An AO Frequency Shifter (AOFS) is a device that modifies the frequency of the optical beam. This is a consequence of the Doppler effect; the travelling acoustic wave causing the frequency of the optical beam to be either increased or decreased by an amount equal to the RF carrier frequency. Since the RF frequency is typically of the order of tens or hundreds of Megahertz, and the optical frequency is typically of the order of 1014Hz, the frequency shift is relatively small and would not normally be perceivable, for example as a visible change in colour.

An AO Frequency Shifter (AOFS) is a device that modifies the frequency of the optical beam. This is a consequence of the Doppler effect; the travelling acoustic wave causing the frequency of the optical beam to be either increased or decreased by an amount equal to the RF carrier frequency. Since the RF frequency is typically of the order of tens or hundreds of Megahertz, and the optical frequency is typically of the order of 1014Hz, the frequency shift is relatively small and would not normally be perceivable, for example as a visible change in colour.