Photonics

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 - 6 May 2019

Cited by 59 | Viewed by 10309

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 3953

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 43 | Viewed by 6085

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 4904

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 24 | Viewed by 6195

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 - 6 Mar 2019

Cited by 10 | Viewed by 4558

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 19 | Viewed by 5355

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 13 | Viewed by 5159

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 56 | Viewed by 11111

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 13 | Viewed by 5981

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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