Exit pupil expander with a large field of view based on diffractive optics

Abstract— The field of view is an important parameter of a near‐to‐eye display. To achieve an immersive viewing experience, the field of view should be as high as possible. Presently, in most of the commercially available devices the field of view is between 15° and 30°. In this paper, a large‐field‐of‐view exit pupil expander that is based on diffractive optics was demonstrated. Usually these types of diffractive expanders cannot have a field of view much more than 25°. Here, an exit pupil expander with an extended field of view, based on two stacked plates, was demonstrated. The expander is designed for green light and it achieves a field of view of more than 40°.     

Micromachined W-band polymeric tunable iris filter

A tunable filter working in the W-band spectrum has been successfully demonstrated using a combined plastic molding and electroplating process. The prototype filter architecture has two deformable membranes of 1.6 mm in diameter on top of a WR-10 waveguide based, two-cavity, polymeric iris filter. The membranes can be actively adjusted to deform and alter the cavity geometry concurrently for frequency tuning applications. The tunable filter was simulated using High Frequency Structure Simulator and theoretically analyzed using the perturbation method. Experimentally, a prototype band-pass filter has bandwidth of 4.05 GHz centered at 94.79 GHz and a minimum insertion loss of 2.37 dB with return loss better than 15 dB. As a tunable filter, a total of 2.59 GHz center frequency change has been recorded when the membranes deflected from 50 μm into, to 150 μm out of the waveguide. These results imply that the demonstrated tunable filter could be potentially applicable for waveguide-based mm-wave systems.     

Development and characterisation of integrated microfluidics on waveguide-based photonic platforms fabricated from hybrid materials

This article reports on a detailed investigation of sol–gel processed hybrid organic–inorganic materials for use in lab-on-a-chip (LoC) applications. A particular focus on this research was the implementation of integrated microfluidic circuitry in waveguide-based photonic sensing platforms. This objective is not possible using other fabrication technologies that are typically used for microfluidic platforms. Significant results on the surface characterisation of hybrid sol–gel processed materials have been obtained which highlight the ability to tune the hydrophilicity of the materials by careful adjustment of material constituents and processing conditions. A proof-of-principle microfluidic platform was designed and a fabrication process was established which addressed requirements for refractive index tuning (essential for waveguiding), bonding of a transparent cover layer to the device, optimized sol–gel deposition process, and a photolithography process to form the microchannels. Characterisation of fluid flow in the resulting microchannels revealed volumetric flow rates between 0.012 and 0.018 μl/min which is characteristic of capillary-driven fluid flow. As proof of the integration of optical and microfluidic functionality, a microchannel was fabricated crossing an optical waveguide which demonstrated that the presence of optical waveguides does not significantly disrupt capillary-driven fluid flow. These results represent the first comprehensive evaluation of photocurable hybrid sol–gel materials for use in waveguide-based photonic platforms for lab-on-a-chip applications.     

Fiber Bragg grating weighing sensor of beam with two parallel holes

Due to the strains of fiber Bragg gratings mounted on the gauge hole of beam with two parallel holes excited by the weight, a fiber Bragg grating weighing sensor is developed. During the double differential operation of the relation shifts of Bragg wavelength of these four mounted gratings, the shifts of Bragg wavelengths caused by the temperature fluctuation and the bending moment caused by the deflection load can be compensated. The loading and unloading experiments indicate that the delay of grating weighing sensor is 0.28%FS, and the repetition is 0.32%FS. Through the least-square algorithm fitting, the load response sensitivity of grating weighing sensor is 9.992 × 10⁻⁶ kg f⁻¹, and the fitting linearity is 0.6%FS. The temperature drift of grating weighing sensor is 0.02%FS/°C at the range of 20–60 °C. The fitting linearity is 1.5%FS under the action of deflection load.     

Wide field of view head-up displays

Head-up displays in current production aircraft have a restricted field of view caused by the relatively small diameter of the collimating optics. There is a growing interest in alternative designs which make a better field of view available to the pilot. Several possible design options for achieving a wide field are outlined. The new methods usually rely on the properties of diffractive optical elements to achieve a satisfactory performance with respect to accuracy, photometric efficiency and sunlight rejection. Some advantages arising from the particular characteristics of diffractive elements are considered. Most wide field of view displays are of the ‘projected porthole’ type, ie the exit pupil of the system is not within the equipment but is instead projected to the observer's eye position. Definitions of the instantaneous and total fields of view are discussed and compared with those for the conventional head-up display. As wide field of view displays become more readily available it is important to establish whether the additional cost and bulk of the equipment is justified by gains in operational efficiency. The paper concludes by outlining some possible uses of the larger field.     

