The last two decades have seen tremendous progress in the design and performance of mid-wavelength infrared (MWIR) type-II superlattices (T2SL) for detectors. The materials of focus have evolved from the InAs/(In)GaSb T2SL to include InAs/InAsSb T2SLs and most recently InGaAs/InAsSb SLs, with each materials system offering particular advantages and challenges. InAs/InAsSb SLs have the longest minority carrier lifetimes, and their best nBn dark current densities are <5X Rule ’07 at high temperatures, while those of InAs/GaSb SLs and InGaAs/InAsSb SLs are <10X Rule ’07. The quantum efficiency of all three SL detectors can still be improved, especially by increasing the diffusion length beyond the absorber length at low temperatures. Evidence of low temperature carrier localization is greatest for the two SLs containing ternary layers; however, the interface intermixing causing the localization is present in all three SLs. Localization likely does not affect the high temperature detector performance (>120 K) where these SL unipolar barrier detectors are diffusion-limited and Auger-limited. The SL barrier detectors remain diffusion-limited post proton irradiation, but the dark current density increases due to the minority carrier lifetime decreasing with increased displacement damage causing an increase in the trap density. For these SL detectors to operate in space, the continued understanding and mitigation of point defects is necessary.

Global efforts to mitigate climate change have largely focused on reducing emissions of carbon dioxide (CO₂), which is responsible for 55-60% of current anthropogenic radiative forcing on warming impact. Because of its long lifetime (~130 years [1]) in the atmosphere, long-lasting CO₂ will remain the primary driver of long-term temperature rise even if new CO₂ emissions dropped to zero. A "fast-action" climate mitigation strategies is therefore strongly needed to provide more sizeable short-term benefits than CO₂ reductions by reducing emission of short-lived climate pollutants (SLCPs), having atmospheric lifetimes of less than 20 years [2], which would allow for short-term drops in atmospheric concentrations and hence slow climate change over the next several decades. Monitoring of climatically and environmentally active SLCPs is important not only for policy-based reporting, but also for basic process-based understanding of climate related processes in the atmosphere. In this talk, we will overview our recent progress in the developments and applications of laser-based optical instruments for the measurements of environmental and livestock emitted methane (CH₄), as well as the measurement of black carbon (BC) absorption. The experimental detail, the preliminary measurement results, the corresponding data processing and analysis will be presented.

A quantum cascade laser-based gas analyzers with table-top size are developed for the acetone and isotope of carbon dioxide. The precision of 0.1 ppm and 0.3 ‰ in delta notation are achieved respectively.

We report here on the realization of a single-tube on-beam quartz-enhanced photoacoustic (QEPAS) spectroscopy sensor employing a custom-made quartz tuning fork (QTF) with a large prong spacing. The prongs of the QTF have been designed in order to provide a quality factor twice higher when the QTF operates in the first overtone flexural mode than in the fundamental mode. The influence of the microresonator tube on the main parameters characterizing the sensing performance of the QEPAS spectrophone, including the quality factor, the magnitude of the QEPAS signal and the associated background noise was investigated in detail.

Nitrogen oxides (NO_x), including nitric oxide (NO) and nitrogen dioxide (NO₂) play important roles in determining the photochemistry of the ambient atmosphere, controlling the production of tropospheric ozone, affecting the concentration levels of the hydroxyl radical, and forming acid precipitation. A sensor system capable of simultaneous measurements of NO and NO₂ by using a commercial 76 m astigmatic multi-pass gas cell (MPGC) was developed in order to enable fastresponse NOx detection. A continuous wave (CW), distributed-feedback (DFB) quantum cascade laser (QCL) and a CW external-cavity (EC) QCL were employed for targeting a NO absorption doublet at 1900.075 cm^-1 and a NO₂ absorption line at 1630.33 cm^-1, respectively. Both laser beams were combined and transmitted through the MPGC in an identical optical path and subsequently detected by a single mid-infrared detector. A frequency modulation multiplexing scheme was implemented by modulating the DFB-QCL and EC-QCL at different frequencies and demodulating the detector signal with two Labview software based lock-in amplifiers to extract the corresponding second-harmonic (2f) components. Continuous monitoring of NO and NO2 concentration levels was achieved by locking the laser frequencies to the selected absorption lines utilizing a reference cell filled with high concentrations of NO and NO₂. The experimental results indicate minor performance degradation associated with frequency modulation multiplexing and no cross talk between the two multiplexed detection channels. The performance of the reported sensor system was evaluated for real time, sensitive and precise detection of NO and NO₂ simultaneously.

We report on a novel quantum cascade laser (QCL) capable of operating in pure amplitude or wavelength modulation configuration thereby allowing the acquisition of background-free gas absorption-line profiles using quartz-enhanced photoacoustic spectroscopy (QEPAS). The QCL is composed of three electrically independent sections: Gain, Phase (PS) and Master Oscillator (MO). The non-uniform pumping of these three QCL sections allows laser wavelength tuning with constant optical power and vice-versa. Pure QEPAS amplitude modulation operating conditions were obtained by modulating the PS current, while pure wavelength modulation was obtained by modulating the MO section and slowly scanning the PS current.

Reliable standoff detection of traces of explosives is still a challenging task. Imaging MIR backscattering spectroscopy has been shown to be a promising technique for non-contact detection of traces of explosives on various surfaces. This technique, which is eye-safe, relies on active imaging with MIR laser illumination at various wavelengths. Recording the backscattered light with a MIR camera at each illumination wavelength, the MIR backscattering spectrum can be extracted from the three-dimensional data set recorded for each point within the laser illuminated area. Applying appropriate image analysis algorithms to this hyper-spectral data set, chemically sensitive and selective images of the surface of almost any object can be generated. This way, residues of explosives can be clearly identified on the basis of characteristic finger print backscattering spectra and separated from the corresponding spectra of the underlying material. To achieve a high selectivity, a large spectral coverage is a key requirement. Using a MIR EC-QCL with a tuning range from 7.5 μm to 9.5 μm, different explosives such as TNT, PETN and RDX residing on different background materials, such as painted metal sheets, cloth and polyamide, could be clearly detected and identified. For short stand-off detection distances (<3 m), residues of explosives at an amount of just a few 10 μg, i .e. traces corresponding to a single fingerprint, could be detected. For larger concentration of explosives, stand-off detection over distances of up to 20 m has already been demonstrated. During the European FP7 projects EMPHASIS and HYPERION several field tests were performed at the test site of FOI in Sweden. During these tests realistic scenarios were established comprising test detonations of IEDs. We could demonstrate the potential of QCL-based imaging backscattering spectroscopy for the detection of trace amounts of hazardous substances in such scenarios.

We are developing a technology for standoff detection of chemicals on surfaces based on active broadband infrared imaging spectroscopy. This approach leverages one or more IR quantum cascade lasers (QCL), tuned to strong absorption bands in the analytes and directed to illuminate an area on a surface of interest. An IR focal plane array is used to image the surface response upon laser illumination. The broadband IR signal is processed as a hyperspectral image cube comprised of spatial, spectral and temporal dimensions as vectors within a detection algorithm. Such standoff spectroscopic imaging applications place stringent stability requirements on the wavelength, power, pulse width and spatial beam profile that pose a challenge for broadly tunable IR QCL. In this manuscript, we discuss methods to mitigate these challenges, including extensive calibration and active feedback stabilization. These mitigation methods should benefit many applications of IR QCL, including those for standoff detection, spectroscopy and imaging.

We report here an analysis of the performance of a quartz-enhanced photoacoustic (QEPAS) system operating in a pulsed mode by employing a quantum cascade laser (QCL). The QEPAS system is based on a quartz tuning fork (QTF) having fundamental resonance frequency of 4.2 kHz and a first overtone resonance of 25.4 KHz. Water vapor was used as a target gas by selecting its absorption line falling at 1296.5 cm^-1 with a line strength of 1.69⋅10^-22 cm/molecule. The QEPAS signal was investigated, while varying the QCL duty-cycle from continuous wave operation, down to 5%, which corresponds to a laser power consumption of 0.17 mW and a pulse-width of 4 μs.

We present mid-infrared vibrational spectroscopy and imaging at the nanoscale of individual cell membranes deposited on ultraflat gold substrate by use of resonantly-enhanced mechanical photoexpansion technique. This platform allows one to measure the energy absorbed by the sample by monitoring its local thermal expansion with a nanometer atomic force microscope tip. The observed Amide-I and Amide-II bands of proteins in the spectrum acquired on individual purple membrane flakes, filled with bacteriorhodopsin (bR) molecules, are in good agreement with the far-field infrared spectrum collected on large numbers of membranes. Differences among the relative intensity of the two Amide bands in the near- and far-field spectra are attributed to different orientation of bR protein molecules in the two samples. Strong vibrational contrast imaging at the Amide-I of proteins with a lateral resolution of around 50 nm is reported for individual flakes of both purple membranes and artificial lipid vesicles loaded with channelrhodospin molecules.

