Polarization mode selectable coupling structures, tunable polarization filters and photonic chips

Abstract

The embodiment of the application provides a polarization mode selectable coupling structure, a tunable polarization filter and a photonic chip, wherein the polarization mode selectable coupling structure comprises: a silicon layer; a silicon micro-ring resonant cavity arranged on the silicon layer; and a bus waveguide arranged on one side of the silicon layer and used as input and output of the polarization mode selectable coupling structure, the bus waveguide and the silicon micro-ring resonant cavity forming a coupling area; wherein base mode transverse electric mode polarized light of the bus waveguide is phase matched and coupled with a first mode of the silicon micro-ring resonant cavity; and base mode transverse magnetic mode polarized light of the bus waveguide is phase matched and coupled with a second mode of the silicon micro-ring resonant cavity.

Description

Technical Field

[0001] This application relates to the field of optical device design technology, and more specifically, to a polarization mode selectable coupling structure, a tunable polarization filter, and a photonic chip. Background Technology

[0002] Currently, devices for polarization filtering or switching mainly include polarization beamsplitters based on multimode interferometers (MMI), polarization beamsplitters based on directional couplers (DC), or devices based on waveguide gratings. However, these devices have the following drawbacks: large size and poor adjustability. Summary of the Invention

[0003] The purpose of this application is to provide a polarization mode selectable coupling structure, a tunable polarization filter, and a photonic chip that can achieve polarization mode selectability using fewer structures.

[0004] In a first aspect, the present invention provides a polarization mode selectable coupling structure, comprising: a silicon layer; a silicon micro-ring resonator disposed on the silicon layer; and a bus waveguide disposed on one side of the silicon layer for serving as the input and output of the polarization mode selectable coupling structure, wherein the bus waveguide forms a coupling region with the silicon micro-ring resonator; wherein the fundamental transverse electric mode polarized light of the bus waveguide is phase-matched and coupled with a first mode of the silicon micro-ring resonator; and the fundamental transverse magnetic mode polarized light of the bus waveguide is phase-matched and coupled with a second mode of the silicon micro-ring resonator.

[0005] In the above implementation, two modes, i.e., tunable polarization, can be achieved with relatively few structural designs. Specifically, by setting a silicon micro-ring resonator on the silicon layer, phase matching and coupling can be achieved in different modes, enabling polarization mode selection. Furthermore, since this application only requires setting a silicon micro-ring resonator on the silicon layer, its footprint is much smaller than that of traditional polarization devices based on interferometers or adiabatic cones, typically within tens of micrometers square, greatly improving integration density.

[0006] In an optional embodiment, a dielectric layer is disposed between the silicon micro-ring resonator and the bus waveguide.

[0007] In the above implementation, a dielectric layer can also be set to create a gap between the silicon micro-ring resonator and the bus waveguide, forming a distance that makes it easier to achieve phase matching and coupling.

[0008] In an optional embodiment, the dielectric layer is a silicon dioxide layer.

[0009] In the above implementation, a silicon dioxide layer is used as the dielectric layer, which is a common cladding material. When used as a coupling spacer layer, it provides a stable, low-loss insulating environment.

[0010] In an optional embodiment, the spacing between the silicon micro-ring resonator and the bus waveguide in a first direction is between 50 nm and 200 nm, where the first direction is perpendicular to the silicon layer.

[0011] In the above implementation, setting the thickness of the dielectric layer in the range of 50 nm to 200 nm can enhance or suppress coupling at a specific operating wavelength, thus achieving wavelength-selective coupling.

[0012] In an optional implementation, the width of the bus waveguide is between 500 nm and 1.5 µm.

[0013] In an optional implementation, the thickness of the bus waveguide is between 200 nm and 800 nm.

[0014] In the above implementation, the width and thickness together define the geometry of the "pipeline" through which light is confined and guided. The width and thickness of the bus waveguide can be set, which directly determines the "mode" characteristics of light propagating in this pipe. In the above implementation logic, the width is limited to between 500 nm and 1.5 µm, and the thickness is limited to between 200 nm and 800 nm, which can better achieve specific polarization and mode-selective coupling.

[0015] In an optional embodiment, the distance between the bus waveguide and the silicon micro-ring resonator in a second direction is a value between -200 nm and 500 nm, where the second direction is parallel to the silicon layer.

[0016] In the above implementation, by setting the distance of the silicon micro-ring resonator in the second direction between -200 nm and 500 nm, the overall required size is relatively smaller, and specific polarization and mode-selective coupling can be better achieved.

[0017] In an optional embodiment, the waveguide width or curvature of the silicon micro-ring resonator is non-uniformly distributed along the loop.

