阅读说明：本技术 起偏器、起偏器制备方法及光纤陀螺仪 (Polarizer, polarizer preparation method and optical fiber gyroscope ) 是由 王兴军 陶子涵 陈睿轩 舒浩文 白博文 王心悦 于 2021-09-22 设计创作，主要内容包括：本发明提供一种起偏器、起偏器制备方法及光纤陀螺仪,本发明涉及集成光电子领域。其中起偏器包括：波导层和金属吸收层,波导层包括多模直波导区、曲率渐变波导区和盘绕型波导区,曲率渐变波导区的首端与多模直波导区的末端连接,曲率渐变波导区的末端与盘绕型波导区的首端连接,金属吸收层与盘绕型波导区相对,金属吸收层与盘绕型波导区之间设置有隔离层。本发明提供的起偏器,通过将波导层分为连续的多模直波导区、曲率渐变波导区和盘绕型波导区,增强对TE偏振态的光场束缚能力,减小TE偏振态的传输损耗,经过盘绕型波导区的长距离盘绕结构后,TM偏振光会被经过隔离层隔开的金属吸收层的金属吸收,从而实现在宽光谱范围内得到高消光比的起偏器。(The invention provides a polarizer, a preparation method of the polarizer and an optical fiber gyroscope, and relates to the field of integrated photoelectron. Wherein the polarizer includes: the waveguide layer comprises a multimode straight waveguide region, a curvature gradual change waveguide region and a coiled waveguide region, the head end of the curvature gradual change waveguide region is connected with the tail end of the multimode straight waveguide region, the tail end of the curvature gradual change waveguide region is connected with the head end of the coiled waveguide region, the metal absorption layer is opposite to the coiled waveguide region, and an isolation layer is arranged between the metal absorption layer and the coiled waveguide region. According to the polarizer provided by the invention, the waveguide layer is divided into the continuous multimode straight waveguide area, the curvature gradient waveguide area and the coiling type waveguide area, so that the optical field constraint capacity to the TE polarization state is enhanced, the transmission loss of the TE polarization state is reduced, and after the long-distance coiling structure of the coiling type waveguide area, TM polarized light can be absorbed by metal of the metal absorption layer separated by the isolation layer, so that the polarizer with high extinction ratio can be obtained in a wide spectrum range.)

1. A polarizer, comprising: the waveguide layer comprises a multimode straight waveguide region, a curvature gradient waveguide region and a coiled waveguide region, the head end of the curvature gradient waveguide region is connected with the tail end of the multimode straight waveguide region, the tail end of the curvature gradient waveguide region is connected with the head end of the coiled waveguide region,

the metal absorption layer is opposite to the coiled waveguide area, and an isolation layer is arranged between the metal absorption layer and the coiled waveguide area.

2. The polarizer according to claim 1, wherein said metal absorbing layer and said waveguide layer are engraved on a chip, said chip comprising a substrate, a buried oxide layer on top of said substrate and a cladding layer, said metal absorbing layer, said isolating layer and said waveguide layer being interposed between said buried oxide layer and said cladding layer.

3. The polarizer according to claim 2, wherein the isolating layer, the substrate, the buried oxide layer and the cladding layer are made of silica materials.

4. The polarizer of claim 1, wherein the width of the waveguide layer is 2 microns and the thickness of the spacer layer is 0.7 microns.

5. The polarizer according to claim 1, wherein the thickness of the metal absorption layer is greater than 50nm and less than or equal to 100 nm.

6. A method for preparing a polarizer according to any one of claims 1 to 5, comprising:

determining the width of the waveguide layer: obtaining evanescent field attenuation coefficients of TE polarized light and TM polarized light of an entering light source along the y-axis direction, and confirming the width of the waveguide layer according to the width of the waveguide layer and the relation between the thickness of the waveguide layer and the evanescent field attenuation coefficients;

determining the position of the metal absorption layer: taking the axial symmetry position of the upper surface of the waveguide layer as a coordinate origin, and taking the position between the amplitude ratio of the TE polarization evanescent field to the amplitude positioned at the coordinate origin by more than 10 times and the amplitude ratio of the TM polarization evanescent field to the amplitude positioned at the coordinate origin by less than 10 times as the position of the metal absorption layer along the evanescent field direction, thereby determining the thickness of the isolation layer;

determining the thickness of the metal absorption layer: obtaining the attenuation coefficient of a light source on the metal absorption layer, determining the skin depth according to the attenuation coefficient of the metal absorption layer, and further determining the thickness of the metal absorption layer;

determining the length of the coiled waveguide region: obtaining the attenuation coefficient of the coiled waveguide area, and determining the length of the coiled waveguide area according to the extinction ratio.

