CN1303443C - Array waveguide raster type comb filter - Google Patents

Abstract

The present invention relates to an array waveguide grating type comb filter which has the function of alternately dividing a column of optical wave signals with equidistant frequency into an odd sequence and an even sequence to output from two channels. The optical transmission is formed by a surface optical waveguide which comprises a base, a lower covering layer, a core layer and an upper covering layer, wherein the lower covering layer is mainly made of silicon dioxide material, and the material of the lower covering layer is arranged on the surface of the base. The core layer is mainly made of germanium-doped silicon dioxide material or silicon material, and is arranged on the lower covering layer of the silicon dioxide. A stripe-shaped rectangular waveguide or a ridge waveguide for optical transmission is etched on the core layer, and the surface of the etched core layer is covered with the silicon dioxide material as the upper covering layer. The functions of the upper covering layer and the lower covering layer are to bind optical waves, and the function of the core layer is to transmit the optical waves.

Description

Arrayed Waveguide Grating Comb Filter

technical field

The invention belongs to the technical field of semiconductors, in particular to an arrayed waveguide grating comb filter.

Background technique

With the vigorous rise of the Internet in the world, the amount of information transmitted in the field of communication is increasing at an accelerated rate. To achieve this purpose, there are usually three multiplexing methods, namely space division multiplexing, time division multiplexing and wavelength division multiplexing. Space division multiplexing is to increase the number of channels by laying new optical fibers, and its cost is the highest; time division multiplexing is to increase the number of channels by dividing time, and the potential to be tapped is very limited; and wavelength division multiplexing is through The principle that different wavelengths can be transmitted in the same optical fiber increases the number of channels, which can double the signal transmission. For this reason, under the limited number of optical fiber cables, most communication systems use time-division multiplexing and wavelength-division multiplexing technologies. At present, according to the regulations of the International Telecommunication Union (ITU), the channel spacing of the channels is 100GHz or 200GHz. If you want to expand the original system at a low price, people prefer the optical comb filter (Interleaver), because it can be used without changing On the basis of the original equipment and system, the channel spacing is halved, that is, for the original system with a channel spacing of 200GHz, use 100GHz Interleaver; for the original system with channel spacing of 100GHz, use 50GHz Interleaver, etc. wait. The function of the filter is to divide a column of equally spaced light wave signals into two columns of odd and even channel signals alternately by expanding the channel spacing, that is, demultiplexing; or to multiplex the two columns of signals into one column by reducing the channel spacing. Because Interleaver can expand without replacing the original equipment, it saves expenses. Therefore, Interleaver plays a very important role in upgrading the existing optical communication wavelength division multiplexing system, and at the same time there is a huge market. The optical interleaver currently on the market is: fiber grating type [1, 2], birefringent crystal type [3, 4], Mach-Zehdner (Mach Zahdner) interference type [5, 6], resonant cavity type [7] etc., the following gives a brief introduction to each type.

The fiber grating comb filter is to engrave the template content with a special period into the optical fiber through ultraviolet light, resulting in periodic disturbance of the refractive index along the axis, forming a fiber grating, thereby adjusting the transmitted and reflected light to achieve comb filtering role.

The birefringent crystal comb filter uses the birefringence effect of the anisotropic crystal to distinguish the ordinary light (o) and the extraordinary light (e) passing through it in space. (caused by different refractive indices n(o) and n(e)) and then recombine, through the interference between o light and e light to achieve the purpose of comb filtering different wavelength signals.

There are many forms of Mach-Zehdner interference comb filters, but they are all composed of two 3dB couplings and two arms of different lengths. When the optical signal passes through the first 3dB coupling, it is divided into two equal beams, each of which passes through arms of different lengths to form a phase difference, and then interferes with each other in the second 3dB coupling, so as to achieve the purpose of comb filtering.

The resonant cavity comb filter uses the multi-beam dry radiation of the resonant cavity for frequency selection, and the selected wavelength satisfies the condition of 2d×sinθ=mλ (where d is the resonant cavity spacing, θ is the incident angle in the cavity, and m is positive integer). For example, Michelson interference, Fabry-Perot interference and the like.

