Mid to far infrared is an important wavelength band for detection of substances. Incandescent sources are often used in infrared spectroscopy because they are simple and cost effective. They are however broadband and quasi isotropic. As a result, the total efficiency in a detection system is very poor. Yet it has been shown recently that thermal emission can be designed to be directional and/or monochromatic. To do so amounts to shape the emissivity. Any real thermal source is characterized by its emissivity, which gives the specific intensity of the source compared to the blackbody at the same temperature. The emissivity depends on the wavelength and the direction of emission and is related to the whole structure of the source (materials, geometry below the wavelength-scale...). Emissivity appears as a directional and chromatic filter for the blackbody radiation. Playing with materials and structure resonances, the emissivity can be designed to optimize the properties of an incandescent source. We will see how it is possible to optimize a plasmonic metasurface acting as an incandescent source, to make it directional and quasi monochromatic at a chosen wavelength. We will target a CO2 detection application to illustrate this topic.

In a non-magnetic dielectric sphere of high-permittivity ( <20), effective magnetic response occurs as a result of the 1st Mie mode, known as the magnetic dipole resonance. This resonance produces a similar effect as split ring resonators, making it possible to use dielectric spheres as metamaterial components. In the terahertz (THz) part of the spectrum, where dielectrics with  ~100 can be found, all-dielectric metamaterials can potentially reduce absorption and provide isotropic and polarization-independent properties. In this contribution, we discuss TiO2 micro-spheres, ~1/10 of the wavelength in diameter. Such spheres are expected to support the magnetic and electric dipole resonances. To detect these resonances in a single TiO2 microsphere we use THz near-field microscopy with the sub-wavelength size aperture probe. This method allows detection of Mie resonances in single sub-wavelength spheres. Fano-type line-shape is observed in the near-field amplitude and phase spectra. The narrow line-width of the magnetic resonance and the subwavelength size of the TiO₂ microspheres make them excellent candidates for realizing low-loss THz metamaterials.

Optical spectroscopy techniques are widely used for the characterization of semiconductors and nanostructures. Confocal Raman microscopy is useful to retrieve chemical and molecular information at the ultimate submicrometer resolution of optical microscopy. Fast imaging capabilities, 3D confocal ability, and multiple excitation wavelengths, have increased the power of the technique while making it simpler to use for material scientists. Recently, the development of the Tip Enhanced Raman Spectroscopy (TERS) has opened the way to the use of Raman information at nanoscale, by combining the resolution of scanning probe microscopy and chemical selectivity of Raman spectroscopy. Significant advances have been reported in the field of profiling the atomic composition of multilayers, using the Glow Discharge Optical Emission Spectroscopy technique, including real-time determination of etched depth by interferometry. This allows the construction of precise atomic profiles of sophisticated multilayers with a few nm resolution. Ellipsometry is another widely used technique to determine the profile of multilayers, and recent development have provided enhanced spatial resolution useful for the investigation of patterned materials. In addition to the advances of the different characterization techniques, the capability to observe the same regions at micrometer scale at different stages of material elaboration, or with different instrument, is becoming a critical issue. Several advances have been made to allow precise re-localization and co-localization of observation with different complementary characterization techniques.

Recently we have improved the efficiency and the output power of our optically pumped continuous-wave THz sources. These sources are based on the beating of two laser lines in a wide bandwidth photodetector. Its intrinsic nonlinear behaviour is used to produce a beatnote at the frequency difference between the two laser lines (photomixing). These photomixers are continuously tunable THz sources working at room temperature. We have developed two kinds of photomixers: GaAs-based for 0.8 μm pumping and InP-based for 1.5 μm pumping. On GaAs the best results has been obtained thanks to low-temperature-grown GaAs (LTG-GaAs) photoconductors (PC). Efficiency and power were optimized by designing a new type of thin PC placed in a Fabry-Pérot resonator. The high impedance of the PC is a wellknown limitation of this device but with our approach it was possible to reduce its impedance by a factor 100. Moreover by designing an impedance matching network it was possible to obtain 1.8 mW at 252 GHz with a total efficiency of 0.5 %. On InP the best results are obtained with uni-travelling-carrier photodiodes (UTC-PD). The device was improved by designing a new heterostructure and new semi-transparent contacts with sub-wavelength apertures. The active layer was also bonded to a silicon substrate thanks to metal thermocompression. It is demonstrated that with this approach it is possible to obtain a power of 0.7 mW at 300 GHz with a total efficiency of 0.7 %. More generally the efficiency of optically pumped terahertz sources will be discussed.

A terahertz quantum cascade laser has been realized from an isotropic disordered hyperuniform design. Such a system presents a photonic band-gap although it is characterized by an efficient depletion of the long range order. Hyperuniform patterns allow greater versatility in engineering band gaps in comparison to standard photonic-crystal materials. Bidimensional hyperuniform patterns were simulated for hexagonal tiles composed of high refractive index disks merged in a low dielectric constant polymeric matrix. Based on this design, quantum cascade lasers were fabricated by standard photolithography, metal evaporation, lift-off and dry-etching techniques in a half-stack bound to continuum active region emitting around 2.9 THz.

The THz part of the spectrum (0.1 to 10 THz) has been gathering increasing interest over the past 10 years as it could enable interesting new applications. Key to its exploitation has been the development of photonic based sources and detectors. However there is a lack of room temperature operating devices for both sources and detectors. We propose the use of uni-travelling carrier photodetectors (UTC-PDs) as both source and detectors for the range up to 2 THz.

Buried heterostructure (BH) lasers are routinely fabricated for telecom applications. Development of quantum cascade lasers (QCL) for sensing applications has largely benefited from the technological achievements established for telecom lasers. However, new demands are to be met with when fabricating BH-QCLs. For example, hetero-cascade and multistack QCLs, with several different active regions stacked on top of each other, are used to obtain a broad composite gain or increased peak output power. Such structures have thick etch ridges which puts severe demand in carrying out regrowth of semi-insulating layer around very deeply etched (< 10 μm) ridges in short time to realize BH-QCL. For comparison, telecom laser ridges are normally only <5 μm deep. We demonstrate here that hydride vapour phase epitaxy (HVPE) is capable of meeting this new demand adequately through the fabrication of BH-QCLs in less than 45 minutes for burying ridges etched down to 10-15 μm deep. This has to be compared with the normally used regrowth time of several hours, e.g., in a metal organic vapour phase epitaxy (MOVPE) reactor. This includes also micro-stripe lasers resembling grating-like ridges for enhanced thermal dissipation in the lateral direction. In addition, we also demonstrate HVPE capability to realize buried heterostructure photonic crystal QCLs for the first time. These buried lasers offer flexibility in collecting light from the surface and relatively facile device characterization feasibility of QCLs in general; but the more important benefits of such lasers are enhanced light matter interaction leading to ultra-high cavity Q-factors, tight optical confinement, possibility to control the emitted mode pattern and beam shape and substantial reduction in laser threshold.

Strained-layer superlattice (SL) structures have been grown by metalorganic vapor phase epitaxy (MOVPE) on metamorphic buffer layers (MBLs) for application in intersubband-transition devices, such as quantum cascade lasers. Using the MBL as an adjustable lattice-parameter platform, we have designed relatively-low-strain quantum-cascade-laser structures that will emit in the 3.0-3.5 μm wavelength range while suppressing carrier leakage from the upper laser level. Thick (10-12 μm) compositionally-graded, hydride-vapor-phase-epitaxy (HVPE)-grown MBL structures are employed. To improve the planarity of the MBL surface, we employ chemical mechanical polishing (CMP) followed by wet chemical etching prior to the growth of the SL/device structures. We find that the wet-chemical etching step is crucial to remove residual damage introduced during CMP. 20-period In_xGa_1-xAs (wells)/Al_yIn_1-yAs (barriers) SLs grown on the MBLs are characterized by x-ray diffraction (XRD). Intersubband electroluminescence emission is observed in the 3.5 μm wavelength range from devices employing such SL structures.

Quantum cascade lasers (QCLs) are promising light sources for real time high-sensitivity gas sensing in the mid-infrared region. For the practical use of QCLs as a compact and portable gas sensor, their power-consumption needs to be reduced. We report a successful operation of a low power-consumption distributed feedback (DFB) QCL. For the reduction of power consumption, we introduced a vertical-transition structure in a core region to improve carrier transition efficiency and reduced the core volume. DFB-QCL epitaxial structure was grown by low-pressure OMVPE. The core region consists of AlInAs/GaInAs superlattices lattice-matched to InP. A first-order Bragg-grating was formed near the core region to obtain a large coupling coefficiency. A mesa-strip was formed by reactive ion etching and a buried-heterostructure was fabricated by the regrowth of semi-insulating InP. High-reflective facet coatings were also performed to decrease the mirror loss for the reduction of the threshold current. A device (5x500μm) operated with a single mode in the wavelength region from 7.23μm to 7.27μm. The threshold current and threshold voltage under CW operation at 20 °C were 52mA and 8.4V respectively. A very low threshold power-consumption as low as 0.44 W was achieved, which is among the lowest values at room temperature to our knowledge.

