An on-chip polarizer for fiber optic gyroscopes based on LNOI

Abstract

The present invention provides an on-chip polarizer for an optical fiber gyroscope based on LNOI. An input waveguide, an intermediate waveguide, and an output waveguide are sequentially arranged on the LNOI material. The intermediate waveguide includes N polarization waveguides connected in sequence, where N≥2. The polarization waveguides are in a bent structure, and the bending directions of adjacent polarization waveguides are opposite, and the adjacent two end faces are connected in a staggered manner. The present invention realizes physical polarization on a small-sized LNOI chip by designing a specific waveguide structure, meeting the polarization requirements of the optical fiber gyroscope.

Description

Technical Field

[0001] The present invention belongs to the technical field of integrated optical chips, and particularly relates to an on-chip polarizer for a fiber optic gyroscope based on LNOI. Background Art

[0002] A fiber optic gyroscope is a sensor that senses the angular velocity of a sensitive carrier based on the Sagnac effect. It has the advantages of no moving parts, fast startup time, and a wide precision coverage range, and has received extensive attention and applications in the fields of aviation, aerospace, navigation, land precision navigation, weapon precision guidance, and automatic control. In order to better meet the development needs of miniaturization and low cost of inertial navigation systems, the next generation of fiber optic gyroscopes urgently needs to develop towards miniaturization. The optical path volume occupies more than 70% of the volume of the fiber optic gyroscope, which is the primary challenge in achieving miniaturization. An integrated optical chip based on integrated optical technology can integrate multiple optical path devices or functions on a chip with a size of mm or less, significantly reducing the optical path volume of the gyroscope and providing a feasible technical solution for the miniaturization of the optical path of the fiber optic gyroscope.

[0003] The polarizer is one of the key devices in the optical path of an interferometric closed-loop fiber optic gyroscope. The polarizer of a traditional fiber optic gyroscope is integrated in a multi-functional integrated optical modulator (MIOC). The MIOC is made of the birefringent crystal lithium niobate through proton exchange or titanium diffusion processes. The TE-mode light wave propagates according to the waveguide structure, and the TM-mode light wave does not satisfy the conduction condition and gradually leaks, forming linearly polarized light with a high polarization extinction ratio. For medium and low-precision fiber optic gyroscopes, the polarization extinction ratio of the polarizer should be better than -30 dB.

[0004] Lithium niobate material has excellent electro-optic properties and a super-wide transparent window, which is an excellent platform for realizing optical devices. The MIOC device is based on bulk lithium niobate (LN) material. Due to the small refractive index difference of the LN material, the device volume is too large, and it is difficult to achieve on-chip integration of multiple devices. The refractive index difference of lithium niobate thin film material (LNOI) is greatly increased, which is a potential platform for realizing on-chip integration of multiple devices and provides a feasible technical solution for the miniaturization of fiber optic gyroscopes.

[0005] Functions such as beam splitting / combining, phase modulation, and coupling are realized based on LNOI, but there are disadvantages in polarization performance. Therefore, it is necessary to design an on-chip polarizer based on a special physical structure. In addition, another challenge is how to obtain an on-chip LNOI polarizer with high polarization performance through a simple structure. Summary of the Invention

[0006] Aiming at the technical problem that the polarization performance of lithium niobate thin film material LNOI in the prior art cannot meet the requirements, the present invention provides an on-chip polarizer for fiber optic gyroscopes based on LNOI, which realizes physical polarization on a small-size LNOI chip by designing a specific waveguide structure to meet the polarization requirements of fiber optic gyroscopes.

[0007] The technical solutions adopted by the present invention to solve the above technical problems are as follows:

[0008] An on-chip polarizer for fiber optic gyroscopes based on LNOI, an input waveguide, an intermediate waveguide, and an output waveguide are sequentially arranged on the LNOI material. The intermediate waveguide includes N polarization waveguides connected in sequence, N≥2, and the polarization waveguides are in a bent structure, and the bending directions of adjacent polarization waveguides are opposite, and the adjacent two end faces are connected in a staggered manner.

[0009] Further, the waveguide structure from top to bottom is a upper cladding layer, a core layer, a buried oxide layer, and a substrate layer. The upper cladding layer is an air layer; the core layer is LN, with a thickness of 200nm to 700nm; the buried oxide layer is SiO 2 , with a thickness greater than 2μm; the substrate layer is Si, with a thickness greater than 700μm.

[0010] Further, the input waveguide and the output waveguide have the same structure; adjacent polarization waveguides are staggered in the waveguide width direction, and the staggering size is less than half of the width of the polarization waveguide.

[0011] Further, the input waveguide and the output waveguide are straight waveguides, and the widths of the input waveguide and the output waveguide do not exceed the width of the polarization waveguide; the input waveguide and the output waveguide are ridge waveguides or strip waveguides, and the intermediate waveguide is a strip waveguide.

