Singular point photon gyroscope chip based on lithium niobate single crystal film

Abstract

The invention discloses a non-Hermite singular point photon gyroscope based on a lithium niobate single crystal film. Comprising a wide-spectrum light source, a spot size converter, a polarizer, a gyroscope sensing unit, a photoelectric detector and a lithium niobate film layer which are positioned in a packaging shell, the wide-spectrum light source, the spot size converter, the polarizer, the gyroscope sensing unit and the photoelectric detector are all located on the upper surface of the lithium niobate thin film layer and are sequentially arranged in the light path direction; light emitted by the wide-spectrum light source sequentially passes through the spot size converter, the polarizer and the gyroscope sensing unit and then is received by the photoelectric detector. By means of the electro-optical effect of lithium niobate, the resonant frequency of the micro-cavity is adjusted by applying voltage to keep the gyroscope sensing unit at a singular point in the initial state, and interference of external factors is counteracted; the anti-space-time inversion symmetric structure is constructed, the sensitivity of the gyroscope sensing unit is improved by utilizing the sensitivity of singular points to external perturbation, and the gyroscope sensing unit has the advantages of high sensitivity, small size, high practicability and integratability.

Description

Technical Field

[0001] The invention relates to the field of integrated optics and inertial sensing, and in particular to a singular point photon gyroscope chip based on a lithium niobate single crystal film. Background Art

[0002] A gyroscope is a tool for measuring the angular velocity of a moving carrier. It plays an extremely important role in inertial navigation, inertial guidance and inertial measurement systems and is widely used. The performance of an inertial system is largely determined by the performance of the gyroscope. According to the basic working principle, it can be divided into a mechanical gyroscope based on classical mechanics and an optical gyroscope based on modern optical effects.

[0003] The presence of moving parts inside the mechanical gyroscope makes its power consumption and volume large. It also has problems such as weak vibration and impact resistance and sensitivity to gravity acceleration, which limits its application in some fields. The emergence of optical gyroscopes based on the optical Sagnac effect provides a new idea for the application selection of gyroscopes. Since the optical Sagnac effect was proposed, optical gyroscopes have experienced a development process from ring laser gyroscopes (RLG) to fiber optic gyroscopes. At present, RLG technology has been very mature and has been applied in many high-precision navigation fields, but it has many internal optoelectronic devices, large volume and high cost, which is not conducive to miniaturization. Although fiber optic gyroscopes have solved the above problems to a certain extent, the signal generated by the Sagnac effect is proportional to the length of the optical fiber and the radius of the optical fiber ring. The improvement of its performance comes at the cost of increasing the length of the optical fiber and the radius of the optical fiber ring. Therefore, there is an inherent contradiction between high sensitivity and miniaturization. With the increasing miniaturization of inertial sensor units, the development of chip-level gyroscopes has become an urgent problem to be solved in the field of inertial navigation.

[0004] In recent years, with the in-depth research in the field of micro-nano optics, integrated optical gyroscopes have received extensive attention from researchers. Their research mainly focuses on the integration of optical devices. By integrating discrete fiber optic devices into a single chip, the size and weight of traditional optical gyroscopes can be minimized, which is an ideal solution for gyroscope miniaturization. However, as mentioned above, the Sagnac effect is proportional to the length and radius of the sensitive ring, making it difficult to achieve miniaturization while taking into account high sensitivity in principle. Summary of the invention

[0005] Research on the enhancement of the Sagnac effect is the key to solving this contradiction. A non-Hermitian system is a system that has energy exchange or gain or loss with the outside world, and its physical quantities can be described by non-Hermitian operators. Unlike the Hermitian system, the non-Hermitian system has singular points (i.e., exceptional points, hereinafter referred to as singular points). The singular point is the degenerate point of the non-Hermitian system. At this point, the real and imaginary parts of the eigenvalues ​​of the system are equal at the same time, the eigenvalues ​​and eigenstates are degenerate at the same time, and the eigenstates can no longer constitute a complete basis vector. Ultra-sensitive optical sensing based on singular points is currently a hot research topic in the field of non-Hermitian optics. It has different degrees of application in particle detection, temperature sensing, refractive index sensing, rotation speed measurement, etc. The application of non-Hermitian optical systems in the field of inertial sensing is expected to develop optical gyroscopes that are both highly sensitive and miniaturized.

[0006] In order to solve the problems in the background technology, the present invention proposes a singular point photonic gyroscope chip based on lithium niobate single crystal film with small size, high sensitivity and easy packaging and integration for non-Hermitian optical systems, which is conducive to the miniaturization of high-sensitivity optical gyroscopes.

[0007] The present invention utilizes the property that the singularity of a non-Hermitian optical system is sensitive to external perturbations, and shrinks the gyroscope to the chip level while maintaining the high sensitivity advantage of the optical gyroscope, which is expected to resolve the contradiction between high sensitivity and miniaturization of the optical gyroscope. In the design of the sensitive unit structure, the electro-optic effect is used to introduce a controllable additional phase into the racetrack annular microcavity, thereby achieving effective control of the singularity of the non-Hermitian system. The present invention has a simple structure and high integration, and is expected to become a solution for miniaturization of high-sensitivity optical gyroscopes.

[0008] The technical solution of the present invention is:

[0009] 1. A singular point photonic gyroscope chip based on lithium niobate single crystal film

[0010] It includes a wide spectrum light source, a spot converter, a polarizer, a gyro sensitive unit, a photodetector and a lithium niobate thin film layer located in a packaging shell;

[0011] The broadband light source, spot converter, polarizer, gyro sensitive unit and photoelectric detector are all located on the upper surface of the lithium niobate film layer and arranged in sequence along the light path; the light emitted by the broadband light source passes through the spot converter, polarizer and gyro sensitive unit in sequence and is received by the photoelectric detector.

