This PDF file contains the front matter associated with SPIE Proceedings Volume 10540, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Gliomas are a deadly class of brain tumor for which surgery is currently standard treatment. However, important functional areas must be avoided during tumor removal. Currently intraoperative stimulation-based mapping addresses this, however it has low spatial resolution (~ 1cm) and requires many stimulations. We explore an alternate approach to functional mapping via infrared thermography. Activated brain tissue recruits additional blood supply (neurovascular coupling), which raises local temperature. Intraoperative thermal imaging (ITI) can map several areas simultaneously with relatively high resolution (~0.1 mm). We present our experiences using ITI on two glioma patients, and compare our findings to the stimulation-based gold standard. Initial data suggests good correspondence between these methods, and opens possibilities for a complementary approach. Ultimately, the goal of ITI is to improve patient outcomes by precisely defining the extent of surgical resection and prevent postoperative neurologic deficits.

Most of reported HPTs in literatures are based on InGaAs compounds that cover NIR spectral region. However, InGaAs compounds provide limited cut-off wavelength tunability. In contrast, type-II superlattices (T2SLs) are a developing new material system with intrinsic advantages such as great flexibility in bandgap engineering, low growth and manufacturing cost, high-uniformity, auger recombination suppression, and high carrier effective mass that are becoming an attractive candidate for infrared detection and imaging from short-wavelength infrared to very long wavelength infrared regime. We present the recent advancements in T2SL-based heterojunction phototransistors in e– SWIR, MWIR and LWIR spectral ranges. A mid-wavelength infrared heterojunction phototransistor based on type-II InAs/AlSb/GaSb superlattices on GaSb substrate has been demonstrated. Then, we present the effect of vertical scaling on the optical and electrical performance of heterojunction phototransistors, where the performance of devices with different base width was compared as the base was scaled from 60 down to 40 nm.

Future and advanced sensor technologies needed for DoD applications will require more efficient semiconductor materials and devices. Pushing sensor device performance beyond present levels requires a deep understanding of the fundamental limiters. Therefore fundamental research is needed to assure transition of technology from demonstration to system deployment. To address this problem, the Army Research Laboratory (ARL) and Boston University (BU) have come together to create a BU led Consortium for semiconductor Modeling of Materials and Devices (CSM). The Consortium brings together government, academia, and industry in a collaborative fashion to continuously push semiconductor research forward to meet DoD needs. The leveraged attributes of the Consortium include combined broad knowledge base in semiconductor modeling, materials growth and device expertise; sharing of computational resources; project continuity; and extension of the bench. Details regarding the Consortium’s first research topic on understanding vertical transport in Type 2 SL will be discussed.

Semiconductor quantum dots (QDs) are solid-state artificial atoms which host spectrally-narrow optical transitions. In this talk, I will review recent results showing that a single QD integrated into a tapered nanowire can find interesting applications to sensing. First, a self-assembled QD integrated at the base of a vertical nanowire constitutes a sensitive probe of the nanowire motion. When the wire oscillates, the QD experiences an oscillating mechanical stress which modulates the spacing between its energy levels. Optical QD spectroscopy then enable to detect the wire motion [1]. Interestingly, the vertical geometry (wire axis parallel to the QD growth axis) optimizes the sensitivity to the oscillating (uniaxial) stress [2]. Furthermore, optimal detection performance are achieved with resonant QD optical spectroscopy: one can then resolve the thermal motion of various mechanical modes, even at liquid helium temperature [3]. Finally, the coupling to a set of vibration modes can be exploited to map the QD position in the wire section with an accuracy as good as one nanometer [4,5]. As a second application to sensing, I will discuss preliminary results showing that nanowire QD can be also used as a scanning probe to map electric field [5]. References: [1] Yeo et al., Nature Nanotech. 9, 106 (2014) [2] P. Stepanov et al., Nano Lett. 16, 3215 (2016) [3] P.-L. De Assis et al., Phys. Rev. Lett. 118, 117401 (2017) [4] M. Munsch et al., Nature Comm. 8, 76 (2017) [5] D. Cadeddu et al., under review at Phys. Rev. Appl.

Reduction of dark current density in microjunction-based InAs/InAs_1-xSb_x type-II superlattice long-wavelength infrared photodetectors was demonstrated. A double electron barrier design was used to suppress both generation-recombination and surface dark currents. The photodetectors exhibited high surface resistivity after passivation with SiO₂, which permits the use of small size features without having strong surface leakage current degrading the electrical performance. Fabricating a microjunction structure (25×25 μm² mesas with 10×10 μm² microjunctions) with this photodetector double barrier design results in a dark current density of 6.3×10^-6 A/cm² at 77 K. The device has an 8 μm cut-off wavelength at 77 K and exhibits a quantum efficiency of 31% for a 2 μm-thick absorption region, which results in a specific detectivity value of 1.2×10¹² cm·Hz^1/2/W at 77 K.

While conventional CMOS scaling has not quit yet, alternatives have been continuously investigated for a wide range of applications. We have been fabricating nanoscale vacuum tubes using entirely and exclusively silicon technology. Vacuum is superior to any semiconductor in terms of electron transport, in addition to being immune to all radiations. We have combined the best of vacuum and silicon technology to fabricate surround gate nanoscale vacuum transistors on 8 " wafers with a channel dimension of 50 nm. These vacuum transistors, operating at a drive voltage of only 2 V, which is remarkable for vacuum devices, have the potential for THz electronics and several other applications. While silicon nanowires have been found to be ideal for a range of applications, the bottom up nanotechnology efforts to date have hindered progress in terms of large scale fabrication. We have developed top down approaches to create silicon nanowires on 8 " wafers and demonstrated their superior performance in BioFETs (field effect transistors) for biosensing, photodetecors and solar cells. This talk will present results to date for these applications. The author thanks Jin-Woo Han, Chang-ki Baek, Kihyun Kim and Taiuk Rim for their contributions.

We report interband cascade light-emitting devices (ICLEDs) emitting at λ ≈ 3.1mm, which produce generate higher radiance, output power, and efficiency than any other mid-infrared LEDs operating in continuous wave (cw) mode near and above room temperature. This is achieved in part by splitting the 22 LED stages into four groups placed at the antinodes of the near-normal optical field when the device is mounted epitaxial-side-down on a reflective metal contact. At an applied bias of 9.4 V and injection current of 0.6 A, an ICLED with mesa diameter 400 mm produces 2.9 mW of cw output power at T = 25°C, which corresponds to a radiance of 0.73 W/cm²/sr. The wall-plug efficiency ranges from 0.4% at low powers to 0.05% at the maximum output power.