[0012] Further, the input waveguide and the output waveguide are dissipative waveguides, and the outer diameters of the two free ends of the input waveguide, the output waveguide and the intermediate waveguide are aligned.

[0013] Further, the widths of the input waveguide and the output waveguide are [0.2, 3.5]μm, the width of the polarization waveguide is w m ∈[0.5, 3.5]μm, the radius of the polarization waveguide is R∈[2.5, 57.7]μm, and the coverage angle of the polarization waveguide is θ∈[60, 270]°.

[0014] Further, the input waveguide and the output waveguide include dissipative waveguides and absorption waveguides respectively arranged on both sides of the dissipative waveguides. The outer diameters of the two free ends of the dissipative waveguides and the intermediate waveguide are aligned; the input waveguide and the output waveguide are ridge waveguides, and the intermediate waveguide is a strip waveguide.

[0015] Further, the widths of the dissipative waveguide and the absorption waveguide are both less than 1 / 3·W m, W m is the width of the polarization waveguide; the distance between the dissipative waveguide and the absorption waveguide is greater than 4·W d and 2·W a , W a is the width of the absorption waveguide, and W d is the width of the dissipative waveguide.

[0016] Furthermore, the width of the dissipative waveguide of the input waveguide and the output waveguide is w d ∈[0.2, 0.8] μm, the width of the absorption waveguide of the input waveguide and the output waveguide is w a ∈[3.4, 11.7] μm, the distance between the dissipative waveguide and the absorption waveguide is D i ∈[1.9, 6.7] μm, the width of the polarization waveguide is w m ∈[0.5, 3.5] μm, the radius of the polarization waveguide is R ∈[2.5, 57.7] μm, and the coverage angle of the polarization waveguide is θ ∈[60, 270]°.

[0017] Furthermore, a modulator is also integrated on the LNOI chip where the polarizer is located.

[0018] Advantages of the present invention compared with the prior art:

[0019] (1) For the polarizer based on LNOI, physical polarization is achieved by designing a special waveguide combination, eliminating process steps such as proton exchange or titanium diffusion, and significantly reducing the device volume, providing a feasible technical approach for the on-chip integration of small-sized polarizers;

[0020] (2) At the current stage, it is difficult to implement a high-performance modulator on SOI. Therefore, it is difficult to achieve monolithic integration of a polarizer and a modulator based on SOI materials; LNOI inherits the excellent electro-optic properties of LN and can achieve high-performance modulators. The polarizer described in the present invention realizes polarization performance without changing the material properties of LNOI, making it possible to achieve monolithic integration of a polarizer and a modulator on LNOI;

[0021] (3) The polarizer described in the present invention is for fiber optic gyroscope applications. The refractive index difference of SOI is large and the device size is very small, resulting in a small output optical mode field, and there are certain difficulties in connecting with optical fibers, and a special coupling structure needs to be designed; the polarizer described in the present invention is based on LNOI, and its refractive index difference is between LN and SOI. While having the advantage of a small size, the output optical mode field is effectively increased, which is more conducive to achieving low-loss connection with optical fibers.

[0022] (4) The polarizer proposed by the present invention has a simple structure. The waveguide characteristic size is much larger than the minimum line width of the existing manufacturing process. The device manufacturing process adopts the general semiconductor manufacturing process without special manufacturing steps, eliminating processes such as proton exchange and titanium diffusion, greatly reducing the device preparation process, lowering the complexity and difficulty of the manufacturing process, and facilitating mass production at low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings included are used to provide a further understanding of the embodiments of the present invention, which form a part of the specification, are used to illustrate the embodiments of the present invention, and together with the written description are used to explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 It is a top view of the simple configuration of the on-chip polarizer for an LNOI-based fiber optic gyroscope provided in Specific Embodiment 1 of the present invention;

[0025] Figure 2 It is a top view of the complete configuration of the on-chip polarizer for an LNOI-based fiber optic gyroscope provided in Specific Embodiment 2 of the present invention;

[0026] Figure 3 It is a schematic top view of the on-chip polarizer for an LNOI-based fiber optic gyroscope (N = 3 polarization modules in series, simple configuration, input and output on the same side) provided in Specific Embodiment 3 of the present invention;

[0027] Figure 4 It is a schematic top view of the on-chip polarizer for an LNOI-based fiber optic gyroscope (N = 3 polarization modules in series, complete configuration, input and output on the same side) provided in Specific Embodiment 4 of the present invention;

[0028] Figure 5 It is a schematic top view of the on-chip polarizer for an LNOI-based fiber optic gyroscope (N = 4 polarization modules in series, simple configuration, input and output on different sides) provided in Specific Embodiment 5 of the present invention;

[0029] Figure 6 It is a schematic top view of the on-chip polarizer for an LNOI-based fiber optic gyroscope (N = 4 polarization modules in series, complete configuration, input and output on different sides) provided in Specific Embodiment 6 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0030] Specific embodiments of the present invention will be described in detail below. In the following description, specific details are set forth for the purpose of explanation and not limitation, in order to help a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may also be practiced in other embodiments without these specific details.

