Diffraction on birefringent elements with sine surface microrelief

Abstract— Light diffraction on optically anisotropic substrates using sine surface microrelief has been calculated by using the OAGSM method. The influence of the microrelief depth and material birefringence on the diffraction intensity on the order of 0–3 is reviewed and discussed. The results are compared with the results of the calculation for a rectangular microrelief. The microrelief depth and material birefringence allows the realization of different polarization states of the light beam transmitted or reflected by the substrate. The approach can be used to control the light‐beam propagation for different applications including LCD backlights.     

Polarized light diffraction on anisotropic substrates with rectangular and sine microrelief

Abstract— Light diffraction on optically anisotropic substrates with surface microrelief has been calculated by using the OAGSM method. Varying the microrelief depth and material birefringence allows us to realize different polarization states of the light beam transmitted or reflected by the substrate. The approach can be used to optimize the LCD backlight and control light‐beam propagation for different puposes.     

Electro‐optical parameters of FLC layers stabilized by a typical polymer net

Abstract— A typical polymer net with microcells of different sizes (from 25 × 25 to 200 × 200 μm) was formed by using a lithographic process, both on glass and flexible polymeric substrates. To investigate the influence of polymeric walls on FLC‐display cell operation, the typical electro‐optical parameters of FLC layers — light transmission and scattering, optical contrast ratio and response time — were measured under different conditions, such as display cell preparation and processing, driving voltage, microcell dimensions, and temperature.     

Narrowing of a light spot at diffraction of linearly-polarized beam on binary asymmetric axicons

To compensate widening of the central light spot which inevitably arises at linear polarization of a beam illuminating high-numerical-aperture axicon we propose to introduce an asymmetry in axicon structure. Experimental research of diffraction of Gaussian beam by three types of binary microaxicons with the period close to wavelength was carried out by means of near-field microscope. Diffractive optical elements with the period of 500 nanometers and various height of a microrelief have been fabricated by e-beam lithography. Narrowing of a central light spot formed by asymmetric microaxicons was experimentally confirmed. Overcoming of the diffraction limit (down to FWHM = 0.32λ) was observed in a near zone.     

Interaction of dielectric substrates in the course of tribometric assessment of the surface cleanliness

We look into theoretical and experimental aspects of tribometric interaction between two dielectric substrates with identical surfaces in the course of rapid analysis of their cleanliness. It is shown that if the coefficient of sliding friction equals that of static friction the surface is can be defined as being of production grade. The tribometric interaction of the substrates is experimentally shown not to result in a mechanical damage of the surface under study. It is suggested that the device should be complemented by a diffraction grating that generates light pulses. Based on the grating parameters, such as light pulse duration, average sum of three pulses, and degree of their deviation from reference values, the level of substrate surface cleanliness is assessed. The use of the diffraction grating of period T = 63 μm and slit width b = 20 μm is shown to pro vide a 16-fold increase in the resolution of the tribometric device. The text was submitted by the authors in English.     

ZnO nanowires for LED and field‐emission displays

Abstract— The use of ZnO nanostructures in various display applications is reported. Single‐crystalline vertically oriented nanowires with typical diameters of 100 nm and a length of 1–2 μm were grown at deposition temperatures below 100°C. Homogeneous growth over areas up to 50 cm² on Si as well as on various metallic, transparent, and flexible substrates were obtained. Visible electroluminescence in the region between 400 and 900 nm and narrow‐line near‐ultraviolet (UV) electroluminescence is demonstrated. The physical conditions leading to single‐crystalline growth at low temperature, the role of defects, and the possibility of doping are discussed. These issues present the main challenges on the road towards high emission rates in LED operation. Under certain conditions, sharply tipped wires can be grown that hold promise for field‐emission applications.     

