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Cu-Ni-Si alloy is the key raw material for the lead frame of large integrated circuits. The disordered grain orientation of alloy billet, high hardening rate, residual stress, and poor surface quality of cold working strips seriously affect its processability. In order to improve the cold-working properties of Cu-Ni-Si alloy, two kinds of C70250 copper alloy strips were produced through hot mold continuous casting (HMCC) and cold mold continuous casting (CMCC) technology. The effects of solidified microstructure on the cold-working deformation behavior, mechanical properties, and residual stress of the alloy were studied. The results show that C70250 copper alloys with columnar grain and equiaxed grain were prepared through HMCC and CMCC. After a 98% reduction in cold rolling, columnar grain strip surface quality was very good, and the elongation was still as high as 3.2%, which is 2.9 times that of equiaxed grain alloy. The residual stress of equiaxed grain strips reached 363 MPa, which is 2.7 times that of columnar grain strips. During the cold rolling process, equiaxed grain strips are prone to cause intersecting plane dislocations, stacking faults, shear bands, and grain breakage during large deformation cold rolling. The columnar grain strip causes parallel plane dislocations, stacking faults, and shearbands. Furthermore, the deformation structure was found to be uniform, and, ultimately, the alloy formed a fibrous structure. Therefore, the elongation and latter distortion of columnar grain strips improved after being put through large deformation cold rolling, which greatly reduced residual stress.

A droplet array which can function as a microlens array (MLA) is prepared by filling a small amount of polyvinyl chloride (PVC) gel into a polymeric cavity. The apex distance of each droplet decreases gradually as the applied DC voltage increases. The lens surface profile presents a spherical shape during actuation. By applying a voltage from 0 to 250 V, the focal length of the MLA changes from 2.75 mm to 3.15 mm and the measured total response time is 360 ms, which is lower operating voltage and much faster than that previously reported. The proposed MLA is free from gravitational effect, shaking, and vibration. It has potential applications in imaging, beam steering, biometrics, sensing, and electronic displays.

In this paper, we demonstrate a large-area optical switch using surface-expandable liquid droplets. These droplets are isolated by polymeric grids. The surrounding of the liquid droplets is filled with another immiscible liquid in order to suppress the gravitational effect. To obtain an optical switch, the droplets are doped with dye. In the voltage-off state, the droplets have minimal surface area-to-volume ratio. As a result, the aperture ratio (AR) is maximal. By applying a voltage, the generated dielectric force can expand the surface of the droplets, leading the AR to decrease. At $V = 60\ {\rm V_{\rm rms}}$ , the AR reduces to zero. The optical switch is polarization insensitive. By further optimizing the device structure, this optical switch has promising applications in light shutters, switchable windows, and displays.

A polymer network liquid crystal (PNLC) lenticular microlens array with no surface treatment is prepared. Before polymerization, the LC and diacrylate monomers are reoriented with gradient refractive index distribution by a fringing field. After polymerization, the oriented LC is stabilized by the polymer network. The prepared PNLC lenticular microlens array is optically anisotropic. Without surface treatment, the device fabrication is simplified, and it can present almost the same optical performance as the PNLC lenticular microlens with surface treatment. Integrating with a 90 $^\circ $ twisted-nematic LC cell, the PNLC lenticular microlens array can be switched between a focusing state and non-focusing state. Such a PNLC lenticular microlens array has potential application in switchable 2D/3D displays.

The authors report an optical switchable lens using an electrowetting liquid lens. The optical switchable lens is obtained through two different paths, either the annular aperture or the central aperture of the liquid lens. Three polarizers and a liquid crystal cell are used as a light shutter for the two-path transition. A prototype is demonstrated, and the authors analyzed the properties of the switchable electrowetting liquid lens. In contrast to the conventional liquid lenses, our lens system can present high optical power with high resolution for the path of annular aperture, while it can reduce the aberrations and extend the depth of field for the path of central clear aperture. Our lens system has potential applications in target tracking, biomedical science, imaging security, and portable electronic devices.