Mid-infrared lasers, emitting in the spectral region of 3-12 μm that contain strong characteristic vibrational transitions of many important molecules, are highly desirable for spectroscopy sensing applications. High efficiency quantum cascade lasers have been demonstrated with up to watt-level output power in the mid-infrared region. However, the wide wavelength tuning, which is critical for spectroscopy applications, is still largely relying on incorporating external gratings, which have stability issues. Here, we demonstrate the development a monolithic, widely tunable quantum cascade laser source emitting between 6.1 and 9.2 μm through an on-chip integration of a sampled grating distributed feedback tunable laser array with a beam combiner. A compact tunable laser system was built to drive the individual lasers within the array and coordinate the driving of the laser array to produce desired wavelength. A broadband spectral measurement (520cm^-1) of methane shows excellent agreement with Fourier transform infrared spectrometer measurement. Further optimizations have led to high performance monolithic tunable QCLs with up to 65 mW output while delivering fundamental mode outputs.

Optically pumped semiconductor lasers (OPSL) have been replacing legacy gas lasers and solid state lasers for over a decade, due to their superior properties such as compactness, high efficiency, low noise, wavelength scalability, and power scalability. It has wide applications in life sciences, medical therapeutics, light show, and other scientific researches. In this work, we present a gain model and couple it to the thermal management of high power OPSL.

Hydrocarbon detection in the gas phase can be a powerful tool to guide downstream operations for the oil & gas industry. This application requires highly sensitive, selective and robust spectroscopic techniques. In this work, a quartz-enhanced photoacoustic sensor system designed to detect methane and ethane concentration levels in the part-per billion concentration range by employing a single interband cascade laser emitting at 3345 nm is reported. Measurements at both low and high pressure were carried out and mixtures simulating typical downhole compositions were analyzed.

We have developed GaInAsP semiconductor photonic crystal nanolaser biosensor, which detects the adsorption of proteins and DNAs from ultralow concentrations via the wavelength shift. In general, bio-chemical sensors based on photonic cavities are considered to detect the environmental refractive index change. In this study, however, we observed various evidence that the wavelength shift of the nanolaser sensor reflects not only the environmental index but also the surface charge of biomolecules and/or environmental ions. Different from the pH-sensitivity in the laser emission intensity we reported previously, the wavelength shift is extremely sensitive to the surface charge and ions so that we can detect the biomolecules from fM to aM. To investigate the mechanism, we exposed the device to plasma or DNA solution, and measured the zeta potential and flatband potential as well as the wavelength shift. From the consistent behaviors between them, we constructed a physical model that the surface charge modifies the Schottky barrier near the semiconductor surface, trap the excited carriers in the barrier, and produce the carrier plasma shift in the wavelength. Since the change of the flatband potential is already observed for fM DNA, we suppose a phenomenon such that a small number of charged molecules act as a trigger for changing the charged functional group on the device surface. These results also suggest the possibility that some other photonic sensors also involves similar electrochemical effects.

Interband cascade IR photodetectors (ICIPs) are multi-stage detectors with discrete absorbers separated by unipolar electron and hole barriers. In this multi-stage detector architecture, the absorber in each stage is designed with a thickness that is thinner than the carrier diffusion length so that photo-generated carriers can be collected efficiently and quickly. This advantage has been validated with the operation of ICIPs at high temperatures (>400 K) and high frequencies (up to 1.3 GHz). Recently, electrical gain exceeding unity was observed in ICIPs. Also, negative differential conductance (NDC) was observed at high temperatures. In this paper, we will discuss the underlying physics of the NDC and a new mechanism that should well explain the electrical gain in ICIPs, as well as our progress towards improved understanding and high temperature performance.

We show that intersubband (ISB) polaritons are robust to inhomogeneous broadening. In a series of multiple quantum well samples with mid-infrared ISB absorption transitions with broadenings varying by a factor of 5 (from 4 meV to 20 meV), we observed polariton linewidths lying in the 4 - 7 meV range only. We have verified the dominantly inhomogeneous origin of the broadening of the ISB transition, and that the linewidth reduction of the modes persists up to room-temperature. The immunity to inhomogeneous broadening is a direct consequence of the coupling of the large number of ISB oscillators to a single photonic mode.

An advanced commercial InfraRed Isotope Ratio (IR²) analyzer has been developed in Arrow Grand Technologies and the hollow waveguide (HWG) is used as the sample tube. By measuring the selected CO₂ absorption peaks in the Mid- IR(MIR), the stable carbon isotope ratio, i.e. ¹³C, is obtained at a fast sampling rate. Combined with a GC and a combustor, it has been successfully employed to measure compound specific ¹³C isotope ratios in the field. By updating the single path HWG to 5-path HWG, we have also demonstrated its application for the environmental and health research. Here, the isotope ratio analyzer is minimized in size and weight to better fulfill the field deployment requirements. The size is reduced from 80cm*51cm*51cm to 74cm*33cm*46cm. After optimizing all subsystems, the minimized isotope ratio analyzer has a better performance. What’s more, the number of HWG paths can be selected to match the specific application. For instance, a 3-pass HWG is selected to conduct ultra-sensitive compound specific isotope analysis for mud gas logging, and a 5+1 pass HWG could measure isotope ratios of carbon with an ultra-broad CO₂ concentration range of 300 ppm-47,500 ppm and a fast sample refresh and data processing rate up to 10Hz.

Short-wave infrared (SWIR) is an interesting region of the electromagnetic spectrum, as it is highly suitable for imaging through biological tissue and the atmosphere, and yet immune from the background thermal photon noise. These properties have led to a rapidly growing interest in the SWIR imaging for exciting new scientific, medical, defense, and consumer applications. In this seminar, I will present our new findings for ultra-sensitive and ultra-fast SWIR cameras. In particular, I will present a SWIR imager that is based on the detection mechanism in the Rod cells in the eye. We are making a very fast, and yet sensitive camera based on this new technology for the direct imaging of Earth-like exoplanets for the first time. This same detector has recently been used in a commercial medical optical tomography system, and achieved ~1000 times higher sensitivity at very low light conditions. I will also present a new approach to add ultra-fast timing to the SWIR imaging. Using this approach we could achieve a timing accuracy of about 30 pico-seconds across the images, which allows us to separate two objects that are only a fraction of centimeter apart from the difference it the time of arrival of the light rays.

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. This is the result of strong and continuous development efforts 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. On one hand the advanced performances of Sofradir product rely on a strong partnership with CEA-LETI materialized in a common laboratory named DEFIR. On the other hand, these cutting edge performances are made possible thanks to Sofradir vertical industrial model. From the CdZnTe (CZT) and HgCdTe (MCT) crystal growth to the last electro-optical characterization recipe before shipping, and all the intermediate steps in between like IDDCA (Integrated Detector Dewar Cooler Assembly) final pumping cycle, all the manufacturing steps are developed, performed and controlled inhouse. This allows direct feedback between IDDCA, system performances and process or material. State of the art relevant performances for IR detection and imaging will be presented, that is to say low excess noise defects, RFPN (Residual Fixed Pattern Noise), NUC (Non Uniformity Correction) table stability for Daphnis product, 10μm pitch XGA extended MW matrix at 110K and HOT (High Operating Temperature) p-on-n technology, VGA format with 15μm pitch MW at 160K.

