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APPLICATIONS-CENTERED RESEARCH IN OPTICS

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Early Posting

Accepted papers to appear in an upcoming issue

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December


(LC2014) Adaptive Exposure Estimation for HDR imaging applied to natural scenes and daylight skies.

  • Miguel Angel Martínez-Domingo, Eva Valero, and Javier Hernandez-Andres
  • received 09/02/2014; accepted 12/17/2014; posted 12/17/2014; Doc. ID 222306
  • [full text: PDF (16139) KB)]
  • Abstract: Digital imaging of natural scenes and optical phenomena present on them (such as shadows, twilights, crepuscular rays, etc) can be a very challenging task due to the range spanned by the radiances impinging on the capture system. We propose a novel method for estimating the set of exposure times (bracketing set) needed to capture the full dynamic range of a scene with high dynamic range (HDR) content. The proposed method is adaptive to scene content and to any camera response and configuration, and works on-line, since the exposure times are estimated as the capturing process is ongoing. Besides, it requires no a-priori information about scene content or radiance values. The resulting bracketing sets are minimal and moreover, the user can set a tolerance for the maximum percentage of pixel population that is underexposed or saturated. This method is based in the use of the Camera Response Function, which is needed for building the HDR radiance map by stitching together several, differently exposed, Low Dynamic Range images of the scene. The use of HDR imaging techniques, converts our digital camera in a tool for measuring the relative radiance outgoing from each point of the scene, and for each color channel. This is important for an accurate characterization of the optical phenomena present in the atmosphere without suffering any loss of information due to its high dynamic range. We have compared our method with the most complete and efficient HDR bracketing set estimation algorithm developed so far (Barakat et al. 2008). Results of the experiments carried out for 30 natural scenes, show that our proposed method equals or outperforms the previously developed best approach, with less shots and shorter exposure times, asserting the advantage of being adaptive to scene content for exposure time estimation.

Keywords (OCIS):

  • (040.1490) Detectors : Cameras
  • (100.2000) Image processing : Digital image processing
  • (110.0110) Imaging systems : Imaging systems
  • (110.1085) Imaging systems : Adaptive imaging
  • (110.1758) Imaging systems : Computational imaging
  • (010.7295) Atmospheric and oceanic optics : Visibility and imaging

Mode-Field Adapter for Tapered-Fiber-Bundle Signal and Pump Combiners

  • Pavel Koska, Yauhen Baravets, Pavel Peterka, Jan Bohata, and Michael Pisarik
  • received 08/28/2014; accepted 12/16/2014; posted 12/16/2014; Doc. ID 221872
  • [full text: PDF (1054) KB)]
  • Abstract: We report on novel mode-field adapter that is proposed to be incorporated inside tapered fused-fiber-bundle pump and signal combiners for high-power double-clad fiber lasers. Such an adapter allows optimization of signal-mode-field matching on the input and output fibers. Correspondingly, losses of the combiner signal branch are significantly reduced. The mode-field adapter optimization procedure is demonstrated on a combiner based on commercially available fibers. Signal wavelengths of 1.55 and 2 μm are considered. The losses can be further improved by using specially designed intermediate fiber and by dopant diffusion during splicing as confirmed by preliminary experimental results.

Keywords (OCIS):

  • (060.2320) Fiber optics and optical communications : Fiber optics amplifiers and oscillators
  • (060.2340) Fiber optics and optical communications : Fiber optics components
  • (140.3510) Lasers and laser optics : Lasers, fiber

High power spectral beam combining of linearly polarized Tm:fiber lasers

  • Lawrence Shah, Pankaj Kadwani, Robert Sims, Christina Willis, Joshua Bradford, Alex Sincore, and Martin Richardson
  • received 09/16/2014; accepted 12/15/2014; posted 12/17/2014; Doc. ID 223099
  • [full text: PDF (896) KB)]
  • Abstract: To date, high power scaling of Tm:fiber lasers has been accomplished by maximizing the power from a single fiber aperture. In this work, we investigate power scaling by spectrally beam combine three linearly polarized Tm:fiber MOPA lasers using dielectric mirrors with a steep transition from highly reflective to highly transmissive that enable a minimum wavelength separation of 6 nm between individual laser channels within the wavelength range from 2030-2050 nm. Maximum output power is 253 W with M2<2, ultimately limited by thermal lensing in the beam combining elements.