Electric and magnetic fields in photoalignment of liquid crystals

The results of investigation of slow surface dynamics (easy axis gliding), induced by secondary illumination of photoaligned substrates with linearly polarized UV or blue light in the presence of electric (magnetic) fields, are presented for the first time. The initial surface orientation of nematic liquid crystal (NLC) was provided, in accordance with the standard photoalignment technique, via preliminary UV treatment of the glass substrates coated by sulfonic azo‐dye SD1 film. The experiments fulfilled for the two geometries, A and B, corresponding to the normal (A) and parallel (B) orientation of fields relatively to liquid crystal (LC) layer, revealed different effects induced by electric (magnetic) fields. For geometry A, strong electric field applied, in combination with a linearly polarized blue light, to the planar layer in a sandwich‐like LC cell with two photoaligned substrates results in simultaneous reorientation of easy axis on both substrates. It demonstrates the possibility of an azimuthal rotation of monodomain planar samples of LCs. For geometry B, usage of “in‐plane” electric (magnetic) fields in the cell, composed of photoaligned and rubbed substrates, speeds up reorientation process of NLC easy axis respectively to pure light‐induced reorientation. It provides electric control of operating times in previously proposed optical rewritable technology.     

Design and experiment of optical transparent microstrip antenna on glass and polycarbonate substrates

Microstrip antennas have the advantages of light weight, low profile, and conformal to the attached surface with antenna feed line. This work presents the design of transparent microstrip antennas by In₂O₃:Sn thin film on glass and polycarbonate substrates. The transparent conducting thin films of 21–300 nm thickness deposited by magnetron sputtering are measured by X‐ray diffraction for microstructure, 4‐point probe for electrical resistance, and spectrometer for optical transmittance. Analyses show that the 2.4 GHz antenna can achieve 5.1 and 4.7 dB antenna gain on glass (1.2 mm) and polycarbonate (0.7 mm) substrate, respectively. Experimental verification on glass substrate shows that the antenna achieves 3.1 dB gain and 86% optical transmittance on 550 nm wave length.     

Mura‐detection method by using a slit‐beam ellipsometer

Abstract— A slit‐beam ellipsometer which performs sensitive mura detection of thin films on transparent substrates has been developed. Mura is a Japanese term which means the non‐uniformity of the thin‐film thickness, the dielectric constant, etc. The mura thickness of polyimide films and the mura thickness of the surface of polyimide films caused by rubbing along a 30‐mm‐long slit beam was observed. This ellipsometer only detects the reflected light from the rubbed polyimide films onto the transparent substrates. As a result, sensitive MURA detection is achieved. The slit beam generated by a cylindrical lens is irradiated onto a sample. The reflected light from the sample becomes collimated light passing through another cylindrical lens and is detected by a 2048‐pixel CCD liner sensor. In addition, the in‐line use of slit‐beam ellipsometer was examined. When the slit‐beam ellipsometer is set up during the rubbing process, the optimum set up, where rubbing mura‐detection becomes highly sensitive, was determined.     

Polarization‐independent modulation for projection displays using small‐period LC polarization gratings

Abstract— Progress in the use of liquid‐crystal polarization grating (LCPG) to modulate unpolarized (and polarized) light with a grating period as small as 6.3 μm is reported. Similar to LCPGs formed at larger periods (11 μm) reported previously, polarization‐independent switching, predominantly three diffraction orders, maximum contrast ratios of ～100:1 for unpolarized broadband light, very low scattering, and diffraction efficiencies >98% continue to be observed. The smaller period led to an expected lower threshold voltage, even though the thickness was greater. Because the smaller grating period enables a brighter result from a Schlieren projection scheme for a microdisplay using the LCPG light valve, the inherent tradeoffs involved with both material and design parameters are discussed, and prospects for a polarization‐independent projection display are commented upon.     

A study of electro‐optical characteristics depending on LC pre‐tilt angle and cell gap in a full‐HD LCOS panel

Abstract— The goal of this work is to achieve a better understanding of the electro‐optical characteristics of a VA‐mode full‐HD LCOS panel via simulations and experiments. The optical parameters, such as reflectance, fill factor, and contrast that vary due to the pre‐tilt angle and cell gap, were also studied. Based on the simulations, the optical fill factor was the highest at an angle of 81° and 2.1 μm under the given conditions. The contrast ratio was the highest at an angle of 89° and 2.4 μm. Five different LCOS panels were fabricated; three different angles (85°, 87°, and 89°) at a 2.1‐μm cell gap and two different cell gaps (1.8 and 2.1 μm) at an angle of 87°. The measured reflected light intensity was compared to the calculated reflectance. The simulated and measured contrasts were compared with each other. The simulation results well‐matched the experimental results and the differences were less than a few percentage points. Based on the comparative studies on reflectance and contrast, the test panel under the condition of an 87° angle and 2.1‐μm gap showed the best performance results.     