In this talk I will reflect on the genesis of the Information and Communications Revolution and through an analysis of the hard case of Nobel Prizes in Physics to show that the causal direction of scientific discovery and radical invention are often reversed. They often arose in a culture of so called “applications oriented research” in industrial laboratories and will use those examples to enumerate the key ingredients of highly successful R&D institutions. My views have been shaped by my own personal experiences in industrial research at the iconic Bell Labs, U.S National Laboratories and research intensive universities. I will highlight the need for institutions which transcend the “basic-applied dichotomy” and which bring research across domains into deeper congress in emerging areas such as nanoscience, biologically inspired engineering and cyber-physical systems. The need for new integrative institutions to address global challenges such as climate change and alternative energy sources will also be discussed.

An InGaAs Single-Photon Avalanche Photodiode (SPAD) array and a hybrid photon-counting image sensor have been developed for time-resolved applications in the near infrared region, especially for Flash LIDAR. The implemented array has a 100 μm pitch 32×32 matrix, and the active area in each pixel has a diameter of 12 μm. A dedicated read-out IC incorporates an active quenching and recharge circuit, and an in-pixel time-to-digital converter with 318 ps resolution for providing stable Geiger-mode operation of the InGaAs SPAD pixels and a simultaneous time-resolving function. The uniformity of the electrical field in the entire two-dimensional area is one of the key characteristics as it affects most performance parameters. The breakdown voltage mapping revealed the SPAD array has an excellent uniformity. Full characterizations of dark count rate, photon detection probability, and timing jitter were performed and will be discussed. Methods of suppressing afterpulses were examined by utilizing an adjustable hold-off function. The results showed that the function worked effectively to reduce the afterpulse probability. Finally we prove that the InGaAs SPAD image sensor has the capability of accurate timing detection for constructing a flash LIDAR in the near future.

Present infrared (IR) detection techniques are limited due to the absence of spectroscopic or “color” detection/imaging abilities. At present all cooled and uncooled MWIR and LWIR detectors are being “bucket” detectors generate integrated spectral images in the binary color format (choices of any two pseudo colors). To date very little research work has been performed on frequency selective detection. On the other hand if we see natural world we find many animals that can see over multiple spectral bands in the visible as well as in the infrared domain. Mantis shrimp eye is an example of a complex eye which is comprised of an elegant 12 channel spectrum sampler that spans the range 300-750 nm, with spectral bandwidth of around 40 nm. These are among the sharpest spectral sensitivities in the animal kingdom. The key aspect of their eye is “biological light funnel” apparatus which collect light over a wide angle with near perfect efficiency. Another biological masterpiece is pit vipers that have heat-sensitive membranes that can detect the difference in temperature between a moving prey—such as a running mouse—and its surroundings on the scale of milli Kelvins. Their infrared eye (“the pit”) has unique abilities to scatter visible light away and transmit only a band of infrared light which reduces background noise substantially. The grand challenge: Can we create an artificial eye/imaging system which has spectral resolving power like Mantis shrimp but viper like detection ability in the infrared domain?

Near-field imaging techniques at terahertz (THz) frequencies are severely restricted by diffraction. To date, different detection schemes have been developed, based either on sub-wavelength metallic apertures or on sharp metallic tips. However high-resolution THz imaging, so far, has been relying predominantly on detection techniques that require either an ultrafast laser or a cryogenically-cooled THz detector, at the expenses of a lack of sensitivity when high resolution levels are needed. Here, we demonstrate two novel near-field THz imaging techniques able to combine strongly sub-wavelength spatial resolution with highly sensitive amplitude and phase detection capability. The first technique exploits an interferometric optical setup based on a THz quantum cascade laser (QCL) and on a near-field probe nanodetector, operating at room temperature. By performing phase-sensitive imaging of THz intensity patterns we demonstrate the potential of our novel architecture for coherent imaging with sub-wavelength spatial resolution improved up to 17 μm. The second technique is a detector-less s-SNOM system, exploiting a THz QCL as source and detector simultaneously. This approach enables amplitude- and phase-sensitive imaging by self-mixing interferometry with spatial resolution of 60-70 nm.

Light-matter interaction can be controlled at the nanometer scale by designing the photonic environment of an emitter. The quantity that drives light-matter interaction is the Local Density of States (LDOS) that counts the number of modes in which the fluorescent emitter can decay, either by emitting fluorescent photons coupled to the far field (radiative modes), or by giving its energy to the environment (coupling to a dark mode or absorption losses). Depending on the targeted application (e.g. an efficient single photon source or an efficient absorber), it can be interesting to characterize and optimize the radiative and the non-radiative contributions to the local density of states separately. We have recently developed a fluorescent probe atomic force microscope that allows us to bring a fluorescent emitter in the near-field of a nanostructured sample for simultaneous mapping of the sample topography, fluorescence intensity and fluorescence decay rate (proportional to the LDOS) with nanometric precision. In this talk, we will show that this device allows a thorough characterization of the electromagnetic response of plasmonic and dielectric nanoantennas, in 3D. Moreover, we will show a novel method to map the radiative and the non-radiative contributions to the LDOS starting from the simultaneous imaging of the fluorescence intensity and decay rate. Finally, a new device for LDOS mapping at the nanometer scale without the need of scanning parts will be shown.

This manuscript presents a survey of the extended short wavelength infrared (SWIR) FPA technologies with the emphasis on In_xGa_1-xAs imagers. We discuss the limitations of 2.5 μm cut-off extended In_xGa_1-xAs photodetector technology arising from the lattice mismatch between the absorber material and the InP substrate, as well as presenting the characteristics of molecular beam epitaxy grown In_0.83Ga_0.17As photodetectors on InP substrates with different buffer layers. It is possible to achieve desirable pixel and large format focal plane array (FPA) characteristics with In_0.83Ga_0.17As epilayers on linearly graded Al_xIn_1-xAs buffer layer. No considerable difference was detected in the G-R components of the dark currents of the detectors with graded AlInAs and InGaAs buffers. Therefore, the utilization of these materials as the buffer layer seems to generate similar trapping centers in the In_0.83Ga_0.17As absorber layer. While no considerable 1/f noise was observed in the extended SWIR In_0.83Ga_0.17As detectors operating under small reverse bias at 200 K, the signal to noise ratio of the detectors was limited by 1/f noise for higher reverse bias voltages. The 1/f noise was found to be related with the shunt leakage and the generation-recombination processes in the depletion region with a relatively larger shunt leakage noise coefficient in the order of 10^-3. We also present a comparison of extended SWIR InGaAs and HgCdTe detector technologies and discuss the potential of these technologies for future developments. While 2.5 μm cut-off mesa type In_0.83Ga_0.17As FPA pixels exhibit dark current densities in the same order with those of the best planar-type HgCdTe sensors on CdZnTe substrates near room temperature, HgCdTe on CdZnTe sensors provide more than an order of magnitude smaller dark current density at the typical operation temperature of these detectors. On the other hand, In_0.83Ga_0.17As sensors on InP substrates and HgCdTe detectors on Si substrates display dark current densities in the same order with different dominancy levels of shunt and G-R leakage currents. High noise coefficient of the shunt leakage is an important limitation for the lattice mismatched detectors narrowing the operation range of these sensors.

