Tunable Lens Research Articles

Monocular depth estimation method using a focus tunable lens.

We propose a method for the passive-type estimation of depth using a focus tunable lens. The proposed method utilizes a lens group and a focus tunable lens and charge coupled device. The target object is imaged by the group of lenses and measured by changing the focal length of the focus tunable lens. The method aims to measure depth information in the image domain and not in the object domain. An autofocusing algorithm finds the best focus position of the target object through the focus value calculated by the Sobel operator. We believe that the proposed method is applicable to depth measurement systems because it offers a simple configuration without any active light source and can operate in real time. The experiment, performed for comparison with theoretical calculations, confirms the feasibility of the proposed method.

All-silicon reconfigurable metasurfaces for multifunction and tunable performance at optical frequencies based on glide symmetry

Dielectric metasurfaces have opened promising possibilities to enable a versatile platform in the miniaturization of optical elements at visible and infrared frequencies. Due to high efficiency and compatibility with CMOS fabrication technology, silicon-based metasurfaces have a remarkable potential for a wide variety of optical devices. Adding tunability mechanisms to metasurfaces could be beneficial for their application in areas such as communications, imaging and sensing. In this paper, we propose an all-silicon reconfigurable metasurface based on the concept of glide symmetry. The reconfigurability is achieved by a phase modulation of the transmitted wave activated by a lateral displacement of the layers. The misalignment between the layers creates a new inner periodicity which leads to the formation of a metamolecule with a new sort of near-field interaction. The proposed approach is highly versatile for developing multifunctional and tunable metadevices at optical frequencies. As a proof of concept, in this paper, we design a bifunctional metadevice, as well as a tunable lens and a controllable beam deflector operating at 1.55 μm.

High-speed color three-dimensional measurement based on parallel confocal detection with a focus tunable lens.

Reflectance confocal microscopy is a widely used optical imaging technique for non-destructive three-dimensional (3D) surface measurement. In confocal microscopy, a stack of two-dimensional (2D) images along the axial position is used for 3D reconstruction. This means the speed of 3D volumetric acquisition is limited by the beam scanning and the mechanical axial scanning. To achieve fast volumetric imaging, simultaneous multiple point scanning by parallelizing the beam instead of transverse point scanning can be considered, using a pinhole array. Previously, we developed a direct-view confocal microscope with a focus tunable lens (FTL) to produce a monochrome 3D surface profile of a sample without any mechanical scanning. Here, we report a high-speed color 3D measurement method based on parallel confocal detection. The proposed method produces a color 3D image of an object by acquiring 180 2D color images with an acquisition time of 1 second. We also visualized the color information of the object by overlaying the color obtained with a color area detector and a white LED illumination on top of the 3D surface profile. In addition, we designed an improved optical system to reduce artifacts caused by internal reflections and developed a new algorithm for noise-resistant 3D measurements. The feasibility of the proposed non-contact high-speed color 3D measurement for use in industrial or biomedical fields was demonstrated by imaging the color 3D shapes of various specimens. We anticipate that this technology can be utilized in various fields, where rapid 3D surface profiles with color information are required.

Ultrathin Tunable Lens Based on Boundary Tension Effect.

Solid and liquid lenses are commonly used in optical design. Such lenses have suitable thicknesses due to their working principle and processing mode. Thus, zoom optical systems comprising solid and liquid lenses are extremely large. This work presents a new ultrathin tunable lens (UTL) comprising two liquid film lenses (LFLs) obtained through aspheric deformation and produced from the surface of a micro-liquid under gravity and boundary tension. The UTL can flexibly change focal lengths between positive and negative lenses when the device thickness is merely 2.15 mm. The proposed lens has the advantages of small volume, light weight, simple fabrication, and independence from external force during zooming. This research makes up for the drawback that traditional solid and liquid lenses cannot further reduce their thicknesses. The proposed UTL provides a new lens form and fabrication method, and can be used to replace solid and liquid lenses for designing miniature zoom optical systems.

Varifocal Occlusion-Capable Optical See-through Augmented Reality Display based on Focus-tunable Optics.

