Characterizing residual reflections within semiconductor lasers, integrated sources, and coupling optics

We describe a method for analyzing reflections within or near semiconductor lasers and more complicated integrated sources. Through Fourier transformation of an optical spectrum from the wavevector to the length domain, reflections are analyzed for strength, round-trip path length, and current or voltage dependence. Identification of reflections from within semiconductor lasers, integrated electro-absorption modulated lasers, and from coupling optics is presented. Spatial resolution in InP of /spl sim/5 /spl mu/m with over two orders of magnitude in dynamic range is demonstrated. Inverse transformation of a spatially resolved feature in a transformed reflection spectrum provides an optical spectrum due to that individual feature of sufficient resolution to study wavelength dependence, for example, of coatings and gratings.