Stability and convergence of sequential methods for coupled flow and geomechanics: Fixed-stress and fixed-strain splits

We analyze stability and convergence of sequential implicit methods for coupled flow and geomechanics, in which the flow problem is solved first. We employ the von Neumann and energy methods for linear and nonlinear problems, respectively. We consider two sequential methods with the generalized midpoint rule for t_n+α, where α is the parameter of time discretization: namely, the fixed-strain and fixed-stress splits. The von Neumann method indicates that the fixed-strain split is only conditionally stable, and that its stability limit is a coupling strength less than unity if α ? 0.5. On the other hand, the fixed-stress split is unconditionally stable when α ? 0.5, the amplification factors of the fixed-stress split are different from those of the undrained split and are identical to the fully coupled method. Unconditional stability of the fixed-stress split is also obtained from the energy method for poroelastoplasticity. We show that the fixed-stress split is contractive and B-stable when α ? 0.5.We also estimate the convergence behaviors for the two sequential methods by the matrix based and spectral analyses for the backward Euler method in time. From the estimates, the fixed-strain split may not be convergent with a fixed number of iterations particularly around the stability limit even though it is stable. The fixed-stress split, however, is convergent for a fixed number of iterations, showing better accuracy than the undrained split. Even when we cannot obtain the exact local bulk modulus (or exact rock compressibility) at the flow step a priori due to complex boundary conditions or the nonlinearity of the materials, the fixed-stress split can still provide stability and convergence by an appropriate estimation of the local bulk modulus, such as the dimension-based estimation, by which the employed local bulk modulus is less stiff than the exact local bulk modulus.We provide numerical examples supporting all the estimates of stability and convergence for the fixed-strain and fixed-stress splits.     

Thin-film sensor based tip-shaped split ring resonator metamaterial for microwave application

The artificially constructed materials based split ring resonators (SRRs) may have exotic electromagnetic properties and have received growing interest in recent years. Moreover, the resonance frequency shift of this material is extraordinarily sensitive to the changes in the capacitance of SRR, which makes SRR suit for microwave thin-film sensing applications. Based on such principle, the tip-shaped SRR metamaterial is presented as thin-film sensor in this paper to reduce device size and resonance frequency as well as to improve the Q-factor. The structure is placed inside an X-band waveguide with dimensions of 22.86 mm × 10.16 mm × 12.8 mm to investigate resonance frequency shift in different cases by numerical method. In contrast to the traditional structures, the tip-shaped design exhibits a miniaturization and sharper dip on resonance in their transmission spectra. Furthermore, the proposed sensor can deliver the sensitivity level of 16.2 MHz/μm and less than a 2 μm nonlinearity error when the uniform benezocyclobutene films from 100 nm to 50 μm thick are coated onto the fixed structure. These results indicate that the proposed thin-film sensor has high sensitivity and low nonlinearity error, and make it great promising application for wireless sensors in future.     

Metamaterial inspired CPW‐fed compact antenna for ultrawide band applications

A small size, planar and co‐planar waveguide fed metamaterial inspired antenna is proposed for ultra‐wideband (UWB) application. The main radiating element consists of three split‐ring resonators (SRR) and placed along one axis. Moreover, coplanar waveguide (CPW)‐fed line along with modified ground plane is used to improve the impedance matching. The physical size of proposed antenna is 25(W) × 22 (L) × 1.6 (H) mm³. The CPW‐fed metamaterial inspired antenna provides bandwidth of 10.4 GHz from 3.1 to 13.5 GHz based on the 3:1 (voltage standing wave ratio [VSWR] <2). Over the range of UWB frequency, peak realized gain varies from 2.5 to 4 dBi. The proposed antenna provides omnidrectional radiation patterns. Further, fidelity factor of the proposed antenna is also calculated and measured. The calculated fidelity factor is suitable for UWB applications. Finally, prototype of the antenna is developed and tested using network analyzer. The simulated and measured results are in good agreement.     

Flow-injection determination of iron(III) in soil by biamperometry using two independent redox couples

A flow-injection biamperometric method for the determination of iron(III) has been described. The detector consists of two chambers separated by a salt bridge, and one platinum wire working electrode is embedded in each chamber, respectively. When iron(III) solution and hydrogen peroxide solution simultaneously flow through two chambers, the reduction of iron(III) at one platinum electrode is associated with the oxidation of hydrogen peroxide at the other platinum electrode, forming such a system as similar to a reversible couple one. The biamperometric system can perform the determination of iron(III) without any external potential difference. The linear relationship is obtained from 1.0 × 10⁻⁶ to 1.0 × 10⁻⁴ mol l⁻¹ with a detection limit of 6.0 × 10⁻⁷ mol l⁻¹. The proposed method exhibits the satisfactory reproducibility with a relative standard derivation (R.S.D.) of 1.4% for 17 successive determinations of 2.0 × 10⁻⁵ mol l⁻¹ iron(III) and is applied to the determination of iron(III) in soil.     

