Frequency-Multiplying Optoelectronic Oscillator With a Tunable Multiplication Factor

A frequency-multiplying optoelectronic oscillator (OEO) with a tunable multiplication factor to generate a frequency-quadrupled, sextupled, or octupled microwave signal without using an optical filter is proposed and experimentally demonstrated, for the first time to the best of our knowledge. In the proposed OEO, a polarization modulator (PolM), a polarization controller (PC), and an optical polarizer (Pol) function jointly as a Mach-Zehnder modulator (MZM). Microwave oscillation is achieved in the OEO by feedbacking the intensity-modulated signal to the PolM after photodetection, and the oscillation frequency is determined by the center frequency of an electrical bandpass filter (EBPF) in the loop. A frequency-multiplied microwave signal is generated by a joint use of the PolM and a second modulator to generate two sidebands at the ±second, ±third, or ±fourth orders with the sidebands at other orders fully suppressed. By beating the two sidebands at a second photodetector (PD), a frequency-quadrupled, sextupled, or octupled microwave signal is generated. An experiment is performed. A fundamental microwave signal at 9.957 GHz is generated in the OEO loop, which is multiplied to generate a frequency-quadrupled, sextupled, or octupled microwave signal at 39.828, 59.742, or 79.656 GHz, respectively. The phase-noise performance of the frequency-multiplying microwave signal is also investigated.