Polarizer, parameter determination method of polarizer and optical gyroscope
By designing a polarizer that includes a coupled waveguide and a bent waveguide, the problem of integrating Bragg reflector polarizers with silicon photonic devices was solved, realizing a low-loss, high polarization extinction ratio optical gyroscope suitable for high-precision measurement of optical gyroscopes.
Patent Information
- Application Number
- CN202511355543.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-22
- Publication Date
- 2026-01-06
AI Technical Summary
Existing Bragg reflector polarizers are difficult to integrate with silicon photonic devices and cannot meet the needs of broadband applications. At the same time, their emission structure is difficult to integrate directly with the light source, resulting in high loss and low polarization extinction ratio.
Design a polarizer comprising first and second coupling waveguides, a bent waveguide and a transmission waveguide, to achieve low-loss, high-selectivity coupling through an adiabatic directional coupler, filter out non-target polarized light and stably transmit it to free space, reduce stray light accumulation and improve polarization extinction ratio.
It achieves integration with silicon photonics devices, reduces insertion loss, improves polarization extinction ratio, and reduces crosstalk in the main optical path, making it suitable for high-precision measurements of optical gyroscopes.
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Figure CN121276702A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical device technology, specifically to a polarizer, a method for determining the parameters of the polarizer, and an optical gyroscope. Background Technology
[0002] With the continuous advancement of integrated optical design and micro / nano fabrication technologies, replacing discrete components in traditional optical gyroscopes with photonic integrated devices has become a key path to achieving miniaturization, low cost, mass production, and high integration. Among these, silicon photonic devices, due to their compatibility with Complementary Metal-Oxide-Semiconductor (CMOS) processes, provide important support for passive integration, heterogeneous integration, and hybrid integration technologies, and have been widely used in optical gyroscopes.
[0003] Since most silicon photonic devices are insensitive to polarization state, the optical engine of an optical gyroscope that realizes integrated polarization, beam splitting / combining, and phase modulation functions needs to design a polarizer with low loss and high polarization extinction ratio to meet the needs of high-precision measurement and integrated development.
[0004] Bragg reflector polarizers selectively reflect light of a specific polarization state through a periodic structure, enabling the output of polarized light with high purity and high light utilization. However, due to the limitation of the Bragg reflection wavelength, Bragg reflector polarizers are theoretically difficult to meet the requirements of broadband applications, and their emission structure is difficult to integrate directly with the light source. Therefore, there is an urgent need for a polarizer that can be integrated with silicon photonics devices and has low loss and a high polarization extinction ratio. Summary of the Invention
[0005] In view of this, the present invention provides a polarizer, a method for determining the parameters of the polarizer, and an optical gyroscope to solve the problem that the polarizer is difficult to integrate with silicon photonic devices while also having low loss and high polarization extinction ratio.
[0006] In a first aspect, the present invention provides a polarizer comprising a first coupled waveguide, a second coupled waveguide, a first bent waveguide, a second bent waveguide, a first transmission waveguide, and a second transmission waveguide disposed on a silicon-based chip; the first coupled waveguide and the second coupled waveguide are spaced apart, and the center lines of the first coupled waveguide and the second coupled waveguide in the optical transmission direction are parallel; one end of the second coupled waveguide is connected to one end of the first bent waveguide, and the other end of the first bent waveguide is connected to one end of the first transmission waveguide, the other end of the first transmission waveguide being disposed at the edge of the silicon-based chip; the other end of the second coupled waveguide is connected to one end of the second bent waveguide, and the other end of the second bent waveguide is connected to one end of the second transmission waveguide, the other end of the second transmission waveguide being disposed at the edge of the silicon-based chip; when the first coupled waveguide transmits an optical signal containing target polarized light and non-target polarized light, the non-target polarized light is coupled to the second coupled waveguide, and the non-target polarized light entering the second coupled waveguide is output from the silicon-based chip through the first bent waveguide and the first transmission waveguide, or is output from the silicon-based chip through the second bent waveguide and the second transmission waveguide.
[0007] The polarizer provided by this invention has a first coupling waveguide and a second coupling waveguide that are fully coupled to filter out unnecessary polarized light. The first and second curved waveguides can ensure the stable transmission of the filtered unnecessary polarized light and reduce unnecessary curved radiation. The first and second transmission waveguides can transmit the filtered unnecessary polarized light to free space, reducing the accumulation of stray light. This can reduce crosstalk in the main optical path and improve the polarization extinction ratio. Moreover, the polarizer can be integrated with silicon photonic devices by filtering unnecessary polarized light through coupling.