Optical see-through augmented reality (AR) systems are a next-generation computing platform that offer unprecedented user experiences by seamlessly combining physical and digital content. Many of the traditional challenges of these displays have been significantly improved over the last few years, but AR experiences offered by today's systems are far from seamless and perceptually realistic. Mutually consistent occlusions between physical and digital objects are typically not supported. When mutual occlusion is supported, it is only supported for a fixed depth. We propose a new optical see-through AR display system that renders mutual occlusion in a depth-dependent, perceptually realistic manner. To this end, we introduce varifocal occlusion displays based on focus-tunable optics, which comprise a varifocal lens system and spatial light modulators that enable depth-corrected hard-edge occlusions for AR experiences. We derive formal optimization methods and closed-form solutions for driving this tunable lens system and demonstrate a monocular varifocal occlusion-capable optical see-through AR display capable of perceptually realistic occlusion across a large depth range.

Electrically Tunable Fresnel Lens in Twisted-Nematic Liquid Crystals Fabricated by a Sagnac Interferometer.

This paper presents an electrically tunable Fresnel lens in a twisted nematic liquid crystal cell fabricated by using a Sagnac interferometer. When the Fresnel-patterned green beam, formed by the Sagnac interferometer, is irradiated on the azo-dye doped liquid crystal mixture, the azo-dye molecules undergo trans–cis photoisomerization and then generate the photo-alignment effect in the bright (odd) zones. The director of the liquid crystal molecules in the odd zones reorients the direction perpendicular to the polarization direction of the linearly polarized green beam. The various structures of liquid crystals in the odd and even zones will result in a phase difference and thus, a Fresnel lens can be generated. The experimental results show that the proposed Fresnel lens has a high diffraction efficiency of 31.5% under an applied alternating-currents (AC) voltage. The focal length of the Fresnel lens can also be tuned by thermally erasing the photo-alignment effect of the azo dyes and rewriting by a different Fresnel-like pattern.

Optical hoovering on plasmonic rinks

Abstract

Parylene based thin-film microfluidic lens array fabricated by iCVD nano-adhesive bonding

Microfluidic lenses that have been fabricated using PDMS have serious limitations due to the high gas permeability of the material, which leads to evaporation of the filling liquid and air bubble formation. We report a fast and reliable method of fabricating flexible, thin-film parylene microfluidic devices, and their application in tunable microfluidic lens arrays. A parylene microfluidic lens was built by molding and bonding 1.4-μm-thick parylene layers using nano-adhesivelayers deposited by initiated chemical vapor deposition (iCVD). The focal length of the lens could be tuned by changing the radius of curvature of the lens and/or changing the refractive indices of the filling liquids. The parylene microfluidic lens showed a large range of focal length tuning, and high reproducibility over hundreds of cycles.

Speeded-Up Focus Control of Electrically Tunable Lens by Sparse Optimization

Electrically tunable lenses (ETL), also known as liquid lenses, can be focused at various distances by changing the electric signal applied on the lens. ETLs require no mechanical structures, and therefore, provide a more compact and inexpensive focus control than conventional computerized translation stages. They have been exploited in a wide range of imaging and display systems and enabled novel applications for the last several years. However, the optical fluid in the ETL is rippled after the actuation, which physically limits the response time and significantly hampers the applicability range. To alleviate this problem, we apply a sparse optimization framework that optimizes the temporal pattern of the electrical signal input to the ETL. In verification experiments, the proposed method accelerated the convergence of the focal length to the target patterns. In particular, it converged the optical power to the target at twice the speed of the simply determined input signal, and increased the quality of the captured image during multi-focal imaging.

Vision with different presbyopia corrections simulated with a portable binocular visual simulator.