Keywords (OCIS):

  • (060.2390) Fiber optics and optical communications : Fiber optics, infrared
  • (140.3510) Lasers and laser optics : Lasers, fiber
  • (140.3298) Lasers and laser optics : Laser beam combining

Waveform reconstruction for ultrasonic fiber Bragg grating sensor demodulated by erbium fiber laser

  • Qi Wu and Yoji Okabe
  • received 11/19/2014; accepted 12/15/2014; posted 12/15/2014; Doc. ID 227139
  • [full text: PDF (718) KB)]
  • Abstract: Fiber Bragg grating (FBG) demodulated by erbium fiber laser (EFL) has been used for ultrasonic detection recently. However, due to the inherent relaxation oscillation of the EFL, detected ultrasonic signals have large deformations, especially in the low frequency range. We proposed a novel data process method to reconstruct actual ultrasonic waveform. The noise spectrum was smoothed firstly; the actual ultrasonic spectrum was then obtained by deconvolution in order to mitigate the influence from the relaxation oscillation of the EFL. We proved this waveform reconstruction method has high precision by experiment, and demonstrated the FBG sensor demodulated by EFL will have large practical application in nondestructive testing.

Keywords (OCIS):

  • (060.2370) Fiber optics and optical communications : Fiber optics sensors
  • (100.3010) Image processing : Image reconstruction techniques
  • (120.4290) Instrumentation, measurement, and metrology : Nondestructive testing
  • (140.3510) Lasers and laser optics : Lasers, fiber
  • (060.3735) Fiber optics and optical communications : Fiber Bragg gratings

Effects of Prestrain Applied to Poly(Ethylene Terephthalate) Substrate on Microstructures and Morphologies of Porous TiO2 Film and Optical Scattering Behaviors of Light

  • Jen-Fin Lin, Tse-Chang Li, and Cheng-Fang Ho
  • received 10/09/2014; accepted 12/15/2014; posted 12/16/2014; Doc. ID 224236
  • [full text: PDF (4873) KB)]
  • Abstract: A mould was designed to simulate a thin ceramic film coating on a soft, flexible substrate using a rotating deposition system. With this mould, three prestrains (2%, 4%, and 6%) were applied to a polyethylene terephthalate (PET) substrate before the deposition of a thin TiO2 film. The contact angle of the substrate and thus the mean TiO2 particle size were affected by the prestrain. The effects of the mean particle size of TiO2 on the surface roughness and cavity area ratio of the porous film and on the scattering behavior of light were investigated. A goniophotometer and Advanced System Analysis Program (ASAP) software were employed for the light analyses of bi-directional scatter distribution functions and their calibration. A spectrometer with an integrating sphere was applied to determine the total scatters (TSs) of transmittance and reflection. An increase in the prestrain increased the mean particle size of TiO2 deposited on the substrate and thus the mean surface roughness, the cavity/void depth and the cavity area ratio. PET/TiO2 specimens with various prestrains were prepared that satisfy the Harvey-like model but without the isotropic, diffusive property in scatter. The bi-directional transmittance distribution function area and (TS)transmittance results are governed by the mean particle size and thus the cavity/void geometries and surface roughness. These values decrease with increasing PET prestrain. The bi-directional reflection distribution function area and (TS)reflection, however, are governed by the adsorbed carbon and its absorption thickness. These values increase with increasing C1s peak value in X-ray photoelectron spectroscopy spectra.

