Invited paper Generation and control of transform-limited optical pulses in subpico- and picosecond regions from semiconductor diode lasers

Abstract

In this paper we summarize and discuss a series of experimental investigations, performed systematically in recent years in our laboratory, for the generation of transform-limited optical pulses with excellent coherence in the picosecond and subpicosecond ranges from semiconductor diode lasers in the near-infrared wavelength region. The two basic methods, mode locking and direct modulation, were developed and fully studied for this first achievement employing AlGaAs and InGaAsP laser diodes. Active and passive mode locking incorporating external cavities with AlGaAs diode lasers were successful in realizing transform-limited optical pulses with durations of 30 ps and 0-58 ps respectively. Moreover, a strong RF modulation scheme superimposed on the forward and backward DC bias current was demonstrated to be the most practical and reliable for generating single-mode ultra short optical pulses with excellent coherence from a distributed feedback (DFB) InGaAsP diode laser. This transform-limited behaviour was achieved only by the laser diode itself, with no requirement for any other optical elements and external cavity or careful optical alignment, and proved to be capable of continuous control of the pulse width from about 25 to 80 ps as well as of the peak output power by adjusting the DC bias current. Thus it can be expected that well-tailored diode lasers and their optically integrated versions should be able to produce transform-limited ultra short and high-peak power optical pulses in the wavelength range from visible to 10 μm or more in the near future.