Photonics

11 pages, 1049 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effects of Performance and Task Duration on Mental Workload during Working Memory Task

by Kosar Khaksari, Emma Condy, John B. Millerhagen, Afrouz A. Anderson, Hadis Dashtestani and Amir H. Gandjbakhche

Photonics 2019, 6(3), 94; https://doi.org/10.3390/photonics6030094 - 28 Aug 2019

Cited by 13 | Viewed by 4684

Abstract

N-back is a working memory (WM) task to study mental workload on the prefrontal cortex (PFC). We assume that the subject’s performance and changes in mental workload over time depends on the length of the experiment. The performance of the participant can change [...] Read more.

N-back is a working memory (WM) task to study mental workload on the prefrontal cortex (PFC). We assume that the subject’s performance and changes in mental workload over time depends on the length of the experiment. The performance of the participant can change positively due to the participant’s learning process or negatively because of objective mental fatigue and/or sleepiness. In this pilot study, we examined the PFC activation of 23 healthy subjects while they performed an N-back task with two different levels of task difficulty (2-, and 3-back). The hemodynamic responses were analyzed along with the behavioral data (correct answers). A comparison was done between the hemodynamic activation and behavioral data between the two different task levels and between the beginning and end of the 3-back task. Our results show that there is a significant difference between the two task levels, which is due to the difference in task complication. In addition, a significant difference was seen between the beginning and end of the 3-back task in both behavioral data and hemodynamics due to the subject’s learning process throughout the experiment. Full article

(This article belongs to the Special Issue Neurophotonics – Optics for the Brain)

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18 pages, 7938 KiB

Open AccessEditor’s ChoiceArticle

Experimental Investigation on the Performances of Innovative PV Vertical Structures

by Gianluca Acciari, Gabriele Adamo, Guido Ala, Alessandro Busacca, Massimo Caruso, Graziella Giglia, Antonino Imburgia, Patrizia Livreri, Rosario Miceli, Antonino Parisi, Filippo Pellitteri, Riccardo Pernice, Pietro Romano, Giuseppe Schettino and Fabio Viola

Photonics 2019, 6(3), 86; https://doi.org/10.3390/photonics6030086 - 31 Jul 2019

Cited by 20 | Viewed by 3599

Abstract

The sustainable development of our planet is considerably related to a relevant reduction of CO₂ global emissions, with building consumption contributing more than 40%. In this scenario, new technological conceptions, such as building-integrated photovoltaic technology, emerged in order to satisfy the requirements [...] Read more.

The sustainable development of our planet is considerably related to a relevant reduction of CO₂ global emissions, with building consumption contributing more than 40%. In this scenario, new technological conceptions, such as building-integrated photovoltaic technology, emerged in order to satisfy the requirements of sustainability imposed by the European Union. Therefore, the aim of this work is to provide a technical and economical comparison of the performances of different vertical-mounted innovative photovoltaic systems, potentially integrated on a building instead of on traditional windows or glass walls. The proposed investigation was carried out by means of experimental tests on three different next-generation vertical structures. The related results are described and discussed, highlighting the advantages and the drawbacks of the proposed technologies. Full article

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15 pages, 2580 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Multi-Distance Frequency-Domain Optical Measurements of Coherent Cerebral Hemodynamics

by Giles Blaney, Angelo Sassaroli, Thao Pham, Nishanth Krishnamurthy and Sergio Fantini

Photonics 2019, 6(3), 83; https://doi.org/10.3390/photonics6030083 - 26 Jul 2019

Cited by 18 | Viewed by 3655

Abstract

We report non-invasive, bilateral optical measurements on the forehead of five healthy human subjects, of 0.1 Hz oscillatory hemodynamics elicited either by cyclic inflation of pneumatic thigh cuffs, or by paced breathing. Optical intensity and the phase of photon-density waves were collected with [...] Read more.

