OEO-Based Microwave Photonics Frequency Conversion without LO Signal Leakag

We propose an optoelectronic oscillator (OEO)-based frequency conversion approach that inherently eliminates the local oscillator (LO) leakage. The core component is a dual-polarization dual-parallel Mach-Zehnder modulator (DP-DPMZM). Radio frequency (RF) signals to be frequency-converted are applied to the x-DPMZM to achieve carrier-suppressed single-sideband modulation. The y-DPMZM is used to construct an OEO loop in order to generate the LO signal. The OEO with low-phase-noise performance releases the use of external microwave sources, effectively mitigating the impact of microwave source quality on frequency- converted signals. Normally, an optical carrier (OC) in the OEO loop is essential to ensure an oscillation. However, the OC is also the main cause of LO leakage by beating with the first-order optical sidebands in a photodetector (PD). We propose a new method in this work to oscillate the LO signal in the OEO loop without the need for an OC. Therefore, the LO leakage naturally does not exist. The OC in the OEO loop is eliminated by carrier-suppressed double sideband modulation. Alternatively, the stable oscillation of the LO signal at the fundamental tone is ensured by using a 1/2 frequency divider after PD. Experimentally, we successfully generate down-converted signals (0.5-4 GHz) and up-converted signals (10.5-14 GHz) with conversion efficiencies of -36.66 ± 1.13 dB and -32.34 ± 1.87 dB, respectively. Vector signal (16 quadrature amplitude modulation) transmission tests demonstrate down-conversion error vector magnitude (EVM) between 4.66%-7.6% and up-conversion EVM between 5.86%-10.07%. The proposed scheme is inherently free from chromatic dispersion-induced power fading. The 25 km fiber transmission experiments show its potential for long-distance Radio over Fiber systems.