Acousto-optic devices for operation with 2 µm fiber Lasers

Ward, J.D., Stevens, G. and Shardlow, P.C. (2016) Acousto-optic devices for operation with 2 µm fiber Lasers. Proceedings of SPIE, 9730. (doi:10.1117/12.2209352).

Abstract

Fibre lasers operating in the 2µm region are of increasing interest for a range of applications, including laser machining and biomedical systems. The large mode area compared to 1µm fibre lasers combined with operation in an “eye-safe” region of the spectrum makes them particularly attractive. When developing fibre lasers at 1µm and 1.5µm manufacturers were able to call upon enabling technologies used by the telecoms industry, but at longer wavelengths, including 2µm, many such components are either unavailable or immature. We report on recent developments of Acousto-Optic Modulators and Tunable Filters that are specifically optimised for use with fibre systems operating at or around 2µm. AO devices are interesting due to their ability to conserve spatial-coherence, making them appropriate for use with single-mode optical fibres. We describe how the choice of interaction medium is an important consideration, particularly affecting the drive power and the polarisation behaviour of the device – the latter being an important parameter when used in a fibre system. We also describe two designs of AO Tunable Filter intended for laser tuning. Both designs have been demonstrated intracavity in 2µm fibre lasers. The first gives exceptionally narrow resolution (δλ/λ<0·1%). The second design is of a novel type of AOTF where a matched pair of AOTFs is configured to give a substantially net zero frequency-shift with little or no loss of pointing stability, any minor deviations in manufacture being self-compensated. Furthermore, small controlled frequency-shifts (up to about 10kHz) may be introduced with little or no detriment to the alignment of the system.

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Contributors

Author: P.C. Shardlow

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