Optical communication systems based on wavelength division multiplexing require devices with wide tunability, narrow passband and low side lobe characteristics. Optical waveguide devices based on control by inhomogeneous surface acoustic waves can provide such features. In this paper an integrated optical directional coupler device controlled by a tapered surface acoustic waveguide is proposed and analysed. Basic formulation is presented for the analysis of tapered SAW guide and the optical directional coupler.

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We propose high gain optical waveguide amplifiers using rare-earth-doped garnet crystalline thin films in place of fiber amplifiers. Recently we find that it is effective to select Er^<3+> as active ion in order to operate near 1.55mm wavelength of the optical fiber transmission window, and fabricate slab waveguides of 1.3 at.% Er^<3+>-doped yttrium alminium garnet (Er : YGG) on the YAG substrates by RF sputtering. In this report, attenuation spectra of the waveguide showing the peaks that are due to absorption of the erbiumions are measured, and then best pumping wavelengths near 0.98μm and 1.48μm are determined. In order to make three-dimensional waveguide amplifier, we suppose strip-loaded waveguide consisting of Er : YGG thin film on YAG substrate with ZnO as loading strip, and analyze the number of modes by effective index method.

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MAN (metropolitan area network) is the future high speed network to connect metropolis. Now DQDB has been adopted as the MAN standard by IEEE 802.6 committee and draws more and more attentions. The performance studies have been carried out in many aspects. However, till now they were mainly performed by simulation method; only a few trials of theoretical analysis have been reported. In this study, we aim at finding a simple and good approximate method to analyze the DQDB system. Based on the traditional independent and geometrical distribution assumptions, we introduce the mean request generation rate and perform the analysis of DQDB system with finite buffer capacity. Our method is simple, and comfirmed by comparing the numerical results with the simulation results, achieves very good accuracy. The throughput in individual stations matches that of simulation very well within the range of traffic up to the channel capacity. Also the delay performance is good up to the moderate traffic load. Based on the results we can conclude that our analysis is valid and effective.

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Precise patterning of optical waveguides is required in integrated-optic circuits such as acousto-optic matrix switches in order to reduce crosstalks and insertion losses. In this paper, an improvement of photomask patterning is discussed in laser drawing system with stepping motors. Mechanical fluctuation and vibration in xy-stages are experimentally clarified. A PID feedback control of the stages improved the patterning accuracy within ±40nm, which is limited by the resolution of deviation measurement. Also, W discuss methods for realizing an accuracy of ±5nm.

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We measured the nonlinear coefficient of dispersion-shifted fibers at 1550nm both by XPM and SPM methods. The nonlinear index n2 for random polarization was 2.31×10^<-20>m^2/W by XPM method, and 2.6×10^<-20>m^2/W by SPM method. The results by the two methods are in agreement with published values, but they are inconsistent when we consider the polarization dependence of n2. It seems that the difficulty is mainly caused by neglecting chromatic dispersion of fibers.

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Transmission delay variations in a bare optical fiber and an Optical Ground Wire (OPGW) link using 32-Mbps transmission were measured to clarify the effect of temperature which is taken to be a dominant factor of the delay variation. The coefficient or delay variation with respect to temperature in a 40km bare optical fiber measured in a constant temperature bath was 49 ps/km/℃. Transmission delays measured on a 257 km round-trip OPGW link can be well expressed in terms of an averaged atmospheric temperature along the link where the coefficient of delay variation with respect to temperature was 62 to 68 ps/km/℃. Based on the measured results, feasibility of time synchronized networks using optical fiber links was investigated.

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This paper describes a field measurement of optical polarization characteristics in actual OPGW (Optical fiber composite Ground Wire) of Hokuriku electric company in the condition of lightning. As a result, transient fluctuations or polarization are detected 51 times in two half months. These waves feature the rise time 0.05-0.2msec and damping oscillation of 2-5kHz in 2-5msec. The maximum shift on Poincare sphere is 165 degree. my estimating the location of lightning with LLS (Lightning Location System) data and power line trip records, the transients of polarization are caused by lightning attacks distant from observed OPGW within 60km.

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Erbium-doped optical amplifier (EDFA) which are suitable for transmission systems used in an electric power company are studied. The amplifiers are designed for bidirectional optical transmission systems which contain one repeater amplifier at most. The signal directions are discriminated by wavelengths, in 1530nm and 1550nm bands. One amplifier having a simple structure with one wavelength selective coupler (WSC) shows modelate optical gain sufficient for a terminal end of the system. The other designed for a repeater of one-relay system owing to a two-stage EDFA and four WCSs, possesses high gain and large output characteristics. Performances of these amplifiers are clarified by transmittion experiments at 2.48BGbit/s using two or eight wavelengths.

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In the analog optical transmission systems, such as subcarrier multiplexing, it is problem to be generated interference noise by double Rayleigh scatters. We report that the noise measured by the quasi-experimental set-up using single Rayleigh scatters is correspond to the noise measured by double Rayleigh scatters experiment. In the results, it is necessary that Rayleigh backscater is less than -30dB in order to be obtained -155dB/Hz RIN (Relative intensity Noise) as same as analog signal sources. We also comfirm that the poralization extinction ratio of Rayleigh scatters is reduced as comparison with the input singal porarization ratio.

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Various investigations are performed for the improvement of EDFA. We report the development of High Power EDFA pumped with high power semiconductor laser diodes bidirectionally. Moreover, we exiamined EDFA's structure for low-NF and reduced it by simultaneously pumping with 980nm and l480nm pumping source. We also examined the characteristics or EDF and the fiber or optical parts which is optical transmission path and reports, as the application of High Power EDFA, dispersion shifted EDFA (DS-EDFA) whose wavelength dispersion is considered and polalization maintaining EDFA (PM-EDFA) Which amplify signal light with preserving its state of polarization.

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