Ink-jet fabrication of polymer microlens for optical-I/O chip packaging

We report on a simple and versatile method of fabricating polymer microlenses that can be easily integrated with optical devices. UV-curable epoxy resin is dropped onto optical devices by an ink-jet apparatus. When the droplets touch the surface, they form into partial spheres due to their surface tension. UV light irradiation for less than five minutes call easily turn them into solid microlenses. Various microlenses, having a geometrical diameter from 20 to 140 mu m with F/1.0 to F/11.0, were successfully produced by controlling the volume and viscosity of the polymer resin and their wettability to the substrate. Their uniformity in a microlens array was measured to be within +/-1% in diameter and +/-3 mu m in pitch. Hybrid integration of an ink-jetted microlens with a wire-bonded vertical-cavity surface-emitting laser (VCSEL) was also demonstrated. When an ink-jetted microlens (45-mu m diameter, F/2.0) was formed on the aperture of an 850-nm VCSEL, the coupling efficiency into a single-mode fiber was 4 dB higher than without the microlens.