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Abnormal refraction and reflection refers to the phenomenon in which light does not follow its traditional laws of propagation and instead is subject to refraction and reflection at abnormal angles that satisfy a generalization of Snell's law. Metasurfaces can realize this phenomenon through appropriate selection of materials and structural design, and they have a wide range of potential applications in the military, communications, scientific, and biomedical fields. This paper summarizes the current state of research on abnormal refractive and reflective metasurfaces and their application scenarios. It discusses types of abnormal refractive and reflective metasurfaces based on their tuning modes (active and passive), their applications in different wavelength bands, and their future development. The technical obstacles that arise with existing metasurface technology are summarized, and prospects for future development and applications of abnormal refractive and reflective metasurfaces are discussed. HIGHLIGHTS: • This paper summarizes the design of and research on anomalous refractive and reflective metasurfaces in recent years and provides a comprehensive understanding of their constituent materials, structures, and application scenarios. • It focuses on the design and preparation of metasurfaces, their classification, and a comparison of the materials used in their fabrication with regard to their capability for active modulation, and it provides a clear description of the materials used to achieve different functions. • A novel classification of anomalous refractive and reflective metasurfaces is adopted in terms of wavelength bands, providing an alternative perspective on their design and application. [ABSTRACT FROM AUTHOR]

Monolithic multi-wavelength VCSEL arrays, with wavelengths of individual VCSELs precisely set in a post-epitaxial growth process, would enable compact multi-color light sources and transmitters for various sensing and datacom applications. Here we report on a numerical study of the requirements of spectral matching and balancing of DBR reflectances, optical confinement factor, and optical gain for uniformity of threshold current and slope efficiency over wavelength with wavelength set by intra-cavity phase tuning. The requirements are verified by an experimental demonstration of intra-cavity phase tuned VCSELs in the spectral range 1043–1067 nm with a wavelength spacing of 8 ± 1 nm enabled by precise Ar ion-beam etching. Small variations of threshold current and slope efficiency are achieved by close to ideal spectral matching and balancing. The VCSELs are GaAs-based with a dielectric SiO2/TiO2 top-DBR. We conclude that high uniformity of threshold current and slope efficiency is demanding in terms of spectral matching and balancing and requires not only very precise etching for intra-cavity phase tuning and precise thickness of the layers in the dielectric top-DBR, but also precise thickness and composition of the layers in the epitaxial semiconductor part. [ABSTRACT FROM AUTHOR]

We use reflection-absorption infrared spectroscopy (RAIRS) to study the photochemistry of NO on Cu(110) in the UV-visible range. We observe that the only photoactive species of NO on Cu(110) is the NO dimer, which is asymmetrically bound to the surface. RAIRS shows that photoinduced dissociation proceeds via breaking of the weak N-N bond of the dimer, photodesorbing one NOg to the gas phase and leaving one NOads adsorbed on the surface in a metastable atop position. We model the measured wavelength-dependent cross sections assuming both electron- and hole-induced processes and find that the photochemistry can be described by either electron attachment to a level 0.3 eV above the Fermi energy EF or hole attachment to a level 2.2 eV below EF. While there is no experimental or theoretical evidence for an electron attachment level so close to EF, an occupied NO-related molecular orbital is known to exist at EF - 2.52 eV on the Cu(111) surface [I. Kinoshita, A. Misu, and T. Munakata, J. Chem. Phys. 102, 2970 (1995)]. We, therefore, propose that photoinduced dissociation of NO dimers on Cu(110) in the visible wavelength region proceeds by the creation of hot holes at the top of the copper d-band. [ABSTRACT FROM AUTHOR]

We report measurements of the temperature dependence of the optical reflectivity, i.e., the thermoreflectance dR/dT, of 18 metallic elements at two laser wavelengths commonly used in ultrafast pump-probe experiments, 1.55 μm and 785 nm. The thermoreflectance is determined using time-domain thermoreflectance combined with measurements of the laser power and spot size and comparisons between the data and quantitative modeling of the temperature evolution at the surface of the sample. At a laser wavelength of 1.55 μm, four elements within this set of samples, Nb, Re, Ta, and V, have dR/dT comparable to or larger than 0.6×10-4 K-1. At a laser wavelength of 785 nm, the highest thermoreflectance is found in Al and Ta, dR/dT≈2.1×10-4 K-1 and 2.2×10-4 K-1, respectively. Alloying Au with 5% Pd increases the optical absorption by a factor of 3 and the thermoreflectance by a factor of 2. [ABSTRACT FROM AUTHOR]