Based on the requirements of project assignment, the paper firstly introduces the needs for principle prototype, and its overall technical solutions, assignment analysis and requirement index. Then it elaborates key technical solutions, prototype technical plan, as well as project design and production of its components, besides, we also developed testing device for debugging and testing needs, when the components design is completed, we conducted components alignment and testing, overall testing, obtaining noise squeezing degree （dB）of quantum squeezed field by principle prototype ≥ 6.4 dB, and the resolution higher than 0.2 mm @ 0.5m. We met the index requirements of principle prototype and realized high resolution imaging, providing significant basis for the following relative projects and for the development of new remote sensing technology with high performance.

We demonstrate a novel active far-field wide-field label-free nano-imaging with high signal-to-noise ratio based on the nanoscale light source, pioneering in utilizing a combination of spatial frequency shift and Stokes frequency shift. Ring shape or polygonal shape nanoscale light sources emit photoluminescence and the light is coupled to a underneath subwavelength film waveguide to produce omnidirectional illuminating evanescent waves to shift high spatial frequencies for the far-field, label-free, 2D subdiffraction imaging. The photoluminescence of the nanostructure enables high-efficiency evanescent wave coupling in a large area for the low-noise wide-field imaging. The field of view is one order of magnitude improved from the previously reported far-field and full-field method. This approach’s versatility has been demonstrated by imaging integrated chips, Blu-ray DVDs, biological cells and various subwavelength 2D patterns. The configuration-----a special NW assisted slide-----is cost-effective, quite compatible with the standard microscope and can conveniently give super resolvability to conventional microscopy as a compact module. This work is significant for physics, materials, biology, chemistry, and other areas that need nanoscale visualization.

In metal nanostructures under illumination, multiple different processes can drive current flow, and in an opencircuit configuration some of these processes lead to the production of open-circuit photovoltages. Structures that have plasmonic resonances at the illumination wavelength can have enhanced photovoltage response, due to both increased interactions with the incident radiation field, and processes made possible through the dynamics of the plasmon excitations themselves. Here we review photovoltage response driven by thermoelectric effects in continuous metal nanowires and photovoltage response driven by hot electron production and tunneling. We discuss the prospects for enhancing and quantifying hot electron generation and response via the combination of local plasmonic resonances and propagating surface plasmon polaritons.

The optimization of nonlinear optical processes at the nanoscale is a key challenge in nanoscience. In this framework, plasmon-enhanced nonlinear effects together with the development of innovative nanoantenna designs and hybrid nanostructures are receiving a lot of attention [1-2]. We recently devised a plasmonic nanoantenna working in the near-infrared region of the electromagnetic spectrum, which allows boosting the SHG efficiency. This is achieved by optimizing the nanoantenna geometry to feature (i) a double resonant response at both the excitation and emission wavelengths, (ii) a spatial overlap between the modes involved in the process and (iii) a broken symmetry, to enable dipole-allowed SHG. We found that this nanoantenna behaves like a strongly coherent nanoscale light source, featuring a marked THG along with an intense SHG [3-4]. We find evidence of a SHG-mediated cascaded effect in THG [5]. We have identified a THG polarization behavior that strongly deviates from that of a bulk (3)-mediated effect and unveils a significant contribution coming from the cascaded coherent sum of a SHG photon and a pump photon. References [1] Kauranen, M.; Zayats, A. V., Nature Photon. 2012, 6, 737-748. [2] Butet, J.; Brevet, P. F.; Martin, O. J. F., ACS Nano 2015, 9, 10545–10562. [3] Celebrano, M.; et al., Nat. Nanotechnol. 2015, 10, 412−417. [4] Sartorello, G.; et al., ACS Photon. 2016, 3, 1517−1522. [5] Mu, X.; et al., Y., Opt. Lett. 2000, 25, 117-119.

Monolayer two-dimensional transition metal dichalcogenides (2D-TMDCs) have gained immense attention for their desirable transport properties and direct bandgap that have led to a plethora of studies on modern nanoelectronic and optoelectronic applications. These properties are known to occur exclusively in TMDCs when thinned down to one or few monolayers. However reduced dimensionality poses a significant challenge for photonics and optoelectronics applications due to poor light absorption and emission dictated by the volume of semiconductor material. Plasmonic nanostructures have been widely studied for enhancing light-matter interactions in wide variety of material systems resulting in increased emission and absorption properties. 2D Materials provide the ultimate lower limit in terms of material thickness, therefore investigation of plasmon/2D Material hybrid material systems with a specific aim to enhance light-matter interactions is essential for practical optoelectronic applications. In this talk, I will discuss increased photoluminescence emission from MoS2 using both periodic plasmonic nanodisc arrays as well as a single plasmonic optical antenna. Additionally, I will describe a systematic study in which we have demonstrated increased light absorption in a monolayer WS2 film.

Low phase noise signal generated in a small structure is required for communication and high resolution imaging. Optoelectronic oscillators with their demonstrated low phase noise are popular due to the increasing demand of very clean local oscillator and clock signal sources. Forced techniques of self-injection locking phase locking (SILDPLL) applied on an OEO system reduces the phase noise and suppresses side mode observed in standard OEO with long delays. However, this novel optical feedback technique using self-ILPLL is also employed for phase noise reduction of free-running microwave oscillators. Phase noise reduction of 27 dB at 10 kHz offset has been demonstrated by applying this technique for a 10 GHz state of art DRO, achieving -137 dBc/Hz at 10 kHz offset. A phase noise prediction of this feedback technique is also presented, which very closely corroborates with experimental results. Analysis of SILPLL using the modeling has shown that further phase noise reductions could be achieved, by reducing the residual phase noise of the long delay lines and microwave amplifiers. In addition, a frequency synthesizer working at K-band is demonstrated using electronically tuned narrowband RF filter in place of fixed narrowband frequency metallic cavity based filters. The synthesizer employs optical transversal filter cascaded with YIG filter to electronically fine and coarse tune the oscillation frequency, as a replacement for fixed frequency high Q metallic filter. Second harmonic generated frequency synthesized signals with close-in to carrier phase noise of -127 dBc/Hz phase noise at 10 kHz are reported by V_π operation of a Mach-Zehnder (MZM) over 18 GHz to 22 GHz with frequency tuning step as small as 20 kHz/pm. A 19’’ rack mount system is also constructed and long term stability of 4.5 kHz over 60 min is measured at K-band, while a 3.5 kHz drift is measured for a tabletop realization. A fully integrated version of this forced OEO is also being pursued to enhance size, power consumption, and cost. A fully monolithic DBR based multi-mode laser is considered with mode-locking method to build frequency stabilized and tunable RF signal generator. The number of the output modes from each laser is adjusted using reflecting bandwidth of distributed Bragg reflector and electro-absorption (EA) modulator for amplitude control, while the phase section in integrated laser system provides frequency tuning. Mode-locking of 60 laser modes results in a highly frequency stable 10 GHz RF beat-notes with a calculated phase noise of -150 dBc/Hz at 10 kHz offset frequency.

