BROADLY TUNABLE ULTRASHORT PULSE GENERATION WITH MODE-LOCKED SEMICONDUCTOR LASERS

Abstract

<p>Wavelength tunable ultrashort pulses are generated with mode-locked InGaAs/GaAs semiconductor lasers mounted in an external cavity. A broad tuning range is achieved through the use of an asymmetric quantum well (AQW) structure in the active region of the devices. Furthermore, the incorporation of a bend in the waveguide of the devices results in a broadband, low modal reflectivity. This allows the lasers to be mode-locked in a compact, linear external cavity. Passive mode-locking of dual asymmetric quantum wen deviceshave produced pulses 2 to 5 ps in duration, tunable from 954 nm to 1015 nm. Compression of the pulses using a modified grating pair compressor has yielded optical pulses as short as 510 fs. Similar devices based on a triple asymmetric quantum well active region are capable of producing pulses 2 to 11 ps in duration under passive mode-locking, tunable from 942 nm to 1017 nm. Preliminary work with long wavelength InGaAs/GaAs lasers has resulted in pulses 2 to 5 ps in duration with average output powers ranging from 750 /-lW to 1.8 mW. Pulse compression yields pulses as short as 570 fs. The synchronization of a passively mode-locked semiconductor laser to a mode-locked Ti:Sapphire laser, using an all-optical synchronization method, is studied. The parameter space is explored in order to determine the operating conditions that yield optimal synchronization of the two lasers. Good qualitative agreement is obtained between a simple theoretical model of the synchronization process and the corresponding experimental measurements. It is also shown that the synchronization of the mode-locked semiconductor laser with a femtosecond laser provides an additional means by which the mode-locked semiconductor laser can be characterized.</p>