A simple length measuring method for single mode fiber coiled around a drum using Sagnac effect, is proposed. Phase difference variation caused by rotating the coil is measured, and fiber length can be derived by processing the measured results. Typically, a length measurement accuracy of 1% is obtained.

In an optical fiber gyroscope consisting of sensing fiber coil, an optical phase modulator and an electronic switching circuit for Sagnac phase shift detection, a ratio of the second and the fourth harmonics in the detected output signal is used to control the modulation index. Experimental results show improved operation with stabilized scale factor.

Feed back control approach for stabilization phase modulator index of PZT phase modulator in all-fiber optic gyroscope is described. Dual core fiber interferometric sensor is applied to detect phase modulating index of PZT cylinder. Fluctuation of modulator versus temperature variation can be approximately eliminated 15 dB by this method.

Data comparison and trigger skip methods are proposed to extract truly synchronized trigger from a high speed repetitive waveform to be observed on a CRT or to be written in a partially sequential digital sampling storage circuit. So far, there have been no way to automatically extract truly synchronized trigger from the input repetitive waveform in a multi-period sampling system, when an external synchronizing signal is not accompanied. Trigger extraction mechanisms from various kinds of repetitive waveform, for which, especially, a number of triggers can generate during its fundamental period are theoretically analysed. Based on the results, the principle and effectiveness of this system for various types of the waveform are described. The input waveform is taken twice in the sampling storage circuit, and successively taken two sample value streams are compared with each other. These two should agree if both are taken in the same portion of the waveform fundamental period. If they do not agree, it is judged to be due to incorrect trigger extraction, and the trigger skip number is increased. Data taking and comparison is repeated by increasing the trigger skip number untill two successively taken data streams agree with each other. Performance estimation tests of fabricated data comparison and trigger skip circuits were made using computer produces test signal, and the results showed the reliable digital data storage and simple operation.

The scale factor temperature dependences of three important optical parts of phase modulation type optical fiber gyroscope, sensing coil, phase modulator and fiber coupler are described. Contribution of each part to the total temperature property is comparable. For each part, more than 5% of scale factor change per 1 is observed in the region from 20 to 45.