Takao Matsumoto

Polarization fluctuations in a single-mode optical fiber

Polarization fluctuation characteristics of single-mode optical fiber output are examined theoretically and experimentally. A fiber model for studying these characteristics from the perspective of probability on the Poinare sphere is proposed. The relationship of the degree of polarization fluctuation to time and fiber length is shown theoretically. Measurements of submarine and underground cables and long-haul fibers up to 270 km in length generally support the proposed model. >

Neural-processing-type optical WDM demultiplexer

A neural-processing-type optical WDM demultiplexer consisting of a multimode waveguide, a detector array, and an electrical neural network (NN) is described. This demultiplexer regenerates the original signals by recognizing the different speckle patterns of each channel with the pattern-recognition function of an NN. The demultiplexing properties can be flexibly changed, in the electrical domain, by modifying the parameters of the NN, and only simple optical components are required for implementation. Three 150-Mb/s WDM signals are successfully demultiplexed with a silica-based multimode planar waveguide, a four-channel detector array, and two high-speed analog neural network integrated circuits (ANNICs), each of which has sixteen modifiable weights and four sigmoidal transfer functions. >

High-gain polarization-insensitive optical amplifier

A polarization-insensitive optical amplifier (PIOA) consisting of two serial semiconductor laser amplifiers (SLAs) is studied theoretically and experimentally. A polarization-insensitive isolator (PII) inserted between the two SLAs serves not only to eliminate the coupling cavity, but also to rotate any polarized forward light by 90 degrees . Experimental results show a maximum fiber-to-fiber gain of 29 dB. PIOA gain deviation for the input polarization launch angle is just 0.6 dB compared to an original value of 5-6 dB in a single SLA. A theoretical analysis shows that it is necessary to achieve a PII rotation design error of less than 0.5 degrees in order to suppress deviation below 0.1 dB. PIOA noise figure deviation, for the input signal polarization launch angle, was only 0.1 dB from both the experimental and theoretical results even though there was a rotation error of 2 degrees . >

Fiber-optic transmission systems in Japan

The current status of optical-fiber communications system in Japan is reviewed. Point-to-point systems in use and under development are described. A 1.6-Gb/s system is highlighted.<<ETX>>