Tunable Microwave Frequency Multiplication by Injection Locking of DFB Laser With a Weakly Phase Modulated Signal

We have demonstrated in this paper a novel tunable microwave frequency multiplication by injecting a weakly phase-modulated optical signal into a DFB laser diode. Signals with multiple weak sidebands are generated by cross-phase modulation of a continuous wave (CW) with short pulses from mode-locked fiber laser. Then, frequency multiplication is achieved by injection and phase locking a commercially available DFB laser to one of the harmonics of the phase modulated signal. The multiplication factor can be tuned by changing the frequency difference between the CW and the free oscillating wavelength of the DFB laser. The experimental results show that, with an original signal at a repetition rate of 1 GHz, a microwave signal with high spectral purity and stability is generated with a multiplication factor up to 60. The side-mode suppression ratio over 40 dB and phase noise lower than -90 dBc/Hz at 10 kHz are demonstrated over a continuous tuning range from 20 to 40.