Open-loop Fiber-optic Gyroscope Research Articles

Suppression of modulation-induced polarization error in spliceless open-loop fiber optic gyroscope [Invited

Suppression of modulation-induced polarization error in spliceless open-loop fiber optic gyroscope [Invited

Compensation of scale factor nonlinear error introduced by harmonic distortion for open-loop fiber optic gyroscopes.

The scale factor (SF) of a gyroscope is the ratio of the detection output rotational rate and the input, and is expected to be a constant. However, for open-loop interferometric fiber optic gyroscopes (IFOGs) with sinusoidal modulation, harmonic amplitudes are inevitably affected by detection defects, such as nonuniform frequency response of the photodetector or unequal gain of amplification circuits. As a result, harmonic distortion leads to SF nonlinearity, which seriously hinders the accuracy of high-precision gyroscopes. In this Letter, the theoretical form of the SF error introduced by harmonic distortion of open-loop gyroscopes is analyzed, and an effective and simple compensation method is proposed. Instead of traversing the whole dynamic range, the proposed method simplifies the calibration pretest, where only a section of the dynamic range needs to be tested. Experimental results on an open-loop IFOG prototype show that, with our proposed method, the SF nonlinear error is suppressed to 2.5 ppm within the range -300 to +300∘/s, which is 33 times less than that before compensation.

Digital Control and Demodulation Algorithm for Compact Open-Loop Fiber-Optic Gyroscope.

With the advantages of small size, low cost, and moderate accuracy, an open-loop fiber-optic gyroscope (FOG) has a wide range of applications around control and automation. For the most cost-sensitive applications, a simple and stable digital algorithm with a reduced control-circuit volume and cost is highly desirable to realize high-precision control of a FOG. In this work, a new algorithm for an open-loop FOG is proposed based on the discrete multi-point demodulation in the sinusoidal modulation period. Utilizing this algorithm, stable control and angular velocity calculation of a gyro are realized with effectively suppressed gyro error. The use of this algorithm greatly reduces the requirements for processing power and simplifies the gyro circuit. Based on this algorithm, a digital FOG with a volume of only 25 × 20 × 40 mm3 achieves a bias instability of less than 0.15°/h, an angle random walk (ARW) of less than 0.015°/√h, a start-up time of less than 1 s, and a 3 dB bandwidth beyond 160 Hz. This low-cost, compact, and high-performance gyro is sufficient to satisfy the requirements of applications in the navigation and control fields such as unmanned driving.

Compact and high-reliability fiber-optic open-loop gyroscope enabled by an in-fiber polarizer.

The performance of an open-loop fiber-optic gyroscope is strongly dependent on the optical characteristics of its polarizer. Here we report the implementation of an in-house fabricated 45° tilted-fiber-grating-based polarizer, for the first time on an ultra-fine diameter polarization-maintaining fiber platform in an open-loop fiber-optic gyroscope. This special in-line polarizer is proven to have the merits of high extinction ratio, broad spectrum, bendability, stretchability, temperature insensitivity, and high reliability, all of which make it a perfect match for practical fiber optic gyros that need to be packaged compactly without affecting performance. Our prototype fiber optic gyroscope has a compact volume of only ϕ35 × 20 mm2, achieving a bias instability of less than 0.1 °/h, full temperature bias stability of less than 1 °/h, and scale factor linearity of better than 200 ppm. This compact and high-performance fiber gyro enabled by TFG polarizer may promise great potential in the field of automation and control.

Open-loop fiber-optic gyroscope with a double sensitivity employing a polarization splitter and Faraday rotator mirror.

In this Letter, a novel open-loop fiber-optic gyroscope configuration with a double sensitivity is proposed. By employing a polarization-maintaining Faraday rotator mirror and a polarization beamsplitter/combiner, light waves propagate twice along the same fiber coil in two orthonormal polarization directions. The reciprocity of the configuration has been verified in theory. The Allan variance analysis of the gyro prototype exhibits 0.03°/h bias stability over 5.5h in the laboratory environment.

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.

