Silicone microlenses and interference gratings

Interference gratings, plano-convex microlenses, and spherical microlenses have been made in silicone. Lenses were fabricated by the melting method. Two substrates have been tried: glass and Teflon. The latter substrate lets us fabricate low-f-number lenses. We made spherical microlenses by placing pieces of silicone near a thermal source and studied resolution of the lenses by investigating the images they gave of a test chart. We made low-spatial-frequency gratings by recording interference patterns and studied parameters involved in the recording. A study of the profile of the gratings and lenses was done with a mechanical surface analyzer.     

Dynamical optical microelements on dye-sensitized gels

We discuss the optical recording and relaxation of low spatial frequency gratings and negative microlenses by a dyed polyacrylamide gel. An analysis of the grating diffraction efficiency and the focal distance of microlenses is shown. A study of the evolution of the surface modulation of both types of elements with an interference microscope is also included.     

Albumen as a relief recording media for spatial distributions of infrared radiation. Fabrication of interference gratings and microlenses

It is shown that a relief is generated when spatial distributions of infrared light (lambda = 10.6 microm) are recorded on albumen films. The relief can be applied to the fabrication of microelements, such as diffraction gratings and microlenses. Examples are shown.     

First-generation holographic, grazing-incidence gratings for use in converging, extreme-ultraviolet light beams

We present two holographic recording solutions that produce gratings suitable for use at grazing incidence in the extreme ultraviolet. The rulings are formed when the interference pattern of two spherical wave fronts is recorded on a planar substrate. Each grating is designed to minimize or eliminate the dominant aberration terms in order to maximize the spectral and spatial resolution of the system. In the first design, the dominant astigmatism term in a power-series expansion of the light path function is eliminated; in the second design, the dominant comatic terms are minimized. Each grating is placed directly in a converging light beam at grazing incidence to provide high system efficiency in the extreme ultraviolet. The aberration control afforded by both recording solutions is excellent, providing detector-limited spatial and spectral resolution over much of the usable bandpass. Furthermore, the aberration control is maintained over a wide range of beam speeds and off-axis angles, thereby outperforming conventional varied line-space gratings for use in the extreme ultraviolet. We discuss the methodology used to develop the recording solutions, model and compare the performance of the gratings, and discuss possible space-based applications for these gratings.     

Analysis of PVA/AA based photopolymers at the zero spatial frequency limit using interferometric methods

One of the problems associated with photopolymers as optical recording media is the thickness variation during the recording process. Different values of shrinkages or swelling are reported in the literature for photopolymers. Furthermore, these variations depend on the spatial frequencies of the gratings stored in the materials. Thickness variations can be measured using different methods: studying the deviation from the Bragg's angle for nonslanted gratings, using MicroXAM S/N 8038 interferometer, or by the thermomechanical analysis experiments. In a previous paper, we began the characterization of the properties of a polyvinyl alcohol/acrylamide based photopolymer at the lowest end of recorded spatial frequencies. In this work, we continue analyzing the thickness variations of these materials using a reflection interferometer. With this technique we are able to obtain the variations of the layers refractive index and, therefore, a direct estimation of the polymer refractive index.     

Spatial-frequency response of holographic gratings photodeposited from inorganic colloids

Surface photodeposition is a photon-assisted process by which thin films are formed on substrates immersed in colloid solutions. We experimentally evaluate the resolution capabilities of the photodeposition process with amorphous selenium colloids by recording holographic gratings at different spatial frequencies, up to 2200 lines/mm. The experimental diffraction efficiencies are analyzed in terms of a theoretical model, which relates the spatial-frequency response to optical recording parameters and colloid particle sizes. The maximal experimental diffraction efficiency reaches 13% with a spatial frequency of f = 1100 lines/mm. The diffraction efficiencies decrease monotonically with spatial frequency, and drop to half of the maximal diffraction efficiency at f ≈ 1500 lines/mm. These resolution capabilities are achieved with colloid particle sizes extending up to 80 nm. The theoretical derivation indicates that to obtain spatial frequencies above 3000 lines/mm, one should restrict the colloid particle size to a(max) ≤ 30 nm.     

