Conical Mounting Research Articles

Polarization Property Associated with Surface Plasmon Resonance in a Palladium Thin-Film Coated Aluminum Grating in a Conical Mounting and Its Application to Hydrogen Gas Detection.

We have investigated a polarization property of the (specularly) reflected light from an aluminum grating, coated with a palladium (Pd) thin-film on its surface. The polarization property, which is associated with surface plasmon resonance (SPR), and occurs in the Pd thin-film on the aluminum grating in a conical mounting, is observed as a rapid change in the normalized Stokes parameter s3, around the resonance angle, θsp, at which point, SPR occurs. The sensing technique used the rapid change in s3 to allow us to successfully detect a small change in the complex refractive index of the Pd thin-film layer upon exposure to hydrogen gas, with a concentration near the lower explosion level. Experimental results showed that the sensing technique provided a sensitive and stable response when the Pd thin-film layer was exposed to gas mixtures containing hydrogen at concentrations of 1 to 4% (by volume) in nitrogen.

Incident angle-tuned filter based on 1D resonant waveguide grating in full conical mounting

Incident angle-tuned filter based on 1D resonant waveguide grating in full conical mounting

Investigation into Ethanol Concentration Changes of Ethanol–Water Solution Using Polarization Property Associated with Surface Plasmon Resonance in Aluminum Grating in Conical Mounting

Investigation into Ethanol Concentration Changes of Ethanol–Water Solution Using Polarization Property Associated with Surface Plasmon Resonance in Aluminum Grating in Conical Mounting

Кремниевые решетки с блеском для мягкого рентгеновского и экстремального ультрафиолетового излучения: влияние формы профиля штриха и случайной шероховатости на дифракционную эффективность

The effect of the groove profile shape and random roughness of the reflecting facet of five silicon diffraction gratings (1°-4° blaze angle, period 0.4, 1.4, 2, and 4 μm, various coatings) operating in the soft X-ray and extreme ultraviolet radiation ranges on the outflow of the diffraction efficiency from working orders is studied. Diffraction gratings were fabricated by wet etching of Si(111) vicinal wafers and characterized by atomic force microscopy to determine the shape of the groove profile and roughness. The diffraction efficiency of gratings operating in classical and conical diffraction mounts was calculated based on realistic groove profiles by computer simulation using the PCGrateTM code and taking into account the scattering intensity using Nevot-Croce or Debye-Waller corrections or using the Monte Carlo method (rigorously). The effect of the groove profile shape and roughness on the diffraction efficiency of the fabricated Si gratings is shown.

Third harmonic generation enhancement from silicon-based multilayer guided mode resonance structures under a conical mounting condition

We experimentally demonstrate more than four-orders of magnitude enhancement in third harmonic generation from an amorphous silicon layer as thin as 10 nm deposited above silicon nitride guided mode resonance (GMR) structures under a conical mounting condition using a rectangular aperture as a pupil plane mask for the fundamental excitation. The multilayer GMR structure studied here consists of shallow etched one-dimensional silicon dioxide gratings with a silicon nitride intermediate layer and an amorphous silicon nonlinear medium. Under conical mounting, by restricting the fundamental excitation angles along the grating vector direction, while retaining the angles supported by the objective lens along the grating lines, the resonances are made angle insensitive. The forward detected THG enhancement increases from 2860 in the absence of any pupil plane mask, with a uniform fundamental excitation angular span of 2.3° to 4740 and 1.7 × 104 in the presence of rectangular apertures that selectively reduce the excitation angular span along the grating vector direction to 0.86° and 0.43°, respectively. Conical mounting using rectangular aperture pupil masks to engineer the fundamental excitation is a promising approach to enhance nonlinear optical processes from angle sensitive GMR structures.

Cr/C lamellar multilayer grating in conical diffraction mounting for beam splitter used in X-ray free-electron lasers.

