Showing papers on "Diffraction grating published in 1995"
TL;DR: In this paper, the authors presented a stable and efficient numerical implementation of the analysis technique for one-dimensional binary gratings for both TE and TM polarization and for the general case of conical diffraction.
Abstract: The rigorous coupled-wave analysis technique for describing the diffraction of electromagnetic waves by periodic grating structures is reviewed. Formulations for a stable and efficient numerical implementation of the analysis technique are presented for one-dimensional binary gratings for both TE and TM polarization and for the general case of conical diffraction. It is shown that by exploitation of the symmetry of the diffraction problem a very efficient formulation, with up to an order-of-magnitude improvement in the numerical efficiency, is produced. The rigorous coupled-wave analysis is shown to be inherently stable. The sources of potential numerical problems associated with underflow and overflow, inherent in digital calculations, are presented. A formulation that anticipates and preempts these instability problems is presented. The calculated diffraction efficiencies for dielectric gratings are shown to converge to the correct value with an increasing number of space harmonics over a wide range of parameters, including very deep gratings. The effect of the number of harmonics on the convergence of the diffraction efficiencies is investigated. More field harmonics are shown to be required for the convergence of gratings with larger grating periods, deeper gratings, TM polarization, and conical diffraction.
2,437 citations
TL;DR: In this paper, the surface of an azoaromatic polymer film is optically altered to produce local highly efficient diffraction gratings, which can be erased by heating the polymer above its glass transition temperature and no permanent damage of the film is observed.
Abstract: The surface of an azoaromatic polymer film is optically altered to produce local highly efficient diffraction gratings. The gratings obtained are stable but can be erased by heating the polymer above its glass transition temperature and no permanent damage of the film is observed. Multiple gratings can be simultaneously written and gratings can be overwritten. Atomic force microscopy was used to investigate the gratings produced on the surfaces. Possible mechanisms responsible for the surface alteration are discussed.
1,183 citations
TL;DR: In this paper, the authors observed holographic surface relief gratings with relatively large amplitude on a second order nonlinear optical polymeric material, which were created upon exposure to polarized Ar+ laser beams at 488 nm without any subsequent processing steps.
Abstract: We report observation of holographic surface relief gratings with relatively large amplitude on a second order nonlinear optical polymeric material. Surface relief gratings on these polymer films were created upon exposure to polarized Ar+ laser beams at 488 nm without any subsequent processing steps. The surface structure of the relief gratings was investigated by atomic force microscopy. The depth of the surface relief in a typical case was 120 nm which is approximately 20% of the original film thickness. The diffraction efficiency of gold‐coated gratings was investigated as a function of wavelength and capability of recording orthogonal gratings on the same film was demonstrated.
1,079 citations
TL;DR: In this paper, the authors describe a compact, economic and versatile diode laser system based on commercial laser diodes, optically stabilized by means of feedback from a diffraction grating, which offers singlemode operation with a linewidth of a few 100 kHz, continuous scans over 25 GHz, high chirp rates (up to 9 GHz/ms) and FM-modulation up to the GHz range.
519 citations
TL;DR: A wideband antireflection structure for glass that consists of a diffraction grating with a dielectric overcoat, which leads to an average reflection of less than 0.6% in the wavelength range between 300 and 2100 nm is presented.
Abstract: Diffractive optical structures for increasing the efficiency of crystalline silicon solar cells are discussed. As a consequence of the indirect band gap, light absorption becomes very ineffective near the band edge. This can be remedied by use of optimized diffraction gratings that lead to light trapping. We present blazed gratings that increase the optically effective cell thickness by approximately a factor of 5. In addition we present a wideband antireflection structure for glass that consists of a diffraction grating with a dielectric overcoat, which leads to an average reflection of less than 0.6% in the wavelength range between 300 and 2100 nm.
410 citations
TL;DR: In this article, an optimal Klopfenstein tapered 2D subwavelength grating is designed to reduce the Fresnel reflections by 20 dB over a broad band from an air-substrate (ns = 3.0) interface.