We demonstrate an adaptive lenticular microlens array (LMA) using Polyvinyl chloride (PVC)/dibutyl phthalate (DBP) gels. The gels form a membrane on the surface of an electrode with interdigitated pattern. By applying a DC voltage, the surface of the membrane can present a wavy configuration due to the electrostatic repulsive force. The membrane with wavy surface functions as a LMA. If the anode and cathode are switched over, the waved surface can rapidly recover to its originally flat surface. Due to the advantages of compact structure, optical isotropy, and good mechanical stability, the demonstrated LMA has potential application in imaging, information processing, biometrics, and switchable 2D/3D displays.

A liquid crystal (LC) lens is prepared by controlling the alignment of a LC using a homogeneous polyimide (PI) layer and a homeotropic PI layer. The rubbed homogeneous PI layer has a concave surface and the homeotropic PI layer is flat. The LC sandwiched between the two PI layers obtains a hybrid alignment which has the largest gradient of refractive index (GRIN) distribution. The LC layer exhibits a lens character because of its convex shape. Since the effective refractive index of the LC is larger than that of the homogeneous PI, the LC lens can focus a light with the shortest focal length in the voltage-off state. By applying an external voltage, the LC molecules can be reoriented along the electric field. As a result, the focal length of the LC lens is reduced. The focal length of the LC lens can be tuned from ~30 to ~120 μm when the voltage is changed from 0 to 7 Vrms. This LC lens has the advantages of no threshold, low operating voltage, and simple fabrication.

A switchable-focus lenticular microlens array (LMA) is an essential component for switchable 2D/3D displays. For 2D display, the LMA has no optical power and it functions as an optical flat plate. To achieve 3D display, each microlens in the array has a focusing effect. Various approaches for preparing LMAs were demonstrated. In this report, we mainly introduce two types of LMAs: polymeric LMA and polyvinyl chloride (PVC)/dibutyl phthalate (DBP) LMA. The polymeric LMA is optically anisotropic and solidified. When it integrates with a twisted-nematic liquid crystal (TN LC) polarized rotator, a switchable focus with a low driving voltage and fast response time can be obtained. As a comparison, the PVC/DBP LMA is optically isotropic and adaptive. Its focal length can be largely changed by reconfiguring its surface profile using a DC voltage. Both LMAs have the merits of compact structure, simple fabrication, and good optical performance. The operation mechanism of each LMA is introduced and their performances are evaluated. They both have potential applications in switchable 2D/3D displays.

Electrically tunable liquid crystal microlenses have attracted strong research attention due to their advantages of tunable focusing, voltage actuation, low power consumption, simple fabrication, compact structure, and good stability. They are expected to be essential optical devices with widespread applications. However, the slow response time of nematic liquid crystal (LC) microlenses has been a significant technical barrier to practical applications and commercialization. LC/polymer composites, consisting of LC and monomer, are an important extension of pure LC systems, which offer more flexibility and much richer functionality than LC alone. Due to the anchoring effect of a polymer network, microlenses, based on LC/polymer composites, have relatively fast response time in comparison with pure nematic LC microlenses. In addition, polymer-stabilized blue phase liquid crystal (PS-BPLC) based on Kerr effect is emerging as a promising candidate for new photonics application. The major attractions of PS-BPLC are submillisecond response time and no need for surface alignment layer. In this paper, we review two types of fast-response microlenses based on LC/polymer composites: polymer dispersed/stabilized nematic LC and polymer-stabilized blue phase LC. Their basic operating principles are introduced and recent progress is reviewed by examples from recent literature. Finally, the major challenges and future perspectives are discussed.

The fringe-field switching-liquid crystal display (FFS-LCD) mode recently became a major component of LCDs for high resolution, high-image quality, low power consumption, and touch screen suitability. This review paper discusses how the FFS technology was developed, how it evolved to its present status, and also about the future advances of the FFS mode in terms of performance and technologies.