Invited speaker: Sources for optical and infrared radiation are traditionally based on transitions between discrete electronic states and are therefore limited by the intrinsic emission properties of the semi-conductor or organic gain medium. Electron tunneling across narrow gaps may induce broadband photon emission due to inelastic transport through a tunneling junction; however, this process suffers from a very low efficiency, typically one photon per 10^5 electrons. Electrically-driven optical antennas could boost this quantum efficiency owing to concentrating photons and electrons within an ultrasmall volume. In my talk, I propose a new class of nanoscopic light sources that are not limited by quantum states, but rather depend on the antenna architecture and the applied bias. These compact light sources, based on electrically-driven nanogap optical antennas, feature a tunable emission wavelength, a high quantum efficiency, and operate at room temperature. As the fluctuations in the tunneling current constitute a broadband source, the electroluminescence can be tuned from the blue to the infrared spectral regions, by changing the antenna dimensions and the applied bias voltage. This implies that differently tuned devices can be integrated on-chip in close proximity on top of a wide variety of substrates or within microfluidic channels. Such multi-spectral sources have the potential to impact today’s Si-based electronic chips by employing fast light pulses as the communication path for higher data flux.

The comprehensive monitoring of the food chain, i.e. from growth to consumer, without gaps is of outstanding importance to consumer health and the food industry alike. Yet, due to the lack of suitable sensing technologies at adequate costs, only selective, critical spots can currently be monitored. While the particular food to be monitored may take any shape or form during processing, gases are always present and their composition is uniquely suited to learn about the state of the system. In this contribution, a universal quantum sensor concept to identify and quantify the components of complex gas matrices is presented. The sensing approach is based on detecting Raman scattered photons from inside a gas sample filled optical cavity. Because of the typically small Raman scattering cross-sections on the order of 10^-30 cm² a Fabry-Perot cavity with a Finesse of about 2,000 is used to enhance the available laser power of an extended cavity diode laser running at 780 nm. The scattered light is funneled onto a spectrometer after Rayleigh scattered photons have been suppressed using a notch filter. To allow in-situ determination of arbitrary gas matrices, the sensor concept relies on the diffusion of ambient air into the cavity. The setup is currently able to simultaneously detect gases with Raman spectra up to 3000 cm^-1, which includes important indicators for food packaging, including nitrogen, oxygen, and carbon dioxide.

Invited Ultra-small light sources which can be controlled electrically or optically are of great interest to nano-photonics. Electroluminescence induced by inelastic tunneling from an STM-junction is such an example, however hampered due to a small quantum efficiency. We observe enhanced emission of photons from such a tunneling junction by almost three orders of magnitudes by additionally exciting a gap-plasmon oscillation with laser irradiation. Either a pristine Au-substrate/Au-tip tunneling junction or a junction (Au-substrate/self-assembled molecular monolayer/Au-tip) with molecules chemically bound to the Au substrate is used. Analyzing the emission spectra from the junction recorded as a function of bias voltage for the Au-Au junction we conclude that the enhanced intensity is induced by laser illumination and originates from the radiative decay of hot electrons closely above the Fermi level via inelastic tunneling into the plasmon modes formed by the tip-substrate gap. In the presence of molecules in the gap, we observe a bias dependent spectral narrowing characteristic for superluminescence. The optically pumped molecular junction behaves as a bias-driven point source, operating at ambient conditions and providing almost three orders of magnitude higher electron-to-photon conversion efficiency than electroluminescence induced by inelastic tunneling without optical pumping. The enhanced emission can be modeled by rate equations taking into account the hole-injection from the tip (anode) into the highest occupied orbital of the closest substrate bound molecule (lower level) and radiative recombination with an electron from above the Fermi-level (upper level), hence feeding photons back by stimulated emission resonant with the gap mode.

Recent works towards the development of Ge-rich SiGe photonic integrated circuits will be presented, such as the demonstration of low-loss waveguides and ultra-wideband Mach Zehnder interferometer from 5.5 to 8.6 μm wavelength, as well as the first steps towards the realization of efficient wideband optical sources.

Antennas play a key role in today’s wireless communication networks and it would be hugely beneficial to extent their use into the optical regime. However, classical signal generators do not work at those frequencies and therefore new concepts are needed. Here, we demonstrate how to electrically drive an optical nanoantenna using an atomic-scale feed gap provided by a gold-particle pushed into a precisely tailored interstice between two antenna arms. Upon applying a voltage, inelastic electron tunneling leads to current fluctuations in the optical regime and, hence, light emission. We show how the antennas spectrally shape the emission, how the exact particle position influences these properties and how to increase the directivity via Yagi-Uda arrangements or plasmonic waveguides structures in order to make electricallydriven optical nanoantennas more suitable for on-chip data communication.

Single-photon avalanche diodes (SPADs) must be integrated on modern highly-scaled process nodes to achieve high array fill factors and imager pixel counts. Integration also enables applications where rapid, complex data processing needs to be co-located with these detectors and other photonic components. In this work we implement 5μm, 10μm, and 15μm-diameter circular SPADs using a p+/n-well structure and an STI guard ring in a 90nm bulk CMOS process, and in contrast to previous work on silicon SPADs carry out detailed study of dark count rate (DCR) and afterpulsing at cryogenic temperatures. With passive quenching these SPADs are saturated by dark counts at room temperature and by afterpulsing at cryogenic temperatures, motivating the development of an active quenching circuit (AQC) to characterize and ultimately suppress the processes responsible for these non-idealities. A novel AQC topology based on a linear output stage, able to detect avalanches and drive SPADs connected by a coaxial cable faster than previously-demonstrated circuits, is proposed and demonstrated. This circuit enables device testing using a coaxial microprobe inside a Helium cryostat. To quantify the SPADs’ performance, we operate them in free-running mode and collect histograms of the pulse interarrival times from which we extract the DCR and afterpulsing probability. We use this technique to measure these parameters with varying temperature and overbias voltage, showing there is an optimal temperature for operating each SPAD. With active quenching we achieve 100Hz-level DCR, <10% afterpulsing probability, >10% 405nm quantum efficiency at 140K, and are presently characterizing the photon detection probability.

We investigate laser energy localization in 2D photonic crystal with Kerr nonlinear response in dependence of the incident femtosecond pulse chirp. Such kind of energy localization appears due to soliton formation in certain elements of photonic crystal. Their positions, in which the soliton appear, depend on the incident pulse chirp and the pulse intensity. It is important to emphasize that a soliton occur in separate elements of the photonic crystal. Therefore, their sizes must be less than sizes of the photonic crystal elements. Consequently, an intensity of the incident pulse must be greater than certain crucial value. A process of energy localization strongly depends on relation between the wave packet carrier frequency and a frequency characterizing a photonic crystal. These solitons move with slow velocity inside the PC elements. Under certain conditions, the soliton can stop. The problem under consideration is described by a nonlinear Schrödinger equation with respect to amplitude slowly varying in time only. We investigate a femtosecond pulse interaction with photonic crystal numerically and analytically.