Keywords (OCIS):

  • (290.5880) Scattering : Scattering, rough surfaces
  • (310.6860) Thin films : Thin films, optical properties
  • (290.1483) Scattering : BSDF, BRDF, and BTDF
  • (290.2648) Scattering : Stray light
  • (290.5835) Scattering : Scattering, Harvey

The Effect of the Morphology on the Anisotropic Light Scattering of Polycarbonate (PC)/Poly(styrene-co-acrylonitrile) (SAN)(70/30) Blend

  • Xianming Dong, ying xiong, Shaoyun Guo, and Guangshun Chen
  • received 10/29/2014; accepted 12/15/2014; posted 12/15/2014; Doc. ID 225791
  • [full text: PDF (1598) KB)]
  • Abstract: The polycarbonate (PC)/poly(styrene-co-acrylonitrile) (SAN) (70/30) anisotropic light scattering sheets with controllable anisotropic degree was prepared by blending and hot stretching process. The morphological evolution of the dispersed particles for PC/SAN (70/30) blend during hot stretching was observed by a Scanning Electron Microscope (SEM) and the effect of stretching deformation on the light scattering properties was investigated. The SEM photographs revealed that SAN particles deformed into ellipsoid during hot stretching. The scattering properties analysis results revealed the appearance of anisotropic light scattering for PC/SAN (70/30) blends with various deformations, and with the increase of stretching deformation, the anisotropic scattering degree increased, verifying the correctness of geometrical optical scattering theoretical analysis.

Keywords (OCIS):

  • (080.0080) Geometric optics : Geometric optics
  • (160.1190) Materials : Anisotropic optical materials
  • (160.5470) Materials : Polymers
  • (290.5850) Scattering : Scattering, particles

Analysis of tunable negative refraction in a lossy and extrinsic semiconductor

  • Chien-Jang Wu, Tsung-Wen Chang, and Yi Min Zeng
  • received 10/22/2014; accepted 12/14/2014; posted 12/15/2014; Doc. ID 225402
  • [full text: PDF (449) KB)]
  • Abstract: In this work, within the framework of inhomogeneous wave, we study the wave transmission at the boundary between air and a lossy extrinsic semiconductor of n-type Indium Antimonide. Transmission property such as the negative refraction is specifically investigated. The choice of such a semiconductor enables us to study the tunable features in the negative refraction because its permittivity is a function of the frequency, the temperature, and the doping concentration. It is found that there exist a threshold temperature and a threshold frequency in order to obtain the negative refraction. The dependence of threshold temperature on the doping concentration and the operating frequency will be numerically demonstrated. The analysis of negative refraction can be used to study the electromagnetic response for a lossy and extrinsic semiconductor.

Keywords (OCIS):

  • (160.4760) Materials : Optical properties
  • (160.6000) Materials : Semiconductor materials
  • (260.0260) Physical optics : Physical optics
  • (260.2110) Physical optics : Electromagnetic optics

Design and implementation of pulsed terahertz experimental systems

  • Christopher Collier, Mark Bergen, Trevor Stirling, Mark DeWachter, and Jonathan Holzman
  • received 10/22/2014; accepted 12/14/2014; posted 12/15/2014; Doc. ID 225411
  • [full text: PDF (2492) KB)]
  • Abstract: In this work, a pulsed terahertz (THz) system is designed and implemented. The work introduces a methodology for implementing such THz systems, through three design processes: collineation, autocorrelation, and electro-polarization. The collineation process establishes spatial alignment between the overlapped pump and probe beams, to ensure that there is similar spatial alignment between the subsequent THz and probe beams. The autocorrelation process characterizes the optical path difference between pulses in the THz and probe beams, to define the precise temporal zero-time of the THz system. The electro-polarization process optimizes the polarization-sensitive optics in the THz system, to maximize the THz-induced modulation on the probe polarization. The processes are applied to design and implement a successful THz system.

Keywords (OCIS):

  • (320.7100) Ultrafast optics : Ultrafast measurements
  • (300.6495) Spectroscopy : Spectroscopy, teraherz

Analytical design and implementation of a compact imaging spectrometer

  • Yiqun Ji, Jose Sasian, Jianxin Li, Jiangkang Zhou, and Weimin Shen
  • received 08/15/2014; accepted 12/13/2014; posted 12/15/2014; Doc. ID 220995
  • [full text: PDF (2324) KB)]
  • Abstract: We present the design and practical implementation of a visible/near infrared (VNIR) imaging spectrometer. The design of the spectrometer is based on an Offner relay. The aberration correction achieves a flat sagittal field condition. This allows for an effective design with minimum astigmatism which is the dominant residual aberration over the full wavelength range of interest and to achieve a large field size. The system works at the wavelength range from 400nm to 1000nm with a high spectral resolution of 0.6nm/pixel, a relatively low f-number of f/2.3, and a large flat field of 12mm. The performance measurement of the achieved prototype shows that only a low smile distortion (<0.1pixel) and a small spectral keystone distortion (<0.07pixel) are present. The instrument has the advantages of a compact configuration and of a light weight. We present some actual images at different working wavelengths.