A lamellar multilayer grating in a conical diffraction mounting was proposed as a beam splitter for X-ray free-electron lasers. Theoretical calculations demonstrated that the distribution of diffraction efficiency can be adjusted by optimizing the groove depth or d-spacing. A Cr/C multilayer lamellar grating with a line density of approximately 2500 L/mm was fabricated. The performance of the element was measured in the Optics Beamline PM-1 (BESSY-II) at an energy of 1500 eV. A five-order diffraction pattern was recognized, and the diffraction efficiencies of the -/+first-order were approximately 12.6 and 4.4%, respectively. The asymmetric distribution of diffraction efficiency can be caused by the different sidewall angles of the grating groove.

Blazed Diffraction Gratings on Si --- First Results

Using direct laser lithography and wet etching of polished vicinal Si(111) wafers, a technology was developed and diffraction gratings 500 grooves/mm with a blaze angle of 4o were fabricated. The manufacturing process of a reflective Si-grating with the triangular profile (sawtooth) can be divided into four main steps: (1) obtaining a pattern of a protective mask for grooves etching; (2) anisotropic etching of grooves in KOH solution; (3) etching to smooth the grating profile and polish the surface of working facets; (4) coating to increase reflectivity. The samples obtained were characterized using scanning electron microscopy and atomic force microscopy methods to determine the shape of the groove profile and roughness: the shape turned out to be close to the ideal triangular, and the RMS roughness was less than 0.3 nm. Using PCGrateTM software and taking into account the measured real groove profile, the diffraction efficiency of gratings operating in classical and conical mounts in soft-X-ray and extreme ultraviolet radiation has been simulated. The obtained efficiency values are close to the record ones for the corresponding spectral range and the Au-coating of the grating. Keywords: diffraction grating, wet etching technology of Si, sawtooth groove profile, AFM, SEM, diffraction efficiency modelling.

Spectral beam combining gratings: high diffraction efficiency at a large deviation angle achieved around conical Littrow mounting.

We theoretically make plausible and numerically verify that when a high-efficiency, polarization-independent grating, designed to work at or near Littrow mounting, is used in conical Littrow mounting, its high efficiency and polarization independence can be very well maintained at a large off-principal-plane deviation angle. This finding provides a new degree of freedom to the design of high-efficiency, more compact spectral beam combining grating systems.

Polarization property associated with surface plasmon resonance in a metal grating in a conical mounting and its application to refractive index sensing.

We focus on the normalized Stokes parameter s3 of the specularly reflected light from a metal grating in a conical mounting in order to accurately and sensitively detect the occurrence of surface plasmon resonance (SPR). Experimental and theoretical investigations into the incident angle dependence of s3 reveal a rapid change in s3 around the resonance angle θsp at which SPR occurs. The rapid change in s3 has features that are successfully applied to SPR sensing: the zero-crossing point of s3 determines θsp, and s3 in the vicinity of θsp varies markedly in response to a small change in the refractive index of a sample. An experiment using gas samples demonstrates that SPR sensing that considers the rapid change in s3 clearly detects a refractive index change on the order of 10-5.

Дифракционные решетки с блеском, получаемые на пластинах Si --- первые результаты

Using direct laser lithography and liquid etching of polished vicinal Si(111) wafers, a technology was developed and diffraction gratings 500 /mm with a blaze angle of 4° were fabricated. The manufacturing process of a reflective Si-grating of a triangular profile (sawtooth) can be divided into four main steps: (1) obtaining a pattern of a protective mask for etching grooves; (2) anisotropic etching of grooves in KOH solution; (3) etching to smooth the grating profile and polish the surface of working facets; (4) coating to increase reflectivity. The samples obtained were characterized using scanning electron microscopy and atomic force microscopy methods to determine the shape of the groove profile and roughness: the shape turned out to be close to the ideal triangular, and the root-mean square roughness was less than 0.3 nm. With the help of the PCGrate™ code, taking into account the measured real groove profile, the diffraction efficiency of gratings operating in classical and conical mounts in soft-X-ray and extreme ultraviolet radiation has been simulated. The obtained efficiency values are close to the record ones for the corresponding spectral range and the Au-coating of the grating.

Guided-mode resonance-based bandpass filter operating at full conical mounting.

