Novel reciprocity resonance interference combined type integrated optical gyroscope sensor and detection method

Abstract

The invention discloses a novel reciprocity resonance interference combined type integrated optical gyroscope sensing and detection method, and belongs to the field of integrated optical gyroscopes. Firstly, an integrated optical gyroscope optical path sensing module is built, light emitted by a laser is split and modulated after sequentially passing through a circulator and a phase modulator and is split again after passing through a straight-through end coupler of a resonant cavity, two light beams are output to a photoelectric detector I and a photoelectric detector II after passing through an isolator from a straight-through end, and the other two light beams are output from a transmission end after entering the cavity for resonance; the light returns to the circulator for light combination interference and is output to a photoelectric detector III; generating a laser frequency locking signal by using light output from the straight-through end, and returning the laser frequency locking signal to the laser to form a closed loop so as to complete establishment of a laser frequency locking detection module; after the laser locks the resonant frequency of the resonant cavity, light is output from the transmission end, construction of a differential interference sensitive angular velocity detection module is completed, and the final gyro angular velocity is output. The invention solves the problem that the optical path scheme of the resonant gyroscope is not reciprocal and is easily influenced by environment temperature change.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of integrated optical gyroscopes, and particularly relates to a novel reciprocal resonant-interference combined integrated optical gyroscope sensing and detection method. BACKGROUND

[0002] Inertial navigation systems have a wide range of applications in weapon equipment, ocean exploration, automobile navigation and mobile phone positioning and orientation due to their completely autonomous navigation and high concealment. As a key component of the inertial navigation system, an optical gyroscope has an important influence on the performance thereof.

[0003] Fiber-optic gyroscopes have a wide application basis in high-precision inertial navigation, but are restricted in small size, low power consumption and light weight application occasions to different degrees. With the development of integrated photonics technology, integrated optical gyroscopes develop towards higher precision, smaller size and higher integration on the basis of laser gyroscopes and fiber-optic gyroscopes.

[0004] The sensing unit of the integrated optical gyroscope is a waveguide instead of an optical fiber, and part or all of active / passive devices such as light sources, modulators, beam splitters and detectors are integrated on a chip by monolithic integration or hybrid integration technology, so as to realize microsystemization. Meanwhile, the integrated optical technology is not sensitive to electromagnetic interference, is less affected by vibration, can be used in harsh environments, and has high scalability, and therefore becomes a research hotspot of a new generation of optical gyroscopes.

[0005] So far, researchers at home and abroad have carried out fruitful work from aspects of integrated optical gyroscope overall scheme, waveguide optical path design and processing and gyroscope signal processing.

[0006] The integrated optical gyroscope overall scheme mainly includes an interference type and a resonant type. The interference type integrated optical gyroscope loop has reciprocity, but the sensitivity thereof is positively related to the length of the interference optical path, and it is difficult to solve the contradiction between miniaturization and high precision, and it is still difficult to process a long-distance interference ring on a small-size chip. The resonant type integrated optical gyroscope doubles the sensitivity through a resonant cavity, and light is circulated in the cavity. The equivalent optical path of the resonant cavity can reach several hundreds or even thousands of times of the geometric perimeter, but the optical path, especially the part from the integrated optical phase modulator to the input resonant cavity, is non-reciprocal, so that the output is susceptible to environmental disturbances. The overall performance is still difficult to meet the actual application requirements. The interference type integrated optical gyroscope has reciprocity, but the sensitivity thereof depends on the length of the sensing ring and is difficult to break through the contradiction between high precision and miniaturization. The resonant type integrated optical gyroscope doubles the sensitivity through resonance, but the principle of detecting the light after clockwise and counterclockwise resonance respectively cannot eliminate the non-reciprocal error of the optical path in the application environment.

[0007] Based on the above considerations, it is particularly important to study a new type of reciprocal resonant interference combined integrated optical gyroscope sensing and detection method. The key is to make the path of light from the modulator beam splitting into clockwise and counterclockwise light to the modulator light combining completely the same, realize the reciprocal optical path sensitive angular velocity, so that the change amount of waveguide light transmission phase caused by thermal effect in the resonant cavity and the additional temperature error caused by inconsistent waveguide preparation outside the resonant cavity are the same, the Sagnac phase signs of clockwise and counterclockwise light are opposite, and the thermal disturbance error is offset when the modulator light combining differential interference. Therefore, the new type of reciprocal resonant interference combined integrated optical gyroscope sensing and detection method not only resists the disturbance of the temperature change environment, but also the Sagnac phase multiplication coefficient is proportional to the resonant cavity clarity, the higher the clarity, the higher the sensitivity of the gyroscope, which can break through the bottleneck that the sensitivity of the optical gyroscope is limited by the size, and lay a foundation for the development of miniaturized and high-precision integrated optical gyroscope. SUMMARY

[0008] In view of the above problems, the present application provides a new type of reciprocal resonant interference combined integrated optical gyroscope sensing and detection method, which combines the strong reciprocity of the optical path of the interference type gyroscope and the resonant multiplication of the optical path of the resonant type gyroscope, breaks through the bottleneck that the sensitivity of the interference type gyroscope is proportional to the size of the waveguide ring and is difficult to balance miniaturization and high precision, and solves the problem that the non-reciprocity of the optical path scheme of the resonant type gyroscope is easily affected by the environmental temperature change.

[0009] The new type of reciprocal resonant interference combined integrated optical gyroscope sensing and detection method has the following specific steps:

[0010] Step one, build a new type of reciprocal resonant interference combined integrated optical gyroscope optical path sensing module;

[0011] The integrated optical gyroscope optical path sensing module comprises a laser, a circulator, a phase modulator, a resonant cavity, two isolators and three photodetectors.

