Showing papers on "Diffraction grating published in 1999"

Fiber Bragg gratings

Abstract: Since the discovery of photosensitivity in optical fibers there has been great interest in the fabrication of Bragg gratings within the core of a fiber. The ability to inscribe intracore Bragg gratings in these photosensitive fibers has revolutionized the field of telecommunications and optical fiber based sensor technology. Over the last few years, the number of researchers investigating fundamental, as well as application aspects of these gratings has increased dramatically. This article reviews the technology of Bragg gratings in optical fibers. It introduces the phenomenon of photosensitivity in optical fibers, examines the properties of Bragg gratings, and presents some of the important developments in devices and applications. The most common fabrication techniques (interferometric, phase mask, and point by point) are examined in detail with reference to the advantages and the disadvantages in utilizing them for inscribing Bragg gratings. Reflectivity, bandwidth, temperature, and strain sensitivity of the Bragg reflectors are examined and novel and special Bragg grating structures such as chirped gratings, blazed gratings, phase-shifted gratings, and superimposed multiple gratings are discussed. A formalism for calculating the spectral response of Bragg grating structures is described. Finally, devices and applications for telecommunication and fiber-optic sensors are described, and the impact of this technology on the future of the above areas is discussed.

Laterally modulated excitation microscopy: improvement of resolution by using a diffraction grating

Abstract: High spatial frequencies in the illuminating light of microscopes lead to a shift of the object spatial frequencies detectable through the objective lens. If a suitable procedure is found for evaluation of the measured data, a microscopic image with a higher resolution than under flat illumination can be obtained. A simple method for generation of a laterally modulated illumination pattern is discussed here. A specially constructed diffraction grating was inserted in the illumination beam path at the conjugate object plane (position of the adjustable aperture) and projected through the objective into the object. Microscopic beads were imaged with this method and evaluated with an algorithm based on the structure of the Fourier space. The results indicate an improvement of resolution.

Surface plasmon resonance sensors based on diffraction gratings and prism couplers: sensitivity comparison

Abstract: Theoretical analysis and comparison of the sensitivity of surface plasmon resonance (SPR) sensors using diffraction at gratings and attenuated total reflection (ATR) in prism couplers for two detection methods-resonant angle interrogation and resonant wavelength interrogation is presented. Analytical expressions for sensitivity of these SPR sensors are derived and the influence of the major design parameters of the sensing structures on the sensor sensitivity is discussed. The analysis shows that grating-based SPR sensors using wavelength interrogation are much less sensitive then their prism coupler-based counterparts. In the angular interrogation mode, the sensitivity of SPR sensors using diffraction gratings depends on the diffraction order and does not differ much from that of SPR sensors based on prism couplers.

Design and fabrication of blazed binary diffractive elements with sampling periods smaller than the structural cutoff

Abstract: We report here on the theoretical performance of blazed binary diffractive elements composed of pillars carefully arranged on a two-dimensional grid whose period is smaller than the structural cutoff. These diffractive elements operate under unpolarized light. For a given grating geometry, the structural cutoff is a period value above which the grating no longer behaves like a homogeneous thin film. Because the grid period is smaller than this value, effective-medium theories can be fully exploited for the design, and straightforward procedures are obtained. The theoretical performance of the blazed binary elements is investigated through electromagnetic theories. It is found that these elements substantially outperform standard blazed echelette diffractive elements in the resonance domain. The increase in efficiency is explained by a decrease of the shadowing effect and by an unexpected sampling effect. The theoretical analysis is confirmed by experimental evidence obtained for a 3λ-period prismlike grating operating at 633 nm and for a 20°-off-axis diffractive lens operating at 860 nm.

Photoinduced surface deformations on azobenzene polymer films

Abstract: Laser-induced surface deformation and surface relief grating formation at different intensity levels on azobenzene-functionalized polymer films were investigated. The surface deformation profile induced by a Gaussian laser beam at low intensities reveals strong polarization dependence and establishes that an optical-field component in the direction of the optical-field gradient is essential for this deformation process. A theoretical analysis based on the optical-field gradient force model is presented to account for the deformation behavior at low intensities. In the higher-intensity regime, however, a different mechanism is found to dominate the surface deformation process. Simultaneous formation of two different types of topographic gratings is observed in a two-beam interference experiment. The phase relationship between these surface relief gratings and the interference intensity pattern was deduced based on the results from the single-beam experiments. The erasing behaviors of the two distinct surface relief gratings were experimentally investigated to highlight the two mechanisms involved in these grating recordings.

