Showing papers on "Diffraction grating published in 1987"

3000 times grating compressor with positive group velocity dispersion: Application to fiber compensation in 1.3-1.6 µm region

Abstract: A compressor is designed that presents an opposite sign of the dispersion to that of standard two grating compressors. This is achieved by placing a telescope between gratings in order to modify in an adequate manner the phase shift for different wavelengths. The telescope simultaneously provides a high magnification in order to compensate more than 90 km of standard monomode fibers in the 1.6 μm region, yielding compression factors as high as 3000. Analytical expressions for Gaussian beams are found and limitations due to lateral spectral walkoff and telescope pupils are discussed.

Antireflection effect in ultrahigh spatial-frequency holographic relief gratings.

Abstract: An interpretation model for low reflectivity in ultrahigh spatial-frequency holographic relief gratings is proposed. The model is based on the concept that the grating effective index, caused by grating ultrahigh spatial frequency, is graded in the depth direction and forms an antireflective constitution similar to the multilayer coating. Numerical results show that a sinusoidal grating is antireflective over wide groove depth, wavelength and incident angle ranges, and a grating with nearly triangular section, having a circle arc index distribution, has a very low reflectivity, >10(-4)%. Reflectivity vs groove depth, obtained experimentally for a holographically recorded photoresist grating, agrees fairly well with the numerical results.

High resolution imagery systems and methods

Abstract: The current limits of resolution of multi-element optical systems are exceeded by reducing the number of elements while introducing at the critical aperture a blazed transmission grating having grating rings of low bending power defined by multiple plateaus. By illuminating the optical train with monochromatic light that constitutes a multiplicity of distributed sources having a substantial temporal coherence but spatial incoherence and by varying the slopes and widths of the grating rings, local phase delays are introduced that adjust aberrations in the optical system, providing an aligned composite wavefront. The system and method may be used for presenting an image, as for a wafer stepper, or for viewing an image, as in a microscope.

Coherent laser addition using binary phase gratings

Abstract: Binary phase diffraction gratings are shown to couple light coherently from a laser array into a single on-axis beam. The diffraction grating, designed to split a single beam into a specific number of equal intensity diffraction orders, is placed inside the cavity formed by the laser array and a common output mirror. The grating superimposes the light beams from the lasers in the array and produces a far-field pattern with the same divergence as that of a single laser. Six GaAlAs lasers from an antireflection-coated linear array were combined with a coupling efficiency of 68.4%. The far field of the combined GaAlAs lasers consisted of a single on-axis Gaussian beam.

Method for aligning first and second objects, relative to each other, and apparatus for practicing this method

Abstract: According to this invention, a method and apparatus for aligning a mask and a wafer arranged to oppose each other, in a direction along their opposing surfaces, relative to each other, are arranged as follows. A first diffraction grating as a one-dimensional diffraction grating, bars of which extend in a direction perpendicular to an alignment direction, is formed on the mask. A second diffraction grating which has a checkerboard-like pattern, is formed on the wafer. The first diffraction grating is irradiated with laser beam emitted from a light source. Light beams diffracted and transmitted through the first diffraction grating is transferred to the second diffraction grating. Light beams diffracted and reflected by said second diffraction grating are transferred to said first diffraction grating. The light beams are diffracted by and transmitted through said first diffraction grating, again. Is detected, one of the diffracted light beams, which do not propagate along a predetermined plane. The light beams reflected and diffracted by the surface of the first diffraction grating, is transferred only in the predetermined plane. For this reason, the detected diffracted light beam will not interfere with reflected diffracted light beams. The mask and wafer can be precisely aligned relative to each other, in accordance with the intensity of the detected diffracted light beam.

Diffraction immunoassay apparatus and method

Abstract: A diffraction immunoassay method in which a diffraction grating design of non-light disturbing primary binding reagent on an insoluble surface is conjugated with analyte in a sample. If the primary binding reagent-analyte conjugate is light disturbing, a diffraction grating is formed. If the primary binding reagent-analyte conjugate is non-light disturbing, the analyte is further conjugated with a secondary binding reagent which is labeled with a light disturbing material to form a diffraction grating. Light from a narrow band light source is then applied to the surface, and the intensity of beams of diffracted light formed by the diffraction grating is determined. The diffraction immunoassay plate for the method comprises a smooth insoluble surface having on the surface thereof, a diffraction grating design of lines of the primary binding reagent. The diffraction immunoassay apparatus comprises a light source, a platform for supporting the diffraction immunoassay plates in the path of a beam of light from the light source, and at least one light detector positioned to detect light diffracted by the diffraction grating.