Presbyopes can choose today among different corrections to provide them with functional vision at far and near, and the outcomes and patient satisfaction depend on the selection. In this study, we present a binocular and portable vision simulator, based on temporal multiplexing of two synchronized tunable lenses allowing see-through and programmable visual simulations of presbyopic corrections. Seventeen binocular corrections were tested: 3 Monofocal (Far, Intermediate, Near), 4 Simultaneous Vision (bifocal, trifocal), 2 Monovision (far and near in either eye) and 8 Modified Monovision corrections (Simultaneous vision in one eye, Monofocal in the other eye). Perceived visual quality was assessed through the simulated corrections in 8 cyclopleged subjects who viewed a composite realistic visual scene with high contrast letters and a landscape at far (4 m) and a high contrast text at intermediate (66 cm) and near (33 cm) distances. Perceptual scores were obtained on a scale of 0 to 5 (low to high perceived quality). Perceptual preference was assessed by judging 36 random image pairs (6 repetitions) viewed through 9 binocular presbyopic corrections using two-interval forced choice procedures. The average score, across far and near distances, was the highest for Monovision (4.4±0.3), followed by Modified Monovision (3.4±0.1), Simultaneous Vision (3.0±0.1) and Monofocal corrections (2.9±0.2). However, the mean difference between far and near was lower for Simultaneous Vision and Monovision (0.4±0.1 PS) than Modified Monovision (1.8±0.7) or monofocal corrections (3.3±1.5). A strong significant correlation was found between the perceptual scores and the percentages of energy in focus, for each correction and distance (R = 0.64, p<0.0001). Multivariate ANOVA revealed significant influence of observation distances (p<10–9) and patients (p = 0.01) on Perceptual Score. In conclusion, we have developed a binocular portable vision simulator that can simulate rapidly and non-invasively different combinations of presbyopic corrections. This tool has applications in systematic clinical evaluation of presbyopia corrections.

Super-sensitive tunable planar lens based on graphene hyperbolic metamaterials.

We theoretically study the topological transition of dispersion types and propose a tunable planar lens based on graphene hyperbolic metamaterials (HMMs). By tuning the chemical potential (μc) of graphene, the dispersion relation of the HMM is topologically switchable between ellipse (μc<0.6 eV) and hyperbola (μc>0.6 eV) where positive and negative refractions occur respectively. Especially, for μc>0.6 eV, a Gaussian light beam is negatively refracted twice and focuses at a far-field point finally, acting well as a planar lens. Furthermore, its focal length l can be sensitively tuned by controlling μc, and Δl reaches 260 μm (from 528 to 268 μm) while μc varies with only 0.05 eV (from 0.65 to 0.7 eV). The physical reason is attributed to the different anisotropy degrees of EFCs for different μc. Such a compact, high-speed, and sensitively tunable planar lens holds great promise in photonic integration, photonic imaging, and directional coupling applications.

Towards a Switchable AR/VR Near-eye Display with Accommodation-Vergence and Eyeglass Prescription Support.

In this paper, we present our novel design for switchable AR/VR near-eye displays which can help solve the vergence-accommodation-conflict issue. The principal idea is to time-multiplex virtual imagery and real-world imagery and use a tunable lens to adjust focus for the virtual display and the see-through scene separately. With this novel design, prescription eyeglasses for near- and far-sighted users become unnecessary. This is achieved by integrating the wearer's corrective optical prescription into the tunable lens for both virtual display and see-through environment. We built a prototype based on the design, comprised of micro-display, optical systems, a tunable lens, and active shutters. The experimental results confirm that the proposed near-eye display design can switch between AR and VR and can provide correct accommodation for both.

Creep deformation in elastomeric membranes of liquid-filled tunable-focus lenses.

Liquid-filled tunable-focus lenses have been demonstrated to be suitable for autofocus eyewear applications. Traditionally, these lenses are constructed using an elastomeric polymer chamber filled with a high-index liquid. In this work, we investigate the effect of elastomeric creep on the deformation and eventual degradation of these tunable lenses. We use numerical analysis of a deformable circular disk representative of the lens and provide rigorous experimental results testing the creep property of a number of elastomers. Finally, we provide a comparative study of different elastomeric materials and select the best one for this application.

Speckle reduction with fast electrically tunable lens and holographic diffusers in a laser projector

We proposed a speckle reduction system in the laser pico-projector. The holographic diffusers and the fast electrically tunable lens (FET lens) were adopted in the method of the speckle reduction. This research focuses on speckle reduction by the different divergence angle of the holographic diffusers. Moreover, the speckle contrast value can be further reduced by the fast electrically tunable lens. Different divergence angle of the holographic diffuser provides the different angular diversity to compare the speckle reduction ability. We propose three experimental methods to explore speckle reduction. In experiment 1, we use a holographic diffuser and the FET lens. The speckle contrast value can be reduced to 0.08353. In experiment 2, the speckle contrast value can be reduced to 0.06403 under the balance between power consumption and speckle reduction. In experiment 3, we adjust different waveforms to get lower speckle contrast value. Finally, the speckle contrast value is 0.048 at 400Hz. That is lower than 0.05 successfully. That caused the speckle phenomenon is undetectable by human eye.

Recent Advances in MEMS Metasurfaces and Their Applications on Tunable Lens.

