WO2011117807A1

WO2011117807A1 - Optical couplers and optically coupled devices

Info

Publication number: WO2011117807A1
Application number: PCT/IB2011/051188
Authority: WO
Inventors: David Brooks; Udi Pariente; Eyal Porat
Original assignee: COLORCHIP (ISRAEL) Ltd
Current assignee: COLORCHIP (ISRAEL) Ltd
Priority date: 2010-03-22
Filing date: 2011-03-22
Publication date: 2011-09-29
Anticipated expiration: 2012-09-22
Also published as: GB201004708D0; GB2478912A

Abstract

Apparatus for multiplexing and demultiplexing optical signals in different wavelength bands respectively into and from a same waveguide formed in an optical substrate, the apparatus comprising: for each of the different wavelength bands, a groove formed in the substrate having a surface in the substrate that intersects the waveguide and reflects light that propagates in the waveguide in the wavelength band and does not reflect light propagating in the waveguide in other of the wavelength bands; for each of at least two grooves in a first group of the grooves, a different source of optical signals that transmits optical signals that are reflected by the groove's reflecting surface into the waveguide; and for each of at least two grooves in a second group of the grooves, a different optical sensor for each groove that receives light reflected by the groove's reflecting surface and generates an output signal responsive to the received light.

Description

OPTICAL COUPLERS AND OPTICALLY COUPLED DEVICES

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims benefit under 35 U.S.C. § 119(a)-(d) of British Application GB 1004708.2 filed March 22, 2010, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to methods and apparatus for optically coupling optical elements.

BACKGROUND

Optical circuits generally comprise discrete optical elements that transmit optical signals to, and/or receive optical signals from, other elements of the circuit. For example, planar light circuits (PLC) often comprise waveguides formed in a glass substrate for transmitting optical signals between optical elements, at least one of which is mounted externally to the substrate. Optical signals from or to the externally mounted optical element are coupled to a waveguide for insertion or extraction by a reflecting surface that intersects the waveguide.

US Patent Publication US 2008/0083699, to some of the same inventors as inventors of the present application, describes forming a reflecting surface in a glass substrate for coupling optical signals to a waveguide in the substrate by forming a groove in the substrate by laser ablating substrate material. The groove is shaped and positioned so that a surface of the groove intersects the waveguide and operates to reflect light from an optical component mounted on a surface of the substrate into the waveguide and/or to reflect light propagating in the waveguide to the optical component. Optionally a reflecting coating is applied to at least a portion of the reflecting surface.

SUMMARY

An aspect of some embodiments of the invention relates to providing an improved method for producing an optical coupler for coupling an optical element to an optical waveguide formed in a substrate. The coupler comprises a reflecting surface that is formed by a groove in the substrate and is covered by an optical "cover plate" that substantially seals the reflecting surface from the environment and protects it from environmental degradation.

An aspect of some embodiments of the invention relates to providing a method for bonding the cover plate to the substrate.

In an embodiment of the invention, the cover plate is adhered to a surface area bordering the groove by first placing the cover plate on the substrate to cover the opening of the groove so that a narrow space separates the cover plate and substrate. A quantity of a bonding agent is deposited along an edge of the cover plate and is drawn into the space between the cover plate and substrate by capillary action to substantially fill the space. The capillary action and surface tension of the bonding agent operate to prevent the bonding agent from flowing into the groove, wetting, and thereby degrading the reflecting surface.

In some embodiments of the invention, a bonding agent flow channel is formed in the surface area bordering the groove to facilitate distribution of the bonding agent throughout the bordering surface and filling of the space between the cover plate and substrate.

Because the groove is sealed from the environment by the cover plate, the reflecting surface generally does not have to be coated with a protective coating to prevent reduction of its reflectivity, which might result from accumulation of environmental dust, dirt, or moisture. Optionally, the cover plate functions as a mounting plate and interfaces the reflecting surface with an optical element that is mounted on the cover plate.

In some embodiments of the invention, the cover plate does not substantially affect light propagating to or from the optical element as it passes through the cover plate from or to the optical waveguide. Optionally, the cover plate is configured to affect light propagating to or from the optical element as it passes through the cover plate from or to the optical waveguide. For example, in some embodiments of the invention, the cover plate comprises a thin film filter, such as a band pass filter.

An aspect of some embodiments of the invention relates to providing an aperture plate for shielding an optical device from effects of stray light. The aperture plate has formed therein an aperture and transmits light to the optical device if the light is incident on the aperture and blocks light incident on the aperture plate from the optical device if the light is not incident on the aperture.

