Tunable Microlens Research Articles

Design of a tunable microlens based on hybrid single-wall carbon nanotube and liquid crystal

: Tunable liquid crystal (LC) lenses have garnered significant interest in recent years for their lightweight, cost-effectiveness, and versatility in applications like augmented reality, ophthalmic devices, and astronomy. Despite numerous proposed structures to enhance LC lens performance, achieving a minimal focal length while preserving image quality and balancing cost and complexity remains a daunting challenge. Adaptive microlenses encounter these obstacles due to physical constraints and diffraction effects. One promising solution lies in using adaptive LC-carbon nanotubes (CNTs) lenses. By adjusting external stimuli like electric or magnetic fields, it is possible to modify the refractive index distribution of the LC medium, thus changing the focal length of the microlens. When paired with CNTs, the LC molecules' orientation and control of focal length can be even more precise. Our research findings suggest that to achieve the shortest focal length in a microlens with a thickness of 22.5 μm, it is recommended that the diameter of the CNT should not exceed 10 nm, and the height of CNT should fall within the range of 10 to 20 μm considering the presence of screening effect. Conversely, for a microlens with low full width at half maximum (FWHM), narrower light spot, it is advisable to use CNT with a diameter larger than 100 nm and a height greater than 13 μm. Additionally, for a microlens with an efficient Fresnel number in the range of 1 to 10, the microlens should have CNT with widths from 100 to 200 nm. Therefore, based on the importance of each factor (focal length, FWHM, and Fresnel number), the dimensions of the carbon nanotube can be selected to suit the desired application.

A Rapid Fabrication Method of Large-Area MLAs with Variable Curvature for Retroreflectors Based on Thermal Reflow.

Retroreflectors are an important optical component, but current retroreflector structures and manufacturing processes are relatively complex. This paper proposes a rapid, low-cost, large-area method for fabricating retroreflectors based on microlens arrays. Tunable microlens arrays with adjustable curvature, fill factor, and sizes were prepared using photolithography and thermal reflow techniques. Subsequently, a two-step nanoimprinting process was used to create a flexible reverse mold and transfer the structure onto the desired substrate. The microlens arrays, with a diameter of 30 μm, a period of 33 μm, a curvature radius ranging from 15.5 to 18.8 μm, and a fill factor ranging from 75.1% to 88.8%, were fabricated this way. In addition, the method also fabricated microlens arrays with diameters ranging from 10 to 80 μm. Retroreflectors were made by sputtering a layer of silver on the MLAs as a reflecting layer, and tests showed that the microlens-based retroreflector exhibited superior retroreflective performance with a wide-angle response of ±75°. Microlens-based retroreflectors have the advantages of simple operation and controllable profiles. The fabrication method in this paper is suitable for large-scale production, providing a new approach to retroreflector design.

Optical design of a tunable microneedle array for photodynamic therapy of metastatic melanomas

The need for photodynamic therapy is increasing with the rise of skin cancer melanoma detection. However, low penetration depth of light in the UV range and higher scattering of skin tissues cause harsh clinical practices and reduced irradiance for the activation of chemicals such as photosensitizers to facilitate cell necrosis of malignant tumors. In this paper, a tunable microlens integrated on a microneedle array is designed for variable focusing to reduce melanomas at multiple sites with an improved intensity for reactive oxygen species production. A light distribution of 36% percent of the input intensity is achieved at the targeted distance of 4.35 mm for blue light. Red light attained a light distribution of 13% of the input intensity at a targeted distance of 6.5 mm. Designing such a light, delivery-based in-vivo biomedical device is of extreme importance for photodynamic therapy of skin cancer on and beyond the epidermal tissue layer.

