Song Ningfang

Effect of radiation-induced mean wavelength shift in optical fibers on the scale factor of an interferometric fiber optic gyroscope at a wavelength of 1300 nm

In order to analyze the effect of wavelength-dependent radiation-induced attenuation (RIA) on the mean transmission wavelength in optical fiber and the scale factor of interferometric fiber optic gyroscopes (IFOGs), three types of polarization-maintaining (PM) fibers are tested by using a 60Co γ-radiation source. The observed different mean wavelength shift (MWS) behaviors for different fibers are interpreted by color-center theory involving dose rate-dependent absorption bands in ultraviolet and visible ranges and total dose-dependent near-infrared absorption bands. To evaluate the mean wavelength variation in a fiber coil and the induced scale factor change for space-borne IFOGs under low radiation doses in a space environment, the influence of dose rate on the mean wavelength is investigated by testing four germanium (Ge) doped fibers and two germanium—phosphorus (Ge—P) codoped fibers irradiated at different dose rates. Experimental results indicate that the Ge-doped fibers show the least mean wavelength shift during irradiation and their mean wavelength of optical signal transmission in fibers will shift to a shorter wavelength in a low-dose-rate radiation environment. Finally, the change in the scale factor of IFOG resulting from the mean wavelength shift is estimated and tested, and it is found that the significant radiation-induced scale factor variation must be considered during the design of space-borne IFOGs.

Reduction of nonreciprocal errors in a differential interferometric fiber optical gyroscope using optically differential processing

The bias stability of differential interferometric fiber optical gyroscope is analyzed. Thermal error causing long-term bias drift are reduced by putting the 90° splice in the middle of the fiber coil and applying a wide spectrum light source. Also, a kind of novel optical differential processing, which is much more precise than the electronic differential processing, is proposed for reducing the residual nonreciprocal error in the final differential output. An experimental setup based on optical differential processing was built. An ∼100 fold reduction in the long-term bias drift is demonstrated experimentally compared with the primary differential interferometric fiber optical gyroscope.

Electrical crosstalk-coupling measurement and analysis for digital closed loop fibre optic gyro

The phase modulation and the closed-loop controller can generate electrical crosstalk-coupling in digital closed-loop fibre optic gyro. Four electrical cross-coupling paths are verified by the open-loop testing approach. It is found the variation of ramp amplitude will lead to the alternation of gyro bias. The amplitude and the phase parameters of the electrical crosstalk signal are measured by lock-in amplifier, and the variation of gyro bias is confirmed to be caused by the alternation of phase according to the amplitude of the ramp. A digital closed-loop fibre optic gyro electrical crosstalk-coupling model is built by approximating the electrical cross-coupling paths as a proportion and integration segment. The results of simulation and experiment show that the modulation signal electrical crosstalk-coupling can cause the dead zone of the gyro when a small angular velocity is inputted, and it could also lead to a periodic vibration of the bias error of the gyro when a large angular velocity is inputted.

Space radiation effect on fibre optical gyroscope control circuit and compensation algorithm

The process of a γ-irradiation experiment of fibre optical gyroscope (FOG) control circuit was described, in which it is demonstrated that the FOG control circuit, except for D/A converter, could endure the dose of 10krad with the protection of cabin material. The distortion and drift in D/A converter due to radiation, which affect the performance of FOG seriously, was indicated based on the elemental analysis. Finally, a compensation network based on adaptive neuro-fuzzy inference system is proposed and its function is verified by simulation.

An Online Smoothing Method Based on Reverse Navigation for ZUPT-Aided INSs

Zero velocity update (ZUPT) is widely discussed for error restriction in land vehicle Inertial Navigation Systems (INSs) and wearable pedestrian INSs to overcome the problems of Global Positioning System (GPS) unavailability in urban canyons or indoor scenarios. In this paper, an online smoothing method for ZUPT-aided INSs is presented. By introducing the Rauch–Tung–Striebel (RTS) smoothing method into the ZUPT-aided INS, position errors can be effectively restrained not only at stop points but during the whole trajectory. By integrating reverse navigation with a ZUPT smoother, the method realises forward and real-time processing. Compared with existing approaches, it can improve the position accuracy in real time without any other sensors, which is well suited for applications on high-accuracy navigation in GPS-challenging environments. Accuracy test results with different Inertial Measurement Units (IMUs) show that the developed method can significantly decrease position errors from hundreds or thousands of metres to below ten metres. During the whole trajectory, the online smoothing method ensures the maximum position errors at non-stop points can reach the same level of accuracy at stop points. A delay test result proves that the delay of the reverse online smoothing method proposed in this paper is much shorter than existing online smoothing methods.

Investigation of Interstice Collapse for Hollow-Core Photonic Bandgap Fiber Fabrication

Hollow-core photonic bandgap fibers (PBGF) have low loss in theory; hence, they have great potential for many applications, such as high-speed big-data fiber communication and fiber sensors. They are fabricated using a two-step fiber drawing method. For PBGF optical properties, fabrication is an important factor. Most studies for microstructure fiber fabrication consider gas pressure, tension, and temperature control in the fiber drawing progress without considering the hexagon fillet in the honeycomb cladding, which could have a significant effect on the bandgap width. This letter focuses on the interstice’s impacts among capillaries in the hexagon fillet forming process via the hydrodynamic mode. Research shows that small interstices could collapse totally when the heating temperature is high enough, and the collapse of interstice can help the honeycomb holes restrain collapse slightly. Interstices might be advantageous for controlling the honeycomb holes and hexagon fillets.

Experimental investigation of pre-irradiation effect on radiation sensitivity of temperature sensing fiber Bragg gratings

The effect of pre-irradiation on radiation sensitivity of fiber Bragg gratings (FBGs) is verified experimentally. FBGs are fabricated in photosensitive optical fibers and single mode fibers with Ge-concentration in a range from 3 mol% to 23.37 mol% in the core. In experiments, the FBGs are subjected to twice ?-radiation exposures to a Co60 source at a dose-rate of 0.1 Gy/s up to a total dose of 50 kGy. Pre-irradiation treatment can reduce the temperature sensitivity variation of FBGs by 18.12%?35.91%, as well as Bragg wavelength shift (BWS) by 8%?27.08%. Our research demonstrates that pre-irradiation treatment is a feasible method to improve the radiation tolerance of FBGs.

The novel arithmetic and realization based on FPGA module design for the real time compensation of the reset error in FOG

In order to reduce the size of the processing circuit, and realize the real time compensation of the reset error in fiber optic gyro (FOG). A new arithmetic and realization base on field programmable gate array (FPGA) is presented in this paper. At first the reset error and the insufficiency of usual compensation scheme are analyzed. Then a novel arithmetic which based on binary algebraic operation is described. And the functional design of arithmetic implementation was completed by using modular design method. Thus the embedded module substitutes part of the processing circuit, and the small volume, light weight, low power consumption are achieved. At last the function of the module was tested, and the result indicates that the arithmetic and implementation are valid and available.