Quarter-wave Reflector Research Articles

Intraband Transition of HgTe Nanocrystals for Long-Wave Infrared Detection at 12 μm

The synthesis of n-doped HgTe colloidal quantum dots was optimized to produce samples with a 1Se-1Pe intraband transition in the long-wave infrared (8-12 μm). The spin-orbit splitting of 1Pe states places the 1Se-1Pe1/2 transition around 10 μm. The narrow line width of 130 cm-1 at 300 K is limited by the size distribution. This narrowing leads to an absorption coefficient about 5 times stronger than is possible with the HgTe CQD interband transition at similar energies. From 300 to 80 K, the intraband transition blueshifts by 90 cm-1, while the interband transition redshifts by 350 cm-1. These shifts are assigned to the temperature dependence of the band structure. With ∼2 electrons/dot doping at 80 K, a photoconductive film of 80 nm thickness on a quarter wave reflector substrate showed a detectivity (D*) of ∼107 Jones at 500 Hz in the 8-12 μm range.

An Antenna Solution for Glacial Environmental Sensor Networks

Antennas used in glacial environmental sensor networks and reported in the last two decades have been reviewed. A link budget framework for designing such antenna systems is presented and used to design an antenna system for deployment at the Thwaites glacier, Antarctica. Design details of two left hand circularly polarized cross dipole antennas, one for englacial sensor probes and the other for supraglacial surface receivers are presented. The probe antenna is a 3D bent cross dipole that fits within a borehole of 8 cm diameter while providing a 1 dBic gain at 433 MHz in ice. The surface receiver antenna is a planar printed antenna providing a gain of 6.1 dBic with a quarter wave reflector. Both antennas provide 3 dB beamwidths of at least 50° in the xz and yz vertical planes catering for transmitter-receiver antenna misalignments caused by extended deployments. The antennas displayed good circular polarization and polarization purity traits. The 3 dB axial ratio bandwidths of both the antennas remained 54.9 %. The total efficiencies of the bent cross dipole and the surface receiver antennas were noted as 69.7 % and 86.9 % respectively. Lastly, the 433 MHz band has been validated for achieving englacial communication ranges of up to 2300 metres.

Angular-adjustable single-channel narrow-band filter based on one-dimensional photonic crystal heterostructure

In this work, we designed a narrow-band filter based on a one-dimensional photonic crystal heterostructure featuring an angle-adjustable single-channel. The design presented here is based on a quarter-wave reflector with a mirror defect layer in the middle of the structure. By combining two defective one-dimensional photonic crystals (PCs), we obtained a heterostructure in which the two sub-PCs had the wavelengths of their defect modes, that is, the same at one incident angle and different at all other incident angles. This structure possessed the single-channel resonant peak in the transmission spectrum under either a normal or an oblique incident angle, and the angle-adjustability was related to the two modifying parameters. The filter based on this heterostructure possessed not only a narrow passband but also a sharp angular pass breadth. These properties have potential applications in angular tunable, single-channel narrow-band filters.

A Self-Stabilizing Phase Decoder for Quantum Key Distribution

Self-stabilization quantum key distribution (QKD) systems are often based on the Faraday magneto-optic effect such as “plug and play” QKD systems and Faraday–Michelson QKD systems. In this article, we propose a new anti-quantum-channel disturbance decoder for QKD without magneto-optic devices, which can be a benefit for the photonic integration and applications in magnetic environments. The decoder is based on a quarter-wave plate reflector–Michelson (Q–M) interferometer, with which the QKD system can be free of polarization disturbance caused by quantum channel and optical devices in the system. The theoretical analysis indicates that the Q–M interferometer is immune to polarization-induced signal fading, where the operator of the Q–M interferometer corresponding to Pauli Matrix σ2 makes it satisfy the anti-disturbance condition naturally. A Q–M interferometer based time-bin phase encoding QKD setup is demonstrated, and the experimental results show that the QKD setup works stably with a low quantum bit error rate about 1.3% for 10 h over 60.6 km standard telecommunication optical fiber.

Seven-Component Model-Based Decomposition for PolSAR Data with Sophisticated Scattering Models

Due to incomprehensive and inaccurate scattering modeling, the state-of-the-art polarimetric synthetic aperture radar (PolSAR) model-based target decompositions are incapable of effectively depicting the scattering mechanism of obliquely oriented urban areas. In this paper, a seven-component model-based decomposition scheme is proposed by constructing several sophisticated scattering models. First, an eigenvalue-based obliquely-oriented dihedral scattering model is presented to reasonably distribute the co-polarization and cross-polarization scattering powers in obliquely oriented urban areas, thus accurately characterizing the urban scattering. Second, the ±45° oriented dipole and ±45° quarter-wave reflector scattering models are incorporated for the purpose of accounting for the real and imaginary components of the T 13 element in the coherency matrix so as to fully utilize polarimetric information. Finally, according to their mathematical forms, several strategies for model parameter solutions are designed, and the seven-component decomposition is fulfilled. Experimental results conducted on different PolSAR data demonstrate that the proposed method considerably improves the PolSAR scattering interpretation in a more physical manner compared to other existing model-based decomposition, which can be applied for urban area detection, classification, and other urban planning applications.