Dynamically reconfigurable complex liquid crystal emulsions

ABSTRACT Complex emulsions, containing liquid crystals (LCs) and immiscible oils such as fluorocarbon or silicone oils, present innovative functionalities in soft materials. These emulsions exhibit dynamic reconfiguration in droplet morphology and internal LC organisation, expanding applications in optics, sensing, and active matter. This review highlights the evolution and potential of LC-containing complex emulsions. Emphasis is placed on emulsions featuring dynamic and reversible morphological transformations and LC reorganisation, underpinning their suitability for tunable micro-lenses, chemical sensing, and biosensing. Nematic LCs within complex emulsions allow for topological defect-driven functionalization, attaching antibodies to induce substantial changes in the LC director field upon interfacial recognition events. This feature may facilitate the development of ultrasensitive chemical and biological sensors. Moreover, cholesteric LCs, through their selective reflection, enable the rapid and sensitive detection of foodborne pathogens. The controlled assembly of magnetic nanoparticles at interfaces illustrates advancements towards magnetic field-responsive and active colloids. Future perspectives include exploiting these properties for intelligent colloidal systems capable of autonomous behaviour, and furthering applications in dynamic photonic devices, high-security identification tags, and responsive lens systems.

Investigation into fabrication and optical characteristics of tunable optofluidic microlenses using two-photon polymerization.

Optofluidic systems, integrating microfluidic and micro-optical technologies, have emerged as transformative tools for various applications, from molecular detection to flow cytometry. However, existing optofluidic microlenses often rely on external forces for tunability, hindering seamless integration into systems. This work presents an approach using two-photon polymerization (TPP) to fabricate inherently tunable microlens arrays, eliminating the need for supplementary equipment. The optofluidic design incorporates a three-layered structure enabling dynamic manipulation of refractive indices within microchannels, leading to tunable focusing characteristics. It is shown that the TPP fabricated optofluidic microlenses exhibit inherent tunable focal lengths, numerical apertures, and spot sizes without reliance on external forces. This work signifies some advancements in optofluidic technology, offering precise and tunable microlenses with potential applications in adaptive imaging and variable focal length microscopy.

Toroidal dipole Fano resonances driven by bound states in the continuum of lithium niobate metasurface for efficient electro-optic modulation

Free-space optical applications benefit greatly from actively reconfigurable metasurfaces. While static metasurfaces have demonstrated remarkable capabilities in manipulating optical wave characteristics, their fixed electromagnetic response faces a challenge for active device demands. This work presents an all-dielectric metasurface of lithium niobate with high Q-factor Fano resonances for enhanced electro-optic modulation. The resonance mechanism is investigated through multipole decomposition and near-field analysis, revealing that toroidal dipole contributions are dominant in all found three resonances. The strongest resonance arises from symmetry-protected bound states in the continuum (SP-BIC), and it is excited in an asymmetric metasurface by introducing a perturbation in the symmetric nanohole clusters, to enable polarization-independent operation. We numerically achieve a tuning efficiency of 0.65 nm/V and π-phase retardation driven by a bias of 0.53 V, due to the strong field confinement of quasi-BIC mode. Our work provides a scheme for compact, high-performance, and electrically tunable metasurfaces that can help in the development of spatial optical switches as well as tunable micro-lenses and displays.

Technologies for depth scanning in miniature optical imaging systems [Invited

Biomedical optical imaging has found numerous clinical and research applications. For achieving 3D imaging, depth scanning presents the most significant challenge, particularly in miniature imaging devices. This paper reviews the state-of-art technologies for depth scanning in miniature optical imaging systems, which include two general approaches: 1) physically shifting part of or the entire imaging device to allow imaging at different depths and 2) optically changing the focus of the imaging optics. We mainly focus on the second group of methods, introducing a wide variety of tunable microlenses, covering the underlying physics, actuation mechanisms, and imaging performance. Representative applications in clinical and neuroscience research are briefly presented. Major challenges and future perspectives of depth/focus scanning technologies for biomedical optical imaging are also discussed.

Electrically Tunable Polymer Stabilized Chiral Ferroelectric Nematic Liquid Crystal Microlenses

AbstractTunable optical lenses are in great demand in modern technologies ranging from augmented and virtual reality to sensing and detection. In this work, electrically tunable microlenses based on a polymer‐stabilized chiral ferroelectric nematic liquid crystal are described. The power of the lens can be quickly (within 5 ms) varied by ≈500 diopters by ramping an in‐plane electric field from 0 to 2.5 V µm−1. Importantly, within this relatively low‐amplitude field range, the lens is optically isotropic; thus, its focal length is independent of the polarization of incoming light. This remarkable performance combines the advantages of electrically tuned isotropic lenses and the field‐controlled shape of the lens, which are unique properties of chiral ferroelectric nematic liquid crystals and have no counterpart in other liquid crystals. The achieved lens performance represents a significant step forward as compared to liquid lenses controlled by electrowetting and opens new possibilities in various applications such as biomimetic optics, security printing, and solar energy concentration.

