Mirror Structure Research Articles

Hyperbolic metamaterials based on Bragg polariton structures

A new hyperbolic metamaterial based on a modified semiconductor Bragg mirror structure with embedded periodically arranged quantum wells is proposed. It is shown that exciton polaritons in this material feature hyperbolic dispersion in the vicinity of the second photonic band gap. Exciton–photon interaction brings about resonant nonlinearity leading to the emergence of nontrivial topological polaritonic states. The formation of spatially localized breather-type structures (oscillons) representing kink-shaped solutions of the effective Ginzburg–Landau–Higgs equation slightly oscillating along one spatial direction is predicted.

Low‐noise readout circuit for thermo‐electrical cooler‐less uncooled microbolometer infrared imager

A low-noise analogue frontend readout circuit is presented for VOx microbolometer infrared imager without thermo-electrical cooler. A modified differential mirror structure with substrate temperature and self-heating effect compensation ability is used, targeting below 40 mK noise equivalent temperature difference (NETD) with 17 μm pixel pitch. Noise characteristics are investigated to give an optimal trade-off approach to reach lower NETD at same power consumption compared with traditional readout structures.

Comparative study on a core-offset fiber temperature sensor between the faraday rotation mirror structure and the double coupling structure

A temperature sensor based on core-offset single mode fiber (SMF) and a Faraday rotation mirror (FRM) has been proposed and experimentally demonstrated in this paper. This sensor was fabricated by splicing in a section of SMF between two SMFs with a core-offset at two splicing joints. The end of the joint is connected to the FRM, which can double the sensitivity and improve the polarization state stabilization at the sensor output. The variation of the transmission spectrum of the sensor with respect to the surrounding temperature has been experimentally studied. A comparison is made between this design and a laser temperature sensor made of the same core-offset fiber utilizing a double coupling (DC) structure. The results show that, within the range of 1539.42–1553.90nm, the sensitivity of the proposed sensor is 0.89039nm/°C and in the range of 47–63°C. Additionally, the power attenuation is 2.257dB/°C. The temperature sensitivity in the SMF and FRM sensor is increased by an order of magnitude in comparison with the DC sensor. The instability and low sensitivity characteristics of a laser temperature sensor constructed with DC structure can be solved through the use of core-offset SMF and FRM.

Simulation of the Golay3 multiple mirror telescope with a conicoidal primary mirror by extending the optical design program

The notion of a sparse aperture system offers a novel solution to decrease the volumes and weight of space telescopes while pursuing higher resolutions. A simulation of the applicable sparse aperture systems is studied. First, the principle of ray tracing used in the optical design program is analyzed. It is pointed out that surface models representing the primary mirror of a sparse aperture system can be established by programming and creating Dynamic Link Library files to define the propagation properties of the passing rays. The method of simulating the Golay3 multiple mirror telescope (MMT) with a conicoidal primary mirror is proposed. Second, the structure of the conicoidal primary mirror of the Golay3 MMT is investigated. Formulas to define the directions, optical path lengths and intensities of rays passing through the primary mirror are deduced. Finally, two Golay3 MMT systems are simulated as examples. Their simulation results are presented and analyzed. The theoretical fill factors, the simulative fill factors, and the normalized modulation transfer functions of the simulated system are calculated to verify the proposed simulation method. They are proved to be in accordance with each other.

Numerical modelling of a fibre reflection filter based on a metal – dielectric diffraction structure with an increased optical damage threshold

Numerical modelling demonstrates the possibility of fabricating an all-fibre multibeam two-mirror reflection interferometer based on a metal – dielectric diffraction structure in its front mirror. The calculations were performed using eigenmodes of a double-clad single-mode fibre. The calculation results indicate that, using a metallic layer in the structure of the front mirror of such an interferometer and a diffraction effect, one can reduce the Ohmic loss by a factor of several tens in comparison with a continuous thin metallic film.

Quantum transmissivity of one-dimensional mirror structure photonic crystals

In this paper, we have studied the transmission characteristic of one-dimensional mirror structure photonic crystals (MSPCs) (AB)ND1D2D3(BA)N with the quantum theory method. We find there are some sharp peaks (quantum transmissivity T=1) in the PBG of MSPCs, and the number of sharp peaks is added with the increasing of thickness, refractive index and numbers of defect layer, which is beneficial to design the optic filter of multiple channel.

