A polarization-rotating beam splitter based on a reverse-tapered coupler structure

Abstract

The application provides a polarization rotation beam splitter based on a reverse taper coupler structure, the main structure of which is constructed by a first straight waveguide, a mode converter, a reverse taper coupler, a second straight waveguide, an S-shaped curved waveguide and a third straight waveguide, when mixed mode TE0 / TM0 light from an input end passes through the mode converter, TM0 mode light is rotated into TE1 mode light, and TE0 mode light does not change, TE0 / TE1 mixed mode light enters the input end of the waveguide group of the reverse taper coupler, and when passing through the waveguide group, TE1 mode is converted and coupled to the fourth tapered waveguide, and finally TE0 mode is output at the second output end of the polarization rotation beam splitter, and TE0 mode is not transformed and finally TE0 mode is output at the first output end of the polarization rotation beam splitter, so that the purpose of a simple polarization rotation beam splitter is achieved. Simulation results show that the application not only can solve polarization dependence, but also has the advantages of low loss, low crosstalk, large bandwidth, and small overall device size.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optics, and relates to a polarization rotation beam splitter based on a reverse taper coupler structure. BACKGROUND

[0002] In the past decade, silicon photonics has attracted much attention due to its potential to realize high-density and low-power components, compatibility with complementary metal-oxide-semiconductor (CMOS) fabrication technology, high refractive index contrast, and compact size, which has been widely studied in many fields such as optical interconnection, sensing, and signal processing. However, the strong polarization dependence of silicon photonic devices based on nanoscale waveguides caused by the large refractive index difference between silicon and silicon dioxide is one of the main challenges for their practical applications, especially if the device is deployed on a fiber link, the polarization state of the optical signal at its input end can change randomly over time, making the standard SOI silicon photonic device no longer compatible with optical processing functions.

[0003] In view of the above problems, a polarization rotation beam splitter (PBSR) is proposed for beam splitting and rotation, which can well solve the polarization dependence. The mechanism of the polarization rotation beam splitter can be designed based on two principles of mode coupling and mode hybridization. In recent decades, there have been many devices designed based on these two principles, such as polarization rotation beam splitters based on symmetric / asymmetric directional coupler structures, polarization rotation beam splitters based on curved waveguide coupler structures, polarization rotation beam splitters based on Y-branch structures, and polarization rotation beam splitters based on double-etch directional coupler structures, which have attracted much attention. Such device structures are relatively compact, but are sensitive to manufacturing processes and wavelengths, and in order to solve the polarization dependence, their performance in insertion loss, crosstalk, and bandwidth is not satisfactory.

[0004] Therefore, how to provide a polarization rotation beam splitter that can well solve the loss, crosstalk, bandwidth, and polarization dependence, and has a relatively compact size, has become an important technical problem to be solved by those skilled in the art. SUMMARY

[0005] In view of the above-mentioned shortcomings of the prior art, the present application aims to provide a polarization rotation beam splitter based on a reverse taper coupler structure, which can solve the problems of high loss, large crosstalk, and small bandwidth of existing polarization rotation beam splitters.

[0006] To achieve the above object and other related objects, the present application provides a polarization-rotating beam splitter based on a reverse-tapered coupler structure, comprising a cladding and a main structure embedded in the cladding, wherein the main structure comprises:

[0007] a first straight waveguide;

[0008] a mode converter comprising a first tapered waveguide, a second tapered waveguide and a third tapered waveguide, wherein the input end of the first tapered waveguide is connected to the output end of the first straight waveguide, the input end of the second tapered waveguide is connected to the output end of the first tapered waveguide, the third tapered waveguide is located on the upper surface of the first tapered waveguide and the second tapered waveguide, and the input end of the third tapered waveguide is connected to the first straight waveguide;

[0009] a reverse-tapered coupler comprising a waveguide group and a fourth tapered waveguide arranged in parallel and spaced apart, wherein the input end of the waveguide group is connected to the output end of the mode converter;

[0010] a second straight waveguide, wherein the input end of the second straight waveguide is connected to the output end of the waveguide group;

[0011] an S-shaped curved waveguide, wherein the input end of the S-shaped curved waveguide is connected to the output end of the fourth tapered waveguide, the S-shaped curved waveguide comprises a first arc-shaped curved segment and a second arc-shaped curved segment connected in sequence, and the average interval distance between the first arc-shaped curved segment and the second straight waveguide is smaller than the average interval distance between the second arc-shaped curved segment and the second straight waveguide;

[0012] a third straight waveguide, wherein the input end of the third straight waveguide is connected to the output end of the S-shaped curved waveguide.

[0013] Optionally, the thicknesses of the first straight waveguide, the waveguide group, the fourth tapered waveguide, the second straight waveguide, the S-shaped curved waveguide and the third straight waveguide are the same, the first tapered waveguide and the second tapered waveguide are located in the same layer and have the same thickness, and the superimposed thickness of the first tapered waveguide and the third tapered waveguide is equal to the thickness of the first straight waveguide.

