A singular point photonic gyroscope chip based on lithium niobate single crystal thin film

Abstract

The application discloses a non-Hermite singular point photon gyroscope based on a lithium niobate single crystal thin film. The gyroscope comprises a wide-spectrum light source, a mode spot converter, a polarizer, a gyroscope sensitive unit, a photoelectric detector and a lithium niobate thin film layer in a packaging shell; the wide-spectrum light source, the mode spot converter, the polarizer, the gyroscope sensitive unit and the photoelectric detector are sequentially arranged on the upper surface of the lithium niobate thin film layer along the light path direction; the light emitted by the wide-spectrum light source is sequentially received by the photoelectric detector after passing through the mode spot converter, the polarizer and the gyroscope sensitive unit. The application utilizes the electro-optic effect of lithium niobate, adjusts the resonant frequency of a microcavity by applying a voltage, keeps the gyroscope sensitive unit at a singular point in an initial state, offsets the interference of external factors, constructs an anti-time reversal symmetry structure, utilizes the sensitivity of the singular point to external perturbation, improves the sensitivity of the gyroscope sensitive unit, and has the advantages of high sensitivity, small volume, strong practicability and integrability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of integrated optics and inertial sensing, and particularly to a singular point photonic gyroscope chip based on a lithium niobate single crystal thin film. BACKGROUND

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

[0003] The existence of internal moving parts of the mechanical gyroscope makes its power consumption and volume larger, and also has the problems of poor anti-vibration and anti-impact ability, sensitivity to gravity acceleration, etc., which limits its application in some fields. The emergence of optical gyroscope based on optical Sagnac effect provides a new way of thinking for the application of gyroscope. Since the optical Sagnac effect was proposed, the optical gyroscope has experienced the development process from ring laser gyroscope (RLG) to fiber optic gyroscope. At present, the RLG technology is very mature and has been applied in many high-precision navigation fields, but its internal photoelectric devices are numerous, large in size and expensive, which is not conducive to miniaturization. Although the fiber optic gyroscope solves the above problems to some extent, the signal generated by the Sagnac effect is proportional to the length of the fiber and the radius of the fiber ring, and the improvement of its performance comes at the cost of the increase of the length of the fiber and the radius of the fiber ring, so there is an inherent contradiction between high sensitivity and miniaturization. Today, with the increasing miniaturization of inertial sensing units, the development of chip-level gyroscope has become a problem to be solved in the field of inertial navigation.

[0004] In recent years, with the in-depth study of the field of micro-nano optics, integrated optical gyroscope has attracted widespread attention from researchers, and its research mainly focuses on the integration of optical devices. By integrating discrete fiber devices onto 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 earlier, the Sagnac effect is proportional to the length and radius of the sensitive ring, making it difficult to achieve miniaturization while maintaining high sensitivity in principle. SUMMARY

[0005] The research on the enhancement of Sagnac effect is the key to solve this contradiction. The non-Hermitian system is a system with energy exchange with the outside world or with gain and loss, and its physical quantity can be described by a non-Hermitian operator. Unlike the Hermitian system, the non-Hermitian system has a singular point (hereinafter referred to as an exceptional point). The exceptional point is a degenerate point of the non-Hermitian system, at which the real part and the imaginary part of the eigenvalue of the system are equal, the eigenvalue and the eigenstate are degenerate, and the eigenstate can no longer form a complete basis vector. The ultra-sensitive optical sensing based on the exceptional point is a research hotspot in the field of non-Hermitian optics at present, and it has different degrees of application in particle detection, temperature sensing, refractive index sensing, and rotational speed measurement. The application of the non-Hermitian optical system in the field of inertial sensing is expected to develop an optical gyroscope with high sensitivity and miniaturization.

[0006] In order to solve the problems in the background art, the present application proposes a lithium niobate single crystal thin film based exceptional point photon gyroscope chip with small volume, high sensitivity and easy packaging integration for non-Hermitian optical system, which is conducive to the miniaturization of high-sensitivity optical gyroscopes.

[0007] The present application utilizes the sensitive nature of the non-Hermitian optical system to external perturbations at the exceptional point, maintains the high sensitivity advantage of the optical gyroscope while reducing the gyroscope to a chip level, and is expected to solve the contradiction between high sensitivity and miniaturization of optical gyroscopes. In the design of the sensitive unit structure, the controllable additional phase is introduced in the racetrack ring-shaped microcavity by using the electro-optic effect, and the effective regulation of the exceptional point of the non-Hermitian system is realized. The present application has simple structure and high integration, and is expected to become a solution for miniaturization of high-sensitivity optical gyroscopes.

