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Photonics, Volume 3, Issue 3 (September 2016)

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Open AccessArticle
Experimental Study of Light Propagation in Apple Tissues Using a Multispectral Imaging System
Received: 9 August 2016 / Revised: 12 September 2016 / Accepted: 12 September 2016 / Published: 18 September 2016
Cited by 3 | Viewed by 1615 | PDF Full-text (3260 KB) | HTML Full-text | XML Full-text
Abstract
This work aimed at highlighting the role played by the skin in the light propagation through the apple flesh. A multispectral Visible-Near Infrared (Vis-NIR) steady-state imaging setup based on the use of four continuous laser sources (633, 763, 784, and 852 nm) and [...] Read more.
This work aimed at highlighting the role played by the skin in the light propagation through the apple flesh. A multispectral Visible-Near Infrared (Vis-NIR) steady-state imaging setup based on the use of four continuous laser sources (633, 763, 784, and 852 nm) and a charge–coupled–device (CCD) camera was developed to record light diffusion inside apple tissues. Backscattering images and light reflectance profiles were studied to reveal optical features of three whole and half-cut apple varieties with and without skin. The optical absorption and scattering properties (μa, μ’s) of intact apples and peeled apples were also retrieved in reflectance mode, using an optimal sensing range of 2.8–10 mm. A relative difference for Δμa ranging from 3.4% to 24.7% was observed for intact apples with respect to peeled apples. Under the same conditions, no significant changes were noted for Δμ’s, which ranged from 0.1% to 1.7%. These findings show that the apple skin cannot be ignored when using Vis-NIR optical imaging as a non-destructive sensing means to reveal major quality attributes of fruits. Full article
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Open AccessArticle
Low Loss Electro-Optic Polymer Based Fast Adaptive Phase Shifters Realized in Silicon Nitride and Oxynitride Waveguide Technology
Received: 29 July 2016 / Revised: 21 August 2016 / Accepted: 23 August 2016 / Published: 26 August 2016
Cited by 3 | Viewed by 1910 | PDF Full-text (2223 KB) | HTML Full-text | XML Full-text
Abstract
We present a comprehensive study on how to design and fabricate low loss electro-optic phase shifters based on an electro-optic polymer and the silicon nitride and silicon oxynitride waveguide material systems. The loss mechanisms of phase shifters with an electro-optic (EO) polymer cladding [...] Read more.
We present a comprehensive study on how to design and fabricate low loss electro-optic phase shifters based on an electro-optic polymer and the silicon nitride and silicon oxynitride waveguide material systems. The loss mechanisms of phase shifters with an electro-optic (EO) polymer cladding are analyzed in detail and design solutions to achieve lowest losses are presented. In order to verify the low loss design a proof of concept prototype phase shifter was fabricated, which exhibits an attenuation of 0.8 dB/cm at 1550 nm and an electro-optic efficiency factor of 27%. Furthermore, the potential of this class of phase shifters is evaluated in numerical simulations, from which the optimal design parameters and achievable figures of merit were derived. The presented phase shifter design has its potential for application in fast adaptive multi stage devices for optical signal processing. Full article
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Open AccessCommunication
Photodynamic Therapy-Induced Microvascular Changes in a Nonmelanoma Skin Cancer Model Assessed by Photoacoustic Microscopy and Diffuse Correlation Spectroscopy
Received: 18 July 2016 / Revised: 31 July 2016 / Accepted: 2 August 2016 / Published: 5 August 2016
Cited by 2 | Viewed by 1524 | PDF Full-text (1338 KB) | HTML Full-text | XML Full-text
Abstract
One of the main mechanisms of action for photodynamic therapy (PDT) is the destruction of tumor vasculature. We observed the PDT-induced vasculature destruction in a mouse model of skin cancer using two techniques: Photoacoustic microscopy (PAM) and diffuse correlation spectroscopy (DCS). PAM showed [...] Read more.
One of the main mechanisms of action for photodynamic therapy (PDT) is the destruction of tumor vasculature. We observed the PDT-induced vasculature destruction in a mouse model of skin cancer using two techniques: Photoacoustic microscopy (PAM) and diffuse correlation spectroscopy (DCS). PAM showed high-resolution images of the abnormal microvasculature near the establishing tumor area at pre-PDT, as well as the subsequent destruction of those vessels post-PDT. DCS indicated a significant blood flow decrease after PDT, confirming the vascular destruction. Noninvasive assessment of vascular changes may be indicative of therapy response. Full article
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Open AccessArticle
Frequency Tuning and Modulation of a Quantum Cascade Laser with an Integrated Resistive Heater
Received: 23 June 2016 / Revised: 25 July 2016 / Accepted: 26 July 2016 / Published: 30 July 2016
Cited by 4 | Viewed by 1726 | PDF Full-text (3508 KB) | HTML Full-text | XML Full-text
Abstract
We present a detailed experimental investigation of the use of a novel actuator for frequency tuning and modulation in a quantum cascade laser (QCL) based on a resistive integrated heater (IH) placed close to the active region. This new actuator is attractive for [...] Read more.