Rigorous three-dimensional coupled-wave diffraction analysis of single and cascaded anisotropic gratings

Abstract: The diffraction by one or an arbitrary number of cascaded anisotropic planar gratings with slanted fringes is analyzed by using rigorous three-dimensional vector coupled-wave theory. Arbitrary angle of incidence and polarization are treated. The existence of uniaxial external regions and the treatment of both phase and amplitude anisotropic slanted gratings are included in the analysis. The anisotropy and the three-dimensionality of the problem cause coupling between orthogonally polarized waves. The Bragg conditions for various combinations of ordinary (O) and extraordinary (E) polarized waves are quantified. Sample calculations are presented for single anisotropic gratings (a lithium niobate hologram in air and an interdigitated-electrode-induced electro-optic grating in an optical waveguide), for two cascaded anisotropic gratings (a pair of interdigitated-electrode-induced gratings satisfying the OOO forward Bragg condition, the EEE forward Bragg condition, and the OOO backward Bragg condition), and for multiple cascaded gratings (a lithium niobate hologram with depth modulation). The same analysis applies in the limiting cases of isotropic materials, a grating vector lying in the plane of incidence, etc. Applications for this analysis include optical storage, switching, modulation, deflection, and data processing.

Second harmonic generation in an optical fibre by self written x(2) grating

Abstract: Measurements of the effective length and wavelength selectivity of a second order susceptibility grating written into a fibre are reported. A weak non-phase matched second harmonic signal at 532nm is generated by the allowed quadrupole polarisation. This signal initiates the self-writing of an axially periodic pattern of defect centres in the fibre which lead to the growth of a chi (2) grating. Phase-matching is achieved automatically because the enhanced chi (2) is written periodically into the fibre at spatial locations where the second harmonic signal is the highest and is in phase with the pump. One particular chi (2) grating extends over 12cm of fibre and has a bandwidth of 0.24nm

Display element and observation apparatus having the same

Abstract: A display element includes a substrate and a display pattern formed on the substrate, the display pattern including a diffraction grating. The width in the direction perpendicular to the grating lines of the diffraction grating of the display pattern is selected so as to prevent re-diffraction of the light diffracted by the one diffraction grating. An observation apparatus includes the afore-said display element, but the display pattern has a first diffraction grating structure and a second diffraction grating structure. An illuminating system and an observation system are added so as to allow for observation of the display pattern. The direction of the grating lines of the first diffraction grating structure differs from that of the grating lines of the second diffraction grating structure, thereby preventing the occurrence of a rainbow-like image.

Experimental evidence of the inverse Smith–Purcell effect

Abstract: Interest in the development of laser-driven linacs has been stimu-lated recently by the advent of the high-power lasers. The use of a laser to accelerate charged particles was first proposed by K. Shimoda in 19621. He noticed that high values of acceleration per metre (acceleration gradient) could be obtained with an intense electric field in the output of a high-power laser. The inverse Smith–Purcell (ISP) effect proposed by us2 is a candidate for laser-driven linacs with a metallic grating as an interaction circuit. In 1953 Smith and Purcell demonstrated that light is emitted when a high-voltage electron beam moves parallel and close to a metallic optical diffraction grating in a direction perpendicular to the grating rulings3. The dispersion relationship is a synchronous condition between the electrons and the wave on the grating. Therefore, the inverse Smith-Purcell effect (ISP), or the extended interaction between electrons and an incident light wave should occur when the same relation is satisfied between the electrons and the incident wave (Fig. 1)2. Lawson pointed out4 that this effect would fail to accelerate relativistic particles. This difficulty was solved by Palmer5, who showed that acceleration is possible either if the particles travel skew to the grating lines, or if the radiation is falling at a skew angle onto the grating. Several authors have described possibilities for producing a grating linac (ISP effect) with accelerating field of a few GeV m−1 in the infrared or optical wave region6. Here we report the first observational evidence for this effect using a submillimetre-wave laser as a driving source. The experimental results give good agreement with theoretical predictions.

