Society Of Photo-Optical Instrumentation Engineers Research Articles

Double-pulse single-longitudinal-mode operation of injection-seeded laser using intracavity phase modulator

A single-longitudinal-mode (SLM) double-pulse injection-seeded neodymium-doped yttrium aluminium garnet (Nd:YAG) laser was established utilizing an RbTiOPO4 electro-optic crystal to modulate the optical path of the slave resonator for generating a resonance condition. The Q-switcher was fired twice during every pump period. This enabled the laser to emit a pair of SLM laser pulses with a time separation of 200 mu s. Each pulse had a pulse energy of 13 mJ at 50-Hz repetition rate, pulse duration of 20 +/- 0.5 ns, and linewidth of 30 +/- 0.3 MHz (within 2 min). The beam quality factor of M-2 was <1.22. A frequency jitter of 1.4 MHz was obtained within 2 min. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Effects of land cover change on evapotranspiration in the Yellow River Delta analyzed with the SEBAL model

This study investigated the associations between land cover changes and evapotranspiration (ET) in the Yellow River Delta during the last 30 years using Landsat imagery. The result showed that the Delta region experienced a distinct increase in area due to sea-land interaction and sediment deposition, accompanied by substantial change in land cover fractions. From 1986 to 2015, 35.48% of land cover changed, mainly due to a transformation into salterns and culture ponds from other land cover types. In general, land cover was converted from less developed into highly developed types. The monowindow algorithm for retrieval of land surface temperature (LST) and the SEBAL model were used to explore the effects of land cover changes on regional ET. The results indicated that the average relative error of daily ET was 9.46%, and there was a significant linear correlation (R-2 >= 0.959, p < 0.001) between ET and LST. Relationships existed between LST, ET, fractional vegetation cover, and other relevant vegetation indices, and there were positive and negative correlations between different threshold ranges. During the study period, the transformation of large areas of different land cover types into salterns and culture ponds led to an average increase of 1.43 mm in daily ET. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Repetition-frequency-controllable double Q-switched Ho:LuAG laser with acousto-optic modulator and Cr2+:ZnS saturable absorber

A repetition-frequency-controllable double Q-switched (DQS) Ho:LuAG laser at 2098.34 nm with acousto-optic modulator (AOM) and Cr2+:ZnS saturable absorber (SA) was investigated. The maximum output power of 5.3 W was obtained at the AOM repetition frequency (RF) of 3.72 kHz, corresponding to the slope efficiency of 29.8%. The largest pulse energy of 2.8 mJ with the shortest pulse width of 54.2 ns was observed at the AOM RF of 2.64 kHz. Compared with the passively Q-switched Ho: LuAG laser, the DQS Ho: LuAG laser could generate shorter pulse width and larger pulse energy, and its RF could be controlled by the AOM RF. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

Investigation of organic semiconductor interlayers in hybrid PEDOT:PSS/silicon solar cells

In the last years, hybrid organic/inorganic solar cells have attracted great interest in photovoltaic research due to their expected potential to combine the advantages of both material classes, the excellent electrical properties and stability of the inorganic and the low-cost proc- essability of the organic semiconductors. This work is focused on hybrid solar cells based on n-doped crystalline Si as the inorganic and the polymer poly(3,4-ethylenedioxythio- phene):poly(styrenesulfonate) as the organic part of the device. The hole-conducting organic semiconductors poly(3-hexylthiophene-2,5-diyl) (P3HT) and 2,2',7,7'-Tetrakis(N;N-di(4- methoxyphenyl)amino)-9,9'-spirobifluorene (Spiro-MeOTAD) are investigated as electron blocking interlayers to reduce the parasitic electron current into the metal top contact and thereby increase the efficiency of the solar cell. In this context, P3HT is identified to be insufficient as an interlayer material due to unfavorable hysteresis effects. On the other hand, for solar cells with a Spiro-MeOTAD interlayer, the power conversion efficiency (PCE) is significantly increased. This is mainly attributed to an increased short-circuit current density. For the best performing device, a PCE of 14.3% is achieved, which is one of the highest values reported for this type of hybrid solar cells so far. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10

Tunable dual-wavelength passively mode-locked thulium-doped fiber laser using carbon nanotube

