Pd grating obtained by direct micromolding for use in high resolution optical diffraction based sensing

Pd grating patterns have been fabricated using the process of micromolding in capillary employing a Pd alkanethiolate precursor, which could be converted to metal in situ by thermolysis. Thus generated Pd grating were uniform in width (~950?nm) and spacing (~450?nm) over millimeter square areas on glass substrates. Importantly, the pattern when used as an optical grating produced a diffraction pattern with a high resolution (>2000); the intensities of widely separated (diffraction angle, ~26·8°) diffracted spots could be measured using a simple photodiode. By varying the concentration of Pd precursor (2?mM to 25?mM), thickness of the resulting gratings could be adjusted in the range of ~15?C115?nm. By adjusting the grating parameters optimally, a maximum diffraction efficiency of 36% has been achieved. Thus fabricated Pd grating was used as seed catalyst to deposit Cu by electroless plating. The Cu deposition process has also been monitored by employing AFM, SEM and EDS analysis. The diffraction efficiency values corroborate well with the changes in the grating thickness due to Cu deposition. The grating structures presented can be reproducibly fabricated for rapidly emerging optical diffraction based sensing applications. This has been demonstrated in the case of aqueous Cu^2?+? by depositing the latter electrolessly on Pd.     

自聚焦变栅距光栅设计、制作及特性研究

利用变栅距光栅的衍射光束自聚焦特性,设计和制作了变栅距透射光栅,并对其自聚焦特性进行了研究.采用变栅距光栅的自动生成宏文件程序,优化设计了变栅距光栅的栅距变化.采用光栅扫描电子束光刻的方法制作了中心线数为300 1/mm、适用于355 mm波长的自聚焦变栅距变狭缝光栅.使用三倍频Nd:YAG激光器,研究了制作的变栅距光栅的聚焦特性,并与对氦氖激光的聚焦特性进行了比较.结果表明,主动式设计的变栅距变狭缝自聚焦光栅可以大幅提高衍射光强度和分辨本领,具有重要的应用价值.     

Tuning of external-cavity semiconductor lasers with chirped diffraction gratings

We present a novel scheme of tunable semiconductor laser based on the use of a chirped grating in an external cavity. The chirped grating is fabricated using a simple holographic technique: two Gaussian beams having wavefronts with different radii of curvature are brought to interfere on a photoresist layer. The tuning properties of chirped gratings have been investigated with semiconductor lasers operated with an external cavity. With this type of grating positioned in Littrow configuration, the wavelength selection can be done by translating the grating without any need to rotate it. This cavity configuration provides a tunable output beam with an angle of propagation that is independent of the wavelength. The translation of chirped gratings was shown to tune a visible diode laser and an infrared diode laser over the same spectral band as the conventional tuning scheme where an unchirped grating is rotated.     

Micropolarizer fabricated from CaCO3 by anisotropic wet etching

A micropolarizer is fabricated on a birefringent crystal, calcite, by anisotropic wet etching. This device consists of a v-groove grating on calcite, covered by an index-matching material. The grating is fabricated by acid wet etching. When its acid concentration and stirring speed are altered, the etching mechanism can be controlled within the surface-reaction regime. This results in anisotropic etching, which produces a v-groove grating on a calcite surface. This v-groove grating can be fabricated to have a period as small as 2 microm. To the best of our knowledge, this type of v-groove calcite grating is reported for the first time. Although the transmission efficiency of this device is wavelength dependent, a broadband micropolarizer can be made by gluing together two devices with periods of 12 and 16 microm.     

High performance short period superlattice digital alloy InSb/Ga(x)In(1-x)Sb laser emitting at 1.9 µm

For the first time, lasers with short period superlattice based quantum wells have successfully been fabricated and characterized on the (AlGaIn)(AsSb) material system. These new quantum wells are composed of alternating InSb/Ga(x)In(1-x)Sb layers with submonolayer thickness. Distributed-feedback lasers fabricated from the epitaxial layers emit in the wavelength range around 1.9?μm. Side mode suppression ratios over 35?dB and very low threshold currents of 23?mA were realized. The laser emission wavelength can be varied from 1.844 to 1.902?μm using grating periods between 255.0 and 263.8?nm.     