Multiplexer-demultiplexer using an elliptical concave garting and producted in integrated optics

Abstract: The device comprises microguides (G1, G2, . . . GN) traversed by light beams with N different wavelengths, a diffraction grating (R) formed by reflecting elliptical facets and a single microguide (G). Point (S) of the end of the single microguide (G) and points (P1, . . . PN) of the ends of microguides (G1, . . . GN) are optically joined by the grating for different wavelengths.

Method and apparatus for optically measuring fluid levels

Abstract: A non-metallic fiber-optic device is provided for measuring the level of fluid in a tank, reservoir, or other vessel. Light from a broadband light source is transmitted through a fiber optic waveguide and an optical coupler to an optical pipe sensor which is immersed in the fluid to be measured. The optical pipe sensor includes a monotonically varied diffraction grating in the surface and along the length of the sensor which serves to retroreflect wavelengths of light as a function of the local spacing of the diffraction grating. For light entering the sensor from the waveguide, wavelengths of light corresponding to the local spacing of the diffraction grating above the fluid level are retroreflected, whereas wavelengths of light corresponding to the diffraction grating spacing below the fluid level either escape into the fluid, are absorbed, or are coupled to a return fiber to be detected. Either the retroreflected wavelengths of light or the non-retroreflected wavelengths of light are emitted by the sensor, separated by a spectrometer, sensed by a photodetector, analyzed by a computer, and converted to an output display indicating measurement of the fluid level.

Design Of A Grating Spectrometer From A 1:1 Offner Mirror System

Abstract: A 1:1 Offner mirror system is modified to work as a grating spectrometer for the infrared by placing a grating on the secondary convex mirror of the system. Slight adjustment of the configuration combined with tilt of the secondary provide the necessary degrees of freedom to correct for astigmatism of the system. Additional control may be obtained by using a holographic optical element (HOE), constructed to add necessary compensating aberrations. Details of the best configuration and the limitations of performance are presented.

Simplified dichromated gelatin hologram recording process

Abstract: A simplified method for making dichromated gelatin (DCG) holographic optical elements (HOE) has been discovered. The method is much less tedious and it requires a period of processing time comparable with that for processing a silver halide hologram. HOE characteristics including diffraction efficiency (DE), linearity, and spectral sensitivity have been quantitatively investigated. The quality of the holographic grating is very high. Ninety percent or higher diffraction efficiency has been achieved in simple plane gratings made by this process.

Direct production of gratings on plastic substrates using 248-nm KrF laser radiation.

Abstract: A technique is described for the direct production of holographic diffraction gratings on polyethylene terephthalate and polyimide films by irradiation with interfering KrF laser beams. Surface relief type gratings with spatial frequencies of 630–2900 lines/mm have been produced and characterized as to their diffraction efficiency in both transmission and reflection modes. The resultant measurements are discussed in terms of predicted diffraction efficiencies and formation mechanisms involving ablation of the surface layer.

Optical transducers with wavelength coding

Abstract: An optical transducer has an optical head mounted above an optically encoded reflective disc. Broad band radiation is supplied to the head via a single fibre cable. This head is a solid glass block with a curved reflecting surface that collimates and reflects radiation onto a diffraction grating. Radiation is dispersed by the grating and reflected back onto the curved reflecting surface. This causes the radiation to be focussed onto the disc as a spectrum. The head combines radiation reflected from the disc and focusses it onto the end of an output fibre. A wavelength decoder at the other end of the output fibre disperses the received radiation so that an array of photodiodes provides an output representing the location of the reflective parts of the disc from which the position of the disc is determined. By measuring the separation between two reflective tracks concentricity errors can be removed and displacement of an encoder in two coordinate directions can be measured by measuring the separation and absolute positions of reflected wavelengths.

Total internal diffraction of plasmon surface polaritons

Abstract: Total internal diffraction of plasmon surface polariton fields by a dielectric phase grating is described. The grating was fabricated by partly desorbing thin organic multilayers deposited on top of the plasmon‐carrying Ag‐air interface through the regularly spaced holes of an electron microscope grid. The diffraction pattern shows for various angles of incidence a characteristic intensity distribution which can be understood taking into account a grating wave vector mediated coupling of the two plasmons corresponding to the two different layer structures.