Current differencing transconductance amplifier (CDTA) with enhanced performance and its application

A CMOS current differencing transconductance amplifier (CDTA) with high transconductance has been proposed. The transconductance (gm) of CDTA is generally increased either by increasing the biasing current IB or by increasing the size of transistors used in differential pair and current mirror structures. The first technique leads to higher power dissipation and limited range of transconductance while the second limits the input/output swing and bandwidth of CDTA due to higher parasitic capacitances. In the proposed design of CDTA, a cross coupled PMOS active load has been used in place of conventional PMOS active load. The cross coupled PMOS active load forms a positive feedback which results in higher transconductance, wider tuning range and less power consumption without any limitations on input/output swing and bandwidth of the CDTA. Mentor Graphics Eldo simulation tool has been used to verify the performance of proposed CDTA with TSMC 0.18 µm technology parameters. A voltage/current mode oscillator circuit of third order has been designed by proposed CDTA.

The fluid control mechanism of bionic structural heterogeneous composite materials and its potential application in enhancing pump efficiency

Studies have shown that the structure of dolphin skin controls fluid media dynamically. Gaining inspiration from this phenomenon, a kind of bionic structural heterogeneous composite material was designed. The bionic structural heterogeneous composite material is composed of two materials: a rigid metal base layer with bionic structures and an elastic polymer surface layer with the corresponding mirror structures. The fluid control mechanism of the bionic structural heterogeneous composite material was investigated using a fluid–solid interaction method in ANSYS Workbench. The results indicated that the bionic structural heterogeneous composite material’s fluid control mechanism is its elastic deformation, which is caused by the coupling action between the elastic surface material and the bionic structure. This deformation can decrease the velocity gradient of the fluid boundary layer through changing the fluid–solid actual contact surface and reduce the frictional force. The bionic structural heterogeneous composite material can also absorb some energy through elastic deformation and avoid energy loss. The bionic structural heterogeneous composite material was applied to the impeller of a centrifugal pump in a contrast experiment, increasing the pump efficiency by 5% without changing the hydraulic model of the impeller. The development of this bionic structural heterogeneous composite material will be straightforward from an engineering point of view, and it will have valuable practical applications.

Thermal Management in Long-Wavelength Flip-Chip Semiconductor Disk Lasers

We address the thermal management of flip-chip semiconductor disk lasers (SDLs) emitting at wavelengths 1.3–1.6 μm. The emphasis of the study is on fabricating thin SDL structures with high thermal conductance. An essential part of this task is to use GaAs-based materials in the distributed Bragg reflector (DBR), because they can provide a combination of high thermal conductivity and high refractive index contrast. Furthermore, the reflectivity of the GaAs-based DBR should preferably be enhanced using a thin dielectric layer and a highly reflecting metal layer. Such a configuration enables very thin mirror structures with a reduced number of DBR layer pairs without compromising the reflectivity. The concept is demonstrated experimentally with a 1.32-μm flip-chip SDL, where the GaAs-based DBR is finished with a thin Al2O3 layer and a highly reflective Al layer. In addition, the design principles, thermal management, and the development issues related to semiconductor–dielectric–metal mirrors in 1.3–1.6-μm flip-chip SDLs are discussed.

The structure of mirrors on regular maps on Platonic surfaces

A Platonic surface is a Riemann surface that underlies a regular map and so we can consider its vertices, edge-centres and face-centres. A symmetry (anticonformal involution) of the surface will fix a number of simple closed curves which we call mirrors. These mirrors may pass through the vertices, edge-centres and face-centres in some sequence which we call the pattern of the mirror. Here we investigate these patterns for various well-known families of Platonic surfaces, including genus 1 regular maps, and regular maps on Hurwitz surfaces and Fermat curves. The genesis of this paper is classical. Klein in Section 13 of his famous 1878 paper (Klein in Math Ann 14:428–471, 1879), worked out the pattern of the mirrors on the Klein quartic and Coxeter in his book on regular polytopes worked out the patterns for mirrors on the regular solids. We believe that this topic has not been pursued since then.

Corrosion barriers for silver-based telescope mirrors: comparative study of plasma-enhanced atomic layer deposition and reactive evaporation of aluminum oxide

Astronomical telescopes continue to demand high-endurance high-reflectivity silver (Ag) mirrors that can withstand years of exposure in Earth-based observatory environments. We present promising results of improved Ag mirror robustness using plasma-enhanced atomic layer deposition (PEALD) of aluminum oxide (AlOx) as a top barrier layer. Transparent AlOx is suitable for many optical applications; therefore, it has been the initial material of choice for this study. Two coating recipes developed with electron beam ion-assisted deposition (e-beam IAD) of materials including yttrium fluoride, titanium nitride, oxides of yttrium, tantalum, and silicon are used to provide variations in basic Ag mirror structures to compare the endurance of reactive e-beam IAD barriers with PEALD barriers. Samples undergo high temperature/high humidity environmental testing in a controlled environment of 80% humidity at 80°C for 10 days. Environmental testing shows visible results suggesting that the PEALD AlOx barrier offers robust protection against chemical corrosion and moisture permeation. Ag mirror structures were further characterized by reflectivity/absorption before and after deposition of AlOx barriers.

