Takashi Touge

Evaluation of 4-Gbit/s optical fiber transmission distance with direct and external modulation

Transmission characteristics for a recently modulated measured distributed-feedbacked (DFB) laser and an externally modulated DFB laser using a Ti:LiNbO/sub 3/, Mach-Zehnder modulator at 4 Gb/s are discussed. The transmission characteristics are estimated by an advanced eye-pattern analysis method. The maximum measured fiber dispersion with a directly modulated laser is 100 to 140 ps/nm when the chirp power penalty is 1 dB. However, for external modulation, there is no power penalty after transmission over a 2220-ps/nm dispersive fiber. This confirms that external modulation has superior transmission characteristics. The modulation scheme for 4-Gb/s systems in terms of these results is discussed. >

New method analyzing eye patterns and its application to high-speed optical transmission system

An advanced method of analyzing eye patterns is proposed which plots the eye pattern as a function of the error rate. The method is applied to high-speed optical-transmission systems and its usefulness is confirmed. Degradation of eye opening due to noise and intersymbol interference is investigated quantitatively using the 10/sup -10/ BER eye. An automatic gain-control system is evaluated from a viewpoint of eye margin, and a gain control system having an improved eye margin performance is proposed. Low-probability abnormal phenomena, such as turn-on fluctuations and mode partitioning in directly modulated distributed feedback (DFB) lasers, are observed using this method. >

4*4 OEIC switch module using GaAs substrate

A compact 4*4 optical switch module consisting of a monolithic 4-channel OEIC receiver chip, a 4*4 GaAs IC chip, and a 4-channel OEIC transmitter chip has been developed for the first time. The module offers good performance, without an optical loss, a bandwidth of more than 600 MHz, and a crosstalk between neighboring channels of less than -20 dB. It has a good switching and distributive performance for high speed optical input signals of 560 Mbit/s. The switch module is attractive for use in high data-rate optical communication systems, particularly in local area networks, CATV systems, and intra-office links. >

Compact transmitter and receiver modules with optoelectronic-integrated circuits for optical LAN's

Compact transmitter and receiver modules with monolithic optoelectronic-integrated circuits, i.e., OEICs, are demonstrated, and 400- and 800-Mbit/s transmission experiments are successfully carried out over up to 4 and 2 km, respectively, with these modules, for the first time. The design of the monolithic-integrated circuits and the compact module structure are presented. The soldering technique based on the use of YAG laser simplifies the packaging procedures, and an efficient and simple scheme for coupling between OEICs and fibers make the OEIC modules compact. Both modules are attractive for applications in high data-rate communication systems, particularly in local area networks, CATV systems, and intra-office links.

Optical wireless modem for office communication

A novel type of optical wireless modem, suitable for office communication, is described. Two types of modems, satellite and terminal, each of which consists of head and body, have been developed. The satellite head is usually attached to a ceiling or wall, and the terminal is placed adjacent to a data terminal. The full-duplex mode of data transmission up to 19.2 kbit/s, with the error rate less than 10-6, is realized between the satellite and the terminal which is placed anywhere in the service area of 10 m radius around the satellite head under the fluorescent light. In this paper, the configurations, specifications, main design features and performances of the modem are described. Some applications are also discussed.

Optical amplification and modulation techniques for multigigabit IM/DD long-haul transmission systems

The authors discuss and compare several representative modulation techniques for IM/DD (intensity modulation/direct detection) systems, focusing on their tolerance of fiber chromatic dispersion. The modulation techniques examined are direct intensity modulation of the laser diode, Mach-Zehnder interferometer external modulation, electroabsorption external modulation and direct-phase-shift and self-homodyne intensity modulation (DPSH-IM). The authors discuss the impact of these techniques on the performance of long-haul systems using optical amplifiers. A 12-Gb/s transmission experiment using an Er-doped fiber amplifier is also described. External modulation and DPSH-IM seem to be more promising than conventional direct intensity modulation for multigigabit long-span transmission systems using optical amplifiers.<<ETX>>

Cumulative waveform distortion in cascaded optical amplifier repeaters for multigigabit IM/DD systems

An analysis was conducted of a cumulative pattern-dependent waveform distortion in cascaded semiconductor laser and Er/sup 3+/-doped fiber amplifiers. At 2.5 Gb/s, cumulative waveform distortion limits the number of cascaded amplifiers to about 20 for the semiconductor amplifiers. The Er/sup 3+/-doped fiber amplifier is relatively unaffected-over 100 stages can be cascaded. The Er/sup 3+/ amplifier is seen to be the better choice for long-haul multigigabit systems.<<ETX>>

Polarization Preserving Fiber-Optic 2X2 Directional Coupler (PPFDC)

A low-loss, wide band, compact, polarization preserving, fiber optic directional coupler (PPFDC) is developed for use in future coherent optical fiber transmission systems or gyroscopes. The PPFDC is made of two 200 μm diameter sapphire ball lenses, a half-mirror and four conical alumina-ceramic ferrules with flat reference plane to preserve polarization at the connection of the fibers. Built-in thermal stress change in the fiber is minimized, because the fiber is polished only for the short length within the straight ferrule. The optical and mechanical axes are tilted, so cross-talk light from the fiber endfaces or lens surfaces is avoided. The optical directivity of the PPFDC is over 50 dB and return loss is over 40 dB in the 1.3 μm wavelength range. The excess loss is under 1 dB in the 1.2 to 1.4 μm wavelength range. The extinction ratio is over 25 dB. The length of the coupling region of the PPFDC is about 1 mm including the two ball lenses and half mirror. Spectral line widths of a fiber interfaced DFB laser diode are measured by a self delayed homodyne detection scheme, using the PPFDC. Experimental results of a novel polarization preserving fiber-optic gyroscope using a phase modulating PPFDC showed reasonable sensitivity and stability. These experimental results verified the above mentioned characteristics of the PPFDC.