Compact polarization rotation beam splitter

Abstract

The invention relates to a compact polarization rotation beam splitter, which comprises an input waveguide, a mode conversion region, a mode coupling region and an output waveguide, a TM0 mode optical signal in the optical signals is converted into a TE mode high-order optical signal in the mode conversion area; the mode coupling region is used for coupling the TE mode high-order optical signal into a TE0 mode optical signal with the first adiabatic coupling waveguide; and the output waveguide is used for outputting a TE0 mode optical signal which is not subjected to mode conversion in the optical signals, and outputting a TE0 mode optical signal obtained after mode conversion of the mode conversion area and the second adiabatic coupling waveguide. According to the invention, the polarization rotation path can be shortened through high-order mode conversion in the mode conversion area, efficient beam splitting is realized by using the asymmetric adiabatic coupling waveguide in the mode coupling area, the size reduction of a redundant structure is avoided through function integration, the performance of the beam splitter is ensured, and the problems of large size and low cost of the existing polarization rotation beam splitter are solved. And the performance is not good.

Description

Technical Field

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

[0002] As an important pillar in the field of modern communication, optical communication technology has undergone a huge transformation from early simple communication systems to today's high-speed, large-capacity, and long-distance transmission systems. The core of an optical communication system lies in the transmission and processing of optical signals, and the polarization state of optical signals, as one of its important characteristics, has a significant impact on the transmission quality of signals. As an important device for polarization control, a polarization rotation beam splitter can effectively separate and convert the polarization state of optical signals, thereby improving the transmission quality of signals and system performance. At the same time, it can also be integrated with other optical devices to construct complex photonic integrated circuits to meet the application requirements of optical communication systems in different scenarios.

[0003] Currently, the technical principles of polarization rotation beam splitters are mainly divided into two types: one is based on the mode coupling mechanism, and the other is based on the mode evolution mechanism. Although the mode coupling mechanism has a simple structure, it is limited by strict phase matching conditions and is difficult to achieve the performance of large bandwidth and high tolerance; while the mode evolution mechanism can achieve efficient polarization rotation, but the long device size and complex structure design increase the manufacturing difficulty and cost. Therefore, how to achieve miniaturization while maintaining high performance is an important direction for the future development of polarization rotation beam splitter technology.

[0004] In view of the problems of large size and poor performance of polarization rotation beam splitters in the related art, no effective solution has been proposed yet. Summary of the Invention

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

[0006] In a first aspect, in the present embodiment, a compact polarization rotation beam splitter is provided, including:

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

[0008] A mode conversion region connected to the input waveguide for converting the TM0 mode optical signal in the optical signal into a TE mode high-order optical signal;

[0009] The mode coupling region includes a first adiabatic coupling waveguide and a second adiabatic coupling waveguide which are asymmetrically arranged; the first adiabatic coupling waveguide is connected to the mode conversion region and is used for transmitting the TE0 mode optical signal in the optical signal that does not undergo mode conversion, and the second adiabatic coupling waveguide is used to couple the higher-order TE mode optical signal with the first adiabatic coupling waveguide into a TE0 mode optical signal;

[0010] The output waveguide includes 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 for outputting the TE0 mode optical signal in the optical signal that does not undergo mode conversion;

[0012] The second output waveguide is connected to the second adiabatic coupling waveguide and is used for outputting the TE0 mode optical signal obtained after mode conversion in 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 axial symmetry;

[0014] Wherein, 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 decreases 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 for converting the TM0 mode optical signal in the optical signal into a higher-order TE mode optical signal.

[0017] In some embodiments, the first ridge waveguide and the second ridge waveguide are composed of two waveguide materials with different etching depths, the middle region is a fully etched region, and the two sides are shallow etched regions.

[0018] In some embodiments, the width of the first adiabatic coupling waveguide decreases from large to small, the width of the second adiabatic coupling waveguide increases from small to large, and the adjacent sides of the first adiabatic coupling waveguide and the second adiabatic coupling waveguide are kept parallel and the spacing is fixed.

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

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

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

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

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

[0024] In some of these embodiments, the material of the compact polarization rotation 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 the TM0 mode optical signal in the optical signal into a TE mode high-order optical signal; a mode coupling region including 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 for transmitting the 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 with the first adiabatic coupling waveguide into a TE0 mode optical signal; 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 the TE0 mode optical signal in the optical signal that has not undergone mode conversion; the second output waveguide is connected to the second adiabatic coupling waveguide for outputting the 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 through high-order mode conversion in the mode conversion region, efficient beam splitting can be achieved by using the asymmetric adiabatic coupling waveguides in the mode coupling region, and the size can be reduced by avoiding redundant structures through function integration, ensuring the performance of the beam splitter and solving the problems of large size and poor performance of the current polarization rotation beam splitters.

