Tunable Focal Distance Research Articles

Spectral characterization of optical aberrations in fluidic lenses

We report an extensive numerical study and supporting experimental results on the spectral characterization of optical aberrations in macroscopic fluidic lenses with tunable focal distance and aperture shape. By using a Shack–Hartmann wavefront sensor, we experimentally reconstruct the near-field wavefront transmitted by the fluidic lenses, and we characterize the chromatic aberrations in terms of Zernike polynomials in the visible range. Moreover, we further classify the spectral response of the lenses using clustering techniques, in addition to correlation and convolution measurements. Experimental results are in agreement with numerical results based on our theoretical model of the nonlinear deformation of thin elastic membranes.

High resolution multispectral spatial light modulators based on tunable Fabry-Perot nanocavities

Spatial light modulators (SLMs) are the most relevant technology for dynamic wavefront manipulation. They find diverse applications ranging from novel displays to optical and quantum communications. Among commercial SLMs for phase modulation, Liquid Crystal on Silicon (LCoS) offers the smallest pixel size and, thus, the most precise phase mapping and largest field of view (FOV). Further pixel miniaturization, however, is not possible in these devices due to inter-pixel cross-talks, which follow from the high driving voltages needed to modulate the thick liquid crystal (LC) cells that are necessary for full phase control. Newly introduced metasurface-based SLMs provide means for pixel miniaturization by modulating the phase via resonance tuning. These devices, however, are intrinsically monochromatic, limiting their use in applications requiring multi-wavelength operation. Here, we introduce a novel design allowing small pixel and multi-spectral operation. Based on LC-tunable Fabry-Perot nanocavities engineered to support multiple resonances across the visible range (including red, green and blue wavelengths), our design provides continuous 2π phase modulation with high reflectance at each of the operating wavelengths. Experimentally, we realize a device with 96 pixels (~1 μm pitch) that can be individually addressed by electrical biases. Using it, we first demonstrate multi-spectral programmable beam steering with FOV~18° and absolute efficiencies exceeding 40%. Then, we reprogram the device to achieve multi-spectral lensing with tunable focal distance and efficiencies ~27%. Our design paves the way towards a new class of SLM for future applications in displays, optical computing and beyond.

Continuous High-Throughput Fabrication of Architected Micromaterials via In-Air Photopolymerization.

Recent advances in optical coding, drug delivery, diagnostics, tissue engineering, shear-induced gelation, and functionally engineered rheology crucially depend on microparticles and microfibers with tunable shape, size, and composition. However, scalable manufacturing of the required complex micromaterials remains a long-standing challenge. Here in-air polymerization of liquid jets is demonstrated as a novel platform to produce microparticles and microfibers with tunable size, shape, and composition at high throughput (>100mL h-1 per nozzle). The polymerization kinetics is quantitatively investigated and modeled as a function of the ink composition, the UV light intensity, and the velocity of the liquid jet, enabling engineering of complex micromaterials in jetting regimes. The size, morphology, and local chemistry of micromaterials are independently controlled, as highlighted by producing micromaterials using 5 different photopolymers as well as multi-material composites. Simultaneous optimization of these control parameters yields rapid fabrication of stimuli-responsive Janus fibers that function as soft actuators. Finally, in-air photopolymerization enables control over the curvature of printed droplets, as highlighted by high-throughput printing of microlenses with tunable focal distance. The combination of rapid processing and tunability in composition and architecture opens a new route toward applications of tailored micromaterials in soft matter, medicine, pharmacy, and optics.

Two-Dimensional Hybrid Photonic Crystal With Graded Low-Index Using a Nonuniform Voltage

Abstract We proposed a new method for designing graded index lens using liquid crystal infiltration into annular photonic crystals. Applying an external nonuniform voltage in the transverse direction perpendicular to the direction of light propagation yields different orientation of liquid crystal molecules inside the photonic crystal unit cells. As a result, a gradient refractive index was modulated. We numerically investigate focusing properties of the designed graded index structure using plane-wave expansion and finite-difference time-domain methods. The gradient refractive index profile was adjusted by varying the nonuniform voltage excitations, which consequently altered the focal distance of the graded index structure. A wide tuning range of 1856 nm was achieved for focal distance by the proposed graded index structure. This feature can be implemented for planning a flat lens with tunable focal distance based on electro-optic effect. These achievements may have future applications in some optical devices such as near-field imaging and scanning.

Tunable fluidic lenses with high dioptric power

We report a complete theoretical model and supporting experimental results on the fabrication and characterization of macroscopic adaptive fluidic lenses with high dioptric power, tunable focal distance, and aperture shape. The lens is 17 mm wide and is made of an elastic polydimethylsiloxane (PDMS) polymer, which can adaptively restore accommodation distance within several cm according to the fluidic volume mechanically pumped in. Moreover, the lens can provide for magnification in the range of +25 diopter to +100 diopter with optical aberrations within a fraction of a wavelength, and overall lens weight of less than 2 g. The agreement between the non-linear theoretical model describing the elastic membrane deformation and the experimental results is apparent. We stress that these features make the proposed lenses appropriate for the low vision segment, as well as for applications in video magnifiers, camera zooms, telescope and microscopes objectives, and other machine vision applications where large magnification is required.

