KR20050013165A - Method and apparatus for detecting multiple optical wave lengths - Google Patents

Abstract

Optical diffraction gratings that perform several functions at various wavelengths are formed in various ways to preserve spectral information in the wavelength band, and functions include: coupling radiation from one waveguide to another A controllable diffraction grating operating at a different wavelength in response to an external control signal.

Description

Method and apparatus for detecting multiple optical wave lengths

Diffraction gratings are optical devices that are used to obtain wavelength dependent properties using optical interference effects. This wavelength dependent optical property may, for example, function to reflect or diffract light of all other wavelengths while reflecting light of a particular wavelength. This feature is useful in a wide range of situations, including extracting individual wavelength channels in a wavelength division multiplex (WDM) optical communication system or providing wavelength specific feedback for tunable or multiwavelength semiconductor lasers. The diffraction grating is usually realized by modulating (variing) the effective refractive index of the waveguide structure. This change in refractive index causes the incident light wavelength to be reflected or diffracted. That is, at the boundary where the two refractive index values change drastically, light incident directly on the interface is reflected according to the well-known Fresnel reflection law.

The term "multi-wavelength grating" generally refers to a diffraction grating that can exhibit optical properties at several wavelengths. For example, a multi-wavelength diffraction grating may be a diffraction grating that reflects light at some selected wavelength (which may correspond to a particular optical communication channel) while transmitting light at other wavelengths. However, in some situations it is necessary to set the optical properties in a continuous range of wavelengths rather than at specific wavelength values. For example, the non-uniformity of the light gain profile in the laser cavity and the optical amplifier is to be compensated using the optical diffraction grating. However, achieving this task in a continuous range of wavelengths is difficult with traditional diffraction grating techniques.

Similarly, a range of optical wavelengths can be used when encoding many communication channels using light of different wavelengths in a single optical cable (more commonly referred to as wavelength division multiplexing (WDM) technology). Periodic gratings are often used to separate or process these channels. However, since the periodic diffraction grating technology processes one wavelength, the device has to adopt a plurality of single diffraction gratings for processing a single wavelength. This is not a desirable solution in that, in addition to the additional losses incurred by each diffraction grating, even a single diffraction grating occupies a significant amount of space in today's integration and refinement standards. Therefore, a single device capable of handling several wavelengths in a space efficient manner is desired.

In the field of semiconductor lasers, the output wavelength of a semiconductor laser is mainly determined by the presence of a "feedback element" around or inside the laser gain, which feedback function serves to reflect light of the desired wavelength back into the laser. Multiwavelength feedback is required for operation at multiple wavelengths. Once again, the single wavelength diffraction grating technique has no choice but to solve this requirement by lining up a simple diffraction grating, which results in the same (and more prominent) loss and space issues described above.

One such wavelength diffraction grating element is a Bragg grating. Bragg diffraction gratings consist of periodic changes in the refractive index, acting as reflectors for single wavelengths of light associated with the periodicity of the refractive index pattern (known as pitch Λ), and are also frequently used in semiconductor systems and fiber optical systems. In fact, however, the Bragg diffraction grating can reflect at several wavelengths substantially corresponding to the overtone of the fundamental pitch. However, these higher-order wavelengths tend to be in a spectral region that is significantly different from the fundamental wavelength, thus making the Bragg diffraction grating less useful as a multiwavelength reflector. In addition, these higher order wavelengths cannot be tuned independently of others.

Other multiwave diffraction grating techniques include: analog superimposed diffraction gratings, sampled gratings (SG), super-structure gratings (SGS), and binary supergrating gratings (Binary Supergrating) ; BSG).

The analog superposition diffraction grating is a generalization of Bragg diffraction gratings, which is rooted in the principle of superposition. That is, a diffraction grating profile consisting of the sum of the refractive index profiles of the single wavelength diffraction gratings reflects at all of its constituent wavelengths. This diffraction grating depends on the change of the analog refractive index. That is, the refractive index changes continuously along the length of the diffraction grating (FIG. 30). However, it is difficult to engrave strong analog diffraction gratings using well-known photorefractive effects because the change in refractive index under illumination changes nonlinearly and is usually saturated at strong exposures. Similarly, the fabrication of the surface relief analog diffraction grating becomes impractical due to the difficulty of reproducibly etching the analog shape onto the surface. The latter difficulty results in the introduction of a binary diffraction grating, i.e., a diffraction grating that depends only on two refractive index values corresponding to whether the diffraction grating is etched or not or illuminated.

Two representatives of the multi-wavelength binary diffraction gratings are sampled diffraction gratings (SG) and superstructure diffraction gratings (SSG). SG is composed of alternating regions of the diffraction grating and the region without the diffraction grating on the waveguide. These alternating regions produce diffraction spectra with multiple reflection peaks (typically) enclosed in symmetrical envelopes. SG is inherently limited in the relative intensities of reflectance peaks and in positional flexibility, and in that the proportion of space without diffraction gratings is large and spatially inefficient. SG is therefore particularly unsuitable for short diffraction gratings or high waveguide losses.

The grating period in the superstructure diffraction grating (SSG) is chirped by changing the grating pitch corresponding to one ridge-gol cycle slightly. It can also be thought of as a sequence of finely tuned phase shifts, where the common phase profile includes linear and quadratic chirping. This implementation allows in principle a relative height corresponding to any peak position and a very small proportion of the size of the floors of the grating, but this is only possible at an expensive cost of extremely high resolution.

Conventional techniques related to the synthesis of binary superimposed diffraction gratings are described by Ivan A. Avrutsky, Dave S. Ellis, Alex Tanger, Hana Anis, and Jimmy M. Xu, "Desing of widely tunable semiconductor icon lasers and the concept of Binary Superimposed Gratings (BSG's). ", IEEE J. Quantum Electron., Vol. 34, pp. 729-740, 1998.

Other methods in the prior art refer to the synthesis of "multi-peak" diffraction gratings-ie, diffraction gratings of properties reflected at several "peaks", which peaks can be controlled by their position and intensity. In these methods the diffraction grating engineer starts with a set of sinusoids, each sinusoid corresponding to a single reflection peak and weighted according to the desired relative intensity of that peak. These peaks are added to each other (ie overlapping, thus BSG is known as superimposed diffraction grating) to create an "analog profile". This profile is digitally quantized by the simple threshold method. For example, if the analog profile value is positive (above the preselected reference value), the corresponding BSG segment has a refractive index value of high or binary 1, and if negative, the corresponding BSG segment is low or binary 0. It has a refractive index value.

FIELD OF THE INVENTION The present invention generally relates to detecting optical signals, and more particularly, to detecting a plurality of optical wavelengths with optical supergrating.

The above described features and other advantages of the present invention are explained in the following detailed description associated with the accompanying drawings.

1 is a schematic diagram of a deep-grating BSG.

FIG. 2 is a k-space diagram illustrating the rationale behind baseband exclusion.

3 is a schematic illustration of the transverse BSG in a ridge waveguide.

4 is a schematic diagram of a two-dimensional (2D) superdiffraction grating.

5 is a schematic diagram of a multi-level one-dimensional (1D) superdiffraction grating implemented with 2D BSG.

6 is a schematic diagram of a three-dimensional (3D) superdiffraction grating.

7A-7D illustrate embodiments of a programmable superdiffraction grating.

8 is a schematic diagram illustrating a forward asymmetric waveguide BSG coupler.

9 is a schematic diagram illustrating a reverse asymmetric waveguide BSG coupler.

10 is a schematic diagram illustrating a reverse symmetric waveguide BSG coupler.

11 is a schematic diagram of a grid-shaped crossbar switch.

12 is a schematic diagram of one embodiment of a four-fiber switch utilizing six switching elements.

FIG. 13 illustrates a one-photon technique for implementing BSG in an optical fiber.

FIG. 14 illustrates a multi-photon technique (here two-photon) for implementing BSG in an optical fiber.

15 is a schematic diagram of a demultiplexer employing 1D BSG.

16 is a schematic diagram of a demultiplexer employing 2D BSG.

17 is a schematic diagram of a static add / drop filter.

18 is a schematic diagram of a Vernier-tuning dynamic add / drop filter.

19 is a schematic diagram of a programmable BSG add / drop filter.

20A-20C are schematic diagrams of an embodiment of a BSG based wavelength stability monitor.

21 is a schematic diagram of a 2-D BSG network monitor.

22 is a schematic diagram of a BSG dynamic WDM equalizer.

23 is a schematic diagram of a gain smoothed optical amplifier.

24A and 24B are schematic diagrams of a lambda router embodiment.

25A-25D are schematic diagrams of a BSG variance-gradient compensator embodiment.

26A and 26B are schematic diagrams of tunable dispersion compensators.

27A-27C are schematic diagrams of a variable feedback super diffraction grating laser.

28 is a schematic diagram of the beam combiner of an embodiment where a waveguide and a 2D BSG are coupled.

FIG. 29A is a schematic diagram of a BSG based separator, and FIGS. 29B and 29C are schematic diagrams of a four port coupled waveguide circulator.

30 is an analog refractive index profile showing the refractive index change Δn over distance x.

31 is a BSG refractive index profile of Δn over distance x, corresponding to a surface relief embodiment.

32 is a block diagram illustrating a standard configuration for delta-sigma modulation.

FIG. 33 is a diagram illustrating a synthesis technique of BSG using induction-symmetry. FIG.

FIG. 34 illustrates a synthesis technique of BSG using super-Nyquist synthesis. FIG.

35 is a flowchart illustrating steps in a method of synthesizing a BSG according to an embodiment of the present invention.

36A and 36B show simplified examples of demultiplexers in comparison with discrete components.

37-45 illustrate embodiments employing a pixel pattern that provides a photonic band gap.

However, this approach is inadequate for at least two reasons. First, the threshold quantization process results in intermodulation, which greatly limits the applicability of the BSG synthesized in this way to practical applications (such as laser feedback elements). Second, this synthesis process is limited to multiple peak diffraction gratings and provides little or no control of the individual peak shapes. For example, the creation of a flattop channel required in some communication applications, or the generation of almost any reflectance spectrum required in some gain and dispersion compensation methods is entirely impossible.

Other methods for BSG synthesis include trial and error, which are almost always computationally difficult and inefficient.

Accordingly, it is desirable to provide a method and apparatus that can overcome the above-mentioned disadvantages and design and synthesize a superdiffraction grating for detecting optical wavelengths.

Although the present invention is described with reference to the embodiments shown in the drawings, it should be understood that the present invention may be practiced with many modified forms of the invention and is not limited to the described embodiments.

For the purposes of the present invention, a diffraction grating is considered to be an optical element used to obtain wavelength dependent properties using the optical interference effect.

First of all, with regard to binary superdiffraction gratings (BSG), it should be recognized that there are two main attributes that differentiate BSG from other diffraction grating technologies. First, BSG is based on a discrete number of refractive index levels. This number is historically two and therefore BSG is known as a binary diffraction grating. Although the description focuses on the binary embodiment of the present invention for the sake of clarity and convenience, it should be understood that in other embodiments discontinuous levels of an appropriate number of refractive indices may be used. Unless otherwise stated in the claims, for convenience the term super diffraction grating will be referred to as a diffraction grating having two or more refractive index values. The second property defining BSG is that the diffraction grating is similar to the sampled structure characterized by the sample length. This means that the transition between refractive index levels of the diffraction grating cannot occur at any location, but rather at multiples of the sample length. The BSG is thus by definition analogous to a digital signal pattern—ie, a discretely sampled waveform. Thus, the BSG can be described by a series of (often binary) numbers indicating the refractive index setting at each sampling point (FIG. 31).

Referring now to FIG. 35, the BSG design involves several important choices. Step 351 selects the refractive index level of the device determined from the material parameters and the constraints of lithography or photoinscription. Step 352 then determines the desired sample length, taking into account the desired wavelength range of the diffraction grating and the resolution of available lithography. Step 353 sets the total element length of the diffraction grating, which is limited by the available physical space and the technical limitations of the engraving process. The method described herein is for determining the grating pattern of the surface relief diffraction grating, and it should be understood that in other embodiments the method may be sufficiently adapted to optical fiber diffraction grating patterns or programmable implementations. The next step 354 converts the diffraction characteristics of the desired diffraction grating into a Fourier region using a Fourier approximation. Such diffraction properties can be reflection, transmission, forward or reverse coupling, or appropriate scattering, or any combination thereof. It is to be understood that "reflection" and "reflection" throughout this specification may be replaced by "cross transmission" and "cross transmission". Guided by the Fourier approximation, the designer can finally design the diffraction grating by its Fourier spectrum. As described below, this step also provides feedback means for various incorrect approximation results to improve the final result. Alternatively, any method suitable for designing the analog refractive index profile to achieve the desired refractive characteristics may be used, and many methods are known in the art.

