Interferometric integrated optic gyroscope usually applies a square wave phase modulation signal, namely two state modulation or four state modulation, between two back-propagation light waves. The amplitude of square wave phase modulation is π/2, and the modulation frequency is the intrinsic frequency of the sensitive loop. Based on this unique demodulation method, it is inevitable to generate a spike pulse signal at the output signal end of the detector. This spike pulse signal can cause transient saturation in the front or rear amplifier of the detector, and signal distortion will occur when the detector recovers from this overload state; The asymmetry of peak pulses can generate odd harmonic interference coupled into useful signals, resulting in errors during demodulation and increasing the output noise of the gyroscope. Therefore, it is necessary to process the spike pulse. This article theoretically analyzes the reasons for the output noise of the gyroscope caused by spike pulses, and adopts a method to avoid the impact of spike pulses. Simulation shows that this method not only eliminates spike pulses, but also eliminates odd harmonic interference induced by spike pulses. The experimental comparison shows that this method significantly improves the accuracy of the gyroscope.
In order to meet the temperature performance requirements of high-precision FOG, the Shupe coefficient of the optical fiber coil must be further reduced. The generation of Shupe error is not only related to the rate of change of temperature with time, but also related to the rate of change of thermal stress with time. In this paper, the effects of thermal conductivity and internal stress of the potting adhesive on the Shupe error of the optical fiber coil were carried out. By designing a hyperbranched molecular structure, the curing stress of the UV potting adhesive was greatly reduced, and a rigid-flexible block structure was prepared by adjusting the formulation components to obtain high modulus (Eˊ) and high glass transition temperature (Tg) performance, which greatly improved the full temperature stability and long-term reliability of the potting adhesive. The potting adhesive is doped with high thermal conductivity particles to obtain high thermal conductivity, reduce the temperature gradient inside the optical fiber coil, and improve the full temperature performance of the coil. The results showed that the glass transition temperature of the developed high-precision optical fiber coil UV potting adhesive is higher than 100℃, and the Young's modulus is higher than 2000MPa. The peak-to-peak value of the coil Shupe is 0.1°/h. Through research, low stress, high thermal conductivity potting adhesive can effectively reduce the Shupe error of the high-precision optical fiber coil, improve the full-temperature performance of the coil, and realize the long-term stability and reliability of the FOG.
The development of high precision fiber optic gyroscope (HFOG) is of great strategic significance to a country's industrial and national defense science and technology. Optical fiber coil is the key to guarantee the accuracy and long-term stability of HFOG, and the adhesive is an important factor for the stability of optical fiber coil performance. In order to improve the temperature characteristics of HFOG, this study carried out the research on the technology of high thermal conductivity adhesive doped with high thermal conductive filler to improve its thermal conductivity (κ), and prepared a high thermal conductivity coil potting adhesive with excellent heat transfer and heat dissipation performance. By designing the composition ratio and block molecular structure with alternating soft and hard segments, the balance of glass transition temperature (Tg) and Yong’s modulus (Eˊ) was obtained, which can make the temperature field distribution of the optical fiber coil more uniformly, reduce the stress in the coil after curing, reduce the coil temperature errors. The above studies suppress the temperature drift and improve the overall accuracy of HFOG.
High-Precision Fiber Optic Gyroscope (HPFOG) is the core sensor of the long-endurance fiber optic inertial navigation system. The improvement of the positioning accuracy of the inertial navigation system depends on the improvement of the bias performance and the scale performance of the gyroscope. The broadband ASE light source can effectively suppress the noise such as Kerr effect and Rayleigh scattering in the optical path of the FOG. The flatness of the output spectrum of the ASE light source also affects the scale of the FOG. In this paper, the influence of broadband fiber light source on the bias performance and scaling performance of HPFOG is analyzed theoretically, and the design of a high-flatness C+L band broadband ASE light source is developed. By analyzing the conditions of the output spectrum of the ASE light source from the C-band to the L-band until the C+L band is formed, the pump light power and the length of the erbium-doped fiber are optimized, and the output spectral width, power and spectral flatness of the ASE light source are simultaneously improved. Performance, the developed C+L band broad-spectrum ASE light source has a spectral width of 80nm and a flatness of less than 1.5dB. Subsequently, this paper compares the performance of HPFOG using traditional Gaussian ASE light sources and high-flatness C+L band light sources. The experimental results show that although the spectral symmetry of the C+L band broad ASE light source is weaker than that of the Gaussian spectrum ASE light source, but the scale factor performance of HPFOG is similar, and there is no obvious impact. The key is that the use of high-flat C+L band broad ASE light source significantly improves the bias stability of HPFOG. The normalized index shows that the 100s bias stability is improved by 30%.
Based on the Sagnac effect, the small changes in thermally induced stresses and microcosmic size of optical fiber coil can cause the drift of the Shupe error and scale factor of fiber optic gyroscope (FOG). As polymer functional resin represents a high proportion in optical fiber coil, its physical and chemical properties determine largely the thermally induced stresses and dimensional stability of the coil, thus influencing the performance of FOG. Given the demands for the long-term stability and temperature characteristics of FOG, this paper studies the influence of molecular chain structure and thermal conductivity of polymer functional resin for optical fiber sensing on FOG. The experimental results suggest: high thermal conductivity can reduce the thermal induced stresses of polymer functional resin of reticular molecular structure, greatly improving the zero bias stability of FOG at all temperature; hyperbranched molecular structure reports outstanding creep-resistant characteristics thanks to the significantly reduced internal free volume of optical fiber coil after encapsulation and insignificant dimensional changes at all temperatures, thus ensuring long-term stability of the scale factor of FOG.
Compared with laser gyro, the scale factor performance of high-precision FOG(HPFOG) restricts its application to high-precision and strategic applications. According to the characteristics of HPFOG with well temperature sensitivity and poor nonlinearity, In this paper, the temperature error model of fiber optic loop and the scale factor error output curve of gyro at different angular rates of each temperature point are analyzed. An optical fiber temperature sensor embedded in the optical fiber loop is proposed to accurately measure the temperature of the optical fiber loop. Compared with the existing single point or multi-point external temperature model, the model can accurately measure the internal temperature field of the optical fiber loop, and establish a reliable Shupe error model of the optical fiber loop temperature. A hybrid model is established by introducing the input angular rate information of gyroscope into the model, and the multi coefficient scale error is compensated according to the model. The experimental results show that the scale factor of HPFOG is greatly improved after compensation based on the accurate error model, and the performance index of the scale factor of HPFOG is effectively improved.
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