Surface plasmonic lightening characteristics through liquid crystal microlens arrays controlled electrically

We demonstrate an efficient method for fabricating high-quality cylindrical microlens arrays (CMLAs) on the surface of fused silica, fully based on spatially shaping of a femtosecond laser beam from Gaussian to Bessel distribution. As the envelope of shaped spatial intensity distribution matches the profile of cylindrical microlens perfectly, a CMLA with more than 50 uniform microlenses is fabricated by simple line scanning. The radius and height of these microlens units can be finely controlled by adjusting the power of laser pulses. Excellent optical imaging and high-speed fabrication performances are also demonstrated by our fabricated CLMA.

The cylindrical microlens array (CMLA) is an important micro-optical component, it has very significant application effects in the fields of naked eye three-dimensional display, laser line generation, and deformed beam shaping. However, the high efficiency and low-cost manufacturing of large-area CMLA is still challenging for industry and academia. Based on the electric-field-driven (EFD) jet printing technique, a new method for manufacturing a large-area CMLA with high efficiency and low cost has been proposed. We use the theoretical analysis and numerical simulation to investigate the basic principle of EFD jet printing. The influence of process parameters on the formation of CMLA was revealed by experiments. Using optimized process parameters, the fabrication of a CMLA with a patterned area of 50 × 50 mm2, a line width of 70 μm, and a period of 100 μm was achieved. The geometric and optical properties of the fabricated CMLA were characterized, showing that the products have the good geometric appearance and focusing effect. The results show that the proposed fabrication method provides a new manufacturing process for large-area manufacturing of CMLA with high efficiency and low cost.

Gradient index micro lenses for laser diode applicationsR. Goering, T. Possner, B. MesserschmidtFraunhofer Institution for Applied Optics and Precision EngineeringSchillerstrasse 1 , 07745 Jena, GermanyABSTRACTCollimating and diverging cylindrical micro lenses with N.A. up to 0.60 fabricated by thermal silver ion exchangein a special designed glass type are reported. Cylindrical microlens arrays are fabricated by field assistet ion-exchange. Applications to fiber coupling as well as to diode bar collimation are discussed.Keywords: ion-exchange, GRIN-components, laser diode beam shaping, laser bar collimation, fiber coupling1. INTRODUCTIONMicrooptical GRIN-lenses with high N.A. are very useful for the transformation of the strongly divergent andasymmetric beam emitted from semiconductor laser diodes and laser diode bars to a well-collimated beam orto a focused spot. Preferred applications are the coupling between laser diodes and optical fibres, the pumpingof solid state lasers as well as optical scanning. High N.A., a nearly diffraction limited pertormance and lensdimensions of a few hundred microns are required. In a previous paper we presented the formation of one-dimensional cylindrical microlenses by a two step silver ion-exchange process1. Here we would like to discussthe optimization of these components and a number of new elements fabricated by similar ion-exchangeprocesses and applications which could not be realized by standard SELFOC-lenses.Figures 1 and 2 show flat GRIN-components and ion-exchange techniques for their realization. The formationof diverging lenses is possible in a single ion-exchange step. For the generation of cylindrical collimating lenseswe use a two step process, proposed by Ohmi2. Cylindrical microlens-arrays are produced by a field-assistedexchange using a masked substrate.Fig. 1: Thermal ion-exchanged GRIN components

