Fixed and Variable – Frequency Shifters

A frequency shifter uses the shift inherent in the acousto-optic interaction to up- or down-shift a laser’s frequency.


AA Opto-Electronic offers acousto-optic (AO) fixed and variable frequency shifters. An acousto-optic device is made up of a radio frequency (RF) driver which is connected to a suitable crystal via a piezo-electric transducer. The piezo-electric transducer converts the radio frequency electric signal from the driver to acoustic (sound) waves in the crystal. The acoustic waves thus act as a “phase grating” which travels through the crystal and can diffract incident laser beams.

An acousto-optic frequency shifter uses the frequency shift of the laser beam inherent to the acousto-optic interaction. The Doppler effect shifts the frequency of the incident laser beam on an AO device. The shift of the diffracted beam equals the frequency of the acoustic wave due to energy conservation. Hence acousto-optical modulators and deflectors also act as fixed frequency shifters and variable frequency shifters respectively. The frequency shift can be positive or negative, depending on the angular sketch configuration.

Additional techniques such as multiple travels inside the shifter to double or triple the frequency shift, or a combination of two frequency shifters to achieve low amount of shift (DC to KHz) can be used. Example applications include optical heterodyning and interferometry, and laser Doppler velocimetry for particle velocity analysis in sprays.

For tables of available products, see AO Deflectors for variable frequency shifters and AO Modulators for fixed frequency shifters in free space.

Also, see the Fibre Pigtailed AO Modulators for fibre coupled fixed frequency shifters.

For a copy of AA catalogue, click CATALOG-AA-OPTO-2019.

A depository of related published articles is available here.

View/ download theory and application notes on accousto-optics.

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