Wafer-scale fabricated thermo-pneumatically tunable microlenses

Abstract

We have developed a self-contained, liquid tunable microlens based on polyacrylate membranes integrated with compact on-chip thermo-pneumatic actuation fabricated using full-wafer processing. Silicone oil is used as the optical liquid, which is pushed or pulled into the lens cavity via an extended microfluidic channel structure without any pumps, valves or other mechanical means. The heat load generated by the thermal actuator is physically isolated from the lens chamber. The back focal length may be tuned from infinity to 4 mm with a maximum power consumption of 300 mW. The principal application is fine tuning of the back focal length, for which tuning time constants as small as 100 ms are suitable. Scientists in Germany have designed a fluid-based microlens with a widely tunable focal length. Developed by Wei Zhang and co-workers at the University of Freiburg, the lens consists of a circular fluidic chamber filled with silicone oil and sandwiched between a glass substrate and a flexible polyacrylate membrane. The fluid chamber is connected to an air chamber via a microfluidic channel and the entire structure is housed in a protective silicon micromachined frame. The lens’ focal length is tuned between values of infinity and 4 mm by applying a voltage to a heating element in the air chamber. Expansion of the heated air forces more oil into the fluid chamber, causing the membrane to deform and thus the shape of the lens to change.