Reflection and transmission coefficients of a thin strip grating for antenna application

Abstract: Reflection and transmission coefficients of thin strip gratings are discussed for plane wave incidence from arbitrary direction. Upon use of the low-frequency approximation, simple closed-form expressions are obtained. They are applicable for the analysis of grid reflector antennas. Physical interpretations of the phenomena are also given and interesting characteristics of the gratings are pointed out. The validity and the applicability of our results is examined numerically by making use of the point matching method (PMM). It is shown that the accuracy is excellent provided the period of gratings is smaller than about 0.3 wavelength.

Picosecond holographic-grating spectroscopy.

Abstract: Interfering light waves produce an optical interference pattern in any medium that interacts with light. This modulation of some physical parameter of the system acts as a classical holographic grating for optical radiation. When such a grating is produced through interaction of pulsed light waves with an optical transition, a transient grating is formed whose decay is a measure of the relaxation time of the excited state. Transient gratings can be formed in real space or in frequency space depending on the time ordering of the interfering light waves. The two gratings are related by a space-time transformation and contain complementary information on the optical dynamics of a system. The status of a grating can be probed by a delayed third pulse, which diffracts off this grating in a direction determined by the wave vector difference of the interfering light beams. This generalized concept of a transient grating can be used to interpret many picosecond-pulse optical experiments on condensed-phase systems. Examples of some low-temperature experiments will be presented. In principle, many of these experiments could also be performed by using stochastic broad-band excitation. In these nonlinear photon-interference experiments the time resolution is determined by the correlation time of the light source rather than its pulse width.

Zero-reflectivity homogeneous layers and high spatial-frequency surface-relief gratings on lossy materials

Abstract: The required thickness and complex refractive index of single homogeneous layers on lossy substrates to produce zero reflectivity are calculated by a rigorous impedance matching approach. The analysis is applicable to both TE and TM polarization and to any angle of incidence. The filling factor and groove depth of a rectangular-groove grating, equivalent to a single homogeneous lossy layer in the long-wavelength limit, are calculated. The method reduces to that previously found for dielectric surface-relief gratings in the limit of no losses. The antireflection behavior of the gratings is verified using the rigorous (without approximations) coupled-wave analysis of metallic surface-relief grating diffraction. It is shown that multiple zero-reflectivity solutions exist for both TE and TM polarizations and for any angle of incidence for an arbitrary complex-refractive-index substrate. Example zero-reflectivity gold gratings for incident free space wavelengths from 0.44 to 12.0 μm are presented.

Aplanatic and quasi-aplanatic diffraction gratings

Abstract: A reflection diffraction grating having a series of transverse minute grooves of progressively varying spacing along a concave surface enables use of such gratings for X-ray or longer wavelength imaging of objects. The variable groove spacing establishes aplanatism or substantially uniform magnification across the optical aperture. The grating may be used, for example, in X-ray microscopes or telescopes of the imaging type and in X-ray microprobes. Increased spatial resolution and field of view may be realized in X-ray imaging.

Photorefractive spatial light modulation by anisotropic self-diffraction in KNbO(3) crystals.

Abstract: Photoinduced anisotropic self-diffraction in photorefractive KNbO3 has been studied It has been shown that this type of diffraction is ideally suited for spatial light modulation or incoherent-to-coherent conversion A phase grating that is photoinduced by two coherent light beams causes the diffraction of one of the beams By spatially modulating the amplitude of the phase grating with an incoherent signal beam it is possible to transfer an incoherent image onto the coherent self-diffracted beam The performance parameters of this modulator are described with a simple model

Optical monomode guidance structure including low resolution grating

Abstract: Optical guidance structure comprising a monomode input guide having a particular direction (De), two monomode output guides having directions (Ds1, Ds2) symmetrically inclined with respect to the direction (De) of the input guide and a widened junction zone between the input guide and the output guides. A diffraction grating is located between the input guide and the junction. The grating has a spacing which defines only two diffraction directions of orders differing from zero, respectively +1 and -1. The spacing is chosen so that these two diffraction directions coincide with the directions of the first two output guides.