Self-aligned positioning of microoptical components by precisionprismatic grooves impressed into metals

Grooves embossed into metallic substrates are proposed for self-aligned positioning of microoptical components like microlenses, optical fibers, glass rods with mirrors or filters, etc. As substrates, both ductile metals such as aluminum or copper, and hard alloys like CrNi steel can be used, which allows adaptation to requirements concerning thermal expansion coefficient, thermal conductance, hardness, mechanical strength, solderability, weldability, etc. Compared to other methods such as anisotropic etching in silicon substrates and LIGA, this technique offers more design flexibility and much lower investment cost and is well suited for medium production numbers. By the embossing process, the shape and surface quality of the embossing die are virtually transferred into the groove. The residual deviation between die and groove is in the order of 5-10 μm. The reproducibility is better than 5 μm, thus allowing self-aligned positioning with multimode fiber applications. Without reconditioning, several thousand embossing cycles can be made with the same die. The manufacturing of embossing dies is based on precision tooling techniques. The paper concludes with two application examples of optical communication components     

Choosing the geometry of a halogenide antireflection grating profile based on etching technique capabilities

This work studies the propagation of middle IR laser radiation through an antireflection relief fabricated on the optical surface (made of silver halohenide). A new technology of microrelief fabrication that allows its antireflection properties to be enhanced is proposed.     

Surface‐treatment effects of a sapphire substrate by He+‐, Ar+‐, and Xe+‐ion implantations for GaN epitaxial layers

Abstract— The structural, electrical, and optical properties of GaN epilayers grown on various ion‐implanted sapphire(0001) substrates by MOCVD were investigated. GaN or AlN buffer layers and pre‐treatment were indispensably introduced before GaN‐epilayer growth. The ion‐implanted substrate's surface had decreased internal free energies during the growth of the ion‐implanted sapphire(0001) substrates. The crystal and optical properties of the GaN epilayers grown in ion‐implanted sapphire(0001) substrates were improved. Also, an excessively roughened and modified surface caused by ions degraded the GaN epilayers. Not only the ionic radius but also the chemical species of implanted sapphire(0001) substrates improved the properties of the GaN epilayers grown by MOCVD. It is obvious that the ion‐implanted pre‐treatment of sapphire(0001) substrates can be an alternative pre‐treatment procedure for GaN deposition and has the potential to improve the properties of the GaN epilayers on sapphire(0001) substrates.     

Digital lithographic processing for large‐area electronics

Abstract— A non‐contact jet‐printed mask‐patterning process is described. By combining digital imaging with jet printing, digital lithography was used to pattern a‐Si:H‐based electronics on glass and plastic substrates in place of conventional photolithography. This digital lithographic process is capable of layer‐to‐layer registration of ±5 μm using electronic mask files that are directly jet printed onto a surface. Aminimum feature size of 50 μm was used to create 180 × 180 element backplanes having 75‐dpi resolution for display and image‐sensor applications. By using a secondary mask process, the minimum feature size can be reduced down to ～15 μm for fabrication of short‐channel thin‐film transistors. The same process was also used to pattern black‐matrix wells in fabricating color‐filter top plates in LCD panels.     

Structural, optical and electrical properties of CdO/Cd(OH)2 thin films grown by the SILAR method

Successive Ionic Layer Adsorption and Reaction (SILAR) was used to form Cd(OH)₂ thin films from aqueous cadmium–ammonia complex on glass substrates at room temperature and the thermal annealing effect on thin films was studied. The as-deposited films were annealed at 200, 300 and 400 °C for 1 h in an oxygen atmosphere for conversion from Cd(OH)₂ to CdO and change in the structural, optical and electrical properties of the films and the effect of the light on the electrical properties of the films were investigated. The structural and surface morphological properties of the films were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that Cd(OH)₂ phase is converted into the cubic CdO films by annealing. The band gap energy values of films decreased from 3.59 to 2.13 eV through increasing annealing temperature. It was found that the current increased with increasing light intensity and CdO films were more conductive than the as-deposited films.     