The objective of this work is to establish molecular beam epitaxy (MBE) growth processes that can produce high quality InAs/GaInSb superlattice (SL) materials specifically tailored for very long wavelength infrared (VLWIR) detection. To accomplish this goal, several series of MBE growth optimization studies, using a SL structure of 47.0 Å InAs/21.5 Å Ga_0.75In_0.25Sb, were performed to refine the MBE growth process and optimize growth parameters. Experimental results demonstrated that our “slow” MBE growth process can consistently produce an energy gap near 50 meV. This is an important factor in narrow band gap SLs. However, there are other growth factors that also impact the electrical and optical properties of the SL materials. The SL layers are particularly sensitive to the anion incorporation condition formed during the surface reconstruction process. Since antisite defects are potentially responsible for the inherent residual carrier concentrations and short carrier lifetimes, the optimization of anion incorporation conditions, by manipulating anion fluxes, anion species, and deposition temperature, was systematically studied. Optimization results are reported in the context of comparative studies on the influence of the growth temperature on the crystal structural quality and surface roughness performed under a designed set of deposition conditions. The optimized SL samples produced an overall strong photoresponse signal with a relatively sharp band edge that is essential for developing VLWIR detectors. A quantitative analysis of the lattice strain, performed at the atomic scale by aberration corrected transmission electron microscopy, provided valuable information about the strain distribution at the GaInSb-on-InAs interface and in the InAs layers, which was important for optimizing the anion conditions.

Temperature dependent measurements of carrier recombination rates using a time-resolved pump-probe technique are reported for mid-wave infrared InAs/InAsSb type-2 superlattices (T2SLs). By engineering the layer widths and alloy compositions a 16 K band-gap of ~235 ± 10meV was achieved for four doped and five undoped T2SLs. Carrier lifetimes were determined by fitting lifetime models of Shockley-Read-Hall (SRH), radiative, and Auger recombination processes simultaneously to the temperature and excess carrier density dependent data. The contribution of each recombination process at a given temperature is identified and the total lifetime is determined over a range of excess carrier densities. The minority carrier and Auger lifetimes were observed to increase with increasing antimony content and decreasing layer thickness for the undoped T2SLs. It is hypothesized that a reduction in SRH recombination centers or a shift in the SRH defect energy relative to the T2SL band edges is the cause of this increase in the SRH minority carrier lifetime. The lower Auger coefficients are attributed to a reduced number of final Auger states in the SL samples with greater antimony content. An Auger limited minority carrier lifetime is observed for the doped T2SLs, and it is found to be a factor of ten shorter than for undoped T2SLs. The Auger rates for all the InAs/InAsSb T2SLs were significantly larger than those previously reported for InAs/GaSb T2SLs.

Detector-relevant material properties are calculated for mid-wavelength infrared and long-wavelength infrared InAs/InAsSb type-II superlattices (T2SLs). The electronic structure, transport, optical and carrier recombination properties are calculated for a series of T2SLs with varying Sb content in the InAsSb layer, and strain balanced for growth on GaSb substrates. The electronic-structure calculations rely on a well-tested envelope-function formalism based on fourteen bulk bands that has been extensively tested for InAs/GaInSb superlattice detectors. Targeted cutoff wavelengths are 5.2 microns and 10 microns. As the Sb composition and the strain in the InAsSb layer is varied the conduction and valence band edges also shift, and the resulting effect of these shifts on the Shockley-Read-Hall recombination rates from defect states in the gap is presented. Anisotropy in the carrier masses can also reduce detector performance; we find that hole mass anisotropy can be moderate for high-performance InAs/InAsSb superlattices.

Superlattice layers in infrared emitters and detectors can be highly anisotropic in their electrical properties, and proper characterization of their in-plane and cross-plane transport can reveal information about the band structure, doping density, impurities, and carrier lifetimes. This work introduces numerical simulation methods for the potential distribution in an anisotropic resistive layer representing a suplerlattice, using both and non-conformal and conformal mapping to simplify the calculation of the potential int he presence of a magnetic field. A shingle strip-line contact is modeled atop the resistive superlattrive layer of interest, which, in turn, contact with a highly conducting back-plane and magnetic field-dependent Neumann boundary conditions at the floating front-plane. To increase cpomputational efficiency, non-conformal an conformal mapping are combined to transform the problem of an intractable infinitely wide anisotropic thin-film smaple to calculable, finite isotropic rectangular shape. The potential calculations introduced here should prove useful for deducing the full conductivity tensor of the superlattice region, including in-plane, cross-plane, and transverse conductivity tensor components.

In this work we investigate the high temperature performance of mid-wavelength infrared InAsSb-AlAsSb nBn detectors with cut-off wavelengths near 4.5μm. The quantum efficiency of these devices is 35% without antireflection coatings and does not change with temperature in the 77 - 325K temperature range, indicating potential for room temperature operation. The device dark current stays diffusion limited in the 150K-325K temperature range and becomes dominated by generation-recombination processes at lower temperatures. Detector detectivities of D*(λ) = 1x10⁹ (cm Hz^0.5/W) at T = 300K and D*(λ) = 5x10⁹ (cm Hz^0.5/W) at T = 250K, which is easily achievable with a one stage TE cooler.

In this communication, we report results obtained on a new InSb/InAlSb/InSb ‘bariode’, grown by MBE on (100)- oriented InSb substrate. Because of a very weak valence band offset with InSb (~ 25meV), InAlSb is a good candidate as a barrier layer for electrons. However, due to lattice mismatch with the InSb substrate, careful growth study of InAlSb was made to insure high crystal quality. As a result, InSb-based nBn detector device exhibits dark current density equals to 1x10^-9A.cm^-2 at 77K: two decades lower than Insb standard pin photodiode with similar cut-off wavelength. Moreover, compared to standard pn (or pin) InSb-based photodetectors fabricated by implanted planar process or by molecular beam epitaxy (MBE), we demonstrate that the reachable working temperature, around 120 K, of the InSbbased nBn detector is respectively higher than 40 K and 20 K than the previous. Such result demonstrates the potentiality of Insb detectors with nBn architecture to reach the high operating temperature.

SOFRADIR is widely present on the IR detector market for high-performance space, military and security applications thanks to a well mastered Mercury Cadmium Telluride (MCT) technology, and to the recent acquisition of the III-V InSb, InGaAs, and QWIP technologies. As a result, strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of sensitivity, spatial and thermal resolution. The actual trend in quantum IR detector development is the design of very small pixel, with high operating temperature. The selfconfinement of neighboring diodes may not be efficient enough to maintain optimal modulation transfert function (MTF). This paper presents the recent developments achieved in Sofradir in terms of MTF measurements protocol challenged by the pitch reduction. An overview of state of the art MTF results with optimized measurement technic will be shown, from SWIR to VLWIR MCT focal plane. In order to optimize device performances and reduce development cycle time, this experimental approach has been coupled with finite elements modelisation (FEM). Optimized MTF results for 10μm pitch and HOT MCT technology will be exposed.

We show here theoretically and experimentally how chaotic Photonic Crystal resonators can be used for en- ergy harvesting applications and the demonstration of fundamental theories, like the onset of superradiance in quantum systems.

Mid-infrared silicon photonics emerge as the dominant technology to bridge photonics and electronics in multifunctional high-speed integrated chips. The transmission and processing of optical signals lying at the mid-infrared wavelength region is ideal for sensing, absorption-spectroscopy and free-space communications and the use of group IV materials becomes principally promising as the vehicle towards their realization. In parallel, optical forces originating from modes and cavities can reach to outstandingly large values when sizes drop into the nanoscale. In this work, we propose the exploitation of large gradient optical forces generated between suspended silicon beams and optomechanical transduction as a means of converting signals from the mid-infrared to the near-infrared region. A midinfrared signal is injected into the waveguide system so as to excite the fundamental symmetric mode. In the 2-5μm wavelength range, separation gaps in the 100nm order and waveguide widths ranging from 300–600nm, the mode is mostly guided in the air slot between the waveguides which maximizes the optomechanical coupling coefficient and optical force. The resulting attractive force deflects the waveguides and the deflection is linearly dependent on the midinfrared optical power. A simple read-out technique using 1.55μm signals with conventional waveguiding in the directional coupler formed by the two beams is analyzed. A positive conversion efficiency (<0dB) is foreseen for waveguides with suspending lengths up to 150μm. The converter could be ideal for use in sensing and spectroscopy rendering the inefficient mid-infrared detectors obsolete. The low-index unconventional guiding in mid-infrared could be a key component towards multifunctional lab-on-a-chip devices.