A Bidirectionally Focus-Tunable Optofluidic Microlens With Miniature Thermoelectric Coolers

The design and fabrication of a novel bidirectionally optofluidic tunable microlens actuated by thermoelectric coolers (TECs) are reported. A high-resolution three-dimensional printing technology is adopted to fabricate the truly three-dimensional structure of an optofluidic chip. Owing to the bidirectional thermal property of the TECs, both upward and downward membrane profiles are available under the control of a programmable direct-current power supply. The focal length of the liquid lens decreases from 25 to 5mm as the voltage is increased from 0.2 to 1.1V whereas the focal length changes from -25 to -5mm as the current is applied in the opposite direction. A finite element simulation with COMSOL software is conducted to assess the temperature distribution on the device. The response functions of the TECs are investigated for the heating and cooling processes, and the imaging properties are characterized.

Enhanced photocatalytic degradation of organic contaminants in water by highly tunable surface microlenses

Photocatalysis is one of the dominant technologies used to enhance the efficiency of water decontamination with light-based treatments. However, the effectiveness of photocatalysts is usually limited by the irradiation conditions and the properties of the water matrix. In this work, we have demonstrated the capability of surface microlenses (MLs) as a clean technology for more efficient photocatalytic water decontamination. Random or ordered surface MLs were fabricated from simple polymerization of nanodroplets produced in a solvent exchange process. Both random microlenses (MLR) and microlenses array (MLA) could enhance the photocatalytic degradation efficiency (η) of four representative organic pollutants, including methyl orange (MO), norfloxacin (NFX), sulfadiazine (SFD), sulfamethoxazole (SMX), spiked in ultra-pure water, synthetic natural water, or real river water. By controlling the conditions of light treatment, η could be enhanced by up to 402%. The effectiveness of surface MLs was validated under both visible LED light and simulated solar light and for two photocatalysts zinc oxide (ZnO) and titanium dioxide (TiO2). By reducing the concentration of the photocatalysts from 100 to 5 mg/L and the intensity of irradiation intensity from 1 Sun to 0.3 Sun, our findings suggest that the enhancement factor by MLs was higher at lower catalyst concentration, or at lower light intensity. Based on optical simulations and experimental results, we demonstrated that surface MLs optimize the light distribution and promote the formation of active species, which results in the enhancement of η. The use of MLs may serve as a novel strategy to improve the photocatalytic degradation of micropollutants, especially in places where the available light source is weak, such as indoors or in cloudy regions.Synopsis: MLs-enhanced photocatalysis degradation of organic contaminants in different water matrices.

Novel Optofluidic Imaging System Integrated with Tunable Microlens Arrays.

Optofluidic tunable microlens arrays (MLAs) can manipulate and control light propagation using fluids. Lately, their applicability to miniature lab-on-a-chip systems is being extensively researched. However, it is difficult to incorporate 3D MLAs directly in a narrow microfluidic channel using common techniques. This has resulted in limited research on variable focal length imaging with optofluidic 3D MLAs. In this paper, we propose a method for fabricating MLAs in polydimethylsiloxane (PDMS)-based microchannels via electrohydrodynamic jet (E-jet) printing to achieve optofluidic tunable MLAs. Using this method, MLAs of diameters 15 to 80 μm can be fabricated in microfluidic channels with widths of 200 and 300 μm. By alternately using solutions with different refractive indices in the microchannel, the optofluidic microlenses exhibit reversible modulation properties while retaining the morphologies and refractive indices of the microlenses. The focal length of the resulting optofluidic chip can have threefold tunability, thereby achieving an imaging depth of approximately 450 μm. This outstanding advantage is useful in observing microspheres and cells flowing in the microfluidic system. Thus, the proposed optofluidic chip exhibits great potential for cell counting and imaging applications.

