Design and Physics of VCSELs for Emerging Applications

Vertical cavity surface emitting lasers (VCSELs) have been widely employed in short distance optical interconnects. Recently however a series of emerging applications are creating a rapidly growing demand for compact, low cost and high-performance light sources. 3D imaging and proximity sensing capabilities based on time of flight and structured light schemes are currently being deployed in a vast amount of consumer hand held devices, in particular in cell phones. Here VCSEL arrays of various sizes, densities and powers are being employed in volumes of multiple hundreds of millions per year. At the same time, wavelength tunable VCSELs with wide tuning range, fast tuning speed and single mode continues wavelength tuning are of tremendous interest for swept source optical coherence tomography (SS-OCT). This work investigates a series of VCSEL architectures that specifically address the requirements of the above-mentioned applications. Inhouse epitaxial growth by metal organic chemical vapor deposition was developed (chapter 2) to supply the wide variety of VCSEL structures investigated and in particular to enable the realization of devices that depend on regrowth steps. Optical pumping of high contrast grating (HCG) enabled devices was tested (chapter 3) as this method has proven successful in DBR based devices. Wavelength tunable VCSELs with a MEMS actuated HCG as sole top reflector where demonstrated (chapter 4 & 5). These devices showed single mode emission and continues electrostatic tuning covering a wide wavelength range. Thus, proving their concepts promising for application as sources in SS-OCT. Two different VCSEL architectures with lithographically defined current apertures have been investigated, one based on a buried InGaP heterostructure (chapter 5) and one based on a buried tunnel junction (chapter 6). Substituting the native oxide confined current aperture by a lithographic aperture of such kind enables a wealth of potential performance improvements. Improvements in reliability, thermal resistance, emitter uniformity, array density, high-power single mode emission and coherently coupled arrays can be reasonably expected of such devices. In combination with the HCG reflector lasing in a stable, single polarization can be achieved. At last, VCSEL arrays were fabricated at 850 nm and 940 nm wavelength in chapter 7