Resonator Fiber Optic Gyro Research Articles

Reducing polarization-fluctuation induced drift in resonant fiber optic gyro by using single-polarization fiber

A novel hybrid single-polarization (SP) fiber ring resonator is demonstrated by using a polarization-maintaining coupler formed by splicing a section of SP fiber into the resonator. The SP fiber selectively eliminates the unwanted resonance by introducing high loss for the unwanted eigenstates of polarization in the resonator. The calculated result shows that this hybrid SP resonator is a good candidate for a tactical-grade performance gyro with a high environmental temperature stability. The experiment shows that the desired resonance in the resonator can keep an excellent stability in a wide temperature range, thus the temperature-dependent polarization-fluctuation drift in the resonant fiber optic gyro is sufficiently suppressed. As a result, a random walk coefficient of 0.08°/√h and a typical bias stability below 0.3°/h for an integration time of 300 s have been carried out.

Wide dynamic range experiments on a resonator fiber optic gyro based on closed-loop frequency locking technique

Wide dynamic range is an important index of the resonator fiber optic gyro (RFOG). The dynamic range is related to the parameters of the fiber ring resonator (FRR). After adopting the appropriate parameters, the resonant curve of a FRR and the synchronous demodulated curve are measured. Based on the closed-loop frequency locking technique, the wide dynamic range is obtained, while the linearity is guaranteed. The experiment’s results show that the dynamic range is ±480 deg/s with less than 1% nonlinearity, and that the bias stability is 0.04 deg/s over 2000 s. This Letter demonstrates the scheme for a RFOG with a wide dynamic range.

Compensation of scale factor nonlinearity in resonator fiber optic gyro

Scale factor nonlinearity (SFN) and dynamic range (DR) are the two significant parameters used to evaluate the performance of a resonator fiber optic gyro (RFOG). The inherent SFN of an open-loop RFOG with triangular phase modulation is first analyzed theoretically, and its relationship with the DR is simulated, showing that the DR is significantly constrained by the SFN. For our system, when the SFN is 1%, the DR is less than ±82 deg/s. To decrease the SFN in a certain DR, a real-time compensation method based on a field-programmable gate array is proposed. The compensation model is set up and the compensation scheme is illustrated. With the proposed method, the SFN of the RFOG is decreased from 1.53% to 0.057% with a DR of ±100 deg/s.

Residual intensity modulation in resonator fiber optic gyros with sinusoidal wave phase modulation

We present how residual intensity modulation (RIM) affects the performance of a resonator fiber optic gyro (R-FOG) through a sinusoidal wave phase modulation technique. The expression for the R-FOG system’s demodulation curve under RIM is obtained. Through numerical simulation with different RIM coefficients and modulation frequencies, we find that a zero deviation is induced by the RIM effect on the demodulation curve, and this zero deviation varies with the RIM coefficient and modulation frequency. The expression for the system error due to this zero deviation is derived. Simulation results show that the RIM-induced error varies with the RIM coefficient and modulation frequency. There also exists optimum values for the RIM coefficient and modulation frequency to totally eliminate the RIM-induced error, and the error increases as the RIM coefficient or modulation frequency deviates from its optimum value; however, in practical situations, these two parameters would not be exactly fixed but fluctuate from their respective optimum values, and a large system error is induced even if there exists a very small deviation of these two critical parameters from their optimum values. Simulation results indicate that the RIM-induced error should be considered when designing and evaluating an R-FOG system.

