Frequency Comb Generation from Semiconductor Laser Diodes
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Optical frequency combs have shown much potential in recent years to be a revolutionary tool in metrology, signals processing, and telecommunications. We investigate the use of single-section semiconductor laser diode as a portable and robust frequency comb source with the proper bandwidth and spectral coherence for spectroscopy applications. Drawing upon previous theoretical studies on pulsed and cascaded stimulated Brillouin scattering, a comprehensive theoretical model of semiconductor laser diodes was developed, including all carrier dynamics, cavity effects, and nonlinear phase shifts. The physics and essential mechanisms of laser diode frequency comb generation were studied, focusing upon the frequency modulated nature of the output without any saturable absorber. Finally, InGaAsP / InP quantum well laser diodes, operating at 1.55 Â µm and 1.3 Â µm were fabricated and characterized, with designs specified by our theoretical models. The fabricated lasers exhibited comb behavior as predicted, outputting combs with bandwidths of about 1 THz and RF linewidths of 100-250 kHz, both at 1.55 Â µm and 1.3 Â µm. These sources show much promise for spectroscopy and other frequency comb applications, paving the way toward integration in portable systems as a truly practical frequency comb source.