Showing papers in "Photonics in 2016"

Recent Advances and Applications of External Cavity-QCLs towards Hyperspectral Imaging for Standoff Detection and Real-Time Spectroscopic Sensing of Chemicals

Abstract: External-cavity quantum cascade lasers (EC-QCL) are now established as versatile wavelength-tunable light sources for analytical spectroscopy in the mid-infrared (MIR) spectral range We report on the realization of rapid broadband spectral tuning with kHz scan rates by combining a QCL chip with a broad gain spectrum and a resonantly driven micro-opto-electro-mechanical (MOEMS) scanner with an integrated diffraction grating in Littrow configuration The capability for real-time spectroscopic sensing based on MOEMS EC-QCLs is demonstrated by transmission measurements performed on polystyrene reference absorber sheets, as well as on hazardous substances, such as explosives Furthermore, different applications for the EC-QCL technology in spectroscopic sensing are presented These include the fields of process analysis with on- or even inline capability and imaging backscattering spectroscopy for contactless identification of solid and liquid contaminations on surfaces Recent progress in trace detection of explosives and related precursors in relevant environments as well as advances in food quality monitoring by discriminating fresh and mold contaminated peanuts based on their MIR backscattering spectrum is shown

Increasing Surface Plasmons Propagation via Photonic Nanojets with Periodically Spaced 3D Dielectric Cuboids

Abstract: A structure based on periodically arranged 3D dielectric cuboids connected by photonic nanojets (PNJs) is proposed with the aim of increasing the propagation distance of surface plasmon polaritons (SPPs) at the telecom wavelength of 1550 nm. The performance of the structure is evaluated and compared with the case without the cuboids demonstrating that the SPPs propagation length is enhanced by a factor greater than 2, reaching a value of approximately 19λ0, when the gap between the cuboids is 2.5λ0. Also, the dependence of the propagation length with the height of the cubes is evaluated, showing that this parameter is critical for a good performance of the chain. A subwavelength resolution is obtained for all the jets generated at the output of the cuboids.

Quantum Control in Qutrit Systems Using Hybrid Rabi-STIRAP Pulses

Abstract: We introduce and analyze theoretically a procedure that combines slow adiabatic stimulated Raman adiabatic passage (STIRAP) manipulation with short nonadiabatic Rabi pulses to produce any desired three-level state in a qutrit system. In this protocol, the fast pulses create superpositions between the ground state and the first excited state, while the slow pulses transfer an arbitrary population to the second excited state via STIRAP. We demonstrate high-fidelity quantum control of the level populations and phases and we characterize the errors incurred under the breakdown of adiabaticity. In a configuration where an ancillary state is available, we show how to realize a nondemolition monitoring of the relative phases. These methods are general and can be implemented on any experimental platform where a quantum system with at least three accessible energy levels is available. We discuss here in detail experimental implementations in circuit quantum electrodynamics (QED) based on the results obtained with a transmon, where the control of population using the hybrid Rabi-STIRAP sequence has been achieved.

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

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.

Heterogeneously Integrated Distributed Feedback Quantum Cascade Lasers on Silicon

Abstract: Silicon integration of mid-infrared (MIR) photonic devices promises to enable low-cost, compact sensing and detection capabilities that are compatible with existing silicon photonic and silicon electronic technologies. Heterogeneous integration by bonding III-V wafers to silicon waveguides has been employed previously to build integrated diode lasers for wavelengths from 1310 to 2010 nm. Recently, Fabry-Perot Quantum Cascade Lasers integrated on silicon provided a 4800 nm light source for mid-infrared (MIR) silicon photonic applications. Distributed feedback (DFB) lasers are appealing for many high-sensitivity chemical spectroscopic sensing applications that require a single frequency, narrow-linewidth MIR source. While heterogeneously integrated 1550 nm DFB lasers have been demonstrated by introducing a shallow surface grating on a silicon waveguide within the active region, no mid-infrared DFB laser on silicon has been reported to date. Here we demonstrate quantum cascade DFB lasers heterogeneously integrated with silicon-on-nitride-on-insulator (SONOI) waveguides. These lasers emit over 200 mW of pulsed power at room temperature and operate up to 100 °C. Although the output is not single mode, the DFB grating nonetheless imposes wavelength selectivity with 22 nm of thermal tuning.