[0008] The technical scheme of the present application is:

[0009] I. A lithium niobate single crystal thin film based exceptional point photon gyroscope chip

[0010] It comprises a wide spectrum light source, a mode spot converter, a polarizer, a gyroscope sensitive unit, a photodetector and a lithium niobate thin film layer located in a packaging shell.

[0011] The wide spectrum light source, the mode spot converter, the polarizer, the gyroscope sensitive unit and the photodetector are all located on the upper surface of the lithium niobate thin film layer and arranged in sequence along the optical path. The light emitted by the wide spectrum light source is received by the photodetector after passing through the mode spot converter, the polarizer and the gyroscope sensitive unit in sequence.

[0012] The mode spot converter is a double-layer inverted cone-shaped waveguide obtained by twice etching, comprising an unetched lithium niobate thin film bottom layer and an etched lower inverted cone-shaped waveguide and an upper inverted cone-shaped waveguide, and the lithium niobate thin film bottom layer, the lower inverted cone-shaped waveguide and the upper inverted cone-shaped waveguide are stacked in sequence from bottom to top.

[0013] The lower inverted taper waveguide and the upper inverted taper waveguide are both ridge waveguides with the width gradually increasing along the light path direction, and the height of the upper surface of the lower inverted taper waveguide is consistent with the height of the upper surface of the lithium niobate thin film layer.

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

[0015] The lower inverted taper waveguide is divided into two sections of taper waveguides connected in sequence along the light path direction, the width of the two sections of taper waveguides gradually increases along the light path direction, and the output end of the first section of taper waveguide and the input end of the second section of taper waveguide are connected and have the same width.

[0016] The polarizer comprises a standard single-mode transmission waveguide, a TM mode coupling waveguide and a TM mode dissipating waveguide.

[0017] The input end of the standard single-mode transmission waveguide is connected with the mode spot converter, the TM mode coupling waveguide is arranged in parallel with the standard single-mode transmission waveguide on one side of the standard single-mode transmission waveguide, the input end of the TM mode dissipating waveguide is connected with the output end of the TM mode coupling waveguide, and the output end is bent and arranged in a direction away from the transmission waveguide of the polarizer.

[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 condition required by mode coupling, while the TE mode cannot meet the phase matching condition, and the height of the TM mode coupling waveguide is consistent with the height of the TM mode dissipating waveguide.

[0019] The TM mode dissipating waveguide is a waveguide with the width narrowed after being bent by 90° along the transmission direction, and the input end of the TM mode dissipating waveguide is connected with the output end of the TM mode coupling waveguide.

[0020] The gyroscopic sensing unit comprises two microcavity electrode assemblies and a gyroscopic sensing unit transmission waveguide, the two microcavity electrode assemblies are arranged on both sides of the gyroscopic sensing unit transmission waveguide, and each microcavity electrode assembly comprises a racetrack ring waveguide microcavity and a pair of electrodes.

[0021] The input end of the gyroscopic sensing unit transmission waveguide is connected with the polarizer, the racetrack ring waveguide microcavity is a waveguide in the shape of a racetrack ring, and the straight racetrack area of the racetrack ring waveguide microcavity is arranged in parallel with and adjacent to the gyroscopic sensing unit transmission waveguide.

[0022] The pair of electrodes comprises two control electrodes, and the two control electrodes are arranged on the side of the racetrack ring waveguide microcavity away from the gyroscopic sensing unit transmission waveguide.

[0023] Each of the racetrack ring resonator microcavities mainly comprises two straight waveguides in parallel and aligned at two ends and two open arc waveguides, the two straight waveguides are aligned at two ends along the light path direction, the aligned ends are respectively connected to two ends of one open arc waveguide, the other ends of the two straight waveguides are respectively connected to two ends of the other open arc waveguide, and the two control electrodes are respectively arranged on the two sides of the straight waveguide away from the transmission waveguide of the gyro sensitive unit.

[0024] The resonant frequency difference of the two racetrack ring resonator microcavities is designed as:

[0025] |ω1-ω2|=μ1μ2

[0026] Wherein ω1, ω2 respectively represent the resonant frequencies of the two racetrack ring resonator microcavities, μ1, μ2 represent the coupling coefficients between the microcavities 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 resonator microcavities can be obtained as:

[0028]

[0029] Wherein c is the speed of light in vacuum, n is the refractive index of the waveguide material, L1, L2 respectively represent the cavity lengths of the two racetrack ring resonator microcavities, m is the resonant order number determined according to the incident wavelength and the cavity length L1, κ1, κ2 respectively are the energy coupling proportions between the two waveguide microcavities and the transmission waveguide.