We report non-invasive, bilateral optical measurements on the forehead of five healthy human subjects, of 0.1 Hz oscillatory hemodynamics elicited either by cyclic inflation of pneumatic thigh cuffs, or by paced breathing. Optical intensity and the phase of photon-density waves were collected with frequency-domain near-infrared spectroscopy at seven source-detector distances (11–40 mm). Coherent hemodynamic oscillations are represented by phasors of oxyhemoglobin (O) and deoxyhemoglobin (D) concentrations, and by the vector D/O that represents the amplitude ratio and phase difference of D and O. We found that, on an average, the amplitude ratio (|D/O|) and the phase difference (∠(D/O)) obtained with single-distance intensity at 11–40 mm increase from 0.1° and −330° to 0.2° and −200°, respectively. Single-distance phase and the intensity slope featured a weaker dependence on source-detector separation, and yielded |D/O| and ∠(D/O) values of about 0.5 and −200°, respectively, at distances greater than 20 mm. The key findings are: (1) Single-distance phase and intensity slope are sensitive to deeper tissue compared to single-distance intensity; (2) deeper tissue hemodynamic oscillations, which more closely represent the brain, feature D and O phasors that are consistent with a greater relative flow-to-volume contributions in brain tissue compared to extracerebral, superficial tissue. Full article

(This article belongs to the Special Issue Neurophotonics – Optics for the Brain)

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9 pages, 1391 KiB

Open AccessEditor’s ChoiceLetter

A Robust Method for Adjustment of Laser Speckle Contrast Imaging during Transcranial Mouse Brain Visualization

by Vyacheslav Kalchenko, Anton Sdobnov, Igor Meglinski, Yuri Kuznetsov, Guillaume Molodij and Alon Harmelin

Photonics 2019, 6(3), 80; https://doi.org/10.3390/photonics6030080 - 13 Jul 2019

Cited by 20 | Viewed by 8179

Abstract

Laser speckle imaging (LSI) is a well-known and useful approach for the non-invasive visualization of flows and microcirculation localized in turbid scattering media, including biological tissues (such as brain vasculature, skin capillaries etc.). Despite an extensive use of LSI for brain imaging, the [...] Read more.

Laser speckle imaging (LSI) is a well-known and useful approach for the non-invasive visualization of flows and microcirculation localized in turbid scattering media, including biological tissues (such as brain vasculature, skin capillaries etc.). Despite an extensive use of LSI for brain imaging, the LSI technique has several critical limitations. One of them is associated with inability to resolve a functionality of vessels. This limitation also leads to the systematic error in the quantitative interpretation of values of speckle contrast obtained for different vessel types, such as sagittal sinus, arteries, and veins. Here, utilizing a combined use of LSI and fluorescent intravital microscopy (FIM), we present a simple and robust method to overcome the limitations mentioned above for the LSI approach. The proposed technique provides more relevant, abundant, and valuable information regarding perfusion rate ration between different types of vessels that makes this method highly useful for in vivo brain surgical operations. Full article

(This article belongs to the Special Issue Biomedical Photonics Advances)

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22 pages, 1073 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Photobiomodulation for Alzheimer’s Disease: Has the Light Dawned?

by Michael R. Hamblin

Photonics 2019, 6(3), 77; https://doi.org/10.3390/photonics6030077 - 04 Jul 2019

Cited by 67 | Viewed by 21194

Abstract

Next to cancer, Alzheimer’s disease (AD) and dementia is probably the most worrying health problem facing the Western world today. A large number of clinical trials have failed to show any benefit of the tested drugs in stabilizing or reversing the steady decline [...] Read more.

Next to cancer, Alzheimer’s disease (AD) and dementia is probably the most worrying health problem facing the Western world today. A large number of clinical trials have failed to show any benefit of the tested drugs in stabilizing or reversing the steady decline in cognitive function that is suffered by dementia patients. Although the pathological features of AD consisting of beta-amyloid plaques and tau tangles are well established, considerable debate exists concerning the genetic or lifestyle factors that predispose individuals to developing dementia. Photobiomodulation (PBM) describes the therapeutic use of red or near-infrared light to stimulate healing, relieve pain and inflammation, and prevent tissue from dying. In recent years PBM has been applied for a diverse range of brain disorders, frequently applied in a non-invasive manner by shining light on the head (transcranial PBM). The present review discusses the mechanisms of action of tPBM in the brain, and summarizes studies that have used tPBM to treat animal models of AD. The results of a limited number of clinical trials that have used tPBM to treat patients with AD and dementia are discussed. Full article

(This article belongs to the Special Issue Neurophotonics – Optics for the Brain)

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13 pages, 11248 KiB

Open AccessEditor’s ChoiceArticle

Long-Range, High-Resolution Camera Optical Design for Assisted and Autonomous Driving

by Furkan E. Sahin

Photonics 2019, 6(2), 73; https://doi.org/10.3390/photonics6020073 - 25 Jun 2019

Cited by 18 | Viewed by 27669

Abstract

High-quality cameras are fundamental sensors in assisted and autonomous driving. In particular, long-range forward-facing cameras can provide vital information about the road ahead, including detection and recognition of objects and early hazard warning. These automotive cameras should provide high-resolution images consistently under extreme [...] Read more.

