Color separation of high-density dielectric rectangular grating in the Fresnel diffraction region

A high-density dielectric rectangular grating is designed for color separation in a Fresnel diffraction field. The Fresnel field distribution is analyzed and the optimization conditions for color separation are given. The process of the modes propagating and energy exchanging with the diffraction orders are expressed by modal method. The color separation for different polarizations can be realized. The energy efficiency is 96.3% at the 633 nm wavelength and 86.9% at the 488 mm wavelength for both TE polarizations, while the energy efficiency is theoretically 96.3% at the 633 nm wavelength for TE polarization and 90.6% at the 488 nm wavelength for TM polarization. The field distributions are scanned by the near-field scanning optical microscopy, and the efficiency is 71.2% for the 633 nm wavelength and 67.3% for the 488 nm wavelength for both TE polarizations experimentally.     

Measurement of duty cycles of metal grating masks formed on dielectric substrates

A nondestructive method for measuring the duty cycles of metal grating masks formed on top of dielectric substrates is proposed. For a near-normal angle of incidence, the zeroth diffracted order transmission efficiency curves for both TE and TM polarized probe lights, as a function of duty cycles, behave linearly in the duty cycle ranging from 0 to 1. By comparing the measured efficiencies, or the ratio of zeroth-order transmission efficiency for TM polarization to that for TE polarization, with that of the rigorous-coupled wave analysis (RCWA) method for a fixed grating period and depth, one can determine the duty cycle of the grating. By selecting the probe light appropriately, the measurement errors originating from deviations of the incident angle and grating depth can be negligible. This method is applicable for all metal gratings, which are not easy to measure nondestructively due to fine grooves smaller than the wavelength. This method is simple, accurate, nondestructive, and low-cost. The results of experimental verification are presented and show excellent agreement with scanning electron microscope images.     

Design of transmission blazed binary gratings for optical limiting with the form-birefringence theory

The structure of transmission blazed binary gratings for optical limiting is designed with the form-birefringence theory. This kind of grating has subwavelength features, can imitate the transmission blazed grating effectively, and has higher efficiencies than a transmission blazed grating with a subwavelength structure. The diffraction efficiencies are calculated and analyzed. For the normal incident light with 10.6 microm wavelength, the transmissivities for the designed grating at 0 degrees deviation angle for TE and TM polarizations are 0.05% and 5.09%, respectively, which are basically identical to the results of the finite-difference time-domain method. The diffraction efficiencies of the first transmitted order for TE and TM polarizations are 93.95% and 83.88%, respectively.     

Broadband and high efficiency metal–multilayer dielectric grating based on non-quarter wave coatings as reflective mirror for 800 nm

A broadband and high efficiency metal–multilayer dielectric grating (MMDG), which was used to compress and stretch an ultra-short laser pulse in a chirped-pulse amplification (CPA) system, was designed. The diffraction characteristics of the MMDG were analyzed using the method of rigorous coupled wave analysis. The reflective mirror used for the broadband and high diffraction grating is made up of non-quarter wave metal–multi-layer dielectric coatings. Taking the diffraction efficiency of the ?1 order as merit function, the parameters such as groove depth, residual thickness and reflective mirror were optimized to obtain broadband and high diffraction efficiency. The optimized MMDG shows an ultra-broadband working spectrum with an average efficiency exceeding 97% over 120?nm wavelength centered at 800?nm and TE polarization. The optimized MMDG should have potential application in CPA systems.     

Unified design of sinusoidal-groove fused-silica grating

A general design rule of deep-etched subwavelength sinusoidal-groove fused-silica grating as a highly efficient polarization-independent or polarization-selective device is studied based on the simplified modal method, which shows that the device structure depends little on the incident wavelength, but mainly on the ratio of groove depth to incident wavelength and the ratio of wavelength to grating period. These two ratios could be used as the design guidelines for wavelength-independent structure from deep ultraviolet to far infrared. The optimized grating profile with a different function as a polarizing beam splitter, a polarization-independent two-port beam splitter, or a polarization-independent grating with high efficiency of -1st order is obtained at a wavelength of 1064 nm, and verified by using the rigorous coupled-wave analysis. The performance of the sinusoidal grating is better than a conventional rectangular one, which could be useful for practical applications.     

Three-port binary reflective grating with high efficiency under second Bragg angle incidence

Abstract

A binary three-port reflective grating under second Bragg angle incidence is designed in this paper. Under second Bragg angle incidence, the grating can separate nearly 33% light wave energy into the 2nd order, the 1st order and the 0th diffractive orders, respectively. Rigorous coupled-wave analysis can give numerical calculation to optimize the three-port grating depths and periods. For the optimized reflective three-port grating, TE polarization and TM polarization can have different values of grating depth and period. Compared with the reported three-port binary grating under Bragg angle incidence, the diffraction efficiencies can be improved. Moreover, the modal method is applied to explain the propagating mechanism. The highly efficient three-port binary reflective grating under second Bragg angle incidence would be manufactured in the emerging industry for its novel performance.     

