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Photonics, Volume 3, Issue 3 (September 2016) – 10 articles

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3260 KiB

Open AccessArticle

Experimental Study of Light Propagation in Apple Tissues Using a Multispectral Imaging System

by Mohamed Lamine Askoura, Fabrice Vaudelle and Jean-Pierre L’Huillier

Photonics 2016, 3(3), 50; https://doi.org/10.3390/photonics3030050 - 18 Sep 2016

Cited by 12 | Viewed by 4677

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 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 (μ_a, 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 Δμ_a 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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2223 KiB

Open AccessArticle

Low Loss Electro-Optic Polymer Based Fast Adaptive Phase Shifters Realized in Silicon Nitride and Oxynitride Waveguide Technology

by Lars Baudzus and Peter M. Krummrich

Photonics 2016, 3(3), 49; https://doi.org/10.3390/photonics3030049 - 26 Aug 2016

Cited by 10 | Viewed by 5946

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 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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1338 KiB

Open AccessCommunication

Photodynamic Therapy-Induced Microvascular Changes in a Nonmelanoma Skin Cancer Model Assessed by Photoacoustic Microscopy and Diffuse Correlation Spectroscopy

by Daniel J. Rohrbach, Hakeem Salem, Mehmet Aksahin and Ulas Sunar

Photonics 2016, 3(3), 48; https://doi.org/10.3390/photonics3030048 - 5 Aug 2016

Cited by 13 | Viewed by 5056

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 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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3508 KiB

Open AccessArticle

Frequency Tuning and Modulation of a Quantum Cascade Laser with an Integrated Resistive Heater

by Kutan Gürel, Stéphane Schilt, Alfredo Bismuto, Yves Bidaux, Camille Tardy, Stéphane Blaser, Tobias Gresch and Thomas Südmeyer

Photonics 2016, 3(3), 47; https://doi.org/10.3390/photonics3030047 - 30 Jul 2016

Cited by 9 | Viewed by 5169

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 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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1680 KiB

Open AccessArticle

Ar⁺-Implanted Si-Waveguide Photodiodes for Mid-Infrared Detection

by Brian Souhan, Christine P. Chen, Ming Lu, Aaron Stein, Hassaram Bakhru, Richard R. Grote, Keren Bergman, William M. J. Green and Richard M. Osgood

Photonics 2016, 3(3), 46; https://doi.org/10.3390/photonics3030046 - 27 Jul 2016

Cited by 4 | Viewed by 4223

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%. 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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Full article ">Figure 1
(a) Cross-sectional diagram of the waveguide photodetector with a mode intensity profile for a wavelength of 2.2 µm; (b) Cross section at center of waveguide showing the overlap of the normalized mode intensity with both the defect density and the ion density as calculated using Stopping Range of Ions in Matter (SRIM) (and prior to any annealing or post processing); (c) Waveguide top view indicating the Si waveguide, the Ar+-implant region, doped “wings,” and at the end, the fan-out tapered coupler. Full article ">Figure 2
(a) Photocurrent and dark current for devices annealed at 300 °C and 350 °C; (b) Linearity for devices annealed at 250 °C and 350 °C. Full article ">Figure 3
(a) Responsivity as a function of bias and annealing temperature for a 250 µm Ar+-implanted PD. Significant increases in responsivity were observed after annealing at 150 °C, 200 °C, and 300 °C; (b) Responsivity at a 5 V reverse bias as a function of annealing temperature for various Ar+-implanted photodetectors (PDs) and Si+-implanted PDs. Unlike the peak seen in responsivity for Si+-implanted devices, the responsivity of Ar+ devices increases with higher temperature annealing [<a href="#B12-photonics-03-00046" class="html-bibr">12</a>]. Due to Al reflow as discussed in the text, we are unable to determine the maximum annealing temperature. Full article ">Figure 4
Measured Responsivity for the 250 µm PD versus wavelength after high-temperature annealing. Full article ">

13829 KiB

Open AccessReview

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

by Jürgen Röpcke, Paul B. Davies, Stephan Hamann, Mario Hannemann, Norbert Lang and Jean-Pierre H. Van Helden

Photonics 2016, 3(3), 45; https://doi.org/10.3390/photonics3030045 - 25 Jul 2016

Cited by 23 | Viewed by 7010

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 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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524 KiB

Open AccessArticle

Development of a Multi-Objective Evolutionary Algorithm for Strain-Enhanced Quantum Cascade Lasers

by David Mueller and Gregory Triplett

Photonics 2016, 3(3), 44; https://doi.org/10.3390/photonics3030044 - 22 Jul 2016

Cited by 7 | Viewed by 4508

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.

