Novel heterostructure design for increased spectral width of superluminescent diodes and dual-wavelength laser diodes

Superluminescent diodes (SLDs) based on amplified spontaneous emission are used in numerous applications such as optical coherence tomography where the short coherence length due to the broad spectral width enables high resolution images. Multiple approaches have been made to broaden the spectrum of SLDs to reduce the coherence length further. These include multi-quantum well (MQW) designs with different effective band gaps formed either by different well widths or different well compositions. These MQWs forming the active region of the device are conventionally located within the intrinsic region of a p-i-n junction diode and have common quasi-Fermi levels determined by the current injection and carrier lifetime. The overall spectral width of these devices however narrows at high injection levels when the injection is increased to reach the desired output power. This spectral narrowing is due to the disproportionate increase in gain for different wavelengths as the injection is increased.