Next step 355 performs quantization of the analog refractive index profile. Delta-sigma modulation can be used as one of these quantization techniques and can be efficiently implemented. Of course, any suitable quantization technique that preserves Fourier information in the spectral band may be used. Synthesis methods using threshold quantization techniques such as those disclosed in Avrutski et al. And the resulting diffraction gratings are not appropriate in that they do not preserve Fourier information in the spectral band, but may be useful in some circumstances. In two- or three-dimensional radiation operations, where it is important for radiation to proceed in two or three dimensions, and it is important for the pixel array to extend in two or three dimensions, any quantization method in designing devices that meet specifications May also be used.

The next step 356 determines the actual diffraction characteristics of the BSG using an accurate technique such as what is known as a transfer matrix technique. This calculation determines the residual error of the Fourier approximation or other synthesis method used and quantifies the error, which can be returned to the Fourier region and if the error exceeds a predetermined threshold in step 357 the Can be added. This process can be repeated as needed, often with one iteration. It goes without saying that any suitable technique may be used to determine the difference between the desired and actual refractive properties.

Turning now to each of the above-described steps in more detail, in step 353, the Fourier approximation is a mathematical relationship that correlates the structure of the refractive index profile with the diffraction characteristics of the diffraction grating (reflection, transmission or appropriate scattering, or any combination thereof). In other words, a single wavelength diffraction grating has a reflectance spectrum that is accurately characterized by a periodic structure, and a simple superimposed diffraction grating has a reflectance spectrum characterized by its wavelength or reflectance spectral component. Thus, the diffraction spectrum of the diffraction grating can be related to the Fourier transform of the structure. Fourier transform is a standardized way to evaluate the "wavelength property" or "frequency property" of a waveform.

Accordingly, the present invention advantageously uses Fourier approximation to provide a means (inverse Fourier transform) for generating an analog refractive index profile from a desired reflectance specification.

It should also be understood that the quantization step (step 355) of the analog refractive index profile can be performed regardless of how the analog profile has been determined. In other words, the analog profile does not necessarily have to be obtained by the Fourier based method.

The following examples illustrate the Fourier approximation for BSG synthesis.

Simple peak synthesis

In some situations, such as laser feedback elements, BSG is preferred for reflecting light at a given set of wavelengths and where it is possible to do so with high wavelength selectivity. In other words, this specification is for simple peaks with a minimum channel width. These peaks can be derived from the overlap of the next trigonometric profile.

Where a _i , ω _i , and φ _i are the phase of the amplitude, spatial frequency and i-th peak, respectively, and x is the position in the longitudinal direction of the diffraction grating. In most cases the amplitude coefficient is known. In many cases, however, no specific details are required for the phases.

In general, the phase of a component should be chosen to minimize the maximum height of overlap under the amplitude of a given component (and consequently flatten the entire contour). The use of phase information to generate flat contours can greatly increase the efficiency of the diffraction grating. This explains the general principles of BSG design. That is, in most cases, the analog refractive index profile (prior to quantization) should be as flat as possible. This is desirable because flat contours represent an even distribution of grating intensities and allow more efficient use of the available refractive index modulation.

The phase optimization step according to the present invention facilitates greatly increasing the reflection efficiency of the BSG. It should be understood that increasing the number of reflection peaks does not result in a linearly proportional increase in the required refractive index modulation. In other words, in order to double the number of peaks while maintaining the reflectance of the same peak, the refractive index step need not be doubled.

Bandpass Channel Synthesis

Diffraction gratings are often required to separate or select wavelength division multiple optical communication channels. These channels are described by their wavelength (location) and bandwidth (width). The diffraction grating is also typically determined by the specification of spectral flatness and reflection intensity in the channel. Such bandpass filter designs are commonly found in FIR filter theory, and therefore there are many approaches for their solution. The technique presented here is based on a windowing technique.

The main principle of the synthesis of structured diffraction grating spectra, such as bandpass filters, is to use analytically determined solutions to approximate design problems. That is, it is known that certain filter shapes, such as flat top filters, correspond to certain mathematical functions. For example, the sinc function of the following form is known to correspond to an ideal lowpass filter with a bandwidth of δω.

Where i is the BSG segment number. This filter can be transformed into a bandpass filter centered at approximately the frequency ω _c by multiplying the appropriate trigonometric function.

The peak here is at about ω _c and has a width of Δω.

Unfortunately, this filter is characterized by an abrupt transition from passband to stopband and requires infinite length for its implementation. Simply cropping the filter to the desired length results in undesirable oscillation characteristics known as Gibbs. This is a common issue in FIR design, and one approach to this solution is the windowing technique.

The windowing technique sees truncation as the product of a window function that is zero in the region to be cropped. Theoretically, it is assumed that the area to keep the cutting operation is 1 and the area to be cut out is multiplied by a "square window" of 0. This theory claims that this rectangular window is responsible for the Gibbs phenomenon.

The window function that can be used for truncation generally makes the bandpass filter non-ideal, which is a finite "transition width between passband and stopband, in contrast to an ideal filter that does not require bandwidth for transition. (transition width) ". The FIR filter theory, though ideal, provides some acceptable window functions.

One such window function is the Kaiser window, which is considered an ideal lowpass (and thus bandpass) filter, allowing designers to adjust the transition characteristics via parameter β. Kaiser windows are therefore suitable for BSG synthesis and provide increased flexibility in adjusting the shape and slope of the reflectance channels. However, this is only one of many FIR techniques that can be used to achieve this result, and BSG synthesis by Fourier techniques is not limited to this particular technique.

It should be understood that the analog profile corresponding to the flat top channel makes use of most of the center of the diffraction grating. In the case of multiple peaks, this situation is undesirable since it leads to inefficient use of resources away from the center of the diffraction grating. A simple solution to this problem is to stagger waveforms with respect to individual channels when they overlap. Together with phase optimization techniques such as those used for multiple peak diffraction gratings, this technique can enable very efficient use of diffraction grating resources.

In some embodiments, the reflectance specifications do not correspond to specific element shapes such as bandpass channels or peaks. The gain compensation profile and dispersion compensation diffraction grating of optical amplifiers fall into this category. In such embodiments the diffraction grating may be synthesized using a Discrete Fourier Transform (DFT).

The Discrete Fourier Transform and associated Fast Fourier Transform (FFT) is a version of the Fourier Transform that operates on a finite number of sampling points. Regarding the normal Fourier transform, the Fourier approximation and its inclusion in the BSG synthesis is passed to the DFT. The DFT operation on the set of points with the actual value of 1 results in a set of 1/2 independent frequency components. Thus, a desired diffraction grating having segments of 1 will be assigned a reflectance value at wavelengths of half, not between wavelengths.

Example of BSG synthesis using DFT is performed as follows.

The frequency domain specifications are input to an array of length l, intended device length (as number of samples), in a manner suitable for inverse DFT operation. This can be done by "sampling" a continuous version of the Fourier region specification at a particular point, or alternatively "drawing" the specification directly into a form suitable for DFT. The inverse DFT of this array is then determined. Various known forms of "smoothing" can be applied to the resulting waveform to reduce oscillation characteristics between frequency samples.

If analog refractive index profiles are synthesized, some variations may be required. One such variant is filtering by a discrete-sum filter. Another variant is to scale the waveform to a level suitable for the subsequent delta-sigma modulation stage. For example, this can be achieved by adjusting to a waveform with amplitude one.

Quantization or Delta-Sigma Modulation (DSM)

Fourier domain synthesis performed so far produces an analog diffraction grating profile. However, BSG requires a discrete profile that utilizes only a small number (usually two) of refractive index values. Of course, other embodiments may use any suitable discrete number of values, such as an octal superdiffraction grating (OSG). One technique for quantization (ie discrete representation) of diffraction grating profiles is delta-sigma modulation. However, any suitable quantization technique can be used.

A desirable requirement for quantization of analog profiles by Fourier technique is to preserve spectral information in critical frequency bands. Delta-sigma modulation is designed, for example, to "filter out" quantization noise in that frequency band while leaving little spectral information in a given frequency band. Other quantization techniques can also be applied, with improvements such as taking into account non-obvious grating effects in the frequency domain. In any case, as required by the Fourier approximation, the selected quantization technique is desirable to preserve low amplitude spectral features in the critical band, which becomes apparent in the low amplitude region.

It should be understood that the BSG synthesis method by the Fourier technique and the quantization technique described below are not limited to delta-sigma quantization.

Referring to FIG. 32, the DSM feedback process 320 is shown, which enhances the quantization performed behind the loop filter 322 by using the measured quantization error 321. That is, the DSM quantizes its input using the threshold of unit 323, but maintains a path of any important information lost by quantization in unit 323 and feeds this information back to the input of filter 322. . Of course, any suitable digital quantizer may be used in other embodiments.

Error feedback and iteration

When the Fourier grating reflectance spectrum is quantized, the synthesis is almost complete. The performance of the diffraction grating can be evaluated using standard tests such as transition matrix techniques to determine the synthesis error. Synthetic error is the difference between the desired reflectance spectrum and the spectrum measured by the transition matrix technique. In one embodiment this error can be evaluated and used to correct the design specification by subtracting the error from the frequency domain specification of the diffraction grating. The new specification can then be used to repeat the synthesis process to create an improved diffraction grating. In another embodiment, the error measured in the frequency domain can be properly converted to the spatial domain and added to the analog grating profile (the grating before quantization). This latter form is a general and powerful technique that can be used independently of the synthesis techniques used in the frequency domain. The error feedback process can be repeated if desired, but is often enough for one iteration. The convergence of the feedback process for the low amplitude frequency domain is ensured by the Fourier approximation described above.

It should be noted that the present invention allows a designer to compare error feedback correction and diffraction grating correction techniques for correcting distortion in the diffraction characteristic region. For example, some peaks may have a characteristic shape that is distorted in the reflectance region, which can correct any of the error feedback described above. The present invention allows designers to evaluate the benefits of error feedback compared to the application of grid resources.

Other Examples of BSG Synthesis

Induced-Symmetry Synthesis

Referring to FIG. 33, the basic property of the sampled signals is that their Fourier spectra show symmetry at approximately integer multiples of the characteristic frequency known as the Nyquist frequency. In some applications, such as a filter with a large number of identical peaks, similar symmetry exists in the reflectance specification. The principle of induction-symmetry synthesis is that the symmetry of this reflectance specification can be reproduced near the Nyquist frequency, and the resources of the diffraction grating can only be used to generate half of the spectral characteristics.

A good example of this technique is the synthesis of a filter with 10 evenly spaced reflectance peaks. Using the principle of induction-symmetry synthesis, the designer can choose a sampling length that places the Nyquist frequency exactly center of the 10 peaks, ie on the line of symmetry of the specification. After that, the designer can synthesize a diffraction grating for the lower five peaks. The top five peaks appear automatically based on frequency domain symmetry.

Super-Nyquist Synthesis

Often the resolution required to engrave the diffraction grating exceeds the available resolution. For example, when designing a BSG for the 1550 nm wavelength range as gallium-arsenide (n = 3.2), placing the Nyquist rate at 1550 nm corresponding to a sample length of about 120 nm (e.g., inductive-symmetric synthesis). Using) is convenient. This feature size is too small for optical photolithography and requires the use of more expensive electron beam lithography.

However, Nyquist said that frequency content above the Nyquist limit consists of a repetition of the spectral information below the Nyquist limit, known as an image. Thus, grating features above the Nyquist rate (super-Nyquist) can be generated by synthesizing those grating images found below the Nyquist limit.

In this way, super-Nyquist synthesis is useful, for example, for reducing the resolution required for the 1550 nm gallium-acenide diffraction grating described above. Selecting "3rd order" synthesis, the designer can select a sample length such that the 1550 nm region corresponds to three times the Nyquist frequency, as shown in FIG. The designer can then shift the Fourier domain grating characteristics by an integer multiple of the sampling rate (double the Nyquist frequency) so that they fall below the "baseband", Nyquist frequency. The diffraction grating synthesized with these shifted properties shows intended grating properties just below three times the Nyquist frequency because of the imaging phenomenon. Furthermore, the sample length of this new diffraction grating is 360 nm, which is a more suitable range for optical lithography. It can be seen that super-Nyquist synthesis can be usefully applied to reduce resolution requirements.