[0008] In one alternative implementation, the first coupling waveguide and the second coupling waveguide are parallel straight waveguides.
[0009] In one optional implementation, the first width of the first coupled waveguide and the second width of the second coupled waveguide are different. The first width and the second width are determined based on the first propagation constant of the first coupled waveguide, the second propagation constant of the second coupled waveguide, a first correspondence, and a second correspondence. The first correspondence is the correspondence between the effective refractive index and the width of the first coupled waveguide, and the second correspondence is the correspondence between the effective refractive index and the width of the second coupled waveguide.
[0010] In one alternative implementation, the second coupling waveguide is composed of at least one first tapered waveguide, and the region corresponding to the first coupling waveguide and the second coupling waveguide is composed of at least one second tapered waveguide.
[0011] In this embodiment, the first and second coupled waveguides are configured as tapered waveguide structures, which can reduce the sensitivity of the polarizer to process deviations.
[0012] In one alternative implementation, the length of the first coupling waveguide is an odd multiple of the coupling length.
[0013] In one alternative implementation, the first and second curved waveguides are formed based on freeform curves, Bezier curves, or Euler curves.
[0014] In this embodiment, for modes that need to be filtered out, a variable curvature curved waveguide is used to maintain the transmission of higher-order modes to free space, which can reduce the impact of curved radiation on the optical gyroscope system.
[0015] In one alternative implementation, a plurality of polarizers are disposed on a silicon-based chip, and a first coupling waveguide is connected between two adjacent polarizers.
[0016] In this embodiment, by setting multiple polarizers on the silicon-based chip, the polarization extinction ratio can be further improved.
[0017] In a second aspect, the present invention provides a method for determining the parameters of a polarizer, wherein the polarizer is the polarizer described in the first aspect above or any corresponding embodiment thereof, and the method includes: obtaining a first correspondence and a second correspondence, wherein the first correspondence is a correspondence between the effective refractive index and the width of a first coupled waveguide, and the second correspondence is a correspondence between the effective refractive index and the width of a second coupled waveguide; determining a first width of the first coupled waveguide and a second width of the second coupled waveguide based on a first propagation constant of the first coupled waveguide, a second propagation constant of the second coupled waveguide, the first correspondence, and the second correspondence.
[0018] In one optional implementation, determining the first width of the first coupled waveguide and the second width of the second coupled waveguide based on the first propagation constant of the first coupled waveguide, the second propagation constant of the second coupled waveguide, the first correspondence, and the second correspondence includes: aiming for the first propagation constant and the second propagation constant to be the same, and determining the first width and the second width based on the first correspondence and the second correspondence, wherein the first propagation constant is determined based on the effective refractive index of the first coupled waveguide, and the second propagation constant is determined based on the effective refractive index of the second coupled waveguide.
[0019] Thirdly, the present invention provides an optical gyroscope, including the polarizer of the first aspect above or any corresponding embodiment thereof. Attached Figure Description
[0020] To more clearly illustrate the technical solutions in the specific embodiments or related technologies of the present invention, the drawings used in the description of the specific embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.
[0021] Figure 1 This is a schematic diagram of the structure of a polarizer according to an embodiment of the present invention;
[0022] Figure 2 This is a schematic diagram of another polarizer according to an embodiment of the present invention;
[0023] Figure 3 This is a schematic diagram of the structure of the first and second coupled waveguides according to an embodiment of the present invention;
[0024] Figure 4 This is a schematic diagram of the effective refractive index curves corresponding to different widths according to an embodiment of the present invention;
[0025] Figure 5 This is a schematic diagram of the undercoupling of the first coupled waveguide and the second coupled waveguide according to an embodiment of the present invention;
[0026] Figure 6 This is a schematic diagram of the critical coupling of the first coupled waveguide and the second coupled waveguide according to an embodiment of the present invention;
[0027] Figure 7 This is a schematic diagram of the overcoupling of the first and second coupled waveguides according to an embodiment of the present invention;
[0028] Figure 8 This is a schematic diagram of optical transmission when TMO mode light is input from the left end of the first coupled waveguide of a polarizer according to an embodiment of the present invention.
[0029] Figure 9 This is a schematic diagram of optical transmission when TMO mode light is input from the right end of the first coupled waveguide of a polarizer according to an embodiment of the present invention.
[0030] Figure 10 This is a schematic diagram of optical transmission when TEO mode light is input from the left end of the first coupled waveguide of a polarizer according to an embodiment of the present invention.
[0031] Figure 11 This is a schematic diagram of optical transmission when TEO mode light is input from the right end of the first coupled waveguide of a polarizer according to an embodiment of the present invention.
