Showing papers on "Diffraction grating published in 1984"

Polarization holography. 2: Polarization holographic gratings in photoanisotropic materials with and without intrinsic birefringence.

Abstract: Results are reported of experimental investigations on the diffraction efficiency and its polarization dependence of holographic phase polarization gratings in a photoanisotropic medium methyl orange/PVA with intrinsic birefringence. A comparative study of layers with different intrinsic birefringence was conducted. The conditions—initial birefringence and a type of polarization recording—were found to have high diffraction efficiency (>30%) and strong dependence on the direction of polarization of the linearly polarized readout beam. The results are in agreement with the theoretical considerations on such gratings.

I Rigorous Vector Theories of Diffraction Gratings

Abstract: Publisher Summary This chapter describes the rigorous vector theories of diffraction gratings. The diffraction grating is a valuable instrument for scientific research. It is mainly used for spectroscopy and filtering. Even though the holographic grating has not eliminated the classical, ruled grating, which remains the most suitable for important applications, it has permitted a considerable extension of the use of gratings for industrial or scientific purposes such as wavelength selectors for tunable lasers, selective surfaces for solar energy, masks for photolithography, beam sampling mirrors for high power lasers, spectrometers in extreme ultraviolet (UV) or x-ray regions for Space Optics. In addition, one can consider that rigorous vector theories of gratings are able to solve almost all the classical problems of gratings encountered by manufacturers and users.

Optical wavelength division multiplexing/demultiplexing system

Abstract: A wavelength division method and system employing a radiation transmissive planar waveguide provided with collimating and focusing lenses and with a periodic radiation transmissive diffraction grating incorporating radiation reflecting elements in spaced array, preselected, in demultiplexing service, to separate into individual entities an optical signal input constituting a multiplicity of coherent radiation signals of different characteristic wavelengths transmitted simultaneously via the waveguide and, in multiplexing service, to consolidate a multiplicity of coherent radiation signals individually introduced to the grating via the waveguide along angular courses substantially coincident with the angular courses taken by individual radiation signals of corresponding wavelengths exiting the grating during demultiplexing service, and means directing the signals to dedicated receptors.

Integrated optical switches and gas sensors

Abstract: We have demonstrated new switching and gas-sensing effects in integrated optics using input and output grating couplers and Bragg reflector gratings with 1200 lines/mm on planar SiO2–TiO2 waveguides. Switching is actuated by adsorption or desorption of water or other adsorbates on the waveguide surface through a change in the effective index of the guided modes under the grating. We derived theoretically the ultimate sensitivity limits of the grating devices employed either as switches or as gas sensors. Switching requires the adsorption and desorption, respectively, of less than one H2O monolayer. Sensors can detect variations in surface coverage of 1/100 of an H2O monolayer.

Multichannel phase-shifted interferometer

Abstract: A new real-time interferometer based on diffraction phenomena is discussed. It consists of a point-diffraction interferometer fabricated on a transmission grating. The real-time data-analysis capability is achieved by simultaneously introducing a phase shift (piston) on the three separate channels of diffracted interferograms. Mathematical analysis and preliminary observational results are included.

Scattering theory for diffraction gratings

Abstract: 1. Physical Theory.- 1. The Physical Problem.- 2. The Mathematical Formulation.- 3. Solution of the Initial-Boundary Value Problem.- 4. The Reference Problem and Its Eigenfunctions.- 5. Rayleigh-Bloch Diffracted Plane Waves for Gratings.- 6. Rayleigh-Bloch Surface Waves for Gratings.- 7. Rayleigh-Bloch Wave Expansions.- 8. Wave and Scattering Operators for Gratings.- 9. Asymptotic Wave Functions for Gratings.- 10. The Scattering of Signals from Remote Sources.- 2. Mathematical Theory.- 1. Grating Domains and Grating Propagators.- 2. Rayleigh-Bloch Waves.- 3. The Reduced Grating Propagator Ap.- 4. Analytic Continuation of the Resolvent of Ap.- 5. Proofs of the Results of 4.- 6. The Eigenfunction Expansion for Ap.- 7. Proofs of the Results of 6.- 8. The Rayleigh-Bloch Wave Expansions for A.- 9. Proofs of the Results of 8.- 10. The Initial-Boundary Value Problems for the Scattered Fields.- 11. Construction of the Wave Operators for AP and Ao,p.- 12. Construction of the Wave Operators for A and Ao.- 13. Asymptotic Wave Functions and Energy Distributions.- 14. Construction and Structure of the S-Matrix.- 15. The Scattering of Signals by Diffraction Gratings.- References.

