A compact polarization rotating beam splitter

Abstract

The present application relates to a compact polarization rotation beam splitter, comprising an input waveguide, a mode conversion region, a mode coupling region, and an output waveguide; the mode conversion region converts the TM0 mode optical signal in the optical signal into a TE mode high-order optical signal; the mode coupling region is used to couple the TE mode high-order optical signal with the first adiabatic coupling waveguide to a TE0 mode optical signal; the output waveguide is used to output the TE0 mode optical signal in the optical signal that has not undergone mode conversion, and to output the TE0 mode optical signal obtained after mode conversion through the mode conversion region and the second adiabatic coupling waveguide. Through the present application, the polarization rotation path can be shortened by high-order mode conversion in the mode conversion region, efficient beam splitting can be achieved by utilizing the asymmetric adiabatic coupling waveguide in the mode coupling region, and redundant structures can be avoided by functional integration to reduce size, thereby ensuring the performance of the beam splitter and solving the problems of large size and poor performance of current polarization rotation beam splitters.

Description

Technical Field

[0001] The present application relates to the technical field of integrated optical devices, and in particular to a compact polarization rotation beam splitter. Background Art

[0002] Optical communication technology, a key pillar of modern communications, has undergone a dramatic transformation from early simple communication systems to today's high-speed, high-capacity, long-distance transmission systems. The core of optical communication systems lies in the transmission and processing of optical signals, and the polarization state of optical signals, as one of their key characteristics, has a significant impact on signal transmission quality. Polarization rotation beam splitters, as key components for polarization control, can effectively separate and convert the polarization state of optical signals, thereby improving signal transmission quality and system performance. They can also be integrated with other optical devices to construct complex photonic integrated circuits, meeting the application requirements of optical communication systems in various scenarios.

[0003] Currently, there are two main technical principles for polarization rotation beam splitters: one based on mode coupling and the other on mode evolution. While the mode coupling mechanism offers a simple structure, it is limited by strict phase matching requirements, making it difficult to achieve wide bandwidth and high tolerance performance. While the mode evolution mechanism can achieve efficient polarization rotation, its long device size and complex structural design increase manufacturing difficulty and cost. Therefore, miniaturization while maintaining high performance is a key direction for the future development of polarization rotation beam splitter technology.

[0004] Currently, no effective solution has been proposed to address the problems of large size and poor performance of polarization rotation beam splitters in related technologies. Summary of the Invention

[0005] Based on this, it is necessary to provide a compact polarization rotation beam splitter that can maintain high performance while achieving miniaturization to address the above technical problems.

[0006] In a first aspect, this embodiment provides a compact polarization rotation beam splitter, comprising:

[0007] An input waveguide, used for inputting an optical signal;

[0008] a mode conversion region connected to the input waveguide, configured to convert a TM0 mode optical signal in the optical signal into a TE mode high-order optical signal;

[0009] a mode coupling region, comprising a first adiabatic coupling waveguide and a second adiabatic coupling waveguide asymmetrically arranged; the first adiabatic coupling waveguide being connected to the mode conversion region and configured to transmit a TE0 mode optical signal that has not undergone mode conversion in the optical signal; and the second adiabatic coupling waveguide being configured to couple the TE mode high-order optical signal to the TE0 mode optical signal with the first adiabatic coupling waveguide.

[0010] output waveguides, including a first output waveguide and a second output waveguide;

[0011] The first output waveguide is connected to the first adiabatic coupling waveguide and is used to output the TE0 mode optical signal in which no mode conversion occurs in the optical signal;

[0012] The second output waveguide is connected to the second adiabatic coupling waveguide, and is used to output the TE0 mode optical signal obtained after mode conversion through the mode conversion region and the second adiabatic coupling waveguide.

[0013] In some embodiments, the mode conversion region includes a first tapered waveguide, a first ridge waveguide, a second ridge waveguide, and a second tapered waveguide connected in sequence; the mode conversion region has axisymmetry;

[0014] The width of the first tapered waveguide increases from small to large, and the effective refractive index of the TE1 mode is less than or equal to the effective refractive index of the TM0 mode;

[0015] The width of the second tapered waveguide is reduced from large to small, and the effective refractive index of the TM0 mode is less than or equal to the effective refractive index of the TE1 mode;

[0016] The first ridge waveguide and the second ridge waveguide are used to convert a TM0 mode optical signal in the optical signal into a TE mode high-order optical signal.

