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Photonics, Volume 5, Issue 4 (December 2018)

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Open AccessReview Terahertz Polarization Imaging and Its Applications
Received: 27 October 2018 / Revised: 30 November 2018 / Accepted: 6 December 2018 / Published: 12 December 2018
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Abstract
This review focuses on several recent research activities regarding precise and fast polarization-sensitive terahertz time-domain spectroscopy systems for imaging purposes, and explains three interesting application examples. Owing to modulation techniques that have recently been developed for the evaluation of the instantaneous terahertz electric-field
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This review focuses on several recent research activities regarding precise and fast polarization-sensitive terahertz time-domain spectroscopy systems for imaging purposes, and explains three interesting application examples. Owing to modulation techniques that have recently been developed for the evaluation of the instantaneous terahertz electric-field (E-field) vector, fast and precise terahertz polarization imaging becomes feasible. This terahertz technology enables high-resolution surface topography, precise understanding of the spatial E-field vector distribution of the focused terahertz pulse, and examination of strain-induced birefringence in polymeric materials. These examples constitute a new application area of terahertz photonics with emphasis on both fundamental optics and industrial applications. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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Open AccessArticle Improving Diagnosis of Cervical Pre-Cancer: Combination of PCA and SVM Applied on Fluorescence Lifetime Images
Received: 15 October 2018 / Revised: 19 November 2018 / Accepted: 26 November 2018 / Published: 10 December 2018
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Abstract
We report a significant improvement in the diagnosis of cervical cancer through a combined application of principal component analysis (PCA) and support vector machine (SVM) on the average fluorescence decay profile of Fluorescence Lifetime Images (FLI) of epithelial hyperplasia (EH) and CIN-I cervical
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We report a significant improvement in the diagnosis of cervical cancer through a combined application of principal component analysis (PCA) and support vector machine (SVM) on the average fluorescence decay profile of Fluorescence Lifetime Images (FLI) of epithelial hyperplasia (EH) and CIN-I cervical tissue samples, obtained ex-vivo. The fast and slow components of double exponential fitted fluorescence lifetimes were found to be higher for EH compared to the lifetimes of CIN-I samples. Application of PCA to the average time-resolved fluorescence decay profiles showed that the 2nd PC, in combination with 1st PC, enhanced the discrimination between EH and CIN-I tissues. Fluorescence lifetime and PC scores were then classified separately by using SVM support vector machine to identify the two. On applying SVM to a combination of fluorescence lifetime and PC scores, diagnostic capability improved significantly. Full article
(This article belongs to the Special Issue Biomedical Photonics Advances)
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Open AccessFeature PaperArticle Super-Oscillatory Metalens at Terahertz for Enhanced Focusing with Reduced Side Lobes
Received: 27 October 2018 / Revised: 16 November 2018 / Accepted: 29 November 2018 / Published: 5 December 2018
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Abstract
In this paper, we design and numerically demonstrate an ultra-thin super-oscillatory metalens with a resolution below the diffraction limit. The zones of the lens are implemented using metasurface concepts with hexagonal unit cells. This way, the transparency and, hence, efficiency is optimized, compared
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In this paper, we design and numerically demonstrate an ultra-thin super-oscillatory metalens with a resolution below the diffraction limit. The zones of the lens are implemented using metasurface concepts with hexagonal unit cells. This way, the transparency and, hence, efficiency is optimized, compared to the conventional transparent–opaque zoning approach that introduces, inevitably, a high reflection in the opaque regions. Furthermore, a novel two-step optimization technique, based on evolutionary algorithms, is developed to reduce the side lobes and boost the intensity at the focus. After the design process, we demonstrate that the metalens is able to generate a focal spot of 0.46λ0 (1.4 times below the resolution limit) at the design focal length of 10λ0 with reduced side lobes (the side lobe level being approximately −11 dB). The metalens is optimized at 0.327 THz, and has been validated with numerical simulations. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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Open AccessReview Broadband Terahertz Spectroscopy of Phonon-Polariton Dispersion in Ferroelectrics
Received: 7 November 2018 / Revised: 28 November 2018 / Accepted: 28 November 2018 / Published: 3 December 2018
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Abstract
Electromagnetic waves at frequencies below the X-ray region strongly couple to the optical vibrational modes in a solid. These coupled excitations have been called phonon polaritons. The relationship of the polariton frequency versus the polariton wavevector shows a remarkable dispersion, especially in the
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Electromagnetic waves at frequencies below the X-ray region strongly couple to the optical vibrational modes in a solid. These coupled excitations have been called phonon polaritons. The relationship of the polariton frequency versus the polariton wavevector shows a remarkable dispersion, especially in the vicinity of the transverse and longitudinal optical mode frequencies. The significant frequency dependence enables valuable applications such as a tunable terahertz radiation source. The polariton dispersion relations of technologically important dielectric and ferroelectric crystals were reviewed in the broad terahertz range using terahertz time-domain spectroscopy, far-infrared spectroscopy, and Raman scattering spectroscopy. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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Open AccessArticle 3D Mueller-Matrix Diffusive Tomography of Polycrystalline Blood Films for Cancer Diagnosis