Abstract: Techniques for the design of continuously tapered two-dimensional (2D) subwavelength surface-relief grating structures for broadband antireflection surfaces are investigated. It has been determined that the Klopfenstein taper [ Proc. IRE44, 31 ( 1956)] produces the optimum graded-index profile with the smallest depth for any specified minimum reflectance. A technique is developed to design the equivalent tapered subwavelength surface-relief grating structure by use of 2D effective-medium theory. An optimal Klopfenstein tapered 2D subwavelength grating is designed to reduce the Fresnel reflections by 20 dB over a broad band from an air–substrate (ns = 3.0) interface. The performance is verified by use of both a 2D effective-medium-theory simulation algorithm and rigorous coupled-wave analysis. These structures are also shown to achieve this low reflectance over a wide field of view (θFOV > 110°). The pyramidal spatial profile, which has generally been assumed to produce the optimal broadband antireflection grating structure, is shown to require a significantly larger depth to achieve the same performance as a Klopfenstein-designed tapered antireflection grating structure.
243 citations
TL;DR: The Talbot effect, the self-imaging of a periodic structure, with atom waves is demonstrated, and the successive recurrence of these self-images is measured as a function of the distance from the imaged grating.
Abstract: We have demonstrated the Talbot effect, the self-imaging of a periodic structure, with atom waves. We have measured the successive recurrence of these self-images as a function of the distance from the imaged grating. This is a near-field interference effect, which has several possible applications that are discussed.
238 citations
TL;DR: In this article, the design and performance of a new type of high-efficiency diffraction grating for use in either transmission or reflection are described, which is produced in a multilayer dielectric coating deposited upon optically flat substrates.
Abstract: The design and performance of a new type of high-efficiency diffraction grating for use in either transmission or reflection are described. The gratings are produced in a multilayer dielectric coating deposited upon optically flat substrates. By proper design of the multilayer stack and grating structure, a diffraction efficiency in excess of 96% for polarized light in the m = -1 order in reflection has been achieved.
225 citations
TL;DR: In this paper, an all-fiber Mach-Zehnder interferometer with photo-induced Bragg gratings was used to drop/insert a single wavelength channel from/into a multiple-wavelength transmission link with 100 GHz channel-spacing at 1550 nm.
Abstract: A wavelength multiplexing/demultiplexing device is fabricated and used to drop/insert a single wavelength channel from/into a multiple wavelength transmission link with 100 GHz channel-spacing at 1550 nm. The device consists of an all-fiber Mach-Zehnder interferometer with photoinduced Bragg gratings. The following performances were measured: extraction/coupling efficiency =99.4%, excess loss 20 dB, and return loss >23 dB. >
219 citations
TL;DR: In this paper, a structure for an electro-optically controlled liquid crystal diffraction grating is proposed, which can dramatically simplify the fabrication process of liquid crystal optical gratings and gives 100% diffraction efficiency and no polarization direction dependence.
Abstract: A structure for an electro‐optically controlled liquid crystal diffraction grating is proposed, which can dramatically simplify the fabrication process of liquid crystal optical gratings. The structure consists of two alternating stripes. Each stripe is a hybrid liquid crystal cell with adjacent stripes oriented perpendicularly. This kind of electro‐optically controlled diffraction grating in principle gives 100% diffraction efficiency and no polarization direction dependence. The detailed fabrication process is presented.
208 citations
TL;DR: It is shown that although the reflection characteristics can be accurately modeled with the second-order EMT, the phase difference created by form birefringence for TE- and TM-polarized waves requires the use of a more rigorous, RCWA approach.
Abstract: Diffraction characteristics of high-spatial-frequency (HSF) gratings are evaluated for application to polarization-selective computer-generated holograms by the use of two different approaches: second-order effective-medium theory (EMT) and rigorous coupled-wave analysis (RCWA). The reflectivities and the phase differences for TE- and TM-polarized waves are investigated in terms of various input parameters, and results obtained with second-order EMT and RCWA are compared. It is shown that although the reflection characteristics can be accurately modeled with the second-order EMT, the phase difference created by form birefringence for TE- and TM-polarized waves requires the use of a more rigorous, RCWA approach. The design of HSF gratings in terms of their form birefringence and reflectivity properties is discussed in conjunction with polarization-selective computer-generated holograms. A specific design optimization example furnishes a grating profile that provides a trade-off between the largest form birefringence and the lowest reflectivities.