[0030] The singular point photonic gyro 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] II. A rotation speed detection method of a singular point photonic gyro chip

[0032] In the initial state, a feedback voltage is applied to the control electrode, the electro-optic effect of the lithium niobate material is used to change the refractive index of the two racetrack ring resonator microcavities, so as to adjust the resonant frequency difference between the racetrack ring resonator microcavities, so that the gyro sensitive unit is in a non-Hermite system singular point in the initial state, 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 photodetector in turn after passing through the mode spot converter, the polarizer and the gyro sensitive unit.

[0034] When the gyro-sensitive unit rotates, due to the Sagnac effect, the resonant frequency of the two racetrack ring resonator microcavities will change, so that the gyro-sensitive unit deviates from the singularity point, causes 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 according to the beat frequency-rotation speed fitting curve.

[0035] The present application has the following beneficial effects:

[0036] All devices are integrated on the silicon substrate, compared with the traditional optical gyro, the volume is smaller, the integration is higher, and the batch production is suitable.

[0037] The present application constructs a second-order non-hermitian system with anti-PT symmetry, uses the characteristics that the singularity point of the non-hermitian system is sensitive to external perturbation, has high sensitivity, small volume and is easy to integrate. And the wide spectrum light source is mixed and integrated on the gyro chip, solving the light source integration problem of the chip level gyro. Two waveguide microcavities with the same loss are constructed, which use the characteristics that the singularity point of the non-hermitian system is sensitive to external perturbation, further improve the sensitivity and reduce the volume of the sensor while maintaining the original advantages of the optical gyro.

[0038] The present application designs a specific mode spot converter for the exit mode spot of the wide spectrum light source tube, uses a partially etched double-layer inverted cone waveguide to obtain an elliptical end face mode field, realizes high efficiency coupling of the wide spectrum light source, and the increase of the transmission optical power on the gyro chip further improves the sensitivity of signal detection.

[0039] The present application adds a pair of electrodes to the straight waveguide area of the two racetrack ring resonator microcavities, introduces additional phase in the microcavity by using electro-optic effect, effectively eliminates the influence of other interference and preparation process tolerance in the application environment of the sensor on the singularity point of the non-hermitian system, realizes continuous controllability of the singularity point of the non-hermitian system, and improves the practicability and preparation tolerance of the sensor.

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

[0041] Figure 1 It is the whole structure schematic diagram of the singularity point photonic gyro chip based on lithium niobate single crystal thin film of the present application;

[0042] Figure 2 It is the structure schematic diagram of the mode spot converter in the present application;

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

[0044] Figure 4 This is a schematic diagram of the gyroscope sensing unit structure in this invention;

[0045] In the figure: 1. Broadband light source, 2. Mode converter, 3. Polarizer, 4. Gyroscope sensing element, 5. Runway-shaped waveguide microcavity, 6. Photodetector, 7. Encapsulation 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 conical waveguide, 25. Upper inverted conical waveguide; 31. Standard single-mode transmission waveguide, 32. TM mode coupled waveguide, 33. TM mode dissipative waveguide, 44. Gyroscope sensing element transmission waveguide, 45. Open arc waveguide, 46. Straight waveguide, 47. Control electrode. Detailed Implementation

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

[0047] like Figure 1 As shown, the singular point photonic gyroscope chip specifically implemented includes a broadband light source 1, a mode converter 2, a polarizer 3, a gyroscope sensing unit 4, a photodetector 6, and a lithium niobate thin film layer 8 located in the package shell 7.

[0048] The broadband light source 1, the mode converter 2, the polarizer 3, the gyroscope sensing unit 4, and the photodetector 6 are all located on the upper surface of the lithium niobate thin film layer 8 and arranged sequentially along the optical path direction; the light emitted from the broadband light source 1 is received by the photodetector 6 after passing through the mode converter 2, the polarizer 3, and the gyroscope sensing unit 4 in sequence.

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

[0050] like Figure 2 As shown, the mode converter 2 is a double-layer inverted conical waveguide obtained through two etching processes. It includes an unetched lithium niobate film substrate 23, and etched lower and upper inverted conical waveguides 24 and 25. Unlike traditional double-layer inverted conical waveguide structures, a portion of the unetched lithium niobate film substrate 23 is retained during the etching of the lower inverted conical waveguide 24. Therefore, the mode spots tend to distribute towards the unetched lithium niobate film substrate 23, making the mode field of the mode converter 2 near the broadband light source 1 elliptical, thus matching the elliptical beam emitted by the broadband light source 1. The lithium niobate film substrate 23, lower inverted conical waveguide 24, and upper inverted conical waveguide 25 are stacked sequentially from bottom to top.

