Rigorous Diffraction Theory Research Articles

Double groove silicon grating polarizer in telecommunication wavelength band

In this paper, we propose an ultra broad band polarizer operating in the telecommunication wavelength band, this device consisting a double groove silicon grating is designed with using the inverse mathematical method and rigorous vector diffraction theory. It is shown from our calculations that the device presents extremely high reflection (R>95%) for TE polarization light and high transmission (T>95%) for TM polarization over ∼400nm wavelength range, moreover, the extinction ratio is ∼30 in the central wavelength 1550nm. Furthermore, it is found with rigorous coupled wave analysis (RCWA) that the extremely wide band property for TE polarization is due to the excitation of strong modulation guided modes in the design wavelength range.

Extremely wide band Rayleigh resonant reflector with sharp angular spectra in near infrared wavelength band

In this paper, we propose an extremely broadband Rayleigh resonant reflector with sharp angular spectra operating in near infrared wavelength band, this device consisting of a single germanium resonant grating layer is designed and analyzed by using with the rigorous vector diffraction theory. At the Rayleigh angle, the first diffracted order can be appear from evanescent to a propagating one, thus, a very sharp angular spectrum characteristics can be presented in the device. Based on the guided mode resonant effect, high index material such as silicon and germanium can be designed as wide band reflector, beam splitter and polarizer in near infrared wavelength region. Through connecting Rayleigh phenomena and guided mode resonant effect, we can design a new kind of optical devices with versatile characteristics such as sharp angular spectra and extremely wide reflection band. In this paper, we present a Rayleigh resonant reflector with extremely high reflection (R>99.5%) for TE polarization light over ∼600nm wavelength range and sharp angular spectral distribution. In addition, it is shown from our calculations that the high-index nano-layer located adjacent to the substrate is seen to critically affect the resulting spectra of Rayleigh resonant reflector.

Improvement of light trapping in thin-film silicon solar cells by combining periodic and random interfaces

The concept of photonic random textures for application as a light-trapping scheme in thin-film solar cells is introduced. Those textures consist of a randomly textured interface, as commonly applied in thin-film solar cells, which is superimposed with a two-dimensional grating structure. The light-scattering properties of those textures are investigated by scalar scattering theory for transmission into the absorber layer and reflection at the back contact. A quantity to describe the light-trapping efficiency is derived and verified by rigorous diffraction theory. The photonic random textures outperform the random textures and the grating structures significantly.

Detection limits of confocal surface plasmon microscopy.

This paper applies rigorous diffraction theory to evaluate the minimum mass sensitivity of a confocal optical microscope designed to excite and detect surface plasmons operating on a planar metallic substrate. The diffraction model is compared with an intuitive ray picture which gives remarkably similar predictions. The combination of focusing the surface plasmons and accurate phase measurement mean that under favorable but achievable conditions detection of small numbers of molecules is possible, however, we argue that reliable detection of single molecules will benefit from the use of structured surfaces. System configurations needed to optimize performance are discussed.

Broadband antireflection enhancement by triangular grating microstructure in the resonance domain

Abstract It is well known that broadband antireflective characteristics are frequently realized by using subwavelength tapered micro- or nanostructures. In this paper, we propose that the triangular grating in the resonance domain with period larger than the incident wavelength can also possesses broadband and wide angle antireflective performance and polarization selection. The diffraction pattern for the external reflection grating and the internal reflection one is demonstrated by the rigorous vector diffraction theory. It is found that the total transmittivity with TE polarized illumination is clearly less than that for TM polarization. The aspect ratio of grating is a significant parameter to broadband antireflection performance. For the external reflection grating, the broadband antireflection function can be achieved with the aspect ratio larger than 1.5 for both polarization modes in the resonant domain. For the internal reflection grating, the narrow band antireflection properties are demonstrated for TE polarization with higher aspect ratio. And the broadband antireflection characteristics can be revealed at the aspect ratio higher than 4.0 in the resonance domain for TM polarization. Besides, in order to determine intuitively diffraction pattern and antireflection performance, the electric field distribution was calculated for both types of triangular profile in the resonant domain, and the aspect ratio of the grating is crucial to the total transmittance.

Theoretical Analysis of Vector-Vortex Fields Generated by Quasi-Periodic Planar Structure

It was experimentally demonstrated that a circularly polarized plane beam passing through a properly designed quasi-periodic planar structure (qPPS) will be converted into the Bessel-like beam with spiral phase structure. This letter provides the analysis of the vector-vortex field diffracted from the qPPS by performing the rigorous vector diffraction theory. Results demonstrate that a vector-vortex beam can be generated by employing such qPPS, and that its polarization profile can be manipulated by changing elliptically polarized field illuminated onto the qPPS. Results derived in this letter are expected to find potential applications in communication, imaging, etc.