A tunable dual-wavelength passively mode-locked thulium-doped fiber laser (TDFL) based on single-wall carbon nanotube is demonstrated. By properly tuning the pump power and the polarization controller, both single-and dual-wavelength mode-locked operation can be achieved. The repetition rates of the single-and dual-wavelength mode-locked operation are both 17.64 MHz. The duration of the ultrashort soliton pulse is about 3.7 ps. By appropriately adjusting the polarization state of the laser, the dual wavelength can be tuned from 1879.8 and 1894.5 nm to 1903.3 and 1914.1 nm. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

Dual-wavelength continuous-wave and passively Q-switched Nd,Y:SrF2 ceramic laser

A polycrystalline ceramic based on an Nd;Y:SrF2 single crystal was successfully fabricated and its laser performance was experimentally investigated. We obtained dual-wavelength continuous-wave operation at the wavelengths of 1050.5 and 1058.0 nm. The maximum output power and slope efficiency were 750 mW and 31.5%, respectively. In the passively Q-switched operation, the shortest pulse with a 169-ns duration was also obtained, and the corresponding maximum repetition rate and single pulse energy were 7.3 kHz and 19.2 mu J, respectively. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

Digital holographic nondestructive testing of laminate composite

Abstract. Opticaldigitalholographictechniquescanbeusedfornondestructivetestingofmaterials.Digitalholo-graphicnondestructivetestingessentiallymeasuresdeformationsonthesurfaceoftheobject.However,thereissufficient sensitivity to detect subsurface and internal defects in metallic and composite specimens. We inves-tigate and discuss the vibration analysis of laminated composite glass-epoxy using time averaging in digitalFresnel holography to visualize the modes of vibration and to test the integrity of the structures of studied mate-rials. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.55.9.095105] Keywords: damage; digital holography nondestructive testing; laminate composite.Paper 160647 received Apr. 29, 2016; accepted for publication Aug. 30, 2016; published online Sep. 23, 2016. 1 IntroductionInrecentdecades,compositematerialshavefoundincreasinguse in structural applications because of their high specifictensile and compressive strengths, and good fatigue and cor-rosion resistance properties.

Soliton all-optical logic AND gate with semiconductor optical amplifier-assisted Mach–Zehnder interferometer

The concept of soliton provides a line in research in telecommunications systems. In the present study, a soliton all-optical logic AND gate with semiconductor optical amplifier (SOA)-assisted Mach- Zehnder interferometer has been numerically simulated and investigated. The dependence of the output quality factor (Q-factor) on the soliton characteristics and SOA parameters has been examined and assessed. The obtained results demonstrate that the soliton AND gate is capable of operating at a data rate of 80 Gb∕s with logical correctness and high-output Q-factor. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10 .1117/1.OE.55.8.087109)

Statistics of accumulated splice-cross talk in weakly coupled few-mode fiber links

Abstract For uncoupled mode-division-multiplexed systems in weakly coupled (WC) few-mode fibers (FMFs),we numerically investigate the effect of splices on the statistical regularities of WC property preservation alongthe transmission link. At each splice, the probability density functions of intermodal cross talk (XT) for thetransmittedlinearlypolarizedmode(s)arenumericallyanalyzedbyusingGaussianfitting.Undertheassessmentcriterion of accumulated intermodal XT affected by discrete splices, we give an empirical evaluation on theuncoupled probability value versus transmission distance, for WC FMF links with different splicing qualities. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.55.7.076118] Keywords: few-mode fibers; mode cross talk; mode-division multiplexing; fiber optics communications.Paper 160703 received May 7, 2016; accepted for publication Jul. 12, 2016; published online Jul. 28, 2016. 1 IntroductionFew-mode fibers (FMF) systems have been considered as apromising solution to overcome the fundamental capacitylimit of single-mode (SM) systems. In an FMF system, inwhich the separation between nondegenerate linearly polarized(LP) modes is preserved [i.e., to use the weakly coupled (WC)approach aimed at minimizing distributed mode coupling],each LP mode(s) can be separately detected using simple 2×2 (nondegenerate LP

