Adjustable hybrid diffractive/refractive achromatic lens

Stimulated-responsive refractive-diffractive biological hydrogel micro-optical element enabling achromatism via femtosecond laser lithography

Herein, we report a novel biological hydrogel-based achromatic refractive-diffractive micro-optical element with single-material apochromatism. Benefiting from the stimulated responsive property of the hydrogel, pH modulation yielded swelling and affected the refractive index of the element, enabling multi-wavelength focusing performance tuning and chromatic aberration adjustment. Using femtosecond laser lithography, we fabricated a separate hydrogel microlens and Fresnel zone plate and measured the tunable focusing performance while varying pH; the results were consistent with our simulation results. Furthermore, we designed and fabricated a hydrogel-based achromatic refractive-diffractive micro-optical element and demonstrated achromatism with respect to three wavelengths using only one material consisting of a microlens and a Fresnel zone plate. We characterized the optical focusing properties and observed smaller chromatic aberration. The potential applications of such hybrid microoptical elements include biomedical imaging and optical biology sensing.

Study of brine-halite phase separation through optical constringence and molecular dynamics

This work presents a study of the reciprocal dispersive power, also known as constringence or Abbe number of an aqueous solution of NaCl in a wide range of concentrations. The constringence exhibited a distinct behavior in the region close to the phase transition between a phase containing exclusively brine and a phase containing brine+halite. Molecular dynamics simulations of this system indicated the existence of halite formation below the known saturation curve, which agreed with the experimental measurements, indicating a crystal growth in the unsaturated region.

A new low-cost, compact, auto-phoropter for refractive assessment in developing countries

Using a phoropter to measure the refractive error is one of the most commonly used methods by ophthalmologists and optometrists. Here, we demonstrate design and fabrication of a portable automatic phoropter with no need for patient’s feedback. The system is based on three tunable-focus fluidic lenses and thin-film holographic optical elements to perform automatic refractive error measurement and provide a diagnostic prescription without supervision. Three separate lenses are deployed to correct the defocus and astigmatism. The refractive error is measured using a Shack-Hartmann wavefront sensor that calculates the Zernike values of an infrared wavefront emerging from the eye. Holographic optical elements steer the emerging wavefront into the wavefront sensor, while simultaneously providing an unobstructed view for the subject. The power of each lens is controlled by pumping a liquid in and out of the lens chamber using servo motor actuated diaphragm pumps. Spherical and cylindrical correction range of −10 to +10 diopters with 0.1 diopter increments is achieved in less than 15 seconds using wavefront sensor feedback to the pumps. This system can be used in rapid screening of large patient populations especially in the developing countries that lack sufficient facilities and specialist doctors.

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 thus axially separate 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.

Chromatic-aberration-corrected diffractive lenses for ultra-broadband focusing

We exploit the inherent dispersion in diffractive optics to demonstrate planar chromatic-aberration-corrected lenses. Specifically, we designed, fabricated and characterized cylindrical diffractive lenses that efficiently focus the entire visible band (450 nm to 700 nm) onto a single line. These devices are essentially pixelated, multi-level microstructures. Experiments confirm an average optical efficiency of 25% for a three-wavelength apochromatic lens whose chromatic focus shift is only 1.3 μm and 25 μm in the lateral and axial directions, respectively. Super-achromatic performance over the continuous visible band is also demonstrated with averaged lateral and axial focus shifts of only 1.65 μm and 73.6 μm, respectively. These lenses are easy to fabricate using single-step grayscale lithography and can be inexpensively replicated. Furthermore, these devices are thin (<3 μm), error tolerant, has low aspect ratio (<1:1) and offer polarization-insensitive focusing, all significant advantages compared to alternatives that rely on metasurfaces. Our design methodology offers high design flexibility in numerical aperture and focal length, and is readily extended to 2D.

Wave-optical design of a combined refractive-diffractive varifocal lens

A novel type of integrated refractive-diffractive varifocal membrane lens is designed and analyzed by wave-optical methods. In contrast to other hybrid devices, the diffractive microstructure is directly imprinted onto the soft deflecting membrane, allowing for a high level of integration. Elastic deformation is taken into account by mechanical simulations with the finite element method (FEM). We show, that the superimposed structure can considerably suppress chromatic and spherical aberration. Furthermore, our algorithm is successfully applied to design a confocal hyperspectral lens.

Dispersion tuning with a varifocal diffractive-refractive hybrid lens

We present a hybrid diffractive-refractive optical lens doublet consisting of a varifocal Moiré Fresnel lens and a polymer lens of tunable refractive power. The wide range of focal tunability of each lens and the opposite dispersive characteristics of the diffractive and the refractive element are exploited to obtain an optical system where both the Abbe number and the refractive power can be changed separately. We investigate the performance of the proposed hybrid lens at zero overall refractive power by tuning the Abbe number of a complementary standard lens while maintaining a constant overall focal length for the central wavelength. As an application example, the hybrid lens is used to tune to an optimal operating regime for quantitative phase microscopy based on a two-color transport of intensity (TIE) approach which utilizes chromatic aberrations rather than intensity recordings at several planes to reconstruct the optical path length of a phase object.

Speed, optical power, and off-axis imaging improvement of refractive liquid crystal lenses

Two design approaches (multicell and addition of phase resets in single cell) are introduced to optimize the performances of tunable refractive liquid crystal lenses, including improvements on the switching speed, optical power, and the off-axis, wide-angle imaging performance. Key parameters and advantages for each method are discussed, and their effects on the performance are demonstrated in detail with numerical calculations.

Nonmechanical zoom system through pressure-controlled tunable fluidic lenses

We have developed a variable-power zoom system that incorporates fluidic lenses and has no moving parts. The designed system applies two single-chamber plano-convex fluid singlets, each with their own distinct design, as well as a conventional refractive lens. In this paper, we combine the two fluid elements to form a variable-power telescope, while the fixed lens enables image formation. In this configuration, the image plane location is fixed. By synchronizing the powers of the two fluidic lenses, we produce a varying magnification zoom system. The design of each lens and the coupled system is analyzed. The coupled device experimentally produced a magnification range of 0.1× to 10× zoom or a 20× zoom magnification range with no moving parts. Furthermore, we expand on optical performance and capabilities of our system with fluidic lenses relative to traditional zoom lenses.

Near-diffraction-limited and low-haze electro-optical tunable liquid crystal lens with floating electrodes

A near-diffraction-limited, low-haze and tunable liquid crystal (LC) lens is presented. Building on an understanding of the key factors that have limited the performance of lenses based on liquid crystals, we show a simple design whose optical quality is similar to a high quality glass lens. It uses 'floating' electrodes to provide a smooth, controllable applied potential profile across the aperture to manage the phase profile.

Physical limitations and fundamental factors affecting performance of liquid crystal tunable lenses with concentric electrode rings

A comprehensive analysis of fundamental factors and their effects on the performance of liquid crystal (LC)-based lenses is given. The analysis adopts numerical LC director and electric field simulation, as well as scalar diffraction theory for calculating the lens performance considering different variable factors. A high-efficiency LC lens with concentric electrode rings is fabricated for verifying and enriching the analysis. The measurement results are in close agreement with the analysis, and a summary of key factors is given with their quantitative contributions to the efficiency.