Optimization of phase noise in an all-optical frequency upconverter utilizing an optical interleaver and a semiconductor optical amplifier for radio-over-fiber applications

An all-optical frequency upconverter using an optical interleaver and a semiconductor optical amplifier (SOA) has been experimentally demonstrated for radio-over-fiber (RoF) applications. An optical radio frequency (RF) signal (fRF=25 GHz) consisting of an optical carrier and a sideband is generated by mixing an optical intermediate frequency (IF) signal (fIF=1 GHz) with an optical local oscillator (LO) signal (fLO=24 GHz). The phase noise characteristic of the all-optical frequency upconverter is limited by that of the LO signal source. However, it is degraded due to path imbalance of two optical signal paths, which can be compensated by the use of a delay line. Compensation of the path imbalance by an optimum delay line produces an optimized phase noise of the upconverted RF signal of approximately −98 dBc/Hz at the offset frequency of 10 kHz.