Recording of concave diffraction gratings in counterpropagating beams using meniscus blanks

The most technological way of recording blazed concave holographic gratings is by using the direct- and back-reflected beams. Usually plano-concave blanks are used for diffraction grating fabrication. To compensate the refraction at the plane back surface of the blank, one has to use additional elements or two-step recording mountings. Another solution is to use diffraction grating blanks having zero optical power. A number of gratings with different groove frequencies have been fabricated using concave—convex blanks. The theoretical investigation of the aberration properties of the recording mountings, and the experimental study of the grating properties are discussed. Using the CODE V program it is shown that a significant reduction in the aberration size of the virtual recording source can be achieved by optimization of the radius of curvature of the blank back surface. The experimental results confirm the possibility of achieving gratings that can be used in flat-field spectrometers with a limit of resolution of about 2–3 nm even in the case where an aberrated virtual recording source is used.     

Photoluminescence and lasing from deoxyribonucleic acid (DNA) thin films doped with sulforhodamine

Thin solid films of salmon deoxyribonucleic acid (DNA) have been fabricated by treatment with a surfactant and used as host for the laser dye sulforhodamine (SRh). The DNA films have an absorption peak at approximately 260 nm owing to absorption by the nitrogenous aromatic bases. The SRh molecules in the DNA films have absorption and emission peaks at 578 and 602 nm, respectively. The maximum emission was obtained at approximately 1 wt. % SRh in DNA, equivalent to approximately 100 DNA base pairs per SRh molecule. A distributed feedback grating structure was fabricated on a SiO(2)-Si substrate using interference lithography. The grating period of 437 nm was selected, corresponding to second-order emission at the amplified spontaneous emission wavelength of 650 nm. Lasing was obtained by pumping with a doubled Nd:YAG laser at 532 nm. The lasing threshold was 3 microJ, corresponding to approximately 30 microJ/cm(2) or 4 kW/cm(2). The emission linewidth decreased from approximately 30 nm in the amplified spontaneous emission mode to <0.4 nm (instrument limited) in the lasing mode. The slope efficiency of the lasing was approximately 1.2%.     

Strain and temperature sensors using multimode optical fiber Bragg gratings and correlation signal processing

Multimode fiber optic Bragg grating sensors for strain and temperature measurements using correlation signal processing methods have been developed. Two multimode Bragg grating sensors were fabricated in 62/125 /spl mu/m graded-index silica multimode fiber; the first sensor was produced by the holographic method and the second sensor by the phase mask technique. The sensors have signal reflectivity of approximately 35% at peak wavelengths of 835 nm and 859 nm, respectively. Strain testing of both sensors has been done from 0 to 1000 /spl mu//spl epsiv/ and the temperature testing from -40 to 80/spl deg/C. Strain and temperature sensitivity values are 0.55 pm//spl mu//spl epsi/ and 6 pm//spl deg/C, respectively. The sensors are being applied in a power-by-light hydraulic valve monitoring system.     

Diffractive optical element used in an external feedback configuration to tune the wavelength of uncoated Fabry-Pérot diode lasers

Abstract

A diffractive optical element (DOE) has been designed, fabricated and used in an external feedback configuration to set the wavelength of operation of uncoated Fabry-Pérot diode lasers. The DOE was designed to replace the conventional elements of an external feedback system, which are a collimating lens and grating in the Littrow configuration. The goal was to simplify use of the external cavity laser by replacing the lens and grating with a single optical element while maintaining the performance that is achieved with a grating and lens. Four DOEs were fabricated with two different focal lengths and two different reflectivities. DOE external cavity lasers were tested for maximum tunable range and stability of the wavelength of operation and compared with an external cavity laser based on a lens and grating in the Littrow configuration. A 40 nm tuning range was achieved with the DOE external cavity laser and this is comparable with the tuning range of the external cavity lasers based on a grating and collimating lens in the Littrow configuration.     