We report an adaptive-focus lens using two immiscible liquids. The two liquids have a spherical interface and their border is confined by an iris diaphragm (ID). Using a bubble actuator to vary the aperture of the ID, the surface profile of the two liquid is changed, which in turn leads to a tunable focal length. In this paper, the liquid lens structure is depicted and the operation mechanism of the bubble actuator is introduced. For the liquid lens, the refractive index (n1) of the convex liquid is smaller than that of the concave (or surrounded) liquid (n2, n2-n1 ~ 0.2), so the lens is a diverging lens. As the aperture of the diaphragm is changed from ~ 5 to ~ 7.5 mm by the actuator, the focal length (f) of the lens could be tuned in the range of -168 mm ≤ f ≤ -55 mm. For the bubble actuator, it has the advantages of voltage control, large actuation pressure, reasonable speed, and low power consumption. Driven by the bubble actuator, our liquid lens can present a large aperture change, reasonable dynamic response, and precise focus control.

We demonstrate a novel adaptive liquid lens actuated by liquid crystal (LC) pistons. The dielectrophoretic force generated by the embedded in-plane-switching electrode causes the reciprocating movement of LC droplets which, in turn, changes the optical power of the resultant liquid lens. Such a microlens array is promising for 3D image processing.

We demonstrate a submillisecond-response tunable-focus cylindrical microlens array based on polymer network liquid crystal. The focal length can be tuned from 1.9 cm to 5 cm by increasing the voltage from 0 to 80V. This microlens array has potential applications in autostereoscopic 3D displays.

We report a dielectrically actuated liquid crystal (LC) pump. A small volume of LC forms a pillar-like droplet in a cylindrical hole which partially touches the bottom substrate with embedded interdigitated electrodes. By applying a voltage, the LC droplet can be largely stretched along the electrode direction by the generated dielectric force, which in turn exerts a pressure to displace a small volume of fluid on the opposite side of the chamber. Once the voltage is removed, the LC droplet returns to its initial state. The LC droplet with such a reciprocating movement behaves like a pump. In this work, the actuation mechanism of the LC pump is presented and the performance evaluated experimentally. Our LC pump has the following advantages: simple structure, easy fabrication, compact size, high precision, low power consumption, and relatively fast response time. It is promising for applications in lens actuators, biotechnology, drug delivery, and other lab-on-a-chip devices.

A tunable-focus liquid lens using an iris diaphragm is demonstrated. In the central opening area, two immiscible liquids with different refractive indices meet, resulting in a curved shape with a contact angle on the blade surface of the diaphragm. The liquids with a curved shape exhibit a lens character. By changing the aperture of the diaphragm, the shape of the liquid is changed accordingly which, in turn, leads to tunable focal length. Based on this operation approach, the focal length (f) of our lens could be tuned in the range of 13 ≤ f ≤ 105 cm when its aperture is changed from 1.3 to 3.2 mm. At f = 105 cm, the resolution of our lens can resolve over 45 line pairs per millimeter at room temperature. Our liquid lens, by changing aperture size, has the advantages of compact structure, easy operation, large optical power, and multistability.

We report a novel optical switch and display using fringing field-induced aperture change of a bracelet-like liquid ring. To prove concept, we demonstrated a 4times4 color pixel array and a black-and-white single pixel for an optical switch. Without an electric field, the pixel has the largest clear aperture. The applied fringing field stretches the liquid surface, leading to a decreased aperture size. For a 230-μm-diameter pixel, the switchable aperture ratio is over 80% and the response time is ∼10 ms. This device has following advantages: polarization independence, fast response time, and easy fabrication.

We demonstrate a single-pixel color display based on voltage-stretchable liquid crystal (LC) droplet. The gray scale is induced by stretching a dye-doped LC droplet from a small circular visible area to different extent through dielectrophoretic force. This polarization-insensitive liquid display shows a relatively low operating voltage, fast response, wide viewing angle and good contrast ratio. Both transmissive and reflective modes can be configured.

