CN117724206A - Polarization separation end face coupler and linear design method thereof - Google Patents

Abstract

The invention provides a polarization separation end face coupler and a linear design method thereof. The waveguide structure is composed of two groups of waveguides positioned on the same horizontal plane, wherein one group of waveguides has two thicknesses and is used for coupling with an optical fiber and transmitting optical signals of transverse electric mode (TE) modes, the other group of waveguides has constant thickness and is used for coupling with the previous group of waveguides and transmitting optical signals of transverse magnetic mode (TM) modes, and based on the planar waveguide coupling structure, a waveguide linear design method is provided, and the optimized design of coupling waveguide linear aiming at different wavelengths realizes the efficient and large-bandwidth mode field coupling and polarization separation functions of the optical field from the optical fiber to the optical chip.

Description

Polarization separation end face coupler and linear design method thereof

Technical Field

The invention relates to the field of design and encapsulation of silicon-based photoelectronic chips, in particular to a polarization separation end face coupler and a linear design method thereof.

Background

In the past few decades, optical communication technologies have been widely used. In recent years, with the development of the AI industry, the large-scale establishment of a data center and the vigorous development of cloud computing and intelligent computing put forward more demands and higher demands on data transmission and interconnection, and high integration and high transmission rate are two important indexes. Silicon-based optoelectronic chips find wide application in these fields.

In addition to the development of the silicon-based optoelectronic integrated platform and the compatibility of CMOS, the preparation and packaging of the silicon optical chip are greatly improved. The coupling of optical fibers and silicon optical chips is a ring of great importance in improving interconnection performance and transmission efficiency, and the development of CMOS compatible coupling devices is great importance. Meanwhile, many silicon optical devices are polarization sensitive and wavelength sensitive devices, so that polarization separation is required to be carried out on input signal light so as to obtain better performance, and therefore, the polarization separation broadband coupler has very wide application prospect and requirement;

the existing silicon optical coupler has two types, namely a vertical grating coupler, has the advantages of large coupling tolerance, can be used for on-chip detection, but has obvious defects, high polarization sensitivity, small bandwidth and large loss. The other is an end-face coupler with ultra-low loss and polarization insensitivity. There are two types of end-face couplers, one is a front cone structure and one is an inverted cone structure. In the inverted cone structure, the cross section of the side close to the optical fiber is smaller to obtain a mode field matched with the optical fiber as much as possible, then the mode field is gradually enlarged, the mode field is gradually bound in the waveguide, and finally the mode field is transmitted to a subsequent optical chip. The mode field diameter of the conventional single-mode fiber is about 10um, and in order to match the mode field of the optical fiber, the cross-sectional area of the coupling section needs to be small to obtain a larger waveguide mode field, which is usually achieved by reducing the waveguide radius at the coupling end face or a waveguide with smaller thickness. However, the top Si thickness of the substrate used in the optical chip fabricated in the standard SOI process is typically 220nm, and the width of the waveguide at the coupling end face (typically less than 100 nm) can only be reduced in order to be compatible with such devices, but the reduced width requires higher fabrication costs. Therefore, devices with interlayer coupling structures are proposed, i.e. the coupling of optical fibers and waveguides is accomplished with thinner or lower refractive index waveguides, and the coupling of the optical field into 220nm thick silicon waveguides is then performed. However, the thickness between two waveguides coupled between the layers cannot be flexibly controlled, and the design freedom is reduced.

Therefore, the invention provides a novel planar structure end face coupler, which firstly utilizes a thinner waveguide (less than 220 nm) to realize the coupling of a chip waveguide and an optical fiber under a larger waveguide width, and realizes the polarization separation coupling of a silicon optical chip prepared by a standard CMOS technology in a waveguide with a thicker (220 nm) thickness prepared by a standard SOI technology for dividing a coupled optical field into TE and TM modes and respectively coupling the TE and TM modes to the same horizontal plane. Because of the coupling of the same horizontal plane, the space between the two coupling waveguides can be freely regulated and controlled besides the width of the coupling waveguides, so that the coupling bandwidth and the coupling efficiency are improved.

