KR20130086651A - Planar polarization rotator - Google Patents

Abstract

The optical polarization rotor includes a first optical waveguide rib and a second optical waveguide rib positioned along the planar surface of the substrate. The second optical waveguide rib is located further from the surface than the first optical waveguide rib. The first segment of the optical waveguide ribs forms a vertical stack over the substrate, and the second segment of the optical waveguide rib is laterally offset in a direction along the planar surface. The first optical waveguide rib and the second optical waveguide rib are formed of a material having different bulk refractive indices.

Description

Planar Polarization Rotors {PLANAR POLARIZATION ROTATOR}

The present invention relates to a polarizing rotor and a method of making and using the polarizing rotor.

This section introduces aspects that may help to facilitate a better understanding of the present invention. Therefore, the description of the section should be read in this respect and should not be understood as an admission of what is in the prior art or what is not in the prior art.

Some optical components process one or two orthogonal linearly polarized components to individually perform functions related to optical communication of the digital data stream. To enable such processing, the polarization splitter can process the received light to separate its two orthogonal linear polarization components. In addition, to enable this process, the polarization rotor can rotate one or both of the discrete linear polarization components of such light. For example, such light rotation can align the polarization of both of the separated polarization components.

One embodiment provides an apparatus including an optical polarization rotor having first and second optical waveguide ribs positioned along a planar surface of a substrate. The second optical waveguide rib is located further from the surface than the first optical waveguide rib. The first segment of the two optical waveguide ribs forms a vertical stack over the substrate. The second segment of the two optical waveguide ribs is laterally offset in the direction along the planar surface. The first and second optical waveguide ribs are formed of a material having different bulk refractive indices.

In some embodiments, the device may further comprise a spacer layer between the first and second optical waveguide ribs. Such a spacer layer can be formed, for example, of a material having a bulk refractive index different from that of the first and second optical waveguide ribs. This spacer layer may be thinner perpendicular to the surface than the first optical waveguide rib.

In some embodiments of any of the above devices, the first optical waveguide ribs may be formed of the same material as the portion of the planar surface of the substrate.

In some embodiments of any of the above devices, one of the optical waveguide ribs may be formed of a semiconductor, and the other of the optical waveguide ribs may be formed of a dielectric.

In some embodiments of any of the above devices, the optical polarization rotor may be configured to rotate the polarization of the received linearly polarized light at least 45 degrees.

In some embodiments of any of the above devices, the device is characterized in that the first optical waveguide rib monotonically decreases from a large value at the boundary of the input planar optical waveguide to a small value in the first segment of the first optical waveguide rib and transverse to the surface. It may include a transition region having a width that is a direction. In some such devices, the second optical waveguide rib monotonically decreases from a small value at the end close to the input optical waveguide to a large value in the first segment of the second optical waveguide rib and has a width transverse to the surface.

In some embodiments of any of the above devices, the device is characterized in that the first optical waveguide rib monotonically decreases from a small value in the second segment of the first optical waveguide rib to a large value at the boundary of the output plane optical waveguide and transverse to the surface. It may include a transition region having a width in the direction.

In some embodiments of any of the above devices, the device comprises a first optical output coupled to transmit light to the first optical waveguide rib, and a first coupled optical output coupled to a first specific output optical waveguide positioned over the substrate transverse to the first optical waveguide rib. It may include a polarizing beam splitter having two light outputs. In some such embodiments, the apparatus may further include a second specific output optical waveguide coupled to the first optical output of the polarizing beam splitter via the optical polarization rotor. The apparatus may be configured to transmit light of substantially the same linearly polarized light to two specific output optical waveguides.

In some embodiments of the device, the device may include a light modulator having a 1 × 2 light splitter, first and second optical waveguide arms, and a 2 × 1 light combiner. Each optical waveguide arm connects the corresponding light output of the 1x2 optical splitter to the corresponding light input of the 2x1 optical combiner and modulates the phase and / or amplitude of the light propagating in response to the received electrical signal. And an electro-optic modulator. In this embodiment, the optical polarization rotor is located in one of the optical waveguide arms.

Another embodiment provides a method. The method includes forming an optical layer over a first optical waveguide rib positioned along a planar surface of the substrate. The optical layer and the first optical waveguide rib are formed of a material having different bulk refractive indices. The method also includes etching the optical layer to form a second optical waveguide rib. The first segment of optical waveguide ribs forms a stack oriented perpendicular to the planar surface. The second segment of the optical waveguide ribs is laterally offset along the relatively planar surface.