The discrepancy of disparity and accommodation in current 3D display systems is one source of discomfort for the audience. To solve this problem, an adaptive focus integral image (InIm) system is proposed, which could adjust the image location according to the video content. To prove concept, a fast-response liquid crystal microlens is proposed and its performance is simulated.

We report the electro-optical properties of dielectric liquid droplets based on dielectrophoretic effect. Due to dielectric force, the surface of each droplet can be reshaped which in turn alters its focusing behaviors. Our experimental results show that a deformed droplet can recover to its original shape with a negligible hysteresis. Both amplitude and frequency of the applied voltage play important roles affecting the droplet's shape change. The rise time is mainly governed by the applied voltage: for a given frequency a higher voltage results in a faster rise time. On the other hand, the decay time is jointly determined by the interfacial surface tensions, droplet size, and viscosity of the employed liquids.

We propose an adaptive dielectric liquid microlens whose focal length can be tuned from negative to positive or vise versa. The biconcave polymer base in the lens cell not only generates an inhomogeneous electric field, inhibits drifting of the droplet, and reduces the operating voltage but also induces a negative optical power. Pairing with the top subliquid lens, the whole lens exhibits a tunable negative and positive optical power under different driving voltages. To prove this concept, we fabricated such a dielectric liquid microlens and evaluated its performance. The biconcave polymer base can be particularly designed to obtain different dynamic range as desired.

We demonstrated a liquid crystal (LC) microlens array by assembling the phase separation morphology of liquid crystal (LC) and liquid monomer using a fringing field. The prepared lenticular microlenses can present a switchable focus with good optical characteristics. Our lenticular microlens array has promising applications in imaging processing and switchable 2D/3D displays.

Based on creep-induced deformation of a polyvinyl chloride (PVC) gel in an electric field, a Fresnel zone plate (FZP) is fabricated. The employed electrode is constructed with a series of concentric zones, and the soft PVC gel coated on the electrode forms a flat membrane. By applying a DC voltage to the electrode, electrons are injected to the PVC gel. Due to the generated electrostatic force, the surface of the PVC membrane is undulated. The configuration of the PVC membrane resembles the pattern of the electrode. As a result, the PVC membrane functions as an FZP. The results show that incident light passing through the FZP can be diffracted, producing a focused spot due to constructive interferences. The maximum diffraction efficiency can reach ∼32.5 % , and the focal length is switchable. The advantages of this FZP are the ease of manufacturability, compactness, large size, and optical isotropy.

We prepared a variable optical attenuator (VOA) at λ ~ 1.55 μm using dielectrically actuated liquids. This VOA works in the principle of absorption. Electro-optical characteristics of this VOA were measured in both transmissive and reflective modes. Compared to transmissive mode, reflective mode could offer much larger attenuation without changing other performances. By applying a voltage of 27 Vrms, this VOA could obtain ~19 dB in transmissive mode, and 38 dB in reflective mode. It had insertion loss (IL) of ~0.76 dB with negligible polarization dependent loss (PDL) at various voltages. Due to its competitive features such as voltage actuation, optical isotropy, and large attenuation with zero PDL, this VOA in reflective mode has potential applications in fiber-optic switches, sensing, and other infrared attenuators.

We report the gravity effects on the shape and focal length changes of liquid droplets. As the droplet size decreases, the gravity effect is gradually weakened. Moreover, if the outside space of the droplet is filled with another immiscible liquid rather than air, the filled liquid helps to offset the gravity effect even though their densities do not match well. Good agreement between experiment and simulation is obtained. The negligible gravity effect enables us to improve the optical performances of the liquid lens by choosing suitable liquids without worrying their density mismatch.