High-quality cameras are fundamental sensors in assisted and autonomous driving. In particular, long-range forward-facing cameras can provide vital information about the road ahead, including detection and recognition of objects and early hazard warning. These automotive cameras should provide high-resolution images consistently under extreme operating conditions of the car for robust operation. This paper aims to introduce the design of fixed-focus, passively athermalized lenses for next-generation automotive cameras. After introducing an overview of essential and desirable features of automotive cameras and state-of-the-art, based on these features, two different camera designs that can achieve traffic sign recognition at 200 m distance are presented. These lenses are designed from scratch, with a unique design approach that starts with a graphical lens material selection tool and arrives at an optimized design with optical design software. Optical system analyses are performed to evaluate the lens designs. The lenses are shown to accomplish high contrast from

- 40

°C to 100 °C and allow for a

4 \times

increase in resolution of automotive cameras. Full article

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15 pages, 4951 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optoacoustic Calcium Imaging of Deep Brain Activity in an Intracardially Perfused Mouse Brain Model

by Oleksiy Degtyaruk, Benedict Mc Larney, Xosé Luís Deán-Ben, Shy Shoham and Daniel Razansky

Photonics 2019, 6(2), 67; https://doi.org/10.3390/photonics6020067 - 12 Jun 2019

Cited by 10 | Viewed by 4965

Abstract

One main limitation of established neuroimaging methods is the inability to directly visualize large-scale neural dynamics in whole mammalian brains at subsecond speeds. Optoacoustic imaging has advanced in recent years to provide unique advantages for real-time deep-tissue observations, which have been exploited for [...] Read more.

One main limitation of established neuroimaging methods is the inability to directly visualize large-scale neural dynamics in whole mammalian brains at subsecond speeds. Optoacoustic imaging has advanced in recent years to provide unique advantages for real-time deep-tissue observations, which have been exploited for three-dimensional imaging of both cerebral hemodynamic parameters and direct calcium activity in rodents. Due to a lack of suitable calcium indicators excitable in the near-infrared window, optoacoustic imaging of neuronal activity at deep-seated areas of the mammalian brain has been impeded by the strong absorption of blood in the visible range of the light spectrum. To overcome this, we have developed and validated an intracardially perfused mouse brain preparation labelled with genetically encoded calcium indicator GCaMP6f that closely resembles in vivo conditions. By overcoming the limitations of hemoglobin-based light absorption, this new technique was used to observe stimulus-evoked calcium dynamics in the brain at penetration depths and spatio-temporal resolution scales not attainable with existing neuroimaging techniques. Full article

(This article belongs to the Special Issue Neurophotonics – Optics for the Brain)

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9 pages, 1026 KiB

Open AccessEditor’s ChoiceArticle

High Concentration Photovoltaics (HCPV) with Diffractive Secondary Optical Elements

by Furkan E. Sahin and Musa Yılmaz

Photonics 2019, 6(2), 68; https://doi.org/10.3390/photonics6020068 - 12 Jun 2019

Cited by 15 | Viewed by 14838

Abstract

Multi-junction solar cells can be economically viable for terrestrial applications when operated under concentrated illuminations. The optimal design of concentrator optics in high concentration photovoltaics (HCPV) systems is crucial for achieving high energy conversion. At a high geometric concentration, chromatic aberration of the [...] Read more.

Multi-junction solar cells can be economically viable for terrestrial applications when operated under concentrated illuminations. The optimal design of concentrator optics in high concentration photovoltaics (HCPV) systems is crucial for achieving high energy conversion. At a high geometric concentration, chromatic aberration of the primary lens can restrict the optical efficiency and acceptance angle. In order to correct chromatic aberration, multi-material, multi-element refractive elements, hybrid refractive/diffractive elements, or multi-element refractive and diffractive systems can be designed. In this paper, the effect of introducing a diffractive surface in the optical path is analyzed. An example two-stage refractive and diffractive optical system is shown to have an optical efficiency of up to 0.87, and an acceptance angle of up to ±0.55° with a 1600× geometric concentration ratio, which is a significant improvement compared to a single-stage concentrator system with a single material. This optical design can be mass-produced with conventional fabrication methods, thus providing a low-cost alternative to other approaches, and the design approach can be generalized to many other solar concentrator systems with different cell sizes and geometric concentration ratios. Full article