The classical theory of electrodynamics cannot explain the existence and structure of electric and magnetic dipoles, yet it incorporates such dipoles into its fundamental equations, simply by postulating their existence and properties, just as it postulates the existence and properties of electric charges and currents. Maxwell’s macroscopic equations are mathematically exact and self-consistent differential equations that relate the electromagnetic (EM) field to its sources, namely, electric charge-density 𝜌𝜌free, electric current-density 𝑱𝑱free, polarization 𝑷𝑷, and magnetization 𝑴𝑴. At the level of Maxwell’s macroscopic equations, there is no need for models of electric and magnetic dipoles. For example, whether a magnetic dipole is an Amperian current-loop or a Gilbertian pair of north and south magnetic monopoles has no effect on the solution of Maxwell’s equations. Electromagnetic fields carry energy as well as linear and angular momenta, which they can exchange with material media—the seat of the sources of the EM field—thereby exerting force and torque on these media. In the Lorentz formulation of classical electrodynamics, the electric and magnetic fields, 𝑬𝑬 and 𝑩𝑩, exert forces and torques on electric charge and current distributions. An electric dipole is then modeled as a pair of electric charges on a stick (or spring), and a magnetic dipole is modeled as an Amperian current loop, so that the Lorentz force law can be applied to the corresponding (bound) charges and (bound) currents of these dipoles. In contrast, the Einstein-Laub formulation circumvents the need for specific models of the dipoles by simply providing a recipe for calculating the force- and torque-densities exerted by the 𝑬𝑬 and 𝑯𝑯 fields on charge, current, polarization and magnetization. The two formulations, while similar in many respects, have significant differences. For example, in the Lorentz approach, the Poynting vector is 𝑺𝑺𝐿𝐿 = 𝜇𝜇0 −1𝑬𝑬 × 𝑩𝑩, and the linear and angular momentum densities of the EM field are 𝓹𝓹𝐿𝐿 = 𝜀𝜀0𝑬𝑬 × 𝑩𝑩 and 𝓛𝓛𝐿𝐿 = 𝒓𝒓 × 𝓹𝓹𝐿𝐿, whereas in the Einstein-Laub formulation the corresponding entities are 𝑺𝑺𝐸𝐸𝐸𝐸= 𝑬𝑬 × 𝑯𝑯, 𝓹𝓹𝐸𝐸𝐸𝐸= 𝑬𝑬 × 𝑯𝑯⁄𝑐𝑐2, and 𝓛𝓛𝐸𝐸𝐸𝐸= 𝒓𝒓 × 𝓹𝓹𝐸𝐸𝐸𝐸. (Here 𝜇𝜇0 and 𝜀𝜀0 are the permeability and permittivity of free space, 𝑐𝑐 is the speed of light in vacuum, 𝑩𝑩 = 𝜇𝜇0𝑯𝑯 + 𝑴𝑴, and 𝒓𝒓 is the position vector.) Such differences can be reconciled by recognizing the need for the so-called hidden energy and hidden momentum associated with Amperian current loops of the Lorentz formalism. (Hidden entities of the sort do not arise in the Einstein-Laub treatment of magnetic dipoles.) Other differences arise from over-simplistic assumptions concerning the equivalence between free charges and currents on the one hand, and their bound counterparts on the other. A more nuanced treatment of EM force and torque densities exerted on polarization and magnetization in the Lorentz approach would help bridge the gap that superficially separates the two formulations. Atoms and molecules may collide with each other and, in general, material constituents can exchange energy, momentum, and angular momentum via direct mechanical interactions. In the case of continuous media, elastic and hydrodynamic stresses, phenomenological forces such as those related to exchange coupling in ferromagnets, etc., subject small volumes of materials to external forces and torques. Such matter-matter interactions, although fundamentally EM in nature, are distinct from field-matter interactions in classical physics. Beyond the classical regime, however, the dichotomy that distinguishes the EM field from EM sources gets blurred. An electron’s wavefunction may overlap that of an atomic nucleus, thereby initiating a contact interaction between the magnetic dipole moments of the two particles. Or a neutron passing through a ferromagnetic material may give rise to scattering events involving overlaps between the wave-functions of the neutron and magnetic electrons. Such matter-matter interactions exert equal and opposite forces and/or torques on the colliding particles, and their observable effects often shed light on the nature of the particles involved. It is through such observations that the Amperian model of a magnetic dipole has come to gain prominence over the Gilbertian model. In situations involving overlapping particle wave-functions, it is imperative to take account of the particle-particle interaction energy when computing the scattering amplitudes. As far as total force and total torque on a given volume of material are concerned, such particle-particle interactions do not affect the outcome of calculations, since the mutual actions of the two (overlapping) particles cancel each other out. Both Lorentz and Einstein-Laub formalisms thus yield the same total force and total torque on a given volume—provided that hidden entities are properly removed. The Lorentz formalism, with its roots in the Amperian current-loop model, correctly predicts the interaction energy between two overlapping magnetic dipoles 𝒎𝒎1 and 𝒎𝒎2 as being proportional to −𝒎𝒎1 ∙ 𝒎𝒎2. In contrast, the Einstein-Laub formalism, which is ignorant of such particle-particle interactions, needs to account for them separately.

Sensitive detection of nitric oxide (NO) at ppbv concentration levels has an important impact in diverse fields of applications including environmental monitoring, industrial process control and medical diagnostics. For example, NO can be used as a biomarker of asthma and inflammatory lung diseases such as chronic obstructive pulmonary disease. Trace gas sensor systems capable of high sensitivity require the targeting of strong rotational-vibrational bands in the mid-IR spectral range. These bands are accessible using state-of-the-art high heat load (HHL) packaged, continuous wave (CW), distributed feedback (DFB) quantum cascade lasers (QCLs). Quartz-enhanced photoacoustic spectroscopy (QEPAS) permits the design of fast, sensitive, selective, and compact sensor systems. A QEPAS sensor was developed employing a room-temperature CW DFB-QCL emitting at 5.26 μm with an optical excitation power of 60 mW. High sensitivity is achieved by targeting a NO absorption line at 1900.08 cm^-1 free of interference by H₂O and CO₂. The minimum detection limit of the sensor is 7.5 and 1 ppbv of NO with 1and 100 second averaging time respectively . The sensitivity of the sensor system is sufficient for detecting NO in exhaled human breath, with typical concentration levels ranging from 24.0 ppbv to 54.0 ppbv.

Hydrogen peroxide (H₂O₂) is a relevant molecular trace gas species, that is related to the oxidative capacity of the atmosphere, the production of radical species such as OH, the generation of sulfate aerosol via oxidation of S(IV) to S(VI), and the formation of acid rain. The detection of atmospheric H₂O₂ involves specific challenges due to its high reactivity and low concentration (ppbv to sub-ppbv level). Traditional methods for measuring atmospheric H₂O₂ concentration are often based on wet-chemistry methods that require a transfer from the gas- to liquid-phase for a subsequent determination by techniques such as fluorescence spectroscopy, which can lead to problems such as sampling artifacts and interference by other atmospheric constituents. A quartz-enhanced photoacoustic spectroscopy-based system for the measurement of atmospheric H₂O₂ with a detection limit of 75 ppb for 1-s integration time was previously reported. In this paper, an updated H₂O₂ detection system based on long-optical-path-length absorption spectroscopy by using a distributed feedback quantum cascade laser (DFB-QCL) will be described. A 7.73-μm CW-DFB-QCL and a thermoelectrically cooled infrared detector, optimized for a wavelength of 8 μm, are employed for theH₂O₂ sensor system. A commercial astigmatic Herriott multi-pass cell with an effective optical path-length of 76 m is utilized for the reported QCL multipass absorption system. Wavelength modulation spectroscopy (WMS) with second harmonic detection is used for enhancing the signal-to-noise-ratio. A minimum detection limit of 13.4 ppb is achieved with a 2 s sampling time. Based on an Allan-Werle deviation analysis the minimum detection limit can be improved to 1.5 ppb when using an averaging time of 300 s.

We report on the design and realization of custom quartz tuning forks with different geometries and sizes aimed to improve the photoacoustic effect in quartz-enhanced photoacoustic (QEPAS) sensor systems. A detailed analysis of the piezoelectric properties in terms of resonance frequencies, quality factors, gas damping was performed.

We report on three different quartz enhanced photoacoustic (QEPAS) sensors operating in the near-IR, mid-IR and THz spectral ranges, employing quartz tuning forks of different sizes and shapes. To test our sensors in the near-IR we used a diode laser working at 2.7 μm, while in the mid-IR we employed a quantum cascade laser (QCL) operating at 7.9 μm, fiber-coupled to the QEPAS cell. In the THz range we employed a QCL emitting at 2.95 THz. H₂S absorption features with line-strength up to 10^-20 cm/mol were selected and QEPAS normalized noise-equivalent absorption in the 10^-10 W•cm^-1•Hz^-1/2 range was achieved..

We describe a prototype trace gas sensor designed for real-time detection of multiple chemicals. The sensor uses an external cavity quantum cascade laser (ECQCL) swept over its tuning range of 940-1075 cm^-1 (9.30-10.7 μm) at a 10 Hz repetition rate. The sensor was designed for operation in multiple modes, including gas sensing within a multi-pass Heriott cell and intracavity absorption sensing using the ECQCL compliance voltage. In addition, the ECQCL compliance voltage was used to reduce effects of long-term drifts in the ECQCL output power. The sensor was characterized for noise, drift, and detection of chemicals including ammonia, methanol, ethanol, isopropanol, Freon- 134a, Freon-152a, and diisopropyl methylphosphonate (DIMP). We also present use of the sensor for mobile detection of ammonia downwind of cattle facilities, in which concentrations were recorded at 1-s intervals.

The first of its kind Gas Chromatograph Infra Red Isotope Ratio (GC-IR2) instruments have been deployed to the field to help the identification of sweet spot during the shale gas exploration. The onsite measurement capability of the GC-IR2 along with its accuracy and speed helped the discovery of the fast dynamics of gas release from shale cuttings. The half life of the isotope change for methane, ethane and propane released from shale cuttings is closely related to the porosity and permeability of the specific shale reservoir, and could be as short as a one hour to a couple of days. Initial δ¹³C values for methane could be extremely fractionated toward heavy ¹³C species that values in the -20~<-10 per mil, which belong to inorganic methane could be measured.

With their large mid-infrared spectral coverage, Quantum Cascade Lasers (QCL) are very promising for probing the molecular fingerprint region. Current applications to high-resolution spectroscopy are mainly limited by their large freerunning frequency instability. A lot of efforts have thus been made recently to characterize and improve their spectral properties, especially the emission line width and the traceability to frequency standards. Here we demonstrate the frequency stabilization of a QCL emitting at 10 μm onto an optical frequency comb (OFC), itself controlled with a remote near-infrared ultra-stable laser. The latter frequency is transferred with an optical fiber link of 43 km from a metrological institute, where its frequency is monitored against frequency standards. From the reference ultra-stable laser stability, one can infer a QCL line width below 1 Hz and a relative frequency stability of 2x10^-15 for an averaging time of 1 s. Moreover the QCL frequency is known with an uncertainty of at most 10^-14 after 100 s averaging time, thanks to the traceability to primary standards. This performance overcome by at least two orders of magnitude what has been demonstrated up to now with a QCL. We further demonstrate the continuous tuning of this stabilized QCL and recorded a few OsO4 molecular absorption lines, some of them being unreported so far to our knowledge. The saturated absorption line width is 25 kHz, well below what has ever been recorded with a QCL. These results open the way to ultra-high precision measurements with molecules with the same performance than currently achieved with atoms.