Keywords (OCIS):

  • (110.0110) Imaging systems : Imaging systems
  • (120.4820) Instrumentation, measurement, and metrology : Optical systems
  • (220.4830) Optical design and fabrication : Systems design
  • (220.4880) Optical design and fabrication : Optomechanics
  • (110.4234) Imaging systems : Multispectral and hyperspectral imaging

Multicore implementation of the windowed Fourier transform algorithms for fringe pattern analysis

  • Ming Zhao and Kemao Qian
  • received 10/20/2014; accepted 12/13/2014; posted 12/15/2014; Doc. ID 225283
  • [full text: PDF (1005) KB)]
  • Abstract: Due to its effectiveness in fringe pattern analysis, a fast implementation of the Windowed Fourier transforms (WFT) based algorithms is desired. In this paper, we speed up the implementation from two aspects. First, we speed up the computation of Fourier transform which is a core component of the WFT based algorithms. Second, we parallelize the main body of these algorithms due to its parallel characteristic. With these two approaches, we obtain a 10× faster implementation than the original MATLAB version.

Keywords (OCIS):

  • (100.2650) Image processing : Fringe analysis
  • (200.4960) Optics in computing : Parallel processing

Proton and gamma irradiation of Fabry-Pérot quantum cascade lasers for space qualification

  • Tanya Myers, Bret Cannon, Carolyn Brauer, Stewart Hansen, and Blake Crowther
  • received 09/05/2014; accepted 12/12/2014; posted 12/15/2014; Doc. ID 221974
  • [full text: PDF (1116) KB)]
  • Abstract: Fabry-Pérot quantum cascade lasers (QCLs) were characterized following irradiation by high energy (64 MeV) protons and Cobalt-60 gamma rays. Seven QCLs were exposed to total accumulated radiation dosages that varied from 20 krad(Si) to 46.3 krad(Si), which are typical dosages for electronic components in a space environment. The QCLs did not show any measurable changes in threshold current or slope efficiency suggesting the suitability of QCLs for use in space-based missions.

Keywords (OCIS):

  • (350.5610) Other areas of optics : Radiation
  • (140.5965) Lasers and laser optics : Semiconductor lasers, quantum cascade

Lensless optical image processing based on two-dimensional Fresnel diffraction for synthetic-aperture imaging ladar

  • Zhiwei Sun, Jianfeng Sun, pei hou, Zhou Yu, Qian Xu, Ning Zhang, and Liren Liu
  • received 09/11/2014; accepted 12/12/2014; posted 12/15/2014; Doc. ID 222948
  • [full text: PDF (893) KB)]
  • Abstract: A principle scheme of lensless optical processor for synthetic-aperture imaging ladar (SAIL) is proposed. The collected data from SAIL is initially digitally added with a quadratic phase in the range direction. These data are then uploaded on a liquid crystal spatial light modulator (LCSLM) to modulate the incident light. The target image is obtained through two-dimensional (2D) free-space Fresnel diffraction. The imaging process is mathematically analyzed using 2D data-collection equation of strip-mode side-looking SAIL. The design equation, imaging resolutions and target-image compression ratios are presented. Based on this principle scheme, we construct an experimental optical SAIL processor and present the imaging result of data obtained from one SAIL demonstrator. The optical processor is found to exhibit the flexible property of digital processing, as well as fast processing capability of optical means, because this optical processor is a lensless system.

