Optical signal polarization state tracking chip

Abstract

The application discloses a kind of optical signal polarization state tracking chips, comprising: first end face coupler, for receiving arbitrary complete polarization state input light;First direct current drive light phase shifter, for adjusting the light phase of input light;First polarization dependent mode converter, for mode conversion to phase-adjusted input light;Dual-mode beam splitter, for mode-converted input light is split into two optical signals;Second direct current drive light phase shifter, for regulating the phase difference between two optical signals;Dual-mode combiner, for the two optical signals of phase difference regulation are combined into a light signal;Second polarization dependent mode converter, for the inverse transformation of mode to the optical signal of combination is executed;Third direct current drive light phase shifter, for adjusting the light phase difference between orthogonal polarization state light of inverse-transformed optical signal;Polarization-insensitive beam splitter, for the first optical signal and second optical signal of phase difference adjusted optical signal are divided.

Description

Technical Field

[0001] This invention belongs to the field of integrated photonics technology, specifically, it relates to an optical signal polarization state tracking chip based on thin-film lithium niobate. Background Technology

[0002] The polarization state of light, as a key physical dimension of light waves, carries a wealth of information and is an important carrier of the interaction between light and matter. In recent years, its applications have rapidly expanded from traditional fields such as optical detection and spectral analysis to cutting-edge technology fields such as fiber optic communication, quantum information processing, high-precision sensing, and lidar.

[0003] Precise manipulation of the polarization state of light enables information encoding, multiplexing and transmission, and sensitive measurement of physical parameters, demonstrating enormous application potential. Therefore, developing efficient and stable polarization state control technology has become a key step in advancing these fields. Summary of the Invention

[0004] To achieve the above objectives, an integrated optical chip based on thin-film lithium niobate is provided according to an embodiment of the present invention, namely, an optical signal polarization state tracking chip based on thin-film lithium niobate. This optical signal polarization state tracking chip has a simple internal structure, can accept input light with any fully polarized state, and on this basis, realizes on-chip control and detection analysis of the light polarization state.

[0005] According to one aspect of an embodiment of the present invention, an optical signal polarization state tracking chip integrates a polarization state control module, the polarization state control module comprising: a first end-face coupler for receiving input light of any fully polarized state; a first DC-driven optical phase shifter for adjusting the optical phase of the input light; a first polarization-related mode converter for performing mode conversion on the phase-adjusted input light; a dual-mode beam splitter for splitting the mode-converted input light into two optical signals; a second DC-driven optical phase shifter for regulating the optical phase difference between the two optical signals; and a dual-mode beam combiner for combining the phase-adjusted input light into two optical signals. Two optical signals, after phase difference modulation, are combined into one optical signal; a second polarization-dependent mode converter is used to perform an inverse mode transformation on the combined optical signal; a third DC-driven optical phase shifter is used to adjust the optical phase difference between the orthogonally polarized light states of the optical signal after inverse mode transformation; a polarization-insensitive beam splitter is used to split the optical signal after phase difference modulation into a first optical signal and a second optical signal according to a preset splitting ratio, wherein the light intensity of the first optical signal is greater than that of the second optical signal, and the second optical signal is used as a polarization state analysis signal; and a second end-face coupler is used to output the first optical signal.

[0006] In one example of the optical signal polarization state tracking chip provided above, the optical signal polarization state tracking chip further integrates a polarization state analysis module. The polarization state control analysis includes: a polarization beam splitter rotator for receiving the second optical signal and splitting the second optical signal into a first optical component and a second optical component with orthogonal polarization states; a first 2×2 multimode interference coupler for receiving the first optical component and generating a first analysis optical signal and a first pre-analysis optical signal based on the first optical component; a second 2×2 multimode interference coupler for receiving the second optical component and generating a second analysis optical signal and a second pre-analysis optical signal based on the second optical component; a 4×4 multimode interference coupler for receiving the first pre-analysis optical signal and the second pre-analysis optical signal and generating a third analysis optical signal and a fourth analysis optical signal based on the first pre-analysis optical signal and the second pre-analysis optical signal; a third end-face coupler for outputting the first analysis optical signal; a fourth end-face coupler for outputting the third analysis optical signal; a fifth end-face coupler for outputting the fourth analysis optical signal; and a sixth end-face coupler for outputting the second analysis optical signal.

