Abstract

Recent growing interest in miniature atomic frequency references and precision magnetometers has motivated investigations of coherent population trapping (CPT) and its use in such applications [1]. System designs based on picosecond mode-locked lasers have been previously reported for generating the CPT effect, using Ti:Sapphire lasers passively mode-locked at a submultiple of the hyperfine splitting ⁸⁷Rb levels [2], or laser diodes modulated electrically [3] or with an external electro-optic modulator [4] at the ⁸⁷Rb splitting frequency. In this work we investigate a novel approach for achieving CPT in ⁸⁷Rb vapour cells. We use a 795nm semiconductor laser passively mode-locked [5] at the ⁸⁷Rb standard frequency (~6.834GHz). This approach eliminates the need for any RF driving circuit, allowing a more compact, integrable and easy to drive implementation of CPT in ⁸⁷Rb. For this purpose we have fabricated 5.678mm long lasers with 3µm wide and 1.2µm deep ridge waveguides, with a 150µm long saturable absorber (SA) at one facet. The laser material used is a 793nm GaAs/Al_xGa_1-xAs single quantum well (QW) graded-index separate confinement heterostructure (GRINSCH), with an epitaxial design similar to the one reported in [6].

© 2011 Optical Society of America