Modern micro- and nanofabrication allows very complex optical systems to be fabricated, with potential applications in classical and quantum communications, sensing and information processing. We now know such systems could perform operations well beyond the classical optics of lenses and mirrors; indeed, any legal linear optical operation can be constructed from a mesh of two-beam interferometers [1,2]. One recently demonstrated example [3] is separating arbitrary overlapping orthogonal beams, without fundamental loss. Surprisingly, not only is there a simple way of designing such meshes, but the mesh can even design itself, without any calculations, opening up a new field of self-configuring, self-correcting, and self-stabilizing optics [1-3], and these meshes are well-suited to silicon photonics and possibly nanophotonic implementations. Potential applications include mode multiplexing/demultiplexing in telecommunications, microwave photonics, self-aligning beam couplers, automatic tracking of targets, automatically finding the best channels through a scattering optical system, networks for quantum applications, and many others. This different way of looking at optics has also led to a surprising fundamental advance in rewriting and extending Kirchhoff’s law of thermal radiation [4]. [1] D. A. B. Miller, “Self-configuring universal linear optical component,” Photon. Res. 1, 1-15 (2013) [2] D. A. B. Miller, “Sorting out light,” Science 347, 1423-1424 (2015) [3] A. Annoni et al., “Unscrambling light – automatically undoing strong mixing between modes,” Light Science & Applications 6, e17110 (2017) [4] D. A. B. Miller, L. Zhu, and S. Fan, “Universal modal radiation laws for all thermal emitters,” PNAS 114, 4336-4341 (2017)

Here we review our journey from metallic nanostructures to dielectric and semiconductor metasurfaces. We show how to employ metal non-linearity to stimulate a strongly anisotropic nonlinear response by symmetry breaking, despite their high Ohmic losses. Furthermore, we show how an ultra-thin surface of subwavelength dielectric nanostructures, e.g. silicon with negligible losses and multipolar characteristics, can enable enhanced light matter interaction for efficient third harmonic generation and ultra-fast light modulation. However, the centrosymmetric structure of silicon and the lack of quadratic nonlinearity, guided us towards exploiting semiconductor nanostructures, particularly III-V semiconductors. Subsequently, we demonstrate dielectric realization of AlGaAs nanoantennas for an efficient second harmonic generation, allowing the control of both directionality and polarization of nonlinear emission. This is enabled through the fabricated high-quality AlGaAs nanostructures embedded in an optically transparent low-index material. Our results open novel applications in ultra-thin light sources, light switches and modulators, ultra-fast displays, night-vision and other nonlinear optical metadevices based on resonant nanoparticles.

Broadband subwavelength optical resonators have the ability to enhance the spontaneous emission rate and brightness of solid-state emitters. Recently, high-index dielectrics have been proposed as an alternative to plasmonic materials to design optical resonators with low ohmic losses. In this study, the interaction between a silicon nanoantenna and solid-state emitters is characterized by tuning the position of a 100 nm diameter fluorescent sphere in the vicinity of an e-beam fabricated silicon disk using scanning-probe microscopy. If the nanodisk resonance matches the emission wavelength of the fluorescent molecules, we observe enhanced decay rates at short distances; while, for an out-of-resonance antenna, the fluorescence lifetime is locally increased. Furthermore, our experiments highlight the ability of silicon antennas to increase far-field collection efficiencies, in agreement with numerical simulations (D. Bouchet et al, Phys. Rev. Applied 6, 064016 (2016)). The intensity of spontaneous emission from fluorescent dye molecules can be further enhanced, by more than two orders of magnitude, in the nanoscale gap between silicon nanodisks. This is evidenced at the single molecule level using fluorescence correlation spectroscopy with freely diffusing emitters (R. Regmi et al, Nano Lett. 16, 5143 (2016)). These results demonstrate the potential of silicon antennas for the manipulation of solid-state emitters at the nanoscale and at room temperature.

Dielectrics represent a new frontier for Surface Enhanced Raman Scattering. They can serve either as a complement or an alternative to conventional, metal-based SERS, offering key advantages in terms of low invasiveness, reproducibility, versatility and recyclability. In comparison to metals, dielectric systems and, in particular, semiconductors, are characterized by a much greater variety of parameters and properties that can be tailored to achieve enhanced Raman scattering or related effects. Light trapping and sub-wavelength focusing capabilities, morphology-dependent resonances, control of band gap and stoichiometry, size-dependent plasmons and excitons, charge transfer between semiconductors and molecules and vice-versa are a few examples of the manifold opportunities associated to use of semiconductors as SERS-active materials. In this talk a few examples [1] of all-dielectric core/shell colloids for plasmon-free SERS,[2] including applications in biochemistry [3-5] and environmental science,[6] will be presented and discussed, with a special focus on the latest results regarding SERS/mass spectrometry multimodal sensing.[7] References: 1) I. Alessandri, J. R. Lombardi, Chem. Rev. (2016) 116, 14921−14981. 2) I. Alessandri, J. Am. Chem. Soc. (2013) 135, 5541-5544. 3) I. Alessandri et. al., Small (2014) 10, 1294-1298. 4) I. Alessandri et al., ACS-Appl. Mater. Interf. (2016) 8, 14944-14951. 5) N. Bontempi et al. Nanoscale 2017, doi: 10.1039/C7NR0249F 6) N. Bontempi et al., Nanoscale (2016), 8, 326-3231. 7) I. Alessandri et al., Sci. Rep. (2016) 6, 34521.

We will present our recent work on III-V micro-cavity lasers monolithically grown on silicon substrates. The III-V material is directly grown using Template-Assisted-Selective-Epitaxy (TASE) within oxide cavities patterned using conventional lithographic techniques on top of the silicon substrate. This allows for the local integration of single-crystal III-V active gain material. Two variations of this technique will be discussed; the direct growth of disc lasers and the two-step approach via a virtual substrate. Room temperature single-mode optically pumped lasing is achieved in GaAs micro-cavity lasers, and devices show a remarkably low shift of the lasing threshold (T₀=170K) with temperature. Dependence on cavity geometry and pump power will be discussed.

Strain-balanced InAs/InAsSb superlattices can be tuned to absorb and emit across the mid- to long-wave infrared, and exhibit appropriate minority carrier lifetimes for high performance infrared photodetectors. The optical quality of this material has been shown to improve with the use of Bi as a surfactant. Specifically, InAs/InAsSb superlattices grown at 425 °C and 430 °C exhibit improved photoluminescence intensity for Bi/In flux ratios up to 1.0%, and optical quality improves further with increasing growth temperature and increasing Bi/In flux ratios up to 5.0%. The identification of optimal growth conditions for InAs/InAsSb superlattices with Bi surfactant, as well as further exploration of the impact of Bi surfactant is an important component to further developing and optimizing this infrared material system.

