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Automatic modulation classification (AMC) has been identified to perform a key role to realize technologies such as cognitive radio, dynamic spectrum management, and interference identification that are arguably pivotal to practical SG communication networks. Random graphs (RGs) have been used to better understand graph behavior and to tackle combinatorial challenges in general. In this research article, a novel modulation classifier is presented to recognize M-Quadrature Amplitude Modulation (QAM) signals using random graph theory. The proposed method demonstrates improved recognition rates for multiple-input multiple-output (MIMO) and single-input single-output (SISO) systems. The proposed method has the advantage of not requiring channel/signal to noise ratio estimate or timing/frequency offset correction. Undirected RGs are constructed based on features, which are extracted by taking sparse Fourier transform (SFT) of the received signal. This method is based on the graph representation of the SFT of the 2nd, 4th, and 8th power of the received signal. The simulation results are also compared to existing state-of-the-art methodologies, revealing that the suggested methodology is superior.

Unstained microscopy of growth cartilage microstructure is crucial for understanding bone formation and related diseases. Here, we compare imaging modalities with unconventional contrast mechanisms applied to the epiphyseal bone-cartilage interface and highlight their comparative merits.

We have constructed a finite element simulation where we investigate the effects of wet-etch-induced surface roughness on transmission and reflection of infrared light in the 8-12um band. A silicon wafer was wet-etched for 2 hours in a 10% KOH solution at 80°C, scanned in an atomic force microscope, and the surface profile was recreated in COMSOL. Simulated plane waves of light and varying angles of incidence were then allowed to pass through this surface and the resulting effects on the reflection and transmission were investigated. Roughness was then amplified to investigate the effects of increased surface roughness. For the wavelengths investigated, an increase in transmission of 8% could be seen up to an RMS surface roughness of 800nm followed by a decrease, while the angles investigated showed an RMS dependent increase in transmission between 20° and 40° for RMS surface roughness' above 1000nm.

Cerium-doped single crystals (Ce:LuAG, Ce:YAG, Ce:GAGG, Ce:GdYAG) have been investigated as stationary phosphor candidates for blue laser driven solid-state lighting without heat sink. The luminous properties of the single crystals are superior compared to the commercial ceramic powder phosphor wheels (Ce3+: Y3Al5O12). The high-power blue laser diode driven temperature increase of the crystals versus quantum efficiency is experimentally measured and discussed. We have carried out realistic measurements at high excitation power levels and at high temperatures. Limitation of phosphors as stationary sources is determined for commercial usage. The measurements were done without any heat sink to see the relative comparison of SCPs in the worst-case scenarios. The results indicate that Gd and Ga addition decreases the luminescence quenching temperature. Based on their superior properties, these single crystals can serve as potential phosphor candidates for high-power blue diode laser driven picture projectors for the green and red channels.

The remarkable performance in perovskite solar cells over the past few years primarily stemmed from an improvement in perovskite film composition and morphology. Antisolvent treatment of perovskite films is one such widely adopted method where a solvent other than that used for precursor solution is introduced to facilitate rapid crystallization of perovskite crystals and to obtain a homogeneous pin-hole free film. Various reports are published recently to understand solvent extraction mechanism, electrical properties and the effect of antisolvent treatment of perovskite film on device performance and stability. Herein, we report some more insights on the charge carrier dynamics, crystallinity and more importantly, the change in energy levels of antisolvent treated perovskite films. The UV–vis absorption, photoluminescence, and photoelectron spectroscopy measurements revealed a downward shift in energy levels of MAPbI3 perovskite when treated with an antisolvent. The energy level shift favoured interfacial charge transfer and resulted in remarkable open-circuit voltage ~1.08 V and photoconversion efficiency 8.21% up from 0.61 V and 1.3% for a non-treated film, respectively for devices prepared at ambient conditions.

Sheet beam vacuum electron tubes are an attractive solution for high-power sources or amplifiers at millimeter-waves. In this article, a novel ${W}$ -band slow wave structure (SWS) for traveling wave tube (TWT) amplifiers supporting a sheet beam is proposed. The SWS is based on a rectangular waveguide with ${H}$ - and ${E}$ -plane loaded (HEL) metal corrugations. A test structure of the proposed HEL SWS with purposely designed input and output couplers was built in the frequency range of 91–98 GHz ( ${W}$ -band). The measured scattering-parameters agree well with the simulations showing ${S}_{11} dB over 10-GHz bandwidth. A TWT was designed and simulated with the HEL SWS. It shows very good gain-bandwidth performance. The SWS is easy to manufacture by low-cost computer numerical controlled (CNC)-milling. The results demonstrated that the HEL SWS is a very good solution to build high-power, wideband millimeter-wave TWTs for a wide range of applications that need high power in a broad frequency range.

