A Wideband Photonic RF Receiver With Lower IF Frequency Enabled by Kramers–Kronig Detection

Featuring the benefits of wideband operation, flexible tunability, and enhanced electromagnetic immunity, photonic down-conversion is a promising technique for future RF heterodyne receiver. However, due to the square-law detection of the photodiode (PD), the down-converted signal suffers from signal-signal beat interference (SSBI). In this paper, we demonstrate a photonics-based RF heterodyne receiver using direct detection and Kramers-Kronig (KK) algorithm. The RF signal and the LO signal are modulated on an optical carrier using carrier-suppressed double-sideband (CS-DSB) modulation. A single-ended PD is severed as the mixing element to produce the intermediate frequency (IF) signal. Thanks to the SSBI mitigating ability provided by KK processing, the need of a frequency gap between the RF signal and the LO signal can be obviated, resulting in a lower IF. This allows a low-speed PD and an analog-to-digital converter with a lower sampling rate to be employed. The performance of the RF receiver is verified via reception of an RF vector signal with 16-quadrature amplitude modulation (QAM). With no frequency gap between the RF signal and the LO signal, the experimental results show that error vector magnitude (EVM) of the down-converted 16-QAM signal is 4.31%, while the EVM is 13.1% without KK processing. To the best of our knowledge, this is the first time KK processing is applied for direct detection of optical CS-DSB signals. Without long-haul fiber transmission, CS-DSB modulation is preferable for photonic RF frequency conversion due to its easy implementation.