Society Of Photo-Optical Instrumentation Engineers Research Articles

PEREGRINATIONS ON THE STUDY OF THE OPTICAL PROPERTIES OF NONSPHERICAL PARTICLES

PEREGRINATIONS ON THE STUDY OF THE OPTICAL PROPERTIES OF NONSPHERICAL PARTICLES

Radio quiet and radio notification zones characteristics for radio astronomy in medium densely populated areas and humid tropical countries

This study proposes general criteria to identify a radio quiet zone (RQZ) and a radio notification zone (RNZ) for the installation of a radio astronomical observatory on-site and safeguard the radio astronomy spectrum specifically in tropical regions. This study focuses on areas with a medium population density. Most RQZs selected in the world are mainly located in regions with a low population density, whereas this work studies the radio frequency interference (RFI) environment in humid tropical regions that have not been studied. The humidity in the tropical regions has a significant effect on radio signal, and this provides a unique perspective to the study. This study implements an algorithm to model the RFI level by considering important humidity factors. The ideal sites are chosen based on the RQZs criteria, whereas the realistic sites are based on the RNZs criteria. In Malaysia, four ideal and another four realistic candidate sites were identified, and the on-site RFI level measurement was conducted. From this study, Kuala Tembeling site is suggested as the RQZ and the Jelebu site as the RNZ in Malaysia. © 2021 Society of Photo-Optical Instrumentation Engineers (SPIE).

Monitoring of Photovoltaic System Performance Using Outdoor Suns-VOC

Summary In-field characterization of photovoltaics is crucial to understand performance and degradation mechanisms, subsequently improving overall reliability and lifespans. Current outdoor characterization is limited by logistical difficulties, variable weather, and requirements to measure during peak production hours. We capitalize on Suns-VOC, which is widely used for laboratory measurements of single solar cells and discuss the barriers in extending the technique to outdoor systems. We demonstrate the normalization of measurements using both backsheet temperature sensors and on-site weather stations. Despite weather variation, VOC, ideality factor, and pseudo fill factor all fall within 1% of the laboratory measurements. It is also demonstrated that monitoring the system VOC at 0.05 to 0.1 suns, during minimal power production, provides a figure of merit that can indicate early degradation of the system. Extensive simulations show that shading portions of a system has minimal effect on measurements, allowing the technique to be used in all weather conditions.

МЕТОД ВИЗНАЧЕННЯ ДІЕЛЕКТРИЧНОЇ ПРОНИКНОСТІ ДІЕЛЕКТРИКІВ У ММ ТА СУБММ ДІАПАЗОНАХ ДОВЖИН ХВИЛЬ НА ПІДСТАВІ ВИМІРЮВАННЯ ПАРАМЕТРІВ ПЛАЗМОН-ПОЛЯРИТОННОГО РЕЗОНАНСУ

МЕТОД ВИЗНАЧЕННЯ ДІЕЛЕКТРИЧНОЇ ПРОНИКНОСТІ ДІЕЛЕКТРИКІВ У ММ ТА СУБММ ДІАПАЗОНАХ ДОВЖИН ХВИЛЬ НА ПІДСТАВІ ВИМІРЮВАННЯ ПАРАМЕТРІВ ПЛАЗМОН-ПОЛЯРИТОННОГО РЕЗОНАНСУ

Performance assessment of dual-polarized 5G waveforms and beyond in directly modulated DFB-laser using Volterra equalizer

We investigate the performance of 25-Gbps dual-polarized orthogonal frequency division multiplexing (OFDM)-based modulation in a directly modulated distributed feedback (DFB)-laser over 25 km of single-mode fiber. A Volterra equalizer is used to compensate for the nonlinear effects of the optical fiber. The results show that FBMC-OQAM modulation outperforms OFDM, universal filtered multicarrier (UFMC), and generalized frequency division multiplexing (GFDM) waveforms. Indeed, a target bit error rate of similar to 3.8 x 10(-3) [forward error correction (FEC) limit] for FBMC, UFMC, OFDM, and GFDM can be achieved at -30.5, -26, -16, and -14.9 dBm, respectively. The effect of the DFB laser is also investigated for UFMC, OFDM, and GFDM, and they undergo a Q penalty of 2.44, 2.77, and 4.14 dB, respectively, at their FEC limit points. For FBMC-OQAM, the signal is perfectly recovered when excluding the DFB laser at -30.5 dBm. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)

Multiresolution and velocity vector average processing algorithm for wind field retrieval based on Doppler radar

