in Quantum Electronics
Henry Baltes, Peter Günter, Ursula Keller,
Fritz K. Kneubühl †, Walter Lukosz,
Hans Melchior, Markus W. Sigrist
MODELOCKING OF SEMICONDUCTOR VERTICAL
EMITTERS: FROM VECSEL TO MIXSEL
1st edition 2009. XXII, 120 pages; € 64,00.
ISBN-10: 3-86628-242-7, ISBN-13: 978-3-86628-242-1
Thanks to their vertical emission and external cavity, optically pumped VECSELs (vertical external cavity surface-emitting lasers) offer excellent single transverse mode beam quality at higher powers than any other semiconductor lasers. The output power can be simply scaled up by increasing the pump spot diameter, enabling output powers as high as 20 W so far, in fundamental transverse mode (M2<1.1). Furthermore, the semiconductor gain offers a great flexibility in design and makes it possible to address a large wavelength range from visible to infrared.
The low gain saturation of VECSELs is moreover favorable for passive modelocking with semiconductor saturable absorber mirrors (SESAMs) and reduces Q-switching instability issues. SESAM-VECSEL modelocking have been demonstrated with high power up to 2.08 W at 4 GHz, as well as high repetition rates up to 50 GHz.
In this thesis, we present a detailed study on modelocked VECSELs, which resulted in a new type of integrated modelocked VECSEL: the MIXSEL (modelocked integrated external-cavity surface emitting laser). The development of quantum dot based SESAMs (QD-SESAMs) with low saturation fluence achieved through a resonant field enhancement in the absorber was a key achievement in the demonstration of the MIXSEL as it enables modelocking with same mode sizes on the gain and absorber sections. With the MIXSEL, where a saturable absorber is integrated in the gain structure, modelocking can be achieved from a simple straight cavity. 185 mW average power was demon-strated at 2.9 GHz with 31.6 ps pulses. We discuss the saturable absorber requirements and challenges for integration in the MIXSEL and for power scaling and pulse shortening.
Finally, we investigated the QD absorber properties for a better understanding and improvement of the MIXSEL design. This study resulted in the demon-stration of antiresonant multiple-layer QD-SESAMs, which are very promising for MIXSEL integration. Antiresonant designs will improve the growth tolerance and lower MIXSEL dispersion, which is especially important for short pulse generation and high repetition rates.
About the Author:
Aude-Reine Bellancourt received her engineer degree in physics and optics from the ‘Institut d’Optique Graduate School’ in 2005. She joined the Institute for Quantum Electronics at ETH Zurich in the same year. Her research focused on development of semiconductor vertical external cavity surface-emitting lasers (VECSELs) as well as passive modelocking of these lasers with SESAMs for ultrafast lasers with multi-GHz repetition rates. She has written and co-authored more than 30 scientific journal articles and conference contributions.
Keywords: vertical external-cavity surface-emitting laser (VECSEL), semiconductor saturable absorber mirror (SESAM), modelocked integrated external-cavity surface emitting laser (MIXSEL), thin disk semiconductor laser, passive modelocking, optically pumped semiconductor lasers
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