[0032] Figure 12This is a schematic diagram of optical transmission when TMO mode light is input from the left end of the first coupled waveguide of another polarizer according to an embodiment of the present invention.
[0033] Figure 13 This is a schematic diagram of optical transmission when TEO mode light is input from the left end of the first coupled waveguide of another polarizer according to an embodiment of the present invention.
[0034] Figure 14 This is a schematic diagram of the structure of another polarizer according to an embodiment of the present invention;
[0035] Figure 15 This is a schematic diagram of optical transmission when TM0 mode light is input from the left end of the first coupled waveguide of another polarizer according to an embodiment of the present invention.
[0036] Figure 16 This is a schematic diagram of optical transmission when TEO mode light is input from the left end of the first coupled waveguide of another polarizer according to an embodiment of the present invention.
[0037] Reference numerals: 10, polarizer; 11, first coupled waveguide; 111, second tapered waveguide; 12, second coupled waveguide; 121, first tapered waveguide; 13, first bent waveguide; 14, second bent waveguide; 15, first transmission waveguide; 16, second transmission waveguide; 20, silicon-based chip. Detailed Implementation
[0038] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the invention, not the entire structure.
[0039] In the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concepts of the present invention. Various structural schematic diagrams according to embodiments of the present invention are shown in the accompanying drawings. These drawings are not to scale, and some details are enlarged for clarity, and some details may be omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate in practice due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed. In the context of the present invention, when a layer / element is referred to as being "on" another layer / element, the layer / element may be directly on the other layer / element, or there may be an intermediate layer / element between them. Additionally, if a layer / element is "on" another layer / element in one orientation, then when the orientation is reversed, the layer / element may be "below" the other layer / element.
[0040] Currently, researchers have proposed various polarizer structures, such as Bragg reflection structures, apodized multimode Bragg structures, and absorptive polarizers. Apodized multimode Bragg polarizers utilize an apodized multimode Bragg structure, converting a specific polarized light into multimode reflections at the incident end, and combining mode multiplexing techniques to reduce reflection. Absorptive polarizers employ a strategy of absorbing specific polarized light through material implantation, thus directionally controlling the polarization state of light. Furthermore, waveguide structure design can be used to modify the confinement ability of polarized light, particularly through curved structures, to filter out unsupported polarized light in the form of radiation during transmission.
[0041] However, as mentioned in the background section, Bragg reflector polarizers are difficult to meet the needs of broadband applications. Furthermore, the conflict between the Bragg reflector's requirement for the incident angle and the divergence of the light source makes it difficult to directly integrate the emitting structure with the light source. While apodized multimode multiplexed Bragg structures can solve the reflection problem, their large size hinders large-scale integration, and their small feature size (<150nm) requires high process precision, making manufacturing difficult.
[0042] Absorption-type polarizers are achieved by introducing additional materials into the waveguide material, but this method increases the complexity of device fabrication, and the introduction of new materials also leads to an increase in the required polarization loss. Bending waveguides alleviate the manufacturing difficulty somewhat, but the bending radiation into the cladding increases the risk of stray light interfering with the main path signal. Furthermore, a larger bending radius is required to achieve the low-loss polarization required, which leads to a decrease in the polarization extinction ratio.
[0043] In view of this, the present invention provides a polarizer, a method for determining the parameters of the polarizer, and an optical gyroscope, which, by coupling and filtering unnecessary polarized light, can bring a high polarization extinction ratio to the system with low insertion loss while being integrated with silicon photonic devices.
[0044] The structure of the polarizer provided by the present invention will be described in detail below with reference to the accompanying drawings.
[0045] like Figure 1 As shown, the polarizer 10 includes a first coupling waveguide 11, a second coupling waveguide 12, a first bent waveguide 13, a second bent waveguide 14, a first transmission waveguide 15, and a second transmission waveguide 16 disposed on a silicon-based chip 20. The silicon-based chip 20 can be a chip with silicon nitride as its substrate. The polarizer on the silicon-based chip can be formed by single-step full etching, reducing the complexity of the manufacturing process.
[0046] Specifically, the first coupling waveguide 11 and the second coupling waveguide 12 are spaced apart, with the centerline O1 of the first coupling waveguide 11 and the centerline O2 of the second coupling waveguide 12 parallel in the optical transmission direction. One end of the second coupling waveguide 12 is connected to one end of the first bent waveguide 13, and the other end of the first bent waveguide 13 is connected to one end of the first transmission waveguide 15, the other end of which is located at the edge of the silicon-based chip 20. The other end of the second coupling waveguide 12 is connected to one end of the second bent waveguide 14, and the other end of the second bent waveguide 14 is connected to one end of the second transmission waveguide 16, the other end of which is located at the edge of the silicon-based chip 20.