[0014] Optionally, the input end width of the first taper waveguide is equal to the output end width of the first straight waveguide, the output end width of the first taper waveguide is greater than the input end width of the first taper waveguide; the input end width of the second taper waveguide is equal to the output end width of the first taper waveguide, the output end width of the second taper waveguide is less than the input end width of the second taper waveguide; the input end width of the third taper waveguide is equal to the input end width of the first taper waveguide, the output end width of the third taper waveguide is greater than the input end width of the third taper waveguide and equal to the output end width of the second taper waveguide; the input end width of the waveguide group is equal to the output end width of the third taper waveguide; the input end width of the second straight waveguide is equal to the output end width of the waveguide group; the output end width of the fourth taper waveguide is greater than the input end width of the fourth taper waveguide; the input end width of the S-shaped curved waveguide is equal to the output end width and equal to the output end width of the fourth taper waveguide, and the width of the third straight waveguide is equal to the output end width of the S-shaped curved waveguide.

[0015] Optionally, the first taper waveguide, the second taper waveguide and the third taper waveguide are all isosceles trapezoidal waveguides, and the fourth taper waveguide is a right trapezoidal waveguide.

[0016] Optionally, the waveguide group comprises a fourth straight waveguide, a first right trapezoidal waveguide, a second right trapezoidal waveguide, a third right trapezoidal waveguide, a fourth right trapezoidal waveguide, a fifth right trapezoidal waveguide, a sixth right trapezoidal waveguide, a seventh right trapezoidal waveguide, an eighth right trapezoidal waveguide and a fifth straight waveguide connected in sequence.

[0017] Optionally, the right angle waists of the first right trapezoidal waveguide, the second right trapezoidal waveguide, the third right trapezoidal waveguide, the fourth right trapezoidal waveguide, the fifth right trapezoidal waveguide, the sixth right trapezoidal waveguide, the seventh right trapezoidal waveguide and the eighth right trapezoidal waveguide are located on the same plane and face the fourth taper waveguide.

[0018] Optionally, the input end width of the first straight rectangular waveguide is equal to the width of the fourth straight waveguide, and the output end width of the first straight rectangular waveguide is smaller than the input end width of the first straight rectangular waveguide; the input end width of the second straight rectangular waveguide is equal to the output end width of the first straight rectangular waveguide, and the output end width of the second straight rectangular waveguide is larger than the input end width of the second straight rectangular waveguide; the input end width of the third straight rectangular waveguide is equal to the output end width of the second straight rectangular waveguide, and the output end width of the third straight rectangular waveguide is smaller than the input end width of the third straight rectangular waveguide; the input end width of the fourth straight rectangular waveguide is equal to the output end width of the third straight rectangular waveguide, and the output end width of the fourth straight rectangular waveguide is smaller than the input end width of the fourth straight rectangular waveguide; the input end width of the fifth straight rectangular waveguide is equal to the output end width of the fourth straight rectangular waveguide, and the output end width of the fifth straight rectangular waveguide is smaller than the input end width of the fifth straight rectangular waveguide; the input end width of the sixth straight rectangular waveguide is equal to the output end width of the fifth straight rectangular waveguide, and the output end width of the sixth straight rectangular waveguide is smaller than the input end width of the sixth straight rectangular waveguide; the input end width of the seventh straight rectangular waveguide is equal to the output end width of the sixth straight rectangular waveguide, and the output end width of the seventh straight rectangular waveguide is smaller than the input end width of the seventh straight rectangular waveguide; the input end width of the eighth straight rectangular waveguide is equal to the output end width of the seventh straight rectangular waveguide, and the output end width of the eighth straight rectangular waveguide is smaller than the input end width of the eighth straight rectangular waveguide; and the width of the fifth straight waveguide is equal to the output end width of the eighth straight rectangular waveguide.

[0019] Optionally, the curvature of the first arc-shaped curved segment and the curvature of the second arc-shaped curved segment are both 90°.

[0020] Optionally, the first straight waveguide is configured to receive TE0 / TM0 hybrid mode light, and the mode converter is configured to convert the TE0 / TM0 hybrid mode light into TE0 / TE1 hybrid mode light; the reverse taper coupler is configured to output TE0 mode light from the TE0 / TE1 hybrid mode light received by the waveguide group to the second straight waveguide, and convert TE1 mode light therefrom into TE0 mode light and couple the TE0 mode light to the fourth tapered waveguide; the S-shaped curved waveguide is configured to output TE0 mode light from the fourth tapered waveguide to the third straight waveguide; the second straight waveguide is configured to output TE0 mode light from the waveguide group, and the third straight waveguide is configured to output TE0 mode light from the S-shaped curved waveguide.