Super Diffraction Grid Application

Reduced Super Diffraction Scattering

1, there is schematically shown a deep grating BSG 14 formed in an upper cladding 13 that forms a structure with a core 12 and a lower cladding 11. Of interest in the superdiffraction grating design is the scattering loss due to the radial cladding mode resulting from the low spatial frequency component of the diffraction grating. This scattering results from incomplete fulfillment of phase matching conditions in a direction perpendicular to the diffraction grating, which is more common in shallow gratings.

The deeper etched features of the present invention reduce this scattering by occupying a greater distance in the vertical direction, which is well known by the Huygens principle and Fourier conditions, which leads to more complete phase matching requirements in the vertical direction. And consequently reduce (unwanted) scattering efficiency. More quantitatively, the lattice shape ideally goes deeper than the material wavelength of the cladding (λ _mat = λ ₀ / n _clad ), and the decay constant of the mode tail should be less than 1 / λ _mat in the diffraction grating region (alternatively) BSG can be implemented in the core region 12 at the center of the mode, in which case the core 12 must be wider than [lambda] _mat , or in this way the refractive index perturbation must span the full mode profile). This ensures a relatively uniform contribution at the normal limit of the diffraction grating, thereby enhancing the disappearance of the scattered components.

Considering the product of the refractive index profile and the mode profile 15, the following analysis results. In other words, the wider and flatr this enemy, the narrower its Fourier transform, and thus the narrower the k-space representation in the vertical direction. This increased constraint on the phase matching condition reduces the range (eg, in terms of output angle) within which the guided wave can be coupled with the radiation mode, thus reducing scattering losses as a whole.

Also shown in FIG. 2 is a k-space illustrating the rationale behind baseband exclusion. Including the k-space baseband (ie, low spatial frequency) as an additional "region of interest" can improve synthesis by drastically reducing unwanted higher order couplings interposed by small k components.

In other embodiments, the superdiffraction grating may be implemented using any means for varying the effective (or mode) refractive index, including surface relief embodiments (see FIG. 31). One alternative is to change the mode refractive index by adjusting the transverse magnitude of the one-dimensional waveguide. This can be accomplished by changing the width from logic 0 to the value of logic 1 in the case of ridge waveguide 30, as shown in FIG. This embodiment has many advantages as follows. That is, the waveguide 30 and the BSG 31 can be patterned and etched together, thus simplifying manufacturing. Waveguides and diffraction gratings can be automatically aligned to reduce tolerances. And a multilevel super diffraction grating can be as easy as a two-level BSG.

2D Super Diffraction Grid

In one embodiment, the BSG takes the form of a one-dimensional sequence line of high refractive index and low refractive index, and can make almost any overlap by varying the magnitude of the k vector (ie, spatial frequency component) in the same direction. The BSG can be extended to two dimensions, in which case a matrix of high and low refractive pixels is implemented in the plane of the planar waveguide, which can further be extended to include any number of discrete levels. . 2D BSG (and more general 2D superdiffraction gratings) can emulate almost any overlap of k vectors by varying their size and direction (in the plane of the diffraction gratings). Practically speaking, this means that the 2D BSG can route and focus light according to wavelength and in-plane input and output angles, thus providing beam-shaping, wavelength selective lensing, and spatial multiplexing and demultiplexing. It allows the same functions.

2D Super Diffraction Grid Example

Referring now to FIG. 4, a schematic 2D “superdiffraction grating” (40, referred to as a BSG represented by a binary superdiffraction grating) is shown. A 2D superdiffraction grating is an optical element having a two-dimensional array of refractive index modulated, effective refractive index modulated, gain modulated, and / or loss modulated pixels, each pixel literally having two or more levels of modulated parameters ( Employs a finite set of light, and the light propagates in the plane of the array. The term "wave layer" will be used when referring to the layer through which light travels. The term "modulation layer" will be used when referring to a layer that performs a physical change causing a change in the mode refractive index of the structure. In some cases, for example, when ion implantation is used, the two layers will be the same. In other cases, they will differ when the cladding layer is etched or when controllable instructions have been applied to cause contact with the propagation layer. Those skilled in the art will fully understand when these terms are used. The pixels may be arranged in any order or periodic structure (eg lattice arrangement), and may employ any arbitrary but repetitive shape. Hatched pixels represent high refractive index values and empty pixels represent low refractive index values. Examples include an array of square pixels on a square array, points that spread out into a triangle network, or hexagon pixels in a hexagonal network. The fabricated form of this device is not binary due to technical difficulties to produce a complete physical structure, or even if the modulation levels are continuous, the pixels are a finite set of parameters corresponding to the level of the ideal set that makes the device a 2D BSG. Engraved by the engraving technique. Such devices can allow for angle and wavelength specific optical processing, in addition to mimicking traditional optical components such as mirrors and lenses.

The pixels of a 2D BSG are quantized representations of analog profiles quantized by a method (without significant additions or deletions) that maintains Fourier information within one or more regions of interest in the two-dimensional spatial frequency representation of the diffraction grating. The region corresponds to the region of interest in terms of diffraction characteristics specific to the angle and wavelength.

Synthesis of 2D Super Diffraction

One way to synthesize a two-dimensional superdiffraction grating is as follows.

A) Determine the set of mathematical conditions that describe the electromagnetic fields at the input and output of the BSG at all operating modes and wavelengths.

B) Calculate the analog profile by solving the equation of the system corresponding to the Born approximation with the boundary conditions corresponding to the input and output conditions.

C) Digitize the analog profile using a two-dimensional technique designed to maintain Fourier components within one or more regions of interest. One suitable technique is Floyd-Steinberg dithering, where the quantization error generated at each pixel is converted to pixels to be quantized using a finite impulse response function containing spectral information in the region of interest (s). Spreads.

The process of diffraction grating synthesis can be described by a simplified example. FIG. 36A shows a simple demultiplexer 36-10 having two wavelengths La and Lb to separate the incoming radiation from under the waveguide 36-2 and exit into two paths 36-4 and 36-6, respectively, of a single wavelength. Illustrated. 36B shows a simple demultiplexer with discrete components that perform the same function. The example of FIG. 36B uses a prism 3 to separate the incoming wavelengths into two paths 24 'and 26' (both bend in the same direction). The separated radiation beam bends back into the correct path entering the output waveguides 4 and 6 by the prisms 34 and 36. The beams are then focused into waveguides 4 and 6 by lenses 34 'and 36'.

36A shows the same functionality performed by the embodiment formed of a planar waveguide by solid-state technology. XY (indicated by arrow 36-15) pixel arrays, represented by lines along the left edge and bottom of box 36-10, split the beam at different angles (angles A1 and A2 and B1 and B2) over distance It forms a BSG that performs the function of (in this case one wavelength to the left and the other to the right). The angles are reversed in the areas indicated by groups 36-34 and 36-36, and the pixels perform an angle change and focus radiation. In the lower part of the box 36-10, the wavefront is indicated by a straight line and in the upper part by a curve to represent the result of focusing to the output waveguides 36-4 and 36-6.

The example of FIG. 36A simplifies the pixels in the upper part simply by processing a single wavelength since radiation is separated in space. In many practical embodiments of the demultiplexer the output paths are close or overlapping and the pixels will have to handle more than one wavelength. An advantageous feature of the present invention is that the synthesis of the refractive index profile to perform the required function is done mathematically, rather than irradiating the material layer with a conventional first interference pattern, with a second pattern and so forth.

Referring to FIG. 5, 2D BSG can be used in applications and devices that use 1D superdiffraction grating 50 or other types of diffraction gratings to provide potential advantages. These advantages stem from the fact that two-dimensional diffraction gratings have well-defined coupling wave vectors in two dimensions of the diffraction grating plane, providing direct control of the coupling in the radiation mode, thus potentially reducing scattering. On the other hand, the 1D diffraction grating 50 often has a coupling wave vector that is not well defined in the direction perpendicular to the waveguide because of its narrow width.

An "effective one-dimensional diffraction grating" corresponding to a given two-dimensional diffraction grating may be regarded as a 1D refractive index profile derived by integrating the 2D diffraction grating along a lateral line perpendicular to the one-dimensional waveguide. This effective 1D diffraction grating has a refractive index level that spans a wide range of values between two binary levels, and can be nearly analogous in nature with sufficiently high lateral sampling (the number of levels is 2 for l binary transverse samples). will be ^l ). As analog diffraction gratings do not have quantization problems, they can be used as a method for multilevel diffraction grating designs that still have the robustness of binary-like physical structures and ease of manufacture.

The method can be summarized including the following steps.

Calculate the analog profile as in the conventional technique.

Convert each pixel to a line of binary (or multi-level) pixels lined transversely perpendicular to the 1D diffraction grating axis, in such a way that the average taken along that line closely matches the desired analog value. This set of pixels is preferably bound to maintain certain symmetry properties to reduce coupling to higher modes (along with a tradeoff that limits the number of available transverse averages). This line can be calculated using a DSM-like process (where the desired average or desired lateral profile is input), in conjunction with a random search optimization technique (for a small number of pixels), or by other techniques.

The 2D superdiffraction grating can be implemented in a one-dimensional configuration by first widening the 1D waveguide to include the 2D superdiffraction grating. The waveguide can extend beyond the area and then reduce to a smaller (possibly single mode) size. In addition, the two waveguides can be extended (and similarly reduced on the other side) to be a 2D diffraction grating region and form a waveguide coupler. The 2D superdiffraction grating also provides reduced scattering when implemented in conjunction with the superdiffraction grating waveguide coupler.

3D Super Diffraction

The BSG can be extended to three dimensions by taking the form of a three-dimensional array of high and low refractive pixels. As before, this definition can be extended to include any number of discrete levels. 3D BSG (and more general 3D superdiffraction gratings) can emulate almost any superposition of k vectors of any size and orientation in one or more regions of interest defined in 3D spatial frequency space. Practically speaking, this allows the 3D BSG to route and focus light according to wavelength and input angles (ie polar and azimuth) and output angles, thus providing features as described in two-dimensional diffraction gratings, And at the azimuth angle.

Referring to FIG. 6, a schematic diagram of a 3D superdiffraction grating 60 is shown, comprising a three dimensional array of refractive index, effective refractive index, gain, and / or loss modulated pixels, each pixel being literally two finite or two. It is a form of optical element that employs more levels of modulated parameter (s). The pixels may be arranged in any order or periodic structure and may employ any but repeating shape. The fabricated form of this device is due to technical difficulties to produce a complete sample, or by design, even if it is not binary or even modulation levels are continuous, the pixels are finite of parameters corresponding to the level of the ideal set that makes the device a 3D BSG. Engraved by the engraving technique as a set. In addition to mimicking traditional optical components such as mirrors and lenses, these devices can allow optical processing specific to angle and color.

Synthesis of 3D Super Diffraction

The synthesis method of the 3D superdiffraction grating includes an approach very similar to that described above for the 2D superdiffraction grating. However, equations are described in three-dimensional space, and the quantization technique also uses a three-dimensional impulse response function to distribute the quantization error.

Two- or three-dimensional superdiffraction gratings can be designed to create structures that characterize complete or incomplete photonic band-gaps (PBGs). This can be done by designing the diffraction grating using any BSG design technique with spectral features to create a gap with sufficient intensity and density in or near the desired band gap. The synthesis may be applied on a smaller scale to cover the entire applicable area, or to create a pattern that covers and covers a wider area. The design may also use higher order synthesis techniques to allow for reduced resolution requirements.

A complete photonic band gap material shows a range of frequencies that cannot propagate through the medium, regardless of its direction of propagation. Applications of these media are reportedly plentiful and abundant. Some examples include optical filters and resonators, optical radiation suppressors or enhancers, (super) prismatic materials, environments of new laser and detector structures, and substrates for light guiding and wiring.

BSG-based photonic band gaps include lower specific refractive index requirements and relaxed resolution requirements (both lead to optical devices and ease of manufacture and higher affinity) compared to conventional PBG materials. It offers a major advantage.

Synthesis of Super Diffraction Grids by Optimization

A general method of designing a one, two or three dimensional change superdiffraction grating is presented as follows in addition to the method described above.