There is a need to better understand the peripheral optics of the human eye and their correction. Current eye models have some limitations to accurately predict the wavefront errors for the emmetropic eye over a wide field. The aim here was to develop an anatomically correct optical model of the human eye that closely reproduces the wavefront of an average Caucasian-only emmetropic eye across a wide visual field. Using an optical design program, a schematic eye was constructed based on ocular wavefront measurements of the right eyes of thirty healthy young emmetropic individuals over a wide visual field (from 40° nasal to 40° temporal and up to 20° inferior field). Anatomical parameters, asymmetries, and dispersion properties of the eye’s different optical components were taken into account. A geometry-independent gradient index model was employed to better represent the crystalline lens. The RMS wavefront error, wavefront shapes, dominant Zernike coefficients, nasal-temporal asymmetries, and dispersion properties of the developed schematic eye closely matched the corresponding measured values across the visual field. The developed model can help in the design of wide-field ophthalmic instruments and is useful in the study and simulations of the peripheral optics of the human eye.

Laser sources have been promised for many years to be better light sources as compared to traditional lamps or light-emitting diodes (LEDs) for projectors, which enable projectors having wide colour gamut for vivid image, super brightness and high contrast for the best picture quality, long lifetime for maintain free operation, mercury free, and low power consumption for green environment. A major technology obstacle in using lasers for projection has been the speckle noise caused by to the coherent nature of the lasers. For speckle reduction, current state of the art solutions apply moving parts with large physical space demand. Solutions beyond the state of the art need to be developed such as integrated optical components, hybrid MOEMS devices, and active phase modulators for compact speckle reduction. In this article, major methods reported in the literature for the speckle reduction in laser projectors are presented and explained. With the advancement in semiconductor lasers with largely reduced cost for the red, green and the blue primary colours, and the developed methods for their speckle reduction, it is hoped that the lasers will be widely utilized in different projector applications in the near future.

For travelling-wave tube in millimeter and submillimeter wave frequency bands, an H-plane and E-plane loaded rectangular waveguide is demonstrated as slow-wave structure. The H-plane and E-plane loaded slow-wave structure is designed at W-band for fast verification of the design concept. The cold-test parameters are compared with measurement results.

An Imaging and a non-imaging Laser Driven Static Phosphor Light Engine which utilizes LuAG:Ce(0.3%) single crystal phosphor is proposed. Both designs are compared and their limitations and advantages are discussed.

The design optimization and simulation for high performance of two types of slow wave structures (SWS) for micro-electro-mechanical system (MEMS) terahertz (THz) sources are presented, e.g., THz staggered double vane (SDV) traveling wave tube (TWT) working at center frequency of 220 GHz, H-plane and E-plane loaded (HEL) rectangular TWT working at center frequency of 400 GHz. The structures are able to realize a larger interaction impedance, thereby resulting in higher gain and improved output power of the devices. To further enhance the energy transferring between the electron beam and THz wave, the maximum length of the interaction section can be extended using the phase velocity tapering technique, where the spent electron beam energy can be reused by resynchronizing the phase velocity of the THz signal with electron velocity at the second section of the TWT. As an achievement, improved power of more than 50% is achieved over the operated bandwidth for both designs. The designs have considered the LIGA fabrication for these vacuum MEMS THz sources.

An analysis of slow-wave structure (SWS) for vacuum-electron traveling wave tube is carried out using COMSOL Multiphysics software. A helix SWS is used as an example to model and perform fully coupled 3D electromagnetics cold-simulations and beam-wave interaction hot-simulations. The preliminary COMSOL simulation results show good agreement with calculations from CST studio software.

In this study, a sequential deposition process is used for the fabrication of PEDOT: PSS based inverted planar perovskite solar cell. A small amount of additive deionized water (DI-H2O) was added into PbI2 + Dimethyl formamide (DMF) precursor solution in order to increase the solubility of PbI2 in DMF, and finally to manipulate the surface morphology of the perovskite films. A morphology transition from needle like structure to hexagonal plates, and then needle-like again has been observed as the DI-H2O was added continuously (0.0 wt% to 3.0wt%). The latter one leads to full surface coverage of the perovskite, which is essential for high performance solar cell., {"references":["Z. Xiao, C. Bi, Y. Shao, Q. Dong, Q. Wang, Y. Yuan, et al., \"Efficient, high yield perovskite photovoltaic devices grown by interdiffusion of solution-processed precursor stacking layers,\" Energy & Environmental Science, vol. 7, pp. 2619-2623, 2014.","L. Zheng, Y. Ma, S. Chu, S. Wang, B. Qu, L. 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A simulation study of lateral current injection 1.55 μm laser with strain-compensated multiple quantum-well (MQW) active region (InGaAsP well, InGaAlAs barrier) is presented using self-consistent 2D numerical simulations. The effects of different mesa width and p-doping in the QWs on the carrier and gain uniformity across the active region are explored. A high p-doping in the quantum wells is found to increases the carrier and gain non-uniformity across the active region. The QW region close to the n-contact side does not provide much gain at high optical powers. An asymmetric optical waveguide design is proposed to help reduce the gain non-uniformity across the active region. By shifting the optical modal peak toward the p-side, the modal overlap between the gain region and the optical mode is improved and a more even carrier and gain distribution is obtained. However, due to reduced bandgap of the quaternary InGaAsP p-cladding, an enhanced electron leakage out of the QWs into the p-cladding degrades the laser efficiency and increases the threshold current. Transient time–domain simulations are also performed to determine the small-signal modulation response of the laser promising a simulated high modulation bandwidth suitable for direct-modulation applications.

