Tunable Narrowband Microwave Radiation Source Based On A Frequency-Locked Superlattice Oscillator

We report on the generation of tunable ultra-narrowband microwave radiation using a frequency locked superlattice oscillator fabricated in a planar design. As active device, a wide-miniband GaAs/AlAs superlattice was used, showing, at room temperature, self-sustained current oscillation giving rise to microwave generation at a natural frequency near 5 GHz and ultraharmonics up to the 7(th) order; the linewidth of the harmonics was near 1 MHz. We observed a drastic reduction of the linewidths to less than 10 Hz by frequency locking the oscillator (similar to 100 mu W) with a weak narrowband driving field (similar to 0.1 mu W). The oscillator was tunable within a locking range of 1 percent of the natural frequency. Besides harmonic also subharmonic Locking was observed.