Broad band beam splitter based on the double-groove fused silica grating

In this paper, we propose a broad band 1×3 beam splitter operating in the telecommunication wavelength band under normal incidence, this device consisting of a double-groove fused silica grating layer is designed with using the inverse mathematical method and rigorous vector diffraction theory. It is shown from our calculations that the device presents excellent beam splitter ability for TE polarization light with the average diffraction efficiencies is more than 95% over ∼100nm wavelength range, moreover, the uniformity of our beam splitter is better than 2% in the whole wavelength band. Furthermore, the physical understanding of the diffraction behaviors taking place inside the beam splitter gratings can be explained by the modal method.

Wide band polarizer with suspended silicon grating

In this paper, we propose an ultra broadband polarizer operating in the telecommunication wavelength band; this device consisting a single silicon suspended resonant grating layer is designed with using the inverse mathematical method and rigorous vector diffraction theory. It is shown from our calculations that the device presents extremely high reflection (R>98%) for TE polarization light and high transmission (T>98%) for TM polarization over ∼330nm wavelength range; moreover, the extinction ratio is ∼100 in the central wavelength 1550nm. Furthermore, it is found with Rigorous Coupled Wave Analysis (RCWA) and near field distribution that the extremely wide band property for TE polarization is due to the excitation of strong modulation guided modes in the design wavelength range.

Free-field characterization via directional transmission through a nanoaperture

We propose a scheme based on extraordinary transmission of light through a single nanoaperture, surrounded by periodic corrugations, for direct characterization of focal-region optical fields with subwavelength-scale structure. We describe the design of the device on the basis of rigorous diffraction theory and fabricate a prototype using a process that involves electron beam lithography, dry etching, and template stripping. First experimental results performed with a transmission-type confocal optical microscope demonstrate the potential of the method.

Phase anomalies in Talbot light carpets of self-images

An interesting feature of light fields is a phase anomaly, which occurs on the optical axis when light is converging as in a focal spot. Since in Talbot images the light is periodically confined in both transverse and axial directions, it remains an open question whether at all and to which extent the phase in the Talbot images sustains an analogous phase anomaly. Here, we investigate experimentally and theoretically the anomalous phase behavior of Talbot images that emerge from a 1D amplitude grating with a period only slightly larger than the illumination wavelength. Talbot light carpets are observed close to the grating. We concisely show that the phase in each of the Talbot images possesses an anomalous axial shift. We show that this phase shift is analogous to a Gouy phase of a converging wave and occurs due to the periodic light confinement caused by the interference of various diffraction orders. Longitudinal-differential interferometry is used to directly demonstrate the axial phase shifts by comparing Talbot images phase maps to a plane wave. Supporting simulations based on rigorous diffraction theory are used to explore the effect numerically. Numerical and experimental results are in excellent agreement. We discover that the phase anomaly, i.e., the difference of the phase of the field behind the grating to the phase of a referential plane wave, is an increasing function with respect to the propagation distance. We also observe within one Talbot length an irregular wavefront spacing that causes a deviation from the linear slope of the phase anomaly. We complement our work by providing an analytical model that explains these features of the axial phase shift.

Hybrid liquid crystal photorefractive system for the photorefractive coupling of surface plasmon polaritons

We present a detailed investigation of a photorefractive surface plasmon polariton system capable of coupling energy between two predefined surface plasmon modes with efficiencies up to 25%. We have investigated the dependence of the diffraction efficiency on the energy, the initial and final wavevectors of the surface plasmon modes, and the cell parameters. We have also developed numerical simulations of the system based upon the defect-free Q-tensor approach and rigorous diffraction theory, which fit the experimental data very well and have allowed us to develop a good theoretical understanding of the performance of these cells. On the basis of the experimental results and theory we discuss the prospects that a hybrid liquid crystal photorefractive system could lead to photorefractive gain for surface plasmon polaritons.

Optical bistability in a doubly resonantχ(2)-nonlinear plasmonic nanocavity

We demonstrate optical bistability in a ${\ensuremath{\chi}}^{(2)}$-nonlinear plasmonic nanocavity. The nanocavity is made from a metal-insulator-metal waveguide possessing stubs as realistic mirrors. The design of the nanocavity is sufficiently flexible to allow for resonances at both the fundamental and the second-harmonic frequency and a phase-matched nonlinear interaction. By using rigorous diffraction theory and a mean-field approach, we establish the conditions required to observe optical bistability and present optimal configurations with regard to a minimum pump power. This work might be useful for employing plasmonic nanocircuits in optical computing schemes.

Surface plasmon microscopy: resolution, sensitivity and crosstalk

This paper develops the theoretical framework to understand the capability of the interferometric surface plasmon microscope to quantify sample properties in a confined region. We use rigorous diffraction theory to quantify the ability of the system to measure local properties and eliminate crosstalk from adjacent regions. We argue that the interferometric system in the defocused condition defines the measured point of excitation and reradiation of the surface plasmons; which greatly improves localisation. We also present results for the noninterferometric microscope, which confirm that the interferometric based system can perform quantitative measurements over smaller regions.