Large area, 38 nm half-pitch grating fabrication by using atomic spacer lithography from aluminum wire grids

We wrapped 150 nm period aluminum wire grid polarizer (WGP) with AlSiOx by using atomic layer deposition at 250 degrees C. The nanometer precision coating defined the spacer to double the spatial frequency of the 100 mm diameter grating fabricated by using a legacy immersion holography setup at 351 nm wavelength. Half-pitch grating of approximately 38 nm was demonstrated with good pattern uniformity, excellent repeatability, and a wide processing window. We believe 10 nm half-pitch grating over even larger areas are viable, overcoming one major hurdle to commercialize nanoimprint.     

Hybrid oxygen-responsive reflective Bragg grating platforms

Oxygen responsive sensor platforms were fabricated by pin printing tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(dpp)(3)](2+)) doped sols onto wavelength tuned reflective Bragg gratings. In an epi-luminescence configuration, these Bragg gratings (Gr) were designed to selectively reflect the O(2) responsive [Ru(dpp)(3)](2+) emission toward the detector to enhance the detected signal magnitude. The xerogel based sensors were formed onto (i) glass (XGl), (ii) directly on top of the grating (XGrGl), or (iii) on the glass substrate opposite the grating (XGlGr). The results show that all sensors exhibit linear, statistically equivalent O(2) sensitivities, and the XGrGl platform yields up to an 8-fold increase in relative detected analytical signal (RDAS) in comparison to the control (XGl) platform.     

Efficiency calibration of the first multilayer-coated holographic ion-etched flight grating for a sounding rocket high-resolution spectrometer

We have fabricated the four flight gratings for a sounding rocket high-resolution spectrometer using a holographic ion-etching technique. The gratings are spherical (4000-mm radius of curvature), large (160 mm x 90 mm), and have a laminar groove profile of high density (3600 grooves/mm). They have been coated with a high-reflectance multilayer of Mo/Si. Using an atomic force microscope, we examined the surface characteristics of the first grating before and after multilayer coating. The average roughness is approximately 3 A rms after coating. Using synchrotron radiation, we completed an efficiency calibration map over the wavelength range 225-245 A. At an angle of incidence of 5 degrees and a wavelength of 234 A, the average efficiency in the first inside order is 10.4 +/- 0.5%, and the derived groove efficiency is 34.8 +/- 1.6%. These values exceed all previously published results for a high-density grating.     

Optimization of diffraction grating profiles in fabrication by electron-beam lithography

We propose a new design method for periodic diffraction gratings to be fabricated with direct-writing electron-beam lithography. When the grating has a small period, the proximity effect of electron scattering restricts the grating profile after developing. Our design method optimizes the electron-dose profile and grating profile simultaneously to obtain the desired diffraction efficiency under the restriction of the proximity effect. The optimization is made with rigorous electromagnetic grating analysis and the resist development simulator. When we designed the diffraction grating with a period of 1.0 microm to obtain the highest efficiency of the first-order diffracted light of a 633-nm wavelength, the calculated grating profile was really different from the profile optimized only with rigorous electromagnetic grating analysis. Moreover, the diffraction grating of the electron-beam resist was fabricated according to the simulation result. The estimated diffraction efficiency was 82%, and the measured efficiency was 70%.     

Hot embossing of grating-based optically variable images in thermoplastic acrylic lacquer

We report the novel use of thermoplastic acrylic lacquer (automotive paint) in the hot embossing of nanoscale structures. Replicas of grating arrays have been produced in coatings of acrylic lacquer using a standard embossing process. The master dies for the experiments comprised grating arrays fabricated by electron beam lithography. Grating patterns with a pitch of 0.7–1.3 μm were configured to produce diffractive images over an area of ∼25 × 25 mm. The embossing experiments used a replicated Ni shim as a die and were performed at 100–150 °C and 80 kN force. A temperature above the glass transition temperature for the lacquer, T = 120–150 °C, was required in order to achieve a uniform impression across the embossed area of ∼80 × 80 mm. The diffractive grating patterns which were embossed into acrylic lacquer have shown optical effects suitable as a security feature including image switching and color movement.     

