Polarization-rotating beam splitter

Abstract

The application discloses a polarization rotation beam splitter, relates to the field of integrated photonics, and comprises the following: an input waveguide for inputting a broadband optical signal containing a TE0 mode or a TM0 mode; a polarization-dependent mode converter for keeping the TE0 mode unchanged and adiabatically evolving the TM0 mode into a TE1 mode; a multimode beam splitter for splitting the TE0 mode into two optical fields with equal amplitude and in-phase and splitting the TE1 mode into two optical fields with equal amplitude and anti-phase; a directional coupler for coupling the optical field corresponding to the TE0 mode to one output channel and the optical field corresponding to the TE1 mode to another output channel according to the phase difference between the two optical fields; an output taper for adiabatically converting the optical field of each channel into a single-mode TE0 mode; and a first output waveguide and a second output waveguide for outputting the single-mode TE0 mode optical signal of the corresponding channel, respectively. The polarization rotation beam splitter can realize efficient polarization beam splitting, low-loss conversion and standard single-mode stable output of the TE0 and TM0 modes under broadband.

Description

Technical Field

[0001] This invention relates to the field of integrated photonics, and particularly to polarization rotating beam splitters. Background Technology

[0002] In the field of integrated photonics, silicon-based optoelectronics technology is widely used in high-speed optical communication, optical interconnection and microwave photonics due to its compatibility with CMOS (Complementary Metal-Oxide-Semiconductor) processes, high integration and low cost. As the core device of polarization diversity circuit, the polarization rotation beam splitter can separate the two orthogonal polarization states of the input and convert the TM0 mode into the TE0 mode, so that subsequent optical signal processing can be completed under a single polarization fundamental mode.

[0003] High-capacity optical communication and intelligent optical networks have placed demands on polarization rotating beamsplitters for large operating bandwidth, stable polarization separation, and unified output modes. Most existing mainstream polarization rotating beamsplitters employ directional coupling structures, relying on strict phase matching and specific coupling lengths. The coupling coefficient is sensitive to wavelength changes, making it difficult to maintain stable polarization separation and mode conversion across a wide spectral range. The use of adiabatic, slowly varying double waveguide structures, thin-film lithium niobate platforms, and MMI interference structures all suffer from limited operating bandwidth. Furthermore, most existing devices can only achieve fixed polarization beam splitting and rotation, failing to achieve directional channel output for different polarization modes. The output mode is also difficult to unify into a standard single-mode TEO mode, increasing the difficulty of backend optical path processing. Moreover, they can only achieve polarization state conversion within a single channel, unable to complete spatial separation and directional output of two orthogonal polarization modes.

[0004] In summary, how to achieve stable separation and directional output of TE0 and TM0 modes over a wide spectral range, and uniformly convert them into single-mode TE0 mode output, is a problem that needs to be solved in this field. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a polarization rotating beam splitter that achieves stable separation and directional output of TE0 and TM0 modes over a wide spectral range, and uniformly converts them into a single-mode TE0 mode output. The specific solution is as follows: In a first aspect, this application discloses a polarization rotating beam splitter, comprising: An input waveguide is used to input broadband optical signals; wherein, the broadband optical signals include TEO mode optical signals and TMO mode optical signals; A polarization-dependent mode converter connected to the input waveguide is used to keep the TE0 mode optical signal in the broadband optical signal unchanged based on the effective refractive index of the broadband optical signal, and to adiabatically evolve the TM0 mode optical signal in the broadband optical signal into the TE1 mode optical signal. The multimode beam splitter connected to the polarization-dependent mode converter is used to split the TE0 mode optical signal into two optical fields in an equal amplitude and in phase manner, and to split the TE1 mode optical signal into two optical fields in an equal amplitude and out-of-phase manner. The directional coupler connected to the multimode beam splitter is used to directionally couple the optical field corresponding to the TE0 mode to one output channel and the optical field corresponding to the TE1 mode to another output channel according to the phase difference between the two optical fields. The output gradient connected to the directional coupler is used to thermally convert the optical field output by each output channel into a single-mode TEO mode optical signal. The first and second output waveguides, which are connected to the output gradient, are used to output single-mode TEO optical signals for the corresponding output channels, respectively.

[0006] Optionally, the polarization rotating beam splitter further includes: A connecting waveguide, whose input end is connected to the multimode beam splitter and whose output end is connected to the directional coupler, is used to transmit two optical fields to the directional coupler.

[0007] Optionally, the connecting waveguide includes: The upper phase shifter waveguide is used to transmit one of the two optical fields to the directional coupler. The lower phase shifter waveguide is used to transmit the other optical field of the two optical fields to the directional coupler.

[0008] Optionally, the polarization rotating beam splitter further includes: The phase shifter, whose input end is connected to the upper phase shifter waveguide and / or the lower phase shifter waveguide and whose output end is connected to the directional coupler, is used to apply a first electrical signal to the optical field in the upper phase shifter waveguide and / or the lower phase shifter waveguide and to flip the parity symmetry of the optical field to switch the output channel of the optical field corresponding to the TE0 mode and the optical field corresponding to the TE1 mode, or to apply a second electrical signal to the optical field in the upper phase shifter waveguide and / or the lower phase shifter waveguide and to compensate for the phase of the optical field to eliminate the phase error of the optical field.

[0009] Optionally, the phase shifter can be any one of the following: thermo-optical control type phase shifter, carrier depletion / injection type electro-optic phase shifter, electro-optic phase shifter based on electro-optic materials, phase change material type phase shifter, microelectromechanical system control type phase shifter, and all-optical control type phase shifter.

[0010] Optionally, the mode hybrid structure of the polarization-dependent mode converter can be any one of the following: an adiabatic graded ridge waveguide structure with a shallowly etched plate, an air cladding structure, a waveguide tilting structure, or a subwavelength grating structure.

[0011] Optionally, the waveguide of the multimode beam splitter is an adiabatic graded ridge waveguide with a shallowly etched plate. The structure of the multimode beam splitter is any one of a three-waveguide adiabatic coupling structure, a Y-branch coupling structure, or a 1×2 multimode interference coupling structure. The three-waveguide adiabatic coupling structure includes a central main waveguide and branch waveguides symmetrically distributed on both sides of the main waveguide. The width of the main waveguide gradually narrows and the width of the branch waveguides gradually widens along the optical transmission direction.

[0012] Optionally, the waveguide of the directional coupler is an adiabatic tapered ridge waveguide with a shallowly etched plate, and the type of the directional coupler is any one of the following: a width-tapered dual-waveguide asymmetric adiabatic coupler, a bent directional coupler, or a combination of a 2×2 multimode interference coupler and a waveguide phase shifter.

[0013] Optionally, the width-gradient dual-waveguide asymmetric thermal coupler includes a first ridge waveguide and a second ridge waveguide arranged along the optical transmission direction. The initial widths of the first ridge waveguide and the second ridge waveguide are equal. Along the optical transmission direction, the width of the first ridge waveguide gradually widens and the width of the second ridge waveguide gradually narrows, forming an asymmetric thermal evolution structure. This structure is used to form an even-symmetric supermode by interfering optical fields with a phase difference of 0 and converge it to the output channel corresponding to the first ridge waveguide, and to form an odd-symmetric supermode by interfering optical fields with a phase difference of π and converge it to the output channel corresponding to the second ridge waveguide.