Liquid immersion deep-ultraviolet interferometric lithography

Abstract: An apparatus for deep-ultraviolet interferometric lithography is described, in which the interfering beams illuminate the substrate through a fused silica prism and a layer of index-matching liquid. The liquid-immersion technique was found to be compatible with a commercially available, chemically amplified photoresist. The apparatus was used with a 257 nm light source to write gratings having a period of 97 nm and linewidth of approximately 40 nm.

Simultaneous multiplane imaging with a distorted diffraction grating

Abstract: We describe a simple technique for simultaneously imaging multiple layers within an object field onto a single camera. The approach uses a binary diffraction grating in which the lines are distorted such that a different level of defocus is associated with each diffraction order. The design of the gratings is discussed, and their ability to image multiple object planes is validated experimentally. Extension of the technique for spherical-aberration correction is described, and it is shown how the gratings can be used as part of a wave-front-sensing system.

A novel high-throughput Raman spectrometer for polarization difference measurements

Abstract: A Raman backscattering instrument which, for the first time, takes full advantage of the enormous etendue of modern holographic transmission grating spectrographs in single sample measurements is described Developed primarily as the basic design of a new generation of Raman optical activity spectrometers, it inherently has the capability also to measure precisely and rapidly the degree of circularity of scattered light, and thus reversal coefficients Its novel dual-channel design allows the simultaneous measurement of right and left circular scattered light and drastically reduces sensitivity to particulate matter and thermal Schlieren in the sample As examples the rapid and precise measurement of the degree of circularity of optically inactive substances and of the vibrational Raman optical activity of D-carnitine·HCl is presented Copyright © 1999 John Wiley & Sons, Ltd

Performance of the grating-crystal monochromator of the ALOISA beamline at the Elettra Synchrotron

Abstract: The new beamline ALOISA, now operational at the Elettra Synchrotron, is designed for surface studies by means of several experimental techniques: surface x-ray diffraction and reflectivity, photoemission spectroscopy, photoelectron diffraction, e−-Auger coincidence spectroscopy. A new monochromator has been specifically designed and realized for this multipurpose beamline: it makes use of a channel-cut Si crystal dispersive element for the 3–8 keV range and of a plane mirror-plane grating element for the 200–2000 eV range. Both dispersive elements share the same optical system. In the low energy range (200–900 eV) the spectral resolving power exceeds 5000 while maintaining a throughput higher than 1010 photons/s/200 mA/0.02% BW. In the case of the N2 1s→π* and Ne 1s→3p transitions, the extremely high signal-to-noise ratio of the absorption spectra allowed a very accurate determination of the corresponding natural linewidth (116±2 and 250±10 eV, respectively). Moreover, the vibrational structure of the CO–...

Dynamical diffraction in metallic optical gratings

Abstract: I show that dynamical diffraction of light in thin metallic gratings causes strong fluctuations in the transmitted intensity when the optical wavelength is comparable to the grating periodicity. The relative excitation of propagating Bloch waves in the grating depends on the incident wave vector. Bloch waves that peak in amplitude in the metal are strongly absorbed, whereas Bloch waves that peak in the holes are weakly absorbed. Anomalously high transmission occurs when the latter Bloch waves are strongly excited. Since surface plasmons are associated with the evanescent modes of the diffracted wavefield, I argue that the propagating diffracted beams and the surface plasmons are both part of the same dynamical scattering process.

High-efficiency dielectric reflection gratings: design, fabrication, and analysis.