TL;DR: A computationally efficient implementation of rigorous coupled-wave analysis is presented in this article, where the eigenvalue problem for a one-dimensional grating in a conical mounting is reduced to two eigen value problems in the corresponding nonconical mounting, yielding two n × n matrices to solve for eigenvalues and eigenvectors.
Abstract: A computationally efficient implementation of rigorous coupled-wave analysis is presented The eigenvalue problem for a one-dimensional grating in a conical mounting is reduced to two eigenvalue problems in the corresponding nonconical mounting This reduction yields two n × n matrices to solve for eigenvalues and eigenvectors, where n is the number of orders retained in the computation For a two-dimensional grating, the size of the matrix in the eigenvalue problem is reduced to 2n × 2n These simplifications reduce the computation time for the eigenvalue problem by 8–32 times compared with the original computation time In addition, we show that with rigorous coupled-wave analysis one analytically satisfies reciprocity by retaining the appropriate choice of spatial harmonics in the analysis Numerical examples are given for metallic lamellar gratings, pulse-width-modulated gratings, deep continuous surface-relief gratings, and two-dimensional gratings
Patent•
29 Sep 1995TL;DR: In this article, the design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described, and methods for fabricating these gratings without the use of ion etching techniques are described.
Abstract: The design and fabrication of dielectric grating structures with high diffraction efficiency used in reflection or transmission is described. By forming a multilayer structure of alternating index dielectric materials and placing a grating structure on top of the multilayer, a diffraction grating of adjustable efficiency, and variable optical bandwidth can be obtained. Diffraction efficiency into the first order in reflection varying between 1 and 98 percent has been achieved by controlling the design of the multilayer and the depth, shape, and material comprising the grooves of the grating structure. Methods for fabricating these gratings without the use of ion etching techniques are described.
TL;DR: Transient and persistent holographic gratings have been observed in dye- and fullerene C(60)-doped nematic liquid-crystal films and the nature and time evolution of the underlying mechanisms, such as space-charge field production, flows, and dielectric- and conductivity-induced torques are examined.
Abstract: Transient and persistent holographic gratings have been observed in dye- and fullerene C60-doped nematic liquid-crystal films. The nature and time evolution of the underlying mechanisms, such as space-charge field production, flows, and dielectric- and conductivity-induced torques, and the resultant director axis reorientation and refractive-index gratings are examined.
Patent•
08 Mar 1995
TL;DR: In this paper, an embedded optical sensor has a plurality of layers (10-20) and an optical fiber (21) with a fiber grating (28), disposed between the layers (14, 16).
Abstract: An embedded optical sensor has a plurality of layers (10-20) and an optical fiber (21) with a fiber grating (28), disposed between the layers (14, 16). The layers (10-20) comprise filaments (22) and resin (24) which have different thermal expansion coefficients and the filaments (22) are oriented so as to create unequal transverse residual stresses that act through the geometry of a resin-rich region that surrounds on the grating (28) in the fiber (21). The unequal transverse residual stresses cause birefringence in the grating (28), thereby causing the grating (28) to reflect light (32) having two wavelengths with a predetermined separation, each along a different polarization axis. The wavelength separation and average wavelength between such separation have different sensitivities to temperature and strain, thereby allowing independent temperature and strain measurements using only a single grating. The birefringence is maximized when the filaments (22) of the adjacent layers (10, 12) are oriented at 90 degrees with respect to the longitudinal (Z-axis) of the fiber (21).
Patent•
30 Aug 1995TL;DR: An electrically-programmable diffraction grating was proposed in this article for optical information processing (e.g. optical correlators and computers), for multiplexing and demultiplexing a plurality of light beams of different wavelengths, and for forming spectrometers.