In this paper recent advances in broadband-tuneable mid-infrared (MIR) external-cavity quantum cascade lasers (EC-QCL) technology are reported as well as their use in spectroscopic process analysis and imaging stand-off detection of hazardous substances, such as explosive and related precursors. First results are presented on rapid scan EC-QCL, employing a custom-made MOEMS scanning grating in Littrow-configuration as wavelength-selective optical feedback element. This way, a scanning rate of 1 kHz was achieved, which corresponds to 2000 full wavelength scans per second. Furthermore, exemplary case studies of EC-QCL based MIR spectroscopy will be presented. These include timeresolved analysis of catalytic reactions in chemical process control, as well as imaging backscattering spectroscopy for the detection of residues of explosives and related precursors in a relevant environment.

We study the dynamics of a Quantum Cascade Laser subject to strong optical feedback in the framework of the Lang-Kobayashi model. In particular, we demonstrate that the continuous wave instability may lead to coherent multimode oscillations that indicate spontaneous phase-locking among external cavity modes. We recently predicted that this unique behavior is linked to the absence of relaxation oscillations in unipolar semiconductor lasers, which are characterized by a fast carriers recombination time (class-A lasers). These theoretical evidences may help understanding the mechanisms possibly leading to spontaneous mode-locking and pulse generation in QCLs.

Quantum Cascade (QC) lasers are widely used in optical communications, high-resolution spectroscopy, imaging, and remote sensing due to their wide spectral range, going from mid-infrared to the terahertz regime. The dynamics of QClasers are dominated by their ultrafast carrier lifetime, typically of the order of a few picoseconds. The combination of optical nonlinearities and ultrafast dynamics is an interesting feature of QC-lasers, and investigating the dynamical properties of such lasers gives unprecedented insights into the underlying physics of the components, which is of interest for the next generation of QC devices. A particular feature of QC-lasers is the absence of relaxation oscillations, which is the consequence of the relatively short carrier lifetime compared to photon lifetime. Optical feedback (i.e. self-injection) is known to be a robust technique for stabilizing or synchronizing a free-running laser, however its effect on QC-lasers remains mostly unexplored. This work aims at discussing the dynamical properties of QC-lasers operating under optical feedback by employing a novel set of rate equations taking into account the upper and lower lasing levels, the bottom state as well as the gain stage’s cascading. This work analyzes the static laser properties subject to optical feedback and provides a comparison with experiments. Spectral analysis reveals that QC-lasers undergo distinct feedback regimes depending on the phase and amplitude of the reinjected field, and that the coherence-collapse regime only appears in a very narrow range of operation, making such lasers much more stable than their interband counterparts.

We demonstrate superresolution in position tracking sensing based on feedback interferometry in quantum cascade lasers (QCLs). QCLs with optical feedback make highly compact sensors since they work as mixer oscillator and detector of infrared radiation. Additionally, QCL continuous-wave emission remains stable at steady state in strong feedback regimes, permitting to gain control on the nonlinearity of the QCL active medium. Here, nonlinear frequency mixing in a QCL-based common-path interferometer is exploited to unveil object’s position with nanometer-scale resolution, far beyond the intrinsic limit of half-wavelength. Experimental results are in excellent agreement with simulations based on Lang-Kobayashi model encompassing multiple-target dynamics.

We report a theoretical and experimental study of laser coupling in hollow-core, fiber-optic waveguides with small-bore diameters of d=200 μm. For the experiments we utilized three mid-infrared quantum cascade lasers with different emission wavelength, which were coupled into the waveguides using lenses with focal lengths in the range 25-76 mm. Measurements of the output beam profiles and propagation losses were obtained as a function of the coupling conditions. With appropriate coupling parameters, single mode beam delivery can be obtained for all laser wavelengths, ranging from λ ~ 5.4 to 10.5 μm.

New advances on Selective Area Growth (SAG) of InGaN/GaN nanostructures by plasma-assisted MBE on GaN/sapphire templates and Si (111) substrates are presented. Both, axial and core-shell structures are considered. Very intense green electroluminescence is achieved on axial nanoLEDs grown on Si(111) with very small emission drift with current injection. First results on core-shell InGaN/GaN structures grown by MBE on GaN templates are also presented. Two approaches are followed: i) top down, where cylindrical micro-rods are etched down by ICP from a 3 micron thick GaN/sapphire template, and bottom up, in which very high aspect ratio GaN cores are used. In both cases, GaN and InGaN shell layers are then grown both in axial and radial directions. Potential advantages of this core-shell structure as compared to the axial one are twofold: the increase of emission surface (lateral area) and the absence of internal electric fields (m-plane). The crystal perfection is much better than that of 2D InGaN films of similar In% composition. Ordered arrays of GaN and InGaN axial nanostructures are also grown on non-polar and semi-polar directions and subsequently merged into a continuous film to produce high quality pseudo substrates. The resulting films exhibit a very strong luminescence, orders of magnitude higher that from the substrate used. Semi-polar GaN templates have a huge density of stacking faults (SFs) most of them are filtered upon coalescence of the nanostructures grown on top. In all cases there is a preferential growth direction along the c-plane (0001). PL and spatially resolved CL measurements on individual nanostructures, either polar, non-polar, or semi-polar show that the In% incorporation depends strongly on the crystal plane considered.

Degenerate two-photon absorption (TPA) is investigated in a 186 nm thick gallium arsenide (GaAs) p-i-n diode embedded in a resonant metallic nanostructure. The full device consists in the GaAs layer, a gold subwavelength grating on the illuminated side, and a gold mirror on the opposite side. For TM-polarized light, the structure exhibits a resonance close to 1.47 μm, with a confined electric field in the intrinsic region, far from the metallic interfaces. A 109 times increase in photocurrent compared to a non-resonant device is obtained experimentally, while numerical simulations suggest that both gain in TPA-photocurrent and angular dependence can be further improved. For optimized grating parameters, a maximum gain of 241 is demonstrated numerically and over incidence angle range of (−30°; +30°). This structure paves the way towards low-noise infrared detection, using non-degenerate TPA, involving two photons of vastly different energies in the same process of absorption in a large bandgap semiconductor material.

Metallic metamaterial structures are used in nanophotonics applications in order to localize and enhance an incident electromagnetic field. We have theoretically and experimentally studied resonant coupling between plasmonic modes of an SRR array and a quantum dot-in-a-well (DWELL) heterostructure. The near-field distribution from the SRRs on the GaAs substrate was first modeled by electromagnetic simulations and optimized SRR dimensions for maximum nearfield coupling at the peak absorption were extracted. The DWELL sample with a ground state emission peak at 1240 nm was grown by molecular beam epitaxy on a semi-insulating GaAs substrate. The sample was uniformly covered with an array of SRRs, and patterned by standard electron-beam-lithography. In order to study the near field coupling of the plasmonic structure into the DWELL, optical characterization was performed on the SRR-DWELL heterostructure, including room temperature photoluminescence, and transmission measurement.

In this work we show that the fabrication method introduced by De Angelis et al.1 is highly versatile and allows to produce three-dimensional (3D) hollow plasmonic nanostructures with a precisely tunable shape and with large scale capabilities. The fabrication process is comprehensively explained and some structure examples are introduced in order to show the versatility of the method. The resulting plasmonic nanoantennas are characterized by Raman spectroscopy in order to evaluate their plasmonic performance in respect to their features.

We proposed and demonstrated the metallic nano-ring structure using polystyrene lift-off process to enhance the sensitivity of an SPR surface. The double layered SPR structures are optimized using the finite-difference time-domain method for the width, thickness, and period of the polystyrene beads. The optimum thickness of the metal film and the metallic nano-ring is 30 and 20 nm in the 214 nm wide nano-hole size, respectively. The metallic nano-ring structures are fabricated with monolayer polystyrene beads of 400 nm wide. The various metallic nano-ring structures have been obtained by transferring method. The sensitivities of the conventional SPR sensor and the metallic nano-ring structures are obtained to 42.2 and 52.1 degree/RIU, respectively.

Researchers all over the world are competing in a technology-driven quest to develop the next generation of ultrasmall, low-power photonic and plasmonic devices. One route to this objective involves hybrid structures that incorporate a phase-changing material into the structure, creating a nanocomposite material in which the optical response of a plasmonic or photonic structure is modulated by a change in phase, crystallinity or dielectric function induced by thermal, optical or electrical stimulus. Vanadium dioxide (VO₂₎ has been considered as a potential electro-optic switching material for electronic and photonic applications ever since its semiconductor-to-metal transition (SMT) was first described half a century ago. This review describes the application of vanadium dioxide as the switching element in (i) a hybrid silicon ring resonator and (ii) a polarization-sensitive, multifunctional plasmonic modulator in the form of a nanoscale heterodimer. As is now widely known, the SMT in VO₂ is also accompanied by a structural phase transition (SPT) from the M1 (monoclinic) to a rutile (tetragonal, R) crystalline form that was believed to prevent a fast recovery after switching. However, recent research has shown that this picture is oversimplified, and that there is a monoclinic metallic state that enables true ultrafast switching. That understanding, in turn, is leading to new concepts in developing hybrid nanocomposites that incorporate VO₂ in silicon photonics and plasmonic modulators, enabling the construction of ultrafast optical switches, modulators and memory elements.

