Quantum Dot Superluminescent laser diodes

An SLD is, in essence, a combination of a laser and an ELED. It bears a unique design that reaps the combined advantages and characteristics of both a laser and ELED. SLDs are similar in geometry to lasers but have no built-in optical feedback mechanism required by laser diodes for stimulated emission to achieve lasing. SLDs have structural features similar to those of ELEDs that suppress the lasing action by reducing the reflectivity of the facets. Hence, SLDs are essentially highly optimized ELEDs. The advantages of SLDs over conventional LEDs include higher coupled power, spectral linewidth, and greater bandwidths.

In our proposed research, the idea of realizing SLDs using quantum dot layers as the active gain medium is put investigated. Fundamentally, a key attribute of a SLD is its spectral linewidth, which ideally should be much broader than what a conventional LD can deliver without too much compromise in optical power output. Unlike quantum well devices, which rely on ex-situ process techniques such as plasma-induced well intermixing to broaden the emission spectrum, quantum dot systems have intrinsic inhomogeneous broadening mechanisms that can be exploited to achieve spectral linewidth broadening. Furthermore, large process latitude exists within which the dot characteristics can be manipulated directly using the epitaxial growth process. These include dot density, lateral size, height, aspect ratio and uniformity. Manipulation of these physical characteristics directly impacts the emission behavior in terms of peak wavelength and spectral linewidth. SLD structures comprising stacked quantum dot layers, each of which is spectrally tuned differently would enable the realization of a wide composite spectrum. This has been demonstrated in preliminary experimental results by the Compound Semiconductor and Quantum Information Group in the School of EEE.