(This article belongs to the Special Issue Nonimaging Optics in Solar Energy)

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17 pages, 4723 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Photonic and Iontronic Sensing in GaInAsP Semiconductor Photonic Crystal Nanolasers

by Toshihiko Baba

Photonics 2019, 6(2), 65; https://doi.org/10.3390/photonics6020065 - 10 Jun 2019

Cited by 10 | Viewed by 4384

Abstract

The GaInAsP semiconductor photonic crystal nanolaser operates at room temperature by photopumping and emits near-infrared light at a wavelength longer than 1.3 μm. Immersion of the nanolaser in a solution causes its laser characteristics to change. Observation of this phenomenon makes it possible [...] Read more.

The GaInAsP semiconductor photonic crystal nanolaser operates at room temperature by photopumping and emits near-infrared light at a wavelength longer than 1.3 μm. Immersion of the nanolaser in a solution causes its laser characteristics to change. Observation of this phenomenon makes it possible to perform biosensing without a fluorescent label or a chromogenic substrate. The most common phenomenon between many photonic sensors is that the resonance wavelength reflects the refractive index of attached media; an index change of 2.5 × 10⁻⁴ in the surrounding liquid can be measured through an emission wavelength shift without stabilization. This effect is applicable to detecting environmental toxins and cell behaviors. The laser emission intensity also reflects the electric charge of surface ions. The intensity varies when an electrolyte or a negatively charged deoxyribonucleic acid (DNA), which is positively or negatively charged in water, is accumulated on the surface. This effect allows us to detect the antigen-antibody reaction of a biomarker protein from only the emission intensity without any kind of spectroscopy. In detecting a small amount of DNA or protein, a wavelength shift also appears from its concentration that is 2–3 orders of magnitude lower than those of the conventional chemical methods, such as the enzyme-linked immuno-solvent assay. It is unlikely that this wavelength behavior at such low concentrations is due to the refractive index of the biomolecules. It is observed that the electric charge of surface ions is induced by various means, including plasma exposure and an electrochemical circuit shifting the wavelength. This suggests that the superhigh sensitivity is also due to the effect of charged ions. Thus, we call this device an iontronic photonic sensor. This paper focuses on such a novel sensing scheme of nanolaser sensor, as an example of resonator-based photonic sensors, in addition to the conventional refractive index sensing. Full article

(This article belongs to the Special Issue Photonic Crystal Laser and Related Optical Devices)

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12 pages, 8488 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Propagation of Cylindrical Vector Laser Beams in Turbid Tissue-Like Scattering Media

by Alexander Doronin, Nicolás Vera, Juan P. Staforelli, Pablo Coelho and Igor Meglinski

Photonics 2019, 6(2), 56; https://doi.org/10.3390/photonics6020056 - 24 May 2019

Cited by 22 | Viewed by 5341

Abstract

We explore the propagation of the cylindrical vector beams (CVB) in turbid tissue-like scattering medium in comparison with the conventional Gaussian laser beam. The study of propagation of CVB and Gaussian laser beams in the medium is performed utilizing the unified electric field [...] Read more.

We explore the propagation of the cylindrical vector beams (CVB) in turbid tissue-like scattering medium in comparison with the conventional Gaussian laser beam. The study of propagation of CVB and Gaussian laser beams in the medium is performed utilizing the unified electric field Monte Carlo model. The implemented Monte Carlo model is a part of a generalized on-line computational tool and utilizes parallel computing, executed on the NVIDIA Graphics Processing Units (GPUs) supporting Compute Unified Device Architecture (CUDA). Using extensive computational studies, we demonstrate that after propagation through the turbid tissue-like scattering medium, the degree of fringe contrast for CVB becomes at least twice higher in comparison to the conventional linearly polarized Gaussian beam. The results of simulations agree with the results of experimental studies. Both experimental and theoretical results suggest that there is a high potential of the application of CVB in the diagnosis of biological tissues. Full article

(This article belongs to the Special Issue Biomedical Photonics Advances)

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7 pages, 2606 KiB

Open AccessEditor’s ChoiceLetter

The Role of Electron Transfer in the Nonlinear Response of Ge₂Sb₂Te₅-Mediated Plasmonic Dimers

by Burak Gerislioglu and Arash Ahmadivand

Photonics 2019, 6(2), 52; https://doi.org/10.3390/photonics6020052 - 16 May 2019

Cited by 13 | Viewed by 2844

Abstract

Here, we study the possibility of exquisitely selective harmonic generation based on the concept of charge transfer plasmons (CTPs) in bridged nanoparticle assemblies. By choosing plasmonic dimer nanoantenna, as a fundamental member of the nanocluster family, and bridging the capacitive gap space between [...] Read more.

