Changes In Diffraction Efficiency Research Articles

HKUST-1-Doped High-Resolution Volume Holographic Gratings

We report on transmission holographic gratings doped with metal organic frameworks (MOFs). As a first attempt, we focused on MOF-199, also known as HKUST-1, which is an efficient adsorbent of VOCs. HKUST-1 is not soluble in the pre-polymerized holographic mixture. For this reason, samples containing HKUST-1 show high light scattering. In this work, the recording of HKUST-1-doped one-dimensional transmission phase gratings is demonstrated. The optical properties of the recorded structures, such as diffraction efficiency and average refractive index changes, are reported by using angular analysis measurements. A first attempt to demonstrate the possibility of using the doped gratings as sensors is also reported.

Uniformity improvement of a reconstructed-holographic image in a near-eye display system using off-axis HOE.

When a near-eye display (NED) device reproduces an image at a location close to the eye, the virtual image is implemented at a large angle. The uniformity of the image is unbalanced due to the change in diffraction efficiency by the hologram recording angle and angular selectivity. This study proposes a method for implementing an optimal uniform image by analyzing the diffraction efficiency and the reconstructed image was analyzed using angular selectivity generated while reproducing the source point of the diffused image as an intermediate element by holographic optical element (HOE). This research provides practical results for displaying high diffraction efficiency and immersive holographic images in the NED system with HOE as uniformed intermediate elements.

Stacked volume holographic gratings for extending the operational wavelength range in LED and solar applications

A novel stacking procedure is presented for volume phase holographic gratings (VPHGs) recorded in photopolymer material using Corning Willow Glass as a flexible substrate in order to achieve broader angular and spectral selectivity in a diffractive device with high efficiency for solar and LED applications. For the first time to our knowledge, we have shown a device designed for use with a white LED that has the same input and output angles and high efficiency when illuminated by different wavelengths. In this paper, two VPHGs were designed, experimentally recorded, and tested when illuminated at normal incidence. The experimental approach is based on stacking two individual gratings in which the spatial frequency and slant have been tailored to the target wavelength and using real-time on-Bragg monitoring of the gratings in order to control the recorded refractive index modulation, thereby optimizing each grating efficiency for its design wavelength. Lamination of the two gratings together was enabled by using a flexible glass substrate (Corning Willow Glass). Recording conditions were studied in order to minimize the change in diffraction efficiency and peak diffraction angle during lamination and bleaching. The final fabricated stacked device was illuminated by a white light source, and its output was spectrally analyzed. Compared to a single grating, the stacked device demonstrated a twofold increase in angular and wavelength range. The angular and wavelength selectivity curves are in good agreement with the theoretical prediction for this design. This approach could be used to fabricate stacked lenses for white light LED or solar applications.

Characterizing profile tilt of nanoscale deep-etched gratings via x-ray diffraction

The authors report the development of fast, nondestructive, and high accuracy metrology for the characterization of profile tilt relative to the surface normal in nanoscale gratings using x-ray diffraction. Gratings were illuminated with a collimated x-ray beam (Cu Kα), similar to variable-angle small-angle x-ray scattering, to record changes of diffraction efficiency (DE) as a function of incidence angle. Simulations using scalar diffraction theory and rigorous coupled wave analysis predict extrema (0th order DE minimized, ±1st order DE maximized) when local grating bars are parallel to the incident x-ray beam. The surface normal was measured independently by reflecting a laser beam from the grating surface. The independent measurements using x rays and laser beams were referenced to each other via a slit reference plane to characterize the bar tilt angle relative to the surface normal. The fast x-ray measurement can be repeated at arbitrary points to study the spatial variation of the bar tilt angle across large gratings. Two test gratings etched with different deep reactive-ion etch chambers were prepared to investigate the performance of the proposed method. The authors report a repeatability of <0.01° and an accuracy of ∼0.08° with a fast scan speed (total integration time of 108 s to scan a line across ∼55 mm large grating samples at an interval of ∼2 mm). High spatial resolution (<50 μm) can be easily achieved at the expense of speed by limiting the incident x-ray spot size. This process is applicable to any periodic nanostructure as long as x-ray diffraction is well modeled.

Effect of ambient temperature and substrate material selection on diffraction efficiency for diffractive optical elements

A mathematical model of the diffraction efficiency change with the ambient temperature for the single-layer diffractive optical elements (SLDOEs) is presented, and its effects are analyzed in this paper. According to the deduced relation, the SLDOEs made of different substrate materials are discussed in the visible and infrared wavebands in a wide temperature range. The results show that the diffraction efficiency for the plastic SLDOE declines faster at the lower ambient temperature, but for the GE SLDOE declines faster at the higher ambient temperature. The diffraction efficiency change is obviously different with the selection of the substrate material. Therefore, the method of substrate material selection is put forward for the SLDOEs to reduce the impact of ambient temperature. The analysis result can be considered during optical engineering design with the DOEs.