Received: 15 October 2018 / Revised: 19 November 2018 / Accepted: 23 November 2018 / Published: 1 December 2018
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Abstract
The decomposition of the Mueller matrix of blood films has been carried out using differential matrices with polarized and depolarized parts. The use of a coherent reference wave is applied and the algorithm of digital holographic reconstruction of the field of complex amplitudes
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The decomposition of the Mueller matrix of blood films has been carried out using differential matrices with polarized and depolarized parts. The use of a coherent reference wave is applied and the algorithm of digital holographic reconstruction of the field of complex amplitudes is used. On this basis, the 3D Mueller-matrix diffuse tomography method—the reconstruction of distributions of fluctuations of linear and circular birefringence of depolarizing polycrystalline films of human blood is analytically justified and experimentally tested. The dynamics of the change in the magnitude of the statistical moments of the first-fourth order, which characterize layer-by-layer distributions of fluctuations in the phase anisotropy of the blood film, is examined and analyzed. The most sensitive parameters for prostate cancer are the statistical moments of the third and fourth orders, which characterize the asymmetry and kurtosis of fluctuations in the linear and circular birefringence of blood films. The excellent accuracy of differentiation obtained polycrystalline films of blood from healthy donors and patients with cancer patients was achieved. Full article
(This article belongs to the Special Issue Biomedical Photonics Advances)
Open AccessArticle Performance Analysis of Optical Spatial Modulation in Atmospheric Turbulence Channel
Received: 9 November 2018 / Revised: 21 November 2018 / Accepted: 23 November 2018 / Published: 1 December 2018
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Abstract
In this paper, spatial pulse position modulation (SPPM) is used as a case study to investigate the performance of the optical spatial modulation (SM) technique in outdoor atmospheric turbulence (AT). A closed-form expression for the upper bound on the asymptotic symbol error rate
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In this paper, spatial pulse position modulation (SPPM) is used as a case study to investigate the performance of the optical spatial modulation (SM) technique in outdoor atmospheric turbulence (AT). A closed-form expression for the upper bound on the asymptotic symbol error rate (SER) of SPPM in AT is derived and validated by closely-matching simulation results. The error performance is evaluated in weak to strong AT conditions. As the AT strength increases from weak to strong, the channel fading coefficients become more dispersed and differentiable. Thus, a better error performance is observed under moderate-to-strong AT compared to weak AT. The performance in weak AT can be improved by applying unequal power allocation to make free-space optical communication (FSO) links more distinguishable at the receiver. Receive diversity is considered to mitigate irradiance fluctuation and improve the robustness of the system to turbulence-induced channel fading. The diversity order is computed as half of the number of detectors. Performance comparisons, in terms of energy and spectral efficiencies, are drawn between the SPPM scheme and conventional MIMO schemes such as repetition coding and spatial multiplexing. Full article
(This article belongs to the Special Issue Lightwave Communications and Optical Networks)
Open AccessArticle Absolute and Precise Terahertz-Wave Radar Based on an Amplitude-Modulated Resonant-Tunneling-Diode Oscillator
Received: 29 October 2018 / Revised: 22 November 2018 / Accepted: 23 November 2018 / Published: 27 November 2018
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Abstract
We present the principle of a terahertz-wave radar and its proof-of-concept experimental verification. The radar is based on a 522 GHz resonant-tunneling-diode oscillator, whose terahertz output power can be easily modulated by superimposing the modulation signal on its bias voltage. By using one
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We present the principle of a terahertz-wave radar and its proof-of-concept experimental verification. The radar is based on a 522 GHz resonant-tunneling-diode oscillator, whose terahertz output power can be easily modulated by superimposing the modulation signal on its bias voltage. By using one modulation frequency and measuring the time delay of the returning signal, a relative measurement of the propagation distance is possible; adding a second modulation frequency removes the ambiguity stemming from the periodicity of the modulation sine wave and allows an absolute distance measurement. We verified this measurement method experimentally and obtained a submillimeter precision, as predicted by theory. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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Open AccessArticle Impact of Chirp in High-Capacity Optical Metro Networks Employing Directly-Modulated VCSELs
Received: 31 October 2018 / Revised: 22 November 2018 / Accepted: 23 November 2018 / Published: 27 November 2018
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Abstract
Directly modulated long-wavelength vertical cavity surface emitting lasers (VCSELs) are considered for the implementation of sliceable bandwidth/bitrate variable transceivers for very high capacity transmission (higher than 50 Gb/s per wavelength) in metropolitan area systems characterized by reduced cost, power consumption, and footprint. The
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Directly modulated long-wavelength vertical cavity surface emitting lasers (VCSELs) are considered for the implementation of sliceable bandwidth/bitrate variable transceivers for very high capacity transmission (higher than 50 Gb/s per wavelength) in metropolitan area systems characterized by reduced cost, power consumption, and footprint. The impact of the frequency chirp measured for InP VCSELs with different kinds of design (high-bandwidth very short cavity and widely-tunable with micro electro-mechanical systems (MEMS) top mirror) is analyzed in case of discrete multitone (DMT) direct modulation in combination with 25-GHz wavelength selective switch (WSS) filtering. The maximum transmitted capacity for both dual side- and single side-band DMT modulation is evaluated as a function of the number of crossed nodes in a mesh metro network, comparing VCSEL based transmitters performance also with the case of external electro-absorption modulator use. Finally, the maximum reach achieved based on the received optical signal to noise ratio (OSNR) and the fiber span length is discussed. The results confirm the possibility to use directly-modulated long-wavelength VCSELs for the realization of sliceable bandwidth/bitrate variable transmitters targeting 50-Gb/s capacity per polarization, also in the presence of 5 crossed WSSs for reaches of hundreds of kilometers in multi-span Erbium-doped fiber amplified (EDFA) metro links supported by coherent detection. Full article