Keywords (OCIS):

  • (010.3640) Atmospheric and oceanic optics : Lidar
  • (100.3010) Image processing : Image reconstruction techniques
  • (110.0110) Imaging systems : Imaging systems
  • (280.6730) Remote sensing and sensors : Synthetic aperture radar

Studies on laser assisted Penning ionization by optogalvanic effect in Ne/Eu hollow cathode discharge

  • VINOD SAINI, Pankaj Kumar, Sudhir Dixit, and Shankar Nakhe
  • received 09/15/2014; accepted 12/12/2014; posted 12/15/2014; Doc. ID 223170
  • [full text: PDF (613) KB)]
  • Abstract: Laser assisted Penning ionization (LAPI) is detected in Ne/Eu hollow cathode discharge lamp using pulsed optogalvanic (OG) method. In Ne/Eu discharge, doubly ionized europium excited energy levels Eu[4f⁷(⁶P₇/₂,₅/₂)] lies within thermal limit (~kT) from laser excited neon’s energy level [2p⁵(²P⁰₃/₂)3p or 2p₈ (in Paschen notation)] lying at 149848 cm-¹. Therefore, Penning ionization of europium atoms likely to occur into its highly excited ionic states, is investigated. To probe Penning ionization of europium, the temporal profile of its counterpart neon OG signal are studied as a function of discharge current for transitions (1s₄→2p₈) and (1s₂→ 2p₂) corresponding to 650.65 and 659.89 nm wavelengths, respectively. It is observed that Penning ionization of europium alters over all discharge characterstics significantly and hence modifies the temporal profile of OG signals accordingly. The quasi-resonant ionizing energy transfer collisions between laser excited Ne ‘2p₈’ atoms and electronically excited Eu ‘¹⁰P₉/₂’ atoms are used to explain the laser assisted Penning ionization mechanism. Such, LAPI studies carried out in hollow cathode discharge could be useful for a discharge of metal-vapour laser with apporopriate Penning mixture.

Keywords (OCIS):

  • (300.6440) Spectroscopy : Spectroscopy, optogalvanic
  • (350.5400) Other areas of optics : Plasmas

Absolute Gauge Block Calibration Using Ultra-Precise Optical Frequency Synthesizer Locked to a Femtosecond Comb

  • Osama Terra, Hatem Hussein, and Niveen Farid
  • received 09/22/2014; accepted 12/12/2014; posted 12/15/2014; Doc. ID 223558
  • [full text: PDF (486) KB)]
  • Abstract: In this paper, we report a gauge block (GB) calibration that is traceable to the SI unit of time, the second. An ultra-stable four optical telecommunication wavelengths near1556 nm are obtained by locking a narrow-tuning-range fiber laser to a fiber-based femtosecond frequency comb. Since the GB calibration system doesn’t operate at this region of spectrum, the superior frequency stability of the laser is transferred to the 778 nm region by using a waveguide periodically polled Lithium Niobate (PPLN) crystal. After applying the locking scheme, the stability and accuracy of the laser become better than 8×10-12. The frequency doubled light is sent through 30 m optical fiber to a gauge block interferometer, which is installed at different laboratory in the same building. Using this calibration scheme, a Gauge block with nominal length of 100 mm is calibrated with uncertainty of ±50 nm. This uncertainty value is still comparable or even better than other metrology laboratories for a similar block length.

Keywords (OCIS):

  • (120.3180) Instrumentation, measurement, and metrology : Interferometry
  • (140.4050) Lasers and laser optics : Mode-locked lasers

Stretched-Pulse and Solitonic Operation of an All-Fiber Thulium/Holmium Doped Fiber Laser

  • Brian Washburn and Rajesh Kadel
  • received 08/15/2014; accepted 12/12/2014; posted 12/15/2014; Doc. ID 220849
  • [full text: PDF (361) KB)]
  • Abstract: Stretched-pulse operation of a mode-locked thulium/holmium doped fiber laser has been demonstrated using a high numerical aperture fiber inside the laser cavity for intracavity dispersion compensation. The high numerical aperture fiber exhibits normal group-velocity dispersion allowing for the net-cavity dispersion to be positive. We experimentally investigate the laser dynamics as a function of the net cavity dispersion, observing the transition from stretched-pulse to solitonic operation as the length of high numerical aperture fiber was reduced. In the stretched-pulse regime the laser produced pulses with a bandwidth of 30 nm and duration of 450 fs. Methods for compensating the third-order dispersion using high numerical aperture fibers are proposed.