Thermal Sensitivity of the Birefringence of Air-Core Fibers and Implications for the RFOG

We present an analytical model of the drift in the resonant fiber optic gyroscope (RFOG) caused by thermally induced changes in the fiber beat length ${\rm L_{B}(T)}$ and find that the relevant metric for thermal-drift performance is not ${\rm dL_{B}/dT}$ but rather ${\rm(1/L_{B}^{2})dL_{B}/dT}$ . This disfavors conventional solid-core PM fibers for which ${\rm L_{B}}$ is very short and ${\rm dL_{B}/dT}$ is large. Because the air core of hollow-core fibers does not support the strains associated with differential thermal expansion in conventional PM fibers, the birefringence of hollow-core fibers should be more thermally stable than conventional fibers with a correspondingly smaller ${\rm (1/L_{B}^{2})dL_{B}/dT}$ . To identify the relative merits of different types of fibers in the RFOG, we measure ${\rm (1/L_{B}^{2})dL_{B}/dT}$ for a variety of air-core and solid-core fibers by recording the shift in the resonance frequencies of an all-fiber ring resonator when its temperature is changed. We find that the PM air-core fiber offers a 270-fold improvement in ${\rm (1/L_{B}^{2})dL_{B}/dT}$ coefficient compared to a Panda fiber.

Eliminating bias drift error in lock-in frequency for a resonant fiber optic gyro.

The accuracy of the resonant frequency servo loop is a major concern for high-performance operation of a resonant fiber optic gyro. This is usually resolved by adopting the central frequency of the laser source to track the resonance of the optical fiber ring resonator in one direction. However, the drift of the resonant frequency arising from resonator temperature fluctuation must be eliminated to maintain this accuracy. The traditional proportional integral (PI) frequency servo loop cannot address this issue very well. For instance, a bias error as large as tens or even hundreds of degrees/hour has been observed at the demodulated output of a resonant frequency servo loop. In this paper, we propose a method to eliminate this bias error by adding a double integral term in the traditional PI-based resonant frequency servo loop. We demonstrate that the double integral term can precisely track the linear resonant frequency drift, evidenced by our experimentally achieved close-to-zero bias error of -0.0009 deg/h at the demodulated output of the resonant frequency servo loop.

Study of Birefringence and Mode Field for Hollow-Core Photonic Bandgap Fiber

Since the Appearance of Hollow-Core Photonic Bandgap Fiber (HC-PBF), it was Widely Concerned for its Excellent Characteristics. in Order to Study the Characteristics of the HC-PBF that can be Used in Resonator Fiber Optic Gyros (R-Fogs), the Model Structure of a Polarization-Maintaining HC-PBF was Built and its Performance was Simulated by Using the Finite Element Method (FEM). its Mode Field Distribution and Birefringence Characteristics were Obtained. the Influences of the Air Core and Cladding Structures on the Mode Field Distribution and Birefringence were Simulated and Analyzed Further. the Result Showed that there are both Core Mode and Surface Mode in the Structure we Built. by Adding Scattering Points into the Fiber Core, the Surface Mode can be Significantly Suppressed. by Matching the Size of Core and Air Holes around the Core, a Birefringence up to 8*10-4 were Obtained.

Suppression of frequency locking noise in resonator fiber optic gyro by differential detection method

Abstract The performance of the resonator fiber optic gyro (RFOG) is influenced by frequency locking noise. This paper proposes a differential detection method (DDM) to suppress the frequency locking noise. First, the frequency locking noise induced by the frequency locking error is described theoretically; the description indicates that it acts as the common-mode noise in the RFOG. In the traditional signal-path detection method (SDM), there is a trade-off between suppressing the frequency locking noise and improving the gyro sensitivity. Thus, a model of the DDM is set up and analyzed. The frequency locking noise can be suppressed using the DDM by adjusting the gains of two lock-in amplifiers. Finally, the experimental setup is established, and the SDM and DDM are compared. When the tested equivalent frequency locking noise is 10.6°/h, the bias stability of the RFOG is improved from 12.9°/h to 1.1°/h by the DDM.