(This article belongs to the Special Issue Lightwave Communications and Optical Networks)
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Open AccessFeature PaperReview Key Technologies for THz Wireless Link by Silicon CMOS Integrated Circuits
Received: 28 October 2018 / Revised: 16 November 2018 / Accepted: 20 November 2018 / Published: 23 November 2018
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Abstract
In terahertz-band communication using ultra-high frequencies, compound semiconductors with superior high-frequency performance have been used for research to date. Terahertz communication using the 300 GHz band has nonetheless attracted attention based on the expectation that an unallocated frequency band exceeding 275 GHz can
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In terahertz-band communication using ultra-high frequencies, compound semiconductors with superior high-frequency performance have been used for research to date. Terahertz communication using the 300 GHz band has nonetheless attracted attention based on the expectation that an unallocated frequency band exceeding 275 GHz can be used for communication in the future. Research into wireless transceivers using BiCMOS integrated circuits with silicon germanium transistors and advanced miniaturized CMOS integrated circuits has increased in this 300 GHz band. In this paper, we will outline the terahertz communication technology using silicon integrated circuits available from mass production, and discuss its applications and future. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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Open AccessArticle Optical Multilevel Pulse Width Modulation for Analog Mobile Fronthaul
Received: 30 October 2018 / Revised: 16 November 2018 / Accepted: 20 November 2018 / Published: 23 November 2018
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Abstract
The evolution of radio access networks is towards a centralized architecture (C-RAN), with massive antenna deployments and large radio-frequency bandwidths. In the next future, traditional optical transport technologies based on digital radio over fiber will no longer be able to support the mobile
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The evolution of radio access networks is towards a centralized architecture (C-RAN), with massive antenna deployments and large radio-frequency bandwidths. In the next future, traditional optical transport technologies based on digital radio over fiber will no longer be able to support the mobile fronthaul traffic connecting antennas hosted at remote radio units and centralized baseband units. Analog radio over fiber can be selected to support the mobile fronthaul (MFH) network and, in particular, pulse width modulation (PWM) is a viable alternative for analog signal transport. In order to increase the MFH spectral efficiency, we propose to exploit multilevel PWM (M-PWM) in a wavelength division multiplexing-passive optical network (WDM-PON) network, comparing its performance with a conventional 2-level PWM solution. Experimental results show successful transmission over 7.5-km standard single mode fiber (SSMF) of up to 16 aggregated LTE-like 20-MHz signals with 64-QAM on each subcarrier, while up to eight aggregated LTE-like 20-MHz signals with 256-QAM could be supported. M-PWM thus allows either using higher order modulation formats or aggregating a higher number of LTE channels. Full article
(This article belongs to the Special Issue Lightwave Communications and Optical Networks)
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Open AccessArticle Comparative Modeling of Infrared Fiber Lasers
Received: 23 October 2018 / Revised: 6 November 2018 / Accepted: 7 November 2018 / Published: 12 November 2018
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Abstract
The modeling and design of fiber lasers facilitate the process of their practical realization. Of particular interest during the last few years is the development of lanthanide ion-doped fiber lasers that operate at wavelengths exceeding 2000 nm. There are two main host glass
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The modeling and design of fiber lasers facilitate the process of their practical realization. Of particular interest during the last few years is the development of lanthanide ion-doped fiber lasers that operate at wavelengths exceeding 2000 nm. There are two main host glass materials considered for this purpose, namely fluoride and chalcogenide glasses. Therefore, this study concerned comparative modeling of fiber lasers operating within the infrared wavelength region beyond 2000 nm. In particular, the convergence properties of selected algorithms, implemented within various software environments, were studied with a specific focus on the central processing unit (CPU) time and calculation residual. Two representative fiber laser cavities were considered: One was based on a chalcogenide–selenide glass step-index fiber doped with trivalent dysprosium ions, whereas the other was a fluoride step-index fiber doped with trivalent erbium ions. The practical calculation accuracy was also assessed by comparing directly the results obtained from the different models. Full article
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Open AccessArticle Influence of a Surface Finishing Method on Light Collection Behaviour of PWO Scintillator Crystals
Received: 7 October 2018 / Revised: 30 October 2018 / Accepted: 31 October 2018 / Published: 4 November 2018
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Abstract
In the field of scintillators, high scintillation and light production performance require high-quality crystals. Although the composition and structure of crystals are fundamental in this direction, their ultimate optical performance is strongly dependent on the surface finishing treatment. This paper compares two surface
