A modified phase diversity wavefront sensor with a diffraction grating

The phase diversity wavefront sensor is one of the tools used to estimate wavefront aberration, and it is often used as a wavefront sensor in adaptive optics systems. However, the performance of the traditional phase diversity wavefront sensor is limited by the accuracy and dynamic ranges of the intensity distribution at the focus and defocus positions of the CCD camera. In this paper, a modified phase diversity wavefront sensor based on a diffraction grating is proposed to improve the ability to measure the wavefront aberration with larger amplitude and higher spatial frequency. The basic principle and the optics construction of the proposed method are also described in detail. The noise propagation property of the proposed method is also analysed by using the numerical simulation method, and comparison between the diffraction grating phase diversity wavefront sensor and the traditional phase diversity wavefront sensor is also made. The simulation results show that the diffraction grating phase diversity wavefront sensor can obviously improve the ability to measure the wavefront aberration, especially the wavefront aberration with larger amplitude and higher spatial frequency.

Detecting High-Refractive-Index Media Using Surface Plasmon Sensor with One-Dimensional Metal Diffraction Grating

We experimentally detect high-refractive-index media (n > 1.5) using a surface plasmon resonance (SPR) sensor with a diffraction grating. While SPR sensors are generally based on the attenuated total reflection method using metal films, here, we focus on a method using a diffraction grating, which can detect relatively higher refractive-index media and is suitable for device miniaturization. In this study, we used the rigorous coupled-wave analysis method to simulate the dependence of the reflectance on an incident angle for media with refractive index values up to 1.700. In the experiment, a medium (n = 1.660 - 1.700) was successfully detected using this grating. Under the conditions of the grating (period: 600 nm, Au thickness: 40 nm) using a red laser (λ: 635 nm), a sharp decline in the reflectance and a rise in the transmittance at certain angles were confirmed, demonstrating the extraordinary transmission enabled by SPR. Because excitation angles changed with changes in the refractive index, we concluded that this method can be applied to sensors that detect high-refractive-index media.

A novel single-order diffraction grating: Random position rectangle grating

Spectral diagnosis of radiation from laser plasma interaction and monochromation of radiation source are hot and important topics recently. Grating is one of the primary optical elements to do this job. Although easy to fabricate, traditional diffraction grating suffers from multi-order diffraction contamination. On the other hand, sinusoidal amplitude grating has the nonharmonic diffraction property, but it is too difficult to fabricate, especially for x-ray application. A novel nonharmonic diffraction grating named random position rectangle grating（RPRG） is proposed in this paper. Theoretical analysis and experiment results show that the RPRG is both higher order diffraction suppressing and not difficult to fabricate. Additionally, it is highly efficient; its first order absolute theoretical diffraction efficiency reaches 4.1%. Our result shows that RPRG is a novel tool for radiation diagnosis and monochromation.

A flat-topped etched diffraction grating demultiplexer with low polarization-dependent loss using a tapered MMI structure

A flat-topped etched diffraction grating (EDG) demultiplexer with a low polarization-dependent loss (PDL) is designed. A design and simulation method based on the method of moment (MoM) is proposed. A 65-channcl EDG demultiplexer with channel spacing of 100 GHz is considered as a design example. A tapered multi-mode interferometer (MMI) is used to flatten the passband of the EDG demultiplexer. The numerical results show that the exit width of the tapered waveguide impacts the loss of the TE case more than that of the TM case. Based on this fact, the exit width of the taper is optimized to obtain the lowest PDL. The tapering angle is also optimized where the minimal ripple is obtained. The designed EDG demultiplexer has an excellent flat-topped spectral response and a very low PDL.

A NEW INTEGRAL EQUATION FORMULATION FOR SCATTERING BY PENETRABLE DIFFRACTION GRATINGS

This paper is concerned with the problem of scattering of time-harmonic electromag- netic waves from penetrable diffraction gratings in the 2D polarization case. We propose a new, weakly singular, integral equation formulation for the scattering problem which is proved to be uniquely solvable. A main feature of the new integral equation formula- tion is that it avoids the computation of the normal derivative of double-layer potentials which is difficult and time consuming. A fast numerical algorithm is also developed for the scattering problem, based on the NystrSm method for the new integral equation. Nu- merical examples are also shown to illustrate the applicability of the new integral equation formulation.

