Kramers–Kronig detected analog RoF link enabling co-frequency RF signal transmission

A spectrally efficient Kramers-Kronig (KK) detected analog radio-over-fiber (RoF) link supporting co-frequency RF signal transmission is proposed and experimentally verified. In the proposed scheme, two identical-frequency radio-frequency (RF) signals are modulated onto the intensity and phase of the light wave of a single polarization state. The separation and demodulation of the co-frequency RF signals are accomplished after the optical field recovery by the KK receiver. The proposed scheme can mitigate chromatic dispersion (CD)-induced crosstalk between co-frequency RF signals and eliminate signal-signal beat interference (SSBI), which enables higher frequency operation and fewer constraints on the laser frequency offset and the RF signal bandwidth. In the experiments, two 16-quadrature amplitude modulation (16-QAM) microwave vector signals at 1.94 GHz with a symbol rate of 100 MSym/s are transmitted over a 25-km single-mode fiber (SMF) and detected. With the suppression of the SSBI, the obtained error vector magnitudes (EVMs) of the two 16-QAM microwave vector signals are 7.8% and 8.17%, respectively. The measured channel isolations for the two transmission channels are 25 and 21 dB, respectively. Additionally, for high-frequency band operation, the mitigation of severe crosstalk induced by fiber CD has been experimentally demonstrated using the same vector signals but with RF carrier frequencies of 6 GHz. The recovered EVMs are 7.53% and 7.79% compared with the non-compensated ones of 30.61% and 30.54%, respectively.