[0012] The laser is connected with the Y waveguide phase modulator through the circulator, the output ends of the phase modulator are connected with the input ends of the resonant cavity, respectively, the two straight-through ends of the resonant cavity are connected with the photodetector I and the photodetector II through the isolators ISO1 and ISO2, respectively; the circulator is connected with the photodetector III, the photodetector III is connected with the Sagnac phase demodulator and the angular velocity closed loop controller in sequence.

[0013] The clockwise and counterclockwise light is combined at an integrated optical phase modulator to output differential interference, the whole path of the clockwise and counterclockwise light from beam splitting to light combination sensitive to Sagnac effect is completely consistent, and the reciprocal optical path sensitive to angular velocity is realized. The reciprocity of the interference type gyroscope and the resonant multiplication sensitive loop of the resonant type gyroscope are ingeniously combined, the sensitivity of the light in the single loop resonant cavity is greatly enhanced, the reciprocal optical path sensitive to angular velocity is realized, the problem that the resonant type gyroscope is easily affected by the temperature change environment is solved, and the bottleneck that the precision of the interference type gyroscope is proportional to the size and cannot be miniaturized is broken through.

[0014] In the aspect of signal detection, a method of differential measurement resonant cavity with cooperative control of key optical parameters of multi-state wave modulation is proposed, the common mode signal obtained by summing the outputs of the detectors of the straight-through end of the clockwise and counterclockwise light is used to cancel the angular velocity information to realize the frequency locking of the laser, and the driving light resonates in the resonant cavity; and the clockwise and counterclockwise light resonates to realize the differential interference sensitive to angular velocity, the environmental disturbance resistance of the reciprocal differential measurement resonant cavity is realized, and the environmental adaptability of the integrated optical gyroscope is effectively improved.

[0015] In step two, in the optical path sensing module of the integrated optical gyroscope, the light emitted by the laser is sequentially split and modulated after passing through the circulator and the phase modulator, and is again split through the through end coupler of the resonant cavity, wherein two beams of light are output to the photodetectors I and II after passing through the isolator from the reflection end (through end) of the resonant cavity, and the other two beams of light are output from the transmission end after resonating in the cavity, and are returned to the circulator through the modulator to output interference to the photodetector III;

[0016] In step three, the two beams of light output from the reflection end are used to generate a laser frequency locking signal, and are returned to the laser to form a closed loop; and the laser frequency locking detection module of the integrated optical gyroscope optical path is built.

[0017] The two beams of light output from the reflection end reach the photodetectors I and II respectively, and are summed after being converted into circuit signals to measure the common mode signal to cancel the Sagnac phase, realize the extraction of the center frequency of the resonant cavity, and generate a laser frequency locking signal after resonant frequency demodulation. At this time, the frequency locking precision only affects the interference light intensity fluctuation and does not affect the closed loop detection of the Sagnac phase, so the laser frequency is locked near the center frequency of the resonant cavity, thereby reducing the requirement for the laser frequency locking precision.

[0018] The output light intensity of the two beams of light output from the reflection end is respectively:

[0019]

[0020]

[0021] I out_r_cw is the output light intensity of the clockwise light; I out_r_ccwis the light intensity of the clockwise light output; I0 is the input light intensity; k c is the coupling ratio of the resonant cavity coupler; q is the electric field intensity of the incident light passing through the two straight-through end couplings and one round of waveguide loss when transmitting one round in the resonant cavity; f0 is the resonant frequency of the resonant cavity, and Δf = f - f0 is the difference between the input light frequency and the static resonant frequency; f bias is the equivalent frequency shift; τ is the transit time.

[0022] The corresponding demodulation results are respectively:

[0023]

[0024]

[0025]

[0026] wherein is the phase shift caused by the Sagnac effect, and the sum of the demodulation results of the clockwise and counterclockwise directions can eliminate the influence of the Sagnac effect. Taking this demodulation result as the error input of the controller, the adjustment coefficient can realize the locking of the laser frequency, so that the laser works at the required resonant frequency.

[0027] Step four, after the laser is locked at the resonant frequency of the resonant cavity, the two beams of light output from the transmission end are used to complete the construction of the integrated optical gyroscope light path differential interference sensitive angular velocity detection module, and the final detected angular velocity of the gyroscope is output.

[0028] The key of the method lies in that the light is split into clockwise and counterclockwise light at the modulator, and then the light reaches the modulator again. The paths of the clockwise and counterclockwise light are completely the same. The change amount of the waveguide light transmission phase caused by the thermal effect in the resonant cavity and the additional temperature error caused by the inconsistent waveguide preparation outside the resonant cavity have the same sign. The Sagnac phase signs of the clockwise and counterclockwise light are opposite, and the thermal effect disturbance error is offset when the light returns to the modulator and interferes. Therefore, the reciprocal sensing optical path not only resists the disturbance of the temperature change environment, but also has a Sagnac phase multiplication coefficient proportional to the resonant cavity clarity. The higher the clarity, the higher the sensitivity of the gyroscope, which can break through the bottleneck of the limited size of the optical gyroscope sensitivity, and lay a foundation for the development of miniaturized and high-precision integrated optical gyroscopes.

[0029] The clockwise and counterclockwise light after entering the cavity forms resonance in the resonant cavity and is output from the transmission end respectively, returns to the circulator through the modulator for light interference, and is output to the photodetector III. After being converted into an electrical circuit signal, Sagnac phase demodulation and angular velocity closed-loop control are performed to obtain the final angular velocity output of the gyroscope;

[0030] Meanwhile, the demodulated bias signal is used as error feedback to the system to generate an additional closed-loop feedback signal, which, together with a modulation signal generated by direct digital synthesis (DDS) in the circuit system, is applied to a phase modulator after digital-to-analog conversion to form a second closed loop.

