Interferometric Fiber Optic Gyroscope Research Articles

Comments on “Simultaneous measurement of angular velocities of two vertical directions in a slow-light structure”

Abstract A recent paper by Gu and Liu reported a fiber double-ring resonator gyroscope that can simultaneously measure rotation in two orthogonal axes, with a sensitivity predicted to be 35 times larger than that of an interferometric fiber optic gyroscope (IFOG). Because the two rings have different lengths, the gyroscope could not be biased properly, and the authors remark that as a result, its sensitivity to a small rotation rate is reduced. We stress that this sensor actually responds quadratically to a small applied rotation rate, and that it is therefore essentially insensitive to a small rotation rate. We point out that it could easily be biased properly and this major issue is eliminated by using two rings with nominally equal lengths. We also show that in general, and unlike claimed, this sensor does not measure rotation on orthogonal axes independently. This cross-sensitivity between axes worsens significantly when the sensor is properly biased, and it is then much too strong for inertial navigation of aircraft. A conceptual method that might reduce this cross-sensitivity is suggested. A simple physical argument is also presented to explain why this gyroscope was entirely expected to be more sensitive than an IFOG, and shows that as a result of algebraic errors, the predicted factor of 35 is actually only at most 11.

Two-level and two-period modulation for closed-loop interferometric fiber optic gyroscopes.

We propose and experimentally demonstrate a modulation technique for closed-loop interferometric fiber optic gyroscopes that improves its scale factor control and allows for the construction of gyroscopes with optimized angle random walk. The proposed two-level and two-period modulation is composed of two intercalated periods of the square wave modulation, one with amplitude of ϕ rad and the other with amplitude of 2π-ϕ rad. As in the two-level modulation, the angular velocity is obtained from the difference of consecutive output levels. Modulation depth error is obtained from the difference of the mean levels of the output from two consecutive periods. The proposed technique eliminates the limitation of square wave modulation: inefficient scale factor control at low angular velocities. Additionally, it requires a slower analog-to-digital converter than four-level modulation.

Six-state phase modulation for reduced crosstalk in a fiber optic gyroscope.

Electrical crosstalk in an interferometric fiber-optic gyroscope (IFOG) is regarded as the most significant factor influencing dead bands. Here, we present a six-state modulation (SSM) technique to reduce crosstalk. Compared to conventional four-state modulation (FSM) or square-wave modulation (SWM), the SSM reduces the correlation between modulation voltage and demodulation reference by separating their fundamental frequencies, and thus reduces the bias error induced by crosstalk. The measured dead band of a 1500-m IFOG is approximately 0.02 °/h using FSM and approximately 0.08 °/h using SWM, whereas there is no evidence of dead band using SSM. The IFOG using SSM also exhibits better angular random walk (ARW) and bias instability performance compared to the same IFOG using FSM or SWM. These results verify the crosstalk reduction effect of SSM. In theory, by using the relative intensity noise (RIN) suppressing technique with the optimal modulation depth of 2π/3, the SSM can eliminate the crosstalk, which offers the potential for a high-performance IFOG with low noise, high sensitivity, wide dynamic range, and no dead band.

Study on phase noise induced by 1/f noise of the modulator drive circuit in high-sensitivity fiber optic gyroscope

Abstract The contribution of modulator drive circuit noise as a 1/f noise source to the output noise of the high-sensitivity interferometric fiber optic gyroscope (IFOG) was studied here. A noise model of closed-loop IFOG was built. By applying the simulated 1/f noise sequence into the model, a gyroscope output data series was acquired, and the corresponding power spectrum density (PSD) and the Allan variance curve were calculated to analyze the noise characteristic. The PSD curve was in the spectral shape of 1/f, which verifies that the modulator drive circuit induced a low frequency 1/f phase noise into the gyroscope. The random walk coefficient (RWC), a standard metric to characterize the noise performance of the IFOG, was calculated according to the Allan variance curve. Using an operational amplifier with an input 1/f noise of 520 nV/√Hz at 1 Hz, the RWC induced by this 1/f noise was 2 × 10−4°/√h, which accounts for 63% of the total RWC. To verify the correctness of the noise model we proposed, a high-sensitivity gyroscope prototype was built and tested. The simulated Allan variance curve gave a good rendition of the prototype actual measured curve. The error percentage between the simulated RWC and the measured value was less than 13%. According to the model, a noise reduction method is proposed and the effectiveness is verified by the experiment.