[0021] Optionally, the material of the main body structure comprises silicon, and the material of the cladding layer comprises silicon dioxide.

[0022] As described above, in the polarization rotation beam splitter based on the reverse tapered coupler structure of the application, the main structure of the polarization rotation beam splitter is constructed by the first straight waveguide, the mode converter, the reverse tapered coupler, the second straight waveguide, the S-shaped curved waveguide and the third straight waveguide, when the mixed mode TE0 / TM0 light from the input end passes through the mode converter, the TM0 mode light is rotated into the TE1 mode light, and the TE0 mode light does not change, and the TE0 / TE1 mixed mode light enters the input end of the waveguide group of the reverse tapered coupler, and when passing through the waveguide group, the TE1 mode is converted and coupled to the fourth tapered waveguide, and finally the TE0 mode is output at the second output end of the polarization rotation beam splitter, and the TE0 mode is not transformed and finally the TE0 mode is output at the first output end of the polarization rotation beam splitter, so as to achieve the purpose of the simple polarization rotation beam splitter. The simulation results show that the polarization rotation beam splitter based on the reverse tapered coupler structure of the application not only can solve the polarization dependence, but also has the advantages of low loss, low crosstalk, large bandwidth, and small overall device size. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A top view structural schematic diagram of the main structure of the polarization rotation beam splitter based on the reverse tapered coupler structure of the application is shown.

[0024] Figure 2 A sectional view of the polarization rotation beam splitter based on the reverse tapered coupler structure of the application at A-A' in Figure 1

[0025] Figure 3 An enlarged structural schematic diagram of the waveguide group in the main structure of the polarization rotation beam splitter based on the reverse tapered coupler structure of the application is shown.

[0026] Figure 4 A simulation transmission spectrum line diagram of the polarization rotation beam splitter based on the reverse tapered coupler structure of the application under the input TE0 mode light source is shown.

[0027] Figure 5 A simulation transmission spectrum line diagram of the polarization rotation beam splitter based on the reverse tapered coupler structure of the application under the input TM0 mode light source is shown.

[0028] ELEMENT NUMBER EXPLANATION

[0029] 1 first straight waveguide

[0030] 2 mode converter

[0031] 201 first tapered waveguide

[0032] 202 second tapered waveguide

[0033] ​203 Third Conical Waveguide

[0034] 3. Reverse tapered coupler

[0035] 301 waveguide group

[0036] 301a Fourth Straight Waveguide

[0037] 301b First Right-Angle Trapezoidal Waveguide

[0038] 301c Second Right-Angle Trapezoidal Waveguide

[0039] 301d Third Right-Angle Trapezoidal Waveguide

[0040] 301e Fourth Right-Angle Trapezoidal Waveguide

[0041] 301f Fifth Right-Angle Trapezoidal Waveguide

[0042] 301g Sixth Right-Angle Trapezoidal Waveguide

[0043] 301h Seventh Right-Angle Trapezoidal Waveguide

[0044] 301i Eighth Right-Angle Trapezoidal Waveguide

[0045] 301j Fifth Straight Waveguide

[0046] 302 Fourth Conical Waveguide

[0047] 4 Second Straight Waveguide

[0048] 5 S-shaped curved waveguide

[0049] 6 Third Straight Waveguide

[0050] 7. Cladding Detailed Implementation

[0051] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0052] Please see Figures 1 to 5 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0053] The application provides a polarization rotation beam splitter based on a reverse taper coupler structure, comprising a cladding and a main structure embedded in the cladding, please refer to Figure 1 , which is shown as a top view structure diagram of the main structure, comprising a first straight waveguide 1, a mode converter 2, a reverse taper coupler 3, a second straight waveguide 4, an S-shaped curved waveguide 5 and a third straight waveguide 6.

[0054] Specifically, the first straight waveguide 1 is used as the input end of the polarization rotation beam splitter, the second straight waveguide 4 is used as the first output end of the polarization rotation beam splitter, and the third straight waveguide 6 is used as the second output end of the polarization rotation beam splitter.

[0055] As an example, the output end face of the second straight waveguide 4 and the output end face of the third straight waveguide 6 are located in the same plane.

[0056] Specifically, the first straight waveguide 1 is used for accessing a TE0 / TM0 mixed mode light source mixed by a TE0 mode (transverse electric wave zero order mode) light source and a TM0 mode (transverse magnetic wave zero order mode) light source, so as to receive the TE0 / TM0 mixed mode light and output to the mode converter 2.

[0057] Specifically, the mode converter 2 is used for converting the TE0 / TM0 mixed mode light into TE0 / TE1 mixed mode light, wherein after the TE0 / TM0 mixed mode light enters the mode converter 2, the TM0 mode light is polarized to rotate into TE1 mode light, and the TE0 mode light does not change, and finally the mode converter 2 outputs the TE0 / TE1 mixed mode light to the waveguide group 301 of the reverse taper coupler 3.