[0026] Details of one or more embodiments of this application are set forth in the following drawings and description to make other features, objects, and advantages of this application more concise and understandable. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0028] Figure 1 is a top view schematic diagram of a compact polarization rotation beam splitter in 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 is a schematic diagram of the waveguide shape of a mode coupling region modulated with different exponents m in an embodiment;

[0031] Figure 4 is a schematic diagram of the change in conversion efficiency of the mode coupling region under modulation with different exponents 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 is a spectral response curve of different wavelengths when the polarization of the input light is TM0 in an embodiment;

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

[0036] In the figures: 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 bent 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 implementation manners

[0037] To more clearly understand the purpose, technical solution and advantages of the present application, the present application will be described and explained 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 those of ordinary skill in the technical field to which this application pertains. In this application, words such as "a", "an", "one", "the", "these", etc. do not denote a limitation in quantity and can be singular or plural. The terms "comprising", "including", "having" and any variations thereof used in this application are intended to cover non-exclusive inclusion. 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 may include other steps or modules (units) inherent in these processes, methods, products or devices. The terms "connected", "coupled" and the like used in this application do not limit to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The term "plurality" used in this application means two or more. "And / or" describes the association relationship of associated objects and indicates that there can be three relationships. For example, "A and / or B" can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. Usually, the character " / " indicates that the objects associated before and after are in an "or" relationship. The terms "first", "second", "third", etc. used in this application only distinguish similar objects and do not represent a specific order for the objects.

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

[0040] An input waveguide 1 for inputting an optical signal;

[0041] A 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] A 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 for transmitting the TE0 mode optical signal in the optical signal that has not undergone mode conversion, and the second adiabatic coupling waveguide 32 is used to couple the TE mode high-order optical signal with the first adiabatic coupling waveguide 31 into a TE0 mode optical signal;

[0043] An output waveguide 4 includes 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 the 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 in the mode conversion region 2 and the second adiabatic coupling waveguide 32.

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

[0046] The input waveguide 1 is used to input an optical signal, guide the optical signal from the outside (such as a laser or an optical fiber) to the internal processing region of the beam splitter (such as the mode conversion region 2), and support both the TE0 (Transverse Electric) mode and the TM0 (Transverse Magnetic) mode, where 0 and 1 represent the mode orders, ensuring that different polarization states (TE / TM) of the input optical signal can be correctly processed by subsequent modules. Correspondingly, the optical signal can include a TE0 mode optical signal and a TM0 mode optical signal.

[0047] The mode conversion region 2 is connected to the input waveguide 1 and includes a ridge waveguide and a tapered waveguide. Through the designed structures of the ridge waveguide and the tapered waveguide, the optical field distribution and the effective refractive index of the confined mode can be controlled by the gradual change of the waveguide width, avoiding mode competition, and only converting the TM0 mode optical signal therein, so that the electric field direction of the TM0 mode gradually rotates from transverse (TM) to longitudinal (TE), and a TE mode higher-order optical signal is obtained by conversion. If there is a TE0 mode optical signal in the optical signal, the electric field distribution of the TE0 mode is matched with the waveguide geometry, no conversion is required, and the TE0 mode optical signal in the optical signal remains unchanged.

[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 realize the 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 on the side of the first adiabatic coupling waveguide 31 and is arranged in parallel with the first adiabatic coupling waveguide 31. Among them, 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 higher-order optical signal (such as TE1) to gradually evolve into the TE0 mode, and through the mode coupling effect of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32, coupling and transferring the TE0 mode optical signal to the second adiabatic coupling waveguide 32. If there is a TE0 mode optical signal in the input optical signal, the TE0 mode optical signal that has not undergone mode conversion continues to be transmitted 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 is 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. Further, in order to avoid mode crosstalk caused by too close a distance, the interval between the first output waveguide 41 and the second output waveguide 42 can be increased. Specifically, an arc-shaped bending waveguide can be designed at the connection between the output waveguide 4 and the mode coupling region 3 for connection.