A comprehensive simulation study of InGaAsP (well)/InGaAlAs(barrier) 1.55 /spl mu/m strain-compensated MQW lasers is presented. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and strain of the barriers and p-doping in the active region. Some preliminary results are also presented for the manufactured lasers using these QWs indicating a good material platform.

We use double reversing wavefront Michelson interferometer to measure the spatial coherence properties of high power broad area Fabry Perot edge emitting blue laser. The measurements are done at different bias current, from lasing threshold up to 1A. The laser is driven in both continuous-wave, CW and pulsed-wave modes. It is found that the magnitude of complex degree of coherence decrease when the laser is driven in pulsed mode. Among driving currents for each mode just for 700 mA bias current more uniform and rather visible interference fringes attained.

In laser projection displays, speckle is the major obstacle which degrades the image quality. In this paper, a demonstration of speckle reduction in a commercial projector by using a Micro-Electro-Mechanical Systems (MEMS) diffuser is presented.

Barker binary phase code of maximum length 13 has previously been used for speckle reduction in line-scan laser projectors, and a speckle contrast factor decreased down to 13% has been achieved. In this article, Barker-like binary phase codes of length longer than 13 are used at an intermediate image plane. It is shown by theoretical calculation that much better speckle reduction with speckle contrast factor up to 6% can be achieved by using longer binary phase codes other than the Barker code. Preliminary experimental results are also presented indictaing good speckle reduction.

Speckle reduction by moving diffuser has been previously studied in display systems with coherent light sources, such as lasers. In this Letter, we propose a motionless diffractive optical element (DOE) for speckle reduction. The DOE was designed based on finite-element method simulations, fabricated using micromachining technology, and characterized for despeckle efficiency. Experiments using a DOE with two gratings have indicated that the speckle was suppressed to 50%, which shows fair agreement with theoretical analysis. With some modification of this DOE, the speckle noise can be reduced to 10% according to the theory.

A nonsequential ray tracing technique is used to calculate the narcissus signature in infrared (IR) imaging cameras having cooled detectors operating in the 7-11 microm waveband. Imaging cameras based on a one-dimensional linear detector array with a scan mirror are simulated. Circularly symmetric diffractive phase surfaces commonly used in modern IR cameras are modeled including multiple diffraction orders in the narcissus retroreflection path to correctly estimate the stray light return signal. An optical design example based on a step-zoom dual field of view optical system is discussed along with the performance curves to elaborate the modeling technique. Optical methods to minimize the narcissus return signal are explained, and modeling results presented. The nonsequential ray tracing technique is found to be an effective method to accurately calculate the narcissus return signal in complex IR cameras having diffractive surfaces.

A Barker binary phase code of maximum length 13 has previously been used for speckle reduction in line-scan laser projectors, and a speckle contrast factor decrease down to 13% has been achieved. In this Letter, Barker-like binary phase codes of lengths longer than 13 are used at an intermediate image plane. It is shown by theoretical calculation that a much better speckle reduction with a speckle contrast factor up to 6% can be achieved by using longer binary phase codes other than the Barker code.

We have recently reported a 980nm GaAs-based three terminal Pnp transistor-vertical-cavity surface-emitting laser (TVCSEL) operating at room temperature with optical power up to 1.8mW. However, the current gain β = ΔIc/ΔIb was near zero just before lasing and became negative after the lasing threshold. The main cause of the negative current gain was found to be a gradual and position-dependent forward-biasing (saturation) of the base-collector junction with increasing bias even before lasing threshold. In this article, detailed multi-physics device simulations are performed to better understand the device physics, and find ways to avoid the premature saturation of the base-collector junction. We have optimized the thickness of the base region as well as its doping concentration and the location of the quantum wells to ensure that the T-VCSEL is in the active mode throughout its range of operation. That is, the emitter-base junction is forward biased and base-collector junction is reversed biased for sweeping the excess charges out of the base region.

We utilize spatial and angular diversity to achieve speckle reduction in laser illumination. Both free-space and imaging geometry configurations are considered. A fast two-dimensional scanning micromirror is employed to steer the laser beam. A simple experimental setup is built to demonstrate the application of our technique in a two-dimensional laser picture projection. Experimental results show that the speckle contrast factor can be reduced down to 5% within the integration time of the detector.

A nonsequential ray tracing technique is used to simulate the narcissus phenomenon in infrared (IR) imaging cameras having cooled detectors. Imaging cameras based on two-dimensional focal plane array detectors are simulated. In a companion article, line-scan imaging cameras based on one-dimensional linear detector arrays are simulated. Diffractive phase surfaces commonly used in modern IR cameras are modeled including multiple diffraction orders in the narcissus retroreflection path to correctly simulate the stray light return signal. Practical optical design examples along with their performance curves are given to elucidate the modeling technique. Optical methods to minimize the narcissus return signal are thoroughly explained, and modeling results are presented. It is shown that the nonsequential ray tracing technique is an effective method to accurately calculate the narcissus return signal in complex IR cameras having diffractive surfaces.