Generate an analog profile by the procedure described in the first synthesis method (this function is called P).

Create a filter H that determines the critical wavelength range (s) (in which spectral features are preserved) and its weight. H essentially assigns weights to each frequency, with higher weights conserving spectral information better than lower weights. The filter H can be written in the form of a matrix operator that leads to a matrix solution of the next step, but can also take the form of an impulse response or a pole-zero.

Solve optimization problems:

Where X is a vector containing the values of BSG, V is a vector of Lagrange multiplier, and L is the type of norm for optimization (L = 2 is, for example, least squares). -square)). The Lagrange product multiplies the BSG values to either of the allowed refractive index values (n _low or n _high ) to derive a binary form. The function can be modified to allow multivalued superdiffraction gratings in accordance with the techniques of the present invention.

Optimization can be performed using any optimization technique, but Newton-type techniques are particularly useful and desirable because of the matrix nature of the equations.

This approach can be applied to the synthesis of 2D and 3D diffraction gratings by taking analog profiles generated by corresponding synthesis techniques and performing similar optimization procedures, in which the matrix equations are properly transformed taking into account dimensions. This can be done by stacking the rows of the two-dimensional diffraction grating into one row of the X variable, and similarly to the P variable, to synthesize the corresponding H matrix. The H matrix can be generated as a Toeplitz matrix of a given impulse response function, or with other techniques, including:

Let h _{f be} a vector representing the importance weight of the spatial frequency f. H is then given by:

H = F ^-1 diag (h _f ) F

Where n-dimensional F is a Fourier matrix given by:

Multiplication by the matrix F is equivalent to taking the Fourier transform of the vector, and the operation can be faster by using the Fast Fourier Transform (FFT) technique. This fact can be used for this type of H filter to speed up the computation of the cost function and its nth derivative, log (n).

Another alternative is to perform optimizations in the Fourier domain by taking into account the Fourier representation (generated by multiplying F) for both P and X variables, and converting their equivalence constraints accordingly:

This expression And / or allowing h _f vectors to be sparse representation, which helps to reduce computation time.

Tuning Mechanism of the Super Diffuser

The spectral characteristics of the superdiffraction grating can be shifted by any mechanism that makes a change in the effective mode refractive index. This can be accomplished by electro-optic, electro-strictive, magneto-optic, electrochromic, and / or photosensitive media, where one or more design parameters are modified using electronic control. It can be achieved if it exists as part of a device that allows it to be. As an alternative, one or more modifications of the design parameters may be performed using changes in temperature, the application of mechanical stress, and / or illumination of the entire device or portion.

Tuning mechanisms may include, but are not limited to: thermal, electro-optical, magneto-optical, opto-restrictive, mechanical strain (external, piezo, electrostatic, electrostatic, acoustical), Current injection, light irradiation, liquid crystal, reconstituted molecules, chemical reactions, and mechanical transitions.

In some devices, the gain corresponds to a shift or change in spectral characteristic intensity, and in others, functionalities appear beyond this. In any case, throughout this patent application and in the following descriptions of all devices, it is absolute that the function of a device employing a static superdiffraction grating can be further improved by replacing it with a tunable superdiffraction grating. .

Programmable Super Diffuser

7A-7D, exemplary embodiments of a programmable superdiffraction grating are shown. The programmable superdiffraction grating comprises, in part, electrically addressable electrodes with a suitable medium, so that the electrodes are a device for building a diffraction grating pattern in the medium. The diffraction grating pattern can be programmable, dynamic or fixed. The diffraction grating pattern utilizes a finite number of modulated levels (eg two levels for BSG, more for a superdiffraction grating), or successive modulation levels.

Another embodiment (FIG. 7A) comprises an array of microelectromechanical system (MEMS) fingers 7a2 located above one or more waveguides 7a3, each finger corresponding to a “bit” of the BSG, and so on. Individually deflected downwards may contact the waveguide 7a2 surface. Alternately, the "off" state corresponds to the contact between the finger and the waveguide, and the "on" is deflected upward and away from the waveguide. In any case, the contact with the waveguide will generally result in a higher effective refractive index, and the absence of contact will result in a lower refractive index. The preferred embodiment facilitates true binary operation by making the off-waveguide separation sufficiently large so that even a small error of this value changes even lower effective refractive index.

Another embodiment includes a plurality of electrodes disposed over the enclosed liquid crystals 7b2 (LCs) that affect propagation, as shown in FIG. 7B. Liquid crystals on the nematic phase are birefringent tuned by voltage, and thus have a means of tuning the effective refractive index. This voltage dependency typically has some threshold voltage V _t (corresponding to the full orientation of the nematic liquid crystal), with little or no refractive index change thereon. Employing voltage control of V = 0 and V> V _t The method allows for true binary operation even in the face of chaotic effects such as electric field edges.

Forward and Reverse Asymmetric Waveguides BSG Couplers

Begin by describing two basic elements of many more complex devices. That is, the forward and reverse asymmetric waveguide BSG coupler. These elements (which can indeed be devices themselves) couple light with the desired spectral response from one waveguide to another parallel waveguide. That is, light at any given wavelength may be fully, partially coupled with the desired phase, or not coupled at all. 7C shows that the effective mode refractive indices (n _eff ) ₁ and (n _eff ) ₂ are different and thus different propagation vectors k ₁ (λ ₀ ) = 2π (n _eff ) ₁ / λ ₀ and k ₂ (λ ₀ ) Two parallel asymmetric waveguides with 2π (n _eff ) ₂ / λ ₀ where λ ₀ is the free-space wavelength. The effective refractive index will generally depend on the wavelength λ ₀ . When a signal from the electronic driver 7c3 is applied to the electrodes referred to as 7c2, the mode distribution is changed to induce coupling.

If each mode profile overlaps, light will be forward coupled from one waveguide to another neighboring waveguide, which is known as inherent coupling and will generally occur at all input waveguides. Inherent coupling is a parasitic effect in the context of BSG enhanced coupling, and the optimal design seeks to ensure that the latter shrinks the former. This condition is likely to be satisfied as the waveguide asymmetry (ie, the difference between (n _eff ) ₁ and (n _eff ) ₂ ) increases.

Forward Asymmetric Waveguide BSG Coupler

Referring to Figure 8, a forward asymmetric waveguide BSG coupler 80 is shown. Forward coupling from one waveguide 81 to a neighboring waveguide 82 (i.e., the mode profile overlaps) indicates that the effective refractive indices of the waveguides have a spatial frequency K _g (λ ₀ ) = k ₁ (λ ₀ ) -k ₂ ( If perturbed with λ ₀ ) it will be enhanced at a particular wavelength λ ₀ . This can be accomplished using any BSG embodiment, including placing the BSG 83 between two waveguides, or translating the BSGs into one or two waveguides, and without limitation. . Any spectral coupling characteristic is achieved by having the BSG 83 emulate the appropriate spectrum K _g (λ ₀ ).

Reverse Asymmetric Waveguide BSG Coupler

Referring to FIG. 9, a schematic diagram of a reverse asymmetric waveguide BSG coupler 90 coupling waveguides 91 and 92 is shown. For a given input wavelength λ ₀ in this embodiment the reverse coupling will occur if the refractive index perturbation instead includes the spatial frequency K _g (λ ₀ ) = k ₁ (λ ₀ ) + k ₂ (λ ₀ ). The BSG 93 should be free from the spatial frequencies 2k ₁ (λ ₀ ) and 2k ₂ (λ ₀ ) throughout the entire spectral band of interest, which creates back reflections within each waveguide, thus reducing coupling efficiency. This will reduce and cause unwanted back reflections. To satisfy this condition, any overlap between the diffraction grating spatial frequencies (K _g 's), which results in coupling between the waveguides and coupling within the waveguide, throughout the wavelength region (s) of interest, can be avoided. It is required that asymmetry be sufficient. This can be expressed mathematically as:

k ₁ (λ ₁ ) + k ₂ (λ ₁ ) ≠ 2 k ₁ (λ ₂ ) and k ₁ (λ ₁ ) + k ₂ (λ ₁ ) ≠ 2k ₂ (λ ₂ )

Where k ₁ and k ₂ are defined first together with the wavelength dependent refractive index, and λ ₁ and λ ₂ are any combination of wavelengths within the region of interest.

If any of the waveguides are multimode, other overlaps, i.e. overlaps with regard to desired and undesired coupling between the range of diffraction grating frequencies (whether forward or reverse), should also be avoided.

Reverse Symmetric Waveguide BSG Coupler

Referring to FIG. 10, a schematic of a reverse symmetric waveguide BSG coupler is shown. The symmetrical BSG reverse coupler performs the same function as the asymmetrical reverse coupler (programmable, dynamic or static) but the two waveguides are weakly asymmetric or even symmetrical at their effective refractive index. Thus, although it usually causes in-waveguide reflections, it can exceed the limitations expressed in the previous equation. The method summarized below enables efficient coupling between neighboring symmetric waveguides while suppressing reflection in the waveguide.

This device includes two waveguides (symmetrical or not) with a BSG 612 located between them. The BSG can be static, tunable, or programmable as needed. Two other BSGs 611 and 622, which are identical to the middle BSG but contrasted in contrast (ones to zeros and zeros to ones), are located on each other side of the two waveguides so that they are towards the center BSG with respect to the corresponding waveguide. Reflect.

The principle of operation is as follows. as mode profile of the waveguide 1 to m ₁ and m ₂ Let mode profile of the waveguide 2. In short, the coupling coefficients for the two waveguides are written as the first order in the diffraction grating intensities:

Where G ₁₂ is the center diffraction grating and G ₁₁ and G ₂₂ are the diffraction gratings outside of waveguides 1 and 2, respectively. The second term is negligible because the two lateral diffraction gratings are very far from the opposite waveguide (more precisely, the mode profile of the opposite waveguide can be ignored in this region).

However, the coupling coefficient from the first waveguide itself (corresponding to the waveguide internal reflection) is:

(Because G ₁₁ = -G ₂₂ and symmetry)

The result is the same for the second waveguide. The only necessary assumption to make this clear is that the mode profiles of the two waveguides are basically symmetrical (for their waveguides, they do not necessarily have to be identical to each other. It should be understood that waveguide coupling generally results in the least asymmetrical element). The diffraction gratings are properly symmetrically arranged with respect to the waveguide. This erasure is independent of many material parameters, such as the effective refractive index of the waveguide, even if these material parameters change independently.

BSG Coupling Using Transverse Waveguide Variation

This particular embodiment of implementing the BSG is specially handled here for its particular advantages, as well as the following particular difficulties, as described below: variation in the optimum width, taking into account the relative BSG strength in each waveguide in asymmetric waveguide coupling; And how to design a reverse-contrast diffraction grating of a symmetric waveguide coupler to minimize internal reflection of the waveguide.

The advantages of this embodiment are similar to those described above. However, there are now two (or more) waveguides, and the alignment of the waveguides is important. It should be noted that the waveguide and BSG can be patterned and etched together to take advantage of the advantages, thus simplifying manufacturing, and furthermore, the waveguide and diffraction grating can be automatically self-aligned to mitigate tolerances.

BSG Crossbar Switch

Referring to Figure 11, a schematic diagram of a grid-shaped crossbar switch is shown. Crossbar switches are devices that route wavelength channels from several input waveguides to several output channels (typically matching the number of input waveguides). Crossbar switches should generally be able to route any wavelength from any input waveguide to any output waveguide. Such switches are typically denoted in the form of N x N, where N represents the product of the number of input / output waveguides and the number of wavelength channels. For example, a switch with four input waveguides, four output waveguides, and 16 wavelength channels per waveguide is called a 64 x 64 switch.

Traditional crossbar switches use a grid shape, where each of the n input waveguides is first demultiplexed into a c wavelength channel such that the n × c input “rows” intersect the n × c output “columns”. These columns are then multiplexed back into the n output waveguide. Routing is done using optical switches located at each intersection of rows and columns. This design is common in that each switch is implemented using a moving mirror, especially using MEMS. Clearly this structure requires a switching element of (n × c) ² .