[0031] The demodulation result of the combined light interference transmission light signal is:

[0032]

[0033] where I0 is the input light intensity, k c is the coupling ratio of the resonant cavity coupler, q is the electric field intensity of the incident light after two straight-through end couplings and one round of waveguide loss in the resonant cavity, f0 is the resonant frequency of the resonant cavity, and Δf = f-f0 is the difference between the input light frequency and the static resonant frequency; f bias is the equivalent frequency shift, τ is the transit time, R is the resonant cavity radius, F is the resonant cavity definition, λ is the light wavelength, and c is the light speed in vacuum, is the total phase difference generated by the Sagnac effect when the clockwise and counterclockwise light transmits one round in the resonant cavity, and Ω is the gyro angular velocity.

[0034] Compared with the prior art, the present application has the following beneficial effects:

[0035] The present application is a novel reciprocal resonant interference combined integrated optical gyro sensing and detection method, which combines the reciprocity of the interference type gyro and the resonant multiplication sensitive loop of the resonant type gyro, greatly enhances the sensitivity of the light in the single loop resonant cavity, and senses the angular velocity of the reciprocal light path.

[0036] The present application is a novel reciprocal resonant interference combined integrated optical gyro sensing and detection method, which not only resists the disturbance of the temperature change environment, but also has a Sagnac phase multiplication coefficient proportional to the resonant cavity definition, and the higher the definition, the higher the gyro sensitivity, solving the problem that the resonant type gyro is easily affected by the temperature change environment, breaking the bottleneck that the precision of the interference type gyro is proportional to the size and cannot be miniaturized. BRIEF DESCRIPTION OF DRAWINGS

[0037] Figure 1 A flow chart of a novel reciprocity resonant interference combined integrated optical gyroscope sensing and detection method of the application;

[0038] Figure 2 A schematic diagram of a novel reciprocity resonant interference combined integrated optical gyroscope optical path sensing module built by the application;

[0039] Figure 3 A relationship diagram of clockwise and counterclockwise output light intensity and phase difference of the resonant cavity and angular velocity when the detector combines light interference of the application;

[0040] Figure 4 A relationship diagram of the limit sensitivity of the gyroscope and the waveguide transmission loss and the coupling ratio in the embodiment of the application;

[0041] Figure 5 A relationship diagram of the gain of Sagnac phase resonance multiplication and the frequency locking error in the embodiment of the application;

[0042] Figure 6 A relationship diagram of short-time / long-time measurement results of the frequency control word of the laser in the embodiment of the application;

[0043] Figure 7 A detector output change and simulation result diagram measured in a period in the embodiment of the application. DETAILED DESCRIPTION

[0044] The embodiments of the application will be described below in detail and with reference to the drawings. Obviously, the described embodiments are only some of the embodiments of the application, but not all the embodiments. Based on the embodiments of the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0045] The novel reciprocity resonant interference combined integrated optical gyroscope sensing and detection method, as shown in Figure 1 The specific steps are as follows:

[0046] Step 1, build a novel reciprocity resonant interference combined integrated optical gyroscope optical path sensing module;

[0047] The integrated optical gyroscope optical path sensing module includes a tunable narrow-line-width laser, a circulator, a Y-waveguide integrated optical phase modulator, a waveguide ring resonant cavity, two isolators ISO1 and ISO2, and three photodetectors I, II, and III.

[0048] The laser is connected with two phase modulators through a circulator, the output ends of the phase modulators are connected with the input ends of the resonant cavity respectively, and the two straight-through ends of the resonant cavity are connected with a photoelectric detector I and a second photoelectric detector II through isolators ISO1 and ISO2 respectively.

[0049] The circulator is also connected with a photoelectric detector III, the photoelectric detector III is connected with a Sagnac phase demodulator and an angular velocity closed-loop controller in sequence.

[0050] In the second step, the light emitted by the laser is split through the circulator and the integrated optical phase modulator after the circulator, and the clockwise light (CW) and the counterclockwise light (CCW) are modulated respectively, and then the two beams of light are split again through the straight-through end couplers C1 and C2 of the resonant cavity, wherein the two beams of light are output to the photoelectric detectors I and II through the isolators respectively, and the other two beams of light enter the cavity and are transmitted in the cavity for multiple turns to form resonance and are output from the transmission end of the resonant cavity, and then are returned to the circulator through the modulator to interfere and output to the photoelectric detector III.

[0051] In the third step, the two beams of light output from the reflection end are used to generate a laser frequency locking signal, and are returned to the laser to form a closed loop, and the laser frequency locking detection module of the integrated optical gyroscope optical path is built.

[0052] The two beams of light output from the reflection end reach the photoelectric detectors I and II respectively, and are converted into electrical signals respectively, and then the common mode signal is measured by summing to cancel the Sagnac phase, the center frequency of the resonant cavity is extracted, and the laser frequency locking signal is generated after the resonant frequency demodulation. At this time, the frequency locking precision only affects the interference light intensity fluctuation and does not affect the closed-loop detection of the Sagnac phase, so the laser frequency is locked near the center frequency of the resonant cavity, thereby reducing the requirement for the laser frequency locking precision.

[0053] The closed loop realizes the laser frequency locking, and ensures that the laser works at the resonant frequency of the resonant cavity.