[0017] In some embodiments, the first ridge waveguide and the second ridge waveguide are composed of two layers of waveguide materials with different etching depths, with a middle area being a fully etched area and two sides being shallowly etched areas.

[0018] In some embodiments, the width of the first adiabatic coupling waveguide decreases from large, the width of the second adiabatic coupling waveguide increases from small, and adjacent sides of the first adiabatic coupling waveguide and the second adiabatic coupling waveguide remain parallel and have a fixed spacing.

[0019] In some embodiments, the widths of the first adiabatic coupling waveguide and the second adiabatic coupling waveguide vary according to an exponential function.

[0020] In some embodiments, the mode conversion region further includes an arc-shaped curved waveguide disposed on a side of the second tapered waveguide; the arc-shaped curved waveguide is connected before the first adiabatic coupling waveguide.

[0021] In some embodiments, the second output waveguide is curved.

[0022] In some embodiments, the output end widths of the first output waveguide and the second output waveguide are the same as the input end width of the input waveguide.

[0023] In some embodiments, the width of the tapered waveguide in the compact polarization-rotating beam splitter varies according to an exponential function, a parabolic function, or a linear function.

[0024] In some embodiments, the material of the compact polarization rotating beam splitter is silicon-based.

[0025] Compared with the related art, a compact polarization rotation beam splitter provided in this embodiment includes an input waveguide for inputting an optical signal; a mode conversion region connected to the input waveguide, for converting a TM0 mode optical signal in the optical signal into a TE mode high-order optical signal; a mode coupling region, including an asymmetrically arranged first adiabatic coupling waveguide and a second adiabatic coupling waveguide; the first adiabatic coupling waveguide is connected to the mode conversion region, for transmitting a TE0 mode optical signal in the optical signal that has not undergone mode conversion, and the second adiabatic coupling waveguide is used to couple the TE mode high-order optical signal into a TE0 mode optical signal with the first adiabatic coupling waveguide; an output waveguide, including a first output waveguide and a second output waveguide; the first output waveguide is connected to the first adiabatic coupling waveguide, for outputting a TE0 mode optical signal in the optical signal that has not undergone mode conversion; and the second output waveguide is connected to the second adiabatic coupling waveguide, for outputting a TE0 mode optical signal obtained after mode conversion through the mode conversion region and the second adiabatic coupling waveguide. Through this embodiment, the polarization rotation path can be shortened by high-order mode conversion in the mode conversion region, efficient beam splitting can be achieved by utilizing the asymmetric adiabatic coupling waveguide in the mode coupling region, and the size can be reduced by avoiding redundant structures through functional integration, thereby ensuring the performance of the beam splitter and solving the problems of large size and poor performance of current polarization rotation beam splitters.

[0026] The details of one or more embodiments of the present application are set forth in the following drawings and description to make other features, objects, and advantages of the present application more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0028] Figure 1 is a schematic top view of a compact polarization rotating beam splitter according to an embodiment;

[0029] Figure 2 is a schematic diagram of the overall structure of a compact polarization rotation beam splitter in an embodiment;

[0030] Figure 3 FIG. 1 is a schematic diagram of a waveguide shape in a mode coupling region using modulations of different indexes m in an embodiment;

[0031] Figure 4 is a schematic diagram of the change in conversion efficiency of the mode coupling region under different modulation indices m in an embodiment;

[0032] Figure 5 is a light field distribution diagram when the polarization of the input optical signal is TM0 in an embodiment;

[0033] Figure 6 is a light field distribution diagram when the polarization of the input optical signal is TE0 in an embodiment;

[0034] Figure 7 spectral response curves of different wavelengths when the polarization of the input light is TM0 in one embodiment;

[0035] Figure 8 spectral response curves of different wavelengths when the polarization of the input light is TE0 in one embodiment.

[0036] In the figure: 1. Input waveguide; 2. Mode conversion region; 21. First tapered waveguide; 22. First ridge waveguide; 23. Second ridge waveguide; 24. Second tapered waveguide; 25. Arc-shaped curved waveguide; 3. Mode coupling region; 31. First adiabatic coupling waveguide; 32. Second adiabatic coupling waveguide; 4. Output waveguide; 41. First output waveguide; 42. Second output waveguide. DETAILED DESCRIPTION

[0037] In order to more clearly understand the purpose, technical solutions and advantages of the present application, the present application is described and illustrated below in conjunction with the accompanying drawings and embodiments.