There is therefore provided in accordance with an embodiment of the invention, method of producing an optical coupler configured to insert light into or extract light from a waveguide formed in an optical substrate, the method comprising: forming a groove in the substrate having a surface in the substrate that reflects light that propagates in the waveguide and an opening rimmed by edges on a substrate surface; placing a cover plate having edges on the substrate so that the cover plate covers the groove opening and leaves a narrow space between the cover plate and the substrate ; and depositing a quantity of an adhesive along an edge of the cover plate so that capillary action between the cover plate and the substrate surface draws the adhesive into the narrow space and adheres the cover plate to a surface of the substrate.

Optionally the narrow space between the cover plate and the surface of the substrate has a height separating the cover plate and substrate surface between about 1 micron and 10 microns. Additionally or alternatively, the method optionally comprises forming a channel in the substrate surface that surrounds the groove opening. Optionally, the method comprises covering the channel with the cover plate. Optionally, the method comprises forming at least one feed channel that communicates with the channel surrounding the groove opening so that at least a part of the at least one feed channel is not covered by the cover plate. Optionally, the at least one feed channel comprises at least two feed channels.

In some embodiments of the invention, at least one of the channels has a depth in the substrate surface equal to between about 5 microns and about 15 microns.

In some embodiments of the invention, the at least one channel has a width equal to between about 50 microns and about 250 microns.

In some embodiments of the invention, all of the channels have a substantially same depth. In some embodiments of the invention, all of the channels have a substantially same width. In some embodiments of the invention, the adhesive has a viscosity between about 200MPa-s to about 300MPa-s. In some embodiments of the invention, the surface in the substrate reflects light by total internal reflection.

There is further provide in accordance with an embodiment of the invention, an optical coupler configured to insert light into or extract light from a waveguide formed in an optical substrate, the coupler comprising: a groove formed in the substrate having a surface in the substrate that reflects light that propagates in the waveguide and an opening rimmed by edges on a substrate surface; a cover plate that covers the groove opening and through which light extracted from or inserted into the waveguide passes; a layer of adhesive that adheres the cover plate to a surface of the substrate and is absent from surfaces of the groove; and a channel that lies under the cover plate and surrounds the groove opening. There is further provide in accordance with an embodiment of the invention, apparatus for demultiplexing optical signals propagating in different wavelength bands in a same waveguide formed in an optical substrate, the apparatus comprising: for each of the different wavelength bands, a groove formed in the substrate having a surface in the substrate that intersects the waveguide and reflects light that propagates in the waveguide in the wavelength band and does not reflect light propagating in the waveguide in other of the wavelength bands; and a different optical sensor for each groove that receives light reflected by the groove's reflecting surface and generates an output signal responsive to the received light.

There is further provide in accordance with an embodiment of the invention, apparatus for multiplexing optical signals in different wavelength bands into a same waveguide formed in an optical substrate, the apparatus comprising: for each of the different wavelength bands, a groove formed in the substrate having a surface in the substrate that intersects the waveguide and reflects light that propagates in the waveguide in the wavelength band and does not reflect light propagating in the waveguide in other of the wavelength bands; and a different source of optical signals for each groove that transmits optical signals that are reflected by the groove's reflecting surface into the waveguide.

Additionally or alternatively, the apparatus comprises a different groove for each wavelength band. In some embodiments of the invention, the apparatus comprises a same groove for at least two wavelength bands.

There is further provide in accordance with an embodiment of the invention, apparatus for multiplexing and demultiplexing optical signals in different wavelength bands respectively into and from a same waveguide formed in an optical substrate, the apparatus comprising: for each of the different wavelength bands, a groove formed in the substrate having a surface in the substrate that intersects the waveguide and reflects light that propagates in the waveguide in the wavelength band and does not reflect light propagating in the waveguide in other of the wavelength bands; for each of at least two grooves in a first group of the grooves, a different source of optical signals that transmits optical signals that are reflected by the groove's reflecting surface into the waveguide; and for each of at least two grooves in a second group of the grooves, a different optical sensor for each groove that receives light reflected by the groove's reflecting surface and generates an output signal responsive to the received light.

Optionally, no groove belonging to the first group also belongs to the second group. Alternatively, at least one groove in the first group of grooves optionally belongs to the second group of grooves. Optionally, the apparatus comprises a same optical waveguide coupled to the source of optical signals and the optical sensor associated with the at least one groove along which optical signals from the source propagate towards the groove's reflecting surface and light from the groove's reflecting surface propagates to the sensor. Optionally, the optical waveguide comprises an optical fiber.

