Optoelectronic Oscillator for Arbitrary Microwave Waveform Generation

An optoelectronic oscillator (OEO) for arbitrary microwave waveform generation based on Fourier domain mode-locking (FDML) is proposed. A reconfigurable optical waveform generator (OWG) is implemented via external electro-optical modulation, which serves as the optical source for the proposed OEO. The optical waveform from the OWG can be seen as a series of frequency-scanning optical wavelengths in the frequency domain. At any instant, the number of wavelengths can be from 0 to infinite. By setting the period of the optical waveform or its multiple equal to the cavity round-trip time, an FDML OEO implemented by a frequency-scanning microwave photonic filter (MPF) is realized based on the phase-modulation-to-intensity-modulation conversion using a phase modulator cascaded with a phase-shifted fiber Bragg grating. The scanning characteristics of the MPF changes according to the optical waveform, which can be utilized to generate low-phase-noise arbitrary microwave waveforms using the inherent low-phase-noise merit of an OEO. An experiment is performed. Linearly chirped microwave waveforms and non-linearly chirped microwave waveforms with a scanning bandwidth of 2 GHz, 2-level frequency hopping (FH) microwave waveforms with an FH range of 500 MHz, and 240- and 250-bit binary and quaternary phase-coded microwave waveforms are generated from the OEO. To the best of our knowledge, this is the first time that an OEO is proposed for arbitrary microwave waveform generation.