[0038] Unless otherwise defined, technical or scientific terms used in this application shall have the ordinary meanings as understood by persons of ordinary skill in the art to which this application belongs. The terms "a," "an," "the," "these," and similar expressions in this application do not denote limitations on quantity and may be singular or plural. The terms "comprise," "include," "have," and any variations thereof, as used in this application, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or device comprising a series of steps or modules (units) is not limited to the listed steps or modules (units) but may include unlisted steps or modules (units) or other steps or modules (units) inherent to the process, method, product, or device. The terms "connected," "connected," "coupled," and similar expressions used in this application are not limited to physical or mechanical connections but may include electrical connections, whether direct or indirect. As used in this application, "plurality" means two or more. "And / or" describes an association between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone; A and B exist simultaneously; or B exists alone. Generally, the character " / " indicates that the objects in the preceding and following relationship are in an "or" relationship. The terms "first", "second", "third", etc. involved in this application are only used to distinguish similar objects and do not represent a specific ordering of the objects.

[0039] In this embodiment, a compact polarization rotating beam splitter is provided. Figure 1 FIG. 1 is a top view schematic diagram of the compact polarization rotation beam splitter in this embodiment. Figure 1 As shown, the compact polarization rotating beam splitter includes:

[0040] Input waveguide 1, used for inputting optical signals;

[0041] Mode conversion region 2, connected to the input waveguide, for converting the TM0 mode optical signal in the optical signal into a TE mode high-order optical signal;

[0042] The mode coupling region 3 includes an asymmetrically arranged first adiabatic coupling waveguide 31 and a second adiabatic coupling waveguide 32; the first adiabatic coupling waveguide 31 is connected to the mode conversion region 2 and is used to transmit the TE0 mode optical signal that has not undergone mode conversion in the optical signal, and the second adiabatic coupling waveguide 32 is used to couple the TE mode high-order optical signal to the TE0 mode optical signal with the first adiabatic coupling waveguide 31;

[0043] Output waveguide 4, including a first output waveguide 41 and a second output waveguide 42;

[0044] The first output waveguide 41 is connected to the first adiabatic coupling waveguide 31 and is used to output the TE0 mode optical signal in which no mode conversion has occurred in the optical signal; the second output waveguide 42 is connected to the second adiabatic coupling waveguide 32 and is used to output the TE0 mode optical signal obtained after mode conversion through the mode conversion region 2 and the second adiabatic coupling waveguide 32.

[0045] Specifically, the input waveguide 1, the mode conversion region 2, the mode coupling region 3 and the output waveguide 4 in the compact polarization rotation beam splitter are connected end to end in sequence, and the widths of the connections are the same.

[0046] Input waveguide 1 is used to input optical signals, guiding them from an external source (such as a laser or optical fiber) to the internal processing area of ​​the beam splitter (such as mode conversion region 2). It supports both the TE0 (transverse electric) and TM0 (transverse magnetic) modes, where 0 and 1 represent the mode order. This ensures that the different polarization states (TE / TM) of the input optical signal can be correctly processed by subsequent modules. Consequently, the optical signal can include both TE0 and TM0 mode signals.

[0047] Mode conversion region 2 is connected to input waveguide 1 and includes a ridge waveguide and a tapered waveguide. The design of these two waveguides allows for gradual width variation in the waveguides to control the optical field distribution and constrain the effective refractive index of the modes, avoiding mode competition. This conversion targets only the TM0 mode optical signal, gradually rotating the TM0 mode's electric field direction from transverse (TM) to longitudinal (TE), generating a TE mode high-order optical signal. If the TE0 mode optical signal exists in the optical signal, the TE0 mode's electric field distribution is aligned with the waveguide geometry, eliminating the need for conversion and maintaining the TE0 mode signal within the optical signal.

[0048] The mode coupling region 3 includes an asymmetrically arranged first adiabatic coupling waveguide 31 and a second adiabatic coupling waveguide 32, which are used to achieve mode conversion and separation of the input optical signal. The first adiabatic coupling waveguide 31 is connected to the mode conversion region 2, and the second adiabatic coupling waveguide 32 is arranged to the side of the first adiabatic coupling waveguide 31 and parallel to the first adiabatic coupling waveguide 31. The widths of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 gradually change according to a specific function, guiding the TE mode high-order optical signal (e.g., TE1) to gradually evolve into the TE0 mode. Through the mode coupling effect of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32, the TE0 mode optical signal is coupled and transferred to the second adiabatic coupling waveguide 32. If a TE0 mode optical signal exists in the input optical signal, the TE0 mode optical signal that has not undergone mode conversion continues to propagate in the first adiabatic coupling waveguide 31.