[0031] It should be noted here that, in order to avoid obscuring the present invention with unnecessary details, only the device structures and / or processing steps closely related to the solution of the present invention are shown in the drawings, while other details less related to the present invention are omitted.

[0032] An on-chip polarizer for an LNOI-based fiber optic gyroscope provided by the present invention sequentially sets an input waveguide, an intermediate waveguide, and an output waveguide on an LNOI material. The intermediate waveguide includes N polarization waveguides connected in sequence, N≥2, and the polarization waveguides are in a bent structure. The bending directions of adjacent polarization waveguides are opposite, and the adjacent end faces are connected in a staggered manner. The present invention guides light waves by connecting adjacent polarization waveguides in a staggered manner, preventing light from overflowing, reducing light loss, ensuring the transmission of effective modes, and ensuring the effective transmission and oscillation of light waves by designing the structural forms of the input waveguide, the intermediate waveguide, and the output waveguide, realizing physical polarization on a small-size LNOI chip and meeting the polarization requirements of the fiber optic gyroscope.

[0033] Further, the waveguide structure from top to bottom is a upper cladding layer, a core layer, a buried oxide layer, and a substrate layer. The upper cladding layer is an air layer, the core layer is LN with a thickness of 200 nm to 700 nm; the buried oxide layer is SiO 2 , with a thickness greater than 2 μm; the substrate layer is Si with a thickness greater than 700 μm.

[0034] Further, the input waveguide and the output waveguide have the same structure; adjacent polarization waveguides are staggered in the waveguide width direction, and the staggering size is less than half of the width of the polarization waveguide.

[0035] Further, the input waveguide and the output waveguide are straight waveguides, and the widths of the input waveguide and the output waveguide do not exceed the width of the polarization waveguide.

[0036] Further, the input waveguide and the output waveguide are dissipative waveguides, and the outer diameters of the two free ends of the input waveguide, the output waveguide and the intermediate waveguide are aligned. By aligning the outer diameters of the two free ends of the input waveguide, the output waveguide and the intermediate waveguide, light is guided to enter, and light loss is reduced.

[0037] Further, the widths of the input waveguide and the output waveguide are [0.2, 3.5] μm, the width of the polarization waveguide is w m ∈[0.5, 3.5] μm, the radius of the polarization waveguide is R∈[2.5, 57.7] μm, and the coverage angle of the polarization waveguide is θ∈[60, 270]°.

[0038] Further, the input waveguide and the output waveguide are ridge waveguides or strip waveguides, and the intermediate waveguide is a strip waveguide.

[0039] Further, the input waveguide and the output waveguide include a dissipative waveguide and absorption waveguides respectively disposed on both sides of the dissipative waveguide. The outer diameters of the two free ends of the dissipative waveguide are aligned with those of the intermediate waveguide. By aligning the outer diameters of the two free ends of the dissipative waveguide with those of the intermediate waveguide, light is guided to enter, reducing optical loss.

[0040] Further, the widths of both the dissipative waveguide and the absorption waveguide are less than 1 / 3·W m , W m being the width of the polarization waveguide; the distance between the dissipative waveguide and the absorption waveguide is greater than 4·W d and 2·W a , W a being the width of the absorption waveguide, and W d being the width of the dissipative waveguide.

[0041] Further, the input waveguide and the output waveguide are ridge waveguides, and the intermediate waveguide is a strip waveguide.

[0042] Further, the width of the dissipative waveguide of the input waveguide and the output waveguide is w d ∈[0.2, 0.8] μm, the width of the absorption waveguide of the input waveguide and the output waveguide is w a ∈[3.4, 11.7] μm, the distance between the dissipative waveguide and the absorption waveguide is D i ∈[1.9, 6.7] μm, the width of the polarization waveguide is w m ∈[0.5, 3.5] μm, the radius of the polarization waveguide is R ∈[2.5, 57.7] μm, and the coverage angle of the polarization waveguide is θ ∈[60, 270]°.

[0043] Further, a modulator is also integrated on the LNOI chip where the polarizer is located.

[0044] The on-chip polarizer for an optical fiber gyroscope based on LNOI proposed by the present invention includes an input waveguide, an intermediate waveguide, and an output waveguide. The input waveguide and the output waveguide can be located on the same side or on different sides. The input waveguide is a straight waveguide in a specific form, the intermediate waveguide is composed of N bent waveguides and misaligned waveguides, and the output waveguide is a straight waveguide in a specific form. The input waveguide and the output waveguide have the same form, and different implementation forms are selected according to different actual application requirements.

[0045] In the complete form, the input waveguide, the output waveguide, and the intermediate waveguide all have polarization and polarization performance. The input waveguide and the output waveguide are both composed of a dissipative waveguide and an absorption waveguide; the input waveguide and the output waveguide are implemented based on ridge waveguides, and the intermediate waveguide is implemented based on strip waveguides.