The reflection notch of cholesteric liquid crystals (CLCs) formed from highly photosenstive azobenzene nematic liquid crystals doped with light-insensitive, large helical twisting power chiral dopants is shown to be widely phototunable by green laser beams. The nonlinear transmission properties of these materials were studied. We have shown that the relative shift in Bragg wavelength is independent of the chiral dopant concentration and develop a predictive theory of such behavior. The theory describes the dynamics of phototuning as well. Reflection shifts greater than 150 nm were driven with low power, cw of 532 nm in these photosensitive CLCs, previously attainable only through UV pre-exposure. A nonlinear feedback mechanism was demonstrated for CLCs of left, right, and both handedness upon laser-induced blueshifting of the reflection notch from a red wavelength using a green cw laser. [ABSTRACT FROM AUTHOR]

Abstract This paper examines the possibility of optical spectral singularity in scattering spectrums of one dimensional multilayer (1DM) structure. We show that the transfer matrix method is not valid in optical spectral singularity situation. Based on the irrational wavelength concept, it is illustrated that discontinuity and optical spectral singularity in scattering spectrums of 1DM structure, physically, is impossible. By using this result, the scattering spectrums of a gained Fabry-Perot structure are obtained. The diverging value and very narrow width of transmission or reflection coefficients are interpreted, successfully. [ABSTRACT FROM AUTHOR]

Abstract Large, thin, prestressed membranes known as 'gossamer' structures have many applications in space, including light reflection and electromagnetic signal collection. The prestress forces applied to these structures usually causes some wrinkling of the membrane to occur, and the degree of wrinkling affects the reflective performance of the structure. The primary aim was to assess whether solar radiation pressure could affect the wrinkle pattern of gossamer structures, with a particular focus on solar sails. Several prestressed rectangular membranes with dimensions and material properties representative of current and future solar sails, a class of membrane structures typically made of Kapton, were modelled to investigate the effects of pressure on the wrinkle pattern. It was shown that increasing the pressure applied normal to the membrane surface increased the amplitude and decreased the wavelength of the wrinkles. However, no significant change in the wrinkle pattern was found to occur until the magnitude of the applied pressure was much greater than that likely to be experienced by gossamer structures due to solar radiation pressure. Therefore it was concluded that the effects of solar pressure will have no significant impact on the future development of larger and thinner gossamer structures than exist at present. [ABSTRACT FROM AUTHOR]

A highly sensitive liquid level sensor based on an optical fiber Michelson interferometer with core-offset structure has been proposed and demonstrated. The sensor was fabricated by offset splicing a section of single-mode fiber (SMF) between another two SMFs and coated the reflection film at the end-face of the pigtail. This sensor was then used to measure liquid level and the dip of the measured reflection spectra caused by Michelson interference shifted obvious when the sensor is immersed in pure water. A good linear relationship between the liquid level and spectrum dip wavelength shift was detected (R 2  = 0.9971), while the dip intensity of the interference fringes fluctuates very little. The measured sensitivity up to 77 pm/mm was shown when the water level changed from 0 to 40 mm. In summary, this optical fiber sensing system would be appreciated in applications to liquid level measurement due to its good linearity, sensitivity, simple structure, and low cost. [ABSTRACT FROM AUTHOR]

The quantification of hemoglobin oxygen saturation (sO2) with multispectral optoacoustic (OA) (photoacoustic) tomography (MSOT) is a complex spectral unmixing problem, since the OA spectra of hemoglobin are modified with tissue depth due to depth (location) and wavelength dependencies of optical fluence in tissue. In a recent work, a method termed eigenspectra MSOT (eMSOT) was proposed for addressing the dependence of spectra on fluence and quantifying blood sO2 in deep tissue. While eMSOT offers enhanced sO2 quantification accuracy over conventional unmixing methods, its performance may be compromised by noise and image reconstruction artifacts. In this paper, we propose a novel Bayesian method to improve eMSOT performance in noisy environments. We introduce a spectral reliability map, i.e., a method that can estimate the level of noise superimposed onto the recorded OA spectra. Using this noise estimate, we formulate eMSOT as a Bayesian inverse problem where the inversion constraints are based on probabilistic graphical models. Results based on numerical simulations indicate that the proposed method offers improved accuracy and robustness under high noise levels due the adaptive nature of the Bayesian method. [ABSTRACT FROM AUTHOR]