7. The method for preparing a polarizer according to claim 6, further comprising the steps of:

determining the curvature and the arc length of the curvature gradient waveguide area: and determining the curvature and the arc length of the curvature gradual change waveguide area according to the parameters of the tail end of the multimode straight waveguide area and the initial end of the coiled waveguide area and an Euler curve or a curvature quadratic change curve.

8. The method for preparing a polarizer according to claim 6, wherein the intrinsic solution of guided electromagnetic wave intrinsic Maxwell's equation for determining the width of the waveguide layer is as follows:

wherein z is the coordinate of the z-axis corresponding to the propagation direction of light, x is the coordinate of the x-axis corresponding to the width direction of the waveguide layer, y is the coordinate of the y-axis corresponding to the height direction of the waveguide layer, t represents the time change, and phi_TE(x,y,z,t)、Φ_TM(x, y, z, t) are two intrinsic solutions of an equation set, which represents that the waveguide layer supports two polarization states of TE and TM, A_0TE、A_0TERepresenting normalized amplitude, beta_TE、β_TMA propagation constant representing the TE, TM polarization state, complex in lossy propagation, f_TE(x，y)、f_TM(x, y) represents the normalized mode field distribution, ω, of the TE, TM polarization state cross-section_TE、ω_TMRepresenting the angular frequency of the TE, TM polarization state.

9. The method for preparing a polarizer according to claim 8, wherein the step of determining the length of the coiled waveguide region comprises:

determining propagation constants beta of TE polarized light and TM polarized light_TEAnd beta_TM；

Will propagation constant beta_TEAnd beta_TMConverting into effective refractive index, and confirming the imaginary part of the effective refractive index;

determining the attenuation coefficient of the coiled waveguide region;

the length of the coiled waveguide region was confirmed based on the extinction ratio.

10. An optical fiber gyroscope comprising an end-tapered coupling waveguide and a polarizer as claimed in any one of claims 1 to 5, the end-tapered coupling waveguide being disposed at the input and output ends of the polarizer.

Technical Field

The invention relates to the technical field of integrated photoelectron, in particular to a polarizer, a polarizer preparation method and an optical fiber gyroscope.

Background

The optical fiber gyroscope is an important high-precision optical inertial measurement instrument and is in an extremely important position in national economic construction and national defense equipment systems. The light source required by the optical fiber gyroscope is a superradiance light emitting diode, a wide spectrum light source can be emitted spontaneously, the center wavelength can be detected more easily by the Gaussian distribution of the light source, and Rayleigh scattering can be inhibited. However, the light source output by the superluminescent light emitting diode cannot ensure a single polarization state, and for the optical fiber gyroscope, the refractive indexes of the two polarization states are different, which may cause an optical path difference, and the extra noise is introduced by the extra polarized interference light during the light intensity detection, which may degrade the detection precision. Therefore, a broad-spectrum polarizer with high extinction ratio and low insertion loss becomes an indispensable device in the optical fiber gyroscope.

Therefore, how to obtain a polarizer with high extinction ratio in a wide spectral range, and reducing the loss of TE polarization state is the direction to be studied at present.

Disclosure of Invention

The invention provides a polarizer, a polarizer preparation method and a fiber optic gyroscope, which are used for solving the defects that a polarizer with a high extinction ratio cannot be obtained in a wide spectral range and the loss of a TE polarization state is reduced in the prior art, realizing that a coiled waveguide region is opposite to a metal absorption layer, arranging an isolation layer with controllable thickness between the metal absorption layer and the metal absorption layer, obtaining the polarizer with the high extinction ratio in the wide spectral range and reducing the loss of the TE polarization state.

The invention provides in a first aspect a polarizer comprising: the waveguide layer comprises a multimode straight waveguide region, a curvature gradient waveguide region and a coiled waveguide region, the head end of the curvature gradient waveguide region is connected with the tail end of the multimode straight waveguide region, the tail end of the curvature gradient waveguide region is connected with the head end of the coiled waveguide region,

the metal absorption layer is opposite to the coiled waveguide area, and an isolation layer is arranged between the metal absorption layer and the coiled waveguide area.