[0014] Optionally, the polarization rotating beam splitter further includes: The width-gradient tapered waveguide, whose input end is connected to the directional coupler and whose output end is connected to the output gradient, adopts a ridge waveguide structure with a shallowly etched plate and has a continuous thermally adiabatic gradient in width along the optical transmission direction, so as to separate the two optical fields in physical space and perform thermally adiabatic transition of the optical fields through the smooth gradient of the waveguide width.

[0015] The beneficial effects of this application are as follows: The polarization rotating beam splitter of this application includes an input waveguide, a polarization-dependent mode converter connected to the input waveguide, a multimode beam splitter connected to the polarization-dependent mode converter, a directional coupler connected to the multimode beam splitter, an output grader connected to the directional coupler, and a first output waveguide and a second output waveguide connected to the output grader; the input waveguide is used to input a broadband optical signal; wherein, the broadband optical signal includes a TEO mode optical signal and a TMO mode optical signal; the polarization-dependent mode converter is used to keep the TEO mode optical signal in the broadband optical signal unchanged based on the effective refractive index of the broadband optical signal, and to convert the TEO mode optical signal into a multimode beam splitter. In a broadband optical signal, the TM0 mode optical signal is adiabatically evolved into the TE1 mode optical signal; a multimode beam splitter is used to split the TE0 mode optical signal into two optical fields in an equal amplitude and in phase manner, and to split the TE1 mode optical signal into two optical fields in an equal amplitude and out-of-phase manner; a directional coupler is used to directionally couple the optical field corresponding to the TE0 mode to one output channel and the optical field corresponding to the TE1 mode to another output channel according to the phase difference between the two optical fields; an output taper is used to adiabatically convert the optical fields output by each output channel into single-mode TE0 mode optical signals; a first output waveguide and a second output waveguide are used to output the single-mode TE0 mode optical signals of the corresponding output channels, respectively.Therefore, this application uses an input waveguide to input broadband optical signals in either TE0 or TM0 mode. A polarization-dependent mode converter connected to the input waveguide maintains the TE0 mode optical signal unchanged based on the effective refractive index difference, while adiabatically evolving the TM0 mode optical signal into a TE1 mode optical signal, thus distinguishing between the two input polarization modes and avoiding mode interference. A multimode beamsplitter connected to the polarization-dependent mode converter splits the TE0 mode optical signal into two optical fields with equal amplitude and in phase, and the TE1 mode optical signal into two optical fields with equal amplitude and out of phase, forming a fixed and distinguishable phase difference characteristic, providing a clear basis for subsequent directional coupling. A directional coupler connected to the multimode beamsplitter couples the optical field corresponding to the TE0 mode to one output channel and the optical field corresponding to the TE1 mode to another output channel based on the phase difference between the two optical fields, completing the processing of different input polarization modes. The proposed polarization rotation beam splitter achieves spatial separation and directional output without relying on strict phase matching and specific coupling lengths, reducing sensitivity to wavelength changes and expanding the operating bandwidth. All the related devices mentioned above perform mode conversion / beam splitting / separation through adiabatic gradation, thus inherently possessing wavelength insensitivity and waveguide size robustness. Therefore, the proposed polarization rotation beam splitter features large bandwidth and large tolerance. The output grader connected to the directional coupler adiabatically converts the optical field of each output channel into a single-mode TE0 optical signal, unifying the output mode to the standard TE0 fundamental mode, reducing the complexity of back-end optical path processing. The signal is then output through the first and second output waveguides, achieving stable separation, rotation, and single-mode output of two orthogonal polarization states in the broadband optical signal. The overall structure is simple, with low transmission loss and low crosstalk, while also possessing a wider operating wavelength range and higher tolerance for process errors. This application introduces an architecture combining an odd-even symmetric supermode beam splitting mechanism with an active phase shifter, enabling the device to receive external control signals and dynamically change interference conditions under software control, thereby achieving efficient and real-time routing switching of polarized light. At the same time, the active phase shifter in the structure can act as a phase adjustment unit in the static working state to actively compensate for residual phase errors caused by waveguide size deviations, thereby improving the performance consistency and yield of the device in actual process fabrication. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of a polarization rotating beam splitter disclosed in this application; Figure 2This is a specific waveguide cross-sectional view disclosed in this application; Figure 3 This is a schematic diagram of a polarization rotating beam splitter disclosed in this application; Figure 4 This is another specific waveguide cross-sectional view disclosed in this application; Figure 5 This is a schematic diagram of a specific active polarization rotating beam splitter disclosed in this application; Figure 6 This is a schematic diagram of a specific passive polarization rotating beam splitter disclosed in this application; Figure 7 This is a schematic diagram of the optical field transmission and mode evolution of a specific polarization-dependent mode converter and multimode beam splitter disclosed in this application; Figure 8 This is a schematic diagram illustrating a specific effective refractive index evolution disclosed in this application; Figure 9 This is a schematic diagram of a specific optical field transmission and mode evolution disclosed in this application; Figure 10 This is a simulation diagram of a specific phase shifter disclosed in this application when it is not working; Figure 11 A simulation diagram of a specific phase shifter disclosed in this application during operation; Figure 12 This is a schematic diagram of a polarization rotating beam splitter structure based on an electro-optic switch disclosed in this application. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Silicon-based optoelectronics technology, due to its compatibility with CMOS processes, high integration, and low cost, is widely used in high-speed optical communication, optical interconnects, and microwave photonics. In polarization multiplexing and coherent optical communication systems, to overcome the polarization correlation loss and dispersion problems caused by the strong birefringence of silicon waveguides, polarization diversity circuits are often used. Polarization rotating beamsplitters are used as core devices to separate the two orthogonal polarization states, TE0 and TM0, and convert the TM0 mode to the TE0 mode, allowing subsequent signal processing to be completed under a single fundamental mode. With the development of communication systems towards full spectrum and intelligence, significant demands are placed on these devices. The requirements for bandwidth and high flexibility are significant. Existing mainstream polarization rotating beam splitters mostly rely on directional coupling structures, which require strict phase matching and fixed coupling length. The coupling coefficient is sensitive to wavelength, resulting in a narrow operating bandwidth. It is difficult to maintain high conversion efficiency and low crosstalk over a wide band. Moreover, most of them are passive and fixed structures, which cannot achieve dynamic routing and port switching of polarization state after fabrication. At the same time, traditional structures are extremely sensitive to waveguide size process errors, have small manufacturing tolerances, and lack the ability to calibrate phase errors and crosstalk after fabrication. When used in cascade, crosstalk is easily amplified, which cannot meet the high yield and high consistency requirements of large-scale integrated chips.