[0049] The output waveguide 4 includes a first output waveguide 41 and a second output waveguide 42. The first output waveguide 41 is connected to the first adiabatic coupling waveguide 31 and is used to output the TE0 mode optical signal in the optical signal that has not undergone mode conversion. The TM0 mode optical signal in the input optical signal is converted into a TE mode high-order optical signal through the mode conversion region 2, and then mode-converted into a TE0 mode optical signal by the second adiabatic coupling waveguide 32. The second output waveguide 42 is connected to the second adiabatic coupling waveguide 32 and is used to output the TE0 mode optical signal obtained after mode conversion through the mode conversion region 2 and the second adiabatic coupling waveguide 32. Furthermore, to avoid mode crosstalk caused by close distance, the spacing between the first output waveguide 41 and the second output waveguide 42 can be increased. Specifically, an arc-shaped curved waveguide can be designed at the junction of the output waveguide 4 and the mode coupling region 3 to achieve connection.

[0050] Figure 2 FIG. 1 is a schematic diagram of the overall structure of the compact polarization rotation beam splitter in this embodiment. Figure 2 As shown in the figure, port a is the optical signal input port, and ports b and c are the output ports. For the input TE0 mode optical signal, it is directly output to port b without conversion. For the input TM0 mode optical signal, after two stages of conversion (TM0 → TE1 → TE0), it is output from port c, completing the polarization rotation and beam splitting of the optical signal.

[0051] Through the above steps, the TM0 mode optical signal in the input optical signal is converted into a TE mode high-order optical signal in the mode conversion region. In the mode coupling region, asymmetrically arranged adiabatic coupling waveguides are used to convert the TE mode high-order optical signal while suppressing coupling to other modes (e.g., TE0), thereby improving the output polarization purity. The mode conversion region and the mode coupling region are closely connected in space, enabling parallel processing of polarization rotation and mode separation, thereby reducing the size of the beam splitter and resolving the issues of large size and poor performance of current polarization rotation beam splitters. The beam splitter in this embodiment boasts excellent performance, including a compact design, wide bandwidth, low insertion loss, and a high extinction ratio, making it widely applicable to the fields of optical communications and optical sensing.

[0052] In some of these embodiments, Figure 1 As shown, the mode conversion region 2 includes a first tapered waveguide 21, a first ridge waveguide 22, a second ridge waveguide 23, and a second tapered waveguide 24 connected in sequence; the mode conversion region 2 has axisymmetry;

[0053] Among them, the width of the first tapered waveguide 21 increases from small to large, and makes the effective refractive index of the TE1 mode less than or equal to the effective refractive index of the TM0 mode; the width of the second tapered waveguide 24 decreases from large to large, and makes the effective refractive index of the TM0 mode less than or equal to the effective refractive index of the TE1 mode; the first ridge waveguide 22 and the second ridge waveguide 23 are used to convert the TM0 mode optical signal in the optical signal into a TE mode high-order optical signal.

[0054] Specifically, the first tapered waveguide 21, first ridge waveguide 22, second ridge waveguide 23, and second tapered waveguide 24 in the mode conversion region 2 are connected end to end. The mode conversion region 2 is axially symmetrical and shares the same axis as the input waveguide 1. Each waveguide has a width ranging from 200 nanometers to 2 microns and a length of less than 100 microns.

[0055] The width of the first tapered waveguide 21 gradually expands from the initial width of the input waveguide, which can preliminarily adjust the expanded waveguide width so that the light field distribution adapts to the subsequent ridge waveguide etching structure. At the same time, during the width gradient process, it ensures that the effective refractive index of the TE1 mode does not exceed the effective refractive index of the TM0 mode to avoid mode competition.

[0056] The first ridge waveguide 22 and the second ridge waveguide 23 are composed of two layers of waveguide material etched to different depths. The center region is fully etched, and the two sides are shallowly etched. By adjusting the ridge width and the width and length of the shallowly etched region, the effective refractive index distribution of the mode is precisely controlled. The etching differences lead to an asymmetric equivalent refractive index distribution in the waveguide, forcing the transverse electric field of the TM0 mode to gradually and completely rotate into the longitudinal electric field of the TE1 mode.