According to the polarizer provided by the invention, the metal absorption layer and the waveguide layer are etched on a chip, the chip comprises a substrate, a buried oxide layer and a cladding layer, wherein the buried oxide layer is arranged on the upper layer of the substrate, and the metal absorption layer, the isolation layer and the waveguide layer are arranged between the buried oxide layer and the cladding layer.

According to the polarizer provided by the invention, the isolating layer, the substrate, the oxygen buried layer and the cladding are made of silicon dioxide materials.

According to the polarizer provided by the invention, the width of the waveguide layer is 2 microns, and the thickness of the isolation layer is 0.7 microns.

According to the polarizer provided by the invention, the thickness of the metal absorption layer is more than 50nm and less than or equal to 100 nm.

The invention provides a preparation method of a polarizer, which comprises the following steps:

determining the width of the waveguide layer: obtaining evanescent field attenuation coefficients of TE polarized light and TM polarized light of an entering light source along the y-axis direction, and confirming the width of the waveguide layer according to the width of the waveguide layer and the relation between the thickness of the waveguide layer and the evanescent field attenuation coefficients;

determining the position of the metal absorption layer: taking the axial symmetry position of the upper surface of the waveguide layer as a coordinate origin, and taking the position between the amplitude ratio of the TE polarization evanescent field to the amplitude positioned at the coordinate origin by more than 10 times and the amplitude ratio of the TM polarization evanescent field to the amplitude positioned at the coordinate origin by less than 10 times as the position of the metal absorption layer along the evanescent field direction, thereby determining the thickness of the isolation layer;

determining the thickness of the metal absorption layer: obtaining the attenuation coefficient of a light source on the metal absorption layer, determining the skin depth according to the attenuation coefficient of the metal absorption layer, and further determining the thickness of the metal absorption layer;

determining the length of the coiled waveguide region: obtaining the attenuation coefficient of the coiled waveguide area, and determining the length of the coiled waveguide area according to the extinction ratio.

The preparation method of the polarizer provided by the invention further comprises the following steps:

determining the curvature and the arc length of the curvature gradient waveguide area: and determining the curvature and the arc length of the curvature gradual change waveguide area according to the parameters of the tail end of the multimode straight waveguide area and the initial end of the coiled waveguide area and an Euler curve or a curvature quadratic change curve.

According to the preparation method of the polarizer provided by the invention, the intrinsic solution of the guided electromagnetic wave intrinsic Maxwell equation for determining the width of the waveguide layer is as follows:

wherein z is the coordinate of the z-axis corresponding to the propagation direction of light, x is the coordinate of the x-axis corresponding to the width direction of the waveguide layer, y is the coordinate of the y-axis corresponding to the height direction of the waveguide layer, t represents the time change, and phi_TE(x,y,z，t)、Φ_TM(x, y, z, t) are two intrinsic solutions of an equation set, which represents that the waveguide layer supports two polarization states of TE and TM, A_0TE、A_0TERepresenting normalized amplitude, beta_TE、β_TMA propagation constant representing the TE, TM polarization state, complex in lossy propagation, f_TE(x，y)、f_TM(x, y) represents the normalized mode field distribution, ω, of the TE, TM polarization state cross-section_TE、ω_TMRepresenting the angular frequency of the TE, TM polarization state.

According to the preparation method of the polarizer provided by the invention, the step of determining the length of the coiled waveguide region comprises the following steps:

determining propagation constants beta of TE polarized light and TM polarized light_TEAnd beta_TM；

Will propagation constant beta_TEAnd beta_TMConverting into effective refractive index, and confirming the imaginary part of the effective refractive index;

determining the attenuation coefficient of the coiled waveguide region;

the length of the coiled waveguide region was confirmed based on the extinction ratio.

A third aspect of the present invention provides an optical fiber gyroscope, an end-face tapered coupling waveguide and the polarizer of the first invention, wherein the end-face tapered coupling waveguide is disposed at a light entrance end and a light exit end of the polarizer.