Near-Field Focused Array Antenna With Frequency-Tunable Focal Distance

An $8\times8$ microstrip planar array antenna with near-field focused beams is presented in this paper, whose elements are series fed in both E- and H-planes. The focus is designed at a distance of 200 mm above the array plane at 10 GHz, and by carefully designing the feed network, the focal distance can be frequency tunable. Eventually, a steerable focal distance from 78 to 249 mm is achieved as frequency varies from 9.25 to 10.5 GHz, with near-field sidelobes below −8 dB. Theoretical analysis is performed first, which is further proven by simulations and experiments. Finally, the method of tuning the sensitivity and range of frequency scan is discussed, which is proven by numerical study. To the best of our knowledge, the proposed design is the first array approach to realize tunable focal distance without any beam-forming components.

Inverse-designed stretchable metalens with tunable focal distance

In this paper, we present an inverse-designed 3D-printed all-dielectric stretchable millimeter wave metalens with a tunable focal distance. A computational inverse-design method is used to design a flat metalens made of disconnected polymer building blocks with complex shapes, as opposed to conventional monolithic lenses. The proposed metalens provides better performance than a conventional Fresnel lens, using lesser amount of material and enabling larger focal distance tunability. The metalens is fabricated using a commercial 3D-printer and attached to a stretchable platform. Measurements and simulations show that the focal distance can be tuned by a factor of 4 with a stretching factor of only 75%, a nearly diffraction-limited focal spot, and with a 70% relative focusing efficiency, defined as the ratio between power focused in the focal spot and power going through the focal plane. The proposed platform can be extended for design and fabrication of multiple electromagnetic devices working from visible to microwave radiation depending on scaling of the devices.

63.1: Invited Paper: Liquid Crystal Devices Based on Photo‐Alignment and Photo‐Patterning Materials

AbstractLiquid crystal devices based on photo‐alignment and photo‐patterning materials, were proposed, including patterned retarders for 3D applications, lenses with electrically tunable focal distance, LC based sensors, switchable q‐plates, and optically rewritable E‐paper. The photoalignment materials were mostly photosensitive azo‐dye layers. The combination of azo‐dye layers and liquid crystal polymers were also used for photo patterned phase retarders. The practical applications of new LC elements in 3D displays and other LC technology areas are envisaged.

Playing with water drops: from wetting to optics through electrostatics

We present a consistent series of activities, including experiments and basic computational studies, investigating the shape and optical properties of water drops in connection with novel technological devices. Most of the work can be carried out with simple teaching equipment and is well suited to undergraduate students. Firstly, we show how the mass variations of a sessile drop can be used to control its curvature and hence to produce lenses with tunable focal distance. Alternatively, the shape of the drop can be varied using electrowetting on dielectric (EWOD). We propose a simple pedagogical approach to this phenomenon in connection with historical electrostatic apparatus. A detailed process for the preparation of an EWOD device is given, together with a focimetric method allowing the analysis of electrowetting effects in practical exercises. Finally, the manipulations of a commercialized variable focus lens illustrate that EWOD is at the heart of most recent technological developments, making practical work in optics more attractive than traditional exercises using conventional lenses.

In vivo three-dimensional imaging of normal tissue and tumors in the rabbit pleural cavity using endoscopic swept source optical coherence tomography with thoracoscopic guidance

The purpose of this study was to develop a dynamic tunable focal distance graded-refractive-index lens rod-based high-speed 3-D swept-source (SS) optical coherence tomography (OCT) endoscopic system and demonstrate real-time in vivo, high-resolution (10-microm) imaging of pleural-based malignancies in an animal model. The GRIN lens-based 3-D SS OCT system, which images at 39 fps with 512 A-lines per frame, was able to capture images of and detect abnormalities during thoracoscopy in the thoracic cavity, including the pleura, chest wall, pericardium, and the lungs. The abnormalities were confirmed by histological evaluation and compared to OCT findings. The dynamic tunable focal distance range and rapid speed of the probe and SS prototype OCT system enabled this first-reported application of in vivo 3-D thoracoscopic imaging of pleural-based malignancies. The imaging probe of the system was found to be easily adaptable to various sites within the thoracic cavity and can be readily adapted to other sites, including rigid airway endoscopic examinations.

Polymer thin film deposited on liquid for varifocal encapsulated liquid lenses

We developed a process for making liquid lenses that have a tunable focal distance. In our process, polymer thin films are directly deposited on liquid droplets in vacuum. Conducting the deposition in vacuum helps preserve the delicate spherical droplet shape so that they can be used as lenses. The polymer film is mechanically stable, which protects the droplets from the ambient, but it is also extremely thin and flexible, which allows the droplets to deform. The droplets are deformed using electrostatic force to change their focal distance. Our lens is structurally simple and can be operated by an electrical input.

Integrated fluidic lenses and optic systems

Functionally integrated fluidic lenses and lens systems were demonstrated. Fluidic optic lenses can function as lenses with tunable focal distance, lens doublets with variable and convertible lens type, zoom lenses, and a lens system possessing both telephoto and reverse telephoto functions. High lens power and broad tuning range were achieved in a single 20-mm aperture device that can be tuned to have a convex or concave shape, with the respective tunable focal distance from 14.3 mm to infinity and from -6.1 mm to negative infinity. For fluidic adaptive zoom-lens-on-a-chip, a zoom ratio of 2.14 was achieved for 20-mm lens aperture, and a zoom ratio of 2.83 for 5-mm lens aperture. For the latter device, a tunable field-of-view from 10/spl deg/ to 80/spl deg/ was demonstrated, suggesting that the functions of telephoto and reverse telephoto systems can be achieved in a single zoom lens chip. Finally, the fluidic devices including the microfluidic pumps can be integrated with the lenses. All these integrated fluidic lenses and lens systems were microfabricated using a modified UV-LIGA process.