Keywords (OCIS):

  • (060.2320) Fiber optics and optical communications : Fiber optics amplifiers and oscillators
  • (140.3070) Lasers and laser optics : Infrared and far-infrared lasers
  • (190.4370) Nonlinear optics : Nonlinear optics, fibers

A new phase quality map based on local multi-unwrapped results for two dimensional phase unwrapping

  • Heping Zhong, Jinsong Tang, and Sen Zhang
  • received 10/01/2014; accepted 12/11/2014; posted 12/12/2014; Doc. ID 223997
  • [full text: PDF (1485) KB)]
  • Abstract: The efficiency of a phase unwrapping algorithm and the reliability of the corresponding unwrapped result are two key problems in reconstructing the digital elevation model (DEM) of a scene from its interferometric synthetic aperture radar (InSAR) or interferometric synthetic aperture sonar (InSAS) data. In this paper, a new phase quality map is designed and implemented in graphic processing unit (GPU) environment, which greatly accelerates the unwrapping process of the quality-guided algorithm and enhances the correctness of the unwrapped result. In a local wrapped phase window, the center point is selected as the reference point, and then two unwrapped results are computed by integrating in two different simple ways. After the two local unwrapped results are computed, the total difference of the two unwrapped results is regarded as the phase quality value of the center point. In order to accelerate the computing process of the new proposed quality map, we have implemented it in GPU environment. The wrapped phase data is first uploaded to the memory of device, and then the kernel function is called in the device to compute the phase quality in parallel by blocks of threads. Unwrapping tests performed on the simulated and real InSAS data confirm the accuracy and efficiency of the proposed method.

Keywords (OCIS):

  • (100.2650) Image processing : Fringe analysis
  • (280.6730) Remote sensing and sensors : Synthetic aperture radar
  • (100.5088) Image processing : Phase unwrapping

Effect of soil temperature on one-way optical frequency transfer through dense-wavelength-division-multiplexing fibre links

  • Tjeerd Pinkert, O. Böll, Lorenz Willmann, G.S.M. Jansen, E. A. Dijck, R. Smets, F. C. Bosveld, Wim Ubachs, Klaus Jungmann, Kjeld Eikema, Jeroen Koelemeij, and B.G.H.M. Groeneveld
  • received 10/17/2014; accepted 12/11/2014; posted 12/12/2014; Doc. ID 225128
  • [full text: PDF (1420) KB)]
  • Abstract: Results of optical frequency transfer over a carrier-grade dense-wavelength-division-multiplexing (DWDM) optical fibre network are presented. The relation between soil temperature changes on a buried optical fibre and frequency changes of an optical carrier through the fibre is modelled. Soil temperatures, measured at various depths by the Royal Netherlands Meteorology Institute (KNMI) are compared with observed frequency variations through this model. A comparison of a nine-day record of optical frequency measurements through the 2 x 298 km fibre link with soil temperature data shows qualitative agreement. A soil temperature model is used to predict the link stability over longer periods (days-months-years). We show that one-way optical frequency dissemination is sufficiently stable to distribute and compare e.g. rubidium frequency standards over standard DWDM optical fibre networks.

Keywords (OCIS):

  • (060.2300) Fiber optics and optical communications : Fiber measurements
  • (120.0120) Instrumentation, measurement, and metrology : Instrumentation, measurement, and metrology
  • (120.5050) Instrumentation, measurement, and metrology : Phase measurement
  • (120.6810) Instrumentation, measurement, and metrology : Thermal effects

Extraction of optical constants from maxima of fringing reflectance spectra

  • Shun-Tung Yen and Pei-Kang Chung
  • received 10/24/2014; accepted 12/11/2014; posted 12/12/2014; Doc. ID 225686
  • [full text: PDF (408) KB)]
  • Abstract: We propose a scheme to extract the refractive index and the extinction coefficient of dielectrics. The extraction needs only a reflectance spectrum with reliable successive maxima of fringing oscillations measured from a dielectric film either free-standing or on metal. With the film thickness known in advance, we determine the refractive index spectrum from the fringing oscillation periods and then the extinction coefficient spectrum from the upper envelope. The method is demonstrated to work well for GaAs and Ge.