[0046] In its simplest form, only the middle waveguide has polarization and polarization characteristics. The input waveguide and the output waveguide are only composed of transmission waveguides. The input waveguide and the output waveguide can be implemented based on ridge waveguides or strip waveguides, and the middle waveguide is implemented based on strip waveguides.

[0047] The middle waveguide has a modular cascading characteristic. The different requirements of the gyro for polarization performance can be met by increasing or decreasing the number N of polarization waveguides. The number is directly proportional to the polarization performance. The input waveguide and the output waveguide have two implementation forms: polarized and non-polarized. When in the polarized form, the different requirements of the gyro for polarization performance can be met by increasing or decreasing the waveguide length. The length is directly proportional to the polarization performance. When the input waveguide and the output waveguide are ordinary straight waveguides, it is in the non-polarized form. The internal connection form of the polarizer: The input waveguide is connected to the first polarization waveguide, the Nth polarization waveguide is connected to the output waveguide, and the different polarization waveguides are connected end to end in sequence.

[0048] The polarizer is implemented based on a strip waveguide structure, which from top to bottom is: upper cladding layer, core layer, buried oxide layer, and substrate layer. The upper cladding layer is an air layer; the core layer is an LN layer with a thickness of n LN ; the buried oxide layer is a SiO 2 layer with a thickness of n SiO2 ; the substrate layer is a Si layer with a thickness of n sub-Si . In the polarized form, the dissipation waveguide width of the said input waveguide and output waveguide is W d , the absorption waveguide width of the input waveguide and output waveguide is W a , W d < 1 / 3·W m , the distance between the dissipation waveguide and the absorption is D i , D i > 4·W d and D i > 2·W a , the bending radius of the polarization waveguide in the middle waveguide is R, the width is W m , the coverage angle is θ, the number of polarization waveguides is N, the outer diameter of the dissipation waveguide of the input waveguide is flush with that of the first polarization waveguide, the outer diameter of the dissipation waveguide of the output waveguide is flush with that of the Nth polarization waveguide, and the offset between the polarization waveguides is D p , and D p < 1 / 2·W m . In the non-polarized form, the width of the said input waveguide is W i , the width of the output waveguide is W o , the bending radius of the polarization waveguide in the middle waveguide is R, the width is W m , the coverage angle is θ, the number of polarization waveguides is N, the outer diameter of the input waveguide is flush with that of the first polarization waveguide, the outer diameter of the output waveguide is flush with that of the Nth polarization waveguide, and the offset between the polarization waveguides is D p , Dp <1 / 2·W m 。

[0049] Principle of operation of the polarizer: The polarization waveguide causes different equivalent refractive indices for different modes, resulting in scattering loss, radiation loss, and mode mismatch loss in the transmission mode, further differentiating the mode propagation rate. A single polarization waveguide can achieve a certain polarization effect, but its performance cannot meet the application requirements of the gyroscope. The dissipative waveguide with a specific aspect ratio has different propagation constants for the transmitted optical waves of different modes, and specifically attenuates specific modes through specific design. The absorption waveguide is set to absorb the leaked optical waves and quickly dissipate the light intensity. Regarding the specific parameter design, the parameters of the polarizer provided by the present invention can be determined through frequency-domain simulation and parameter scanning time-domain simulation of the waveguide. The specific parameter design methods of this kind are not elaborated here.

[0050] In the complete form, the optical wave first passes through the input waveguide. The dissipative waveguide attenuates specific modes and polarizes the optical wave. The polarized light enters the first polarization waveguide of the intermediate waveguide, and birefringence occurs at the curved waveguide. Different effective refractive indices of the TE and TM modes result in different transmission limitation conditions. The TE mode is more strongly restricted, while the restriction on the TM mode is significantly reduced. Therefore, the TE mode can maintain low-loss transmission, while the TM mode leaks. After passing through N polarization waveguides, the TM mode is significantly attenuated. The dissipative waveguide at the output waveguide can further attenuate the TM mode, and finally linearly polarized light with a high polarization extinction ratio is output to meet the application requirements of the polarization performance for medium and low-precision fiber optic gyroscopes.

[0051] In the simple form, the optical wave first passes through the input waveguide. The transmission waveguide in it only provides a guiding function for the transmission direction of the optical wave. The optical wave enters the first polarization waveguide of the intermediate waveguide, and birefringence occurs at the curved waveguide. Different effective refractive indices of the TE and TM modes result in different transmission limitation conditions. The TE mode is more strongly restricted, while the restriction on the TM mode is significantly reduced. Therefore, the TE mode can maintain low-loss transmission, while the TM mode leaks. After passing through N polarization waveguides, the TM mode is significantly attenuated. The output waveguide outputs linearly polarized light with a high polarization extinction ratio to meet the application requirements of the polarization performance for medium and low-precision fiber optic gyroscopes.

[0052] The on-chip polarizer for an LNOI-based fiber optic gyroscope shown in the present invention has a waveguide structure of: a waveguide core layer, an upper cladding layer, a buried oxide layer, and a substrate layer, and the waveguide structure is a standard LNOI structure.