[0018] In the above implementation, the curvature and waveguide width of the silicon micro-ring resonator are non-uniformly distributed at different locations (especially in the uncoupled curved region), which enables it to support at least two modes while suppressing the bending loss of higher-order modes and inter-mode crosstalk.

[0019] In an optional embodiment, the resonant wavelength of the silicon micro-ring resonator satisfies: Where m represents a positive integer; L represents the ring length of the silicon micro-ring resonator; Indicates the operating wavelength; This indicates the resonant wavelength of the silicon micro-ring resonator.

[0020] Secondly, the present invention provides a tunable polarization filter, comprising: a polarization mode selectable coupling structure as described in any of the foregoing embodiments; a tuning device disposed within or around the silicon micro-ring resonator for adjusting the refractive index of the silicon micro-ring resonator; wherein, when a first voltage is applied to the tuning device, one of the resonance peaks in the first mode is aligned with a preset operating wavelength, and the resonance peak in the second mode is moved away from the preset operating wavelength; when a second voltage is applied to the tuning device, one of the resonance peaks in the second mode is aligned with the preset operating wavelength, and the resonance peak in the first mode is moved away from the preset operating wavelength.

[0021] In the above-described implementation of this application, the tuning of the silicon micro-ring resonator is achieved based on a tuning device. Typically, only a few nanometers of resonant wavelength needs to be moved to achieve state switching. Compared with devices that require a wide range of tuning, the power consumption is significantly reduced.

[0022] In an optional embodiment, the tuning device includes a thermal tuner for adjusting the effective refractive index of the silicon microring resonator by applying a tuning signal.

[0023] In an optional embodiment, the tuning device includes an electrical tuner for adjusting the effective refractive index of the silicon microring resonator by applying a tuning signal.

[0024] In the above implementation, the tuning device can be either a thermal tuner or an electric tuner, making the tuning method relatively more flexible.

[0025] Thirdly, the present invention provides a photonic chip including the tunable polarization filter described in any of the foregoing embodiments. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1a A schematic diagram of a polarization mode selectable coupling structure provided in an embodiment of this application;

[0028] Figure 1b for Figure 1a A schematic diagram of the coupling structure with selectable polarization modes from another perspective;

[0029] Figure 2a A schematic diagram of the resonance spectrum provided in the embodiments of this application;

[0030] Figure 2b Another schematic diagram of the resonance spectrum provided in this application embodiment;

[0031] Figure 3 This is a schematic diagram of the structure of a tunable polarization filter provided in an embodiment of this application.

[0032] Icons: 100 - Polarization mode selectable coupling structure; 110 - Silicon layer; 111 - Top layer; 112 - Middle layer; 113 - Bottom layer; 120 - Bus waveguide; 130 - Silicon micro-ring resonator; 200 - Tunable polarization filter; 210 - Tuning device. Detailed Implementation

[0033] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.

[0034] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0035] In the description of this application, it should be noted that the terms "upper", "lower", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations of this application.

[0036] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set," "install," and "connect" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0037] With the development of optical communication, optical computing, and optical sensing systems, the demand for refined processing of optical signals is increasing. Polarization is one of the fundamental properties of light, and polarization management (such as polarization separation, rotation, or filtering) is crucial in many photonic systems.

[0038] In silicon photonics platforms, due to the high refractive index difference and submicron waveguide size of silicon waveguides, their optical properties have a strong polarization dependence. However, the current polarization-related devices have relatively high losses, and there is a demand for polarization processing devices based on this background. At present, the devices that realize polarization filtering or switching mainly include polarization beam splitters based on multimode interferometers (MMI), polarization beam splitters based on directional couplers (DC), or devices based on waveguide gratings. The polarization filtering devices obtained by these methods often have the following disadvantages: (1) Traditional polarization beam splitters (PBS) are usually broadband and static. Their function is to separate the transverse electric mode (TE) and transverse magnetic mode (TM) to different output ports, but they cannot achieve "selective pass" (i.e., select TE or TM at the same output port). (2) To achieve a high extinction ratio, the length of many traditional polarization devices (such as adiabatic tapered couplers) may reach hundreds of micrometers or even millimeters, which is not conducive to high-density integration. (3) The function of most polarization devices is fixed after manufacturing, making it difficult to dynamically adjust their polarization response during use. Based on the above situation, there is an urgent need for a device that is compact, has low power consumption, is compatible with standard CMOS processes, and can achieve dynamically tunable polarization filtering function.

[0039] Based on the above research, embodiments of this application provide a polarization mode selectable coupling structure, a tunable polarization filter, and a photonic chip, which belong to the fields of integrated optics and silicon-based optoelectronics. In particular, it relates to a novel optical filter, specifically an on-chip tunable polarization filter capable of selectively passing between transverse electric mode polarization and transverse magnetic mode polarization.

