Switchable polarization rotator

Abstract

The invention relates to a switchable polarization rotator, to a structure of a polarization rotator and to a method of manufacturing a structure of a polarization rotator. The structure comprises a substrate, a first waveguide core located above the substrate, and a second waveguide core located above the substrate. The second waveguide core is arranged in proximity to a segment of the first waveguide core. The second waveguide core is composed of a material having a refractive index that reversibly changes in response to a stimulus.

Description

Technical Field

[0001] This invention relates to photonic chips, and more particularly to the structure of a polarization rotator and a method for manufacturing the structure of a polarization rotator. Background Technology

[0002] Photonic chips are used in many applications and systems, including but not limited to data communication and computing systems. Photonic chips integrate optical components (such as waveguides, optical switches, and directional couplers) with electronic components (such as field-effect transistors) on a unified platform. Among other factors, layout area, cost, and operational overhead can be reduced by integrating both types of components onto the same chip.

[0003] Polarization rotators are another common optical component in photonic chips. A polarization rotator can be configured to receive an optical signal with a given polarization state (e.g., a fundamental transverse magnetic (TM0) mode) as input and output a different polarization state (e.g., a fundamental transverse electric (TE0) mode). Polarization rotators are passive optical components with optical properties that cannot be adjusted, switched, or otherwise configured.

[0004] The structure of the polarization rotator that needs improvement, and the method for manufacturing the structure of the polarization rotator. Summary of the Invention

[0005] In one embodiment of the present invention, a structure for a polarization rotator is provided. The structure includes a substrate, a first waveguide core located above the substrate, and a second waveguide core located above the substrate. The second waveguide core is positioned adjacent to a section of the first waveguide core. The second waveguide core is composed of a material having a reversibly changing refractive index in response to a stimulus.

[0006] In one embodiment of the invention, a method for forming a structure of a polarization rotator is provided. The method includes forming a first waveguide core over a substrate and forming a second waveguide core over the substrate. The second waveguide core is disposed adjacent to a segment of the first waveguide core, and the second waveguide core is composed of a material having a reversibly changing refractive index in response to stimuli. Attached Figure Description

[0007] The accompanying drawings, which are included and constitute a part of this specification, illustrate various embodiments of the invention and, together with the foregoing general description of the invention and the following detailed description of these embodiments, serve to explain these embodiments of the invention. In these drawings, similar reference numerals denote similar features in different views.

[0008] Figure 1 A top view showing a structure in the initial manufacturing stage of a process method according to an embodiment of the present invention.

[0009] Figure 2 Showing the general outline Figure 1 The cross-sectional view of the structure is shown in line 2-2.

[0010] Figure 3 Display in Figure 1 A top view of the structure during the subsequent manufacturing phase.

[0011] Figure 4 Showing the general outline Figure 3 The cross-sectional view of the structure is shown in line 4-4.

[0012] Figure 5 Display in Figure 3 , 4 A cross-sectional view of the structure during the subsequent manufacturing phase.

[0013] Figure 6 A top view showing a structure according to an alternative embodiment of the present invention.

[0014] Figure 7 Showing the general outline Figure 6 The cross-sectional view of the structure is shown in line 7-7.

[0015] Figure 8 A top view showing a structure according to an alternative embodiment of the present invention.

[0016] Figure 9 Showing the general outline Figure 8 The cross-sectional view of the structure is shown in line 9-9.

[0017] Figure 10 A top view showing a structure according to an alternative embodiment of the present invention.

[0018] Figure 11 Showing the general outline Figure 10 The cross-sectional view of the structure is shown by line 11-11 in the figure.