Although the above methods have their own advantages and disadvantages, one of the disadvantages is that they cannot be integrated with silicon-based microelectronics. The second is that the future 1×N comb filter can only be formed through multiple cascades, which will inevitably result in excessive insertion. loss. In response to this problem, the comb filter involved in this patent application is prepared based on the principle of arrayed waveguide grating (AWG), which is a flat optical waveguide circuit device, so it can be integrated with silicon-based microelectronics, and can also be Other planar optical waveguide circuit device integration. Not only that, AWG itself is an N×N wavelength division multiplexing device, using its periodicity (one of the four characteristics), it is designed as a 1×N (N=2, 3,...) Interleaver, forming The advantages of one-time filtering in place, such as various favorable conditions such as small crosstalk and uniform output signal strength, and further development can form AWG cascades with periodic characteristics.

Contents of the invention

One of the purposes of the present invention is to provide an arrayed waveguide grating comb filter, which can meet the requirements of a large path difference between adjacent arrayed waveguides and a small size of the device by changing the shape and parameters of the AWG (the path difference ≥0.8mm). To this end, increase the bending curvature of the arrayed waveguide (that is, reduce the bending radius r) so that the bending radius r≤10mm; combine two Roland circular slab waveguides into one to form a closed-loop array waveguide; the periphery of the slab waveguide is composed of four Different arcs are formed. The arcs ab and gh on both sides connecting the input and output waveguides are Rowland arcs, and their curvature radius is half the diameter of the flat waveguide; the arcs cd and ef on both sides of the array waveguide are concave gratings. The radius of curvature is the diameter of the slab waveguide; the angle  between the two central axes is between 10 and 170 degrees.

The second object of the present invention is to alleviate the large angular dispersion in the slab waveguide by adjusting the size of the Rowland circle. Since the angular dispersion (Δθ/Δλ) in this device is much larger than the angular dispersion (≤0.5 degrees/nm) in the usual AWG, for this reason, the distance between the strip waveguide and the flat waveguide is widened to make it between 6~ Between 30 μm; increase the diameter of the Rowland circle so that it is between 1 and 4 mm; in this way, the angular dispersion can be reduced from 5.0 degrees/nm to 1.0 degrees/nm. For the sequence signal of Δλ=0.4nm, the opening angle Δθ of adjacent waveguides on the Rowland circle to a certain point at the center of the grating circle is between 0.4 and 2.0 degrees, Δθ/Δλ≥1.0 degrees/nm).

The third purpose of the present invention is to emphasize the odd-even characteristics of the input and output and the arrayed waveguide. According to the requirements of Interleaver with one input and two outputs, the input waveguides are odd numbers such as 1, 3, 5, and 7, the output waveguides are even numbers such as 2, 4, 6, and 8, and the array waveguides are odd numbers between 7 and 25. strip.

Technical scheme of the present invention is:

An arrayed waveguide grating comb filter, whose function is to alternately divide a column of light wave signals at equal intervals into two columns of odd sequence and even sequence, and alternately divide them into two columns of odd sequence and even sequence, and from the two channels output; characterized in that it includes:

Two overlapping and intersecting Rowland circular slab waveguides;

An array waveguide, the intersection of the array waveguide is the two overlapping and intersecting Roland circular slab waveguides, the input end of the array waveguide is connected to the concave grating output end of the two overlapping and intersecting Roland circular slab waveguides, The output end of the arrayed waveguide is connected to the concave grating input end of two overlapping and intersecting Roland circular slab waveguides;

An input waveguide, the input end of the input waveguide is the input port of the whole device, the output end of the input waveguide is connected with the Rowland circle input ends of two overlapping and intersecting Rowland circle slab waveguides;

The output waveguide, the input end of the output waveguide is connected with the Rowland circle output end of two overlapping and intersecting Rowland circle slab waveguides, and the output end of the output waveguide is the output port of the whole device.