Relief optical microelements fabricated with dichromated gelatin

Relief microlenses and micromirrors are fabricated in dichromated gelatin layers. Microelements typically have diameters of approximately a few hundred micrometers and have focal distances ranging from 4 to 15 mm.     

Influences of Recording Geometry Parameters on Diffraction Efficiency in Bleached Silver Halide Transmission Holograms

Abstract

The experimental results of diffraction efficiency as a function of the geometrical disposition of recording beams in bleached silver halide transmission thick-holographic gratings are presented. Two variables have been used to relate these results with certain geometric parameters. These variables are spatial frequency and the slant angle of the interference fringes in the material. The experimental results obtained show that while maximum diffraction efficiency and refractive index modulation depend strongly on spatial frequency, they vary little with slant angle.     

High-Frequency Relief-Phase Holographic Gratings on Dichromated Gelatin Processed by Short-Wave UV Radiation

Technical Physics Letters - The possibility of creating relief-phase holographic gratings with high spatial frequency (1500 mm–1) on dichromated gelatin layers processed by destructive effect...     

Hyperbolic holographic gratings: analysis and interferometric tests

The aberrations of hyperbolic diffraction gratings produced with two spherical waves are analyzed theoretically and experimentally. The behavior of these gratings in collimated illumination indicates that for a grating of a given size there is a critical spatial frequency above which the aberration remains constant for all spatial frequencies. Aberrations associated with geometrical errors in the recording geometry are derived. With simple interferometric tests, misalignments in the recording process can be identified easily.     

Fabrication of chirped gratings on GaAs optical waveguides

After a brief review of the applications and fabrication techniques of gratings in integrated and guided wave optics, a new method of fabricating chirped gratings is presented. The method is based on the interference of two spherical laser beams after spatial filtering by pinholes. The experimental conditions required for fabricating antisymmetric linearly chirped gratings, symmetric quadratically chirped gratings and uniform gratings are presented by way of example. By this method chirped gratings with small variations in the period can be fabricated on GaAs thin film optical waveguides. Profiles and patterns of chemically etched corrugations are quite uniform, mainly because of the direct interference of beams immediately after spatial filtering.     

Wavelength demultiplexing with layered multiple Bragg gratings in LiNbO3:Fe crystal

Dense wavelength division multiplexing (DWDM) is an important technology for expanding the capacity of optical network. The optical component based on the superimposed Bragg gratings shows that it can be used as one of advantageous multichannel components because of its excellent angle and wavelength selectivities. An optimized method for recording multiple Bragg gratings for wavelength demultiplexing in optical telecommunication band is proposed to achieve gratings with equal diffraction efficiency. A structure of three layers with twenty four gratings is demonstrated in a LiNbO(3):Fe crystal by employing the optimized recording method. Then an initial wavelength demultiplexing experiment based on the formed gratings is carried out in optical telecommunication C-band. The results obtained by measuring and analyzing the transmitted spectra of the fabricated gratings show that the diffraction efficiencies of the gratings are uniform. It is suggested that this kind of multiple gratings can be used for increasing the number of the demultiplexed wavelengths in recording medium with unit volume for WDM.     

Optimization of a photopolymerizable holographic recording material based on polyvinylalcohol using angular responses

Acrylamide-based holographic recording materials have significant advantages and the composition of these materials has been optimized in terms of energetic sensitivity and diffraction efficiency. As a result, diffraction gratings with an efficiency of almost 80% for energetic exposures of 35 mJ/cm² and a spatial frequency of 1000 lines/mm in photosensitive films 65 μm thick have been obtained. In this paper we present the effects of intensity, thickness, and variation in the concentration of each component by studying the angular responses of the diffraction gratings recorded in each composition.     