[0047] The two ends of the first coupling waveguide 11 can also be located at the edge of the silicon-based chip 20, with one end being the optical signal input end and the other end being the optical signal output end. The optical signal generated by the light source enters the first coupling waveguide 11 from the optical signal input end, and the optical signal output from the optical signal output end can be transmitted to the optical receiving module of the optical gyroscope.
[0048] The first coupling waveguide 11 and the second coupling waveguide 12 constitute an adiabatic directional coupler (ADC). Based on the principle of adiabatic transmission, the ADC can achieve low-loss and high-selectivity coupling of optical signals between the two waveguides, thereby completing the polarization separation of light.
[0049] The first coupling waveguide 11 and the second coupling waveguide 12 are fully coupled (coupling efficiency ≥ 90%). When the first coupling waveguide 11 transmits an optical signal containing both target polarized light and non-target polarized light, the non-target polarized light is coupled to the second coupling waveguide 12. The non-target polarized light entering the second coupling waveguide 12 is output to the silicon-based chip 20 through the first bent waveguide 13 and the first transmission waveguide 15, or through the second bent waveguide 14 and the second transmission waveguide 16. The target polarized light in the first coupling waveguide 11 is output from the optical signal output end.
[0050] The first curved waveguide 13 and the second curved waveguide 14 are used to ensure stable transmission of non-target polarized light and reduce unnecessary bending radiation. The first transmission waveguide 15 and the second transmission waveguide 16 are used to transmit non-target polarized light (i.e., non-main optical path polarized light) to free space, reducing stray light accumulation. Compared with the inverted conical waveguide structure used to radiate stray light to the cladding, the method of stably transmitting stray light to free space by the first transmission waveguide 15 and the second transmission waveguide 16 can more effectively avoid stray light interference with the main optical path, with a return loss greater than 60dB.
[0051] Light can be classified into transverse electric (TE) and transverse magnetic (TM) modes based on its polarization characteristics, and into fundamental (0th order) and higher-order modes (1st order and above) based on their mode order. The target polarized light is the light in the mode required for measurement by the optical gyroscope. For example, the target polarized light can be TE0 mode light, in which case other modes (such as TM0 mode) are non-target polarized light.
[0052] Taking the optical signal including TE0 mode and TM0 mode, and the target polarized light being in TE0 mode as an example, the transmission process of the optical signal is explained.
[0053] Specifically, if the left end of the first coupling waveguide 11 is the optical signal input end, the optical signals including TEO mode and TMO mode are transmitted from left to right. During the transmission, the TMO mode light is coupled to the second coupling waveguide 12, and then the TMO mode light is transmitted from the second coupling waveguide 12 to the second curved waveguide 14, and then through the second transmission waveguide 16 to be stably output to the silicon-based chip 20 to reach free space. Meanwhile, the TEO mode light is guided by the first coupling waveguide 11 and output from the optical signal output end (the right end of the first coupling waveguide 11).
[0054] If the right end of the first coupling waveguide 11 is the optical signal input end, the optical signals including TEO mode and TMO mode are transmitted from right to left. During the transmission, the TMO mode light is coupled to the second coupling waveguide 12, and then the TMO mode light is transmitted from the second coupling waveguide 12 to the first curved waveguide 13, and then through the first transmission waveguide 15 to be stably output to the silicon-based chip 20 to reach free space. Meanwhile, the TEO mode light is guided by the first coupling waveguide 11 and output from the optical signal output end (the left end of the first coupling waveguide 11).
[0055] This invention does not specifically limit the structure of the first coupling waveguide 11 and the second coupling waveguide 12, as long as the first coupling waveguide 11 and the second coupling waveguide 12 are sufficiently coupled. For example, the width of the first coupling waveguide 11 and the width of the second coupling waveguide 12 can be fixed, such as... Figure 1 As shown, the first coupling waveguide 11 and the second coupling waveguide 12 are parallel straight waveguides.
[0056] For example, the width of the first coupled waveguide 11 and the width of the second coupled waveguide 12 can also be gradually changed. For example... Figure 2 As shown, the second coupling waveguide 12 is composed of at least one first tapered waveguide 121, and the regions corresponding to the first coupling waveguide 11 and the second coupling waveguide 12 are composed of at least one second tapered waveguide 111. Figure 2Taking the example that the second coupling waveguide 12 is composed of two symmetrically arranged first tapered waveguides 121, and the region corresponding to the first coupling waveguide 11 and the second coupling waveguide 12 is composed of two symmetrically arranged second tapered waveguides 111, but it is not limited to this.
