Abstract

Microwave-modulated light can be down-converted to generate high frequency electrical signals and passively mode-locked semiconductor lasers are promising candidates as sources of short pulses at high repetition rates [1,2]. For this purpose we combine the use of high power laser epistructures [3] with harmonic mode-locking configurations (HML) [1,2]. In this work we investigate the mode-locking (ML) operation of a multiple colliding-pulse mode locked (MCPM) laser with multiple saturable absorbers (SA) placed in the 3.7mm long cavity [4]. The 830nm laser material we use is a GaAs/Al_xGa_1-xAs double quantum well (QW) graded-index separate confinement heterostructure (GRINSCH), with an epitaxial design similar to the one reported in [3]. As shown in Fig. 1(a), the 148µm long SAs are placed at ¼, ½ and ¾ of the laser length, allowing the selection of the harmonic of the round-trip frequency (~10GHz). Sputtering-induced disordering (SID) quantum well intermixing (QWI) is used to integrate non-absorbing mirrors (NAM) in the cavity, as they improve the output power limit due to cathastrophic optical mirror damage (COMD) [5]. The 2^nd (~20GHz) or the 4^th (~40GHz) harmonics of the round-trip frequency are selected when the SA₂ or the SA₃ are reverse biased, respectively. On the other hand, no ML operation is observed when two SAs are reverse biased at the same time, preventing the selection of the 3^rd harmonic. The intensity autocorrelation traces relative to the 20 and 40GHz ML regimes are shown in Fig. 1(b) and Fig. 1(c), respectively.

© 2011 Optical Society of America