Laser-induced controllable chirped-pitch circular surface-relief diffraction gratings on AZO glass

Chirped-pitch nanoscale circular surface-relief diffraction gratings were photoinscribed on thin films of a Disperse Red 1 functionalized material using a holographic technique. A truncated conical mirror splits and redirects a converging or diverging laser beam, resulting in an interference pattern of concentric circles with a chirped pitch that can be controlled by varying the wavefront curvature. The resulting circular gratings have a diameter of 12 mm and have the advantage of being produced in a fast, single-step procedure with no requirement for a master grating,photomask, or milling equipment.

An Adaptive Finite Element Method with a Modified Perfectly Matched Layer Formulation for Diffraction Gratings

For numerical simulation of one-dimensional diffraction gratings both in TE and TM polarization,an enhanced adaptive finite element method is proposed in this paper.A modified perfectly matched layer(PML)formulation is proposed for the truncation of the unbounded domain,which results in a homogeneous Dirichlet boundary condition and the corresponding error estimate is greatly simplified.The a posteriori error estimates for the adaptive finite element method are provided.Moreover,a lower bound is obtained to demonstrate that the error estimates obtained are sharp.

On a Fast Integral Equation Method for Diffraction Gratings

The integral equation method for the simulation of the diffraction by optical gratings is an efficient numerical tool if profile gratings determined by simple crosssection curves are considered.This method in its recent version is capable to tackle profile curves with corners,gratings with thin coated layers,and diffraction scenarios with unfavorably large ratio period over wavelength.We discuss special implementational issues including the efficient evaluation of the quasi-periodic Green kernels,the quadrature algorithm,and the iterative solution of the arising systems of linear equations.Finally,as an example we present the simulation of echelle gratings which demonstrates the efficency of our approach.

Single order soft X-ray diffraction with quasi-random radius pinhole array spectroscopic photon sieves

A novel single order diffraction grating in the soft X-ray region, called quasi-random radius pinhole array spectro- scopic photon sieves （QRSPS）, is proposed in this paper. This new grating is composed of pinholes on a substrate, whose radii are quasi-random, while their centers are regular. Analysis proves that its transmittance function across the grating bar is similar to that of sinusoidal transmission gratings. Simulation results show that the QRSPS can suppress higher-order diffraction effectively. And the QRSPS would still retain its characteristic of single order diffraction when we take the effect of X-ray penetration into account. These properties indicate that the QRSPS can be used in the soft X-ray spectra measurement.

High-efficiency asymmetric diffraction based on PT-antisymmetry in quantum dot molecules

We present preparation of asymmetric grating with higher diffraction efficiency in quantum dot molecules by combining the tunneling effect and parity-time antisymmetry.In the presence of tunneling between two quantum dots,the system exhibits the striking PT antisymmetry via spatially modulating the driving field and the detuning with respect to the driven transition.For this reason,the asymmetric grating could be achieved.The results show that the diffraction efficiency can be adjustable via changing the driving intensity,detuning,tunneling strength,and interaction length,and then the high-order diffraction can be reached.The scheme provides a feasible way to obtain the direction-controlled diffraction grating,which can be helpful for optical information processing and realization of controllable optical self-image.