Single-Polarization Coupler Based on Air-Core Photonic Bandgap Fibers and Implications for Resonant Fiber Optic Gyro

A single-polarization (SP) coupler based on air-core photonic bandgap fibers (PBFs) is proposed and numerically simulated. The physical mechanism is the decoupling phenomenon occurring at special separations between the cores of the dual-core PBFs called decoupling points. The coupling length of one polarization in the coupler tends to be infinite while the coupling length of other polarization remains in normal level. The coupling ratio for the primary polarization can vary by adjusting the length of the coupler since the other polarization is always decoupled out at any length of the coupler. When this novel SP coupler is incorporated into a PBFs based fiber ring resonator, its unique polarization property is theoretically simulated. In this full-PBFs configuration, the SP coupler functions as the power splitter and the polarizer simultaneously. By the finite element method, the feasibility of the SP coupler to filter the secondary eigenstate of polarization (ESOP) propagating in the resonator is proved. And the performance of the SP coupler to suppress the temperature-related polarization fluctuation in the resonant fiber optic gyro is promised to be more significant to the in-line polarizer integrating in the resonator. Furthermore, the mechanism of decoupling phenomenon in the SP coupler and the influence of polarization-axis angular misalignment are discussed. In conclusion, an optimized SP coupler can couple the primary ESOP properly, and a polarization extinct ratio larger than 30 dB can be achieved within the angular misalignment of 0.9 degree. The aforementioned unique properties make this novel SP coupler attractive for the resonant fiber optic gyro.

高Q光纤环谐振腔陀螺角速度传感研究

The transmission spectrum and demodulation curve of the fiber ring resonator were simulated.As can be seen,the lowest value of transmission spectrum was corresponding to the modulation resonance point,the linear zone of demodulation curve was the dynamic range of gyroscope,the midpoint of the linear region was corresponds to the resonance point and it could be used as the maximum of scale factor.In order to achieve the high accuracy and steady frequency locked of the resonance point,resonant gyroscope angular velocity measurement scheme was designed,which used proportional integral circuit to lock the resonant frequency and sine wave to scan the piezoelectric transducer of narrow linewidth laser(linewidth is less than 1kHz),so that the length of laser resonant cavity was changed to adapt the changes of the fiber ring resonator which real-time tracked and locked with the external environment.Through the method of linewidth,calculated quickly that the quality value of fiber ring resonator was 107.The real-time output of the fiber ring cavity in resonant and non-resonant points frequency locked were compared and analyzed,the continuous rotation in the two kinds condition was obtained by rotation test.The detection sensitivity of fiber optic gyro system in the theory was calculated finally.The results show that the output level of the gyro value in the resonant point is 3times than the non-resonant point,which proves the importance of the resonator fiber optic gyroscope resonant frequency locking.

Reduction of reset pulse in resonant frequency servo loop for resonant fiber-optic gyro by an auto-controlled reset technique

Resonant fiber-optic gyro (RFOG) based on the Sagnac effect has the potential to achieve the inertial navigation system requirement with a short sensing coil. A high-accuracy resonant frequency servo loop is indispensable for a high-performance RFOG. A digital proportional-integral (PI) controller is always adopted in the resonant frequency servo loop. The resonant frequency of the optical fiber ring resonator drifts with environmental temperature changes. When the resonant frequency drift is beyond the tracking range of the resonant frequency servo loop, the digital PI controller overflows and outputs a reset signal. A large reset pulse, which is equivalent to a rotation rate error of 26°/h, has been observed at the output of the RFOG, while a long time is required for returning to the lock-in state simultaneously. To reduce the effect of the overflow resetting in the digital PI controller, an auto-controlled reset technique is proposed and experimentally demonstrated. As a result, the time for returning to the lock-in state is reduced to 5ms from 8s. With the integration time of 1s, the equivalent accuracy of the resonant frequency servo loop is improved to 0.18°/h.