Hybrid Bulk Acoustic Wave Structure for Temperature Stability in LTE Applications

A novel structure of hybrid bulk acoustic wave (BAW) resonator with low temperature coefficient of frequency (TCF) is presented. Implemented with a pair of quarter-wave reflectors on air-cavity reflector, the hybrid BAW resonator exhibits a TCF of as low as -11.5 ppm/°C and an effective electro-mechanical coupling coefficient (kt2) of 5.1% at the frequency of 2.5 GHz. The hybrid BAW resonator also shows excellent Q-factors of 1627 and 1842 at resonance and anti-resonance frequency, respectively. RF duplexer configured with the hybrid BAW resonators is provided as well. The fabricated RF duplexer for long term evolution (LTE) band-7, which should be designed to prevent the co-existence problem with WiFi having extremely narrow fractional band-gap of 0.7%, achieves an attenuation of 36.8 dB and an insertion loss of 2.4 dB.

Monte Carlo Study on Optimization of Reflectors in Pixelated CsI Film for Mammographic Application

Isotropic light spread in the scintillator film decreases the spatial resolution of scintillator-based digital X-ray imaging systems such as digital radiography and mammography. Pixelation of the scintillator film could be a good solution to overcome this limitation. This has been demonstrated with pixilated CsI:Tl layers which was made by thermal evaporation process on a pre-patterned substrate or which was post-patterned by laser after preparation. Additionally, in order to minimize cross-talk between pixels and to maximize light collection efficiency, a reflection material can be coated on the top and side surfaces of each pixilated scintillator block. In This paper, several materials such as Al, and quarter-wave multilayer reflector with SiO2 and TiO2 were considered as the reflector materials of pixilated CsI:Tl scintillator blocks. Through a serious of simulations given below on these simple 2-dimensional scintillator blocks coated by a reflector, reflectivity, cross-talk, and modulation transfer function were calculated to find the optimum reflector.

Development of an optical refractometer by analysis of one-dimensional photonic bandgap structures with defects.

A theoretical analysis of an optical fiber photonic-bandgap-based refractometer is presented. The design is based on a quarter-wave reflector with one defect. By modifying both the real and the imaginary parts of the index of refraction of the defects we begin to change either the frequency or the amplitude of the localized optical mode. So we could fabricate a specific optical fiber refractometer by combining all the variables: index of refractive index of the defects and the rest of layers, thickness of the defect, number of layers, etc. to yield a large set of design possibilities, for example, detecting wider or thinner ranges of refractive indices, or controlling the detection accuracy. Some rules for the practical implementation of the refractometer are given.

Finite Element Analysis of Optical Bistability in One-Dimensional Nonlinear Photonic Band Gap Structures with a Defect

We present a new approach based on the recently reported finite element scheme16 to study the optical response of a finite one-dimensional nonlinear grating. Using the transmitted wave amplitude as a numerical input parameter, we are able to find all stable and unstable solutions related to a specific incident wave which build up the complete bistability curve. The method is applied to investigate the optical bistability in a nonlinear quarter-wave reflector with a defect. With a proper choice of the incident light frequency, a very low bistability threshold is predicted for an optimized defect structure.

Analysis of one-dimensional photonic band gap structures with a liquid crystal defect towards development of fiber-optic tunable wavelength filters

A theoretical analysis of a fiber optical photonic band gap based tunable wavelength filter is presented. The design presented here is based on the quarter wave reflector with a liquid crystal defect layer in the middle of the structure. The filter generated by the structure is shifted in wavelength as the voltage applied to the structure is modified. Some critical parameters are analyzed: the effect of the consideration of fiber as the first layer and not the input medium in the shape of the filter, the number of layers of the structure, and the thickness of the defect layer. This last parameter determines the width of the wavelength sweep of the filter, but is limited by the creation of more defects. Some rules of practical implementation of this device are also given.

Study of (Al,Ga)N Bragg Mirrors Grown on Al2O3(0001) and Si(111) by Metalorganic Vapor Phase Epitaxy

A series of selective (Al,Ga)N quarter-wave reflectors has been grown on sapphire and silicon substrates by metalorganic vapor phase epitaxy. The microstructure of the mirror structures, consisting of GaN quarter-wave layers alternating with AlN. AIGaN or AlN/GaN short-period superlattices, has been assessed in terms of a joint X-ray diffraction (XRD) and transmission electron microscopy (TEM) study.

Study of (Al,Ga)N Bragg Mirrors Grown on Al2O3(0001) and Si(111) by Metalorganic Vapor Phase Epitaxy

A series of selective (Al,Ga)N quarter-wave reflectors has been grown on sapphire and silicon substrates by metalorganic vapor phase epitaxy. The microstructure of the mirror structures, consisting of GaN quarter-wave layers alternating with AlN, AlGaN or AlN/GaN short-period superlattices, has been assessed in terms of a joint X-ray diffraction (XRD) and transmission electron microscopy (TEM) study.