Here, we study the possibility of exquisitely selective harmonic generation based on the concept of charge transfer plasmons (CTPs) in bridged nanoparticle assemblies. By choosing plasmonic dimer nanoantenna, as a fundamental member of the nanocluster family, and bridging the capacitive gap space between the proximal nanoparticles with an optothermally controllable substance, we judiciously showed that variations in the generation of third harmonic light in the visible regime can be possible by considering distinct states of the functional bridge. To this end, the conductive connection between the nanoparticles is mediated with Ge₂Sb₂Te₅ (GST) with inherently opposite optical and electrical properties below (dielectric, amorphous state) and above 477 °C (conductive, crystalline state). This helped to actively control the transition of charges across the bridge and thereby control the excitation of CTP resonances and provide a switching feature between dipolar and CTP modes. This versatile approach also allowed for production of the intended harmonic signal at different wavelengths depending on the conductivity of the interparticle nanojunction. Full article

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24 pages, 2713 KiB

Open AccessEditor’s ChoiceReview

Multifunctional Smart Optical Fibers: Materials, Fabrication, and Sensing Applications

by Zhengyong Liu, Zhi Feng Zhang, Hwa-Yaw Tam and Xiaoming Tao

Photonics 2019, 6(2), 48; https://doi.org/10.3390/photonics6020048 - 06 May 2019

Cited by 46 | Viewed by 8372

Abstract

This paper presents a review of the development of optical fibers made of multiple materials, particularly including silica glass, soft glass, polymers, hydrogels, biomaterials, Polydimethylsiloxane (PDMS), and Polyperfluoro-Butenylvinyleth (CYTOP). The properties of the materials are discussed according to their various applications. Typical fabrication [...] Read more.

This paper presents a review of the development of optical fibers made of multiple materials, particularly including silica glass, soft glass, polymers, hydrogels, biomaterials, Polydimethylsiloxane (PDMS), and Polyperfluoro-Butenylvinyleth (CYTOP). The properties of the materials are discussed according to their various applications. Typical fabrication techniques for specialty optical fibers based on these materials are introduced, which are mainly focused on extrusion, drilling, and stacking methods depending on the materials’ thermal properties. Microstructures render multiple functions of optical fibers and bring more flexibility in fiber design and device fabrication. In particular, micro-structured optical fibers made from different types of materials are reviewed. The sensing capability of optical fibers enables smart monitoring. Widely used techniques to develop fiber sensors, i.e., fiber Bragg grating and interferometry, are discussed in terms of sensing principles and fabrication methods. Lastly, sensing applications in oil/gas, optofluidics, and particularly healthcare monitoring using specialty optical fibers are demonstrated. In comparison with conventional silica-glass single-mode fiber, state-of-the-art specialty optical fibers provide promising prospects in sensing applications due to flexible choices in materials and microstructures. Full article

(This article belongs to the Special Issue Polymer Optical Fibre)

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7 pages, 2622 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Exploiting the Nonlinear Dynamics of Optically Injected Semiconductor Lasers for Optical Sensing

by Maria S. Torre and Cristina Masoller

Photonics 2019, 6(2), 45; https://doi.org/10.3390/photonics6020045 - 24 Apr 2019

Cited by 4 | Viewed by 3421

Abstract

Optically injected semiconductor lasers are known to display a rich variety of dynamic behaviours, including the emission of excitable pulses, and of rare giant pulses (often referred to as optical rogue waves). Here, we use a well-known rate equation model to explore the [...] Read more.