Only recently, a novel type of intensity autocorrelator in the time-domain has been reported for the Terahertz frequency range. The technique is based on fast electro-optic sampling in a double beam configuration and its temporal resolution is ultra-fast, as short as only few hundreds of femtoseconds. In particular, the self-referencing character of the technique is suitable for any type of source, including free-running sources. These unique characteristics enable therefore the investigation of the output profile of Terhertz Quantum Cascade Laser based Frequency Combs, with typical roundtrip times of few tens of picoseconds. The output dynamics of such devices have been investigated theoretically by Maxwell-Bloch equations and experimentally using Shifted Wave Interference Fourier Transform Spectroscopy. In this work, we present the results of the direct measurement of intensity autocorrelations of a Terahertz comb around 2.5 THz, when operated in the comb and high-noise regime, with radio-frequency beatnotes of 800 Hz and few MHz, respectively. We find the laser to be both amplitude- and frequency-modulated in both regimes, with a modulation ratio of the intensity of roughly 90 percent.The technique might come to use in future for the measurement of free-running pulses at Terahertz frequencies with high temporal resolution.

Plasmonic nanoantenna designs are quickly evolving in the direction of practical molecular sensing applications hence their wavelength range is being extended from the visible towards the mid-infrared. The problem of obtaining, in the mid-infrared, the same degree of plasmonic confinement obtained with gold in the visible range is related to the perfect conductor behavior of metals at long wavelengths. Here we fabricated bow-tie nanoantennas made of bottom-up assembled “metallic germanium” with free electron density of the order of 10²⁰ cm^-3 and therefore short plasma wavelength of 4.5 μm. We demonstrate the existence in the antenna gaps of confined hotspots with radius of the order of 100 nm, which we imaged by near-field photoexpansion microscopy at a wavelength of 5.8 μm in order to provide a clear proof of strong field confinement in the mid-infrared.

While much of the previous work on interband cascade lasers (ICLs) has been limited to the 3-4 μm spectral range, it was recently demonstrated at NRL and elsewhere that the low threshold current and power densities characteristic of ICLs can be extended to longer wavelengths. Here we report on the performance of ICLs operating in the 4.6-6.1 μm spectral range. The pulsed threshold current density at room temperature for an ICL emitting at λ = 4.8 μm is 220 A/cm², the lowest ever reported for a semiconductor laser at such a long emission wavelength. Broad-area devices emitting in the 4.6-4.9 μm range are observed to maintain pulsed external differential quantum efficiencies (EDQEs) of 11-17% when operating at 375 K. An ICL emitting at λ = 5.7 μm exhibits a threshold current density of 450 A/cm² and EDQE of 27% at room temperature. The Auger coefficients extracted from these thresholds indicate a systematic increase with wavelength, with the value at 6 μm being 3-4 times higher than that at λ = 3.5 μm.

In this work we present latest achievements on gain chips as sources for single-frequency tunable laser absorption spectroscopy and sensing. External cavity lasers based on Brolis Semiconductors (2.05 – 2.45) μm wavelengths GaSb gain chips exhibited single mode laser emission with linewidths <100 kHz and output powers of <5 mW in the entire tuning range of <100 nm per chip. Continuous current tuning of 60 GHz and mode-hop free piezo tuning of 26 GHz were demonstrated. Additionally, we report on extended wavelengths range by demonstrating low spectral modulation 850 nm GaAs-based gain chips. Finally, experimental results on GaSb-based gain chip integration with silicon photonics are presented.

Interband cascade lasers (ICLs) are a promising light source for the mid-infrared (mid-IR) spectral range. However, for certain applications such as spectroscopic techniques for chemical sensing and non-invasive disease diagnostics, a broadband incoherent radiation source such as an LED may be more desirable. Here we investigate both ICLs and interband cascade light emitting devices (ICLEDs). The ICLEDs follow the example of ICLs by cascading multiple active stages in series to improve efficiency and increase output power, but without an optical cavity to provide feedback. In this work we will present studies of these devices using high hydrostatic pressure techniques to determine the key efficiency limiting processes so that they might be mitigated. The application of hydrostatic pressure causes reversible changes to the band structure, increasing the energy of the conduction band gamma point and moving other key points in the band structure. This makes it a useful technique to probe recombination processes that depend on band gap and offsets, independently of temperature. For a laser dominated by CHCC Auger recombination, as is typical in narrow band gap devices for the mid-IR, one would expect a decrease in threshold current with increasing pressure, as the Auger process decreases with increasing band gap. However, the lasers studied here exhibit an increase in threshold current with pressure, indicating that other processes also play a significant role. We will discuss the relative contributions from Auger recombination and other processes such as defect-related recombination and carrier leakage in these devices, with respect to relevant modelling.

The family of interband cascade (IC) IR devices includes: interband cascade lasers (ICLs), interband cascade IR photodetectors (ICIPs), and thermophotovoltaics (ICTPVs). To date, developments at the component level have resulted in power-efficient mid-IR ICLs with CW operation at room temperature and above as well as uncooled mid-IR low-noise and high-speed ICIPs. However, there has been little effort to integrate these devices on a single chip for an IR photonic system. Since an appropriately designed ICL can operate as an IR photodetector at zero bias, ICLs and ICIPs can be grown and fabricated on a single chip, enabling the on-chip integration of IR lasers and photodetectors for mid- and long-IR wavelengths. We report the first demonstration of monolithically integrated mid-IR IC devices operating at room temperature. The unit consists of a monolithically integrated ICL and ICIP fabricated using focused ion beam (FIB) milling. The base structure is a type-I ICL with quaternary GaInAsSb active regions. The laser peak emission wavelength is 3.1 μm at 20 ◦C and the 10% cut-off wavelength of the corresponding ICIP is 3.3 μm, which ensures sufficient photon absorption at the lasing wavelength. For a laser/detector unit (at 20 ◦C) with a 12 μm gap between laser mirror and detector, the open-circuit voltage of the ICIP is 1.06 V and its short-circuit current is 106 μA, resulting from the laser emission (2.6 mW/facet). These preliminary results demonstrate the practical application of integrated IC devices for high-temperature, high-bandwidth and power-efficient on-chip sensors and optical communication mid-IR photonic systems.

Narrow gap semiconductors and superlattices relevant to optoelectronics often host multiple conducting species, such as electrons and holes, requiring a mobility spectral analysis (MSA) method to separate contributions to the conductivity. Building on the Fourier-domain MSA (FMSA) method proposed previously by the authors, we introduce a background subtraction step prior to FMSA to more accurately extract the spectral mobilities below what is normally considered the low mobility threshold μth = 1/B_max, where B_max is the maximum magnetic field of the experimental data under analysis. This preliminary step subtracts a linear background from the magnetotransport data and enables a more accurate fit in the low mobility range by several orders of magnitude. Background subtraction extends the useful low-mobility limit by a factor of 5 to μ_min = 1/5Bmax, and can be easily applied in other MSA techniques where low mobilities are of interest.

We demonstrate sub-wavelength electromagnetic resonators operating in the THz spectral range, whose resonant properties and optical response can be engineered using lumped elements, similarly to what is done in electronic circuits and antennas. We discuss the device concept, and we experimentally study the tuning of the resonant frequency as a function of variable capacitances and inductances. The advantages of this ‘circuit-tunable’ platform to realize novel THz meta-devices featuring an ultra-small semiconductor core are then discussed. As an application, we show that these micro-resonators have a strong potential for ultra-fast THz detection, when combined to a tiny quantum well photodetector active core.

Plasmonic terahertz (THz) resonators provide a promising route for exploring strong light-matter coupling phenomena. Double-metal resonator designs in particular enable strong enhancement of the THz field and provide well-defined field orientation and confinement within a sub-wavelength size volume. The strong field confinement however limits access to the internal fields essential for investigations of light-matter coupling. We propose and investigate a method for mapping and spectroscopic analysis of the internal fields in double-metal plasmonic THz resonators. We use aperture-type scanning near-field THz microscopy to access strongly confined fields with sub-wavelength spatial resolution of ~5 μm (~λ/100). Combined with the THz time-domain spectroscopy technique, the near-field method allows us to perform spectroscopic studies and investigate the field evolution inside the resonator. This experimental method opens doors to studies of strong light-matter coupling at THz frequencies in individual plasmonic resonators.

Terahertz quantum cascade lasers (THz QCL) are a very promising source for efficient frequency comb generation at terahertz frequencies. They do not only provide an output power of the order of milliwatts but are also covering a large spectral bandwidth. Octave spanning devices have recently been reported by our group. They provide a very low intrinsic dispersion due to the flat gain curve and the flat losses of the resonator. This allows frequency comb operation up to more than 600 GHz bandwidth with standard broadband metal-metal waveguide Fabry-Pérot QCLs. Frequency combs at terahertz frequencies are especially interesting for spectroscopic applications employing the powerful dual-comb setup. Such a setup requires a fast detector which is difficult to get with a sufficient sensitivity at terahertz frequencies. We present here an alternative approach, which does not need a fast detector but rather uses one of the two THz QCL frequency combs as an ultrafast multiheterodyne detector integrating local oscillator (LO) and detector in one single device. Two laser ridges are fabricated on the same chip at a distance of 500 um. Part of the light from the sample laser is coupled into the LO laser via the metallic ground plane. The downconverted multiheterodyne beatnote can be measured through the laser power supply line with a bias Tee. The obtained dual-comb covers a bandwidth of 630 GHz with a central frequency of 2.5 THz. The frequency comb spacing was analysed using frequency counting techniques revealing an accuracy down to _frep=fcarrier 10^(-12) at the carrier frequency of 2.5 THz.