We present an analytical scheme for the design of realistic metagratings for wide-angle engineered reflection. These recently proposed planar structures can reflect an incident plane wave into a prescribed (generally nonspecular) angle with very high efficiencies, using only a single meta-atom per period. Such devices offer a means to overcome the implementation difficulties associated with standard metasurfaces (consisting of closely packed subwavelength meta-atoms) and the relatively low efficiencies of gradient metasurfaces. In contrast to previous work, in which accurate systematic design was limited to metagratings unrealistically suspended in free space, we derive herein a closed-form formalism allowing the realization of printed circuit board (PCB) metagrating perfect reflectors, comprised of loaded conducting strips defined on a standard metal-backed dielectric substrate. The derivation yields a detailed procedure for the determination of the substrate thickness and conductor geometry required to achieve unitary coupling efficiencies, without requiring even a single full-wave simulation. Our methodology, verified via commercial solvers, ultimately allows one to proceed from a theoretical design to synthesis of a full physical structure, avoiding the time-consuming numerical optimizations typically involved in standard metasurface design. [ABSTRACT FROM AUTHOR]

An algorithm that selects optimal wavelengths for spectral fitting of diffuse light reflectance spectra using a nonnegative least squares method is presented. Oxyhemoglobin, deoxyhemoglobin, and water are considered representative absorbers, but the approach is not constrained or limited by absorber selection provided native basis spectra are available. The method removes wavelengths iteratively from a scattering-modulated absorption matrix by maximizing the product of its singular values and offers considerable improvements over previously published wavelength selection schemes. Resulting wavelength selections are valid for a broad range of optical properties and yield lower RMS errors than other wavelength combinations. The method is easily modified and broadly applicable to tissue optical spectroscopy. Adaptation of the algorithm to select optimal light-emitting diodes for fitting blood is described. [ABSTRACT FROM AUTHOR]

The optical reflection in periodic structures based on a semiconductor AlGaAs matrix containing two-dimensional arrays of plasmonic AsSb nanoinclusions was studied. The number of periods was 12 or 24. The spatial period was near 110 nm in both cases. In the experimental optical reflection spectra at normal incidence we observed resonant Bragg diffraction with the main peaks at wavelengths of 757 or 775 nm, depending on the spatial period of the nanostructure. The magnitudes of the resonance peaks reached 19 and 31% for the systems of 12 and 24 AsSb-AlGaAs layers, while the volume fraction of the nanoinclusions was much less than 1%. In the case of light incident at inclined angles, the Bragg-diffraction pattern shifted according to Wulff-Bragg’s law. Numerical calculations of the optical reflection spectra were performed using the transfer-matrix method by taking into account the spatial geometry of the structures and the resonance characteristics of the plasmonic AsSb layers. [ABSTRACT FROM AUTHOR]

For answering the growing demand of innovative micro-fluidic devices able to measure the refractive index of samples in extremely low volumes, this paper presents an overview of the performances of a micro-opto-fluidic sensing platform that employs rectangular, miniature hollow glass tubings. The operating principle is described by showing the analytical model of the tubing, obtained as superposition of different optical cavities, and the optical readout method based on spectral reflectivity detection. We have analyzed, in particular, the theoretical and experimental optical features of rectangular tubings with asymmetrical geometry, thus with channel depth larger than the thickness of the glass walls, though all of them in the range of a few tens of micrometers. The origins of the complex line-shape of the spectral response in reflection, due to the different cavities formed by the tubing flat walls and channel, have been investigated using a Fourier transform analysis. The implemented instrumental configuration, based on standard telecom fiberoptic components and a semiconductor broadband optical source emitting in the near infrared wavelength region centered at 1.55 µm, has allowed acquisition of reflectivity spectra for experimental verification of the expected theoretical behavior. We have achieved detection of refractive index variations related to the change of concentration of glucose-water solutions flowing through the tubing by monitoring the spectral shift of the optical resonances. [ABSTRACT FROM AUTHOR]

In this paper, a novel InP-based hybrid plasmonic (HP) bowtie nanoantenna with director was proposed that can serve as a good alternative to the silicon-on-insulator based ones. The proposed bowtie HP nanoantenna is capable of monolithic integration with laser and photodetector at optical communication wavelengths. By using the finite-element method, it was observed that the device can radiate and receive the optical field with a gain of about 9 dB at frequency range of 180 to 220 THz. In addition, the results showed that this device is expandable in array structure. Antenna gains with two diverse array arrangements of single row and square array were also determined. [ABSTRACT FROM AUTHOR]

Suppression of visible-light reflection from material surfaces is an important technology for many applications such as flat-panel displays, camera lenses, and solar panels. In this study, we developed an anti-reflective coating design based on a silver nanodisc metasurface. The effective refractive index of a 10-nm-thick monolayer of silver nanodiscs was less than 1.0, which enabled strong suppression of reflection from the underlying substrate. The nanodisc structure was easy to fabricate using a conventional roll-to-roll wet-coating method. The anti-reflective structure was fabricated over a large area. [ABSTRACT FROM AUTHOR]

