HIGHLY ATTENUATING EXTERNAL-CAVITY FOR PICOSECOND-TUNABLE PULSE GENERATION FROM GAIN Q-SWITCHED LASER-DIODES

We analyze in detail the behavior of gain/Q-switched Fabry-Perot laser diodes coupled to a highly attenuating, selective external cavity. Radical differences are shown as compared to the case of strong external feedback used in mode locking. Actually, we evidence a strong analogy with the case of pulsed lasers with a small quasi-monochromatic injection signal. Unlike previous experiments on laser diodes with selective external cavity, strong chirping is observed in single-mode emission, leading to tunable picosecond pulses after compression. Experiments are carried out on two types of devices. Picosecond pulses with very high tunability (40 nm) and repetition rates (> 10 GHz) are obtained from 1.3 mum gain-switched laser diodes, the minimum pulsewidth being 2.5 ps. Ultrashort (approximately 1 ps), high-power (> 5 W) tunable pulses are achieved with 0.8 mum Q-switched lasers.