Integration of Single-Photon Sources and Detectors on GaAs

Abstract: Quantum photonic integrated circuits (QPICs) on a GaAs platform allow the generation, manipulation, routing, and detection of non-classical states of light, which could pave the way for quantum information processing based on photons. In this article, the prototype of a multi-functional QPIC is presented together with our recent achievements in terms of nanofabrication and integration of each component of the circuit. Photons are generated by excited InAs quantum dots (QDs) and routed through ridge waveguides towards photonic crystal cavities acting as filters. The filters with a transmission of 20% and free spectral range ≥66 nm are able to select a single excitonic line out of the complex emission spectra of the QDs. The QD luminescence can be measured by on-chip superconducting single photon detectors made of niobium nitride (NbN) nanowires patterned on top of a suspended nanobeam, reaching a device quantum efficiency up to 28%. Moreover, two electrically independent detectors are integrated on top of the same nanobeam, resulting in a very compact autocorrelator for on-chip g(2)(τ) measurements.

Absorption Properties of Simply Fabricated All-Metal Mushroom Plasmonic Metamaterials Incorporating Tube-Shaped Posts for Multi-Color Uncooled Infrared Image Sensor Applications

Abstract: Wavelength-selective infrared (IR) absorbers have attracted considerable interest due to their potential for a wide range of applications. In particular, they can be employed as advanced uncooled IR sensors that identify objects through their radiation spectra. Herein, we propose a mushroom plasmonic metamaterial absorber incorporating tube-shaped metal posts (MPMAT) for use in the long-wavelength IR (LWIR) region. The MPMAT design consists of a periodic array of thin metal micropatches connected to a thin metal plate via tube-shaped metal posts. Both the micropatches and posts can be constructed simultaneously as a result of the tube-shaped structure of the metal post structure; thus, the fabrication procedure is both simple and low cost. The absorption properties of these MPMATs were assessed both theoretically and experimentally, and the results of both investigations demonstrated that these devices exhibit suitable levels of LWIR absorption regardless of the specific tube-shaped structures employed. It was also found to be possible to tune the absorption wavelength by varying the micropatch width and the inner diameter of the tube-shaped metal posts, and to obtain absorbance values of over 90%. Focal plane array structures based on such MPMATs could potentially serve as high-performance, low-cost, multi-spectral uncooled IR image sensors.

Dual-Section DFB-QCLs for Multi-Species Trace Gas Analysis

Abstract: We report on the dynamic behavior of dual-wavelength distributed feedback (DFB) quantum cascade lasers (QCLs) in continuous wave and intermittent continuous wave operation. We investigate inherent etaloning effects based on spectrally resolved light-current-voltage (LIV) characterization and perform time-resolved spectral analysis of thermal chirping during long (>5 µs) current pulses. The theoretical aspects of the observed behavior are discussed using a combination of finite element method simulations and transfer matrix method calculations of dual-section DFB structures. Based on these results, we demonstrate how the internal etaloning can be minimized using anti-reflective (AR) coatings. Finally, the potential and benefits of these devices for high precision trace gas analysis are demonstrated using a laser absorption spectroscopic setup. Thereby, the atmospherically highly relevant compounds CO2 (including its major isotopologues), CO and N2O are simultaneously determined with a precision of 0.16 ppm, 0.22 ppb and 0.26 ppb, respectively, using a 1-s integration time and an optical path-length of 36 m. This creates exciting new opportunities in the development of compact, multi-species trace gas analyzers.

Wide Spectral Characteristics of Si Photonic Crystal Mach-Zehnder Modulator Fabricated by Complementary Metal-Oxide-Semiconductor Process

Abstract: Optical modulators for optical interconnects require a small size, small voltage, high speed and wide working spectrum. For this purpose, we developed Si slow-light Mach-Zehnder modulators via a 180 nm complementary metal-oxide-semiconductor process. We employed 200 μm lattice-shifted photonic crystal waveguides with interleaved p-n junctions as phase shifters. The group index spectrum of slow light was almost flat at ng ≈ 20 but exhibited ±10% fluctuation over a wavelength bandwidth of 20 nm. The cutoff frequency measured in this bandwidth ranged from 15 to 20 GHz; thus, clear open eyes were observed in the 25 Gbps modulation. However, the fluctuation in ng was reflected in the extinction ratio and bit-error rate. For a stable error-free operation, a 1 dB margin is necessary in the extinction ratio. In addition, we constructed a device with varied values of ng and confirmed that the extinction ratio at this speed was enhanced by larger ng up to 60. However, this larger ng reduced the cutoff frequency because of increased phase mismatch between slow light and radio frequency signals. Therefore, ng available for 25 Gbps modulation is limited to up to 40 for the current device design.