[0019] Figure 12 Display in Figure 10 , 11 A cross-sectional view of the structure during the subsequent manufacturing phase. Detailed Implementation

[0020] Please refer to Figure 1 , 2According to an embodiment of the present invention, the structure 10 of the switchable polarization rotator includes a waveguide core 12 disposed on a dielectric layer 14 and above a substrate 16. The waveguide core 12 may be composed of a single-crystal semiconductor material, such as single-crystal silicon derived from the device layer of a silicon-on-insulator (SOI) wafer. The SOI wafer also includes a buried oxide layer composed of a dielectric material (e.g., silicon dioxide) to provide the dielectric layer 14, and the substrate 16 may be composed of a semiconductor material (e.g., single-crystal silicon). The waveguide core 12 may be patterned from the device layer of the SOI wafer during front-end process fabrication using photolithography and etching processes. The device layer of the SOI wafer may be fully etched to define a ridge waveguide (as shown), or alternatively, only partially etched near the waveguide core 12 to define a rib waveguide.

[0021] Waveguide core 12 includes segments 18, 20, and 22 aligned, adjacent, and connected along longitudinal axis 24. Segment 20 is disposed between segments 18 and 22. Segment 20 tapers (i.e., widens) in the reverse direction from segment 18 to segment 22, and conversely tapers (i.e., narrows) in the direction from segment 22 to segment 18. The widening direction may be the direction of light propagation through structure 10. Segment 20 may intersect segment 18 at one end and segment 22 at its opposite end. The width of segment 20 varies along its length from width W1 at its intersection with segment 18 to width W2 at its intersection with segment 22. In one embodiment, width W2 is greater than width W1. In one embodiment, segments 18 and 22 may be non-tapered or straight. The portion of segment 18 adjacent to segment 20 along its length may have width W1, and the portion of segment 22 adjacent to segment 20 along its length may have width W2.

[0022] Please refer to Figure 3 , 4 Similar reference numerals indicate Figure 1 , 2 Similar features are present in the waveguide core 12, and in the next manufacturing stage, a dielectric layer 32 is formed over the waveguide core 12. The dielectric layer 32 may be composed of a dielectric material (e.g., silicon dioxide), which is deposited by chemical vapor deposition and planarized by, for example, chemical mechanical polishing to remove morphology and provide a flat surface for subsequent deposition. The waveguide core 12 is disposed in the dielectric material of the dielectric layer 32, which acts as a low-refractive-index cladding layer.

[0023] Additional dielectric layers 34, 36, and 38 may be formed on dielectric layer 32. Dielectric layers 34 and 38 may be composed of silicon dioxide, and dielectric layer 36 may be composed of silicon nitride. In one embodiment, dielectric layer 36 may be omitted from this layer stack.

[0024] Waveguide core 40 may be disposed above substrate 16 and on dielectric layer 38. Waveguide core 40 may be formed by depositing a layer on dielectric layer 38 and patterning the deposited layer using photolithography and etching processes. For this purpose, an etch mask is formed on the deposited layer by photolithography, and the unmasked portions of the deposited layer are etched and removed using an etching process such as reactive ion etching. The shape of the etch mask determines the patterned shape of waveguide core 40. The etching process may be selected to stop on the material of dielectric layer 38 after completely penetrating the deposited layer.

[0025] In one embodiment, the waveguide core 40 may be composed of an active material having a refractive index that can be tuned (i.e., switched) by applying a stimulus (e.g., electrical, optical, or thermal). In one embodiment, the waveguide core 40 may be composed of a material characterized by a refractive index that changes reversibly between different states by the stimulus, these different states being characterized by significantly different refractive indices and light absorption properties. In one embodiment, the refractive index of the active material may exhibit multiple different states, with significantly different real and imaginary parts. For example, the refractive index of the active material may have a higher real part and a lower imaginary part in one state compared to another. In one embodiment, the stimulus used to facilitate this reversible change between the different refractive index states may be heating from a resistive heater providing temperature changes, an electric field provided by an applied voltage, a current provided by an applied voltage, or optical pumping by pump light provided by an external laser.

[0026] In one embodiment, the active material included in the waveguide core 40 may be a conductive oxide, such as indium tin oxide, whose real and imaginary parts of refractive index are approximately 2 and approximately 0, respectively, in one adjusted state, and approximately 1 and approximately 0.3, respectively, in another adjusted state. In one embodiment, the active material included in the waveguide core 40 may be a phase change material, such as vanadium oxide or germanium antimony telluride. For example, vanadium oxide undergoes a reversible metal-insulator phase transition between its metallic and insulating states at temperatures close to 68°C. In one embodiment, the active material included in the waveguide core 40 may be a two-dimensional material, such as graphene or molybdenum disulfide. In one embodiment, the active material included in the waveguide core 40 may be an electro-optic polymer.

