Rotating-waveplate optical-frequency shifting in lithium niobate

A rotating-waveplate optical frequency shifter using lithium niobate (LiNbO3) has been constructed and fully evaluated. The experimental modulator frequency shifts the incoming 6328-Å light by 110 MHz, requires 15 W of drive power, and has an inherent 12-MHz bandwidth. The output beam has high spectral purity with very little power in unwanted sidebands and closely matches the TEM00mode of the input beam. An analysis of the effects of electrical and optical maladjustments on modulator performance shows only moderate requirements on optical and electrical alignment. Heating due to the absorbed drive power slightly degrades the modulator in agreement with a temperature analysis of the modulator. An increase in insertion loss due to diffraction of the light by acoustic waves in the LiNbO3crystal was observed.