[0040] Figure 1a and Figure 1b This is a schematic diagram of the polarization mode selectable coupling structure 100 provided in an embodiment of this application. (See attached diagram.) Figure 1a and Figure 1b As shown, the polarization-mode selectable coupling may include: a silicon layer 110, a silicon micro-ring resonator 130, and a bus waveguide 120. Wherein, Figure 1b The perspective shown is the same as... Figure 1aThe angles shown are perpendicular to each other.

[0041] In this embodiment, the silicon micro-ring resonator 130 is disposed on the silicon layer 110. Exemplarily, the silicon micro-ring resonator 130 can be formed on the silicon layer 110.

[0042] Optionally, the silicon layer 110 can be silicon-on-insulator (SOI). It can contain a multilayer structure, such as... Figure 1b As shown, it may include a bottom layer 113, a middle layer 112 and a top layer 111.

[0043] For example, the bottom layer 113 may be a silicon substrate. The intermediate layer 112 may be a buried oxide layer, i.e., an insulating layer, typically silicon dioxide. The top layer 111 may be a single-crystal silicon thin film used to fabricate transistors or photonic devices.

[0044] In this embodiment, the bus waveguide 120 can be disposed on one side of the silicon layer 110 and used as the input and output of the polarization mode selectable coupling structure 100.

[0045] Optionally, the bus waveguide 120 is positioned above or below the silicon micro-ring resonator 130.

[0046] Specifically, the fundamental transverse electric mode polarized light of the bus waveguide 120 is phase-matched and coupled with the first mode of the silicon micro-ring resonator 130; the fundamental transverse magnetic mode polarized light of the bus waveguide 120 is phase-matched and coupled with the second mode of the silicon micro-ring resonator 130.

[0047] Optionally, the first mode can be the TE00 mode. The TE00 mode is a type of transverse electric mode. In a transverse electric mode, the electric field is entirely in the transverse plane (perpendicular to the direction of light propagation), while the magnetic field has a component in the longitudinal direction (propagation direction).

[0048] In this context, the subscript "00" in TE00 mode indicates that the field distribution of this TE00 mode in both orthogonal dimensions (e.g., x and y) of the waveguide cross-section is the fundamental mode (zero-order variation). The TE00 mode is the lowest-order transverse electric mode that the waveguide can support.

[0049] The electric field of the TE00 mode lies entirely within the cross-sectional plane of the waveguide (e.g., only along the x-direction) and has zero components in the propagation direction (z-direction). Its intensity is strongest at the center of the cross-section and smoothly decays towards the edges according to a specific function (such as the Gaussian approximation, Bessel function, etc.). The magnetic field of the TE00 mode has components in both the transverse and longitudinal directions. The field pattern of the TE00 mode is typically a single-peak, nodeless bell-shaped distribution on the cross-section.

[0050] The TE00 mode is a fundamental mode that never cuts off. It exists as long as the waveguide structure is present, regardless of its size (up to the nanoscale, although losses become extremely high). The TE00 mode produces linearly polarized light with a fixed electric field vector direction.

[0051] In this embodiment, the optional coupling structure is designed to enable phase matching and coupling between the fundamental transverse electric mode polarized light of the bus waveguide 120 and the TE00 mode of the silicon micro-ring resonator 130.

[0052] Optionally, the second mode can be the TE01 mode, which is a higher-order horizontal electric mode.

[0053] In the TE01 mode, the subscript "01" indicates that the TE01 mode has a uniform (unchanging) field distribution along the wide side direction, and a "two-lobed" field distribution along the narrow side direction with a zero point (node) in the middle.

[0054] The electric field in the TE01 mode typically has only one transverse component, such as E*x* (or E*y*, depending on the coordinate system definition, but usually E in TE01 is parallel to the wide side). Along the x-direction: the electric field strength is uniformly distributed and remains constant. Along the y-direction: the electric field strength follows a sinusoidal (or cosine) function distribution. At the center point of the narrow side (y=b / 2), the electric field strength is zero (at the node). At the two boundaries of the narrow side (y=0 and y=b), the electric field amplitude is maximum but in opposite directions (one positive and one negative).

[0055] The magnetic field of the TE01 mode has components in both the transverse and longitudinal directions, and its distribution is determined by the electric field. It also has a complex structure at the center of the narrow side.

[0056] The TE01 mode is a higher-order mode with a cutoff frequency or cutoff wavelength. For a rectangular waveguide, the cutoff wavelength λ is... c The calculation formula is: λ c (TE01) = 2b, where b represents the length of the smaller side in the cross-section of the bus waveguide 120, i.e., the inner wall dimension of the narrow side; λ c (TE01) indicates the cutoff wavelength in TE01 mode.

