Hybrid radio-intermediate-frequency oscillator with photonic-delay-matched frequency conversion pair.

A low-phase-noise, single-loop radio-frequency (RF) oscillator is proposed and experimentally demonstrated where part of the oscillation is in intermediate-frequency (IF) domain by a pair of frequency conversions. Single-mode operation is achieved by IF filtering. The key design is the matched photonic delay between the two conversions, by which the large phase noise of the common external RF local oscillation (LO) shows no impact on the RF carrier passing through the conversion pair and the low-phase-noise oscillation is guaranteed. The phase-noise performance of the delay-matched conversion pair plus IF filtering is theoretically and experimentally studied. With the proposed scheme, we achieve 120 dBc/Hz phase noise at 10-kHz offset from 10-GHz carrier frequency through a 1-μs loop cavity.