Silicon photonics is being considered as the future photonic platform for low power consumption optical communications. However, silicon is a centrosymmetric crystal, i.e. silicon doesn’t have Pockels effect. Nevertheless, breaking the crystal symmetry of silicon can be used to overcome this limitation. This crystal modification is achieved by depositing a SiN high-stress overlayer. In this work, we present recent developments on the subject taking into account parasitic effects including plasma dispersion effect and fixed charge effect under an electric field. We theoretically and experimentally investigated Pockels effect in silicon waveguides and last results will be presented.

Ternary GaAsP nanowires (NWs) have gained great attention due to their structure-induced novel properties and band gap that can cover the working wavelength from green to infrared. However, the growth and hence applications of selfcatalyzed GaAsP NWs are troubled by the difficulties in controlling P and the complexities in growing ternary NWs. In this work, self-catalyzed core-shell GaAsP NWs were successfully grown and demonstrated almost stacking-fault-free zinc blend crystal structure. By using these core-shell GaAsP NWs, single NW solar cells have been fabricated and a single NW world record efficiency of 10.2% has been achieved. Those NWs also demonstrated their potential application in water splitting. A wafer-scale solar-to-hydrogen conversion efficiency of 0.5% has been achieved despite the low surface coverage. These results open up new perspectives for integrating III−V nanowire photovoltaics on a silicon platform by using self-catalyzed GaAsP core−shell nanowires.

Gallium Nitride (GaN) materials are the backbone of emerging solid state lighting. To date, GaN research has been primarily focused on hexagonal phase devices due to the natural crystallization. This approach limits the output power and efficiency of LEDs, particularly in the green spectrum. However, GaN can also be engineered to be in cubic phase. Cubic GaN has a lower bandgap (~200 meV) than hexagonal GaN that enables green LEDs much easily. Besides, cubic GaN has more isotropic properties (smaller effective masses, higher carrier mobility, higher doping efficiency, and higher optical gain than hexagonal GaN), and cleavage planes. Due to phase instability, however, cubic phase materials and devices have remained mostly unexplored. Here we review a new method of cubic phase GaN generation: Hexagonal-to-cubic phase transition, based on novel nano-patterning. We report a new crystallographic modelling of this hexagonal-to-cubic phase transition and systematically study the effects of nano-patterning on the GaN phase transition via transmission electron microscopy and electron backscatter diffraction experiments. In summary, silicon-integrated cubic phase GaN light emitters offer a unique opportunity for exploration in next generation photonics.

SHG is used in many practical applications such as a substance diagnostics, and imaging of various processes as well as for frequency conversion. Well known that the frequency doubling is used also for a generation of tripled frequency wave due to mixing of optical radiation at basic frequency with optical radiation at doubled frequency. In this case an important role plays a relation between phases of interacting waves with basic frequency and doubled frequency. Therefore, a derivation of the corresponding law for phase evolutions is an urgent problem. Below we provide such derivation for a SHG of high intensive femtosecond pulse with taking into account an influence of a cubic nonlinear response on the frequency doubling. Using the frame-work of long pulse duration approximation and plane wave approximation as well as an original approach we derive the solution of Schrodinger equations describing the SHG for femtosecond pulse without using the basic wave energy non-depletion approximation. It should be stressed, that the frequency conversion in conditions under consideration possesses multi-stability: there are many modes of SHG efficiency. We write a wave phase evolution for each of the modes. The derived formulas are verified by computer simulation based on using the corresponding Schrodinger equations.

We studied the Ga-free InAs/InAsSb type-II superlattice (T2SL) period, thickness and antimony composition, in order to define an optimized structure suitable for detection of the full mid-wavelength infrared domain (MWIR). The SL structures were fabricated by MBE on n-type GaSb substrates and exhibited cut-off wavelengths between 5μm and 5.5μm at 150K. The growth procedure used to achieve strain-balanced structures is reported and first structural and optical results, made of high-resolution Xray diffraction pattern, AFM image scan, photoluminescence (PL) and time resolved photoluminescence measurements (TRPL), are presented and analyzed.

High temperature operation of long wavelength interband cascade infrared photodetectors (ICIPs) has been demonstrated with a working temperature above 300 K. We conducted a comparison study of three sets of ICIP structures, which comprise single absorber barrier detectors and multi-stage ICIPs with four, six and eight discrete absorbers. The 90% cutoff wavelength of these detectors was between 7.5 and 11.5 μm from 78 to 340 K. Advantages of the multi-stage ICIPs over the one-stage devices are demonstrated in terms of lower dark current density, higher detectivity (D*) and higher operating temperatures. Multiple stage ICIPs were able to operate at temperatures up to 340 K with a monotonically increasing bias-independent responsivity up to 280 K, while the one-stage detectors operated at temperatures up to 250 K with the responsivity decreased at 200 K with bias dependence. The D* values for these ICIPs at 200 and 300 K were higher than 1.0×10⁹ and 1.0×10⁸ cmˑHz^1/2/W at 8 μm, respectively, which is more than a factor of two higher than the corresponding values for photovoltaic HgCdTe detectors with similar cutoff wavelengths. Interestingly, negative differential conductance (NDC) was observed in these detectors at high temperatures. The underlying physics of the NDC was investigated and correlated with the number of cascade stages and electron barriers. With enhanced electron barriers in the multiple-stage ICIPs, the NDC was reduced, and the device performance, in terms of D*, was improved.

We investigated a novel approach to extend a cut-off wavelength of Sb-based nBn detectors. We incorporated a series of single InSb monolayer into InAsSb bulk that allowed to realize a digital alloy absorber with an extended cut-off wavelength of λ = 4.6 μm at T = 200 K. The cut-off wavelength extension to 4.6μm is technologically important for realization of detectors covering CO₂ absorption line at 4.26μm.

In the short wavelength infrared (SWIR) region, InGaAs/GaAsSb type-II quantum well absorption structures are proposed as an attractive material for realizing low dark current. Recently QVGA format (array size 320×256) focal plane array (FPA) with cutoff-wavelength of 2.35 μm was demonstrated for commercial use by our group. We succeeded in extending cut-off wavelength of FPA consisting of InGaAs/GaAsSb type-II quantum well up to 2.5 μm. The 250-pairs InGaAs/GaAsSb quantum well structure lattice matched to InP substrate was grown by metal organic vapor phase epitaxy (MOVPE). The p-n junction of each pixel was formed by selective zinc diffusion method. Dark current of pixel showed the diffusion current limited mode and slightly better than that of HgCdTe with a same cutoff-wavelength. We present the electrical and optical characteristics of InGaAs/GaAsSb type-II quantum well FPA with cutoff-wavelength of 2.5 μm.

Midwave-midwave dual color detection has been successfully demonstrated by using pixel filters fabricated on top of InAs/GaSb focal plane arrays (FPAs). The pixel filters used in these FPAs were designed to transmit infrared radiation in the 3.5 - 4.1 μm wavelength region and to completely block light shorter than 3.5 μm. By comparing the signals of filtered and unfiltered pixels, excellent contrast between the two bands were obtained. This design concept offers a great flexibility to tailor the transmission window to any wavelength range within the 3-5 μm wavelength region. In particular, this dual color detector concept has been used for gas detection of volatile organic compounds which have main absorption peaks at 3.3 μm.

Timely technology transition with minimal risk requires an understanding of fundamental and technology limitations of material synthesis, device operation and design controllable parameters. However, this knowledge-based approach requires substantial investment of resources in the Science and Technology (ST) stage of development. For low volume niche semiconductor technologies of Department of Defense (DoD) relevance, there is little drive for industry to expend their limited resources towards basic research simply because there is no significant return on investment. As a result, technology transition from ST to product development is often delayed, expensive and carries risks. The Army Research Laboratory (ARL) is addressing this problem by establishing a Center for Semiconductor Modeling of Materials and Devices (CSM) that brings together government, academia, and industry in a collaborative fashion to address research opportunities through its Open Campus initiative. This Center leverages combined core competencies of partner organizations, which include a broad knowledge base in modeling, and its validation; sharing of computational, characterization, materials growth and device processing resources; project continuity; and ‘extension of the bench’ via exchange of researchers between affiliated entities. A critical DoD technology is sensing in the infrared (IR) spectrum, where understanding of materials, devices and methods for sensing and processing IR information must continually improve to maintain superiority in combat. In this paper we focus on the historical evolution of IR technology and emphasize the need for understanding of material properties and device operation to accelerate innovation and shorten the cycle time, thereby ensuring timely transition of technology to product development and manufacturing. There are currently two competing IR technologies being pursued, namely the incumbent II-VI Hg₁- _xCd_xTe technology and the III-V Type 2 Superlattices (SLs) technology. A goal of the CSM is to develop physics based models for Type 2 SLs with the capability to timely understand the knowledge gap between what is built and what is designed.

