Study of Optoelectronic Sampler Linearity for Analog-to-Digital Conversion of RF Signals

Photoconductive sampling of 10-GHz radio- frequency (RF) signal is demonstrated using interdigitated photoswitches made from low-temperature grown GaAs. We study the linearity of the device for RF input power ranging from -3 to 20 dBm. For moderate levels, the sampler shows a spurious-free dynamic range (SFDR) better than 40 dB. For the largest values, it exhibits a nonlinear response that deteriorates both SFDR and resolution. This nonlinearity is attributed to drift velocity saturation in the semiconductor material.