OPTICAL STORAGE MECHANISM AND HIGH-ORDER DIFFRACTION PROPERTIES OF NITROAZOBENZENE-CONTAINING POLYESTER FILMS

Using Nd:YAG second harmonic pulse (100 ps), the optical storage properties of two novel polyesters, poly [4'-bis (N, N-oxyethylene) imino-4-nitroazobenzene succinyl] and poly [2'-chloro-4'-bis (N, N-oxyethylene) imino-4-nitroazobenzene succinyl] have been studied by multiwave mixing. The high-order diffractions of the orientation gratings induced by anisotropy via the reorientation of nitroazobenzene groups and optical information storage with long-term stability have been realized by multiwave mixing in their films. Up to 3rd order forward diffraction was detected in two wave mixing, while up to 4th order backward diffraction was observed in degenerated four wave mixing. The recording mechanism was explained by the trans-cis-trans isomerization cycles of azobenzene groups. The isomerization of these azobenzene groups probably undergoes with inversion mechanism under the experimental conditions. The information recorded in these films has been kept for more than 6 months.

Asymmetric dynamic phase holographic grating in nematic liquid crystal

A new scheme for recording a dynamic phase grating with an asymmetric profile in C60-doped homeotropically aligned nematic liquid crystal（NLC） was presented.An oblique incidence beam was used to record the thin asymmetric dynamic phase holographic grating.The diffraction efficiency we achieved is more than 40%,exceeding the theoretical limit for symmetric profile gratings.Both facts can be explained by assuming that a grating with an asymmetric saw-tooth profile is formed in the NLC.Finally,physical mechanism and mathematical model for characterizing the asymmetric phase holographic grating were presented,based on the photo-refractive-like（PR-like） effect.

Experimental implementation of phase triplicator gratings in a spatial light modulator

In this work,we compare different methods for implementing a triplicator,a phase grating that generates three equiintense diffraction orders.The design with optimal efficiency features a continuous phase profile,which cannot be easily reproduced,and is typically affected by quantization.We compare its performance with binary and sinusoidal phase profiles.We also analyze the effect of quantizing the phase levels.Finally,a random approach is adopted to eliminate the additional harmonic orders.In all cases,a liquid-crystal-on-silicon spatial light modulator is employed to experimentally verify and compare the different approaches.

Novel Even Beam Splitters Based on Subwavelength Binary Simple Periodic Rectangular Structure

In this paper, a novel method of a subwavelength binary simple periodic rectangular structure is presented to realize even beam splitting by combining the rigorous couple-wave analysis with the genetic algorithm. Several even splitters in the terahertz region were designed and one of the silicon-based beam splitters designed to separate one incident beam into four emergent beams has total efficiency up to 92.23 %. Zero-order diffraction efficiency was reduced to less than 0.192 % and the error of uniformity decreased to 6.51 9 10-6. These results break the limitation of even beam splitting based on the traditional scalar theory. In addition, the effects of the incident angle, wavelength, as well as the polarizing angle on the diffraction efficiency and uniformity were also investigated.

MEASUREMENT OF 2-DIMENSIONAL DISPLACEMENT USING 2-D ZERO-REFERENCE MARKS

Several 2-D displacement sensing methods are reviewed. As to the crossdiffraction grating, there is no absolute zero-reference. In regards to the optical fiber method,the output signal is affected greatly by the quality of the reflecting surface and it is hard to gethigh resolution. Considering the concentric-circle gratings, the displacement can only be gainedwith complicated calculating of the experiment data. Compared with the advantages and limitations ofthe methods above, a novel 2-D zero-reference mark is especially proposed and demonstrated. Thiskind of mark has an absolute zero-reference when used in pair, and the experimental result is simpleto dispose. By superimposing a pair of specially coded 2-D marks, the correct alignment position ofthe two marks can be detected by the maximum output of the sharp intensity peak. And each slope ofthe peak is of good linearity which can be used to achieve high resolution in positioning andalignment in two dimensions. Design and fabrication of such 2-D zero-reference marks are introducedin detail. The experiment results are agreed with the theoretical ones.

