Abstract

The input and reference signals for the optical A/D converter are generated by two laser diodes operating at 850 nm. Circuits for both the high speed current drive and thermal compensation have been designed. The two optical signals illuminate input and reference holograms. The input hologram replicates the input signal onto the input diodes of 256 FET-SEED comparators. The reference hologram produces 256 gray levels that provide the trigger level input for each of the corresponding comparators. The digital signal value is determined by the position in the FET-SEED array where the output changes from high to low reflectance. The position in the array is decoded by another opto-electronic circuit. The output of this circuit is an array of 256 CVSEL’s, only one of which will be on for a given signal level. Each VCSEL illuminates a lookup tahle hologram to generate the corresponding digital word. The archeticture of the system is given in Fig. 2.

© 1996 Optical Society of America