Remote broadband RF signal down-conversion with stable phase and high efficiency using a sideband optical phase-locked loop

We propose a phase-stable high-efficiency down-conversion approach for broadband radio frequency signals transmitted from a remote site. A high power coherent optical local oscillator signal is used at the local site to increase the conversion gain and the spurious-free dynamic range (SFDR) at the same time. A sideband optical phase-locked loop ensures the suppression of the phase noise induced by the fiber transmission and the relative frequency drift of the remote and local lasers, which are essential for the signal transmission and the down-conversion. We first experimentally demonstrate the down-conversion of a single frequency signal at 16.45 GHz to a 250 MHz intermediate frequency (IF) signal with 3 dB gain and 103 dB/Hz²/³ SFDR after 10 km fiber transmission. Then we show the broadband down-conversion capability by down-converting a 1 GHz wide linear frequency modulated pulse signal centered at 11 GHz to 1 GHz with 3 dB gain. Along with a positive gain, the SFDR of the IF signal down-converted from 5 GHz to 40 GHz has reached 97.6 dB/Hz²/³ on average. This approach is suitable for weak broadband remote signal down-conversion with a simple-structured remote end.