Optimization design and analysis of reflecting polarizing beam splitter based on metal–multilayer dielectric grating for 800 nm

A new reflecting polarizing beam splitter (RPBS), based on a metal–multilayer dielectric grating (MMDG), was designed using rigorous coupled wave analysis method and a genetic algorithm. The RPBS reflects the TE wave in the ?1st order and TM wave in the 0th order for 800?nm. The optimized RPBS has an extinction ratio of over 20 dB, from 765?nm to 823?nm, and a large angle, from 43.8° to 60°. At 800?nm, the extinction ratios of the 0th and ?1st orders reach a maximum of 41.0 dB and 53.2 dB, respectively. Furthermore, analysis suggests that the designed RPBS allows sufficient manufacture tolerance. These results show the potential of MMDGs in fabrication of a RPBS, which can be widely used in optical systems.     

Narrowband, polarization-independent free-space wave notch filter

A two-dimensional-corrugated-slab-waveguide add/drop filter providing 100% resonant reflection at 1.55 microm wavelength for both TE and TM polarizations with identical FWHM is designed. The fabricated device exhibits a reflectivity spectrum of more than 95% peak reflection for both polarizations at 1.537 microm. The coupling scheme involves the TE0 guided mode only; it is made relatively tolerant by means of a double-sided crossed grating.     

Efficiency of a grazing-incidence off-plane grating in the soft-x-ray region

Efficiency measurements of a grazing-incidence diffraction grating in the off-plane mount were performed using polarized synchrotron radiation. The grating had 5000 grooves/mm, an effective blaze angle of 14 degrees, and was gold coated. The efficiencies in the two polarization orientations (TM and TE) were measured in the 1.5-5.0 nm wavelength range and were compared with the efficiencies calculated using the PCGrate-SX code. The TM and TE efficiencies differ, offering the possibility of performing unique science studies of astrophysical, solar, and laboratory sources by exploiting the polarization sensitivity of the off-plane grating.     

Polarizing color filter based on a subwavelength metal-dielectric grating

We propose a polarizing color filter based on a one-dimensional subwavelength metal-dielectric grating combining the functions of a polarizer and a color filter. The proposed device consists of three parts: a substrate, a dielectric grating, and a metal grating. The effects of the dielectric grating and the metal grating are investigated in detail by rigorous coupled-wave analysis. Performance is enhanced effectively by utilizing a dielectric grating of high equivalent refractive index. Typical optimized structural parameters are obtained, in which more than 72.6% broadband transmission with >21 dB polarization extinction ratio are simultaneously achieved for a tricolor filter. For transverse electric (TE) polarized light, its reflection efficiency is more than 71.8% in the broad passband light range, which can be recycled by rotating the TE polarization in part into transverse magnetic polarization and reimpinging on the designed device to increase the total energy efficiency. Numerical results show that peak transmission efficiency (PTE) is increased by at least 12.9% using recycled TE-polarized light.     

Polarization dependence of diffraction gratings that have total internal reflection facets

The total internal reflection (TIR) grating is an integrated optical diffraction grating designed to achieve high efficiency for the retrodiffracted order by use of total internal reflection twice within a groove of the grating rather than by use of metalized grooves. Numerical calculations are presented for both TE and TM polarizations of incident light. When the TIR grating was used in the -mth-order Littrow mount with m > 13, the diffraction efficiency was found to decrease linearly with 1/m. The polarization dependence of the retrodiffraction efficiency exceeds 3 dB for TIR gratings formed in silica glass (n = 1.5) but is very small for gratings with InP-based technology (n = 3.2).     

Polarization independence of a one-dimensional grating in conical mounting

We demonstrate theoretically a polarization-independent guided-mode resonant filter with only a one dimensional grating. A rigorous method, the modal method by Fourier expansion, is used to compute the diffracted efficiencies of the grating. Wave-vector analysis fails to correctly design a polarization-independent structure. We show that a rigorous analysis of the resonances must be employed to obtain such a device; using a pole approach, we study the effects of grating parameters on the resonances of both polarizations.     

Stable and efficient bloch-mode computational method for one-dimensional grating waveguides

We present a stable and efficient method for the Bloch-mode computation of one-dimensional grating waveguides. The approach uses the Fourier modal method and the S-matrix algorithm to remove numerical instabilities. The use of perfectly matched layers provide a high accuracy. Numerical results obtained for different lamellar grating waveguides and for both TE and TM polarizations illustrate the performance of the approach.     

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Abstract

A rigorous modal analysis of lamellar gratings, i.e. gratings having rectangular grooves, in conical mountings is presented. It is an extension of the analysis of Botten et al. which considered non-conical mountings. A key step in the extension is a decomposition of the electromagnetic field in the grating region into two orthogonal components. A computer program implementing this extended modal analysis is capable of dealing with plane wave diffraction by dielectric and metallic gratings with deep grooves, at arbitrary angles of incidence, and having arbitrary incident polarizations. Some numerical examples are included.     