Fe-ions implantation to modify TiO2trilayer films for dye-sensitized solar cells

A series of Fe-doped TiO2 trilayer films were prepared successfully by using the ion-implantation technique. The aim of the ion implantation was to enhance charge transfer and to reduce charge recombination. A maximum conversion efficiency of 4.86% was achieved in cells using Fe-ion-implanted electrodes with the illumination of 6 × 10 15 atom∕cm 2 . It is 14.1% higher than that of the cells without ion implantations. The sig- nificant improvement in conversion efficiency by Fe-ion implantation could be contributed to the enhancement of dye uptake and charge transfer, as indicated from the incident photon-to-collected electron conversion efficiency and ultraviolet-visible measurements. Furthermore, the implanted Fe-ions introduce impurity levels in the bandgap of TiO2, and this improves the electron injection efficiency from lowest unoccupied molecular orbital of excited N719 into the conduction band of TiO2. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1. OE.55.6.067107)

Study on the electrical properties of ZnO thin film transistors using pyrochlore Bi1.5Zn(1+y)Nb1.5O(7+y)gate insulators fabricated by RF sputtering

Abstract. A series of ZnO thin film transistors (TFTs) using pyrochlore Bi 1.5 Zn ð1þyÞ Nb 1.5 O ð7þyÞ (BZN) thin filmsas gate insulators by RF sputtering has been fabricated. The relations between the zinc content and perfor-mance of BZN thin films and ZnO-TFTs are studied. The electrical properties of the ZnO-TFTs with BZNgate insulators as a function of Zn content are discussed. The research results showed that excess Zn(5 mol.%) can significantly enhance the performance of BZN thin films and ZnO-TFTs, which is mainly attributedto the compensation of Zn volatility during fabrication of BZN thin films. At an applied electric field of 250 kV∕cm,the leakage current density of BZN thin films with 5 mol.% excess Zn is approximately four order of magnitudelower than that of BZN thin films without excess Zn. The subthreshold and surface state density of ZnO-TFTswere decreased from 684 and 350 mV∕dec to 4.5×10 12 and 2×10 12 cm −2 , respectively, as Zn content wasincreased. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.55.6.067106]

Construction of an unmanned aerial vehicle remote sensing system for crop monitoring

We constructed a lightweight unmanned aerial vehicle (UAV) remote sensing system and determined the ideal method for equipment setup, image acquisition, and image processing. Fields of rice paddy (Oryza sativa cv. Unkwang) grown under three different nitrogen (N) treat- ments of 0, 50, or 115 kg∕ha were monitored at Chonnam National University, Gwangju, Republic of Korea, in 2013. A multispectral camera was used to acquire UAV images from the study site. Atmospheric correction of these images was completed using the empirical line method, and three-point (black, gray, and white) calibration boards were used as pseudo references. Evaluation of our corrected UAV-based remote sensing data revealed that correction efficiency and root mean square errors ranged from 0.77 to 0.95 and 0.01 to 0.05, respectively. The time series maps of simulated normalized difference vegetation index (NDVI) produced using the UAV images reproduced field variations of NDVI reasonably well, both within and between the different N treatments. We concluded that the UAV-based remote sensing tech- nology utilized in this study is potentially an easy and simple way to quantitatively obtain reli- able two-dimensional remote sensing information on crop growth. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JRS.10.026027)

Polarization maintaining highly nonlinear photonic crystal fiber with closely lying two zero dispersion wavelengths

A simple hexagonal photonic crystal fiber is proposed to simultaneously achieve ultrahigh birefrin- gence, large nonlinear coefficient, and two zero dispersion wavelengths (ZDWs). The finite element method with circular perfectly matched layer boundary condition is used to simulate the designed structure. Simulation results show that it is possible to achieve two closely lying ZDWs of 1.08 and 1.29 μm for x-polari- zation with 0.88 and 1.20 μm for y-polarization modes, respectively. In addition, an ultrahigh birefringence of 3.15 × 10 −2 and a high nonlinear coefficient of 58 W −1 km −1 are also obtained at the excitation wavelength of 1.55 μm. The proposed fiber can have important applications in supercontinuum generation, parametric ampli- fication, four-wave mixing, and optical sensors design. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10 .1117/1.OE.55.5.056107)

Horizontal wind velocity retrieval using a Levenberg–Marquardt algorithm for an airborne wind lidar

