GaAs-based superluminescent diodes with window-like facet structure for low spectral modulation at high output powers

We demonstrate a GaAs-based superluminescent diode ( SLD ) based on the incorporation of a window-like back facet into a self-aligned stripe structure in order to reduce the effective facet reflectivity. This allows the realisation of SLDs with low spectral modulation depth ( SMD ) at high power spectral density ( PSD ) , without the application of anti-reflection coatings to either facet. This approach is therefore compatible with ultra-broadband gain active elements. We show that 30 mW output power can be attained in a narrow bandwidth, corresponding to 2.2 mW nm−1 PSD with only 5% SMD, centred about 990 nm. We discuss the design criteria for high power and low SMD and the deviation from a linear dependence of SMD on output power, resulting from Joule heating in the self-aligned stripe.