[0007] In one example of the optical signal polarization state tracking chip provided above, the optical signal polarization state tracking chip is based on an X-cut or Y-cut thin-film lithium niobate wafer, which includes a substrate layer and a buried oxide layer, a lithium niobate ridge waveguide layer and an upper cladding layer sequentially stacked on the substrate layer.

[0008] In one example of the optical signal polarization state tracking chip provided above, the first to sixth end face couplers are used to connect optical fibers outside the optical signal polarization state tracking chip to couple optical signals in or out.

[0009] In one example of the optical signal polarization state tracking chip provided above, the first polarization-dependent mode converter and the second polarization-dependent mode converter are respectively used to perform mode conversion operations according to the polarization state or mode of the received optical signal; wherein, when the received optical signal is in TE0 mode, the mode of the output optical signal remains in TE0 mode; when the received optical signal is in TM0 mode, the mode of the output optical signal is converted to TE1 mode.

[0010] In one example of the optical signal polarization state tracking chip provided above, the dual-mode beam splitter is used to perform beam splitting processing according to the mode of the received optical signal and to impart a fixed optical phase difference between the two output optical signals; wherein, when the received optical signal is in TE0 mode, the two output optical signals are two TE0 mode optical signals and the optical phase difference between the two TE0 mode optical signals is 0°; when the received optical signal is in TE1 mode, the two output optical signals are two TE0 mode optical signals and the optical phase difference between the two TE0 mode optical signals is 180°.

[0011] In one example of the optical signal polarization state tracking chip provided above, the dual-mode beam combiner and the dual-mode beam splitter have the same geometry; the dual-mode beam splitter and the dual-mode beam combiner are reversible devices, and the dual-mode beam combiner is used to take the two outputs of the dual-mode beam splitter as inputs and the inputs of the dual-mode beam splitter as outputs.

[0012] In one example of the optical signal polarization state tracking chip provided above, the polarization beam splitter is used to perform beam splitting and polarization rotation operations according to the polarization state of the received optical signal.

[0013] In one example of the optical signal polarization state tracking chip provided above, the polarization beam splitter is used to split the received optical signal into two optical signals with orthogonal polarization states, and to rotate the polarization state of one of the optical signals, and output the other optical signal and the optical signal after the polarization state rotation.

[0014] In one example of the optical signal polarization state tracking chip provided above, the polarization-insensitive beam splitter is used to split the received optical signal at a preset splitting ratio when the signal is in TE0 mode or TM0 mode.

[0015] Beneficial effects: The optical signal polarization state tracking chip according to embodiments of the present invention has at least one of the following advantages: First, this optical signal polarization state tracking chip is the first to integrate polarization state control and polarization state analysis functions on a single chip. The chip acquires polarization data through an analysis module and uses this data in a closed-loop feedback control to activate a DC-driven optical phase shifter, thereby locking the polarization state in real time and ultimately outputting highly stable polarized light.

[0016] Second, compared to existing technologies, this optical signal polarization state tracking chip has a simple internal structure and can be monolithically integrated with an electro-optic modulator on a thin-film lithium niobate platform, thus eliminating the need for bulky external polarization control components. Furthermore, through its built-in polarization state analysis module, this optical signal polarization state tracking chip can perform real-time tracking and closed-loop feedback adjustment of the polarization state of the main output light, significantly improving the performance and long-term stability of the thin-film lithium niobate modulator under polarization variation environments, while greatly reducing system size and packaging complexity. Attached Figure Description

[0017] The above and other aspects, features, and advantages of embodiments of the present invention will become clearer from the following description taken in conjunction with the accompanying drawings, in which: Figure 1 This is a system architecture diagram of an optical signal polarization state tracking chip according to an embodiment of the present invention; Figure 2 This is a cross-sectional view of an optical signal polarization state tracking chip according to an embodiment of the present invention. Detailed Implementation

[0018] Hereinafter, specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention can be implemented in many different forms, and should not be construed as limited to the specific embodiments set forth herein. Rather, these embodiments are provided to explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the various embodiments of the invention and various modifications suitable for particular intended applications.