The realization and control of radiation sources is the key for proper development of THz-based metrology. Quantum Cascade Lasers (QCLs) are crucial, towards this purpose, due to their compactness and flexibility and, even more important, to their narrow quantum-limited linewidth. We recently generated an air-propagating THz comb, referenced to an optical frequency comb by nonlinear optical rectification of a mode-locked femtosecond Ti:Sa laser and used it for phase-locking a 2.5 THz QCL. We have now demonstrated that this source can achieve a record low 10 parts per trillion absolute frequency stability (in tens of seconds), enabling high precision molecular spectroscopy. As a proof-ofprinciple, we measured the frequency of a rotational transition in a gas molecule (methanol) with an unprecedented precision (4 parts in one billion). A simple, though sensitive, direct absorption spectroscopy set-up could be used thanks to the mW-level power available from the QCL. The 10 kHz uncertainty level ranks this technique among the most precise ever developed in the THz range, challenging present theoretical molecular models. Hence, we expect that this new class of THz spectrometers opens new scenarios for metrological-grade molecular physics, including novel THzbased astronomy, high-precision trace-gas sensing, cold molecules physics, also helping to improve present theoretical models.

We present a THZ quantum cascade laser operating in continuous wave with an emission covering more than one octave in frequency, and displaying homogeneous power distribution among the lasing modes. The gain medium is based on a heterogeneous quantum cascade structure operating in the THz range. Laser emission takes place from 1.64 THz to 3.35 THz with optical powers of 3 mW and 84 modes above threshold. For narrow waveguides a collapse of the free-running beatnote to linewidths of 980 Hz, limited by jitter, indicate frequency comb operation on a spectral bandwidth as wide as 624 GHz.

Infrared (IR) digital holography (DH) based on CO₂ lasers has proven to be a powerful coherent imaging technique due to the reduced sensitivity to mechanical vibrations, to the increased field of view, to the high optical power and to possible vision through scattering media, such as smoke. In this contribution we report IR DH based on the combination of quantum cascade laser (QCL) sources and a high resolution microbolometric camera. QCLs combine highly desirable features for coherent imaging, such as compactness, high optical power, and spectral purity. The present availability of external cavity mounted QCLs having a broad tuning range, makes them suitable sources for multiple wavelength holographic interferometry. In addition, QCL emission covers several windows throughout a large portion of the IR spectrum, from the mid-IR to the terahertz region. This allows taking advantage of the different optical response of the imaged objects at different frequencies, which is crucial for applications such as non-destructive testing and biomedical imaging. Our holographic system is suitable for the acquisition of both transmission holograms of transparent objects and speckle holograms of scattering objects, which can be processed in real time to retrieve both amplitude and phase.

We develop a spectroscopy platform for industrial applications based on semiconductor quantum cascade laser (QCL) frequency combs. The platform’s key features will be an unmatched combination of bandwidth of 100 cm^-1, resolution of 100 kHz, speed of ten to hundreds of μs as well as size and robustness, opening doors to beforehand unreachable markets. The sensor can be built extremely compact and robust since the laser source is an all-electrically pumped semiconductor optical frequency comb and no mechanical elements are required. However, the parallel acquisition of dual-comb spectrometers comes at the price of enormous data-rates. For system scalability, robustness and optical simplicity we use free-running QCL combs. Therefore no complicated optical locking mechanisms are required. To reach high signal-to-noise ratios, we develop an algorithm, which is based on combination of coherent and non-coherent averaging. This algorithm is specifically optimized for free-running and small footprint, therefore high-repetition rate, comb sources. As a consequence, our system generates data-rates of up to 3.2 GB/sec. These data-rates need to be reduced by several orders of magnitude in real-time in order to be useful for spectral fitting algorithms. We present the development of a data-treatment solution, which reaches a single-channel throughput of 22% using a standard laptop-computer. Using a state-of-the art desktop computer, the throughput is increased to 43%. This is combined with a data-acquisition board to a stand-alone data processing unit, allowing real-time industrial process observation and continuous averaging to achieve highest signal fidelity.

The mid-infrared (mid-IR, wavelength range between 2 and 10 μm) is of great interest for a huge range of applications such as medical and environment sensors, security, defense and astronomy. I will give a broad overview of the different activities recently launched in INL Lyon, in close collaboration with several French and Australian institutions, under the umbrella of “Mid-IR integrated photonics” with a particular focus on novel integrated sources for the Mid-IR including hybrid III-V semiconductors on SiGe sources, thermal sources and nonlinear sources.

Integrated optics is becoming increasingly important for applications in quantum information processing, quantum sensing and for advanced measurement. Intrinsically stable and low-loss it provides essential routing and coupling for quantum optical experiments offering functions such as interconnects, couplers, phase delays and routing. Silica-onsilicon has particular attractions, and in this work the fabrication approaches and advantages of the technique will be explored. In particular, UV direct writing of waveguides and Bragg gratings proves useful for its rapid-prototyping capability and its ability to provide grating for characterization of components for loss, birefringence and coupling ratio. This review concentrates on the fabrication of planar waveguide devices, and ways in which direct UV writing provides important functionality. Examples of applications of silica-on-silicon waveguides include quantum enhanced interferometry, teleportation, boson sampling as well as hybrid operation for single photon detection with transition edge sensors directly placed onto waveguide devices.

Staring infrared focal plane arrays (FPAs) require pixel-level, three-dimensional (3D) integration with silicon readout integrated circuits (ROICs) that provide detector bias, integrate detector current, and may further process the signals. There is an increased interest in ROIC technology as a result of two trends in the evolution of infrared FPAs. The first trend involves decreasing the FPA pixel size, which leads to the increased information content within the same FPA die size. The second trend involves the desire to enhance signal processing capability at the FPA level, which opens the door to the detector behaving like a smart peripheral rather than a passive component—with complex signal processing functions being executed on, rather than off, the FPA chip. In this paper, we review recent advances in 3D integration process technologies that support these key trends in the development of infrared FPAs. Specifically, we discuss approaches in which the infrared sensor is integrated with 3D ROIC stacks composed of multiple layers of silicon circuitry interconnected using metal-filled through-silicon vias. We describe the continued development of the 3D integration technology and summarize key demonstrations that show its viability for pixels as small as 5 microns.

Efficient coupling of nanoemitters to photonic or plasmonic structures requires the control of the orientation of the emitting dipoles related to the emitter. Nevertheless the knowledge of the dipole orientation remains an experimental challenge. Many experiments rely on the realization of large sets of samples, in order to be able to get one nanostructure coupled to a well aligned dipole. In order to avoid these statistical trials, the knowledge of the nature of the emitter (single or double dipole) and its orientation are both crucial for a deterministic approach. Based on the theoretical development of the point-dipole emission, we propose in this paper to determine the nature and the polarization of two types of nanoemitters (spherical nanocrystals and dot-in-rod) by the analysis of their emission polarization [1,2]. The nanoemitters we considered in this study are colloidal semiconductor (CdSe/CdS) nanocrystals with different sizes and aspect ratio, allowing us to establish a relationship between the geometry of a nanoemitter and the nature and orientation of its associated radiating dipole.

Here we present a 2D slit-box electromagnetic nanoantenna inspired by the acoustic Helmholtz resonator. It is able to concentrate the energy into tiny volumes, and a giant field intensity enhancement is observed throughout the slit. Noteworthily, we have shown that this field intensity enhancement can also be obtained in three dimensional structures that are polarization independent. In the Helmholtz nanoantenna, the field is enhanced in a hot volume and not a hot point, which is of great interest for applications requiring extreme light concentration, such as SEIRA, non-linear optics and biophotonics.

Single-photon detectors are the best option for applications where low noise measurements and/or high timing resolution are required. At wavelengths between 900 nm and 1700 nm, however, low noise detectors have typically been based on cryogenic superconducting technology, precluding their extended use in industrial or clinical applications. Here we present a practical (i.e. compact, reliable and affordable) detector, based on a negative feedback InGaAs/InP avalanche photodiode and exhibiting dark counts < 1 count-per-second at 10% efficiency, and with efficiencies of up to 27%. We show how this detector enables novel applications such as singlet-oxygen luminescence detection for Photo Dynamic Therapy (PDT) but can be an enabling technology also for a diverse set of applications in both quantum communication (e.g. long-distance quantum key distribution) and biomedical imaging.

We present a new InGaAs/InP Single-Photon Avalanche Diode (SPAD) with high detection efficiency and low noise, which has been employed in a sinusoidal-gated setup to achieve very low afterpulsing probability and high count rate. The new InGaAs/InP SPAD has lower noise compared to previous generations thanks to the improvement of Zinc diffusion conditions and the optimization of the vertical structure. A detector with 25 μm active-area diameter, operated in gated-mode with ON time of tens of nanoseconds, has a dark count rate of few kilo-counts per second at 225 K and 5 V of excess bias, 30% photon detection efficiency at 1550 nm and a timing jitter of less than 90 ps (FWHM) at 7 V of excess bias. In order to reduce significantly the afterpulsing probability, these detectors were operated with a sinusoidal gate at 1.3 GHz. The extremely short gate ON time (less than 200 ps) reduces the charge flowing through the junction, thus reducing the number of trapped carriers and, eventually, lowering the afterpulsing probability. The resulting detection system achieves a maximum count rate higher than 650 Mcount/s with an afterpulsing probability of about 1.5%, a photon detection efficiency greater than 30% at 1550 nm and a temporal resolution of less than 90 ps (FWHM).

