Society Of Photo-Optical Instrumentation Engineers Research Articles

Frequency- and time-domain simulations of semiconductor optical amplifiers using equivalent circuit modeling

Abstract. We propose an equivalent circuit modeling for a chip-on-carrier and for two encapsulated semicon-ductor optical amplifiers (SOAs). The models include main parasitic leaks and were used in reflection and trans-mission simulations, showing good agreement with experimental data. The model for each SOA is validated,comparing the simulated results with experimental data from SOAs operating as high-speed electro-opticalswitches, reaching rise times below 200 ps. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.54.11.114107] Keywords: optical communications; electro-optics; switching; simulations.Paper 150396 received Mar. 26, 2015; accepted for publication Oct. 28, 2015; published online Nov. 30, 2015. 1 IntroductionDigital computing systems require high-speed interconnec-tions between processors and from processors to their cor-responding memories and processing nodes. Performancescaling of such digital systems demands interconnects withhigh bandwidth, high density, low latency, long reach, andhigh energy efficiency.

Measurement of birefringence using polarization phase-shifting Mach–Zehnder interferometer

An interferometric method for quantitative evaluation of the magnitude and direction of birefringence of an arbitrarily oriented birefringent sample is developed and presented. The analysis shows that full-field analysis of a spatially varying birefringence is possible by suitably combining several interferogram frames obtained by varying the polarization parameters involved. The preliminary experimental result for a uniformly birefringent sample with a known direction of birefringence is presented. © 2015 Society of Photo-Optical Instrumentation Engineers

Single-crystal diamond pyramids: synthesis and application for atomic force microscopy

Here we present the results of investigations aimed at the development and testing of robust, chemically inert single-crystal diamond probes for atomic force microscopy (AFM). The probes were prepared by assembling common silicon probes with micrometer-sized pyramid- shaped single-crystal diamonds (SCD). The SCD were obtained by the selective thermal oxi- dation of the polycrystalline films grown by chemical vapor deposition. Electrostatic spray of adhesive coating onto silicon probes was used to attach individual SCD. Geometrical parameters of produced AFM SCD probes were revealed with transmission electron microscopy: the apex angle of the pyramidal diamond crystallite was ∼10 deg, and the curvature radius at the apex was ∼2 to 10 nm. The diamond AFM probes were used for surface imaging of deoxyribonucleic acid deposited on graphite substrate. Obtained results demonstrate high efficiency of the dia- mond AFM probes, allowing improvement of the image quality compared to standard silicon probes. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JNP.10

Resolving multiple propagation paths in time of flight range cameras using direct and global separation methods

Time of flight (ToF) range cameras illuminate the scene with an amplitude-modulated continuous wave light source and measure the returning modulation envelopes: phase and amplitude. The phase change of the modulation envelope encodes the distance travelled. This technology suffers from measurement errors caused by multiple propagation paths from the light source to the receiving pixel. The multiple paths can be represented as the summation of a direct return, which is the return from the shortest path length, and a global return, which includes all other returns. We develop the use of a sinusoidal pattern from which a closed form solution for the direct and global returns can be computed in nine frames with the constraint that the global return is a spatially lower frequency than the illuminated pattern. In a demonstration on a scene constructed to have strong multipath interference, we find the direct return is not significantly different from the ground truth in 33∕136 pixels tested; where for the full-field measurement, it is significantly different for every pixel tested. The variance in the estimated direct phase and amplitude increases by a factor of eight compared with the standard time of flight range camera technique. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10 .1117/1.OE.54.11.113109)

Rice yield estimation using Landsat ETM + Data

Paddy rice areas in Larkana district in Sindh province, Pakistan, were mapped over eight years. Landsat 7 ETMþ satellite imagery was classified for rice areas using training data collected through visual interpretation and using a bagged decision tree approach. Within the rice areas, we estimated yield for the 2013 season using regression models based on Landsat-derived normalized difference vegetation index (NDVI) and ratio vegetation index (RVI) values against historic, reported yield values. The annual cropped rice area estimated from satellite imagery was between 19% and 24% lower than the area reported by the Crop Reporting Service, Sindh. A positive and strong relationship with coefficient of determination (R 2 ) of 0.94 was observed between the reported rice crop yield and NDVI at the peak of the growing season for the years 2006 to 2013. A fair relation (R 2 ¼ 0.875) between rice crop yield and RVI was observed for the same years. A strong relationship between observed and predicted rice production with model efficiency ¼ 0.925, mean bias error ¼ −85;016 t ,a ndRMSE ¼ 80;726 t was obtained. Thus, Landsat ETMþ has a high potential for estimating rice yield and production at the district level in Pakistan and elsewhere. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JRS.9.095986)