Strip gratings at a dielectric interface and application of Babinet’s principle: erratum

Abstract: In this paper, we consider the transmission-line model used to calculate the transmittance of thin metallic strip gratings (at wavelengths longer than the grating period) to resolve a conflict of published expressions for the effect of a thick dielectric substrate on the equivalent circuit capacitance of capacitive gratings. By using rigorous diffraction theory we establish the correct expression and derive a modified form of Babinet’s principle for use with strip gratings on dielectric boundaries. It is found that the equivalent circuit capacitance of a strip grating on the boundary between media of refractive indices n1 and n2 is larger than its free-space value by a factor (n12+n22)/2. The result is applicable in general to the capacitive part of the equivalent circuit of grid reflectors, which are widely used at submillimeter wavelengths. A useful set of rigorously calculated transmission curves for strip gratings is presented, and these are used to establish the range of validity of the transmission-line model.

Static deflection device for an infrared beam

Abstract: The diffraction grating principle is used to deflect an infrared beam in a series of discrete predetermined directions. A periodic control voltage having a staircase waveform with N steps is applied across a liquid crystal layer to create local variations of refractive index therein, thereby setting up an infrared diffraction grating of adjustable pitch.

Diffraction characteristics of photoresist surface-relief gratings

Abstract: Theoretical results from rigorous coupled-wave analysis are compared with experimental diffraction characteristics for holographically formed dielectric photoresist surface-relief gratings with deep grooves (greater than a grating period) and high diffraction efficiency (>85%). The angular selectivity (at a fixed wavelength) and the wavelength selectivity (at a fixed angle of incidence) are presented for both TE and TM incident polarizations. Modeling the gratings as a surface-relief modulated half-space and using rigorous coupled-wave analysis are shown to produce good general agreement with the experimentally measured diffraction characteristics.

Dielectric surface-relief gratings with high diffraction efficiency

Abstract: Diffraction properties of dielectric surface-relief gratings were investigated by solving Maxwell’s equations numerically using the differential method. The diffraction efficiency of a grating with a groove depth about twice as deep as the grating period is comparable with the efficiency of a volume phase grating. Dielectric surface-relief gratings interferometrically recorded in photoresist can possess a high diffraction efficiency of up to 94% (throughput efficiency 85%). Calculated results were also found in good agreement with the experimental data.

Enhancement of Smith–Purcell radiation from a grating with surface-plasmon excitation

Abstract: The Smith–Purcell radiation from a charge moving across a penetrable grating is studied. We account for the finite permittivity and the absorption effect of the grating and find that enhancement of the radiation will occur near particular angles of observation at which the phase-matching condition for the excitation of the surface-plasmon mode is satisfied.

Optical instrument for measuring displacement

Abstract: Optical intrument for measuring displacement comprising a movable diffraction grating used as a scale, a semiconductor laser device (1), photodetectors (10, 11) and means (2, 4, 5, 6, 7) for making two light beams diffracted by the diffraction grating interfere with eath other in which displacement of said diffraction grating is measured, based on variations of interference signals. The laser device has a suitable coherency for making selectively two necessary light beams with equal optical path lengths interfere with each other.

Apparatus and method for coherently adding laser beams

Abstract: The disclosed apparatus includes a diffraction grating illuminated by a plurality of lasers. Apparatus is provided for summing the plurality of lasers coherently by, (a) phase locking the plurality of lasers and by, (b) diffracting the plurality of beams into a single beam. The diffraction grating has a configuration to generate upon illumination substantially equal intensities of diffraction orders corresponding to the number of lasers while suppressing higher unwanted orders. The phase locking can be accomplished by a single master laser, or by a cavity mirror to generate reference beams. Then, the output beams of the plurality of lasers propagating in the reverse direction are coherently superimposed by that grating. It is preferred that the diffraction grating be binary. Both one and two-dimensional diffraction grating arrays are disclosed. In one embodiment, the phase of the plurality of lasers is locked together by means of a separate injection lock laser, in another embodiment the grating is part of a multielement cavity. In a preferred embodiment, the binary grating is a periodic pattern, where the structure of the periodicity is determined by the number of laser beams. Then, an injection lock laser illuminates that grating and locks together the phases of the plurality of lasers whose beams are to be added. Or, alternatively, a mirror is substituted for the injection lock laser and it provides the illumination beam to the grating which then generates the plurality of beams.

On the Numerical Study of Deep Conducting Lamellar Diffraction Gratings

Abstract: A root-finding algorithm for the solution of the eigenvalue equation linked with the theoretical study of lossy lamellar gratings is outlined. The computation time seems to be shorter than required when using a method proposed by Botten et al. (1981). The agreement is found to be excellent.

