Hisashi Sawada

A new method for low noise automatic gain control of EDFAs for WDM systems in metropolitan networks

We propose a new hybrid automatic gain controlled (HAGC) EDFA which has electrical and optical feedback. The conventional optical automatic gain clamped (OAGC EDFA) has higher noise figure (NF) than the normal EDFA for its optical feedback. However the HAGC EDFA has low NF equal to the normal EDFA by the new feedback method (electrical and optical hybrid) which maintains the state just before oscillation in the optical loop. The HAGC EDFA has equal temporal response characteristics. Additionally the HAGC EDFA has lower power consumption than the OAGC EDFA by virtue of the low pump laser power, controlled by the electrical feedback.

Environmentally Stable Ytterbium-Doped Fiber Pulse Laser Composed of All-Polarization-Maintaining Fiber System with a Broad Tuning Range

Self-starting pulse generation from a ytterbium-doped fiber (YDF) ring laser is presented. The laser consisted of an all-polarization-maintaining (PM) fiber system, specifically a single-mode PM-YDF with a side hole. Environmentally stable pulses and a wide tuning range of 60 nm were obtained with a polarization extinction ratio >20 dB. The YDF oscillator described in this study is compact, reliably self-starting, and has excellent long-term stability in light of its robustness to thermal and mechanical disturbances.

Self-Controlled Short Pulse Generator from All-Fiber Coupled Fabry-Perot Cavity

Self-controlled sub-nanosecond pulse generator was demonstrated with an ytterbium-doped fiber. This fiber laser consisted simply of all non-polarization fiber without any devices for polarization control and birefringence compensation. The self-pulse operation system gave an average output power of 0.9 mW in 800-ps duration pulses.

Self-oscillating optoelectronic up-converter using a heterojunction bipolar transistor

Summary form only given. In summary, a self-oscillating optoelectronic up-converter using a single heterojunction bipolar transistor (HBT) is demonstrated for the first time. This upconverter will help simplify the configuration of radio base stations in fiber-optic subcarrier transmission links, especially when the up-converted signal frequency is high such as millimeter-wave band.

Development of Air-Hole Type Double-Clad Fiber Lasers

Transversal single mode fiber laser at 1116nm constructed by both a high optical output diode laser and an air-hole type double-clad fiber has been developed for the 1310nm Raman amplification. The special edge filters without substrates make possible to manufacture the laser system using the air-hole type double-clad fiber easily. The laser system and its characteristics are introduced in this report.