Estimation of BER from Error Vector Magnitude for Optical Coherent Systems

Abstract: This paper presents the estimation of bit error ratio (BER) from error vector magnitude (EVM) for M-ary quadrature amplitude modulation (QAM) formats in optical coherent systems employing carrier phase recovery with differential decoding to compensate for laser phase noise. Simulation results show that the relationship to estimate BER from EVM analysis for data-aided reception can also be applied to nondata-aided reception with a correction factor for different combined linewidth symbol duration product at the target BER of 10 − 3 . It is demonstrated that the calibrated BER, which would otherwise be underestimated without the correction factor, can reliably monitor the performance of optical coherent systems near the target BER for quadrature phase shift keying (QPSK), 16-QAM, and 64-QAM.

Advanced fabrication of single-mode and multi-wavelength MIR-QCLs

Abstract: In this article we present our latest work on the optimization of mid-infrared quantum cascade laser fabrication techniques. Our efforts are focused on low dissipation devices, broad-area high-power photonic crystal lasers, as well as multi-wavelength devices realized either as arrays or multi-section distributed feedback (DFB) devices. We summarize our latest achievements and update them with our most recent results.

Progress in Rapidly-Tunable External Cavity Quantum Cascade Lasers with a Frequency-Shifted Feedback

Abstract: The recent demonstration of external cavity quantum cascade lasers with optical feedback, controlled by an acousto-optic modulator, paves the way to ruggedized infrared laser systems with the capability of tuning the emission wavelength on a microsecond scale. Such systems are of great importance for various critical applications requiring ultra-rapid wavelength tuning, including combustion and explosion diagnostics and standoff detection. In this paper, recent research results on these devices are summarized and the advantages of the new configuration are analyzed in the context of practical applications.

Influence of Ethanol on Breath Acetone Measurements Using an External Cavity Quantum Cascade Laser

Abstract: Broadly tunable external cavity quantum cascade lasers (EC-QCLs) in combination with off-axis integrated cavity enhanced spectroscopy (OA-ICOS) provide high molecular gas sensitivity and selectivity. We used an EC-QCL in the region of 1150–1300 cm−1 in both broadband scan mode, as well as narrow scanning mode around 1216 cm−1, respectively, for detection of acetone in exhaled breath. This wavelength region is essential for accurate determination of breath acetone due to the relative low spectral influence of other endogenous molecules like water, carbon dioxide or methane. We demonstrated that ethanol has a strong spectroscopic influence on the acetone concentration in exhaled breath, an important detail that has been overlooked so far. An ethanol correction is proposed and validated with the reference measurements from a proton-transfer reaction mass spectrometer (PTR-MS) for the same breath samples from ten persons. With the ethanol correction, both broadband and narrowband molecular spectroscopy represent an attractive way to accurately assess the exhaled breath acetone. The importance of considering spectroscopic ethanol influence is essential, especially for the narrowband scans, (e.g., 1216 cm−1), for which the error in determining the acetone concentrations can rise up to 39% if it is not considered.

Design and Analysis of Enhanced Modulation Response in Integrated Coupled Cavities DBR Lasers Using Photon-Photon Resonance

Abstract: In the last few decades, various solutions have been proposed to increase the modulation bandwidth and, consequently, the transmission bit-rate of semiconductor lasers. In this manuscript, we discuss a design procedure for a recently proposed laser cavity realized with the monolithic integration of two distributed Bragg reflector (DBR) lasers allowing one to extend the modulation bandwidth. Such an extension is obtained introducing in the dynamic response a photon-photon resonance (PPR) at a frequency higher than the modulation bandwidth of the corresponding single-section laser. Design guidelines will be proposed, and dynamic small and large signal simulations results, calculated using a finite difference traveling wave (FDTW) numerical simulator, will be discussed to confirm the design results. The effectiveness of the design procedure is verified in a structure with PPR frequency at 35 GHz allowing one to obtain an open eye diagram for a non-return-to-zero (NRZ) digital signal up to 80 GHz . Furthermore, the investigation of the rich dynamics of this structure shows that with proper bias conditions, it is possible to obtain also a tunable self-pulsating signal in a frequency range related to the PPR design.

