Interferometric Technique for the Spectral Characterization of High Frequency Current-Modulated Mid-Infrared Semiconductor Lasers

Abstract

We describe two methods, based on Michelson interferometery, that enable the determination of the absolute wavelength of current-modulated semiconductor lasers. By non-linear regression of the instantaneous frequency of the interference signal, the rate of change of the wavelength of the radiation can be inferred. Alternatively, the absolute wavelength can be directly calculated from the maxima and minima of the interference signal. In both cases a reference absorption line enables the determination of the absolute wavelength. Both methods offer respective advantages. The methods allow a highly resolved wavelength measurement under lower kilohertz range current-modulation with relatively little effort. As a result, we present the rates of wavelength change and absolute wavelengths exemplarily for a specific interband cascade laser. It is furthermore shown that the spectral dynamic range of the laser decreases with increasing modulation frequency.