Widely Tunable Opto-Electronic Oscillator Based on a Dual-Frequency Laser

We report on an opto-electronic oscillator (OEO) widely tunable from 2.5 to 5.5 GHz. It is based on an Er,Yb:glass Dual-Frequency Laser operating at 1.53 μm which naturally provides an electrically-tunable beatnote. Inserted in an optical frequency-locked loop including a long fiber delay line, the laser beatnote reaches a spectral purity comparable to the one obtained with classical fixed frequency OEOs. As the oscillator scheme does not require an RF filter, the tunability is simply achieved by tuning the laser beatnote frequency. A fine optimization of the loop has allowed reaching a -27 dBc/Hz (respectively -108 dBc/Hz) phase noise power spectral density at 10 Hz (respectively 10 kHz) of the carrier with only 100 m optical fiber, this performance being independent of the frequency.