[0057] The polarizer provided by this invention has a first coupling waveguide 11 and a second coupling waveguide 12 that are fully coupled to filter out unnecessary polarized light. The first curved waveguide 13 and the second curved waveguide 14 can ensure the stable transmission of the filtered unnecessary polarized light and reduce unnecessary curved radiation. The first transmission waveguide 15 and the second transmission waveguide 16 can transmit the filtered unnecessary polarized light to free space, reduce the accumulation of stray light, reduce crosstalk in the main optical path, and improve the polarization extinction ratio. Moreover, the polarizer can be integrated with silicon photonic devices by filtering unnecessary polarized light through coupling.
[0058] like Figure 3 As shown, the first coupling waveguide 11 and the second coupling waveguide 12 are parallel straight waveguides. The first width W1 of the first coupling waveguide 11 and the second width W2 of the second coupling waveguide 12 are different. The first width and the second width determine whether the phase between the fundamental mode in the first coupling waveguide 11 and the higher-order mode in the second coupling waveguide 12 is matched. Only when the phase between the fundamental mode and the higher-order mode is matched can the fundamental mode in the first coupling waveguide 11 and the higher-order mode in the second coupling waveguide 12 be coupled. The coupling length between the first coupling waveguide 11 and the second coupling waveguide 12 determines whether the first coupling waveguide 11 and the second coupling waveguide 12 can be fully coupled.
[0059] For example, such as Figure 3 As shown, when the fundamental mode and the higher-order mode are phase matched, TM0 in the first coupled waveguide 11 can be coupled with TM1 in the second coupled waveguide 12, and the coupling length determines the coupling efficiency between TM0 and TM1.
[0060] The first width W1 and the second width W2 are determined based on the first propagation constant of the first coupled waveguide 11, the second propagation constant of the second coupled waveguide 12, a first correspondence, and a second correspondence. That is, the first width W1 and the second width W2 are determined through numerical calculation to satisfy the phase matching between the fundamental mode and higher-order modes. Specifically, the first correspondence is the correspondence between the effective refractive index and the width of the first coupled waveguide 11, and the second correspondence is the correspondence between the effective refractive index and the width of the second coupled waveguide 12.
[0061] Specifically, the eigenmode solution method can be used to obtain, for example... Figure 4 The effective refractive index curves corresponding to different widths shown are for... Figure 4 Fitting the curve in the curve yields a function of the width corresponding to the effective refractive index, which represents the first and second correspondences. Figure 4The horizontal axis represents the width (in μm), and the vertical axis represents the effective refractive index (neff).
[0062] Considering the lossless waveguide, based on perturbation theory and the waveguide coupling in coupled mode theory, the normalized power of the first coupled waveguide 11 can be expressed as Equation (1), and the normalized power of the second coupled waveguide 12 can be expressed as Equation (2):
[0063]
[0064] Where x represents the distance in the waveguide transmission direction, P1 represents the normalized power of the first coupled waveguide, σ represents the phase difference, σ=(β1-β2) / 2, β1 represents the first propagation constant, which is determined by the following formula (3), β2 represents the second propagation constant, which is determined by the following formula (4), k represents the cross-coupling coefficient, which is obtained by superimposing and integrating the electric fields inside the waveguide, and P2 represents the normalized power of the second coupled waveguide.
[0065]
[0066] Where, λ 01 n represents the wavelength of the optical signal transmitted in the first coupled waveguide in vacuum. eff1 λ represents the effective refractive index of the first coupled waveguide. 02 n represents the wavelength of the optical signal transmitted in the second coupled waveguide in vacuum. eff2 This represents the effective refractive index of the second coupled waveguide.
[0067] Specifically, it can be seen from the above formulas (1) and (2) that satisfying When the optical power of the second coupled waveguide reaches its maximum value, the coupling length Lc can be characterized by formula (5).
[0068]
[0069] From the above formulas, it can be deduced that when the phase difference σ = 0, and the length of the first coupled waveguide is an odd multiple of the coupling length, the optical power is completely transmitted to the second coupled waveguide. At this time, the above formula (1) can be simplified to formula (6), the above formula (2) can be simplified to formula (7), and the above formula (5) can be simplified to formula (8).