[0027] Waveguide core 40 is disposed close to waveguide core 12 and offset vertically from waveguide core 12. Waveguide core 40 is located in a different layer within structure 10 than waveguide core 12. In this respect, waveguide core 12 is disposed in a layer between the layer containing substrate 16 and the layer containing waveguide core 40. The proximity of waveguide core 40 to waveguide core 12 provides sufficient spatial proximity to provide switching behavior through light absorption.

[0028] Waveguide core 40 includes segments 48, 50, and 52 aligned, continuously adjacent, and connected along a longitudinal axis 54, the longitudinal axis changing direction in different segments 48, 50, and 52. In one embodiment, segment 48 of waveguide core 40 may be arranged in an overlapping manner with segment 18 of waveguide core 12, and segment 50 of waveguide core 40 may be arranged in an overlapping manner with segment 20 of waveguide core 12. Segment 50 is arranged between segments 48 and 52. Segment 50 tapers (i.e., narrows) along the direction from segment 48 to segment 52, and conversely tapers (i.e., widens) in the opposite direction from segment 52 to segment 48. Segment 50 may intersect segment 48 at one end and segment 52 at its opposite end. The width of segment 50 varies along its length from a width W3 at its intersection with segment 48 to a width W4 at its intersection with segment 52. In one embodiment, width W4 is greater than width W3. In one embodiment, segments 48 and 52 may be non-conical or straight. The portion of segment 48 adjacent to segment 50 along its length may have a width W3, and the portion of segment 52 adjacent to segment 50 along its length may have a width W4.

[0029] Waveguide core 40 may terminate at end 42 and at end 44 opposite to end 42. A segment 48 of waveguide core 40 may extend from end 42 at an angle relative to waveguide core 12, and segment 48 may be positioned to overlap with segment 18 of waveguide core 12. A segment 50 of waveguide core 40 may be arranged to partially overlap with waveguide core 12 and may be primarily positioned above segment 20 of waveguide core 12. A segment 52 of waveguide core 40 may be angled away from waveguide core 12 and may terminate at end 44.

[0030] In an alternative embodiment, the waveguide core 40 can be shaped using an adiabatic bend. As used herein, the adiabatic bend comprises a gradual change along the direction to allow the optical signal to propagate without a significant reduction in optical confinement.

[0031] Please refer to Figure 5 Similar reference numerals indicate Figure 4 Similar features are present in the dielectric layer 38, and in the next manufacturing stage, a dielectric layer 55 can be formed over the dielectric layer 38 and the waveguide core 40. The dielectric layer 55 may be composed of a dielectric material (e.g., silicon dioxide), which is deposited by chemical vapor deposition or atomic layer deposition. In one embodiment, the dielectric layer 55 may be composed of a dielectric material (e.g., silicon dioxide), which is deposited by chemical vapor deposition using tetraethoxysilane (TEOS) as a reactant.

[0032] The back-end process stack 56 can be formed over the dielectric layer 55 via a back-end process. The back-end process stack 56 may include one or more dielectric layers that may be composed of dielectric materials such as silicon dioxide or low-k dielectric materials.

[0033] In one embodiment, a heater 58 may be disposed close to the waveguide core 40. In this representative embodiment, the heater 58 is disposed close to the waveguide core 40 in a back-end process stack 56. This proximity of the heater 58 to the waveguide core 40 is spatially close and sufficient to provide stimulation for changes in the refractive index of the active material of the waveguide core 40 through temperature variations.

[0034] Heater 58 may be composed of a metal such as nickel-chromium, tantalum nitride, or titanium nitride, which is deposited and patterned. Heater 58 is powered by a power supply 64 coupled to metal features 60, 62 located in the back-end process stack 56, thereby providing a temperature variation that induces a change in the refractive index of the active material of waveguide core 40. During operation, heat is transferred from the powered heater 58 to the waveguide core 40 through the dielectric material of the back-end process stack 56. The temperature of waveguide core 40 can be varied above and below the state transition temperature by selectively applying heat as a stimulus to provide different refractive indices.