[0020] Among existing polarization processing devices, one type uses an adiabatic, slowly varying dual waveguide structure to achieve passive polarization beam splitting and rotation. This type can only perform static polarization processing by fixing the waveguide morphology, cannot dynamically switch the output port, lacks a process error compensation mechanism, and has limited operating bandwidth. Another type is based on a thin-film lithium niobate platform, using a fixed-width waveguide to form a static phase shifter in conjunction with conventional MMI (Multimode Interference) interference to achieve beam splitting. The phase shift structure is not adjustable, so dynamic switching cannot be achieved, and the self-image principle of MMI has an inherent bandwidth bottleneck. Yet another type uses on-chip mode conversion and MZI (Mach-Zehnder Interferometer) interference structure to achieve polarization control. This type can only convert polarization states within a single channel, cannot achieve spatial separation of TE0 and TM0 modes and unified TE0 fundamental mode output, and the MZI interference mechanism is highly sensitive to wavelength, with bandwidth shrinking significantly during dynamic control.

[0021] To address this, this application provides a polarization rotating beam splitter that achieves stable separation and directional output of TE0 and TM0 modes over a wide spectral range, and uniformly converts them into single-mode TE0 mode output.

[0022] See Figure 1 As shown in the figure, this application discloses a polarization rotating beam splitter, including: Input waveguide 101 is used to input broadband optical signals; wherein, the broadband optical signals include TE0 mode optical signals and TM0 mode optical signals.

[0023] The polarization-dependent mode converter 102 connected to the input waveguide 101 is used to keep the TE0 mode optical signal in the broadband optical signal unchanged based on the effective refractive index of the broadband optical signal, and to adiabatically evolve the TM0 mode optical signal in the broadband optical signal into the TE1 mode optical signal.

[0024] The multimode beam splitter 103 connected to the polarization-dependent mode converter 102 is used to split the TE0 mode optical signal into two optical fields in an equal amplitude and in phase manner, and to split the TE1 mode optical signal into two optical fields in an equal amplitude and out-of-phase manner.

[0025] The directional coupler 104 connected to the multimode beam splitter 103 is used to directionally couple the optical field corresponding to the TE0 mode to one output channel and the optical field corresponding to the TE1 mode to another output channel according to the phase difference between the two optical fields.

[0026] The output gradient 105, connected to the directional coupler 104, is used to thermally convert the optical field output by each output channel into a single-mode TEO optical signal.

[0027] The first output waveguide 106 and the second output waveguide 107, which are connected to the output gradient 105, are used to output single-mode TEO optical signals of the corresponding output channels, respectively.

[0028] In this embodiment, a broadband optical signal containing dual polarization signals is input to a polarization rotation beam splitter via an input waveguide. That is, the input waveguide is used to input a broadband optical signal including TEO mode optical signals and TMO mode optical signals.

[0029] Next, the broadband optical signal enters a polarization-dependent mode converter connected to an input waveguide. In this embodiment, the mode hybridization structure of the polarization-dependent mode converter is any one of the following: an adiabatic graded ridge waveguide structure with a shallowly etched plate, an air cladding structure, a waveguide tilting structure, or a subwavelength grating structure. The polarization-dependent mode converter maintains the TE0 mode optical signal in the broadband optical signal unchanged based on the effective refractive index of the broadband optical signal, and adiabatically evolves the TM0 mode optical signal in the broadband optical signal into the TE1 mode optical signal. Specifically, both the waveguide and the shallowly etched plate of the polarization-dependent mode converter gradually widen, thereby introducing an adiabatic graded waveguide with a specific asymmetric cross-section. Besides using a shallowly etched plate, the polarization-dependent mode converter can also use other hybridization methods such as air cladding, tilted waveguides, and subwavelength grating structures to separate the two polarization modes. According to the principle of mode evolution, when the input light is in TE0 mode, its effective refractive index does not satisfy the mode hybridization condition, and the light field will continue to propagate forward in TE0 mode. When the input light is in TM0 mode, the mode hybridization condition is satisfied during the gradual transition, and it will adiabatically evolve into TE1 mode. Figure 2(a1) top view and Figure 2 As shown in the cross-sectional view of (a2), the polarization-dependent mode converter employs a ridge waveguide structure with a shallowly etched plate at the bottom. By introducing the shallowly etched plate at the bottom, the symmetry of the waveguide in the vertical direction is broken. Figure 2 (a1) shows a tapered design with a gradually increasing width of the waveguide core region, which enables the waveguide region of a specific width to meet the effective refractive index anti-crossing condition of the TM0 mode and the TE1 mode, thereby achieving efficient, broadband adiabatic mode hybridization from TM0 to TE1.

[0030] Furthermore, the TE0 mode optical signal and the TE1 mode optical signal enter the multimode beam splitter. The multimode beam splitter splits the TE0 mode optical signal into two optical fields in the form of equal amplitude and in phase, and splits the TE1 mode optical signal into two optical fields in the form of equal amplitude and out of phase.

[0031] In other words, the optical field processed by the polarization-dependent mode converter enters the multimode beamsplitter, which acts as a power distribution unit and has different phase responses to different modes. Specifically, if the input to the beamsplitter is the TE0 mode, the optical field will be equally split into two beams, which will enter the upper and lower phase shifter waveguides respectively, and the optical fields in the two arms will remain in phase (i.e., the initial phase difference is 0). If the input is the hybridized TE1 mode (odd-symmetric mode), the optical field will also be equally split into the upper and lower phase shifter arms, but the optical fields in the two arms will be out of phase (i.e., the initial phase difference is pi).

[0032] In this embodiment, the waveguide of the multimode beamsplitter is an adiabatic graded ridge waveguide with a shallowly etched flat plate. The structure of the multimode beamsplitter is any one of a three-waveguide adiabatic coupling structure, a Y-branch coupling structure, or a 1×2 multimode interference coupling structure. The three-waveguide adiabatic coupling structure includes a central main waveguide and branch waveguides symmetrically distributed on both sides of the main waveguide. The width of the main waveguide gradually narrows and the width of the branch waveguides gradually widens along the optical transmission direction.

[0033] like Figure 2 (b1) top view and Figure 2As shown in the cross-sectional view of (b2), the multimode beamsplitter preferably employs a three-waveguide adiabatic coupling structure. This structure includes a central main waveguide and symmetrically distributed branch waveguides on both sides. In the optical transmission direction, the width of the central main waveguide gradually narrows, while the width of the branch waveguides on both sides gradually widens. When the input to the central main waveguide is an even-symmetric TE0 mode, the optical energy is adiabatically transferred to the two side waveguides, exciting equal-amplitude, in-phase (phase difference 0) TE0 modes in the two side waveguides. When the input to the central main waveguide is an odd-symmetric TE1 mode, after adiabatic transfer, equal-amplitude, out-of-phase (phase difference pi) TE0 modes are excited in the two side waveguides. This adiabatic evolution beamsplitter structure significantly reduces wavelength sensitivity, providing a core guarantee for achieving ultra-high bandwidth. Besides the three-waveguide adiabatic coupling structure, other structures that can split the optical fields of two modes into two beams, such as Y-branch and 1×2 MMI, can also be used for multimode beams.