[0057] In this embodiment, the polarization mode selectable coupling structure 100 is designed to enable phase matching and coupling between the fundamental transverse magnetic mode polarized light of the bus waveguide 120 and the TE01 mode of the silicon micro-ring resonator 130.

[0058] The above explanation uses TE00 and TE01 modes as examples. In practical applications, other modes can be selected for the first and second modes based on the needs of the application scenario where the polarization mode of the coupling structure 100 is selectable. For example, TE10 mode, TM01 mode, etc.

[0059] In this embodiment, the silicon micro-ring resonator 130 can be a closed waveguide loop, and its curvature and waveguide width can be optimized at different locations. Specifically, it can be optimized in the uncoupled curved region of the silicon micro-ring resonator 130. Based on the optimized design, the silicon micro-ring resonator 130 can support the fundamental mode TE00 and TE01 modes, while suppressing the bending loss and inter-mode crosstalk of higher-order modes.

[0060] Optionally, the curvature and waveguide width of the silicon micro-ring resonator 130 can be designed through simulation.

[0061] Optionally, the effective refractive index of the silicon microring resonator 130 can be altered using the plasma dispersion effect or thermo-optic effect of silicon. With different effective refractive indices, different types of light can be brought into a resonant state. Light in a resonant state can be coupled into the silicon microring resonator 130 and lost within it, resulting in extremely low intensity of the resonant light at the output of the bus waveguide 120. For light not in a resonant state, it hardly interacts with the silicon microring resonator 130 and passes directly through the bus waveguide 120.

[0062] In an alternative embodiment, the bus waveguide 120 may be a silicon nitride bus waveguide 120. The width, thickness, and lateral position of the silicon nitride bus waveguide 120 relative to the silicon microring resonator 130 are designed to achieve specific polarization and mode-selective coupling.

[0063] In this embodiment, in the region where the bus waveguide 120 and the silicon micro-ring resonator 130 are close to each other, the optical field undergoes evanescent wave coupling, and the region where the bus waveguide 120 and the silicon micro-ring resonator 130 are close to each other forms a coupling region.

[0064] Optionally, the bus waveguide 120 is positioned above or below the silicon micro-ring resonator 130 along a first direction. The first direction is perpendicular to the silicon layer 110. The bus waveguide 120 and the silicon micro-ring resonator 130 can cooperate to form a vertical coupling region.

[0065] For example, the regions where the silicon nitride bus waveguide 120 and the silicon micro-ring resonator 130 are close to each other can form a three-dimensional coupling structure of SiN-on-Si.

[0066] In the above implementation, a silicon micro-ring resonator 130 is formed on the silicon layer 110. The effective refractive index of the silicon micro-ring resonator 130 can be easily adjusted. Therefore, by setting this structure, a polarization mode selectable coupling structure 100 can be formed. Switching between multiple operating modes can be accomplished using auxiliary devices that can interfere with the effective refractive index of the silicon micro-ring resonator 130.

[0067] In an alternative implementation, a dielectric layer is disposed between the silicon micro-ring resonator 130 and the bus waveguide 120.

[0068] The dielectric layer can space the silicon micro-ring resonator 130 from the bus waveguide 120.

[0069] Optionally, the dielectric layer is a silicon dioxide layer 110. Optionally, the dielectric layer may also be a silicon nitride layer 110.

[0070] Optionally, the spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the first direction can be verified by simulation to show the working effect of different spacings in the first and second modes, thereby selecting a suitable spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the first direction.

[0071] In this embodiment, the spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the first direction is between 50 nm and 200 nm.

[0072] For example, the spacing between the silicon microring resonator 130 and the bus waveguide 120 in the first direction can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 110 nm, 120 nm, 150 nm, 160 nm, 180 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, or 250 nm, etc. It is understood that the above are merely examples of a few possible values, and the spacing between the silicon microring resonator 130 and the bus waveguide 120 in the first direction can also be some values ​​that are not multiples of 10, or some values ​​between the various examples described above.

[0073] By setting the spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the first direction to the value described above, switching between the required operating modes can be better achieved.

[0074] Optionally, the width of the bus waveguide 120 can be verified by simulation to show the working effect of different widths in the first and second modes, thereby selecting a suitable width for the bus waveguide 120.

[0075] In this embodiment, the width of the bus waveguide 120 is between 500 nm and 1.5 µm.

[0076] For example, the width of the bus waveguide 120 can be 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 µm, 1.2 µm, 1.3 µm, 1.4 µm, or 1.5 µm. It is understood that the above are merely examples of a few possible values, and the width of the bus waveguide 120 can also be any of the values ​​listed above.