An array of 32x32 Single-Photon Avalanche-Diodes (SPADs) and Time-to-Digital Converters (TDCs) has been fabricated in a 0.35 μm automotive-certified CMOS technology. The overall dimension of the chip is 9x9 mm2. Each pixel is able to detect photons in the 300 nm – 900 nm wavelength range with a fill-factor of 3.14% and either to count them or to time stamp their arrival time. In photon-counting mode an in-pixel 6-bit counter provides photon-numberresolved intensity movies at 100 kfps, whereas in photon-timing mode the 10-bit in-pixel TDC provides time-resolved maps (Time-Correlated Single-Photon Counting measurements) or 3D depth-resolved (through direct time-of-flight technique) images and movies, with 312 ps resolution. The photodetector is a 30 μm diameter SPAD with low Dark Count Rate (120 cps at room temperature, 3% hot-pixels) and 55% peak Photon Detection Efficiency (PDE) at 450 nm. The TDC has a 6-bit counter and a 4-bit fine interpolator, based on a Delay Locked Loop (DLL) line, which makes the TDC insensitive to process, voltage, and temperature drifts. The implemented sliding-scale technique improves linearity, giving 2% LSB DNL and 10% LSB INL. The single-shot precision is 260 ps rms, comprising SPAD, TDC and driving board jitter. Both optical and electrical crosstalk among SPADs and TDCs are negligible. 2D fast movies and 3D reconstructions with centimeter resolution are reported.

Nitrogen Vacancy (NV) centers are point defects in diamond that allow magnetic field sensing based on Optically Detected Magnetic Resonance (ODMR). They are processed in ultrapure single-domain CVD grown diamond crystals and can be operated at room temperature. This results in solid-state sensors with a wide variety of applications. Ensemble of NV centers can be used to perform wide-field magnetic imaging with sensitivity in the nT range. Single NV centers can also be processed, which allows sensing at the atomic scale. This possibility, combined with its unique coherence properties, make NV center an ideal candidate for quantum sensing.

Rising efforts concerning the reduction of CO₂ emission promote the use of fiber reinforced plastics, e.g. in automotive or aircraft engineering due to their low mass compared to classical materials. Although fiber reinforced plastics have critical properties such as low mass and high stiffness compared to classical materials, they also may suffer unpredictable failures due to hidden structural damage. Thus structural health monitoring is vital for the development of modern lightweight structures. Our concept of material integrated sensor technology is based on a combination of a piezoelectric foil with a quantum dot polymer composite. By application of a mechanical (over-) load, electrical charges are generated and injected into the nanocrystals causing PL quenching, which is detectable as local optical contrast. A very efficient charge injection is crucial for sensitive load detection, because of limited amount of generated charges and transport losses. Consequently we have investigated the charge injection and charge storage properties of various types of quantum dots, in particular core shell types CdSe/ZnS and InP/ZnS, embedded in semi-conducting poly(9-vinylcarbazole) (PVK). PL quenching was realized by application of external voltages smaller than 20 V. Initial results indicated a longer charge storage time in InP/ZnS quantum dots, which we attribute to a difference in band level alignment between valence band levels of respective quantum dots and PVK.

For decades, the potential for automation in particular, in the form of smart wheelchairs to aid those with motor, or cognitive, impairments has been recognized. It is a paradox that often the more severe a person's motor impairment, the more challenging it is for them to operate the very assistive machines which might enhance their quality of life. A primary aim of my lab is to address this confound by incorporating robotics autonomy and intelligence into assistive machines turning the machine into a kind of robot, and offloading some of the control burden from the user. Robots already synthetically sense, act in and reason about the world, and these technologies can be leveraged to help bridge the gap left by sensory, motor or cognitive impairments in the users of assistive machines. This paper overviews some of the ongoing projects in my lab, which strives to advance human ability through robotics autonomy.

InAs/GaSb superlattice (SL) is a peculiar quantum system for infrared detection, where electrical and optical properties are directly governed by the composition and the periodicity of the InAs/GaSb cell. Indeed, several structures with different InAs to GaSb thickness ratios in each SL period, can target the same cut-off wavelength. Likewise, the type of conductivity of the non-intentionally doped SL structure is also linked to the InAs/GaSb SL period. The objective of this communication is to use the flexibility properties of InAs/GaSb SL to design and then to fabricate by MBE a pin photodiode where the active zone is made of different SL periods. Electrical and electro-optical characterizations are reported. The results show that SL structure for the MWIR domain can be designed by combining the best of each SL periods.

SCD has developed a range of advanced infrared detectors based on III-V semiconductor heterostructures, grown on GaSb. The XBn/XBp family of detectors enables diffusion limited behavior with dark currents comparable with MCT Rule-07 and with high quantum efficiencies. InAsSb/AlSbAs based XBn focal plane array detectors with a cut-off wavelength of ~ 4.1 μm and formats presently up to 1024×1280 / 15 μm, operate with background limited performance up to ~175 K at F/3. They have a sensitivity and image quality comparable with those of standard InSb detectors working at 77K. In an XBp configuration, the same concept has been applied to an InAs/GaSb type II superlattice (T2SL) detector with a cut-off wavelength of ~ 9.5 μm, which operates with background limited performance up to ~100 K at F/2. In order to design our detectors effectively, a suite of simulation algorithms was developed based on the k ⋅ p and optical transfer matrix methods. In a given T2SL detector, the complete spectral response curve can be predicted essentially from a knowledge of the InAs and GaSb layer widths in a single period of the superlattice. Gallium free T2SL detectors in which the GaSb layer is replaced with InAs1-xSbx (x ~ 0.15-0.5) have also been simulated and the predicted spectral response compared for the two detector types.

Sofradir recently presented Daphnis, its latest 10μm pitch XGA and HD720 products. Daphnis XGA is a 10μm pitch 1024x768 mid-wave infrared focal plane array. The development of small pixel pitch is opening the way to very compact products with high spatial resolution. This new product is key contribution to the HOT technology competition allowing reductions in size, weight and power of the overall package. This paper presents the recent developments achieved at Sofradir to make this 10μm pitch HgCdTe focal plane array. Electrical and electro-optical characterizations are presented to define the appropriate design of 10μm pitch diode array. The technological tradeoffs are explained to lower the dark current, to keep high quantum efficiency with a high operability above 110K, F/4.

The e-SWIR wavelength band is a performance gap for infrared detectors. At both shorter and longer wavelengths, high performance detector technologies exist: SWIR InGaAs detectors (1.7 micron cutoff), and MWIR (3-5 micron) detectors such as InAs-based and GaSb-based Unipolar Barriers, MCT, and InSb. This work discusses development of high performance e-SWIR detectors with cutoff wavelengths in the 2.7 - 2.8 micron range. Two approaches for e-SWIR detector absorber materials were evaluated, lengthening the wavelength response of the SWIR InGaAs technology and shortening the wavelength response of MWIR GaSb-based technology. The InGaAs e- SWIR approach employs mismatched InGaAs absorber layers on InP substrates, using graded AlInAs buffer layers. The GaSb-based approach uses lattice-matched InGaAsSb absorber layers on GaSb substrates. Additionally, two device architectures were examined, pn-based photodiodes and unipolar barrier photodiodes. For both of the absorber materials, the unipolar barrier device architecture was found to be superior. The unipolar barrier device architecture enables both types of device to be free of effects of surface leakage currents and generation-recombination dark currents. InGaAsSb-based devices show excellent performance, with diffusion-limited dark current within a factor of 2-4 of the HgCdTe standard, Rule 07. They achieve background-limited (BLIP) performance at T=210K, which is accessible by thermo-electric coolers. As expected, defects associated with latticemismatch increase dark currents of the InP-based approach. The dark currents of the mismatched unipolar barrier photodiodes are 30x larger than those of the lattice-matched GaSb approach, however despite the defects, the devices still exhibit diffusion-limited operation, and achieve BLIP operation at T=190K Further improvements in the InP-based approach are expected with refinements in the epitaxial structures. Both types of detector approaches are excellent alternatives to conventional e-SWIR detectors.

The recent developments in high-performance infrared sensor technology are opening up new opportunities for exploitation in the defence and security domains. In this paper, the focal plane array developments in the UK on low noise techniques, avalanche photodiodes, high operating temperature devices and large format cameras are reviewed and impact upon military capability is discussed. These technological developments are focused towards enduring challenges including the stand-off identification of hazardous materials and long range target recognition and are enabling exploitation of high performance thermal imaging onto a wide range of smaller platforms.

We present different methods of generating light in the blue-green spectral range by nonlinear frequency conversion of tapered diode lasers achieving state-of-the-art power levels. In the blue spectral range, we show results using single-pass second harmonic generation (SHG) as well as cavity enhanced sum frequency generation (SFG) with watt-level output powers. SHG and SFG are also demonstrated in the green spectral range as a viable method to generate up to 4 W output power with high efficiency using different configurations.