[0051] The lower inverted taper waveguide 24 and the upper inverted taper waveguide are both ridge waveguides with the width gradually increasing along the light 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 the upper surface of the lower inverted taper waveguide is flush with the upper surface of the lithium niobate film layer 8, and the height of the upper surface of the upper inverted taper waveguide 25 is higher than the height of the upper surface of the lithium niobate film layer 8.

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

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

[0054] The etching depth is determined according to the optimized structure parameters. According to the preparation process, the thickness of the lower inverted taper 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 taper waveguide 24 is flush with the upper surface of the lithium niobate film layer 8.

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

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

[0057] The lower inverted taper waveguide 24 is divided into two tapered waveguides arranged in sequence along the light path direction, the width of the two tapered waveguides gradually increases along the light path direction, the output end of the first tapered waveguide and the input end of the second tapered waveguide are connected and have the same width, and the lengths of the two tapered waveguides are obtained by optimizing the designed input end and output end width, so as to realize low-loss transmission of light.

[0058] In actual design, the end face width and thickness of the lower inverted taper waveguide 24 and the upper inverted taper waveguide 25 and the thickness of the lithium niobate film bottom layer 23 should be optimized according to the actual mode field size of the selected wide-spectrum light source 1, so that the wide-spectrum light source 1 and the mode spot converter 2 can achieve the highest coupling efficiency.

[0059] As shown in Figure 3 The polarizer 3 includes a standard single-mode transmission waveguide 31, a TM mode coupling waveguide 32 and a TM mode dissipation waveguide 33.

[0060] The input end of the standard single-mode transmission waveguide 31 is connected to the upper inverted taper waveguide 25 of the mode spot converter 2, the TM mode coupling waveguide 32 is arranged on one side of the standard single-mode transmission waveguide 31 and parallel to the standard single-mode transmission waveguide 31, the input end of the TM mode dissipating waveguide 33 is connected to the output end of the TM mode coupling waveguide 32, and the output end is arranged to bend and extend away from the polarizer transmission waveguide 31;

[0061] The height and width of the TM mode coupling waveguide 32 are not equal to those of the standard single-mode transmission waveguide 31, so that the TM mode satisfies the phase matching condition required by mode coupling, while the TE mode does not satisfy the phase matching condition. The height of the TM mode coupling waveguide 32 is consistent with that of the TM mode dissipating 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 completely coupled into the TM mode coupling waveguide 32 by evanescent wave, and the TE mode continues to transmit in the standard single-mode transmission waveguide 31 of the polarizer 3.

[0063] The TM mode dissipating waveguide 33 is a waveguide that narrows in width after bending 90° in the transmission direction. The input end of the TM mode dissipating waveguide 33 is connected to the output end of the TM mode coupling waveguide 32, and other parameters are the same as those of the TM mode coupling waveguide 32. The design of bending in the transmission direction makes the transmission direction of the TM mode perpendicular to that of the TE mode, so as to reduce the signal interference on the TE mode. The gradually narrowing width increases the loss of the TM mode, so that the TM mode is quickly lost after coupling, achieving the effect of polarization. Finally, the standard single-mode transmission waveguide 31 of the polarizer 3 only outputs the TE mode into the gyro sensitive unit 4.

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

[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, and the output end of the gyro sensitive unit transmission waveguide 44 is connected to the input end of the photodetector 6. The racetrack ring waveguide microcavity 5 is a waveguide in the shape of a racetrack ring. The straight racetrack area of the racetrack ring waveguide microcavity 5 is parallel to and adjacent to the gyro sensitive unit transmission waveguide 44.

[0066] The pair of electrodes is composed of two modulation electrodes 47 arranged on the side of the racetrack ring resonator microcavity 5 away from the transmission waveguide 44 of the gyro sensitive unit.

[0067] Each racetrack ring resonator microcavity 5 is mainly composed of two straight waveguides 46 parallel to each other and aligned at both ends, and two open arc waveguides 45, the two ends of the two straight waveguides 46 are respectively aligned, and the aligned ends are respectively connected to the two ends of one open arc waveguide 45, the other ends of the two straight waveguides 46 are respectively connected to the two ends of the other open arc waveguide 45, and the two modulation electrodes 47 are respectively arranged in parallel and spaced apart on the two sides of the straight waveguide 46 away from the transmission waveguide 44 of the gyro sensitive unit.