Abstract: We report on reflection gratings produced entirely of dielectric materials. This gives the opportunity to enhance the laser damage threshold over that occurring in conventional metal gratings used for chirped-pulse-amplification, high-power lasers. The design of the system combines a dielectric mirror and a well-defined corrugated top layer to obtain optimum results. The rules that have to be considered for the design optimization are described. We optimized the parameters of a dielectric grating with a binary structure and theoretically obtained 100% reflectivity for the -1 order in the Littrow mounting for a 45° angle of incidence. Subsequently we fabricated gratings by structuring a low-refractive-index top layer of a multilayer stack with electron-beam lithography. The multilayer system was fabricated by conventional sputtering techniques onto a flat fused-silica substrate. The parameters of the device were measured and controlled by light scatterometer equipment. We measured 97% diffraction efficiency in the -1 order and damage thresholds of 4.4 and 0.18 J/cm2 with 5-ns and 1-ps laser pulses, respectively, at a wavelength of 532 nm in working conditions.

Broadband form birefringent quarter-wave plate for the mid-infrared wavelength region.

Abstract: We discuss the design, fabrication and optical performance of a broadband form-birefringent quarter-wave plate for the 3.5 to 5 aem wave-length region. Rigorous coupled wave analysis (RCWA) was used to design the requisite subwavelength grating for silicon substrates in ambient air. Fabricated samples yield a measured phase retardation of 89o to 102o over the desired wavelength range.

10-GHz, over 20-channel multiwavelength pulse source by slicing super-continuum spectrum generated in normal-dispersion fiber

Abstract: We demonstrate a multiwavelength pulse source which utilizes the super-continuum generated in a normal group-velocity dispersion fiber and an arrayed-waveguide grating filter. Over 20-channels of pulse train with a repetition rate of 10 GHz are realized, and each channel has almost the same pulsewidth. This uniformity originates from the fact that the super-continuum pulse generated in a normal-dispersion fiber has a rectangular waveform and a linear chirp.

Fabrication of a new broadband waveguide polarizer with a double-layer 190 nm period metal-gratings using nanoimprint lithography

Abstract: We fabricated a new waveguide polarizer, that has a double-layer 190 nm period metal grating at the interface between the waveguide core and waveguide cladding layer. Both silicon nitride and polymethylmethancrylate were used as waveguide cores. 190 nm period gratings were patterned by nanoimprint lithography. The new type waveguide polarizer works as a broadband and highly efficient transverse magnetic-pass polarizer with transverse electric-polarized light highly attenuated. The new polarizer structure can be applied to almost any waveguide structures. The simple fabrication process, which is compatible with conventional device processing, makes it very attractive for integrated optoelectronic system.

A slit grating spectrograph for quantitative soft x-ray spectroscopy

Abstract: In this article we describe a new slit grating spectrograph which is based on an e-beam written 10 000 linepairs/mm freestanding transmission diffraction grating. In combination with a thinned, back-illuminated charge coupled device (CCD), the spectrograph allows for real-time spectroscopy of laser-produced plasma x-ray sources within the wavelength region λ=1–20 nm. Calibration of grating and CCD allow for the possibility to measure absolute photon fluxes, currently within the wavelength region λ=1–6 nm. The compact spectrograph is easy to align and flexible in its use. Absolutely calibrated spectra were obtained from a liquid-jet laser-plasma source in the water window, with a spectral resolution λ/Δλ⩾330 at λ=3.37 nm. A simple change in experimental geometry allowed single-shot spectra to be recorded with λ/Δλ⩾60 at the same wavelength. In addition, spectra from this laser-plasma source were measured within the range λ=9–20 nm.

Reconfigurable diffraction gratings based on elastomeric microfluidic devices

Abstract: This paper describes the fabrication and operating principles of a reconfigurable diffraction grating based on a microfluidic device. The device consists of an array of microscopic channels (50 μm wide and 20 μm deep) defined by the conformal contact between a transparent elastomeric material that has an embossed surface relief and a flat glass substrate. The microchannels can be filled reversibly with fluids (gas, aqueous solutions, or organic solutions). The difference in index of refraction between the fluid in the array of microchannels and the structural elastomeric solid generates a difference in the phase of the light passing through the device; absorption by the fluid changes the amplitude of the light. Both of these effects give rise to diffraction. The gratings are reconfigured by pumping liquids with different indices of refraction and optical densities through the microchannels. In these experiments, the devices exhibited maximum depths of modulation of ∼20 dB and switching times of ∼50 ms; the volume of liquid sampled by the incident light was about 8 nl. The potential application of these devices as sensing elements in micro total analysis systems (μTAS) and as actuators is evaluated.