A high-temperature sensor based on a peanut flat-end reflection structure is demonstrated. The sensor can be simply fabricated by splicing the spherical end-faces of two segments of single-mode fibers and then cleaving one other end as a flat reflect surface. The proposed structure works as a reflected interferometer. When the ambient temperature changes, the resonant dip wavelength of the interferometer will shift due to the linear expansion or contraction and the thermo-optic effect. As a result, the temperature measurement can be achieved by monitoring the resonant dip wavelength of the interferometer. Experimental results show that the proposed sensor probe based on the peanut flat-end reflection structure works well and it can measure the temperature range from 100 °C to 900 °C with the sensitivity of 0.098 nm/ °C with R 2  =  0.988. When temperature ranges from 400 °C to 900 °C, the sensitivity of 0.11 nm/ °C can be achieved with R 2 = 0.9995. Due to its compact and simple configuration, the proposed sensor is a good high temperature sensor probe. [ABSTRACT FROM AUTHOR]

Nanostructured optical materials, for example, metamaterials, have unique spectral, directional, and polarimetric properties. Samples designed and fabricated for infrared (IR) wavelengths have been characterized using broadband instruments to measure specular polarimetric transmittance or reflectance as in ellipsometry or integrated hemisphere transmittance or reflectance. We have developed a wavelength-tunable IR Mueller-matrix (Mm) polarimetric scatterometer which uses tunable external-cavity quantum-cascade lasers (EC-QCLs) to tune onto and off of the narrowband spectral resonances of nanostructured optical materials and performed full polarimeteric and directional evaluation to more fully characterize their behavior. Using a series of EC-QCLs, the instrument is tunable over 4.37-6.54 μm wavelengths in the mid-wave IR and 7.41-9.71 μm in the long-wave IR and makes measurements both at specular angles, acting as a Mm polarimeter, and at off-specular angles, acting as a Mm scatterometer. Example measurements of an IR thermal metamaterial are shown. [ABSTRACT FROM AUTHOR]

We propose a new way to enlarge gain bandwidth of a miniaturized reflectarray antenna (MRA), a new type of reflectarray antenna (RA) with significantly reduced volume. To extend the gain bandwidth, we have used meander-line based sub-wavelength elements as reflectarray cells, which can fully cover a required reflection phase range ideally, 360°. As a result, we have accomplished a three times wider gain bandwidth than that of our previous MRAs. In addition, the proposed MRA can also provide high gain with good aperture efficiency even though a main beam directs toward a tilted direction. Furthermore, remarkably reduced electrical volume, which is 700 times smaller than the smallest conventional RAs, is still maintained. Measured aperture efficiency of the proposed MRA is 41.1% which is comparable with conventional RAs. And the measurement results show that the main lobe direction is very stable around the target direction within the given −1 dB gain bandwidth without any degradation in other performances. As a result, the proposed MRAs with wide gain bandwidth stands out as a good alternative of the conventional RAs. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the near-field enhanced optical absorption and far-field radiation characteristics of plasmonic dipole nano-antenna with different geometries which are rectangular, square, circular, and ellipse dipoles. Localized E-field enhancement at the excitation gap and reflection profile in an infinite 2D array of each nano-antenna are characterized and optimized at the resonant frequency of 375 THz, which corresponds to the incident wavelength of 800 nm. Numerical results show that the ellipse nano-antenna produces the most enhanced electric field at the excitation gap whereas the circular nano-antenna yields the best reflection and far-field radiation characteristics. This research is useful for the researchers and designers in choosing appropriate plasmonic dipole nano-antennas when incorporating with a photoconductive antenna for terahertz radiation enhancement. [ABSTRACT FROM AUTHOR]

An apodized fiber Bragg grating formation using a phase mask with variable duty cycle is numerically analyzed. In particular, an impact of position of an optical fiber behind the phase mask with Gaussian apodization profile on Bragg grating reflection efficiencies at Bragg wavelength and its harmonics is extensively studied. It is shown that reflection efficiency of each harmonic strongly depends on the optical fiber location with respect to the adjacent Talbot planes during the grating inscription. An analytical formula for calculation such periodical changes of reflection strength is proposed. It is also proved, that the smaller optical fiber diameter the higher fluctuations of reflectivity for particular harmonic occur. Results presented for such general case (i.e. phase mask with variable duty cycle with all non-zero diffraction orders) directly correspond to less complex structures, such as uniform phase masks and those with variable groove depth. They are also useful in optimization of Bragg wavelength and harmonic reflection efficiencies as well as in deep understanding of apodized FBG formation using aforementioned phase masks. [ABSTRACT FROM AUTHOR]