Disclosure of Invention

The invention aims to provide a polarization separation end face coupler and a linear design method thereof, which realize optical field separation coupling from an optical fiber to an optical chip waveguide TE and a TM mode through a novel device structure and a linear design method, solve the problem of mismatching of the optical fiber and the chip waveguide mode field in the optical chip, and also meet the problem of polarization sensitivity of a polarization sensitive device to an input optical signal.

The first aspect of the invention: there is provided a polarization splitting end-face coupler composed of a first waveguide and a second waveguide located in the same horizontal plane xy, the first waveguide including an optical fiber coupling waveguide, the first coupling waveguide and a TE coupling transmission waveguide; the transverse electric mode TE polarization of the optical field coupled in by the optical fiber is output into the optical chip by the TE coupling transmission waveguide, and the transverse magnetic mode TM polarization is coupled and transmitted into the optical chip by the second coupling waveguide, the third coupling waveguide and the TM transmission waveguide, so that the optical field polarization separation and the coupling between the optical fiber and the optical chip are realized.

Specifically, the thickness of the first waveguide has a primary mutation along the x direction, the thicknesses of the optical fiber coupling waveguide and the first coupling waveguide are consistent and smaller than that of the TE coupling transmission waveguide, and the optical fiber coupling waveguide and the first coupling waveguide are flexibly selected according to the process and the actual thickness and can be realized through a double etching process.

Specifically, in the first waveguide, the optical fiber coupling waveguide is a waveguide with gradually-changed width, and the width of the waveguide is gradually increased from the optical fiber coupling end face to the direction of the first coupling waveguide, and is finally connected with the first coupling waveguide; the thickness and width of the first coupling waveguide remain unchanged, and the height and width of the first coupling waveguide are consistent with those of the tail end of the optical fiber coupling waveguide.

Specifically, the TE coupling transmission waveguide in the first waveguide is located above the first coupling waveguide, and includes a section of wedge waveguide and a section of straight waveguide, where the width of the tip of the wedge waveguide is smaller than that of the first coupling waveguide, and the width of the wedge waveguide is gradually changed linearly, and finally the wedge waveguide is consistent with the first coupling waveguide; the first coupling waveguide and the TE coupling transmission waveguide are closely connected up and down, and the thickness of the first coupling waveguide and the TE coupling transmission waveguide is matched with that of a standard SOI substrate.

Specifically, the waveguide thickness of the second waveguide is kept unchanged, the interval and the width between the second waveguide and the first waveguide are changed, and the interval between the two waveguides is the distance between the two waveguide edges; the waveguide interval and the waveguide width can be designed according to different working wavelengths to improve the coupling efficiency and increase the working bandwidth; the second coupling waveguide and the third coupling waveguide are used for performing TM mode coupling, the initial width of the third coupling waveguide is consistent with the tail end width of the second coupling waveguide, the tail end width is consistent with the initial width of the TM transmission waveguide, and the width of the TM transmission waveguide is unchanged; the interval between the third coupling waveguide and the TM transmission waveguide and the first waveguide is consistent with the interval between the tail end of the second coupling waveguide and the first waveguide, and the interval is kept unchanged; its third coupling waveguide functions to prevent the TM mode in the TM transmission waveguide from being coupled again.

Specifically, the waveguide spacing and the waveguide width use a planar structure to enable the TM mode to be coupled between different waveguides, and the TE mode generates low loss when transmitted in the first waveguide, so that the TM mode is coupled from the first waveguide to the second waveguide, the TE mode is kept to be transmitted in the first waveguide, and TM and TE polarization separation coupling is realized.