[0077] Optionally, the thickness of the bus waveguide 120 can be verified by simulation to show the working effect of different thicknesses in the first and second modes, thereby selecting a suitable thickness for the bus waveguide 120.

[0078] In this embodiment, the thickness of the bus waveguide 120 is between 200 nm and 800 nm.

[0079] For example, the thickness of the bus waveguide 120 can be 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, or 800 nm. It is understood that the above are just a few examples, and the thickness of the bus waveguide 120 can also be some of the values ​​between the various examples mentioned above.

[0080] Optionally, the spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the second direction can be verified by simulation to show the working effect of different spacings in the first and second modes, thereby selecting a suitable spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the second direction.

[0081] In this embodiment, the spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the second direction is a value between -200 nm and 500 nm.

[0082] For example, the spacing between the silicon microring resonator 130 and the bus waveguide 120 in the second direction can be -200 nm, -100 nm, 0 nm, 100 nm, 130 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm, etc. It is understood that the above are merely examples of a few possible values; the spacing between the silicon microring resonator 130 and the bus waveguide 120 in the second direction can also be a value that is not a multiple of 10, or it can be one of the values ​​between the various examples described above.

[0083] Optionally, the design of the bus waveguide 120 dimensions can be verified through simulation.

[0084] For example, the width of the bus waveguide 120 can be predetermined. With the width determined, the thickness of the bus waveguide 120 and the spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the second direction are adjusted during simulation to verify the performance of the polarization mode selectable coupling structure 100 in different operating modes with different bus waveguide 120 thicknesses and spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the second direction. This verifies the selective passage effect of TE and TM polarization at the same output port. For example, in the first operating state, the amount of TM polarized light passing through the bus waveguide 120 and the amount of TM polarized light coupled into the silicon micro-ring resonator 130 and filtered out; and in the second operating state, the amount of TM polarized light passing through the bus waveguide 120 and the amount of TM polarized light coupled into the silicon micro-ring resonator 130 and filtered out.

[0085] For example, the thickness of the bus waveguide 120 can be predetermined. With the thickness determined, the width of the bus waveguide 120 and the spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the second direction are adjusted during simulation to verify the performance of the polarization mode selectable coupling structure 100 in different operating modes with different widths of the bus waveguide 120 and spacing between the silicon micro-ring resonator 130 and the bus waveguide 120 in the second direction. This verifies the effect of selective transmission of TM polarized light and TM polarized light at the same output port. For example, in the first operating state, the amount of TM polarized light passing through the bus waveguide 120 and the amount of TM polarized light coupled into the silicon micro-ring resonator 130 and filtered out; and in the second operating state, the amount of TM polarized light passing through the bus waveguide 120 and the amount of TM polarized light coupled into the silicon micro-ring resonator 130 and filtered out.

[0086] For example, the spacing between the silicon microring resonator 130 and the bus waveguide 120 in the second direction can be predetermined. With the spacing between the silicon microring resonator 130 and the bus waveguide 120 in the second direction determined, the width and thickness of the bus waveguide 120 during simulation are adjusted to verify the performance of the polarization-mode selectable coupling structure 100 in different operating modes with different bus waveguide widths and thicknesses, and the effect of selective transmission of TM-polarized light and TM-polarized light at the same output port. For example, in the first operating state, the amount of TM-polarized light passing through the bus waveguide 120 and the amount of TM-polarized light coupled into the silicon microring resonator 130 and filtered out; and again, in the second operating state, the amount of TM-polarized light passing through the bus waveguide 120 and the amount of TM-polarized light coupled into the silicon microring resonator 130 and filtered out.

[0087] Optionally, during simulation, the spacing between the silicon microring resonator 130 and the bus waveguide 120 in the second direction, the width of the bus waveguide 120, and the thickness of the bus waveguide 120 can be adjusted simultaneously to verify the performance of the polarization mode selectable coupling structure 100 under different operating modes with different bus waveguide widths, bus waveguide thicknesses, and spacing between the silicon microring resonator 130 and the bus waveguide 120 in the second direction. This verifies the effect of selective transmission of TM-polarized light and TM-polarized light at the same output port. For example, in the first operating state, the amount of TM-polarized light passing through the bus waveguide 120 and the amount of TM-polarized light coupled into the silicon microring resonator 130 and filtered out; and again, in the second operating state, the amount of TM-polarized light passing through the bus waveguide 120 and the amount of TM-polarized light coupled into the silicon microring resonator 130 and filtered out.