[0058] As an example, the mode converter 2 comprises a first taper waveguide 201, a second taper waveguide 202 and a third taper waveguide 203, the input end of the first taper waveguide 201 is connected to the output end of the first straight waveguide 1, the input end of the second taper waveguide 202 is connected to the output end of the first taper waveguide 201, the third taper waveguide 203 is located on the upper surface of the first taper waveguide 201 and the second taper waveguide 202, and the input end of the third taper waveguide 203 is connected to the first straight waveguide 1.

[0059] As an example, the first taper waveguide 201, the second taper waveguide 202 and the third taper waveguide 203 are all isosceles trapezoidal waveguides.

[0060] Specifically, the reverse taper coupler 3 is used for outputting the TE0 mode light in the TE0 / TE1 mixed mode light received by the waveguide group 301 to the second straight waveguide 4, and converting the TE1 mode light therein into TE0 mode and coupling to the fourth taper waveguide 302.

[0061] As an example, the reverse tapered coupler 3 includes a waveguide group 301 and a fourth tapered waveguide 302 arranged in parallel intervals. The input end of the waveguide group 301 is connected to the output end of the mode converter 2; the input end of the second straight waveguide 4 is connected to the output end of the waveguide group 301. In this embodiment, the input end face of the waveguide group 301 and the input end face of the fourth tapered waveguide 302 are located in the same plane, and the output end face of the waveguide group 301 and the output end face of the fourth tapered waveguide 302 are located in the same plane.

[0062] As an example, the fourth tapered waveguide 302 is a right-angled trapezoidal waveguide, and the right-angled waist of the fourth tapered waveguide 301 faces the waveguide group 301.

[0063] Specifically, the S-shaped curved waveguide 5 is used to output the TE0 mode light from the fourth tapered waveguide 302 to the third straight waveguide 6, and the third straight waveguide 6 is used to output the TE0 mode light from the S-shaped curved waveguide 5; the second straight waveguide 4 is used to output the TE0 mode light from the waveguide group 301, thereby achieving the purpose of a simple polarization rotating beam splitter.

[0064] As an example, the input end of the S-shaped curved waveguide 5 is connected to the output end of the fourth tapered waveguide 302, and the input end of the third straight waveguide 6 is connected to the output end of the S-shaped curved waveguide 5.

[0065] As an example, the S-shaped curved waveguide 5 is formed by bending a straight waveguide twice, including a first arc-shaped curved segment and a second arc-shaped curved segment connected in sequence. The average spacing between the first arc-shaped curved segment and the second straight waveguide 4 is less than the average spacing between the second arc-shaped curved segment and the second straight waveguide 4.

[0066] As an example, the arc of the first arc-shaped bending segment and the arc of the second arc-shaped bending segment of the S-shaped bending waveguide 5 are both 90°.

[0067] For example, please refer to Figure 2 Displayed as Figure 1 The A-A' cross-sectional view shows that, in this embodiment, the first tapered waveguide 201 and the second tapered waveguide 202 in the mode converter 2 are located on the same layer and have the same thickness.

[0068] As an example, as an example Figure 2 The cladding layer 7 is also shown. In this embodiment, the material of the main structure includes silicon, and the material of the cladding layer 7 includes silicon dioxide.

[0069] As an example, the thicknesses of the first straight waveguide 1, the waveguide group 301, the fourth tapered waveguide 302, the second straight waveguide 4, the S-shaped curved waveguide 5 and the third straight waveguide 6 are the same, and the superimposed thicknesses of the first tapered waveguide 201 and the third tapered waveguide 203 are equal to the thickness of the first straight waveguide 1. In this embodiment, the upper surfaces of the first straight waveguide 1, the third tapered waveguide 203, the waveguide group 301, the fourth tapered waveguide 302, the second straight waveguide 4, the S-shaped curved waveguide 5 and the third straight waveguide 6 are located in the same plane, and the lower surfaces of the first straight waveguide 1, the first tapered waveguide 201, the second tapered waveguide 202, the waveguide group 301, the fourth tapered waveguide 302, the second straight waveguide 4, the S-shaped curved waveguide 5 and the third straight waveguide 6 are located in the same plane.

[0070] As an example, the input end width of the first tapered waveguide 201 is equal to the output end width of the first straight waveguide 1, and the output end width of the first tapered waveguide 201 is greater than the input end width of the first tapered waveguide 202; the input end width of the second tapered waveguide 202 is equal to the output end width of the first tapered waveguide 201, and the output end width of the second tapered waveguide 202 is smaller than the input end width of the second tapered waveguide 202; the input end width of the third tapered waveguide 203 is equal to the input end width of the first tapered waveguide 201, and the output end width of the third tapered waveguide 203 is greater than the input end width of the third tapered waveguide 203 and equal to the output end width of the second tapered waveguide 202; the input end width of the waveguide group 301 is equal to the output end width of the third tapered waveguide 203; the input end width of the second straight waveguide 4 is equal to the output end width of the waveguide group 301; the output end width of the fourth tapered waveguide 5 is greater than the input end width of the fourth tapered waveguide 5; the input end width of the S-shaped curved waveguide 5 is equal to the output end width, and the width of the third straight waveguide 6 is equal to the output end width of the S-shaped curved waveguide 5.