[0035] During use, an optical signal propagating in transverse magnetic (TM) mode can be guided onto a photonic chip via waveguide core 12 for input to structure 10. When the active material of waveguide core 40 is conditioned (e.g., by a temperature below the phase transition temperature) to a refractive index state, waveguide cores 12 and 40 cooperate to rotate the polarization mode of the light contained in the optical signal from the TM mode to the transverse electric (TE) mode, thereby outputting from structure 10. In particular, the overlapping arrangement of segment 18 of waveguide core 12 and segment 48 of waveguide core 40 and / or the overlapping arrangement of segment 20 of waveguide core 12 and segment 50 of waveguide core 40 can provide polarization, wherein the polarization mode of the light is rotated. Depending on the length of waveguide cores 12 and 40, the light emitted from structure 10 can be polarized to include only the TE mode light, or, alternatively, a polarization mixture can be included, comprising light containing a TE mode component and light containing a TM mode component. When the active material of waveguide core 40 is tuned (e.g., by a temperature greater than the phase transition temperature) to another refractive index state, waveguide core 40 can effectively block light transmission through structure 10 by absorbing and dissipating the input light signal, thereby providing optical switching.

[0036] In any embodiment of structure 10 described herein, structure 10 may be integrated into a photonic chip including electronic components and additional optical components. For example, the electronic components may include field-effect transistors manufactured using a CMOS front-end-of-line (FEOL) process.

[0037] Please refer to Figure 6 , 7According to an alternative embodiment of the invention, waveguide core 60 may be disposed above substrate 16 in an overlapping relationship with waveguide core 12, and waveguide core 40 may be laterally offset to be disposed in a non-overlapping relationship with waveguide core 12. Waveguide core 60 may be disposed close to waveguide core 40 and located in the same layer within structure 10. Therefore, the two waveguide cores 40 and 60 are located in different layers within structure 10 from waveguide core 12. In this respect, waveguide core 12 is disposed in a layer between the layer containing substrate 16 and the layer containing waveguide cores 40 and 60.

[0038] Waveguide core 60 can be formed by depositing a dielectric layer 38 and patterning the deposited layer using photolithography and etching processes. For this purpose, an etch mask is formed over the deposited layer using photolithography, and the unmasked portions of the deposited layer are etched and removed using an etching process (e.g., reactive ion etching). The shape of the etch mask determines the patterned shape of the waveguide core 60. The etching process can be selected to stop on the material of the dielectric layer 38 after completely penetrating the deposited layer. In one embodiment, waveguide core 60 may be composed of a dielectric material (e.g., silicon nitride). In an alternative embodiment, waveguide core 60 may be composed of polysilicon. Waveguide core 60 may be masked during the formation of waveguide core 40.

[0039] Waveguide core 60 includes segments 68, 70, and 72 aligned, continuously adjacent, and connected along a longitudinal axis 74, the longitudinal axis changing direction in different segments 68, 70, and 72. Segment 70 is arranged between segments 68 and 72. Segment 70 tapers (i.e., narrows) along the direction from segment 68 to segment 72, and conversely tapers (i.e., widens) in the opposite direction from segment 72 to segment 68. Segment 70 may intersect segment 68 at one end and segment 72 at its opposite end. The width of segment 70 narrows along its length from where it intersects segment 68 to where it intersects segment 72. In one embodiment, segments 68 and 72 may be non-tapered or straight.

[0040] Waveguide core 60 can be perpendicularly offset from waveguide core 12 and laterally offset from waveguide core 40. In this representative embodiment, segment 68 of waveguide core 60 can be arranged in an overlapping manner with segment 18 of waveguide core 12, and segment 70 of waveguide core 60 can be arranged in an overlapping manner with segment 20 of waveguide core 12. Segment 68 of waveguide core 60 can be tilted at a certain angle relative to waveguide core 12. Segment 72 of waveguide core 60 can be tilted at a certain angle to offset from waveguide core 12.