We present a detailed experimental investigation of the use of a novel actuator for frequency tuning and modulation in a quantum cascade laser (QCL) based on a resistive integrated heater (IH) placed close to the active region. This new actuator is attractive for molecular spectroscopy applications as it enables fast tuning of the QCL wavelength with a minor influence on the optical output power, and is electrically-controlled. Using a spectroscopic setup comprising a low-pressure gas cell, we measured the tuning and modulation properties of a QCL emitting at 7.8 μm as a function of the active region and IH currents. We show that a current step applied to the IH enables the laser frequency to be switched by 500 MHz in a few milliseconds, as fast as for a step of the current in the active region, and limited by heat dissipation towards the laser sub-mount. The QCL optical frequency can be modulated up to ~100 kHz with the IH current, which is one order of magnitude slower than for the QCL current, but sufficient for many spectroscopic applications. We discuss the experimental results using a thermal model of the heat transfer in terms of cascaded low-pass filters and extract the respective cut-off frequencies. Finally, we present a proof-of-principle experiment of wavelength modulation spectroscopy of a N2O transition performed with a modulation of the IH current and show some potential benefits in comparison to QCL current modulation, which results from the reduced associated amplitude modulation. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle
Ar+-Implanted Si-Waveguide Photodiodes for Mid-Infrared Detection
Received: 30 June 2016 / Revised: 18 July 2016 / Accepted: 22 July 2016 / Published: 27 July 2016
Cited by 1 | Viewed by 1414 | PDF Full-text (1680 KB) | HTML Full-text | XML Full-text
Abstract
Complementary metal-oxide-semiconductor (CMOS)-compatible Ar+-implanted Si-waveguide p-i-n photodetectors operating in the mid-infrared (2.2 to 2.3 µm wavelengths) are demonstrated at room temperature. Responsivities exceeding 21 mA/W are measured at a 5 V reverse bias with an estimated internal quantum efficiency of 3.1%–3.7%. [...] Read more.
Complementary metal-oxide-semiconductor (CMOS)-compatible Ar+-implanted Si-waveguide p-i-n photodetectors operating in the mid-infrared (2.2 to 2.3 µm wavelengths) are demonstrated at room temperature. Responsivities exceeding 21 mA/W are measured at a 5 V reverse bias with an estimated internal quantum efficiency of 3.1%–3.7%. The dark current is found to vary from a few nanoamps down to less than 11 pA after post-implantation annealing at 350 °C. Linearity is demonstrated over four orders of magnitude, confirming a single-photon absorption process. The devices demonstrate a higher thermal processing budget than similar Si+-implanted devices and achieve higher responsivity after annealing up to 350 °C. Full article
(This article belongs to the Special Issue Advanced Photodetectors Devices and Technologies)
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Open AccessReview
Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics
Received: 22 June 2016 / Revised: 19 July 2016 / Accepted: 21 July 2016 / Published: 25 July 2016
Cited by 6 | Viewed by 2161 | PDF Full-text (13829 KB) | HTML Full-text | XML Full-text
Abstract
The considerably higher power and wider frequency coverage available from quantum cascade lasers (QCLs) in comparison to lead salt diode lasers has led to substantial advances when QCLs are used in pure and applied infrared spectroscopy. Furthermore, they can be used in both [...] Read more.
The considerably higher power and wider frequency coverage available from quantum cascade lasers (QCLs) in comparison to lead salt diode lasers has led to substantial advances when QCLs are used in pure and applied infrared spectroscopy. Furthermore, they can be used in both pulsed and continuous wave (cw) operation, opening up new possibilities in quantitative time resolved applications in plasmas both in the laboratory and in industry as shown in this article. However, in order to determine absolute concentrations accurately using pulsed QCLs, careful attention has to be paid to features like power saturation phenomena. Hence, we begin with a discussion of the non-linear effects which must be considered when using short or long pulse mode operation. More recently, cw QCLs have been introduced which have the advantage of higher power, better spectral resolution and lower fluctuations in light intensity compared to pulsed devices. They have proved particularly useful in sensing applications in plasmas when very low concentrations have to be monitored. Finally, the use of cw external cavity QCLs (EC-QCLs) for multi species detection is described, using a diagnostics study of a methane/nitrogen plasma as an example. The wide frequency coverage of this type of QCL laser, which is significantly broader than from a distributed feedback QCL (DFB-QCL), is a substantial advantage for multi species detection. Therefore, cw EC-QCLs are state of the art devices and have enormous potential for future plasma diagnostic studies. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle
Development of a Multi-Objective Evolutionary Algorithm for Strain-Enhanced Quantum Cascade Lasers
Received: 1 June 2016 / Revised: 16 July 2016 / Accepted: 18 July 2016 / Published: 22 July 2016
Cited by 1 | Viewed by 1767 | PDF Full-text (524 KB) | HTML Full-text | XML Full-text
Abstract
An automated design approach using an evolutionary algorithm for the development of quantum cascade lasers (QCLs) is presented. Our algorithmic approach merges computational intelligence techniques with the physics of device structures, representing a design methodology that reduces experimental effort and costs. The algorithm [...] Read more.