Linking Diffractive and Geometrical Optics Surface Scattering at a Fundamental Level

Optical surface scattering analyses based on diffractive optics (DO) are typically applied to one surface;however, there is a need for simulating surface scattering losses for devices having many surface interactions such as light pipes. Light pipes are often simulated with geometric optics (GO) using ray tracing, where surface scattering is driven by the surface slope distribution. In the DO case, surface scattering analyses depend on the spatial frequency distribution and amplitude as well as wavelength, with the sinusoidal grating as a fundamental basis. A better understanding of the link, or transition, between DO and GO scattering domains would be helpful for efficiently incorporating scattering loss analyses into ray trace simulations. A formula for the root-mean-square (rms) scattered angle width of a sinusoidal reflection grating that depends only on the surface rms slope is derived from the nonparaxial scalar diffraction theory, thereby linking it to GO. The scatter angle’s mean and rms width are evaluated over a range of grating amplitudes and periods using scalar theory and full vector simulations from the COMSOL® wave optic module for a sinusoidal reflection grating. The conditions under which the diffraction-based solution closely approximates the GO solution, as predicted by the rms slope, are identified. Close agreement is shown between the DO and GO solutions for the same surface rms slope scattering loss due to angular filtering near the critical angle of a total internal reflection (TIR) glass-to-air interface.

Sensitivity Analysis of a Bioinspired Refractive Index Based Gas Sensor

It was found out that the change of refractive index of ambient gas can lead to obvious change of the color of Morpho butterfly＇s wing. Such phenomenon has been employed as a sensing principle for detecting gas. In the present study, Rigorous Coupled-Wave Analysis （RCWA） was described briefly, and the partial derivative of optical reflection efficiency with respect to the refractive index of ambient gas, i.e., sensitivity of the sensor, was derived based on RCWA. A bioinspired grating model was constructed by mimicking the nanostructure on the ground scale of Morpho didius butterfly＇s wing. The analytical sensitivity was verified and the effect of the grating shape on the reflection spectra and its sensitivity were discussed. The results show that by tuning shape parameters of the grating, we can obtain desired reflection spectra and sensitivity, which can be applied to the design of the bioinspired refractive index based gas sensor.

Single-order soft x-ray spectra with spectroscopic photon sieve

A single-order diffraction transmission grating named spectroscopic photon sieve(SPS)for soft x-ray region is proposed and demonstrated in this paper.The SPS consists of many circular pinholes located randomly,and can realize both free-standing diffractions and the suppression of higher-order differations.In this paper,the basic concept,numerical simulations,and calibration results of a 1000-lines/mm SPS for soft x-ray synchrotron radiation are presented.As predicted by theoretical calculations,the calibration results of a 1000-lines/mm SPS verify that the higher-order diffractions can be significantly suppressed along the symmetry axis.With the current nanofabrication technique,the SPS can potentially have a higher line density,and can be widely used in synchrotron radiation,laser-induced plasma diagnostics,and astrophysics.

Higher order harmonics suppression in extreme ultraviolet and soft x-ray

The extreme ultraviolet and soft x-ray sources are widely used in various domains. Suppressing higher order harmonics and improving spectral purity are significant. This paper describes a novel method of higher order harmonics suppression with single order diffraction gratings in extreme ultraviolet and soft x-ray. The principle of harmonic suppression with single order diffraction grating is described, and an extreme ultraviolet and soft x-ray non-harmonics grating monochromator is designed based on the single order diffraction grating. The performance is simulated by an optical design software. The emergent beams of a monochromator with different gratings are measured by a transmission grating spectrometer. The results show that the single order diffraction grating can suppress higher order harmonics effectively, and it is expected to be widely used in synchrotron radiation, diagnostics of laser induced plasma, and astrophysics.

Holograms in Albumins and Optical Properties Recorded in Real Time

Holographic recording analysis was performed on the films that were sensitized with ammonium dichromate with albumin of hen and quail (Gallus gallus and Callipepla cali) as abiopolymeric photosensitive matrix. The samples were exposed to an He-Cd laser, λ = 442 nm, at various concentrations, and diffraction efficiencies were measured as a function to the energy, thickness, protein density, aging time, and spatial frequencies. The photosensitivity was measured as a function of storage time, and the gratings were recorded in real time. The photochemical processes involved in the formation of holographic image are described. The results indicate the behavior of colloidal systems based on albumin bird build holographic recording materials.