Closed-loop Interferometric Fiber Optic Gyroscope Research Articles

Improved Thermal Stability of a Fiber Optic Gyroscope Using a Geometric Birefringence-Enhanced Polarization- Maintaining Fiber

In this paper, we propose and experimentally demonstrate an interferometric fiber optic gyroscope (IFOG) composed of an optimized elliptical-core Panda polarization-maintaining fiber (PMF) based on a comprehensive analysis of the design principle of PMFs for IFOGs. The improvement mechanism of the geometric birefringence on the performance of the Panda PMF was analyzed using the finite element model, and the optimized structural parameters were selected for fiber fabrication. The extinction ratio, polarization crosstalk, and assembled closed-loop IFOG output were tested and compared for fiber coils wound by different fiber structures under different temperature loads. An angle random walk performance of 0.001723 °/√h was achieved, which is a significant improvement over the traditional IFOG. The experimental results confirmed the proposed design basis that the elliptical-core Panda PMF with both higher birefringence and lower effective mode refractive index can improve the temperature stability of the IFOG.

Experimental study and analysis of high sensitivity interferometric fiber optic gyroscope using multi-core fiber

In this paper, multi-core fiber (MCF) is integrated in interferometric fiber optic gyroscope (IFOG) as the sensing coil to improve its sensitivity without increasing the fiber length or Shupe error. We have used a 300-m long 7-core fiber and connected 4 cores of MCF to each other by fan-in and fan-out (FIFO) devices of fused taper in closed-loop IFOG to replace the traditional single-core fiber (SCF). Before experiment, the main benefits and certain possible problems of using MCF are explained and analyzed. The angular random walk (ARW) of 0.006°/√h and drift of 0.01°/h have been achieved, which is close to the performance of IFOG using the 1200-m long SCF. Besides having a lower Shupe sensitivity, the MCF-IFOG also has small crosstalk effect when using broadband light source. The results show that the scheme of MCF for IFOG is expected to be used in practical application in the foreseeable future.

Low-Drift Closed-Loop Fiber Optic Gyroscope of High Scale Factor Stability Driven by Laser With External Phase Modulation

In view of the poor scale factor stability of the interferometric fiber optic gyroscope (IFOG), it is a creative method to use laser to drive the IFOG for its better frequency stabilization characteristics instead of the broadband light source. As the linewidth of laser is narrow, the errors of coherent backscattering, polarization coupling, and Kerr effect are reintroduced which cause more noise and drift. This paper studies laser spectrum broadening based on external phase modulation of Gaussian white noise (GWN). The theoretical analysis and test results indicate that this method has a good effect on spectrum broadening and can be used to improve the performance of the laser-driven IFOG. In the established closed-loop IFOG, a four-state modulation (FSM) is adopted to avoid temperature instability of the multifunction integrated-optic chip (MIOC) and drift caused by the electronic circuit in demodulation. The experimental results show that the IFOG driven by broadened laser has the angular random walk noise of 0.003 8 °/√h and the drift of 0.017 °/h, which are 62% and 66% better than those without modulation respectively, of which the drift has reached the level of the broadband light source. Although the noise still needs further reduction, its scale factor stability is 0.38 ppm, which has an overwhelming advantage compared with the traditional IFOG.

Temperature modeling of modulation phase error in the integrated optical chip for closed-loop interferometric fiber optic gyroscope

An integrated optical chip (IOC) is the phase modulation actuator in a closed-loop interferometric fiber optic gyroscope (IFOG). Research on temperature characteristic of IOC is meaningful for high-precision IFOG working in harsh environment. We focus on the temperature modeling of the IOC modulation phase error. In theoretical analysis, based on the temperature dependence of the IOC equivalent capacitance, a model between IOC modulation phase error and temperature is proposed. Through experiments, the variation tendency of the IOC equivalent capacitance with temperature is first presented. Subsequently, the IOC modulation phase error is demonstrated to be linear with temperature, which verifies the effectiveness of the proposed model. We provide an error research direction of IOC for high-precision fiber optic gyroscopes.

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.

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.

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.

Improved hybrid filter for fiber optic gyroscope signal denoising based on EMD and forward linear prediction

Fiber optic gyroscope (FOG) has been widely applied in strapdown inertial navigation system (SINS) as an ideal component. However the slowly varying drift of FOG that often submerged in noise will degrade the precision of SINS over time. The main objective of this paper is to focus on eliminating noise and extracting the slowly varying drift using a newly proposed hybrid filter called EMD-G-FLP. The implementation of EMD-G-FLP mainly consists of two steps. First, improved empirical mode decomposition (EMD) method is used to decompose original drift. Then a prediction filtering method named G-FLP is adopted to denoise obtained intrinsic modes. EMD-G-FLP is compared with methods based on wavelet packet translation (WPT) and G-FLP, respectively, using signals detected from a closed-loop interferometric FOG. The deficiencies of WPT-based method are analyzed by employing static and dynamic FOG drift. Experimental results show that, G-FLP and EMD-G-FLP retain the slowly varying drift without distorting the trend. Furthermore, compared with G-FLP, EMD-G-FLP reduces the noises including quantization noise, random walk and bias instability by about 82%, 75% and 53%, respectively.