[0034] In a specific passive implementation, the multimode beamsplitter is connected to a directional coupler. Two optical fields converge into the combining region of the directional coupler. Based on the phase difference between the two optical fields, the directional coupler combines and directionally couples the optical field corresponding to the TE0 mode to one output channel and the optical field corresponding to the TE1 mode to another output channel. Specifically, if the phase difference of the optical fields input to the combining region is 0, according to the asymmetric evolution rule, the optical field will mainly evolve and converge to the upper channel of the coupler; if the phase difference between the two input optical fields is pi, the optical field will evolve and converge to the lower channel of the coupler. Because this process is based on adiabatic evolution rather than strict interferometric phase matching, it exhibits excellent bandwidth performance over a large bandwidth and has high tolerance for waveguide size errors, demonstrating strong robustness.

[0035] In this embodiment, the waveguide of the directional coupler is an adiabatic tapered ridge waveguide with a shallowly etched plate. The type of the directional coupler is any one of the following: a width-tapered dual-waveguide asymmetric adiabatic coupler, a bent directional coupler, or a combination of a 2×2 multimode interference coupler and a waveguide phase shifter.

[0036] In this embodiment, the width-gradient dual-waveguide asymmetric thermally adiabatic coupler includes a first ridge waveguide and a second ridge waveguide arranged along the optical transmission direction. The initial widths of the first ridge waveguide and the second ridge waveguide are equal. Along the optical transmission direction, the width of the first ridge waveguide gradually widens and the width of the second ridge waveguide gradually narrows, forming an asymmetric thermal evolution structure. This structure is used to form an even-symmetric supermode by interfering optical fields with a phase difference of 0 and converging it to the output channel corresponding to the first ridge waveguide, and to form an odd-symmetric supermode by interfering optical fields with a phase difference of π and converging it to the output channel corresponding to the second ridge waveguide.

[0037] like Figure 2 (c1) top view and Figure 2 As shown in the cross-sectional diagram of (c2), the dual-waveguide asymmetric directional coupler employs a dual-waveguide asymmetric adiabatic evolution structure. Its cross-section contains two ridge-shaped waveguides of unequal width. Due to the asymmetry in the widths of the two waveguides, the effective refractive indices of the supported local modes differ. When the phase difference between the two input optical fields is 0, the interference forms an even-symmetric supermode of the system, which, after adiabatic evolution, will be mainly localized in the wider waveguide. When the phase difference between the two input optical fields is pi, the interference forms an odd-symmetric supermode, which, after evolution, will be localized in the narrower waveguide. This directional coupling based on asymmetric supermode evolution completely eliminates the dependence of traditional directional couplers on strict phase matching and precise coupling length, further improving the device's fabrication tolerance and operating bandwidth. In addition to the width-gradient dual-waveguide asymmetric directional coupler, other devices capable of generating a 180° phase difference structure, such as curved directional couplers and 2×2 MMI+waveguide phase shifters, can also be used.

[0038] In this embodiment, the polarization rotating beam splitter further includes: a width-gradient tapered waveguide with its input end connected to the directional coupler and its output end connected to the output gradient. The waveguide adopts a ridge waveguide structure with a shallowly etched flat plate and its width is continuously and thermally gradient along the optical transmission direction to separate the two optical fields in physical space and to achieve thermal transition of the optical fields through the smooth gradient of the waveguide width.

[0039] The optical field output from the upper or lower side of the dual-waveguide asymmetric directional coupler then enters a tapered waveguide with a continuously tapered width. This tapered waveguide physically separates the two waveguides to avoid crosstalk while simultaneously enabling a smooth transition of the optical field through an adiabatic gradient in waveguide width. In other words, the tapered waveguide employs a ridge waveguide structure with a shallowly etched slab, and its width exhibits a continuous, adiabatic gradient along the optical transmission direction to physically separate the two optical fields and achieve an adiabatic transition of the optical field through a smooth gradient in waveguide width.

[0040] Then, the optical field is thermally narrowed by the output gradient through the shallow etched plate, converting the mode field into a single-mode TE0 output from the first and second output waveguides, that is, thermally converting the optical field into a single-mode TE0 optical signal.

[0041] Finally, the first and second output waveguides, which are connected to the output gradient, output the single-mode TEO optical signal of the corresponding output channel to the next-stage optical path.

[0042] The beneficial effects of this application are as follows: The polarization rotating beam splitter of this application includes an input waveguide, a polarization-dependent mode converter connected to the input waveguide, a multimode beam splitter connected to the polarization-dependent mode converter, a directional coupler connected to the multimode beam splitter, an output grader connected to the directional coupler, and a first output waveguide and a second output waveguide connected to the output grader; the input waveguide is used to input a broadband optical signal; wherein, the broadband optical signal includes a TEO mode optical signal and a TMO mode optical signal; the polarization-dependent mode converter is used to keep the TEO mode optical signal in the broadband optical signal unchanged based on the effective refractive index of the broadband optical signal, and to convert the TEO mode optical signal into a multimode beam splitter. In a broadband optical signal, the TM0 mode optical signal is adiabatically evolved into the TE1 mode optical signal; a multimode beam splitter is used to split the TE0 mode optical signal into two optical fields in an equal amplitude and in phase manner, and to split the TE1 mode optical signal into two optical fields in an equal amplitude and out-of-phase manner; a directional coupler is used to directionally couple the optical field corresponding to the TE0 mode to one output channel and the optical field corresponding to the TE1 mode to another output channel according to the phase difference between the two optical fields; an output taper is used to adiabatically convert the optical fields output by each output channel into single-mode TE0 mode optical signals; a first output waveguide and a second output waveguide are used to output the single-mode TE0 mode optical signals of the corresponding output channels, respectively.Therefore, this application uses an input waveguide to input broadband optical signals in either TE0 or TM0 mode. A polarization-dependent mode converter connected to the input waveguide maintains the TE0 mode optical signal unchanged based on the effective refractive index difference, while adiabatically evolving the TM0 mode optical signal into a TE1 mode optical signal, thus distinguishing between the two input polarization modes and avoiding mode interference. A multimode beamsplitter connected to the polarization-dependent mode converter splits the TE0 mode optical signal into two optical fields with equal amplitude and in phase, and the TE1 mode optical signal into two optical fields with equal amplitude and out of phase, forming a fixed and distinguishable phase difference characteristic, providing a clear basis for subsequent directional coupling. A directional coupler connected to the multimode beamsplitter couples the optical field corresponding to the TE0 mode to one output channel and the optical field corresponding to the TE1 mode to another output channel based on the phase difference between the two optical fields, completing the processing of different input polarization modes. The proposed polarization rotation beam splitter achieves spatial separation and directional output without relying on strict phase matching and specific coupling lengths, reducing sensitivity to wavelength changes and expanding the operating bandwidth. All the related devices mentioned above perform mode conversion / beam splitting / separation through adiabatic gradation, thus inherently possessing wavelength insensitivity and waveguide size robustness. Therefore, the proposed polarization rotation beam splitter features large bandwidth and large tolerance. The output grader connected to the directional coupler adiabatically converts the optical field of each output channel into a single-mode TE0 optical signal, unifying the output mode to the standard TE0 fundamental mode, reducing the complexity of back-end optical path processing. The signal is then output through the first and second output waveguides, achieving stable separation, rotation, and single-mode output of two orthogonal polarization states in the broadband optical signal. The overall structure is simple, with low transmission loss and low crosstalk, while also possessing a wider operating wavelength range and higher tolerance for process errors. This application introduces an architecture combining an odd-even symmetric supermode beam splitting mechanism with an active phase shifter, enabling the device to receive external control signals and dynamically change interference conditions under software control, thereby achieving efficient and real-time routing switching of polarized light. At the same time, the active phase shifter in the structure can act as a phase adjustment unit in the static working state to actively compensate for residual phase errors caused by waveguide size deviations, thereby improving the performance consistency and yield of the device in actual process fabrication.