Optically diffracting security element

Abstract: A security element for authenticating bank notes, credit cards, security passes and the like is disclosed. The security element incorporates a reflective-type diffraction grating, which grating comprises a continuous layer of reflecting material on which is deposited a layer of dielectric material. Non-continuous reflecting layer portions are embedded in the dielectric material. It is practically impossible to lay bare the diffraction grating without destroying it.

High resolution digital diffraction grating scale encoder

Abstract: An optical scale reader comprises a light source for radiating a beam of coherent light on a reflective scale, a half mirror for mixing light beams from the light source which are reflected and diffracted by the scale for interference with each other, an optical system for causing the interfering light beams leaving the half mirror on its opposite sides to be 90° out of phase with each other so that the light beams will fall on the half mirror at a particular angle of incidence, photodetectors for detecting the interfering light beams, respectively, which have left the half mirror, and a signal processor for processing first and second electric signals which are supplied from the photodetectors and 90° out of phase with each other to generate a signal indicative of the distance which the scale has moved. There is also disclosed a position control device incorporating the optical scale reader.

Aberrations of varied line-space grazing incidence gratings in converging light beams

Abstract: Analyses of the imaging properties of several designs for varied-line space gratings in converging beams of light in grazing-incidence spectrometers are presented. An explicit model is defined for the case of a plane-reflection grating intercepting light that converges and is reflected to a stigmatic point associated with the zero-order image of the grating. Smooth spatial variation of the grating constant then permits aberration correction. The aberrations are expressed as polynomials in the grating lens coordinates using power series expansions. Application of the model is illustrated in terms of aberrations experienced with the short wavelength spectrometer on the EUVE satellite. Attention is given to straight and parallel in-plane grooves, curved groove in-plane designs and off-plane grooves. Aberrations due to dispersions and misalignment are also considered.

Wavelength Division Multiplexing/Demultiplexing (WDM) Using Diffraction Gratings

Abstract: This paper reviews the present status of diffraction grating based wavelength division multiplexer/demultiplexers (WDM). A comparison is made of WDM's currently in commercial use with both monomode and multimode fibres. Devices are described ranging from an industrial system multiplexing and demultiplexing 49 channels to a 12-channel monomode demultiplexer. The discussion includes multi-multiplexers in which several multiplexers share a common optical element.

Wavelength-selective multiplexer-demultiplexer

Abstract: A multiplexer-demultiplexer for different wavelengths carried by optical fibers (10) the ends of which are disposed in the immediate vicinity of the focus of a concave mirror (18) associated with a plane diffraction grating (15) is disclosed. The multiplexer-demultiplexer consists of four elements that are adhesively attached to one another, namely, a fiber-carrying element (1); a grating-carrying element (15); an intermediary element (3) of the same index as the element (2); and a mirror element (4) having an index of refraction different from that of element (3) and selected to compensate for longitudinal spherical aberration of the mirror (18) for at least one of the wavelengths being utilized.

Range measurement using Talbot diffraction imaging of gratings.

Abstract: A range measurement technique is presented which allows real-time range data acquisition for all points in an image. The technique relies upon the systematic variation in the Fresnel diffraction pattern of a grating as a function of propagation distance. The technique uses a single view of the volume in question so there are no hidden points. Furthermore, there is no need for beam scanning or is any off-line processing required. An extensive theory of operation is presented along with grating and illumination design methods which allow one to tailor the technique to specific measurement requirements. Qualitative experimental results are given along with quantitative results.

Dissimilar superimposed grating precision alignment and gap measurement systems

Abstract: A substrate having a diffraction grating of a first periodicity formed thereon, a mask having a diffraction grating of a second periodicity formed thereon, the mask and substrate being positioned such that the respective mask and substrate gratings are generally parallel opposing one another on the mask and substrate, means for providing collimated coherent light directed so as to impinge on the mask and substrate gratings, and means for separately collecting, recombining, and detecting the intensity of at least a first given order of diffracted light beams as respectively diffracted by the mask and substrate gratings.

Layered synthetic microstructure technology considerations for the extreme ultraviolet

Abstract: It is demonstrated that layered synthetic microstructures (LSMs) can provide mirrors with enhanced normal incidence reflectance in the 300-A spectral region Experimental results are presented for Pt-Si and Ir-Si structures fabricated by electron-beam deposition at pressures of about 10 to the -6th Torr, and it is shown that the enhancement is realized over a limited bandwidth of 75 A One potential application of LSMs is their use as coatings on diffraction gratings to enhance normal incidence reflection efficiencies Preliminary results for the Ir-Si combination on a diffraction grating show that LSMs enhance grating efficiencies in the EUV by a factor of about 3

Coupled wave analysis for out-of-phase mixed thick hologram gratings

Abstract: A coupled wave analysis is given for mixed volume hologram gratings. The effect of spatial dephasing between the absorption and phase grating is considered and evaluated numerically for a number of cases. The analysis is motivated by the photorefractive effect in electro-optic crystals.

