Abstract

We present a novel method to phase lock two lasers with a controllable frequency difference. A microwave frequency-modulated vertical-cavity surface-emitting laser is used to phase connect two diode lasers by a two-step injection locking. The phase fluctuations of the two lasers are measured to be $6.4\times {10}^{-4}{\mathrm{rad}}^2$, corresponding to 99.94% phase coherence. The frequency difference of the two lasers is tunable up to tens of gigahertz. The sideband suppression of the slave laser is more than $30\mathrm{dB}$ at $30\mathrm{\mu }\mathrm{W}$ seed power. A narrow linewidth spectrum of coherent population trapping in rubidium is achieved using such beams.

© 2008 Optical Society of America

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