A multiresolution and velocity vector average processing algorithm is proposed to retrieve the wind field. When the radar echo area is divided into many square grids with sides of 5 km, the radar radial velocities on the edges and in the center of these grids are obtained through velocity vector averaging in the grid region. In order to solve the problem of a nonuniform wind field caused by different distances from echo to radar, the wind field is retrieved with a different angular resolution, whereas the Cartesian grid resolution remains unchanged. Through comparison and research, the correctness of this retrieval method is proven. At the same time, superposition application between geographic information and radar wind field is completed. The application based on this method can provide support for gale disaster early warning. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)

Fabrication of micropyramid structure by fly-cutting

Microgroove cutting by fly-cutting is studied to obtain the optimized parameters to get a smooth groove with less burr and chip. We analyzed the reason for the second groove and reduced the cutting times to fade the effect of machine reposition error. Introducing additional empty cut further reduced the burr and chip. To get the ideal micropyramid arrays, all factors must be considered and controlled. Finally, processed pyramid arrays with the depth of 1 mu m whose structure distributed the entire surface evenly and with no obvious chip. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)

Highly stable mode-locked fiber laser with graphene oxide-coated side-polished D-shaped fiber saturable absorber

A highly stable mode-lock fiber laser with a thin film coating of graphene oxide (GO) nanoparticles on a D-shaped fiber is proposed and demonstrated. The GO-coated D-shaped fiber, which serves as the cavity's saturable absorber (SA), is fabricated by drop-casting GO nanoparticles on the smooth and consistently polished area of the D-shaped fiber made using a disk-polishing machine. Mode-locking is induced through the interaction of the evanescent field from the D-shaped fiber and GO nanoparticle layer. The cavity has a length of 12.5 m with a fundamental frequency of 16.5 MHz and operates in the anomalous dispersion regime. Stable soliton modelocking is obtained above a pump power of 76.6 mW, with a central lasing wavelength of 1555.7 nm and welldefined Kelly's sidebands. The generated pulses have a repetition rate of 16.5 MHz and pulse duration of 1.18 ps over a pump power range of 76.6 to 280.5 mW, with only minor fluctuations observed. A signal-to-noise ratio of 58.3 dB is computed, indicating a highly stable output. The proposed SA fabrication technique provides a simple, cost-effective, and consistent method of generating mode-locked pulses in fiber lasers. © 2018 Society of Photo-Optical Instrumentation Engineers (SPIE).

Photonic crystal ring resonator-based four-channel dense wavelength division multiplexing demultiplexer on silicon on insulator platform: design and analysis

A micro/nanofabrication feasible compact photonic crystal (PC) ring-resonator-based channel drop filter has been designed and analyzed for operation in C and L bands of communication window. The four-channel demultiplexer consists of ring resonators of holes in two-dimensional PC slab. The proposed assembly design of dense wavelength division multiplexing setup is shown to achieve optimal quality factor, without altering the lattice parameters or resonator size or inclusion of scattering holes. Transmission characteristics are analyzed using the three-dimensional finite-difference time-domain simulation approach. The radiation loss of the ring resonator was minimized by forced cancelation of radiation fields by fine-tuning the air holes inside the ring resonator. An average cross talk of -34 dB has been achieved between the adjacent channels maintaining an average quality factor of 5000. Demultiplexing is achieved by engineering only the air holes inside the ring, which makes it a simple and tolerant design from the fabrication perspective. Also, the device footprint of 500 mu m(2) on silicon on insulator platform makes it easy to fabricate the device using e-beam lithography technique. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

NiCrNx interlayer thickness dependence of spectral performance and environmental durability of protected-silver mirrors

Gemini-style protected-silver mirror (Sub/NiCrNx/Ag/NiCrNx/SiNx/Air) is a suitable choice for optical instruments requiring both long-term environmental durability and high broadband reflectance. Three Gemini-style protected-silver mirrors with NiCrNx interlayer thicknesses between 0.1 and 0.6 nm were prepared by magnetron sputtering, and the dependences of spectral properties and environmental durability of these protected-silver mirrors on the thickness of NiCrNx interlayer between the silver layer and SiNx layer were investigated in-depth. The reflectance, transmittance and total scattering loss measurements, optical microscope, and scanning electron microscope imaging were employed to characterize the spectral properties and surface morphology, and accelerated environmental tests, including humidity test and salt fog test, were applied to investigate the environmental durability. The experimental results showed that both optical and corrosion-resistant properties of protected-silver mirrors were NiCrNx interlayer thickness dependent, and an optimum NiCrNx interlayer thickness should be similar to 0.3 nm for Gemini-style protected-silver mirrors to have reasonably both high reflectance in a broadband spectral range from visible to far infrared and good corrosion resistance for long-lifetime applications in harsh environments. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Characterizing the responses of vegetation to climate change in the Tibet Plateau using remote sensing data