Tailoring the optical properties of wide-bandgap based microcavities via metal films

We report on the tuning of the optical properties of II-VI-material-based microcavity samples, which is achieved by depositing Ag films on top of the structures. The micro-reflectivity spectra show a spectral shift of the sample resonance dependent on the metal layer thickness. By comparison of the experimental findings with the theoretical calculations applying the transfer matrix method on a metal-dielectric mirror structure, the influence of the metal layer particularly with regard to its partial oxidation was explored. Tamm plasmon modes are created at the interface between an open cavity with three ZnSe quantum wells and a metal layer on top. When tuning the excitonic emission relative to the mode by changing the sample temperature, an anticrossing of the resonances was observed. This is a clear indication that the strong coupling regime has been achieved in that sample configuration yielding a Rabi splitting of 18.5 meV. These results are promising for the realization of polariton-based optical devices with a rather simple sample configuration.

Design of a Vertical Cavity Optical Micro-Electromechanical Filter

Based on Micro-Opto-Electro-Mechanical System (MOEMS) technology, vertical cavity devices with an air-gap enable very efficient ultra-wide continuous tuning with only a single control parameter. The vertical cavity filters and Lasers consist of an air-gap cavity embedded between two highly reflective Bragg mirrors. Vertical Cavity Surface Emitting Lasers (VCSELs) have an active layer additionally integrated in the cavity. The ultra-wide continuous tuning is achieved by micro-electromechanical actuation of the mirror membranes. Our research activities concentrated on Bragg mirror material system with InP/air-gap mirror structures. The resonator quality depends on the refractive index contrast between the Bragg mirror layer materials and on the number of periods. The advantage of the semiconductor/air-gap system is the very high refractive index contrast ensuring a high reflectivity of more than 99.8% with only three layer periods. The semiconductor/air-gap structures forming the membranes of one Bragg mirror are n-doped while the other mirror membranes are p-doped forming a diode structure. Due to device miniaturization very efficient tuning is achieved by electrostatic actuation. The investigations presented focus on an InP/air-gap Fabry-Perot-filter for air =1.55μm with an air-gap cavity thickness equal to a multiple of ½ air embedded between two InP/air Bragg mirrors. The InP membranes have a thickness of of ¾ InP, the air-gaps in between are ¼air thick. The tuning behaviour is determined by the mechanical flexibility of the membranes and by the optical properties of the vertical cavity. The electrostatic deflection due to a reverse voltage is calculated with FEM simulations incorporating the effect of stress in the membranes. The results of the model calculations compared very well with measured values. This study describes the optical micro-electromechanical design of the novel low cost device structure applicable in optical filters, vertical cavity surface emitting lasers (VCSELs) and a host of other optical applications. We also present a solution to one of the most challenging problems in the design of micro-electromechanical devices consisting of thin-walled structures - that is residual stress. Residual stress alters device characteristics if not taken into consideration during design and characterisation.

MEMS-based air-gap cavity for entangled photon generation via polariton-polariton scattering

A structure for entangled photon generation via polariton-polariton scattering is proposed. We have designed an air-gap planar cavity with embedded quantum wells, in which the photonic modes are in strong coupling regime with excitons of quantum wells. An electrical tuning mechanism is designed by introducing an air-gap layer and an integrated electrical actuator to the distributed Bragg reflector (DBR) mirror structure. Our structure consists of 40 (17) bottom (top) DBRs with 12 GaAs/AlAs (7/3 nm) quantum wells at the antinodes of the electromagnetic field working at 767-nm wavelength. Initial air-gap thickness is 1500 nm. The Q factor and Rabi splitting of the structure are 1742 and 14 meV, respectively. Reflectivity of cavity/air interface is 0.32, and suspended DBR reflectivity is 0.97. Average indices of suspended mirror and cavity are 3.2062 and 3.1901, respectively. According to our simulation results, by changing air-gap thickness from 1000 to 1350 nm, the wavelength tuning range is extended to 30 nm via applying a maximum voltage of 12 V.