[0053] According to an embodiment of the present invention, the waveguide core layer material is LN, with a thickness of 200 nm to 700 nm; the upper cladding layer is air; the buried oxide layer material is silicon dioxide, with a thickness greater than 2 μm; the substrate layer material is silicon, with a thickness greater than 700 μm.

[0054] The on-chip polarizer for an optical fiber gyroscope based on LNOI proposed by the present invention includes an input waveguide 10, an intermediate waveguide 11, and an output waveguide 12. Among them, the polarization waveguide 111 of the intermediate waveguide has a modular series connection characteristic, and the number N of polarization waveguides can be increased or decreased according to different requirements of the gyroscope for polarization performance, and the polarization waveguides are connected in the way of "successively connecting end to end".

[0055] In the present invention, the waveguide width refers to the waveguide size in the direction perpendicular to the waveguide extension direction and parallel to the substrate layer direction.

[0056] Embodiment 1:

[0057] As Figure 1 shown, this embodiment is the basic configuration in a simple form. The polarizer is composed of an input waveguide 10, an intermediate waveguide 11, and an output waveguide 12. The polarizer is in a simple form, that is, both the input waveguide and the output waveguide are straight waveguides. The straight waveguide can be an ordinary straight waveguide or a dissipative waveguide. The dissipative waveguide has a polarization effect and can improve the polarization performance. The intermediate waveguide is composed of N polarization waveguides 111. The adjacent polarization waveguides are connected by a misaligned waveguide 112. The misaligned waveguide 112 means that the docking surfaces of the two polarization waveguides are misaligned in the width direction, so that the communication area between them is reduced. The input waveguide and the output waveguide can be realized based on a ridge waveguide or a strip waveguide, and the intermediate waveguide is realized based on a strip waveguide. The widths of the input waveguide and the output waveguide are w o ∈[0.2, 3.5] μm, that is, the value range of the widths of the input waveguide and the output waveguide is from 0.3 to 2.5 μm. The width of the polarization waveguide is w m ∈[0.5, 3.5] μm, that is, the value range of the width of the polarization waveguide is from 0.5 to 3.5 μm. The radius of the polarization waveguide is R ∈ [2.5, 57.7] μm, that is, the value range of the radius of the polarization waveguide is from 2.5 to 57.7 μm. The coverage angle of the polarization waveguide is θ ∈ [60, 270]°, that is, the value range of the coverage angle of the polarization waveguide is from 60° to 270°. The outer diameter of the input waveguide is flush with the input end of the first polarization waveguide (that is, the output end plane of the input waveguide 10 is butt-jointed with the input end plane of the polarization waveguide 111, and one side of the input waveguide 10 overlaps with the outer diameter tangent of the input end of the polarization waveguide 111). The outer diameter of the output waveguide is flush with the output end of the last polarization waveguide (that is, the input end plane of the output waveguide 12 is butt-jointed with the output end plane of the second polarization waveguide, and one side of the output waveguide 12 overlaps with the outer diameter tangent of the output end of the second polarization waveguide). When N is odd, the input waveguide and the output waveguide are on the same side of the intermediate waveguide; when N is even, the input waveguide and the output waveguide are on the opposite sides of the intermediate waveguide. As Figure 2 shown in the basic configuration, the input waveguide and the output waveguide are on the opposite sides of the intermediate waveguide.

[0058] According to an embodiment of the present invention, in accordance with the above waveguide structure, the polarizer can differentially limit different polarization states of the input optical wave, greatly attenuate the TM mode, and maintain low-loss transmission of the TE mode, thereby realizing linearly polarized light with a high polarization extinction ratio. According to an embodiment of the present invention, the polarization extinction ratio of the polarizer can reach -15 dB to -25 dB.

[0059] Embodiment Two:

[0060] As Figure 2 shown, this embodiment is a basic configuration in a complete form. The polarizer is composed of an input waveguide 10, an intermediate waveguide 11, and an output waveguide 12. The polarizer is in a complete form, that is, both the input waveguide and the output waveguide are composed of a dissipative waveguide and an absorption waveguide. The intermediate waveguide is composed of N bent waveguide structures, and the adjacent polarization waveguides are connected by misaligned waveguides. The input waveguide and the output waveguide are based on ridge waveguides, and the intermediate waveguide is based on strip waveguides. The width of the dissipative waveguide of the input waveguide and the output waveguide is w d ∈[0.2, 0.8] μm, that is, the value range of the width of the dissipative waveguide of the input waveguide and the output waveguide is from 0.2 to 0.8 μm. The width of the absorption waveguide of the input waveguide and the output waveguide is w a ∈[3.4, 11.7] μm, that is, the width of the absorption waveguide of the input waveguide and the output waveguide is from 3.4 to 11.7 μm. The distance between the dissipative waveguide and the absorption waveguide is D i ∈[1.9, 6.7] μm, that is, the distance between the dissipative waveguide and the absorption waveguide is from 1.9 to 6.7 μm. The width of the polarization waveguide is w m ∈[0.5, 3.5] μm, that is, the value range of the width of the polarization waveguide is from 0.5 to 3.5 μm. The radius of the polarization waveguide is R ∈[2.5, 57.7] μm, that is, the value range of the radius of the polarization waveguide is from 2.5 to 57.7 μm. The coverage angle of the polarization waveguide is θ ∈[60, 270]°, that is, the value range of the coverage angle of the polarization waveguide is from 60° to 270°. The outer diameter of the input waveguide is flush with the input end of the first polarization waveguide, and the outer diameter of the output waveguide is flush with the output end of the last polarization waveguide. When N is odd, the input waveguide and the output waveguide are on the same side of the intermediate waveguide; when N is even, the input waveguide and the output waveguide are on the opposite sides of the intermediate waveguide. As Figure 2 shown in the basic configuration, the input waveguide and the output waveguide are on opposite sides of the intermediate waveguide.

