10.3 - A low drive-power light modulator using a readily available material ADP

A video-frequency transverse electrooptic light amplitude modulator utilizing the matrix element γ41in ADP is described and compared favorably with other modulator configurations using ADP, KDP, and KD*P. It utilizes two crystals to compensate for stemperature and angular dependences of birefringence, and has more than adequate stability for normal laboratory use. A useful built-in optical bias control is provided. Frequency response has been measured between 50 Hz and 5 MHz and found to be flat. Video signals have been transmitted over a laser communication link using only 50-volt peak-to-peak drive. Half-wave voltage is 220 volts and capacity is 53 pF, giving a drive-power requirement of 2.6 watts per MHz of bandwidth for 100-percent modulation depth, or 290 mW for 50-percent modulation depth. Optical transmission was 70 percent achieved by using an index matching liquid. An extinction ratio of 30:1 was obtained using a laser light source.