Demonstration of the waveguide-based LCD

Abstract— We demonstrate a waveguide-based liquid-crystal display. Instead of using polarizers to control light intensity, high optical efficiency is obtained by using a liquid crystal to switch light out of a waveguide. Wide viewing angle is obtained by using a scattering screen.     

Three‐dimensional split‐step‐fourier and finite difference time domain‐based rectangular waveguide filter simulators: Validation,verification, and calibration

The split‐step‐Fourier‐based three‐dimensional wave propagation prediction and finite‐difference time‐domain‐based simulators are developed to show network scattering parameters of rectangular waveguide filters with horizontal and/or vertical windows as capacitive and/or inductive irises, respectively. The three‐dimensional‐split‐step parabolic equation simulator is applied to rectangular waveguide filters, and the results are compared with finite‐difference time‐domain model through tests inside a rectangular waveguide. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:660–667, 2016.     

Bayesian modelling of algal mass occurrences—using adaptive MCMC methods with a lake water quality model

Our study aims to estimate confounded effects of nutrients and grazing zooplankton (Crustacea) on phytoplankton groups—specifically on nitrogen-fixing Cyanobacteria—in the shallow, mesotrophic Lake Pyhäjärvi in the northern hemisphere (Finland, northern Europe, lat. 60°54′–61°06′, long. 22°09′–22°22′). Phytoplankton is modelled with a non-linear dynamic model which describes the succession of three dominant algae groups (Diatomophyceae, Chrysophyceae, nitrogen-fixing Cyanobacteria) and minor groups summed together as a function of total phosphorus, total nitrogen, temperature, global irradiance and crustacean zooplankton grazing. The model is fitted using 8 years of in situ observations and adaptive Markov chain Monte Carlo (MCMC) methods for estimation of model parameters. The approach offers a way to deal with noisy data and a large number of weakly identifiable parameters in a model. From our posterior simulations we calculate the lower limit for zooplankton carbon mass concentration (45 μgC L⁻¹) and the upper limit for total phosphorus concentration (16 μg L⁻¹) that satisfy with 0.95 probability our predefined water quality criteria (Cyanobacteria concentration during late summer period does not exceed the value 0.86 mg L⁻¹). Within the observational range total phosphorus has marginal effect on Cyanobacteria compared to the zooplankton grazing effect, which is temperature-dependent. Extensive fishing efforts are needed to attain the criteria.     

Ultracompact two‐way and four‐way SIW/HMSIW power dividers loaded by complementary split‐ring resonators

In this paper, two ultracompact power dividers based on the substrate integrated waveguide (SIW) and half‐mode SIW (HMSIW) technologies loaded by complementary split‐ring resonators (CSRRs) are presented. The presented structures are designed based on the theory of evanescent mode propagation. To obtain a size reduction, the CSRR unit cells are etched on the metallic surface of the SIW and HMSIW structures. First, a two‐way HMSIW power divider is reported. In this circuit, the concept of HMSIW is utilized aiming at a further size reduction in addition to the size reduction by the CSRR unit cells. Then, a four‐way SIW power divider is designed so that the direct coaxial feed is used for the input port and microstrip transmission lines are used for the output ports. Both two‐way and four‐way SIW/HMSIW power dividers at 5.8 GHz covering WLAN are designed, fabricated, and measured. They respectively have 0.18 × 0.21 λg² and 0.38 × 0.21 λg² total size. A fair agreement between simulated and measured results is achieved. The measured insertion losses are 0.5 ± 0.5 and 0.6 ± 0.5 dB for the two‐way and four‐way SIW/HMSIW power dividers, respectively, in the operating band of interest.     

Influence of high magnetic field on peritectic transformation during solidification of Bi–Mn alloy

The influence of high magnetic fields up to 10 T on the peritectic temperature of Bi–Mn alloys has been investigated experimentally. A method for measuring the peritectic temperature in a gradient magnetic field has been developed by relating the change of magnetic levitation force to the phase transformation due to the change in magnetic susceptibility while the transformation occurs. By measuring the temperature at which the magnetizing force changes abruptly, the phase transformation can be detected. It is shown that along with the increase of magnetic field, the temperature of the peritectic phase transformation BiMn_1.08+ L→BiMn increased significantly, and in a 10 T field the temperature increase was about 20 ^°C. It is found that with the high magnetic field, a split and separation of the BiMn grains in the direction perpendicular to the magnetic field occurred, and its morphology changed from flakes to small blocks. This is attributed to the repulsive force among the peritectic BiMn grains generated by the magnetization during the phase transformation. It seems that the precipitation of ferromagnetic phase results in stress in the grains.     