[0061] According to an embodiment of the present invention, in accordance with the above waveguide structure, the polarizer can differentially limit different polarization states of the input optical signal, greatly attenuate the TM mode, and maintain low-loss transmission of the TE mode, thereby realizing linearly polarized light with a high polarization extinction ratio. According to an embodiment of the present invention, the polarization extinction ratio of the polarizer is better than -23 dB.

[0062] Embodiment Three:

[0063] As Figure 3 shown, this embodiment is an upgraded configuration in a simple form. The polarizer is composed of an input waveguide 10, an intermediate waveguide 11, and an output waveguide 12. The polarizer is in a simple form, that is, both the input waveguide 10 and the output waveguide 12 are straight waveguides. The straight waveguide can be a common straight waveguide or a dissipative waveguide. The intermediate waveguide 11 is a bent waveguide (1111, 1112, 1113) structure, and the adjacent polarization waveguides are connected by misaligned waveguides (1121, 1122). The input waveguide and the output waveguide can be realized based on a ridge waveguide or a strip waveguide, and the intermediate waveguide is realized based on a strip waveguide. The widths of the input waveguide and the output waveguide are w o ∈[0.2, 3.5] μm, that is, the value range of the widths of the input waveguide and the output waveguide is 0.3 to 2.5 μm, and the width of the polarization waveguide is w m ∈[0.5, 3.5] μm, that is, the value range of the width of the polarization waveguide is 0.5 to 3.5 μm, the radius of the polarization waveguide is R ∈[2.5, 57.7] μm, that is, the value range of the radius of the polarization waveguide is 2.5 to 57.7 μm, and the coverage angle of the polarization waveguide is θ ∈[60, 270]°, that is, the value range of the coverage angle of the polarization waveguide is 60° to 270°. The outer diameter of the input waveguide is flush with the input end of the first polarization waveguide 1113, and the outer diameter of the output waveguide is flush with the output end of the last polarization waveguide 1111. In this example, N is an odd number, and the input waveguide and the output waveguide are on the opposite sides of the intermediate waveguide. N can be 3, 5, 7, 9, …. The polarizer can obtain an output light wave with a polarization extinction ratio of at least -40 dB.

[0064] Embodiment 4:

[0065] As Figure 4 shown, this embodiment is an upgraded configuration in a complete form. The polarizer is composed of an input waveguide 10, an intermediate waveguide 11, and an output waveguide 12. The polarizer is in a complete form, that is, both the input waveguide 10 and the output waveguide 12 are composed of a dissipative waveguide (101, 121) and an absorption waveguide (102, 103, 122, 123). The intermediate waveguide 11 is a bent waveguide (1111, 1112, 1113) structure, and the adjacent polarization waveguides are connected by misaligned waveguides (1121, 1122). The input waveguide and the output waveguide are realized based on a ridge waveguide, and the intermediate waveguide is realized based on a strip waveguide. The widths of the dissipative waveguides of the input waveguide and the output waveguide are w d ∈[0.2, 0.8] μm, that is, the value range of the widths of the dissipative waveguides of the input waveguide and the output waveguide is 0.2 to 0.8 μm, and the widths of the absorption waveguides of the input waveguide and the output waveguide are w a ∈[3.4, 11.7] μm, that is, the widths of the absorption waveguides of the input waveguide and the output waveguide are 3.4 to 11.7 μm, and the distance between the dissipative waveguide and the absorption waveguide is Di ∈[1.9, 6.7] μm, that is, the distance between the dissipative waveguide and the absorption waveguide is from 1.9 to 6.7 μm, and the width of the polarization waveguide is w m ∈[0.5, 3.5] μm, that is, the value range of the width of the polarization waveguide is from 0.5 to 3.5 μm, the radius of the polarization waveguide is R ∈[2.5, 57.7] μm, that is, the value range of the radius of the polarization waveguide is from 2.5 to 57.7 μm, and the coverage angle of the polarization waveguide is θ ∈[60, 270]°, that is, the value range of the coverage angle of the polarization waveguide is from 60° to 270°. The outer diameter of the input waveguide 10 is flush with the input end of the first polarization waveguide 1113, and the outer diameter of the output waveguide 12 is flush with the output end of the last polarization waveguide 1111. In this example, N is an odd number, and the input waveguide and the output waveguide are on the same side of the middle waveguide. N can be 3, 5, 7, 9, …. The polarizer can obtain an output optical wave with a polarization extinction ratio of at least -40 dB.