[0019] As used herein, the term "comprising" and its variations are open terms meaning "including but not limited to". The terms "based on", "according to", etc., mean "at least partially based on" or "at least partially according to". The terms "one embodiment" and "an embodiment" mean "at least one embodiment". The term "another embodiment" means "at least one other embodiment". The terms "first", "second", etc., may refer to different or the same objects. Other definitions, whether explicit or implicit, may be included below. Unless explicitly indicated by the context, the definition of a term remains consistent throughout the specification.

[0020] Figure 1 This is a system architecture diagram of an optical signal polarization state tracking chip according to an embodiment of the present invention.

[0021] Reference Figure 1 The optical signal polarization state tracking chip according to an embodiment of the present invention integrates a polarization state control module and a polarization state analysis module. It should be noted that in other embodiments of the present invention, the polarization state analysis module can be omitted when polarization state analysis is not required.

[0022] Specifically, the polarization state control module includes: a first end-face coupler SSC1 for receiving input light in any fully polarized state; a first DC-driven optical phase shifter PS1 for adjusting the optical phase of the input light; a first polarization-related mode converter PDMC1 for performing mode conversion on the phase-adjusted input light; a dual-mode beam splitter DMPS for splitting the mode-converted input light into two optical signals; a second DC-driven optical phase shifter PS2 for regulating the optical phase difference between the two optical signals; and a dual-mode beam combiner DMPC for combining the two optical signals after optical phase difference regulation. The optical signal is combined into a single optical signal; a second polarization-dependent mode converter (PDMC2) is used to perform an inverse mode transformation on the combined optical signal; a third DC-driven optical phase shifter (PS3) is used to adjust the optical phase difference between the orthogonally polarized light states of the optical signal after inverse mode transformation; a polarization-insensitive beam splitter (OC) is used to split the optical signal after phase difference adjustment into a first optical signal and a second optical signal according to a preset splitting ratio, wherein the light intensity of the first optical signal is greater than that of the second optical signal, and the second optical signal is used as a polarization state analysis signal; and a second end-face coupler (SSC2) is used to output the first optical signal.

[0023] Furthermore, the polarization state control analysis includes: a polarization beam splitter (PSR) for receiving the second optical signal and splitting it into a first optical component and a second optical component with orthogonal polarization states; a first 2×2 multimode interference coupler (MMI1) for receiving the first optical component and generating a first analysis optical signal and a first pre-analysis optical signal based on the first optical component; a second 2×2 multimode interference coupler (MMI2) for receiving the second optical component and generating a second analysis optical signal and a second pre-analysis optical signal based on the second optical component; a 4×4 multimode interference coupler (MMI3) for receiving the first pre-analysis optical signal and the second pre-analysis optical signal and generating a third analysis optical signal and a fourth analysis optical signal based on the first pre-analysis optical signal and the second pre-analysis optical signal; a third end-face coupler (SSC3) for outputting the first analysis optical signal; a fourth end-face coupler (SSC4) for outputting the third analysis optical signal; a fifth end-face coupler (SSC5) for outputting the fourth analysis optical signal; and a sixth end-face coupler (SSC6) for outputting the second analysis optical signal.

[0024] The first end-face coupler SSC1 to the sixth end-face coupler SSC6 are used to connect optical fibers outside the optical signal polarization state tracking chip to couple optical signals in or out.

[0025] The first polarization-dependent mode converter PDMC1 and the second polarization-dependent mode converter PDMC2 are respectively used to perform mode conversion operations according to the polarization state or mode of the received optical signal; wherein, when the received optical signal is in TE0 mode, the mode of the output optical signal is maintained in TE0 mode; when the received optical signal is in TM0 mode, the mode of the output optical signal is converted to TE1 mode.