In some embodiments, the method may further include forming a spacer layer over the first optical waveguide ribs prior to forming the optical layer. The spacer layer is formed of a material having a bulk refractive index different from that of the optical layer and the first optical waveguide layer.

In some embodiments of any of the above methods, the portion of the first optical waveguide and the planar surface may be formed of the same optical material. In some such embodiments, the etching may be performed such that the optical material acts as a stop layer during the etching.

In some embodiments of any of the above methods, one of the optical layer and the first optical waveguide rib may be formed of a semiconductor, and the other of the optical layer and the first optical waveguide rib may be formed of a dielectric.

In some embodiments of any of the above methods, the third and fourth segments of the first optical waveguide rib can be positioned transverse to the second optical waveguide rib and the first and second segments of the first optical waveguide rib It may be wider in the transverse direction. In this embodiment, the first and second segments of the first optical waveguide rib are connected between the third and fourth segments thereof.

Another embodiment provides a second method, the method comprising receiving linearly polarized light from a planar waveguide at a first end of a segment of the hybrid optical waveguide, and hybrid optical waveguide to rotate the linear polarization of light. Propagating light through segments of the substrate. The segment of the hybrid optical waveguide comprises one segment in which the second optical waveguide rib is positioned vertically above the first optical waveguide rib, wherein the second optical waveguide rib is substantially laterally offset from the corresponding segment of the first optical waveguide rib. Include other segments. The first and second optical waveguide ribs are formed of a material having different bulk refractive indices.

In some embodiments of the second method, one of the first and second optical waveguide ribs may be a semiconductor rib and the other of the first and second optical waveguide ribs may be a dielectric rib.

In any of the above embodiments of the second method, the segment of the hybrid optical waveguide comprises a spacer layer positioned between the first and second optical waveguide ribs and made of a material having a bulk refractive index different from that of the optical waveguide ribs. It may include.

1A and 1B are plan and side views, respectively, showing an optical polarization rotor.
2A, 2B and 2C schematically illustrate the evolution of the light power distribution of the first light propagation mode of the optical polarization rotor of FIGS. 1A-1B in the transverse planes A, B and C of FIGS. 1A-1B, respectively. It is a cross section.
3A, 3B and 3C schematically illustrate the rotation of the light power distribution of the second relatively orthogonal light propagation mode of the optical polarization rotor of FIGS. 1A-1B in the same transverse planes A, B and C of FIGS. 1A-1B, respectively. It is sectional drawing to illustrate.
4A, 4B and 4C are respective plan, side and oblique views illustrating schematically the optical polarization rotor of FIGS. 1A-1B.
5 is a flow chart schematically illustrating a method of manufacturing an optical polarization rotor, for example the optical polarization rotor illustrated schematically in FIGS. 4A-4C.
6 is a flow diagram schematically illustrating a method of rotating the polarization of linearly polarized light in the optical polarization rotor illustrated schematically in FIGS. 1A-1B and 4A-4C, for example.
FIG. 7 is a block diagram schematically illustrating an optical modulator incorporating an optical polarization rotor, eg, one of the optical polarization rotors of FIGS. 1A-1B or 4A-4C, to produce a polarization multiplexed, data multiplexed optical carrier. It is also.
FIG. 8 schematically illustrates an optical receiver configured to separately demodulate data from two linearly polarized components of a data modulated optical carrier that is polarized multiplex, for example, an optical carrier produced schematically by FIG. 7. It is a block diagram.

In this specification, an optical waveguide represents an optical structure that allows received light to propagate along a predefined light guide direction. An optical waveguide is different from an optical structure that simply defines the light received to propagate in a plane. In this specification, an optical waveguide may refer to an unclad optical waveguide or an optical core of a clad optical waveguide. That is, the expression optical waveguide encompasses two types of structures.

1A and 1B show an optical polarization rotor 10 formed from an optical waveguide. The optical waveguide has a first transition region 12, a polarization rotation region 14, and a second transition region 16. The first transition region 12 optically connects the polarization rotation region 14 to an input optical waveguide 18, for example a planar optical waveguide. The polarization rotation region 14 rotates the linear polarization of the received light in one or two substantially linear polarization propagation modes. The second transition region 16 optically connects the polarization rotation region 14 to an output optical waveguide 20, for example a planar optical waveguide.

The first and second transition regions 12, 16 are regions in optical coupling with the respective input and output optical waveguides 18, 20. In some embodiments, the transition regions 12, 16 also redistribute light power densities that propagate the light mode vertically or transversely relative to the near surface of the substrate 22 without rotating linearly polarized light, for example. The first transition region 12 can include a gradual tapering of the optical waveguide that can adiabatically redistribute the light power density over a large vertical region. The second transition region 16 may comprise a gradual reduction of the optical waveguide that thermally redistributes the received light power density through a small vertical region.