[0070] P1(x) = cos 2 (kx) (6)
[0071] P2(x)=sin 2 (kx) (7)
[0072]
[0073] At this point, the insertion loss can be expressed as shown in Equation (9) and the polarization extinction ratio can be expressed as shown in Equation (10):
[0074] IL(x) = 10log 10 cos 2 (kx) (9)
[0075] PDL(x) = IL(x) TE0 -IL(x) TM0 (10)
[0076] Where IL represents insertion loss and PDL represents polarization extinction ratio.
[0077] Based on the above formula, the coupling states (overcoupling, critical coupling, and undercoupling) of the first and second coupled waveguides under different phase differences and coupling lengths can be simulated and calculated. The coupling states can be as follows: Figure 5 , Figure 6 and Figure 7 As shown, from Figures 5 to 7 It can be seen that coupling (i.e., phase matching) only occurs when the phase difference between the fundamental mode and higher-order modes is within ±0.1, and the coupling length has a significant impact on the coupling efficiency. Therefore, based on the coupling state and combined with the effective refractive index and waveguide width function, the first width, the second width, and the coupling length are determined to achieve complete optical power transmission to the second coupling waveguide and narrow the scope of device optimization.
[0078] Specifically, after determining the phase difference (e.g., σ = 0) that makes the fundamental mode and the higher-order modes phase-matched, the correspondence between β1 and β2 can be determined based on σ = (β1 - β2) / 2 (if σ = 0, then β1 = β2). At this point, by combining formulas (3) and (4), the n that satisfies the condition (e.g., β1 = β2) can be determined. eff1 and n eff2 Then, by combining the first correspondence and the second correspondence, we can obtain the first width and the second width.
[0079] After determining the first and second widths, the coupling length can be determined through simulation with the goal of maximizing coupling efficiency. Optionally, the length of the first coupling waveguide can be set to an odd multiple of the coupling length to ensure full coupling between the first and second coupling waveguides.
[0080] When the silicon-based chip is a silicon nitride platform and the target polarized light is in TE0 mode, the numerical calculations above determine that the widths of the TM0 mode in the first coupled waveguide and the TM1 mode in the second coupled waveguide that satisfy the phase matching condition are 0.72 μm and 2.5 μm, respectively, with a coupling length of approximately 7.8 μm. Then, a geometric model of the polarizer is established using these parameters, and optimization calculations are performed using the finite-difference time-domain (FDTD) method. The results show that the optimal coupling length is 9 μm when the first and second coupled waveguides only couple between the TM modes.
[0081] At this point, the coupling efficiency of TM mode is greater than 99.5%, no coupling occurs in TE mode, the transmittance is greater than 99.3%, the insertion loss is less than 0.03 dB, the polarization extinction ratio is greater than 25 dB, and the structural parameters are basically consistent with the theoretical calculations. The optimized optical field transmission can be as follows: Figures 8 to 11 As shown. Among them, Figures 8 to 11 The horizontal axis represents the length of the first coupled waveguide in the x-direction. Figures 8 to 11 The vertical axis represents the length of the second coupled waveguide, the bent waveguide, and the transmission waveguide in the y-direction. Figure 8 This diagram illustrates the optical transmission when TM0 mode light is input from the left end of the first coupled waveguide. Figure 9 This diagram illustrates the optical transmission when TM0 mode light is input from the right end of the first coupled waveguide. Figure 10 This diagram illustrates the optical transmission when TE0 mode light is input from the left end of the first coupled waveguide. Figure 11 This diagram illustrates the optical transmission when TE0 mode light is input from the right end of the first coupled waveguide.
[0082] In this embodiment, based on perturbation and coupling mode theory, the width and coupling length of the parallel straight waveguide that satisfy full coupling are numerically calculated, which can simplify the simulation complexity.
[0083] For example, the first curved waveguide 13 and the second curved waveguide 14 are formed based on freeform curves, Bezier curves, or Euler curves. In this embodiment, for modes that need to be filtered out, the variable curvature curved waveguide is used to maintain the transmission of higher-order modes to free space, which can reduce the impact of curved radiation on the optical gyroscope system.
[0084] Specifically, the first curved waveguide 13 and the second curved waveguide 14 adopt an Euler curve design, which can prevent stray light from radiating to the cladding from the constant curvature curved waveguide. The Euler curvature radius R can be characterized by formulas (11) and (12):
[0085]
[0086]
[0087] Where L represents the length of the Euler curve, θ represents the angle, Lt represents the total length of the Euler curve, and R min R represents the minimum radius of curvature. max This represents the maximum radius of curvature.
