mid-IR Wavelength Range Research Articles

Infrared Plasmonics via ZnO

Conventional plasmonic devices involve metals, but metal-based plasmonic resonances are mainly limited to λres < 1 μm, and thus metals interact effectively only with light in the UV and visible ranges. We show that highly doped ZnO can exhibit λres ≥ 1 μm, thus moving plasmonics into the IR range. We illustrate this capability with a set of thin (d = 25–147 nm) Al-doped ZnO (AZO) layers grown by RF sputtering on quartz glass. These samples employ a unique, 20-nm-thick, ZnON buffer layer, which minimizes the strong thickness dependence of mobility (μ) on thickness (d). A practical waveguide structure, using these measurements, is simulated with COMSOL Multiphysics software over a mid-IR wavelength range of 4–10 μm, with a detailed examination of propagation loss and plasmon confinement dimension. In many cases, Lplas < λlight, thus showing that IR light can be manipulated in semiconductor materials at dimensions below the diffraction limit.

Mid-infrared wavelength division (de)multiplexer using an interleaved angled multimode interferometer on the silicon-on-insulator platform

A low-cost and high-performance wavelength division (de)multiplexing structure in the mid-IR wavelength range is demonstrated on the silicon-on-insulator platform using an interleaved angled multimode interferometer (AMMI). As compared to a single AMMI, the channel count was doubled and the channel spacing halved with negligible extra insertion loss and crosstalk and with only a slight increase in device footprint. The device requires only single lithography and etching steps for fabrication. Potential is also shown for achieving improved performance with further optimized design.

Generating mid-IR octave-spanning supercontinua and few-cycle pulses with solitons in phase-mismatched quadratic nonlinear crystals

We discuss a novel method for generating octave-spanning supercontinua and few-cycle pulses in the important mid-IR wavelength range. The technique relies on strongly phase-mismatched cascaded second-harmonic generation (SHG) in mid-IR nonlinear frequency conversion crystals. Importantly we here investigate the so-called noncritical SHG case, where no phase matching can be achieved but as a compensation the largest quadratic nonlinearities are exploited. A self-defocusing temporal soliton can be excited if the cascading nonlinearity is larger than the competing material self-focusing nonlinearity, and we define a suitable figure of merit to screen a wide range of mid-IR dielectric and semiconductor materials with large effective second-order nonlinearities $d_{\rm eff}$. The best candidates have simultaneously a large bandgap and a large $d_{\rm eff}$. We show selected realistic numerical examples using one of the promising crystals: in one case soliton pulse compression from 50 fs to 15 fs (1.5 cycles) at $3.0\mic$ is achieved, and at the same time a 3-cycle dispersive wave at $5.0\mic$ is formed that can be isolated using a long-pass filter. In another example we show that extremely broadband supercontinua can form spanning the near-IR to the end of the mid-IR (nearly 4 octaves).

Broadband focusing grating couplers for suspended-membrane waveguides

We propose and demonstrate broadband focusing grating couplers for suspended-membrane waveguides on silicon-on-insulator both in near-infrared (near-IR) and in mid-IR wavelength range. Finite-difference time-domain simulation predicts ∼100 nm 3dB bandwidth with -1.7 dB coupling efficiency for an apodized grating in near-IR. -3.5 dB maximum coupling efficiency and ∼90 nm 3dB bandwidth are realized experimentally. In mid-IR, -5.5 dB maximum coupling efficiency from a uniform focusing grating is measured at 2.75μm, and ∼500 nm 3dB bandwidth is predicted theoretically.

High-Q microresonators for mid-IR light sources and molecular sensors

We propose and demonstrate a simple and reliable method for fabricating high-quality whispering-gallery mode (WGM) optical microresonators in "mid-IR relevant" low-loss ZrF(4)-BaF(2)-LaF(3)-AlF(3)-NaF (ZBLAN) glasses. Intrinsic quality factors of 10(7) have been demonstrated, providing great promise for WGM-based mid-IR (MIR) devices. Absorption-limited Q-factors of over 3×10(8) are anticipated over the 2.0 to 3.2 μm MIR wavelength range in ZBLAN microcavities in the foreseeable future.

Young Stellar Objects in the Low-Metallicity Small Magellanic Cloud

AbstractThe Spitzer Legacy Program “Surveying the Agents of Galaxy Evolution in the Tidally-Stripped, Low-Metallicity Small Magellanic Cloud” (SAGE-SMC; Gordon et al. 2011) allows a global study of star formation in the SMC at high enough resolution to resolve individual cores and protostars at a range of mid-IR wavelengths. Using the SAGE-SMC IRAC (3.6 - 8.0 μm) and MIPS (24 and 70 μm) catalogs and images combined with the near-IR and optical data, we identified a population of ∼1100 intermediate- to high-mass Young Stellar Objects (YSOs) in the SMC (3 × more than previously known). We investigate the properties of the YSOs and how they relate to the galaxy's structure and gas and dust distribution.