HgCdTe avalanche photodiodes offers a new horizon for observing spatial or temporal signals containing only a few infrared (IR) photons, enabling new science, telecommunication and defence applications. A large number of HgCdTe APD based detectors have been developed at CEA LETI to address the increasing number of applications in which a faint photonic information needs to be extracted from the noise of the proximity electronics used to sample the signal. The performance of HgCdTe APDs is directly related to the multiplication process and the dark current generation in the APDs. The impact of these parameters is presented as a function of the Cd composition and geometry of the APDs. The obtained and expected performance of HgCdTe APD detectors is reported for applications ranging from very low flux observations with long observations times to high data rate telecommunications with up to single photon resolution.

Type II Strained-Layer Superlattice detectors are currently being incorporated into hybridized infrared camera focal plane arrays for commercial applications. The detectors offer significant advantages over InSb and MCT detectors for certain application spaces, particularly high-speed imaging for industrial purposes, and military test ranges. The advantage over MWIR InSb sensors is driven by blackbody physics, which results in much higher emitted photon radiance values for target temperatures around ambient, as well as increased temperature dynamic range as a result of the lower thermal derivative in the LWIR band relative to the MWIR band.

Type II superlattices (T2SLs) based on alternating layers of InAs and GaSb exhibit rather unique properties, including a zero band gap at a critical value of the layer thicknesses. In this respect, T2SLs bear a close relationship to the alloy, Hg_1-xCd_xTe (“MCT”), where the band gap vanishes at a critical value of the composition parameter, x. A 15 μm pitch T2SL Long Wave Infrared array detector has recently been developed by SCD, based on a new XBp barrier architecture and a new and robust passivation process. This detector is made entirely from III-V materials and exhibits performance comparable to high quality MCT detectors. The SCD T2SL XBp detector contains both an InAs/GaSb active layer (AL) and an InAs/AlSb barrier layer. A k • p simulation method is described which can predict both the quantum efficiency and dark current with reasonable precision, from a basic definition of the superlattice period and the AL stack thickness. Results are compared with simulations for type I HgTe/CdTe superlattices. The method introduces a number of novel features including the use of an interface matrix, and a way of calculating the Luttinger parameters from standard reference values. For layer thicknesses greater than the critical values, both InAs/GaSb/AlSb and HgTe/CdTe superlattices undergo a transition to a Topological Insulator (TI) phase. The TI phase exhibits unusual spin polarized transport and optical properties which may be useful in future spintronic and THz devices.

This paper reports studies on spatial characteristics of Mid Wave InfraRed (MWIR) InAs/GaSb superlattices (T2SL) photodetectors. Modulation Transfer Function (MTF) measurements on commercial T2SL MWIR Focal Plane Array (FPA) are reported, using a Continuously Self Imaging Grating (CSIG). We find that measurements of the pixel size can be reliably achieved thanks to a new approach of data processing. Next, a new class of radiometric characterization, called "correctability", or ability for FPA pixels to durably keep the same behavior when exposed to a given radiometric flux, has been investigated on. Gain and offset corrections and Residual Fixed Pattern Noise (RFPN) measurements have also been made. The results obtained confirm the potentiality of high performance T2SL infrared photodetectors.

The knowledge of carrier concentration of doped or non-intentionally doped layer structures grown by Molecular Beam Epitaxy (MBE) is crucial to fabricate and manage design of new advanced photodetectors called "barrier structures". This communication reports on capacitance-voltage (C-V) study on MOS structure. Simulation to define specific MOS design, allowing doping layer concentration extraction by measurements, is performed. MOS structures based on InAs/GaSb Longwave infrared (LWIR) superlattice have been fabricated and characterized. Results obtained were analyzed and compared with simulations.

Time-Correlated Single Photon Counting (TCSPC) is acknowledged as one of the most effective techniques for measuring weak and fast optical signals, since it provides very high temporal resolution and sensitivity. Nevertheless, the long acquisition time needed to perform a measurement it’s still the main drawback. To overcome this limitation, multidimensional TCSPC systems have been developed, but they still suffer for a strong trade-off between performance and number of channels: the higher the number of channels, the poorer the performance. In this work we present the design of a complete TCSPC acquisition system which is meant to overcome this trade-off. Since the best state-of-the-art detectors and sensing circuits developed so far are designed with different technologies, following the same approach those circuits will be designed onto different chips to achieve the best performance from both sides. Through Silicon Vias (TSVs) will be investigated as a possible solution for connecting a custom technology SPAD array to a CMOS pick-up circuit. Since a high number of detectors will cause the count rate to saturate due to the limited transfer rate of a PC, the target throughput has been set to 10 Gb/s, well beyond the state of the art. Consequently, the number of acquisition chains has been tailored on the affordable throughput, and a dynamic-routing logic connects the detectors to this lower number of acquisition channels. Five fast Time-to-Amplitude Converters (TACs), able to reach 80 Mconv/s, have been designed to get high temporal resolution along with low dead time.

Nanoparticles composed of high refractive index semiconductors can support strong localized Mie-type resonances of electric and magnetic multipolar character that can be tuned by the nanoresonator geometry [1]. In addition, such semiconductor nanoresonators can exhibit very low absorption losses at optical frequencies. Based on these unique optical properties, semiconductor nanoresonators represent versatile building blocks of functional photonic nanostructures with tailored optical properties. This talk will provide an overview of our recent advances in controlling the generation and propagation of light with dielectric nanostructures composed of silicon or other high-index semiconductor nanoresonators. First, I will focus on passive and linear silicon metasurfaces designed to impose a spatially variant phase shift onto an incident light field, thereby providing control over its wave front. Based on the simultaneous excitation of electric and magnetic dipole resonances, silicon nanoresonators can be tailored to emulate the behaviour of the forward-propagating elementary wavelets known from Huygens’ principle [2]. This concept allows for the realization of various wave front shaping devices with high transmittance efficiency, full phase coverage, and a polarization insensititve response [3,4]. I will then discuss how we can utilize semiconductor nanoresonators for tailoring spontaneous emission from nanoscale light sources as well as for the manipulation of nonlinear effects in semiconductor nanoparticles. [1] I. Staude et al., ACS Nano 7, 7824 (2013). [2] M. Decker et al., Adv. Opt. Mater. 3, 813 (2015). [3] K. E. Chong et al., Nano Lett. 15, 5369–5374 (2015). [4] K. E. Chong et al., ACS Photonics 3, 514-519 (2016).

We demonstrate monolithic aluminum gallium arsenide (AlGaAs) optical nanoantennas for enhanced second harmonic generation (SHG) at telecom wavelengths. From measurements on nanocylinders of 400 nm height and varying radius pumped with femtosecond pulses delivered at 1554-nm wavelength, we estimated a peak conversion efficiency exceeding 10⁻⁵. Our measurements are in excellent agreement with frequency-domain numerical simulations, revealing the microscopic nature of the SHG process in our nanoresonators.

Plasmonic nano-antennas provide broadband spontaneous emission control by confining light on highly sub-wavelength volumes. We realize a plasmonic patch antenna by positioning a emitter within a ultrathin slab of dielectric limited by an optically thick gold layer and a thin gold patch. A single CdSe/CdS colloidal quantum dot is deterministically located just in the center of the antenna by an original in situ optical lithography protocol [1]. Depending on the dimension of the patch antenna and the emitter orientation, different Purcell factors could be achieved leading to different optical properties. For moderate Purcell factors, patch nanoantennas are plasmonic directive single photon sources. For higher Purcell factors, the spontaneous emission acceleration makes the multiexciton radiative recombination more efficient than Auger non radiative recombination. Emission of photons due to multiexcitons recombination could be observe at very short time scale. Such antennas can be very efficiently excited. Such antenna appear to be extremely bright as their luminescence exceed by more than one order of magnitude the one of single nanocrystals. References: [1] Dousse, A. et al. Controlled light-matter coupling for a single quantum dot embedded in a pillar microcavity using far-field optical lithography. Phys. Rev. Lett. 101, 267404 (2008). [2] C. Belacel, B. Habert, F. Bigourdan, F. Marquier, J-P. Hugonin, S. Michaelis de Vasconcellos, X. Lafosse, L. Coolen, C. Schwob, C. Javaux, B. Dubertret, J-J. Greffet, P. Senellart, A. Maître, Controlling spontaneous emission with plasmonic optical patch antennas, Nanoletters 13 1516 (2013)

Epsilon-Near-Zero (ENZ) metamaterials (MMs), whose dielectric permittivity approaches zero at specific wavelengths, exhibit exotic physical properties and promising optoelectronic applications. Here we exploit the effective medium approach to obtain the ENZ condition by stacking metal and dielectric materials, with individual subwavelength thickness. Based on this configuration, we investigate optical activity (dichroism and circular birefringence) of 1D chiral MMs enhanced by the ENZ effect and the all-optical transition of ENZ MMs, from metallic to dielectric, as a function of the pumping optical power.