[0068] The side of the two racetrack ring resonator microcavities 5 away from the modulation electrodes 47 is close to but not in contact with the transmission waveguide 44, so that the coupling between each racetrack ring resonator microcavity 5 and the transmission waveguide 44 of the gyro sensitive unit can occur through evanescent waves, and the spacing between the racetrack ring resonator microcavity 5 and the transmission waveguide 44 of the gyro sensitive unit determines the coupling coefficient between them, and the gyro sensitive unit is at the singularity point, which requires that the coupling coefficient and the resonant frequency of the microcavity satisfy the relationship:

[0069] |ω1-ω2|=μ1μ2

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

[0071] Due to the existence of micro-nano processing errors and the interference of external factors such as environment, the above-mentioned singularity point condition is usually difficult to meet, resulting in that the gyro sensitive unit 4 deviates from the singularity point, affecting the measurement of the rotation speed. The modulation electrodes 47 change the refractive index of the two racetrack ring resonator microcavities 5 by applying corresponding feedback voltages and using the electro-optic effect of lithium niobate, so that the resonant frequency of the microcavity can be adjusted, so that the gyro sensitive unit 4 is at the non-Hermite system singularity point in the initial state. The design of the modulation electrodes 47 realizes the continuous controllability of the singularity point, effectively inhibiting the influence of preparation errors and environmental interference on the performance of the gyro sensitive unit 4.

[0072] In the working process of the singularity point photon gyroscope chip:

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

[0074] When working, the modulation electrodes 47 are applied with corresponding feedback voltages, the refractive index of the two racetrack ring resonator microcavities 5 is changed by using the electro-optic effect of lithium niobate, so as to adjust the resonant frequency difference between the microcavities, so that the gyro sensitive unit 4 is at the non-Hermite system singularity point in the initial state, and the sensor is in working state;

[0075] In working state, the light emitted by the broadband light source 1 is sequentially detected by the photoelectric detector 6 after passing through the mode spot converter 2, the polarizer 3 and the gyro sensitive unit 4.

[0076] When the gyro sensitive unit 4 rotates, the resonant frequencies of the two racetrack ring resonator microcavities 5 will change due to the Sagnac effect, so that the gyro sensitive unit 4 deviates from the singularity point, causing the output of the sensor to change, which is manifested as a beat frequency signal in the photoelectric detector 6. According to the beat frequency-rotation speed relationship by substituting the pre-fitted curve, the current rotation speed can be obtained.

[0077] No voltage is applied to the control electrode 47, and the singularity point photonic gyroscope chip does not work.

[0078] The resonant frequency difference of the two racetrack ring resonator microcavities 5 is designed as:

[0079] |ω1-ω2|=μ1μ2

[0080] Where ω1, ω2 represent the resonant frequencies of the two racetrack ring resonator microcavities 5, and μ1, μ2 represent the coupling coefficients between the microcavities 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 resonator microcavities 5 can be obtained as:

[0082]

[0083] 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 resonator microcavities 5, respectively, m is the resonant order number determined according to the incident wavelength and the cavity length L1, and κ1 and κ2 are the energy coupling proportions between the two waveguide microcavities and the transmission waveguide 44, which can be flexibly determined within the range of 0-1.

[0084] In actual design, the energy coupling proportion can be set according to the way of κ1=κ2, then one of the cavity lengths L1 of the two racetrack ring resonator microcavities 5 is set according to the size requirement of the sensor, the resonant order number m is calculated according to the wavelength of the light source, and the other cavity length L2 of the racetrack ring resonator microcavity 5 is obtained by substituting the above formula. As can be seen from the above formula, the cavity lengths of the two racetrack ring resonator microcavities 5 are slightly different, so their resonant frequencies are also different. At the same time, in order to construct a non-Hermite system, the same loss is artificially introduced in the two racetrack ring resonator microcavities 5.

[0085] The two racetrack ring resonator microcavities 5 in the gyro-sensitive unit 4 only have energy coupling with the middle gyro-sensitive unit transmission waveguide 44, and the energy coupling is completed through evanescent waves. The two racetrack ring resonator microcavities 5 do not have direct energy coupling, but have indirect coupling through the middle gyro-sensitive unit transmission waveguide 44, and are used to construct a non-Hermite system satisfying the anti-time reversal symmetry.

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

[0087] The wide-spectrum light generated by the wide-spectrum light source 1 is coupled into the waveguide structure through the mode spot converter 2. The TM mode light passes through the polarizer 3 and is coupled into the TM mode coupling waveguide 32. Then, the TM mode light is quickly lost through the TM mode dissipating waveguide 33, so as to achieve the polarization effect. The remaining TE mode light is transmitted to the gyro-sensitive unit 4 through the polarizer transmission waveguide 31. Part of the light passing through the polarizer 3 is coupled into the straight waveguide 46 of the two racetrack ring resonator microcavities 5 close to the gyro-sensitive unit transmission waveguide 44, and then is transmitted along the racetrack ring resonator microcavities 5, coupled back into the gyro-sensitive unit transmission waveguide 44 again, and the above process is repeated. The other part of the light passing through the gyro-sensitive unit transmission waveguide 44 is directly output into the photodetector 6.