[0026] The dual-mode beam splitter (DMPS) is used to perform beam splitting processing according to the mode of the received optical signal and to assign a fixed optical phase difference between the two output optical signals. Specifically, when the received optical signal is in TE0 mode, the two output optical signals are two TE0 mode optical signals, and the optical phase difference between the two TE0 mode optical signals is 0°. When the received optical signal is in TE1 mode, the two output optical signals are two TE0 mode optical signals, and the optical phase difference between the two TE0 mode optical signals is 180°.

[0027] The dual-mode beam combiner (DMPC) and the dual-mode beam splitter (DMPS) have the same geometry. However, the dual-mode beam splitter (DMPS) and the dual-mode beam combiner (DMPC) are reversible devices. Therefore, the dual-mode beam combiner (DMPC) is used to take the two outputs of the dual-mode beam splitter (DMPS) as inputs and the inputs of the dual-mode beam splitter (DMPS) as outputs.

[0028] The polarization beam splitter (PSR) is used to perform beam splitting and polarization rotation operations based on the polarization state of the received optical signal. Further, the PSR splits the received optical signal into two orthogonal optical signals, rotates the polarization state of one of the optical signals, and outputs the other optical signal and the polarization-rotated optical signal.

[0029] The polarization-insensitive beam splitter OC is used to split the received optical signal at a preset splitting ratio when it is in TE0 or TM0 mode.

[0030] In one example, the second DC-driven optical phase shifter PS2 may be, for example, a Mach-Zehnder interferometer, but the invention is not limited thereto.

[0031] Figure 2 This is a cross-sectional view of an optical signal polarization state tracking chip according to an embodiment of the present invention.

[0032] Reference Figure 2According to an embodiment of the present invention, the optical signal polarization state tracking chip is based on an X-cut or Y-cut thin-film lithium niobate wafer, which includes a substrate layer 100 and a buried oxide layer 200, a lithium niobate ridge waveguide layer 300, and an upper cladding layer 400 sequentially stacked on the substrate layer 100. The substrate layer 100 may be, for example, a silicon substrate; the buried oxide layer 200 may be, for example, a silicon dioxide layer; and the upper cladding layer 400 may be, for example, a silicon dioxide or silicon oxynitride layer, but the present invention is not limited thereto.

[0033] The optical signal processing procedure of the optical signal polarization state tracking chip according to an embodiment of the present invention will be described in detail below.

[0034] The trajectory of the electric vector of a plane light wave (i.e., the input light) can be described in the following form: (1); in, and These are the horizontal and vertical electron components of a plane light wave. , These are their corresponding amplitudes. , It is their initial phase. It is the angular frequency of the light wave. The polarization state of light is usually defined by... The polarization extinction ratio and the The given phase difference This is used to characterize it. Therefore, it can be seen that when the polarization extinction ratio and phase difference are adjusted... At that time, the polarization state of light can be freely controlled.

[0035] When the input optical field of the first polarization-dependent mode converter PDMC1 satisfies At that time, the polarization state control module outputs a light field. satisfy: (2); in, and These are the transmission matrices for the first DC-driven optical phase shifter PS1 and the third DC-driven optical phase shifter PS3, respectively. It is a polarization controller transmission matrix composed of the first polarization-dependent mode converter PDMC1, the dual-mode beam splitter DMPS, the second DC-driven optical phase shifter PS2, the dual-mode beam combiner DMPC, and the second polarization-dependent mode converter PDMC2. They are represented as follows: (3); (4); (5); in, , and The phase changes are caused by the first DC-driven optical phase shifter PS1, the second DC-driven optical phase shifter PS2, and the third DC-driven optical phase shifter PS3, respectively. , and This is the phase difference caused by waveguide birefringence in the three DC-driven optical phase shifters. Using the transfer matrix given above, the performance of the polarization state control module can be clearly evaluated.

[0036] Furthermore, in order to verify and lock the output polarization state of the polarization state control module, the optical signal polarization state tracking chip according to an embodiment of the present invention also includes a feedback mechanism. For example... Figure 1 As shown, the optical signal processed by the third DC-driven optical phase shifter PS3 is split into beams by a 90:10 polarization-insensitive beam splitter OC; 10% of the optical power is coupled to the polarization state analysis module for real-time detection, and the analysis results are fed back to the polarization state control module to correct the deviation; at the same time, the remaining 90% of the optical power is output as the stabilized main signal by the second end coupler SSC2.