[0054] The output light intensities of the two beams of light output from the reflection end for the laser frequency locking module are:

[0055]

[0056]

[0057] wherein, I out_r_cw is the output light intensity of the clockwise light; I out_r_ccw is the output light intensity of the counterclockwise light; I0 is the input light intensity; k cq is the coupling ratio of the resonant cavity coupler; q is the electric field strength of the incident light after two direct-end couplings and one waveguide loss during a single turn of propagation within the resonant cavity; f0 is the resonant frequency of the resonant cavity; Δf = f - f0 is the difference between the input light frequency and the resonant frequency under static conditions; f bias τ is the equivalent frequency shift; τ is the transit time.

[0058] The corresponding demodulation results are as follows:

[0059]

[0060]

[0061]

[0062] in To eliminate the phase shift caused by the Sagnac effect, the demodulation results in both clockwise and counterclockwise directions are summed. The demodulation results are then used as an error input controller, and the adjustment coefficient is used to lock the laser frequency.

[0063] For a resonant cavity with known parameters, the curve of the signal received by the detector can be calculated using the above formula. When the laser frequency changes continuously, there will be a modulation frequency with the largest demodulation result at each modulation frequency. Summing the demodulation results clockwise and counterclockwise can eliminate the influence of the Sagnac effect.

[0064] Based on the PDH frequency locking scheme, this demodulation result is used as the error input controller. Adjusting the PID coefficients can achieve laser frequency locking. A single-channel direct-through output is used to lock the laser frequency. The full-scan range of the light source drive current corresponds to the frequency control word value of 0–512, and its full-scale adjustment range is slightly larger than one free spectral range (FSR) to ensure the gyroscope can always find a resonant peak. Experimental testing showed that after multiple adjustments to the frequency locking controller parameters, the frequency locking error with a 0.1s sampling time was approximately 3.5 × 10⁻⁶. -5 FSR. Measurement results of the laser frequency control word are attached. Figure 6 As shown, it can be seen that the laser's operating state drifts relatively quickly when the state has just changed, but the frequency locking program can enable the optical frequency to track the resonant frequency rapidly over time.

[0065] Step 4: After the laser is locked at the resonant frequency of the resonant cavity, the two beams of light output from the transmission end are used to complete the construction of the integrated optical gyroscope optical path differential interference sensitive angular velocity detection module, and the final detected gyroscope angular velocity is output.

[0066] The key to this method lies in the fact that light is split into clockwise and counterclockwise beams at the modulator and then recombined at the modulator. The clockwise and counterclockwise beams follow identical paths. The changes in waveguide propagation phase caused by thermal effects in the resonant cavity and the additional temperature error due to inconsistent fabrication of the external waveguide have the same sign. The Sagnac phase signs of the clockwise and counterclockwise beams are opposite, and the differential interference of the recombined beams at the modulator cancels out the thermal effect disturbance error. Therefore, the proposed reciprocal sensing optical path is not only resistant to temperature-dependent environmental disturbances, but also the Sagnac phase multiplication factor is proportional to the resonant cavity resolution. Higher resolution results in higher gyroscope sensitivity, which can overcome the bottleneck of optical gyroscope sensitivity being limited by size, laying the foundation for the development of miniaturized, high-precision integrated optical gyroscopes.

[0067] The clockwise and counterclockwise transmitted light follows the same path from beam splitting to beam combining, achieving a reciprocal optical path sensitive angular velocity. Simultaneously, the light resonates significantly in the single-ring resonant cavity, greatly enhancing sensitivity. The thermal effect within the resonant cavity causes a change in the waveguide light transmission phase, and the additional temperature error due to inconsistent waveguide fabrication outside the resonant cavity has the same sign. The clockwise and counterclockwise Sagnac phases have opposite signs. When the beam combines back to the modulator and differentially interferes, it cancels out the thermal effect disturbance error. This combines the advantages of the reciprocity of an interferometric gyroscope and the resonant multiplication sensitive loop of a resonant gyroscope. The beam combining interference at detector III cancels out the thermal effect disturbance error in the transmitted light signal I. out_T The calculation is as follows:

[0068]

[0069] Where E0 is the photoelectric field intensity output by the laser, k c α is the coupling ratio of the coupler. L / 2 Let q be the half-turn transmission loss of a single-ring resonant cavity, and q be the change in electric field intensity of the incident light as it propagates through the resonant cavity for one turn, passing through two direct-end couplings and one turn of waveguide loss, expressed as q = (1 - k c )(1-α L / 2 ω is the angular frequency of the laser output light, τ is the transit time, which is the time it takes for the light to travel one revolution in the resonant cavity. Near the resonant frequency, ωτ~0; θ Sag θ is the total phase difference caused by the Sagnac effect when clockwise and counterclockwise light travels one revolution in the resonant cavity. Sag =8π 2 R 2 / λc, where R is the radius of the single-ring resonant cavity, λ is the wavelength of light, and c is the speed of light in vacuum; φ out_T_cw φ out_T_ccw These represent the phases of the light arriving at detector III in clockwise and counterclockwise directions, respectively, and have

[0070]

[0071]

[0072]

[0073] Where φ i,i＝1-4 These represent the phase change of light as it propagates through waveguides 1-4 outside the cavity, thereby eliminating the phase change of waveguide light propagation caused by thermal effects in the resonant cavity and the additional temperature error caused by inconsistent fabrication of the waveguides outside the resonant cavity.

[0074] The demodulation result of the transmitted light signal from the combined interference is as follows:

[0075]

[0076] Where R is the radius of the resonant cavity, F is the sharpness of the resonant cavity, λ is the wavelength of light, and c is the speed of light in a vacuum. The total phase difference caused by the Sagnac effect when clockwise and counterclockwise light travels one revolution in the resonant cavity is represented by Ω, where Ω is the gyro angular velocity. This demodulation result outputs the final detected gyro angular velocity.