[0071] It should be noted that the length direction is the direction in which the first straight waveguide 1 points to the waveguide group 301, and the thickness direction is the stacking direction of the first tapered waveguide 201 and the third tapered waveguide 203. In this embodiment, the width refers to the width of the corresponding waveguide in the direction perpendicular to the length direction and the thickness direction.

[0072] As an example, the input end face of the first tapered waveguide 201 and the input end face of the third tapered waveguide 203 are located in the same plane, and the input end faces of the first tapered waveguide 201 and the third tapered waveguide 203 are combined to be completely coincident with the output end face of the first straight waveguide 1; the input end face of the second tapered waveguide 202 is completely coincident with the output end face of the first tapered waveguide 201; the output end face of the second tapered waveguide 202 and the output end face of the third tapered waveguide 203 are located in the same plane, and the output end faces of the second tapered waveguide 202 and the third tapered waveguide 203 are combined to be completely coincident with the input end face of the waveguide group 301; the input end face of the second straight waveguide 4 is completely coincident with the output end face of the waveguide group 301; the input end face of the S-shaped curved waveguide 5 is completely coincident with the output end face of the fourth tapered waveguide 302; and the input end face of the third straight waveguide 6 is completely coincident with the output end face of the S-shaped curved waveguide 5.

[0073] As an example, refer to Figure 3 , which shows an enlarged structural schematic diagram of the waveguide group 301 in the reverse tapered coupler 3. The waveguide group 301 includes a fourth straight waveguide 301a, a first straight-angle trapezoidal waveguide 301b, a second straight-angle trapezoidal waveguide 301c, a third straight-angle trapezoidal waveguide 301d, a fourth straight-angle trapezoidal waveguide 301e, a fifth straight-angle trapezoidal waveguide 301f, a sixth straight-angle trapezoidal waveguide 301g, a seventh straight-angle trapezoidal waveguide 301h, an eighth straight-angle trapezoidal waveguide 301i, and a fifth straight waveguide 301j connected in sequence.

[0074] As an example, the straight-angle waists of the first straight-angle trapezoidal waveguide 301b, the second straight-angle trapezoidal waveguide 301c, the third straight-angle trapezoidal waveguide 301d, the fourth straight-angle trapezoidal waveguide 301e, the fifth straight-angle trapezoidal waveguide 301f, the sixth straight-angle trapezoidal waveguide 301g, the seventh straight-angle trapezoidal waveguide 301h, and the eighth straight-angle trapezoidal waveguide 301i are located in the same plane and face the fourth tapered waveguide 302.

[0075] As an example, the lengths of the first straight-angle trapezoidal waveguide 301b, the second straight-angle trapezoidal waveguide 301c, the third straight-angle trapezoidal waveguide 301d, the fourth straight-angle trapezoidal waveguide 301e, the fifth straight-angle trapezoidal waveguide 301f, the sixth straight-angle trapezoidal waveguide 301g, the seventh straight-angle trapezoidal waveguide 301h, the eighth straight-angle trapezoidal waveguide 301i, and the fifth straight waveguide 301j are equal.

[0076] As an example, the input end width of the first rectangular trapezoidal waveguide 301b is equal to the width of the fourth straight waveguide 301a, and the output end width of the first rectangular trapezoidal waveguide 301b is smaller than the input end width of the first rectangular trapezoidal waveguide 301b; the input end width of the second rectangular trapezoidal waveguide 301c is equal to the output end width of the first rectangular trapezoidal waveguide 301b, and the output end width of the second rectangular trapezoidal waveguide 301c is larger than the input end width of the second rectangular trapezoidal waveguide 301c; the input end width of the third rectangular trapezoidal waveguide 301d is equal to the output end width of the second rectangular trapezoidal waveguide 301c, and the output end width of the third rectangular trapezoidal waveguide 301d is smaller than the input end width of the third rectangular trapezoidal waveguide 301d; the input end width of the fourth rectangular trapezoidal waveguide 301e is equal to the output end width of the third rectangular trapezoidal waveguide 301d, and the output end width of the fourth rectangular trapezoidal waveguide 301e is smaller than the input end width of the fourth rectangular trapezoidal waveguide 301e; the input end width of the fifth rectangular trapezoidal waveguide 301f is equal to the output end width of the fourth rectangular trapezoidal waveguide 301e, and the output end width of the fifth rectangular trapezoidal waveguide 301f is smaller than the input end width of the fifth rectangular trapezoidal waveguide 301f; the input end width of the sixth rectangular trapezoidal waveguide 301g is equal to the output end width of the fifth rectangular trapezoidal waveguide 301f, and the output end width of the sixth rectangular trapezoidal waveguide 301g is smaller than the input end width of the sixth rectangular trapezoidal waveguide 301g; the input end width of the seventh rectangular trapezoidal waveguide 301h is equal to the output end width of the sixth rectangular trapezoidal waveguide 301g, and the output end width of the seventh rectangular trapezoidal waveguide 301h is smaller than the input end width of the seventh rectangular trapezoidal waveguide 301h; the input end width of the eighth rectangular trapezoidal waveguide 301i is equal to the output end width of the seventh rectangular trapezoidal waveguide 301h, and the output end width of the eighth rectangular trapezoidal waveguide 301i is smaller than the input end width of the eighth rectangular trapezoidal waveguide 301i; the width of the fifth straight waveguide 301j is equal to the output end width of the eighth rectangular trapezoidal waveguide 301i. The end faces of any two adjacent waveguides in the waveguide group 301 face each other and completely coincide.