Abstract: An electrically-programmable diffraction grating. The programmable grating includes a substrate having a plurality of electrodes formed thereon and a moveable grating element above each of the electrodes. The grating elements are electrostatically programmable to form a diffraction grating for diffracting an incident beam of light as it is reflected from the upper surfaces of the grating elements. The programmable diffraction grating, formed by a micromachining process, has applications for optical information processing (e.g. optical correlators and computers), for multiplexing and demultiplexing a plurality of light beams of different wavelengths (e.g. for optical fiber communications), and for forming spectrometers (e.g. correlation and scanning spectrometers).
TL;DR: In this paper, the interference field produced by a periodic mask and the near-field energy density and fluence distribution for varying degrees of order content when exposed using an excimer laser with finite spatial and temporal coherence were analyzed.
TL;DR: In this paper, the performance of grating and crystal monochromators is compared in the 1-2 keV photon energy range. And the performance data of a plane grating focusing condition was presented.
Abstract: During the last 10 years various types of soft x‐ray monochromators have been developed, which are optically based on the plane grating focusing condition introduced in 1980. These instruments as well as those using the original 1980 optical configuration are reviewed and compared to the other type of high performance soft x‐ray grating monochromator, the Rowland circle based spherical grating monochromator (SGM). Performance data of a plane grating monochromator (HE‐PGM‐3), which was recently commissioned at BESSY and which offers a broad spectral range (40–2000 eV) and very high spectral resolution (up to E/ΔE∼10 000) are given in more detail. The performance of grating and crystal monochromators is compared in the 1–2 keV photon energy range.
TL;DR: In this article, achromatic interferometric lithography was used to fabricate large-area coherent gratings and grids with spatial periods of 100 nm, which is the minimum required for the fabrication of periodic structures.
Abstract: For the fabrication of periodic structures with spatial periods of 100 nm or less, achromatic interferometric lithography is preferred over other lithographic techniques. We report on processes we have developed, using achromatic interferometric lithography, to fabricate large‐area coherent gratings and grids with spatial periods of 100 nm.
TL;DR: In this article, the authors used standard coupledmode theory together with transfer-matrix formalism, and showed that by introducing several phase shift regions and properly choosing their locations and magnitudes the transmission spectrum can be tailored into a nearly rectangular shape.
Abstract: Standard Bragg filters (dielectric waveguides with a grating overlay) show a stopband only in reflection. Filters with quarter-wave-shifted gratings have an extremely narrow transmission peak the center of the stopband but its shape (a sharp triangle with a broad bottom) is not suitable for system design. Using standard coupled-mode theory together with transfer-matrix formalism, we show that by introducing several phase-shift regions and properly choosing their locations and magnitudes the transmission spectrum can be tailored into a nearly rectangular shape. For InP-InGaAsP based Bragg-grating filters estimates are made of achievable channel spacings in wavelength-division multiplexing systems.
TL;DR: The design and fabrication of large-area, high-efficiency metallic gratings for use in high-power laser systems is described and a simple theory for optical damage to metallic diffraction gratings is developed.
Abstract: The design and fabrication of large-area, high-efficiency metallic gratings for use in high-power laser systems is described. The gratings exhibit a diffraction efficiency in excess of 95% in the m = −1 order (Littrow mount) and have a high threshold for laser damage. Computations and experimental measurements are presented that illustrate the effect of grating shape and polarization on efficiency. A simple theory for optical damage to metallic diffraction gratings is developed and compared with experimental measurements of the laser-damage threshold over the pulse range from 400 fs to >1 ns.
Patent•
19 May 1995
TL;DR: In this paper, a diffraction grating is inserted between a mask and a projection optical system, and the mask is obliquely emitted from a different direction by diffracting the light passed through the pattern of a mask via projection optical systems, and reproducing a mask pattern on a sample from the diffracted light to be exposed.