The electromagnetic (EM) properties of metasurfaces depend on both structural design and material properties. microelectromechanical systems (MEMS) technology offers an approach for tuning metasurface EM properties by structural reconfiguration. In the past 10 years, vast applications have been demonstrated based on MEMS metasurfaces, which proved to have merits including, large tunability, fast speed, small size, light weight, capability of dense integration, and compatibility of cost-effective fabrication process. Here, recent advances in MEMS metasurface applications are reviewed and categorized based on the tuning mechanisms, operation band and tuning speed. As an example, the pros and cons of MEMS metasurfaces for tunable lens applications are discussed and compared with traditional tunable lens technologies followed by the summary and outlook.

White-light interferometer without mechanical scanning

We introduce an optical 3D sensor that can measure the shape of objects with rough surface. The proposed sensor is based on white-light interferometry but it does not require a mechanical movement of the measured object relative to the measuring device. The output of a fiber optical interferometer is used as the light source for the measuring interferometer. The built-in fiber stretcher changes the optical path difference and replaces the mechanical movement. A focus tunable lens is a part of the imaging system. This lens secures that the measured part of the surface is imaged sharply onto the camera during the measurement process.

Dynamic control of plasmonic beams.

We experimentally demonstrate dynamic, electrically controlled shaping of plasmonic beams, propagating at the boundary between a metal and a dielectric, by using the thermo-optic effect. The concept is based on selectively heating a specific region in which the plasmonic beam passes by injecting electrical current to an isolated metal layer. This leads to transverse modulation of the wavefront through the thermal dispersion of the dielectric layer above this metal region. We demonstrate two active plasmonic devices: a plasmonic mode converter between the fundamental and first-order Hermite-Gauss modes and a tunable plasmonic lens with a dynamically varying focal length.

Smart Compound Eyes Enable Tunable Imaging

AbstractCompound eyes are natural multiaperture optical imaging systems and have substantial potential in the field of modern optics. However, both natural and artificial compound eyes are composed of ommatidia with fixed focal lengths, and thus incapable of variable‐focus imaging. In this study, inspired by the tunable crystalline lens of human eyes, smart stimuli‐responsive compound eyes based on the bovine serum album (BSA) protein are fabricated via femtosecond laser direct writing. Due to the swelling and shrinking effect of BSA under different pH conditions, a tunable field of view (FOV, 35°–80°) and variable focal length of ommatidia are achieved. In addition to the direct prototyping of an entire protein‐based compound eye, the ability to flexibly integrate the smart protein ommatidia with a conventional optical lens (an SU‐8 lens in this study) to form a composite compound eye is shown. The composite compound eye achieves nearly 400% of focal length tuning at a fixed FOV. It is anticipated that femtosecond laser fabrication and the integration of smart protein‐based compound eyes may emerge as an enabler for fabricating miniature tunable imaging systems.

VIEW-MOD: a versatile illumination engine with a modular optical design for fluorescence microscopy.

We developed VIEW-MOD (Versatile Illumination Engine with a Modular Optical Design): a compact, multi-modality microscope, which accommodates multiple illumination schemes including variable angle total internal reflection, point scanning and vertical/horizontal light sheet. This system allows combining and flexibly switching between different illuminations and imaging modes by employing three electrically tunable lenses and two fast-steering mirrors. This versatile optics design provides control of 6 degrees of freedom of the illumination source (3 translation, 2 tilt, and beam shape) plus the axial position of the imaging plane. We also developed standalone software with an easy-to-use GUI to calibrate and control the microscope. We demonstrate the applications of this system and software in biosensor imaging, optogenetics and fast 3D volume imaging. This system is ready to fit into complex imaging circumstances requiring precise control of illumination and detection paths, and has a broad scope of usability for a myriad of biological applications.

Electrically variable liquid crystal lenses for ophthalmic distance accommodation.

We present the example of a specific design of an electrically tunable liquid crystal lens (TLCL) with floating electrode to analyze experimentally the potential of using TLCLs in intraocular implants. An optimized voltage-frequency driving technique is demonstrated to achieve high optical powers (up to 4 diopters) with very low aberrations (below 0.1μm) for an optical aperture of 3mm. In addition, the continuous character of distance accommodation and the absence of granularity across the aperture of the lens (pixel-free) make this component an excellent choice for various ophthalmic applications.