[0088] Through the above-mentioned multi-round verification, the resonant spectra of the TE00 mode and the TE01 mode can be shifted by changing the effective refractive index of the silicon micro-ring resonator 130, so that the light that needs to be filtered out can be lost in the silicon micro-ring resonator 130, thereby achieving the purpose of filtering out, so as to provide different working states (filtering out different light and allowing the required light to pass through).

[0089] In this embodiment, in order to optimize the transmission loss and mode crosstalk of the TE01 mode, the waveguide width or curvature of the silicon micro-ring resonator 130 is non-uniformly distributed along the loop.

[0090] Optionally, the resonant wavelength of the silicon micro-ring resonator 130 satisfies:

[0091] ;

[0092] Where m represents a positive integer; L represents the ring length of the silicon micro-ring resonator 130; Indicates the operating wavelength; This indicates the resonant wavelength of the silicon micro-ring resonator 130.

[0093] The polarization mode selectable coupling structure 100 provided in this application embodiment has a fundamental transverse electric mode polarized light in the bus waveguide 120 whose effective refractive index is designed to match the fundamental TE00 mode in the silicon micro-ring resonator 130. Therefore, the fundamental transverse magnetic mode polarized light can be efficiently coupled to the fundamental TE00 mode of the silicon micro-ring resonator 130.

[0094] The polarization mode selectable coupling structure 100 provided in this application embodiment has a fundamental transverse magnetic mode polarized light in the bus waveguide 120 whose effective refractive index is designed to match the first-order TE01 mode in the silicon micro-ring resonator 130. Therefore, the fundamental transverse magnetic mode polarized light is efficiently coupled to the first-order TE01 mode of the silicon micro-ring resonator 130.

[0095] Because the effective refractive indices of the TE00 and TE01 modes in the silicon micro-ring resonator 130 are significantly different, the TE00 and TE01 modes will resonate at different wavelengths, producing two independent sets of resonance spectra (transmission function curves), which can be specifically described as follows: Figure 2a and Figure 2b As shown, the horizontal axis represents wavelength (nm) and the vertical axis represents transmittance. Figure 2a and Figure 2b The red curve shown is the curve of the silicon micro-ring resonator 130 in TE01 mode, and the blue curve is the curve of the silicon micro-ring resonator 130 in TE00 mode. Figure 2a In the example shown, with the silicon microring resonator 130 at the first effective refractive index and an operating frequency of 1306 nm, all resonance peaks of the TE01 mode are far from this operating frequency, allowing TM polarized light to pass through while TE polarized light is absorbed by the silicon microring resonator 130; whereby... Figure 2b In the example shown, with the silicon micro-ring resonator 130 at the second effective refractive index and the operating frequency at 1306 nm, all resonance peaks of the TE00 mode are far from this operating frequency, allowing TE polarized light to pass through while TM polarized light is absorbed by the silicon micro-ring resonator 130.

[0096] This application also provides a tunable polarization filter 200, such as... Figure 3 As shown, the tunable polarization filter 200 may include a polarization mode selectable coupling structure 100 and a tuning device 210.

[0097] The polarization mode selectable coupling structure 100 mentioned in this embodiment can be similar to the polarization mode selectable coupling structure 100 in the previous embodiment. Other details about the polarization mode selectable coupling structure 100 in this embodiment can be found in the description in the previous embodiment, and will not be repeated here.

[0098] Tuning device 210 can be disposed within or around silicon micro-ring resonator 130, and is used to adjust the refractive index of silicon micro-ring resonator 130. Tuning device 210 can be thermally or electrically coupled to silicon micro-ring resonator 130.

[0099] Specifically, when a first voltage is applied to the tuning device 210, one of the resonant peaks in the first mode is aligned with a preset operating wavelength, and the resonant peak in the second mode is moved away from the preset operating wavelength; when a second voltage is applied to the tuning device 210, one of the resonant peaks in the second mode is aligned with a preset operating wavelength, and the resonant peak in the first mode is moved away from the preset operating wavelength.

[0100] When the first mode is TE00, and a first voltage is applied to the tuning device 210, the silicon micro-ring resonator 130, at its current effective refractive index, causes a certain resonance peak of the TE00 mode to be precisely aligned with the preset operating wavelength, while all resonance peaks of the TE01 mode are far from the preset operating wavelength. Figure 2a For example, when the preset working wavelength is 1306nm, a certain resonance peak of the TE00 mode is exactly aligned with the preset working wavelength, while all the resonance peaks of the TE01 mode are far away from the preset working wavelength, or all the resonance peaks of the TE01 mode are offset from the preset working wavelength of 1306nm.

