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Advances in OptoElectronics
Volume 2017 (2017), Article ID 5283850, 6 pages
Research Article

Fundamental Transverse Mode Selection (TMS#0) of Broad Area Semiconductor Lasers with Integrated Twice-Retracted 4f Set-Up and Film-Waveguide Lens

Integrated Optoelectronics and Microoptics Research Group, Physics Department, University of Kaiserslautern, P.O. Box 3049, 67653 Kaiserslautern, Germany

Correspondence should be addressed to Henning Fouckhardt

Received 4 September 2017; Accepted 22 November 2017; Published 14 December 2017

Academic Editor: Vasily Spirin

Copyright © 2017 Henning Fouckhardt et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Previously we focused on fundamental transverse mode selection (TMS#0) of broad area semiconductor lasers (BALs) with two-arm folded integrated resonators for Fourier-optical spatial frequency filtering. The resonator had a round-trip length of 4f, where f is the focal length of the Fourier-transform element (FTE), that is, a cylindrical mirror in-between the orthogonal resonator branches. This 4f set-up can be called “retracted once” due to the reflective filter after 2f; that is, the 2f path was used forwards and backwards. Now the branches are retracted once more resulting in a compact 1f long linear resonator (called “retracted twice”) with a round-trip length of 2f. One facet accommodates the filter, while the other houses the FTE, now incorporating a film-waveguide lens. The BAL facet with the filter represents both the Fourier-transform plane (after 2f, i.e., one round-trip) as well as the image plane (after 4f, two round-trips). Thus filtering is performed even after 4f, not just after 2f. Experimental results reveal good fundamental TMS for pump currents up to 20% above threshold and a one-dimensional beam quality parameter = 1.47. The BALs are made from AlGaInAsSb, but the concept can equally well be employed for BALs of any material system.