BRIEF DESCRIPTION OF FIGURES

Embodiments of the invention will be more clearly understood by reference to the following description of embodiments thereof read in conjunction with the figures attached hereto. In the figures, identical structures, elements or parts that appear in more than one figure are generally labeled with a same numeral in all the figures in which they appear. Dimensions of components and features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale. The figures are listed below.

Fig. 1 schematically shows an optical coupler comprising a cover plate covering a groove formed in an optical substrate, in accordance with an embodiment of the invention;

Figs. 2A-2D schematically show views of the cover plate and grooved substrate shown in Fig. 1 to illustrate adhering the cover plate to the substrate to protect the groove, in accordance with an embodiment of the invention;

Figs. 3A and 3B schematically show a process for adhering a cover plate over a groove using a bonding agent flow channel, in accordance with an embodiment of the invention;

Figs. 4A-4D schematically show an optical coupler coupling an optical element to a waveguide, in accordance with an embodiment of the invention;

Fig. 5A schematically shows the optical coupler coupling an optical element to a waveguide shown in Fig. 4A and stray light that affects operation of the optical element, in accordance with an embodiment of the invention;

Fig. 5B schematically shows the optical coupler and optical element shown in Fig. 4A and an aperture plate for reducing effects of stray light, in accordance with an embodiment of the invention;

Fig. 6A schematically shows a demultiplexer, in accordance with an embodiment of the invention; Fig. 6B schematically shows another demultiplexer, in accordance with an embodiment of the invention;

Fig. 6C schematically shows a multiplexer, in accordance with an embodiment of the invention;

Fig. 6D schematically shows a transceiver, in accordance with an embodiment of the invention;

Fig. 6E schematically shows a multiplexer-demultiplexer, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

Fig. 1 schematically shows a perspective view of an optical coupler 20 comprising a cover plate 22 mounted on a surface 24 of an optical substrate 26 to cover a groove 30, shown in dashed lines, formed in the substrate, in accordance with an embodiment of the invention. Groove 30 has an opening 32 in substrate surface 24 rimmed by edges 34. The groove is bounded by a surface 40, i.e. a "reflecting surface", that intersects a waveguide 42 formed in substrate 26 for propagating optical signals in the substrate from or to an optical component (not shown) coupled to, or formed in, the substrate. Waveguide 42 may be formed using any of various methods known in the art. Optionally, the waveguide is formed by an Ag+ ion exchange process such as described in PCT Publication WO 2006/054302. Groove 30 is formed, optionally using a laser ablation method described in PCT Publication WO 2008/044237. The disclosures of the above noted PCT Publications are incorporated herein by reference.

Groove 30 is formed, so that light propagating along waveguide 42 toward groove 30 is incident on reflecting surface 40 at a desired angle of incidence θχ, schematically indicated for light propagating in the waveguide represented by a wavy arrow 44. 9j is defined by a direction of propagation of light 44 indicated by a line 45, and a normal 46 to surface 40. Optionally, the angle of incidence is greater than the critical angle for reflecting surface 40 so that light 44, upon incidence on the reflecting surface is totally internally reflected, optionally to exit substrate 26 in a direction perpendicular to surface 24. By way of example, assuming that the index of refraction of substrate 26 is typical of glass, ~ 1.5, and groove 30 is filled with air, the critical angle is equal to about 42°. To reflect light 44 out of substrate 26 at about 90° to surface 24, groove 30 is formed so that 9_j and an angle at which reflecting surface 40 intersects waveguide 42 are equal to about 45°. Whereas reflecting surface 40 is described as being used to extract light from waveguide 42 and reflect the extracted light to exit substrate 26 at about 90° to surface 24, the reflecting surface can of course be used to insert light into the waveguide. Insertion is accomplished by transmitting light into the substrate 26 at an appropriate location and at 90° to surface 24 so that the reflecting surface 40 reflects the transmitted light into the waveguide.

Because groove 30 is covered by cover plate 22, reflecting surface 40 is isolated from an ambient environment in which substrate 26 is used and is substantially protected from degradation and damage from the environment. For example, cover plate 22 protects reflecting surface 40 from environmental dust and moisture. As a result, reflecting surface 40 does not, generally, require a reflective coating to protect and stabilize its optical characteristics.

In some embodiments of the invention, cover plate 22 is substantially transparent to light propagating in waveguide 42. However, the cover plate may be formed to interact with and modify light propagating in the waveguide. For example, cover plate 22 may optionally comprise a lens, such as a holographic lens, and/or an optical band pass, low pass, or high pass filter.