[0050] Figure 2 is the overall structural schematic diagram of the compact polarization rotation beam splitter in this embodiment, as Figure 2 shown, port a is the input port of the optical signal, 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-stage conversion (TM0→TE1→TE0), it is output from port c to complete 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, and the TE mode high-order optical signal is converted by using the asymmetrically arranged adiabatic coupling waveguide in the mode coupling region, while suppressing other mode couplings (such as TE0), thereby improving the output polarization purity. The mode conversion region and the mode coupling region are closely connected in space to realize the parallel processing of polarization rotation and mode separation, thereby reducing the size of the beam splitter and solving the problems of large size and poor performance of the current polarization rotation beam splitters. The beam splitter in this embodiment has excellent performances such as a compact structural design, a large bandwidth, a low insertion loss, and a high extinction ratio, and is widely applicable to the fields of optical communication and optical sensing.

[0052] In some of the embodiments, as Figure 1 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 axial symmetry;

[0053] Among them, the width of the first tapered waveguide 21 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; the width of the second tapered waveguide 24 decreases 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; 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, in the mode conversion region 2, the first tapered waveguide 21, the first ridge waveguide 22, the second ridge waveguide 23, and the second tapered waveguide 24 are connected end to end in sequence. The mode conversion region 2 has axial symmetry and the same axis as the input waveguide 1. The width of each waveguide is in the range of 200 nanometers to 2 micrometers, and the length is within 100 micrometers.

[0055] The width of the first tapered waveguide 21 gradually expands from the initial width of the input waveguide, which can initially adjust and expand the waveguide width, so that the optical field distribution adapts to the etching structure of the subsequent ridge waveguide. At the same time, during the process of gradual width change, it is ensured that the effective refractive index of the TE1 mode does not exceed the effective refractive index of the TM0 mode, avoiding mode competition.

[0056] The first ridge waveguide 22 and the second ridge waveguide 23 are composed of two waveguide materials with different etching depths. The middle region is a fully etched region, and the two sides are shallow etched regions. By adjusting the ridge width, the width and length of the shallow etched region, the effective refractive index distribution of the mode is precisely controlled. The etching difference causes the equivalent refractive index distribution of the waveguide to be asymmetric, 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 restricting the effective refractive index of the TM0 mode not to exceed that of the TE1 mode, the conversion unidirectionality is ensured, preventing reverse mode interference. At the same time, the waveguide width is reduced, making the optical field concentrate again, providing an adapted optical field distribution for connecting to the subsequent arc-shaped bent waveguide 25.

[0058] Through the cascaded design of the tapered waveguide and the ridge waveguide in this embodiment, the optical field regulation, polarization rotation, and mode stabilization are completed in stages, and finally the efficient conversion of the TM0 mode optical signal to the TE mode high-order optical signal is realized. The gradual change design of the tapered waveguide realizes the effective refractive index regulation with a small physical length. The etching difference of the ridge waveguide is directly integrated into the waveguide body without additional complex structures, and the overall layout is highly compact.

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

[0060] Specifically, the arc-shaped bent waveguide 25 is connected before the first adiabatic coupling waveguide 31, and the spacing between the arc-shaped bent waveguide 25 and the second tapered waveguide 24 gradually decreases in the transmission direction, 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, as Figure 1 shown, the width of the first adiabatic coupling waveguide 31 decreases from large to small, 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 shrinks from large to small from the input end to the output end, which can guide the slow evolution of the optical field of the high-order TE mode and provide the initial conditions for subsequent mode order reduction. The waveguide width of the second adiabatic coupling waveguide 32 gradually increases from small to large 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 adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 vary in an exponential function to ensure the satisfaction of the adiabatic condition (slow change). That is, the adjacent sides of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 are parallel and the spacing is fixed, ensuring that the mode coupling process is controllable and stable. The other sides of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 both vary in an exponential function, and the width gradient directions are opposite. 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 and evolves into the low-order TE mode. During the gradual change of the waveguide width, the effective refractive index of the waveguide is regulated, so that the phase matching condition between the TE high-order mode and the TE0 mode is gradually satisfied, realizing efficient energy transfer.

[0065] The spacing between the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 is usually in the range of 90 nanometers to 300 nanometers. The larger the spacing, the longer the waveguide. When the waveguide width varies in an exponential function at an appropriate spacing, the waveguide length can be shortened while ensuring the waveguide conversion efficiency, and the beam splitter structure is more compact.