[0066] Example Five:

[0067] As Figure 5 shown, this embodiment is an upgraded configuration in a simple form. The polarizer is composed of an input waveguide 10, a middle waveguide 11, and an output waveguide 12. The polarizer is in a simple form, that is, both the input waveguide 10 and the output waveguide 12 are straight waveguides. The straight waveguide can be a common straight waveguide or a dissipative waveguide. The middle waveguide 11 is a curved waveguide (1111, 1112, 1113, 1114) structure, and the adjacent polarization waveguides are connected by misaligned waveguides (1121, 1122, 1123). The input waveguide and the output waveguide can be realized based on a ridge waveguide or a strip waveguide, and the middle waveguide is realized based on a strip waveguide. The width of the input waveguide and the output waveguide is w o ∈[0.2, 3.5] μm, that is, the value range of the width of the input waveguide and the output waveguide is from 0.3 to 2.5 μm, and the width of the polarization waveguide is w m ∈[0.5, 3.5] μm, that is, the value range of the width of the polarization waveguide is from 0.5 to 3.5 μm, the radius of the polarization waveguide is R ∈[2.5, 57.7] μm, that is, the value range of the radius of the polarization waveguide is from 2.5 to 57.7 μm, and the coverage angle of the polarization waveguide is θ ∈[60, 270]°, that is, the value range of the coverage angle of the polarization waveguide is from 60° to 270°. The outer diameter of the input waveguide 10 is flush with the input end of the polarization waveguide 1114, and the outer diameter of the output waveguide 12 is flush with the output end of the polarization waveguide 1111. In this example, N is an even number, and the input waveguide and the output waveguide are on different sides of the middle waveguide. N can be 2, 4, 6, 8, …. The polarizer can obtain an output optical wave with a polarization extinction ratio of at least -40 dB.

[0068] Example Six:

[0069] As Figure 6As shown, this embodiment is an upgraded configuration in a complete form. The polarizer is composed of an input waveguide 10, an intermediate waveguide 11, and an output waveguide 12. The polarizer is in a complete form, that is, both the input waveguide 10 and the output waveguide 12 are composed of a dissipative waveguide (101, 121) and an absorption waveguide (102, 103, 122, 123). The intermediate waveguide 11 is of a curved waveguide (1111, 1112, 1113, 1114) structure, and the adjacent polarization waveguides are connected by misaligned waveguides (1121, 1122, 1123). The input waveguide and the output waveguide are implemented based on a ridge waveguide, and the intermediate waveguide is implemented based on a strip waveguide. The width of the dissipative waveguide of the input waveguide and the output waveguide is w d ∈[0.3, 0.7] μm, that is, the width of the dissipative waveguide of the input waveguide and the output waveguide is w d ∈[0.2, 0.8] μm, that is, the value range of the width of the dissipative waveguide of the input waveguide and the output waveguide is from 0.2 to 0.8 μm. The width of the absorption waveguide of the input waveguide and the output waveguide is w a ∈[3.4, 11.7] μm, that is, the width of the absorption waveguide of the input waveguide and the output waveguide is from 3.4 to 11.7 μm. The distance between the dissipative waveguide and the absorption waveguide is D i ∈[1.9, 6.7] μm, that is, the distance between the dissipative waveguide and the absorption waveguide is from 1.9 to 6.7 μm. The width of the polarization waveguide is w m ∈[0.5, 3.5] μm, that is, the value range of the width of the polarization waveguide is from 0.5 to 3.5 μm. The radius of the polarization waveguide is R ∈[2.5, 57.7] μm, that is, the value range of the radius of the polarization waveguide is from 2.5 to 57.7 μm. The coverage angle of the polarization waveguide is θ ∈[60, 270]°, that is, the value range of the coverage angle of the polarization waveguide is from 60° to 270°. The outer diameter of the input waveguide is flush with the input end of the polarization waveguide 1114, and the outer diameter of the output waveguide is flush with the output end of the polarization waveguide 1111. In this example, N is an even number, and the input waveguide and the output waveguide are on the opposite sides of the intermediate waveguide. N can be 2, 4, 6, 8,.... The polarizer can obtain an output optical wave with a polarization extinction ratio of at least -40 dB.

