Dynamically variable focal length microlens by microfluidic and electroactive polymer approaches.

摘要

This research is on a development of a variable focusing microlens system. The studies of modern researchers have thrown new light on this subject, which has aroused intense interest in making tunable focusing microlenses. The most well-known methods are liquid crystal and electrowetting. Both methods require electrodes immersed in the electrolyte solution, causing severe optical distortion, and require complicated fabrication processes. Few attempts have thus far been developed to make variable focusing lens using other approaches.; However, two novel actuation mechanisms have been developed in this work for generating significant forces to change the physical dimensions of an elastic polymeric lens structure to control the focal length. The two proposed actuation mechanisms are: (1) the microfluidic and (2) the Electro-Active Polymer (EAP) actuations. By pneumatically regulating the pressure of the microfluidic chamber, the elastic lens can be deformed, causing the changes in the focal length. EAP is another method to transfer electrical energy to mechanical deformation. This energy transformation causes the deflection on the lens and induces its focal plane to be shifted.; For the microfluidic lens system, a novel PDMS to PDMS casting process to fabricate 3D convex elastic microlens diaphragm is developed. This new fabrication technique has a potential for producing low-cost elastic microlens arrays. Microlenses, with a diameter of 600∼1400 mum, are fabricated using this fabrication technique. The curvature changes of the microlens were from 1210mum to 3238mum. With this wide range of curvature changes, one can control the back focal length from 3.82 mm to 10.64 mm, and the numerical aperture from 0.09 to 0.24. The numerical aperture of this optical device can then reach 0.24, about 4 times that of a conventional planar diaphragm (NA = 0.05).; Moreover, a new "two-step copolymerization" technique has been developed to fabricate an elastic silicone-based gradient refractive index (GRIN) lens. This is a flat lens with a gradient refractive index distribution within the lens structure. Moreover, this GRIN lens is elastic, so it is deformable with high elongation under mechanical stresses. Finally, this lens is made by a dielectric material, and can be integrated easily into an EAP actuator, generating enough mechanical force to cause the deflection on the GRIN lens and induce a shift in focal length. The characteristics of GRIN lenses and EAP actuation have been studied in this work. It appears that this is the first reported work proposing a dynamically tunable focusing GRIN lens with an EAP actuation. Further research needs to be carrying out for optimizing the proposed approach for its desired application.