Diffractive Protein Gratings as Optically Active Transducers for High-Throughput Label-free Immunosensing.

A novel label-free biosensing approach based on bioreceptor networks patterned as diffractive gratings (biogratings) has been developed. Nanogrooved structures were used as optically active scaffolds for producing arrays of functional BSA biogratings on low energy surfaces by a water-assisted variant of microcontact printing. An analytical scanner, comprising a LightScribe compact disk drive, was developed to measure the diffraction patterns of these biogratings, thus allowing biointeractions to be quantitatively sensed in a multiplex and label-free fashion by means of diffraction efficiency changes. The approach was demonstrated by immunoassaying IgGs, reaching well-correlated responses with quantification and detection limits of 1.3 and 5.2 nM, respectively. These results provide appealing insights into cost-effective, portable, and scalable alternatives for designing new analytical technologies based on diffractive gratings of bioreceptors.

Advantage of the circular polarization of light in the updatable holographic response in an azo-carbazole monolithic dye dispersed acrylate matrix

The advantage of the circular polarization of light in updatable holographic responses in an azo-carbazole monolithic dye dispersed acrylate matrix has been investigated. Compared to linear polarization holography, four times higher diffraction efficiency was measured without the depression of the response time. The rise time of the holographic recording becomes faster with the increase in the cycled recording time, and no change in diffraction efficiency was observed in the cycled updatable holographic recording using a circularly polarized light. On the other hand, a significant depression in the diffraction efficiency and a slower rise time were observed in a cycled updatable hologram recording using a linearly polarized light. The advantage of the orthogonal circular polarization of light in updatable holographic responses is discussed on the basis of the difference in the photo-oriented state of the azo-carbazole molecules under the orthogonal circular polarization holographic recording and the parallel linear polarization state.

Electrically tunable diffraction efficiency from gratings in Al-doped ZnO

Transparent conducting aluminum-doped zinc oxide (AZO) can be used as part of an active plasmonic device due to its electrically tunable permittivity, which is accomplished by changing the carrier concentration with electrical biasing. In this letter, we report a continuous electrical tuning of diffraction efficiency from AZO gratings in the visible range (specifically 532 nm) when the AZO is under bias voltages between −1 V and −3.5 V. The carrier concentration in AZO under negative bias has been measured and simulated. The diffraction efficiency changes have been explained by the carrier concentration variation and induced complex refractive index change at the Al2O3 and AZO interface. The reported results can lead toward the application of post-fabrication tuning of optoelectronic devices using AZO.

Liquid-crystal-grating-based optical displacement sensors.

The optical properties of liquid crystal (LC) gratings with a mobile glass substrate, which can be used for optical displacement applications, were investigated. LC gratings are composed of homogeneous and twisted nematic domains. The displacement measurement principle is based on the change in diffraction efficiency induced by varying the mixing ratio of two orientation domains, in response to the lateral shift of the mobile substrate. Improved conditions for the polarization direction of incident light, as well as the application of voltage for achieving higher sensitivities, were explored. A simple demonstration of an LC-grating-based displacement sensor was also conducted.

Controlling the duty cycle of holographic crossed gratings by in situ endpoint detection during development.

A method of in situ development endpoint detection is proposed to control the duty cycle of holographic crossed gratings. Based on the observation that after the developer first touches the substrate surface the topography of the crossed grating undergoes an evolution process from a hole array of increasing diameter to a pillar array of decreasing diameter, we set up a development model. In this model, the shapes of both holes and pillars are assumed to have square in-plane cross sections, rotated 45° with respect to the main periodic directions, and straight side walls perpendicular to the grating plane. Thus, the main development process, including the transition from a hole array to a pillar array, can be characterized by a single parameter continuously, and the change of diffraction efficiency during the process can be theoretically calculated. Two different in situ development monitoring conditions were simulated and tested experimentally. Using this method, crossed gratings with various duty cycles were fabricated under different incident and monitoring conditions.