Room temperature lasing at blue wavelengths in gallium nitride microcavities

Lasing action has been demonstrated at blue wavelengths in vertical cavity surface-emitting lasers at room temperature. The microcavity was formed by sandwiching indium gallium nitride multiple quantum wells between nitride-based and oxide-based quarter-wave reflectors. Lasing action was observed at a wavelength of 399 nanometers under optical excitation and confirmed by a narrowing of the linewidth in the emission spectra from 0.8 nanometer below threshold to less than 0.1 nanometer (resolution limit) above threshold. The result suggests that practical blue vertical cavity surface-emitting lasers can be realized in gallium-nitride-based material systems.

Highly reflective GaN/Al0.34Ga0.66N quarter-wave reflectors grown by metal organic chemical vapor deposition

Quarter-wave reflectors consisting of sets of GaN and Al0.34Ga0.66N layers have been grown on sapphire substrates by atmospheric-pressure metal organic chemical vapor deposition. A periodic structure with flat interfaces was observed by high-resolution scanning electron microscopy. X-ray diffraction measurements were performed to characterize the structures, from which the Al content x in the AlxGa1−xN layers was determined to be 0.34. No cracks could be seen on the surface of the reflectors by optical microscopy. The measured peak reflectivity at 390 nm increases with the number of pairs and reaches as high as 96±2% in the 35-pair reflector.

Optical limiting and switching of short pulses by use of a nonlinear photonic bandgap structure with a defect

An extension of the recently introduced nonlinear finite-difference time-domain technique [Opt. Lett.21, 1138 (1996)] for the study of electromagnetic wave propagation in a non-linear Kerr medium to include absorption is presented. The optical limiting and switching of short pulses by use of a nonlinear quarter-wave reflector (a one-dimensional photonic bandgap structure) with a defect is studied. Comparison with an optical limiter and with an optical switch with a perfect nonlinear quarter-wave reflector shows that introducing a defect can improve the performance of these devices.

A gratingless wavelength stabilized semiconductor laser

A single frequency laser structure is obtained by coupling a high order mode of a semiconductor waveguide to a low index polymer waveguide. The device does not require a grating or regrowth, emits in a mode compatible with optical fibers, and may be immune to catastrophic mirror damage. The epilayers of the semiconductor waveguide use quarterwave reflectors to support a mode with a low enough effective index to phase match to the polymer waveguide. The coupling between the two waveguides is highly frequency selective and therefore stabilizes the wavelength. Preliminary structures emit in a single longitudinal and spatial mode, have 30 dB of sidemode suppression, and emit about 6 mW into a fiber compatible mode.

Wide bandwidth AlAs/AlGaAs tandem Bragg reflectors grown by organometallic vapor phase epitaxy

Wide bandwidth AlAs/Al0.6Ga0.4As tandem Bragg reflectors were grown by organometallic vapor phase epitaxy. Quarter-wave reflector stacks designed for different wavelengths were placed in cascade in epitaxially grown structures to expand the high reflectance bands. Intermediate low-index layers were put in between every two stacks to suppress the transmission peaks in the centers of the combined high reflectance bands. While a single-stack structure showed a full width half-maximum bandwidth of 500 Å, the two-stack and the three-stack structures effectively doubled and tripled this bandwidth to approximately 1000 and 1500 Å, respectively.

AlN-GaN quarter-wave reflector stack grown by gas-sourceMBE on (100) GaAs

A 15 period, wurtzite-structure AlN-GaN reflector stack has been grown on (100) GaAs by gas-source molecular beam epitaxy. A peak reflectance of over 90% has been realised, in agreement with a matrix-method computer simulation. Our results support the feasibility of vertical Fabry-Perot cavity optoelectronics using nitride materials.

Moisture patches in Al2O3/SiO2 quarterwave reflectors studied by fringes of equal chromatic order like experiments

Moisture patches in Al2O3/SiO2 quarterwave reflectors studied by fringes of equal chromatic order like experiments

Simple expressions for predicting substrate, volume, and interface absorption and reflective phase shifts in high-reflectance quarter-wave stacks at oblique angles of incidence

Approximate closed-form expressions are developed for predicting the substrate absorption, volume absorption, and interface absorption at oblique angles of incidence for quarter-wave stack reflectors. At normal incidence the results for S- and P-polarized radiation reduce to those obtained by Sparks [ SparksM., J. Opt. Soc. Am.67, 1590 ( 1977)] and Bennett and Burge [ BennettH. E.BurgeD. K., J. Opt. Soc. Am.70, 268 ( 1980)]. The significant difference in the interface absorption for S- and P-polarized light at large angles of incidence is of interest in damage threshold theory, especially damage due to surface defects or contamination. Simple expressions are also derived for the S- and P-polarization phase shift caused by layer-thickness errors or operation at non-quarter-wave wavelengths. A difference in the S and P phase shifts is of importance in annular resonator design and in assessing the uncorrectable beam degradation due to uneven mirror heating. Exact computer results based on the matrix methods are compared with the predictions of the simple expressions, and agreement to well within 1% is found in most cases of interest.