It is of great significance to investigate the changes in vegetation and its response to climate change in Tibet due to the sensitivity and vulnerability of the area to climate change. The spatiotemporal pattern of the normalized difference vegetation index (NDVI) and its trends between 2001 and 2015 were depicted using NDVI from the moderate resolution imaging spectroradiometer (MODIS). The responses of vegetation to climatic variables were analyzed through linear regression and correlation analysis with tropical rainfall measuring mission precipitation data and MODIS land surface temperature (LST) data. The results showed that (1) the average annual NDVI gradually decreased from the southeast to the northwest in accordance with the variations in LST and precipitation, (2) the annual NDVI increased from 2001 to 2015 at a rate of 0.3 x 10(-3) per year. The LST exhibited an average annual increase of 0.05 degrees C while precipitation remained relatively stable, (3) the correlation between NDVI and precipitation was positive in the central region, whereas it became negative in the southeast and northeast. The correlation between NDVI and LST was opposite of that between NDVI and precipitation, and (4) the increases in NDVI in the tropical monsoon rain forest and rain forest, subalpine coniferous forest, and alpine meadow vegetation types in the southeast depended more on LST than precipitation. In contrast, the increases in NDVI responded strongly to precipitation in the alpine bush and meadow, alpine grassland, alpine desert, and alpine desert steppe vegetation types in the northwest. (c) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

UFCN: a fully convolutional neural network for road extraction in RGB imagery acquired by remote sensing from an unmanned aerial vehicle

Road extraction in imagery acquired by low altitude remote sensing (LARS) carried out using an unmanned aerial vehicle (UAV) is presented. LARS is carried out using a fixed wing UAV with a high spatial resolution vision spectrum (RGB) camera as the payload. Deep learning techniques, particularly fully convolutional network (FCN), are adopted to extract roads by dense semantic segmentation. The proposed model, UFCN (U-shaped FCN) is an FCN architecture, which is comprised of a stack of convolutions followed by corresponding stack of mirrored deconvolutions with the usage of skip connections in between for preserving the local information. The limited dataset (76 images and their ground truths) is subjected to real-time data augmentation during training phase to increase the size effectively. Classification performance is evaluated using precision, recall, accuracy, F1 score, and brier score parameters. The performance is compared with support vector machine (SVM) classifier, a one-dimensional convolutional neural network (1D-CNN) model, and a standard two-dimensional CNN (2D-CNN). The UFCN model outperforms the SVM, 1D-CNN, and 2D-CNN models across all the performance parameters. Further, the prediction time of the proposed UFCN model is comparable with SVM, 1D-CNN, and 2D-CNN models. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Adaptive optics-corrected solar image quality assessment based on image power spectrum and human visual system

In ground-based large aperture solar telescopes, the speckle image reconstruction technique combined with adaptive optics (AO) correction is generally used to get near diffraction-limited solar images. In order to select the high quality images from the AO-corrected high resolution solar image sequence, an automated no-reference image quality assessment (IQA) is needed. According to the noise characteristics of solar AO images, an IQA metric based on an image power spectrum and human visual system is developed. By the incorporation of noise masking and shifting the spatial frequency range of summation, our IQA metric could select sharper images with less noise than previous works based on the image power spectrum, even if there is image scaling. Compared with existing general-purpose IQA metrics and previous metrics specifically designed for solar IQA, experimental results verify that the proposed metric gains better performance whether on robustness to blur and noise, or on selecting high quality frames containing solar granulations, sunspots, or both of them. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)

Simultaneous change region and pattern identification for very high-resolution images

By taking advantages of fine details obtained by the improved spatial resolution, very high-resolution images are promising for detecting change regions and identifying change patterns. However, high overlaps between different change patterns and the complexities of multiclass classification make it difficult to reliably separate change features. A framework named simultaneous change region and pattern identification (SCRAPI) is proposed for simultaneously detecting change regions and identifying change patterns, whose components are aimed at capturing overlaps between change patterns and reducing overlaps driven by user-specific interests. To validate the effectiveness of SCRAPI, a supervised approach is illustrated within this framework, which starts with modeling the relationship between change features by interclass couples and intraclass couples, followed by metric learning where structural sparsity is captured by the mixed norm. Experiments demonstrate the effectiveness of the proposed approach. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Performance analysis of 1-km free-space optical communication system over real atmospheric turbulence channels