The second aspect of the invention: a linear design method of a polarization separation end-face coupler, the design method comprising the steps of:

(1) After determining the width w1 and the height h1 of the first coupling waveguide 102, performing simulation and calculation to obtain the effective refractive indexes n1, λ of the individual first waveguides at the wavelength λ;

(2) Setting the height of the 2 nd waveguide as h2, simulating and calculating to obtain the effective refractive index n2 of the independent second waveguide at the wavelength lambda, wherein lambda changes along with the width of the second waveguide, and obtaining the width w2 of the second waveguide when n1, lambda=n2 and lambda through interpolation fitting;

(3) Fixing w1 and w2, and performing simulation calculation on the two waveguide intervals Gap, h1 and h2 to obtain the effective refractive index neff of the system of the two waveguides;

(4) Subtracting n1 from neff, and obtaining coupling strength g of two waveguides when the working wavelength is lambda by lambda (n 2, lambda);

(5) Repeating the step (3) and the step (4) to change Gap, simulating to obtain coupling strength g under different gaps, and obtaining the relation between the Gap and the coupling strength g through interpolation fitting;

(6) For a set of wavelengths { λ1, λ2, λ3 … … λi }, giving a set of initial coupling strengths { g1, g2, g3 … … gi }, and obtaining a set of waveguide intervals { Gap1, gap2, gap3 … … Gap }, based on the relationship between the coupling strengths g and Gap; repeating step (1) and step (2) to obtain the widths { w21, w22, w23 … … w2i } of the set of second waveguides (2) corresponding to the set of wavelengths;

(7) Performing linear interpolation fitting on { Gap1, gap2, gap3 … … Gapi } and { w21, w22, w23 … … w2i }, and connecting the fitting results, and further taking a group of waveguide intervals and waveguide widths at linear equal intervals, and marking the waveguide intervals and the waveguide widths as { (Gap 1, w 1), (Gap 2, w 2), (Gap 3, w 3), … … (Gapn, wn) }, wherein n is an integer greater than or equal to i, and the number and the value range of n are taken in a connecting line segment;

(8) Obtaining the y-axis relative coordinates of the first waveguide and the second waveguide according to a group of points (Gapn, wn) taken at equal intervals;

(9) Uniformly distributing n groups of relative coordinates along an x-axis, wherein the total length is L;

(10) The method comprises the steps of fixing the length value of a coupled waveguide, modeling and simulating by using a finite difference method FDTD in a time domain, and performing iterative optimization on the Gap value for a plurality of times until the coupling efficiency of each working wavelength lambda under the specified coupling waveguide length reaches the maximum value or approximately the maximum value, so that the working bandwidth meeting the requirements is obtained, and the line shape of a second coupling waveguide in a second waveguide is obtained;

(11) Adding a section of third coupling waveguide behind the second coupling waveguide, wherein the width of the third coupling waveguide is consistent with the width of the tail end of the second coupling waveguide, and then adjusting the coupling length L through simulation to obtain a required coupling waveguide structure; the coupling length L is the sum of the lengths of the second coupling waveguide and the third coupling waveguide.

Further, the sum of the thicknesses of the TE coupling transmission waveguide and the first coupling waveguide is the same as the thickness of the second waveguide, the thickness is compatible with a standard SOI optical chip based on a CMOS process, and the width and the thickness of the waveguide do not limit a design method.

A third aspect of the invention: there is provided an electronic device comprising:

one or more processors;

a memory for storing one or more programs;

when the one or more programs are executed by the one or more processors, the one or more processors implement the linear design method of a polarization splitting end-face coupler.

A fourth aspect of the invention: a computer readable storage medium having stored thereon computer instructions which when executed by a processor perform the steps of a method of linear design of a polarization splitting face coupler is provided.