[0037] Of the four output terminals (SSC3 to SSC6) of the polarization state analysis module, the optical signals output from SSC3 to SSC6 are respectively converted into electrical signals by the first photodetector, the second photodetector, the third photodetector, and the fourth photodetector. The first and fourth photodetectors correspond to the TE0 and TM0 components of the optical field under test, respectively, and their equivalent polarization modulation corresponds to linear polarization at 0° and 90°, respectively. The corresponding Jones matrix can be expressed as: (6); Among them, the coefficients in front of the two matrices The beam splitting effect is derived from a 2×2 multimode interference coupler. Assume the light field to be measured... The optical powers measured by the first photodetector and the fourth photodetector are respectively: (7).

[0038] Next, considering the outputs of the second and third photodetectors, we first need to calculate the transfer matrix of the 4×4 multimode interferometric coupler MMI3. For an N×N multimode interferometric coupler, the phase relationship between its output and input is as follows: (8); Where p = 1, 2, 3...N are the indices of the input ports of the multimode interference coupler from bottom to top, and q = 1, 2, 3...N are the indices of the output ports of the multimode interference coupler from top to bottom. Therefore, the transmission matrix of the 4×4 multimode interference coupler MMI3 can be expressed as: (9).

[0039] The polarization state analysis module uses only two inputs (p=2, 4) and two outputs (q=2, 4) of a 4×4 multimode interferometer coupler MMI3. Therefore, the actual transfer matrix can be simplified as follows: (10).

[0040] Therefore, the optical powers measured by the second and third photodetectors are respectively: (11).

[0041] Therefore, the Stokes parameters of the light to be measured can be represented by four measured optical powers: (12).

[0042] The Stokes vector fully characterizes any polarization state of light through four parameters (S0, S1, S2, S3). S0 represents the total intensity of the light, while S1, S2, and S3 describe the intensity differences in the linear polarization directions (0° vs. 90°), +45° vs. -45°, and the right-handed vs. left-handed circular polarization components, respectively. It is through this specific combination of three relative components that the vector can uniquely and precisely describe all polarization states from linear and elliptical to circular polarization, forming a complete physical system for quantitatively describing polarization states.

[0043] In summary, the optical signal polarization state tracking chip according to embodiments of the present invention has at least one of the following advantages: First, this optical signal polarization state tracking chip is the first to integrate polarization state control and polarization state analysis functions on a single chip. The chip acquires polarization data through an analysis module and uses this data in a closed-loop feedback control to activate a DC-driven optical phase shifter, thereby locking the polarization state in real time and ultimately outputting highly stable polarized light.

[0044] Second, compared to existing technologies, this optical signal polarization state tracking chip has a simple internal structure and can be monolithically integrated with an electro-optic modulator on a thin-film lithium niobate platform, thus eliminating the need for bulky external polarization control components. Furthermore, through its built-in polarization state analysis module, this optical signal polarization state tracking chip can perform real-time tracking and closed-loop feedback adjustment of the polarization state of the main output light, significantly improving the performance and long-term stability of the thin-film lithium niobate modulator under polarization variation environments, while greatly reducing system size and packaging complexity.

[0045] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

Claims

1. A polarization state tracking chip for optical signals, characterized in that, The optical signal polarization state tracking chip integrates a polarization state control module, which includes: The first end-face coupler is used to receive input light in any fully polarized state; A first DC-driven optical phase shifter is used to adjust the optical phase difference of the input light; The first polarization-dependent mode converter is used to convert the mode of the phase-adjusted input light; A dual-mode beam splitter is used to split the input light after mode conversion to form two optical signals; The second DC-driven optical phase shifter is used to regulate the optical phase difference between the two optical signals; A dual-mode beam combiner is used to combine two optical signals that have undergone optical phase difference modulation into a single optical signal. The second polarization-dependent mode converter is used to perform inverse mode transformation on the combined optical signal. The third DC-driven optical phase shifter is used to adjust the optical phase difference between the orthogonally polarized states of the optical signal after mode inverse transformation; A polarization-insensitive beam splitter is used to split a single optical signal that has been adjusted by optical phase difference into a first optical signal and a second optical signal according to a preset splitting ratio. The light intensity of the first optical signal is greater than that of the second optical signal, and the second optical signal is used as a polarization state analysis signal. The second end-face coupler is used to output the first optical signal.