According to the polarizer provided by the invention, the waveguide layer is divided into the continuous multimode straight waveguide area, the curvature gradient waveguide area and the coiling type waveguide area, so that the optical field constraint capacity to the TE polarization state is enhanced, the transmission loss of the TE polarization state is reduced, and after the long-distance coiling structure of the coiling type waveguide area, TM polarized light can be absorbed by metal of the metal absorption layer separated by the isolation layer, so that the polarizer with high extinction ratio can be obtained in a wide spectrum range.

Further, in the method for manufacturing a polarizer and the optical fiber gyroscope provided by the present invention, since the polarizer is provided as described above, various advantages as described above are also provided.

Drawings

In order to more clearly illustrate the technical solutions of the present invention or the prior art, the drawings needed for the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.

FIG. 1 is a schematic partial cross-sectional view of a polarizer provided by the present invention;

FIG. 2 is a schematic view of a waveguide layer of a polarizer provided by the present invention;

FIG. 3 is a schematic structural diagram of an optical fiber gyro provided by the present invention;

FIG. 4 is a schematic flow chart of a method for preparing a polarizer provided by the present invention;

FIG. 5 is a schematic diagram of the polarizer provided by the present invention;

FIG. 6 is a second schematic flow chart of the preparation method of the polarizer provided by the present invention;

FIG. 7 is a graph showing the simulation results of the wavelength and extinction ratio of the polarizer provided by the present invention.

Reference numerals:

100: a waveguide layer; 200: a metal absorption layer;

300: an isolation layer; 400: a polarizer;

101: a multimode straight waveguide region; 102: a curvature-graded waveguide region;

103: a coiled waveguide region; 110: an end-tapered coupling waveguide;

301: a substrate; 302: an oxygen burying layer;

303: a cladding layer; 401: a superluminescent light emitting diode;

402: a circulator; 403: a coupler;

404: a sagnac loop.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings, and it is obvious that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In the description of the embodiments of the present invention, it should be noted that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of describing the embodiments of the present invention and simplifying the description, but do not indicate or imply that the referred devices or elements must have a specific orientation, be configured in a specific orientation, and operate, and thus, should not be construed as limiting the embodiments of the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the embodiments of the present invention, it should be noted that, unless explicitly stated or limited otherwise, the terms "connected" and "connected" are to be interpreted broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; may be directly connected or indirectly connected through an intermediate. Specific meanings of the above terms in the embodiments of the present invention can be understood in specific cases by those of ordinary skill in the art.

In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of an embodiment of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.

An embodiment of the present invention will be described below with reference to fig. 1 to 7. It is to be understood that the following description is only exemplary embodiments of the present invention and is not intended to limit the present invention.

As shown in fig. 1 and 2, the present invention provides a polarizer 400 comprising: the waveguide layer 100 comprises a multimode straight waveguide region 101, a curvature gradual change waveguide region 102 and a coiled waveguide region 103, the head end of the curvature gradual change waveguide region 102 is connected with the tail end of the multimode straight waveguide region 101, the tail end of the curvature gradual change waveguide region 102 is connected with the head end of the coiled waveguide region 103, the metal absorption layer 200 is opposite to the coiled waveguide region 103, and an isolation layer 300 is arranged between the metal absorption layer 200 and the coiled waveguide region 103.

Specifically, a light source firstly enters the multi-mode straight waveguide region 101, and according to the optical waveguide theory, the multi-mode straight waveguide region 101 can enhance the optical field constraint capacity on the TE polarization state and reduce the transmission loss of the TE polarization state; then, the waveguide enters a curvature gradual change waveguide area 102 for adiabatic evolution, and a straight waveguide mode is converted into a bent waveguide mode without generating multimode crosstalk; thereby coupling light into the coiled waveguide region 103 without loss.

The metal absorption layers 200 are arranged above the disc surface of the coiled waveguide region 103 at intervals, the intervals are the isolation layers 300, TM polarized light can be absorbed by metal of the metal absorption layers 200 after passing through the long-distance coiled structure of the coiled waveguide region 103, a surface plasma effect cannot be excited in a TE polarization state, and energy is completely reserved; the TM polarized light evanescent field interacts with the metal absorption layer 200 to excite a surface plasmon effect and absorb the energy of the TM polarized light, so that high extinction ratio is realized.

In addition, the thickness of the isolation layer 300 is required to be slightly equal to that of the metal absorption layer 200 and an evanescent field of a TM polarization state, so that unwanted reflection due to abrupt change of a light field is avoided.