[0043] Reference Figure 3 As shown, this embodiment of the invention discloses a specific polarization rotating beam splitter. Compared with the previous embodiment, this embodiment further explains and optimizes the technical solution. Specifically: The polarization rotating beam splitter further includes a connecting waveguide 108 whose input end is connected to the multimode beam splitter 103 and whose output end is connected to the directional coupler, for transmitting two optical fields to the directional coupler 104.

[0044] The connecting waveguide 103 includes: an upper phase shifter waveguide 1031 for transmitting one of the two optical fields to the directional coupler 104; and a lower phase shifter waveguide 1032 for transmitting the other of the two optical fields to the directional coupler 104.

[0045] The polarization rotating beam splitter further includes a phase shifter 109, whose input end is connected to the upper phase shifter waveguide 1031 and / or the lower phase shifter waveguide 1032 and whose output end is connected to the directional coupler 104. The phase shifter 109 is used to apply a first electrical signal to the optical field in the upper phase shifter waveguide 1031 and / or the lower phase shifter waveguide 1032 and flip the parity symmetry of the optical field to switch the output channels of the optical field corresponding to the TE0 mode and the optical field corresponding to the TE1 mode, or to apply a second electrical signal to the optical field in the upper phase shifter waveguide 1031 and / or the lower phase shifter waveguide 1032 and compensate for the phase of the optical field to eliminate the phase error of the optical field.

[0046] Furthermore, the polarization rotating beam splitter also includes a connecting waveguide, i.e., a phase shift arm, which connects the input end to the multimode beam splitter and the output end to the directional coupler. The TE0 mode optical signal and the TE1 mode optical signal of the multimode beam splitter are split into two optical fields and then enter the connecting waveguide.

[0047] The connecting waveguides include an upper phase-shifting waveguide and a lower phase-shifting waveguide, which together form the two arms of an interferometer. The upper phase-shifting waveguide transmits one of the two optical fields to the directional coupler, and the lower phase-shifting waveguide transmits the other of the two optical fields to the directional coupler.

[0048] In a specific active embodiment, the polarization rotating beam splitter further includes a phase shifter. The input end of the phase shifter is connected to the upper phase shift arm waveguide and / or the lower phase shift arm waveguide, and the input end is connected to a directional coupler. The phase shifter is integrated on at least one arm to receive external control signals, i.e., electrical signals, and to dynamically adjust the relative phase difference between the two arms.

[0049] The phase shifter can realize the routing switching function. Specifically, the phase shifter receives a first electrical signal and applies the first electrical signal to the optical field in the upper phase shift arm waveguide and / or the lower phase shift arm waveguide, and flips the parity symmetry of the optical field to switch the output channel of the optical field corresponding to the TE0 mode and the optical field corresponding to the TE1 mode. By applying a specific electrical signal, an additional 0 or pi phase difference is generated between the two arms, thereby flipping the parity symmetry of the optical field in the waveguide (such as changing the 0 phase difference to the pi phase difference, and vice versa), realizing the dynamic switching of the output port.

[0050] Phase shifters can achieve active error compensation. Specifically, the phase shifter receives a second electrical signal and applies it to the optical field in the upper and / or lower phase-shifting waveguides, compensating for the phase of the optical field to eliminate phase errors. In actual fabrication, due to process variations, static phase errors can easily occur in the two waveguide arms, leading to polarization crosstalk. In this case, a small compensation phase can be applied by the phase shifter to actively calibrate and eliminate these residual phase errors, greatly improving the device's manufacturing tolerance and actual wafer fabrication yield.

[0051] In this embodiment, the phase shifter is any one of the following: thermo-optical control type phase shifter, carrier depletion / injection type electro-optic phase shifter, electro-optic phase shifter based on electro-optic materials, phase change material type phase shifter, microelectromechanical system control type phase shifter, and all-optical control type phase shifter.

[0052] like Figure 4 (a1) top view and Figure 4 As shown in the cross-sectional view of (a2), the phase shifter in this embodiment is preferably a thermo-optical phase shifter. Its waveguide body still adopts a ridge waveguide, with a metal heating electrode deposited on the upper cladding (usually silicon dioxide). Joule heating is generated by applying a control voltage to the metal electrode, and the effective refractive index of the waveguide arm is changed by utilizing the large thermo-optic coefficient of silicon material, thereby achieving dynamic and continuous control of the relative phase difference between the upper and lower phase shift arms. Alternatively, the phase shifter can be replaced with an electro-optical phase shifter based on carrier dispersion effects (such as a PN junction) to achieve faster switching. Besides thermo-optical switching, the phase shifter can also use carrier depletion / injection type electro-optical phase shifters, electro-optical phase shifters based on electro-optical materials, phase change material phase shifters, microelectromechanical systems (MEMS) control, all-optical control, and any other switching method that can achieve this.

[0053] The following is based on Figure 5 Taking a specific active polarization rotating beamsplitter as an example, this application will be described accordingly. The polarization rotating beamsplitter includes an input waveguide 201, a polarization correlation mode converter 202, a multimode beamsplitter 203, an upper phase shifter waveguide 204, a lower phase shifter waveguide 205, a phase shifter 206, a dual-waveguide asymmetric directional coupler 207, a width-gradient tapered waveguide 208, an output tapered waveguide 209, and a first output waveguide 210 and a second output waveguide 211. The specific optical field transmission and evolution process is as follows: 1) Input and Mode Hybridization: A broadband optical signal containing dual polarization signals is input through the input waveguide. The optical signal then enters the polarization-dependent mode converter (PDM). According to the principle of mode evolution, when the input light is in TE0 mode, its effective refractive index does not satisfy the mode hybridization condition, and the optical field will continue to propagate in TE0 mode. When the input light is in TM0 mode, the mode hybridization condition is satisfied during the gradual transition, and the light will adiabatically evolve into TE1 mode.

[0054] 2) Odd-Even Symmetric Supermode Beam Splitting: The optical field processed by the polarization-dependent mode converter enters the multimode beam splitter. Specifically, if the input to the beam splitter is the TE0 mode, the optical field will be equally split into two beams, which will enter the upper and lower phase shifter waveguides respectively, and the optical fields in the two arms will remain in phase (i.e., the initial phase difference is 0). If the input is the hybridized TE1 mode (odd-symmetric mode), the optical field will also be equally split into the upper and lower phase shifter arms, but the optical fields in the two arms will be out of phase (i.e., the initial phase difference is pi).