Influence of aberrations in microholographic recording

The influence of various types of aberrations (spherical, coma, and astigmatic) of recording and read- out beams on the readout signal in a microholographic recording was investigated through a numerical simu- lation. The simulation conditions were that the wavelength of the laser was 405 nm and the numerical aperture of the objective lenses was 0.85. The tolerance of the root-mean-square (RMS) wavefront aberrations was defined as the aberration when the normalized signal level decreased to 0.8. Among the three types of aberrations, the influence of the spherical aberration was the most significant. When both the recording and readout beams were aberrated and the signs of the aberrations were in the worst case, the tolerance of the RMS wavefront aberra- tions was less than half of the Marechal's criterion. Moreover, when the RMS wavefront aberrations of the record- ing and readout beams were within the above tolerance, the bit intervals of 0.13 and 0.65 μm in the inplane and vertical directions, respectively, which correspond to the recording density of 91 bit∕μm 3 (recording capacity of 16 TB for a 120-mm-diameter optical disk having a 300-μm-thick recording layer), were shown to be feasible for confocal detection with an allowable signal-to-noise ratio. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.OE.54.11.117104)

Impact of atmospheric correction and image filtering on hyperspectral classification of tree species using support vector machine

Hyperspectral images can be used to identify savannah tree species at the landscape scale, which is a key step in measuring biomass and carbon, and tracking changes in species distributions, including invasive species, in these ecosystems. Before automated species map- ping can be performed, image processing and atmospheric correction is often performed, which can potentially affect the performance of classification algorithms. We determine how three processing and correction techniques (atmospheric correction, Gaussian filters, and shade/ green vegetation filters) affect the prediction accuracy of classification of tree species at pixel level from airborne visible/infrared imaging spectrometer imagery of longleaf pine savanna in Central Florida, United States. Species classification using fast line-of-sight atmospheric analysis of spectral hypercubes (FLAASH) atmospheric correction outperformed ATCOR in the majority of cases. Green vegetation (normalized difference vegetation index) and shade (near-infrared) filters did not increase classification accuracy when applied to large and continu- ous patches of specific species. Finally, applying a Gaussian filter reduces interband noise and increases species classification accuracy. Using the optimal preprocessing steps, our classifica- tion accuracy of six species classes is about 75%. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JRS.9.095990)

Phase retrieval–based distribution detecting method for transparent objects

A distribution detecting method to recover the distribution of transparent objects from their diffraction intensities is proposed. First, on the basis of the Gerchberg-Saxton algorithm, a wavefront function involving the phase change of the object is retrieved from the incident light intensity and the diffraction intensity, then the phase change of the object is calculated from the retrieved wavefront function by using a gradient field- based phase estimation algorithm, which circumvents the common phase wrapping problem. Finally, a linear model between the distribution of the object and the phase change is set up, and the distribution of the object can be calculated from the obtained phase change. The effectiveness of the proposed method is verified with simulations and experiments. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.OE.54.11.113103)

Combined line-of-sight error and angular position to generate feedforward control for a charge-coupled device–based tracking loop

A feedforward control based on data fusion is proposed to enhance closed-loop performance. The target trajectory as the observed value of a Kalman filter is recovered by synthesizing line-of-sight error and angular position from the encoder. A Kalman filter based on a Singer acceleration model is employed to estimate the target velocity. In this control scheme, the control stability is influenced by the bandwidth of the Kalman filter and time misalignment. The transfer function of the Kalman filter in the frequency domain is built for analyzing the closed loop stability, which shows that the Kalman filter is the major factor that affects the control stability. The feedforward control proposed here is verified through simulations and experiments. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Algorithm for camera parameter adjustment in multicamera systems

Multicamera systems have many advantages and are widely used. However, many situations require camera parameters that are more accurate than those that are currently available. A new algorithm is proposed to improve the accuracy and consistency of these systems by adjusting the camera parameters. The algorithm assumes that the distribution of the measured point positions follows the Gaussian mixture model. Based on this model, point positions in space are estimated, and new camera parameters are computed from the estimation. A metric is defined to describe the difference between the newly computed and precalibrated camera parameters, following which the parameters are adjusted by minimizing this difference. Finally, the validity of the algorithm is confirmed by conducting experiments. Two indicators that describe the accuracy and consistency are defined and applied to analyze the experimental data. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Use of nanostructures based on silver nanospike prepared by oblique angle deposition as broadband optical polarizer