[0077] The demodulated signal is controlled by an angular velocity closed loop to generate a sawtooth wave feedback signal. This signal is then summed with the modulated signal and returned to the phase modulator via a digital-to-analog converter to form a second closed loop, thus achieving differential interference sensitive angular velocity.

[0078] The differential interference sensitive angular velocity module's angular velocity closed-loop controller modulates one of the light beams with a sawtooth wave phase, causing its equivalent frequency shift to be Δf. shift When an angular velocity of Ω exists, the clockwise and counterclockwise phase difference of the light is:

[0079]

[0080] Where, Δφ out The clockwise and counterclockwise phase difference of light, where n represents the waveguide refractive index, when At that time, the equivalent frequency shift is:

[0081]

[0082]

[0083] In other words, frequency shifting can lock the phase difference of the combined light interference, enabling stable closed-loop control of the gyroscope's angular velocity and improving the detection accuracy and dynamic performance of the reciprocal integrated optical gyroscope. Since the entire optical path after clockwise and counterclockwise beam splitting, returning to the circulator, and interfering again is exactly the same, the differential interference of the combined light cancels out the phase changes in the waveguide within the resonant cavity and in waveguides 1-4 outside the cavity. and This eliminates thermal effects and additional temperature errors caused by inconsistencies in waveguide fabrication width, depth, and symmetry. Since Sagnac phase closed-loop feedback is achieved at the modulator, and the fiber optic paths in other external devices undergo the same clockwise and counterclockwise light splitting and combining processes, phase changes at the fiber optic locations of other devices do not affect the Sagnac phase closed-loop detection accuracy. The multi-state wave applied to the modulator includes a sinusoidal signal operating in the optimal linear region of the modulation optics, a sawtooth wave for Sagnac phase feedback, and a triangular wave to suppress backscattering / backscattering noise.

[0084] The proposed multi-state wave modulation technique can not only demodulate the Sagnac phase from the output of photodetector III for feedback tracking of angular velocity, but also demodulate the modulation coefficient of the modulator with temperature by using the light intensity information before and after sawtooth wave reset.

[0085] Example:

[0086] A novel reciprocal resonant interference combined integrated optical gyroscope optical path sensing module was constructed, such as... Figure 2 As shown, when using a narrow linewidth laser (linewidth ~5kHz), the output light is considered as clockwise and counterclockwise light undergoing multi-beam interference and then summed. The electric field expression for the laser output light is:

[0087] E = E0e iωt (1)

[0088] Where E0 is the electric field strength, i is the imaginary unit, ω is the angular frequency of the incident light, and t represents time.

[0089] The following analysis examines the propagation model of clockwise and counterclockwise light from beam splitting, resonating within the resonant cavity, to the combined light interference:

[0090] Suppose two couplers C1 and C2 divide the cavity into two symmetrical parts, and the coupling ratio of each coupler is k. c Considering the thermal effect causing phase changes in optical waveguide transmission, and also taking into account the additional temperature disturbances caused by inconsistencies in waveguide fabrication width, depth, and symmetry, let the phase change during optical transmission in the external waveguides 1-4 of the resonant cavity be φ. i,i＝1-4 And let θ be the total phase difference caused by the Sagnac effect when the clockwise and counterclockwise light travels one revolution in the resonant cavity. sag The time required for one transmission cycle is τ = nL / c, where n is the refractive index and L is the cavity length.

[0091] When the light beam first reaches detector III, the path it takes is two cross-couplings and a half-loop waveguide. The phase abrupt change of the evanescent wave cross-coupling is π / 2, and the loss of the light passing through the half-loop waveguide is α. L / 2=βL / 2, where β is the waveguide unit transmission loss; the generated sagnac phase difference is ±θsag / 4. Therefore, the electric field expression for the first output and return to the modulator is:

[0092]

[0093] After the light travels through the cavity once, each subsequent light exiting from the transmission end undergoes two more direct-end couplings and one more waveguide path compared to the previous light exiting. The electric field of the k-th output is:

[0094]

[0095] Calculate the total output light intensity of clockwise and counterclockwise light by summing the electric fields:

[0096]

[0097]

[0098] Near the resonant frequency, ωτ ~ 0. First, calculate the phase change of the electric field of the output light in the clockwise and counterclockwise directions, and then calculate the phase difference of the interference.

[0099]

[0100]

[0101] The final expression for the output light intensity is:

[0102]

[0103] As can be seen from the above formula, the output is not affected by the input phase error caused by temperature, stress, etc. Due to the influence of the rotational speed, when the rotational speed is 0, the output light intensity of the combined light interference is 4 times that of the output light intensity at the single transmission end of the resonant cavity. From equation (7), it can be seen that the phase difference of the combined light interference under low rotational speed conditions is independent of the laser frequency locking error and has a linear relationship with the single-turn Sagnac phase difference, with a slope of (1+q) / [2(1-q)]. That is, the sensitivity of the hybrid gyroscope to the Sagnac effect is increased by (1+q) / [2(1-q)] times compared with the ring optical path with the same perimeter as the resonant cavity.

[0104] In this embodiment, the parameters of the novel reciprocal resonant interference combined integrated optical gyroscope are set as follows: coupling ratio k c =0.0093, loss α L / 2=0.0054 corresponds to a waveguide loss of 0.5dB / m, a cavity diameter of 60mm, and a resolution of F=213. A RIO semiconductor laser is used to continuously scan the laser frequency, while simultaneously measuring the light intensity at the direct-through end of the resonant cavity and the output end of the beam combining interference. During the frequency sweep, the optical frequency control word changes every 200µs, much longer than the resonance settling time. When the laser is locked at the cavity's static resonant frequency, during beam combining interference at detector III, the relationship between the clockwise and counterclockwise output light intensity and phase difference of the resonant cavity and the angular velocity is as follows: Figure 3 As shown, the sensitivity to the Sagnac effect is increased by 68 times compared to a ring optical path with the same resonant cavity perimeter.