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In the field of scintillators, high scintillation and light production performance require high-quality crystals. Although the composition and structure of crystals are fundamental in this direction, their ultimate optical performance is strongly dependent on the surface finishing treatment. This paper compares two surface finishing methods in terms of the final structural condition of the surface and the relative light yield performances. The first polishing method is the conventional “Mechanical Diamond Polishing” (MDP) technique. The second polishing technique is a method applied in the electronics industry which is envisaged for finishing the surface treatment of scintillator crystals. This method, named “Chemical Mechanical Polishing” (CMP), is efficient in terms of the cost and material removal rate and is expected to produce low perturbed surface layers, with a possible improvement of the internal reflectivity and, in turn, the light collection efficiency. The two methods have been applied to a lead tungstate PbWO4 (PWO) single crystal due to the wide diffusion of this material in high energy physics (CERN, PANDA project) and diagnostic medical applications. The light yield (LY) values of both the MDP and CMP treated crystals were measured by using the facilities at CERN while their surface structure was investigated by Scanning Electron Microscopy (SEM) and Grazing Incidence X-ray Diffraction (GID). We present here the corresponding optical results and their relationship with the processing conditions and subsurface structure. Full article
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Open AccessArticle Pancharatnam–Berry Optical Elements for Spin and Orbital Angular Momentum Division Demultiplexing
Received: 21 September 2018 / Revised: 28 October 2018 / Accepted: 31 October 2018 / Published: 3 November 2018
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Abstract
A Pancharatnam–Berry optical element is designed, fabricated, and optically characterized for the demultiplexing of beams with different polarization and orbital angular momentum states at the telecom wavelength of 1310 nm. The geometric phase control is achieved by fabricating properly-oriented subwavelength gratings on a
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A Pancharatnam–Berry optical element is designed, fabricated, and optically characterized for the demultiplexing of beams with different polarization and orbital angular momentum states at the telecom wavelength of 1310 nm. The geometric phase control is achieved by fabricating properly-oriented subwavelength gratings on a silicon substrate, inducing a spatially-variant form birefringence. The digital grating pattern is transferred to the silicon substrate with a two-step nanofabrication protocol, using inductively coupled plasma reactive ion etching to transfer the resist pattern generated with high-resolution electron beam lithography. The optical characterization of the sample confirms the expected capability to sort circularly polarized optical beams with different handedness and orbital angular momentum. Encompassing optical element design and silicon photonics, the designed silicon metasurface paves the way to innovative devices for total angular momentum mode division multiplexing with unprecedented levels of integration. Full article
(This article belongs to the Special Issue Optical Angular Momentum in Nanophotonics)
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Open AccessArticle TDM-PON PAM Downstream Transmission for 25 Gbit/s and Beyond
Received: 15 October 2018 / Revised: 29 October 2018 / Accepted: 31 October 2018 / Published: 2 November 2018
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Abstract
The optical access network is currently driving studies on transmissions beyond 10 Gbit/s. This paper reports an analysis of Pulse Amplitude Modulation (PAM), seen as a promising candidate for future Passive Optical Networks (PON). Previous 25 Gbit/s real-time PAM4 results are extrapolated here
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The optical access network is currently driving studies on transmissions beyond 10 Gbit/s. This paper reports an analysis of Pulse Amplitude Modulation (PAM), seen as a promising candidate for future Passive Optical Networks (PON). Previous 25 Gbit/s real-time PAM4 results are extrapolated here with simulations to higher bit rates and a higher number of PAM levels. Our main goal is to evaluate the compliancy of PAM with the existing standards and legacy networks as far as fiber length, optical budget class, and wavelength plan are concerned. The simulations enlighten us as to the challenges of multilevel modulation formats, such as noise and jitter, compared to the currently adopted Non-Return-to-Zero (NRZ). Full article
(This article belongs to the Special Issue Lightwave Communications and Optical Networks)
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Open AccessArticle Spectroscopic Optical Coherence Tomography by Using Multiple Multipole Expansion
Received: 12 August 2018 / Revised: 19 October 2018 / Accepted: 24 October 2018 / Published: 30 October 2018
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Abstract
This paper presents a pre-processing method to remove multiple scattering artifacts in spectroscopic optical coherence tomography (SOCT) using time–frequency analysis approaches. The method uses a multiple multipole expansion approach to model the light fields in SOCT. It is shown that the multiple scattered
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This paper presents a pre-processing method to remove multiple scattering artifacts in spectroscopic optical coherence tomography (SOCT) using time–frequency analysis approaches. The method uses a multiple multipole expansion approach to model the light fields in SOCT. It is shown that the multiple scattered fields can be characterized by higher order terms of the multiple multipole expansion. Hence, the multiple scattering artifact can thus be eliminated by applying the time–frequency transform on the SOCT measurements characterized by the lower order terms. Simulation and experimental results are presented to show the effectiveness of the proposed pre-processing method. Full article
(This article belongs to the Special Issue Biomedical Photonics Advances)
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Open AccessLetter On Stiffness of Optical Self-Injection Locking
Received: 28 September 2018 / Revised: 19 October 2018 / Accepted: 25 October 2018 / Published: 30 October 2018
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Abstract