Electrically tunable efficient broad-band fiber filter

Abstract: We demonstrate a new type of fiber-optic electrically tunable filter that enables a tuning range of 60 mm with an electrical power of 0.17 W, corresponding to a tuning efficiency of approximately 320 nm/W. The device is based on a metal coated long-period fiber grating written in a specially designed "air-clad" fiber that is filled with a polymer whose index of refraction is a sensitive function of temperature. Resistive heating, caused by current flowing through the metal coating, heats the polymer and induces changes in its index of refraction; these changes induce shifts in the position of the attenuation dip associated with the long-period grating. The air-clad structure has two benefits: (1) it enables the introduction of temperature sensitive materials into the fiber thus enabling power efficient operation of the device and (2) ensures that the cladding modes are insensitive to the surrounding environment and thus are unaffected by the metal coating on the surface of the fiber.

Efficient grating-tuned mid-infrared Cr2+:CdSe laser.

Abstract: Room-temperature, all-solid-state, broadly tunable laser operation of Cr2+-doped CdSe has been demonstrated. Pumping with a Q-switched Tm, Ho:YLF laser running at a 1-kHz repetition rate achieved broadband output of 500 mW at 2.6 µm with 48% absorbed power slope efficiency. With reduced efficiency, as much as 815 mW of power was obtained. With a diffraction grating, the Cr2+:CdSe laser was tuned from 2.3 to 2.9 µm with 10-nm bandwidth (FWHM) and output power up to 350 mW.

Light guide plate for point source

Abstract: Rays of light from three light-emitting diodes 5 incident at a thicker side end edge 2 c of a light guide plate 2 made of a transparent plate. A ratio of grating part width/non-grating part width in a unit width of a diffraction grating 3 provided on a rear surface 2 b of the light guide plate 2 is varied, and grating constant of a diffraction grating 4 of a front surface 2 a provided perpendicularly to the diffraction grating 3 , is set to a fixed value smaller than a mean grating constant of the diffraction grating of the rear surface 2 b , so that uniform, high brightness at the front surface 2 a of the light guide plate 2 can be obtained. Therefore, the light guide plate can perform high, uniform brightness over a whole illuminating surface even with a point light source, and yet can prolong life of batteries by virtue of reduction in power consumption of the light source.

Fiber optic network using space and wavelength multiplexed data channel arrays

Abstract: A network for multi-bit word parallel communication between optoelectronic chips on a two dimensional array of optical input and output channels carried on a single dimension of optical fibers. Each bit of a word is carried on a different wavelength and the multiple wavelengths carrying a word are wavelength multiplexed onto a single optical fiber. Multiple fibers can be joined into a one dimensional array of fibers. A transceiver for transmitting and receiving along the optical data channels comprises an array of modulators powered by individual wavelength light beams, either from individual monochromatic light sources and a light beam from a single broadband light source made to pass through a diffraction grating. The modulators are positioned so that each modulator reflects a different wavelength light beam, thereby providing multiple optical channels. Alternatively, multiple wavelengths are generated from CMOS integrated light sources. These multiple optical channels are then collimated and guided into one single mode fiber or multiple multimode fibers at its transmitting end. At the receiving end a diffraction grating is used to separate the distinct data channels by their individual wavelengths. The multiple wavelengths are then caused to fall on an array of optical detectors spaced according to the individual wavelengths to be detected. By constructing a one dimensional array of these fibers, a two dimensional array of optical data channels is realized. The size of the array is determined by the number of fibers and the number of distinct wavelengths combined in each fiber.

Fibre optic load sensors with high transverse strain sensitivity based on long-period gratings in B/Ge co-doped fibre

Abstract: A novel application is reported of long-period fibre gratings produced in non-high-birefringence fibre as fibre optic load sensors based on the measurement of the transverse strain induced birefringence. A transverse strain sensitivity some 800 times higher than that previously reported for fibre Bragg gratings has been achieved.