High power, tunable two color lasers are highly suitable for the new wavelengths generation thanks to various nonlinear conversion phenomena. Vertical external cavity surface emitting lasers (VECSELs) are of special interest due to the access to the high intracavity circulating power and wavelength control. We report a novel VECSEL cavity design, which can deliver high power, tunable two color emission. The VECSEL setup is based on a two-chip T-shape cavity configuration which utilizes a polarizing beam splitter to combine two VECSEL cavities. This allows for two-color orthogonally polarized high-power collinear outputs. The two color emission of this kind is ideal for type II nonlinear frequency conversion. A high-Q folded T-cavity is utilized to achieve the combined beams circulating power in excess of 175 W. Intracavity birefringent filters are used to facilitate tunability and wavelength separation between two colors. A configuration of this type is used for high power intracavity type II sum frequency generation, which resulted in tunable blue emission with above 750 mW output, and in the second case a tunable green emission with more than 1.4 W output was obtained. A signal around 1 THz was achieved through type II difference frequency generation in tilted periodically poled lithium niobate. Lastly, a silver thiogallate was utilized to generate mid-IR wavelength around 5.36 μm through type II difference frequency generation.

An effective approach to achieve efficient phase matching for second order nonlinearities, in multilayer structures will be discussed. It uses dispersion engineering in Bragg reflection waveguides to harness parametric processes in conjunction with concomitant dispersion and birefringence engineering in active devices. This technology enables novel coherent light sources using frequency conversion in a self-pumped chip form factor. These sources can also provide continuous coverage of spectral regions, which are not accessible by other technologies including quantum cascade lasers. This approach has been recently demonstrated in multi-layer Silicon-Oxy-Nitride (SiON) waveguides. Harnessing χ⁽²⁾ in SiON offers a route for integration of broadband infrared sources using frequency mixing with opto-fluidics. Different approaches for implementing opto-fluidic structures on Si will be discussed, where the root cause of enhancing the retrieved Raman and infrared signals in these structures will be explained. Recent progress in using this approach to study different nanostructures and biological molecules will be presented.

We report corrugated narrow-ridge interband cascade lasers emitting at λ ≈ 3.5 mm that have been fabricated using CH₄/Cl₂- and BCl3-based inductively coupled plasma reactive ion etch processes, with largely similar results from both types of etches. The highest brightness figure of merit was obtained at intermediate ridge width (28 mm), for which the maximum cw output power at T = 25 °C was 522 mW and the corresponding wallplug efficiency and beam quality factor were 10.3% and M² = 3.1, respectively. The high output power may be attributed to a 7-stage design that employs thicker separate confinement layers for lower internal loss.

Distributed feedback (DFB) laser sources are key components of modern gas analyzers based on tunable laser absorption spectroscopy. While the current induced tuning range of DFB lasers is usually limited to a few nanometers, there are a number of applications which will benefit from lasers with a wider tunability, e.g. multi-gas sensing or spectroscopy of liquids. In this paper, we present monolithic widely tunable laser devices in the 3.6 μm wavelength region based on interband cascade laser material. Using the concept of binary superimposed (BSG) grating structures and two-segment Vernier-tuning, stable single-mode emission is realized at discrete wavelength channels in the 3560 nm to 3620 nm region. A total tuning range around 60 nm in three channels is demonstrated. Within a single channel, the emission wavelength can be tuned mode hop free over up to 5 nm. The wavelength channels can be arbitrarily placed in the range of the material gain, allowing BSG lasers to sweep over several gas absorption lines. The number of channels can be chosen as well. Within a wavelength channel, the lasers show DFB like spectral performance with setup limited sidemode suppressino ratios around 25 dB and milliwatt levels of continuous wave output powers around room temperature. This paper will present an overview of the laser concept, simulations, performance data and applications.

A trace gas absorption sensor for formaldehyde (H2CO) detection was developed using a continuous wave, room temperature, low-power consumption interband cascade laser (ICL) at 3.6 μm. The recent availability of ICLs with wavelength ranged between 3−4 μm enables the sensitive detection of trace gases such as formaldehyde that possesses a strong absorption band in this particular wavelength region. This absorption sensor detected a strong formaldehyde line at 2778.5 cm^-1 in its v1 fundamental band. Wavelength modulation spectroscopy with second harmonic detection (WMS-2f) combined with a compact and novel multipass gas cell (7.6 cm physical length, 32 ml sampling volume, and 3.7 m optical path length) was utilized to achieve a sensitivity of ~6 ppbv for H2CO measurements at 1 Hz sampling rate. The Allan- Werle deviation plot reveals that a minimum detection limit of ~1.5 ppbv can be achieved for an averaging time of 140 seconds.

Laser diodes emitting at different wavelengths can address various applications. 852nm or 894nm single frequency low linewidth laser diodes are needed for Cs pumping for realization of atomic clocks. 780nm high power low linewidth laser diodes and amplifiers are needed for Rb pumping for realization of cooled atoms based inertial sensors. High power lasers at 793nm and 975nm with wavelength stabilization are required to pump Tm and Yb doped fibres respectively. We have developed the building blocks and have realize the different kinds of laser diodes needed for various pumping applications. One of these key building blocks are the Al free active region laser structures, which allow epitaxial regrowth on a Bragg grating necessary to get single frequency or wavelength stabilized lasers.

We present our recent progress in the development of novel lasers with tapered InAs/GaAs quantum-dot devices at their core, unlocking the access to record-high output power from tunable and ultrafast laser diodes, in the spectral region between 1.2 - 1.3 μm.

Mid-infrared spectral region (2-4 μm) is gaining significant attention recently due to the presence of numerous enabling applications in the field of gas sensing, medical, and defense applications. Gas sensing in this spectral region is attractive due to the presence of numerous absorption lines for such gases as methane, ethane, ozone, carbon dioxide, carbon monoxide, etc. Sensing of the mentioned gas species is of particular importance for applications such as atmospheric LIDAR, petrochemical industry, greenhouse gas monitoring, etc. Defense applications benefit from the presence of covert atmospheric transmission window in the 2.1-2.3 micron band which is more eye-safe and offers less Rayleigh scattering than the conventional atmospheric windows in the near-infrared. Major requirement to enable these application is the availability of high-performance, continuous-wave laser sources in this window. Type-I GaSb-based laser diodes are ideal candidates for these applications as they offer direct emission possibility, high-gain and continuous wave operation. Moreover, due to the nature of type-I transition, these devices have a characteristic low operation voltage, which results in very low input powers and high wall-plug efficiency. In this work, we present recent results of 2 μm – 3.0 μm wavelength room-temperature CW light sources based on type-I GaSb developed at Brolis Semiconductors. We discuss performance of defense oriented high-power multimode laser diodes with < 1 W CW power output with over 30 % WPE as well as ~ 100 mW single TE00 Fabry-Perot chips. In addition, recent development efforts on sensing oriented broad gain superluminescent gain chips will be presented.

This work presents a new type of polarization-free GaN emitter. The unique aspect of this work is that the ultraviolet and visible emission originates from the cubic phase GaN and the cubic phase InGaN/GaN multi-quantum-wells, respectively. Conventionally, GaN emitters (e.g. light emitting diodes, laser diodes) are wurtzite phase thus strong polarization fields exist across the structure contributing to the “droop” behavior – a phenomenon defined as “the reduction in emitter efficiency as injection current increases”. The elimination of piezoelectric fields in GaN-based emitters as proposed in this work provide the potential for achieving a 100% internal efficiency and might lead to droopfree light emitting diodes. In addition, this work demonstrates co-integration of GaN emitters on cheap and scalable CMOS-compatible Si (100) substrate, which yields possibility of realizing a GaN laser diode uniquely – via forming mirrors along the naturally occurring cubic phase GaN-Si(100) cleavage planes.

We report a new method for injecting angular momentum in a polariton superfluid. Rather than stirring, such as what is done in atomic BECs, we resonantly inject a ring-shaped rotating superfluid in a planar semiconductor cavity. The resonant injection avoids any significant exciton populations and ensures a high level of control in the system. A Spatial Light Modulator is used to create a Laguerre-Gaussian laser beam that pumps the system and creates a rotating polariton population. By using a ℓ = 8 Laguerre-Gaussian mode we have studied the steady-state condition for observing the nucleation of angular momentum in freely propagating polaritons at the center. We find that, likely due to the fixed border conditions, the angular momentum in weak cavity disorder areas does not spontaneously nucleates at the center, and we observe a single ℓ = 8 vortex. For larger cavity disorder vortex-antivortex pairs can nucleate and we present numerical simulations that explain the role of this disorder to observe such a nucleation.

We create exciton-polariton quasi-particles by exciting optically a microcavity filled with a ladder-type conjugated polymer in the strong coupling regime. At room temperature thermalization of these quasi-particles occurs while it is suppressed at low temperature due to a relaxation bottleneck. Above a certain excitation threshold with incoherent offresonant picosecond laser pulses, we observe the emergence of non-equilibrium Bose-Einstein condensation in the lower polariton branch. This is evidenced by several distinct features such as a blue-shifted emission peak at zero in-plane momentum, accompanied by a nonlinear increase in the emission intensity and a sudden drop of the line width. In contrast to conventional lasing, we find a strong increase in threshold when decreasing the temperature, which can be explained by the peculiar thermalization properties. Single-shot measurements of the emission spectrum allow studying single realizations of the condensate, giving access to non-averaged properties from each individual condensation process. Our approach demonstrates a radically simplified route to investigate Bose-Einstein condensation physics at ambient conditions with easy-to-process non-crystalline materials.