The all-optical magnetization reversal of magnetic layers, by picosecond optical pulses, is of particular interest as it shows the potential for energy-efficient and fast magnetic tunnel junction (MTJ) elements. This approach requires memory elements that are optically and electronically accessible, for optical writing and electronic read-out. In this paper, we propose the integration of indium tin oxide (ITO) as a transparent conducting electrode for magnetic tunnel junctions in integrated spintronic–photonic circuits. To provide light with sufficient energy to the MTJ free layer and allow electrical read-out of the MTJ state, we successfully integrated indium tin oxide as a top transparent electrode. The study shows that ITO film deposition by physical vapor deposition with conditions such as high source power and low O2 flow achieves smooth and conductive thin films. Increase in grain size was associated with low resistivity. Deposition of 150 nm ITO at 300 W, O2 flow of 1 sccm and 8.10−3 mbar vacuum pressure results in 4.8 × 10−4 Ω.cm resistivity and up to 80% transmittance at 800 nm wavelength. The patterning of ITO using CH4/H2 chemistry in a reactive ion etch process was investigated showing almost vertical sidewalls for diameters down to 50 nm. The ITO based process flow was compared to a standard magnetic tunnel junctions fabrication process flow based on Ta hard mask. Electrical measurements validate that the proposed process based on ITO results in properties equivalent to the standard process. We also show electrical results of magnetic tunnel junctions having all-optical switching top electrode fabricated with ITO for optical access. The developed ITO process flow shows very promising initial results and provides a way to fabricate these new devices to integrate all-optical switching magnetic tunnel junctions with electronic and photonic elements.

We propose a multi-view 2D/3D switchable display by using cylindrical liquid crystal (LC) lens array with a low operating voltage and fast response time. The cylindrical LC lens array is composed of three parts: the LC layer, a top-plane indium tin oxide (ITO) electrode, and bottom periodic strip ITO electrodes. In the voltage-off state, the cylindrical LC lens array is equivalent to a transparent glass substrate and the viewers can see a clear 2D image. In the 3D mode, the cylindrical LC lens array can be used as a cylindrical lens array under a suitable operating voltage. As a result, the 2D and 3D images can be switched according to the state of the cylindrical LC lens array. The experimental result shows that the 2D/3D switchable display with the cylindrical LC lens array has a wider viewing angle, has no moiré pattern, and is much thinner compared to the other 2D/3D switchable display devices.

Light-field imaging is a crucial and straightforward way of measuring and analyzing surrounding light worlds. In this paper, a dual-polarized light-field imaging micro-system based on a twisted nematic liquid-crystal microlens array (TN-LCMLA) for direct three-dimensional (3D) observation is fabricated and demonstrated. The prototyped camera has been constructed by integrating a TN-LCMLA with a common CMOS sensor array. By switching the working state of the TN-LCMLA, two orthogonally polarized light-field images can be remapped through the functioned imaging sensors. The imaging micro-system in conjunction with the electric-optical microstructure can be used to perform polarization and light-field imaging, simultaneously. Compared with conventional plenoptic cameras using liquid-crystal microlens array, the polarization-independent light-field images with a high image quality can be obtained in the arbitrary polarization state selected. We experimentally demonstrate characters including a relatively wide operation range in the manipulation of incident beams and the multiple imaging modes, such as conventional two-dimensional imaging, light-field imaging, and polarization imaging. Considering the obvious features of the TN-LCMLA, such as very low power consumption, providing multiple imaging modes mentioned, simple and low-cost manufacturing, the imaging micro-system integrated with this kind of liquid-crystal microstructure driven electrically presents the potential capability of directly observing a 3D object in typical scattering media.

In order to optimize the preparation process of microlens arrays, improve preparation efficiency, and reduce preparation costs, 248 nm KrF excimer laser direct writing is combined with a motion mask to prepare microlens arrays on PMMA substrates. Firstly, a specific exposure mask based on the contour characteristics of the microlens unit was designed, and the preparation principle was analyzed. Using COMSOL Multiphysics 6.3 simulation software, a microlens preparation model was built to intuitively describe the process of preparing microlenses by the motion mask method. Secondly, a preparation system was built, and the laser processing technology was optimized. Finally, microlens arrays were prepared based on the optimized process, and an optical microscope and white-light interferometer were used to observe their morphology. The experimental results show that this method can effectively prepare cylindrical and circular microlens arrays. The width of the cylindrical microlens array unit exceeded 90 μm, the height was 7.08 μm, and the roughness was 0.09 μm. The diameter of the circular microlens array unit was φ100 μm, the height was 4 μm, and the curvature radius was 230 μm. The geometric dimensions of the mask can be adjusted to obtain microlens units of the desired size, achieving personalized preparation of microlens arrays. The excimer laser motion mask method can prepare various types of microlens arrays, and the array units have a high consistency and high surface quality, which helps to improve the efficiency, flexibility, stability, and specificity of microlens array preparation.