Optically anisotropic, electrically tunable microlens arrays formed via single-step photopolymerization-induced phase separation in polymer/liquid-crystal composite materials

Optically anisotropic, electrically tunable microlens arrays formed via single-step photopolymerization-induced phase separation in polymer/liquid-crystal composite materials

ITO-activated reconfigurable micro-lens array for dynamic reversible focusing and collimation

Micro-scale optical components with varifocal manipulation, play a crucial role in imaging and display technology, beam shaping, optical switching, and wavefront-analysis. In order to provide dynamic reversible functionality, these lenses require varifocal capability. Herein, we demonstrate droplet-based micro-lens array for continuous shape regulation from focusing to collimation. Based on high transmittance of 80.41% at 808 nm wavelength and photothermal effect of surface plasmon wave, these ITO-activated microlenses can be dynamically reconfigured and thus display reversible focusing state of convex profile and collimation state of plane profile. As a result, the excellent vision of varifocal ability is unprecedentedly tuned from 155 µm to 1300 µm within a short time of 30 s. Meanwhile, these tunable micro-lenses accurately control the focal length by changing the irradiation duty ratio of laser pulse. Therefore, we demonstrate the fundamental characteristics and promising opportunities of ITO-activated microlenses for fluid-based refractive optical system. • Cormorant eye-inspired reconfigurable microlens arrays display reversible focusing state. • ITO-activated microlenses actuated by remote NIR exhibit the high transmittance. • Photothermal effect of surface plasmon wave facilitates light-responsive microlens arrays behaving varifocal ability. • ITO-activated microlens is promising as a novel remote-driven refraction optical system.

Tunable and Dynamic Optofluidic Microlens Arrays Based on Droplets.

Microlens arrays (MLAs) are acquiring a key role in the micro-optical system, which have been widely applied in the fields of imaging processing, light extraction, biochemical sensing, and display technology. Compared with solid MLAs, liquid MLAs have received extensive attention due to their natural smooth interface and adjustability. However, manufacturing tunable liquid MLAs with ideal structures is still a key challenge for current technologies. In this paper, a novel and simple optofluidic method is demonstrated, enabling the tunable focusing and high-quality imaging of liquid MLAs. Tunable droplets are fabricated and self-assembled into arrays as the MLAs, which can be easily adjusted to focus, form images, and display different focal lengths. Tuning of MLAs' focusing properties (range from 550 to 5370 μm) is demonstrated by changing the refractive index (RI) of the droplets with a fixed size of 200 μm, which can be changed by adjusting the flow rates of the two branch streams. Also, the corresponding numerical apertures of the MLAs range from 0.026 to 0.26. Furthermore, the MLAs' functionality for microparticle imaging applications is also illustrated. Combining the MLAs with a 4× objective, microparticle imaging is magnified two times, and the resolution has also been improved on the original basis. Besides, both the size and RI of the MLAs in an optofluidic chip can be further adjusted to detect samples at different positions. These MLAs have the merits of high optical performance, a simple fabrication procedure, easy integration, and good tunability. Thus, it shows promising opportunities for many applications, such as adaptive imaging and sensing.

Surface Topographical Control of a Liquid Crystal Microlens Array Embedded in a Polymer Network

A novel approach for fabricating a microlens array with a tunable surface topographical structure and focal length is proposed in the present study. The microlens array was manufactured through the photoinduced molecular reorientation of nematic liquid crystals (LCs) stabilized by a polymer network. The fabricated microlens array had a mountain-shaped topographical structure due to the accumulation of polymers and LC molecules. The molecular orientation of the LC inside the microlens was disordered, while the outer side of the microlens was ordered. The thermal expansion of the polymer network and the phase transition of the LC molecules within the microlens array allowed the surface topographical structure and the focal length to be reversibly tuned under heat treatment. The results of this research work will enable future implementations to provide a thermally tunable microlens array.