We propose a cost-effective narrow bandpass filter based on a guided-mode resonance (GMR) structure, operating at full conical mounting configuration. Two additional layers above the GMR structure with designed geometry is considered to create a large angle of incidence (AOI) on the GMR structure with an almost normal AOI on the entire structure. In the visible wavelength range, the transmission spectrum contains three peaks: two peaks that are due to the GMR effect and one that is due to thin-film interference. The modal characteristic of the two GMR peaks is identified using a matrix method for the n-layer waveguide structure. The two GMR peaks with bandwidths of ∼1nm and ∼0.5nm correspond to the fundamental TE and TM modes, respectively. The GMR peaks can be pushed away from the thin-film interference peak by modulating the grating depth.

High azimuthal angle tolerant dual-channel wavelength filter from visible to NIR using conically mounted guided mode resonance structures.

We present a concept to design narrow linewidth dual-channel wavelength filters using the principle of wavelength tuning under conical mounting of guided mode resonance structure. The general procedure for the design of such filters from visible to NIR wavelength range is presented and validated experimentally. We show that already fabricated guided mode resonance structures that do not show dual wavelength filtering at these wavelengths in classical mounting can exhibit dual wavelength filtering in conical mounting. Using this principle, we design high azimuthal angle tolerant guided mode resonance dual wavelength filters at C-band communication wavelengths (1310 and 1550 nm) that are insensitive to azimuthal angle over a range of up to 20 deg, achieved in expense of a tolerance in the angle of incidence that is less than 3 deg.

Polarization-independent absorption enhancement in graphene for light incidence in conical mounting

A terahertz graphene tunable absorber consisting of monolayer graphene on a dielectric grating and a substrate separated by a waveguide layer is designed and investigated. The absorber exhibits polarization-independent absorption enhancement at resonance for fully conical light incidence, which is attributed to the simultaneous excitation of two identical guided modes in the waveguide layer. Moreover, the absorber possesses an ultranarrow absorption profile with an ultrahigh quality factor. To intuitively confirm the potential physical mechanism of such phenomena, the electromagnetic field distributions for both polarized light are described. Finally, the influences of Fermi level and relaxation time on the absorption properties are investigated, which present the flexible tunability of the proposed device. It is believed that the conclusions will enable the development of optoelectronic devices by simply combining graphene with a guided-mode resonance structure.

Flat-top Brewster filter based on guided mode resonance effect

We have analyzed and discussed a flat-top Brewster filter that works in full conical mounting. Results reveal that flat-top reflection band can be formed by merging double peaks that corresponded to guided modes with different polarization states. Merging is achieved by adjusting the incident angle in the design. When the proposed single-layer waveguide grating structure is irradiated with transverse magnetic (TM) polarized plane wave at the Brewster angle, the filter has a highly efficient flat-top reflection spectral response with central wavelength of 547 nm, bandwidth of 15.5 nm (R > 90%), and sideband reflectance of <2.3%.

Polarization-independent guided-mode resonance filtering by all-dielectric gratings in the terahertz region.

We propose an angular-dependent polarization-insensitive filter in the terahertz (THz) region, based on the guided-mode resonance of one-dimensional zero-contrast grating architectural design. Particle swarm optimization combined with the rigorous coupled-wave analysis method is used to design the filter and investigate the influences of the planes of incidence on the characteristics of the proposed all-dielectric THz filter. With the planes of incidence set at 0°, 30°, 45°, and 60°, the polarization-independent resonances occur at 0.458 THz, 0.459 THz, 0.461 THz, and 0.465 THz under oblique incidences of 9.3°, 10.8°, 13.3°, and 19.2°, respectively, which means the oblique incident angle of the polarization-independent THz filter increases with the rotation of the planes of incidence from classic mounting to fully conical mounting. In addition, for the fully conical mounting case, the resonance has high angular stability and is no longer split, compared with classic incidence; meanwhile, there is only a tiny blue shift in resonance of less than 3 GHz when changing the incident angle from 0° to 10°. The physical mechanism of the spectral characteristics is also analyzed in detail. The spectral properties proposed herein enable significant potential application in the fields of spectroscopy, image sensors, communication, etc., in the THz region.