Figs. 2A -2D schematically show cross section views of cover plate 22 and substrate 26 shown in Fig. 1 that illustrate adhering the cover plate to the substrate to cover and seal groove 30, in accordance with an embodiment of the invention. In an embodiment of the invention, the process of adhering cover plate 22 to substrate 26 and sealing groove 30 is performed in an atmosphere of dry gas, such as dry Nitrogen. The dry optical gas atmosphere provides a controlled environment in which to seal groove 30 and for trapping a gas of known, desired optical characteristics in the sealed groove.

Fig. 2A schematically shows cover plate 22 positioned on substrate 26, optionally by a pick and place machine (not shown), to cover opening 32 of groove 30. By way of numerical example, opening 32 of the groove may be characterized by width and length of about 50 microns and 100 microns respectively, and cover plate 22 may be square, having a side of length between about 1/2 and about 1 mm, and be about 200 microns thick. Trapped gas, and roughness of substrate surface 24 and the surface of cover plate 22 that contacts substrate surface 24, produces a narrow space 50 between the cover plate and substrate surface 24.

In accordance with an embodiment of the invention, a quantity of a liquid adhesive 60 is then deposited by a suitable dispenser (not shown) along an edge of cover plate 22. The liquid adhesive is chosen so that forces between the adhesive, cover plate 22 and substrate surface 24 promote capillary action that draws the liquid adhesive into space 50

In some embodiments of the invention, the choice of adhesive is determined responsive to its viscosity and height of space 50 to promote flow of the adhesive 60 into space 50. Advantageously, space 50 has a "height" perpendicular to substrate surface 24 between about 1 and about 10 microns. In some embodiments of the invention, height of space 50 is adjusted responsive to viscosity of adhesive 60. For example, substrate surface 24 may be polished, using any of various methods and material known in the art, to an appropriate degree of smoothness to control height of space 50, and/or capillary forces, and thereby flow of adhesive in space 50.

Fig. 2B schematically shows a cross section view of liquid adhesive 60 being drawn into space 50 by capillary action. In an embodiment of the invention, a suitable amount of adhesive is deposited on surface 24 along an edge of cover plate 22 so that the adhesive flows up to and surrounds edges 34 of groove 30 along opening 32 of the groove in substrate surface 24.

Fig. 2C schematically shows a plan view of cover plate 22 and substrate 26 that shows adhesive 60 being drawn into space 50 by capillary action to surround and "lip" edges 34 of the groove. Capillary action and surface tension of adhesive 60 prevents the adhesive flowing into space 50 from flowing over edges 34 and entering groove 30 and adhering to reflective surface 24. Optionally, a sufficient amount of adhesive 60 is deposited on substrate surface 24 so that the adhesive substantially fills all of space 50 between cover plate 22 and substrate surface 24. Fig. 2D schematically shows a cross section view of cover plate 22 and substrate 26 after the adhesive has filled space 50 (Figs. 2A-2C)

Any of various transparent adhesives having characteristics suitable for supporting capillary action and after setting, bonding cover plate to substrate surface 24 may be used in the practice of the invention. Advantageously, the adhesives have low viscosity, 200MPa-s to 300MPa-s and high glass transition temperature, Tg, 120° C to 150° C and an index of refraction after curing that mitigates reflections at interfaces between cover plate 22, cured adhesive 60 and between the cured adhesive and substrate 26. Optionally, the adhesives are UV cured optical epoxies. The inventors have determined that commercial, optical UV curing epoxies, such as NTT AT6001, AT9390 marketed by NTT AT Nippon Telegraph & Telephone Advanced Technology, Luvantix WR346, Daikin UV2100, marketed by Okura Chem-Tech Corp. EB Luventix Division, or Daikin OPTODYNE UV1100 marketed by Daikin America Inc are suitable for practicing the invention.

Figs. 3A and 3B schematically show plan views of a cover plate 22 shown in dashed lines and a substrate 26 that illustrate adhering the cover plate to the substrate to cover and protect groove 30 using a flow channel formed in the substrate, in accordance with an embodiment of the invention.

Fig. 3A schematically shows an optionally circular "adhesive" flow channel 70 having two feed channels 72 formed in substrate surface 24. Circular flow channel 70 surrounds opening 32 of groove 30 and the flow channel and feed channels 72 are optionally cut to a depth equal to between about 5 to about 15 microns in substrate surface 24 and have width between about 50 microns to about 250 microns. Optionally, adhesive channel 70 and feed channels 72 have a same depth. Optionally, they have a same width. Cover plate 22 covers groove 30, flow channel 70 and a portion, but not all, of each of feed channels 72.