Six-Degrees-of-Freedom Alignment of Two-Dimensional Array Components by Use of Off-Axis Linear Fresnel Zone Plates

A novel six-degrees-of-freedom (six-DOFs) alignment technique for assembling two-dimensional array components is presented. The technique uses off-axis linear Fresnel zone plates on one component that are combined with alignment targets on the other. The technique is compact and sensitive to all six DOFs; it was used to package an array of microlenses with a 32 x 32 array of GaAs multiple-quantum-well modulators flip-chip bonded to a 9 mm x 9 mm complementary-metal-oxide-semiconductor chip. By use of interference fringes to control the tilt misalignment, the worst-case misalignment of the microlenses relative to the chip is calculated to be as follows: lateral = 3.0 mum, rotational = 0.023 degrees , longitudinal = 13 mum, and tilt = 0.022 degrees . We also propose alternative implementations of the technique, including one that uses on-chip photodetectors to automate this six-DOF alignment technique.     

线性啁啾相位掩模的设计

啁啾相位掩模法是啁啾光纤光栅的一种非常重要的制作方法。本文研究讨论了用全息干涉方法制作线性啁啾位相掩模的设计方法,提出用两球面波干涉产生条纹密度随空间距离线性变化的干涉条纹记录啁啾位相光栅,按设定光栅端点空频和端点空频差两种优化设计方法设计了长度100mm、啁啾量1nm/mm的线性啁啾光栅,理论和实验结果给出两种设计方案的非线性系数分别为2.5%和1.6%,理论设计和实验结果相符。     

Statistical Model for Noise Gratings Recorded in Volume Holograms

Abstract

A statistical model is used to study the formation of noise gratings in holograms and the mechanism that causes radiation scattering in them. The theoretical model presented describes noise scattering in terms of diffraction due to the high number of spurious gratings formed during the recording stage by the interference of a single reference beam with its own scattered radiation. Numerical results calculated from the theory showing the dependence of noise grating efficiency on exposure are compared with experimental results obtained with bleached emulsions, and good agreement is found.     

Spatial frequency filtering in holographic image reconstruction

We show that reconstructing a hologram by its object beam leads to spatial filtering, namely, to the suppression of spatial frequency components that are perpendicular to the plane of the recording beams. We conduct experiments by rotating the transparencies of Ronchi gratings and crossed gratings and measuring the corresponding diffraction efficiencies. Good agreement is found with a theory based on image reconstruction with a beam that does not quite satisfy the Bragg condition.     

Design, fabrication, and performance of preferential-order volume grating waveguide couplers

Both a nonfocusing and a focusing preferential-order volume grating waveguide coupler were designed, fabricated, and tested. These volume grating couplers are designed to outcouple a 633-nm wave guided in an adjacent polyimide waveguide film. The slanted-fringe volume gratings are recorded holographically by the interference of two 364-nm waves. The dynamics of the holographic photopolymer HRF600X001 are investigated in relation to the interaction with the guided wave. The fabricated couplers exhibited a preferential coupling of 98%, a spatial coupling rate of 3.6 mm(-1), and a coupling efficiency of 95%. The focusing grating coupler focused the outcoupled beam to a focal line with a full width at half-maximum of 10.49 mum located 25 mm above the grating.     

Polarization Holographic Gratings

Abstract

The photoinduced anisotropy (dichroism and birefringence) in AgCl emulsions is studied as well as the possibility for chemical fixing of this anistropy. A theoretical relation between the diffraction efficiency of amplitude—phase polarization holographic gratings and the photoanisotropy of the recording medium is derived. Based on this relationship an estimation of the properties of the gratings is presented. Polarization holographic gratings with spatial frequencies of 200 to 2000 mm^?1 and diffraction efficiency up to 1·8% are recorded. The gratings are stable, and do not change in time for more than a year.     

Writing long holographic diffraction gratings by use of a novel scanning method

A novel method for writing holographic diffraction gratings is proposed in which the two interfering beams are moved together across the recording medium in such a way that the interference pattern at the medium is unchanged. The phase compensation is discussed both for an idealized setup and for a realistic experimental arrangement.