Measurement of the Phase and Intensity Profile of Surface Plasmon Laser Emission

Abstract: We study the near- and far-field radiation patterns of surface plasmon (SP) lasers in metal hole arrays and observe radially polarized vortex-vector laser beams in both near and far field. Besides the intensity profile, also the complementary phase profile is obtained with a beam block experiment, where we block part of the beam in the near field, measure the resulting changes in the far field, and retrieve the phase using an iterative algorithm. This phase profile provides valuable information on the feedback mechanisms and coherence of the laser and shows that our SP laser operates in a phase-slip mode instead of a pure dark mode. To explain our observations, we extend the standard model for distributed feedback lasers by introducing a position dependence in the optical gain and refractive index.

Applying Quantum Cascade Laser Spectroscopy in Plasma Diagnostics

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.

Quantum Transport Simulation of High-Power 4.6-μm Quantum Cascade Lasers

Abstract: We present a quantum transport simulation of a 4.6- μ m quantum cascade laser (QCL) operating at high power near room temperature. The simulation is based on a rigorous density-matrix-based formalism, in which the evolution of the single-electron density matrix follows a Markovian master equation in the presence of applied electric field and relevant scattering mechanisms. We show that it is important to allow for both position-dependent effective mass and for effective lowering of very thin barriers in order to obtain the band structure and the current-field characteristics comparable to experiment. Our calculations agree well with experiments over a wide range of temperatures. We predict a room-temperature threshold field of 62 . 5 kV/cm and a characteristic temperature for threshold-current-density variation of T 0 = 199 K . We also calculate electronic in-plane distributions, which are far from thermal, and show that subband electron temperatures can be hundreds to thousands of degrees higher than the heat sink. Finally, we emphasize the role of coherent tunneling current by looking at the size of coherences, the off-diagonal elements of the density matrix. At the design lasing field, efficient injection manifests itself in a large injector/upper lasing level coherence, which underscores the insufficiency of semiclassical techniques to address injection in QCLs.

A High-Temperature Solar Selective Absorber Based upon Periodic Shallow Microstructures Coated by Multi-Layers Using Atomic Layer Deposition

Abstract: Regarding the fabrication of solar selective absorbers, the ability to create microstructures on top of metal surfaces is a promising technology. Typically, these materials are able to possess spectrally-selective absorption properties for high-temperature usage. Solar-selective absorbers that function at temperatures up to 700 °C and possess shallow honeycomb cylindrical microcavities coated with a metal-dielectric multi-layer have been investigated. Honeycomb array cylindrical microcavities were fabricated on W substrate with interference lithography and multi-layers consisting of Pt nano-film sandwiched by Al2O3 layers were created for a uniform coating via atomic layer deposition. The absorbance spectrum of fabricated samples reveals results consistent with a simulation based on a rigorous coupled-wave analysis method. A solar absorbance value of 0.92 and a hemispherical total emittance value of 0.18 at 700 °C was determined from the fabricated solar-selective absorber. Additionally, thermal stability of up to 700 °C was confirmed in vacuum.

Aluminum Nitride Ceramic as an Optically Stimulable Luminescence Dosimeter Plate

Abstract: Photostimulable storage phosphors have been used in a wide range of applications including radiation measurements in one- and two-dimensional spaces, called point dosimetry and radiography. In this work, we report that an aluminum nitride (AlN) ceramic plate, which is practically used as a heat sink (SHAPAL®, Tokuyama Corp., Yamaguchi, Japan), shows good optically-stimulated luminescence (OSL) properties with sufficiently large signal and capability for imaging applications, and we have characterized the AlN plate for OSL applications. Upon interaction with X-rays, the sample color turns yellowish, due to a radiation-induced photoabsorption band in the UV-blue range below ~500 nm. After irradiating the sample with X-rays, an intense OSL emission can be observed in the UV (360 nm) spectral region during stimulation by red light. Although our measurement setup is not optimized, dose detection was confirmed as low as ~3 mGy to over 20 Gy. Furthermore, we have successfully demonstrated that the SHAPAL® AlN ceramic plate has great potential to be used as an imaging plate in radiography.

WDM-PON Network for Simultaneous Upstream Transmission with ONU Interconnection Capability

Abstract: To provide dedicated downstream and upstream transmission with direct ONU interconnection, a WDM-PON architecture is proposed. This offers efficient bandwidth utilization and reduces transmission latency, cost and energy consumption of the network.