[0101] When the second mode is TE01, and a second voltage is applied to the tuning device 210, the silicon micro-ring resonator 130, at its current effective refractive index, ensures that a certain resonance peak of the TE01 mode is precisely aligned with the preset operating wavelength, while all resonance peaks of the TE00 mode are far from the preset operating wavelength. Figure 2b For example, when the preset working wavelength is 1306nm, a certain resonance peak of the TE00 mode is exactly aligned with the preset working wavelength, while all the resonance peaks of the TE01 mode are far away from the preset working wavelength, or all the resonance peaks of the TE01 mode are offset from the preset working wavelength of 1306nm.

[0102] Optionally, the tuning device 210 includes a thermal tuner for adjusting the effective refractive index of the silicon micro-ring resonator 130 by applying a tuning signal.

[0103] For example, the tuning device 210 may be a doped silicon resistor disposed inside or on the side of the silicon micro-ring resonator 130.

[0104] For example, the tuning device 210 may be a metal heater disposed above the silicon micro-ring resonator 130.

[0105] Tuning device 210 is used to change the effective refractive index of silicon micro-ring resonator 130 by applying a tuning signal, thereby shifting the resonant spectra of the TE00 and TE01 modes. See details in [link to documentation]. Figure 2a and Figure 2b As shown, the resonant spectra of the TE00 and TE01 modes have been shifted.

[0106] The tuning signal can be a current signal or a voltage signal.

[0107] When a tuning signal is applied to the tuning device 210, the effective refractive index of the silicon micro-ring resonator 130 can be changed by utilizing the plasma dispersion effect or thermo-optic effect of silicon.

[0108] Optionally, the tuning device 210 includes an electrical tuner for adjusting the effective refractive index of the silicon micro-ring resonator 130 by applying a tuning signal.

[0109] In this embodiment, by controlling the tuning signal of the tuning device 210, the tunable polarization filter 200 can switch between a first operating state (TE polarized light is resonantly filtered out, TM polarized light passes through) or a second operating state (TM polarized light is resonantly filtered out, TE polarized light passes through) at a preset operating wavelength.

[0110] The following is combined Figure 2a and Figure 2b The example shown illustrates that, in Figure 2a and Figure 2b In this context, the preset operating wavelength can be 1306nm.

[0111] In the first case, when the first voltage is applied to the tuning device 210, the silicon micro-ring resonator 130 is designed so that a certain resonance peak m1 of the TE00 mode is exactly aligned with the working wavelength 1306nm, while all resonance peaks of the TE01 mode are far away.

[0112] At this point, the input TE-polarized light (coupled to TE00) is in a resonant state. The light is coupled into the silicon micro-ring resonator 130 and lost within the ring, resulting in extremely low intensity of the TE-polarized light at the output of the bus waveguide 120. The input TM-polarized light (coupled to TE01) is in a non-resonant state, and the light hardly interacts with the ring, passing directly through the bus waveguide 120. In this case, the tunable polarization filter 200 acts as a filter for the TM-polarized light.

[0113] In the second scenario, when a second voltage is applied to the tuning device 210, the silicon micro-ring resonator 130 heats up due to the thermo-optical effect, leading to an increase in the refractive index of silicon and a redshift in the resonant spectra of both TE00 and TE01. Since the optical field distributions of the TE00 and TE01 modes are different, their thermo-optical tuning efficiencies (wavelength shift) may also differ. By precisely controlling the tuning amount, the resonant peak m1 of the TE00 mode is shifted away, while a certain resonant peak m2 of the TE01 mode is shifted to the operating wavelength of 1306 nm.

[0114] At this point, the input TE-polarized light (coupled to TE00) becomes non-resonant and passes directly through the bus waveguide 120. The input TM-polarized light (coupled to TE01) becomes resonant and is coupled into the silicon micro-ring resonator 130 and filtered out. In this case, the tunable polarization filter 200 acts as a filter for TM-polarized light.

[0115] In the example above, by applying different voltages to the tuning device 210, selective passage of TE-polarized light and TM-polarized light can be achieved at the same output port.

[0116] This application also provides a photonic chip, which may include a tunable polarization filter 200.

[0117] The tunable polarization filter 200 mentioned in this embodiment can be similar to the tunable polarization filter 200 in the previous embodiment. Other details about the tunable polarization filter 200 in this embodiment can be found in the description in the previous embodiment, and will not be repeated here.

[0118] The polarization mode selectable coupling structure 100, tunable polarization filter 200 and photonic chip provided in the embodiments of this application are novel, compact and low power consumption structures that can realize tunable polarization filtering with fewer components.

[0119] Specifically, it can utilize the coupling characteristics of different polarization modes and different order modes to achieve a polarization mode selectable structure. The "switchable" polarization filter allows it to selectively pass TE polarized light or TM polarized light at the same operating wavelength through tuning with an external electrical signal (current / voltage) in a single waveguide path.