In-line polarizer used in all-0°-splice resonator fiber-optic gyro

A method to suppress the polarization-fluctuation-induced drift in a resonator fiber-optic gyro is proposed in this paper. By inserting one in-line polarizer whose polarization extinction ratio is 30 dB into a polarization-maintaining fiber resonator with 0° polarization-axis splices, the unwanted resonance is introduced to high loss and therefore the ratio of the resonance height of the desired eigen-states of polarization (ESOP) to the unwanted ESOP is 74 dB theoretically; thus the polarization-fluctuation-induced drift is adequately suppressed. The new scheme has excellent operability and high temperature stability simultaneously. Compared to the resonator with twin 90° polarization-axis rotated splices, this scheme does not need precise length difference control. This work is of great importance in the research on resonator integrated optic gyros.

Closed-loop resonant fiber optic gyro with an improved digital serrodyne modulation

To widen the linear dynamic range and improve the linearity, a closed-loop resonant fiber optic gyro (RFOG) is proposed and experimentally demonstrated. To overcome the effect of the imperfect serrodyne modulation, an improved frequency shifting module is designed and constructed on a LiNbO3 phase modulator. Its frequency resolution is improved to 0.01 Hz which is equivalent to a rotation rate of 0.04°/h for an RFOG with a 12-cm diameter fiber ring resonator. With the frequency shifter applied in the RFOG, a closed-loop detection is demonstrated, whose bias stability is around 2 °/h, close to that of the open-loop output. Moreover, good linearity and wide dynamic range are also experimentally demonstrated thanks to the closed-loop operation. The measured result shows that the open-loop linear detection range of ± 215°/s is improved to ± 1076°/s. It is improved by a factor of 5. The open-loop scale factor nonlinearity of 1.2% is decreased to 0.02% (200 ppm), which is improved by a factor of 60. These are the best results reported to date, to the best of our knowledge, for closed-loop RFOGs.

Design and analysis of a dual-axis resonator fiber-optic gyroscope employing a single source

In this paper, design of a resonator fiber-optic gyroscope comprised of a single laser source and two optical fiber resonator rings is presented. A typical gyroscope measures angular rotation around a fixed axis, whereas the proposed design can sense simultaneous rotation about two orthogonal axes. Two variants of the design are proposed and analyzed using a mathematical model based on Jones matrix methodology.

Automated Suppression of Polarization Fluctuation in Resonator Fiber Optic Gyro With Twin 90$^{\circ}$ Polarization-Axis Rotated Splices

A method for automatically suppressing the polarization fluctuation in a resonator fiber optic gyro by adopting a resonator with twin 90° polarization-axis rotated splices is proposed and demonstrated experimentally. The scheme ensures that the input electric field excites only the desired eigenstate of polarization in the resonator by automatically setting the length difference of the fiber segments between the two 90° polarization-axis rotated splicing points at one half of the beat length of the polarization maintaining fiber. The feasibility of the proposed scheme is shown by simulation using a mathematical model based on the Jones transfer matrix. It is also demonstrated experimentally that the bias stability is enhanced when the feedback scheme is adopted.

Improving thermal stability of a resonator fiber optic gyro employing a polarizing resonator

To improve the thermal stability of a resonator fiber optic gyro (R-FOG), a transmission-type polarizing resonator by inserting two in-line polarizers in a polarization-maintaining fiber resonator with twin 90° polarization-axis rotated splices is proposed and experimentally demonstrated. The in-line polarizers attenuate the unwanted resonance by introducing high loss for the unwanted eigenstates of polarization in the resonator. The desired resonance in the resonator can keep excellent stability in a wide temperature range, thus the temperature-related polarization error in the R-FOG is dramatically suppressed. Both our numerical simulation and experimental verification are carried out, which for the first time to our best knowledge demonstrate that the open-loop output of the R-FOG is insensitive to environmental temperature variations. A bias stability below 2°/h in the temperature range of 36.2°C to 33°C is successfully demonstrated.

