Abstract
Photonic generations of both tunable ultra broadband and high frequency microwave signals and their applications utilizing nonlinear laser dynamics are investigated experimentally. New injection schemes including optical pulse injection and dual-beam injection are proposed and studied, which can generate microwave signals with very broad bandwidths and high frequencies. The proposed systems have the advantages of compactness, low power consumption, high reliability, less system complexity, good spectral purity, and high stability. Nonlinear dynamics of semiconductor lasers under optical pulse injection in a hybrid system are investigated and studied for ultra broadband microwave generation. By varying the delay time, regular pulsing states with different pulsing frequencies are generated from a master laser subject to optoelectronic feedback. After injecting a pulse train optically into the slave laser, the microwave frequency combs with bandwidths greater than 20 GHz within a ±5-dB amplitude variation and very low phase noise are obtained benefiting by the bandwidth enhancement effect through optical injection. To analyze their stabilities and spectral purities, single-sideband (SSB) phase noise of each microwave frequency comb line is measured. At an offset frequency of 200 kHz, a single sideband phase noise of -60 dBc/kHz (-90 dBc/Hz estimated) in the 1st harmonic is measured while a noise suppression relative to the injected regular pulsing state of the master laser of more than 25 dB in the 17th harmonic is achieved. A pulsewidth of 29 ps and a rms timing jitter of 5.7 ps are obtained in the time domain for the microwave frequency comb generated. Furthermore, utilizing the microwave frequency comb generated, frequency conversion, broadcasting, and arbitrary channel selection are demonstrated experimentally. Demonstration of ultra-wideband (UWB) over fiber based on optical pulse-injected semiconductor laser is also realized. The UWB signals generated are fully in compliant with the Federal Communications Commission (FCC) mask for indoor radiation, while a large fractional bandwidth of 93\% is achieved. To show the feasibility of the UWB-over-fiber with the proposed scheme, the quality of the UWB signals transmitted through a 2 km single-mode fiber and a pair of broadband horn antenna are examined. Moreover, utilizing a dual-beam optical injection scheme, photonic generation of broadly tunable microwave signals of around 120 GHz is also investigated without the need for a microwave reference source. Optical and power spectra of the microwave signals generated with the dual-beam optical injection scheme are compared with those generated with the optical mixing, the single-beam injection, and the unlocked dual-beam injection schemes. The signal generated with the dual-beam injection scheme shows better tunability and less power fluctuation. As have been demonstrated in this study, compared to commercial products and microwave signals generated by conventional means using laser dynamics, the proposed schemes have the advantages of narrow linewidths, low SSB phase noise, good spectral purity, widely tunable range, and less system complexity in generating ultra broadband and high frequency microwave signals.