[0041] Waveguide core 40 includes segment 48, which is laterally offset from segment 68 of waveguide core 60, and segment 50, which is laterally offset from segment 70 of waveguide core 60. Segments 48 and 50 are arranged at an angle relative to each other, and segment 50 may be non-conical. The longitudinal axis 54 of segment 48 of waveguide core 40 may be arranged parallel or substantially parallel to the longitudinal axis 74 of segment 68 of waveguide core 60, such that segment 48 and segment 68 are tilted at the same angle or substantially the same angle relative to segment 18 of waveguide core 12. The longitudinal axis 54 of segment 50 of waveguide core 40 may be arranged parallel or substantially parallel to the longitudinal axis 74 of segment 70 of waveguide core 60, such that segment 50 and segment 70 are tilted at the same angle or substantially the same angle relative to segment 20 of waveguide core 12.

[0042] In an alternative embodiment, an adiabatic bend-shaped waveguide core 60 may be utilized. As used herein, the adiabatic bend comprises a gradual change along the direction so that the optical signal can propagate without a significant reduction in optical confinement.

[0043] During use, when the active material of waveguide core 40 is adjusted (e.g., by a temperature below the phase transition temperature) to a refractive index state, waveguide cores 12 and 60 cooperate to rotate the polarization mode of the light contained in the optical signal from the TM mode to the transverse electric (TE) mode, thereby outputting from structure 10. Specifically, the overlapping arrangement of segment 18 of waveguide core 12 and segment 68 of waveguide core 60 and / or the overlapping arrangement of segment 20 of waveguide core 12 and segment 70 of waveguide core 60 can provide a polarization region in which the polarization mode of the light is rotated. Depending on the length of waveguide cores 12 and 60, the light emitted from structure 10 can be polarized to include only the TE mode light, or alternatively, a polarization mixture can be included, comprising light containing both the TE mode component and the TM mode component. When the active material of waveguide core 40 is adjusted (e.g., by a temperature above the phase transition temperature) to another refractive index state, waveguide core 40 can effectively block light transmission through structure 10 by absorbing and dissipating the input optical signal, thereby providing optical switching.

[0044] Please refer to Figure 8 , 9 According to an alternative embodiment of the invention, waveguide core 40 may be vertically offset from waveguide core 60 and may be configured to overlap with waveguide core 60. In this respect, waveguide core 40 may be disposed in a different layer within structure 10 than waveguide core 60. Therefore, each waveguide core 12, 40, 60 is located in a different layer within structure 10, with waveguide core 60 disposed vertically between waveguide core 40 and waveguide core 12.

[0045] During use, when the active material of waveguide core 40 is adjusted (e.g., by a temperature below the phase transition temperature) to a refractive index state, waveguide cores 12 and 60 cooperate to rotate the polarization mode of the light contained in the optical signal from the TM mode to the transverse electric (TE) mode, thereby outputting from structure 10. Specifically, the overlapping arrangement of segment 18 of waveguide core 12 and segment 68 of waveguide core 60 and / or the overlapping arrangement of segment 20 of waveguide core 12 and segment 70 of waveguide core 60 can provide a polarization region in which the polarization mode of the light is rotated. Depending on the length of waveguide cores 12 and 60, the light emitted from structure 10 can be polarized to include only the TE mode light, or alternatively, a polarization mixture can be included, comprising light containing both the TE mode component and the TM mode component. When the active material of waveguide core 40 is adjusted (e.g., by a temperature above the phase transition temperature) to another refractive index state, waveguide core 40 can effectively block light transmission through structure 10 by absorbing and dissipating the input optical signal, thereby providing optical switching.

[0046] Please refer to Figure 10 , 11 According to an alternative embodiment of the invention, the waveguide core 40 may be laterally offset from the waveguide core 12 and disposed close to the waveguide core 12 in a parallel and non-overlapping relationship, and located in the same layer as the waveguide core 12 within the structure 10.