The polarization rotation region 14 includes a light stack and a substrate 22. The optical stack includes a first optical waveguide rib 24 positioned on the substrate 22, and a second optical waveguide rib 26 located further away from the planar surface of the substrate 22 than the first optical waveguide rib 24. It includes. The first and second optical waveguide ribs 24, 26 are formed of materials having different bulk refractive indices. For example, one of the optical waveguide ribs 24, 26 may be made of a semiconductor, and the other of the optical waveguide ribs 26, 24 may be made of a dielectric. Alternatively, the first and second optical waveguide ribs 24, 26 may be made of different dielectrics or different semiconductors.

In some embodiments, first optical waveguide rib 24 may be an integral part of substrate 22. The first optical waveguide rib 24 is then formed of the same material as the portion of the near planar surface of the substrate 22.

Alternatively, the first optical waveguide rib 24 may be formed of a material different from a near portion of the planar surface of the substrate 22, for example, a material of different refractive index.

In fact, the first optical waveguide ribs 24 may be positioned in direct contact over the near planar surface of the substrate 22 or may be located over the near planar surface of the substrate 22 without directly contacting the planar surface.

The second optical waveguide ribs 26 may be in direct contact (not shown) over the first optical waveguide ribs 24, or a spacer layer of a material that is positioned over the first optical waveguide ribs 24 and is substantially optically transparent ( 28 may be separated from the first optical waveguide rib 24. This spacer layer 28 is generally thinner vertically than the first optical waveguide rib 24.

In the polarization rotating region 14, the central axes of the first and second optical waveguides 24, 26 are directed along the transverse transverse direction. For this reason, the vertical overlap between the transverse widths corresponding to the segments of the first and second optical waveguides 24, 26 decreases along the direction of propagation of light in the polarization rotation region 14, ie in FIGS. 1A-1B. Decrease to the right. Thus, some corresponding segments of the first and second optical waveguide ribs 24, 26 may be laterally offset along the planar surface of the substrate 22, ie at the rightmost part of the polarization rotation region 14. .

In the polarization rotation region 14, each of the first and second optical waveguide ribs 24, 26 may have a constant transverse width or may have a non-uniform width. For example, the width of the first optical waveguide rib 24 may increase along the direction of propagation of light in the polarization rotation region 14. In addition, the width of the second optical waveguide rib 26 may decrease along the direction of propagation of light in the polarization rotation region 14.

The vertical widths of the first and second optical waveguide ribs 24, 26 are generally substantially constant through the optical polarization rotor 10.

2A, 2B and 2C schematically illustrate the expected light power distribution of the first propagating light mode in the continuous transverse planes A, B and C of FIGS. 1A-1B. The first propagation mode is initially a transverse magnetic (TM) propagation light mode with initial linear polarization.

In the initial transverse plane A, the cross sections of the first and second optical waveguide ribs 24, 26 are aligned perpendicular to the planar surface PS of the substrate 22. In the initial transverse plane A, the optical power of the first propagating light mode, ie the TM mode, is concentrated in the first rectangular region OR1 whose main axis is directed perpendicular to the plane surface PS of the substrate 22.

Later in the transverse plane B, the centers of the cross sections of the first and second optical waveguide ribs 24, 26 are substantially laterally offset, and the optical power of the first propagating light mode is concentrated in the second rectangular area OR2. . The rectangular region OR2 is inclined considerably with respect to the normal direction to the planar surface PS of the substrate 22 such that the major axis of the rectangular region is oriented almost along the diagonal between the centers of the two optical waveguide ribs 24 and 26.

In the final transverse plane C, the cross sections of the first and second optical waveguide ribs 24, 26 are separated by a large transverse gap, and the optical power of the first propagation light mode is the principal axis of the substrate 22 It is concentrated in the third rectangular area OR3 which is almost parallel to the surface.

Therefore, the slow turning of the light stack gradually rotates the rectangular area where the optical power of the first light propagation mode is concentrated. During progressive rotation, the linearly polarized light of the first propagated light mode rotates into a rectangular region where the optical power of the mode is concentrated. In the illustrated example, polarization rotation consists of about π / 2 radians to change the initial TM propagation light mode to the final transverse electric (TE) propagation light mode.

3A, 3B and 3C schematically illustrate the expected light power distribution of the second propagating light mode in the same respective transverse planes A, B and C of FIGS. 1A-1B. The first propagation mode is initially a TE propagation light mode with initial linear polarization and is relatively orthogonal to the first propagation light mode.