[0105] Like other passive optical systems, the limiting sensitivity of an optical gyroscope is limited by shot noise. The limiting sensitivity of a reciprocal gyroscope scheme is considered below:

[0106] In this embodiment, the relationship between the combined light intensity of the gyroscope's output light from the transmissive connection and the Sagnac phase can be expressed as:

[0107]

[0108] Where P Laser Let η be the optical power of the laser, and η be the transmittance of the output port of the resonant cavity participating in the interference. F represents the amplified Sagnac phase difference, and F represents the resonant cavity sharpness.

[0109] To achieve maximum sensitivity, it is assumed that the added phase modulation causes the gyroscope to operate at the point where the slope of the Sagnac phase response curve is maximum. At this point, the bias power is ηP. Laser / 2, photon number is Where h is Planck's constant.

[0110] From the definition of shot noise, the standard deviation of the photon number is:

[0111] The noise power received by the detector is: Where η PD This represents the quantum efficiency of the detector.

[0112] The noise equivalent interference phase difference is:

[0113] Equivalent to angular velocity, the minimum detectable angular velocity determined by shot noise is obtained, i.e., the gyroscope's limiting sensitivity is:

[0114]

[0115] Where σ ΔΩ Indicates the limiting sensitivity of the gyroscope; Δf bwTo determine the detection bandwidth, a smoothed result of 0.1 Hz (10 s) is typically used; h is Planck's constant; P is the optical power received by the detector; F is the resonant cavity resolution; η PD η is the quantum efficiency of the detector; η is the transmittance of the output port of the resonant cavity participating in the interference; P Laser f is the output optical power of the laser; f is the output optical frequency.

[0116] It can be seen that the limiting sensitivity is inversely proportional to the square root of the optical power reaching the detector and inversely proportional to the amplification factor of the Sagnac effect. For a given source power, the bias power is determined by the transmittance of the resonant cavity. Therefore, when the resonant cavity size remains constant, the key parameters of the resonant cavity—transmission loss and coupling ratio—determine the gyroscope's limiting sensitivity by affecting the cavity's sharpness and transmittance. Figure 4 The diagram illustrates the relationship between the gyroscope's limiting sensitivity and waveguide transmission loss and coupling ratio. With advancements in waveguide fabrication technology, the clarity of the resonant cavity is expected to continue to increase, further enhancing the detection capabilities of novel gyroscope designs.

[0117] The novel reciprocal resonant interference combined integrated optical gyroscope signal detection scheme includes: a laser frequency locking module and a differential interference sensitive angular velocity module.

[0118] The laser frequency-locking module works as follows: The clockwise and counterclockwise optical signals received by detectors I and II through the direct-through end of the resonant cavity are converted into electrical signals and fed into the circuit system. The two output electrical signals are summed to obtain common-mode signal cancellation angular velocity information, thus achieving laser frequency locking and driving the light to resonate within the resonant cavity. In optical gyroscopes operating on the resonance principle, the error and noise of laser frequency locking affect the gyroscope output. When the frequency-locking point has a fixed bias from zero, it is called steady-state error; however, fluctuations during the actual locking process cause noise in the locked frequency.

[0119] First, we analyze the impact of frequency locking error on the resonant multiplication effect of the Sagnac effect.

[0120] The relationship between the combined light interference phase difference and the frequency locking error is calculated according to equation (5). When the rotation speed is 0, the clockwise and counterclockwise light do not have an additional phase difference. However, when the frequency locking error exists, the slope of the combined light interference phase difference with respect to the single-turn Sagnac phase is:

[0121]

[0122] That is, the amplification factor of the Sagnac phase decreases as the frequency locking error increases. For example... Figure 5The figure illustrates the relationship between the gain of the Sagnac phase resonant multiplication and the frequency locking error. When the frequency locking error is 50 kHz, this gain decreases by 0.15%. This demonstrates that in reciprocal optical gyroscopes, frequency locking error leads to a change in the gyroscope's scaling factor. Modulation and demodulation require balancing laser frequency locking and the detection of interference phase differences.

[0123] First, the output light intensity at the direct end of the resonant cavity is calculated using the beam superposition method, i.e., the output light intensities of the two beams output from the reflecting end are as follows: In step three, the output light intensities of the two beams output from the reflecting end are as follows:

[0124]

[0125] Among them, I out_r_cw I represents the output light intensity of the clockwise light. out_r_ccw I0 is the light intensity of the counterclockwise output light; I0 is the input light intensity; k c q is the coupling ratio of the resonant cavity coupler; q is the electric field strength of the incident light after two direct-end couplings and one waveguide loss during a single turn of propagation within the resonant cavity; f0 is the resonant frequency of the resonant cavity; Δf = f - f0 is the difference between the input light frequency and the resonant frequency under static conditions; f bias This is the equivalent frequency shift amount;

[0126] The corresponding demodulation results are as follows:

[0127]

[0128] in To eliminate the phase shift caused by the Sagnac effect, the demodulation results in both clockwise and counterclockwise directions are summed. The demodulation results are then used as an error input controller, and the adjustment coefficient is used to lock the laser frequency.