[0047] Please refer to Figure 12 Similar reference numerals indicate Figure 10 , 11 Similar features are present in the waveguide cores 12 and 40. In the next manufacturing stage, dielectric layers 34, 36, and 38 can be formed above the waveguide cores 12 and 40, and waveguide core 60 can be formed on dielectric layer 38 at a different level than waveguide cores 12 and 40. Waveguide core 60 can be perpendicularly offset from waveguide core 12 and arranged in an overlapping relationship with waveguide core 12.

[0048] During use, when the active material of waveguide core 40 is adjusted (e.g., by a temperature below the phase transition temperature) to a refractive index state, waveguide cores 12 and 60 cooperate to rotate the polarization mode of the light contained in the optical signal from the TM mode to the transverse electric (TE) mode, thereby outputting from structure 10. Specifically, the overlapping arrangement of segment 18 of waveguide core 12 and segment 68 of waveguide core 60 and / or the overlapping arrangement of segment 20 of waveguide core 12 and segment 70 of waveguide core 60 can provide a polarization region in which the polarization mode of the light is rotated. Depending on the length of waveguide cores 12 and 60, the light emitted from structure 10 can be polarized to include only the TE mode light, or alternatively, a polarization mixture can be included, comprising light containing both the TE mode component and the TM mode component. When the active material of waveguide core 40 is adjusted (e.g., by a temperature above the phase transition temperature) to another refractive index state, waveguide core 40 can effectively block light transmission through structure 10 by absorbing and dissipating the input optical signal, thereby providing optical switching.

[0049] The method described above is used for the manufacture of integrated circuit chips. Manufacturers can distribute the resulting integrated circuit chips in raw wafer form (e.g., as a single wafer with multiple unpackaged chips), as bare chips, or in packaged form. The chip can be integrated with other chips, discrete circuit elements, and / or other signal processing devices as part of an intermediate or final product. The final product can be any product including the integrated circuit chip, such as a computer product with a central processing unit or a smartphone.

[0050] The terms used herein, modified by approximate language such as “approximately,” “roughly,” and “substantially,” are not limited to the specified precise values. This approximate language may correspond to the accuracy of the instrument used to measure the value, and may represent + / - 10% of the value unless otherwise dependent on the accuracy of that instrument.

[0051] The terms "vertical" and "horizontal" are used in this document as examples to establish a reference framework and are not intended to be limiting. The term "horizontal" as used herein is defined as a plane parallel to the conventional plane of the semiconductor substrate, regardless of its actual three-dimensional spatial orientation. The terms "vertical" and "orthogonal" refer to directions perpendicular to the horizontal plane as defined above. The term "lateral" refers to a direction within that horizontal plane.

[0052] A feature "connected" or "coupled" to another feature may be directly connected or coupled to that other feature, or one or more intermediate features may exist. If no intermediate features exist, the feature may be "directly connected" or "directly coupled" to the other feature. If at least one intermediate feature exists, the feature may be "indirectly connected" or "indirectly coupled" to the other feature. A feature "on" or "in contact" with another feature may be directly on or in contact with that other feature, or one or more intermediate features may exist. If no intermediate features exist, the feature may be directly "on" or in contact with that other feature. If at least one intermediate feature exists, the feature may not be "directly" on or in contact with that other feature. If one feature extends over and covers a portion of another feature, the different features may "overlap".

[0053] The descriptions of various embodiments of the invention are for illustrative purposes only and are not intended to be exhaustive or limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the embodiments. The terminology used herein has been chosen to best explain the principles of the embodiments, their practical application, or improvements upon technical techniques known in the market, or to enable those skilled in the art to understand the embodiments disclosed herein.

Claims

1. A structure for a polarization rotator, characterized in that, The structure includes: Substrate; A first waveguide core, located above the substrate, comprises segments; A second waveguide core is located above the substrate, the second waveguide core is positioned close to the segment of the first waveguide core, and the second waveguide core is perpendicularly offset from the first waveguide core; and A third waveguide core, perpendicularly offset from the first waveguide core, includes a segment that overlaps with the segment of the first waveguide core. The second waveguide core includes a first material having a refractive index that changes reversibly in response to stimuli, the first waveguide core includes a second material different from the first material, and the third waveguide core includes a third material different from both the first and second materials.

