Photonic-assisted broadband RF receivers with low IF frequencies based on Kramers-Kronig processing

A simplified photonic-based radio frequency (RF) receiver with a low intermediate frequency (IF) is proposed and experimentally demonstrated by utilizing direct detection and Kramers-Kronig (KK) processing. In the proposed approach, the RF and local oscillator (LO) signals are modulated onto an optical carrier using a dual-drive Mach-Zehnder modulator (DDMZM) biased at a minimum transmission point. The modulated optical signal is then directed to a single photodetector (PD) to produce the IF signal, which is designed to fall within 1.5 times the bandwidth of the RF signal. KK processing effectively mitigates the signal-signal beat interference (SSBI) when the frequency gap between the RF signal and the LO signal is 1.5 times less than the bandwidth of the RF signal, thus enabling the generation of a low IF signal. This allows for subsequent processing with a low-speed PD and an analog-to-digital converter operating at a lower sampling rate. Experimental validation using a 16-QAM RF vector signal shows that KK processing reduces the error vector magnitude (EVM) of the down-converted 16-QAM signal to 4.61%, compared to 18.57% without it when no frequency gap exists. This approach provides a streamlined design and straightforward implementation for photonic RF down-conversion.