[0066] Figure 3 is a schematic diagram of the waveguide shape of the mode coupling region modulated by different exponents m in this embodiment, as Figure 3As shown, from top to bottom are the schematic diagrams of the first adiabatic coupled waveguide and the second adiabatic coupled waveguide in the mode coupling region when the exponent 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 m is, the sharper 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 is a schematic diagram of the change in the conversion efficiency of the mode coupling region in this embodiment under different exponent m modulations. As Figure 4 shown, the FDTD simulation software was used to simulate the conversion efficiency of the conversion from the TE1 mode to the TE0 mode in the mode coupling region under different exponents m. The abscissa is the coupling length (the length of the mode coupling region), and the ordinate is the coupling efficiency. Under a suitable line type, the coupling length to reach the same mode conversion efficiency is the shortest when m = 4. Under this line type, when the waveguide spacing is 150 nanometers, a length of only 55 micrometers is required to achieve a mode conversion efficiency greater than 99%. Compared with the original double-tapered adiabatic coupling structure, the waveguide length in the mode coupling region of this embodiment is significantly shortened.

[0068] By keeping the adjacent sides of the first adiabatic coupled waveguide 31 and the second adiabatic coupled waveguide 32 in this embodiment parallel and the spacing fixed, and the width changing in an exponential function, the waveguide length can be shortened while ensuring the waveguide conversion efficiency, and the beam splitter structure is more compact.

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

[0070] Specifically, in order to ensure that there is no coupling between the first output waveguide 41 and the second output waveguide 42 during output, the interval 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-through waveguide, and the second output waveguide 42 can be designed as a curved type, and the spacing from the first output waveguide 41 in the transmission direction gradually increases. As Figure 1 shown, the first output waveguide 41 and the second output waveguide 42 can also be designed as a multi-segment structure. For example, the first output waveguide 41 is composed of two segments of tapered waveguides or straight-through waveguides, and the second output waveguide 42 is composed of an S-shaped waveguide and a tapered waveguide or a straight-through 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, it 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 structures.

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

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

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

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

[0076] The following describes and illustrates this embodiment through preferred embodiments.

[0077] The compact polarization rotation beam splitter in this embodiment is as Figure 1 and Figure 2 shown. The input optical signal is input from input port a and output from port b and port c respectively according to different polarization states of the input optical signal. When the mode of the input optical signal is the TE0 mode, it is output from port b. When the mode of the input optical signal is the TM0 mode, the light is output from port c.

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

[0079] The input waveguide 1 is used to input an optical signal, guide the optical signal from the outside (such as a laser or an optical fiber) to the internal processing region of the beam splitter (such as the mode conversion region 2), and support both the TE0 (Transverse Electric) mode and the TM0 (Transverse Magnetic) mode. Here, 0 and 1 represent the mode orders, ensuring that different polarization states (TE / TM) of the input optical signal can be correctly processed by subsequent modules. Correspondingly, the optical signal can include a TE0 mode optical signal and a TM0 mode optical signal.

[0080] In the mode conversion region 2, the first tapered waveguide 21, the first ridge waveguide 22, the second ridge waveguide 23, and the second tapered waveguide 24 are connected end to end in sequence. The mode conversion region 2 has axial symmetry and the same axis as the input waveguide 1. The width of the first tapered waveguide 21 gradually expands from the initial width of the input waveguide, which can initially adjust and expand the waveguide width, enabling the light field distribution to adapt to the etching structure of the subsequent ridge waveguide. At the same time, during the process of the width gradual change, it is ensured that the effective refractive index of the TE1 mode does not exceed that of the TM0 mode, avoiding mode competition.

[0081] The first ridge waveguide 22 and the second ridge waveguide 23 are composed of two waveguide materials with different etching depths. The middle region is a fully etched region, and the two sides are shallow etched regions. By adjusting the ridge width, the width and length of the shallow etched region, the effective refractive index distribution of the mode is precisely controlled. The etching difference causes the equivalent refractive index distribution of the waveguide to be asymmetric, 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 restricting the effective refractive index of the TM0 mode not to exceed that of the TE1 mode, the unidirectionality of the conversion is ensured, preventing reverse mode interference. At the same time, the waveguide width is reduced, causing the light field to concentrate again, providing an adapted light field distribution for subsequent connection to the arc-shaped bent waveguide 25.

[0083] The mode conversion region 2 further includes an arc-shaped bent waveguide 25 arranged on the side of the second tapered waveguide 24; the arc-shaped bent 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. Moreover, the adjacent sides of the first adiabatic coupling waveguide 31 and the second adiabatic coupling waveguide 32 are kept parallel and the spacing is fixed, and the waveguide width changes in an exponential function.

[0085] In the output waveguide 4, the first output waveguide 41 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 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 in the mode conversion region 2 and the second adiabatic coupling waveguide 32. The first output waveguide 41 is composed of two tapered waveguides or a straight waveguide, and the second output waveguide 42 is composed of an S-shaped waveguide and a tapered waveguide or a straight waveguide.