2. The optical signal polarization state tracking chip according to claim 1, characterized in that, The optical signal polarization state tracking chip also integrates a polarization state analysis module, which includes: A polarization beam splitter is used to receive the second optical signal and split the second optical signal into a first optical component and a second optical component with orthogonal polarization states. A first 2×2 multimode interference coupler is used to receive the first optical component and generate a first analysis optical signal and a first pre-analysis optical signal based on the first optical component. A second 2×2 multimode interference coupler is used to receive the second optical component and generate a second analysis optical signal and a second pre-analysis optical signal based on the second optical component. A 4×4 multimode interference coupler is used to receive the first pre-analysis optical signal and the second pre-analysis optical signal, and generate a third analysis optical signal and a fourth analysis optical signal based on the first pre-analysis optical signal and the second pre-analysis optical signal; The third end-face coupler is used to output the first analysis optical signal; The fourth end-face coupler is used to output the third analytical optical signal; The fifth end-face coupler is used to output the fourth analytical optical signal; The sixth end-face coupler is used to output the second analysis optical signal.

3. The optical signal polarization state tracking chip according to claim 1 or 2, characterized in that, The optical signal polarization state tracking chip is based on an X-cut or Y-cut thin-film lithium niobate wafer, which includes a substrate layer and a buried oxide layer, a lithium niobate ridge waveguide layer and an upper cladding layer sequentially stacked on the substrate layer.

4. The optical signal polarization state tracking chip according to claim 2, characterized in that, The first to sixth end couplers are used to connect optical fibers outside the optical signal polarization state tracking chip to couple optical signals in or out.

5. The optical signal polarization state tracking chip according to claim 1 or 2, characterized in that, The first polarization-dependent mode converter and the second polarization-dependent mode converter are respectively used to perform mode conversion operations according to the polarization state or mode of the received optical signal; Specifically, when the received optical signal is in TE0 mode, the output optical signal remains in TE0 mode; when the received optical signal is in TM0 mode, the output optical signal is converted to TE1 mode.

6. The optical signal polarization state tracking chip according to claim 1 or 2, characterized in that, The dual-mode beam splitter is used to perform beam splitting processing according to the mode of the received optical signal and to impart a fixed optical phase difference between the two output optical signals. Specifically, when the received optical signal is in TE0 mode, the two output optical signals are two TE0 mode optical signals, and the optical phase difference between the two TE0 mode optical signals is 0°; when the received optical signal is in TE1 mode, the two output optical signals are two TE0 mode optical signals, and the optical phase difference between the two TE0 mode optical signals is 180°.

7. The optical signal polarization state tracking chip according to claim 1 or 2, characterized in that, The dual-mode beam combiner and the dual-mode beam splitter have the same geometry; the dual-mode beam splitter and the dual-mode beam combiner are reversible devices, and the dual-mode beam combiner is used to take the two outputs of the dual-mode beam splitter as inputs and the inputs of the dual-mode beam splitter as outputs.

8. The optical signal polarization state tracking chip according to claim 2, characterized in that, The polarization beam splitter is used to perform beam splitting and polarization rotation operations according to the polarization state of the received optical signal.

9. The optical signal polarization state tracking chip according to claim 8, characterized in that, The polarization beam splitter is used to split the received optical signal into two optical signals with orthogonal polarization states, rotate the polarization state of one of the optical signals, and output the other optical signal and the optical signal with the rotated polarization state.

10. The optical signal polarization state tracking chip according to claim 1, characterized in that, The polarization-insensitive beam splitter is used to split the received optical signal at a preset splitting ratio when it is in TE0 or TM0 mode.

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