In the initial transverse plane A, the cross sections of the first and second optical waveguide ribs 24, 26 are vertically aligned, and the optical power of the second propagating light mode, ie TE mode, is concentrated in the other first rectangular area OR1 '. do. The first rectangular area OR1 'has a major axis which is oriented horizontally parallel to the planar surface of the substrate 22.

Later in the transverse plane B, the centers of the cross sections of the first and second optical waveguide ribs 24, 26 are substantially laterally offset, and the optical power of the second propagating light mode is directed to another second rectangular area OR2 '. Are concentrated. The rectangular region OR2 'is inclined considerably with respect to the normal direction to the planar surface of the substrate 22 such that the major axis of the rectangular region is oriented almost along the diagonal between the centers of the two optical waveguide ribs 24, 26.

In the final transverse plane C, the cross sections of the first and second optical waveguide ribs 24, 26 are separated by a large transverse gap, and the optical power of the second propagation light mode is mainly the plane of the substrate 22 It is concentrated in another third rectangular area OR3 'which is oriented almost perpendicular to the surface.

Thus, slow turning of the light stack also gradually rotates the rectangular region where the optical power of the second propagated light mode is concentrated. During progressive rotation, the linearly polarized light of the second propagated light mode rotates around the major axis of the rectangular region where the light power of the mode is concentrated. In the illustrated example, the rotation is made by about [pi] / 2 radians to change the initial TE propagation light mode to the final TM propagation light mode.

4A, 4B and 4C show specific examples 10 ′ of the optical waveguide 10 shown in FIGS. 1A-1B. The optical waveguide 10 ′ has a first transition region 12, a polarization rotation region 14, and a second transition region 16. In the segments of the polarization rotation region 14 and the first transition region 12, the optical waveguide 10 ′ includes first and second optical waveguide ribs 24, 26. The first optical waveguide rib 24 is repositioned closer to the planar surface of the substrate 22 than the second optical waveguide rib 26.

In the first transition region 12, the cross section of the optical waveguide 10 ′ gradually changes so that the transverse light power distribution of the propagating light mode turns to become schematically illustrated in FIG. 2A or 3A. In this example, the change includes the transverse change of the two optical waveguide ribs 24, 26. The change includes a smooth tapering that monotonously reduces the lateral width of the first optical waveguide rib 24 along the direction of propagation. The inventors believe that this gradual decrease in lateral width causes many of the optical power of the initial TE and TM propagating light modes to be redistributed out of the first optical waveguide rib 24. This change also includes a smooth gradual decrease that monotonously increases the transverse width of the second optical waveguide rib 26 along the direction of propagation. The inventor also believes that this gradual increase in lateral width causes many of the optical power of the initial TM propagating light mode to be redistributed from the first optical waveguide rib 24 to the second optical waveguide rib 26. In the absence of progressively reduced segments of the first and second optical waveguide ribs 24, 26, the inventors believe that the light injected from the input optical waveguide probably generates a higher amount of scattering, reflection and excitation in a higher mode, i.e., light It is believed that this results in higher insertion loss in the canal rotor 10 '.

In the polarization rotation region 14, for example as schematically shown in FIGS. 2A-2C and 3A-3C, the optical waveguide 10 ′ is substantially adapted to pivot the propagation mode of linear polarization such that the linear polarization is rotated. Undergo smooth changes. Here, the change includes the smoothing of the lateral overlap between the cross sections of the first and second optical waveguide ribs 24, 26 along the propagation direction. This reduction is at least in part due to the angular misalignment between the axes of the first and second optical waveguide ribs 24, 26. In some embodiments, the reduction may also be due, in part, to a selective monotonous smooth decrease in the lateral width of the second optical waveguide rib 26 along the propagation direction. Here, the change may also comprise a smooth and monotonous reduction of the lateral width of the first optical waveguide rib 24 along the direction of propagation.

In the second transition region 16, the cross section of the optical waveguide 10 ′ gradually changes so that the lateral light power distribution of the final propagation light mode couples more efficiently to the propagation light mode of the output optical waveguide 20. Here, the change is a smooth gradual decrease that monotonously increases the transverse width of the first optical waveguide rib 24 along the propagation direction. The second optical waveguide ribs 26 are not in the second transition region 16 or, for example, so as not to significantly affect the turning of the propagation light mode in the second transition region 16. Offset by a large transverse distance from the figure 24).