[0057] The waveguide width of the second tapered waveguide 24 gradually decreases from large to small, further regulating the effective refractive index of the mode. By constraining the effective refractive index of the TM0 mode to not exceed that of the TE1 mode, the unidirectional conversion is ensured and reverse mode interference is prevented. At the same time, the waveguide width is reduced to re-centralize the light field, providing an adaptive light field distribution for the subsequent connection of the arc-shaped curved waveguide 25.

[0058] Through the cascade design of the tapered waveguide and ridge waveguide in this embodiment, light field control, polarization rotation, and mode stabilization are completed in stages, ultimately achieving efficient conversion of TM0 mode optical signals to TE mode high-order optical signals. The tapered waveguide's gradual design achieves effective refractive index control with a small physical length. The etching differences of the ridge waveguide are directly integrated into the waveguide body, eliminating the need for additional complex structures and making the overall layout highly compact.

[0059] In some of these embodiments, Figure 1 As shown, the mode conversion region 2 further includes an arc-shaped curved waveguide 25 arranged on the side of the second tapered waveguide 24 ; the arc-shaped curved waveguide 25 is connected before the first adiabatic coupling waveguide 31 .

[0060] Specifically, the arc-shaped curved waveguide 25 is connected before the first adiabatic coupling waveguide 31, and the distance between the arc-shaped curved waveguide 25 and the second tapered waveguide 24 in the transmission direction gradually decreases, which can reduce the insertion loss caused by the introduction of the first adiabatic coupling waveguide 31, optimize the optical signal transmission path, reduce the loss and ensure the mode stability.

[0061] In some of these embodiments, Figure 1 As shown, the width of the first adiabatic coupling waveguide 31 decreases from large to large, and the width of the second adiabatic coupling waveguide 32 increases from small to large, and the adjacent sides of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 remain parallel and the spacing is fixed.

[0062] Furthermore, the widths of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 vary in an exponential function.

[0063] Specifically, the waveguide width of the first adiabatic coupling waveguide 31 gradually decreases from the input end to the output end, guiding the slow evolution of the light field of the high-order TE mode and providing the initial conditions for subsequent mode reduction. The waveguide width of the second adiabatic coupling waveguide 32 gradually increases from the input end to the output end, forming a complementary gradient with the first adiabatic coupling waveguide. Through the adiabatic coupling effect, the energy of the high-order TE mode is gradually transferred to the low-order TE0 mode and guided to the output port.

[0064] The widths of the first and second adiabatic coupling waveguides 31, 32 vary exponentially, ensuring that the adiabatic condition (slow variation) is met. Specifically, the adjacent sides of the first and second adiabatic coupling waveguides 31, 32 are parallel and spaced a fixed distance apart, ensuring a controllable and stable mode coupling process. The other sides of the first and second adiabatic coupling waveguides 31, 32 also vary exponentially, with their widths tapering in opposite directions. The optical field energy of the high-order TE mode gradually transfers from the first adiabatic coupling waveguide 31 to the second adiabatic coupling waveguide 32, evolving into a low-order TE mode. During the waveguide width gradient, the effective refractive index is manipulated, ensuring that the phase matching condition between the high-order TE mode and the TE0 mode is gradually met, achieving efficient energy transfer.

[0065] The spacing between the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 is generally in the range of 90 nm to 300 nm. The larger the spacing, the longer the waveguide. At a suitable spacing, the waveguide width changes in an exponential function, which can shorten the waveguide length while ensuring the waveguide conversion efficiency, and the beam splitter structure is more compact.

[0066] Figure 3 Schematic diagram of the waveguide shape in the mode coupling region using different index m modulation in this embodiment, as shown in FIG. Figure 3As shown in the figure, from top to bottom are schematic diagrams of the first adiabatic coupled waveguide and the second adiabatic coupled waveguide in the mode coupling region when the index m is 1, 4, and 8 respectively. It can be seen that when m=1, the change in the outer width of the waveguide is close to a linear change. The larger the m is, the more rapid the initial width change of the first adiabatic coupled waveguide and the ending width change of the second adiabatic coupled waveguide are.