Single Microwave Photon Detection with a Trapped Electron

Abstract: We investigate theoretically the use of an electron in a Penning trap as a detector of single microwave photons. At the University of Sussex we are developing a chip Penning trap technology, designed to be integrated within quantum circuits. Microwave photons are guided into the trap and interact with the electron’s quantum cyclotron motion. This is an electric dipole transition, where the near field of the microwave radiation induces quantum jumps of the cyclotron harmonic oscillator. The quantum jumps can be monitored using the continuous Stern-Gerlach effect, providing the quantum non demolition signal of the microwave quanta. We calculate the quantum efficiency of photon detection and discuss the main features and technical challenges for the trapped electron as a quantum microwave sensor.

Fabrication of 3D Photonic Crystals toward Arbitrary Manipulation of Photons in Three Dimensions

Abstract: The creation of large-area, unintentional-defect-free three-dimensional (3D) photonic crystals in the optical regime is a key challenge toward the realization of the arbitrary 3D manipulation of photons. In this article, we discuss an advanced fabrication method of 3D silicon photonic crystals based on the highly accurate alignment and wafer bonding of silicon-on-insulator (SOI) wafers. We introduce an advanced alignment system, in which the alignment process is automated by image recognition and feed-back control of stages, and show that it achieves an alignment accuracy better than ~50 nm. The bonding of SOI wafers is also investigated to obtain 3D crystals composed of highly pure crystalline silicon. We show the fabrication results of large-area 3D photonic crystals based on such considerations and demonstrate the successful introduction of artificial defects as functional components, such as coupled waveguide pairs or waveguides/nanocavities. We expect that these will be pioneering results toward the arbitrary 3D control of photons using 3D photonic crystals.

Multimode, Aperiodic Terahertz Surface-Emitting Laser Resonators

Abstract: Quasi-crystal structures are conventionally built following deterministic generation rules although they do not present a full spatial periodicity. If used as laser resonators, they open up intriguing design possibilities that are simply not possible in conventional periodic photonic crystals: the distinction between symmetric (vertically radiative but low quality factor Q) and anti-symmetric (non-radiative, high Q) modes is indeed here fully overcome, offering a concrete perspective of highly efficient vertical emitting resonators. We here exploit electrically pumped terahertz quantum cascade heterostructures to devise two-dimensional seven-fold quasi-crystal resonators, exploiting rotational order or irregularly distributed defects. By lithographically tuning the lattice quasi-periodicity and/or the hole radius of the imprinted patterns, efficient multimode surface emission with a rich sequence of spectral lines distributed over a 2.9–3.4 THz bandwidth was reached. We demonstrated multicolor emission with 67 mW of peak optical power, slope efficiencies up to ≈70 mW/A, 0.14% wall plug efficiencies and beam profile results of the rich quasi-crystal Fourier spectrum that, in the case of larger rotational order, can reach very low divergence.

Cascade Type-I Quantum Well GaSb-Based Diode Lasers

Abstract: Cascade pumping of type-I quantum well gain sections was utilized to increase output power and efficiency of GaSb-based diode lasers operating in a spectral region from 1.9 to 3.3 μm. Carrier recycling between quantum well gain stages was realized using band-to-band tunneling in GaSb/AlSb/InAs heterostructure complemented with optimized electron and hole injector regions. Coated devices with an ~100-μm-wide aperture and a 3-mm-long cavity demonstrated continuous wave (CW) output power of 1.96 W near 2 μm, 980 mW near 3 μm, 500 mW near 3.18 μm, and 360 mW near 3.25 μm at 17–20 °C—a nearly or more than twofold increase compared to previous state-of-the-art diode lasers. The utilization of the different quantum wells in the cascade laser heterostructure was demonstrated to yield wide gain lasers, as often desired for tunable laser spectroscopy. Double-step etching was utilized to minimize both the internal optical loss and the lateral current spreading penalties in narrow-ridge lasers. Narrow-ridge cascade diode lasers operate in a CW regime with ~100 mW of output power near and above 3 μm and above 150 mW near 2 μm.

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

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 (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.