We established a model for an airborne wind lidar. Numerical optimization algorithms should be used to solve this nonlinear model. We designed a Levenberg-Marquardt (L-M) algo- rithm and tested it with the modeled data. The retrieved velocity and the true velocity agree very well, and the adjusted R 2 is 0.99947. We have carried out an airborne coherent wind lidar experi- ment in January 2015, and we used the model and the L-M algorithm to process the wind lidar experiment data, and compared the retrieved results with the radiosonde wind profile. The con- sistency is very good, especially at an altitude above 1.8 km. We may speculate that when the atmosphere flows are not so dramatic, the lidar and the radiosonde measurements are strictly synchronous, it is possible to retrieve horizontal wind speeds and directions consistently with the radiosonde using our wind lidar model and the L-M algorithm. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JRS.10.026009)

Errata: Integrating pan-sharpening and classifier ensemble techniques to map an invasive plant (Spartina alterniflora) in an estuarine wetland using Landsat 8 imagery

Accurate mapping of invasive species in a cost-effective way is the first step toward understanding and predicting the impact of their invasions. However, it is challenging in coastal wetlands due to confounding effects of biodiversity and tidal effects on spectral reflectance. The aim of this work is to describe a method to improve the accuracy of mapping an invasive plant (Spartina alterniflora), which is based on integration of pan-sharpening and classifier ensemble techniques. A framework was designed to achieve this goal. Five candidate image fusion algorithms, including principal component analysis fusion algorithm, modified intensity-huesaturation fusion algorithm, wavelet-transform fusion algorithm, Ehlers fusion algorithm, and Gram-Schmidt fusion algorithm, were applied to pan-sharpening Landsat 8 operational land imager (OLI) imagery. We assessed the five fusion algorithms with respect to spectral and spatial fidelity using visual inspection and quantitative quality indicators. The optimal fused image was selected for subsequent analysis. Then, three classifiers, namely, maximum likelihood, artificial neural network, and support vector machine, were employed to preclassify the fused and raw OLI 30-m band images. Final object-based S. alterniflora maps were generated through classifier ensemble analysis of outcomes from the three classifiers. The results showed that the introduced method obtained high classification accuracy, with an overall accuracy of 90.96% and balanced misclassification errors between S. alterniflora and its coexistent species. We recommend future research to adopt the proposed method for monitoring long-term or multiseasonal changes in land coverage of invasive wetland plants. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

Application of Taguchi’s method to optimize fiber Raman amplifier

Abstract. Taguchi’s method is introduced to perform multiobjective optimization of fiber Raman amplifier (FRA).Theoptimizationrequirementsaretomaximizegainandkeepgainrippleminimumovertheoperatingbandwidthof a wavelength division multiplexed (WDM) communication link. Mathematical formulations of FRA and corre-sponding numerical solution techniques are discussed. A general description of Taguchi’s method and how itcan be integrated with the FRA optimization problem are presented. The proposed method is used to optimizetwo different configurations of FRA. The performance of Taguchi’s method is compared with genetic algorithmand particle swarm optimization in terms of output performance and convergence rate. Taguchi’s method isfound to produce good results with fast convergence rate, which makes it well suited for the nonlinear optimi-zation problems. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.55.4.046103] Keywords: Raman amplifier; Taguchi’s method; optimization.Paper 160173 received Feb. 4, 2016; accepted for publication Mar. 14, 2016; published online Apr. 7, 2016.

Experimental testing of focusing properties of subwavelength photon sieves using exposure method

An exposure method is proposed to test the focusing properties of subwavelength photon sieves. To solve the problems caused by the subwavelength photon sieves (such as short focal length and small focal spot size), a grating moire fringe phase detection technique and a microcontact sensor with lead zirconium titanate (PZT) stepping hybrid technique are used in the experimental setup. The focusing properties of the subwavelength photon sieves are tested by this setup. The results show that the focal length and the focal spot size are close to the designed value. Finally, the intensity distribution of the focal spot is proposed. This research result will be beneficial for understanding the focusing properties of subwavelength photon sieves, will help us to improve the imaging quality, and will provide a good experimental basis for practical applications in the nanolithography field. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.10.026003) With requirements for increasingly high resolution, the diameters of the outermost pinholes of photon sieves are becoming smaller and smaller, and the focal spot dimensions are even smaller than the wavelength of the incident light. It is, therefore, necessary to study the focusing properties of subwavelength photon sieves, including their focal lengths, and their focal spot dimensions and energy distributions. These parameters all have a major impact on the overall imaging quality. Many techniques that can be used to test the focusing properties of lenses have been reported, 8 and they can be classified into two types: conventional geometric optical or mechani- cal methods, and the various modern techniques based on interference or diffraction theory. The techniques that have been reported in the first category include charge coupled device (CCD) imaging, 9 knife-edge scanning, 10 and fiber scanning. 11,12 The CCD imaging method suffers from aberrations and energy distribution variations caused by amplification of the small focal spot under testing, and the measurement precision is poor. The knife-edge scanning method is suit- able for the testing of optical spots with regular shapes and symmetrical energy distributions. The

