Nonlinear Power Response in Heterodyne Photonic Radiometers for Microwave Remote Sensing

Microwave photonic circuits are capable of processing large bandwidths of radiometric data (
$>$
100 GHz) in an unprecedented number of analog spectrometer channels (
$>$
100) at narrow spectral resolutions (< 100 MHz) and a small device footprint. However, simultaneously processing this entire bandwidth requires a large dynamic range. In this work, a heterodyne photonic radiometer is assembled and tested with a microwave thermal noise source. We model and demonstrate the 1 dB output power compression point occurs at approximately half of the average input power for a thermal noise signal compared to a continuous wave signal. These results have a significant impact on future photonic radiometer design considerations.