The beneficial effects of the invention are as follows:

1. the structure of the planar end face coupler is provided, the coupling with the optical fiber is realized by a thinner waveguide, the thinner waveguide thickness means that the lower the requirement on the photoetching line width is, the lower the preparation cost is, and then the light is coupled into a standard SOI (silicon on insulator) process silicon waveguide with the thickness of 220 nm;

2. according to the characteristics of a planar coupling structure, namely that the intervals between waveguides are easy to adjust, a waveguide linear design method is provided, different intervals are designed according to the coupling strength under different wavelengths, so that the coupling strength of different working wavelengths can reach an optimal value or an approximate optimal value under a certain coupling length to improve the working bandwidth of the whole device;

3. the whole device and the linear design only need a simple double etching process, and are compatible with a standard CMOS process.

Drawings

FIG. 1 is a three-dimensional schematic diagram of a polarization splitting end-face coupler in accordance with one embodiment of the invention;

FIG. 2 is a schematic top view of a polarization splitting face coupler according to one embodiment of the invention;

FIG. 3 is a graph showing the coupling strength of different wavelengths as a function of waveguide spacing in one embodiment of the present invention;

FIG. 4 is a schematic diagram of a TM coupling segment in line form in accordance with one embodiment of the invention;

FIG. 5 is a mode field distribution diagram of a TM coupling region in one embodiment of the invention;

FIG. 6 is a mode field distribution diagram of TE coupling regions in an embodiment of the present invention.

Reference numerals: 1-a first waveguide; 2-a second waveguide; 3-upper cladding; a 4-silicon oxide buried layer; 5-a substrate; 6-an optical fiber coupling end face; 7-an output end face; an 8-TM mode coupling region; a 9-TE transmission region; 10-incident optical fiber; 11-a light chip system; 101-an optical fiber coupling waveguide; 102-a first coupling waveguide; 103-TE coupled transmission waveguides; 201-a second coupling waveguide; 202-a third coupling waveguide; 203-TM transmission waveguide.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden on the person of ordinary skill in the art based on the embodiments provided herein, are intended to be within the scope of the present application.

It is apparent that the drawings in the following description are only some examples or embodiments of the present application, and it is possible for those of ordinary skill in the art to apply the present application to other similar situations according to these drawings without inventive effort. Moreover, it should be appreciated that while such a development effort might be complex and lengthy, it would nevertheless be a routine undertaking of design, fabrication, or manufacture for those of ordinary skill having the benefit of this disclosure, and thus should not be construed as having the benefit of this disclosure.

Reference in the specification to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearances of such phrases in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. It is to be expressly and implicitly understood by those of ordinary skill in the art that the embodiments described herein can be combined with other embodiments without conflict.

The present embodiment provides a polarization separation end face coupler, and fig. 1 and fig. 2 are schematic structural diagrams of the polarization separation end face coupler of the present embodiment. Wherein the specific alignment of TM mode coupling region 8 can be seen with reference to fig. 4; the optical signal is input from the optical fiber, enters the end face coupler through the optical fiber coupling end face 6, and enters the optical chip system 11 through the output end face 7 after polarization separation and coupling.

In this embodiment, parameters such as the length, thickness, etc. of each waveguide are as follows:

the device is formed by a first waveguide 1 and a second waveguide 2 which are located in the same horizontal plane (xy); the first waveguide 1 comprises an optical fiber coupling waveguide 101, a first coupling waveguide 102 and a TE coupling transmission waveguide 103; the optical fiber coupling waveguide 101 is used for coupling with an optical fiber and transmitting light to the first coupling waveguide 102, and the first coupling waveguide 102 couples the light of the coupled TM mode to another waveguide on the same plane; the tip of the optical fiber coupling waveguide 101 has a thickness of 150nm, a width of 160nm, and then is linearly tapered, the width of the end of the optical fiber coupling waveguide 101 is 1100nm, the height of the optical fiber coupling waveguide 101 is 150nm, and the length of the optical fiber coupling waveguide 101 in the x direction is 120um. Followed by a TM mode coupling region 8, the first coupling waveguide 102 having a width and thickness of 1100nm and 150nm, respectively, in which TM mode is coupled into the second waveguide 2, the TM mode coupling region 8 having a total length of 160um. The TE transmission region 9 is formed by a part of the first coupling waveguide 102 and the TE coupling transmission waveguide 103, and is used for transmitting the TE mode optical field, the TE coupling transmission waveguide 103 has a thickness of 70nm, a tip width of 180nm, and the width of the TE coupling transmission waveguide is kept consistent with 1100nm after passing through a section of gradual change region (30 um), and then the TE mode optical field is output to the polarization sensitive optical chip system.