Effective suppression of residual coherent phase error in a dual-polarization fiber optic gyroscope.

The impact of residual coherent phase error in a dual-polarization interferometric fiber optic gyroscope (IFOG) is investigated. Although it has been intuitively assumed that the coherence of a light source can be eliminated by a sufficient long fiber delay, the experiment and theory indicate that it still contributes a remarkable portion to long-term instability. After the residual coherent phase error is well handled, we demonstrate a dual-polarization IFOG with bias instability of 3.56×10-4°/h. Comparisons show that such performance is even better than the conventional "minimal scheme" that operates on one polarization.

光程倍增光纤陀螺偏振误差相关抵消的研究

光程倍增光纤陀螺偏振误差相关抵消的研究

Compensation of thermal strain induced polarization nonreciprocity in dual-polarization fiber optic gyroscope.

Dual-polarization interferometric fiber optic gyroscope (IFOG) is a novel scheme in which the polarization nonreciprocal (PN) phase error of the two orthogonal polarizations can be optically compensated. In this work, we investigate the effective of PN phase error compensation under varying temperature. It is proved that, the thermally induced strain deforms the fiber, and results in perturbations on the birefringence and polarization cross coupling which degrades the IFOG's stability. A wave propagation model and analytical expressions of PN phase error are derived by using coupled-wave equation and Jones matrix. We theoretically and experimentally verify that, although the single-mode (SM) and polarization-maintaining (PM) fiber coils behave different owing to their intrinsic properties of wave propagation, the thermal strain induced PN phase error can still be compensated under slow and adiabatic temperature variations. This could be a promising feature to overcome the temperature fragility of IFOG.

Thermal-induced rate error of a fiber-optic gyroscope considering various defined factors

As a high-precision angular sensor, the interferometric fiber-optic gyroscope (FOG) usually shows high sensitivity to disturbances of the environmental temperature. To research the related influencing factors of influencing the thermal-induced rate error of an FOG is essential to enhance precision and environmental suitability. This paper starts with the factors neglected in past research to derive the thermal-induced error model of a fiber coil including various factors of equivalent radius, asymmetry of fiber tail, cross-layer leap, and so on in detail, and then translates this error into the inner product form of penalty factor matrix and temperature field matrix. Then, the mathematical model and the three-dimensional temperature field model of the fiber coil with the quadrupolar winding pattern is built, which includes the optic core, coating, glue, packing paper, and accurate temperature boundary conditions. The penalty factor matrix and temperature field matrix can be obtained from these models. Finally, the advancement of this revised the thermal-induced rate error model has been verified through simulation and experimental comparison.

Temperature Dependence of Faraday Effect-Induced Bias Error in a Fiber Optic Gyroscope.

Improving the performance of interferometric fiber optic gyroscope (IFOG) in harsh environments, such as magnetic field and temperature field variation, is necessary for its practical applications. This paper presents an investigation of Faraday effect-induced bias error of IFOG under varying temperature. Jones matrix method is utilized to formulize the temperature dependence of Faraday effect-induced bias error. Theoretical results show that the Faraday effect-induced bias error changes with the temperature in the non-skeleton polarization maintaining (PM) fiber coil. This phenomenon is caused by the temperature dependence of linear birefringence and Verdet constant of PM fiber. Particularly, Faraday effect-induced bias errors of two polarizations always have opposite signs that can be compensated optically regardless of the changes of the temperature. Two experiments with a 1000 m non-skeleton PM fiber coil are performed, and the experimental results support these theoretical predictions. This study is promising for improving the bias stability of IFOG.

An analog modulation and demodulation method employing LVDT signal conditioner for fiber-optic interferometric sensors

An analog method to modulate and demodulate fiber-optic interferometric sensors employing a linear variable differential transformer signal conditioner to generate sine modulation wave and demodulate phase-modulated signal from the photodetector’s output is presented in this letter. No external lock-in amplifiers or digital components are used in this design. All the necessary components for signal processing are integrated in a single analog electronic microchip AD698, which reduces the system’s complexity significantly. After implementation on an interferometric fiber-optic gyroscope as an example, this method demonstrates a bias stability of 0.063 deg h−1 (i.e. 0.220 µrad).