[0077] As an example, in a specific implementation, the first straight waveguide 1 has a length of 5 μm, a width of 500 nm, and a thickness of 220 nm. In the mode converter 2, the first tapered waveguide 201 has a length of 12.5 μm, an input end width of 500 nm, an output end width of 1.2 μm, and a thickness of 130 nm; the second tapered waveguide 202 has a length of 12.5 μm, an input end width of 1.2 μm, an output end width of 750 nm, and a thickness of 130 nm; and the third tapered waveguide 203 has a length of 25 μm, an input end width of 500 nm, an output end width of 750 nm, and a thickness of 90 nm. In the reverse tapered coupler 3, the fourth straight waveguide 301a has a length of 0.5 μm, and the first straight trapezoidal waveguide 301b, the second straight trapezoidal waveguide 301c, the third straight trapezoidal waveguide 301d, the fourth straight trapezoidal waveguide 301e, the fifth straight trapezoidal waveguide 301f, the sixth straight trapezoidal waveguide 301g, the seventh straight trapezoidal waveguide 301h, the eighth straight trapezoidal waveguide 301i, and the fifth straight waveguide 301j all have a length of 1 μm. The fourth straight waveguide 301a, the first straight trapezoidal waveguide 301b, the second straight trapezoidal waveguide 301c, the third straight trapezoidal waveguide 301d, the fourth straight trapezoidal waveguide 301e, the fifth straight trapezoidal waveguide 301f, the sixth straight trapezoidal waveguide 301g, the seventh straight trapezoidal waveguide 301h, the eighth straight trapezoidal waveguide 301i, and the fifth straight waveguide 301j all have a height of 220 nm. The fourth straight waveguide 301a has a width of 750 nm, the first straight trapezoidal waveguide 301b has an input end width and an output end width of 750 nm and 680 nm respectively, the second straight trapezoidal waveguide 301c has an input end width and an output end width of 680 nm and 670 nm respectively, the third straight trapezoidal waveguide 301d has an input end width and an output end width of 670 nm and 770 nm respectively, the fourth straight trapezoidal waveguide 301e has an input end width and an output end width of 770 nm and 690 nm respectively, the fifth straight trapezoidal waveguide 301f has an input end width and an output end width of 690 nm and 590 nm respectively, the sixth straight trapezoidal waveguide 301g has an input end width and an output end width of 590 nm and 550 nm respectively, the seventh straight trapezoidal waveguide 301h has an input end width and an output end width of 550 nm and 530 nm respectively, the eighth straight trapezoidal waveguide 301i has an input end width and an output end width of 530 nm and 450 nm respectively, and the fifth straight waveguide 301j has a width of 450 nm. The fourth tapered waveguide 302 has a length of 9.5 μm, an input end width of 100 nm, an output end width of 300 nm, and a thickness of 220 nm.The second straight waveguide 4 has a length of 20 μm, a width of 450 nm, and a thickness of 220 nm. The gap between the waveguide group 301 and the fourth tapered waveguide 302 has a width of 200 nm. The vertical distance between the input and output faces of the S-shaped curved waveguide 5 is 15 μm. The S-shaped curved waveguide 5 has a width of 300 nm and a thickness of 220 nm. The vertical distance between the plane containing the front face and the plane containing the rear face of the S-shaped curved waveguide 5 is 1.5 μm. The third straight waveguide 6 has a length of 5 μm, a width of 300 nm, and a thickness of 220 nm.

[0078] It should be noted that in other embodiments, the specific dimensions of each waveguide can be adjusted as needed, and are not limited to this embodiment.