Measuring topological charges of Laguerre–Gaussian vortex beams using two improved Mach–Zehnder interferometers

Abstract. We demonstrate, theoretically and experimentally, a new method to measure high-order topologicalcharges (TCs) of Laguerre–Gaussian vortex beams, including the magnitude and the sign, by analyzing theinterference intensity patterns. The magnitude is determined by analyzing the interference intensity patternsbetween the vortex beam and its conjugate beam, and using an improved Mach–Zehnder interferometerwith a dove prism. Counting the number of interference bright petals attests to the magnitude of high-orderTCs through half of the bright petal number. After the TC is modulated by a spiral phase plate, the sign isacquired by comparing the counting results of two charge-coupled devices. Just by this method, we havebeen able to measure both the magnitude and the sign of the TCs up to l ¼ 90. Our experimental resultsare in good agreement with the numerical simulations. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)[DOI: 10.1117/1.OE.55.3.035104] Keywords: topological charge; interference; spiral phase plate; measurement.Paper 160085 received Jan. 18, 2016; accepted for publication Mar. 1, 2016; published online Mar. 22, 2016.

Magnetic quenching of photonic activity in Fe3O4-elastomer composite

We report a quenching phenomenon within the visible region of the electromagnetic spectrum in the photonic response of a passive Fe3O4-silicone elastomer composite film due to magnetically aligned Fe3O4 nanoparticles. We performed systematic studies of the polarization dependence, the effect of particle size, and an in- and out-of-plane particle alignment on the optical response of the Fe3O4-silicone elastomer composites using a UV/vis/NIR spectrometer. We observed systematic redshifts in the response of the out-of-plane composite films with increasing particle alignment and weight that are attributed to dipole-induced effects. There were no observable shifts in the spectra of the in-plane films, suggesting the orientation of the magnetic dipole and the induced electric dipole play a crucial role in the optical response. A dramatic suppression to near quenching of the photonic response occurred in films containing moderate concentrations of the aligned nanoparticles. This is attributed to the interplay between the intra- and the interparticle dipoles. This occurred even when low magnetic fields were used during the curing process, suggesting that particle alignment and particle size limitation are criti- cal in the manipulation of the photonic properties. A dipole approximation model is used to explain the quenching phenomenon. An active system of such a composite has a potential appli- cation in magneto-optic switches. © 2016 Society of Photo-Optical Instrumentation Engineers (SPIE)

Rectilinear-motion space inversion-based detection approach for infrared dim air targets with variable velocities

Dim targets are extremely difficult to detect using methods based on single-frame detection. Radiation accumulation is one of the effective methods to improve signal-to-noise ratio (SNR). A detection approach based on radiation accumulation is proposed. First, a location space and a motion space are established. Radiation accumulation operation, controlled by vectors from the motion space, is applied to the original image space. Then, a new image space is acquired where some images have an improved SNR. Second, quasitargets in the new image space are obtained by constant false-alarm ratio judging, and location vectors and motion vectors of quasitargets are also acquired simultaneously. Third, the location vectors and motion vectors are mapped into the two spaces, respectively. Volume density function is defined in the motion space. Location extremum of the location space and volume density extremum of motion space will confirm the true target. Finally, actual location of the true target in the original image space is obtained by space inversion. The approach is also applicable to detect multiple dim targets. Experimental results show the effectiveness of the proposed approach and demonstrate the approach is superior to compared approaches on detection probability and false alarm probability. c 2016 Society of Photo-Optical Instrumentation Engineers (SPIE).