The above description shows the direction of propagation of light from left to right during the operation of the optical polarization rotors 10, 10 ′ schematically shown in FIGS. 1A-1B and 4A-4C. Nevertheless, the optical polarization rotors 10, 10 ′ also work when light propagates in the opposite direction here. That is, the optical polarization rotors 10 and 10 'will also rotate the linear polarization of the light injected from the optical waveguide 20 shown to the right of FIGS. 1A-1B and 4A-4C.

Illustrative example

4A-4C show an example of an optical waveguide 10 ′ that can be fabricated, for example, using a complementary metal oxide semiconductor process from a commercially available silicon on insulator (SOI) substrate.

In the example, the first and second optical waveguide ribs 24, 26 and the input and output optical waveguides 18, 20 are configured as described herein. The first optical waveguide ribs 24 are formed as part of the silicon layer of the initial SOI substrate and have a thickness of about 200 nanometers (nm). The second optical waveguide ribs 26 are formed of silicon nitride and have a thickness of about 400 nm. Input and output optical waveguides 18 and 20 are formed as part of the silicon layer of the initial SOI substrate and have a thickness of about 200 nm and a lateral width of about 500 nm to 600 nm.

In an example, the optical waveguide 10 'includes an optional spacer layer 28 that is about 100 nm of silicon dioxide located between the first and second optical waveguide ribs 24 and 26.

In the example, the first transition region 12, the polarization rotation region 14 and the second transition region 16 have a lateral size and shape as described below.

In the first transition region 12, the first and second optical waveguide ribs 24, 26 have a central axis that is laterally aligned, for example, the region 12, which may be about 50 micrometers (μm) in length. ) Extends over the entire length. The first optical waveguide rib 24 has an initial transverse width of about 500 nm to 600 nm at the boundary with the input optical waveguide 18. The initial lateral width, which nearly coincides with that of the input optical waveguide 18, decreases linearly with distance up to a value of about 200 nm at or near the boundary of the polarization rotation region 16. The second optical waveguide rib 26 has an initial transverse width of about 100 nm or less at or near the boundary with the input optical waveguide 18, the transverse width of which is about at or near the boundary of the polarization rotation region 16. The distance increases linearly to a value of 200 nm.

In some embodiments, the transverse width of one or both of the first and second optical waveguide ribs 24, 26 in the first transition region 12 is about 200 nm shortly before the boundary of the polarization rotation region 14. To reach. For example, this transverse width can reach a value of 200 nm at a distance of about 100 nm or more from the boundary, and then remains constant up to the boundary of the polarization rotation region 14.

In the polarization rotation region 14, the first and second optical waveguide ribs 24, 26 extend to the full length of the region 14, which may be, for example, 250 μm to 300 μm in length. The first optical waveguide rib 24 has an initial transverse width of about 200 nm at the boundary with the first transition region 12, and its transverse width is about 260 nm at the boundary with the second transverse region 16. Increases linearly. The second optical waveguide rib 26 has a lateral width of about 200 nm at the boundary with the first transition region 12, and its lateral width is about 150 nm or less at the boundary with the second transition region 14. The value can be constant or decrease linearly. Due to the divergent lateral alignment between the central axes of the first and second optical waveguide ribs 24, 26 in the polarization rotation region 14, the second optical waveguide rib 26 has a second transition region. It has a lateral offset of about 150 nm to about 200 nm from the corresponding portion of the first optical waveguide rib 24 near the boundary with (16).

In the second transition region 16, the first optical waveguide rib 24 extends over the entire length of the region 16, which may be, for example, about 50 μm. The first optical waveguide rib 24 has an initial transverse width of about 260 nm at the boundary with the polarization rotation region 14, and its transverse width is about 500 nm to 600 nm at the boundary with the output optical waveguide 20. The distance increases linearly to.

The second optical waveguide rib 26 may or may not project to the initial portion of the second transition region 16. When the second optical waveguide rib 26 projects into the second transition region 16, the lateral width of the second optical waveguide rib 26 may continue to decrease smoothly from about 150 nm to about 100 nm. . In the second transition region 16, the gradual outward gradual reduction of the first optical waveguide rib 24 is insufficient to substantially reduce the lateral offset between the first and second optical waveguide ribs 24, 26. Do. Due to the large initial lateral offset, the second optical waveguide ribs 26 propagate in the second transition region 16 and do not generate substantial polarization rotation of the light.

In various embodiments of the polarization rotors 10, 10 ′ of FIGS. 1A-1B and 4A-4C, the difference between the material composition of the first optical waveguide rib 24 and the material composition of the second optical waveguide rib 26 is It may be advantageous during manufacture. In particular, different material compositions may be applied to the first optical waveguide ribs 24 and / or the first optical waveguide ribs 24 as an etch stop for anisotropic etching of the second optical waveguide ribs 26 and / or the optional spacer layer 28. ) And the material of the optional spacer layer 28 between the second optical waveguide rib 26 may be made available. Such different compositions, if present, may support simpler and / or accurate etch fabrication of the optical waveguide ribs 24, 26 and spacer layer 28.