New Trends in Amplifiers and Sources via Chalcogenide Photonic Crystal Fibers

Rare-earth-doped chalcogenide glass fiber lasers and amplifiers have great applicative potential in many fields since they are key elements in the near and medium-infrared (mid-IR) wavelength range. In this paper, a review, even if not exhaustive, on amplification and lasing obtained by employing rare-earth-doped chalcogenide photonic crystal fibers is reported. Materials, devices, and feasible applications in the mid-IR are briefly mentioned.

Guided mode resonance in subwavelength metallodielectric free-standing grating for bandpass filtering

We present the experimental study of a free-standing metallic guided-mode resonant structure, for bandpass filtering applications in the mid-IR wavelength range. Structure consists of a subwavelength gold grating with narrow slits deposited on a silicon nitride membrane. High optical transmission is measured with up to 78% transmission at resonance. Angularly resolved spectra are presented revealing Fano-type resonance.

Strong absorption and selective thermal emission from a midinfrared metamaterial

We demonstrate thin-film metamaterials with resonances in the midinfrared (mid-IR) wavelength range. Our structures are numerically modeled and experimentally characterized by reflection and angularly resolved thermal emission spectroscopy. We demonstrate strong and controllable absorption resonances across the mid-IR wavelength range. In addition, the polarized thermal emission from these samples is shown to be highly selective and largely independent of emission angles from normal to 45°. Experimental results are compared to numerical models with excellent agreement. Such structures hold promise for large-area, low-cost metamaterial coatings for control of gray- or black-body thermal signatures, as well as for possible mid-IR sensing applications.

Application of thin-film interference coatings in infrared reflection spectroscopy of organic samples in contact with thin metal films

A thin dielectric IR-transparent interlayer is introduced between an IR-transparent medium of incidence and a thin metal film. The interlayer increases the intensity of light on the metal/sample interface at certain wavenumbers. By computations, the reflectivities of the system "calcium fluoride (CaF)-germanium (Ge)-gold (Au) sample" are analyzed as a function of incidence angle and Ge layer thickness. Absorbance spectra with acetonitrile as a sample are recorded for different angles of incidence and polarizations and compared to computations. A characteristic feature of the absorbance spectra is the occurrence of interference fringes distributed between 1000 and 6000 cm(-1), i.e., over the complete mid-IR wavelength range into the near-IR. These fringes could be used in analytical spectroscopy.

High-performance InP-based midinfrared quantum cascade lasers at Northwestern University

We present recent performance highlights of midinfrared quan- tum cascade lasers (QCLs) based on an InP material system. At a repre- sentative wavelength around 4.7 μm, a number of breakthroughs have been achieved with concentrated effort. These breakthroughs include watt-level continuous wave operation at room temperature, greater than 50% peak wall plug efficiency at low temperatures, 100-W-level pulsed mode operation at room temperature, and 10-W-level pulsed mode oper- ation of photonic crystal distributed feedback quantum cascade lasers at room temperature. Since the QCL technology is wavelength adaptive in nature, these demonstrations promise significant room for improvement across a wide range of mid-IR wavelengths. C 2010 Society of Photo-Optical

Effect of Applied Stress on IR transmission of Spark Plasma-Sintered Alumina

The effect of applied stress on IR transmittance of nanocrystalline alumina prepared by spark plasma sintering was evaluated. Transparent alumina with maximum transmittance >80% was obtained over the entire mid-IR wavelength range of 3–5 μm by applying a high stress of 275 MPa at 1150°C using specially designed high-strength compound dies. The transmittance observed was similar to previous reports at identical wavelengths, but at a lower sintering temperature. The transparent samples have an average grain size of 0.3 μm and a hardness of 23 GPa. At lower stresses and sintering temperatures, transmittance reduced drastically due to remnant pores in the matrix as observed from the microstructural analysis. The effect of porosity was found to be critical in developing transparency as even a marginal decrease in porosity led to substantial increase in transmittance.

Simulation of mid-IR amplification in Er 3+-doped chalcogenide microstructured optical fiber

This paper deals with the design of an erbium doped microstructured optical fiber (MOF) amplifier operating in the mid-infrared (mid-IR) wavelength range, more precisely around 4.5 μm wavelength. A home-made numerical code which solves the rate equations and the power propagation equations has been ad hoc developed to theoretically investigate the feasibility of mid-IR MOF amplifier. On the basis of the measured energy level transition parameters of a Er 3+-doped Ga 5Ge 20Sb 10S 65 chalcogenide glass, the amplifier feasibility is demonstrated exhibiting high gain and low noise figure.

Mid-IR fibre optics spectroscopy in the 3300–600 cm −1 range

The latest development in IR fibre optics enables to expand spectral range of process spectroscopy from 3300 to 600 cm −1. Mid-IR wavelength range from 5000 to 1700–1000 cm −1may be covered by chalcogenide IR glass (CIR) fibres while polycrystalline infrared (PIR) fibres made of silver halides solid solutions transmit radiation of the whole most informative “finger-print” part of the spectrum from 3300 to 600 cm −1. PIR fibre based immersion ATR probes had been manufactured and successfully tested with FTIR spectrometers in the field of remote spectroscopy of chemical reaction and fuel analysis. The sensitivity of different ATR elements, performance and permanence of the probes are considered in temperature range 20–150 °C.