Other architectures can use 2x2 switches. That is, the switching element has two inputs (I ₁ and I ₂ ) and two outputs (O ₁ and O ₂ ), and I ₁ and O ₁ and I ₂ and O ₂ , or I ₁ and O ₂ and I ₂ and O Connect any of ₁ . The problem lies in choosing the arrangement and number of switches so that the input optical signals can be rearranged to the output of all possible permutations. We can say that what is required to determine the number of switches is that since there is a permutation of possible inputs of (n × c)! And all 2x2 switches provide one bit of control bits:

O (log ₂ (nc)!) = O ((nc) log ₂ (nc))

A programmable BSG (eg, the tunable forward or reverse coupler described above) can be used to form a 2x2 switch. Thus, each BSG switching element can provide a 2x2 function independently of each input wavelength. This is very advantageous in that it eliminates the need to demultiplex the input wavelengths first and reduces the number of switches needed:

Number of switching elements = O (nlog ₂ n)

Where n is only the number of input waveguides, and has nothing to do with the number of wavelength channels c (see FIG. 12, which shows a schematic diagram of one embodiment of a four-fiber switch utilizing six switching elements 120).

Other embodiments may use stacked 2x2 BSG switching elements, where each layer has the same number of switching elements of n / 2, where n represents the number of input waveguides, each carrying a c wavelength channel. . In this embodiment, the switches are connected to each other in the following manner.

Ensure that the waveguide w is connected to the waveguide w + 2 ^l-1 . Where l is the floor number (starting at 1).

Rewrite (rewind) the above equation by setting l = 1 when 2 ^l = n.

This is only one special wiring technique and many other techniques can be thought of as drawing from the prior art, particularly with regard to binary switching tree design.

The number of switching elements employed in this type of design is given by:

Here the ceil function produces the smallest integer greater than its argument.

The savings resulting from this design technique can be enormous and are shown in Table 1.

Input waveguide (n) Wavelength channel per input (c) Switching element Grid design Single wavelength stack design Multiwavelength Lamination Design 4 16 256 96 6 6 32 1152 384 12 8 64 4096 1024 16

The number of switching elements in the case of superdiffraction grating is given by the above formula, but in the case of grid design the number of switches is specified as c · n ² , and in the stacked design the number of single wavelength switches is the switching elements in the BSG design. C times the number of fields.

In addition, embodiments using a programmable BSG can further reduce the need for multiplexers and demultiplexers. Single wavelength designs can be implemented with forward and reverse couplers employing Bragg diffraction gratings instead of BSGs.

Direct Wiring of BSG to Fiber Optics

The following describes a technique for implementing BSG in an optical fiber in which its refractive index and / or effective mode refractive index can be changed by exposure to intense and / or high energy laser light.

One-photon process

Referring to Figure 13, a single photon technique for implementing BSG in an optical fiber is shown. In this embodiment, the diffraction grating employing binary or multilevel features (refractive or effective refractive index change, elimination, loss modulation, etc.) uses a focused focused laser beam 13-10 over the photosensitive optical fiber 13-1. Engraved. Here the laser beam engraves the diffraction grating information directly on the optical fiber, as indicated by the arrow, as the optical fiber moves at a constant or variable speed relative to the laser's focus. In another embodiment, the optical fiber is stationary and the laser focus is manipulated to scan the optical fiber.

Multi-photon process

Referring to FIG. 14, there is shown a multi-photon device (here two-photon) 140 implementing BSG in an optical fiber. This technique involves the fact that two or more laser beams 144, 145 are employed in the process, where the information (ie, shift in refractive index) preferentially intersects and / or structurally interferes with the intersection 143 of these beams. Similar to the above, except that it is engraved. This embodiment provides advantages depending on whether the underlying photosensitive mechanism is intensity dependent or energy dependent. In the former case the structural interference of the N beam (same amplitude) is N ² times the intensity of the single beam, and in the latter case the collective light energy is set at only the intersection of the beams so that the transition of the problem occurs.

This embodiment allows increased control over the area of the fiber where information is engraved (e.g., the index of refraction can only change in the core 141 when the beam is allowed to cross the core) and has been required in a single photon processor. An external cladding such as this does not have to be stripped off, simplifying the manufacturing process.

The following is a description of other embodiments of the present invention employing certain combinations of superdiffraction gratings and module elements in the previous description. It should be understood that any of the BSGs mentioned herein may be replaced with more general multilevel superdiffraction embodiments in accordance with the teachings of the present invention, and furthermore may be replaced with tunable and / or programmable embodiments.

Wavelength Demultiplexer

The demultiplexer separates the multiwavelength (ie multichannel) input into its designated channel. This demultiplexer function may be achieved using the BSG of various embodiments described in detail below.

Multilevel superdiffraction gratings in accordance with the teachings of the present invention are also suitable for demultiplexers and filters having non-uniform channel spacing (or any other channel spacing structure). It will be appreciated that the advantages of this demultiplexer embodiment of the present invention effectively alleviate problems such as stimulated raman scattering (SRS) generated when channels are spaced at equal intervals in terms of optical frequency (energy).

Demultiplexer with 1D Super Diffraction

Referring to FIG. 15, a schematic diagram of a demultiplexer employing 1D BSG is shown. This device, in part, as described above, comprises a set of waveguides coupled using reverse and / or forward BSG couplers 15-1 to 15-3, which enter the device through a particular input port. It splits the multiwavelength light into its wavelength components and leaves the device through its assigned output port.

This embodiment is a forward and reverse serial connection of the BSG that divides the channels into two subbands in sequence until the individual channels are extracted, and a sequence of sloped single channel diffraction gratings that direct the individual channels to their respective output waveguides. It includes.

Demultiplexer with 2D Super Diffraction

This embodiment includes a 2D BSG, as shown in FIG. 16, which splits the multiwavelength light incident on the device through a particular input port into its wavelength component and leaves the device through its assigned output port. .

Add / drop filter

In this embodiment, as shown in FIG. 17, the optical add / drop filter includes an " input " port 171 that accepts multiple wavelength channel inputs, " routed " one or more channels to be separated from the " input " stream. Optical element 170 including a "drop" port 172 and a "pass" port 174 through which the remaining channels exit. There may be additional "extra" ports, which accept and route input to the "pass" output where the wavelength channel is dropped from the "input" stream.

Static add / drop filter

Referring to FIG. 18, there is shown an optical device embodiment of the present invention that includes one or more 2D BSG and / or a reversely coupled set of waveguides and / or forward BSG couplers. In this embodiment, one or more wavelength components of light entering the device through a particular input (“input”) port 181 are separated and leave the device through a particular output (“drop”) port 184. The remainder of the input light leaves the device through another output ("pass") port 182. Additionally, the device may include an additional input (“additional”) port 183 having the property that certain or all wavelength components enter the device through the port, and the incoming light may also be a “pass” port. Leaving through 182 adds to the light routed from the "input" port.

18, BSG 1 couples a subset of the input lambda from waveguide A to waveguide B. BSG 2 couples a subset of the first subset from B to C. This process continues until only the desired wavelength (s) remain in the drop waveguide. It should be noted that BSG 1 and BSG 2 can be tuned to select the desired λ in the range beyond the original tuning range Δλ / λ ≒ Δn / n. Furthermore, of course, reverse coupling may be employed in other embodiments. In this embodiment the additional port 183 can be made lambda selectively via a similar Vernier approach.

Dynamic add / drop filter

Referring to FIG. 19, there is shown an optical device embodiment 190 that includes the following elements. That is, the optics are coupled using one or more 2D BSG, and / or tunable or fixed reverse and / or forward BSG couplers to achieve the same functionality as a static BSG add / drop filter, but additionally “input” The wavelength (s) directed from the "port" to the "drop" port and / or the wavelength (s) directed from the "additional" port to the "pass" port comprise a set of waveguides controllable by an external control signal.

This embodiment uses the vernier tuning principle as a design motivated by the fact that spectral shifts accessible through refractive index tuning are often much less than the overall desired tuning range. The multichannel inputs enter one waveguide, and light is coupled to adjacent waveguides by multiple peaks (peak spacing generally less than the available tuning range) tunable BSG. Subsequent tunable BSGs (typically with different spacing peaks, which are less than the tuning range available) couple a subset of the first set of these channels to a third waveguide. This decimation process can continue as desired and the BSGs are independently tuned to the channel (s) they wish to drop relative to each other. The channel selection range may thus greatly exceed the available refractive index tuned spectral shifts. The same set of BSGs can be used as shown in FIG. 18 to add the dropped channels at the second input.

Another embodiment may employ a programmable BSG to have a structure as shown in FIG. 19 to dynamically add and drop any subset of the input channels.

Wavelength stability monitor

Optical networks functionally require channel wavelengths to stay within some range of their nominal value. Drifting is caused by a number of factors, including changes in environmental conditions, device aging, and mechanical disruption.

Wavelength drift can be monitored using a 1D superdiffraction grating, as shown in FIG. 20A in accordance with the teachings of the present invention. Light incident at a given angle of incidence on the inclined 1D diffraction grating 20a3 will be diffracted only at a particular exit angle, but if detuned at the central peak reflectance wavelength will actually detune at an angle and reduce diffraction efficiency.

This reaction can be used to detect wavelength shifts. Or, assuming that the wavelength is normal, the shift in device characteristics can be compensated for through various mechanisms (such as temperature control). In one embodiment, photodetector arrays 20a4 symmetrically arranged along the diffraction path 20a2 of the desired center wavelength may be used to detect wavelength shifts. In this configuration, if the local wavelength matches the desired value, the signals from each will match (note that usually the diffraction efficiency will be intentionally low, so most of the power will pass through). The deviation in the local wavelength then appears as a change in the relative value of the photodetector 20a4 and can be monitored as it passes through the logarithmic subtraction processor 20a5 (other more sensitive means may be employed).

Similarly, another embodiment may be implemented with 2D BSG 20b4, as shown in FIG. 20B, which focuses diffracted light onto detector 20b3 and / or wavelengths of various channels. Pseudo-1D (i.e. point source) attribute 20c3 etched along waveguide 20c2, which will simultaneously detect drift in or induce symmetrical diffraction in both transverse directions, as shown in FIG. 20C. It can be implemented with a sequence of (detection and processing take place in units 20c3 and 20c4). One side of the mirror may optionally be etched to optimize the collection of scattered light.

Tap-off network monitor

For dynamic reconfiguration channel assignment (“wavelength monitoring”), the network requires feedback of channel usage, and this reconfigurability is particularly necessary for metropolitan optical networks (MONs).

Network monitoring is a 1-D or 2-D superdiffraction where a portion of the input light (typically small in design) is removed, separated and sent to separate channels in accordance with the spirit of the present invention (FIG. 21 is an embodiment of a 2D network monitor). This can be done using a grid. Separated channels are focused on detector array 212, where the power is measured and information is converted into a single electrical signal. This signal may be processed by the processor 214 and transmitted over an electrical network to a monitoring base (not shown) in a metropolitan network to provide diagnostic data to facilitate wavelength monitoring, or to troubleshoot To show where you are losing power, to generate load statistics, and to measure fault tolerances.

Multiwavelength Equalizer and Gain Smoothing Filter

For optimized functionality, optical networks typically require wavelength channels to have balanced power. Balancing typically occurs within or following the amplification step, and is correspondingly called "gain smoothing" or "equalization", respectively. The power balancing element may additionally function to suppress undesirable signals such as pump wavelengths in the optical amplifier.

Dynamic multiwavelength equalizer

In this equalizer embodiment, dynamic equalization is accomplished by routing the input wavelengths through a branch network monitor (FIG. 22A) that separates the channels and monitors their respective power levels (see FIG. 22B showing the curve of power versus wavelength). Can be achieved. The signals are passed to an electronic processor, the output of which equalizes power over the channels by tuning (or programming) the sequence of BSGs and removing power in various wavelength bands, for example. 22C shows an example of power removed as a function of wavelength. Suitable methods for cutting wavelength power include using BSG to couple input channels to the output waveguide at low efficiency or using BSG to impose higher scattering losses. 22D shows the result of subtracting an appropriate amount of power from one set of wavelength bands to produce substantially equivalent power in each band.

One embodiment employs a series of BSGs including "basis functions" that can be tuned independently to achieve the loss spectrum required for equalization, with the appropriate base functions being a step-shift that can be shifted relative to each other. Includes similar spectra

Gain smoothed optical amplifier

23 illustrates another channel balancing embodiment. In this embodiment the BSG 23-1 (FIG. 23A), which shapes the gain spectrum into the desired shape, is integrated directly into the amplifier. The gain spectrum (not shown as not perturbed in FIG. 23B) may be smoothed and possibly tailored to any other profile in anticipation of wavelength dependent losses following amplification. FIG. 23C shows a loss factor spectrum matched to the gain spectrum of FIG. 23B. Figure 23d shows the combined gain factor spectrum, which combines the gain of the medium with the losses imposed on it. It should be noted that this embodiment provides much greater efficiency than typical post-amplification equalization, which is useful in recognizing that smoothing the gain coefficient (gain per unit length in the amplifier) is much less power consuming than post-amplification gain smoothing. Result.