FIG. 5 schematically illustrates an exemplary method 30 of manufacturing an optical polarization rotor, for example the polarization rotors 10, 10 ′ of FIGS. 1A-1B and / or 4A-4C.

The method 30 includes performing an etching of a top layer of a substrate, such as a silicon layer of an SOI substrate, to form the first optical waveguide ribs 24 of FIGS. 4A-4C (step 32). . The same etching may be used to form additional silicon optical waveguides transverse to the first optical waveguide ribs 24, for example to form the input and output optical waveguides 18, 20 of FIGS. 1A-1B and 4A-4C. Can be used for Etching may use any existing process for mask controlled etch silicon, such as anisotropic dry etching of silicon dioxide, of silicon dioxide on this exemplary SOI substrate.

The method 30 optionally forms a layer of different material over the first optical waveguide rib 24, for example also on a transversely adjacent portion and / or on a transversely adjacent optical waveguide of the planar surface of the substrate 22. Step (step 34). Layers of different materials can be formed by, for example, conventional deposition processes that form light quality silicon dioxide layers.

Once step 34 is performed, the method 30 may utilize layers of different materials formed in step 34 to produce a suitable spacer layer, for example the spacer layer 28 of FIGS. 1A-1B and 4A-4C. Chemical mechanical polishing. Chemical mechanical polishing may, for example, produce a flat spacer layer of silicon dioxide having a thickness of about 100 nm or less, for example, on the first optical waveguide rib formed in step 32. The chemical mechanical polishing step may utilize existing processes known to those skilled in the art to be effective in polishing the layers of different materials formed in step 34.

The method 30 also includes forming an optical layer (step 38) over a portion of the first optical waveguide rib 24, for example over a portion of the planar surface of the substrate 22. Forming 38 may include, for example, depositing a layer of about 400 nm of silicon nitride on the optional spacer layer, using any existing process known to those skilled in the art to deposit an optical layer of silicon nitride. Can be. The optical layer, the first optical waveguide ribs 24 and the spacer layer are generally formed of materials having different bulk refractive indices.

The method 30 also includes etching the optical layer to form a second optical waveguide rib 26, for example directly on the optional spacer layer 28 or directly on the first optical waveguide rib 24. 40). The second optical waveguide ribs 26 form a stack in which the first segments of the first and second optical waveguide ribs 24, 26 are oriented perpendicular to the planar surface of the substrate 22 and the optical waveguide ribs 24, The second segment of 26 is formed to be relatively transversely offset in the direction along the planar surface of the substrate 22. In embodiments where the optical layer is silicon nitride, etching step 40 may use any existing process, for example for etching silicon nitride. For example, the etching step stops substantially at the silicon dioxide of the exemplary spacer layer 28 and / or the silicon of the first optical waveguide rib 24 of the exemplary silicon and / or the silicon of the exemplary substrate 22. And anisotropic dry etching for silicon nitride that substantially stops at the surface.

The method may also include depositing a cladding layer, such as a silicon dioxide layer (step 42), on the waveguide structure created in step 40 above. For example, the cladding layer may have a thickness of several micrometers or more. Deposition step 42 may utilize any existing process, for example depositing a thick light cladding layer of silicon dioxide.

6 schematically illustrates a method 50 of rotating a polarization of a linear polarization component in a planar optical polarization rotor, for example the optical polarization rotors 10, 10 ′ illustrated in FIGS. 1A-1B and 4A-4C. Illustrated.

The method 50 includes receiving (step 52) light from a planar waveguide, for example an input optical waveguide 18, at the first end of the polarization rotor. The received light is generally a combination of a linear polarization mode, for example a near in-phase of TE or TM propagated light mode or TE and TM propagated light mode.

The method 50 optionally optically polarizes such that a substantial portion of the light power of the optical polarization rotor is redistributed laterally and / or vertically in the first transition region 12 of FIGS. 1A-1B and 4A-4C, for example. Propagating the received light through the first progressive reduction waveguide segment of the rotor (step 54). Transverse and / or vertical redistribution of light power is generally performed without substantial change to the polarization of the received light.

