Shiro Ryu

Signal linewidth broadening due to nonlinear Kerr effect in long-haul coherent systems using cascaded optical amplifiers

Signal spectral linewidth broadening due to the interaction between nonlinear Kerr effect and spontaneous emission from optical amplifiers in long-haul coherent optical fiber communication systems using optical amplifiers is examined theoretically and experimentally. By theoretical consideration and recirculating-loop experiments, it is shown that this effect becomes an essential limitation on maximum transmission length in transoceanic coherent optical fiber submarine cable systems. >

Field Trial of 160-Gbit/s, Polarization-Division Multiplexed RZ-DQPSK Transmission System using Automatic Polarization Control

We have successfully demonstrated a field trial of 160-Gbit/s, RZ-DQPSK polarization-division multiplexed transmission system over 214 km using automatic polarization control. Q-factors of the signals have been kept stable for more than five days.

Novel coherent heterodyne optical time domain reflectometry for fault localization of optical amplifier submarine cable systems

A coherent, heterodyne-detection, optical time-domain reflectometry technique suitable for an all-optical repeater system is proposed. Rayleigh backscatter measurement through a 309-km bidirectional optical transmission line with six cascaded in-line semiconductor laser amplifiers is demonstrated using this technique. The possibility of fault localization on an optical amplifier system with optical isolators is shown.<<ETX>>

Use of an optical amplifier in a coherent receiver

The application of an optical amplifier in a coherent receiver is examined theoretically and experimentally. It is shown that in a preamplifier application an optical amplifier with a low noise figure is effective for improving the performance of a receiver which operates in thermal-noise dominant condition. It is also made clear that in an enhanced local oscillator system (ELOS), in which a local oscillator light is amplified by an optical amplifier with high output power, the improvement of a common-mode rejection ratio (CMRR) of a balanced receiver leads the system performance to nearly shot-noise-limited operation.<<ETX>>

Over 1000 km FSK heterodyne transmission system experiment using erbium-doped optical fiber amplifiers and conventional single-mode fibers

The influence of spontaneous emission noise on coherent transmission systems using multistage erbium-doped optical fiber amplifiers is experimentally examined. A frequency-shift keying (FSK) heterodyne transmission experiment was successfully performed at 560 Mb/s through 1028 km of fiber using ten cascaded fiber amplifiers and conventional single-mode fibers with a zero dispersion wavelength of around 1.3 mu m. In the experiment, no transmission penalty due to accumulated spontaneous emission noise or to fiber chromatic dispersion was observed.<<ETX>>

Field Trial of All-Optical 2R Regeneration in 40-Gbit/s WDM Transmission Systems with Optical Add/Drop Multiplexing

Optical signal processing is one of essential technologies for improving the flexibility of all-optical network. Above all, recently there have been a lot of studies regarding all-optical 2R/3R regeneration technology. However, there are few studies about all-optical 2R/3R technologies that are carried out in field environment. In this paper, we report the successful results of field trials of an all-optical 2R regeneration system based on an electro-absorption modulator for 40-Gbit/s WDM transmission systems with optical add/drop multiplexing. It was made sure that by applying the all-optical 2R regeneration system to the optical add/drop multiplexer in the 320-km-long transmission systems the transmission characteristics of the express signal after 320-km transmission and those of the dropped signal at 160-km can be made nearly the same. It is quite important that the transmission characteristics are equal for both the dropped and express channel from a point of view of the system design, and the results in this paper suggests one possible solution for this matter.

Field trial of automatic chromatic dispersion compensation for 40-Gb/s-based wavelength path protection

We report the results of the field trial of generalized multiprotocol label switching-based 40-Gb/s wavelength path protection by photonic cross-connect. In the trial, an automatic chromatic dispersion (CD) compensator was applied to maintain the quality of a signal after protection operation to compensate for the residual CD along the wavelength path. From the results of the field trial, we have made sure that the automatic CD compensation system is essential for the future all-optical wavelength path network.

Polarization diversity techniques for the use of coherent optical fiber submarine cable systems

Recent research and development work on coherent transmission systems, with emphasis on its application to optical-fiber submarine cable systems, are described. The authors demonstrated the feasibility of a polarization diversity scheme in a laboratory environment as well as in the first sea trial of a coherent frequency-shift-keying (FSK) system. The authors propose a novel external cavity laser module and a polarization coupling/dividing module in order to improve the system performance. The polarization fluctuation speed in optical-fiber submarine cable reaches 50 Hz in the worst case, and the polarization diversity scheme is a simple and very powerful technique under such polarization fluctuation conditions. >

Influence of nondegenerate four-wave mixing on coherent transmission system using in-line semiconductor laser amplifiers

Three-channel coherent frequency-shift-keying (FSK) transmission experiments using in-line semiconductor laser amplifiers under the influence of nondegenerate four-wave mixing in laser amplifiers are discussed. The experiments show that the effect of four-wave mixing is reduced by applying modulation to the interfering carriers and enlarging the frequency separation of each carrier. However, transmission quality degradation becomes serious in multistage amplifier systems. >

Frequency stabilization of FDM optical signals using an electronic counter

A new scheme is demonstrated for the frequency stabilization of FDM optical signals. This scheme uses an electronic counter to count signals detected by a scanning Fabry-Perot interferometer, instead of an A/D converter. The frequency measurement accuracy is within 50 MHz, and the frequency stability is within /spl plusmn/200 MHz over 50 hours. Using this scheme, it is possible to stabilize, with high accuracy, the frequencies of FDM carriers with unequal spacings.<<ETX>>