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. Light: Science & Applications (2013) 2, e98; doi:10.1038/lsa.2013.54; published online 13 September 2013Keywords: aberrations; active or adaptive optics; micro-optical devices; polymers INTRODUCTION A broad spectrum of tunable micro-optical components using a wide variety of physical effects has been proposed and demonstrated. 1 One approach with considerable potential is the mechanical deformation of microlenses entirely made of flexible elastomers: by controlled application of radial strain, resulting in a change in lens curvature, it has been shown that the focal length can be tuned over a considerable range. 2,3 To date, strain has only been applied symmetrically around these tunable elastomeric lenses, such that only refractive power (focal length), but not other optical properties, have been tuned. A number of other tunable devices have considered the astigmatism. For example, Beadie et al. 4 presented a tunable composite lens, one part being a fixed focal length lens made of poly(methylmetacrylate) and the tunable part using a membrane with a poly(dimethylsiloxane) (PDMS) elastomer as a filling; the surface profiles showed an inherent astigmatism.Alternatively, singlet polymer lenses with thermal actuation have been reported by Lee et al. 5 By choosing an anisotropic heater structure, Lee et al. were able to tune astigmatism along one axis, while the other axis remains fixed. A more versatile approach with a combination of several membrane lenses was pursued by Marks et al. 6 Here two perpendicularly oriented cylindrical lenses provide variable astigmatism, whose total focus is compensated with a rotational symmetric membrane lens.We show here that application of azimuthally varying strain to a deformable elastomer lens can result in controlled variation of aberrations, particularly astigmatism. As a result, the microlens is not only tunable in focal length, but the concomitant aberrations can be increased or decreased at will.

A fast and reliable, fully integrated optofluidic optical attenuator is demonstrated. The concept employs only liquid and thus has no mechanically moving parts. Transparent and opaque aqueous liquid droplets are displaced using an on-chip electrowetting actuator and, due to the flexibility in the choice of liquids, various transmission spectra can be defined. The microfluidic attenuator system is fabricated using wafer-level bonding and dry film resists resulting in an ultra-compact (11×23×1.6 mm3) device requiring no external components for operation. The measured dynamic range of optical transmission is up to 47 dB, while the response times are below 100 ms for a 2 mm input beam. Using a novel double-actuator configuration, actuation speeds of the liquids of up to 39 mm s−1 were measured.

We present novel biconvex solid-body elastomer (polydimethylsiloxane) lenses, which can be tuned in focal length by using magnetic or mechanical actuation. The focal length change is induced by applying radial elastic strain and is investigated for different initial radii of curvature of the lenses and different actuation designs. In all cases, a linear correlation between induced strain and focal length tuning, in the range of about 10% (approximately 3 mm), is found. These results compare favorably with finite element simulations.

Tunable multi-chamber microfluidic membrane microlenses with achromaticity over a given focal length range are demonstrated. In analogy to a fixed-focus achromatic doublet lens, the multi-lens system is based on a stack of microfluidic cavities filled with optically optimized liquids with precisely defined refractive index and Abbe number, and these are independently pneumatically actuated. The membranes separating the cavities form the refractive optical surfaces, and the curvatures as a function of pressure are calculated using a mechanical model for deformation of flexible plates. The results are combined with optical ray tracing simulations of the multi-lens system to yield chromatic aberration behavior, which is verified experimentally. A focal length tuning range of 5-40 mm and reduction in chromatic aberration of over 30% is demonstrated, limited by the availability of optical fluids.

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