Photonic Generation of Frequency-Multiplied Microwave Signals With Constant Amplitudes

This letter presents a photonic scheme to generate frequency-multiplied microwave signals with nearly constant amplitude. Optical injection locking and an optical fiber active loop filter are utilized to generate a frequency-multiplied microwave signal and equalize its amplitude, respectively. The significance of the scheme is that optical injection locking and nonlinear modulation are simultaneously implemented by a semiconductor distributed feedback laser, making this system compact and low-cost compared with other similar photonic implementations. Corresponding experiments display the effects of amplitude equalization for 10th and 11th harmonics with an initial frequency of 1.5 GHz and an 18th harmonic with an initial frequency of 1 GHz, respectively. The harmonic suppression ratios reach over 20 dB, and the SSB phase noises (<;-92 dBc/Hz at 10 kHz offset frequency) are somewhat decreased with respect to the conventional optical injection locking.