Gain smoothing in accordance with the teachings of the present invention is applicable to any optical amplifier, including Raman amplifiers, erbium doped fiber amplifiers (EDFAs), and semiconductor optical amplifiers (SOAs), as well as multi-wavelength light sources such as tunable lasers. Can be applied.

Gain smoothing not only improves efficiency, but also greatly expands the amplifier bandwidth, especially when the original gain spectrum has a strong peak. This is especially true for semiconductor optical amplifiers (SOAs) where the bandwidth is too narrow to provide only a very small (usually) gain.

Lambda router

Lambda routers-also called wavelength routers-or optical cross-connects. Devices located at the junction of a network that route wavelength (s) from one fiber-optic input side to another. Lambda routers are typically NxN devices (ie, there are N input fibers and N output fibers), and typically each input fiber carries a single wavelength channel.

In the lambda routing embodiment of the present invention, lambda routing may be performed by coupling the demultiplexed input from the BSG based device to the waveguide array, as shown in FIGS. 24A and 24B (ie, one channel per waveguide). . It should be noted that Figures 24A and 24B represent lambda routers when there is one input / output fiber and crossbar switches when there are multiple input and output fiber.

A second waveguide array is below the first set, and each pair of top waveguides and bottom waveguides is separated by a BSG with a flat top spectrum centered at the channel wavelength (ie, forward or reverse coupling). Crossbar operation (i.e., coupling channel light on one waveguide to the other waveguide, vice versa, or staying in the same waveguide) is achieved by locally tuning the BSG to be in alignment with or away from the alignment of the channel wavelength. Is achieved.

In FIG. 24B, the grid-shaped router receives multiplexed inputs on the left side, with one or more incident wavelengths on the channel in the lower waveguide. At each intersection, a bandpass BSG couples the wavelengths in a particular channel into the waveguide in the upper waveguide that extends vertically in the figure. The result is that λ _{i, j} (wavelength lambda with the wavelength of the jth channel entering the ith waveguide) is combined with radiation of the same channel from the other input.

FIG. 24A with the same topology as shown in FIG. 12 is a more efficient arrangement for obtaining the same result.

Dispersion-slope compensator

Optical networks generally have struggled with the property of dispersion, especially when interfering with long transmission distances and high bit rates. Dispersion is due to the wavelength dependence of the effective refractive index, which in turn creates a wavelength dependent group delay spectrum for a given type and length of optical fiber. This spectrum of optical pulses is inevitably finite in width (ie, non-zero), and therefore the dispersion spreads as a pulse traveling along the optical fiber since the various wavelength components will progress at slightly different rates.

Dispersion compensation can be performed by "chirping" the Bragg diffraction grating. That is, as shown in FIG. 25, the pitch of the diffraction grating is modulated along the length z. FIG. 25A illustrates an embodiment in which a chirped diffraction grating is coupled with a circulator. The radiation is directed towards the diffraction grating, processed and returned to the circulator. 25B shows a delivery optical fiber design. FIG. 25C shows a reverse BSG in which the diffraction grating performs chipping while coupling two optical fibers. 25D shows the forward design. These designs produce a wavelength dependent phase spectrum that can be tailored to the desired group delay spectrum: τ _g = -dφ / dω. The delay at a given free space wavelength λ _{0 then follows} from the round trip distance where the local pitch has λ ₀ as the Bragg wavelength: τ _g (λ ₀ ) = 2n _eff z (λ ₀ ), where z (λ ₀ ) Is the spatial coordinate where Λ (z) = λ ₀ / 2n _eff .

The distributed embodiment of the present invention begins by determining the ideal (analog) input chirping function derived from the group delay spectrum τ _g (λ ₀ ) (as opposed to the delay imposed by the diffraction grating). The ideal analog profile is input to a quantization filter to create a binary profile that mimics the desired phase characteristics. The quantization filter can be further optimized for minimizing phase noise.

Other distributed embodiments derive more directly from the desired group delay spectrum.

It should be appreciated that this type of embodiment is very diverse. One embodiment is a three-port circulator that directs light entering port 1 to the waveguide via port 2 (light entering port i is at port i + 1 and port 3 “turns” to port 1). It includes. In accordance with the teachings of the present invention, the reflective BSG enables the desired compensation group delay spectrum in the waveguide, thereby causing the dispersion compensated light to return to port 2 of the circulator and then appear at output port 3.

Another embodiment shown in FIGS. 26A and 26B employs a forward and / or reverse BSG coupler to avoid the need (and cost thereof) of the circulator, where the BSG coupler directs light from the input waveguide to the subsequent waveguide (s). To couple the desired group delay spectrum. Depending on factors such as compensation bandwidth, temporal extension of the group delay spectrum, and whether the compensation is full band or channelized, the device internal propagation length may exceed the desired maximum device size. In this case, dispersion compensation is effected by continuous waveguide coupling arranged in the form of a winding cascade in which the coupled waveguide is wound.

The BSG-based dispersion compensator embodiment employs a complex chirping function in current methods (current methods deal with consecutive terms in Taylor evolution of the dispersion characteristic, or with a relatively small input parameter, It should be noted that it offers many advantages, such as emulating in a simpler form than "get the most suitable". Embodiments using the BSG element in accordance with the teachings of the present invention may also provide dispersion compensation that is individually tailored to multiple simultaneous channels, provides an improvement to the solution, and imposes the same correction across all channels. In addition, in contrast to the approach of the chirped diffraction grating, embodiments using BSG devices in accordance with the teachings of the present invention may be designed to have a flat in-channel reflectance spectrum.

Tunable Dispersion Compensator

Tunable dispersion compensation can be achieved through the configuration similar to the combination of the series connection of the forward and reverse BSG described above, and through the Vernier tuning technique described above, and also with the dynamic multi-wavelength equalizer described above. Referring to FIG. 26A, the series connection of the BSG includes a group delay "basal function" that can be tuned independently of the other to achieve the desired group delay spectrum.

One embodiment shown in FIG. 26B employs two tunable reverse BSG couplers, each implemented with a second order variance function D ₁ and D ₂ of the form:

D ₁ = a ₁ (λ-λ ₁ ) ² + C ₁ and D ₂ = a ₂ (λ-λ ₂ ) ² + C ₂

Wherein the central wavelengths λ ₁ and λ ₂ can be independently shifted along the tuning mechanism as described above. If the BSGs are connected in series and are designed such that a ₂ = -a ₁ , then the resulting variance is:

D _net = D ₁ + D ₂ = [2a ₁ (λ ₂ -λ ₁ )] λ + [(λ ₁ ² -λ ₂ ² ) + (C ₁ -C ₂ )], and Δλ = λ ₂ -λ _If you rearrange it using ₁ ,

D _net = [2a ₁ (Δλ)] λ + [(2λ ₁ + Δλ) (2λ ₁ -Δλ) + (C ₁ -C ₂ )]

Therefore, the dispersion gradient 2a ₁ (Δλ) can be adjusted as desired by appropriately selecting Δλ, and the intercept is determined by appropriately setting λ ₁ . This approach can be applied by optionally employing a higher order variance basis function even for higher order variances.

Variable-feedback superdiffraction lasers (tunable and / or multiwavelength)

27A-27C, an embodiment of a variable feedback super diffraction grating laser is shown. In this embodiment a programmable BSG is combined with an optical gain medium to produce a tunable single wavelength or multiwavelength laser. In FIG. 27A, two programmable BSGs may resonate at one or more wavelengths. In FIG. 27B, the programmable BSG diffraction grating in the gain medium can also control the output spectrum and its power distribution. In FIG. 27C, programmable BSGs can change wavelength and angle so that the wavelength and phase of the output radiation can be controlled.

Any configuration employing a diffraction grating as a feedback element, including but not limited to DBR, DFB, alpha-laser, and ring oscillator configurations, may, in accordance with the teachings of the present invention, be part or equivalent of the diffraction element (s) in a traditional design or It can be updated by replacing everything with a programmable BSG.

In a single wavelength laser embodiment, the BSG-based device can adjust the position of the laser line, its line width, and / or its intensity. In addition, a feedback system can be formed in conjunction with the monitoring of the parameters described above to control one or more of the parameters.

The BSG design (or “program”) can be modified to produce a multiwavelength laser in another similar configuration, to control each of several laser wavelengths independently or to select a single wavelength. The lasing channels can be independently tuned, added or dropped, and their relative output power can be balanced as desired. As mentioned above, monitoring may be added to form a feedback loop to control any of these parameters.

Beam combiner (inverse of beam splitter)

The beam combiner as an embodiment receives inputs from one or more light sources and streams and outputs them as a common output, as shown in FIG. 28. In FIG. 28A, a continuous BSG coupler adds power at one or more wavelengths to power flowing from left to right in the horizontal waveguide. In FIG. 28B, the two-dimensional BSG receives three inputs and radiates along the waveguide. Applications that include a combination of power from multiple lasers ("power combiners" in this context) can achieve sufficient pump power, for example, as performed with Raman amplifiers. In this case it is desirable to integrate this device directly with the semiconductor laser array, which BSG is very well suited for this purpose.

Various embodiments are possible, including a combination of one or more BSG couplers and 2D superdiffraction gratings combined with multiple beams (possibly the same wavelength). In the case of a 2D superdiffraction grating, this essentially corresponds to the inverse of dividing one input into multiple output beams.

Multiwavelength / Wideband Separator / Circulator

An optical splitter is a device that blocks the passage through a waveguide of one or more wavelengths in one or two directions. They are used to suppress back reflection, crosstalk, and / or unwanted wavelength bands (such as pump wavelengths).

The circulator is an N-port element that routes incident light from port i to port (i + 1) and "returns" input to port N to port 1, which often causes the output to come out of the input port (e.g., optical delay). Particular examples of lines, dispersion compensators, and lambda routers).

29A, 29B and 29C show schematic diagrams of a BSG based separator embodiment and a four port coupled waveguide circulator, respectively. Both separators and circulators employ some means of overturning time-reversal symmetry. That is, light traveling through the device in one direction is treated differently from light traveling in the opposite direction. This is accomplished by using magneto-optical and / or optically active materials (such as Faraday rotors), in conjunction with birefringent and / or polarizing elements.

FIG. 29A shows the separator where, for example, radiation entering the polarizer on the left is rotated by 45 degrees through the Faraday rotor and passes through the second polarizer. Radiation entering to the left is polarized, rotated by the rotor and blocked by the second polarizer.

FIG. 29B shows an example of a circulator in which radiation entering port 1 on the right is rotated (eg 45 degrees) by the rotor, reflected back and rotated back on port 3 and directed to port 2 through the splitter.

29C shows an example of a rotor that can be used with the aforementioned or other devices. The radiation incident to the left of the upper waveguide is coupled to the lower waveguide by the BSG coupler in the presence of the Faraday material and thus the polarization direction is rotated.

Superdiffraction gratings in accordance with the teachings of the present invention can be combined with magneto-optical materials and / or polarizers to provide wavelength selective operation on preselected channels, or to create separators and circulators over broad wavelengths.

BSG Photonic Band Gap Material

An important advance in optical theory over the last few decades is the concept of photonic band gap (PBG). The fact that two- or three-dimensional periodic modulation of the refractive index of a material can produce a range of wavelengths in which no light can propagate, regardless of direction, has proved to be rich in applications. Applications include micro dot lasers, sharp turns of waveguides, high-Q optical filters, wavelength selective optical couplers, and the like.

Nevertheless, PBG is essentially a two or three dimensional extension of the Bragg diffraction grating. The BSG concept of Bragg diffraction grating into the wavelength space can be combined with PBG to create a whole new class of optical materials.

A very advantageous feature of the BSG-PBG material may be that it leaves away from the high specific refractive index differences required by conventional PBG materials. If implemented as a periodic grating of refractive index features, conventional PBGs show different periodicities in different directions. Each direction is thus characterized by a different effective Bragg diffraction grating, each of which in turn relates to a particular band gap-the wavelength range in which propagation is prohibited in that direction as a result of the diffraction grating. The width of this wavelength gap is directly proportional to the intensity of the effective diffraction grating, which in turn corresponds to the specific refractive index difference of the PBG. However, in order to inhibit the propagation of a particular wavelength in all directions, thus forming a "full" band gap that defines the PBG, all individual wavelength gaps must overlap at the wavelengths in question, and thus to those skilled in the art It is known that a minimum specific refractive index difference should be imposed on the PBG.