Plasmonics have enabled the realization of new optical components in nanostructures such as polar- izers. We construct nanostructures by polycarbonate grating comprising silver nanospikes prepared by an oblique angle deposition technique. Surface, wavelength, and polarization properties of these devices have been investigated by atomic force microscopy, fiber-coupled spectrometer, and rotating analyzer, respectively. Our results show that we can reach 31% polarization ratio with the aid of two pieces of metalized gratings placed back to back by index-matching gel. Also, we can reach the broadband optical polarizer in the visible region according to the concentration and direction of nanospike in each of metalized nanogratings, which can open up directions toward cheap and one-dimensional optical polarizers. © 2015 Society of Photo-Optical Instrumentation Engineers

Slitless spectroscopy of geosynchronous satellites

A preliminary investigation into the use of slitless spectroscopy for characterization of geosynchro- nous satellites is described. A 100 line∕mm diffraction grating is used as the dispersing device, and the spectral data obtained are compared to a model with good results. A method used to collect and calibrate slitless spectral observations accounting for pixel to wavelength conversion, pixel response as a function of wavelength, and solar features is presented. Observations of several geosynchronous satellites throughout a night reveal reflec- tance with noticeable and different profiles indicating that slitless spectroscopy offers the potential for another modality for identifying and discriminating satellites.©2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI:10.1117/ 1.OE.54.10.104103)

Near ultraviolet-visible radial wire grid polarizer for tight focusing applications

Abstract. A circular wire grid polarizer (WGP) as a device to produce high quality radially polarized light at nearUV wavelength range (in particular at the wavelength of λ ¼ 405 nm) is presented starting from design modelingfollowed by fabrication and performance analysis. The wire grid consists of concentric subwavelength metalliccylinders covering a high quality glass substrate and fabricated using an electron beam pattern generator andetchingtechniques.Thetheoreticalmodelingusingtherigorousfinite-elementmethodandmeasurementsofthetransmittedlightthroughthemaskhavebeenevaluated.AnanalysisonadjustmentsofthegeometryoftheWGPto produce the optimum focused spot of the longitudinal component of the electric field, its implementation, andqualitative testing are also presented. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) [DOI: 10.1117/1.OE.54.10.104101] Keywords: wire grid polarizer; radially polarized light; metallic grating; finite-element method; near ultraviolet wavelength range;physical optics; diffractive optics.Paper 150862 received Jun. 24, 2015; accepted for publication Aug. 31, 2015; published online Oct. 6, 2015.

Modified iterative algorithm for the design of wide-diffraction angle diffraction optical element

Abstract. Afastandeffectivealgorithmfordesigningthediffractionopticalelement(DOE)withawide-diffractionangle is presented. DOE hadbeen widely used in many fields in recent years, but there are finite methods whichcandesignDOEwithwide-diffractionanglequicklyoccupyingasmallquantityofcomputingresource.Bytheuseof a nonparaxial scalar diffraction equation as the light transmission operator, a modified iterative algorithm isproposed. To verify our algorithm, the checkerboard image, binary image, and gray-scale image are numericallysimulated, respectively. The simulation results show that the final variance between the preset image and finalpattern is very small, the value is generally lower than 10 −5 , and the natural images even have a final varianceless than 10 −12 . At the same time, the diffraction efficiency has been significantly increased to be larger than90%, which indicates that the design method is effective and practical. © 2015 Society of Photo-Optical InstrumentationEngineers (SPIE) [DOI: 10.1117/1.OE.54.9.093106]

Correction of amplitude-phase distortion for polarimetric active radar calibrator

The polarimetric active radar calibrator (PARC) is extensively used as an external test target for system distortion compensation and polarimetric calibration for the high-resolution polarimetric radar. However, the signal undergoes distortion in the PARC, affecting the effec- tiveness of the compensation and the calibration. The system distortion compensation resulting from the distortion of the amplitude and phase in the PARC was analyzed based on the of paired echoes. Then the correction method was proposed, which separated the ideal signals from the distorted signals. Experiments were carried on real radar data, and the experimental results were in good agreement with the theoretical analysis. After the correction, the PARC can be better used as an external test target for the system distortion compensation. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.JRS.9.096009)

Hybrid bidirectional radio-over-fiber-based orthogonal frequency division multiple access-passive optical network supporting 60 / 120 GHz using offset quadrate phase shift keying

A hybrid bidirectional orthogonal frequency division multiple access-passive optical network (OFDMA- PON) based on offset quadrate phase shift keying (OQPSK) to support 60- and 120-GHz radio-over-fiber system is proposed. The system can support wired/wireless applications and enable the dynamic bandwidth allocation according to a subscriber's application. It is successfully achieved by using the millimeter waves (MMWs) gen- eration and the carrier-reuse technique. In the proposed scheme, the MMW bands used for downlink (DL) and uplink transmissions are generated at the optical line terminal by the dual-arm Mach-Zehnder modulators. Both 60- and 120-GHz MMWs are obtained for the transmission of the high bit-rate services in source-free optical network units (ONUs), only using a single 15-GHz sinusoidal wave source. The Rayleigh backscattering effect is considered in the proposed OQPSK-based OFDMA-PON. For DL transmission over a 30-km single-mode fiber, the power penalties are less than 0.8 and 1 dB for the OQPSK-OFDM wired data at 10 Gb∕s and the OQPSK- OFDM wireless data at 5 Gb∕s, respectively. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.OE.54 .9.096108)