The performance of a free-space optical communication system is highly affected by the atmospheric turbulence in terms of scintillation. An optical communication system based on intensity-modulation direct-detection was built with 1-km transmission distance to evaluate the bit error rate (BER) performance over real atmospheric turbulence. 2.5-,5-, and 10-Gbps data rate transmissions were carried out, where error-free transmission could be achieved during over 37% of the 2.5-Gbps transmissions and over 43% of the 5-Gbps transmissions. In the rest of the transmissions, BER deteriorated as the refractive-index structure constant increased, while the two measured items have almost the same trend. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Digital shoreline analysis system-based change detection along the highly eroding Krishna–Godavari delta front

Copyright 2017 Society of Photo Optical Instrumentation Engineers (SPIE). One print or electronic copy may be made for personal use only. Systematic reproduction and distribution, duplication of any material in this publication for a fee or for commercial purposes, or modification of the contents of the publication are prohibited.

Plug-in module acceleration feedback control for fast steering mirror-based beam stabilization systems

A plug-in module acceleration feedback control (Plug-In AFC) strategy based on the disturbance observer (DOB) principle is proposed for charge-coupled device (CCD)-based fast steering mirror (FSM) stabilization systems. In classical FSM tracking systems, dual-loop control (DLC), including velocity feedback and position feedback, is usually utilized to enhance the closed-loop performance. Due to the mechanical resonance of the system and CCD time delay, the closed-loop bandwidth is severely restricted. To solve this problem, cascade acceleration feedback control (AFC), which is a kind of high-precision robust control method, is introduced to strengthen the disturbance rejection property. However, in practical applications, it is difficult to realize an integral algorithm in an acceleration controller to compensate for the quadratic differential contained in the FSM acceleration model, resulting in a challenging controller design and a limited improvement. To optimize the acceleration feedback framework in the FSM system, different from the cascade AFC, the accelerometers are used to construct DOB to compensate for the platform vibrations directly. The acceleration nested loop can be plugged into the velocity loop without changing the system stability, and the controller design is quite simple. A series of comparative experimental results demonstrate that the disturbance rejection property of the CCD-based FSM can be effectively improved by the proposed approach. © 2017 Society of Photo-Optical Instrumentation Engineers (SPIE).

Optical thresholder consisting of two cascaded Mach–Zehnder interferometers with nonlinear microring resonators

We propose an optical thresholder having a flat power transfer function both in low-and high-level outputs. The optical thresholder consists of two cascaded Mach-Zehnder interferometers (MZIs) with a nonlinear microring resonator in each MZI. We theoretically analyze the power transfer function and the response speed of the thresholder made of silicon waveguides. A thresholder having the threshold of 7 mW with a response speed of 13 GHz was obtained with a ring radius of 5 mu m. The response speed can be increased to 23.7 GHz by adjusting device parameters with the same ring radius at the cost of increased threshold of 22 mW. Further increased response frequency can be realized by reducing the ring radius. A thresholder with a ring radius of 2 mu m shows the response frequency of 40.5 GHz. (C) 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

Split-nanotube-based negative index metamaterial for midinfrared wavelengths

A design of split-nanotube-based negative index metamaterial for the infrared spectrum has been proposed. The proposed design and its operation are similar to that of a split-ring resonator (SRR) without inheriting the fabrication difficulties associated with conventional SRR. A negative refractive index has been achieved using a split-nanotube in combination with a periodic array of metallic wires between 1.5 and 3.3 μ m . © 2017 Society of Photo-Optical Instrumentation Engineers (SPIE)

2 - μ m numerical analysis of linear-cavity FP structures based on fiber Bragg gratings

Abstract. The linewidth performance of all-fiber, linear-cavity Fabry–Perot structures based on fiber Bragggratings operating at 2-μm band has been investigated numerically. The output linewidth performance oftwo symmetrical and asymmetrical cavities has been theoretically studied and comprehensively compared.The numerical analysis is based on the transmission matrix method with the simplified parameters. The sim-ulationresultsshowthatcavitylengths,cavitylengthsratio,gratinglengths,gratinglengthsratio,aswellasindexmodulationdepths, affectthe outputlinewidthperformance. Thetoleranceability ofthe asymmetricalstructure isfirst proposed and investigated under 1 mm accuracy, and single-frequency output can be realized by properlyadjusting the properties of the proposed composite linear cavity structure. © 2017 Society of Photo-Optical InstrumentationEngineers (SPIE) [DOI: 10.1117/1.OE.56.5.056107] Keywords: 2-μm band; fiber Bragg grating; linear cavity; narrow linewidth.Paper 170162 received Feb. 4, 2017; accepted for publication May 8, 2017; published online May 23, 2017.