Study on parasitic and channel resistance of poly‐Si thin‐film transistors by metal‐induced crystallization

Abstract— The channel‐length‐dependent transfer characteristics of TFTs using poly‐Si by metal‐induced crystallization through a cap (MICC) of a‐Si to evaluate the parasitic and channel resistances have been studied. The MICC p‐channel TFTs studied in the present work showed a maximum field‐effect mobility, threshold voltage, and gate swing of 53 cm²/V‐sec, −4.4 V, and 0.8 V/dec for W/L = 12 μm/6 μm, 71 cm²/V‐sec, −5.3 V, and 0.9 V/dec for W/L = 12 μm/12 μm, and 113 cm²/V‐sec, −7 V, and 1 V/dec for W/L = 12 μm/24 μm, respectively. It is found that the parasitic resistance is higher than the channel resistance, and both decrease with increasing temperature.     

Vertically integrated,double stack oxide TFT layers for high‐resolution AMOLED backplane

We developed a novel vertically integrated, double stack oxide thin‐film transistor (TFT) backplane for high‐resolution organic light‐emitting diode (OLED) displays. The first TFT layer is bulk‐accumulation mode, and the second TFT layer is a single gate with back‐channel etched structure. The extracted mobilities and threshold voltages are higher than 10 cm²/Vs and 0 ~ 1 V, respectively. Both TFTs are found to be extremely stable under the bias and temperature stress. The gate driver with width of 530 μm and a pitch of 18.6 μm was developed, exhibiting well shifted signal up to the last stage of 900 stages without output degradation, which could be used for 1360 ppi TFT backplane.     

Dimensioning a full color LED microdisplay for augmented reality headset in a very bright environment

This paper focuses on the dimensioning of a very bright full color 10 μm‐pitch light‐emitting device (LED) microdisplay for avionics application. Starting from the specifications of head‐mounted display to be used in an augmented reality optical system, a theoretical approach is proposed that enables predicting the specifications of the main technology building blocks entering into the microdisplay manufacturing process flow. By taking into account various material and technological parameters, kept as realistic as possible, it is possible to assess the feasibility of a very bright LED microdisplay (1 Mcd/m² full white) and to point out the main limitations. The theoretical specifications are then compared with the technical results obtained so far in the framework of the H2020 Clean Sky “HILICO” project. It shows that 350 000 cd/m² of white emission may be accessible with the present gallium nitride (GaN)‐micro‐LED technology provided a color conversion solution with stable external quantum efficiency of 30% is available. Beyond such level of luminance, the inherent limitations of driving circuit (4 V, 15 μA per pixel) commands working with materials enabling higher external quantum efficiency (EQE). In particular, 10‐μm‐pitch micro‐LEDs with electroluminescence EQE of 15% and color conversion EQE approaching 60% are needed, opening the way to future challenging material and technology research developments.     

Low‐temperature‐applicable polymer‐stabilized blue‐phase liquid crystal and its Kerr effect

Abstract— A type of polymer‐stabilized blue‐phase liquid crystal, which can be used in a low‐temperature environment, is proposed. The blue‐phase range after polymerization was widened to more than 73°C, and the blue‐phase texture is very stable even at a temperature as low as ?35°C. The electro‐optical performances dependence on polymer concentration was investigated. The results indicate that the saturation voltage increases and the hysteresis enhances as the polymer concentration increases. The rise and decay times could reach as low as 391 and 789 μsec, respectively. Such material also shows good electro‐optical behavior at a temperature of ?35°C. In addition, the Kerr constant was tested under a uniformly distributed electric field to be 2.195 nm/V² at room temperature and 2.077 nm/V² at ?35°C. The Kerr constant tested under white‐light illumination was 1.975 nm/V², which shows a small dispersion.