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Factors Affecting Reciprocity Characteristics In FOG And Possible Solutions To These Factors

Oct 11, 2019

In the actual FOG, there are many factors affecting the reciprocity characteristics. These factors and their possible solutions are summarized as follows:

(l) Suppressing Scattering Noise in Fibers The backward Rayleigh scattering in the fiber and the backscattering from the optical interface are the main sources of noise for the FOG. These scattered light causes measurement errors by parasitic interference with its origin. The effective methods for suppressing these scattering noises are mainly: a. using low-coherence light sources such as super-light-emitting diodes; b. providing frequency difference for backscattered light and pulse-modulating the light source; c. using optical isolators; d. A laser, a frequency hopping laser, a phase modulator, or the like is used as a light source to destroy the temporal coherence of the light source such that the interference of the backscattered light is zero on average.

(2) Improving the noise characteristics of the semiconductor laser light source The detection sensitivity and accuracy of the FOG are directly limited by noise. In order to improve the accuracy and resolution of FOG, in addition to low-loss polarization-maintaining fiber and high-power light source, the noise characteristics of the light source should be improved and a photo-detector with high quantum efficiency should be developed to minimize the harmful effects generated inside the FOG. noise. (3) Reducing system drift due to temperature Temperature is another important cause of system drift. For high sensitivity FOG, it is especially important to overcome the effects of temperature. Since the temperature field around the fiber coil is not uniform to the fiber coil, which causes random drift of the non-reciprocal phase shift, the fiber coil must be thermostated, such as shielding with lead foil and appropriate Temperature compensation, etc., to reduce system drift caused by temperature.

(4) Improving the performance of functional components There are many functional components in FOG, such as polarizers, beam splitters, beam combiners, phase modulators, and photodetectors, which further improve the matching and phase shift of these functional components. Detection sensitivity and accuracy, reducing the guarantee of short-term drift rate.

(5) Suppression of noise of photodetector and circuit The shot noise of the photodetector and the white noise of the circuit are also important factors affecting the detection sensitivity and measurement accuracy of the FOG. For white noise of the circuit, phase modulation frequency higher than l khz can be selected to reduce noise (!l/ !); low noise preamplifier circuit with high input impedance can also be selected to improve signal to noise ratio; for photodetector The shot noise, in the current situation, uses a high quantum efficiency photodetector, a low loss polarization-maintaining fiber and a high-power laser source, etc., which has a good suppression effect.

(6) Improve the environmental adaptability of FOG Improve the stability of FOG under vibration, deformation and acceleration conditions and expand the dynamic range of measuring rotational speed, which can improve its reliability and environmental adaptability. It is also missile guidance, aircraft and naval navigation. And the basic requirements for FOG under harsh environmental conditions such as satellite and terrain matching tracking. Reducing the measurement error of the FOG and increasing its resolution and sensitivity are prerequisites for obtaining many of the above characteristics. The causes of FOG measurement errors include: a. Faraday effect. For example, the typical measurement error caused by the Earth's magnetic field is l0 /1. By using electromagnetic shielding and using polarization-maintaining fiber, the distortion distortion error of every cycle in the loop can be eliminated. b. Optical Kerr effect. The optical Kerr effect is a third-order nonlinear optical effect, and the use of low-coherence light sources may be an effective solution. c. Fresnel reflection of the fiber end face. Fresnel reflection can be reduced by eliminating backscattering (such as using a low coherent light source such as a superluminescent diode or pulsing a light source) or by using an index matching solution. d. The birefringence characteristics of the fiber. The polarization controller is set in the optical path, and the diversity receiving technology and the polarization-maintaining fiber technology can reduce the FOG measurement error caused by the birefringence characteristics of the fiber. e. Polarization changes. It can be solved by polarization-maintaining fiber or polarization plane compensation device and depolarizer. f. The optical path difference between the two beams. Intensity compensation can be performed, and the effect of returning light is eliminated by an optical isolator. g. Time-varying temperature disturbance (S1upe). The fiber coil can be wound by a four-pole method and compensated in a signal processing circuit. h. Acoustic noise and vibration. Acoustic noise and vibration can cause large non-reciprocal parasitic effects, which can be overcome by symmetrically winding fiber coils and ensuring coil stability.

Single Axis Fiber Optic Gyroscope

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