Optically sampled analog-to-digital converters

Optically sampled analog-to-digital converters (ADCs) combine optical sampl ing with electronic quantization to enhance the performance of electronic A DCs. In this paper, we review the prior and current work in this field, and then describe our efforts to develop and extend the bandwidth of a lineari zed sampling technique referred to as phase-encoded optical sampling. The t echnique uses a dual-output electrooptic sampling transducer to achieve bot h high linearity and 60-dB suppression of laser amplitude noise. The bandwi dth of the technique is extended by optically distributing the post-samplin g pulses to an array of time-interleaved electronic quantizers. We report o n the performance of a 505-MS/s (megasample per second) optically sampled A DC that includes high-extinction LiNbO3 1-to-8 optical time-division demult iplexers. Initial characterization of the 505-MS/s system reveals a maximum signal-to-noise ratio of 51 dB (8.2 bits) and a spur-free dynamic range of 61 dB. The performance of the present system is limited by electronic quan tizer noise, photodiode saturation, and preliminary calibration procedures. None of these fundamentally limit this sampling approach, which should ena ble multigigahertz converters with 12-b resolution. A signal-to-noise analy sis of. the phase-encoded sampling technique shows good agreement with meas ured data from the 505-MS/s system.