Metal nanoantennas make it possible to manipulate the light, and in particular to control its absorption. According to Kirchhoff's law, emissivity equals absorptivity and nanoantennas may become light sources operating by thermal emission. These sources exhibit properties that deviate from those of the ideal blackbody described by Planck's law. We will show that it is possible to develop a metasurface based on metal-insulator-metal nanoantennas, wherein each antenna has dimensions smaller than the wavelength, and acts as a transmitter at given polarization state and wavelength of light, independent of the adjacent antennas. It is thus possible to obtain spatial, spectral and polarization control of the emitted light, and thus to encode complex images. Other nanoantennas concepts will be presented, such as optical Helmholtz resonators.

In this work, we take advantage of the resistive losses induced by plasmons excited at optical frequencies to design, fabricate and characterize a metal grating based CMOS-compatible light detector. A change of resistance is caused by increased electron scattering introduced by localized and delocalized surface plasmons in an applied current. We realize a spectral and polarization dependent detector that can be read out electronically. The optical response of the sensor can be tuned from the visible to IR regime by changing the geometry of the metal grating, which enables a variety of applications for an on-chip ultra-wideband plasmonic detector.

Invited abstract. The extreme light confinement provided by nanophotonic structures pushes toward revisiting the photodetector design. On the other hand introducing absorbing layers in nano-resonators demands dedicated electromagnetic design. This context opens the way for performance improvements and new functionalities, introducing the fourth generation of photo-detectors with promising features such as ultra-thin absorbing layers, device area much smaller than its optical cross-section and carved optical response. In this talk, I present a GMR InGaAs photo-detector dedicated for FPA applications, illustrating this global design and the cross-linked properties of the optical and semiconductor structures. In this "guided mode resonator", the semiconductor stack works as an optical guide. Its bottom part is structured in order to generate the first order diffraction modes in the semiconductor. Adjusting the coupling between the optical modes of the guide and those of the grating, allows optimizing this structure for various applications as optimum absorption at 1.55 μm or in the SWIR band [M. Verdun et al, Appl. Phys. Lett. 108 053501 (2016)]. The photodiode is based on an InP/InGaAs double heterojunction. The small thickness of the InGaAs absorbing layer (100 – 200 nm) allows suppressing the diffusion currents as well as reducing the generation-recombination currents in the space charge layer. It will be shown that the minimum value of the dark current is not necessarily reached for the thinnest absorbing layers. As a result, experimental data show at λ = 1.55 μm an external quantum efficiency of 75% and a specific detectivity of up to 1013 cm.√Hz.W-1.

Wavelength conversion via quadratic optical nonlinearity in AlGaAs waveguiding devices will be presented. Devices reported in this article include periodically inverted quasi-phase matching (QPM) devices and thin- rectangular high-index-contrast birefringence phase matching devices. Special emphasis will be placed on GaAs/AlGaAs QPM waveguides fabricated based on epitaxial growth technique (sublattice reversal epitaxy) we have developed for growing spatially inverted semiconductors. We have succeeded in demonstrating QPM second-harmonic generation and difference-frequency generation with reasonably high efficiencies.

Optical frequency combs currently represent enabling components in a wide number of fast-growing research fields, from frequency metrology to precision spectroscopy, from synchronization of telecommunication systems to environmental and biomedical spectrometry. As recently demonstrated, quadratic nonlinear media are a promising platform for optical frequency combs generation, through the onset of an internally pumped optical parametric oscillator in cavity enhanced second-harmonic generation systems. We present here a proposal for quadratic frequency comb generation in AlGaAs waveguide resonators. Based on the crystal symmetry properties of the AlGaAs material, quasi-phase matching can be realized in curved geometries (directional quasi-phase matching), thus ensuring efficient optical frequency conversion. We propose a novel design of AlGaAs waveguide resonators with strongly reduced total losses, compatible with long-path, high-quality resonators. By means of a numerical study, we predict efficient frequency comb generation with threshold powers in the microwatt range, paving the way for the full integration of frequency comb synthesizers in photonic circuits.

Antibacterial items are one of the major queries from the medical community in the fight against medical infections. Indeed, bacteria are resistant and their multiplication and biofilm formation on devises are one of the major causes of infections. Finding antibacterial surfaces, which are biocompatible, cost-effective, not toxic, and spreadable over large and irregular surfaces, is not easy. However, we created an antibacterial cloak by laser printing of Graphene Oxide (GO) hydrogels by mimicking the Cancer Pagurus carapace. This surface provides up to 90% reduction of bacteria cells through a bacteriostatic and bactericidal effect. Indeed, Laser treating allows GO sheets gel to cut and wrap microorganisms. Our findings are confirmed by a theoretical active matter model. This new technology based on antibiotic-free biomimetic Graphene Oxide gels opens untrodden roads to the fight against infections in biomedical applications and chirurgical equipment.

From latest nanotechnology advances, low-dimensional matter confinement delivered by nanostructuration or few-layer stacking offer new opportunities for ultimate light absorption performances. In this field, semiconducting 2D materials and photonic crystals have already demonstrated promising flexible optical properties from monoatomic to bulk structuration covering visible to IR spectral range. Today, these emerging materials such as Phosphorene, allow reconsideration of some physical effects such as photoconductivity. Indeed, its exploitation in integrated planar structures become c in terms of efficient local contactless control with a high degree of tunability by optics in association with high dark resistivity, fast carrier dynamics, and sub-wavelength light coupling solutions compatibility. Multiscale modeling and design tools implementing material anisotropic parameters from atomic configuration up to mesoscale, in complement with multiscale optical characterization in a large frequency bandwidth opens routes to new microwave signal processing functionalities such as switching, generation, amplification and emission over a large frequency bandwidth, that could not be achieved by full electronic solutions. This paper will report on latest demonstrations of high performance photoconductive structures for high frequency applications and review state-of-the-art research work in this area, with a specific focus on latest demonstrations for airborne applications.

This paper reviews recent advancement on the research toward graphene-based terahertz (THz) lasers. Optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the THz spectral range, which may lead to new types of THz lasers. A forward-biased graphene structure with a lateral p-i-n junction was implemented in a distributed-feedback (DFB) dual-gate graphene-channel FET and observed a single mode emission at 5.2 THz at 100K. The observed spectral linewidth fairly agrees with the modal gain analysis based on DFB-Fabry-Perrot hybrid-cavitymode modeling. Although the results obtained are still preliminary level, the observed emission could be interpreted as THz lasing in population-inverted graphene by carrier-injection.

A prototypical experiment in cavity quantum electrodynamics involves controlling the light-matter interaction by tuning the frequency of a cavity mode in- and out-of resonance with the frequency of a quantum emitter,^1-3 while the field amplitude is generally unaltered. The opposite situation, where one perturbs the spatial pattern of a cavity mode without changing its frequency, has been considered only recently in a few works.^{4, 5} Changing the amplitude of the field at the emitter's position has important applications, at it allows a real-time control of the light-matter coupling rate, and therefore a direct control of processes such as spontaneous emission and Rabi oscillations. In view of this large potential, in this paper we discuss general design principles that allow obtaining large variations of the electromagnetic field, without change of the frequency, upon an external perturbation of the cavity. We showcase the application of these rules to two photonic structures, a single Fabry-Perot cavity and a coupled three-cavity system. As showed by our analysis and by the examples provided, a small frequency spacing between the modes of the unperturbed cavity is an important requirement to obtain large field variations upon small perturbations. In this regard, a coupled-cavity system, where the frequency spacing is controlled by the interaction rates between the single cavities, constitutes the most promising system to achieve large modulations of the field amplitude.

Optical resonators have enabled the label-free measurement of nanoparticles suspended in liquids, down to the resolution of individual viruses and large molecules, but are only able to quantify optical properties (refractive index, scattering, fluorescence). Additionally, these sensors are fundamentally limited by the random diffusion of particles to the sensing region, and thus only measure a tiny fraction of the analyte. We have developed a microfluidic optomechanical resonator capable of sensing freely flowing nanoparticles using the action of phonons that are coupled to light. The phonon mode of the system casts a nearly perfect net for measuring density, viscoelasticity, and compressibility of the particles that flow through, without being limited by random diffusion. Information on the mechanical properties of the particles is encoded in the light scattered from the thermal fluctuations of the phonon mode. We have also developed a new electro-opto-mechanical method for improving the sensing speed achievable with this technique. We demonstrate real-time particle transit measurements as fast as 400 microseconds, without any post-processing. We discuss how this novel technique can be used for ultra-high throughput analysis of mechanical properties of biological particles in liquids, enabling a new form of flow cytometry. (invited by Prof. Giuseppe Leo)

First, we will provide some recent advances on low-frequency phononic and acoustic insulators based on metasurfaces. We will introduce a new concept of acoustic absorption based on the coiling-up space design which exhibits extreme acoustic properties. A new acoustic absorber operating at 125Hz with deep-subwavelength thickness (~ λ/230) acting as an “acoustic sink” is designed and its functionalities are discussed. Second, as we are dealing with how to reduce or to absorb low-frequency sound/noise, we will explore a novel idea on the use in a positive manner these noises as a source of energy. We theoretically and numerically show the properties of a novel acoustic energy harvester resulting from the confinement and conversion of low-frequency acoustic/noise disturbances to electrical energy. We indeed present preliminary results showing a metamaterial structure producing an electrical power density of 0.54μw/cm³ for one confined frequency, which presents a very good value compared the others acoustic energy harvesting approaches.