Bias Error Caused by the Faraday Effect in Fiber Optical Gyroscope With Double Sensitivity

We present an investigation of bias error caused by the Faraday effect in interferometric fiber optical gyroscopes (IFOGs) with double sensitivity. Jones matrix method is utilized to formulize the bias error in IFOGs with double sensitivity under the action of radial magnetic field. Theoretical results show that the bias error caused by the Faraday effect can be suppressed effectively in IFOGs with double sensitivity. Experiments with different lengths and twists of fiber coils are performed, and the experimental results support these theoretical predictions. For 490- and 1020-m polarization maintaining fiber coils, the maximum errors generated by a 1-mT radial magnetic field are 0.8°/h and 0.5°/h, respectively. This letter is promising for improving the bias stability of IFOGs.

Symmetry evaluation for an interferometric fiber optic gyro coil utilizing a bidirectional distributed polarization measurement system.

We propose a dual-channel measurement system for evaluating the optical path symmetry of an interferometric fiber optic gyro (IFOG) coil. Utilizing a bidirectional distributed polarization measurement system, the forward and backward transmission performances of an IFOG coil are characterized simultaneously by just a one-time measurement. The simple but practical configuration is composed of a bidirectional Mach-Zehnder interferometer and multichannel transmission devices connected to the IFOG coil under test. The static and dynamic temperature results of the IFOG coil reveal that its polarization-related symmetric properties can be effectively obtained with high accuracy. The optical path symmetry investigation is highly beneficial in monitoring and improving the winding technology of an IFOG coil and reducing the nonreciprocal effect of an IFOG.

Study of double-ring slow-light gyroscope with two input–output waveguides

A novel structure of double-ring slow-light gyroscope with two input–output waveguides is studied. We utilize interferometric detection method, and sufficiently combine the advantages of Interferometric Fiber Optic Gyro (I-FOG) and Resonator Optic Gyro (ROG). The responses of the structure are derived and simulated. Here two experimental schemes are also proposed. By applying a square wave to the integrated phase modulator, we can make the structure work at the highest sensitivity. After applied the square wave, the system runs at linear zone, thus the angular velocity can be obtained according to the linear relationship between the phase difference and the angular velocity. The optimal parameters for the largest phase difference of light signal monitored at different output ports are investigated. Some comparisons are done in the condition of various values of transmission loss coefficients.

Simultaneous measurement of angular velocities of two vertical directions in a slow-light structure

Abstract A dual-axis optical velocity sensor comprising an asymmetrical double-ring slow-light structure (ADRSLS) coupled by a 3 × 3 coupler is presented. The phase difference caused by the ADRSLS between the counter-propagating waves is derived and discussed. We design and built the experimental system and successfully realize the simultaneous measurement of angular velocities of two vertical directions. The maximum sensitivity of the slow light gyroscope in our case is about 35 times higher than that of an interferometric fiber optic gyroscope (IFOG).

Drift suppression in a dual-polarization fiber optic gyroscope caused by the Faraday effect

An investigation of the drift caused by the Faraday effect in a dual-polarization interferometric fiber optic gyroscope (IFOG) is presented. Both theoretical analysis and experimental results indicate that the Faraday effect phase drifts in two orthogonal polarizations of polarization-maintaining fiber always have opposite polarities that can be compensated effectively. When the interference signals of the two orthogonal polarized light waves are added up, the bias stability of the IFOG is improved significantly. This study is promising for reducing the drift of IFOG caused by the Faraday effect.

Fault Diagnosis of Space-borne Fiber Optic Gyros Based on Random Walk Coefficient Prediction and In-Orbit Calculation

A novel fault diagnosis method for the space-borne interferometric fiber-optic gyroscope (IFOG) is presented in this paper. The noise source of the fiber-optic gyroscope is analyzed first. Then, the prediction model of the random walk coefficient (RWC) is established based on the radiation-induced attenuation effect on optical fiber, and the estimation model of RWC is developed by using the detected signal acquired by the photo-detector. In addition, an improved iterative method to calculate the RWC with the output data of the IFOG in orbit is proposed. The three RWC values mentioned above are compared to determine the operational state of the gyroscope. And an in-situ fault diagnosis strategy for the IFOG is proposed finally. Based on the ground simulation and fault injection, the feasibility of the strategy is proved.