[0088] The singularity 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. The waveguide structure of the mode spot converter 2, the polarizer 3 and the gyro-sensitive unit 4 is obtained by etching the lithium niobate thin film once or multiple times.

[0089] A rotation speed detection method of a singularity point photon gyroscope chip:

[0090] In the initial state, a feedback voltage is applied to the control electrode 47, and the electro-optic effect of the lithium niobate material is used to change the refractive index of the two racetrack ring resonator microcavities 5, so as to adjust the resonance frequency difference between the two racetrack ring resonator microcavities 5, so that the gyro-sensitive unit 4 is in a non-Hermite system singularity point in the initial state, and the singularity point photon gyroscope chip is in a working state.

[0091] In the working state, the light emitted by the wide-spectrum light source 1 is sequentially detected and received by the photodetector 6 after passing through the mode spot converter 2, the polarizer 3 and the gyro-sensitive unit 4.

[0092] When the gyro-sensitive unit 4 rotates, the resonance frequencies of the two racetrack ring resonator microcavities 5 will change due to the Sagnac effect, so that the gyro-sensitive unit 4 deviates from the singularity point, causing the output of the gyro-sensitive unit 4 to change. A beat frequency signal is detected in the photodetector 6. According to the beat frequency-rotation speed curve fitted in advance, the current rotation speed can be obtained.

[0093] The detection process is specifically:

[0094] S1, in the static state, i.e. 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 the singular point, at which time there is no beat frequency signal;

[0095] S2, in the rotating state, i.e. when the external rotation speed is not zero, the resonant frequency of the two racetrack ring resonators 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 photoelectric detector 6, the beat frequency is detected, and the corresponding rotation speed can be obtained according to the relationship between the beat frequency and the rotation speed.

[0096] In specific embodiments, 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 center wavelength of 1550 nanometers and a bandwidth greater than 30 nanometers, and the light power coupling ratio between the two racetrack ring resonators 5 and the gyro-sensitive unit transmission waveguide 44 is 90:10, i.e. 90% of the light is coupled from the gyro-sensitive unit transmission waveguide 44 into the racetrack ring resonator 5; According to the condition of the singular point of the non-Hermitian system, the relationship between the lengths of the two racetrack ring resonators 5 can be obtained as:

[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 lengths of the two racetrack ring resonators 5, respectively, and m is the resonance order determined according to the incident wavelength and L1. Specifically, after the wavelength λ and the light 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 resonators 5 can be given according to the chip size requirement, the resonance order m is calculated using the resonance condition, and the parameters are substituted into the above formula to calculate the design length L2 of the other racetrack ring resonator 5.

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

[0101]

[0102] where t represents time, j is imaginary unit, a1 represents the energy amplitude in one of the racetrack ring resonator microcavities 5, a2 represents the energy amplitude in the other racetrack ring resonator microcavity 5, ω1, ω2 represent the resonant frequencies of the two racetrack ring resonator microcavities 5 respectively, κ = μ1μ2 / 2 represents the indirect coupling coefficient between the two racetrack ring resonator microcavities, γ represents the loss of the racetrack ring resonator 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 resonator microcavities 5 and the gyro-sensitive unit transmission waveguide 44, and μ2 represents the coupling coefficient between the other racetrack ring resonator microcavity 5 and the gyro-sensitive unit transmission waveguide 44.

[0103] wherein:

[0104]

[0105] wherein μ 1,2 represents the coupling coefficients between the two racetrack ring resonator microcavities 5 and the gyro-sensitive unit transmission waveguide 44 respectively, L 1,2 represents the cavity length of the two racetrack ring resonator microcavities 5, and in practical applications, the resonant frequency difference and the coupling coefficient need to satisfy the relationship:

[0106] |ω1-ω2| = μ1μ2

[0107] so that the gyro-sensitive unit 4 is in the singular point of the non-Hermite system in the initial state.

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

[0109] S out = S in -jμ1a1-jμ2a2

[0110] wherein S out represents the optical power output from the output end of the gyro-sensitive unit 4, and thus the transfer function of the gyro-sensitive unit 4 can be written as:

[0111]

[0112] wherein T represents the transfer function of the gyro-sensitive unit, and the poles of the transfer function are calculated to obtain the eigenfrequency:

[0113]

[0114] wherein ω ±ω1-ω2=μ1μ2, the under-root of the above formula is 0 at the singular point, and no beat frequency signal is generated in the photodetector 6.