We study a tunable-focus lens with convex and flat electrodes in a homogeneous liquid crystal (LC) cell. In a voltage-on state, a centro-symmetric gradient refractive index is generated within the LC layer, which causes the focusing behavior for the extraordinary wave. There have been experimental studies of the systems with spherical or parabolic shape of the top electrodes and there is a need in the theoretical modeling. We present a theoretical model of the lens with spherical top electrode and analyze its properties. We solve the Maxwell equations that are coupled to the Euler–Lagrange equations from the variational principle applied to the total free energy minimization. LC director spatial profile is found subject to the applied voltage. After that the phase retardation profile of the test light beam is calculated and thus a focal length dependence on the applied field. The simulation results agree well with experimental data. This LC lens has advantages in relatively large focal length range and low operating voltage.

Soft electroactive materials including dielectric elastomer actuators (DEAs) and polyvinyl chloride (PVC) gels have recently been extensively investigated. These smart materials can effectively respond to an electric field, resulting in shape deformation. In addition to artificial muscles, actuators, sensors, and micro-electromechanical systems, they can be used to prepare various adaptive lenses with unique features such as a simple fabrication, compact structure, good flexibility, and light weight. In contrast to DEAs, PVC gels can provide exciting opportunities for emerging applications in imaging, sensing, optical communication, biomedical engineering, and displays. In this review paper, the underlying physical mechanisms of these two electroactive materials are explained first, and then some recent progress in their application in macro-sized lenses and microlens arrays is presented. Finally, future perspectives of the PVC gels are discussed.

Tight focusing of laser light using a polarization converter and an adaptive lens is demonstrated. The polarization converter is used to convert the linearly polarized light into a radially polarized light. The adaptive lens is used to focus the radially polarized light on a spot. At the focused spot, a large component of the electric field is along the longitudinal direction, and the focused power density is enhanced. The size of the focused spot can be changed by changing the focal length of the lens. When the focal length of the lens becomes shorter, the focused spot becomes tighter. The mechanisms of the two devices are introduced, and the theory of tight focusing is experimentally supported. Tight focusing of radially polarized laser light with a controllable spot size has potential applications in super-resolution imaging, material processing, and microparticle trapping.

A polymer-dispersed liquid crystal (PDLC)-based variable optical attenuator (VOA) was demonstrated to exhibit a relatively small polarization dependent loss (PDL) in the optical communication C band. The influence of the PDLC characteristics, the temperature, as well as the wavelength of the laser irradiation, on the PDLC VOA performance was analyzed. The PDL, the insertion loss at saturated voltage, and the operating voltage of the PDLC-based VOA were reduced by optimizing the fabrication conditions and applying a bias voltage to the PDLC cells during polymerization-induced phase separation.

We report a new approach to preparing a lenticular microlens array (LMA) using polyvinyl chloride (PVC)/dibutyl phthalate (DBP) gels. The PVD/DBP gels coated on a glass substrate form a membrane. With the aid of electrostatic repulsive force, the surface of the membrane can be reconfigured with sinusoidal waves by a DC voltage. The membrane with wavy surface functions as a LMA. By switching over the anode and cathode, the convex shape of each lenticular microlens in the array can be converted to the concave shape. Therefore, the LMA can present a large dynamic range. The response time is relatively fast and the driving voltage is low. With the advantages of compact structure, optical isotropy, and good mechanical stability, our LMA has potential applications in imaging, information processing, biometrics, and displays. (C) 2016 Optical Society of America

We demonstrate a thin flat polymeric microlens for improving the aperture ratio and light efficiency of an LCD; a tunable-focus LC lens for imaging processing and switchable 2D/3D displays, and a liquid lens with large focal length tenability for beam steering and machine vision. Detailed device structure and operation mechanism of each lens will be described.

