Matched Pair of AOTFs with Net Zero Frequency-Shift

Jon Ward

Gooch and Housego (UK) LTD

Date: Monday 11 may 2015 from 17:00 to 17:15

Room: Claude Lefebvre

Abstract :
Acousto-Optic Tunable Filters are used in many applications where their fast agile tuning characteristics can be used to advantage. In addition, their ability to conserve spatial-coherence is useful in specialist applications, for example with single-mode optical fibres. Since, as is common with most AO devices, AOTFs generally use a travelling acoustic wave, the diffracted beam is frequency-shifted by an amount that is essentially equal to the RF drive frequency. This can be inconvenient, especially in applications where the AOTF is deployed in a multi pass configuration such as a recirculating-ring or laser-cavity. Often in such configurations a second AO device (usually similar to the first) is deployed in such a way so as to compensate for the frequency- shift. For an AO device using the isotropic AO interaction this is relatively straightforward since there is a symmetry about the device and interaction. However, an AOTF uses the anisotropic interaction which is asymmetric, and this is frequently further complicated by the inclusion of pointing-stability compensation. We describe and characterise a pair of matched AOTFs operating in opposite quadrants of the “K-space” diagram that when combined have true reciprocity and give a net zero frequency shift whilst maintaining excellent pointing- stability. Any minor deviations in manufacture are self-compensated making these components ideal for use within a single-mode fibre network, or laser cavity. 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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