ALL-OPTICAL ANALOG-TO-DIGITAL AND DIGITAL-TO-ANALOG CONVERSION IMPLEMENTED BY A NONLINEAR FIBER INTERFEROMETER

We propose all-optical analog-to-digital and digital-to-analog converters using cross-phase modulation in a nonlinear interferometer. The proposed devices use the optical Kerr effect and are thus potentially very fast. Preliminary experimental results on 3-bit A/D and 2-bit D/A converters in a single-mode fiber Sagnac interferometer are presented. In the A/D conversion experiment, the interaction length of the fiber loop was 200 m and the input pump power was 1.55 W for bit 0 at the end of the dynamic range. In the D/A conversion, the interaction lengths were 100 m and 200 m for bit 0 and bit 1, respectively; when the bit value "1" of the input digital word was 0.26 W, the nonlinear phase shifts were pi/3, 2-pi/3, and pi for the input digital words 01, 10, and 11, respectively, demonstrating the linear phase response; we could linearize the output too by limiting and biasing the input pump power.