[0129] For a resonant cavity with known parameters, the curve of the signal received by the detector can be calculated using the above formula. When the laser frequency changes continuously, there will be a modulation frequency with the largest demodulation result at each modulation frequency. Summing the demodulation results clockwise and counterclockwise can eliminate the influence of the Sagnac effect. According to the PDH frequency locking scheme, this demodulation result is used as the error input controller, and adjusting the PID coefficient can achieve precise locking of the laser frequency. The full scan range of the light source drive current corresponds to the frequency control word value of 0 to 512, and its full-scale adjustment range is slightly greater than 1FSR to ensure that the gyroscope can always find a resonant peak. After experimental testing, after adjusting the frequency locking controller parameters multiple times, the frequency locking error with a sampling of 0.1s is approximately 3.5*10. -5 FSR. Short-time / long-time measurement results of the laser frequency control word, as shown below. Figure 6As shown, it can be seen that the laser's operating state drifts relatively quickly when the state has just changed, but the frequency locking program can enable the optical frequency to track the resonant frequency rapidly over time.

[0130] The differential interference sensitive angular velocity module works as follows: the optical signal of differential interference after clockwise and counterclockwise optical resonance received by detector III is converted into an electrical signal and sent to the circuit system for demodulation. The result is sent to the angular velocity closed-loop controller to generate a gyroscope output and a sawtooth wave feedback signal. The feedback signal is summed with the modulation signal and then added to the phase modulator to realize the closed-loop control of the angular velocity.

[0131] The demodulation result of the transmitted light signal from the combined interference is as follows:

[0132]

[0133] Where I0 is the input light intensity; k c q is the coupling ratio of the resonant cavity coupler; q is the electric field strength of the incident light after two direct-end couplings and one waveguide loss during a single turn of propagation within the resonant cavity; f0 is the resonant frequency of the resonant cavity; Δf = f - f0 is the difference between the input light frequency and the resonant frequency under static conditions; f bias λ is the equivalent frequency shift; τ is the transit time; R is the resonant cavity radius; F is the resonant cavity sharpness; λ is the wavelength of light; and c is the speed of light in vacuum. The total phase difference caused by the Sagnac effect when clockwise and counterclockwise light travels one revolution in the resonant cavity is represented by Ω, where Ω is the gyro angular velocity. This demodulation result outputs the final detected gyro angular velocity.

[0134] For a resonant cavity with known parameters, the signal received by the detector can be calculated using the above formula. Following the constructed optical path, after locking the laser frequency, the combined interference waveform is observed as the modulation depth changes. The applied modulation frequency is 2.5MHz, and the modulation depth is continuously scanned. The detector output change measured within one period of 0.4µs ​​and the simulation results are as follows. Figure 7 As shown, the simulation and experiment are in agreement. By locking the laser frequency to the cavity resonant frequency, the Sagnac effect can be multiplied, enabling the measurement of angular velocity. However, directly measuring large angular velocities presents problems such as large scaling factor nonlinearity and susceptibility to intensity noise. In particular, the output light intensity of semiconductor lasers changes drastically with the current-tuned frequency lock point. Therefore, closed-loop control of the gyroscope angular velocity is required.

[0135] In the novel reciprocal resonant interference combined with integrated optical gyroscope signal detection scheme, the differential interference sensitive angular velocity module's angular velocity closed-loop controller adds sawtooth wave phase modulation to one of the light beams, causing its equivalent frequency shift to be Δf. shift When an angular velocity of Ω exists, the clockwise and counterclockwise phase difference of the light is:

[0136]

[0137] Where, Δφ out The clockwise and counterclockwise phase difference is given by q, where q is the change in electric field intensity after two direct-end couplings and one waveguide loss during a single turn of propagation within the resonant cavity, f is the output light frequency, τ is the transit time, R is the radius of the single-ring resonant cavity, λ is the wavelength of light, c is the speed of light in vacuum, and n represents the refractive index of the waveguide. At that time, the equivalent frequency shift is:

[0138]

[0139] In other words, frequency shifting can lock the phase difference of the combined light interference, enabling stable closed-loop control of the gyroscope's angular velocity and improving the detection accuracy and dynamic performance of the reciprocal integrated optical gyroscope.

[0140] As can be seen, the key to a novel reciprocal resonant interference combined integrated optical gyroscope sensing and detection method lies in the fact that light is split into clockwise and counterclockwise beams at the modulator and then recombined at the modulator. The clockwise and counterclockwise beams follow identical paths, and the changes in waveguide light transmission phase caused by thermal effects in the resonant cavity, as well as the additional temperature error due to inconsistent fabrication of the external waveguide, have the same sign. The Sagnac phase signs of the clockwise and counterclockwise beams are opposite, and the differential interference of the recombined beams at the modulator cancels out the thermal effect disturbance error. Therefore, the proposed reciprocal sensing optical path is not only resistant to temperature-varying environmental disturbances, but also the Sagnac phase multiplication coefficient is proportional to the resonant cavity resolution. Higher resolution results in higher gyroscope sensitivity, which can overcome the bottleneck of optical gyroscope sensitivity being limited by size, laying the foundation for the development of miniaturized, high-precision integrated optical gyroscopes.