[0088] This embodiment reduces mode matching loss by optimizing the maximum radius of curvature and avoids exciting higher-order modes by optimizing the minimum radius of curvature, thus enabling stable transmission of the TE1 mode to free space. When the TE / TM fundamental mode is input to the polarizer, the optical field transmission is as follows: Figures 8 to 11 As shown, the reverse input performance is consistent, ensuring bidirectional filtering of unnecessary polarized light in optical gyroscopes, with a single device size length of less than 150μm.
[0089] Specifically, when the first coupling waveguide 11 and the second coupling waveguide 12 are parallel straight waveguides, due to the width deviation of the fabrication process, the actual value of the insertion loss deviates from the optimal value by more than 0.1 dB, and the polarization extinction ratio deviates by more than 10 dB.
[0090] Therefore, in some embodiments, such as Figure 2 As shown, the first and second coupled waveguides are configured as tapered waveguide structures to reduce the sensitivity of the polarizer to process deviations.
[0091] The minimum width W3 and maximum width W4 of the first tapered waveguide 121 can be determined based on the second width W2, and the minimum width W5 and maximum width W6 of the second tapered waveguide 111 can be determined based on the first width W1. Other widths of the first and second tapered waveguides 121 can be obtained through linear interpolation. For example, W3 = W2 or 1.1 × W2, W4 = 1.6 × W2 or 2 × W2, W5 = W1 or 1.1 × W1, and W6 = 1.6 × W1 or 2 × W1.
[0092] According to simulation calculations, such as Figure 2 The polarizer shown can have an insertion loss of less than 0.05 dB and a polarization extinction ratio greater than 20 dB. Under the same fabrication process deviation, the insertion loss is less than 0.05 dB, the polarization extinction ratio is less than 2 dB, and the optical field transmission can be as follows: Figure 12 and Figure 13 As shown. Figure 12 and Figure 13 The horizontal axis represents the length of the first coupled waveguide in the x-direction. Figures 12 to 13 The vertical axis represents the length of the second coupled waveguide, the bent waveguide, and the transmission waveguide in the y-direction. Figure 12 This diagram illustrates the optical transmission when TM0 mode light is input from the left end of the first coupled waveguide. Figure 13 This diagram illustrates the optical transmission when TE0 mode light is input from the left end of the first coupled waveguide.
[0093] In some embodiments, to further improve the polarization extinction ratio, such as Figure 14 As shown, a plurality of polarizers 10 are disposed on the silicon-based chip 20, and the first coupling waveguides 11 of two adjacent polarizers 10 are connected. Figure 14 Taking the cascaded polarizers on a silicon-based chip 20 as an example, but not limited to this, for example, a two-stage, three-stage, or six-stage cascaded polarizer can be set on the silicon-based chip 20.
[0094] Simulation results show that the increase in polarization extinction ratio is linearly related to the number of cascaded polarizers, expressed as PDL(n) = PDL0 × n, where PDL0 is the polarization extinction ratio of a single polarizer, and n represents the number of cascaded polarizers. The optical field transmission of a two-stage cascaded polarizer can be as follows: Figure 15 and Figure 16 As shown, Figure 15 This diagram illustrates the optical transmission when TM0 mode light is input from the left end of the first coupled waveguide of a two-stage cascaded polarizer. Figure 16 This diagram illustrates the optical transmission when TE0 mode light is input from the left end of the first coupled waveguide of a two-stage cascaded polarizer.
[0095] The polarizer provided by this invention requires only a single-step etching process, and the waveguide width is much larger than the process limit. The waveguide in the coupling region adopts a gradient width, which reduces the complexity and sensitivity of the process fabrication. It has low insertion loss, a polarization extinction ratio of a single device greater than 25dB, a small overall device size, and a linear increase in polarization extinction ratio in the cascaded structure. The filtered mode is transmitted to free space through the waveguide, which reduces the risk of stray light interfering with the main path signal.
[0096] This invention also provides a method for determining the parameters of a polarizer, which can be used in terminal devices such as computer equipment. The method includes the following steps:
[0097] Step S101: Obtain the first correspondence and the second correspondence.
[0098] The first correspondence is the correspondence between the effective refractive index and the width of the first coupled waveguide, and the second correspondence is the correspondence between the effective refractive index and the width of the second coupled waveguide.
[0099] Specifically, the first and second correspondences can be obtained through the intrinsic mode solution method.
[0100] Step S102: Determine the first width of the first coupled waveguide and the second width of the second coupled waveguide based on the first propagation constant of the first coupled waveguide, the second propagation constant of the second coupled waveguide, the first correspondence, and the second correspondence.
[0101] For example, with the goal of having the same first propagation constant and the same second propagation constant, the first width and the second width can be determined based on the first correspondence and the second correspondence. The first propagation constant is determined based on the effective refractive index of the first coupled waveguide, and the second propagation constant is determined based on the effective refractive index of the second coupled waveguide.
