Tunable Microlens Array Research Articles

Optically Isotropic Polymer Stabilized Liquid Crystals with Fast and Large Field‐Induced Refractive Index Variation

AbstractOptically isotropic polymer stabilized liquid crystals with low haze (≈1% at 550 nm), large (≈0.09) field induced refractive index variation, and fast (<0.1 ms) relaxation time are reported. The impressive improvement compared to previous studies using conventional nematic liquid crystals are due to both the addition of novel highly polar ferroelectric nematic liquid crystals that decrease the required field to achieve the theoretically predicted refractive index variation and of the 6 wt.% of chiral dopant with high helical twisting power that suppressed the haze and made the system reversible with fast relaxation. It is also shown that the field induced refractive index variation can be increased over to 0.1 by using high intensity UV light for polymer stabilization. Although such polymer structure is not completely isotropic, it still provides polarization independent optical properties for normal incidence. Since fast and large switching of focal length is essential in AR/VR glasses, these systems offer significant potential for applications in highly tunable microlens arrays.

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.

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.

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

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.

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 microlens array fabricated by a silicone oil-induced swelled polydimethylsiloxane (PDMS) membrane bonded to a micro-milled microfluidic chip.

Microlens arrays (MLAs) nowadays are critical micro-optical components and they can be applied in many application fields, such as optical communication systems and flat panel display modules. This article describes a novel approach to the fabrication of tunable, highly reliable, and uniform polydimethylsiloxane (PDMS) MLAs. A polydimethylsiloxane (PDMS) membrane is bonded to a micro-milled poly(methyl methacrylate) (PMMA) microfluidic chip and exposed to silicone oil of a specific viscosity. Molecules in the oil insert themselves into the molecular structure of the PDMS membrane, causing it to swell and subsequently form dome-shaped MLAs. From our experiments, we derived the following conclusions. First, the homogeneous swelling of the PDMS resulted in MLAs with a high numerical aperture (0.5), high uniformity illumination (CV of the illumination intensity is between 2.5%∼5.1%), and high uniformity (CV of sag height of MLAs is less than 0.05). Second, the shorter molecular chains in low-viscosity oils diffused more readily into the PDMS membrane, which increased the effects on swelling, resulting in MLAs with higher sag height and higher numerical aperture. For example, the 5 cst silicone oil resulted in sag height of 191 µm with NA of 0.50, whereas the 100 cst silicone oil resulted in sag height of 86 µm with numerical aperture of 0.33. Finally, the integrated mixer module enabled the simultaneous tuning of the 7 × 7 MLAs simply by adjusting the injection flow rates of the constituent silicone oils.

Polyvinyl chloride gel tunable lenticular microlens array with fast dynamic response

A facial method was used to enhance the dynamic response of polyvinyl chloride (PVC) gel tunable lenticular microlens array (LMA). The response time could be reduced using a discontinuous hydrophobic layer-modified electrode substrate due to a decrease in friction between the substrate surface and PVC gel. The application of DC voltage (V = − 45 V) to LMA induced a response time <240 ms. The proposed PVC gel LMA looks promising for use in image processing and two/three-dimensional switchable displays due to its fast-dynamic response, good stability, compact structure, and easy fabrication.

Scalable and ultrafast epitaxial growth of single-crystal graphene wafers for electrically tunable liquid-crystal microlens arrays

The scalable growth of wafer-sized single-crystal graphene in an energy-efficient manner and compatible with wafer process is critical for the killer applications of graphene in high-performance electronics and optoelectronics. Here, ultrafast epitaxial growth of single-crystal graphene wafers is realized on single-crystal Cu90Ni10(1 1 1) thin films fabricated by a tailored two-step magnetron sputtering and recrystallization process. The minor nickel (Ni) content greatly enhances the catalytic activity of Cu, rendering the growth of a 4 in. single-crystal monolayer graphene wafer in 10 min on Cu90Ni10(1 1 1), 50 folds faster than graphene growth on Cu(1 1 1). Through the carbon isotope labeling experiments, graphene growth on Cu90Ni10(1 1 1) is proved to be exclusively surface-reaction dominated, which is ascribed to the Cu surface enrichment in the CuNi alloy, as indicated by element in-depth profile. One of the best benefits of our protocol is the compatibility with wafer process and excellent scalability. A pilot-scale chemical vapor deposition (CVD) system is designed and built for the mass production of single-crystal graphene wafers, with productivity of 25 pieces in one process cycle. Furthermore, we demonstrate the application of single-crystal graphene in electrically controlled liquid-crystal microlens arrays (LCMLA), which exhibit highly tunable focal lengths near 2 mm under small driving voltages. By integration of the graphene based LCMLA and a CMOS sensor, a prototype camera is proposed that is available for simultaneous light-field and light intensity imaging. The single-crystal graphene wafers could hold great promising for high-performance electronics and optoelectronics that are compatible with wafer process.

