Ultra-low-phase-noise Ka band microwave optoelectronic oscillator and its application in frequency conversion

In this paper, we develop and demonstrate a proof-of-principle OEO, which features ultra-low phase noise in a Ka frequency band. The prototype of the whole OEO is in a cylindrical form. The optical fibers are wound on the outside, while all the optoelectronic devices are in the center. The fiber transmission noise is suppressed via phase modulation for the power redistribution. The spur-level improvement and steady state operation is guaranteed by dual-loop structure with 8.7 km and 11.6 km fiber spools, respectively. The optical power loss is reduced by the dual-output electro-optical intensity modulator (DEOM) instead of another 50:50 optical coupler. The noise floor for the fiber link from laser intensity and phase noises is suppressed by the balanced photodetector (PD) with specialized working conditions. Performance is investigated in detail. The OEO operates at the frequency of 30 GHz with the spur suppression of 74.6 dBc. The phase noise of -130.7 dBc/Hz (-149.1 dBc/Hz) @1 kHz (10 kHz), respectively, are achieved. The spectral purity is much higher than the current commercial signal source and equipment. Further, the developed OEO is applied to the frequency conversion. The RF signal, to be converted with a frequency of 7 GHz, is coupled into the OEO. Each beat results with OEO are observed clearly. All these results show that OEO has broad prospects in high precision infrastructure and projects.