[0012] The pattern spot converter is a double-layer inverted tapered waveguide obtained by etching twice, including an unetched lithium niobate film bottom layer and an etched lower inverted tapered waveguide and an upper inverted tapered waveguide, wherein the lithium niobate film bottom layer, the lower inverted tapered waveguide and the upper inverted tapered waveguide are stacked in sequence from bottom to top;

[0013] The lower inverted tapered waveguide and the upper inverted tapered waveguide are both ridge waveguides whose width increases along the optical path direction, and the height of the upper surface of the lower inverted tapered waveguide is consistent with the height of the upper surface of the lithium niobate film layer;

[0014] The input end of the upper inverted tapered waveguide is located in the middle of the lower inverted tapered waveguide, and the output end of the upper inverted tapered waveguide is aligned with the output end of the lower inverted tapered waveguide.

[0015] The lower inverted tapered waveguide is divided into two sections of tapered waveguides which are sequentially connected along the optical path. The widths of the two sections of tapered waveguides gradually increase along the optical path. The output end of the tapered waveguide of the first section and the input end of the tapered waveguide of the second section are connected and have the same width.

[0016] The polarizer includes a standard single-mode transmission waveguide, a TM mode coupling waveguide and a TM mode dissipative waveguide;

[0017] The input end of the standard single-mode transmission waveguide is connected to the mode spot converter, the TM mode coupling waveguide is placed at one side of the standard single-mode transmission waveguide and is parallel to the standard single-mode transmission waveguide, the input end of the TM mode dissipative waveguide is connected to the output end of the TM mode coupling waveguide, and the output end is bent and extended in a direction away from the polarizer transmission waveguide;

[0018] The height and width of the TM mode coupling waveguide are not equal to the height and width of the standard single-mode transmission waveguide, so that the TM mode can meet the phase matching conditions required for mode coupling, while the TE mode does not meet the phase matching conditions, and the height of the TM mode coupling waveguide is consistent with the height of the TM mode dissipative waveguide.

[0019] The TM mode dissipative waveguide is a waveguide whose width is narrowed after being bent 90 degrees along the transmission direction. The input end of the TM mode dissipative waveguide is connected to the output end of the TM mode coupling waveguide.

[0020] The gyro sensitive unit comprises two microcavity electrode assemblies and a gyro sensitive unit transmission waveguide, the two microcavity electrode assemblies are respectively arranged on both sides of the gyro sensitive unit transmission waveguide, and the two microcavity electrode assemblies comprise a racetrack annular waveguide microcavity and a pair of electrode pairs;

[0021] The input end of the gyro sensitive unit transmission waveguide is connected to a polarizer, the racetrack annular waveguide microcavity is a waveguide in a racetrack annular shape, and the straight racetrack region of the racetrack annular waveguide microcavity is parallel to the gyro sensitive unit transmission waveguide and is placed adjacently and spaced apart;

[0022] The pair of electrodes consists of two control electrodes, and the two control electrodes are arranged on a side of the racetrack annular waveguide microcavity away from the transmission waveguide of the gyro sensitive unit.

[0023] Each of the racetrack annular waveguide microcavity is mainly composed of two parallel straight waveguides with both ends aligned and two open arc waveguides, the two straight waveguides are aligned at both ends along the optical path direction, one of the aligned ends is connected to the two ends of an open arc waveguide, the other aligned ends of the two straight waveguides are connected to the two ends of another open arc waveguide, and the two control electrodes are arranged on both sides of the straight waveguide away from the transmission waveguide of the gyro sensitive unit.

[0024] The resonant frequency difference between the two racetrack ring waveguide microcavities is designed to be:

[0025] |ω1-ω2|=μ1μ2

[0026] Where ω1 and ω2 represent the resonant frequencies of the two racetrack ring waveguide microcavities, and μ1 and μ2 represent the coupling coefficients between the microcavity and the transmission waveguide of the gyro sensitive unit;

[0027] According to the calculation formula of the resonant frequency and the coupling coefficient, the relationship between the cavity lengths of the two racetrack ring waveguide microcavities can be obtained as follows:

[0028]

[0029] Where c is the speed of light in vacuum, n is the refractive index of the waveguide material, L1 and L2 represent the cavity lengths of the two racetrack ring waveguide microcavities, m is the resonance order determined according to the incident wavelength and the cavity length of L1, and κ1 and k2 are the energy coupling ratios between the two waveguide microcavities and the transmission waveguide, respectively.

[0030] The singular point photon gyroscope chip further comprises a silicon substrate and a silicon dioxide buffer layer, the lithium niobate thin film layer is arranged on the silicon dioxide buffer layer, and the silicon dioxide buffer layer is arranged on the silicon substrate.

[0031] 2. A method for detecting the rotation speed of a singular point photon gyroscope chip

[0032] In the initial state, a feedback voltage is applied to the control electrode, and the refractive index of the two racetrack ring waveguide microcavities is changed by utilizing the electro-optical effect of the lithium niobate material, thereby adjusting the resonant frequency difference between the racetrack ring waveguide microcavities, so that in the initial state, the gyro sensitive unit is at the singular point of the non-Hermitian system, and the singular point photonic gyro chip is in a working state;

[0033] In the working state, the light emitted by the wide-spectrum light source is detected and received by the photoelectric detector after passing through the spot converter, polarizer, and gyro sensitive unit in sequence;

[0034] When the gyro sensitive unit rotates, due to the Sagnac effect, the resonant frequencies of the two runway ring waveguide microcavities will change, so that the gyro sensitive unit deviates from the singularity point, causing the output of the gyro sensitive unit to change. The beat frequency signal is detected in the photodetector, and the current rotation speed can be obtained by substituting the beat frequency-rotation speed into the pre-fitted curve.