[0055] 3) Phase modulation and error compensation: The upper and lower phase shifter waveguides form the two arms of an interferometer, with at least one arm ( Figure 5 The diagram shows a configuration with both arms, each integrated with a phase shifter. The phase shifter receives external control signals and dynamically adjusts the relative phase difference between the two arms. This phase shifter has two core functions: 3.1) Routing switching function: By applying a specific electrical signal, an additional 0 or pi phase difference is generated between the two arms, thereby reversing the parity symmetry of the optical field in the waveguide (such as converting the 0 phase difference into the pi phase difference, and vice versa), realizing the dynamic switching of the output port.

[0056] 3.2) Active error compensation function: In actual fabrication, due to process deviations, static phase errors are easily generated in the two-arm waveguide, leading to polarization crosstalk. At this time, a small compensation phase can be applied by a phase shifter to actively calibrate and eliminate these residual phase errors, which greatly improves the manufacturing tolerance of the device and the actual wafer yield.

[0057] 4) Mode Interference and Evolution: After phase modulation, the two optical signals converge into a dual-waveguide asymmetric directional coupler. This region utilizes the evolution principle of odd and even modes for wave combining interference. If the phase difference between the optical fields input to the combining region from the upper and lower arms is 0, according to the asymmetric evolution rule, the optical field will primarily evolve and converge to the upper channel of the coupler; if the phase difference between the optical fields input from the two arms is pi, the optical field will evolve and converge to the lower channel of the coupler.

[0058] 5) Mode Field Adaptation and Output Stage: The optical field output from the upper or lower side of the dual-waveguide asymmetric directional coupler then enters a tapered waveguide with a gradually tapered width. While physically separating the two waveguides to avoid crosstalk, the thermally tapered waveguide width ensures a smooth transition of the optical field. Finally, via an output tapered converter and thermally narrowed through a shallowly etched plate, the mode field is converted into a single-mode TE0 output from the first and second output waveguides.

[0059] The following is based on Figure 6 Taking a specific passive polarization rotation beamsplitter as an example, this application will be described accordingly. The passive structure mainly includes: an input waveguide 301, a polarization-dependent mode converter 302, a multimode beamsplitter 303, a connecting waveguide 304, a dual-waveguide asymmetric directional coupler 305, a tapered waveguide 306, an output tapered waveguide 307, a first output waveguide 308, and a second output waveguide 309. The regions containing the polarization-dependent mode converter, multimode beamsplitter, connecting waveguide, dual-waveguide asymmetric directional coupler, tapered waveguide, and output tapered waveguide all employ a ridged waveguide structure with shallowly etched flat plates. The specific optical field transmission and evolution process is as follows: 1) Input and Mode Hybridization: The TE0 or TM0 mode, containing a broadband optical signal, is injected into the input waveguide. When passing through a polarization-dependent mode converter with an asymmetric shallow-etched slab structure, the input optical field undergoes mode-dependent evolution: the effective refractive index of the TE0 mode does not satisfy the hybridization condition, and its mode state remains unchanged; while the TM0 mode satisfies the hybridization condition and adiabatically evolves into the TE1 mode.

[0060] 2) Odd-even mode beam splitting: The optical field then enters the multimode beam splitter. If the input is TE0 mode, the beam splitting is equal amplitude and in phase in both connecting waveguides, and the phase difference between the two branches is 0; if the input is TE1 mode (odd symmetry) evolved from hybridization, the beam splitting is equal amplitude and out of phase in both connecting waveguides, and the phase difference between the two branches is pi.

[0061] 3) Wideband Directional Sorting Based on Asymmetric Supermode Evolution: Two optical signals with a phase difference of 0 or pi directly enter a dual-waveguide asymmetric directional coupler. This coupler utilizes the principle of adiabatic supermode separation to route modes by setting an asymmetric width gradient structure for the two waveguides, thereby reducing sensitivity to wavelength changes. Specifically, two input optical fields with a phase difference of 0 excite an even-symmetric supermode in the coupling region. As the waveguide asymmetry evolves, the optical energy of this supermode undergoes adiabatic transfer, directionally localized to the wider channel of the coupler; two input optical fields with a phase difference of pi excite an odd-symmetric supermode, which is then directionally localized to the narrower channel of the coupler. This physical separation process based on effective refractive index evolution does not rely on strict phase matching at a specific wavelength, thus ensuring the device's beam splitting and rotation performance over a wide spectral range.

[0062] 4) Mode field adaptation and output: Finally, the separated optical fields are smoothly transitioned into standard TE0 optical fields that meet the single-mode transmission conditions through the width-gradient tapered waveguide and the output gradient, respectively, and output to the next-stage optical path from the first output waveguide and the second output waveguide.

[0063] like Figure 7 As shown, a detailed simulation verification and explanation of the working principle and ultra-wide bandwidth physical mechanism of the key front-end components of the polarization rotating beam splitter (i.e., the polarization-dependent mode converter and the multimode beam splitter) are presented. The figure visually illustrates the propagation trajectory and mode state of the light field as it sequentially passes through an adiabatic tapered waveguide with a shallowly etched plate and a three-waveguide adiabatic coupling structure.

[0064] 1) The evolution of the light field input in TE0 mode (e.g.) Figure 7 (a) shows that when the TE0 fundamental mode is input, since its effective refractive index does not satisfy the hybridization condition in the tapered waveguide region, the optical field maintains the TE0 mode and propagates adiabatically along the polarization-dependent mode converter 102 without mode hybridization. Subsequently, this even-symmetric mode enters the three-waveguide adiabatic coupling structure (multimode beam splitter). As the width of the middle main waveguide gradually narrows and the width of the two side branch waveguides gradually widens, the optical field energy is smoothly and adiabatically transferred to both sides. The two side branch waveguides eventually excite two modes with completely consistent field strength distributions. This proves that the TE0 mode is perfectly split into two and forms an even-symmetric supermode with equal amplitude and in-phase (i.e., phase difference of 0) in the two side waveguides.

[0065] 2) The evolution of the optical field input in TM0 mode (e.g.) Figure 7 (b) shows that when the TM0 fundamental mode is input, the shallowly etched plate at the bottom introduced by the polarization-dependent mode converter breaks the symmetry of the waveguide in the vertical direction. Combined with the adiabatic gradient of the waveguide core width, the TM0 mode satisfies the effective refractive index anti-crossing condition with the TE1 mode in a waveguide region of a specific width. The TM0 mode undergoes efficient broadband adiabatic hybridization in this region, smoothly evolving into an odd-symmetric higher-order TE1 mode. Subsequently, this odd-symmetric TE1 mode enters the three-waveguide adiabatic beamsplitter, and the optical energy is also adiabatically transferred to the two waveguides. The mode field distribution diagram of the output cross section (showing obvious positive and negative polarity contrast / bright and dark phase reversal characteristics) can intuitively confirm that an odd-symmetric supermode with equal amplitude and opposite phase (i.e., an intrinsic phase difference of pi) was successfully excited in the two branch waveguides.