Mid-infrared detection with semiconductor based pixel arrays attracted constant research interest over the past years. Remaining challenges for intersubband detectors are high device performance at elevated temperatures in combination with cost effective scalability to large pixel counts needed for applications in remote sensing and high resolution infrared imaging. In this field, quantum cascade detectors may offer promising advantages such as photovoltaic room temperature operation at a designable operation wavelength with compatibility to stable material systems and growth technology. We present a high performance InGaAs/InAlAs quantum cascade detector design suitable for pixel devices. The design is based on a vertical optical transition and resonant tunneling extraction. The 20 period active region is optimized for a high device resistance and thereby high detectivity up to room temperature. The pixels are fully compatible with standard processing technology and material growth to provide scalability to large pixel counts. An enhanced quantum cascade detector simulator is used for design optimization of the resistance and extraction efficiency while maintaining state of the art responsivity. The device is thermo-compression bonded to a custom read out integrated circuit with substrate bottom side illuminated pixels utilizing a metal grating coupling scheme. The operation wavelength is designed to align with the strong CO2 absorption around 4.3µm. A room temperature responsivity of 16mA/W and a detectivity of 5∙10^7 cm√Hz/W was achieved in good agreement with our simulation results. Device packaging and thermo-electric cooling in an N2 purged 16 pin TO-8 housing has been investigated.

A high photoresponse in a room-temperature quantum cascade detector (QCD) based on a coupled quantum-well design is demonstrated with a peak detection wavelength of 5.4 μm. In this design, forward electron transfer is engineered to be five times as large as relaxation back to ground level. In this situation, the coupled quantum-well QCD indicates a high responsivity of 22 mA/W as well as a specified detectivity (D*) of 8.0×10⁷ cmW^-1Hz^1/2, both at room-temperature with commonly used 45° wedge configuration. Applying a waveguide configuration for the proposed QCD, an elevated responsivity of ~130 mA/W with a D* of 1.1×10⁸ cmW^-1Hz^1/2 was obtained at room-temperature. A laser absorption spectroscopy for N₂O gas with proposed QCD and a distributed feedback quantum cascade laser has been also demonstrated.

Bi-functional active regions, capable of light generation and detection at the same wavelength, allow a straightforward implementation of the mid-infrared quantum cascade technology for integrated photonics. Different parts of the chip can be used for laser and for photodetectors. Potential applications are on-chip integrated sensors or lasers with integrated power monitoring capabilities. In the first bi-functional designs, wavelength matching was achieved using thicker barriers and reduced energy splitings between the extraction levels, but with the drawback of a reduced laser performance. The following introduction of the horizontal-vertical extraction scheme was a significant step towards high performance laser operation. In this work, we combine our design experience with optimized, laterally overgrown waveguides and refined bandstructure modelling. The device was designed for emission at 8 μm to show that wavelength matching can also be achieved at longer wavelengths, where it becomes increasingly difficult due to the smaller ratio between photon energy and LO-phonon energy. Graded interfaces were used in the bandstructure design to consider the behaviour of the MOVPE growth. In pulsed mode a threshold current density of 1.3 kA/cm 2 and a total wallplug efficiency of over 10% was achieved. In continuous-wave operation, the device emits 80mW output power in an episide-up configuration. A much higher performance can be expected after episide-down mounting on AlN substrates. In detector operation the device has a responsivity at the emission wavelength of about 20mA/W.

Quantum cascade lasers are semiconductor lasers based on intersubband transitions that have developed rapidly and become the most suitable mid-infrared laser sources, due to their compactness, efficiency and high room temperature performances. High-power mid-infrared quantum cascade lasers are performant sources for optical countermeasures, including night vision blinding and missile out steering. However, some drawbacks arise with high power lasers that usually lead to a strong degradation of the beam quality. For instance, beam steering is known to be one of the limiting factors inducing an irregular distribution of the optical power within the near-field beam profile. This phenomenon has already been observed in high power quantum cascade lasers before and can be explained by four-wave mixing interaction among the existing transverse modes. It dramatically degrades the far-field of the laser emission, and prevents its use for applications where high beam quality is required. In this work, we show for the first time that the use of a small amount of optical feedback reinjected into a high power quantum cascade laser emitting at 4.6 μm and with poor beam quality allows a total suppression of the beam steering effect without sacrificing the near-field profile.

In this contribution, we report on real-time mid-IR spectroscopy enabled by rapidly tunable External Cavity Quantum Cascade Lasers (EC-QCLs). High speed spectral scanning in a Littrow-type resonator is realized by employing a resonantly driven micro-opto-electro-mechanical-systems (MOEMS) grating as wavelength selective element. Oscillating at a frequency of 1 kHz with mechanical amplitudes of up to 10°, the MOEMS grating is able to cover the whole spectral range provided even by broad-gain QCL chips in just 500 μs. In addition to the high spectral scanning frequency, the MOEMS approach also allows for a miniaturized and rugged design of the EC-QCL. An evaluation of this laser source with regard to spectral reproducibility of consecutive scans, pulse intensity noise, and spectral resolution will be given. Furthermore, we present spectroscopic measurements in backscattering as well as in transmission geometry, demonstrating the real-time capability in different scenarios.

SOFRADIR is the worldwide leader on the cooled IR detector market for high-performance space, military and security applications thanks to a well mastered Mercury Cadmium Telluride (MCT) technology, and recently thanks to the acquisition of III-V technology: InSb, InGaAs, and QWIP quantum detectors. As a result, strong and continuous development efforts are deployed to deliver cutting edge products with improved performances in terms of spatial and thermal resolution, dark current, quantum efficiency, low excess noise and high operability. The actual trend in quantum IR detector development is the design of very small pixel, with the higher achievable operating temperature whatever the spectral band. Moreover maintaining the detector operability and image quality at higher temperature moreover for long wavelength is a major issue. This paper presents the recent developments achieved at Sofradir to meet this challenge for LW band MCT extrinsic p on n technology with a cut-off wavelength of 9.3μm at 90K. State of the art performances will be presented in terms of dark current, operability and NETD temperature dependency, quantum efficiency, MTF, and RFPN (Residual Fixed Pattern Noise) stability up to 100K.

In this talk, monolithic photonics architectures that enable deterministic splitting of entangled states of light will be discussed. In addition, quantum state engineering using the same architectures will be presented exhibiting characteristics that are unique to integrated architectures.

In view of real world applications of quantum information technologies, the combination of miniature quantum resources with existing fibre networks is a crucial issue. Among such resources, on-chip entangled photon sources play a central role for applications spanning quantum communications, computing and metrology. Here, we use a semiconductor source of entangled photons operating at room temperature in conjunction with standard telecom components to demonstrate multi-user quantum key distribution, a core protocol for securing communications in quantum networks. The source consists of an AlGaAs chip emitting polarization entangled photon pairs over a large bandwidth in the main telecom band around 1550 nm without the use of any off-chip compensation or interferometric scheme; the photon pairs are directly launched into a dense wavelength division multiplexer (DWDM) and secret keys are distributed between several pairs of users communicating through different channels. We achieve a visibility measured after the DWDM of 87% and show long-distance key distribution using a 50-km standard telecom fibre link between two network users. These results illustrate a promising route to practical, resource-efficient implementations adapted to quantum network infrastructures.

The performance of superconducting-nanowire single-photon detectors depends on the efficiency of light absorption in the ultrathin (3-8 nm) superconducting nanowire. In this work, we will discuss two approaches to boost light absorption: coupling the nanowire to the evanescent field propagating in a waveguide and enclosing the nanowire in an optical cavity. The latter method is the most widely used, but it is intrinsically very sensitive to the polarization of light. To overcome this issue, we propose some innovative cavity designs which make use of high-index (n >2) dielectrics. With this technique, highly-efficient polarization-insensitive devices can be easily implemented.

Quantum imaging uses entangled photons to overcome the limits of a classical-light apparatus in terms of image quality, beating the standard shot-noise limit, and exceeding the Abbe diffraction limit for resolution. In today experiments, the spatial properties of entangled photons are recorded by means of complex and slow setups that include either the motorized scanning of single-pixel single-photon detectors, such as Photo-Multiplier Tubes (PMT) or Silicon Photo- Multipliers (SiPM), or the use of low frame rate intensified CCD cameras. CMOS arrays of Single Photon Avalanche Diodes (SPAD) represent a relatively recent technology that may lead to simpler setups and faster acquisition. They are spatially- and time-resolved single-photon detectors, i.e. they can provide the position within the array and the time of arrival of every detected photon with <100 ps resolution. SUPERTWIN is a European H2020 project aiming at developing the technological building blocks (emitter, detector and system) for a new, all solid-state quantum microscope system exploiting entangled photons to overcome the Rayleigh limit, targeting a resolution of 40nm. This work provides the measurement results of the 2nd order cross-correlation function relative to a flux of entangled photon pairs acquired with a fully digital 8×16 pixel SPAD array in CMOS technology. The limitations for application in quantum optics of the employed architecture and of other solutions in the literature will be analyzed, with emphasis on crosstalk. Then, the specifications for a dedicated detector will be given, paving the way for future implementations of 100kpixel Quantum Image Sensors.

