Phase-encoded optical sampling for analog-to-digital converters

A high-speed optical sampling system for electrical signals has been developed using a gain-switched diode laser and a dual-output Mach-Zehnder interferometer. The optical phase shift between the branches of the interferometer is highly linear in the applied electrical signal. The phase shift is encoded in the two outputs of the interferometer and is recovered through digital signal processing. Analog-to-digital (A/D) conversion with 78-dB spur-free dynamic range is demonstrated. Our phase-encoded sampling technique allows high-resolution (12-bit) conversion with high linearity at practical laser power levels.