[0079] Please see Figure 4 The image shows a simulated transmission spectrum of the polarization rotating beam splitter based on the reverse conical coupler structure of this invention under an input TEO mode light source. Please refer to... Figure 5 The image shows the simulated transmission spectrum of the polarization rotating beamsplitter based on the reverse tapered coupler structure of this invention under an input TM0 mode light source. Simulation results show that, in the entire 1500-1600 nm wavelength range, the TE0 mode light source has the lowest insertion loss of 0.027 dB and crosstalk of -35.6 dB, while the TM0 mode light source has the lowest insertion loss of 0.19 dB and crosstalk of -25.88 dB. Furthermore, the bandwidth of the entire polarization rotating beamsplitter below -15 dB is close to 100 nm. Therefore, the polarization rotating beamsplitter based on the reverse tapered coupler structure of this invention not only solves the polarization dependence problem but also effectively addresses the issues of insertion loss, crosstalk, and bandwidth, thus possessing the advantages of low loss, low crosstalk, and large bandwidth, while maintaining a relatively small overall device size.

[0080] In summary, in the polarization-rotating beam splitter based on the reverse taper coupler structure, the main structure of the polarization-rotating beam splitter is constructed by a first straight waveguide, a mode converter, a reverse taper coupler, a second straight waveguide, an S-shaped curved waveguide and a third straight waveguide. When the mixed mode TE0 / TM0 light from the input end passes through the mode converter, the TM0 mode light is rotated to TE1 mode light, and the TE0 mode light does not change. The TE0 / TE1 mixed mode light enters the input end of the waveguide group of the reverse taper coupler, and when passing through the waveguide group, the TE1 mode is converted and coupled to the fourth tapered waveguide, and finally the TE0 mode is output at the second output end of the polarization-rotating beam splitter. The TE0 mode does not change and is finally output as the TE0 mode at the first output end of the polarization-rotating beam splitter, so as to achieve the purpose of a simple polarization-rotating beam splitter. Simulation results show that the polarization-rotating beam splitter based on the reverse taper coupler structure not only solves the polarization dependence, but also has the advantages of low loss, low crosstalk, large bandwidth, and small overall device size. Therefore, the present application effectively overcomes the various shortcomings in the prior art and has high industrial utilization value.

[0081] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought of the present application should be covered by the claims of the present application.

Claims

1. A polarization-rotating beam splitter based on an inverse-tapered coupler structure comprising a cladding and a body structure embedded within the cladding, characterized in that, The main body structure comprises: a first straight waveguide; a mode converter comprising a first tapered waveguide, a second tapered waveguide and a third tapered waveguide, an input end of the first tapered waveguide being connected to an output end of the first straight waveguide, an input end of the second tapered waveguide being connected to an output end of the first tapered waveguide, the third tapered waveguide being located on upper surfaces of the first tapered waveguide and the second tapered waveguide, and an input end of the third tapered waveguide being connected to the first straight waveguide; a reverse tapered coupler comprising a waveguide group and a fourth tapered waveguide, the waveguide group being parallelly and spacedly arranged, and an input end of the waveguide group being connected to an output end of the mode converter; a second straight waveguide, an input end of the second straight waveguide being connected to an output end of the waveguide group; an S-shaped curved waveguide, an input end of the S-shaped curved waveguide being connected to an output end of the fourth tapered waveguide, the S-shaped curved waveguide comprising a first arc-shaped curved segment and a second arc-shaped curved segment connected in sequence, an average interval distance between the first arc-shaped curved segment and the second straight waveguide being smaller than an average interval distance between the second arc-shaped curved segment and the second straight waveguide; a third straight waveguide, an input end of the third straight waveguide being connected to an output end of the S-shaped curved waveguide.

2. The polarization-rotating beam splitter based on a reversed-taper coupler structure according to claim 1, characterized in that: The first straight waveguide, the waveguide group, the fourth tapered waveguide, the second straight waveguide, the S-shaped curved waveguide and the third straight waveguide have the same thickness, the first tapered waveguide and the second tapered waveguide are located on the same layer and have the same thickness, and a superimposed thickness of the first tapered waveguide and the third tapered waveguide is equal to the thickness of the first straight waveguide.

3. The polarization-rotating beam splitter based on a reversed-taper coupler structure of claim 1, wherein: An input end width of the first tapered waveguide is equal to an output end width of the first straight waveguide, an output end width of the first tapered waveguide is greater than the input end width of the first tapered waveguide, an input end width of the second tapered waveguide is equal to the output end width of the first tapered waveguide, an output end width of the second tapered waveguide is smaller than the input end width of the second tapered waveguide, an input end width of the third tapered waveguide is equal to the input end width of the first tapered waveguide, an output end width of the third tapered waveguide is greater than the input end width of the third tapered waveguide and equal to the output end width of the second tapered waveguide, an input end width of the waveguide group is equal to the output end width of the third tapered waveguide, an input end width of the second straight waveguide is equal to an output end width of the waveguide group, an output end width of the fourth tapered waveguide is greater than an input end width of the fourth tapered waveguide, an input end width of the S-shaped curved waveguide is equal to an output end width of the S-shaped curved waveguide, and the output end width of the S-shaped curved waveguide is equal to the output end width of the fourth tapered waveguide, and a width of the third straight waveguide is equal to the output end width of the S-shaped curved waveguide.

