Ink-Jets Produce Microlenses
Dr. Tsuyoshi Asaeda
Ink-jets are not just for printing anymore. A team from NTT Telecommunications Energy Laboratories in Tokyo has demonstrated the mass production of microlens arrays for optical-input/output packaging using commercial180-dpi ink-jet printing heads.
The ink-jet method offers noncontact fabrication of microlenses on a target, such as a vertical-cavity surface-emitting laser (VCSEL). Resin is ejected onto the substrate from the nozzle, and ultraviolet radiation cures the droplets into hemispherical lenses. By selecting the viscosity and volume of a droplet, the researchers can vary the diameters of the lenses from 20 to 140 µm and the f numbers from 1.0 to 11.0.
The scientists demonstrated the technique by packaging a microlens and VCSEL in a plastic ball grid array substrate. They solder bump bonded the unit to a printed circuit board and used thermal-resistive resin for the microlens. This enabled them to assemble the package using conventional reflow soldering equipment.
The connection required relatively loose tolerance for alignment because the optical coupling is performed with the parallel beam from the microlens. The prototype optical interface using a polymer waveguide displayed a coupling efficiency 4 dB higher than conventional coupling.
Yuzo Ishii of NTT reported the work, which received the Paper Award at the fall meeting of the Japan Society of Applied Physics. The company is also investigating the use of alternative dispensers for microlens materials that cannot be ejected by ink-jet nozzles.
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