All-digital signal-processing open-loop fiber-optic gyroscope with enlarged dynamic range

We propose and realize a new open-loop fiber-optic gyroscope (FOG) with an all-digital signal-processing (DSP) system where an all-digital phase-locked loop is employed for digital demodulation to eliminate the variation of the source intensity and suppress the bias drift. A Sagnac phase-shift tracking method is proposed to enlarge the dynamic range, and, with its aid, a new open-loop FOG, which can achieve a large dynamic range and high sensitivity at the same time, is realized. The experimental results show that compared with the conventional open-loop FOG with the same fiber coil and optical devices, the proposed FOG reduces the bias instability from 0.259 to 0.018 deg/h, and the angle random walk from 0.031 to 0.006 deg/h(1/2), moreover, enlarges the dynamic range to ±360 deg/s, exceeding the maximum dynamic range ±63 deg/s of the conventional open-loop FOG.

Digital Signal Processing for Open-Loop Fiber-Optic Gyroscope

Digital open-loop fiber-optic gyroscope detection scheme based on sinusoidal phase modulation is introduced. A novel implementation of the detection scheme is developed with digital signal processor (DSP) and field programmable gate array (FPGA). The design and implementation of the detection system are discussed. Timing control and open-loop signal preprocessing are realized in FPGA. Rotation rate calculation is finished in DSP. Experiments result shows that good performances have been achieved and the implementation scheme is of great practical value.

All DSP 기반의 비편광 FOG 설계 및 제작

The interferometric fiber optic gyroscopes (FOGs) are well known as sensors of rotation, which are based on Sagnac effect, and have been under development for a number of years to meet a wide range of performance requirements. This paper describes the development of open-loop FOG and digital signal processing techniques implemented on FPGA. Our primary goal was to obtain intermediate accuracy (pointing grade) with a good bias stability (0.22deg) and scale factor stability, extremely low angle random walk (0.07deg) and significant cost savings by using a single mode fiber. A secondary goal is to design all digital FOG signal processing algorithms with which the SNR at the digital demodulator output is enhanced substantially due to processing gain. The Cascaded integrator bomb(CIC) type of decimation filter only requires adders and shift registers, low cost processors which has low computing power still can used in this all digital FOG processor.

New digital closed-loop processor for a fiber-optic gyroscope

An all-digital closed-loop (ADCL) signal processor is developed for optically open-loop fiber-optic gyroscope. The processor is designed to provide high performance of more than 30 bits of phase resolution over 2/spl pi/ and unlimited measurement range. The random walk of the processor was measured to be about 0.57 /spl mu/rad/Hz/sup 1/2/.

Signal distortion induced by Fresnel reflection in open-loop fiber-optic gyroscopes

The signal distortion that is due to Fresnel reflection in open-loop fiber-optic gyroscopes was theoretically analyzed to determine the relationship between the reflection ratio and the scale factor error of the gyroscopes. The analysis showed that the in-phase component of each Fourier harmonic of the gyroscope signal deviates from the true sinusoidal function, a quadrature-phase component appears, and the pi/2 rotation rates of harmonic components disagree. We evaluated the degree of scale factor degradation by defining the harmonic distortion ratio, which can be used as a measure for the reflectional quality of the gyroscopic optical system. The theory was verified by the response of an experimental gyroscope. The Fresnel reflection was eliminated by optical and electrical means, and the signal distortion of the experimental gyroscope was suppressed.

Feedback effects in erbium-doped fiber amplifier/source for open-loop fiber-optic gyroscope

We have investigated rotation-dependent feedback effects in an erbium-doped fiber source for an open-loop fiber-optic gyroscope with fiber amplifier/source configuration. Average power and optical spectrum of the source output as well as of the amplified signal output were found to vary depending on the rotation rate, resulting in the distortion of the gyroscope output. The distorted gyroscope output could be quantitatively explained by a theoretical model with the assumption that the source power and the gain variation due to feedback depends primarily on the average feedback signal power. It was found that the distortion in gyroscope output due to rotation-dependent feedback can be minimized when the phase difference is modulated with an amplitude of 2.405 rad where the average feedback signal power becomes independent of the rotation rate.