Parameters optimization of interferometric fiber optic gyroscope for improvement of random walk coefficient degradation in space radiation environment

A random walk coefficient (RWC) prediction model of interferometric fiber optic gyroscope (IFOG) in radiation environment has been developed, combining a radiation-induced attenuation (RIA) model of fiber and a RWC expression of digital closed-loop IFOG, and verified by the radiation experiments results of two fiber coils and an experimental IFOG. Using the RWC prediction model the effects of source power, fiber length and modulation phase on the RWC of IFOG were investigated in space radiation environments. Based on the prediction model and its parameters analysis, a parameters optimization method was proposed for IFOG design to improve the RWC degradation in space radiation environments. Finally, the three parameters of the experimental IFOG were redesigned according to the optimization method.

Method to control the gain in modulation chain of closed-loop fiber optic gyroscope with periodical biasing modulation

Both methods to control the gain in the modulation chain of interferometric fiber optic gyroscope (IFOG) are analyzed: One is based on the square wave biasing modulation, and the other is based on the four-state wave biasing modulation. The analysis results indicate that the method based on square wave is less efficient at low angular rate because of long reset time, and the method based on four-state wave may give the wrong or reverse gain error at high angular rate because of frequent resets. To eliminate the limitation of the existing methods, a novel demodulation method of the gain in the modulation chain based on periodical biasing modulation is proposed. This method is independent of the 2π phase ramp resets and the input angular rate. Experimental results indicate that the method effectively improves the scale factor stability and linearity of closed-loop IFOG.

Application of the Scaled Unscented Kalman Filter with Augmented State in the Fiber Optic Gyroscope

Abstract The interferometric fiber optic gyroscope (IFOG) is a nonlinear response system. The noise, which results from the optic and electrical parts of the gyro for the environmental disturbance, includes both nonlinear noise and additive noise, and degrades the bias stability of the gyro. In this paper, the nonlinear state equation about the closed-loop IFOG is deduced from analyzing the sources, characteristic and effect of noise, and then the scaled unscented Kalman filter (SUKF) with augmented state is presented to reduce the noise. The experiment showed that: by adjusting SUKF parameters, it evidently decreases the standard deviation and Allan variance of the bias stability. Therefore this algorithm achieves better performance of filtering and improves effectively the bias stability of the gyro.

Design details and characterization of all digital closed-loop interferometric fiber optic gyroscope with superluminescent light emitting diode

This paper describes the design details and the characterization of an all digital closed-loop (ADCL) interferometric fiber optic gyroscope (IFOG) Prototype with sine wave biasing modulation and SLED emiting at 1288.9 nm, constructed in TUBITAK UME. Electronic feedback section of ADCL-IFOG is composed of 16 bit AD7714YN ADC, 14 bit-LTC1667CG DAC, fully controlled and synchronized by 89C51 microcontroller. The averaged sensitivity of the ADCL-IFOG prototype in unit of error voltage applied to the phase modulator was calculated as 132.65 μV/(°/h) which equals to a scale factor of 7.53888 (°/h)/mV with a standard deviation of 0.85% for a range of 1–15270 (°/h) rotation rate, corresponding to a range of Sagnac phase shifts varying from 0.00115 to 17.57448 (°). The maximum peak to peak noise and the bias stability of the prototype were determined as 4.97 and 1.48 (°/h) at 23.0°C, respectively. The variation of the noise and bias stability on a temperature range of 23.0–42.0°C was observed.

Proton‐induced degradation in interferometric fiber optic gyroscopes

Recent advances in Interferometric Fiber Optic Gyroscope (IFOG) technology have enabled these devices to equal, and in some respects exceed, the performance of the floated, spinning wheel rate integrating gyroscope. However, their ability to perform in a space radiation environment has been a significant concern. Test results are presented addressing the effects of space radiation on the performance of a high precision pointing grade IFOG. Proton-induced degradation of the optical components of an IFOG is evaluated based on testing performed at the Harvard Cyclotron Laboratory (HCL). Rationale is provided for using the HCL proton accelerator as a reasonable simulation of the space environment. An analysis is presented which prioritizes the component-level dose tests based on expected radiation sensitivities. The evaluation addresses both total dose (to about 12 krad) and dose rate effects. Testing was performed at the component level as well as the system level with an expanded version of a closed-loop operational IFOG. Primary concerns include permanent attenuation and spectral transmission (wavelength) sensitivity to total dose, and angle random walk and bias stability degradation as a function of dose rate. Component level results are presented for a superfluorescent light source, integrated optics chip (IOC), coupler, and polarization maintaining fiber coils. Closed-loop transient noise results are evaluated based on dose rate testing of the IOC, coupler, and fiber coil.