Extending the frequency tuning range of a self-injection locked DFB laser diode by artificially enhancing Rayleigh...

Laser diodes self-injection locked to a high Q-factor microresonator through Rayleigh scattering based feedback usually demonstrate narrow linewidth, low frequency noise but limited frequency tuning range. Here, we present a method for extending the frequency tuning range of a DFB laser diode self-injection locked to a microresonator by artificially enhancing Rayleigh scattering based optical feedback. Taking a packaged silica spherical microresonator as an example, we dope zinc oxide nanoparticles to artificially enhance Rayleigh scattering. Experimental results show that the intrinsic linewidth of the DFB laser diode is narrowed to 1.3 kHz and the white frequency noise is reduced to the level of 10² Hz²/Hz by such a doped microresonator with a loaded Q-factor of ∼2 million. A linear frequency tuning range up to 1.884 GHz is also experimentally achieved by thermo-optically tuning the resonance of the microresonator, which is 3.6 times larger than that of another microresonator with Rayleigh scattering signal weakened by 4 times, experimentally verifying the fact that the frequency tuning range of a self-injection locked DFB laser diode can be extended by enhancing Rayleigh scattering based optical feedback. Such a method can also be used in a laser diode self-injection locked to an optically or electrically tunable microresonator, by which fast tuning speed and wide tuning range can be simultaneously achieved.