Abstract

Compact high-power multi-GHz optical sources are of high interest for many applications, such as optical clocking, photonic switching or optical sampling. VECSELs (vertical external cavity surface emitting lasers) modelocked with semiconductor saturable absorber mirrors (SESAMs) [1] achieve excellent beam quality, and high power operation at high repetition rates (486-fs pulses with 30 mW average power at 10 GHz [2], 1.4 W in 6.1-ps pulses at 10 GHz [3], and 50 GHz with 102 mW [4]). However, the laser contains two separate semiconductor elements in a folded cavity, which is an issue for both cost-efficient high volume fabrication and for higher repetition rates. Modelocked integrated external-cavity surface emitting lasers (MIXSELs) [5, 6] combine gain and absorber within one semiconductor wafer. This enables modelocking in a simple straight cavity which can be extended towards a quasi-monolithic design [6]. Since the first MIXSEL demonstration in 2007 (40 mW in 35-ps pulses at 2.8 GHz) [5], we improved our MIXSEL design by introducing novel low saturation fluence quantum dot (QD) saturable absorbers. This allows for an antiresonant MIXSEL design with high growth tolerance. Additionally, thermal management was substantially improved by direct soldering the MIXSEL semiconductor chip onto a CVD diamond heat spreader and subsequent substrate removal. At 2.5 GHz repetition rate, we recently demonstrated power scaling up to 6.4 W [7].

© 2011 Optical Society of America