A resonant-cavity thyristor photodetector based on the GaAs/AlGaAs material system is fabricated and characterized. The device is triggered with an optical input between a high impedance OFF-state and a low impedance ON-state. Peak linear slope efficiency of 4 A/W is obtained in the OFF-state at the resonant wavelength of 986.6 nm, and is greater than 1 A/W across a 5-nm spectral bandwidth. Operated as an optoelectronic switch, turn-ON is enabled with 20~\mu \textW of optical input power yielding a large-signal current gain of 125 and an output voltage of 1.9 V. [ABSTRACT FROM AUTHOR]

The features of the effect of selective reflection from rubidium vapor in a nanocell with the thickness L ≈ λ/2 and L ≈ λ/4, where λ = 795 nm is the wavelength of laser radiation resonant with the Rb D line, are studied. It is shown that, because of the behavior of the nanocell as a low- Q-factor Fabry-Pérot etalon, the sign of the derivative of the selective reflection spectra changes near L ≈ λ/2 from negative at L > λ/2 to positive at L < λ/2. The simplicity of the experimental implementation, large amplitude, and sub-Doppler width (40MHz) of a detected signal at an atomic transition frequency are appropriate for applications in metrology and magnetometry. In particular, selective reflection from the nanocell is a convenient frequency marker of atomic transitions; in this case, the amplitudes of peaks are proportional to the transition probabilities. The remote optical monitoring of a magnetic field with a spatial resolution L = λ/4 ≈ 199 of nm is possible on the basis of the splitting of selective reflection peaks in a strong magnetic field (up to 3 kG). A theoretical model describes well the experimental results. [ABSTRACT FROM AUTHOR]

We investigate beam scanning by lateral feed displacement in novel metasurface-based reflector antennas with extremely short focal distances. Electric field distributions of the waves reflected from the antenna are studied numerically and experimentally for defocusing angles up to 24°. The results show that despite their subwavelength focal distances, the scanning ability of the metamirrors is similar to that of short-focus reflectarrays (focal distance about several wavelengths). In addition to offering a possibility to realize extremely small focal distances, metamirror antennas are practically penetrable and invisible for any radiation outside of the operating frequency range. [ABSTRACT FROM PUBLISHER]

We propose and demonstrate a reflective-distributed surface plasmon resonance (SPR) sensor based on the twin-core fiber. Firstly, we study the effects of the fiber dual tapered (DT) probe grinding angle on the SPR dynamic range. The results show that for larger grinding angles, the resonance wavelength increases, resulting in a higher testing sensitivity. By using this method, we can make the sensor operate in an optimal waveband. Secondly, on the basis of the results above, we grind the DT probe to be an asymmetric wedge shape to configure two grinding angles (6° and 17°) to realize the distributed sensing. Results show that, with the refractive index detecting a range of 1.333–1.385, we can get two separated sensing zones, 591–715 nm and 729–966 nm, the testing sensitivity are 2385 nm/RIU and 4558 nm/RIU respectively. By using this method, we can detect multiple analytes in the same sensing area simultaneously, besides that we can also effectively compensate for the errors caused by background index interference, and the refractive index change resulting from the non-specific binding, or physical absorption and others. It worth to say that by using this method, we can adjust and control the resonance wavelength by changing the fiber grinding angle, while keeping the testing sensitivity is not reduced. For practical applications, this reflective distributed fiber-based sensor is much suitable for biochemical sensing, it has small size and can enter a small testing spaces (μm scale). The diameter of the twin-core fiber is the only 125 μm, which helps to be integrated into a micro-fluidic chip. In this paper, we integrate the fiber probe into an infusion needle to simulate blood vessels on-line monitoring. [ABSTRACT FROM AUTHOR]

The anisotropy of reflection, transmission and wavelength modulated reflection and transmission optical spectra of ZnAl 2 Se 4 crystals doped by cobalt were investigated at 10 and 300 K. Intersections of refractive indices spectral dependences of ordinary and extraordinary waves (isotropic wavelengths λ 0 , λ 01 , λ 02 and λ 03 ) were revealed in the region of electron transitions from Co 2+ ions and in the depth of absorption band ( λ 04 , λ 05 , λ 06 and λ 07 ). It was found, that the spectral dependence Δ n = n (E⊥c)− n (E||c) intersects the zero axis in all values of isotropic wavelengths as in transmission region and in the depth of absorption band. The bands observed in reflection spectra of crystals in parallel and crossed polarizers at isotopic wavelengths have half-widths around 7–15 Å. Refractive indices in isotropic wavelengths change in 10 1 –10 3 times. Narrow-band filters of different wavelengths could be created on the base of ZnAl 2 Se 4 crystals doped by cobalt. [ABSTRACT FROM AUTHOR]