Optically injected semiconductor lasers are known to display a rich variety of dynamic behaviours, including the emission of excitable pulses, and of rare giant pulses (often referred to as optical rogue waves). Here, we use a well-known rate equation model to explore the combined effect of excitability and extreme pulse emission, for the detection of variations in the strength of the injected field. We find parameter regions where the laser always responds to a perturbation by emitting an optical pulse whose amplitude is above a pre-defined detection threshold. We characterize the sensing capability of the laser in terms of the amplitude and the duration of the perturbation. Full article

(This article belongs to the Special Issue Semiconductor Laser Dynamics: Fundamentals and Applications)

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18 pages, 6508 KiB

Open AccessEditor’s ChoiceReview

Latest Achievements in Polymer Optical Fiber Gratings: Fabrication and Applications

by Rui Min, Beatriz Ortega and Carlos Marques

Photonics 2019, 6(2), 36; https://doi.org/10.3390/photonics6020036 - 29 Mar 2019

Cited by 35 | Viewed by 5231

Abstract

Grating devices in polymer optical fibers (POFs) have attracted huge interest for many potential applications in recent years. This paper presents the state of the art regarding the fabrication of different types of POF gratings, such as uniform, phase-shifted, tilted, chirped, and long [...] Read more.

Grating devices in polymer optical fibers (POFs) have attracted huge interest for many potential applications in recent years. This paper presents the state of the art regarding the fabrication of different types of POF gratings, such as uniform, phase-shifted, tilted, chirped, and long period gratings, and explores potential application scenarios, such as biosensing and optical communications. Full article

(This article belongs to the Special Issue Polymer Optical Fibre)

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12 pages, 5224 KiB

Open AccessEditor’s ChoiceArticle

Verification of Non-thermal Effects of 0.3–0.6 THz-Waves on Human Cultured Cells

by Noriko Yaekashiwa, Hisa Yoshida, Sato Otsuki, Shin’ichiro Hayashi and Kodo Kawase

Photonics 2019, 6(1), 33; https://doi.org/10.3390/photonics6010033 - 25 Mar 2019

Cited by 10 | Viewed by 4184

Abstract

Recent progress has been made in the development of terahertz (THz) waves for practical applications. Few studies that have assessed the biological effects of THz waves have been reported, and the data currently available regarding the safety of THz waves is inadequate. In [...] Read more.

Recent progress has been made in the development of terahertz (THz) waves for practical applications. Few studies that have assessed the biological effects of THz waves have been reported, and the data currently available regarding the safety of THz waves is inadequate. In this study, the effect of THz wave exposure on two cultured cells was assessed using a widely tunable THz source with a 0.3–0.6 THz frequency range, which can be used and increased in one GHz increments. The THz waves applied to the cultured cells were weak enough such that any thermal effects could be disregarded. The influence of THz wave exposure on both the proliferative and metabolic activities of these cells was investigated, as well as the extent of the thermal stress placed on the cells. In this work, no measurable effect on the proliferative or metabolic activities of either cell type was observed following the exposure to THz waves. No differences in the quantity of cDNA related to heat shock protein 70 was detected in either the sham or exposure group. As such, no differences in cellular activity between cells exposed to THz waves and those not exposed were observed. Full article

(This article belongs to the Special Issue Terahertz Photonics)

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8 pages, 1886 KiB

Open AccessEditor’s ChoiceArticle

Long Wavelength (λ > 17 µm) Distributed Feedback Quantum Cascade Lasers Operating in a Continuous Wave at Room Temperature

by Hoang Nguyen Van, Zeineb Loghmari, Hadrien Philip, Michael Bahriz, Alexei N. Baranov and Roland Teissier

Photonics 2019, 6(1), 31; https://doi.org/10.3390/photonics6010031 - 21 Mar 2019

Cited by 19 | Viewed by 5144

Abstract

The extension of the available spectral range covered by quantum cascade lasers (QCL) would allow one to address new molecular spectroscopy applications, in particular in the long wavelength domain of the mid-infrared. We report in this paper the realization of distributed feedback (DFB) [...] Read more.