[0035] Beneficial effects of the present invention:

[0036] The present invention integrates all devices on a silicon substrate, is smaller in size and more integrated than a traditional optical gyroscope, and is suitable for mass production.

[0037] The present invention constructs a second-order non-Hermitian system with anti-PT symmetry, and utilizes the characteristic that the singular point of the non-Hermitian system is sensitive to external perturbations, which has high sensitivity, small size and is easy to integrate. The wide-spectrum light source is mixed and integrated into the gyroscope chip, solving the problem of light source integration of chip-level gyroscopes. The two constructed waveguide microcavities with the same loss utilize the characteristic that the singular point of the non-Hermitian system is sensitive to external perturbations, further improving the sensitivity and reducing the size of the sensor while maintaining the original advantages of the optical gyroscope.

[0038] The present invention designs a targeted mode spot converter for the emission mode spot of the wide-spectrum light source tube core, obtains an elliptical end face mode field by utilizing a partially etched double-layer inverted tapered waveguide, realizes high-efficiency coupling of the wide-spectrum light source, and the increase in the transmitted light power on the gyroscope chip further improves the sensitivity of signal detection.

[0039] An additional pair of electrodes is added to the straight waveguide area of ​​the two racetrack ring waveguide microcavities constructed by the present invention, and an additional phase is introduced into the microcavity by utilizing the electro-optical effect, thereby effectively eliminating the influence of other interferences that may exist in the sensor application environment and the tolerance of the preparation process on the singular points of the non-Hermitian system, achieving continuous controllable singular points of the non-Hermitian system and improving the practicality and preparation tolerance of the sensor.

[0040] The present invention designs a chip-type polarizer suitable for lithium niobate film, which ensures that the input light of the gyro sensitive unit is a single polarization light source, avoids the interference of deviation error on the gyro signal, and is compatible with the traditional waveguide etching process in terms of process, which is conducive to realizing monolithic integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the overall structure of the singular point photon gyroscope chip based on lithium niobate single crystal film of the present invention;

[0042] Figure 2 It is a schematic diagram of the structure of the pattern spot converter in the present invention;

[0043] Figure 3 It is a schematic diagram of the structure of the polarizer in the present invention;

[0044] Figure 4 It is a schematic diagram of the structure of the gyro sensitive unit in the present invention;

[0045] In the figure: 1. broadband light source, 2. spot converter, 3. polarizer, 4. gyro sensitive unit, 5. racetrack ring waveguide microcavity, 6. photodetector, 7. packaging shell, 8. lithium niobate thin film layer; 21. silicon substrate, 22. silicon dioxide buffer layer, 23. lithium niobate thin film bottom layer, 24. lower inverted cone waveguide, 25. upper inverted cone waveguide; 31. standard single-mode transmission waveguide, 32. TM mode coupling waveguide, 33. TM mode dissipative waveguide, 44. gyro sensitive unit transmission waveguide, 45. open arc waveguide, 46. straight waveguide, 47. control electrode. DETAILED DESCRIPTION

[0046] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0047] like Figure 1 As shown, the singular point photon gyroscope chip specifically implemented includes a wide spectrum light source 1, a pattern spot converter 2, a polarizer 3, a gyroscope sensitive unit 4, a photodetector 6 and a lithium niobate thin film layer 8 located in a packaging shell 7;

[0048] The broadband light source 1, the pattern spot converter 2, the polarizer 3, the gyro sensitive unit 4 and the photodetector 6 are all located on the upper surface of the lithium niobate thin film layer 8 and are arranged in sequence along the optical path; the light emitted by the broadband light source 1 passes through the pattern spot converter 2, the polarizer 3 and the gyro sensitive unit 4 in sequence and is received by the photodetector 6.

[0049] All waveguide structures of the spot converter 2 , the polarizer 3 and the gyro sensitive unit 4 are formed by etching the lithium niobate thin film layer 8 , and the broadband light source 1 and the photodetector 6 are located in the fixed groove formed by etching the lithium niobate thin film layer 8 .

[0050] like Figure 2 As shown, the mode spot converter 2 is a double-layer inverted tapered waveguide obtained by two etchings, including an unetched lithium niobate film bottom layer 23 and an etched lower inverted tapered waveguide 24 and an upper inverted tapered waveguide 25. Different from the traditional double-layer inverted tapered waveguide structure, a portion of the unetched lithium niobate film bottom layer 23 is retained during the etching of the lower inverted tapered waveguide 24, so the mode spot has a tendency to distribute toward the unetched lithium niobate film bottom layer 23, so that the mode field of the mode spot converter 2 close to the broadband light source 1 is elliptical, so as to match the elliptical light spot emitted by the broadband light source 1. The lithium niobate film bottom layer 23, the lower inverted tapered waveguide 24 and the upper inverted tapered waveguide 25 are stacked in sequence from bottom to top;

[0051] The lower inverted tapered waveguide 24 and the upper inverted tapered waveguide are both ridge waveguides whose width increases along the optical path direction. The height of the upper surface of the lithium niobate film bottom layer 23 is lower than the height of the upper surface of the lithium niobate film layer 8, and is concave in shape. The height of the upper surface of the lower inverted tapered waveguide is consistent with the height of the upper surface of the lithium niobate film layer 8, and the height of the upper surface of the upper inverted tapered waveguide 25 is higher than the height of the upper surface of the lithium niobate film layer 8.