Abstract: PURPOSE: To simultaneously satisfy the large exposure field and the high resolution by diffracting the light passed through the pattern of a mask via a projection optical system, and reproducing a mask pattern on a sample from the diffracted light to be exposed. CONSTITUTION: A diffraction grating A is inserted between a mask 1 and a projection optical system 2, and a diffraction grating B is inserted between the system 2 and a wafer 4. The mask is obliquely emitted from a different direction. In this case, both the gratings A and B are assumed to be phase gratings and that the illuminated lights R, L from the two directions are coherent to each other. A zero order light R0 reaches a point A0 on the grating A, where the light diffracted in + primary direction is passed through the left end of a pupil 3, and arrived at a point B0 on the grating B. Thereafter, it is diffracted by the grating B in + primary and - primary directions, and arrived at Q and P on image surfaces. The + primary diffracted light R1 arrives at the point A1 on the grating A, where the light diffracted in the + primary direction is passed through the right end of the pupil, and arrived at the point B1 on the grating B.
Patent•
30 Aug 1995TL;DR: In this article, the authors describe an optical apparatus consisting of a plurality of diffractive optical elements on a common substrate for forming first and second gratings that alternately intercept the incident light for different units of time.
Abstract: Optical apparatus for forming correlation spectrometers and optical processors. The optical apparatus comprises one or more diffractive optical elements formed on a substrate for receiving light from a source and processing the incident light. The optical apparatus includes an addressing element for alternately addressing each diffractive optical element thereof to produce for one unit of time a first correlation with the incident light, and to produce for a different unit of time a second correlation with the incident light that is different from the first correlation. In preferred embodiments of the invention, the optical apparatus is in the form of a correlation spectrometer; and in other embodiments, the apparatus is in the form of an optical processor. In some embodiments, the optical apparatus comprises a plurality of diffractive optical elements on a common substrate for forming first and second gratings that alternately intercept the incident light for different units of time. In other embodiments, the optical apparatus includes an electrically-programmable diffraction grating that may be alternately switched between a plurality of grating states thereof for processing the incident light. The optical apparatus may be formed, at least in part, by a micromachining process.
TL;DR: In this paper, a simulation tool based on the finite-difference time-domain (FDTD) technique is developed to model the electromagnetic interaction of a focused optical Gaussian beam in two dimensions incident on a simple model of a corrugated dielectric surface plated with a thin film of realistic metal.
Abstract: A simulation tool based on the finite-difference time-domain (FDTD) technique is developed to model the electromagnetic interaction of a focused optical Gaussian beam in two dimensions incident on a simple model of a corrugated dielectric surface plated with a thin film of realistic metal The technique is a hybrid approach that combines an intensive numerical method near the surface of the grating, which takes into account the optical properties of metals, with a free-space transform to obtain the radiated fields A description of this technique is presented along with numerical examples comparing gratings made with realistic and perfect conductors In particular, a demonstration is given of an obliquely incident beam focused on a uniform grating and a normally incident beam focused on a nonuniform grating The gratings in these two cases are coated with a negative-permittivity thin film, and the scattered radiation patterns for these structures are studied Both TE and TM polarizations are investigated Using this hybrid FDTD technique results in a complete and accurate simulation of the total electromagnetic field in the near field as well as in the far field of the grating It is shown that there are significant differences in the performances of the realistic metal and the perfect metal gratings
TL;DR: By locally varying the index, using fabricated two-dimensional arrays of dielectric cylinders, this work can achieve a desired phase modulation to produce a diffractive phase element in one processing step.
Abstract: We have designed, fabricated, and tested a blazed artificial dielectric transmission grating in fused quartz for use at the 633-nm wavelength. By locally varying the index, using fabricated two-dimensional arrays of dielectric cylinders, we can achieve a desired phase modulation to produce a diffractive phase element in one processing step. The effective index depends on the fill fraction of the cylinders.
TL;DR: In this article, a chirped Bragg gratings are used as stretchers and compressors for distortionless amplification of femtosecond pulses in chirping pulse amplification system.