Secondary-phase-modulation method for open-loop fiber-optic gyroscopes

A proposed method of secondary phase modulation for open-loop fiber-optic gyroscopes is examined in general terms. To detect the rotation rate of a system through a beat-frequency channel, we employ linearly combined signals with different frequencies for the optical phase modulation. We find that the proper combinations of the modulation frequencies can optimize the sensitivity of gyroscopes. With this method we can employ a high-frequency band for optical phase modulations while keeping relative a lower-frequency band of the detection channel. The theoretically derived result is experimentally confirmed by using a lithium-niobate (LiNbO(3)) optical phase modulator. We also discuss the combination setup with an optical integrated-circuit device and digital signal processing.

Open Loop Fiber Optic Gyroscope : A Technical Note

This technical note describes the design and fabrication of a prototype open-loop interferometric fiber-optic gyroscope (IFOG). The gyro transfer function is transposed from that of a raised-cosine to a sine function using AC modulation, giving maximum sensitivity at rest. Among various signal processing methods, lock-in principle is used to detect the Sagnac phase shift due to rotation. Initial work is done with bulk-optic components. Finally, all-fiber gyroscope is built using laser diode (1300 nm), PINFET detector, fiber couplers and PZT phase modulator. An effort is made to develop compact IFOG with sensing coil diameter of 10 cm and signal processing card of size 10 x 6.5 sq cm. The present set-up is able to detect the direction of rotation at a rotation rate of 5 x 10/sup -4/ radian per second. Presently, the performance of the set-up is limited by the difficulty in achieving complete reciprocity.

Digital signal processing for an open-loop fiber-optic gyroscope

Open-loop fiber-optic gyroscopes (FOG's) are generally less stable than closed-loop FOG's, yet they offer simpler implementation. We propose a modification of the harmonic division algorithm for an open-loop FOG, which is more stable and also simpler for implementation than the original one. It is shown that when the analog signal is properly sampled and quantized, the performance of our algorithm reaches that of closed-loop FOG's. Our algorithm may be implemented by the use of off-the-shelf component, and does not require an integrated optics circuit.

A quadrature phase tracker for open-loop fiber-optic gyroscopes

A phase detection system for open-loop fiber-optic gyroscopes which is able to determine the Sagnac phase over several interference fringes is presented. It employs two quadrature signals of the Sagnac phase, as well as an electronic feedback signal that is a first-order estimate of the phase. Linearity is achieved by means of a trigonometric transformation, several of which have been identified, and a first-order control system that generates the feedback signal. The dynamic properties such as ramp and step response of the phase tracker have been studied. It is shown that the introduction of a simple feedforward loop completely eliminates the velocity error which is inherent in the first-order feedback system. For the particular loop gain used in the experimental system, a ramp of 280*10/sup 3/ rad/s could be tracked without detectable velocity error. The introduction of feedforward improved the risetime for a step input of 0.86 rad from 2.4 mu s to 550 ns.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Open-loop fiber optic gyroscope with wide dynamic range

An open-loop, wide dynamic range, fiber optic gyroscope has been demonstrated by using the PLL phase tracking technique. This technique provides a linear output of an open-loop gyroscope with the Sagnac phase shift up to 2Nπ rad, N=2n, is where n an integer number.

Digital integrating fiber-optic gyroscope with electronic phase tracking

A novel demodulation scheme for interferometers with optical phase modulation is described. The optical phase shift is measured by mixing a train of square digital pulses with a photodetector current and adjusting the pulse spacing by using an electronic closed loop. The optical phase shift is tracked with deviation less than 0.007 rad, which can be easily corrected by using a look-up table. An experimental optically open-loop fiber-optic gyroscope that uses this demodulation shows a linear scale factor in good agreement with theory.

Deep phase-modulation approach to an open-loop fiber optic gyroscope

A new approach to an open-loop, all-fiber gyroscope with a wide dynamic range and linear scale factor is described. For signal processing, the Sagnac phase lift is converted into a phase shift in the low-frequency electrical signal by using a deep sinusoidal phase-modulation waveform followed by gate switching. With the duty cycle of the gating signal selected to be in the range between 20 and 70%, the scale factor is stable with respect to change in the amplitude of the phase modulation signal by as much as 15%. The basic principle of the technique and experimental results are reported.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>