Spectrally pure semiconductor lasers produced via self-injection locking to high quality factor monolithic optical resonators demonstrate sub-kHz instantaneous linewidth. The lasers are used in photonic sensor systems and microwave photonic oscillators benefitting from the improved spectral purity, the stability and the reduced environmental
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Spectrally pure semiconductor lasers produced via self-injection locking to high quality factor monolithic optical resonators demonstrate sub-kHz instantaneous linewidth. The lasers are used in photonic sensor systems and microwave photonic oscillators benefitting from the improved spectral purity, the stability and the reduced environmental sensitivity of the lasers. The laser frequency stability is defined by both the optical resonator and the optical path of the entire system comprising the laser, the resonator, and the miscellaneous optical components. The impacts of the various destabilization factors are usually convoluted, and it is hardly possible to separate them. In this paper, we report on an experimental study of an influence of the variations of the optical path on the laser frequency stability. We have created a whispering gallery mode optical resonator having the record small thermal sensitivity, on the order of 0.1 ppm/ C, and demonstrated a self-injection locked laser based on this resonator. The measured laser stability is characterized with 1 s Allan deviation of 10 12 , limited by the thermal sensitivity of the optical path between the laser and the resonator. The thermal stabilization on the order of 10 μ K at 1 s is achieved using a standard thermo-electric element. The long term drift of the laser frequency is determined by both the fluctuations of the atmospheric pressure in the laboratory impacting the monolithic resonator and by the optical path instability. Full article
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Open AccessArticle Advances in Optomechatronics: An Automated Tilt-Rotational 3D Scanner for High-Quality Reconstructions
Received: 7 September 2018 / Revised: 23 October 2018 / Accepted: 25 October 2018 / Published: 29 October 2018
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Abstract
3D vision systems are more and more required in a large variety of applications and mostly for mechanical and medical purposes. This paper presents the study and realization of a prototype of a structured light automated tilt-rotational 3D vision system for high-quality reconstructions
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3D vision systems are more and more required in a large variety of applications and mostly for mechanical and medical purposes. This paper presents the study and realization of a prototype of a structured light automated tilt-rotational 3D vision system for high-quality reconstructions of components of various sizes and in cases of freeform and complex surfaces. The main goal of this research work was to develop an instrument with the following main novelties: configurability for different object sizes, high precision and resolution levels and ability to automatically generate the mesh representing the full scanned objects without any intervention of the operator by means of a 2 degrees of freedom automated tilt-rotational mechanical positioning system. A detailed analysis of the instrument and the procedures and results of the performance tests are presented, together with the examination of possible strategies to obtain a better performance, especially by the calibration and the synchronization between the optical and the mechanical systems. As a result, the prototype and the performance parameters resulting from the experimental campaigns, are reported. Full article
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Open AccessArticle Effect of Die Shape and Size on Performance of III-Nitride Micro-LEDs: A Modeling Study
Received: 2 October 2018 / Revised: 22 October 2018 / Accepted: 25 October 2018 / Published: 27 October 2018
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Abstract
Flip-chip truncated-pyramid-shaped blue micro-light-emitting diodes (μ-LEDs), with different inclinations of the mesa facets to the epitaxial layer plane, are studied by simulations, implementing experimental information on temperature-dependent parameters and characteristics of large-size devices. Strong non-monotonous dependence of light extraction efficiency (LEE) on the
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Flip-chip truncated-pyramid-shaped blue micro-light-emitting diodes (μ-LEDs), with different inclinations of the mesa facets to the epitaxial layer plane, are studied by simulations, implementing experimental information on temperature-dependent parameters and characteristics of large-size devices. Strong non-monotonous dependence of light extraction efficiency (LEE) on the inclination angle is revealed, affecting, remarkably, the overall emission efficiency. Without texturing of emitting surfaces, LEE to air up to 54.4% is predicted for optimized shape of the μ-LED dice, which is higher than that of conventional large-size LEDs. The major factors limiting the μ-LED performance are identified, among which, the most critical are the optical losses originated from incomplete light reflection from metallic electrodes and the high p-contact resistance caused by its small area. Optimization of the p-electrode dimensions enables further improvement of high-current wall-plug efficiency of the devices. The roles of surface recombination, device self-heating, current crowding, and efficiency droop at high current densities, in limitation of the μ-LED efficiency, are assessed. A novel approach implementing the characterization data of large-size LED as the input information for simulations is tested successfully. Full article
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Open AccessFeature PaperArticle A Highly Sensitive, Polarization Maintaining Photonic Crystal Fiber Sensor Operating in the THz Regime
Received: 21 September 2018 / Revised: 17 October 2018 / Accepted: 23 October 2018 / Published: 25 October 2018
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Abstract
In this paper, a high sensitivity, polarization preserving photonic crystal fiber (PCF), based on circular air holes for sensing in the terahertz (THz) band, is presented. The finite element method, a practical and precise computational technique for describing the interactions between light and