[0052] The preparation process of the pattern converter 2 is as follows:

[0053] The first etching is performed to prepare the upper inverted tapered waveguide 25 structure and other waveguide structures of the sensor. The etching depth is consistent with that of other waveguide structures of the sensor. Therefore, the thickness of the upper inverted tapered waveguide 25 is the same as that of other waveguides.

[0054] Overlay is performed to prepare the lower inverted tapered waveguide 24 structure, and the etching depth is determined according to the optimized structural parameters. According to the preparation process, the sum of the thickness of the lower inverted tapered waveguide 24 and the thickness of the lithium niobate film bottom layer 23 should be the same as the thickness of the lithium niobate film layer 8, so the upper surface of the lower inverted tapered waveguide 24 is flush with the upper surface of the lithium niobate film layer 8.

[0055] The input end of the upper inverted tapered waveguide 25 is located in the middle of the lower inverted tapered waveguide 24 , and the output end of the upper inverted tapered waveguide 25 is aligned with the output end of the lower inverted tapered waveguide 24 .

[0056] The broadband light source 1 and the spot converter 2 are coaxially arranged, and the output end of the upper inverted tapered waveguide 25 of the spot converter 2 is connected to one end of the standard single-mode transmission waveguide 31 of the polarizer 3 .

[0057] The lower inverted tapered waveguide 24 is divided into two sections of tapered waveguides which are connected in sequence along the optical path. The widths of the two sections of tapered waveguides gradually increase along the optical path. The output end of the tapered waveguide of the first section and the input end of the tapered waveguide of the second section are connected and have the same width. The lengths of the two tapered waveguides are optimized according to the designed widths of the input and output ends to achieve low-loss transmission of light.

[0058] In actual design, the actual mode field size of the selected broadband light source 1 should be determined by optimizing the end face width and thickness of the lower inverted tapered waveguide 24 and the upper inverted tapered waveguide 25 and the thickness of the lithium niobate film bottom layer 23 to achieve the highest coupling efficiency between the broadband light source 1 and the mode spot converter 2.

[0059] like Figure 3 As shown, the polarizer 3 includes a standard single-mode transmission waveguide 31, a TM mode coupling waveguide 32 and a TM mode dissipative waveguide 33;

[0060] The input end of the standard single-mode transmission waveguide 31 is connected to the upper inverted tapered waveguide 25 of the mode spot converter 2, the TM mode coupling waveguide 32 is spaced apart and placed on one side of the standard single-mode transmission waveguide 31 and is parallel to the standard single-mode transmission waveguide 31, the input end of the TM mode dissipative waveguide 33 is connected to the output end of the TM mode coupling waveguide 32, and the output end is bent and extended in a direction away from the polarizer transmission waveguide 31;

[0061] The height and width of the TM mode coupling waveguide 32 are not equal to the height and width of the standard single-mode transmission waveguide 31, so that the TM mode can meet the phase matching conditions required for mode coupling, while the TE mode does not meet the phase matching conditions. The height of the TM mode coupling waveguide 32 is consistent with the height of the TM mode dissipative waveguide 33.

[0062] The length of the TM mode coupling waveguide 32 is selected according to the phase matching condition satisfied by the TM mode, so that the TM mode can be fully coupled into the TM mode coupling waveguide 32 through the evanescent wave, and the TE mode continues to be transmitted in the standard single-mode transmission waveguide 31 of the polarizer 3.

[0063] The TM mode dissipative waveguide 33 is a waveguide that is narrowed after bending 90° along the transmission direction. The input end of the TM mode dissipative waveguide 33 is connected to the output end of the TM mode coupling waveguide 32. The other parameters are the same as those of the TM mode coupling waveguide 32. The design of bending along the transmission direction makes the TM mode transmission direction perpendicular to the TE mode to reduce the signal interference to the TE mode. The gradually narrowing width increases the loss of the TM mode, causing the TM mode to lose quickly after coupling, achieving the effect of polarization, and finally making the standard single-mode transmission waveguide 31 of the polarizer 3 only output the TE mode to enter the gyro sensitive unit 4.

[0064] like Figure 4 As shown, the gyro sensitive unit 4 includes two microcavity electrode assemblies and a gyro sensitive unit transmission waveguide 44. The gyro sensitive unit transmission waveguide 44 is in a strip shape. The two microcavity electrode assemblies are respectively arranged approximately symmetrically on both sides of the gyro sensitive unit transmission waveguide 44. The two microcavity electrode assemblies include a racetrack annular waveguide microcavity 5 and a pair of electrode pairs.

[0065] The parameters of the gyro sensitive unit transmission waveguide 44 are the same as those of the standard single-mode transmission waveguide 31 of the polarizer 3. The input end of the gyro sensitive unit transmission waveguide 44 is connected to the standard single-mode transmission waveguide 31 of the polarizer 3. The output end of the gyro sensitive unit transmission waveguide 44 is connected to the input end of the photodetector 6. The racetrack annular waveguide microcavity 5 is a waveguide whose main body is in the form of a racetrack annular shape. The straight racetrack region of the racetrack annular waveguide microcavity 5 is parallel to the gyro sensitive unit transmission waveguide 44 and is placed adjacently and spaced apart.

[0066] One electrode pair is composed of two control electrodes 47 , and the two control electrodes 47 are arranged on a side of the racetrack ring waveguide microcavity 5 away from the gyro sensitive unit transmission waveguide 44 .

[0067] Each racetrack annular waveguide microcavity 5 is mainly composed of two parallel straight waveguides 46 with both ends aligned and two open arc waveguides 45. The two ends of the two straight waveguides 46 are aligned along the optical path direction, and one of the aligned ends is connected to the two ends of an open arc waveguide 45, and the other ends of the two straight waveguides 46 are connected to the two ends of another open arc waveguide 45, and two control electrodes 47 are arranged in parallel and at intervals on both sides of the straight waveguide 46 away from the gyro sensitive unit transmission waveguide 44.