[0067] Figure 4 Schematic diagram of the conversion efficiency change of the mode coupling region under different index m modulation in this embodiment, as shown in FIG. Figure 4 As shown, FDTD simulation software was used to simulate the conversion efficiency of the TE1 mode to the TE0 mode in the mode coupling region at different exponents m. The abscissa represents the coupling length (mode coupling region length), and the ordinate represents the coupling efficiency. Under a suitable linear configuration, m = 4 achieves the shortest coupling length for the same mode conversion efficiency. Under this linear configuration, when the waveguide spacing is 150 nanometers, a length of only 55 microns is required to achieve a mode conversion efficiency exceeding 99%. Compared to the existing bi-tapered adiabatic coupling structure, the waveguide length in the mode coupling region of this embodiment is significantly shortened.

[0068] In this embodiment, by keeping the adjacent sides of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 parallel and at a fixed distance, and by varying the width in an exponential function, the waveguide length can be shortened while ensuring the waveguide conversion efficiency, and the beam splitter structure can be made more compact.

[0069] In some embodiments, the second output waveguide 42 is curved.

[0070] Specifically, in order to ensure that coupling does not occur between the first output waveguide 41 and the second output waveguide 42 during output, the distance between the first output waveguide 41 and the second output waveguide 42 can be increased. Specifically, the first output waveguide 41 can be designed as a tapered waveguide or a straight waveguide, and the second output waveguide 42 can be designed as a curved shape, and the distance between the first output waveguide 41 and the second output waveguide 42 in the transmission direction gradually increases. Figure 1 As shown, the first output waveguide 41 and the second output waveguide 42 can also be designed as a multi-section structure, such as the first output waveguide 41 is composed of two sections of tapered waveguides or straight waveguides, and the second output waveguide 42 is composed of an S-shaped waveguide and a tapered waveguide or straight waveguide.

[0071] Furthermore, the output end widths of the first output waveguide 41 and the second output waveguide 42 are the same as the input end width of the input waveguide 1. On the one hand, this can ensure the symmetry of the two output optical signals and maintain the consistency of the extinction ratio of the two outputs. On the other hand, it can optimize the manufacturing process of the beam splitter, improve the compatibility in the optical communication system, and avoid redundant structure.

[0072] In some embodiments, the width of the tapered waveguide in the compact polarization-rotating beam splitter varies according to an exponential function, a parabolic function, or a linear function.

[0073] Specifically, the width variation functions of the tapered waveguides such as the input waveguide, the first tapered waveguide, the second tapered waveguide, and the first output waveguide in the above embodiments include but are not limited to exponential functions, parabolic functions, linear functions, etc.

[0074] In some embodiments, the material of the compact polarization-rotating beam splitter is silicon-based.

[0075] Specifically, the compact polarization rotation beam splitter in this embodiment is a silicon-based beam splitter, in which the core layers of waveguides such as the input waveguide, mode conversion region, mode coupling region, and output waveguide are generally composed of silicon (Si) material, which can be prepared by standard semiconductor processes (such as photolithography and etching) and is suitable for large-scale integration. At the same time, the high refractive index of silicon allows the waveguide size to be miniaturized (submicron level), realizing compact device design.

[0076] The present embodiment is described and illustrated below through preferred embodiments.

[0077] The compact polarization rotating beam splitter in this embodiment is as follows Figure 1 and Figure 2 As shown in the figure, the input optical signal is input through input port a and output through ports b and c, respectively, depending on the polarization state of the input optical signal. When the input optical signal mode is TE0 mode, the light is output through port b, and when the input optical signal mode is TM0 mode, the light is output through port c.

[0078] The beam splitter comprises an input waveguide 1, a mode conversion region 2, a mode coupling region 3 and an output waveguide 4 which are connected end to end in sequence, and the widths of the connection parts are the same.

[0079] Input waveguide 1 is used to input optical signals, guiding them from an external source (such as a laser or optical fiber) to the internal processing area of ​​the beam splitter (such as mode conversion region 2). It supports both the TE0 (transverse electric) and TM0 (transverse magnetic) modes, where 0 and 1 represent the mode order. This ensures that the different polarization states (TE / TM) of the input optical signal can be correctly processed by subsequent modules. Consequently, the optical signal can include both TE0 and TM0 mode signals.

