Spectral stabilization of an InGaAsP semiconductor laser by injection-locking

Laboratoire Lasers Ultra-Stables, Etablissement Technique Central de l'Armement, 16 bis Avenue Prieur de la Côte d'or, 94114 Arcueil Cedex, France

Abstract

This report presents both experimental and theoretical results about phase-locking and spectral purity transfer by light injection in InGaAsP semiconductor lasers. From an experimental point of view, only a few tens of nanowatts are sufficient to impose the injected beam frequency to the slave laser. To make injection-locking more confortable to study, the master laser frequency noise is reduced by resonant optical coupling to an external cavity. The master laser spectral purity transfer and the stability of the slave laser along the locking range are examined in detail. The spectral purity transfer between a monomode beam and a multimode mode laser is also studied. From a theoretical point of view, the nonlinear evolution of the phase-locking mechanisms over the three injection regimes is fully explained. In the multimode case, the spectral purity transfer is due to the saturation sharing between the spectral components of the gain. In the monomode case, the calculation of the frequency noise spectral density of the slave diode laser injected with a low frequency noise beam shows that the master laser spectral purity is fully transmitted to the slave laser up to a frequency which is proportional to the square root of the injected power. The final section presents two injection-locking based methods for measuring the Henry factor, and a comparison with evaluation from a method independent to injection-locking techniques.