To adhere the cover plate to substrate surface 24 and seal groove 30, an adhesive, such as any of the UV adhesives noted above, is deposited in one of feed channels 72 in a quantity sufficient to fill flow channel 70 and space 50 (Fig 2A) between the cover plate and substrate surface 24. The deposited adhesive is drawn into flow channel 70 and space between cover plate 22 and substrate surface 24 by capillary action. Gas, which might prevent capillary spread of the adhesive in the flow channel and space between the cover plate and substrate 24, vents via the other feed channel 72 in which adhesive is not deposited.

Fig. 3B schematically shows substrate 26 and cover plate 22 when an adhesive 60 has filled flow channel 70 (Fig. 3A) and space between the cover plate and substrate surface 24. As in the method shown in Figs. 2A-2D, the method of employing a flow channel to adhere a cover plate in accordance with an embodiment of the invention is advantageously carried out in a suitable dry optical gas atmosphere.

Fig. 4A shows, very schematically, an optical coupler 20 comprising a substrate 26 formed having a groove 30 covered by a cover plate 22, coupling light 44 propagating in waveguide 42 to an optical detector 80 mounted on the cover plate, in accordance with an embodiment of the invention. Optionally, detector 80 comprises a photodiode that generates electrical signals responsive to light incident on a light sensitive region 81 of the photodiode. Fig. 4A illustrates a reflecting surface 40 of groove 30 reflecting light 44 propagating in waveguide 42 to extract the light from the waveguide and transmit it to detector 80 so that it is incident on light sensitive region 81 of photodiode 80. Fig. 4B schematically shows a groove 30 and cover plate 22 inserting light into waveguide 42. In accordance with an embodiment of the invention, an optical concentrator lens 90 is mounted on cover plate 22. A laser diode 92 is held and positioned over lens 90 by a laser diode support 94 optionally mounted to cover plate 22. Light 44 emitted by laser diode 92 is focused on reflecting surface 40 by concentrator lens 90 and reflected into waveguide 42 by the reflecting surface.

In some embodiments of the invention, an optical element is large enough and configured in such a manner that it can function as its own cover plate when optically coupled to a waveguide comprised in a substrate by a reflecting surface of a groove formed in the substrate. By way of example, Fig. 4C schematically shows a photodiode 180 comprising a rectangular semiconductor plate 181, conventionally referred to as a "die 181", having a photosensitive region 182 located closer to a first end 183 of the die than to a second end 184 of the die. The die is adhered to substrate 26 so that it covers and seals a groove 30 having a reflecting surface 40 formed in the substrate. Optionally the die is adhered to the substrate using materials and methods described above. Die 181 is sufficiently large and photosensitive region 182 sufficiently offset towards end 183 so that, as shown in Fig. 4C, when positioned to cover and seal groove 30 photosensitive region 182 is aligned over reflecting surface 40 so that light in waveguide 42 that is incident on the reflecting surface is reflected to photosensitive region 182.

By way of another example, Fig. 4D schematically shows a laser diode 192 optically coupled to a waveguide 42 comprised in a substrate 26 via a groove 30 formed in the substrate and having a reflecting surface 40. Laser diode 192 is attached to a laser diode support 194 that is adhered to an upper surface 24 of substrate 26 and is large enough so that it covers and seals groove 30 without requiring a cover plate. The laser diode is positioned on support 194 so that it is sufficiently close to surface 24 of the substrate that a satisfactory amount of light 44 emitted by the laser diode enters the substrate and is reflected by reflecting surface 40 into waveguide 40 without use of a concentrator lens mounted to surface 24. In an embodiment of the invention the laser diode is butt coupled to surface 24.

In many optical systems, light propagating in a waveguide of an optical system, such as waveguide 42 comprised in substrate 26 shown in Fig 4A, is accompanied by stray light that does not propagate in the waveguide but bounces around in a substrate. The stray light may for example be generated by insertion losses when light is introduced into the waveguide, or from light that escapes or leaks from other components (not shown) of the optical system. Fig 5A schematically shows optical coupler 20 shown in Fig. 4A in which in addition to light 44 propagating in waveguide 42, stray light 144 is repeatedly reflected from surfaces of substrate 26 so that it bounces around inside the substrate. Some of the stray light reaches reflecting surface 40 and is reflected by the surface to light sensitive region 81 of detector 80. Generally, such stray light is undesirable and degrades response of the detector to light propagating in the waveguide.

For example, assume light 44 in Figs 4A and 5A is comprised in short light pulses of a high data transmission rate communication system. Stray light 144 contributes to background illumination of detector 80 and reduces signal (light traveling in waveguide 30) to noise. And since stray light 144 generated by insertion loss travels different, and generally longer, path lengths to light sensitive region 81 of detector 80 than signal light propagating in waveguide 42, the stray light contributes to pulse dispersion.