[0086] Figure 5 and Figure 6They are respectively the optical field distribution diagrams when the polarization of the input optical signal is TM0 and TE0. In the diagrams, the abscissa x (m) and the ordinate 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. As Figure 5 shown, when the mode of the input light is TM0 polarization, the optical signal with TM0 polarization is converted into TE1 mode through the mode conversion region, and then converted into TE0 through the mode coupling region and output by the second output waveguide. As Figure 6 shown, when the mode of the input light is TE0 polarization, the optical signal with TE0 polarization passes through the mode conversion region and the mode coupling region and is output by the first output waveguide. In this mode, no mode conversion occurs through the mode conversion region and the mode coupling region.

[0087] Figure 7 and Figure 8 They are respectively the spectral response curves of different wavelengths when the polarization of the input light is TM0 and TE0. The abscissa is different wavelengths, and the ordinate is the transmission loss. As Figure 7 shown, when the polarization of the input light is TM0, the change of the transmission loss of the two output ports b and port c. As Figure 8 shown, when the polarization of the input light is TE0, the change of the transmission loss of the two output ports b and port c. It can be seen that this beam splitter still has low insertion loss and crosstalk within a 100-nanometer wavelength range.

[0088] Through the compact polarization rotation beam splitter provided in this embodiment, it has a compact structural design and a large working bandwidth characteristic. This device not only has the advantages of simple process and simple structure, but also stands out in terms of size compactness, and can effectively meet the requirements of the on-chip integrated system for miniaturization. At the same time, its large bandwidth characteristic enables it to adapt to the optical signal processing requirements of multiple wavelengths, providing possibilities for a wide range of applications in the fields of optical communication and optical sensing. In addition, this device also exhibits excellent performances such as high extinction ratio and low loss, further improving its transmission efficiency and signal quality in the optical communication system, and providing strong support for the development of future on-chip optical communication and optical sensing technologies.

[0089] It should be understood that the specific embodiments described here are only used to explain this application, rather than to limit it. According to the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of this application.

[0090] Obviously, the accompanying drawings are only some examples or embodiments of the present application. For those of ordinary skill in the art, the present application can also be applied to other similar situations based on these drawings without creative efforts. Additionally, it can be understood that although the work done during the development process here may be complex and time-consuming, for those of ordinary skill in the art, certain design, manufacturing, or production changes based on the technical content disclosed in the present application are only routine technical means and should not be regarded as insufficient disclosure of the present application.

[0091] The term "embodiment" in this application means that the specific features, structures, or characteristics described in connection with the embodiments may be included in at least one embodiment of the present application. The phrase appears in various positions in the specification and does not necessarily mean the same embodiment, nor does it mean independence or alternative to other embodiments that are mutually exclusive. Those of ordinary skill in the art can clearly or implicitly understand that the embodiments described in this application can be combined with other embodiments without conflict.

[0092] The above-described embodiments merely represent several implementation manners of the present application. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of patent protection. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all fall within the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the appended claims.

Claims

1. A compact polarization rotation beam splitter, characterized in that, Comprising: An input waveguide for inputting an optical signal; A mode conversion region connected to the input waveguide for converting the TM0 mode optical signal in the optical signal into a TE mode high-order optical signal; A mode coupling region including 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 for transmitting the 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 with the first adiabatic coupling waveguide into a TE0 mode optical signal; 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 the TE0 mode optical signal in the optical signal that has not undergone mode conversion; The second output waveguide is connected to the second adiabatic coupling waveguide for outputting the TE0 mode optical signal obtained after mode conversion in the mode conversion region and the second adiabatic coupling waveguide.

2. The compact polarization rotation beam splitter according to claim 1, characterized in that 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; Wherein, 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; The width of the second tapered waveguide decreases 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; 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.

3. The compact polarization rotation beam splitter according to claim 2, characterized in that, The first ridge waveguide and the second ridge waveguide are composed of two waveguide materials with different etching depths, the middle region is a fully etched region, and the two sides are shallow etched regions.

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

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

6. The compact polarization rotation beam splitter according to claim 2, wherein The mode conversion region further includes an arc-shaped bending waveguide arranged on the side of the second tapered waveguide; the arc-shaped bending waveguide is connected before the first adiabatic coupling waveguide.

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

8. 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.

9. 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 in an exponential function, a parabolic function, or a linear function.

10. 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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