Focus tunable, adaptive lenses provide several advantages over traditional lens assemblies in terms of compactness, cost, efficiency, and flexibility. To further improve the simplicity and compact nature of adaptive lenses, we present an elastomer-liquid lens system which makes use of an inline, transparent electroactive polymer actuator. The lens requires only a minimal number of components: a frame, a passive membrane, a dielectric elastomer actuator membrane, and a clear liquid. The focal length variation was recorded to be greater than 100% with this system, responding in less than one second. Through the analysis of membrane deformation within geometrical constraints, it is shown that by selecting appropriate lens dimensions, even larger focusing dynamic ranges can be achieved.

/pdf/tunable-lenses-using-transparent-dielectric-elastomer-1tqoxalb72.pdf

Tunable Lenses Using Transparent Dielectric Elastomer Actuators

Neural circuitry has evolved to form distributed networks that act dynamically across large volumes. Conventional microscopy collects data from individual planes and cannot sample circuitry across large volumes at the temporal resolution relevant to neural circuit function and behaviors. Here we review emerging technologies for rapid volume imaging of neural circuitry. We focus on two critical challenges: the inertia of optical systems, which limits image speed, and aberrations, which restrict the image volume. Optical sampling time must be long enough to ensure high-fidelity measurements, but optimized sampling strategies and point-spread function engineering can facilitate rapid volume imaging of neural activity within this constraint. We also discuss new computational strategies for processing and analyzing volume imaging data of increasing size and complexity. Together, optical and computational advances are providing a broader view of neural circuit dynamics and helping elucidate how brain regions work in concert to support behavior.

/pdf/technologies-for-imaging-neural-activity-in-large-volumes-26ow5htq3t.pdf

Technologies for imaging neural activity in large volumes

We present a class of display designs combining holographic optics, directional backlighting, laser illumination, and polarization-based optical folding to achieve thin, lightweight, and high performance near-eye displays for virtual reality. Several design alternatives are proposed, compared, and experimentally validated as prototypes. Using only thin, flat films as optical components, we demonstrate VR displays with thicknesses of less than 9 mm, fields of view of over 90° horizontally, and form factors approaching sunglasses. In a benchtop form factor, we also demonstrate a full color display using wavelength-multiplexed holographic lenses that uses laser illumination to provide a large gamut and highly saturated color. We show experimentally that our designs support resolutions expected of modern VR headsets and can scale to human visual acuity limits. Current limitations are identified, and we discuss challenges to obtain full practicality.

/pdf/holographic-optics-for-thin-and-lightweight-virtual-reality-15wd12tcxg.pdf

Holographic optics for thin and lightweight virtual reality

A tunable-focus large aperture liquid lens is constructed using shape memory alloy (SMA) springs as actuators. The lens mainly consists of a shallow liquid-filled cylindrical cavity bound by a thin compressible annular rim and encapsulated by a flexible circular membrane on the top of the rim and a rigid circular plate at the rim bottom. The lens optical power is adjusted by a controlled compression of the annular rim via actuation of the three shape-memory alloy (SMA) springs. Since the volume of the cavity liquid is constant, the rim compression bulges the flexible membrane outward thus reducing its radius of curvature and the lens focal length. The fabricated tunable lens demonstrated an optical power range of 0-4 diopters utilizing a driving voltage less than 3V. Lens optical wavefront profiling was done using a Shack-Hartmann sensor displaying a RMS wave front error of 0.77 µm and 1.68 µm at 0 D and + 4 D. The aperture diameter and thickness of the fabricated lens are 34 mm and 9 mm, respectively, while weighing 16.7 g.

Large aperture tunable-focus liquid lens using shape memory alloy spring.

Modal noise in optical fibers imposes limits on the signal-to-noise ratio (S/N) and velocity precision achievable with the next generation of astronomical spectrographs. This is an increasingly pressing problem for precision radial velocity spectrographs in the near-infrared (NIR) and optical that require both high stability of the observed line profiles and high S/N. Many of these spectrographs plan to use highly coherent emission-line calibration sources like laser frequency combs and Fabry-Perot etalons to achieve precision sufficient to detect terrestrial-mass planets. These high-precision calibration sources often use single-mode fibers or highly coherent sources. Coupling light from single-mode fibers to multi-mode fibers leads to only a very low number of modes being excited, thereby exacerbating the modal noise measured by the spectrograph. We present a commercial off-the-shelf solution that significantly mitigates modal noise at all optical and NIR wavelengths, and which can be applied to spectrograph calibration systems. Our solution uses an integrating sphere in conjunction with a diffuser that is moved rapidly using electrostrictive polymers, and is generally superior to most tested forms of mechanical fiber agitation. We demonstrate a high level of modal noise reduction with a narrow bandwidth 1550 nm laser. Our relatively inexpensive solution immediately enables spectrographs to take advantage of the innate precision of bright state-of-the art calibration sources by removing a major source of systematic noise.

Suppression of fiber modal noise induced radial velocity errors for bright emission-line calibration sources

Several approaches have been demonstrated to build focus tunable lenses. The additional degree of freedom enables the
design of elegant, compact optical systems, typically with less mechanics. We present a new range of electrically and
mechanically focus tunable lenses of different sizes and tuning ranges and discuss their characteristics. We show how
tunable lenses can be used to improve optical design for auto-focus and zoom in terms of size, quality and speed.
Furthermore, we present an LED-based spot light with variable illumination angle, which shows optimal performance in
terms of spot quality and optical efficiency.

Compact optical design solutions using focus tunable lenses

Based on selected liquid and elastic polymers, Optotune has developed adaptive optical components, such as focus
tunable lenses and laser speckle reducers.
The lenses range from 2 to 55mm in aperture, are mechanically or electrically actuated and offer a continuous range of
focal powers of several 10 diopters. This additional degree of freedom enables the design of compact optical systems,
typically with less mechanics. We show how tunable lenses can be used to improve optical designs for imaging and
illumination systems in terms of size, quality and speed.
The speckle reducers are based on electroactive polymers and offer an extremely compact and low cost solution for
removing speckles, which is a key benefit for laser projectors and illumination systems.

M. Büeler

Papers

Compact optical design solutions using focus tunable lenses

Optotune focus tunable lenses and laser speckle reduction based on electroactive polymers