[0115] Rotation will cause the change of the resonant frequencies of the two microcavities, one of which is the same as the rotation direction of the light transmission direction in the racetrack ring waveguide microcavity 5, and the other is opposite to the rotation direction of the light transmission direction in the racetrack ring waveguide microcavity 5, and the expressions of the eigenfrequencies ω1 and ω2 are respectively rewritten as ω1+Δω S1 and ω2-Δω S2 , and by using the singular point condition and simplifying, the eigenfrequencies under the rotation condition can be obtained:

[0116]

[0117] where Δω S1 and Δω S2 are the change amounts of the resonant frequencies caused by the Sagnac effect in the two waveguide microcavities, and are related to the rotation speed:

[0118]

[0119] where Δω S1,S2 represents the change amount of the resonant frequencies caused in the two waveguide microcavities, A 1,2 respectively represent the areas of the two racetrack ring waveguide microcavities 5, Ω represents the rotation speed, and λ represents the wavelength. The change of the microcavity resonant frequencies caused by the rotation is manifested as the splitting of the eigenfrequencies in the gyro sensitive unit 4, and at this time, a beat frequency signal can be detected in the photodetector 6. According to the beat frequency-rotation speed relationship given in the above formula, the current rotation speed can be obtained.

[0120] The embodiment constructs a second-order non-Hermite system with anti-PT symmetry, uses the characteristics that the singular point of the non-Hermite system is sensitive to external perturbations, has high sensitivity, small volume and is easy to integrate. The wide-spectrum light source is mixed and integrated on the gyro chip, and the problem of light source integration of the chip-level gyro is solved. Two racetrack ring waveguide microcavities with the same loss are constructed, which uses the characteristics that the singular point of the non-Hermite system is sensitive to external perturbations, further improves the sensitivity while maintaining the original advantages of the optical gyro, and reduces the volume of the sensor.

[0121] A specific mode spot converter is designed for the mode spot of the wide-spectrum light source tube, an elliptical end face mode field is obtained by using a partially etched double-layer inverted conical waveguide, high-efficiency coupling of the wide-spectrum light source is realized, and the increase of the transmission light power on the gyro chip further improves the sensitivity of signal detection.

[0122] The straight waveguide area of the two racetrack ring waveguide microcavities is additionally added with a pair of electrodes, the refractive index of the waveguide microcavity is changed by using the electro-optic effect, the resonant frequency of the microcavity is adjusted, the sensor is placed at the singular point, the influence of other interference possibly existing in the application environment of the sensor and the tolerance of the preparation process on the singular point of the non-Hermitian system is effectively eliminated, the continuous controllability of the singular point of the non-Hermitian system is realized, and the practicability and preparation tolerance of the sensor are improved.

[0123] The embodiment designs a chip type polarizer suitable for lithium niobate thin film, ensures that input light of a gyro sensitive unit is a single polarized light source, avoids interference of deviation error on a gyro signal, is compatible with a traditional waveguide etching process in a process, and is favorable for realizing monolithic integration.