By filling a liquid droplet in the hole of a dielectric elastomer (DE) film directly, we prepared two small liquid lenses. The aperture of one lens is macro size and the other is micro size. The liquid droplet in each hole of the DE film exhibits a lens character due to its biconvex shape. In relaxed state, the focal length of each liquid droplet is the longest. When a sufficiently high DC voltage is applied, the diameter of each DE hole is decreased by the generated Maxwell stress, causing the curvature of its droplet to increase. As a result, the focal length of each lens is reduced. Here the DE film functions as an actuator. In contrast to previous approaches, our miniature liquid lenses possess the advantages of simple fabrication, fast response time (~ 540 ms), and high optical performance (~ 114 lp/mm). Moreover, the micro-sized liquid lens presents good mechanical stability.

A dielectric liquid lens is prepared based on our previous work. By optimizing the device structure, the liquid lens presents a converging focus with good resolution and changes its focal length over a broad range with a low driving voltage. For a liquid lens with ~2.3 mm diameter in the relaxed state, it can resolve ~40 lp/mm. The resolution does not degrade during focus change. Its focal length can be varied from ~12 to ~5 mm when the applied voltage is changed from 0 to 28 Vrms. The response time of one cycle is ~2.5 s. Our liquid lens, with a low driving voltage for a large dynamic range, has potential applications in imaging, biometrics, optoelectronic, and lab-on-chip devices.

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 similar to 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. (C) 2015 Optical Society of America

We have developed a new guest-host reflective display using a dye-doped dualfrequency liquid crystal (DFLC) gel. By combining dye absorption and maximal light scattering, the display is polarization independent and exhibits a high contrast (� 230:1). The high reflectivity (R � 50%) is because of the vertical aligned structure at 0 Vrms. The fast response time (� 5ms) is also fast due to the frequency modulation. A black and white segmented-alphabet reflective display prototype is also demonstrated.

A polymer-based flat microlens array is demonstrated. Within each pixel of the array, the polymer presents a circular central-symmetric inhomogeneous orientation. Pixel with such a structure behaves a lens-like character. A suitable amount of liquid crystal mixed in the polymer host can improve not only the lens flexibility but also the lens performance. Moreover, the polymer-based microlens array has the advantages of real planar surface, ultra-thin thickness, and can be designed with any aperture size.

A lightweight in-plane-switching liquid crystal display (IPS-LCD) using a single glass substrate and an anisotropic polymeric film is demonstrated. The liquid crystal molecules are aligned by the elongated polymer grain of the film. The alignment capability of the anisotropic film is comparable to a buffed polyimide layer. Compared to the LCD using two glass substrates, our new device exhibits a comparable contrast ratio (/spl sim/514:1), driving voltage, and response time because of good LC alignment. Such an anisotropic film can also function as a phase compensation film for widening the viewing angle. This technology is particularly attractive for making single-substrate displays and also has potential for a double-layered guest-host display and a flexible display using IPS LCDs.

A high-contrast, fast-response, and polarizer-free reflective display using a dye-doped dual-frequency liquid crystal gel is demonstrated. The high contrast ratio originates from the combination of light scattering from the microdomain polymer gel and absorption from the black dyes. The fast response is due to the frequency modulation of the dual-frequency liquid crystal.

A flat microlens array whose focal length can be switched from positive to negative by electric field is demonstrated experimentally and confirmed by computer simulations. To generate the required gradient refractive index, an inhomogeneous electric field is created by a spherical indium-tin-oxide (ITO) electrode which is imbedded in the top flat substrate. The bottom substrate has a planar ITO electrode on its inner surface. A thin polymeric layer is overcoated on top of the spherical ITO to create a flat surface. The disclination lines are eliminated. Because of the employed dual-frequency liquid crystal, the microlens array has fast response times.

A microlens array made of polymer/nanosized polymer-dispersed liquid crystal (nano-PDLC) is demonstrated. The polymer was first patterned into microlens array cavities on a planar substrate and the molded polymer cavities were filled with nano-PDLC material. The nano-PDLC-based microlens is optically transparent. The focal length of the microlens is electrically tunable and the response time is about 200 μs during focus change. Such an electrically tunable-focus lens is a broadband device and its performance is independent of light polarization. A tradeoff is the high operating voltage.