4. The polarization-rotating beam splitter based on a reversed-taper coupler structure of claim 1, wherein: The first tapered waveguide, the second tapered waveguide and the third tapered waveguide are all isosceles trapezoidal waveguides, and the fourth tapered waveguide is a right trapezoidal waveguide.

5. The polarization-rotating beam splitter based on a reversed-taper coupler structure of claim 1, wherein: The waveguide group comprises a fourth straight waveguide, a first right trapezoidal waveguide, a second right trapezoidal waveguide, a third right trapezoidal waveguide, a fourth right trapezoidal waveguide, a fifth right trapezoidal waveguide, a sixth right trapezoidal waveguide, a seventh right trapezoidal waveguide, an eighth right trapezoidal waveguide and a fifth straight waveguide connected in sequence.

6. The polarization-rotating beam splitter based on a reversed-taper coupler structure according to claim 5, characterized in that: The end faces of the right-angle waist of the first, second, third, fourth, fifth, sixth, seventh and eighth right-angle trapezoidal waveguides are located in the same plane and face the fourth tapered waveguide.

7. The polarization-rotating beam splitter based on a reversed-taper coupler structure of claim 5, wherein: The input end width of the first right-angle trapezoidal waveguide is equal to the width of the fourth straight waveguide, and the output end width of the first right-angle trapezoidal waveguide is smaller than the input end width of the first right-angle trapezoidal waveguide; the input end width of the second right-angle trapezoidal waveguide is equal to the output end width of the first right-angle trapezoidal waveguide, and the output end width of the second right-angle trapezoidal waveguide is larger than the input end width of the second right-angle trapezoidal waveguide; the input end width of the third right-angle trapezoidal waveguide is equal to the output end width of the second right-angle trapezoidal waveguide, and the output end width of the third right-angle trapezoidal waveguide is smaller than the input end width of the third right-angle trapezoidal waveguide; the input end width of the fourth right-angle trapezoidal waveguide is equal to the output end width of the third right-angle trapezoidal waveguide, and the output end width of the fourth right-angle trapezoidal waveguide is smaller than the input end width of the fourth right-angle trapezoidal waveguide; the input end width of the fifth right-angle trapezoidal waveguide is equal to the output end width of the fourth right-angle trapezoidal waveguide, and the output end width of the fifth right-angle trapezoidal waveguide is smaller than the input end width of the fifth right-angle trapezoidal waveguide; the input end width of the sixth right-angle trapezoidal waveguide is equal to the output end width of the fifth right-angle trapezoidal waveguide, and the output end width of the sixth right-angle trapezoidal waveguide is smaller than the input end width of the sixth right-angle trapezoidal waveguide; the input end width of the seventh right-angle trapezoidal waveguide is equal to the output end width of the sixth right-angle trapezoidal waveguide, and the output end width of the seventh right-angle trapezoidal waveguide is smaller than the input end width of the seventh right-angle trapezoidal waveguide; the input end width of the eighth right-angle trapezoidal waveguide is equal to the output end width of the seventh right-angle trapezoidal waveguide, and the output end width of the eighth right-angle trapezoidal waveguide is smaller than the input end width of the eighth right-angle trapezoidal waveguide; the width of the fifth straight waveguide is equal to the output end width of the eighth right-angle trapezoidal waveguide.

8. The polarization-rotating beam splitter based on a reversed-taper coupler structure of claim 1, wherein: The radii of the first and second arc-shaped curved segments are both 90°.

9. The polarization-rotating beam splitter based on a reversed-taper coupler structure of claim 1, wherein: The first straight waveguide is configured to receive TE0 / TM0 hybrid mode light, the mode converter is configured to convert the TE0 / TM0 hybrid mode light into TE0 / TE1 hybrid mode light, the reverse tapered coupler is configured to output TE0 mode light from the TE0 / TE1 hybrid mode light received by the waveguide group to the second straight waveguide, and convert TE1 mode light thereinto into TE0 mode and couple it to the fourth tapered waveguide, the S-shaped curved waveguide is configured to output TE0 mode light from the fourth tapered waveguide to the third straight waveguide, the second straight waveguide is configured to output TE0 mode light from the waveguide group, and the third straight waveguide is configured to output TE0 mode light from the S-shaped curved waveguide.

10. The polarization-rotating beam splitter based on a reversed-taper coupler structure of claim 1, wherein: The material of the body structure comprises silicon, and the material of the cladding comprises silicon dioxide. The material of the body structure comprises silicon, and the material of the cladding comprises silicon dioxide.

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