Keywords (OCIS):

  • (120.2230) Instrumentation, measurement, and metrology : Fabry-Perot
  • (120.2650) Instrumentation, measurement, and metrology : Fringe analysis
  • (120.4530) Instrumentation, measurement, and metrology : Optical constants
  • (120.5700) Instrumentation, measurement, and metrology : Reflection
  • (300.6270) Spectroscopy : Spectroscopy, far infrared
  • (300.6470) Spectroscopy : Spectroscopy, semiconductors

Full-field Measurement of Surface Topographies and Thin Film Stresses at Elevated Temperatures by Digital Gradient Sensing Method

  • Xue Feng, Changxing Zhang, Zhe Qu, Xuefei Fang, and Keh-Chih Hwang
  • received 09/12/2014; accepted 12/11/2014; posted 12/12/2014; Doc. ID 223045
  • [full text: PDF (1528) KB)]
  • Abstract: Thin film stresses distribution in thin film/substrate systems at elevated temperatures, which results from the thermal mismatch strain between the film and substrate, usually decides the reliability and safety of such structures in microelectronic devices. The reflection mode of digital gradient sensing (DGS) method, a real-time full-field optical technique, is applicable to measure deformations of reflective surface topographies. In this paper, the reflection mode DGS method was developed for measuring topographies and thin film stresses of thin film/substrate systems at elevated temperatures. The air convection at elevated temperatures, which is a serious problem for optical techniques, is calibrated and compensated. The principles for surface topography measurements by the reflection-mode DGS method at elevated temperatures and the governing equations for removing the air convection effects are introduced in detail. The proposed method is applied to successfully measure the full-field topography and deformation of a NiTi thin film on a silicon substrate at elevated temperatures. The evolution of thin film stresses obtained by the extended Stoney’s formula implies the “non-uniform” effect featured by the experimental results.

Keywords (OCIS):

  • (100.2000) Image processing : Digital image processing
  • (120.6780) Instrumentation, measurement, and metrology : Temperature
  • (240.0310) Optics at surfaces : Thin films
  • (310.4925) Thin films : Other properties (stress, chemical, etc.)

Integration of an Opto-Chemical Detector based on Group III-Nitride Nanowire Heterostructures

  • Roman Kleindienst, Pascal Becker, Volker Cimalla, Adrian Grewe, Mathias Krüger, Ulrich Schwarz, Pascal Hille, Jörg Schörmann, Jörg Teubert, Martin Eickhoff, and Stefan Sinzinger
  • received 10/31/2014; accepted 12/11/2014; posted 12/15/2014; Doc. ID 226073
  • [full text: PDF (2340) KB)]
  • Abstract: The photoluminescence (PL) intensity of group III-Nitrides (III-N) nanowires (NWs) and heterostructures (NWHs) strongly depends on the environmental H2 and O2 concentration. We used this opto-chemical transducer principle for the realization of a novel type gas detector. To make this technology prospectively available to commercial gas monitoring applications a large scale laboratory setup was miniaturized. To this end the gas sensitive NWHs were integrated with electro-optical components for optical addressing and read out within a compact and robust sensor system. This paper covers the entire realization process of the device from its conceptual draft and optical design to its fabrication and assembly, respectively. The applied approaches are verified with intermediate results of profilometric characterizations and optical performance measurements of subsystems. Finally the gas sensing capabilities of the integrated detector are experimentally proven and optimized.

Keywords (OCIS):

  • (130.3120) Integrated optics : Integrated optics devices
  • (220.0220) Optical design and fabrication : Optical design and fabrication
  • (220.4830) Optical design and fabrication : Systems design
  • (230.3120) Optical devices : Integrated optics devices
  • (280.1545) Remote sensing and sensors : Chemical analysis
  • (280.4788) Remote sensing and sensors : Optical sensing and sensors

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