Several strain-balanced InAs/InAsSb superlattices are grown using molecular beam epitaxy at temperatures ranging from 425 °C to 475 °C using Bi/In flux ratios ranging from 0.0% to 10.0%. The structural and optical properties of the samples are evaluated using X-ray diffraction, secondary ion mass spectrometry, and photoluminescence spectroscopy. Analysis of the mass spectrometry data indicates that surfactant Bi incorporates into the InAs/InAsSb material system with a sticking coefficient of 0.3% at 450 °C, yielding dopant-level concentrations for typical Bi/In surfactant flux ratios. Analysis of the integrated photoluminescence intensity indicates that photoluminescence efficiency is greatest with a 1.0% Bi/In flux ratio for growth at 425-430 °C, and a 5.0% Bi/In flux ratio for growth at 450-475 °C. The improvement in photoluminescence efficiency is associated with a longer Shockley-Read-Hall lifetime in the superlattices grown with Bi surfactant.

The convergence of microelectronics and photonics on a single chip is one of the greatest challenges of present research. To make it happen, it is necessary to develop an entire novel class of optoelectronic devices exhibiting far beyond the state-of-the-art performance in term of compactness, speed and power efficiency. Silicon photonics enhanced with III-V semiconductors such as InP-based materials is the key technology to provide a platform able with all the necessary functionalities but it is only through the exploitation of nanophotonics concepts that disruptive performance can be reached. During this presentation, we will show our latest results obtained on electrically powered InP-on-SOI photonic crystal devices. These results will concern first the demonstration of nanolaser diodes emitting at 1.55µm in a SOI waveguide with a wall-plug efficiency higher than 10%. The developed electrical injection scheme allows us, also, to conceive nano-amplifiers and electro-optical modulators which show promising features for their integration in a photonic circuit.

Here we propose a new wide band gap logic circuitry providing emerging power electronics with reliable logic control capabilities with 500 MHz+ switching speeds and withstanding 300V+. Particularly, a three-stage ring oscillator composed of NMOS (μ_e = 1000 cm²/V-s) and PMOS (μ_h = 250 cm²/V-s) cubic phase GaN devices (with V_T of 0.77 V and –0.84 V, respectively) is simulated. The propagation delay is minimized by optimizing the width-to-length ratio (W/L) between the NMOS and PMOS devices. Transient response of the simulation illustrates the ability of the CMOS inverter to operate at a maximum frequency of 1.22 GHz with a full voltage swing between V_DD of 2.5 V and 0 V. The proposed cutting-edge p-channel GaN high hole mobility transistor (HHMT) solves one of the most longstanding problems in power electronics and constitutes the basis of an innovative reduced total life cycle cost that will serve as the cornerstone of the next generation of integrated, scalable, and reliable power systems.

We present the Kerr phase-interrogator as a novel optical processing unit based on the nonlinear Kerr effect for sensing application. The Kerr phase-interrogator enables a variety of point sensors for displacement, temperature, and vibrations measurement, and enables distributed sensing based on incoherent optical frequency domain reflectometry. We highlight some of the unique advantages of the Kerr phase-interrogator including sensitivity enhancement beyond the wavelength limit of standard interferometers, and increasing the sensing range beyond the laser coherence-length using incoherent optical frequency-domain reflectometry. We believe the Kerr phase-interrogator represents a breakthrough in optical sensing because it allows for overcoming fundamental limitations of existing sensors that are based on linear optical effects.

The Quantum Cascade Laser is becoming a key tool for plenty of applications, from the IR to the THz range. Progress in nearby areas, such as the development of ultra-low loss crystalline microresonators, optical frequency standards and optical fiber networks for time&frequency dissemination, are paving the way to unprecedented applications in many fields. For the most demanding applications, a thorough control of quantum cascade lasers (QCLs) emission must be achieved. In the last few years, QCLs unique spectral features have been unveiled, while multifrequency, comb-like QCLs have been demonstrated. Ultra-narrow frequency linewidths are necessary for metrological applications, ranging from cold molecules interaction and ultra-high sensitivity spectroscopy to infrared/THz metrology. In our group, we are combining crystalline microresonators, with a combined high quality factor in the infrared and ultra-broadband spectral coverage, with QCLs and other nonlinear highly coherent and frequency referenced sources. Frequency referencing to optical fiber-distributed optical primary standards offers astonishing stability values of 10^-16 @1-sec timescales in laboratory environments but several hundred kilometres far away from the primary clocks. A review will be given of the present status of research in this field, with a view to perspectives and future applications.

Since the first demonstration of quantum-cascade lasers (QCLs) in 1994, remarkable progress has been made from the mid-infrared (mid-IR) to terahertz (THz) spectral range. The 1–6 THz spectral range is very attractive for many applications, such as imaging, chem-/bio-sensing, heterodyne detection, and spectroscopy. However, this spectral range still lacks high-performance compact continuous-wave (CW) light sources operable at room temperature. Recently, THz sources based on intracavity difference-frequency generation (DFG) in dual-wavelength mid-IR QCLs have been demonstrated. These devices, known as THz DFG-QCLs, have their active region engineered to exhibit giant intersubband nonlinear susceptibility χ⁽²⁾ for THz DFG. Recently, we developed THz DFG-QCLs containing an homogeneous active region with dual-upper states (DAU), which exhibit a THz output power of 301 μW with a high mid-IR-to-THz conversion efficiency of 1.2 mW/W². The DAU active region approach provides a broadband gain bandwidth, and as a result, two wavelength emissions can be obtained without a heterogeneous cascade that has been used previously; this leads to a low threshold current density compared with that obtained from the use of a heterogeneous active region. Here, we present a low threshold THz DFG-QCL based on a λ~6.8 μm DAU active region. The λ~6.8 μm DAU-QCLs have exhibited very low threshold current density as well as broad gain bandwidth. By applying the λ~6.8 μm DAU design approach, the device demonstrates room temperature CW operation without an epidown mounting scheme, where a threshold current density for THz emission has been shown to be low, at 1.3 kA/cm². Besides, ultra-broadband emission covering 1.6–3.5 THz has been obtained in CW mode below 200 K.

The combination of spectral broadly tunable quantum cascade laser chips in an external cavity (EC-QCL) with a rapid scanning MOEMS grating as wavelength selective element has attracted a lot of attention in recent years. Spectral tuning ranges of more than 350 cm-1 in the mid-infrared fingerprint region combined with scan frequencies of up to 1 kHz for a complete wavelength scan have enabled several new sensing applications such as contactless real time identification of chemical substances via backscattering spectroscopy. Moreover, the technological approach of a MOEMS EC-QCL allows for a dense integration of the electro optical components resulting in a footprint size for the laser source comparable to that of a matchbox. This makes the MOEMS EC-QCL especially attractive for handheld sensing systems. In this talk we present the recent advances on the MOEMS EC-QCL technology made at Fraunhofer IAF and IPMS within the European projects MIRPHAB, Aquarius and Chequers. A detailed analysis of spectral reproducibility of consecutive scans, amplitude noise, and spectral resolution in pulsed and cw operation of the laser source is shown and several showcase applications from online process control in chemical and pharmaceutical industry such as transmission measurements on liquids and gases are discussed.