[0080] In mode conversion region 2, the first tapered waveguide 21, first ridge waveguide 22, second ridge waveguide 23, and second tapered waveguide 24 are sequentially connected end to end. Mode conversion region 2 is axially symmetrical and shares the same axis as input waveguide 1. The width of the first tapered waveguide 21 gradually increases from the initial width of the input waveguide, enabling preliminary adjustment and expansion of the waveguide width to adapt the optical field distribution to the subsequent ridge waveguide etch structure. Furthermore, during this gradual width change, the effective refractive index of the TE1 mode does not exceed that of the TM0 mode, thus preventing mode competition.

[0081] The first ridge waveguide 22 and the second ridge waveguide 23 are composed of two layers of waveguide material etched to different depths. The center region is fully etched, and the two sides are shallowly etched. By adjusting the ridge width and the width and length of the shallowly etched region, the effective refractive index distribution of the mode is precisely controlled. The etching differences lead to an asymmetric equivalent refractive index distribution in the waveguide, forcing the transverse electric field of the TM0 mode to gradually and completely rotate into the longitudinal electric field of the TE1 mode.

[0082] The waveguide width of the second tapered waveguide 24 gradually decreases from large to small, further regulating the effective refractive index of the mode. By constraining the effective refractive index of the TM0 mode to not exceed that of the TE1 mode, the unidirectional conversion is ensured and reverse mode interference is prevented. At the same time, the waveguide width is reduced to re-centralize the light field, providing an adaptive light field distribution for the subsequent connection of the arc-shaped curved waveguide 25.

[0083] The mode conversion region 2 further includes an arc-shaped curved waveguide 25 arranged on the side of the second tapered waveguide 24 ; the arc-shaped curved waveguide 25 is connected before the first adiabatic coupling waveguide 31 .

[0084] The mode coupling region 3 includes an asymmetrically arranged first adiabatic coupling waveguide 31 and a second adiabatic coupling waveguide 32. The width of the first adiabatic coupling waveguide 31 decreases from large to small, and the width of the second adiabatic coupling waveguide 32 increases from small to large. The adjacent sides of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 remain parallel and the spacing is fixed. The waveguide width changes according to an exponential function.

[0085] The first output waveguide 41 of the output waveguides 4 is connected to the first adiabatic coupling waveguide 31 and is used to output the TE0 mode optical signal that has not undergone mode conversion. The second output waveguide 42 is connected to the second adiabatic coupling waveguide 32 and is used to output the TE0 mode optical signal obtained after mode conversion through the mode conversion region 2 and the second adiabatic coupling waveguide 32. The first output waveguide 41 is composed of two tapered waveguides or straight waveguides, while the second output waveguide 42 is composed of an S-shaped waveguide and a tapered waveguide or straight waveguide.

[0086] Figure 5 and Figure 6The following are the optical field distribution diagrams when the polarization of the input optical signal is TM0 and TE0, respectively. In the figure, the horizontal axis x(m) and the vertical axis y(m) represent the spatial position of the optical signal in the beam splitter when the distance between the first adiabatic coupling waveguide and the second adiabatic coupling waveguide is 150 nanometers. Figure 5 As shown, when the input light mode is TM0 polarization, the TM0 polarization optical signal is converted into TE1 mode through the mode conversion region, and then converted into TE0 through the mode coupling region and output from the second output waveguide. Figure 6 As shown, when the mode of the input light is TE0 polarization, the TE0 polarized optical signal passes through the mode conversion region and the mode coupling region and is output from the first output waveguide. In this mode, no mode conversion occurs in the mode conversion region and the mode coupling region.

[0087] Figure 7 and Figure 8 The following are the spectral response curves of different wavelengths when the polarization of the input light is TM0 and TE0, respectively. The horizontal axis is the different wavelengths, and the vertical axis is the transmission loss. Figure 7 As shown in Figure 2, when the polarization of the input light is TM0, the transmission loss of the two output ports b and c changes. Figure 8 Figure 2 shows the transmission loss changes at the two output ports b and c when the input light is polarized with TE0. It can be seen that the beam splitter still has low insertion loss and crosstalk within the 100 nm wavelength range.

[0088] The compact polarization rotation beam splitter provided in this embodiment features a compact structural design and a large operating bandwidth. This device not only offers advantages such as simple processing and a simple structure, but also excels in compact size, effectively meeting the miniaturization requirements of on-chip integrated systems. Furthermore, its wide bandwidth enables it to accommodate the processing of optical signals at multiple wavelengths, opening up possibilities for widespread application in optical communications and optical sensing. Furthermore, the device exhibits excellent performance, such as a high extinction ratio and low loss, further enhancing its transmission efficiency and signal quality in optical communication systems, providing strong support for the future development of on-chip optical communications and optical sensing technologies.