Electrically Tunable Microlens Array Enabled by Polymer‐Stabilized Smectic Hierarchical Architectures

AbstractLiquid crystals (LCs) are key functional materials that are broadly adopted in various fields due to their stimuli‐responsiveness. Recently, LCs with hierarchical architectures have brought new effects to optics and attracted intensive attention. In smectic A phase, the parallel molecular layers are periodically wrapped to form toric focal conic domains (TFCDs) under antagonistic boundary conditions (i.e., hybrid alignment conditions). TFCD shows great potential in nanofabrication and integral imaging. However, the arbitrary tailoring of TFCD is still challenging, and the robustness of hierarchical configuration hinders the tunability. Here, a radial alignment lattice is adopted to guide the local orientation of LCs and thus facilitates predefining the lattice symmetry and domain size of TFCDs. By introducing polymer stabilization and optimizing the composition, the sample simultaneously maintains the director distribution inside smectic layers and possesses the stimuli‐responsiveness of nematic phase at room temperature. By this means, microlens arrays are demonstrated with reversible electrical tunability. The strategy can be extended to other smectic configurations and may upgrade existing dynamic optics.

Tunable optofluidic microbubble lens.

Optofluidic microlenses are one of the crucial components in many miniature lab-on-chip systems. However, many optofluidic microlenses are fabricated through complex micromachining and tuned by high-precision actuators. We propose a kind of tunable optofluidic microbubble lens that is made by the fuse-and-blow method with a fiber fusion splicer. The optical focusing properties of the microlens can be tuned by changing the refractive index of the liquid inside. The focal spot size is 2.8 µm and the focal length is 13.7 µm, which are better than those of other tunable optofluidic microlenses. The imaging capability of the optofluidic microbubble lens is demonstrated under a resolution test target and the imaging resolution can reach 1 µm. The results indicate that the optofluidic microbubble lens possesses good focusing properties and imaging capability for many applications, such as cell counting, optical trapping, spatial light coupling, beam shaping and imaging.

Enhanced Photocatalytic Degradation of Organic Contaminants in Water by Highly Tunable Surface Microlenses

Enhanced Photocatalytic Degradation of Organic Contaminants in Water by Highly Tunable Surface Microlenses

In Situ Electrohydrodynamic Jet Printing-Based Fabrication of Tunable Microlens Arrays

Tunable microlens arrays (MLAs) with controllable focal lengths have been extensively used in optical sensors, biochips, and electronic devices. The commonly used method is electrowetting on dielectric (EWOD) that controls the contact angle of the microlens to adjust the focal length. However, the fabrication of tunable MLAs at the microscale remains a challenge because the size of MLAs is limited by the external electrodes of EWOD. In this study, a highly integrated planar annular microelectrode array was proposed to achieve an electrowetting tunable MLA. The planar microelectrode was fabricated by electrohydrodynamic jet (E-jet) printing and the liquid microlens was then deposited in situ on the microelectrode. This method could realize 36 tunable liquid microlenses with an average diameter of 24 μm in a 320 × 320 μm2 plane. The fabricated tunable MLAs with higher integration levels and smaller sizes can be beneficial for cell imaging, optofluidic systems, and microfluidic chips.

Tunable liquid crystal microlens array with negative and positive optical powers based on a self-assembled polymer convex array

ABSTRACT In this report, an LCMLA with a negative-positive tunable focal length is designed using a self-assembled highly uniform polymer convex array. The polymer convex array was prepared by scribing UV-sensitive glue onto the indium tin oxide (ITO) substrate modified with a microhole array patterned hydrophobic layer. This substrate is assembled with another ITO substrate coated with a homogeneous polyimide alignment layer and rubbed in one direction, then filled with an LC material to form a sandwich structure. The refractive index of the selected polymer is kept between ne and no of the LC materials. By rotating the polarisation direction of the incident light for 90°, the focal length of the LCMLA can be switched from negative to positive. Otherwise, by varying the electric field, the continuous negative-to-positive tuning of the focal length of the LCMLA is implemented. For instance, an LCMLA with the aperture of 200 μm and a fill factor of 82.2%, the cell gap is 20 μm. Changing the voltage from 0 to 0.7 Vrms allows the focal length to be adjusted from −4 mm to ∞; in turn, varying the voltage from 1 to 10 Vrms results in the focal length from 6.0 to 4.5 mm.