The width and spacing of the second waveguide 2 from the first waveguide 1 are determined by the operating wavelength, which in this embodiment is selected to be 1260nm-1360nm. The transverse magnetic mode (TM) polarization is output by the second waveguide 2 into the optical chip, thereby achieving optical mode field polarization separation and coupling between the optical fiber and the optical chip. The second waveguide 2 is composed of three parts, a second coupling waveguide 201 and a third coupling waveguide 202 for coupling a TM mode, and a TM transmission waveguide 203 for outputting TM mode light. The initial width of the second coupling waveguide 201 is 0.19um, the end width is 0.213um, and the length is 150um; specifically, in the present embodiment, the initial width of the waveguide 202 is 0.213um, the end is linearly changed to 0.5um, the width of the tm transmission waveguide 203 is consistent with that of the third coupling waveguide 202, which is 0.5um and remains unchanged, and the length of the third coupling waveguide 202 is 10um;

because of planar coupling (two coupling waveguides are in the same horizontal plane), the distance between the two waveguides can be freely adjusted unlike the traditional vertical coupling (two waveguides are distributed up and down), so that the waveguide line type and the distance design of the coupling area are more flexible. Based on the present invention, a linear design method of a polarization separation end-face coupler is provided, specifically, the linear design of the second coupling waveguide 201 and the third coupling waveguide 202 includes the parameters of width and the like of each waveguide, and the design method is as follows:

1) After determining the width (w 1) and the height h1 of the first coupling waveguide 102, the effective refractive indexes n1, λ of the individual first coupling waveguides 101 at the wavelength λ are obtained by simulation calculation;

2) The height of the second waveguide 2 is set to 220nm, the effective refractive index n2 of the individual second waveguide 2 at the wavelength λ is obtained by simulation and calculation, λ is a function of the width of the second waveguide 2, and the width (w 2) of the second waveguide 2 when n1, λ=n2, λ is obtained by interpolation fitting.

3) Fixing w1 and w2, and performing simulation calculation on the interval (Gap) between the two waveguides and the interval (h 1 and h 2) to obtain the effective refractive index neff of the system of the two waveguides;

4) Subtracting n1 and lambda (or n2 and lambda) from neff to obtain the coupling strength g of the two waveguides when the working wavelength is lambda;

5) Changing Gap to repeat 3) and 4), simulating to obtain coupling strength g under different gaps, and obtaining the relation between the gaps and the coupling strength g through interpolation fitting;

6) Given a set of initial coupling strengths { g1, g2, g3 … … gi } for a set of wavelengths { λ1, λ2, λ3 … … λi }, a set of waveguide spacings { Gap1, gap2, gap3 … … Gap }, based on the relationship between coupling strengths and Gap, can be obtained; repeating step 2) to obtain a group of widths { w21, w22, w23 … … w2i }, of the second waveguides 2

7) Performing linear interpolation fitting on { Gap1, gap2, gap3 … … Gapi } and { w21, w22, w23 … … w2i }, and linearly taking a group of waveguide intervals and waveguide widths from the fitting result, denoted as { (Gap 1, w 1), (Gap 2, w 2), (Gap 3, w 3), … … (Gapn, wn) }, wherein n is an integer greater than or equal to i, and the number and value range of n are valued in a line segment; for example, n may be 1,2,3,4, … …,2000, i.e., 2000 pairs;

