VCSEL arrays with integrated optics

Abstract

Systems with arrays of VCSELs can realize multi kilowatt output power. The inherent simplicity of VCSELs enables a performance and cost breakthrough in solutions for thermal processing and the pumping of solid state lasers. The use of an array of micro-optics i.e. one micro-lens per VCSEL enables multiple advantages: firstly it can function as a collimating lens in order to realize a brightness of an array which is similar to the brightness of a single VCSEL. Secondly the micro-lens can be part of an imaging system for tailored intensity distributions. Last but not least the microlens with moderate feedback into the VCSEL can help to select laser modes in order to increase brightness and mode stability. Wafer-level integrated micro-optics allow keeping the VCSEL advantage of realizing complete and operational lasers on wafer level including the micro-optics. This paper presents our approach to bond a 3” GaAs wafer with a micro-optics wafer of the same size. The type of glass used for the optics wafer has been selected to match the coefficient of thermal expansion of GaAs and is suitable for hot pressing of the lens structures. An alignment strategy with corresponding markers on both wafers is used to allow the alignment on a standard mask aligner thus realizing many thousand lens adjustments in a single process step. The technology can be combined with VCSEL wafers with thinned substrate as well as with complete substrate removal. The basic technology and illustrative prototype systems are described here.