The extension of the available spectral range covered by quantum cascade lasers (QCL) would allow one to address new molecular spectroscopy applications, in particular in the long wavelength domain of the mid-infrared. We report in this paper the realization of distributed feedback (DFB) QCLs, made of InAs and AlSb, that demonstrated a continuous wave (CW) and a single mode emission at a wavelength of 17.7 µm, with output powers in the mW range. This is the longest wavelength for DFB QCLs, and for any QCLs or semiconductor lasers in general, operating in a CW at room temperature. Full article

(This article belongs to the Special Issue Selected papers from “International Quantum Cascade Laser School and Workshop 2018”)

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11 pages, 2574 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Design of Optical Circuit-Analog Absorbers through Electrically Small Nanoparticles

by Alessio Monti, Andrea Alù, Alessandro Toscano and Filiberto Bilotti

Photonics 2019, 6(1), 26; https://doi.org/10.3390/photonics6010026 - 06 Mar 2019

Cited by 10 | Viewed by 3963

Abstract

In the last few years, the perfect absorption of light has become an important research topic due to its dramatic impact in photovoltaics, photodetectors, color filters and thermal emitters. While broadband optical absorption is relatively easy to achieve using bulky devices, today there [...] Read more.

In the last few years, the perfect absorption of light has become an important research topic due to its dramatic impact in photovoltaics, photodetectors, color filters and thermal emitters. While broadband optical absorption is relatively easy to achieve using bulky devices, today there is a strong need and interest in achieving the same effects by employing nanometric structures that are compatible with modern nanophotonic components. In this paper, we propose a general procedure to design broadband nanometer-scale absorbers working in the optical spectrum. The proposed devices, which can be considered an extension to optics of microwave circuit-analog absorbers, consist of several layers containing arrays of elongated nanoparticles, whose dimensions are engineered to control both the absorption level and the operational bandwidth. By combining a surface-impedance homogenization and an equivalent transmission-line formalism, we define a general analytical procedure that can be employed to achieve a final working design. As a relevant example, we show that the proposed approach allows designing an optical absorber exhibiting a 20% fractional bandwidth on a thickness of λ/4 at the central frequency of operation. Full-wave results confirming the effectiveness of the analytical findings, as well as some considerations about the experimental realization of the proposed devices are provided. Full article

(This article belongs to the Special Issue Metamaterials for Advanced Photonic and Plasmonic Applications – Selected Papers from Metamaterials’2018)

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13 pages, 1097 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

International System of Units (SI) Traceable Noise-Equivalent Power and Responsivity Characterization of Continuous Wave ErAs:InGaAs Photoconductive Terahertz Detectors

by Anuar de Jesus Fernandez Olvera, Axel Roggenbuck, Katja Dutzi, Nico Vieweg, Hong Lu, Arthur C. Gossard and Sascha Preu

Photonics 2019, 6(1), 15; https://doi.org/10.3390/photonics6010015 - 13 Feb 2019

Cited by 15 | Viewed by 4498

Abstract

A theoretical model for the responsivity and noise-equivalent power (NEP) of photoconductive antennas (PCAs) as coherent, homodyne THz detectors is presented. The model is validated by comparison to experimental values obtained for two ErAs:InGaAs PCAs. The responsivity and NEP were obtained from the [...] Read more.

A theoretical model for the responsivity and noise-equivalent power (NEP) of photoconductive antennas (PCAs) as coherent, homodyne THz detectors is presented. The model is validated by comparison to experimental values obtained for two ErAs:InGaAs PCAs. The responsivity and NEP were obtained from the measured rectified current, the current noise floor in the PCAs, and the incoming THz power for the same conditions. Since the THz power measurements are performed with a pyroelectric detector calibrated by the National Metrology Institute of Germany (PTB), the experimentally obtained values are directly traceable to the International System of Units (SI) for the described conditions. The agreement between the presented model and the experimental results is excellent using only one fitting parameter. A very low NEP of 1.8 fW/Hz at 188.8 GHz is obtained at room temperature. Full article

(This article belongs to the Special Issue Terahertz Photonics)

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12 pages, 6513 KiB

Open AccessEditor’s ChoiceArticle

A Bio-Compatible Fiber Optic pH Sensor Based on a Thin Core Interferometric Technique

by Magnus Engholm, Krister Hammarling, Henrik Andersson, Mats Sandberg and Hans-Erik Nilsson

Photonics 2019, 6(1), 11; https://doi.org/10.3390/photonics6010011 - 30 Jan 2019

Cited by 10 | Viewed by 4351

Abstract

There is an increasing demand for compact, reliable and versatile sensor concepts for pH-level monitoring within several industrial, chemical as well as bio-medical applications. Many pH sensors concepts have been proposed, however, there is still a need for improved sensor solutions with respect [...] Read more.