In accordance with an embodiment of the invention, to reduce deleterious effects of stray light 144, an aperture plate is introduced to shield detector 80. Fig. 5B schematically shows an optical coupler 120 similar to optical coupler 20 shown in Fig. 4A but comprising an aperture plate 150, in accordance with an embodiment of the invention.

Aperture plate 150 is formed having an aperture 151 and blocks light incident on the aperture plate from propagating towards detector 80 unless the light is incident on the aperture. In an embodiment of the invention, aperture plate 150 comprises an optically transparent substrate 160 having a thickness H, a front surface 161 and a back surface 162. Front surface 161 is optionally coated with an optically reflecting coating everywhere except for an area of the front surface where aperture 151 is located. Optionally, back surface 162 does not block light incident on aperture plate 150 that passes through aperture 151. In an embodiment of the invention, as shown in Fig. 5B, front surface 161 of aperture plate 150 is contiguous with a top surface cover plate 22 covering groove 30.

Let light sensitive region 81 of detector 80 be a circular region having a diameter W and aperture 151 be circular and have a diameter D. Then from geometry it is seen that stray light 144 that is incident on aperture 151 reaches sensitive region 81 of detector 80 only if it is incident on the aperture at an angle measured from a normal 163 to front surface 161 that is less than an angle a = arctan(W+D)/2H. By way of a numerical example, in some embodiments of the invention D = 20μ (micrometers); W = 60μ and H = 200μ so that only light incident on aperture 151 at an angle less than or equal to a = arctan(0.2) = 11.3° . As a result, aperture plate 150 reduces an amount of stray light that reaches detector 80, improves signal to noise and reduces pulse dispersion due to stray light generated by insertion loss. It is noted that an amount of stray light that is prevented from reaching detector 80 increases with H.

Fig. 6 A schematically shows an optical demultiplexer 200 comprising aperture plates for mitigating effects of stray light, in accordance with an embodiment of the invention.

Demultiplexer 200 comprises a substrate 200 having a waveguide 42 formed therein in which optical signals 202, represented by arrows 202, are respectively transmitted at wavelengths in a plurality of different wavelength bands along a direction in the waveguide indicated by a direction of the arrows. The demultiplexer is shown, by way of example, separating and extracting optical signals transmitted in three of the plurality of different wavelength bands. The three wavelength bands, and wavelengths in the three bands, are denoted respectively by λ , λ2, and λ3 and optical signals in the three bands are represented by arrows 202 labeled with the wavelength λ , λ2, or λ3 of the wavelength band in which it is transmitted. The optical signals are referred to generically by the numeral 202 labeling the arrows. Upstream and downstream directions in waveguide 42 are directions that are opposite to and the same as the direction indicated by arrows 202. In the figure, three optical signals 202, each in a different wavelength band λι , λ2, and λ3 are shown propagating downstream from a right end 205 of waveguide 42. Whereas in Fig. 6A, signals in only three wavelength bands are shown, the number of the plurality of wavelength bands is not limited to three bands and a demultiplexer in accordance with an embodiment of the invention may be configured to demultiplex signals in more or less than three wavelength bands.

For each wavelength band λι , λ2, and λ3 a groove 231, 232, and 233 respectively is formed in substrate 26 that intersects waveguide 42. Each groove 231, 232, and 233 is delimited by an upstream, entry surface 236, and a downstream, reflecting surface 238. Optionally, entry surface 236 of each groove is perpendicular to waveguide 42 and the reflecting surface of the groove is oriented at an angle β optionally equal to 45° to the waveguide. It is noted that whereas in Figs. 6A and 6B, β is schematically shown equal to about 45°, it can be advantageous to use values for β other than 45°. For example, to reduce back reflections of light from the interface of aperture plate 150 and substrate 26 into waveguide 42, β is advantageously, optionally equal to 41° or 49°. The reflecting surfaces of grooves 231, 232, and 233 are covered respectively with reflectors R231, R232, and R233 that reflect light in wavelength bands λι , λ2, and λ3 respectively and transmit light in the other of the wavelength bands. Optionally, reflectors R231, R232, and R233 are thin film filters (TFFs) formed using any of various suitable methods, such as sputtering or evaporating, and materials, such as titanium oxide (T1O2), silicon dioxide (S1O2), and magnesium dioxide (Mg02) known in the art. Each groove 231, 232, and 233 is filled with an optical gel or adhesive indicated by shading 239 that has an index of refraction substantially the same as that of substrate 26 so that the gel or adhesive operates to reduce reflections of light from optical signals 202 propagating in waveguide 42 that are incident on upstream entry surface 236 of the groove.