The arrayed waveguides are odd-numbered, respectively connected to the concave gratings of two overlapping and intersecting Roland circular slab waveguides.

The input waveguides are odd-numbered, respectively connected to the Rowland circle input ends of two overlapping and intersecting Rowland circle slab waveguides.

The output waveguides are even-numbered and respectively connected to the Rowland circle output ends of two overlapping and intersecting Rowland circle slab waveguides.

Description of drawings

In order to further illustrate the technical content of the present invention, the following detailed description is as follows in conjunction with the embodiments and accompanying drawings, wherein:

Figure 1 is a functional diagram of an AWG comb filter.

Fig. 2 is a cross-sectional view of the silicon-based dioxygen silicon strip waveguide, where A, B, and C are three processes.

Fig. 3 is a cross-sectional view of the fabrication of a silicon-on-insulator ridge waveguide, where A, B, and C are three process steps.

Figure 4A is a top view of an AWG comb filter, "1" on the right is the input end, "2" in the middle is a slab waveguide as a diffraction area, "3" on the top is a curved array waveguide, and "4" on the left is the output end;

Fig. 4B is part "2" of the central box in Fig. 4A, and the two slab waveguides are superimposed on the same level.

Fig. 5 is a schematic diagram of the arrayed waveguide grating.

Fig. 6 is a numerical simulation diagram of an optical signal with a frequency interval of 50 GHz passing through an AWG comb filter (Fig. 4).

Detailed ways

Please refer to Fig. 1 and Fig. 2, a kind of arrayed waveguide grating type comb filter of the present invention, its function is to alternately divide the light wave signal of a column frequency interval into two columns of odd sequence and even sequence, and output from two channels ; Its optical transmission is composed of surface light guides, including:

a base 10;

The lower cladding layer 11 is mainly made of silicon dioxide material, which is prepared on the surface of the substrate 10;

A core layer 12, mainly germanium-doped silicon dioxide material, or silicon material, the core layer is prepared on the lower cladding layer of silicon dioxide;

On the core layer, the rectangular waveguide 13 or ridge waveguide of light transmission strip is etched, wherein the shape of light transmission strip waveguide 13 is composed of input and output strip waveguides, two Roland circular slab waveguides 1, 4, and curves. The arrayed waveguide is formed by connecting 3 phases, two Roland circular slab waveguides 1 and 4 overlap and intersect to form a closed loop arrayed waveguide, as shown in Figure 4, the bending radius r≤10mm is reduced; the input waveguide is an odd number, and the output waveguide The waveguide is an even number, and the array waveguide is an odd number;

The surface of the etched core layer is covered with silicon dioxide material as the upper cladding layer 14;

The function of the upper and lower cladding layers 11 and 14 is to confine light waves, while the core layer 12 is to transmit light waves.

Please refer to Figure 2, which is a cross-sectional view of the silicon-on-insulator ridge waveguide preparation, which is basically the same as Figure 1, including:

a base 20;

The lower cladding layer 21 is mainly made of silicon dioxide material, which is prepared on the surface of the substrate 20;

A core layer 22, mainly silicon material, the core layer 22 is prepared on the lower cladding layer 21 of silicon dioxide;

An upper cladding layer 14, made of silicon dioxide material, is formed on the core layer 22.

The difference is that the strip-shaped rectangular waveguide 13 etched on the core layer 12 shown in FIG. 1 is etched to the lower cladding layer 11 . As shown in FIG. 2 , the strip-shaped rectangular waveguide 23 for light transmission is etched on the core layer 22 , which is etched to a part of the core layer 22 and then covers the upper cladding layer 14 .

1. Merge Roland circular slab waveguides to form a closed array waveguide

Since the AWG type Interleaver has a large path difference between adjacent array waveguides (≥0.8mm, usually the path difference of AWG≤0.1mm), and the flat optical circuit does not allow a large size, so we increase the array waveguide Bending curvature (decrease the bending radius r, and r≤10mm), when the waveguide is long enough, make two Roland circular slab waveguides intersect and coincide (intersection angle  is between 10 and 170 degrees), forming a closed array waveguide circuit.