Light beam combining method and apparatus

Abstract: A plurality of light beams emitted by a plurality of light sources are combined together to obtain a power-multiplication effect of the beams by use of a holographic diffraction grating. The holographic diffraction grating diffracts a plurality of light beams incident thereto into such directions that the diffracted light beams advance in parallel to one another or are collimated, advance toward a point or converge, or advance as if they were emitted from a point or diverge so that the diffracted light beams can be focused to a point by use of or without a focusing optical system to multiply the power of the beams in effect. The holographic diffraction grating may be of area division type which diffracts the light beams at different portions thereof or of a multiple type which diffracts the light beams at the same portion thereof. By the former type holographic diffraction grating a single combined light beam in which the original light beams are fully merged into a single light beam is obtained, and by the latter type grating the original light beams are diffracted into collimated, converging or diverging beams.

Introduction to classical and modern optics

Abstract: Preface. 1. Reflection and Refraction. 2. Thin Lenses. 3. Thick Lenses and Combinations of Lenses. 4. Mirrors. 5. Aberrations. 6. Stops and Pupils. 7. Gradient-Index, Fiber, and Integrated Optics. 8. Lens Design. 9. Optical Systems. 10. Systems Evaluation. 11. Interference. 12. Thin Films. 13. Coherence. 14. Diffraction. 15. Diffraction Gratings. 16. Light Scattering. 17. Polarization of Light. 18. Optical Data Processing. 19. Holography. 20. Light Sources and Detectors. 21. Radiometry/Photometry. 22. Absorption. 23. Lasers. 24. Relativistic Optics. Answers to Odd-Numbered Problems. Index.

Semiconductor light emitting device

Abstract: PURPOSE:To strength the selectivity for TE polarization without causing the increase threshold value current by using a super grating structure for an active layer, in a semiconductor laser wherein a diffraction grating of strong wavelength selectivity is integrated to a laser wave guide CONSTITUTION:A DBR laser is formed of an N-GaAs substrate 1, an N-clad layer 2, an active layer 11, a P-clad layer 3, P-contact layer 4, Bragg reflection type (DBR) reflection parts 8 and 9, and electrodes 6 and 7 Here, the active layer 11 is composed of a GaAs/Al GaAs super grating layer, and has the super grating structure wherein a GaAs well layer and an AlXGa1-XAs barrier layer are alternately stacked to a multilayer Thereby, the selectivity for TE polarization is strengthened by a difference of large gains of TE polarization and TM polarization due to the super grating structure, without damaging of a characteristic of excellence in the singleness of the vertical mode which the DBR laser has, and of excellence in the temperature stability of the laser oscillation wavelength; therefore a deflection surface can be stabilized

Real-time depth measurement and display using Fresnel diffraction and white-light processing

Abstract: An optical method of measuring and displaying depth information has been developed which is based on the Fresnel diffraction properties of coherently illuminated gratings. Cosine modulated gratings are found to be more flexible than simple gratings for depth measurement. A pair of gratings crossed at right angles is used to provide two independent depth measurement channels. A real-time white-light processor has been developed to convert the depth information into pseudocolor. The depth signal is input to a white-light processor by a liquid crystal light valve. The two depth channels are filtered to produce different color images such that the hue of the combined image is a function of depth.

Optical waveguide spectrum analyzer and method

Abstract: System and method for analyzing spectral data from an optical fiber waveguide. Light from the waveguide is directed to a diffraction grating which separates the light into its spectral components and directs these components toward a light responsive detector. The grating is rotated to cause spectral components of different wavelengths to sweep across the detector, and a sensor provides a signal corresponding to the angular position of the grating. A table of calibration data is generated by introducing monochromatic light of known wavelength into the waveguide, positioning the grating to cause the light at two known points in the spectrum of the monochromatic light to impinge upon the detector, and utilizing the wavelength of the monochromatic light and the values of the sensor signal at the two known points to define the relationship between the sensor signal and the detected wavelength for a plurality of grating positions. The calibaration data and the sensor signal are utilized to determine the wavelength of light peaks produced by a sample, and they are also utilized to generate a control signal for positioning the grating very accurately to detect light of a given wavelength. In one disclosed embodiment, two detectors having different spectral responses are employed, and light in different portions of the spectrum is detected by respective ones of the detectors.

Bistable optical device

Abstract: An optical bistable device comprising a semiconductor laser including a diffraction grating which diffracts light parallel to the grating for laser resonance and additionally diffracts a higher order Bragg beam perpendicular to the grating. An optical detector receives the higher order beam and produces an electrical signal which is used as a partial exciting current for the semiconductor laser. Thereby, the two optical ports of the laser can be used for other purposes.