Technique for suppressing the electronic offset drift of interferometric open-loop fiber optic gyroscopes.

A technique to eliminate the offset drift in the demodulator circuitry of open-loop interferometric fiber optic gyroscopes is presented. This technique employs a demodulation scheme that uses the area of the negative half-cycles of the output signal of a sinusoidally modulated gyroscope to obtain the angular velocity. We propose an electronic circuitry that periodically reverses the demodulator input, allowing for the acquisition of two samples of the gyroscope signal with the same magnitude and opposite polarities. The angular velocity is obtained from the subtraction of these two samples, suppressing the electronic offset. Experiments showed that the proposed method reduces the demodulator offset drift from 4.4 μV/°C to about 14 nV/°C, which is equivalent to a reduction, from 0.2 deg/h/°C to about 0.0006 deg/h/°C in the tested gyroscope. The proposed technique improved the bias stability of the tested gyroscope from 0.0162 to 0.0071 deg/h.

Detection method for the singular angular velocity intervals of the interferometric fiber optic gyroscope scale factor

The scale factor is an important parameter used to characterize a fiber optic gyroscope. A scale factor test was performed on the B-215 closed-loop interferometric fiber optic gyroscope and the scale factor was observed to change considerably in some angular velocity intervals, which are defined as singular angular velocity intervals. To determine the singular angular velocity intervals accurately, we implemented the free-pendulum experiment and proposed a new method based on the Daubechies wavelet transform to detect the intervals. The results show that the method can calculate the singular angular velocity intervals efficiently and accurately, and the detection results are consistent with the scale factor test results at discrete angular velocity points. Moreover, the free-pendulum signal reflects the changes of the scale factor in detail. Therefore, this study further improves the scale factor test method by using the following approach: in addition to the scale factor test at discrete angular velocity points, it is necessary to implement the free-pendulum experiment to determine whether singular angular velocity intervals exist.

Fiber Splicing Process Research for High-Precision Optical Path Assembly of IFOG

A series of assembly processes are developed to improve the optical path performance of a kind of interferometric fiber optic gyroscope (IFOG). The assembly process of IFOG optical path mainly points to the fiber splicing operation of different fibers. First, a thermal exfoliation process is developed to decrease the surface exfoliation defect of fiber. Second, a loss-damage cutting method is proposed to control the end-face verticality degree of fiber. Third, several arc discharge functions of fiber splicer are designed to carry out the high-quality splicing. Three kinds of fibers, i.e., the single-mode fiber, the polarization maintaining fiber, and the erbium-doped fiber, are utilized. The arc discharge functions of different fiber combination modes are designed. Finally, when evaluating the process improvement effect of optical path assembly, the splicing loss of total IFOG optical path, the Weibull distribution-based reliability index, and some integrated evaluation indexes of IFOG, are considered to estimate the assembly quality. Many experiment results have proved the correctness and the effectiveness of proposed techniques.

Modeling for IFOG Vibration Error Based on the Strain Distribution of Quadrupolar Fiber Coil.

Improving the performance of interferometric fiber optic gyroscope (IFOG) in harsh environment, especially in vibrational environment, is necessary for its practical applications. This paper presents a mathematical model for IFOG to theoretically compute the short-term rate errors caused by mechanical vibration. The computational procedures are mainly based on the strain distribution of quadrupolar fiber coil measured by stress analyzer. The definition of asymmetry of strain distribution (ASD) is given in the paper to evaluate the winding quality of the coil. The established model reveals that the high ASD and the variable fiber elastic modulus in large strain situation are two dominant reasons that give rise to nonreciprocity phase shift in IFOG under vibration. Furthermore, theoretical analysis and computational results indicate that vibration errors of both open-loop and closed-loop IFOG increase with the raise of vibrational amplitude, vibrational frequency and ASD. Finally, an estimation of vibration-induced IFOG errors in aircraft is done according to the proposed model. Our work is meaningful in designing IFOG coils to achieve a better anti-vibration performance.