[0089] It should be understood that the specific embodiments described herein are only used to explain this application and are not used to limit it. Based on the embodiments provided in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0090] Obviously, the accompanying drawings are merely examples or embodiments of the present application. A person skilled in the art can also apply the present application to other similar situations based on these drawings without inventive effort. Furthermore, it is understandable that, although the work involved in this development process may be complex and lengthy, certain design, manufacturing, or production changes based on the technical content disclosed in this application are merely routine technical means for a person skilled in the art and should not be considered to constitute a deficiency in the disclosure of the present application.

[0091] The term "embodiment" as used in this application refers to specific features, structures, or characteristics described in conjunction with the embodiment that can be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor does it mean that it is mutually exclusive with other embodiments and is independent or optional. It is understood, either explicitly or implicitly, by those skilled in the art that the embodiments described in this application can be combined with other embodiments when there is no conflict.

[0092] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of patent protection. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

Claims

1. A compact polarization rotating beam splitter, characterized in that: include: An input waveguide, used for inputting an optical signal; a mode conversion region connected to the input waveguide, configured to convert a TM0 mode optical signal in the optical signal into a TE mode high-order optical signal; A mode coupling region comprising a first adiabatic coupling waveguide and a second adiabatic coupling waveguide arranged asymmetrically; The first adiabatic coupling waveguide is connected to the mode conversion region and is used to transmit the TE0 mode optical signal that has not undergone mode conversion in the optical signal, and the second adiabatic coupling waveguide is used to couple the TE mode high-order optical signal to the TE0 mode optical signal with the first adiabatic coupling waveguide; output waveguides, including a first output waveguide and a second output waveguide; The first output waveguide is connected to the first adiabatic coupling waveguide and is used to output the TE0 mode optical signal in which no mode conversion occurs in the optical signal; The second output waveguide is connected to the second adiabatic coupling waveguide and is used to output the TE0 mode optical signal obtained after mode conversion through the mode conversion region and the second adiabatic coupling waveguide; The mode conversion region includes a first tapered waveguide, a first ridge waveguide, a second ridge waveguide, and a second tapered waveguide connected in sequence; the mode conversion region has axial symmetry; the width of the first tapered waveguide increases from small to large, and makes the effective refractive index of the TE1 mode less than or equal to the effective refractive index of the TM0 mode; the width of the second tapered waveguide decreases from large to large, and makes the effective refractive index of the TM0 mode less than or equal to the effective refractive index of the TE1 mode; the first ridge waveguide and the second ridge waveguide are used to convert the TM0 mode optical signal in the optical signal into a TE mode high-order optical signal.

2. The compact polarization rotation beam splitter according to claim 1, wherein: The first ridge waveguide and the second ridge waveguide are composed of two layers of waveguide materials with different etching depths, the middle area is a fully etched area, and the two sides are shallowly etched areas.

3. The compact polarization rotation beam splitter according to claim 1, wherein: The width of the first adiabatic coupling waveguide decreases from large, the width of the second adiabatic coupling waveguide increases from small, and adjacent sides of the first adiabatic coupling waveguide and the second adiabatic coupling waveguide remain parallel and the spacing is fixed.

4. The compact polarization rotation beam splitter according to claim 3, wherein: The widths of the first adiabatic coupling waveguide and the second adiabatic coupling waveguide vary in an exponential function.

5. The compact polarization rotation beam splitter according to claim 1, wherein: The mode conversion region further includes an arc-shaped curved waveguide arranged on the side of the second tapered waveguide; the arc-shaped curved waveguide is connected before the first adiabatic coupling waveguide.

6. The compact polarization rotation beam splitter according to claim 1, wherein: The second output waveguide is curved.

7. The compact polarization rotation beam splitter according to claim 1, wherein: The output end widths of the first output waveguide and the second output waveguide are the same as the input end width of the input waveguide.

8. The compact polarization rotation beam splitter according to claim 1, wherein: The width of the tapered waveguide in the compact polarization rotation beam splitter changes with an exponential function, a parabolic function, or a linear function.

9. The compact polarization rotation beam splitter according to claim 1, wherein: The material of the compact polarization rotation beam splitter is silicon-based.

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