Metasurfaces can achieve nearly arbitrary wavefront control based on manipulation of the wave phase profile. We propose a metasurface based on double graphene cut-wire resonators which can cover the complete 2π phase region with high reflection efficiency. This full phase coverage is essential for efficient wavefront manipulation, without reflecting energy into unwanted channels. A mirror capable of focusing multiple wavelengths is demonstrated numerically based on the proposed structure. The mirror can effectively focus terahertz (THz) waves from 1.2 to 1.9 THz to the same focal point by changing the Fermi level of each graphene resonator separately. The presented metasurface could provide a powerful platform for controlling THz waves, including focusing, beam steering, beam shaping, and holography. [ABSTRACT FROM AUTHOR]

The propagation and mode conversion of lower hybridwaves in an inhomogeneous plasma are investigated by using the nonlinear δf algorithm in a two-dimensional particle-in-cell simulation code based on the gyrokinetic electron and fully kinetic ion (GeFi) scheme [Lin et al., Plasma Phys. Controlled Fusion 47, 657 (2005)]. The characteristics of the simulated waves, such as wavelength, frequency, phase, and group velocities, agree well with the linear theoretical analysis. It is shown that a significant reflection component emerges in the conversion process between the slow mode and the fast mode when the scale length of the density variation is comparable to the local wavelength. The dependences of the reflection coefficient on the scale length of the density variation are compared with the results based on the linear full wave model for cold plasmas. It is indicated that the mode conversion for the waves with a frequency of 2.45 GHz (ω~3ωLH, where ωLH represents the lower hybrid resonance) and within Tokamak relevant amplitudes can be well described in the linear scheme. As the frequency decreases, the modification due to the nonlinear term becomes important. For the low-frequency waves (ω~1.3ωLH), the generations of the high harmonic modes and sidebands through nonlinear mode-mode coupling provide new power channels and thus could reduce the reflection significantly. [ABSTRACT FROM AUTHOR]

During the thickness assessment of an optical flat with wavelength-tuning interferometry, the second-order harmonics generated by double reflection inside the optical flat and nonlinear wavelength tuning reduce the accuracy of interferometric assessment. In this study, a harmonic phase-iterative analysis was proposed for the thickness assessment with the elimination of the effects of double reflection and nonlinearity. The harmonic phase-iterative analysis was derived by combining the intensity signal, including the harmonic components, with the partial least-squares method. Then, the proposed iterative analysis was integrated with the harmonic convergence condition and the selected pixel technique to improve the computational ability of the phase-iterative analysis. For evaluation, a numerical simulation and experimental thickness assessment using wavelength-tuning Fizeau interferometer were performed employing a five-frame harmonic phase-iterative analysis. The standard deviation of the experimental thickness assessment was 2.561 nm, which was smaller than those by other phase-detection technique. Based on the simulated and experimental results, it can be seen that the proposed harmonic phase-iterative analysis could determine the target phase with enhanced computational ability and compensation for the combined error between the second-order harmonics and the nonlinearity of the wavelength tuning. [ABSTRACT FROM AUTHOR]

This paper discusses the pulse signal of a highly sensitive lateral deformable optical microelectromechanical systems (MEMS) displacement sensor based on Wood's anomalies and its corresponding tolerance. The optical reflection amplitude of the device changes with the displacement of the nanostructured grating elements. Unexpectedly, the device s original sinusoidal signal develops into a new signal form (i.e., a pulse signal), when the air gap between the two layers of gratings decreases. Since the slope of the pulse signal, namely 2.5%/nm (i.e., 0.65 dB/nm), is eight times higher than that of the original signal form, namely 0.3%/nm (i.e., 0.03 dB/nm), the sensitivity of the structure improves by eight times. However, this device is very sensitive to parameters such as its wavelength, period, duty ratio, and air gap. In this paper we used rigorous coupled wavelength analysis (RCWA) to analyze and optimize the respective influence of each parameter on the device's performance. We have intro- duced two methods to search for the optimal setting and have demonstrated the optimal settings of different incident lights. The simulation results indicate that it is close to 85% possible to achieve an actual device with the highest slope superior to 0.5%/nm and it is 64% possible that the highest slope of an actual device falls in the interval ranging from 1.0%/nm to 2.0%/nm. All the simulated data helped us better understand the tolerance of the pulse signal and guide us toward the development of an actual device. [ABSTRACT FROM AUTHOR]