Reversible change of diffraction efficiency in Cl-containing 3-glycidoxypropyl silsesquioxane films co-doped with Ag and Cu

Reversible change of diffraction efficiency in Cl-containing 3-glycidoxypropyl silsesquioxane films co-doped with Ag and Cu

Nanoimprinted, Submicrometric, MOF‐Based 2D Photonic Structures: Toward Easy Selective Vapors Sensing by a Smartphone Camera

In this work, a soft‐lithographic approach to fabricate submicrometer metal organic framework (MOF)‐based 2D photonic structures is described. Nanometric zeolitic imidazole framework material ZIF‐8 (zinc) is chosen as the sensible MOF material because of its chemical stability and its vapor selective adsorption properties. Two different systems are fabricated: nanopatterned colloidal ZIF‐8 homo‐ and ZIF‐8/TiO2 heterostructures. Several features (stripes, squares, etc.) with dimensions of 200 nm are replicated on different substrates such as silicon, flexible plastics, and even aluminum cans, over relatively large surfaces (up to 1 cm2). In addition, the use of these photonic MOF‐heterostructures as very low‐cost sensing platforms compatible with smartphone technology is demonstrated. This method relies on the evaluation of the change in diffraction efficiency of the photonic MOF‐patterns, induced by the MOF refractive index variation, which is simply detected by a charge coupled device (CCD) camera, as those integrated in smartphones, without need for complex optical instrumentations for transduction data processing. Performances of the sensors are first evaluated using isopropyl alcohol adsorption/desorption cycling as a model case. In addition, a “real” environmental issue is tackled. Selective detection of styrene in presence of interfering water is demonstrated at concentrations below the human permissible exposure limit. In situ ellispometric analyses are also carried out in order to confirm the sensor performances and to propose a mechanism for styrene uptake into the nanoMOFs.

Dark relaxation of holographic gratings in azobenzene and chalcogenide films

Studies of transmission holographic grating (HG) relaxation (recorded with s-s, p-p, s-p, L- L, L-R laser beam polarizations) have been carried out in organic molecular azobenzene glassy films W- 50 and W-75, and in chalcogenide glassy a-As2S3 film. Results previously obtained with azobenzene molecular glassy K-RJ-9 films also are used for comparison. HG with the periods of 0.50, 2.0 and 8.6 μm were studied in these films. It is found that recording efficiency in the same sa mple depends on both recording polarizations and HG period. The HG stability in the course of relaxation also depends on these factors. Anticorrelation has been observed of HG recording efficiency and stability. Recording was efficient with p-p or L-R polarizations at 2.0 μm HG period whereas it was stable with s-s L-L polarizations at 8.6μm HG period. As a rule, HG stability was higher in the samples with higher glass transition temperature. The HG dark (relaxational) self-enhancement of HG was observed in the case of W-75 (L-R polarizations, 0.50μm; s-s polarizations, 2.0μm) and in previously studied K-RJ-9 (p-p polarizations, 8.6μm) samples. Relaxational changes in diffraction efficiency are explained in terms of post-recording mass transfer under the influence of photoinduced spatially periodic mechanical stress.

Porous silicon based on multilayer dielectric-grating optical sensors with enhanced biosensing

This paper reports on the use of a novel all-porous-silicon configuration consisting of a surface grating and a high-reflectivity quarter-wave stack, arranged as both an all-porous-silicon grating diffractive device, and a highly sensitive and inexpensive biosensor. The diffraction efficiency of the top surface grating in this structure can be considerably improved for biosensing. Moreover, a porous-silicon high-reflectivity multilayer can not only prevent the signal energy from radiating to the substrate, but also increase the internal surface area of the sensing platform for detecting more probing molecules. When 3-aminopropyltriethoxysilane (APTES) was employed as a probing molecule, the sensitivity of the proposed structure increased up to 1 order higher than the porous-silicon diffraction-grating biosensors without a high-reflectivity quarter-wave stack. It has been shown by experimentation that before and after the APTES, −3-order diffraction efficiency changes from 1.30 × 10−3 to 1.25 × 10−4. Excellent agreement is achieved between the experimental results and simulations based on the rigorous coupled-wave analysis.

Diffraction efficiency change of multilayer diffractive optics with environmental temperature

In this paper, the effect of an environmental temperature change on multilayer diffractive optical elements (MLDOEs) is studied in terms of the diffraction efficiency and the polychromatic integral diffraction efficiency (PIDE). The relation between the diffraction efficiency of MLDOEs and environmental temperature is analyzed theoretically, and examples of different MLDOEs are discussed in the visible and infrared wavebands. The result shows that the diffraction efficiency reduction is no more than 5% and the PIDE reduction is less than 1.5% for optical plastic MLDOEs in the visible waveband when the environmental temperature ranges from −62 to 71 °C, and that the decrease of both the diffraction efficiency and PIDE for MLDOEs is more significant in the mid-wave infrared than in the long-wave infrared. The analysis result can be considered during optical engineering design with MLDOEs.