In this study, indium tin oxide (ITO) films were deposited at 300°C on glass substrates by low-frequency (60 Hz) magnetron sputtering technique. The influence of oxygen flow rate on the structural, electrical and optical properties of ITO thin films was investigated. The oxygen flow rate was varied from 0 to 8 sccm. We obtained the most superior property of ITO films at oxygen flow rate of 0.5 sccm. The films are found to show preferential orientation both (222) and (400) planes in the XRD patterns. The resistivity of the films with the thickness of 140 nm is 2.1 × 10−4 ohm · cm with 88% optical average transmittance in visible range (500–800 nm). Therefore, we conclude that transparent conducting ITO films prepared by low-frequency magnetron sputtering can be applied for various flat panel displays.

The liquid crystal (LC) device with the circle aperture electrode can be used as a convex lens. The index of refraction of the LC lens can be easily changed by the voltage signal; the arrayed LC lens can be used in the imaging sensors. Comparing with the traditional optical lens, the LC lens has a more effective architecture. In this paper, we present an imaging sensor with a new type LC structure composed of three layers of top electrodes and a joint bottom electrode, and simulating the tunable spatial resolution architecture carried out by applying voltage signal over different ITO electrode in LC lenses coupled with arrayed imaging sensors. From the result of the simulation, we can find that changing the spatial resolution by our architecture can be achieved.

PbLaZrTiOx (PLZT) thin films were deposited on Pt(111) substrate by the sol-gel method, then aluminum-doped zinc oxide (AZO) and indium tin oxide (ITO) top electrodes were deposited by pulsed laser deposition (PLD). We evaluated degradation characteristics by 3% hydrogen atmosphere annealing in 200°C, 1Torr. The polarization ratio of PLZT capacitors with 200 nm top electrodes thickness was maximum value at the same Pb contents. We also evaluated fatigue behavior by applying 10 V, 100 μs pulse width and 1 ms interval cycles. PLZT capacitors with AZO and ITO top electrodes were robust electrodes over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> cycles compared with Pt top electrodes.

Sputtered indium tin oxide (ITO) fulfills the requirements of top transparent electrodes (TTEs) in semitransparent perovskite solar cells (PSCs) and stacked tandem solar cells (TSCs), as well as of the recombination layers in monolithic TSCs. However, the high-energy ITO particles will cause damage to the devices. Herein, the interface reactive sputtering strategy is proposed to construct cost-effective TTEs with high transmittance and excellent carrier transporting ability. Polyethylenimine (PEI) is chosen as the interface reactant that can react with sputtered ITO nanoparticles,so that, coordination compounds can be formed during the deposition process, facilitating the carrier transport at the interface of C60/PEI/ITO. Besides, the impact force of energetic ITO particles is greatly alleviated, and the intactness of the underlying C60 layer and perovskite layer is guaranteed. Thus, the prepared semitransparent subcells achieve a significantly enhanced power conversion efficiency (PCE) of 19.17%, surpassing those based on C60/ITO (11.64%). Moreover, the PEI-based devices demonstrate excellent storage stability, which maintains 98% of their original PCEs after 2000 h. On the strength of the interface reactive sputtering ITO electrode, a stacked all-perovskite TSC with a PCE of 26.89% and a monolithic perovskite-organic TSC with a PCE of 24.33% are successfully fabricated.