Universal properties of mirror mode turbulence in the Earth's magnetosheath

AbstractWe use more than 7 years of Time History of Events and Macroscale Interactions during Substorms observations to quantify the non‐Gaussian properties associated with mirror mode turbulence in the Earth's magnetosheath. We find that non‐Gaussian statistics of mirror modes lead to the parabolic collapse of kurtosis as the square of the skewness (K = aS2+B with a ∼ 1.3 and b ∼− 1). The parabolic scaling is a global constraint for the magnetosheath and is dictated by kinetic processes. This parabolic scaling is qualitatively independent of the distance to the magnetopause or bow shock, which implies that, even though the bow shock is driving the mirror mode instability, the dynamical evolution of mirror structures is independent of the source region and due to local processes. The parabolic relationship and coefficients between kurtosis and skewness for mirror modes in the Earth's magnetosheath are also similar to those found in a wide range of geophysical and laboratory turbulent environments, providing further evidence that turbulent systems dominated by non‐Gaussian fluctuations hold universal statistical properties.

A transconductance boosted CMOS current differencing transconductance amplifier (TBCDTA) and its application

This paper presents a transconductance (gm) boosted CMOS current differencing transconductance amplifier (TBCDTA). The transconductance amplifier of CDTA has been modified in TBCDTA, which results in higher and wide range of transconductance with power dissipation lying in the same range as that of existing CDTA. It has been observed that the transconductance (gm) of CDTA is varied by changing the biasing current IB which leads to higher power dissipation and limited range of transconductance. In the proposed TBCDTA, the biasing current IB is kept constant and transconductance has been boosted by connecting `N' number of MOSFETs in parallel in place of conventional MOSFETs of differential pair and current mirror structures. The workability of the proposed TBCDTA has been verified by using Mentor Graphics Eldo simulation tool with TSMC CMOS 0.18 µm process parameters. A new resistorless third order voltage/current mode quadrature sinusoidal oscillator has been designed. The KHN filter designed by proposed TBCDTA gives better performance than the KHN filter designed by an existing CDTA.

Conception of broadband stigmatic high-resolution spectrometers for the soft X-ray range

We formulate an approach to the development of stigmatic high-resolution spectral instruments for the soft X-ray range , which is based on the combined operation of normal-incidence multilayer mirrors (including broadband aperiodic ones) and grazing-incidence reflection gratings with nonequidistant grooves (so-called VLS gratings). A concave multilayer mirror serves to produce a slightly astigmatic image of the radiation source (for instance, an entrance slit), and the diffraction grating produces a set of its dispersed stigmatic spectral images. The width of the operating spectral region is determined by the aperiodic structure of the multilayer mirror and may range up to an octave in wavelength.

Variational approach for static mirror structures

Anisotropic static plasma equilibria where the parallel and perpendicular pressures are only functions of the amplitude of the local magnetic field are shown to be amenable to a variational principle with a free energy density given by the parallel tension. This approach is used to demonstrate that two-dimensional small-amplitude static magnetic holes constructed from a Grad-Shafranov type equation slightly below the (subcritical) mirror instability threshold identify with lump solitons of KPII equation, but turn out to be unstable. Differently, large-amplitude magnetic structures, which are stable as they realize a minimum of the free energy, are computed using a gradient method within two-dimensional numerical simulations where the regularizing effect of finite Larmor radius corrections is retained. Interestingly, these structures transform from stripes to bubbles when the angle of the magnetic field with the coordinate plane is increased.

Angular Distributions of EUV Generated by Electrons with 5.7 MeV Energy in a Multilayer Mo/Si Structure

The article considers the dynamics of the changes in the intensity and shape of the angular distributions of the backward transition radiation and quasi-monochromatic radiation emitted by the periodic structure of a multilayer mirror in a vacuum ultraviolet region for electrons with the energy of 5.7 MeV, depending on the orientation of the target. It has been shown that the dynamics of the changes in the intensity and shape of the angular distributions of the backward transition radiation and those of the periodic structure radiation observed after directing the radiation through an absorption edge filter display opposite tendencies. These opposite tendencies may be used as an indicator in the experiments aimed at detecting the effect of the periodic structure radiation in the ultraviolet region of the analog of parametric X-ray in crystals.

High performance wafer-fused semiconductor disk lasers emitting in the 1300 nm waveband

We report for the first time on the performance of 1300 nm waveband semiconductor disc lasers (SDLs) with wafer fused gain mirrors that implement intracavity diamond and flip-chip heat dissipation schemes based on the same gain material. With a new type of gain mirror structure, maximum output power values reach 7.1 W with intracavity diamond gain mirrors and 5.6 W with flip-chip gain mirrors, using a pump spot diameter of 300 µm, exhibiting a beam quality factor M(2)< 1.25 in the full operation range. These results confirm previously published theoretical modeling of these types of SDLs.