Diffraction gratings inside bulk azodye-doped hybrid inorganic-organic materials by a femtosecond laser

We have investigated diffraction gratings fabricated inside bulk azodye-doped hybrid inorganic-organic materials by a focused near-IR 800 nm femtosecond laser directly. The first-order diffraction of the grating was measured using a 632.8 nm He-Ne laser. By changing the laser parameters such as the laser power, the scanning speed, and the grating period, we found that the first-order Bragg diffraction efficiency was strongly dependent on the parameters of the femtosecond laser. The results showed that the first-order Bragg diffraction efficiency can be increased when decreasing the laser power or increasing the grating periods and the scanning speed of the laser. The mechanisms were also analyzed briefly.     

滚压印圆柱母光栅的微刻划制造

精密长光栅作为高档数控机床中的核心部件,其制造能力和精度直接决定高精密机床的制造水平．本文对纳米滚压印技术制造长光栅中的核心部件——圆柱母光栅的制造开展研究,建立了高精度的母光栅刻划制造平台,保证了母光栅制造的精度要求;分析了微尺度毛刺的形成机理和抑制方法,对母光栅材料选择及微尺度刻划工艺参数进行了优化,实现了直径110mm,周期分别为20μm、10μm和4μm整圈圆柱母光栅的高精度微刻划制造．母光栅刻划总条数为数万条,4μm周期母光栅连续刻划时间超过62h,最终实现母光栅的首尾拼接误差控制小于300mm．另外,针对滚压印加工中的填充问题,利用聚焦离子束（FIB）技术制备了V形、梯形等形状金刚石刀具,获得了良好的光栅压印结果．     

Diffraction efficiency of a grating coupler for an array illuminator

The diffraction efficiency of a grating coupler having a surface-relief grating is calculated by the use of coupled-wave theory. The grating couplers are fabricated to examine the validity of the calculated result. The dependence of the measured diffraction efficiency on the groove depth of the grating coupler agrees well with the calculated results. The array illuminator, which emits 10 and 20 beams with equal intensity, is designed and fabricated through the use of these numerical results. The uniformity error of the output beam caused by the error of the diffraction efficiency is also discussed.     

Characterization of a quasi-sinusoidal transmission grating without membrane substrate in the 200–1500 eV photon energy regions

A 1000-line/mm quasi-sinusoidal transmission grating (QSTG) without membrane substrate has been designed and fabricated, which is utilized to eliminate the higher order diffraction for soft X-ray spectrum measurement in the experiments of inertial confinement fusion. The grating was calibrated using an X-ray beam on synchrotron radiation facility. It shows that the QSTG has the desired diffraction property and the higher order diffraction components are efficiently suppressed in the photon energy ranges from 200 to 1500 eV.     

Replication of continuous-relief diffractive optical elements by conventional compact disc injection-molding techniques

Continuous-relief diffractive optical elements have been replicated by use of conventional compact disc injection-molding techniques. Two continuous-relief microstructures, a blazed grating and a fan-out element, were chosen to evaluate the replication process. Original elements were fabricated by direct-write electron-beam lithography. Optical measurements and atomic force microscopy were used for investigating the replication fidelity.     

Pitch-modulated phase grating and its application to displacement encoder

Abstract

A binary phase grating with modulated pitch is investigated for a simple displacement encoder. The grating consists of a binary phase grating to eliminate the zeroth-order diffraction, and the pitch of the grating is modulated to compensate the higher harmonics of the encoder displacement signal. Therefore, an undistorted sinusoidal signal as a function of displacement is obtained by simply superimposing a conventional binary grating on the pitch-modulated phase gratings for any air gap between the gratings. The characteristics of the proposed gratings and the encoder signal are investigated by the Fresnel diffraction theory. The proposed grating has been fabricated lithographically, and the signal was examined experimentally. Considering these results, the proposed technique can suppress interpolation error and will be useful for an encoder in precision machining.