Injection-locking mechanisms in semiconductor lasers

Abstract

Injection locking is known to allow both frequency locking of a slave oscillator and spectral purity transfer from the master to the slave oscillator. In the case of semiconductor lasers, a lot of problems still remain to be explained. Systematic investigation has been realized, both on theoretical and on experimental points of view. Two experiments, using InGaAsP semiconductor lasers, enabled to study precisely phase locking mechanisms and spectral purity transfer from master to slave lasers: the former, with a multimode Fabry-Perot diode laser, coupled to a mirror, as master oscillator. The injection-locked slave laser became monomode like the master laser. The latter, with a DFB laser coupled to a Fabry-Perot interferometer of finesse 300, as master oscillator. The injection-locked slave laser beam had then a 1 kHz linewidth, like the master laser. Moreover, the phase difference between injection-locked slave diode laser and master laser is analyzed over the locking range. This leads to full comprehension of the stability of a diode laser under optical injection, with the possibility of simply calculating all the injection parameters. Besides, this enables to answer the question: 'Are the locking ranges symmetrical or not?'. Fascinating applications of the technique are considered.