A double-layer guided-mode resonance (GMR) filter with a non-subwavelength grating period is proposed for light reflection at oblique incidence. A zinc oxide coated photo-resist grating GMR filter was fabricated, which exhibits good filter properties. For a transverse magnetic-polarized wave, the grating period is larger than the resonance wavelength, which will reduce the difficulties associated with pattern production. The grating structure with a 750 nm period was fabricated utilizing a low cost two-beam interference system, with resonance obtained at 659.76 nm. In addition, the fabrication tolerance concerning the fill factor and the grating thickness were discussed. The device was designed utilizing numerical methods based on a rigorous coupled-wave analysis. Our design may promote the practical application of GMR filters. [ABSTRACT FROM AUTHOR]

The modeling of Cavity Resonator Integrated Grating Filter (CRIGF) structures, which are long but finite sub wavelength-patterned structures composed with a grating in-out coupler flanked with two Bragg reflectors, is challenging for any numerical method. We show how a numerical code based on RCWA, usually dedicated to model periodic structures, can be used, with minor modifications, to model CRIGFs within a reasonable time of calculation with a personal computer. Our results are in agreement with the calculations based on the FDTD method published in the literature. [ABSTRACT FROM AUTHOR]

The effects of temperature variation on photonic properties of cholesteric liquid crystal elastomers (CLCEs) are investigated in mechanically unconstrained and constrained geometries. In the unconstrained geometry, cooling in the cholesteric state induces both a considerable shift of the selective reflection band to shorter wavelengths and a finite degree of macroscopic expansion in the two directions normal to the axis of the helical director configuration. The thermal deformation is driven by a change in orientational order of the underlying nematic structure S and the relation between the macroscopic strain and S is explained on the basis of the anisotropic Gaussian chain network model. The helical pitch varies with the film thickness in an affine manner under temperature variation. The CLCEs under the constrained geometry where thermal deformation is strictly prohibited show no shift of the reflection bands when subjected to temperature variation. This also reveals the strong correlation between the macroscopic dimensions and the pitch of the helical director configuration. [ABSTRACT FROM AUTHOR]

A method for approximating light scattering properties of strongly absorbing facetted particles which are large compared to the wavelength is presented. It consists in adding the approximated external diffraction and reflection far fields and is demonstrated for a smooth hexagonal prism. This computationally fast method is extended towards prisms with slightly rough surfaces by introducing a surface scaling factor in order to account for edge effects on subfacets forming the rough surface. These effects become more pronounced with decreasing subfacet dimension to wavelength ratio. Azimuthally resolved light scattering patterns, phase functions and degree of linear polarisation obtained by this method and by the discrete dipole approximation are compared for hexagonal prisms with smooth and slightly rough surfaces, respectively. [ABSTRACT FROM AUTHOR]

A quantum cascade laser (QCL) with an output power of 203 W is demonstrated in pulsed mode at 283 K with an angled cavity. The device has a ridge width of 300 μm, a cavity length of 5.8 mm, and a tilt angle of 12°. The back facet is high reflection coated, and the front facet is anti-reflection coated. The emitting wavelength is around 4.8 μm. In distinct contrast to a straight cavity broad area QCL, the lateral far field is single lobed with a divergence angle of only 3°. An ultrahigh brightness value of 156 MW cm-2 sr-1 is obtained, which marks the brightest QCL to date. [ABSTRACT FROM AUTHOR]

Reflection and refraction at an abrupt dielectric interface at normal incidence are evaluated using an amplitude and phase (amph) formalism. The optical properties of a stack with two quarter-wavelength layers are then calculated. The characteristics of a mirror constructed with quarter-wavelength layers are discussed using the amplitude and phase representation. Floquet nonlinear theorem is invoked to describe the multi-layered system. Results are consistent with Fresnel formulae and conventional matrix methods for stratified periodic media. However, the amph formalism offers several advantages: (i) it is capable of showing the field properties as it propagates though the stack, (ii) it gives a lucid physical insight because the variables involved have a clear physical meaning, and (iii) the mathematical description is simple. [ABSTRACT FROM PUBLISHER]

We derive periodic multilayer absorbers with effective uniaxial properties similar to perfectly matched layers (PML). This approximate representation of PML is based on the effective medium theory and we call it an effective medium PML. We compare the spatial reflection spectrum of the layered absorbers to that of a PML material and demonstrate that after neglecting gain and magnetic properties, the absorber remains functional. This opens a route to create electromagnetic absorbers for real and not only numerical applications and as an example we introduce a layered absorber for the wavelength of 8 $$\upmu \hbox {m}$$ made of $$\hbox {SiO}_2$$ and NaCl. We also show that similar cylindrical core-shell nanostructures derived from flat multilayers also exhibit very good absorptive and reflective properties despite the different geometry. [ABSTRACT FROM AUTHOR]