Talbot images of wavelength-scale amplitude gratings

By means of experiment and simulation, we achieve unprecedented insights into the formation of Talbot images to be observed in transmission for light diffracted at wavelength-scale amplitude gratings. Emphasis is put on disclosing the impact and the interplay of various diffraction orders to the formation of Talbot images. They can be manipulated by selective filtering in the Fourier plane. Experiments are performed with a high-resolution interference microscope that measures the amplitude and phase of fields in real-space. Simulations have been performed using rigorous diffraction theory. Specific phase features, such as singularities found in the Talbot images, are discussed. This detailed analysis helps to understand the response of fine gratings. It provides moreover new insights into the fundamental properties of gratings that often find use in applications such as, e.g., lithography, sensing, and imaging.

Coherence–polarization mixing in resonance gratings

We show, using rigorous diffraction theory, that resonance gratings can be used to transfer partial spatial correlation to partial polarization even if the incident light beam is fully polarized. The phenomenon is based on the fact that either of the two orthogonal polarization components can be coupled into the leaky waveguide mode, leading to a strong phase delay, while the other one is reflected without being coupled into the grating. Numerical demonstrations are based on a Gaussian Schell-model beam and a grating analysis performed by rigorous Fourier modal method.

Wide band polarizer with suspended germanium resonant grating

An ultra broad band polarizer that operates in the telecommunication wavelength band is proposed. This device, which consists of a single suspended germanium resonant grating layer, is designed using the inverse mathematical method and the rigorous vector diffraction theory. Calculated results indicate that the ultra broad band polarizer exhibits extremely high reflection (R>99%) for TE polarization light and high transmission (T>99%) for TM polarization at the wavelength range greater than 300 nm, and it has an extinction ratio of approximately 1 000 at the 1 550-nm central wavelength. The results of the rigorous coupled wave analysis indicate that the extremely wide band property of the TE polarization is caused by the excitation of strong modulation guided modes in the design wavelength range.

Scattering in elements of plasmon optics suppressed by two-layer dielectric structures

Based on the results of simulations in the framework of a rigorous electromagnetic theory of diffraction, it is shown that a structure comprising two isotropic dielectric layers on a metal surface can be used to suppress parasitic scattering in elements of plasmon optics. The proposed dielectric structure makes possible a tenfold decrease (to 1–3%) in the level of scattering losses. This approach can also be applied in creating various elements of plasmon optics, in particular, lenses and Bragg reflection gratings.

Theory of hybrid photorefractive plasmonic liquid crystal cells

We use the theory of optical waveguides to study analytically the voltage-dependent response of a surface plasmon polariton (SPP) at the interface between a photorefractive liquid crystal cell and a semi-infinite gold layer. For sufficiently large electric fields the alignment of the liquid crystal can be calculated analytically. The resulting correction to the SPP dispersion relation is then determined in terms of the applied field and the liquid crystal surface alignment relative to the SPP propagation direction. The approximate analytic techniques developed here are shown to be accurate when compared to rigorous diffraction theory and experimental measurements. The approximate equations are a powerful tool of general application. They can be used to study SPP propagation at the interface between a metal and any nonhomogeneous or anisotropic dielectric and are also applicable to self-assembled monolayers and biosensing applications.

Nanofabrication of Broad-Band Antireflective Surfaces Using Self-Assembly of Block Copolymers

We present a simple and cost-effective method for the fabrication of antireflective surfaces by self-assembly of block copolymers and subsequent plasma etching. The block copolymers create randomly oriented periodic patterns, which are further transferred into fused silica substrates. The reflection on the patterned fused silica surface is reduced to well below 1% in the ultraviolet, visible, and near-infrared ranges by exploiting subwavelength nanostructures with periodicities down to 48 nm. We show that by choosing the appropriate block copolymers and pattern transfer parameters the optical properties of the antireflective surface can be easily tuned, and the spectral measurements verify a significant reduction of the reflectivity by a factor of 10. The experiments, confirmed with simulations based on rigorous diffraction theory, also show that the tapered shape of the nanostructures gives rise to a graded index surface, resulting in a broad-band antireflective behavior.

Light absorption in textured thin film silicon solar cells: A simple scalar scattering approach versus rigorous simulation

Rigorous diffraction theory is a reliable tool to quantify the absorption enhancement in textured thin film solar cells. We provide a line of arguments that make the insights from such an involved analysis accessible to a broader community by using a scalar approach. We show that the scattering response from a textured surface as calculated by a simple scalar model can be related to the measured external quantum efficiency of a solar cell and double-check this model by rigorous calculations. This approach allows estimating the performance of a textured thin film to a certain extent without any sophisticated numerical analysis.