A short birefringent launching fiber is proposed to reduce the fluctuation of backscattering from single-mode fibers. The fluctuation is due to polarization-sensitive measurements. It is analyzed that the polarization direction of linearly polarized inputted light is required to make an angle of 27.4 with respect to the principal axes of the birefringent launching fiber. It is also clarified that degree of coherence should vanish at the group delay of τ and 2 τ where τ is the group delay difference of the orthogonal polarization modes in the birefringent launching fiber. Experiments reveal that the birefringent launching fiber of only 3-m length makes it possible to reduce the backscattered power fluctuation to less than 0.05 dB. Required properties of laser diodes are discussed by considering the coherency of the laser diodes with multi-longitudinal modes.

Optical soliton transmissions at 10 and 20Gbit/s over 1000km with the use of erbium-doped fiber amplifiers are described in detail. For the 10Gbit/s experiment, a bit error rate (BER) of below 110-13 was obtained with 220-1 pseudorandom patterns and the power penalty was less than 0.1dB. In the 20Gbit/s experiment optical multiplexing and demultiplexing techniques were used and a BER of below 110-12 was obtained with 223-1 pseudorandom patterns under a penalty-free condition. A new technique for sending soliton pulses over ultralong distances is presented which incorporates synchronous shaping and retiming using a high speed optical modulator. Some experimental results over 1 million km at 7.210Gbit/s are described. This technique enables us to overcome the Gordon-Haus limit, the accumulation of amplified spontaneous emission (ASE), and the effect of interaction forces between adjacent solitons. It is also shown by computer runs and a simple analysis that a one hundred million km soliton transmission is possible by means of soliton transmission controls in the time and frequency domains. This means that limit-free transmission is possible.

The purpose of this study was to identify the key variables that determine the quality of the auditory environment, for the purposes of workplace auditory design and assessment. To this end, we characterized changes in oscillatory neural activity in electroencephalographic (EEG) data recorded from subjects who performed an intellectual activity while exposed to fluctuating ambient noise. Seven healthy men participated in the study. Subjects performed a verbal and spatial task that used the 3-back task paradigm to study working memory. During the task, subjects were presented with auditory stimuli grouped by increasing high-frequency content: (1) a sound with frequencies similar to Brownian noise and no modulation; (2) an amplitude-modulated sound with frequencies similar to white noise; (3) amplitude-modulated pink noise; and (4) amplitude-modulated Brownian noise. Upon presentation, we observed a characteristic change in three EEG bands: theta (4-8Hz), alpha (8-13Hz), and beta (13-30Hz). In particular, a frequency-dependent enhancement and reduction of power was observed in the theta and beta bands, respectively.