Through the above method, it can not only meet the requirement of large path difference between adjacent arrayed waveguides, but also reduce the surface area of the device; at the same time, place the reduced input and output waveguides on both sides (both sides) of the chip, so that the operator can debug with two The stations independently perform accurate measurement and packaging of the die.

2. Slow down the large angle dispersion in the slab waveguide

Adjust the spacing between the strip waveguide on the Rowland circle and the grating circle between 6 and 30 μm, and adjust the diameter of the slab waveguide between 1 and 4 mm, then the angular dispersion Δθ/Δλ in the slab waveguide is 1.0 to 5.0 degrees/nm Between; for the sequence signal of Δλ=0.4nm, the opening angle Δθ of the adjacent input (or output) waveguide on the Rowland circle corresponding to a certain point of the concave grating is between 0.4 and 5.0 degrees. The larger the diameter of the slab waveguide and the wider the waveguide spacing, the smaller the angular dispersion and opening angle.

3. Parity setting of input waveguide, output waveguide and array waveguide

Set the input waveguides as odd numbers such as 1, 3, 5, and 7, the output waveguides as even numbers such as 2, 4, 6, and 8, and the array waveguides as odd numbers between 7 and 25.

Principle Description

1. Arrayed Waveguide Grating (AWG)

The structure of the AWG is shown in Figure 5. It consists of N input waveguides, N output waveguides, two slab waveguides (slab) and waveguide arrays, all of which are integrated on the same substrate. One end of the slab waveguide connected to the input and output waveguides is a Rowland circle arc (indicated by a dotted line), and the other end of the slab waveguide connected to the array waveguide is a concave grating (indicated by a long dotted line). The circle where the concave grating is located is called the grating circle. The whole device is centered on the array waveguide, and the two slab waveguides and the input and output waveguides are symmetrically distributed respectively.

The radius of curvature of the grating circle is the diameter of the Rowland circle. It can be proved that the light from any point on the Rowland circle will be approximately reflected by the grating circle to another point on the circle, and will be diffracted to other focal points on the circle at the same time. Arrayed waveguide gratings operate according to this principle. First, light enters the input slab waveguide from the input waveguide, and diffracts; then, these diffracted waves are absorbed by the array waveguide through the concave grating, and their phases are periodically modulated by the path difference between adjacent waveguides; when these are modulated After the filtered light waves enter the output slab waveguide, they will be focused to different positions of the output Rowland circle with different channel wavelengths, and then output through the output waveguide. Therefore, the demultiplexing process of optical signals containing different wavelengths is realized, and in turn, the optical waves of different wavelengths can be multiplexed.

2. Single slab waveguide in AWG type Interleaver

Since the path difference (ΔL) between adjacent arrayed waveguides in the AWG is inversely proportional to the free spectrum width (FSR), that is, the smaller the FSR, the greater the path difference ΔL. For example, for FSR=200GHz, its ΔL≈0.4mm; for FSR=100GHz, its ΔL≈0.8mm; for FSR=50GHz, its ΔL≈1.6mm. Therefore, under the same signal resolution, the two output Interleavers have the largest ΔL. And as the signal resolution decreases, ΔL will become larger and larger.

The increase of the path difference (ΔL) between adjacent arrayed waveguides will definitely increase the area of the Interleaver device. Therefore, we meet the dual requirements of large path difference and small area by increasing the bending curvature of the arrayed waveguide (that is, reducing the bending radius r, and r≤10mm). When the bending is performed at a large angle and the arrayed waveguide is long enough, the input and output waveguides, or the arrayed waveguide, will intersect. The intersection of strip waveguides will disturb the mode field of light, which will cause energy loss, so the intersection point is determined at the Roland circular plate waveguide, and the intersection angle  is between 10 and 170 degrees, as shown in Figure 4. Since the cross-transmission of light waves does not change its own amplitude and phase, and there is no limitation of the transverse mode field in a slab waveguide, this choice will not have any impact on the input and output signals. On the other hand, two Rowland circular slab waveguides intersect and overlap to form input and output waveguides on both sides of the chip (double sides), which is beneficial to the measurement and packaging of the chip.