As shown in fig. 1, in one embodiment of the present invention, the metal absorber layer 200 and the waveguide layer 100 are etched on a chip, the chip including a substrate 301, a buried oxide layer 302 overlying the substrate 301, and a cladding layer 303, the metal absorber layer 200, the isolation layer 300, and the waveguide layer 100 being disposed between the buried oxide layer 302 and the cladding layer 303. The large-scale mass production with low cost can be realized, the index requirement of the optical fiber gyroscope can be met, different extinction ratios can be obtained by adjusting the distance between the metal absorption layer 200 and the waveguide layer 100, namely the thickness of the isolation layer 300, in the preparation process, and the different index requirements can be met.

In other words, the metal absorption layer 200 and the waveguide layer 100 implement chip fabrication of the polarizer 400 by using micron-scale photolithography process. The polarizer chip comprises a substrate 301, a buried oxide layer 302, a waveguide layer 100, an isolating layer 300, a metal absorbing layer 200 and a cladding layer 303 from bottom to top. The electric field direction of the TE polarization state is parallel to the substrate 301, and the electric field direction of the TM polarization state is perpendicular to the substrate 301.

In addition, in another embodiment of the present invention, the isolation layer 300, the substrate 301, the buried oxide layer 302 and the cladding layer 303 are made of silicon dioxide materials.

Further, in an alternative embodiment of the present invention, waveguide layer 100 has a width of 2 microns and spacer layer 300 has a thickness of 0.7 microns. Under the parameter, the TE polarization state can realize low-loss transmission, and the TM polarization state and the metal of the metal absorption layer 200 generate a surface plasmon effect, and are inhibited after passing through the metal absorption layer 200, so that the polarizer with high extinction ratio is obtained.

In other embodiments of the present invention, the metal absorber layer has a thickness greater than 50nm and equal to or less than 100 nm.

As shown in fig. 2, the present invention further provides an optical fiber gyroscope, which includes an end-face tapered coupling waveguide 110 and the polarizer 400, where the end-face tapered coupling waveguide 110 is disposed at the light-incoming end and the light-outgoing end of the polarizer 400. The multi-polarized light generated at the superluminescent light source is coupled into the polarizer 400 through the end-tapered coupling waveguide 110 with low loss.

As shown in fig. 3, in an alternative embodiment of the present invention, the optical fiber gyro may further include a superluminescent light emitting diode 401, a circulator 402, the polarizer 400, a coupler 403, and a sagnac loop 404, which are connected in this order. After passing through the circulator 402, a light source generated by the superluminescent light-emitting diode 401 enters the polarizer 400, and unnecessary TM polarized light is filtered out, so that light entering the sagnac loop 404 is only in a TE polarized state, and the test precision of the optical fiber gyroscope is improved.

As shown in fig. 4, a method for preparing the polarizer 400 includes the following steps:

s1: determining the width of the waveguide layer 100: and obtaining the evanescent field attenuation coefficients of the TE polarized light and the TM polarized light of the entering light source along the y-axis direction, and confirming the width of the waveguide layer 100 according to the relationship between the width of the waveguide layer 100, the thickness of the waveguide layer 100 and the evanescent field attenuation coefficients.

As shown in fig. 5, the wider the width of the waveguide layer 100, the stronger the confinement capability to the TE polarization state, and the smaller the absorption loss upon entering the metal absorption layer 200. The electric field of the TE polarization state is weakly contacted with the metal absorption layer 200, and the evanescent field of the TM polarization state is more contacted with the metal absorption layer 200, so that a stronger surface plasma effect is excited.

In other words, since the electric field direction of the TE polarization state is parallel to the substrate 301, for the refractive index step waveguide, the wider the width of the waveguide layer 100, the stronger the optical field confinement capability of the waveguide layer 100 to the TE polarization state, and the less evanescent field of the TE polarization state leaking outside the waveguide layer 100, the less susceptible to the influence of the structure outside the waveguide layer 100. The thickness of the waveguide layer 100 is a known constant value, which is much smaller than the width of the waveguide layer 100.