FIG. 37 shows a hexagonal configuration of points representing regions having different refractive indices in FIG. 37A. 37B shows the corresponding hexagon in wavenumber space. Those skilled in the art will appreciate that the common material exhibiting the PBG effect is normal in its geometric composition to outline its shape in wavenumber space. In FIG. 37B, for example, the hexagonal array of points in FIG. 37A is reflected in hexagon in k space. In order to suppress radiation propagation in all directions (of any wavelength represented by dashed circles), the thickness of the hexagon in k-space must therefore be such that the circle representing the relevant wavelength can fit within the band gap hexagon. do. This requirement imposes the need for unnecessary band gap suppression. For example, in FIG. 37B, since the dotted line is inside the corner, the outer region of the hexagonal corner is not necessary. Similarly, areas in the center are not needed because the dotted line is outside of the area edge.

Unlike conventional PBGs, BSGs are not limited to periodic gratings and nested periodic directional strains. Instead, a two or three dimensional BSG can be designed that exhibits an effective period of almost any band in any direction. This corresponds directly to the control for that diffraction spectrum of the one-dimensional BSG. The freedom of this design eliminates the dependence of the diffraction grating on the specific refractive index difference, thickening the individual band gaps until they overlap. Instead, the refractive index change pattern can be set to reinforce the refractive index pattern of the band gap which geometrically results in an overlap in the first position. Any extra intensity provided by the available refractive index difference can be applied to subject more wavelengths to the PBG effect. FIG. 38 shows aperiodic arrangements of pixels providing suppression of transmission in a particular wavelength range in any direction with the utilization of more economical resources in FIG. 38A. The angle dependence of the pixel pattern is set such that the dotted line (same as the dotted line in FIG. 37) stays within a smaller and more uniform margin. If desired, the margin of FIG. 38 can be increased to cover a larger wavelength range.

Thus, for a given refractive index modulation technique (eg ion implantation), the BSG-PBG material may block a larger wavelength range than conventional PBG materials.

In addition, the new material according to the invention can block radiation in the first wavelength range and handle radiation in one or more other wavelength ranges within the same region-for example, deflection against radiation in the resulting wavelength band, When pumping is blocked while focusing.

The significant reduction in the required specific refractive index difference provided by BSG-PBG synthesis may overcome major practical problems in PBG fabrication. However, this reduction requires another cost. That is, the lower refractive index diffraction grating also contains a longer required response length as a path through which the diffraction grating affects light. However, this is also true for PBGs, where the effect is an important consideration in some applications, but in many other applications it may have been significantly alleviated, overcome, or proved to be efficient.

BSG can do more than simply improve on practicality in the implementation of PBG. For example, BSG shows several photonic band gaps and allows materials that derive directly from the ability to emulate some of the superimposed diffraction gratings that fueled our first quest. Such materials can be useful in many applications, wavelength converters, as well as applications that mainly employ multiple light wavelengths, such as systems with separation pumps and signal wavelengths. More generally, the BSG enables complete control over the optical band structure, including the optical gap and position of the band gap as well as the optical density and dispersion relationship of the states.

Figure 39 shows a cross section of a high efficiency solar cell or other photodetector using PBG material in accordance with the present invention. Substrate 39-10 is a conventional material that exhibits a photoelectric effect, such as silicon. Layers 39-20 are materials that normally allow propagation of light of associated wavelengths. According to the present invention, the BSG-PBG pattern is engraved on the material 39-20 to suppress propagation in the transverse direction indicated by arrows 39-17. If there is radiation propagating in the transverse direction it is scattered by the BSG-PBG pattern and preferentially wound up and scattered with a vertical component (eg according to arrow 39-15). More of the incident light is thus absorbed by the photoelectric material 39-10.

40 shows an array of PBG materials 40-1 arranged in a customary pattern. Two dots 40-2 of the pattern were removed and a pair of micro dot lasers were constructed (ordinary pump radiation was omitted for clarity). As many micro dot lasers as desired can be arranged in any desired geometric layout.

41 is a top view of BSG-PBG material 41-5 that blocks radiation in the associated wavelength range. The BSG pattern does not extend to the waveguide 41-10, allowing passage of radiation in that wavelength range. A curve with a curvature radius R of less than the normal limit, i.e. the reference value, was formed in the waveguide. Those skilled in the art will appreciate that in conventional materials, excessive amounts of scattering occur when passing a curve with a radius of curvature less than the reference value. BSG-PBG materials allow the formation of waveguides with little loss.

42 shows a pair of waveguides 42-10 and 42-12 formed in the BSG-PBG material 42-5. As an optional feature, the region 42-25 between the two waveguides was provided with BSG-PBG material 42-25 having a longer attenuation length at the wavelength transmitted by the waveguides 42-10 and 42-12. Thus, coupling between waveguides can be easily achieved. No other material is required and the same material may be used at appropriate intervals between waveguides (or BSG-PBG material between waveguides may be omitted).

As an additional option, there is no need for a general provision of the PBG and a PBG can be placed between the waveguides 42-10 and 42-12. The material between the two waveguides can be made to allow coupling between the waveguides. For example, the PBG pattern does not allow propagation in a direction parallel to the waveguides, and allows propagation (ie, coupling) between the waveguides.

The above is an example of a directional PBG material, which means that a material having a pixel pattern suppresses propagation in a wavelength band only in a selected direction.

43 is a plan view of a unit employing a nonlinear effect. Squares 43-05 represent regions of material engraved with a PBG pattern that exhibits a nonlinear effect and also inhibits propagation at wavelengths λ ₁ , λ ₂ and λ ₃ . In this example, λ ₁ and λ ₂ propagate along the waveguides 43-10 and 43-15 at the pump wavelength, respectively, and λ ₃ propagates along the output waveguide 43-20 at the output wavelength of the associated nonlinear reaction. The initial portion of the waveguide 43-20 can be used as an optional waveguide in this device to supply input radiation, for example at λ ₃ , which will add to the result of the nonlinear reaction.

The radiation at λ ₁ and λ ₂ , as known by the prior art, is combined in the overlapping region to produce radiation at λ ₃ . The PBG pattern outside the waveguide defines the radiation. In region 43-12 of waveguide 43-20, pixel patterns 43-26 focus output radiation to a point as shown. Area 43-25 of waveguide 43-20 reflects radiation at the output wavelength, directing it in the required direction (upper in the figure) and not wasted. If desired, or required by limited resources, the PBG pattern on the left, referred to as 43-07, is set to limit the emission of λ ₁ and the pattern on the right, referred to 43-06, is set to limit the emission of λ ₂ and , λ ₃ can be limited to j8rm only in the pattern in the region 43-12. Thus, the capacity of the (limited) PBG pattern will be preserved for use only where needed.

It should be understood that the above description is only for explaining the present invention. Various alternatives and modifications may be suggested by those skilled in the art without departing from the present invention. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as fall within the scope of the appended claims.

Claims (62)