[0066] like Figure 8 , 9As shown, the physical working mechanism of the core back-end component (dual-waveguide asymmetric directional coupler) of the polarization rotating beam splitter of this application and the technical principle for achieving ultra-large bandwidth are described in detail. This application completely abandons the strict phase interference mechanism of traditional interferometers, and instead uses a carefully designed asymmetric gradient waveguide to guide the supermode for adiabatic separation.

[0067] 1) The separation and evolution mechanism of the effective refractive index of the supermode (combined with...) Figure 8 This study reveals the physical evolution of the effective refractive index of even-symmetric supermode (solid line) and odd-symmetric supermode (dashed line) in a dual-waveguide asymmetric directional coupler as a function of the width difference between the two waveguides.

[0068] 1.1) Symmetric initial state: When the optical field just enters the coupling region, the widths of the upper and lower waveguides are basically the same (the difference in waveguide width is close to 0 nm), and the system is in a symmetrical state. At this time, the mode field energy of even mode and odd mode is uniformly distributed in the two waveguides.

[0069] 1.2) Asymmetric Adiabatic Evolution: Along the direction of optical signal transmission, the width difference between the upper and lower waveguides is designed to gradually increase smoothly and adiabatably (gradually increasing to 100 nm in the simulation example). As the symmetry is broken, the effective refractive index curves of the two supermodes separate significantly. For example... Figure 8 As shown in the upper-middle mode field inset, the optical energy of a even mode with a high effective refractive index is gradually "drawn" and completely localized into a wider waveguide as the width difference increases; for example... Figure 8 As shown in the lower center mode field inset, the optical energy of odd modes with lower effective refractive index gradually localizes to a narrower waveguide. This evolution curve objectively demonstrates that as long as the length of the asymmetric gradient structure satisfies the adiabatic condition, the optical energy transfer path is determined solely by the intrinsic symmetry (odd / even) of the mode, and no longer depends on the periodic coupling length for a specific wavelength. This mode evolution is wavelength insensitive and can achieve mode separation over a very large bandwidth. Furthermore, it has a very high tolerance for waveguide width; a specific width is not required, only a certain width difference between waveguides is needed.

[0070] 2) Actual propagation and directional gating trajectory of the light field (combined with...) Figure 9 This demonstrates the actual transmission trajectory and cross-sectional mode distribution of the light field in the asymmetric directional coupler under the guidance of the aforementioned physical mechanism.

[0071] 2.1) Even-symmetric supermode ( Figure 9(a) When the optical signal from the front interferometer arm is of equal amplitude and in phase (phase difference is 0), an even-symmetric supermode is excited in the coupling region. During propagation along the x-axis, the optical field energy of this even-symmetric supermode is smoothly and losslessly transferred to a region with a higher effective refractive index due to the asymmetric gradual change in waveguide width. As can be seen from the output cross-section on the right, the optical field is eventually completely localized and output from the wide waveguide port.

[0072] 2.2) Odd-symmetric supermode ( Figure 9 (b) When the optical signal from the front interferometer arm is of equal amplitude and out of phase (phase difference pi), an odd-symmetric supermode is excited in the coupling region. Similarly, during adiabatic transmission, the optical energy of this odd-symmetric supermode smoothly transfers to the region with a lower effective refractive index. As can be seen from the output cross-section on the right, the optical field is eventually completely localized and output from the narrow waveguide port.

[0073] Combination Figure 8 and Figure 9 The results show that the back-end combining and routing mechanism of this application is based on supermode adiabatic separation guided by asymmetric gradient of dual waveguide width. This mechanism mainly relies on the change of effective refractive index and mode evolution, rather than on coherent interference conditions at a specific wavelength. Therefore, this structure has low sensitivity to changes in the operating wavelength, which helps the device maintain a relatively stable operating state in the SL band. At the same time, the adiabatic evolution mechanism is less dependent on local etching size fluctuations, which improves the device's fabrication tolerance to some extent.

[0074] The following detailed simulation process illustrates this application. A specific embodiment of this application uses a silicon nanowire waveguide based on silicon insulator (SOI) material: its core layer is silicon material, with a waveguide thickness of 220 nm and a refractive index of 3.4744; the ridge waveguide plate has a thickness of 70 nm and a refractive index of 3.4744; and both its lower and upper cladding layers are made of SiO2, with a thickness of 2 μm and a refractive index of 1.444.

[0075] The input waveguide width satisfies the single-mode condition for both polarization fundamental modes.

[0076] The width range of the ridge waveguide for the polarization-dependent mode converter should span the mode hybridization widths of both TM0 and TE1 modes.

[0077] The multimode beam splitter should have a sufficiently wide center waveguide and sufficiently narrow side waveguides at the starting end, and a sufficiently narrow center waveguide and sufficiently wide side waveguides at the output end.

[0078] The S-bends of the upper and lower phase shifter waveguides should be able to separate the two arms of light to a sufficient distance to avoid crosstalk during modulation.

[0079] The phase shifter uses a thermo-optical phase shifter, which changes the refractive index of the waveguide by heating the electrodes, thereby changing the phase of the light.

[0080] The upper and lower waveguides of the dual-waveguide asymmetric directional coupler have the same width at the beginning, and as the light propagates, one arm gradually widens and the other arm gradually narrows, thus achieving adiabatic mode evolution.

[0081] The width-gradient tapered waveguide and output gradient need to have a sufficient width change rate to achieve the adiabatic evolution from the ridge waveguide mode to the strip waveguide mode.

[0082] The widths of the first and second output waveguides satisfy the single-mode condition for the TE0 polarization fundamental mode.

[0083] Simulation Result Analysis 1: Initial State When the Phase Shifter is Not Working ( Figure 10 )

[0084] When the phase shifter is in an inactive state (i.e., no external control signal is applied, and the additional phase difference between the upper and lower arms is 0), the broadband transmission spectrum and optical field evolution diagram of the device are as follows: Figure 10 As shown: For TE0 mode input: such as Figure 10 As shown in (a), in the wide band range of 1460nm to 1625nm, the input light is mainly emitted from output port 1 with extremely low insertion loss; while the crosstalk of output port 2 is below -20dB throughout the entire band. Figure 10 (c) clearly shows the physical process of the TE0 mode being in phase split in a multimode beam splitter, then undergoing adiabatic evolution in a dual-waveguide asymmetric directional coupler and smoothly converging to output port 1.

[0085] For TM0 mode input: such as Figure 10 As shown in (b), within the same wide band of 1460nm to 1625nm, after mode hybridization and odd-even beam splitting, the optical field is directionally evolved to be emitted from output port 2 with extremely low insertion loss, and the polarization crosstalk of output port 1 is maintained below -20dB. Figure 10 (d) The optical field transmission diagram visually shows the complete trajectory of TM0 being converted into TE1, splitting into antiphase beams, and finally converging at output port 2.