Optimum parallel-face slanted surface-relief gratings

Using a combination of rigorous coupled-wave analysis and simulated annealing, parallel-face slanted surface-relief gratings (PFSSRGs) are optimized. For substrate-mode optical interconnects, profiles are presented for both polymer and silicon PFSSRGs for both TE and TM polarizations at normal incidence with grating periods designed to give a 45 degrees output angle in the negative-first forward-diffracted order. The resulting diffraction efficiencies range from 70% to 99%, with a majority of the optimized profiles yielding over 90%. Optimized polymer profiles for TE and TM polarizations exhibit similar high diffraction efficiencies, but the TM profiles generally require greater groove depths. Silicon profiles optimized for TM polarization have greater diffraction efficiencies than those for TE polarization. Profiles that can feasibly be fabricated are identified, and sensitivities to groove depth, filling factor, slant angle, and incident angle are shown to be modest.     

Preferential-order waveguide grating couplers: a comparative rigorous analysis using the finite-difference time-domain method

We rigorously analyze and compare preferential-order waveguide grating output couplers using the finite-difference time-domain method in the total-field/scattered-field formulation for TE and TM polarizations. Four kinds of preferential-order grating couplers are studied: volume holographic grating couplers, slanted parallelogrammic surface-relief grating couplers, double-corrugated surface-relief grating couplers, and reflecting-stack surface-relief grating couplers. The outcoupling efficiencies and branching ratios of the couplers, revealing their preferentiality, are calculated and compared with the rigorous coupled-wave analysis leaky-mode method. In addition, their performance is examined in terms of the main design parameters and the excitation wavelength.     

A simplified broadband coupling approach applied to chemically robust sol-gel, planar integrated optical waveguides

A new generation waveguide spectrometer with broadband coupling capabilities has been developed. As opposed to previous devices, this attenuated total reflection (ATR) spectrometer is much simpler in design, is more chemically robust, and transmits light down to at least 400 nm. The attenuated total reflection element consists of a single-mode, planar integrated optical waveguide fabricated by dip-coating a approximately 300 nm thick, sol-gel composite layer on a glass substrate. A commercially available prism is used as the incoupler with an integral holographic diffraction grating acting as the dispersive outcoupling element. The transmission of narrow band-pass filters was used to compare the response of the waveguide spectrometer to that of a conventional transmission instrument. Spectral resolution was assessed by measuring the fwhm of various laser lines, which were found to range from 0.5 to 1.3 nm. The measured limits of detection for the waveguide spectrometer from 400 to 600 nm are 8.0 and 10.1 milliabsorbance units for TE and TM polarizations, respectively. Finally, to demonstrate the application of this technology to a molecular film confined to a solid-liquid interface, visible ATR spectra of an adsorbed submonolayer of horse heart cytochrome c were acquired. A procedure to correct the waveguide spectra for the wavelength dependence in ATR path length is described.     

Design of retrodiffraction gratings for polarization-insensitive and polarization-sensitive characteristics by using the Taguchi method

We present the design of retrodiffraction gratings that utilize total internal reflection (TIR) in a lamellar configuration to achieve high performance for both TE and TM polarized light and polarization-sensitive performance for gratings behaving as polarizer filters; the design was based on rigorous coupled wave analysis (RCWA) and the Taguchi method. The components can thus be fabricated from a single dielectric material and do not have to be coated with a metallic or dielectric film layer to enhance the reflectance. The effects of the structural and optical parameters of lamellar gratings were investigated, and the TIR gratings in a lamellar configuration were structurally and optically optimized in terms of the signal-to-noise ratio (S/N) and a statistical analysis of variance (ANOVA) of the refractive index, grating period, filling factor, and grating depth as control factors and the estimated efficiency by RCWA as a noise factor. For more accurate robustness, a two-step optimization process was used for each purpose. For TIR gratings designed to perform similarly for TE and TM incident polarization, the -1st-order efficiencies were estimated to be up to 92.0% and 88.5% for TE and TM polarization, respectively. Also, for the TIR gratings designed to achieve polarization-sensitive performance when behaving as a polarizer filters, the -1st-order diffraction efficiencies for TE and TM polarization were estimated to be up to 95.5% and 2.7%, respectively. From these analysis results, it was confirmed that the Taguchi method shows feasibility for an optimization approach to a technique for designing optical devices.     

Cylinder and metal grating polarization beam splitter

We propose a novel and compact metal grating polarization beam splitter (PBS) based on its different reflected and transmitted orders. The metal grating exhibits a broadband high reflectivity and polarization dependence. The rigorous coupled wave analysis is used to calculate the reflectivity and the transmitting spectra and optimize the structure parameters to realize the broadband PBS. The finite-element method is used to calculate the field distribution. The characteristics of the broadband high reflectivity, transmitting and the polarization dependence are investigated including wavelength, period, refractive index and the radius of circle grating. When grating period d = 400 nm, incident wavelength λ = 441 nm, incident angle θ = 60° and radius of circle d/5, then the zeroth reflection order R₀ = 0.35 and the transmission zeroth order T₀ = 0.08 for TE polarization, however, T₀ = 0.34 and R₀ = 0.01 for TM mode. The simple fabrication method involves only single etch step and good compatibility with complementary metal oxide semiconductor technology. PBS designed here is particularly suited for optical communication and optical information processing.