Diffraction grating using birefringence and optical head in which a linearly polarized beam is directed to a diffraction grating

Abstract: A diffraction grating comprises a birefractive sheet (11) having a corrugated surface with at least each groove filled with a mass (12) of a material of a refractive index which is substantially equal to one of ordinary and extraordinary indices of the birefractive sheet. The diffraction grating is effective in an optical head device when made to have a plurality of grating regions of different patterns of corrugations. In this event, a linearly polarized beam should be supplied to the diffraction grating with electric vectors directed parallel to those of ordinary and extraordinary components when the refractive index is substantially equal to the ordinary and extraordinary indices, respectively. Alternatively, such an optical head device may comprise a reflection grating in which reflective corrugations are substantially parallel in the respective grating regions. In this event, a linearly polarized beam is supplied from an optical source to the reflective corrugations as a p-polarized beam. When either the birefringence grating or the reflection grating is used, the optical head device should further comprise a quarterwave plate for receiving the linearly polarized beam which is exited from the grating.

Optical type displacement detecting device

Abstract: An optical type displacement detecting device including a main scale and an index scale, wherein a pitch of a first optical grating formed on the main scale is set at P and a pitch of a second optical grating formed on the index scale is set at P/n, thereby producing divided detection signal having pitch P/n. Furthermore, the pitch of the second optical grating is set at (u+v) P/u or (u+v) P/(2u) (u is a gap between a diffusive light source and the first optical grating and v is a gap between the first and second optical gratings), so that a collimator lens can be dispensed with. Further, higher harmonic components of the first optical grating are utilized, whereby the pitch of the second optical grating is set at substantially (u+v) Q/u or (u+v) Q/(2u) (Q=P/m, and m is a whole number of 2 or more), thereby preventing the pitch of the second optical grating from being divided into small ones.

Analysis of waveguide gratings: a comparison of the results of Rouard’s method and coupled-mode theory

Abstract: Recently we introduced a new computational tool for the analysis of waveguide diffraction gratings based on Rouard’s method, a recursive technique used in thin-film coating design. In this paper we compare the reflectivities predicted by Rouard’s method with those found by using the ideal mode expansion of coupled-mode theory for both periodic and aperiodic gratings. We find empirically that the two methods are in excellent agreement, with typical differences in reflectivity of less than 1%.

An automatic mask alignment technique using moiré interference

Abstract: This paper deals with an automatic and precise alignment technique for x‐ray lithographic masks, using two pairs of moire gratings, with their respective moire signals 180° out of phase with each other. The moire signals are detected in the 0th order beams, and the difference between these two signals are used to control the alignment of an x–y stage through a stepping motor. Experiments were carried out by using a transmission grating pitch of 200 μm, a displacement corresponding to one step of the stepping motor as 28 nm, a pulse frequency of 15 Hz and a response time of 0.13 s. With these parameters a precision better than 120 nm was obtained. Experiments were carried out by using a reflection grating of 25 μm pitch. The minimum displacement corresponding to one step of the stepping motor was 14 nm. The resolution of the A/D converters was 12 bits and the response time was 1.2 s. With these parameters a control reproducibility better than 32 nm was obtained. Improvement in the control precision by an o...

Holographic beam coupling in anisotropic photorefractive media

Abstract: The process of two-beam holographic coupling in optically anisotropic media is analyzed. We consider holographic media possessing birefringence, optical activity, and spatial modulation of these effects. Coupled equations are derived, and expressions for diffraction efficiency, angular and wavelength sensitivity, and polarization properties of the interacting beams are obtained. Results are compared with those of experiments with holograms formed in photorefractive Bi12SiO20 crystals.

Frequency stabilized light source

Abstract: Disclosed is a frequency stabilized light source including a semiconductor laser chip and a finite Fourier diffraction grating with a corrugated profile with a continuous first order differential coefficient. The laser chip emits the output light from its one facet into the diffraction grating with the diffracted light from the grating being fed back to the laser chip, so that the laser chip emits the output light with a stable wavelength from its another facet. The arrangement produces the output light with high frequency purity and high adjustment accuracy and yet wide frequency tunable range.

Diffraction grating having a plurality of different grating constants

Abstract: In a diffraction grating grooves having at least two kinds of grating constants are alternately arranged so as to repetitive at a constant period.