Tunable liquid microlens arrays actuated by infrared light-responsive graphene microsheets

In this work, liquid microlens arrays are fabricated by the template assisted liquid self-assembly method and the corresponding focus adjustment is realized by the photothermal conversion of graphene microsheets. Under the infrared laser irradiation, the deposited graphene microsheets layer can convert the light energy into thermal energy, which can increase the temperature of liquid microlens and induce the change of the lenslet curvature. As a result, the liquid microlens array can realize a reversible and programmable focus by selectively confining infrared laser to an expectant region. In contrast with traditional microlens arrays, graphene-based liquid microlens arrays are versatile and practicable with the advantages of non-contact actuation, remote and local control, and omitted connecting wires and electrodes. All these excellent advantages make the graphene-based microlens arrays available for remote-driven optoelectronic applications.

73‐4L: Late‐News Paper: Wavelength‐independent Electrically Tunable Microlens Array with a Chiral Nematic Liquid Crystal

A liquid crystal microlens array (LCMLA) with a chiral nematic liquid crystal material in twisted vertical alignment configuration is demonstrated. The proposed LCMLA has merits of low operation voltage and wavelength‐independent, electrically‐tunable focal length, which are suitable for full color 3D microscopy and endoscope application.

AR/VR, Digital Signage, Display Materials, Vehicular Displays, and Wearables Headline Display Week 2017 Technical Program in Los Angeles

A bumper crop of papers submitted to this year's symposium ensures that the field will be broad as well as deep. Highlights include novel technologies like aerial displays, perovskites, full‐windshield automotive head‐up displays, and tunable microlens arrays, as well as practical advances in manufacturing and metrology that will help you do your job better. This is your once‐a‐year opportunity to find out what's happening in the field of displays. The discoveries you'll make at Display Week will inform your business plans for months and years to come.

Tunable mirolens array with a large fill-factor: Self-assembly fabrication and electrodrodynamic actuation

Because a tunable microlens can focus the incident light and shift the focal point, a tunable microlens array (TMLA) with a large fill-factor was fabricated by a self-assembly method. Interestingly, each microcavity was filled completely with a liquid droplet, forming a hemispherical profile by capillary forces. The TMLA had a large fill-factor of up to 98% and various sag heights. Moreover, when a gated square-wave voltage was applied, the focal length of TMLA could be tuned from the initial 540μm to 140μm by electrohydrodynamic force simultaneously; both of the rise and decay time were within 50ms. These results indicate that this novel method can construct TMLA with a large fill-factor, thus providing a new perspective towards portability, miniaturization, and low-cost applications.

Electrically tunable microlens arrays based on polarization-independent optical phase of nano liquid crystal droplets dispersed in polymer matrix.

Electrically tunable focusing microlens arrays based on polarization independent optical phase of nano liquid crystal droplets dispersed in polymer matrix are demonstrated. Such an optical medium is optically isotropic which is so-called an optically isotropic liquid crystals (OILC). We not only discuss the optical theory of OILC, but also demonstrate polarization independent optical phase modulation based on the OILC. The experimental results and analytical discussion show that the optical phase of OILC microlens arrays results from mainly orientational birefringence which is much larger than the electric-field-induced birefringence (or Kerr effect). The response time of OILC microlens arrays is fast~5.3ms and the tunable focal length ranges from 3.4 mm to 3.8 mm. The potential applications are light field imaging systems, 3D integrating imaging systems and devices for augment reality.

Simulation Study on Polarization-Independent Microlens Arrays Utilizing Blue Phase Liquid Crystals with Spatially-Distributed Kerr Constants

Polarization independent liquid crystal (LC) microlens arrays based on controlling the spatial distribution of the Kerr constants of blue phase LC are simulated. Each sub-lens with a parabolic distribution of Kerr constants results in a parabolic phase profile when a homogeneous electric field is applied. We evaluate the phase distribution under different applied voltages, and the focusing properties of the microlens arrays are simulated. We also calculate polarization dependency of the microlenses arrays at oblique incidence of light. The impact of this study is to provide polarizer-free, electrically tunable focusing microlens arrays with simple electrode design based on the Kerr effect.

Polarization-independent and fast tunable microlens array based on blue phase liquid crystals

This work investigates a polarization-independent and fast response microlens array. This array is composed of a concave polymer microlens array and blue phase liquid crystals (BPLCs). The microlens array can be either positive or negative, depending on the birefringence of the BPLCs. The experimental results show that the microlens array is fast switched between positive and negative focal lengths via controlling the electric fields, and the response time is a few hundred microseconds. Additionally, the focusing efficiency is independent of the polarization of the incident light.

Solvent‐Responsive Surface via Wrinkling Instability

Solvent-responsive surfaces are fabricated by osmotically-driven wrinkling with hierarchical morphology and controlled wavelength. By taking advantage of reversible wrinkling mechanisms and controlling the region with moduli-mismatch, we demonstrate several applications such as reversible channels, tunable microlens arrays, and guided colloidal pattern formation.