[0070] The present invention provides an on-chip polarizer for an LNOI-based fiber optic gyroscope, which realizes physical polarization on a small-size LNOI chip by designing a specific waveguide structure to meet the polarization requirements of the fiber optic gyroscope; at the same time, the device has large characteristic dimensions and low requirements for processing technology, which is beneficial to reducing costs and improving the device yield. In addition, the implementation of the present invention is beneficial to realizing the monolithic integration of the polarizer and the phase modulator.

[0071] The features described and / or illustrated for one embodiment above can be used in the same or similar manner in one or more other embodiments, and / or combined with the features in other embodiments or replace the features in other embodiments.

[0072] It should be emphasized that the term "comprising / including" as used herein refers to the presence of features, whole units, steps or components, but does not exclude the presence or addition of one or more other features, whole units, steps, components or combinations thereof.

[0073] Many features and advantages of these embodiments will be apparent from this detailed description, and thus the appended claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. In addition, since many modifications and variations are readily envisioned by those skilled in the art, the embodiments of the present invention are not to be limited to the exact structures and operations illustrated and described, but may cover all suitable modifications and equivalents that fall within their scope.

[0074] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

[0075] The parts of the present invention not described in detail are well-known technologies to those skilled in the art.

Claims

1. An on-chip polarizer for an LNOI-based fiber optic gyroscope, characterized in that, an input waveguide, an intermediate waveguide, and an output waveguide are sequentially arranged on the LNOI material. The intermediate waveguide includes N polarization waveguides connected in sequence, N≥2. The polarization waveguides are in a bent structure, the bending directions of adjacent polarization waveguides are opposite, the adjacent end faces are connected in a staggered manner, and adjacent polarization waveguides are staggered in the waveguide width direction. The staggering size is less than half of the width of the polarization waveguide.

2. The on-chip polarizer for an LNOI-based fiber optic gyroscope according to claim 1, characterized in that, The waveguide structure includes, from top to bottom, an upper cladding layer, a core layer, a buried oxide layer, and a substrate layer. The upper cladding layer is an air layer; the core layer is LN with a thickness of 200 nm to 700 nm; the buried oxide layer is SiO 2 , with a thickness greater than 2 μm; the substrate layer is Si, with a thickness greater than 700 μm.

3. The on-chip polarizer for an LNOI-based fiber optic gyroscope according to claim 1, characterized in that, the input waveguide and the output waveguide have the same structure.

4. The on-chip polarizer for an LNOI-based fiber optic gyroscope according to claim 1, characterized in that, the input waveguide and the output waveguide are straight waveguides, and the widths of the input waveguide and the output waveguide do not exceed the width of the polarization waveguide; the input waveguide and the output waveguide are ridge waveguides or strip waveguides, and the intermediate waveguide is a strip waveguide.

5. The on-chip polarizer for an LNOI-based fiber optic gyroscope according to claim 4, characterized in that, the input waveguide and the output waveguide are dissipative waveguides, and the outer diameters of the two free ends of the input waveguide, the output waveguide and the intermediate waveguide are aligned.

6. The on-chip polarizer for an LNOI-based fiber optic gyroscope according to claim 5, characterized in that, The widths of the input waveguide and the output waveguide are in the range of [0.2, 3.5] μm, and the width of the polarization waveguide is W m ∈[0.5, 3.5] μm, the radius of the polarization waveguide is R ∈ [2.5, 57.7] μm, and the coverage angle of the polarization waveguide is θ ∈ [60, 270]°.

7. The on-chip polarizer for an LNOI-based fiber optic gyroscope according to claim 1, characterized in that, the input waveguide and the output waveguide include dissipative waveguides and absorption waveguides respectively arranged on both sides of the dissipative waveguides. The outer diameters of the two free ends of the dissipative waveguides and the intermediate waveguide are aligned; the input waveguide and the output waveguide are ridge waveguides, and the intermediate waveguide is a strip waveguide.

8. The on-chip polarizer for an LNOI-based fiber optic gyroscope according to claim 7, characterized in that, The widths of the dissipative waveguide and the absorption waveguide are both less than 1 / 3·W m , W m being the width of the polarization waveguide; the distance between the dissipative waveguide and the absorption waveguide is greater than 4·W d and 2·W a , W a being the width of the absorption waveguide, and W d being the width of the dissipative waveguide.

9. The on-chip polarizer for an LNOI-based fiber optic gyroscope according to claim 7, characterized in that, The dissipation waveguide widths of the input waveguide and the output waveguide are W d ∈ [0.2, 0.8] μm, and the absorption waveguide widths of the input waveguide and the output waveguide are W a ∈ [3.4, 11.7] μm. The distance between the dissipation waveguide and the absorption waveguide is D i ∈ [1.9, 6.7] μm, and the polarization waveguide width is W m ∈ [0.5, 3.5] μm, the polarization waveguide radius is R ∈ [2.5, 57.7] μm, and the polarization waveguide coverage angle is θ ∈ [60, 270]°.

10. The on-chip polarizer for an LNOI-based fiber optic gyroscope according to any one of claims 1 to 9, characterized in that, a modulator is also integrated on the LNOI chip where the polarizer is located.

Images