Claims

1. A novel integrated optical gyroscope sensing and detection method combining reciprocal resonant interference, characterized in that, The specific steps are as follows: Step 1: Construct a novel reciprocal resonant interference combined integrated optical gyroscope optical path sensing module; The integrated optical gyroscope optical path sensing module includes: a laser, a circulator, a phase modulator, a resonant cavity, two isolators, and three photodetectors; Step 2: In the integrated optical gyroscope optical path sensing module, the light emitted by the laser passes through the circulator and phase modulator in sequence for beam splitting and modulation. After passing through the straight-through coupler of the resonant cavity, it is split again. Two beams of light are output from the straight-through end of the resonant cavity to photodetectors I and II after passing through the isolator, respectively. The other two beams of light enter the cavity for resonance and are output from the transmission end. They return to the circulator through the modulator for beam combining interference and are output to photodetector III. Step 3: Use the two beams of light output from the through end to generate a laser frequency-locking signal and return it to the laser to form a closed loop; complete the construction of the integrated optical gyroscope optical path laser frequency-locking detection module; The two beams of light output from the reflection end reach photodetectors I and II respectively. After being converted into circuit signals, they are summed to measure the common-mode signal to cancel the Sagnac phase, thereby realizing the extraction of the center frequency of the resonant cavity and generating the laser frequency-locked signal after demodulation of the resonant frequency. Step 4: After the laser locks the resonant frequency of the resonant cavity, the two beams of light output from the transmission end are used to complete the construction of the integrated optical gyroscope optical path differential interference sensitive angular velocity detection module, and the final detected gyroscope angular velocity is output. The light is split into clockwise and counterclockwise beams at the modulator and then recombined at the modulator. The clockwise and counterclockwise beams follow the same path. The change in the waveguide light transmission phase caused by the thermal effect in the resonant cavity and the additional temperature error due to the inconsistency in the fabrication of the waveguide outside the resonant cavity have the same sign. The Sagnac phase signs of the clockwise and counterclockwise beams are opposite. When the beams are combined back to the modulator and differentially interfered, the thermal effect disturbance error is canceled out. The combined light interference cancels out the thermal effect disturbance error in the transmitted light signal I. outT The calculation is as follows: Where E0 is the photoelectric field intensity output by the laser, k c α is the coupling ratio of the resonant cavity coupler. L / 2 ω is the half-turn transmission loss of the single-ring resonant cavity, q is the electric field intensity of the incident light during a single turn of transmission within the resonant cavity after two direct-end couplings and one turn of waveguide loss, ω is the angular frequency of the laser output light, τ is the transit time, and θ is the electric field intensity. Sag φ is the total phase difference caused by the Sagnac effect when clockwise and counterclockwise light travels one revolution in the resonant cavity. out_T_cw φ out_T_ccw These represent the phases of the clockwise and counterclockwise light arriving at photodetector III, respectively, and have Where φ i i = 1-4 represents the phase change during optical transmission in external waveguide 1-4, i.e. This eliminates the change in waveguide optical transmission phase caused by thermal effects in the resonant cavity, as well as the additional temperature error caused by inconsistent fabrication of the external waveguide.

2. The method as described in claim 1, characterized in that, In step one, after the clockwise and counterclockwise single-ring resonant multiplication Sagnac effect, the combined light differential interference output is achieved at the integrated optical phase modulator. The entire path of the clockwise and counterclockwise light from beam splitting to beam combining is completely consistent, realizing the reciprocal optical path sensitive angular velocity. The clockwise and counterclockwise light beams are fed through the detector output of the through-hole to obtain the common-mode signal, which cancels the angular velocity information and achieves laser frequency locking, driving the light to resonate in the resonant cavity. Furthermore, the clockwise and counterclockwise light beams resonate and then interfere with the sensitive angular velocity, realizing the reciprocal optical path differential measurement resonant cavity to resist environmental disturbances.

3. The method as described in claim 1, characterized in that, In step three, the output light intensities of the two beams of light output from the reflecting end are as follows: Among them, I out_r_cw I represents the output light intensity of clockwise light. out_r_ccw I0 is the light intensity of the counterclockwise output light; I0 is the input light intensity; Δf = f - f0 is the difference between the input light frequency and the resonant frequency under static conditions; f0 is the resonant frequency of the resonant cavity; f bias This is the equivalent frequency shift amount; The corresponding demodulation results are as follows: in To eliminate the phase shift caused by the Sagnac effect, the demodulation results in both clockwise and counterclockwise directions are summed. The demodulation result is then used as the resonant frequency f0 of the resonant cavity as the frequency locking error input to the frequency locking controller to achieve laser frequency locking.

4. The method as described in claim 1, characterized in that, The demodulation result of the transmitted light signal in step four, involving the combined light interference, is as follows: Where R is the resonant cavity radius and F is the resonant cavity sharpness. λ is the wavelength of light, c is the speed of light in vacuum, and Ω is the gyroscope angular velocity; this demodulation result outputs the final detected gyroscope angular velocity.

5. The method as described in claim 1, characterized in that, This method is based on sensing and detection devices, specifically including an optical path sensing module, a laser frequency locking detection module, and a differential interference sensitive angular velocity detection module; The optical path sensing module splits light into clockwise and counterclockwise beams at the modulator and then recombines them at the modulator. The clockwise and counterclockwise beams follow the same path, which is used to achieve optical path reciprocity transmission. When the light is recombined at the modulator and differentially interfered, it eliminates the change in waveguide light transmission phase caused by thermal effects in the resonant cavity and the additional temperature error caused by inconsistent fabrication of the waveguide outside the resonant cavity. The laser frequency locking detection module includes a resonant frequency demodulation unit and a laser frequency control unit. It sums the demodulation results clockwise and counterclockwise to obtain a common-mode signal, eliminating the influence of the Sagnac effect. This is used to accurately lock the laser frequency at the operating frequency of the resonant cavity to form a first closed loop. The differential interference sensitive angular velocity detection module includes a Sagnac phase demodulation unit, an angular velocity closed-loop controller, a direct digital synthesis unit, and a digital-to-analog conversion unit, which are used to output the final detected gyro angular velocity and apply modulation and feedback signals to form a second closed loop.

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