[0124] The above merely describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A singular point photonic gyroscope chip based on lithium niobate single crystal thin film, characterized in that: it comprises a wide spectrum light source (1), a mode 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); the wide spectrum light source (1), the mode spot converter (2), the polarizer (3), the gyroscope sensitive unit (4) and the photodetector (6) are all located on the upper surface of the lithium niobate thin film layer (8) and arranged in sequence along the light path direction; the light emitted by the wide spectrum light source (1) is received by the photodetector (6) after passing through the mode spot converter (2), the polarizer (3) and the gyroscope sensitive unit (4) in sequence; the gyroscope sensitive unit (4) comprises two microcavity electrode assemblies and a gyroscope sensitive unit transmission waveguide (44), the two microcavity electrode assemblies are arranged on the two sides of the gyroscope sensitive unit transmission waveguide (44) respectively, and each microcavity electrode assembly comprises a racetrack ring waveguide microcavity (5) and a pair of electrodes; the input end of the gyroscope sensitive unit transmission waveguide (44) is connected with the polarizer (3), the racetrack ring waveguide microcavity (5) is a waveguide in the shape of a racetrack ring, the straight racetrack area of the racetrack ring waveguide microcavity (5) is parallel to the gyroscope sensitive unit transmission waveguide (44) and is placed in adjacent space; the pair of electrodes is composed of two control electrodes (47), and the two control electrodes (47) are arranged on the side of the racetrack ring waveguide microcavity (5) away from the gyroscope sensitive unit transmission waveguide (44). 2.The singular point photonic gyroscope chip according to claim 1, characterized in that: the mode spot converter (2) is a double-layer inverted taper waveguide obtained by twice etching, comprising an unetched lithium niobate thin film bottom layer (23), an etched lower inverted taper waveguide (24) and an upper inverted taper waveguide (25), and the lithium niobate thin film bottom layer (23), the lower inverted taper waveguide (24) and the upper inverted taper waveguide (25) are sequentially stacked from bottom to top; the lower inverted taper waveguide (24) and the upper inverted taper waveguide are both ridge waveguides with increasing width along the light path direction, and the height of the upper surface of the lower inverted taper waveguide is consistent with the height of the upper surface of the lithium niobate thin film layer (8); the input end of the upper inverted taper waveguide (25) is located in the middle of the lower inverted taper waveguide (24), and the output end of the upper inverted taper waveguide (25) is aligned with the output end of the lower inverted taper waveguide (24). 3.The singular point photonic gyroscope chip according to claim 2, characterized in that: the lower inverted taper waveguide (24) is divided into two taper waveguides which are connected and arranged in sequence along the light path direction, the width of the two taper waveguides gradually increases along the light path direction, and the output end of the first taper waveguide and the input end of the second taper waveguide are connected and have the same width. 4.The singular point photonic gyroscope chip according to 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 dissipation 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 arranged on one side of the standard single-mode transmission waveguide (31) and parallel to the standard single-mode transmission waveguide (31), the input end of the TM mode dissipating waveguide (33) is connected to the output end of the TM mode coupling waveguide (32), and the output end is arranged to extend and bend away from the standard single-mode 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 condition required by mode coupling, and the TE mode does not meet the phase matching condition, and the height of the TM mode coupling waveguide (32) is consistent with the height of the TM mode dissipating waveguide (33).

5. The singularity point photonic gyroscope chip of claim 4, wherein: The TM mode dissipating waveguide (33) is a waveguide that narrows in width after bending 90° in the transmission direction, and the input end of the TM mode dissipating waveguide (33) is connected to the output end of the TM mode coupling waveguide (32).

6. The singularity point photonic gyroscope chip of claim 1, wherein: Each of the racetrack ring waveguide microcavities (5) mainly consists of two straight waveguides (46) parallel to each other and aligned at both ends, and two open arc waveguides (45), the two straight waveguides (46) are aligned at both ends along the optical path direction, the aligned ends of the two straight waveguides (46) are respectively connected to the two ends of one open arc waveguide (45), the other ends of the two straight waveguides (46) are respectively connected to the two ends of the other open arc waveguide (45), and two control electrodes (47) are respectively arranged on the two sides of the straight waveguides (46) away from the transmission waveguide (44) of the gyroscope sensing unit.

7. The singularity point photonic gyroscope chip of claim 6, wherein: The resonant frequency difference of the two racetrack ring waveguide microcavities (5) is designed as: |ω1-ω2|=μ1μ2 Where ω1, ω2 represent the resonant frequencies of the two racetrack ring waveguide microcavities (5), and μ1, μ2 represent the coupling coefficients between the microcavities and the transmission waveguide (44) of the gyroscope sensing unit. 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: 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 (5), m is the resonant order number determined according to the incident wavelength and the cavity length L1, and κ1 and κ2 are the energy coupling proportions between the two waveguide microcavities and the transmission waveguide (44).

8. The singularity point photonic gyroscope chip of claim 1, wherein: The singularity point photonic 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).

9. A rotation speed detection method applied to the singularity point photonic gyroscope chip of claim 7, wherein: In the initial state, the feedback voltage is applied to the control electrode (47), the refractive index of the two racetrack ring resonator microcavities (5) is changed by using the electro-optic effect of lithium niobate material, so as to adjust the resonance frequency difference between the racetrack ring resonator microcavities (5), so that the gyro sensitive unit (4) is in the non-Hermite system singular point in the initial state, and the singular point photonic gyroscope chip is in the working state; In the working state, the light emitted by the wide-spectrum light source (1) is sequentially converted by the mode spot converter (2), the polarizer (3) and the gyro sensitive unit (4), and then is detected and received by the photoelectric detector (6); When the gyro sensitive unit (4) rotates, due to the Sagnac effect, the resonance frequencies of the two racetrack ring resonator microcavities (5) will change, so that the gyro sensitive unit (4) deviates from the singular point, the output of the gyro sensitive unit (4) changes, the beat frequency signal is detected in the photoelectric detector (6), and the current rotation speed can be obtained according to the beat frequency-rotation speed fitting curve.

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