In an embodiment of the invention, grooves 231, 232, and 233 are covered with aperture plates 150 having an aperture 151. Optionally, apertures in the aperture plates 150 covering grooves 231, 232, and 233 are covered with thin film band pass filters having band passes substantially coincident with wavelength bands λ , λ2, and λ3 respectively. A photodiode 80 having a light sensitive region 81 is mounted, optionally, to each aperture plate 150. Aperture plate 150 and photodiode 80 associated with each groove 231, 232, and 233 are aligned so that light reflected respectively by the groove's reflector R231, R232, and R233 from light propagating in waveguide 42 is incident on light sensitive region 81 of the photodiode.

As schematically shown in Fig. 6 A demultiplexer 200 operates to demultiplex optical signals 202 propagating in waveguide 42 and generate electrical signals responsive to the optical signals. As optical signals 202 in transmission bands λι , λ2, and λ3 propagate downstream in waveguide 42 from end 205 they enter groove 231 and are incident on the groove's reflector R231. Reflector R231 reflects light from optical signals 202 transmitted in wavelength band λ and transmits optical signals 202 in wavelength bands λ2 and Light reflected by reflector R231 passes through aperture 151 and is incident on light sensitive region 81 of photodiode 80 mounted over groove 231. The photodiode generates an electrical signal responsive to the incident light and thereby to the optical signal 202 in wavelength band λι . Grooves 232 and 233 similarly extract light from optical signals 202 in wavelength bands λ2 and λ3 respectively, which extracted light is converted to electrical signals by the groove's associated photodiode 80. The presence of aperture plates 150 shielding photodiodes 80 provides demultiplexer 200 with improved resistance to signal degradation by stray light. A demultiplexer, in accordance with an embodiment of the invention, is not limited to comprising aperture plates. Fig. 6B, by way of example, schematically shows a demultiplexer 250 in which photodiodes 251 are mounted directly over grooves 239 so that their respective photosensitive regions 252 are aligned to receive light reflected from waveguide 42 by reflecting surfaces 238 in the grooves. Optionally, as shown in Fig. 6B, photodiodes 251 are large enough so that when mounted over grooves 238, they completely cover and seal the grooves.

It is noted that by replacing photodiodes 80 or 251 with light sources, such as lasers or light emitting diodes, demultiplexer 200 is converted to a multiplexer, in accordance with an embodiment of the invention. Fig. 6C schematically shows a multiplexer 300 in accordance with an embodiment of the invention constructed similarly to demultiplexer 200 with laser diodes LD , LD 2, and LD i,, mounted over grooves 231, 232, and 232 respectively and replacing photodiodes 80 in the demultiplexer. Light emitting diodes LD , Ι ⁾λ2, and LD i, generate light in wavelength bands λι , λ2, and λ3 respectively. In an embodiment of the invention, each laser diode LD \, Ι >λ2, and LO ^ is supported by a diode support 94 mounted to a cover plate 22 positioned over the diode' s respective groove 231, 232 and 233. Optionally, cover plate 22 is mounted with an optical concentrator 90 that receives light from the laser diode and focuses the light on its associated reflector R231, R232 and R233 so that the reflector reflects the light into waveguide 42.

In Fig. 6C each LD \ , LD 2, and LO ^ is schematically shown emitting light in its respective wavelength band λι , λ2, and λ3 to form pulses of light represented by arrows 302 labeled and their wavelength bands λ , λ2, and λ3 . The emitted light pulses 302 from diodes LD , Ι ⁾λ2, and LD i, are focused by the LDs' concentrators 94 on their respective reflectors R231, R232 and R233 which reflect the light pulses so that they enter into and are multiplexed by waveguide 42.

Demultiplexer 200 and multiplexer 300 may be combined to form a transceiver 400, in accordance with an embodiment of the invention, which is schematically shown in Fig. 6D. Transceiver 400 comprises a waveguide 42, M light emitting diodes LD_m (l<m<M) mounted over M grooves 401 having reflectors R_m and N photodiodes PD_n (M<n<N) mounted over (N-M) grooves 402 having reflectors R_n. Light emitting diodes LD_m emit light and reflectors R_m reflect light in wavelength bands _m respectively to generate optical signals 405 that are multiplexed to propagate "upstream" in waveguide 42. Reflectors R_n reflect light in wavelength bands λ_η and reflect optical signals 406 in wavelength bands λ_η propagating downstream in waveguide 42 to photodiodes PD_n to demultiplex and generate electrical signals responsive to the optical signals. By way of example, in Fig. 6C, M = 3 and N =6.

