Tunable microlens actuated via a thermoelectrically driven liquid heat engine

Abstract

We have developed a thermally actuated liquid microlens. An embedded thermoelectric element is used to actuate the liquid based heat engine. A closed-loop system is harnessed to drive and stabilize the temperature of the heat engine. Direct contact between the thermoelectric device and the water results in greatly improved, sub-second thermal rise time (0.8 s). The water based heat engine reacts to the variation in the temperature via expansion and contraction. In turn, the shape of a pinned water-oil meniscus at a lens aperture is deformed in response to the net volume change in the water, creating a tunable microlens. A method to fabricate microfluidic devices with relatively high thickness (250-750 lm) and large length-to-depth aspect ratio (280:1) was developed and used in the process. After fabrication and thermal calibration, optical characteristic of the microlens was assessed. Back focal length of the microlens was shown to vary continuously from À19.6 mm to À6.5 mm as the temperature increased from 5 C to 35 C. A thin film air was further introduced to insulate the heat engine from the substrate to protect the microlens area from the temperature fluctuation of the heat engine, thus preventing the change of the refractive indices and thermally induced aberrations. Wavefront aberration measurement was conducted. Surface profile of the microlens was mapped and found to have a conical shape. Both 3-dimensional and 1-dimensional thermal models for the device structure were developed and thermal simulation of the device was performed. V

New insights in presbyopia: impact of correction strategies

“…Further, while the majority of techniques described herein are designed to restore near vision, we are yet to see a clinically approved method that restores dynamic accommodation to the presbyopic eye. Hitherto, a range of candidate methods using hydrogel,168 thermopneumatic,169 thermoelectric,170 electrohydrodynamic,171 electroactive polymer172 and magnetic173 actuators have been explored to create a tuneable, artificial crystalline lens. Perhaps one emerging approach that may gain further traction can be seen in work using graphene-based compound eyes inspired by vertebrates174 that allow programmable and remote focusing of crystalline lens-shaped lenslet arrays 175.…”

Capillary number encouraged the construction of smart biomimetic eyes

“…Remarkably, the fill-factor is much higher than other adjustable eyes based on external fields or microfluidic devices. 10,12 Moreover, the fill-factor can be further increased through reducing gap distances. Therefore, for practical applications, this strategy is versatile and reliable to construct smaller microlenses by a proper silicon microfabrication process.…”

“…Yet another actuator that has been utilized to induce a shape modification of liquid lenses is the thermally actuated hydrogel. 11,12 Previous experiments showed promising optical performance. However, these heat-responsive hydrogels were generally explored as the microfluidic configuration which induces a technical difficulty in creating a high-density lenslet array.…”

Double-Sided Design of Electrodes Driving Tunable Dielectrophoretic Miniature Lens

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