Modeling of the Interminiband Absorption Coefficient in InGaN Quantum Dot Superlattices

Abstract: In this paper, a model to estimate minibands and theinterminiband absorption coefficient for a wurtzite (WZ) indium gallium nitride (InGaN) self-assembled quantum dot superlattice (QDSL) is developed. It considers a simplified cuboid shape for quantum dots (QDs). The semi-analytical investigation starts from evaluation through the three-dimensional (3D) finite element method (FEM) simulations of crystal mechanical deformation derived from heterostructure lattice mismatch under spontaneous and piezoelectric polarization effects. From these results, mean values in QDs and barrier regions of charge carriers’ electric potentials and effective masses for the conduction band (CB) and three valence sub-bands for each direction are evaluated. For the minibands’ investigation, the single-particle time-independent Schrodinger equation in effective mass approximation is decoupled in three directions and resolved using the one-dimensional (1D) Kronig–Penney model. The built-in electric field is also considered along the polar axis direction, obtaining Wannier–Stark ladders. Then, theinterminiband absorption coefficient in thermal equilibrium for transverse electric (TE) and magnetic (TM) incident light polarization is calculated using Fermi’s golden rule implementation based on a numerical integration into the first Brillouin zone. For more detailed results, an absorption coefficient component related to superlattice free excitons is also introduced. Finally, some simulation results, observations and comments are given.

Overall/ Subgroup ONU Intercommunication based on Two Stage Flexible PON Network

Abstract: Two-stage remote node based PON-architecture is proposed. Architecture provides inter-ONU communication within all ONUs and/or within subgroup of nearby located ONUs to utilize resources efficiently with minimum power and bandwidth requirement.

Semiconductor Three-Dimensional Photonic Crystals with Novel Layer-by-Layer Structures

Abstract: Three-dimensional photonic crystals (3D PhCs) are a fascinating platform for manipulating photons and controlling their interactions with matter. One widely investigated structure is the layer-by-layer woodpile structure, which possesses a complete photonic bandgap. On the other hand, other types of 3D PhC structures also offer various possibilities for controlling light by utilizing the three dimensional nature of structures. In this article, we discuss our recent research into novel types of layer-by-layer structures, including the experimental demonstration of a 3D PhC nanocavity formed in a -layered diamond structure and the realization of artificial optical activity in rotationally stacked woodpile structures.

Rapid and Sensitive Quantification of Isotopic Mixtures Using a Rapidly-Swept External Cavity Quantum Cascade Laser †

Abstract: A rapidly-swept external-cavity quantum cascade laser with an open-path Herriott cell is used to quantify gas-phase chemical mixtures of D2O and HDO at a rate of 40 Hz (25-ms measurement time). The chemical mixtures were generated by evaporating D2O liquid near the open-path Herriott cell, allowing the H/D exchange reaction with ambient H2O to produce HDO. Fluctuations in the ratio of D2O and HDO on timescales of <1 s due to the combined effects of plume transport and the H/D exchange chemical reaction are observed. Noise-equivalent concentrations (1σ) (NEC) of 147.0 ppbv and 151.6 ppbv in a 25-ms measurement time are determined for D2O and HDO, respectively, with a 127-m optical path. These NECs are improved to 23.0 and 24.0 ppbv with a 1-s averaging time for D2O and HDO, respectively. NECs <200 ppbv are also estimated for N2O, 1,1,1,2–tetrafluoroethane (F134A), CH4, acetone and SO2 for a 25-ms measurement time. The isotopic precision for measurement of the [D2O]/[HDO] concentration ratio of 33‰ and 5‰ is calculated for the current experimental conditions for measurement times of 25 ms and 1 s, respectively.

Surface Plasmon-Coupled Enhanced Transmission

Abstract: For distances less 10 nm, a total energy transfer occurs from a quantum emitter to a nearby metallic surface, producing evanescent surface waves that are plasmonic in nature. When investigating a metallic nanohole supported on an optically dense substrate (such as diamond with nitrogen vacancy center), the scattering occurred preferentially from the diamond substrate towards the air for dipole distances less 10 nm from the aperture. In addition, an enhancement to the dipole's radiative decay rate was observed when resonance of the aperture matched the emitters wavelength. The relationship between an emitter and a nearby resonant aperture is shown to be that of the resonance energy transfer where the emitter acts as a donor and the hole as an acceptor. In conjunction with the preferential scattering behavior, this has led to the proposed device that operates in transmission mode, eliminating the need for epi-illumination techniques and optically denser than air superstrates in the collection cycle, hence making the design simpler and more suitable for miniaturization. A design criterion for the surface grating is also proposed to improve the performance, where the period of the grating differs significantly from the wavelength of the surface plasmon polaritons. Response of the proposed device is further studied with respect to changes in nitrogen vacancy's position and its dipolar orientation to identify the crystallographic planes of diamond over which the performance of the device is maximized.