Tunable and reconfigurable fundamental, frequency-doubled, and dual-frequency RF signal generator

A photonic scheme for generating a reconfigurable single- and dual-frequency RF signal with low phase noise and high sidemode suppression is proposed and experimentally demonstrated. It is based on an optoelectronic oscillator (OEO) loop comprising a dual-polarisation binary phase-shift keying (DP-BPSK) modulator and a rotating polariser connected to the output of the OEO loop. Adjusting the polariser device angle alters the amplitudes of the carrier and the RF modulation sidebands produced by the OEO, which leads to the generation of an RF signal at the fundamental and/or twice the OEO oscillating wave frequency after photodetection. The polariser device angles for generating different output RF signals are theoretically analyzed and compared with that obtained using photonic simulation software. Using a high-speed tunable bandpass filter inside the OEO loop, the proposed structure can also generate a reconfigurable fundamental-frequency, frequency-doubled, and dual-band linear frequency modulation (LFM) signal. Experiments are conducted using optimized system parameters and components to minimize the sidemode amplitudes and the phase noise of the generated RF signal. Results demonstrate the generation of an RF signal at either or both 10 GHz and 20 GHz frequencies. The phase noise at a 10 kHz frequency offset for a fundamental 10 GHz RF signal, a frequency-doubled 20 GHz RF signal, and a dual-frequency RF signal at 10 and 20 GHz are -134.6 dBc/Hz, -129.1 dBc/Hz, and -133.5 dBc/Hz (10 GHz) and -128 dBc/Hz (20 GHz) respectively. In all three cases, the sidemode suppression ratio is above 55.4 dB. The frequency tunability of the proposed structure and the ability to generate a reconfigurable LFM signal with different bandwidths using a high-speed tunable bandpass filter inside the OEO loop are also demonstrated.