The method 50 is for example to rotate the linear polarization of light by a significant angle, for example an angle greater than 45 degrees and often an angle of about 90 degrees in the polarization rotation region 16 of FIGS. 1A-1B and 4A-4C. Propagating laterally redistributed light power along the hybrid optical waveguide segment of the polarization rotor (step 56). The hybrid optical waveguide segment includes one segment in which the second optical waveguide rib is positioned vertically above the first optical waveguide rib, for example as in the left portion of the polarization rotation region 14 of FIGS. 1A-1B and 4A-4C, respectively. do. Since the two optical waveguide ribs are directed along the diverging direction in the hybrid optical waveguide segment of the polarization rotor, the hybrid optical waveguide segment is another segment in which the second optical waveguide rib is substantially laterally offset from the corresponding segment of the first optical waveguide rib. It includes. In the hybrid optical waveguide segment, the first and second optical waveguide ribs are formed of a material having different bulk refractive indices.

The method 50 finally reduces progressively the optical polarization rotor such that a substantial portion of the light power is redistributed transversely and / or vertically in the second transition region 16 of FIGS. 1A-1B and 4A-4C, for example. Propagating light from the hybrid optical waveguide segment through the configured waveguide segment (step 58). This final lateral redistribution of light power can be performed without substantially changing the polarization of the transmitted light. This lateral redistribution more efficiently couples polarized rotated light to the propagation light mode of the output planar waveguide, for example the output optical waveguide 20 of FIGS. 1A-1B and 4A-4C.

7 illustrates an optical modulator 43 that supports polarization mode multiplexing of digital data. The light modulator 43 includes 1 × 2 light splitter 44, first and second optical waveguide arms 45, 46 and 2 × 1 light combiner 47.

The 1 × 2 optical splitter 43 receives substantially linearly polarized light from the light source, for example laser light in TE or TM mode, and directs a portion of the received light to the two optical waveguide arms 45 and 46. Split into two light beams. In FIG. 7, the light source is illustrated as transmitting light of an exemplary TE mode to a 1 × 2 light splitter 44.

Each optical waveguide arm 45, 46 couples the corresponding light output of the 1 × 2 light splitter 43 to the corresponding light input of the 2 × 1 light combiner 47. The 1 × 2 optical splitter 43 transmits light of approximately the same linearly polarized light, illustrated in the exemplary TE propagation light mode, to the two optical waveguide arms 45, 46. Each of the optical waveguide arms (45, 46) comprises an electro-optical modulator (48_1, 48_2) is electrically connected to in order to receive the electrical digital data signal, i.e. a stream of DATA 1 or DATA _{_ _} 2. Each electro-optical modulator (48_1, 48_2) modulates the phase and / or amplitude of light propagating in order to transport the received stream of the received digital data signal, i.e., DATA or DATA _{_} 1 _{_} 2. The second optical waveguide arm 46 also includes an optical polarization rotor 49 that rotates linearly polarized light of light, for example optical polarization rotors 10, 10 ′ of FIGS. 1A-1B and 4A-4C. . The polarization rotor 49 is for example at least 45 degrees, more preferably such that the light flux modulated from the two optical waveguide arms 45, 46 has a substantially orthogonal polarization when recombined in the 2 × 1 light combiner 47. Rotate the linearly polarized light by about 90 degrees. The light beams modulated from the two optical waveguide arms 45 and 46 are combined in the 2x1 light combiner 47 to polarize multiplex the two data modulated light carriers.

In some other embodiments, the order of the optical polarization rotator (49) and the electro-optical modulator (48 _{_} 2) may be reversed in the optical waveguide arm 46.

The light modulator 43 may be manufactured in a fully optically integrated device or in a partially optically integrated device.

Figure 8 illustrates a part of an optical receiver (60) configured to demodulate data from the optical carrier, and optical carriers are multiplexed stream data DATA and DATA _{_} l _{_} 2 with polarized light. The optical receiver 60 includes a first optical polarization beam splitter 62, an optical polarization rotor 64, and first and second optical demodulators 66, 68. The optical polarization rotor 64 is connected to receive an optical signal from one optical output of the first optical polarization beam splitter 62 and to optically rotate the linear polarization of the received optical signal. Due to the action of the optical polarization rotor 64, both optical demodulators receive light of substantially similar or identical linear polarization, which is illustrated, for example, in the exemplary TE propagation light mode in FIG. 8. Thus, each of the light demodulators (66, 68) the digital data from the different linear polarization component of the received light at the input of the optical receiver 60, for example, the data stream DATA _{_} l 'and DATA _{_} 2' demodulates In the meantime, the two optical demodulators 66, 68 process light beams of substantially similar or identical linearly polarized light.