[0102] Specifically, by combining formulas (3) and (4), the n that satisfies the condition (β1 = β2) can be determined. eff1 and n eff2 Then, by combining the first correspondence and the second correspondence, we can obtain the first width and the second width.
[0103] The present invention also provides an optical gyroscope, which includes the polarizer provided in any of the above embodiments.
[0104] In the description of this specification, the references to terms such as "this embodiment," "an embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.
[0105] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.
[0106] The above description does not provide detailed explanations of the technical aspects such as the patterning and etching of each layer. However, those skilled in the art should understand that layers and regions of the desired shape can be formed using various technical means. Furthermore, although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be effectively combined.
[0107] The above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described above, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention.
[0108] Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention.
Claims
1. A polarizer characterized by, The polarizer comprises a first coupling waveguide, a second coupling waveguide, a first bending waveguide, a second bending waveguide, a first transmission waveguide and a second transmission waveguide arranged on a silicon-based chip; The first coupling waveguide and the second coupling waveguide are arranged in parallel, and the center lines of the first coupling waveguide and the second coupling waveguide in the light transmission direction are parallel; One end of the second coupling waveguide is connected to one end of the first bending waveguide, the other end of the first bending waveguide is connected to one end of the first transmission waveguide, and the other end of the first transmission waveguide is arranged at the edge of the silicon-based chip; The other end of the second coupling waveguide is connected to one end of the second bending waveguide, the other end of the second bending waveguide is connected to one end of the second transmission waveguide, and the other end of the second transmission waveguide is arranged at the edge of the silicon-based chip; When the first coupling waveguide transmits a light signal containing target polarized light and non-target polarized light, the non-target polarized light is coupled into the second coupling waveguide, and the non-target polarized light entering the second coupling waveguide is output from the silicon-based chip through the first bending waveguide and the first transmission waveguide or through the second bending waveguide and the second transmission waveguide.
2. The polarizer of claim 1, wherein The first coupling waveguide and the second coupling waveguide are parallel straight waveguides.
3. The polarizer of claim 2, wherein The first width of the first coupling waveguide and the second width of the second coupling waveguide are different, and the first width and the second width are determined based on a first propagation constant of the first coupling waveguide, a second propagation constant of the second coupling waveguide, a first correspondence relationship and a second correspondence relationship, the first correspondence relationship is a correspondence relationship between the effective refractive index and the width of the first coupling waveguide, and the second correspondence relationship is a correspondence relationship between the effective refractive index and the width of the second coupling waveguide.
4. The polarizer of claim 1, wherein The second coupling waveguide is composed of at least one first tapered waveguide, and the corresponding region of the first coupling waveguide and the second coupling waveguide is composed of at least one second tapered waveguide.
5. The polarizer according to any one of claims 1 to 4, characterized in that The length of the first coupling waveguide is an odd multiple of the coupling length.
6. The polarizer according to any one of claims 1 to 4, characterized in that The first bending waveguide and the second bending waveguide are formed based on a free-form curve, a Bezier curve or an Euler curve.
7. The polarizer according to any one of claims 1 to 4, characterized in that A plurality of the polarizers are arranged on the silicon-based chip, and the first coupling waveguides in adjacent two of the polarizers are connected.
8. A method of determining parameters of a polarizer, characterized by The polarizer is the polarizer of any one of claims 1 to 7, and the method comprises: obtaining a first correspondence relationship and a second correspondence relationship, wherein the first correspondence relationship is a correspondence relationship between the effective refractive index and the width of the first coupling waveguide, and the second correspondence relationship is a correspondence relationship between the effective refractive index and the width of the second coupling waveguide; determining a first width of the first coupling waveguide and a second width of the second coupling waveguide according to a first propagation constant of the first coupling waveguide, a second propagation constant of the second coupling waveguide, the first correspondence relationship and the second correspondence relationship.
9. The method of claim 8, wherein, The determining the first width of the first coupling waveguide and the second width of the second coupling waveguide according to the first propagation constant of the first coupling waveguide, the second propagation constant of the second coupling waveguide, the first correspondence relationship and the second correspondence relationship comprises: The first width and the second width are determined based on the first correspondence relationship and the second correspondence relationship, with the same target of the first propagation constant and the second propagation constant, wherein the first propagation constant is determined based on an effective refractive index of the first coupling waveguide, and the second propagation constant is determined based on an effective refractive index of the second coupling waveguide.
10. An optical gyroscope, characterized by The polarizer comprises any one of claims 1 to 7.