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In this paper, a high sensitivity, polarization preserving photonic crystal fiber (PCF), based on circular air holes for sensing in the terahertz (THz) band, is presented. The finite element method, a practical and precise computational technique for describing the interactions between light and matter, is used to compute the modal properties of the designed fiber. For the designed PCF, comprising of circular air holes in both the cladding and in the porous core, a relative sensitivity of 73.5% and a high birefringence of 0.013 are achieved at 1.6 THz. The all circular air-hole structure, owing to its simplicity and compatibility with the current fiber draw technique for PCF fabrication, can be realized practically. It is anticipated that the designed fiber can be employed in applications such as detection of biological samples and toxic chemicals, imaging, and spectroscopy. Full article
(This article belongs to the Special Issue Terahertz Photonics)
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Open AccessCommunication Quantification of Cardiomyocyte Beating Frequency Using Fourier Transform Analysis
Received: 26 September 2018 / Revised: 11 October 2018 / Accepted: 17 October 2018 / Published: 19 October 2018
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Abstract
Pacemaker cardiomyocytes of the sinoatrial node (SAN) beat more rapidly than cells of the working myocardium. Beating in SAN cells responds to β-adrenergic and cholinergic signaling by speeding up or slowing, respectively. Beat rate has traditionally been assessed using voltage or calcium sensitive
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Pacemaker cardiomyocytes of the sinoatrial node (SAN) beat more rapidly than cells of the working myocardium. Beating in SAN cells responds to β-adrenergic and cholinergic signaling by speeding up or slowing, respectively. Beat rate has traditionally been assessed using voltage or calcium sensitive dyes, however these may not reflect the true rate of beating because they sequester calcium. Finally, in vitro differentiated cardiomyocytes sometimes briefly pause during imaging giving inaccurate beat rates. We have developed a MATLAB automation to calculate cardiac beat rates directly from video clips based on changes in pixel density at the edges of beating areas. These data are normalized to minimize the effects of secondary movement and are converted to frequency data using a fast Fourier transform (FFT). We find that this gives accurate beat rates even when there are brief pauses in beating. This technique can be used to rapidly assess beating of cardiomyocytes in organoid culture. This technique could also be combined with field scanning techniques to automatically and accurately assess beating within a complex cardiac organoid. Full article
(This article belongs to the Special Issue Biomedical Photonics Advances)
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Open AccessReview High-Power Passive Fiber Components for All-Fiber Lasers and Amplifiers Application—Design and Fabrication
Received: 26 September 2018 / Revised: 9 October 2018 / Accepted: 15 October 2018 / Published: 18 October 2018
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Abstract
The most important components for application in high-power all-fiber lasers and amplifiers are, most of all, power combiners, but also mode field adaptors. This paper summarizes recent achievements in the area of development and fabrication of high-power passive fiber components. The principles of
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The most important components for application in high-power all-fiber lasers and amplifiers are, most of all, power combiners, but also mode field adaptors. This paper summarizes recent achievements in the area of development and fabrication of high-power passive fiber components. The principles of operation and basic design and fabrication criteria, which have to be taken into account while designing the aforementioned components, are explained in detail. The most recent impressive achievements are summarized and described. Full article
(This article belongs to the Special Issue Fiber Lasers)
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Open AccessArticle Design of Silica Multimode Optical Fibers with Extremely Enlarged Core Diameter for Laser-Based Multi-Gigabit Short-Range Optical Networks
Received: 9 September 2018 / Revised: 5 October 2018 / Accepted: 8 October 2018 / Published: 16 October 2018
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Abstract
This work presents an alternative fast and simple method for the design of a refractive index profile of silica multimode optical fibers (MMFs) with extremely enlarged core diameters of up to 100 µm for laser-based multi-gigabit short-range optical networks. We demonstrate some results
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This work presents an alternative fast and simple method for the design of a refractive index profile of silica multimode optical fibers (MMFs) with extremely enlarged core diameters of up to 100 µm for laser-based multi-gigabit short-range optical networks. We demonstrate some results of 100 µm core MMF graded index profile optimization performed by a proposed solution, which provides a selected mode staff differential mode delay (DMD) reduction over the “O”-band under particular launching conditions. Earlier on, a developed alternative model for a piecewise regular multimode fiber optic link operating in a few-mode regime for the computation of laser-excited optical pulse dynamics during its propagation over an irregular silica graded-index MMF with an extremely large core diameter, is utilized to estimate the potentiality of fiber optic links with the described MMFs. Here, we also present the comparison results of the simulation of 10GBase-LX optical signal transmission over 100 µm core MMFs with conventional and optimized graded-index refractive index profiles. Full article
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Open AccessArticle Hairy Polydopamine Particles as Platforms for Photonic and Magnetic Materials
Received: 13 September 2018 / Revised: 9 October 2018 / Accepted: 11 October 2018 / Published: 12 October 2018
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Abstract
By selecting the core materials and grafted-hair polymers, hairy particles with polymer brushes can create various types of functional materials. In recent years, polydopamine (PDA) particles that are obtained by polymerizing dopamine, which is an amino acid derivative, have attracted attention for various