2. The structure as described in claim 1, characterized in that, The first material includes conductive oxides, phase change materials, two-dimensional materials, or electro-optic polymers.

3. The structure as described in claim 2, characterized in that, The second material includes monocrystalline silicon, and the third material includes silicon nitride.

4. The structure as described in claim 3, characterized in that, The second material includes monocrystalline silicon, and the third material includes polycrystalline silicon.

5. The structure as described in claim 1, characterized in that, The segment of the third waveguide core and the segment of the first waveguide core define a polarization region configured to rotate the polarization mode of light, and the second waveguide core is configured to absorb the light when the stimulus is applied to the first material.

6. The structure as described in claim 1, characterized in that, The second waveguide core and the third waveguide core are arranged in an overlapping relationship, and the third waveguide core is arranged vertically between the first waveguide core and the second waveguide core.

7. The structure as described in claim 1, further comprising: A heater, located near the second waveguide core, is configured to selectively transfer heat to the second waveguide core as the stimulus.

8. A polarization rotation structure, characterized in that, The structure includes: Substrate; A first waveguide core, located above the substrate, comprises segments; A second waveguide core, located above the substrate, is positioned close to the segment of the first waveguide core, and is laterally offset from the first waveguide core in a non-overlapping relationship; and A third waveguide core is perpendicularly offset from the first waveguide core, and the third waveguide core includes a segment that overlaps with the segment of the first waveguide core. The second waveguide core includes a first material having a refractive index that changes reversibly in response to stimuli, the first waveguide core includes a second material different from the first material, and the third waveguide core includes a third material different from both the first and second materials.

9. The structure as described in claim 8, characterized in that, The segment of the third waveguide core and the segment of the first waveguide core define a polarization region configured to rotate the polarization mode of light, and the second waveguide core is configured to absorb the light when the stimulus is applied to the first material.

10. The structure as described in claim 8, characterized in that, The second waveguide core is positioned adjacent to the third waveguide core.

11. The structure as described in claim 8, characterized in that, The third waveguide core includes a segment that overlaps with the segment of the first waveguide core.

12. The structure as described in claim 11, characterized in that, The segment of the third waveguide core and the segment of the first waveguide core define a polarization region configured to rotate the polarization mode of light, and the second waveguide core is configured to absorb the light when the stimulus is applied to the first material.

13. The structure as described in claim 8, characterized in that, The first material includes conductive oxides, phase change materials, two-dimensional materials, or electro-optic polymers.

14. The structure as described in claim 8, characterized in that, The second material includes monocrystalline silicon, and the third material includes silicon nitride or polycrystalline silicon.

15. The structure of claim 8, further comprising: A heater, located near the second waveguide core, is configured to selectively transfer heat to the second waveguide core as the stimulus.

16. A structure for a polarization rotator, characterized in that, The structure includes: Substrate; A first waveguide core, located above the substrate, comprises segments; A second waveguide core, located above the substrate, is positioned close to the segment of the first waveguide core; and A third waveguide core is located above the substrate, close to the first and second waveguide cores, perpendicularly offset from the first waveguide core, and includes a segment that overlaps with a segment of the first waveguide core. The second waveguide core includes a first material having a refractive index that changes reversibly in response to stimuli, the first waveguide core includes a second material different from the first material, and the third waveguide core includes a third material different from both the first and second materials.

17. The structure as described in claim 16, characterized in that, Also includes: A heater, located near the second waveguide core, is configured to selectively transfer heat to the second waveguide core as the stimulus.

18. The structure as described in claim 16, characterized in that, The first material includes conductive oxides, phase change materials, two-dimensional materials, or electro-optic polymers.

19. The structure as described in claim 16, characterized in that, The second material includes monocrystalline silicon, and the third material includes silicon nitride.

20. The structure as described in claim 16, characterized in that, The second material includes monocrystalline silicon, and the third material includes polycrystalline silicon.

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