A fully integrated thermo-pneumatic tunable microlens

A thermo-pneumatically actuated tunable microlens has been developed as a completely integrated system with on-chip actuation and temperature sensing. The focal length of the microlens can be adjusted over a wide range without any external pressure controller. The module consists of a structured silicon chip, a spin-coated PDMS membrane, an optical fluidic chamber, a thermal cavity, and a heating and temperature sensing structure. The focal length is controlled by the applied voltage to the heater and could be tuned in the range between 3.3 and 18.2 mm, corresponding to a temperature variation of 37°C to 24°C, and a change in the numerical aperture from 0.303 to 0.055. At the same time, the cutoff frequency of the optical transfer function, referring to a contrast of 0.2, varies from 30 lines/mm at 27°C to 65 lines/mm at 34°C.