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 +2.3 mm for approximately 10% applied strain. The range of directly tunable Zernike polynomials representing astigmatism is about 3 µm, while the secondary lens errors, which cannot be tuned directly, vary only by about 0.2 µm. Hans Zappe and colleagues at the University of Freiburg in Germany have realized elastic lenses whose properties can be controlled by strain. Small, tunable polymer lenses are of interest for micro-optical applications, for example, in miniaturized imaging systems. The focal length of such a lens can be adjusted by an externally applied strain, as this changes the shape of the lens. The researchers used eight mechanical anchors placed around the circumference of the lens to apply different strains at various lens positions. This achieved a complex deformation pattern on the surface, which allowed control over not only the lens’ focal length, but also its astigmatism. Controlling such lens aberrations is important for micro-optical devices that, unlike the multiple-lens arrays used in microscope objectives, use as few lenses as possible.