[0068] The side of the two racetrack ring waveguide microcavities 5 where the control electrode 47 is not distributed is close to the transmission waveguide 44 but not in contact, so that each racetrack ring waveguide microcavity 5 and the gyro sensitive unit transmission waveguide 44 can be coupled through evanescent waves. The spacing between the racetrack ring waveguide microcavity 5 and the gyro sensitive unit transmission waveguide 44 determines the coupling coefficient between the two. The gyro sensitive unit is at a singular point and requires that the coupling coefficient and the resonant frequency of the microcavity satisfy the relationship:

[0069] |ω1-ω2|=μ1μ2

[0070] Wherein ω1 and ω2 represent the resonance frequencies of the two racetrack ring waveguide microcavities 5 respectively, and μ1 and μ2 represent the coupling coefficients between the microcavity and the gyro sensitive unit transmission waveguide 44.

[0071] Due to the existence of micro-nano processing errors and interference from external factors such as the environment, the above-mentioned singular point conditions are usually difficult to meet, causing the gyro sensitive unit 4 to deviate from the singular point, affecting the measurement of the rotation speed. The control electrode 47 applies a corresponding feedback voltage and uses the electro-optical effect of lithium niobate to change the refractive index of the two racetrack ring waveguide microcavities 5, thereby adjusting the resonant frequency of the microcavity so that the gyro sensitive unit 4 is at a non-Hermitian system singular point in the initial state. The design of the control electrode 47 realizes the continuous control of the singular point and effectively suppresses the influence of the preparation error and environmental interference on the performance of the gyro sensitive unit 4.

[0072] During the operation of the singularity point photon gyroscope chip:

[0073] In the initial state, due to the interference of external factors such as preparation errors and environment, the gyro sensitive unit 4 may deviate from the singular point of the non-Hermitian system.

[0074] When working, a corresponding feedback voltage is applied to the control electrode 47, and the refractive index of the two racetrack ring waveguide microcavities 5 is changed by utilizing the electro-optical effect of lithium niobate, thereby adjusting the resonant frequency difference between the microcavities, so that in the initial state, the gyro sensitive unit 4 is at the singular point of the non-Hermitian system, and the sensor is in a working state;

[0075] In the working state, the light emitted by the wide-spectrum light source 1 passes through the spot converter 2, the polarizer 3, and the gyro sensitive unit 4 in sequence and is detected and received by the photodetector 5.

[0076] When the gyro sensitive unit 4 rotates, due to the Sagnac effect, the resonant frequencies of the two racetrack ring waveguide microcavities 5 will change, causing the gyro sensitive unit 4 to deviate from the singularity point, causing the output of the sensor to change, which is manifested as a beat frequency signal in the photodetector 5. The current rotation speed can be obtained by substituting the pre-fitted curve into the relationship between the beat frequency and the rotation speed.

[0077] If no voltage is applied to the control electrode 47, the singular point photon gyroscope chip will not work.

[0078] The resonant frequency difference between the two racetrack ring waveguide microcavities 5 is designed to be:

[0079] |ω1-ω2|=μ1μ2

[0080] Wherein ω1 and ω2 represent the resonance frequencies of the two racetrack ring waveguide microcavities 5 respectively, and μ1 and μ2 represent the coupling coefficients between the microcavity and the gyro sensitive unit transmission waveguide 44.

[0081] According to the calculation formula of the resonant frequency and the coupling coefficient, the relationship between the cavity lengths of the two racetrack ring waveguide microcavities 5 can be obtained as follows:

[0082]

[0083] Wherein c is the speed of light in vacuum, n is the refractive index of the waveguide material, L1 and L2 represent the cavity lengths of the two racetrack ring waveguide microcavities 5, respectively, m is the resonance order determined according to the incident wavelength and the cavity length of L1, k1 and κ2 are the energy coupling ratios between the two waveguide microcavities and the transmission waveguide 44, respectively, which can be flexibly determined within the range of 0-1.

[0084] In actual design, the energy coupling ratio can be set in the manner of κ1=κ2, and then the cavity length L1 of one of the racetrack ring waveguide microcavities 5 is set according to the sensor size requirements, and the resonance order m is calculated according to the wavelength of the light source, and the cavity length L2 of the other racetrack ring waveguide microcavity 5 is obtained by substituting it into the above formula. It can be seen from the above formula that the cavity lengths of the two racetrack ring waveguide microcavities 5 are slightly different, so the resonant frequencies of the two are also different. At the same time, in order to construct a non-Hermitian system, the same loss is artificially introduced in the two racetrack ring waveguide microcavities 5.

[0085] The two racetrack ring waveguide microcavities 5 in the gyro sensitive unit 4 are only energy coupled with the middle gyro sensitive unit transmission waveguide 44. The energy coupling is completed through the evanescent wave. There is no direct energy coupling between the two racetrack ring waveguide microcavities 5. Instead, indirect coupling is generated through the middle gyro sensitive unit transmission waveguide 44, which is used to construct a non-Hermitian system that satisfies anti-parity-time reversal symmetry.

[0086] The wide spectrum light source 1 adopts a SLD light source for a fiber optic gyroscope.

