Novel components for tunable micro-optics

We will present some technologies and devices employed for the fabrication of tunable micro-optics. Tunable liquid lenses and lens arrays as well as polymer membrane-based microlenses and scanning mirrors are of both academic and industrial interest in this area.

Elastomeric lenses with tunable astigmatism

Microlenses fabricated using flexible elastomers can be tuned in focal length by application of controlled strain.By varying the strain azimuthally,the lenses may be deformed asymmetrically such that aberrations may be controlled.This approach is used to tune the astigmatism of the tunable lenses,and it is shown that the generated wavefront may be accurately controlled.The lens presented here has an initial focal length of 32.6 mm and a tuning range of 12.3 mm for approximately 10%applied strain.The range of directly tunable Zernike polynomials representing astigmatism is about 3 mm,while the secondary lens errors,which cannot be tuned directly,vary only by about 0.2 mm.

Variable optofluidic slit aperture

The shape of liquid interfaces can be precisely controlled using electrowetting,an actuation mechanism which has been widely used for tunable optofluidic micro-optical components such as lenses or irises.We have expanded the considerable flexibility inherent in electrowetting actuation to realize a variable optofluidic slit,a tunable and reconfigurable two-dimensional aperture with no mechanically moving parts.This optofluidic slit is formed by precisely controlled movement of the liquid interfaces of two highly opaque ink droplets.The 1.5mmlong slit aperture,with controllably variable discrete widths down to 45 mm,may be scanned across a length of 1.5mmwith switching times between adjacent slit positions of less than 120 ms.In addition,for a fixed slit aperture position,the width may be tuned to a minimum of 3 mmwith high uniformity and linearity over the entire slit length.This compact,purely fluidic device offers an electrically controlled aperture tuning range not achievable with extant mechanical alternatives of a similar size.

The engineered eyeball, a tunable imaging system using soft-matter micro-optics

We demonstrate a tunable imaging system based on the functionality of the mammalian eye using soft-matter micro-optical components.Inspired by the structure of the eye,as well as by the means through which nature tunes its optical behavior,we show that the technologies of microsystems engineering and micro-optics may be used to realize a technical imaging system whose biomimetic functionality is entirely distinct from that of conventional optics.The engineered eyeball integrates a deformable elastomeric refractive structure whose shape is mechanically controlled through application of strain using liquid crystal elastomer(LCE)actuators;two forms of tunable iris,one based on optofluidics and the other on LCEs with embedded heaters;a fixed lens arrangement;and a commercial imaging sensor chip.The complete microsystem,optimized to yield optical characteristics close to those of the human eye,represents the first fully functional,soft-matter-based tunable single-aperture eye-like imager.

An imaging spectrometer employing tunable hyperchromatic microlenses

We present the design,fabrication and characterization of hydraulically-tunable hyperchromatic lenses for two-dimensional(2D)spectrally-resolved spectral imaging.These hyperchromatic lenses,consisting of a positive diffractive lens and a tunable concave lens,are designed to have a large longitudinal chromatic dispersion and the images of different wavelengths from each other.2D objects of different wavelengths can consequently be imaged using the tunability of the lens system.Two hyperchromatic lens concepts are demonstrated and their spectral characteristics as well as their functionality in spectral imaging applications are shown.

Wafer-scale fabricated thermo-pneumatically tunable microlenses

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.

Cascading optofluidic phase modulators for performance enhancement in refractive adaptive optics

We discuss the implementation and performance of an adaptive optics(AO)system that uses two cascaded deformable phase plates(DPPs),which are transparent optofluidic phase modulators,mimicking the common woofer/tweeter-type astronomical AO systems.One of the DPPs has 25 electrodes forming a keystone pattern best suited for the correction of low-order and radially symmetric modes;the second device has 37 hexagonally packed electrodes better suited for high-order correction.We also present simulation results and experimental validation for a new open-loop control strategy enabling simultaneous control of both DPPs,which ensures optimum correction for both large-amplitude low-order,and complex combinations of low-and high-order aberrations.The resulting system can reproduce Zernike modes up to the sixth radial order with stroke and fidelity up to twice better than what is attainable with either of the DPPs individually.The performance of the new AO configuration is also verified in a custom-developed fluorescence microscope with sensorless aberration correction.