Kumio Kasahara

208-W TEM00 operation of a diode-pumped Nd:YAG rod laser.

208-W average-power TEM(00) -mode operation from a diode-pumped Nd:YAG rod laser was demonstrated. The side-pumping method of generating a high-gain aberration-free rod, the bifocusing-compensation technique with two identically pumped rods, and a suitable choice of beam spot size were employed in the design of this laser. At the maximum pump power of 1.1 kW the fundamental transverse-mode operation (M(2)<1.1) was characterized by 7.6% electrical efficiency. The extraction efficiency was almost 60% of full multimode operation. Stable operation was obtained within a pump-power range of 15% of the maximum pump power.

An electroabsorption modulator module for digital and analog applications

This paper presents an electroabsorption modulator (EAM) module for digital and analog (D/A) applications. Optically broad-band operation of the EAM module is studied for such digital application as wavelength division multiplexing (WDM) systems. Utilizing anisotropic electroabsorption of a multiple quantum-well (MQW) EAM, 40- and 100-nm bandwidth operations in 2.5-Gb/s digital signal transmission over 200-km standard fiber are confirmed by the experiments and the simulations, respectively. For analog applications, low distortion and high link gain characteristics of the EAM module are investigated at the wavelength of 1535 nm. High spurious-free dynamic range of 123 dB/spl middot/Hz/sup 4/5/ and high link gains of -10.3 dB with matching circuit and -20.6 dB without matching circuit are obtained using the EAM module.

A channel-number insensitive erbium-doped fiber amplifier with automatic gain and power regulation function

The design scheme for an erbium-doped fiber amplifier (EDFA) with automatic channel-by-channel gain and power regulation function is discussed with much emphasis on the pump power control scheme and the requirement for feedback circuitry. Based on both wavelength and time-resolved simulation technique, an amplifier repeater employing novel high-speed automatic gain control (AGC) and automatic level control (ALC) functions is designed and implemented. The AGC and ALC scheme can suppress the transient power fluctuation of a surviving channel caused by adding or dropping all other channels less than 0.45 dB and keep output power constant over 9-dB input power range.

High-average power Q-switched operation of a Nd:YAG rod laser

Summary form only given. Ranging from fundamental physics to the engineering field, high-power diode-pumped solid-state lasers are attractive light sources for various applications. In particular Q-switched operation, used to generate high peak power IR output or green output, is important for material processing, energy applications and environment measurements. It is known that efficient-operation in the Q-switched regime requires a repetition rate higher than the inverse of the medium spontaneous fluorescence lifetime. But in the condition of continuously pumping with fixed power, the pulse duration increases and the pulse peak-power decreases. A way to shorten the pulse duration is to shorten the resonator length as much as possible. This solution is suitable for miniature lasers, but very difficult to fulfil in a high-power system, because intracavity optical elements must be used, as example to optimize the laser-beam spot-size or to compensate for thermal aberration induced by pumping. Another way to shorten the pulse duration is to increase the pump power and increase the gain in the active medium. Our approach to these problems is a quasi-continuous pumping regime which increases gain in the active medium under the fixed condition of thermal effects. We report our results on a high-average power Q-switched Nd:YAG rod laser which is quasi-continuous pumped.

Investigation of the effect of injection locking between pump lasers on a redundant pumping scheme for erbium-doped fiber amplifiers

The stability of the redundant pumping scheme for an erbium-doped fiber amplifier is investigated. It is shown experimentally that an unstable operation occurs in the redundant pumping configuration and that the instability stems from the injection locking due to coupling between pump lasers. Two countermeasures for reducing the interaction between pump lasers are proposed for practical use-by using optical isolators and by using fiber gratings to obtain coherence collapse phenomenon. A theoretical model for the redundant pumping scheme is investigated, and the requirement for the isolation between the pump lasers to suppress the instability is verified.