[0087] The broadband light generated by the broadband light source 1 is coupled into the waveguide structure for transmission through the mode spot converter 2, wherein the TM mode light is coupled into the TM mode coupling waveguide 32 through the polarizer 3, and then the TM mode light is rapidly lost through the TM mode dissipative waveguide 33 to achieve the polarization effect, and the retained TE mode light is transmitted to the gyro sensitive unit 4 through the polarizer transmission waveguide 31, and a part of the light passing through the polarizer 3 is coupled into the straight waveguide 46 of the runway ring waveguide microcavity 5 on both sides close to the gyro sensitive unit transmission waveguide 44, and then transmitted along the runway ring waveguide microcavity 5, and coupled back into the gyro sensitive unit transmission waveguide 44 again, and the above process is repeated, and another part of the light passing through the gyro sensitive unit transmission waveguide 44 is directly output to the photodetector 6.

[0088] The singular point photonic gyroscope chip also includes a silicon substrate 21 and a silicon dioxide buffer layer 22, a lithium niobate thin film layer 8 is arranged on the silicon dioxide buffer layer 22, and the silicon dioxide buffer layer 22 is arranged on the silicon substrate 21. The waveguide structures of the pattern spot converter 2, the polarizer 3, and the gyroscope sensitive unit 4 are all obtained by etching the lithium niobate thin film once or multiple times.

[0089] A method for detecting the rotation speed of a singular point photon gyroscope chip:

[0090] In the initial state, a feedback voltage is applied to the control electrode 47, and the refractive index of the two racetrack ring waveguide microcavities 5 is changed by utilizing the electro-optical effect of the lithium niobate material, thereby adjusting the resonant frequency difference between the racetrack ring waveguide microcavities 5, so that in the initial state, the gyro sensitive unit 4 is at the singular point of the non-Hermitian system, and the singular point photon gyro chip is in a working state;

[0091] In the working state, the light emitted by the wide-spectrum light source 1 is detected and received by the photodetector 5 after passing through the spot converter 2, the polarizer 3, and the gyro sensitive unit 4 in sequence;

[0092] When the gyro sensitive unit 4 rotates, due to the Sagnac effect, the resonant frequencies of the two racetrack ring waveguide microcavities 5 will change, so that the gyro sensitive unit 4 deviates from the singularity point, causing the output of the gyro sensitive unit 4 to change, and the beat frequency signal is detected in the photodetector 5. The current rotation speed can be obtained by substituting the beat frequency-rotation speed into the pre-fitted curve.

[0093] The specific detection process is as follows:

[0094] S1, in a stationary state, that is, when the external rotation speed is zero, the voltage on the control electrode 47 is adjusted according to the detection result of the photoelectric detector (6) until the gyro sensitive unit 4 is at a singular point, at which time there is no beat frequency signal;

[0095] S2. In the rotating state, that is, when the external rotation speed is not zero, the resonant frequency of the two racetrack ring waveguide microcavities 5 will change due to the Sagnac effect, so the gyro sensitive unit 4 will deviate from the singular point of the non-Hermitian system, which will generate a beat frequency signal in the photodetector 6. The beat frequency is detected, and the corresponding rotation speed can be obtained based on the relationship between the beat frequency and the rotation speed.

[0096] In a specific embodiment, the acceleration sensitive unit of the singular point optical microcavity acceleration sensor is designed as follows:

[0097] In this example, the wide-spectrum light source 1 uses an SLD light source tube core with a central wavelength of 1550 nanometers and a bandwidth greater than 30 nanometers. The optical power coupling ratio between the two racetrack ring waveguide microcavities 5 and the gyro sensitive unit transmission waveguide 44 is 90:10, that is, 90% of the light is coupled from the gyro sensitive unit transmission waveguide 44 into the racetrack ring waveguide microcavity 5; according to the conditions of the singular point of the non-Hermitian system, the relationship between the cavity lengths of the two racetrack ring waveguide microcavities 5 can be obtained as follows:

[0098]

[0099] Where c is the speed of light in vacuum, n represents the refractive index of the waveguide material, L1 and L2 represent the cavity lengths of the two racetrack ring waveguide microcavities 5, respectively, and m is the resonance order determined according to the incident wavelength and L1. Specifically, after the wavelength λ and the optical power coupling ratio between the waveguide microcavity and the gyro sensitive unit transmission waveguide 44 are given, the length L1 of one of the racetrack ring waveguide microcavities 5 can be given according to the chip size requirements, and the resonance order m can be calculated using the resonance condition, and the parameters can be substituted into the above formula to calculate the design length L2 of the other racetrack ring waveguide microcavity 5.

[0100] At the same time, the following two time-domain coupled mode equations of the racetrack ring waveguide microcavity 5 can be established:

[0101]

[0102] Wherein, t represents time, j is an imaginary unit, a1 represents the energy amplitude in one of the racetrack ring waveguide microcavities 5, a2 represents the energy amplitude in the other racetrack ring waveguide microcavity 5, ω1 and ω2 represent the resonant frequencies of the two racetrack ring waveguide microcavities 5, κ=μ1μ2 / 2 represents the indirect coupling coefficient between the two racetrack ring waveguide microcavities, γ represents the loss of the racetrack ring waveguide microcavity 5, S in represents the optical power entering the gyro sensitive unit 4 from the output end of the polarizer 3, μ1 represents the coupling coefficient between one of the racetrack ring waveguide microcavity 5 and the gyro sensitive unit transmission waveguide 44, and μ2 represents the coupling coefficient between the other racetrack ring waveguide microcavity 5 and the gyro sensitive unit transmission waveguide 44.

[0103] in:

[0104]

[0105] In the formula, μ 1，2 represents the coupling coefficient between the two racetrack ring waveguide microcavities 5 and the gyro sensing unit transmission waveguide 44, L 1，2 represents the cavity length of the two racetrack ring waveguide microcavities 5. In practical applications, it is necessary to ensure that the resonant frequency difference and the coupling coefficient satisfy the relationship:

[0106] |ω1-ω2|=μ1μ2

[0107] This makes the gyro sensitive unit 4 be at a singular point of a non-Hermitian system in the initial state.

