Resarch on an Oscillation, Mechanism for an Extremely Short-External-Cavity Laser Diode

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Tunable laser diodes using the extremely short-external-cavity configuration (ESEC LD) are desirable for optical communication, optical data storage, spectroscopy and a variety of sensing and measurement systems. Nevertheless, the wavelength variation mechanism for such ESEC LDs has not been clarified until now, because of the lack of the experimental data for various coupled conditions.We experimentally and theoretically analyzed how the parameters of the coupling system affect the ESEC LD operation. Not only the wavelength but also the side-mode suppression ratio, the spectrum line width and the mode interval are investigated, with the external-cavity length, the reflectivity of the LD facet, and the drive current as parameters.As the results, a strongly coupled (low LD facet reflectivity facing an external mirror and high mirror reflectivity) short external-cavity length is the key to achieve a wide wavelength tuning range, but multi-mode tuning occurs for an anti-reflection coated laser diode. More than 20 nm is simply demonstrated by changing the external-cavity length (varying disk rotation speed) for an InGaAsP/InP anti-reflection coated laser diode with a drive current, I/I_<th> of 1.4, where I/I_<th> is the threshold current at the external-cavity length for the maximum light-output.