Simultaneous RF self-interference cancellation and high-frequency wideband instantaneous reception using optical frequency comb-based optical undersampling

Continuous-wave (CW) carrier-based radio-frequency self-interference cancellation (RF SIC) is key to in-band full-duplex (IBFD) technology, but it cannot achieve instantaneous reception of high-frequency wideband signals. This Letter proposes an optical frequency comb (OFC)-based undersampling for wideband RF SIC and reception, which significantly enhances signal reception capabilities across ultra-wide bandwidths. To address the cancellation failures caused by misaligned optical pulse phases in OFC-based reception links, this study proposes, for the first time to the best of our knowledge, an optical path matching criterion. This extends the conventional RF SIC theory, originally developed for CW carriers, to the OFC-based reception. The new cancellation criterion is applicable to both CW- and OFC-based reception systems. Based on the proposed criterion, we designed an innovative and ingenious wavelength-division multiplexing common-path transmission architecture that effectively satisfies both the optical path matching condition and the conventional electrical path matching requirement without introducing errors. The experimental results validated the effectiveness of the proposed method. Within the 48 MHz to 9.98 GHz frequency band, the achieved RF SIC depths were at least 41.5 dB for single-tone signals and exceeded 26 dB for QPSK-modulated interference signals with a symbol rate of 60 Msps/s. The constellation diagram of the SOI (signal of interest) is successfully recovered, with an error vector magnitude (EVM) below 16.8%, meeting the 3GPP international standard requirements for QPSK signals.