In the last years, Time Correlated Single Photon Counting (TCSPC) has become the technique of choice in fluorescence lifetime measurements, given its remarkable sensitivity, accuracy and timing resolution. Nevertheless, a major drawback of this technique lies in the relatively long acquisition time. In order to overcome this issue, many multichannel systems have been proposed in literature, but the presence of many independent acquisition chains gives rise in principle to a huge data rate at the output, which cannot be processed in real time by a PC. Typically adopted solutions involve a limitation of the maximum detection frequency of each channel, so the measurement speed of currently available systems has not increased accordingly with the number of acquisition chains and is still limited well below the saturation of the transfer rate towards the elaboration unit. We present a completely different approach: starting from the maximum manageable data rate imposed by the transfer towards the PC, a proper number of high-performance external channels has been chosen to be shared among a much larger number of Single Photon Avalanche Diode (SPAD) detectors. Then, at each excitation period a dynamic routing mechanism performs a selection among the whole set of detectors carrying a valid signal and routes them towards the external channels. The selection logic relies on a pixelated architecture and on 3D-stacking techniques to connect each SPAD to its dedicated electronic, leading to a minimization of the number of interconnections crossing the integrated system.

In this talk I will present our recent results on efficient room temperature single photon emitters based on core/shell colloidal semiconductor nanocrystals. By using asymmetric core/shell nanoparticles with a spherical CdSe core surrounded by a rod-like CdS shell (dots-in rods), blinking effects, multi-excitonic emission and polarization of the emitted photons can be separately controlled by tuning shell dimensions. This allows an unprecedented capability in radiative channels engineering, making dot-in-rods “state of the art” blinking-free sources of polarized single photons on-demand. In the last part of the talk I will discuss the different strategies we are pursuing to develop hybrid photonic devices by coupling single nanocrystals with various photonic structures like optical nanofibers, deep parabolic mirrors, liquid crystals and semiconductor nanowires.

In this article we discuss the infrared properties of self-doped nanocrystals and in particular the case of HgSe. HgSe colloidal quantum dots have recently been reported for their tunable optical features all over the mid infrared from 3 to 20 μm. Their optical absorption is a combination of interband absorption at high energy and intraband absorption at low energy. The latter results from the self-doped character of HgSe. The origin of this self-doping is also discussed. We demonstrated that the doping results from the combination of the narrow band gap and high work function of HgSe, which leads to a reduction of the CQD by the water in the environment. In addition, we demonstrated that the doping density can be tuned over an order of magnitude thanks to the control of the capping ligands.

We present magnetooptical and transport properties of metamorphic periodic structures containing InAsSb layers with controllable modulated Sb composition [1]. The modulation period is determined by the thicknesses of the strain compensated InAsSbx/InAsSby pairs grown on a virtual AlGaInSb substrate with a lattice constant of 6.25 A. We demonstrate that the bandgap energy of ordered InAsSb0.3/InAsSb0.75 alloy varies from 100mev to a few meV as a result of the well-regulated variation of the modulation period from ∼3 to ∼7.5 nm. The material effective masses and the specific character of the energy spectra will be discussed. 1. G. Belenky, Y. Lin, L. Shterengas, D. Donetsky, G. Kipshidze and S. Suchalkin, Electron. Lett. 51 (19), 1521, (2015)

Efficient extraction of photons from quantum emitters is an important prerequisite for the use of such emitters in quantum optical applications as single photons sources or sensors. One way to achieve this is by coupling to a suited photonics structure, which guides away the emitter light. Here, we show the coupling of a single defect in hexagonal boron nitride (hBN) to a tapered optical fiber via a nanomanipulation technique. Defects in hBN are capable of emitting single photons at room temperature while being photostable at the same time – two properties that make them ideal candidates for integration in single photon sources. The high control the manipulation technique provides avoids covering the whole nanofiber with emitters. We characterize the coupled system in terms of achievable count rates, saturation intensity, and spectral properties. Antibunching measurements are used to proof the single emitter nature of the defect. Our results pave the way for integration of single defects in hBN into photonic structure and their use as single photon sources in quantum optical applications such as quantum crypthography.

We report measurements of optically detected magnetic resonance spectra of ensembles of nitrogen-vacancy (NV-) centers in diamonds in the presence of electromagnetic fields. To reduce inhomogeneous broadening, the spectra are acquired from a region of 20 cubic microns in a CVD(Chemical Vapor Deposition) diamond through a confocal microscope. The Stark shift from transverse electric fields is enhanced at avoided crossings between the hyperfine levels that arise from interaction with ¹⁴N(I = 1) nuclei in the diamond lattice. As expected from previous reports, the Stark shift of the spectral lines is stronger when there is no magnetic field along the NV axis. The shift is also strong, but for different transitions, at a field of about 100 uT.

We present our activities on the development of narrow linewidth tunable optical parametric sources and their integration in gas sensing instruments. In particular, we have introduced the nested cavity optical parametric oscillator (NesCOPO) scheme that enables to implement very compact devices. The NesCOPO was successfully demonstrated in the microsecond to nanosecond regime and in spectral ranges from short- to long-wave infrared. Its high potential was demonstrated both for local photoacoustic spectroscopy and standoff detection using lidar instruments. We also present our recent advances on rapidly tunable picosecond OPOs based on aperiodic quasi-phase matching and their application to gas detection.

Optical fibres functionalised with chemically sensitive layers offer a powerful platform for the development of sensing systems with a wide range of potential applications, ranging from the monitoring of industrial processes to healthcare. Sensors based upon optical fibres to probe the optical characteristics of nanomaterials that exhibit changes in their optical properties upon exposure to targeted chemical species are particularly attractive, due to their potential high sensitivity, selectivity, the ready ability to multiplex arrays of sensors, and the prospect for remote sensing. This paper provides examples of the application of optical fibres sensors to improve the functionality of the medical devices, for biomarker detection and drug monitoring, and draws upon work that has been conducted as collaboration between teams at the Universities of Kitakyushu, Cranfield and Nottingham.

We present Time-of-Flight (TOF) distance, velocity and acceleration characterisation of a multi-event Time-to-Digital- Converter (TDC) optical sensor featuring a 32x32 Single Photon Avalanche Diode (SPAD) array, a 14 GS/s TDC and on-chip histogram generation. Events are continuously recorded on-chip in 264 70 ps-wide histogram bins. High TDC throughput enables the device to be operated in Doppler mode with pulse-trains moving at hypervelocity speeds relative to the operational sensor frequency. Electrical frequency-detuned signals of 50 kHz are resolved by the TDC module. Optical frequency-detuned signals of 1 kHz are resolved, corresponding to a TOF velocity resolution of 15.8 km/s. Linear, sine-wave, and chirp frequency modulation techniques are used to demonstrate these characteristics.

Micro-scale whispering gallery mode lasers are demonstrated as sensors for remote sensing. We exploit its potential applications in the field of biological and mechanical engineering and different remote sensing applications will be reported. These micro-resonators are fabricated by mixing a solution of rhodamine 6G and methanol with different polymers. The micro-resonators are optically pumped using a Nd:YAG laser and their emission spectrum is observed using a spectrometer. The excited optical resonances are very sensitive to a change in the morphology of the resonators. Therefore, any perturbation of the morphology of the resonator such as size shape and index of refraction leads to a shift of the frequency of the optical resonances. By tracking the shift of the optical resonances, the external physical effect causing the morphology change can be monitored.

Time-frequency applications need high accuracy and high stability clocks. Compact industrial optically pumped Cesium beam standards are promising to address various demands. In this context we are developing Al-free active region distributed-feedback diode (DFB) lasers at 852nm and 894nm for, respectively, the D2 and D1 line Cesium pumping. In order to address the long term reliability of these lasers, long duration ageing tests (more than one year targeted) are being carried out for both wavelengths at 20mW and 25°C. The laser diodes have been ageing for 4950 hours and 3120 hours respectively with very low increase of the operating current.

With the advent of modern experimental techniques the low dimensional structures having quantum confinement in one, two and three dimensions such as (quantum well (QWs), quantum well wires (QWWs) and quantum dots (QDs) ultrathin films have in the last few years attached much attention not only because of their potential in uncovering new phenomena in computational and theoretical nanoscience but also for new technological applications. In ultrathin films, the restriction of the motion of the carriers in the direction normal to the films leads to the quantum size effect allowing two-dimensional carrier transport parallel to the surface of the film. In this context I shall study the DMR in ultrathin films of IIIV semiconductors.