Sputtered transparent electrodes for optoelectronic devices: Induced damage and mitigation strategies

A conjugated polymer in neutral state is semiconductive. It becomes conductive after it is doped by oxidation or reduction. The optical properties of neutral conjugated polymers are predominantly determined by the electron transition from the highest occupied molecular orbital (HOMO) to the lowest unoccupied molecular orbital (LUMO), whereas the optical properties of conducting polymers are related to new energy levels, polaron and bipolaron levels, which are generated during oxidation or reduction. The appearance of the new energy levels significantly changes the optical properties. Some conjugated polymers with low energy band gap can have high transparency in the visible range after they are oxidized and become conductive. Poly(3,4-ethylenedioxythiophene) (PEDOT), its derivatives and analogues are the most popular transparent conducting polymers. This chapter reviews the preparation, structure, properties, and application of transparent conducting polymers, particularly the PEDOTs. PEDOTs can be prepared by solution chemical polymerization, vapor-phase polymerization, or electrochemical polymerization of its monomer. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) prepared by chemical polymerization in solution is particularly interesting because it can be dispersed in water and some polar organic solvents. High-quality PEDOT:PSS films can be readily prepared through solution processing techniques. Less conductive PEDOT:PSS has been used as the buffer layer in optoelectronic devices, such as organic and polymer light-emitting diodes (OLEDs and PLEDs) and organic and polymer solar cells (OSCs and PSCs). However, as-prepared PEDOT:PSS films from aqueous solution cannot be directly used as the transparent electrode of optoelectronic devices because its conductivity is below 1 S cm−1. This conductivity is lower than the conductivity of indium tin oxide (ITO), the conventional transparent electrode material, by three to four orders of magnitude. A couple of methods have been developed to improve significantly the conductivity of PEDOT:PSS. Conductivity of more than 3000 S cm−1 was recently observed with PEDOT:PSS films after treatment with acids. This conductivity is higher than that of ITO on plastic and comparable to ITO on glass. It is anticipated that the conductivity of PEDOT:PSS can be further increased if the molecular weight of PEDOT can be increased. Thus, transparent conducting polymers are very promising candidates to replace ITO as the next-generation of transparent electrode materials.

The effect of various electrode materials has been studied for organic nonvolatile memory devices using a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin film. The bottom electrodes (BEs) were indium tin oxide (ITO) and Al, while the top electrodes (TEs) were Al, Ti, Cr, ITO, Au, Ni, Pd, and Pt. The ITO/PEDOT:PSS/TE devices only had a bipolar switching behavior, while the Al/PEDOT:PSS/TE devices did not have any switching behavior unless a compliance current (CC) was used in the write-operation method. Then, they had a unipolar switching behavior irregardless of the TE material. Therefore, the BE material and the CC have crucial roles in the switching behavior and characteristics.

Using indium tin oxide (ITO) substrates as the bottom electrode and eutectic gallium and indium (EGaIn) as the top electrode, we successfully formed alkyl phosphate self-assembled monolayers (SAMs) on ITO and molecular junctions in the form of ITO-PO3(CH2)nH//GaOx/EGaIn (n = 8, 10, 12, 14, or 16). The tunneling decay coefficient (β, decay of charge transport rate vs. n) of junctions obtained from direct current (DC) methods is 0.90 n-1 with a log-injection current density (log10|J0|) of 1.87 A cm-2 at an applied bias of 0.5 V, which is confirmed by the impedance spectroscopy results from the resistance of the SAM (RSAM), indicating that the evolution of RSAM with molecular length is the main origin of decay of charge transport rate in the phosphate junctions. The dielectric constant (εr) values of PO3(CH2)nH SAMs measured in junctions range from 2.28 to 2.60, indicating that the semiconductor ITO substrates do not affect the dielectric and electrical responses of junctions. This work provides a compatible platform for studying the interfacial charge transport, dielectric responses, and even potential optical properties of a hybrid electronic system of organic molecules with phosphonic acid anchoring groups, semiconducting substrates and metallic electrodes.