Fig. 6E schematically shows a multiplexer demultiplexer (Mux-Demux) 500 comprising reflectors Rj (l<j<J) formed in grooves Gj in a substrate 26 that operate to both multiplex and demultiplex optical signals S j propagating in a waveguide 42 formed in the substrate, in accordance with an embodiment of the invention. Optical signal S j comprises light in a wavelength band of J wavelength bands in which optical signals are propagated in waveguide 42 but relatively very little, or no light, from other of the J wavelength bands. Reflector Rj reflects light in wavelength band and transmits light in the other of the J wavelength bands. By way of example in Fig. 6E J = 3.

Grooves Gj are optionally covered with a protective cover plate 22 to which an array of optic fibers Fj is coupled with each fiber Fj aligned with reflector Rj so that an optical signal S j transmitted in the fiber towards groove Gj enters the groove and is reflected into waveguide 42 to propagate upstream, and be multiplexed with, other signals in the fiber. An optical signal S j propagating downstream in waveguide 42 to groove Gj enters the groove and is reflected out of the waveguide and into fiber Fj to be demultiplexed from other optical signals propagating in waveguide 42. Each fiber Fj is coupled to a suitable detector (not shown), such as a photodiode for detecting signals S j demultiplexed from waveguide 42 and a suitable light source, such as a laser or light emitting diode (not shown) , for transmitting signals S j along the fiber to be multiplexed in waveguide 42.

In the description and claims of the present application, each of the verbs, "comprise" "include" and "have", and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily an exhaustive listing of members, components, elements or parts of the subject or subjects of the verb.

The invention has been described with reference to embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the described invention and embodiments of the invention comprising different combinations of features than those noted in the described embodiments will occur to persons of the art. The scope of the invention is limited only by the following claims.

Claims

1. Apparatus for multiplexing and demultiplexing optical signals in different wavelength bands respectively into and from a same waveguide formed in an optical substrate, the apparatus comprising:

for each of the different wavelength bands, a groove formed in the substrate having a surface in the substrate that intersects the waveguide and reflects light that propagates in the waveguide in the wavelength band and does not reflect light propagating in the waveguide in other of the wavelength bands;

for each of at least two grooves in a first group of the grooves, a different source of optical signals that transmits optical signals that are reflected by the groove's reflecting surface into the waveguide; and

for each of at least two grooves in a second group of the grooves, a different optical sensor for each groove that receives light reflected by the groove's reflecting surface and generates an output signal responsive to the received light.

2. Apparatus according to claim 1 wherein no groove belonging to the first group also belongs to the second group.

3. Apparatus according to claim 2 wherein at least one groove in the first group of grooves belongs to the second group of grooves.

4. Apparatus according to claim 3 and comprising a same optical waveguide coupled to the source of optical signals and the optical sensor associated with the at least one groove along which optical signals from the source propagate towards the groove's reflecting surface and light from the groove's reflecting surface propagates to the sensor.

5. Apparatus according to claim 4 wherein the optical waveguide comprises an optical fiber.

6. Apparatus for generating a signal responsive to light that propagates in a waveguide formed in an optical substrate, the apparatus comprising: a groove formed in the substrate and having a reflecting surface that intersects the waveguide; and

a photodiode that covers the groove and has a photosensitive region that receives light reflected by the reflecting surface from light that propagates in the waveguide and generates a signal responsive to the received light.

7. Apparatus for inserting light into a waveguide formed in an optical substrate, the apparatus comprising:

a groove formed in the substrate and having a reflecting surface that intersects the waveguide; and

a laser diode butt coupled to a surface of the substrate so that light that it emits is reflected by the reflecting surface into the waveguide.

8. Apparatus according to claim 7 wherein the laser diode is attached to a laser diode support that covers and seals the groove.

9. Apparatus for demultiplexing optical signals propagating in different wavelength bands in a same waveguide formed in an optical substrate, the apparatus comprising:

for each of the different wavelength bands, a groove formed in the substrate having a surface in the substrate that intersects the waveguide and reflects light that propagates in the waveguide in the wavelength band and does not reflect light propagating in the waveguide in other of the wavelength bands; and

a different optical sensor for each groove that receives light reflected by the groove's reflecting surface and generates an output signal responsive to the received light.

10. Apparatus for multiplexing optical signals in different wavelength bands into a same waveguide formed in an optical substrate, the apparatus comprising:

a different source of optical signals for each groove that transmits optical signals that are reflected by the groove's reflecting surface into the waveguide.

11. Apparatus according to claim 9 or claim 10 and comprising a different groove for each wavelength band.

12. Apparatus according to claim 9 or claim 10 and comprising a same groove for at least two wavelength bands.