8) From (Gapn, wn) the y-axis relative coordinates of the first waveguide 1 and the second waveguide 2 can be obtained (coordinate axes see FIG. 1)

9) Uniformly distributing n groups of relative coordinates along an x-axis, wherein the total length is L1;

10 The length value of the fixedly coupled waveguide is modeled and simulated by utilizing a finite difference time domain method (FDTD), and the Gap value is optimized for multiple iterations until the coupling efficiency of each working wavelength lambda under the specified coupling waveguide length reaches the maximum value or the approximate maximum value, so that the working bandwidth meeting the requirements is obtained;

11 Thus, the line shape of the second coupling waveguide 201 in the second waveguide 2 is obtained, a section of third coupling waveguide 202 with the length of L2 is added after the second coupling waveguide 201, and the coupling length L2 is finely tuned by simulation, thus obtaining the required coupling waveguide structure. The sum of the length L1 of the second coupling waveguide 201 and the length L2 of the third coupling waveguide 202 is the total length of the TM mode coupling region 8.

Wherein, in steps 1) -6), the width w1 of the first waveguide 1 is 1100um, the h1 is 150nm, the working wavelength is 1 wavelength every 10nm between 1250nm and 1370nm, it should be noted that the selected wavelength can be any range of values, and the number is larger, but the larger the wavelength range is, the larger the number is, the larger the calculation and simulation amount is needed, and in order to obtain better bandwidth in the O wave band (1260 nm to 1360 nm) after comprehensive consideration, the embodiment takes a wavelength every 10nm between 1250nm and 1370 nm. Simulation calculation was performed by using the finite difference time domain method (FDTD), the refractive index of the waveguide material and the substrate material silicon was set to 3.503, and the refractive index of the buried silicon oxide layer 4 and the upper cladding layer 3 was set to 1.4579.

In the present invention, the TM mode is coupled from the first waveguide 1 to the second waveguide 2, and thus the effective refractive index calculated in this embodiment is the effective refractive index of the TM mode. But the linear design method can also be applied to TE mode. The data obtained by simulation calculation according to steps 1) -2) are shown in table 1, and table 1 shows effective refractive index, waveguide width and coupling strength simulation data at different wavelengths:

TABLE 1

Therefore, the initial width of the second coupling waveguide 201 is selected to be 0.19um, the end width is 0.213um, and particularly, in this embodiment, the initial width of the third coupling waveguide 202 is 0.213um, the end is linearly changed to 0.5um, and the width of the tm transmission waveguide 203 is consistent with the width of the third coupling waveguide 202, is 0.5um and remains unchanged.

The relation between the coupling strength and Gap under different wavelengths obtained in the steps 3) to 6) is shown in figure 3; a schematic diagram of the line shape of the TM coupling region 8 waveguide obtained according to steps 1) to 10) of the line shape design method of a polarization separation end-face coupler is shown in FIG. 4.

Through the steps, the structure and parameters of the device in the embodiment are obtained, modeling and simulation are performed by using a finite difference time domain method (FDTD), the length L1 of the second coupling waveguide 201 of the waveguide is determined to be 150um, the length L2 of the third coupling waveguide 202 is determined to be 10um, namely the total length of the TM mode coupling region 8 is 160um; and meanwhile, the field distribution of TE and TM modes is obtained, the results are shown in fig. 5 and 6, and simulation results show that the mode field input from the optical fiber is separated into TE and TM modes and transmitted to a subsequent waveguide, so that the end face coupling of polarization separation is realized.

Furthermore, the present invention provides an electronic apparatus including:

one or more processors;

a memory for storing one or more programs;

when the one or more programs are executed by the one or more processors, the one or more processors implement the linear design method of a polarization splitting end-face coupler.

The invention also provides a computer readable storage medium having stored thereon computer instructions which when executed by a processor perform the steps of the linear design method of a polarization splitting end-face coupler.

Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the application following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the application pertains.