Specular spectroscopic scatterometry in DUV lithography

Abstract: Scatterometry is a one of the few types of metrology that has true in-situ potential for deep submicron CD and profile analysis. To date, commercial prototypes have been used to establish scatterometry based on single wavelength, multiple incident angle inspection. We extend this idea by deploying specular spectroscopic scatterometry (SSS). Conventional scatterometry is designed to measure either many diffraction orders or variable incident/collection angle at a single wavelength. Specular spectroscopic scatterometry is designed to measure the 0th order diffraction responses at a fixed angle of incidence. Specular spectroscopic scatterometry can make direct use of the existing spectroscopic ellipsometry equipment. We show that SSS provides an accurate, inexpensive, and non-destructive CD metrology solution.

Polarization analysis of diffracted orders from a birefringence grating recorded on azobenzene containing polymer

Abstract: Polarization analyses of transmitted and first-diffracted orders have been performed on photoinduced gratings in azopolymers. The polarization states of diffracted orders depend strongly on irradiation time because of the contribution from both a phase grating at short time and a surface relief grating at longer time. These results are nicely explained using a Jones’ matrix approach which predicts the polarization states of transmitted and diffracted orders of polarization holographic gratings.

Azopolymer Holographic Diffraction Gratings: Time Dependent Analyses of the Diffraction Efficiency, Birefringence, and Surface Modulation Induced by Two Linearly Polarized Interfering Beams

Abstract: Dynamical experimental studies of the diffraction efficiency, birefringence, and surface relief modulation were carried out on functionalized azopolymer films of p(DR1M-co-MMA) with a 12% mole fraction of DR1M The gratings were recorded using two linearly polarized pump beams (λ = 5145 nm) either with a parallel configuration (p+p) or (s+(-s)) or with orthogonal polarizations (p+s) A general Jones matricial approach in conjuction with real-time polarization analyses of the first order diffracted beam (S+1) appears to be a quite sensitive method to extract relevant parameters such as birefringence (Δn) and surface relief modulation (2Δd) The phase matrices have been developed considering the pump polarization of the two interfering beams and taking into account the orientational “angular hole-burning” model under low pump irradiances Numerical calculations allow us to extract the time variations of Δn and 2Δd and to compare the various efficiencies in grating formation The obtained values for Δn are

Study on polarizing visible light by subwavelength-period metal-stripe gratings

Abstract: One method for influencing the polarization of light is the use of wire-grid polarizers. For the visible region, this type of element can be realized as a metal-stripe grating with periods less than the wavelength. We fabricate metal-stripe gratings with periods down to 190 nm in thin chromium layers of 35-nm thickness using electron-beam lithography and ion-beam etching. A detailed investigation of the influence of grating period and duty cycle on the polarization effect is carried out to verify the conformity of rigorous diffraction theory and experimental results. The comparison between the two indicates good performance. Polarization ratios of the order of 5 with transmission efficiencies of about 60% in TM polarization are obtained. The connection of the polarization effect real- izable and the fabrication technology used is discussed. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)00902-2)

Observation of quantum accelerator modes

Abstract: We have realized a quantum accelerator mode using a system consisting of ultracold cesium atoms falling through a pulsed standing wave of off resonant light. We present a picture of this system based on diffraction and show that the effect arises from the application of blazed matter wave diffraction gratings. The implications of our results for quantum chaos and the prospect of constructing a large angular separation matter wave beam splitter are discussed.

Integrated polarization compensator for WDM waveguide demultiplexers

Abstract: An integrated polarization compensator for wavelength-division-multiplexed waveguide demultiplexers is proposed and experimentally demonstrated. It is simple to fabricate, has many advantages over previously reported polarization compensation schemes, and is effective in both etched diffraction grating and arrayed waveguide grating based devices.

Low-threshold high-quantum-efficiency laterally gain-coupled InGaAs/AlGaAs distributed feedback lasers

Abstract: We have developed gain-coupled lasers based on metal gratings patterned laterally to the laser ridge. For narrow ridge waveguides, the evanescent field of the laser mode couples to the grating. The fabrication requires no overgrowth steps and can be applied to all material systems. Ridge-waveguide gain-coupled lasers with threshold current densities of 600 A/cm2 were obtained from InGaAs/AlGaAs GRINSCH structures. The continuous wave threshold currents are around 9 mA for a cavity with 600 μm length and 2.5 μm width. Monomode emission up to output power levels of 64 mW and sidemode suppression ratios of over 45 dB have been obtained.