[0108] Depend on Figure 1 The input-output relationship can be established as follows: the optical power S output from the output end of the gyro sensitive unit 4 out The expression is:

[0109] S out =S in -jμ1a1-jμ2a2

[0110] In the formula, S out represents the optical power output from the output end of the gyro sensitive unit 4, so the transfer function of the gyro sensitive unit 4 can be written as:

[0111]

[0112] Where T represents the transfer function of the gyro sensitive unit. By calculating the poles of the transfer function, the eigenfrequency can be obtained:

[0113]

[0114] In the formula, ω ±represents the eigenfrequency. At the singular point, |ω1-ω2|=μ1μ2, the square root of the above equation is 0, and no beat frequency signal is generated in the photodetector 6.

[0115] The rotation will cause the resonant frequencies of the two microcavities to change. The transmission direction of light in one of the racetrack ring waveguide microcavity 5 is the same as the rotation direction, and the transmission direction of light in the other racetrack ring waveguide microcavity 5 is opposite to the rotation direction. The expressions of eigenfrequency ω1 and ω2 are rewritten as ω1+Δω respectively. S1 ω2-Δω S2 , and using the conditions of the singular point to simplify, we can get the eigenfrequency under rotation:

[0116]

[0117] Where Δω S1 , Δω S2 is the change in resonant frequency caused by the Sagnac effect in the two waveguide microcavities, which is related to the rotation speed:

[0118]

[0119] Among them, Δω S1，S2 A represents the change in the resonant frequency caused by the two waveguide microcavities. 1，2 Respectively represent the area of ​​the two racetrack annular waveguide microcavities 5, Ω represents the rotation speed, and λ represents the wavelength. The change of the microcavity resonance frequency caused by the rotation is manifested as the splitting of the eigenfrequency in the gyro sensitive unit 4. At this time, a beat frequency signal can be detected in the photodetector 6. According to the beat frequency-rotation speed relationship given by the above formula, the current rotation speed can be obtained.

[0120] This embodiment constructs a second-order non-Hermitian system with anti-PT symmetry, which utilizes the characteristics of the non-Hermitian system singular point being sensitive to external perturbations, and has high sensitivity, small size and easy integration. The broadband light source is mixed and integrated into the gyroscope chip, solving the problem of light source integration of chip-level gyroscopes. The two runway ring waveguide microcavities with the same loss are constructed to utilize the characteristics of the non-Hermitian system singular point being sensitive to external perturbations, further improving the sensitivity and reducing the size of the sensor while maintaining the original advantages of the optical gyroscope.

[0121] A targeted mode spot converter was designed for the output mode spot of the wide-spectrum light source core. An elliptical end face mode field was obtained by using a partially etched double-layer inverted tapered waveguide, achieving efficient coupling of the wide-spectrum light source. The increase in the transmitted light power on the gyroscope chip further improved the sensitivity of signal detection.

[0122] An additional pair of electrodes was added to the straight waveguide area of ​​the two racetrack ring waveguide microcavities constructed. The electro-optic effect was used to change the refractive index of the waveguide microcavity, thereby adjusting the resonant frequency of the microcavity so that the sensor is at the singularity point. This effectively eliminates the influence of other interferences that may exist in the sensor application environment and the tolerance of the preparation process on the singularity point of the non-Hermitian system, realizes continuous control of the singularity point of the non-Hermitian system, and improves the practicality and preparation tolerance of the sensor.

[0123] This embodiment designs a chip-type polarizer suitable for lithium niobate film to ensure that the input light of the gyro sensitive unit is a single polarization light source, avoiding the interference of deviation error on the gyro signal. At the same time, the process is compatible with the traditional waveguide etching process, which is conducive to monolithic integration.

[0124] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A singular point photon gyroscope chip based on lithium niobate single crystal film, characterized in that: It comprises a wide-spectrum light source (1), a pattern spot converter (2), a polarizer (3), a gyro sensitive unit (4), a photodetector (6) and a lithium niobate thin film layer (8) located in a packaging shell (7); The broadband light source (1), the pattern spot converter (2), the polarizer (3), the gyro sensitive unit (4) and the photodetector (6) are all located on the upper surface of the lithium niobate thin film layer (8) and are arranged in sequence along the direction of the light path; the light emitted by the broadband light source (1) passes through the pattern spot converter (2), the polarizer (3) and the gyro sensitive unit (4) in sequence and is then received by the photodetector (6).

2. The singular point photon gyroscope chip according to claim 1, characterized in that: The pattern spot converter (2) is a double-layer inverted tapered waveguide obtained by etching twice, comprising an unetched lithium niobate film bottom layer (23) and an etched lower inverted tapered waveguide (24) and an upper inverted tapered waveguide (25), wherein the lithium niobate film bottom layer (23), the lower inverted tapered waveguide (24) and the upper inverted tapered waveguide (25) are stacked in sequence from bottom to top; The lower inverted tapered waveguide (24) and the upper inverted tapered waveguide are both ridge waveguides whose width increases along the optical path direction, and the height of the upper surface of the lower inverted tapered waveguide is consistent with the height of the upper surface of the lithium niobate film layer (8); The input end of the upper inverted tapered waveguide (25) is located in the middle of the lower inverted tapered waveguide (24), and the output end of the upper inverted tapered waveguide (25) is aligned with the output end of the lower inverted tapered waveguide (24).

