Matched Pair of AOTFs with Net Zero Frequency-Shift
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.