A first waveguide and a second input port of said waveguide comprising at least two waveguides in a propagation layer of at least one diffraction grating material and carrying input radiation from the first input port to output radiation exiting the first output port A second waveguide of the waveguides carrying input radiation from the first output port and output radiation propagated along a corresponding waveguide from one of the first and second input ports; An optical element comprising one or two-dimensional (binary) superdiffraction gratings in a modulating layer of diffraction grating material for coupling to another of the second waveguides. The second waveguide coupler of claim 1, wherein the one or two-dimensional super-diffraction grating couples the input radiation in the first waveguide traveling in the first direction in a second direction substantially parallel to the first direction. Device for ringing. The second waveguide coupler of claim 1, wherein the one or two-dimensional super-diffraction grating couples the input radiation in the first waveguide traveling in the first direction in a second direction substantially opposite to the first direction. Device for ringing. The center and high refractive indexes of claim 1, wherein the first and second waveguides are symmetrical, and the one or two-dimensional super-diffraction grating has a first pattern having a high refractive index and a low refractive index between the first and second waveguides. By including a first refractive index and a second outer portion having a second pattern opposite to the first pattern as a low refractive index pattern, the one or two-dimensional super-diffraction grating suppresses rear reflection inside the first and second waveguides. Device characterized in that. The device of claim 1, wherein the two-dimensional superdiffraction grating comprises an array of controllable means in response to a set of control signals, the array being configured to determine the refractive index value of the mode in the corresponding pixel in the array. A first mode coupling the input radiation in the first waveguide traveling in one direction to the second waveguide traveling in a second direction substantially parallel to the first direction and the device traveling in the first direction And modifying the input radiation in the first waveguide in at least two modes including a second mode for coupling the second waveguide traveling in a second direction substantially opposite the first direction. 6. The method of claim 5, wherein the one or two-dimensional super-diffraction grating is any one of N different wavelengths between the first and second waveguides in the first and second modes in response to a corresponding value of the control signal. By including an array of controllable means responsive to a set of control signals provided to switch radiation, the device emits radiation in any one of N wavelengths from any of the input ports to the output ports. Can be controlled to pass through to form a wavelength dependent superdiffraction 2x2 coupler. 2. The apparatus of claim 1, wherein the one or two-dimensional superdiffraction grating comprises an array of controllable means in response to a set of control signals, the array having the refractive index values in corresponding pixels in the array. Modifying within at least two modes including a first mode of coupling input radiation in a first waveguide to the second waveguide and a second mode of coupling the input radiation in the second waveguide to the first waveguide. A device characterized by the above-mentioned. 8. The method of claim 7, wherein the one- or two-dimensional superdiffraction grating has any one of N different wavelengths between the first and second waveguides in the first and second modes in response to a corresponding value of the control signal. By including an array of controllable means responsive to a set of control signals provided to switch radiation, the device emits radiation in any one of N wavelengths from any of the input ports to the output ports. Can be controlled to pass through to form a wavelength dependent superdiffraction 2x2 coupler. A set of wavelength dependent superdiffraction couplers arranged to accept radiation coming within an input wavelength range and to couple radiation entering any of the N input ports to any of the M output ports, An NxM system for controllably directing radiation from any one of the N input ports to any of the M output ports, the first row of N / 2 input couplers, the M / 2 coupler And a set of intermediate mixing couplers for coupling the radiation from one or more couplers of the last row and the preceding row to one or more couplers of the next row. 10. The set of claim 9, wherein said one or two-dimensional superdiffraction grating is provided to switch any one of N different wavelengths between said first and second waveguides in response to a corresponding value of said control signal. By including an array of controllable means responsive to a control signal of the element, the device can be controlled to pass radiation in any one of N wavelengths from any of the input ports to any of the output ports. And forming a wavelength-dependent superdiffraction grating crossbar coupler. An apparatus for receiving optical radiation of N input wavelengths and dividing it into N physically separated channels, An input channel, a set of wavelength dependent superdiffraction couplers connected in series with the input channel, each of the set of couplers configured to couple radiation in an emission band from the input channel to an output channel device. 12. The device of claim 11, wherein each of the couplers handles a single one of the radiation of the N channel. 12. The device of claim 11, wherein at least some of the couplers handle radiation of channels in one region and subsequent couplers complete the process of separating each of the N channels. An apparatus for receiving optical radiation of N input wavelengths and dividing it into N physically separated channels, An input channel, a device comprising a two-dimensional wavelength dependent superdiffraction adapted to deflect radiation of different wavelengths and to direct the deflected radiation to a set of output channels. 15. The method of claim 14, wherein the one- or two-dimensional wavelength-dependent superdiffraction deflects radiation at an angle that depends on the wavelength so that it is away from the direction of input travel and focuses the radiation into a set of waveguides for each wavelength channel. Device to be made. A device for processing optical radiation within a set of wavelengths, the device comprising a set of waveguides having at least one input port and at least one output port, wherein the radiation input beam traveling over the input waveguide is inside the input waveguide. Or through at least one wavelength dependent superdiffraction coupler coupling an outer selected wavelength band, wherein the remaining optical beams in the input waveguide have wavelength bands added or subtracted by the selected wavelength band. 17. The device of claim 16, wherein the wavelength dependent superdiffraction coupler adds radiation from a second input port to the input beam. 17. The device of claim 16, wherein the wavelength dependent superdiffraction coupler subtracts radiation within the wavelength reduction range from the input beam. 17. The method of claim 16, wherein at least two superdiffraction couplers are connected in series, wherein the first superdiffraction coupler controls the first wavelength range and the second superdiffraction coupler controls the second wavelength range. Element. A device for monitoring the intensity of radiation in a waveguide, An input waveguide capable of containing radiation within a selected wavelength range; And A wavelength dependent superdiffraction grating whose radiation is intercepted in the waveguide and deflecting a portion of the radiation to a radiation meter responsive to the power of the radiation impinging upon it, the magnitude of the deflected radiation being measured as the magnitude of the radiation traveling inside the waveguide. A device comprising a coupler. An optical element for changing an input power spectrum of an input beam and converting the input beam into an output beam having an output power spectrum, A set of N controllable wavelength sensing power removal modules for removing a controllable amount of power within a wavelength range from the input beam, thereby subtracting power at a selected wavelength range to thereby reduce the output power spectrum to the output power spectrum. The optical element that is converted to. An optical amplifier comprising a gain medium that receives an input beam having an input power spectrum and increases its energy to form an output beam having an output power spectrum. And a power control unit for removing a controllable amount of power within at least one wavelength range from the input beam, wherein the input power spectrum can be adjusted such that the output power spectrum has a desired profile. An array of waveguides arranged on a grid comprising a set of input waveguides for receiving multiplexed inputs, At least one wavelength that intersects a set of output waveguides, each of the input waveguides having a series of wavelength dependent superdiffraction couplers, each of the couplers output radiation corresponding to radiation of a selected output wavelength range; By coupling into an array of waveguides, the radiation coming in with a plurality of wavelengths on the input waveguide is classified into a set of output waveguides each carrying an output wavelength range. The device of claim 23, wherein at least some of said output wavelength ranges cover a single wavelength channel. An optical element for generating an output beam by receiving an input beam having an input wavelength dependent group delay spectrum and applying a compensation group delay spectrum, An input port for receiving the input beam; At least one wavelength dependent supergraft grating for imposing a compensation wavelength dependent delay on the radiation traveling therethrough; And Device containing an output port. 26. The apparatus of claim 25, wherein the input port is coupled to an optical circulator that couples input radiation to a reflective superdiffraction grating, wherein the superdiffraction grating reflects back radiation to the circulator and the wavelength dependent delay is engraved thereon. Device characterized in that. 27. The device of claim 25, wherein the input port is a first end of a first waveguide with a transmissive superdiffraction grating, through which the radiation passes the radiation to the second end of the first waveguide and the wavelength dependent delay. An element characterized by engraved thereon. 27. The device of claim 25, wherein the input port is connected to a reflective superdiffraction grating, the superdiffraction grating being in a second direction substantially opposite the first direction for input radiation in the first waveguide traveling in the first direction. Coupling to an advancing second waveguide, wherein the wavelength dependent delay is engraved thereon. 26. The method of claim 25, wherein the input port is coupled to a transfer superdiffraction grating, the superdiffraction grating having a second direction substantially parallel to the first direction for input radiation in the first waveguide traveling in a first direction. Coupling to a second waveguide, the wavelength dependent delay being engraved thereon. An optical element comprising an input port for receiving input radiation and directing the radiation onto an array of pixels comprising a superdiffraction grating, Each pixel has a refractive index in a mode selected from a set of refractive index values, the array of pixels collectively processing the incident radiation and directing at least one beam of output radiation to at least one output port, wherein the array of pixels At least partly connected to control means for controllably setting the refractive index value of the mode of the corresponding pixel in response to the control signal, such that the processing applied to the input radiation can be determined by the control signal applied to the control means. . A laser comprising: a gain medium, pumping means for causing reversal in the gain medium and means for resonating optical radiation in the gain medium, The means for resonating radiation in the gain medium comprises at least one array of pixels comprising a superdiffraction grating, each pixel having a refractive index of a mode selected from a set of refractive index values, wherein the array of pixels collectively At least a portion of the array of pixels is coupled to control means for controllably setting the refractive index value of the corresponding pixel in response to the control signal such that a process applied to the input radiation is applied to the control means. Laser that can be determined by a control signal. 32. The laser of claim 31 wherein said superdiffraction grating resonates with radiation with respective losses set by said control signal in at least two wavelength ranges, thereby constructing a power spectrum determined by said control signal. 32. The laser of claim 31 wherein said superdiffraction grating is located outside of said gain medium. 32. The laser of claim 31 wherein said superdiffraction grating is located inside said gain medium. 32. The device of claim 31, wherein the superdiffraction grating is located inside of the gain medium and the superdiffraction grating is capable of directing wavelength dependent lengths through the resonator by directing radiation of different wavelengths along different paths through the gain medium. Laser, characterized in that the building. An apparatus for receiving optical radiation of at least two input wavelengths on at least one physically separate channel and combining them into a single output channel, At least two input channels; A one or two-dimensional wavelength dependent superdiffraction grating that deflects radiation of other wavelengths and directs the deflected radiation towards the output channel. 37. A device according to claim 36, wherein the one or two dimensional wavelength dependent superdiffraction deflects radiation at an angle dependent on the wavelength so as to be away from the direction of input travel and focuses the radiation to a waveguide for the output wavelength channel. . An optical element comprising at least one input port and at least one output port connected to asymmetric optical means having different attenuation in opposite directions, the optical element comprising: And a superdiffraction grating for coupling radiation in the pass band from the input port to the output port. 39. The device of claim 38, wherein the superdiffraction grating couples radiation from the first waveguide traveling in the first direction into radiation running in the first direction in the second waveguide. 39. The device of claim 38, wherein the superdiffraction grating couples radiation from an input waveguide traveling in a first direction to radiation traveling in a second direction opposite to the first direction in the output waveguide. 41. The device of claim 40, wherein the input waveguide and the output waveguide are the same. 41. The device of claim 40, wherein the input waveguide and the output waveguide are physically separated. An optical element comprising at least one input port and at least one output port connected to asymmetric optical means having different attenuation in opposite directions, the optical element comprising: And a superdiffraction grating coupling the radiation sequentially in the pass band from the input port to the next port. 10. An optical element comprising an input port and an output port disposed along an optical axis and connected to a superdiffraction grating, said superdiffraction grating coupling radiation from an input port to an output port in a pass band, And a set of two transversely extending transverse pixels representing an analog profile forming a wavefront design set. 46. The device of claim 45, wherein the pixels of the superdiffraction grating are controlled by controllable means for changing the refractive index values of corresponding pixels of the array in response to a set of control signals. At least one waveguide in a first propagation layer of diffraction grating material, and an input propagating from a first port of the first propagation layer, carrying input radiation from the first input port to output radiation exiting the first output port A quantization formed within the modulating layer of diffraction grating material for coupling radiation to at least one other propagation layer disposed at a location different from the first propagation layer along a third dimensional axis, the quantization formed therein for processing the radiation. Superdimensional diffraction grating having pixelated pixels; And Means for directing the processed radiation towards the first output port. A material comprising a layer of optically propagating material in a reference plane that transmits radiation in one wavelength range, the material having a refractive index change pattern engraved therein to suppress propagation within the reference plane, the refractive index change pattern being an analog refractive index. A material characterized by digitizing from a profile. 48. The material of claim 47, wherein the refractive index change pattern is modified to allow propagation of radiation in a defined region and in a defined direction in the wavelength range. 48. The material of claim 47, wherein by being disposed on a substrate of photovoltaic material, propagation of radiation impinging on the photoelectric material is readily compared to propagation of radiation that does not impinge on the photoelectric material. 48. The method of claim 47, wherein the excited emission at the laser wavelength is within the localized region by having at least one localized region capable of causing a laser response at the laser wavelength and allowing propagation of radiation at the laser wavelength. A material, characterized in that it is limited to resonate at. 48. The material of claim 47, wherein a waveguide is included in the absence of the refractive index change pattern such that radiation propagates within the waveguide, wherein the waveguide follows a curve having a curvature radius less than a reference value. . 48. The material of claim 47, comprising two waveguides between the separation regions therebetween, the separation regions having the ability to propagate radiation at least within attenuation lengths. 53. The material of claim 52, wherein the isolation region has a refractive index change pattern that allows propagation within a greater attenuation length than separation between the waveguides. 48. The method of claim 47, wherein: the material supports a nonlinear reaction between two input wavelengths producing radiation of an output wavelength and the refractive index change pattern inhibits propagation of the two input wavelengths and output wavelengths; And And at least one waveguide formed within the material for propagation of the input and output wavelengths. A method of forming a two-dimensional superdiffraction grating in a modulation layer of diffraction grating material to convert input radiation propagating from an input light source through a propagation layer of diffraction grating material into output radiation exiting the at least one output path from the diffraction grating. To Generating, in the modulation layer, a two-dimensional analog refractive index profile that implements a transfer function associated with electromagnetic fields of input radiation and output radiation; A pixel having a digitized refractive index value in the modulation layer by digitizing the analog refractive index profile using a two-dimensional technique that preserves Fourier information in one or more regions of the two-dimensional spatial frequency representation of the two-dimensional analog refractive index profile Creating an array of; And Imposing an array of pixels representing the digitized refractive index profile on the modulation layer. The method of claim 55, Selecting a two-dimensional sampling grating of grating pixels; Setting the overall device length and width; The digitizing step includes setting a refractive index value in each grating pixel of the entire sampling grating. 56. The method of claim 55, wherein digitizing comprises calculating an intermediate sampled index of refraction profile wherein a value at each sampling point of the pleated refractive index profile is determined by the analog index of refraction profile at a corresponding point of the sampling grating. And a refractive index value equivalent. The method of claim 55, Converting a reflectance specification of the transfer function into a Fourier region; Specifying a diffraction grating parameter in the Fourier region; And Determining the analog profile in the spatial domain by converting the diffraction grating parameter into the spatial domain. The method of claim 55, Specifying a phase component of the analog refractive index profile such that the maximum refractive index value of the analog refractive index profile is minimum. A method of forming an effective one-dimensional superdiffraction grating in a modulation layer of diffraction grating material to convert input radiation propagating through the propagation layer of diffraction grating material from an input light source along an axis to output radiation exiting from the diffraction grating. To Generating, in the modulation layer, a two-dimensional analog refractive index profile that implements a transfer function associated with electromagnetic fields of input radiation and output radiation; Digitize the analog refractive index profile using a two-dimensional technique that maintains Fourier information within one or more regions of the two-dimensional spatial frequency representation of the two-dimensional analog refractive index profile to produce an array of pixels having a digitized refractive index value in the modulation layer. Generating; And Imposing an array of pixels representing the digitized refractive index profile on a portion extending a lateral distance from the axis of the modulation layer. A method of forming a three-dimensional superdiffraction grating in a modulator of diffraction grating material to convert input radiation propagating through an diffraction grating material from an input light source into output radiation exiting the at least one output path from the diffraction grating, Generating, in the modulator, a three-dimensional analog refractive index profile that implements a transfer function associated with electromagnetic fields of input radiation and output radiation; Digitize the analog refractive index profile using a three-dimensional technique that preserves Fourier information in one or more regions of the three-dimensional spatial frequency representation of the two-dimensional analog refractive index profile to produce an array of pixels having a digitized refractive index value in the modulation layer. Generating; And Imposing an array of pixels representing the digitized refractive index profile on the modulation layer. One or two or three-dimensional superdiffraction gratings in the modulation layer of diffraction grating material to convert input radiation propagating from the input light source through the propagation layer of diffraction grating material into output radiation exiting the diffraction grating in at least one output path. In the method of forming, Creating, in the modulation layer, a one-dimensional analog refractive index profile, P, which implements a transfer function associated with electromagnetic fields of input radiation and output radiation; Generating a filter function H for selecting spatial frequencies, to which spectral information is preserved and assigned weights; Calculating the refractive index profile X of the binary superdiffraction grating in the modulation layer by converting the input radiation into an output radiation by solving an optimization problem represented by the following equation; And (Where X is a vector containing the refractive index values of the binary superdiffraction grating, V is a vector of Lagrange multiplier, L determines the type of optimization, and n _low and n _high are binary superdiffraction gratings, respectively) Low and high refractive index values. Imposing an array of pixels representing the digitized refractive index profile on the modulation layer, whereby the input radiation is converted to the output radiation.