There is an increasing demand for compact, reliable and versatile sensor concepts for pH-level monitoring within several industrial, chemical as well as bio-medical applications. Many pH sensors concepts have been proposed, however, there is still a need for improved sensor solutions with respect to reliability, durability and miniaturization but also for multiparameter sensing. Here we present a conceptual verification, which includes theoretical simulations as well as experimental evaluation of a fiber optic pH-sensor based on a bio-compatible pH sensitive material not previously used in this context. The fiber optic sensor is based on a Mach-Zehnder interferometric technique, where the pH sensitive material is coated on a short, typically 20-25 mm thin core fiber spliced between two standard single mode fibers. The working principle of the sensor is simulated by using COMSOL Multiphysics. The simulations are used as a guideline for the construction of the sensors that have been experimentally evaluated in different liquids with pH ranging from 1.95 to 11.89. The results are promising, showing the potential for the development of bio-compatible fiber optic pH sensor with short response time, high sensitivity and broad measurement range. The developed sensor concept can find future use in many medical- or bio-chemical applications as well as in environmental monitoring of large areas. Challenges encountered during the sensor development due to variation in the design parameters are discussed. Full article

(This article belongs to the Special Issue Advanced Optical Materials and Devices)

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40 pages, 14703 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Trends and Advances of Silicon-Based Integrated Microwave Photonics

by Reza Maram, Saket Kaushal, José Azaña and Lawrence R Chen

Photonics 2019, 6(1), 13; https://doi.org/10.3390/photonics6010013 - 30 Jan 2019

Cited by 43 | Viewed by 9043

Abstract

Multitude applications of photonic devices and technologies for the generation and manipulation of arbitrary and random microwave waveforms, at unprecedented processing speeds, have been proposed in the literature over the past three decades. This class of photonic applications for microwave engineering is known [...] Read more.

Multitude applications of photonic devices and technologies for the generation and manipulation of arbitrary and random microwave waveforms, at unprecedented processing speeds, have been proposed in the literature over the past three decades. This class of photonic applications for microwave engineering is known as microwave photonics (MWP). The vast capabilities of MWP have allowed the realization of key functionalities which are either highly complex or simply not possible in the microwave domain alone. Recently, this growing field has adopted the integrated photonics technologies to develop microwave photonic systems with enhanced robustness as well as with a significant reduction of size, cost, weight, and power consumption. In particular, silicon photonics technology is of great interest for this aim as it offers outstanding possibilities for integration of highly-complex active and passive photonic devices, permitting monolithic integration of MWP with high-speed silicon electronics. In this article, we present a review of recent work on MWP functions developed on the silicon platform. We particularly focus on newly reported designs for signal modulation, arbitrary waveform generation, filtering, true-time delay, phase shifting, beam steering, and frequency measurement. Full article

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13 pages, 6890 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Multi-Spectral Quantum Cascade Lasers on Silicon With Integrated Multiplexers

by Eric J. Stanton, Alexander Spott, Jon Peters, Michael L. Davenport, Aditya Malik, Nicolas Volet, Junqian Liu, Charles D. Merritt, Igor Vurgaftman, Chul Soo Kim, Jerry R. Meyer and John E. Bowers

Photonics 2019, 6(1), 6; https://doi.org/10.3390/photonics6010006 - 24 Jan 2019

Cited by 11 | Viewed by 5157

Abstract

Multi-spectral midwave-infrared (mid-IR) lasers are demonstrated by directly bonding quantum cascade epitaxial gain layers to silicon-on-insulator (SOI) waveguides with arrayed waveguide grating (AWG) multiplexers. Arrays of distributed feedback (DFB) and distributed Bragg-reflection (DBR) quantum cascade lasers (QCLs) emitting at ∼4.7 µm wavelength are [...] Read more.

Multi-spectral midwave-infrared (mid-IR) lasers are demonstrated by directly bonding quantum cascade epitaxial gain layers to silicon-on-insulator (SOI) waveguides with arrayed waveguide grating (AWG) multiplexers. Arrays of distributed feedback (DFB) and distributed Bragg-reflection (DBR) quantum cascade lasers (QCLs) emitting at ∼4.7 µm wavelength are coupled to AWGs on the same chip. Low-loss spectral beam combining allows for brightness scaling by coupling the light generated by multiple input QCLs into the fundamental mode of a single output waveguide. Promising results are demonstrated and further improvements are in progress. This device can lead to compact and sensitive chemical detection systems using absorption spectroscopy across a broad spectral range in the mid-IR as well as a high-brightness multi-spectral source for power scaling. Full article

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