Effective-medium permittivity of one-dimensional gratings of vertically invariant and laterally arbitrary permittivity distribution

ABSTRACTDerivation of effective-medium permittivities (in the traditional sense) of one-dimensional gratings is revisited. In the present derivation, carried out in Fourier-space and for conical mounting, systematic treatment and mathematical rigour are emphasized. An error of a previous paper published in this journal concerning the 2nd-order effective permittivity in TM polarization is corrected. The derived formulas of the 4th-order effective permittivity and the 2nd-order effective permittivity, when restricted to TE and TM polarizations respectively, agree well with the previous results. The symmetry of the effective permittivities with respect to the sign of the Floquet exponential factor and the sign of grating period is noted and proven.

Polarization-insensitive one-dimensional guided-mode resonance filter operating at conical mounting.

We report the design and implementation of a one-dimensional guided-mode resonance filter (1D-GMRF) aiming to achieve polarization insensitivity at conical mounting. (The incident plane is aligned neither perpendicularly nor parallelly to the grating bars.) The design guideline indicates that, at conical mounting, polarization insensitivity of the 1D-GMRF can be achieved by optimizing the grating parameters to excite the fundamental TE and the fundamental TM waveguide modes simultaneously. Moreover, it is revealed that, at conical mounting, the polarization-insensitive GMR position in the angle-resolved resonance spectra is azimuthal angle ϕ-dependent. The experimental results demonstrate that polarization insensitivity of the fabricated 1D-GMRF occurs at the resonance wavelength of ∼673 nm for the conical mounting of azimuthal angle ϕ≈30° and incident angle θ≈11.2°, which agree with the simulated results.

Polarization-Insensitive Filter for Incidence Between Classic and Full Conical Mountings

An angular-dependent polarization-insensitive filter in the telecommunication region is demonstrated in this letter, which is based on a zero-contrast grating for incident plane between classic and full conical mountings. Particle swam optimization combined with the rigorous coupled wave analysis method is applied to design the filter and perform the reflectance spectra. Realization of the polarization-insensitive filter is based on the split feature of a 1D guided mode resonant filter, under oblique incidence in classic mounting. Results show that polarization-independent resonances occur near $1.454~\mu \text{m}$ under the oblique incidences of 4.8°, 5.3°, 6.5°, and 9.3°, with the incident plane angle being set as 15°, 30°, 45°, and 60°, respectively. During the process of varying the incident plane angle from classical mounting to full conical mounting, the mechanism of the increased angle of oblique incidence is also analyzed in detail.

Cross-polarization mode coupling and exceptional points in photonic crystal slabs

We study exceptional points that occur in photonic crystal slabs due to cross-polarization (TE-TM) mode coupling. To do this, we develop spatiotemporal coupled-mode theory that describes optical properties of photonic crystal slabs supporting TE and TM modes in the case of conical mount. The developed theory suggests that by tuning the in-plane wave numbers of the incident light one can make two modes of the structure coalesce, which results in an exceptional point. The developed theory provides simple analytical expressions for the exceptional point position and the line shape of the corresponding resonance. The parameters of the proposed model can be rigorously estimated by a numerical calculation of the S-matrix poles of the structure. We show that the proposed analytical model with the estimated parameters is in good agreement with the presented full-wave simulations.

Robust overlay metrology with differential Mueller matrix calculus.

Overlay control is of vital importance to good device performances in semiconductor manufacturing. In this work, the differential Mueller matrix calculus is introduced to investigate the Mueller matrices of double-patterned gratings with overlay displacements, which helps to reveal six elementary optical properties hidden in the Mueller matrices. We find and demonstrate that, among these six elementary optical properties, the linear birefringence and dichroism, LB' and LD', along the ± 45° axes show a linear response to the overlay displacement and are zero when the overlay displacement is absent at any conical mounting. Although the elements from the two 2 × 2 off-diagonal blocks of the Mueller matrix have a similar property to LB' and LD', as reported in the literature, we demonstrate that it is only valid at a special conical mounting with the plane of incidence parallel to grating lines. The better property of LB' and LD' than the Mueller matrix elements of the off-diagonal blocks in the presence of overlay displacement verifies them to be a more robust indicator for the diffraction-based overlay metrology.