Abstract: In‐fiber chirped Bragg gratings are used as stretchers and compressors for distortionless amplification of femtosecond pulses in chirped pulse amplification system. It is shown that using opposite directions of pulse propagation the effects of higher order dispersion and grating irregularities can be eliminated and the original pulse shape and duration can be recovered. Using these gratings a compact all‐fiber system consisting of a mode‐locked fiber oscillator and an erbium‐doped fiber amplifier was built. 330 fs bandwidth‐limited pulses from a fiber oscillator were stretched to 30 ps, amplified and recompressed back to 408 fs. The maximum energy of the pulses after the amplifier was 6 nJ and was at the threshold of nonlinear effects for a 30 ps stretched pulse.
TL;DR: The thermal stability of Bragg gratings written in hydrogen-loaded and unloaded germanium-doped optical fiber was studied in this paper, and it was shown that the species responsible for the index change in the hydrogenloaded fiber are less stable than those in the unloaded fiber.
Abstract: We have conducted a detailed study of the thermal stability of Bragg gratings written in hydrogen‐loaded and unloaded germanium‐doped optical fiber. Interference of either continuous‐wave or pulsed ultraviolet light was used to induce the index modulation gratings. Some gratings were kept at room temperature and others were annealed at fixed temperatures for 10–20 h. For temperatures between room temperature and 350 °C, gratings in the hydrogen‐loaded fiber showed significantly greater decay than those in the unloaded counterpart. The ultraviolet‐induced index modulation in hydrogen‐loaded fiber was reduced by 40% after 10 h at 176 °C, whereas it was reduced by only 5% in unloaded fiber under the same conditions. The annealing behavior of gratings written using the pulsed source was identical to that of gratings written with the continuous‐wave source, and the thermal stability of gratings in hydrogen‐loaded fiber did not depend on the magnitude of the index modulation. We also observed that the annealing of ultraviolet‐induced OH absorption in the hydrogen‐loaded fiber was not correlated with the grating decay. Our annealing results show that the species responsible for the index change in the hydrogen‐loaded fiber are less stable than those in the unloaded fiber.
TL;DR: In this paper, a six-wavelength laser array with an integrated amplifier and modulator designed for transmission of a single selectable wavelength is demonstrated, with thresholds of ~20 mA and the single-step printed gratings yield an average channel spacing of 200 GHz.
Abstract: A six-wavelength laser array with an integrated amplifier and modulator designed for transmission of a single selectable wavelength is demonstrated. The lasers have thresholds of ~20 mA, and the single-step printed gratings yield an average channel spacing of 200 GHz. Output powers through the modulator of several milliwatts are obtained from all six lasers when 75 mA is applied to the amplifier.
Patent•
01 May 1995
TL;DR: In this paper, a singlemode laser source tunable in wavelength with a self-aligned external cavity was proposed, consisting of a resonant cavity having an output face that is partially reflecting and a retroreflecting dispersive device.
Abstract: This invention relates to a singlemode laser source tunable in wavelength with a self-aligned external cavity, comprising: a resonant cavity having an output face that is partially reflecting (331) and a retroreflecting dispersive device (31, 39), defining a main collimating axis (351) and a secondary collimating axis (381), an amplifier wave guide (33) placed in position inside the resonant cavity The retroreflecting dispersive device comprises a plane diffraction grating (31) having dispersion planes and an orthogonal reflecting dihedral (39) whose line of intersection (391)is parallel to the dispersion plane of the diffraction grating containing the collimating axes (351, 352)
TL;DR: The design and performance of a new type of high-efficiency diffraction grating for use in either transmission or reflection with diffraction efficiency in excess of 96% for polarized light in the m = -1 order in reflection has been achieved.
Abstract: The design and performance of a new type of high-efficiency diffraction grating for use in either transmission or reflection are described. The gratings are produced in a multilayer dielectric coating deposited upon optically flat substrates. By proper design of the multilayer stack and grating structure, a diffraction efficiency in excess of 96% for polarized light in the m = -1 order in reflection has been achieved.