Abstract
An optimized setup for fiber optic injection of a kilowatt peak power laser diode stack emitting in the SWIR spectral range is proposed. Starting from a fast axis collimated (FAC) and slow axis collimated (SAC) 15 bars, 19 emitters off the shelf laser diode stack, the beam is transformed using spatial beam combining and polarization coupling. Both techniques integrated in a compact design enable to couple the kilowatt level beam into a standard 600 μm core, 0.22 numerical aperture (NA) multimode optical fiber. An application in the field of long range SWIR laser illuminator for gated viewing is presented. A comparison between two illuminators is realized both based on the same laser diode stack but one using beam parameter product (BPP) reduction and one without. It could be demonstrated that BPP reduction is the best way for efficient, narrow divergence and compact semi-conductor based laser illuminators design and realization. The global laser illuminator efficiency could be improved by 75% for the narrowest divergences thanks to this approach.
Highlights
IntroductionMedium average power illuminators are needed for eye safe and long range active imaging applications [1] [2] [3]
Pulsed high repetition rate, medium average power illuminators are needed for eye safe and long range active imaging applications [1] [2] [3]
Beam shaping operations are described allowing the reduction of the beam parameter product (BPP) of an SWIR laser diode stack in the kilowatt power range
Summary
Medium average power illuminators are needed for eye safe and long range active imaging applications [1] [2] [3]. The pitch between each bar is equal to 1.6 mm resulting in a total emitting area of 24 mm × 10 mm The divergences of both fast and slow axis are reduced to 15 mrad and 35 mrad respectively by using micro lens arrays provided by the manufacturer. Improving brightness can considerably increase fiber coupling and relax the requirements of the collimating optics used to control the divergence of a laser illuminator. This complete optimization process is described and experimented in this paper with the support of simulation
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