We demonstrate a single-channel 1.28 Tbit/s-525 km transmission using OTDM of subpicosecond DQPSK signals. In order to cope with transmission impairments due to time-varying higher-order PMD, which is one of the major limiting factors in such a long-haul ultrahigh-speed transmission, we newly developed an ultrafast time-domain optical Fourier transformation technique in a round-trip configuration. By applying this technique to subpicosecond pulses, transmission impairments were greatly reduced, and BER performance below FEC limit was obtained with increased system margin.

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.

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.

In a coherent optical communication system, a polarization fluctuation of an optical fiber is one of the most important problem. On the other hand, for a realization of optical devices, dielectric waveguides with sinusoidally varying width are investigated. Knowledge of the electromagnetic field distribution in a dielectric waveguide with boundary perturbed time by time becomes a very interesting problem. This paper shows a numerical method to simulate the effect of the external disturbance against the dielectric waveguide from time to time. The author has discussed body fitted grid generation with moving boundary for the Poisson's equation and the Laplace's equation. Here we apply this theory for the dielectric waveguide. The technique employs a kind of an expanded numerical grid generation. As the author added time component to grid generation, the time dependent coordinate system which coincides with a contour of moving boundary could be transformed into fixed rectangular coordinate system. Two cases of the perturbations against the dielectric waveguide are treated. In the first case, we present the electric distribution in the dielectric waveguide perturbed along a propagation path. While in the second case, the electric field in the waveguide perturbed perpendicular to the propagation path. Such phenomena that the phase of the electric field modulated by the external perturbation are clarified by numerical results. This technique makes it possible not only to analyze the effect of the external disturbance in a coherent optical communication system but also to fabricate optical modulators or couplers.