Intrinsic linewidths of quantum-cascade lasers are found to be extremely narrow, ~100 Hz. However, the free running linewidths (usually ~1 MHz) of existing quantum-cascade lasers are governed by flicker frequency-noise that is identified to originate from electrical flicker-noise in the devices. Obviously, substantial suppression of the electrical flicker noise is required for substantial narrowing of free-running LWs. In this presentation, we show systematic experimental results of flicker voltage-noise power-spectral density obtained with mid-infrared quantum-cascade lasers of designed positioning of impurities in injectors. The measured noise-levels depending strongly on impurity position as well as device-temperature are evaluated with an ad hoc model based on fluctuating charge-dipoles induced by trapping and de-trapping at impurity states in their injectors. It is shown that quasi-delta doping of impurities leads to strong suppression of electrical flicker noise by minimization of the dipole-length at a certain temperature, for instance ~300 K and, in turn, is expected to narrow astonishingly the free-running line-width down below 10 kHz without assistances of any types of feedback schemes.

In this work we present a significant step toward monolithic multiplexed distributed feedback (DFB) quantum cascade lasers (QCL) array on indium phosphide (InP). A multi-wavelength DFB-QCL array evanescently coupled to an underlying InGaAs waveguide on iron doped InP wafer is presented. We introduce the design, optimization, simulation and fabrication of the adiabatic coupler ensuring high transfer efficiency from the active to the passive waveguide. The active region designed in 7 μm - 10 μm wavelength range is grown by molecular beam epitaxy on top of an InGaAs waveguide. Components are defined during postgrowth processing, which eliminates the need for material regrowth or bonding techniques. With the present design, one could realize a broadly tunable, mechanically robust, single-mode output source which can be used in spectroscopic applications.

Low-dimensional II-VI oxide-based semiconductor nanostructure photodetectors for light sensing are described. Depending on the absorption edge and energy bandgap of the nanostructured materials, the detection wavelength range can be controlled. The physical properties of the fabricated nanostructures are investigated. The p-n junction property of n-ZnO and p-CuO nanostructures is obtained. This growth of the ZnO nanorod arrays on CuO nanostructures may be useful for photodetection applications. The NiO/ZnO nanostructures are also synthesized. Metal-semiconductor-metal (MSM) type photodetectors are fabricated by integrating the oxide-based (i.e., ZnO and CuO) semiconductor nanostructures. Using the solution-based ZnO seed layer, the UV MSM type photodetectors with the vertically-aligned ZnO nanorod arrays are also fabricated. Their photoresponse characteristics are evaluated in a specific spectral range.

Optical frequency combs have great potential for ultra-high bit rate telecommunications e.g. optical orthogonal frequency-division multiplexing superchannels. For frequency comb generation, monolithic Quantum Dash semiconductor mode-locked lasers are very attractive candidates owing to their broadband optical spectrum, inherent intrinsic low noise and compactness. The active region is based on InAs nanostructures grown on InP for operation in the 1.55 μm window. Owing to enhanced nonlinear effects, a single gain section generates short pulses in the modelocking regime without resorting to an absorber section. An optical bandwidth over 1.3 THz yielding over 100 channels, 10 GHz spaced, is reported. Mode-locking properties are analyzed in the frequency domain using the concept of supermodes. An Allan deviation down to ~ 10^-9 is reported for these passively mode-locked lasers. The low timing jitter, longterm stability and high channel count of these QD based combs are of great potential for Tb/s data transmission with only one single FP type laser source.

Time-Resolved Emission (TRE) is a truly non-invasive technique based on the detection of intrinsic light emitted by integrated circuits that is used for the detection of timing related faults from the backside of flip-chip VLSI circuits. Single-photon detectors with extended sensitivity in the Near Infrared (NIR) are used to perform time-correlated single-photon counting measurements and retrieve the temporal distribution of the emitted photons, thus identifying gates switching events. The noise, efficiency and jitter performance of the detector are crucial to enable ultra-low voltage waveform sensitivity. For this reason, cryogenically cooled Superconducting Nanowire Single-Photon Detectors (SNSPDs) offer superior performance compared to state-of-the-art Single-Photon Avalanche Diodes (SPADs). In this paper we will discuss how detector front-end electronics parameters, such as bias current, RF attenuation and comparator threshold, can be tailored to optimize the measurement Signal-to-Noise Ratio (SNR), defined as the ratio between the switching emission peak amplitude and the standard deviation of the noise in the time interval in which there are no photons emitted from the circuit. For example, reducing the attenuation and the threshold of the comparator used to detect switching events may lead to an improvement of the jitter, due to the better discrimination of the detector firing, but also a higher sensitivity to external electric noise disturbances. Similarly, by increasing the bias current, both the detection efficiency and the jitter improve, but the noise increases as well. For these reasons an optimization of the SNR is necessary. For this work, TRE waveforms were acquired from a 32 nm Silicon On Insulator (SOI) chip operating down to 0.4 V using different generations of SNSPD systems.

Compounds and heterostructures in optical devices often host multiple carrier species that contribute simultaneously to the total electrical conduction, making it difficult to distinguish the characteristics of each type. Here a Fourier-domain Mobility Spectrum Analysis (FMSA)¹ is introduced to sort the conductivity contributions of different carrier species from magnetotransport measurements. Using simulated magnetotransport data from 0 to 15 T of a simple initial trial spectrum, FMSA iteratively adjusts the spectral points in either the mobility domain or its Fourier reciprocal space to fit a mobility range spanning over three orders of magnitude (μ = 670 ~ 1,000,000 cm2/V·s). With its alternating local and global adjustments, FMSA is able to recover the mobility distribution of test data, as verified in convergence plots of the total error as a function of iteration number. This technique resolves the mobility spectra as well or better than competing MSA techniques with a simple and elegant algorithm, while precisely resolving the smoothness and width of mobility peaks without artificial broadening.

We present recent studies on a set of three different long wave IR interband cascade infrared photodetectors with Type-II InAs/GaSb absorbers. Two of these detectors were two- and three-stage structures with regular-illumination configuration and the other was a two-stage structure with reverse-illumination configuration. The 100% cutoff wavelength for these detectors was 6.2 μm at 78 K and extended to 8 μm at 300 K. At T=125 K and higher temperatures we were able to observe the benefits of the three-stage detector over the two-stage device in terms of lower dark current and higher detectivity. We conjecture that the imperfections from the device growth and fabrication had a substantial effect on the low-temperature device performance and were responsible for unexpected behavior at these temperatures. We also found that the zero-bias photo-response increased for temperatures up to 200 K, which was indicative of efficient collection of photo-generated carriers at relatively high temperatures. Electroluminescence and X-ray diffraction measurements suggest that all three grown structures had comparable material qualities. However, the twostage detectors with the reverse-illumination had significantly lower performance than the other two detectors. The activation energy for the two-stage detectors with the reverse-illumination was 37 meV for T=78-100 K, which was much lower than the activation energies of the other two detectors (~140 meV). This low activation energy was attributed to shunt leakage observed in detectors with the reverse-illumination configuration.

In this paper an all-optical reservoir computing scheme is modeled, that paves an alternative route to photonic high bit rate header identification in optical networks and allow direct processing in the analog domain. The system consists of randomly interconnected InGaAsP micro-ring-resonators, whereas the computation efficiency of the scheme is based on the ultra-fast Kerr effect and two-photon absorption. Validation of the system’s efficiency is confirmed through detailed numerical modeling and two application orientated benchmark tests that consists in the classification of 32bit digital headers, encoded an NRZ optical pulses, with a bitrate of 240Gbps,and the identification of pseudo-analog patters for real time sensing applications in the analog domain.

Higher Order Bessel Beams (HOBBs) have many useful applications in optical trapping experiments. The generation of HOBBs is achieved by illuminating an axicon by a Laguerre-Gaussian beam generated by a spiral phase plate. It can also be generated by a Holographic Optical Element (HOE) containing the functions of the Spiral Phase Plate (SPP) and an axicon. However the HOBB’s large focal depth reduces the intensity at each plane. In this paper, we propose a multifunctional Diffractive Optical Element (DOE) containing the functions of a SPP, axicon and a Fresnel Zone Lens (FZL) to generate higher efficiency higher order Bessel-like-beams with a reduced focal depth. The functions of a SPP and a FZL were combined by shifting the location of zones of FZL in a spiral fashion. The resulting element is combined with an axicon by modulo-2π phase addition technique. The final composite element contains the functions of SPP, FZL and axicon. The elements were designed with different topological charges and fabricated using electron beam direct writing. The elements were tested and the generation of a higher order Bessel-like-beams is confirmed. Besides, the elements also generated high quality donut beams at two planes equidistant from the focal plane of the FZL.

Fiber Bragg Grating (FBG) sensors have been extensively used for strain and temperature sensing. However, there is still a need to measure multiple environmental parameters with a single sensor system. We demonstrate a multiplexed FBG sensor with various nano materials (polyallylamine-amino-carbon-nanotube, carbon nanotubes, polyelectrolyte and metals) coated onto the surface of the core/cladding FBG for sensing multiple environmental parameters such as pH (64 pm/pH), protein concentration (5 pm/μg/ml), temperature (15 pm/oC), humidity (31 pm/%RH), gas concentration (7 pm/1000 ppm), and light intensity (infrared: 33 pm/mW, visible: 12 pm/mW and UV: 1 pm/mW) utilizing the same FBG based platform.

We show here that n-type InAs/InGaSb superlattices can be electrically isolated from lightly doped n-type GaSb substrates at much higher temperatures than from the more common undoped p-type GaSb substrates without the use of a large band gap insulating buffer layer. Temperature dependent Hall effect measurements show superlattice conduction up to near room temperature, which is significantly higher than the 20 K observed for p-type substrates. Multi-carrier analysis of magnetic field dependent transport data demonstrate the absence of a substrate related conduction channel. We argue that the isolation is due to the depletion layer at the p-n junction between the p-type buffer layer and the n-type substrate.