Pseudo-random-bit-sequence phase modulation for reduced errors in a fiber optic gyroscope.
Low noise and drift in a laser-driven fiber optic gyroscope (FOG) are demonstrated by interrogating the sensor with a low-coherence laser. The laser coherence was reduced by broadening its optical spectrum using an external electro-optic phase modulator driven by either a sinusoidal or a pseudo-random bit sequence (PRBS) waveform. The noise reduction measured in a FOG driven by a modulated laser agrees with the calculations based on the broadened laser spectrum. Using PRBS modulation, the linewidth of a laser was broadened from 10 MHz to more than 10 GHz, leading to a measured FOG noise of only 0.00073  deg/√h and a drift of 0.023  deg/h. To the best of our knowledge, these are the lowest noise and drift reported in a laser-driven FOG, and this noise is below the requirement for the inertial navigation of aircraft.
Eigen frequency measurements of a fiber optic gyroscope based on a staircase waveform with large temperature range.
The eigen frequency is a key parameter of a fiber optic gyroscope (FOG). We present an online eigen frequency tracking method for FOG technology based on the staircase waveform and a four-step frequency perturbation. Results show that the measurement accuracy of the eigen frequency does not exceed 1.7 Hz for a temperature range of 27.5°C-62.5°C and a variation rate of 0.24°C/min. This is in good agreement with the theoretical model. The method, which exhibits a low time-space complexity, simply requires the addition of a low-rate digital-to-analog converter to the existing gyro system. There is no requirement for the type of staircase waveform in the phase modulation, and the staircase waveform remains unchanged. Thus, this method can be easily transplanted into other algorithms.
On the Graph Edit Distance Cost: Properties and Applications
We model the edit distance as a function in a labeling space. A labeling space is an Euclidean space where coordinates are the edit costs. Through this model, we define a class of cost. A class of cost is a region in the labeling space that all the edit costs have the same optimal labeling. Moreover, we characterize the distance value through the labeling space. This new point of view of the edit distance gives us the opportunity of defining some interesting properties that are useful for a better understanding of the edit distance. Finally, we show the usefulness of these properties through some applications.