An automated design approach using an evolutionary algorithm for the development of quantum cascade lasers (QCLs) is presented. Our algorithmic approach merges computational intelligence techniques with the physics of device structures, representing a design methodology that reduces experimental effort and costs. The algorithm was developed to produce QCLs with a three-well, diagonal-transition active region and a five-well injector region. Specifically, we applied this technique to Al x Ga 1 - x As/In y Ga 1 - y As strained active region designs. The algorithmic approach is a non-dominated sorting method using four aggregate objectives: target wavelength, population inversion via longitudinal-optical (LO) phonon extraction, injector level coupling, and an optical gain metric. Analysis indicates that the most plausible device candidates are a result of the optical gain metric and a total aggregate of all objectives. However, design limitations exist in many of the resulting candidates, indicating need for additional objective criteria and parameter limits to improve the application of this and other evolutionary algorithm methods. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle
Fractional Effective Charges and Misner-Wheeler Charge without Charge Effect in Metamaterials
Received: 22 May 2016 / Revised: 6 July 2016 / Accepted: 6 July 2016 / Published: 8 July 2016
Viewed by 1389 | PDF Full-text (2544 KB) | HTML Full-text | XML Full-text
Abstract
Transformation optics enables engineering of the effective topology and dimensionality of the optical space in metamaterials. Nonlinear optics of such metamaterials may mimic Kaluza-Klein theories having one or more kinds of effective charges. As a result, novel photon blockade devices may be realized. [...] Read more.
Transformation optics enables engineering of the effective topology and dimensionality of the optical space in metamaterials. Nonlinear optics of such metamaterials may mimic Kaluza-Klein theories having one or more kinds of effective charges. As a result, novel photon blockade devices may be realized. Here we demonstrate that an electromagnetic wormhole may be designed, which connects two points of such an optical space and changes its effective topological connectivity. Electromagnetic field configurations, which exhibit fractional effective charges, appear as a result of such topology change. Moreover, such effects as Misner-Wheeler “charge without charge” may be replicated. Full article
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Open AccessReview
Recent Advances in Room Temperature, High-Power Terahertz Quantum Cascade Laser Sources Based on Difference-Frequency Generation
Received: 3 June 2016 / Accepted: 1 July 2016 / Published: 7 July 2016
Cited by 10 | Viewed by 2405 | PDF Full-text (2379 KB) | HTML Full-text | XML Full-text
Abstract
We present the current status of high-performance, compact, THz sources based on intracavity nonlinear frequency generation in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources in the power and wall plug efficiency are achieved by systematic optimizing the device’s active [...] Read more.
We present the current status of high-performance, compact, THz sources based on intracavity nonlinear frequency generation in mid-infrared quantum cascade lasers. Significant performance improvements of our THz sources in the power and wall plug efficiency are achieved by systematic optimizing the device’s active region, waveguide, and chip bonding strategy. High THz power up to 1.9 mW and 0.014 mW for pulsed mode and continuous wave operations at room temperature are demonstrated, respectively. Even higher power and efficiency are envisioned based on enhancements in outcoupling efficiency and mid-IR performance. Our compact THz device with high power and wide tuning range is highly suitable for imaging, sensing, spectroscopy, medical diagnosis, and many other applications. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Open AccessArticle
Engineering Multi-Section Quantum Cascade Lasers for Broadband Tuning
Received: 1 June 2016 / Revised: 17 June 2016 / Accepted: 17 June 2016 / Published: 27 June 2016
Cited by 3 | Viewed by 2050 | PDF Full-text (1730 KB) | HTML Full-text | XML Full-text
Abstract
In an effort to overcome current limitations to electrical tuning of quantum cascade lasers, a strategy is proposed which combines heterogeneous quantum cascade laser gain engineering with sampled grating architectures. This approach seeks to not only widen the accessible spectral range for an [...] Read more.
In an effort to overcome current limitations to electrical tuning of quantum cascade lasers, a strategy is proposed which combines heterogeneous quantum cascade laser gain engineering with sampled grating architectures. This approach seeks to not only widen the accessible spectral range for an individual emitter, but also compensate for functional non-uniformity of reflectivity and gain lineshapes. A trial laser with a dual wavelength core is presented which exhibits electroluminescence over a 750 cm−1 range and discrete single mode laser emission over a 700 cm−1 range. Electrical tuning over 180 cm−1 is demonstrated with a simple sampled grating design. A path forward to even wider tuning is also described using more sophisticated gain and grating design principles. Full article
(This article belongs to the Special Issue Quantum Cascade Lasers - Advances and New Applications)
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Photonics EISSN 2304-6732 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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