[0120] Because its design is based solely on the SOI basic structure, it can better ensure compatibility with mainstream silicon-based optoelectronic standard processes (especially platforms with silicon nitride (SiN) deposition processes), and is easy to manufacture and integrate.

[0121] Furthermore, the structure implemented in this application embodiment is based on a silicon micro-ring resonator 130, which occupies a much smaller area than traditional polarization devices based on interferometers or adiabatic cones, typically within tens of micrometers square, greatly improving the integration density.

[0122] Furthermore, dynamically tunable polarization filtering, rather than static polarization separation, is achieved. This has important applications in reconfigurable optical networks and polarization-coded optical communications.

[0123] Because it is based on the thermal tuning of a silicon microring resonator 130, state switching can typically be achieved by shifting only a few nanometers of the resonant wavelength (e.g., moving from one resonant peak to the period of an adjacent resonant line, or moving half a period of the resonant line). Compared to devices that require a wide range of tuning, power consumption is significantly reduced. The wavelength range required for switching based on this method can be very small, such as half a period of the resonant line, and power consumption can be expected to be controlled in the mW range.

[0124] The polarization mode selectable coupling structure 100 provided in this application uses a SiN-on-Si vertical stacking structure, which is the standard process for current silicon photonics multilayer integration platforms (commonly used to realize 3D integration, edge couplers or double-layer grating couplers). It does not require additional special processes, has low manufacturing cost and high yield.

[0125] Furthermore, by utilizing the "notch" characteristics of the silicon micro-ring resonator 130, a very deep (>20dB) transmission drop can be achieved at the resonant point, thereby providing a high extinction ratio filter for the selected polarization state.

[0126] The above description is merely an optional embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application. It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0127] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A tunable polarization filter, characterized in that, include: Polarization mode selectable coupling structure; A tuning device disposed within or around a silicon micro-ring resonator for adjusting the refractive index of the silicon micro-ring resonator; Specifically, when a first voltage is applied to the tuning device, one of the resonant peaks in the first mode is aligned with a preset operating wavelength, and the resonant peak in the second mode is moved away from the preset operating wavelength; when a second voltage is applied to the tuning device, one of the resonant peaks in the second mode is aligned with a preset operating wavelength, and the resonant peak in the first mode is moved away from the preset operating wavelength. The coupling structure for the selected polarization mode includes: a silicon layer; Silicon micro-ring resonant cavity disposed on the silicon layer; A bus waveguide disposed on one side of the silicon layer is used as the input and output of the polarization mode selectable coupling structure. The bus waveguide forms a coupling region with the silicon micro-ring resonator. The waveguide width of the silicon micro-ring resonator is non-uniformly distributed along the loop. Specifically, the fundamental transverse electric mode polarized light of the bus waveguide is phase-matched and coupled with the first mode of the silicon micro-ring resonator; the fundamental transverse magnetic mode polarized light of the bus waveguide is phase-matched and coupled with the second mode of the silicon micro-ring resonator. The resonant wavelength of the silicon micro-ring resonator satisfies: Where m represents a positive integer; L represents the ring length of the silicon micro-ring resonator; Indicates the operating wavelength; This indicates the resonant wavelength of the silicon micro-ring resonator.

2. The tunable polarization filter according to claim 1, characterized in that, A dielectric layer is disposed between the silicon micro-ring resonator and the bus waveguide.

3. The tunable polarization filter according to claim 2, characterized in that, The dielectric layer is a silicon dioxide layer.

4. The tunable polarization filter according to claim 2, characterized in that, The spacing between the silicon micro-ring resonator and the bus waveguide in a first direction is between 50 nm and 200 nm, where the first direction is perpendicular to the silicon layer.

5. The tunable polarization filter according to claim 1, characterized in that, The width of the bus waveguide is between 500 nm and 1.5 µm.

6. The tunable polarization filter according to claim 1, characterized in that, The thickness of the bus waveguide is between 200 nm and 800 nm.

7. The tunable polarization filter according to claim 1, characterized in that, The distance between the bus waveguide and the silicon micro-ring resonator in the second direction is between -200 nm and 500 nm, and the second direction is parallel to the silicon layer.

8. The tunable polarization filter according to claim 1, characterized in that, The tuning device includes a thermal tuner for adjusting the effective refractive index of the silicon micro-ring resonator by applying a tuning signal.

9. The tunable polarization filter according to claim 1, characterized in that, The tuning device includes an electrical tuner for adjusting the effective refractive index of the silicon micro-ring resonator by applying a tuning signal.

10. A photonic chip, characterized in that, Includes the tunable polarization filter according to any one of claims 1 to 9.

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