A photonic switching system is expected to have advantages over a conventional electronic switching system in exchanging broadband signals. Extensive studies have recently done on various photonic switching systems. State-of-art technology in photonic switching systems is surveyed in this paper. Small-capacity space-division switching systems using waveguide optical matrix switches are most practical and expected to be introduced to broadband local-area network in the near future. Wavelength division switching technology is important in extending switching capacity to large value. Application of photonic switching technology for ATM switching systems is also recently extensively studied to achieve switching throughput larger than that of electronic ATM switches.

This paper examines the key technologies and applications of optical frequency division multiplexing (OFDM) systems. It is clarified that a 100-channel OFDM system is feasible as a result of multichannel frequency stabilization, common optical amplification and channel selection utilizing a tunable optical filter. Transmission limitation due to fiber four-wave mixing is also described. Major functions and applications of the OFDM are summarized and the applicability of OFDM add/drop multiplexing is examined.

According to the development of optical communication technologies, it is getting easier to handle new devices, such as optical fibers, semiconductor light sources, guided wave devices, and optical integrated circuits. These devices have recently given considerable impact on the optical sensing field. The optical sensing shares the optical devices and the concepts of signal processing or system configuration with the optical communication. In this paper, the advanced lightwave sensing technology is discussed, considering the relation to the advanced optical communication technology. Distributed fiber sensors and the application of coherence characteristics of semiconductor light sources are the topics to be mainly discussed. In the distributed fiber sensors, the fiber plays both a role of low-loss transmission line and a role of lengthwise deployed sensing element. According to the change of characteristics of light propagating in the fiber, distribution of various physical parameters can be measured, such as the fiber loss, temperature, and strain. Optical Time Domain Reflectometry is employed to determine the location. Another tendency in the lightwave sensing field is the use of coherence characteristics of various semiconductor light sources. Low coherent source provide a highly sensitive inertial rotation sensor, that is, interferometric fiber optic gyroscope. Another type of optical gyroscope, optical passive ring-resonator gyro, has been studied as an application of a high coherence source. Frequency tunability of the semiconductor laser, especially that of tunable DFB or DBR lasers, can provide new ways in signal processing in the sensors. Optical coherence function can be synthesized also by utilizing the tunability. In conjunction with the progress in optical communication, lightwave sensing fields are steadily increasing.

An application of wavelength conversion laser diodes (WCLDs) to a photonic cross-connect system using wavelength-division (WD) technology is presented. We propose a novel WD photonic cross-connect node architecture with multiwavelength selective filters. By using the filters, we can construct a nonblocking cross-connect switch by 2-stage connection. Next we describe the requirements to the optical devices in our switch, especially to the wavelength conversion devices in configuring a multistage connection of our switch. Finally, we have conducted the wavelength switching experiments using our wavelength conversion laser diode at a bit rate of 125Mb/s and shown its applicability to a WD photonic cross-connect system with over 3,000 channels.

A frame-installed lightwave synthesizer is constructed for optical frequency-division-multiplexing (FDM) communication. The synthesizer consists of two DFB diode lasers, electrical feedback loops, and an HCN gas cell used as a frequency reference at v₀=192,843GHz (1.55459µm in wave-length). Output frequency can be stabilized at anywhere within v₀(220) GHz. The beat note observed between the synthesizer and another HCN-stabilized DFB laser is constant within 2MHz over 100 hours. Frequency stability better than 410^-10 (80kHz, without normalization) is obtained for an averaging time of 200s.

A new type of optical frequency domain reflectometry is demonstrated. Optical carrier frequency is swept so that a phase of the backscattered light is shifted. Then, an interference output of the backscattered light is Fourier transformed. The farther the scattering point locates, the faster the phase of the backscattered light changes. Hence, the Fourier spectrum of the interference output displays the fault distribution along a wave-guide. In the present scheme, the theoretical resolution is inversely proportional to the frequency sweeping range of the optical source and is given by z=c/2nf, where f is the frequency sweeping range of the optical source. In a preliminary experiment, a Michelson type interferometer in which a target fiber of 20cm length is inserted in a probing arm. The reference arm is adjusted to be longer than the probing arm by about 1.8m. This is because the interference term between the backscattering light and the reference light should be separated from the interference term formed by the backscattering light itself. A LD pumped Nd: YAG ring laser whose frequency sweeping range is 20GHz is used as a variable wavelength source. The calculated resolution is 5mm for n=1.5 in fiber. A resultant spectrum in which the two peaks correspond to the reflections at both the fiber ends is obtained.

This paper investigates a method of dynamically adjusting inter-packet gaps in accordance with network conditions, and demonstrates that the number of dropped packets is a critical parameter for adjusting inter-packet gaps. This technique, known as rate flow control, can prevent overruns in high-speed, low-delay, low-error-rate networks.

Multiple-site diversity systems are foreseen for earth to satellite paths operating at frequencies above 10GHz in localities with high rain-induced attenuation. In some severe cases double-site protection can be proved to be inadequate and consequently triple-site diversity becomes indispensable. In the present paper, an approach for the prediction of the triple-site diversity performance based on an appropriate three-dimensional gamma distribution is proposed. The model is oriented for application to earth-space paths located in Japan and other locations with similar climatic conditions. Numerical results are compared with the only available set of experimental data taken from some parts of the United States. Some useful conclusions are deduced.