Inkjet Printing for Optical/Electrical Interfacing of VCSEL and PD Arrays

Vertical cavity surface emitting laser (VCSEL) arrays and photodiode (PD) arrays have emerged on the market for short reach fiber communications and other applications. However, the lack of efficient, low-cost methods for light coupling and electrical connection has become a barrier to new products incorporating their high-density and parallel advantages. To address these challenges, we have developed a wafer-level integration of micro-optics with VCSEL array and a direct 90° solder bonding of linear array die. The micro-optic structure consists of a cylindrical pedestal processed by verythick film coating-patterning and a microlens fabricated on top of the pedestal by pre-polymer printing. The alignment of pedestal to VCSEL is ensured within the photolithographic process, and that of microlens to pedestal has a selfcentering nature. The solder bonding, which connects the bond pads on VCSEL/PD array with the metal leads on substrate, is accomplished by molten solder printing. The test results on the fabricated parts demonstrated that the microoptic structure improves the coupling efficiency from VCSEL to multimode optical fiber, while not altering the VCSEL’s emission characteristics. Also, the solder printing is compatible with these optoelectronic devices by the direct applicability and by not altering the emission characteristics or the responsivity of the dies. Because of the wafer-level processing, the new interfacing method offers both technical advantage and cost-effectiveness for manufacturing.