[0086] Simulation Result Analysis 2: Switching State During Phase Shifter Operation ( Figure 11 )

[0087] When the phase shifter is in operation (e.g., a control signal is applied to one arm, causing a relative phase difference of pi between the upper and lower arms), the broadband transmission spectrum and optical field evolution diagram of the device are as follows: Figure 11 As shown: For TE0 mode input: such as Figure 11As shown in (a), after introducing the pi phase difference, the interference condition is reversed. Within the 1460nm to 1625nm wavelength band, the light field is perfectly switched to output port 2, and crosstalk at output port 1 is effectively suppressed to below -20dB across the entire wavelength band. (Compare the light field transmission...) Figure 11 (c) It can be seen that the optical path has been successfully reconstructed.

[0088] For TM0 mode input: such as Figure 11 As shown in (b), similarly, the change in interference conditions causes the output port of the TM0 mode to flip, and the optical field is switched to be emitted from output port 1 in a wide band. The crosstalk of output port 2 is also maintained below -20dB. Figure 11 The optical field transmission diagram in (d) further verifies the smoothness and efficiency of the switching process.

[0089] The polarization rotation beam splitter of this application can be implemented not only on a silicon platform, but also on existing integrated platforms such as silicon nitride, indium phosphide, lithium niobate, and lithium tantalate, including the active and passive solutions mentioned above. A schematic diagram of the electro-optical switching structure based on lithium niobate and lithium tantalate is shown below. Figure 12 As shown, the polarization rotating beam splitter includes an input waveguide 401, a polarization correlation mode converter 402, a multimode beam splitter 403, an upper phase shifter waveguide 404, a lower phase shifter waveguide 405, a phase shifter 406, a dual-waveguide asymmetric directional coupler 407, a width-gradient tapered waveguide 408, an output tapered waveguide 409, a first output waveguide 410, and a second output waveguide 411.

[0090] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0091] The above provides a detailed description of a polarization rotating beam splitter provided by the present invention. Specific examples have been used to illustrate the principle and implementation of the present invention. The description of the above embodiments is only intended to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation and application scope based on the idea of ​​the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A polarization rotating beam splitter, characterized in that, include: An input waveguide is used to input broadband optical signals; wherein, the broadband optical signals include TEO mode optical signals and TMO mode optical signals; A polarization-dependent mode converter connected to the input waveguide is used to keep the TE0 mode optical signal in the broadband optical signal unchanged based on the effective refractive index of the broadband optical signal, and to adiabatically evolve the TM0 mode optical signal in the broadband optical signal into the TE1 mode optical signal. The multimode beam splitter connected to the polarization-dependent mode converter is used to split the TE0 mode optical signal into two optical fields in an equal amplitude and in phase manner, and to split the TE1 mode optical signal into two optical fields in an equal amplitude and out-of-phase manner. The directional coupler connected to the multimode beam splitter is used to directionally couple the optical field corresponding to the TE0 mode to one output channel and the optical field corresponding to the TE1 mode to another output channel according to the phase difference between the two optical fields. The output gradient connected to the directional coupler is used to thermally convert the optical field output by each output channel into a single-mode TEO mode optical signal. The first and second output waveguides, which are connected to the output gradient, are used to output single-mode TEO optical signals for the corresponding output channels, respectively.

2. The polarization rotating beam splitter according to claim 1, characterized in that, The polarization rotating beam splitter further includes: A connecting waveguide, whose input end is connected to the multimode beam splitter and whose output end is connected to the directional coupler, is used to transmit two optical fields to the directional coupler.

3. The polarization rotating beam splitter according to claim 2, characterized in that, The connecting waveguide includes: The upper phase shifter waveguide is used to transmit one of the two optical fields to the directional coupler. The lower phase shifter waveguide is used to transmit the other optical field of the two optical fields to the directional coupler.

4. The polarization rotating beam splitter according to claim 3, characterized in that, The polarization rotating beam splitter further includes: The phase shifter, whose input end is connected to the upper phase shifter waveguide and / or the lower phase shifter waveguide and whose output end is connected to the directional coupler, is used to apply a first electrical signal to the optical field in the upper phase shifter waveguide and / or the lower phase shifter waveguide and to flip the parity symmetry of the optical field to switch the output channel of the optical field corresponding to the TE0 mode and the optical field corresponding to the TE1 mode, or to apply a second electrical signal to the optical field in the upper phase shifter waveguide and / or the lower phase shifter waveguide and to compensate for the phase of the optical field to eliminate the phase error of the optical field.

5. The polarization rotating beam splitter according to claim 4, characterized in that, The phase shifter is any one of the following: thermo-optical control type phase shifter, carrier depletion / injection type electro-optic phase shifter, electro-optic phase shifter based on electro-optic materials, phase change material type phase shifter, microelectromechanical system control type phase shifter, and all-optical control type phase shifter.

6. The polarization rotating beam splitter according to claim 1, characterized in that, The mode hybrid structure of the polarization-dependent mode converter can be any one of the following: an adiabatic graded ridge waveguide structure with a shallowly etched plate, an air cladding structure, a waveguide tilting structure, or a subwavelength grating structure.

7. The polarization rotating beam splitter according to claim 1, characterized in that, The waveguide of the multimode beam splitter is an adiabatic graded ridge waveguide with a shallowly etched plate. The structure of the multimode beam splitter is any one of a three-waveguide adiabatic coupling structure, a Y-branch coupling structure, or a 1×2 multimode interference coupling structure. The three-waveguide adiabatic coupling structure includes a central main waveguide and branch waveguides symmetrically distributed on both sides of the main waveguide. The width of the main waveguide gradually narrows and the width of the branch waveguides gradually widens along the optical transmission direction.

8. The polarization rotating beam splitter according to claim 1, characterized in that, The waveguide of the directional coupler is an adiabatic tapered ridge waveguide with a shallowly etched plate. The type of the directional coupler is any one of the following: a width-tapered dual-waveguide asymmetric adiabatic coupler, a bent directional coupler, or a combination of a 2×2 multimode interference coupler and a waveguide phase shifter.

9. The polarization rotating beam splitter according to claim 8, characterized in that, The width-gradient dual-waveguide asymmetric thermally adiabatic coupler includes a first ridge waveguide and a second ridge waveguide arranged along the optical transmission direction. The initial widths of the first ridge waveguide and the second ridge waveguide are equal. Along the optical transmission direction, the width of the first ridge waveguide gradually widens and the width of the second ridge waveguide gradually narrows, forming an asymmetric thermal evolution structure. This structure is used to form an even-symmetric supermode by interfering optical fields with a phase difference of 0 and converging it to the output channel corresponding to the first ridge waveguide, and to form an odd-symmetric supermode by interfering optical fields with a phase difference of π and converging it to the output channel corresponding to the second ridge waveguide.

10. The polarization rotating beam splitter according to claim 1, characterized in that, The polarization rotating beam splitter further includes: The width-gradient tapered waveguide, whose input end is connected to the directional coupler and whose output end is connected to the output gradient, adopts a ridge waveguide structure with a shallowly etched plate and has a continuous thermally adiabatic gradient in width along the optical transmission direction, so as to separate the two optical fields in physical space and perform thermally adiabatic transition of the optical fields through the smooth gradient of the waveguide width.

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