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By selecting the core materials and grafted-hair polymers, hairy particles with polymer brushes can create various types of functional materials. In recent years, polydopamine (PDA) particles that are obtained by polymerizing dopamine, which is an amino acid derivative, have attracted attention for various applications. Herein, we present a novel approach for creating photonic and magnetic materials from hairy PDA particles. By grafting a hydrophilic hair polymer, we have succeeded in producing photonic materials capable of structural color changes. Furthermore, we have demonstrated the preparation of magnetic materials by immobilizing holmium, which is one of the lanthanide elements, by electrostatic interactions onto a cationic hair polymer. These results demonstrate the possibility of hairy PDA particles for a wide range of applications, such as for photonic and magnetic materials. Full article
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Open AccessReview Disaster-Resilient Optical Network Survivability: A Comprehensive Survey
Received: 30 July 2018 / Revised: 3 September 2018 / Accepted: 7 September 2018 / Published: 12 October 2018
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Abstract
Network survivability endeavors to ensure the uninterrupted provisioning of services by the network operators in case of a disaster event. Studies and news reports show that network failures caused by physical attacks and natural disasters have significant impacts on the optical networks. Such
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Network survivability endeavors to ensure the uninterrupted provisioning of services by the network operators in case of a disaster event. Studies and news reports show that network failures caused by physical attacks and natural disasters have significant impacts on the optical networks. Such network failures may lead to a section of a network to cease to function, resulting in non-availability of services and may increase the congestion within the rest of the network. Therefore, fault tolerant and disaster-resilient optical networks have grasped the attention of the research community and have been a critical concern in network studies during the last decade. Several studies on protection and restoration techniques have been conducted to address the network component failures. This study reviews related previous research studies to critically discuss the issues regarding protection, restoration, cascading failures, disaster-based failures, and congestion-aware routing. We have also focused on the problem of simultaneous cascading failures (which may disturb the data traffic within a layer or disrupt the services at upper layers) along with their mitigating techniques, and disaster-aware network survivability. Since traffic floods and network congestion are pertinent problems, they have therefore been discussed in a separate section. In the end, we have highlighted some open issues in the disaster-resilient network survivability for research challenges and discussed them along with their possible solutions. Full article
(This article belongs to the Special Issue Lightwave Communications and Optical Networks)
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Open AccessArticle Holographic Fabrication and Optical Property of Graded Photonic Super-Crystals with a Rectangular Unit Super-Cell
Received: 25 September 2018 / Revised: 9 October 2018 / Accepted: 9 October 2018 / Published: 11 October 2018
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Abstract
Recently developed graded photonic super-crystals show an enhanced light absorption and light extraction efficiency if they are integrated with a solar cell and an organic light emitting device, respectively. In this paper, we present the holographic fabrication of a graded photonic super-crystal with
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Recently developed graded photonic super-crystals show an enhanced light absorption and light extraction efficiency if they are integrated with a solar cell and an organic light emitting device, respectively. In this paper, we present the holographic fabrication of a graded photonic super-crystal with a rectangular unit super-cell. The spatial light modulator-based pixel-by-pixel phase engineering of the incident laser beam provides a high resolution phase pattern for interference lithography. This also provides a flexible design for the graded photonic super-crystals with a different ratio of length over the width of the rectangular unit super-cell. The light extraction efficiency is simulated for the organic light emitting device, where the cathode is patterned with the graded photonic super-crystal. The high extraction efficiency is maintained for different exposure thresholds during the interference lithography. The desired polarization effects are observed for certain exposure thresholds. The extraction efficiency reaches as high as 75% in the glass substrate. Full article
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Open AccessReview New Generation Wearable Antenna Based on Multimaterial Fiber for Wireless Communication and Real-Time Breath Detection
Received: 31 August 2018 / Revised: 20 September 2018 / Accepted: 30 September 2018 / Published: 11 October 2018
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Abstract
Smart textiles and wearable antennas along with broadband mobile technologies have empowered the wearable sensors for significant impact on the future of digital health care. Despite the recent development in this field, challenges related to lack of accuracy, reliability, user’s comfort, rigid form
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Smart textiles and wearable antennas along with broadband mobile technologies have empowered the wearable sensors for significant impact on the future of digital health care. Despite the recent development in this field, challenges related to lack of accuracy, reliability, user’s comfort, rigid form and challenges in data analysis and interpretation have limited their wide-scale application. Therefore, the necessity of developing a new reliable and user friendly approach to face these problems is more than urgent. In this paper, a new generation of wearable antenna is presented, and its potential use as a contactless and non-invasive sensor for human breath detection is demonstrated. The antenna is made from multimaterial fiber designed for short-range wireless network applications at 2.4 GHz frequency. The used composite metal-glass-polymer fibers permits their integration into a textile without compromising comfort or restricting movement of the user due to their high flexibility, and shield efficiently the antenna from the environmental perturbation. The multimaterial fiber approach provided a good radio-frequency emissive