Polarization-induced noise in resonator fiber optic gyro

An optical fiber ring resonator (OFRR) is the key rotation-sensing element in the resonator fiber optic gyro (R-FOG). In comparing between different OFRR types, a simulation model that can apply to all cases is set up. Both the polarization crosstalk and polarization-dependent loss in the coupler are fully investigated for the first time to our knowledge. Three different splicing schemes, including a single 0°, a single 90°, and twin 90° polarization axis rotated spices, are compared. Two general configurations of the OFRR are considered. One is a reflector OFRR, the other is a transmitter OFRR. This leads to six different OFRR types. The output stability of the R-FOG with six OFRR types is fully investigated theoretically and experimentally. Additional Kerr noise due to the polarization fluctuation is discovered. The OFRR with twin 90° polarization axis rotated splices is of lower additional Kerr noise and hence has better temperature stability. As the coupler is polarization dependent, we notice that in a reflector OFRR, the straight-through component of the output lightwave, which can be isolated by a transmitter configuration, would produce large polarization fluctuation-induced noise. The experimental results show that the bias stability of the transmitter OFRR is 8 times improved over that of the reflector OFRR, which is in accord with the theoretical analysis. By the analysis and experiments above, it is reasonable to make a conclusion that an R-FOG based on a transmitter OFRR with twin 90° polarization axis rotated splices is of better temperature stability and smaller additional Kerr effect noise.

Reduction of polarization-fluctuation induced drift in resonator fiber optic gyro by a resonator integrating in-line polarizers

A method to decrease the polarization-fluctuation induced drift in a resonator fiber optic gyro (R-FOG) is demonstrated by inserting two in-line polarizers in a polarization-maintaining fiber resonator with twin 90° polarization-axis rotated splices. The in-line polarizers attenuate the unwanted resonance by introducing high loss for the unwanted eigenstates of polarization in the resonator. Compared to the resonator without in-line polarizers, the polarization-fluctuation induced drift is reduced by 6×10(3) times. The desired resonance in the resonator can keep excellent stability in a wide temperature range; thus the temperature-dependent polarization-fluctuation drift in the R-FOG is sufficiently suppressed. A typical bias stability of 4.7°/h over 6500 s with an integration time of 10 s has been carried out. To the best of our knowledge, the long-term bias stability and high temperature stability are the best ever demonstrated in an R-FOG.

Analysis of a hollow core photonic bandgap fiber ring resonator based on micro-optical structure

The fiber ring resonator (FRR) is the key component of resonator fiber optic gyros (R-FOGs). The configuration of a novel hollow core photonic bandgap fiber (HC-PBF) ring resonator is proposed based on the usage of micro-optical structure. The normalized transfer function of such kind of FRR is derived, and the effects of different FRR parameters' on the resonant depth, resonant finesse and sensitivity limited by the shot noise of the detector are simulated. The laboratory sample of integrated HC-PBF ring resonator is fabricated and tested experimentally and the optimal scheme is proposed based on the acquired test data. The experimental setup and results verify the feasibility of the micro-optical coupling structure used in the HC-PBF ring resonator and also support the integration and miniaturization of R-FOGs composed of HC-PBFs.

Full investigation of the resonant frequency servo loop for resonator fiber-optic gyro

Resonator fiber-optic gyro (RFOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect. A high-accuracy resonant frequency servo loop is indispensable for a high-performance RFOG. It is composed of a frequency discriminator, a loop filter, and a laser actuator. Influences of the loop parameters are fully developed. Optimized loop parameters are obtained by considering the noise reduction and wide dynamic performance of the RFOG. As a result, with the integration time of 10 s, the accuracy of the resonant frequency loop is increased to 0.02 Hz (1σ). It is equivalent to a rotation rate of 0.067°/h, which is close to the shot noise limit for the RFOG, while a minimum rotation of ±0.05°/s has been carried out simultaneously. These are the best results reported to date, to the best of our knowledge, for an RFOG using the miniature semiconductor laser that benefits from the optimization of the resonant frequency servo-loop parameters.