It is to be understood that the present application is not limited to the precise arrangements and instrumentalities shown in the drawings, which have been described above, and that various modifications and changes may be effected without departing from the scope thereof.

Claims (10)

1. A polarization splitting end-face coupler, characterized in that the coupler is composed of a first waveguide (1) and a second waveguide (2) which are positioned on the same horizontal plane xy, the first waveguide (1) comprises an optical fiber coupling waveguide (101), a first coupling waveguide (102) and a TE coupling transmission waveguide (103); the transverse electric mode TE polarization of the optical field coupled in by the optical fiber is output into the optical chip by the TE coupling transmission waveguide (103), and the transverse magnetic mode TM polarization is coupled and transmitted into the optical chip by the second coupling waveguide (201), the third coupling waveguide (202) and the TM transmission waveguide (203), so that the optical field polarization separation and the coupling between the optical fiber and the optical chip are realized.

2. The polarization splitting end face coupler according to claim 1, wherein the first waveguide (1) has a single abrupt change in waveguide thickness along the x-direction, the optical fiber coupling waveguide (101) and the first coupling waveguide (102) have uniform thicknesses and are smaller than the TE coupling transmission waveguide (103), and the optical fiber coupling waveguide (101) and the first coupling waveguide (102) are flexibly selected according to the process and the actual thickness and can be realized by a double etching process.

3. The polarization splitting end face coupler according to claim 2, wherein in the first waveguide (1), the optical fiber coupling waveguide (101) is a waveguide with gradually-changed width, and the width of the waveguide is gradually increased from the optical fiber coupling end face (6) to the direction of the first coupling waveguide (102), and finally the waveguide is connected with the first coupling waveguide (102); the thickness and width of the first coupling waveguide (102) remain unchanged, and the height and width of the first coupling waveguide and the tail end of the optical fiber coupling waveguide (101) remain consistent.

4. A polarization splitting end face coupler according to claim 2, wherein the TE coupling transmission waveguide (103) of the first waveguide (1) is located above the first coupling waveguide (102), and comprises a section of wedge waveguide and a section of straight waveguide, the width of the wedge waveguide tip is smaller than that of the first coupling waveguide (102), and the width of the wedge waveguide is linearly graded, and finally the wedge waveguide tip is consistent with that of the first coupling waveguide (102); the first coupling waveguide (102) and the TE coupling transmission waveguide (103) are closely connected up and down, and the thickness of the first coupling waveguide and the TE coupling transmission waveguide is matched with that of a standard SOI substrate.

5. A polarization splitting end face coupler according to claim 1, characterized in that the waveguide thickness of the second waveguide (2) is kept constant, the spacing and width from the first waveguide (1) is varied, the two waveguides being spaced apart by the distance of the two waveguide edges; the waveguide interval and the waveguide width can be designed according to different working wavelengths to improve the coupling efficiency and increase the working bandwidth; the second coupling waveguide (201) and the third coupling waveguide (202) are used for performing TM mode coupling, the initial width of the third coupling waveguide (202) is consistent with the end width of the second coupling waveguide (201), the end width is consistent with the initial width of the TM transmission waveguide (203), and the width of the TM transmission waveguide (203) is unchanged; the interval between the third coupling waveguide (202) and the TM transmission waveguide (203) and the first waveguide (1) is consistent with the interval between the tail end of the second coupling waveguide (201) and the first waveguide (1) and is kept unchanged; the third coupling waveguide (202) thereof functions to prevent the TM mode in the TM transmission waveguide (203) from being coupled again.

6. A polarization splitting end face coupler according to claim 5, characterized in that the waveguide spacing and waveguide width are such that the coupling of TM modes between different waveguides is achieved by using a planar structure, the TE modes being low-loss when transmitted in the first waveguide (1), thus coupling the TM modes from the first waveguide (1) to the second waveguide (2), keeping the TE modes transmitted in the first waveguide (1), achieving TM and TE polarization splitting coupling.