In some embodiments, the light output of optical polarization rotor 64 may be directly connected to an optional second optical polarization beam splitter (not shown), after which one of the optical outputs of the second optical polarization beam splitter is 2 Connect directly to the optical input of the optical demodulator 68. In this embodiment, the second optical polarization beam splitter serves as a clean up polarization filter for the optical polarization rotor 64.

In the optical receiver 60, an intermediate conversion of linear polarization of one luminous flux can be useful to ensure that the processing of each data carrier optical carrier is substantially similar. That is, intermediate conversion can be used to avoid problems related to the polarization dependence of the optical properties of the waveguides and media of the optical demodulators 66, 68.

The detailed description of exemplary embodiments and figures merely illustrates the principles of the invention. Accordingly, it will be appreciated that those skilled in the art, although not explicitly described or shown herein, may practice various principles of the present invention and to devise various devices included in the claimed invention. Moreover, all examples listed herein are intended in principle only for educational purposes to assist in understanding the principles of the inventions and concepts contributed to the technological development by the inventor, and are not limited to the examples and conditions specifically enumerated above. Should be interpreted as not. Moreover, all descriptions herein that list the principles, aspects, and examples of the present invention, as well as specific examples thereof, are intended to include equivalents thereof.

Claims (10)

A first optical waveguide rib and a second optical waveguide rib positioned along a planar surface of the substrate, wherein the second optical waveguide rib comprises an optical polarization rotor positioned further away from the surface than the first optical waveguide rib. and,
The first segment of the optical waveguide ribs forms a vertical stack over the substrate, the second segment of the optical waveguide rib is laterally offset in a direction along the surface,
The first optical waveguide ribs and the second optical waveguide ribs are formed of a material having a different bulk refractive index
Device.
The method of claim 1,
And a spacer layer positioned between the first optical waveguide rib and the second optical waveguide rib and formed of a material having a bulk refractive index different from that of the first and second optical waveguide ribs.
Device.

The method of claim 1,
One of the optical waveguide ribs is formed of a semiconductor, and the other of the optical waveguide ribs is formed of a dielectric
Device.
The method of claim 1,
And further comprising a transition region, wherein in the transition region
The first optical waveguide rib has a width transverse to the surface, monotonically decreasing from a large value in the input planar optical waveguide to a small value in the first segment of the first optical waveguide rib.
Device.
The method of claim 1,
And a polarizing beam splitter having a first optical output coupled to transmit light to the first optical waveguide rib, and a second optical output coupled to an output optical waveguide, the output optical waveguide transverse to the first optical waveguide rib. Positioned above the substrate
Device. The method of claim 1,
1 × 2 optical splitter, a first optical waveguide arm and a second optical waveguide arm, and a 2 × 1 light combiner, each optical waveguide arm having a corresponding light output of the 1 × 2 optical splitter; Further comprising a light modulator coupling to a corresponding light input of the light combiner,
Each optical waveguide arm includes an electro-optic modulator capable of modulating the phase and / or amplitude of light passing through and propagating in response to the received electrical signal,
An optical polarization rotor is located on one of the optical waveguide arms
Device.
Forming an optical layer over the first optical waveguide rib positioned along the planar surface of the substrate, wherein the optical layer and the first optical waveguide rib are formed of a material having different bulk refractive indices;
Etching the optical layer to form a second optical waveguide rib, wherein the first segment of the optical waveguide ribs forms a stack oriented perpendicular to the planar surface and the second segment of the optical waveguide ribs is the planar surface Relatively transversely offset along
Way.
The method of claim 7, wherein
Third and fourth segments of the first optical waveguide rib are positioned transverse to the second optical waveguide rib and are laterally wider than the first and second segments of the first optical waveguide rib. Wherein the first segment and the second segment of the first optical waveguide rib are connected between the third segment and the fourth segment of the first optical waveguide rib.
Way.
Receiving linearly polarized light from the planar waveguide at the first end of the segment of the hybrid optical waveguide,
Propagating the light through a segment of the hybrid optical waveguide to rotate the linear polarization of the light,
The segment of the hybrid optical waveguide comprises one segment in which a second optical waveguide rib is positioned vertically above the first optical waveguide rib, wherein the second optical waveguide rib is substantially transverse from the corresponding segment of the first optical waveguide rib. Contains other segments that are offset by
The first optical waveguide rib and the second optical waveguide rib are formed of a material having different bulk refractive indices
Way.
The method of claim 9,
The segment of the hybrid optical waveguide includes a spacer layer positioned between the first optical waveguide rib and the second optical waveguide rib and formed of a material having a bulk refractive index different from that of the optical waveguide ribs.
Way.

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