Intersubband quantum-box semiconductor lasers

It is shown that semiconductor lasers utilizing intersubband transitions in quantum boxes, so-called intersubband quantum-box (IQB) lasers, can have significantly lower threshold current densities and operating voltages than quantum cascade (QC) lasers. In order to achieve this result, an enhancement factor of about 20 in the LO-phonon-assisted electron relaxation time is necessary. The increased gain for the radiative stage in an IQB laser eliminates the need for a multiradiative-stage structure (typically 25 stages in QC lasers). In turn, the electron injector and Bragg mirror regions on either side of the active region can be separately optimized. Due to their inherently lower input power requirements, IQB lasers operating in the mid-IR wavelength range should be capable of higher average-output powers than QC lasers at all temperatures. Furthermore, continuous-wave (CW) operation at room temperature with high wallplug efficiency becomes possible.

High-confinement waveguides for mid-IR devices

We analyze the use of heavily doped semiconductor layers as a means to tightly confine light. The very low refractive index ( n≈1) that is present just above the plasma frequency renders large index steps possible. Slab waveguide structures with InP or GaAs cladding layers doped to n D ∼10 19 cm −3 are analyzed in the mid-IR wavelength range, λ=4– 15 μm . The performance of the waveguide in terms of achieved overlap with an active region of a given thickness versus the waveguide absorption, is compared to waveguides based on surface plasmons. The calculated results indicate that these plasma effect waveguides should be favourable in this respect for wavelengths λ≈6–10 μm using heavily doped InP as a cladding. In GaAs efficient use of the plasma effect is limited to wavelengths λ≳9 μm . Guidelines for required doping levels are given.

Infrared Site Testing in Antarctica

AbstractSite testing campaigns in the mid-IR wavelength range have been carried out in Antarctica in the last two southern summer seasons. A description of the experimental apparatus and some preliminary results are presented in this work. Future plans are also discussed.

Raman studies of InAs/In0.53Ga0.47As single quantum wells grown on InP substrate by M.B.E.

We analyzed using the Raman technique a series of single quantum wells of InAs/In 0.53Ga0.47As at different thicknesses of InAs layer grown on a (100) InP substrate by MBE. These high lattice mismatch systems are particularly interesting for potential applications in the mid-IR wavelength range. The well thickness was between 6 and 12 monolayers. The In 0.53 Ga0.47As grown on an InAs layer is subject to a tensile biaxial strain and the InAs to a compressive one. In the Raman spectra we observed an intense narrow line corresponding to the LO phonon of the InAs layer between a GaAs-like LO mode and a smaller InAs-like LO phonon typical of In0.53Ga0.47As. With the increase of the well thickness the experimental energy shift of the LO phonon of the InAs layer decreases, indicating a smaller strain, whereas the GaAs-like LO phonon of the alloy remains constant and the intensity ratio of these two modes becames smaller. The dominant and sharp features of the InAs LO and GaAs-like LO characterize the good quality of our structures. With the increase of the InAs layer thickness we also observed the appearance and the intensity rise of a weak peak around the frequency of the InAs TO mode. This peak could be associated with the TO mode that is forbidden in our scattering geometry. We believe that this is indicative of a slight deterioration of the structural perfection of the sample with the increase of the well thickness. To our knowledge, this is the first study of vibrational properties of InAs/In 0.53 Ga0.47As single quantum wells grown on InP substrates.

Low-density band-filling in strained InAs quantum wells

We study the low-temperature photoluminescence (PL) of strained InAs single quantum wells (SQWs) embedded in a Ga0.47In0.53As matrix grown on InP substrates by modified solid-source molecular beam epitaxy. The spectra are interpreted in the frame of a two-level rate equation model describing the carrier dynamics in the structures. We show that band-filling occurs in these QWs for an excitation power as low as 30 Wcm−2. Moreover, the spectra reveal that the band-filling results from the rapid population of the hole subband. This observation highlights the low in-plane heavy-hole mass in the compressively strained film. Our results therefore demonstrate the high potential of InAs/Ga0.47In0.53As QW nonlinear optical devices operating in the mid-IR wavelength range.

InAs/Ga0.47In0.53As quantum wells: A new III-V materials system for light emission in the mid-infrared wavelength range

We propose the use of strained InAs/Ga0.47In0.53As quantum wells (QWs) for light emission in the technologically important mid-IR wavelength range. Temperature dependent photoluminescence measurements on single QWs demonstrate that light emission at room temperature is obtained from all samples having InAs QW widths between 2 and 23 monolayers. Luminescence up to 2.4 μm is obtained at 300 K, which is the longest wavelength achieved so far for QWs grown on InP. These results demonstrate the potential of the InAs/Ga0.47In0.53As QW materials system for the fabrication of optoelectronic devices operating in the mid-IR.