Analysis of a shielded elevated coupled coplanar waveguide using a modified finite element method

An elevated coupled coplanar waveguide is proposed and analyzed with a view to exploit the advantage of miniaturization that is possible with elevated coplanar waveguide structures. The influence of elevation on the directional characteristics of the elevated coupled coplanar waveguide has also been studied. The proposed structure is analyzed using a modified universal matrices finite element method. © 1996 John Wiley & Sons, Inc.     

Routes to polymer-based photonics

The advances in polymer materials and technologies for telecom applications are reported. The polymers include new highly halogenated acrylates, which possess absorption losses less than 0.25 dB/cm and refractive indices ranging from 1.3 to 1.5 in the 1.5 μm wavelength region. The halogenated liquid monomers are highly intermixable, photocurable under UV exposure and exhibit high contrast in polymerization. The polymer technologies developed at the Institute on Laser and Information Technologies of the Russian Academy of Sciences (ILIT RAS) include:

Evaluation of thermal and evaporative resistances in cricket helmets using a sweating manikin

The main objective of this study is to establish an approach for measuring the dry and evaporative heat dissipation cricket helmets. A range of cricket helmets has been tested using a sweating manikin within a controlled climatic chamber. The thermal manikin experiments were conducted in two stages, namely the (i) dry test and (ii) wet test. The ambient air temperature for the dry tests was controlled to ∼23 °C, and the mean skin temperatures averaged ∼35 °C. The thermal insulation value measured for the manikin with helmet ensemble ranged from 1.0 to 1.2 clo. The results showed that among the five cricket helmets, the Masuri helmet offered slightly more thermal insulation while the Elite helmet offered the least. However, under the dry laboratory conditions and with minimal air movement (air velocity = 0.08 ± 0.01 ms⁻¹), small differences exist between the thermal resistance values for the tested helmets. The wet tests were conducted in an isothermal condition, with an ambient and skin mean temperatures averaged ∼35 °C, the evaporative resistance, R_et, varied between 36 and 60 m² Pa W⁻¹. These large variations in evaporative heat dissipation values are due to the presence of a thick layer of comfort lining in certain helmet designs. This finding suggests that the type and design of padding may influence the rate of evaporative heat dissipation from the head and face; hence the type of material and thickness of the padding is critical for the effectiveness of evaporative heat loss and comfort of the wearer. Issues for further investigations in field trials are discussed.     

Development of a nanostructural microwave probe based on GaAs

In order to develop a new structural microwave probe, we studied the fabrication of an AFM probe on a GaAs wafer. A waveguide was introduced by evaporating Au film on the top and bottom surfaces of the GaAs AFM probe where a tip 7 μm high with a 2.0 aspect ratio was formed and the dimensions of the cantilever were 250 × 30 × 15 μm. The open structure of the waveguide at the tip of the probe was obtained by FIB fabrication. An AFM image and profile analysis for a standard sample, obtained by the fabricated GaAs microwave probe and a commercial Si AFM probe, indicate that the fabricated probe has a similar capability for measurement of material topography as compared to the commercial probe.     

Theoretical studies on kinetics,mechanism and thermochemistry of gas-phase reactions of HFE-449mec-f with OH radicals and Cl atom

A theoretical study on the mechanism and kinetics of the gas phase reactions of CF₃CHFCF₂OCH₂CF₃ (HFE-449mec-f) with the OH radicals and Cl atom have been performed using meta-hybrid modern density functional M06-2X using 6-31+G(d,p) basis set. Two conformers have been identified for CF₃CHFCF₂OCH₂CF₃ and the most stable one is considered for detailed study. Reaction profiles for OH-initiated hydrogen abstraction are modeled including the formation of pre-reactive and post-reactive complexes at entrance and exit channels. Our calculations reveal that hydrogen abstraction from the CH₂ group is thermodynamically and kinetically more facile than that from the CHF group. Using group-balanced isodesmic reactions, the standard enthalpies of formation for HFE-449mecf and radicals generated by hydrogen abstraction, are also reported. The calculated bond dissociation energies for CH bonds are in good agreement with experimental results. The rate constants of the two reactions are determined for the first time in a wide temperature range of 250–450 K. The calculated rate constant values are found to be 9.10 × 10⁻¹⁵ and 4.77 × 10⁻¹⁷ cm³ molecule⁻¹ s⁻¹ for reactions with OH radicals and Cl atom, respectively. At 298 K, the total calculated rate coefficient for reactions with OH radical is in good agreement with the experimental results. The atmospheric life time of HFE-449mec-f is estimated to be 0.287 years.