3. The singular point photon gyroscope chip as claimed in claim 2, characterized in that: The lower inverted tapered waveguide (24) is divided into two sections of tapered waveguides which are sequentially connected and arranged along the optical path. The widths of the two sections of tapered waveguides gradually increase along the optical path. The output end of the tapered waveguide of the first section and the input end of the tapered waveguide of the second section are connected and have the same width.

4. The singular point photon gyroscope chip as claimed in claim 1, characterized in that: The polarizer (3) comprises a standard single-mode transmission waveguide (31), a TM mode coupling waveguide (32) and a TM mode dissipative waveguide (33); The input end of the standard single-mode transmission waveguide (31) is connected to the mode spot converter (2); the TM mode coupling waveguide (32) is placed at one side of the standard single-mode transmission waveguide (31) and is parallel to the standard single-mode transmission waveguide (31); the input end of the TM mode dissipative waveguide (33) is connected to the output end of the TM mode coupling waveguide (32); and the output end is bent and extended in a direction away from the polarizer transmission waveguide (31); The height and width of the TM mode coupling waveguide (32) are not equal to the height and width of the standard single-mode transmission waveguide (31), so that the TM mode can meet the phase matching conditions required for mode coupling, while the TE mode does not meet the phase matching conditions. The height of the TM mode coupling waveguide (32) is consistent with the height of the TM mode dissipative waveguide (33).

5. The singular point photon gyroscope chip as claimed in claim 4, characterized in that: The TM mode dissipative waveguide (33) is a waveguide whose width is narrowed after being bent 90 degrees along the transmission direction. The input end of the TM mode dissipative waveguide (33) is connected to the output end of the TM mode coupling waveguide (32).

6. The singular point photon gyroscope chip as claimed in claim 1, characterized in that: The gyro sensitive unit (4) comprises two microcavity electrode assemblies and a gyro sensitive unit transmission waveguide (44), the two microcavity electrode assemblies are respectively arranged on both sides of the gyro sensitive unit transmission waveguide (44), and the two microcavity electrode assemblies comprise a racetrack annular waveguide microcavity (5) and a pair of electrode pairs; The input end of the gyro sensitive unit transmission waveguide (44) is connected to a polarizer (3), the racetrack annular waveguide microcavity (5) is a waveguide in the shape of a racetrack annulus, and the straight racetrack region of the racetrack annular waveguide microcavity (5) is parallel to the gyro sensitive unit transmission waveguide (44) and is placed adjacently and spaced apart; The pair of electrodes consists of two control electrodes (47), and the two control electrodes (47) are arranged on a side of the racetrack annular waveguide microcavity (5) away from the gyro sensitive unit transmission waveguide (44).

7. The singular point photon gyroscope chip as claimed in claim 6, characterized in that: Each of the racetrack annular waveguide microcavities (5) is mainly composed of two parallel straight waveguides (46) with both ends aligned and two open arc waveguides (45), the two straight waveguides (46) are aligned at both ends along the optical path direction, one of the aligned ends is respectively connected to the two ends of an open arc waveguide (45), and the other aligned ends of the two straight waveguides (46) are respectively connected to the two ends of another open arc waveguide (45), and two control electrodes (47) are respectively arranged on both sides of the straight waveguide (46) away from the gyro sensitive unit transmission waveguide (44).

8. The singular point photon gyroscope chip as claimed in claim 7, characterized in that: The resonant frequency difference between the two racetrack annular waveguide microcavities (5) is designed to be: |ω1-ω2|=μ1μ2 Wherein ω1 and ω2 represent the resonant frequencies of the two racetrack annular waveguide microcavities (5), respectively, and μ1 and μ2 represent the coupling coefficients between the microcavity and the gyro sensitive unit transmission waveguide (44); According to the calculation formula of the resonance frequency and the coupling coefficient, the relationship between the cavity lengths of the two racetrack ring waveguide microcavities (5) can be obtained as follows: Wherein c is the speed of light in vacuum, n is the refractive index of the waveguide material, L1 and L2 represent the cavity lengths of the two racetrack annular waveguide microcavities (5), m is the resonance order determined according to the incident wavelength and the cavity length of L1, and κ1 and κ2 are the energy coupling ratios between the two waveguide microcavities and the transmission waveguide (44), respectively.

9. The singular point photon gyroscope chip as claimed in claim 1, characterized in that: The singular point photon gyroscope chip further comprises a silicon substrate (21) and a silicon dioxide buffer layer (22); the lithium niobate thin film layer (8) is arranged on the silicon dioxide buffer layer (22); and the silicon dioxide buffer layer (22) is arranged on the silicon substrate (21).

10. A rotation speed detection method for a singular point photon gyroscope chip according to any one of claims 1 to 9, characterized in that: In the initial state, a feedback voltage is applied to the control electrode (47), and the refractive index of the two racetrack ring waveguide microcavities (5) is changed by utilizing the electro-optical effect of the lithium niobate material, thereby adjusting the resonance frequency difference between the racetrack ring waveguide microcavities (5), so that in the initial state, the gyro sensitive unit (4) is at a non-Hermitian system singular point, and the singular point photon gyro chip is in a working state; In the working state, the light emitted by the wide-spectrum light source (1) is sequentially passed through the pattern spot converter (2), the polarizer (3), and the gyro sensitive unit (4) and then detected and received by the photoelectric detector (5); When the gyro sensitive unit (4) rotates, due to the Sagnac effect, the resonance frequency of the two racetrack annular waveguide microcavities (5) will change, thereby causing the gyro sensitive unit (4) to deviate from the singular point, causing the output of the gyro sensitive unit (4) to change, and a beat frequency signal is detected in the photoelectric detector (5). The current rotation speed can be obtained by substituting the beat frequency-rotation speed into the pre-fitted curve.

Images