A compact mid-infrared (MIR) dual-gas sensor system was demonstrated for simultaneous detection of methane (CH4) and ethane (C₂H₆) using a single continuous-wave (CW) interband cascade laser (ICL) based on tunable laser absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS). Ultracompact custom electronics were developed, including a laser current driver, a temperature controller and a lock-in amplifier. These custom electronics reduce the size and weight of the sensor system as compared with a previous version based on commercial electronics. A multipass gas cell with an effective optical length of 54.6 m was employed to enhance the absorption signal. A 3337 nm ICL was capable of targeting a C2H6 absorption line at 2996.88 cm^-1 and a CH₄ line at 2999.06 cm^-1. Dual-gas detection was realized by scanning both the CH4 and C2H6 absorption lines. Based on an Allan deviation analysis, the 1 σ minimum detection limit (MDL) was 17.4 ppbv for CH₄ and 2.4 ppbv for C₂H₆ with an integration time of 4.3 s. TDLAS based sensor measurements for both indoor and outdoor mixing ratios of CH₄ and C₂H₆ were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost without influencing the midinfrared sensor detection sensitivity, selectivity and reliability.

A near-infrared (NIR) dual-channel differential gas sensor system was experimentally demonstrated based on tunable laser absorption spectroscopy (TLAS) and wavelength modulation spectroscopy (WMS). The sensor consists of four modules, including distributed feedback (DFB) lasers for the detection of targeted gases, a custom portable DFB driver compatible for butterfly-packaged DFB lasers, a 20cm-long open-reflective gas-sensing probe and a custom costeffective lock-in amplifier for harmonic signal extraction. The optical and electrical modules were integrated into a standalone sensor system, which possesses advantages of user-friendly operation, good stability, small volume and low cost. With different DFB lasers, the sensor system can be used to detect different gases. Two DFB diode lasers with emission wavelengths of 1.65 μm and 1.53 μm were used to detect CH₄ and C₂H₂, respectively. Standard CH₄ and C₂H₂ samples were prepared and experiments were carried out to evaluate the performance of the two-gas TLAS sensor system. The relation between the second harmonic amplitudes (2f) and gas concentrations was obtained for the two gases by means of calibration. Both the detection error and the limit of detection (LoD) were determined experimentally. The sensor system will be useful in industrial trace gas monitoring due to its use of a low-loss optical fiber and an openreflective gas-sensing probe.

A photoacoustic (PA) spectrophone was developed for filter-free measurement of black carbon (BC) mass absorption coefficient (MAC) in the spectral region of ~ 442 nm using a blue diode laser. The PA sensor was characterized and calibrated using NO2 at standard calibrated concentrations, as well as at indoor and outdoor air concentrations via a side-by-side intercomparison with a commercial NOx analyzer. Black carbon (graphite) and volcanic ash samples were measured under laboratory condition. MAC of BC and volcanic ash sample were determined based on the measured particles optical absorption coefficient by the PA spectrophone, in combination with the mass concentration measured using a scanning mobility particle sizer (SMPS). A minimum detectable absorption coefficient (1σ) of ~ 1.2 Mm^-1 for BC was achieved with a time solution of 1 second.

In this presentation, we report on the high-sensitivity and high-selectivity measurement of HONO by off-beam quartz-enhanced photoacoustic spectroscopy (QEPAS) in a very small gas sample volume (of ~ 40 mm³) resulting in a ultrashort residence time of less than 10 ms (compared to ~ 7 min for a conventional 210 m multipass cell or ~ 10-min. integration time for currently used chemical analytical instruments). A minimum detection limit of 66 ppbv (1σ) HONO was achieved at 70 mbar using a laser output power of 50 mW and 1 s integration time. This MDL was down to 7 ppbv at the optimal integration time of 150 s.

In this work, we investigated photonic crystal (PhC) based double nanocavity resonator biosensor. The sensor performance has confirmed by both sucrose and prostate specific antigen (PSA, a protein biomarker associated with prostate cancer). The device sensitivity and quality factor in sucrose solution are 1571 nm/RIU (Refractive Index Unit) and 2×10⁵ respectively. By using special antigen-antibody reaction, we successfully detected PSA concentration as low as 0.5 ng/mL.

Five-period GaAs_1−xN_x/GaAs multiple quantum wells (MQWs) were grown on GaAs(001) substrates under different nitrogen background pressures through solid-source molecular beam epitaxy and the structural and optical properties at low temperature were investigated. High resolution x-ray diffraction revealed sharper satellite peaks observed for GaAs_0.978N_0.022/GaAs MQWs as compared to GaAs_0.982N_0.018/GaAs MQWs, indicating better interfaces. The MQWs with higher nitrogen content exhibited high photoluminescence (PL) intensity, whereas a degraded PL intensity was observed for the latter, attributed to reduction in surface recombination with high nitrogen incorporation. Moreover, the spectrum for the MQWs with higher nitrogen content was observed to be consisted of several Gaussian spectra, indicating thickness variation of QWs caused by randomness in distribution of N atoms. In the low energy regime of PL, a long asymmetric tail was observed because of nitrogen introduced potential fluctuations. Rapid thermal annealing enhanced PL intensity by multi-fold and substantially reduced the full width at maximum because of homogenization of MQWs. This investigation could enhance understandings of the MQWs-based optoelectronic devices.

Resonant tunnelling diodes (RTDs) are a strong candidate for future wireless communications in the THz region, offering compact, room-temperature operation with Gb/s transfer rates. We employ the InGaAs/AlAs/InP material system, offering advantages due to high electron mobility, suitable band-offsets, and low resistance contacts. We describe an RTD emitter operating at 353GHz, radiating in this atmospheric transmittance window through a slot antenna. The fabrication scheme uses a dual-pass technique to achieve reproducible, very low resistivity, ohmic contacts, followed by accurate control of the etched device area. The top contact connects the device via the means of an air bridge. We then proceed to model ways to increase the resonator efficiency, in turn improving the radiative efficiency, by changing the epitaxial design. The optimization takes into account the accumulated stress limitations and realities of reactor growth. Due to the absence of useful in-situ monitoring in commercially-scalable metal-organic vapour phase epitaxy (MOVPE), we have developed a robust non-destructive epitaxial characterisation scheme to verify the quality of these mechanically shallow and atomically thin devices. A dummy copy of the active region element is grown to assist with low temperature photoluminescence spectroscopy (LTPL) characterisation. The resulting linewidths limits the number of possible solutions of quantum well (QW) width and depth pairs. In addition, the doping levels can be estimated with a sufficient degree of accuracy by measuring the Moss-Burstein shift of the bulk material. This analysis can then be combined with high resolution X-ray diffractometry (HRXRD) to increase its accuracy.

High Contrast Gratings (HCGs) become an attractive alternative for Distributed Bragg Reflectors (DBRs) used as high reflecting mirrors for VCSELs. In this paper we propose to implement HCG or monolithic HCG as a top mirror of the 1650nm InP-based VCSEL intended for use as a methane sensing device. Its unique feature is related to the fact that light taking part in the resonance can be accessed without opening the laser cavity due to the slow light phenomenon which occurs in HCG. Particular designs of HCGs allow to concentrate significant part of the mode between the HCG stripes. In such constructions the presence of the substance in the vicinity of the HCG which interacts with light resonating in the laser will change its emission properties. This enables sensing absorption or change to the refractive index in proximity of the laser based on the emission parameters of the laser. We present a numerical analysis of 1650nm MHCG and HCG mirrors based on fully vectorial optical model. We found optimal parameters of HCGs and MHCGs to detect absorption and refractive index variations in the vicinity of the gratings, based on changes in power reflectance of analysed mirrors. Additionally we consider HCG and MHCG constructions which allow for broad wavelength tuning by the change of the refractive index of substance surrounding mirror.

Graphene is a one-atom thick two-dimensional sp² carbon arrangement. Its ultrahigh surface area, excellent electric conductivity, chemical and physical stability made it a promising material in different research fields. Chemical approaches to the large-scale production of graphene have been realized, and the production of RGO (Reduced Graphene Oxide) in quantity has considerably advanced the development of applications for RGO in photocatalysis, capacitive deionization, and solar cells. In the present study, the improvement of synthesis process of RGO was made in terms of temperature, time and safety, as well as introduction of RGO based nanocomposite material. RGO was synthesized by the two step process which is very simple and easy; the conversion of graphite to GO by oxidation and then reduction of the GO to RGO by hydrothermal treatment. The synthesized RGO was combined with nano-size CdS and CuS compounds. The photocatalytic performance of the composite were investigated with the reduction of Cr(VI) by using RGO-CdS nanocomposite. This results may give an insight for the possibility of RGO-CdS in application for the remover of Cr(VI) ion. The hydrothermally synthesized RGO-CuS contains hexagonal structured CuS. The adsorption kinetics of methylene blue on RGO-CuS nanoparticles were compared with bare CuS. It suggests that RGO-CuS nanocomposite can be used for the adsorbent of methylene blue.

At the beginning of 2001, Professor Siwen Bi first proposed the new direction of quantum remote sensing at home and abroad. Based on the research of fundamental theory and information mechanism of quantum remote sensing, a new concept of quantum spectral imaging was put forward in August 2006. 10 years, quantum spectral imaging research has made breakthrough progress and stage results. Firstly, the research status of spectral imaging and the background of quantum spectrum imaging are introduced. Secondly, the concept and research methods of quantum spectrum imaging, the relationship between quantum spectrum imaging and spectral imaging and advantages are introduced. The basic theory of quantum spectroscopy is described, especially the research of quantum spectroscopy imaging and quantum spectroscopy. Finally, the significance and application prospect of quantum spectrum imaging are described.