非均匀混合调制光栅衍射效率计算方法及特性分析

A method for calculating diffraction efficiencies of non-ideal volume phase holographic gratings is presented by introducing a function between modulation profiles and depths of gratings. By applying Kamiya rigorous delamination-calculation method, rigorous coupled-wave equation for the non-ideal conditions, such as mixed modulation and attenuated modulation profiles, is expressed. The diffraction characteristics of the phase gratings, mixed gratings, out-of-phase gratings and attenuated gratings are investigated. The response degree of diffraction efficiency to the numbers of sub-regions that have been divided is discussed. Comparing with Kogelnik theory and Sabol model, the accuracy of the algorithm is further demonstrated. The results show that, the peaks of diffraction efficiency change over average absorption constants, attenuated constants and the spatial dephasing between the absorption and phase gratings; absorption modulation causes a modest increase of the peak, but average absorption constants drag the efficiencies of the whole transmission orders. The effect of the numbers of sub-regions that have been divided on the angle selectivity and angular spectrum widths of the grating is small, but it decides the accuracy of the algorithm. The work have a certain reference value for calculating the efficiencies and analyzing the diffraction characteristics of the non-ideal modulation of volume holographic gratings.

Humidity and temperature effect on properties of transmission gratings recorded in PVA/AA-based photopolymer layers

This paper explores the effects of humidity on gratings recorded in a polyvinylalcohol–acrylamide photopolymer medium. Investigation of the behaviour of transmission gratings exposed to high humidity is of significant interest for two reasons, firstly because the grating’s sensitivity to humidity can be exploited for the development of irreversible humidity indicators, secondly because too much sensitivity to humidity can limit the use of these materials in applications where an environmentally stable hologram is needed. In this paper we focus on the effect of high humidity on the properties of volume phase transmission gratings recorded in PVA/AA photopolymer layers in the temperature range 8–24 ° C. It has been found that although exposure to humidity changes the diffraction efficiency and Bragg angle of gratings, the effects are fully reversible if the temperatures are kept low. For example, when gratings were subjected to relative humidities of 80% and 90% at a temperature of 8 ° C the observed changes were fully reversible. However, irreversible changes in diffraction efficiency, thickness, refractive index modulation and Bragg angle were observed when the temperature during the humidity exposure was higher than 16 ° C. The magnitude of the irreversible changes depends strongly on the ambient temperature during the humidity exposure, the humidity level and also on the duration of the humidity exposure.

Optical label free biodetection based on the diffraction of light by nanoscale protein gratings

In this work, we use a label free biosensing technique based on the diffraction of light by molecular gratings. Molecular gratings are employed as diffractive probe arrays for protein interaction analysis. Indeed, the diffraction efficiency changes in response to analyte binding, due to a shift in line thickness and/or refractive index of the grating. In this perspective, we have developed a scanning instrument, capable of collecting at high speed the diffracted intensity emitted by molecular gratings. Nanogratings composed of anti-GST antibodies lines (500nm width at a pitch of 1μm) were immobilized through Microcontact printing on a PLL-g-dextran coated substrate. By monitoring the diffracted intensity of the anti-GST antibodies gratings, we have detected GST molecules at a concentration of 0.1μM. This biodetection technique appears sensitive to low molecular weight molecules, such as GST (glutathione S-transferase, 26kDa), which is an interesting result in comparison to other label free detection methods.

Electrically Driven Diffraction Grating Designed for Visible-Wavelength Region

We report on an electrically driven diffraction grating designed for visible light, where the refractive index of a liquid crystal (LC) was modulated periodically at an interval of 700 nm by applying an external dc bias to a metallic nanograting (NG). The LC-NG structure exhibited a maximum refractive index variation (Δn) of 0.088 and a diffraction efficiency (η) change of 0%-16% with a large diffraction angle of 64° for incident light of 633-nm wavelength. This approach, with the help of faster electronics, provides an opportunity of developing active holograms for real 3-D displays.

Multilayer porous silicon diffraction gratings operating in the infrared

Transmission diffraction gratings operating at 1,565 nm based on multilayer porous silicon films are modeled, fabricated, and tested. Features down to 2 μm have been patterned into submicron-thick mesoporous films using standard photolithographic and dry etching techniques. After patterning of the top porous film, a second anodization can be performed, allowing an under-layer of highly uniform porosity and thickness to be achieved. High transmission greater than 40% is measured, and modeling results suggest that a change in diffraction efficiency of 1 dB for a 1% change in normalized refractive index can be achieved. Preliminary measurement of solvent vapor shows a large signal change from the grating sensor in agreement with models.