7. A linear design method of a polarization separation end face coupler is characterized by comprising the following steps:

(1) After determining the width w1 and the height h1 of the first coupling waveguide (102), performing simulation and calculation to obtain the effective refractive indexes n1, lambda of the single first waveguide (1) at the wavelength lambda;

(2) Setting the height of the 2 nd waveguide as h2, simulating and calculating to obtain the effective refractive index n2 of the single second waveguide (2) at the wavelength lambda, wherein lambda changes along with the width of the second waveguide (2), and obtaining the width w2 of the second waveguide (2) when n1, lambda=n2 and lambda through interpolation fitting;

(3) Fixing w1 and w2, and performing simulation calculation on the two waveguide intervals Gap, h1 and h2 to obtain the effective refractive index neff of the system of the two waveguides;

(4) Subtracting n1 from neff, and obtaining coupling strength g of two waveguides when the working wavelength is lambda by lambda (n 2, lambda);

(5) Repeating the step (3) and the step (4) to change Gap, simulating to obtain coupling strength g under different gaps, and obtaining the relation between the Gap and the coupling strength g through interpolation fitting;

(6) For a set of wavelengths { λ1, λ2, λ3 … … λi }, giving a set of initial coupling strengths { g1, g2, g3 … … gi }, and obtaining a set of waveguide intervals { Gap1, gap2, gap3 … … Gap }, based on the relationship between the coupling strengths g and Gap; repeating step (1) and step (2) to obtain the widths { w21, w22, w23 … … w2i } of the set of second waveguides (2) corresponding to the set of wavelengths;

(7) Performing linear interpolation fitting on { Gap1, gap2, gap3 … … Gapi } and { w21, w22, w23 … … w2i }, and connecting the fitting results, and further taking a group of waveguide intervals and waveguide widths at linear equal intervals, and marking the waveguide intervals and the waveguide widths as { (Gap 1, w 1), (Gap 2, w 2), (Gap 3, w 3), … … (Gapn, wn) }, wherein n is an integer greater than or equal to i, and the number and the value range of n are taken in a connecting line segment;

(8) Obtaining y-axis relative coordinates of the first waveguide (1) and the second waveguide (2) from a set of points (Gapn, wn) taken at equal intervals;

(9) Uniformly distributing n groups of relative coordinates along an x-axis, wherein the total length is L;

(10) The method comprises the steps of fixedly coupling waveguide length values, modeling and simulating by using a time domain finite difference method FDTD, and performing iterative optimization on Gap values for a plurality of times until the coupling efficiency of each working wavelength lambda under the specified coupling waveguide length reaches the maximum value or approximately the maximum value, so that the working bandwidth meeting the requirements is obtained, and the line shape of a second coupling waveguide (201) in a second waveguide (2) is obtained;

(11) Adding a section of third coupling waveguide (202) behind the second coupling waveguide (201), wherein the width of the third coupling waveguide (202) is consistent with the width of the tail end of the second coupling waveguide (201), and then adjusting the coupling length L through simulation to obtain a required coupling waveguide structure; the coupling length L is the sum of the lengths of the second coupling waveguide (201) and the third coupling waveguide (202).

8. The linear design method of the polarization splitting end-face coupler according to claim 7, wherein the sum of the thicknesses of the TE coupling transmission waveguide (103) and the first coupling waveguide (102) is the same as the thickness of the second waveguide (2), the thickness is compatible with a standard SOI optical chip based on CMOS technology, and the width and thickness of the waveguides do not constitute a limitation on the design method.

9. An electronic device, comprising:

one or more processors;

a memory for storing one or more programs;

the one or more programs, when executed by the one or more processors, cause the one or more processors to implement the method of any of claims 7-8.

10. A computer readable storage medium having stored thereon computer instructions which, when executed by a processor, implement the steps of the method according to any of claims 7-8.