In another alternative embodiment of the present invention, the intrinsic solution of guided electromagnetic wave intrinsic Maxwell's equations is used to determine the width of the waveguide layer 100. The intrinsic solution of guided electromagnetic wave intrinsic maxwell's equations is as follows:

wherein z is a coordinate of the z-axis corresponding to the propagation direction of the light, x is a coordinate of the x-axis corresponding to the width direction of the waveguide layer 100, y is a coordinate of the y-axis corresponding to the height direction of the waveguide layer 100, t represents a time change, Φ_TE(x,y,z,t)、Φ_TM(x, y, z, t) are two eigensolutions of the equation system, which represents that the waveguide layer 100 supports two polarization states of TE and TM, A_0TE、A_0TERepresenting normalized amplitude, beta_TE、β_TMA propagation constant representing the TE, TM polarization state, complex in lossy propagation, f_TE(x,y)、 f_TM(x, y) represents the normalized mode field distribution, ω, of the TE, TM polarization state cross-section_TE、ω_TMRepresenting the angular frequency of the TE, TM polarization state.

Specifically, in some embodiments of the present invention, the evanescent field distribution is the evanescent field distribution at the periphery of the waveguide layer 100, so that the evanescent field distribution relation outside the waveguide layer 100 can be obtained based on formula (1), as follows:

wherein the content of the first and second substances,represents the evanescent field distribution outside the waveguide layer 100, and takes the axial symmetry position of the upper surface of the waveguide layer 100 as the origin of coordinates, A_1TE、A_1TMRepresenting the normalized amplitude of the evanescent field. The evanescent field decays exponentially along the y-axis outside the waveguide layer 100 with a decay coefficient ofDecays exponentially along the x-axis with a decay coefficient of

Moreover, by solving the formula (2) through a modern electromagnetic numerical calculation method, the evanescent field attenuation coefficient of two polarization states of TE and TM along the y-axis direction can be obtainedAttenuation coefficient of evanescent fieldInfluenced by both the width w of the waveguide layer 100 and the thickness H of the waveguide layer 100, the greater w,the larger, theThe variation is not significant. The thickness H of the waveguide layer 100 is a known constant value, much smaller than the waveguide width w. The width w of the waveguide layer 100 can thus be determined in the actual production process.

S2: determining the position of the metal absorber layer 200: the position where the amplitude ratio of the evanescent field in the TE polarization state is more than 10 times lower than the amplitude at the origin of coordinates and the position where the amplitude ratio of the evanescent field in the TM polarization state is less than 10 times lower than the amplitude at the origin of coordinates are taken as the position of the metal absorption layer 200 along the direction of the evanescent field with the axially symmetric position of the upper surface of the waveguide layer 100 as the origin of coordinates, thereby determining the thickness of the isolation layer 300.

In other words, the metal absorption layer 200 is located at any position between the amplitude of the evanescent field in the TE polarization state being more than 10 times lower than the amplitude at the origin of coordinates and the amplitude of the evanescent field in the TM polarization state being less than 10 times lower than the amplitude at the origin of coordinates. Wherein the metal absorber layer 200 is parallel to the waveguide layer 100.

Furthermore, in an alternative embodiment of the invention, in order to achieve a low loss of TE polarization, the amplitude of the evanescent field for the TE polarization propagates to the metal layer at least 10 times below the origin²Multiplying, and calculating to obtain that when the width of the waveguide layer 100 is 2 microns, the amplitude of the electric field of the evanescent field of the TE polarization state at 0.7 micron on the upper side of the waveguide layer 100 is less than 10 of the original point²In addition, the TE polarization state can realize low-loss transmission, while the TM polarization state generates surface plasmon effect with the metal absorption layer 200, and is suppressed after passing through the metal absorption layer 200.

S3: determination of the thickness of the metal absorber layer 200: obtaining the attenuation coefficient of the light source on the metal absorption layer 200, determining the skin depth according to the attenuation coefficient of the metal absorption layer 200, and further determining the thickness of the metal absorption layer 200.

In one embodiment of the present invention, copper is selected as the metal that excites the surface plasmon effect, i.e., the metal material of the metal absorption layer 200 is selected from copper, which is compatible with CMOS processes. Also, in the present embodiment, the attenuation coefficient of the metal absorption layer 200 is determined by the following formula:

α_mk represents the attenuation coefficient of light in the metal absorption layer 200, and θ is the propagation constant of light wave_iThe angle at which light is incident on the metal absorption layer 200 is selected to be 90 DEG ε in the present embodiment_rIs the relative dielectric constant of the metallic material, sigma is the electrical conductivity of the metallic material, epsilon₀ω is the dielectric constant in vacuum and ω is the angular frequency.