This paper presents the optical absorptance and reflectance in Lead zirconate titanate grating for the solar cells. By properly selected the appropriate grating periods, grating height, duty rate and the film thickness, the related devices could be developed to have bright performance. This study revealed that the grating with 200 nm square grating, 200 nm grating height on the 100 nm film thickness, application of the proposed related devices to an appreciable high absorptance, which reaches up to 99.6% in the wavelength from 200 nm to 550 nm. These advantages make our design showed the great potential in such as imaging, detection, and solar energy applications. [ABSTRACT FROM AUTHOR]

This work presents a validated optical fluence rate model optimised for ultraviolet light-emitting diodes (UV-LEDs), which allow a very wide range of emission wavelengths and source geometries to be used in water treatment units. The model is based on a Monte Carlo approach, in which an incremental ray-tracing algorithm is used to calculate the local volumetric rate of energy absorption and subsequently convert it to the local fluence rate distribution for an UV-LED water treatment chamber of arbitrary design. The model includes contributions from optical reflections and scattering by treatment chamber walls and from scattering due to particulates and/or microorganisms. The model successfully predicts optical fluence rates in point-of-use water treatment units, as verified using biodosimetry with MS-2 bacteriophage at a UV-LED emission wavelength of 254 nm. The effects of chamber geometry are also modelled effectively and are consistent with the inactivation data for E. coli at 254 nm. The data indicate that this model is suitable for application in the design and optimisation of UV-LED-based water treatment systems. [ABSTRACT FROM AUTHOR]

We report on an experimental study of the injected optical power required for polarization switching (PS) in a vertical-cavity surface-emitting laser (VCSEL) subject to orthogonal optical injection. This power is found as a function of the frequency detuning between the injected light and suppressed linear polarization of the solitary VCSEL. Increasing the injected power, we found two types of PS when injecting light with wavelength close to the wavelength of the suppressed linear polarization and to that of the linear polarization of the solitary VCSEL. These two types of PS are, respectively: 1) single and double (with two minima of injected power necessary for PS) and 2) double PS (with two islands of PS and a separate region with a single minimum of injected power). Our experimental results confirm the theoretical predictions of Torre et al. Double PS is observed around the elliptically polarized injection locked states found by Lin et al. Different dynamics are found in the route to PS. [ABSTRACT FROM AUTHOR]

A single-layer broadband polarizer has been designed for operating in the telecommunication wavelength band. The rigorous coupled-wave analysis (RCWA) is applied to study the optical spectrum for the optimized structure. High polarization efficiency, high extinction ratio with a broad wavelength range (1.45–1.75 μm) are obtained. Both of the transmission efficiencies of TM-polarization and reflection efficiencies of TE-polarization are over 95%. The extinction ratio of transmission is over 30 dB in the 1.45–1.75 μm wavelength range, and the value is 114 dB for the central wavelength. The designed polarizer may lead to potential application in optical communication and infrared imaging polarimetry. [ABSTRACT FROM AUTHOR]

We propose a method for measuring the thickness of the exfoliated MoSe2 layers deposited on Si/SiO2 substrate, based on the reflectance measurements performed with laser light illumination at two different wavelengths: red and green from confocal microscope at room temperature. We demonstrate the correlation between the number of layers in a flake and the value of its relative reflection difference. We applied the transfer matrix method to calculate the reflectivity and verify our experimental results. The approach proposed by us allows for fast and automatic verification of the exfoliated MoSe2 layers thickness on large areas of the substrate. [ABSTRACT FROM AUTHOR]

A mixed metal dielectric sandwiched grating is described for polarization-selective reflection. The novel grating is composed of substrate, metal slab, two dielectric grating layers, and covering layer. The polarization-selective grating is optimized by using rigorous coupled-wave analysis for the usual duty cycle of 0.5. With the optimized grating parameters, reflective efficiency of 96.49% can be diffracted into the -1st order for TE polarization. And two-port output of 48.26%/48.27% can be diffracted into the 0th and the -1st orders for TM polarization. Polarization-selective reflection with good performance can be obtained by the mixed metal dielectric sandwiched grating. The usual duty cycle of 0.5 makes it easy and simple to be fabricated for practical applications. Moreover, the polarization-selective beam splitter based on the mixed metal dielectric sandwiched grating has advantages of wide incident wavelength range for TE polarization and angular bandwidth for TM polarization. [ABSTRACT FROM AUTHOR]