3. Optimization of angle dispersion in AWG type Interleaver

The angular dispersion (Δθ/Δλ) in the slab waveguide is proportional to ΔL/d (d is the spacing of the waveguide on the grating circle), so after ΔL is determined, increasing the value of d can slow down the large angular dispersion. On the other hand, the value of d should not be too large. This is not only because increasing the d value will increase the diameter of the slab waveguide in a quadratic relationship, but also increasing the d value must open the horn mouth. There is no fixed mode field in the horn mouth, so an excessively large horn mouth will also increase the insertion loss (IL). Therefore, under specific process conditions, the spacing d of the arrayed waveguides in the comb filter on the grating circle has an optimal value.

4. Setting of waveguide odd and even number in AWG type Interleaver

Since the optical interleaver requires one input and two outputs, the input waveguide should be placed at the zero-order position of the input Rowland circle, that is, on the central axis of the input Rowland circle; the output waveguide should be placed at the ±1-order position of the input Rowland circle ( No zero order), that is, on the symmetrical positions on both sides close to the central axis of the output Rowland circle. From the consideration of process error, it is necessary to fine-tune the system by changing the input waveguide; from the consideration of process stability, it is necessary to add some auxiliary waveguides on both sides of the strip waveguide to protect the central waveguide from damage; therefore, the number of input waveguides It should be increased to an odd number (such as: 3, 5, 7, etc.); the output optical waveguide should also be correspondingly increased to an even number (such as: 4, 6, 8, etc.), that is, there is always a waveguide at the zero-order position of the input Rowland circle There is a waveguide at the position ±1 of the output Rowland circle. In addition, because the diameter of the Rowland circular slab waveguide is small, the diffraction signal is mostly concentrated in the center of the grating circle, corresponding to the zero-order input waveguide, so the number of arrayed waveguides is determined as an odd number.

Figure 6 shows the numerical simulation diagram of an optical signal with a frequency interval of 50 GHz passing through the AWG comb filter (Figure 4), input from the zero-order input end of the input slab waveguide, and output from the ±1-order output end of the output slab waveguide .

Claims (4)

1. An arrayed waveguide grating comb filter, whose function is to alternately divide a column of light wave signals with equal intervals in frequency into two columns of odd sequence and even sequence, and alternately divide them into two columns of odd sequence and even sequence, and from the two Channel output; It is characterized in that, including: Two overlapping and intersecting Rowland circular slab waveguides; An array waveguide, the intersection of the array waveguide is the two overlapping and intersecting Roland circular slab waveguides, the input end of the array waveguide is connected to the concave grating output end of the two overlapping and intersecting Roland circular slab waveguides, The output end of the arrayed waveguide is connected to the concave grating input end of two overlapping and intersecting Roland circular slab waveguides; An input waveguide, the input end of the input waveguide is the input port of the whole device, the output end of the input waveguide is connected with the Rowland circle input ends of two overlapping and intersecting Rowland circle slab waveguides; The output waveguide, the input end of the output waveguide is connected with the Rowland circle output end of two overlapping and intersecting Rowland circle slab waveguides, and the output end of the output waveguide is the output port of the whole device. 2. The arrayed waveguide grating comb filter according to claim 1, wherein the arrayed waveguide is an odd number, respectively connected to the concave gratings of two overlapping and intersecting Loran circular slab waveguides. 3. The arrayed waveguide grating comb filter according to claim 1, wherein there are an odd number of input waveguides, which are respectively connected to the Rowland circle input ends of two overlapping and intersecting Rowland circle slab waveguides. 4. The arrayed waveguide grating comb filter according to claim 1, wherein the even-numbered output waveguides are respectively connected to the Rowland circle output ends of two overlapping and intersecting Rowland circle slab waveguides.

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