Wherein the skin depth is a depth at which the intensity of the outgoing wave attenuates to 1/e or less. The thickness of the metal absorbent layer 200 exceeds the skin depth to ensure sufficient extinction of the metal absorbent layer 200. It is calculated that in an alternative embodiment of the present invention, the thickness of the metal absorber layer 200 should be above 50nm, and the thickness of the metal absorber layer 200 should not exceed 100nm due to the limitation of the lift-off process.

S4: determining the length of the coiled waveguide region 103: the attenuation coefficient of the coiled waveguide region 103 is obtained, and the length of the coiled waveguide region 103 is determined according to the extinction ratio.

In another alternative embodiment of the present invention, as shown in fig. 6, the step of determining the length of the coiled waveguide region 103 comprises:

s11: determining propagation constants beta of TE polarized light and TM polarized light_TEAnd beta_TM(ii) a Specifically, the propagation constant β of TE and TM polarization states is obtained from the formula (1) to the formula (3)_TEAnd beta_TMThis value is complex due to the presence of the metal absorber layer 200.

S12: will propagation constant beta_TEAnd beta_TMConverted to an effective index of refraction, identifying the imaginary part of the effective index of refraction.

In this embodiment, the formula of the converted effective refractive index is:

wherein the content of the first and second substances,effective refractive indices, n, representing TE, TM polarization states_TEAnd n_TMRepresents the real part of the effective refractive index,andrepresents the imaginary part of the effective refractive index, λ₀Representing the wavelength. Further, whenAndwhen the value is not 0, it means that loss occurs when light is transmitted in the polarizer of the present invention, and the imaginary part is extracted from the propagation constantAnd

s13: determining the attenuation coefficient of the coiled waveguide region 103; in an alternative embodiment of the present invention, the attenuation coefficient of the coiled waveguide region 103 is calculated using the following equation:

the losses for the TE and TM polarization states can be calculated for a unit distance.

S14: the length of the coiled waveguide region 103 is confirmed based on the extinction ratio. And the coiled waveguide region 103 is coiled by means of an archimedes spiral, so that the final length of the coiled waveguide region 103 is obtained.

In addition, in an embodiment of the present invention, the method for preparing the polarizer 400 further includes the steps of:

determining the curvature and arc length of the curvature-graded waveguide region 102: and determining the curvature and the arc length of the curvature gradual change waveguide area 102 according to the parameters of the tail end of the multimode straight waveguide area 101 and the initial end of the coiled waveguide area 103 and an Euler curve or a curvature quadratic change curve.

Wherein, in an alternative embodiment of the present invention, the tangential angle of the multi-mode straight waveguide region 101 is 0 degree, and the curvature is 0 degree.

The head end of the curvature gradient waveguide is connected with the tail end of the straight waveguide, so that the tangential angle of the head end of the curvature gradient waveguide is 0 degrees, and the curvature is also 0 degrees. The curvature-gradient waveguide is connected to the coiled waveguide region 103 through a primary change curve (euler curve) or a secondary change curve of curvature along with the arc length, and ensures that the tangential angle and the curvature of the tail end of the curvature-gradient waveguide are the same as those of the head end of the coiled waveguide region 103, thereby realizing mode matching.

As shown in FIG. 7, the insertion loss and extinction ratio of the polarizer 400 in the 820nm-880nm spectral range obtained by the preparation method of the polarizer 400 of the embodiment of the invention can achieve the extinction ratio as high as 30dB in the 60nm spectral range, and the device insertion loss is below 0.5dB, which proves that the polarizer 400 of the invention can have good extinction effect.

According to the polarizer 400 provided by the invention, the waveguide layer 100 is divided into the continuous multimode straight waveguide region 101, the curvature gradient waveguide region 102 and the coiling type waveguide region 103, so that the optical field constraint capacity to the TE polarization state is enhanced, the transmission loss of the TE polarization state is reduced, and after the long-distance coiling structure of the coiling type waveguide region 103, TM polarized light can be absorbed by metal of the metal absorption layer 200 separated by the isolation layer 300, so that the polarizer with high extinction ratio can be obtained in a wide spectrum range.

Further, in the method for manufacturing a polarizer and the optical fiber gyroscope provided by the present invention, since the polarizer is provided as described above, various advantages as described above are also provided.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.