Time-domain characteristics of the signal of an open-loop fiber optic gyroscope were analyzed. The waveform moments of the gyroscope signal were dependent upon the rotation-induced Sagnac phase, just as the signal frequency spectra are. The peak positions of the time signal also varied with the supplied rotation, and the Sagnac phase could be read out, with optimum sensitivity, from the intervals between peaks. To demonstrate the time-domain measurement technique, the gyroscope signal was transferred to lower frequencies and the signal period was lengthened. This equivalent-time scheme lowered the operational speed requirement on the signal processing electronics and improved measurement resolution.

This paper describes a novel theory analysing the baseband transfer function of mode-coupled multi-mode optical fiber. The treatment of this method is based on the scattering matrix. This theory is direct, correct and self-consistent. Most transmission characteristics of the multimode optical fiber can be analyzed.

This paper describes an analytical consideration for mode-coupled multimode optical fibers. First in this paper a novel theory for analysing the baseband transfer function of mode-coupled multi-mode fiber is briefly described. This theory is based on Scattering Matrix method and makes it possible to analyse the baseband transfer function for arbitrary mode dispersion, attenuation, coupling coefficient and excitation condition. Second the results of the simulation based on this theory is compared with the experimental study of the transmission characteristics of multimode W-type fibers with various numerical apertures. This theoretical and experimental approach leads to the necessity of the introduction of the selection rule or the restriction of the maximum difference of the wave constants of the coupled modes. It is shown that coupling intensity and selection rule of mode coupling dominate the transmission characteristics. As for multimode W-Fiber, almost all transmission characteristics such as the transmission loss and bandwidth vs. the intermediate layer width, fiber length and the excitation condition can be analysed by introducing suitable selection rule and coupling intensity. From the view point of the optical fiber transmission system design up to about ten kilometers, it may become convenient that the only two factors: selection rule and coupling intensity are the design parameters. Finally the heuristic fact that multimode W-fiber has smaller microbending loss than singly clad step index fiber on the basis of the same dispersion is proved theoretically.

The phase-modulated optical fiber gyroscope signal was analyzed in a time-domain. The rotation rate detected by the gyroscope optics was extracted from the gyroscope signal as time-domain characteristics at the maximum sensitivity.

A down sampling technique was applied to signal processing of fiber optic gyroscopes with optical phase modulation. The technique shifts the frequency spectrum of the gyroscopic signal down to low frequencies, and lowers the speed requirements for analog-to-digital (A/D) conversion and numerical operations. A single-chip digital signal processor (DSP) with a built-in A/D converter and timers was used to demonstrate the proposed technique. The DSP internally generated a phase modulation signal and sampling trigger timing. The reference signals for digital lock-in discrimination of gyroscopic spectrum are generated by using an external binary counter, and their phases were adjusted optimally by DSP software. The DSP compensated for fluctuations in laser source intensity and phase modulation index, using the signal spectrum extracted, and linearized the gyroscopic response. The measured resolution of rotation detection was 0.9 deg/s (with a full scale of 100 deg/s) and it agreed with the resolution in A/D conversion.

This paper describes an analytical investigation of mode-coupled graded index (GI) fibers. The analysis is based on the Scattering Matrix Method. The mode coupling parameters of the fibers are clarified in calculations and experiments, and the results obtained are used to determine the actual transmission characteristics of long, spliced GI fibers, for the wavelength region near 1.3 µm, as well as for the region near 0.85 µm. It is determined that coupling between adjacent modes is dominant and that a microbending loss of an order of about 0.1 dB/km results in an extremely large increase in the bandwidth of GI fibers larger than 20 km. In this paper the propagation constant for mode groups with the same propagation angle is derived directly from a WKB analysis.

A down sampling technique was applied to signal processing for optical fiber gyroscopes. It lowered the higher speed requirement for the sampling system and numerical operations. Utilizing the technique, a digital signal processing circuit extracted rotational information from the gyroscope signal.

Secondary phase modulation was proposed for lowering the signal frequency band of open-loop optical fiber gyroscopes. Extracting the lowered frequency spectra, the rotation rate was derived from the gyroscope signal and the drift in the optical parameters were compensated.