Green route for preparing extra-small TiO2nanoparticles using aloe extracts and their application in degradation of methyl orange

TiO2 nanoparticles (NPs) with high-photocatalysis properties both in ultraviolet and visible-light regions were synthesized via a simple sol-gel method, and an aloe leaf extract (ALE) was used as the cap. When the Ti(OC4H9)(4):(CH3)(2) CHOH:ALE volume ratio was equal to 0.5:8:40, the reaction time was 6 h, and crystallization occurred at 80 degrees C for 2 h, the TiO(2)NPs had been synthesized. XRD analysis showed that the structure of TiO(2)NPs without thermal treatment was anatase. Transmission electron microscopy images confirmed their average size, which was around 5 nm. The products showed an excellent photocatalytic property for methyl orange in the presence of UV and sunlight with the characterization of UV-vis. The photocatalytic activity was optimized by adjusting the amount of TiO2, the pH value, and the calcination temperature. Results indicated that ALE acted as a cap and nano-TiO2 could be synthesized without calcination. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Large-area land subsidence monitoring and mechanism research using the small baseline subset interferometric synthetic aperture radar technique over the Yellow River Delta, China

The Yellow River Delta, the largest and most rapidly growing delta in China, has undergone severe land subsidence. However, land subsidence has not been regularly and fully measured in this large region and no consensus has been reached as to the primary cause. Here, the small baseline subset interferometric synthetic aperture radar (InSAR) method is applied to retrieve time-series deformation and the full land subsidence pattern in the Yellow River Delta. Spirit leveling data and a standard deviation map are used to verify the InSAR results and measurement accuracy. The major subsidence regions, which have a maximum subsidence rate ranging from 20 to more than 70 mm/year, cover a total of similar to 800 km(2) and are mainly concentrated in the groundwater source areas. An intimate connection of surface deformation with groundwater suggests that land subsidence is primarily caused by excessive exploitation of groundwater. In addition, comparison of the surface deformation with the precipitation record indicates that the seasonal land subsidence correlates with the rainfall rate, with a lag time of around 1 to 2 months between the precipitation peak and the minimum land subsidence displacement. The results provide new insights into land subsidence mechanisms in the Yellow River Delta. A key policy priority should, therefore, be to plan for controlling anthropogenic activities and better management of groundwater. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Single-walled carbon nanotube solution-based saturable absorbers for mode-locked fiber laser

The report proposed a saturable absorber based on a D-shaped fiber embedded in a single-walled carbon nanotube solution. Such a saturable absorber solution method with a D-shaped fiber has the virtues of good antioxidant capacity, excellent scattering resistance, high heat dissipation, and high damage threshold. The nonsaturable loss of this kind of saturable absorber was evaluated to be 3%. To the best of our knowledge, this is the lowest value compared with other carbon nanotube saturable absorbers. By incorporating the saturable absorber into a Yb-doped fiber laser cavity, a mode-locked fiber laser was achieved with a central wavelength of 1054.16 nm. The repetition rate was 23 MHz with a signal-to-noise ratio of 60 dB, and the pulse duration was measured to be 194 ps. The long-term working stability of working is also good. The results indicated that the solution method with a D-shaped fiber possesses a potential for fiber laser stability applications. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Investigation of coupling of a laser diode to photonic crystal fiber via hyperbolic microlens on the fiber tip by ABCD matrix formalism

A simple and accurate theoretical investigation is presented, based on a novel, effective, and straight- forward ABCD matrix technique, in relation to estimation of optimum coupling efficiency between the laser diode and the photonic crystal fiber (PCF) with a hyperbolic microlens (HML) on its tip. By tailoring different parameters, such as the air-filling factor and lattice constant of the PCF, the criteria for achieving maximum coupling are predicted and reported for two different light wavelengths of practical interest. It is observed that such fiber parameters play a crucial role in predicting the optimum focal length of HML for a particular wavelength. The formulation should find application in the design of HML, for achieving a long working distance between the laser source facet and the fiber tip. © 2015 Society of Photo-Optical Instrumentation Engineers (SPIE) (DOI: 10.1117/1.OE.54.8 .086102)