properties, while preserving the mechanical and cosmetic properties of the garments. With a smart textile featuring a spiral shape fiber antenna placed on a human chest, a significant shift of the operating frequency of the antenna was observed during the breathing process. The frequency shift is caused by the deformation of the antenna geometry due to the chest expansion, and to the modification of the dielectric properties of the chest during the breath. We demonstrate experimentally that the standard wireless networks, which measure the received signal strength indicator (RSSI) via standard Bluetooth protocol, can be used to reliably detect human breathing and estimate the breathing rate in real time. The mobile platform takes the form of a wearable stretching T-shirt featuring a sensor and a detection base station. The sensor is formed by a spiral-shaped antenna connected to a compact Bluetooth transmitter. Breathing patterns were recorded in the case of female and male volunteers. Although the chest anatomy of females and males is different compared, the sensor’s flexibility allowed recording successfully a breathing rate of 0.3 Hz for the female and 0.5 Hz for the male, which corresponds to a breathing rate of 21 breaths per minutes (bpm) and 30 bpm, respectively. Full article
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Open AccessArticle Mid-Infrared Photonic-Crystal Surface-Emitting Lasers with InGaAs/GaAsSb ‘W’-Type Quantum Wells Grown on InP Substrate
Received: 10 September 2018 / Revised: 28 September 2018 / Accepted: 30 September 2018 / Published: 2 October 2018
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Abstract
InP-based InGaAs/GaAsSb ‘W’-type quantum well (QW) photonic-crystal (PC) surface- emitting lasers (SELs) of 2.2 μm wavelength range are fabricated and room-temperature lasing emissions by optical pumping are demonstrated for the first time. Photonic-crystal surface-emitting laser (PCSEL) devices are investigated in terms of PC
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InP-based InGaAs/GaAsSb ‘W’-type quantum well (QW) photonic-crystal (PC) surface- emitting lasers (SELs) of 2.2 μm wavelength range are fabricated and room-temperature lasing emissions by optical pumping are demonstrated for the first time. Photonic-crystal surface-emitting laser (PCSEL) devices are investigated in terms of PC parameters of etch depth, lattice period, and filling factor. The lasing emissions cover wavelengths from 2182 nm to 2253 nm. The temperature-dependent lasing characteristics are also studied in terms of lattice period. All PCSELs show consistent lasing wavelength shift against temperature at a rate of 0.17 nm/K. The characteristic temperatures of PCSELs are extracted and discussed with respect to wavelength detuning between QW gain peak and PC cavity resonance. Full article
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Open AccessArticle Time- and Phase-Domain Thermal Tomography of Composites
Received: 5 September 2018 / Revised: 24 September 2018 / Accepted: 26 September 2018 / Published: 28 September 2018
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Abstract
Active infrared (IR) thermographic nondestructive testing (NDT) has become a valuable inspection method for composite materials due to its high sensitivity to particular types of defect and high inspection rate. The computer-implemented thermal tomography, based on the analysis of heat diffusion in solids,
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Active infrared (IR) thermographic nondestructive testing (NDT) has become a valuable inspection method for composite materials due to its high sensitivity to particular types of defect and high inspection rate. The computer-implemented thermal tomography, based on the analysis of heat diffusion in solids, involves a specialized treatment of the data obtained by means of active IR thermographic NDT, thus allowing for the “slicing” of materials under testing for a few layers where discontinuity-like defects can be underlined on the noise-free background (binary thermal tomograms). The time-domain thermal tomography is based on the fact that, in a one-sided test, temperature “footprints” of deeper defects appear later in regard to shallower defects. The phase-domain tomography can be applied to collected IR data in a direct way, for instance, by using the Fourier transform, but quantification of results is more difficult because the relationships between phase and defect depth depend on experimental parameters, and the corresponding “phase vs. defect depth” calibration functions are ambiguous. In this study, the time- and phase-domain thermal tomography techniques have been compared on simulated IR thermograms and experimentally applied to the evaluation of carbon fiber reinforced plastic composite containing impact damage defects characterized by impact energy 10, 18, and 63 J. Both tomographic techniques have demonstrated similar results in the reconstruction of thermal tomograms and, in some cases, supplied complementary information about the distribution of single defect zones within impacted areas. Full article
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Open AccessArticle Coupled Chiral Optical Tamm States in Cholesteric Liquid Crystals
Received: 29 August 2018 / Revised: 21 September 2018 / Accepted: 26 September 2018 / Published: 28 September 2018
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Abstract
The modes formed by two coupled chiral optical Tamm states localized at the interfaces between a photonic cholesteric liquid crystal conjugated with polarization-preserving anisotropic mirrors have been analytically and numerically investigated. These modes are only excited at the diffracting polarization of incident light.
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The modes formed by two coupled chiral optical Tamm states localized at the interfaces between a photonic cholesteric liquid crystal conjugated with polarization-preserving anisotropic mirrors have been analytically and numerically investigated. These modes are only excited at the diffracting polarization of incident light. As the cholesteric layer thickness decreases, the spectral splitting of the localized state frequency is predicted. The splitting value depends on the crystal layer thickness. At the nondiffracting circular polarization, the localized modes are not excited, and the system becomes similar to the Fabry–Pérot cavity containing an anisotropic helical structure. Full article
(This article belongs to the Special Issue Nonlinear Dielectric Photonics and Metasurfaces)
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