_{x}

_{1 - x}

As/In

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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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2544 KiB

Open AccessArticle

Fractional Effective Charges and Misner-Wheeler Charge without Charge Effect in Metamaterials

by Igor Smolyaninov

Photonics 2016, 3(3), 43; https://doi.org/10.3390/photonics3030043 - 8 Jul 2016

Cited by 1 | Viewed by 3936

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. 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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Graphical abstract

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Full article ">Figure 1
(a) “Optical space” in an anisotropic uniaxial metamaterial may mimic such topologically non-trivial 3D space as R2 × S1, which is a product of a 2D plane R2 and a circle S1. (b) Schematic view of the “layered” 3D hyperbolic metamaterial made of subwavelength metal and dielectric layers, which can be used to emulate the R2 × S1 space. (c) Example of numerical calculations of electromagnetic field distribution in the xz plane inside the R2 × S1 metamaterial space using Comsol Multiphysics 4.2a (COMSOL, Inc., Burlington, MA, USA). The distances in the xz plane are measured in the units of wavelength. The power flow distribution (calculated using the scattering boundary conditions) is similar to power flow in a multimode planar waveguide. Full article ">Figure 2
(a) Schematic view of a toroidal handlebody, which connects two points of the R2 × S1 metamaterial space and changes its effective topology. (b,c) Numerical simulations of the electromagnetic wormhole performed using the scattering boundary conditions: (b) spatial distribution of ε1, and (c) corresponding spatial distribution of By. The distances in the xz plane are measured in the units of wavelength. Full article ">Figure 2 Cont.
(a) Schematic view of a toroidal handlebody, which connects two points of the R2 × S1 metamaterial space and changes its effective topology. (b,c) Numerical simulations of the electromagnetic wormhole performed using the scattering boundary conditions: (b) spatial distribution of ε1, and (c) corresponding spatial distribution of By. The distances in the xz plane are measured in the units of wavelength. Full article ">Figure 3
Numerical simulations of power flow near the electromagnetic wormhole in the same geometry as in <a href="#photonics-03-00043-f002" class="html-fig">Figure 2</a>b,c, which demonstrates “charge without charge” effect. The average Poynting vector direction is indicated by black arrows. Near the wormhole openings the z components of the Poynting vector S3 are nonzero and have opposite signs, which according to Equations (11)–(14) leads to appearance of opposite contributions to the effective charge of the wormhole openings (the openings are marked by dashed lines). Full article ">Figure 4
If the wormhole geometry exhibits some symmetry (such as symmetry under rotation by either π (a) or 2π/3 (b) radian, the allowed values of effective charges of the wormhole openings may become restricted to some simple fractions of the “elementary charge” e: if such a rotational symmetry is imposed on electromagnetic field configurations, the integer effective charge inside A must be divided equally between the wormhole openings. Full article ">Figure 4 Cont.
If the wormhole geometry exhibits some symmetry (such as symmetry under rotation by either π (a) or 2π/3 (b) radian, the allowed values of effective charges of the wormhole openings may become restricted to some simple fractions of the “elementary charge” e: if such a rotational symmetry is imposed on electromagnetic field configurations, the integer effective charge inside A must be divided equally between the wormhole openings. Full article ">

2379 KiB

Open AccessReview

Recent Advances in Room Temperature, High-Power Terahertz Quantum Cascade Laser Sources Based on Difference-Frequency Generation

by Quanyong Lu and Manijeh Razeghi

Photonics 2016, 3(3), 42; https://doi.org/10.3390/photonics3030042 - 7 Jul 2016

Cited by 40 | Viewed by 6964

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 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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Graphical abstract
Full article ">Figure 1
Schematic of the DFG process between the electron states in a band structure of quantum cascade laser. Full article ">Figure 2
(a) Band structure of a SPR structure at λ ~ 9 µm with large nonlinear DFG susceptibility based on a lattice-matched Ga0.47In0.53As/Al0.48In0.52As material system; and (b) band structure of a strongly-coupled SPR structure at λ ~ 7.8 µm based on a strain-balanced Al0.63In0.37As/Ga0.35In0.65As/Ga0.47In0.53As material system. Full article ">Figure 3
(a) SEM images and (b) the Fourier analysis of the composite DFB gratings with 1 and 4 THz frequency spacing. The white bar in (a) corresponds to 4 µm. Full article ">Figure 4
(a) Schematic of Čerenkov phase matching in a mid-IR quantum cascade lasers; (b) The thermal distributions of the epi-up and epi-down mounted Čerenkov devices; and (c,d) schematic of the epi-down mounting scheme and the SEM image of an epi-down mounted device. Full article ">Figure 5
(a) Recently-demonstrated THz power records of the THz sources based on DFG QCLs at room temperature. THz power (b); spectra (c); and far field (d), as functions of currents for a high-power THz source based on DFG QCLs. Full article ">Figure 6
SEM images of a buried ridge (a) and buried composite DFB grating waveguide (b); the white bars in (a) and (b) correspond to 10 and 2 µm, respectively; (c) P-I-V of a composite DFB THz device at room-temperature CW operation. Inset: CW lasing mid-IR spectrum at 1.62 A; and (d) THz CW power as a function of current. Inset: CW THz spectrum at 1.62 A. Full article ">

1730 KiB

Open AccessArticle

Engineering Multi-Section Quantum Cascade Lasers for Broadband Tuning

by Steven Slivken and Manijeh Razeghi

Photonics 2016, 3(3), 41; https://doi.org/10.3390/photonics3030041 - 27 Jun 2016

Cited by 5 | Viewed by 5669

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 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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