Wideband tunable opto-electronic oscillator based on frequency translation

We demonstrate a new method to obtain a widely tunable low phase-noise opto-electronic oscillator (OEO), based on translating the OEO signal into a lower intermediate frequency (IF) signal. The OEO signal is downconverted to IF by using a local oscillator (LO) signal, filtered by a high-Q filter; its frequency is then upconverted back into the high OEO frequency. The combination of a narrowband filter at a fixed central frequency with a tunable LO forms a tunable high-Q bandpass filter (BPF) that can be used to change the OEO frequency over a broad frequency region. The effect of the LO phase noise on the OEO is suppressed by the dual frequency conversions. Hence, a tunable LO with a high phase noise can be used to control the frequency of a very low phase-noise OEO. The use of a BPF with a lower center frequency than that of the OEO signal also enables increasing the effective Q-factor of the OEO filter.