Terahertz quantum-cascade lasers based upon active reflectarray metasurfaces are shown to be a viable platform for scalable power with high-quality beams. The “metasurface” is made up of sub-wavelength arrays of antenna-coupled sub-cavities loaded with quantum-cascade active material. One has the ability to spatially engineer the amplitude, phase, spectral, and polarization response of the metasurface. We present several recent results. By placing the metasurface as part of external cavity, focusing QC-VECSELs have been demonstrated with high slope efficiency, high cw power, and near diffraction-limited beam quality. Additionally, VECSELs with electrically switchable polarization have been demonstrated.

Quantum cascade lasers (QCL) are semiconductor lasers based on ultrafast intersubband transitions with picosecond timescale that have become the most suitable laser sources from the mid-infrared to the THz range, due to their compactness, efficiency and high room temperature performances. In particular, high-power QCLs are powerful sources for optical countermeasures, including night vision blinding and missile out steering. This work investigates the nonlinear dynamical features of coupling of linear arrays of emitters in the so-called Talbot configuration for phase-locking operation using broad area emitters. These initial results are of paramount importance for creating future bright infrared sources with Watt-level power.

Quantum cascade lasers (QCLs) exploit radiative intersubband transitions within the conduction band of semiconductor heterostructures. The wide range of wavelengths achievable with QCLs, from mid-infrared to terahertz range, leads to a large number of applications including absorption spectroscopy, optical countermeasures and free space communications requiring stable single-mode operation with a narrow linewidth, high output power and high modulation bandwidth. Prior work has unveiled the occurrence of temporal chaos in a QCL subjected to optical feedback, with a scenario involving oscillations at the external cavity frequency and low-frequency fluctuations. The purpose of this work is to further investigate the temperature dependence of a mid-infrared QCL with optical feedback. When the semiconductor device is cooled down to 170K, experiments unveil that the laser destabilization appears at a lower feedback ratio and that the chaotic bubble slightly expands owing to a different carrier lifetime dynamics. These results are of paramount importance for new mid-infrared applications such as chaos-encrypted free-space communications or unpredictable countermeasures.

Sensing method with Quantum Cascade Laser (QCL) as a light source is expected to offer a high sensitivity, a short measurement time, and a good portability compared to conventional methods. However, commercially available QCLs have high power-consumption of several W. Therefore, a large power supply is required to drive QCL, and most of the input power is released as heat, leading to the necessity for a large cooling system. For these reasons, portable gas sensors using QCL have not been realized. To address this issue, we had recently developed a low power-consumption DFB-QCL in the 7μm wavelength region. In this study, we developed a compact and low power consumption QCL module with Φ 15.4 mm To-CAN package. The QCL device, a thermoelectric cooler (TEC), a thermistor and a window were assembled in this package. The threshold power-consumption and the maximum output power were 0.97 W and 37 mW at 20°C, respectively under continuous wave driving. In addition, it maintained a single mode operation between 20°C and 80°C without a mode hopping. The performance of this QCL module as a light source for gas sensing was evaluated by measuring the mid-infrared absorption spectrum of the methane gas with a multi pass type gas cell. High sensitive methane gas detection was achieved, which was comparable to that of the conventional high heat load (HHL) packaged QCL module reported by other group. It is expected that a compact and low-cost MIR gas sensor with high-sensitivity can be realized with our QCL module.

Progress on the modeling, fabrication, and characterization of the transistor-injected quantum-cascade laser (TI-QCL) is presented. As a novel variant of the quantum cascade laser, the TI-QCL has been projected to have advantages over conventional QCLs in certain applications because of its 3-terminal nature. The separation of field and current is expected to allow separate amplitude and frequency modulation, and the location of the cascade structure in a p-n junction depletion region is expected to reduce free carrier absorption and improve efficiency. At the same time, the added complexity of the structure creates challenges in the realization of working devices. An overview of the basic operating principles of the TI-QCL is first given, and projected advantages discussed. Next, work on modeling GaAsbased TI-QCLs is presented, and a design for devices in this system is presented. Finally, work on fabrication and characterization of devices is examined and ongoing challenges are discussed. The role of quantum state alignment in the QCL region on electron-hole recombination in the base is also examined, showing the capability of using basecollector voltage to modulate the optical output from the direct-bandgap transistor base.

We report on the development of a gas sensor system based on quartz-enhanced photoacoustic spectroscopy (QEPAS) for the detection of trace levels of ethylene using a quantum cascade laser operating at ~ 10.3 μm. To realize a compact sensor architecture, a dedicated acoustic detection module was designed and implemented. The module includes a QEPAS spectrophone, composed of a quartz tuning fork, a micro-resonator tube and a low-noise pre-amplifier chip for the signal readout. The volume of the ADM is ~30 cm³. A minimum detection limit of 30 part-per-billion in concentration was obtained with a data acquisition time of 10 s.

Optimization of spin-lasers relies on the proper design of the active medium but also on a thorough understanding of the vectorial dynamics of the electromagnetic field in the laser cavity itself. A vectorial approach based the Jones formalism associated to the resonant condition of the field in the laser cavity is derived in order to draw the main guidelines for developing functional spin-controlled VCSELs. This general modelling framework, which accounts for spin injection effects as a gain circular dichroism in the active medium, shows that any residual phase anisotropy in the laser has a detrimental role on polarization switching. The same framework, is used to propose two solutions enabling to overcome this drawback: either by compensating the phase anisotropy or by preparing the laser cavity so that its eigenstates are circularly polarized. Moreover, unlike in spin-LED, we show that the leverage effect existing in the laser due to eigenmodes coupling makes it possible to switch the laser from a polarized oscillation to the orthogonal one despite the weak spin injection efficiency due to spin decoherence. All these predictions are confirmed using external cavity VCSELs which offer an ideal playing field for experimental investigations. Based on these developments, future trends towards the achievement of efficient and compact spin-lasers will be given.

We experimentally demonstrate and test a new type of laser where emission is mediated by water waves. Our device is similar to Brillouin lasers, but exploits water-waves (instead of acoustical waves). In our study, we fabricate resonators that co-host capillary and optical modes, control them to operate at their non resolved sideband regime, and observe stimulated capillary scattering and coherent excitation of capillary resonances at kHz rates. In more details, we experimentally measure optical quality factor near million, capillary quality factor near 20 and lasing threshold at 70 microwatt. Knee shaped power dependance, that is typical to lasers, is measured together with line narrowing as power increases. By exchanging energy between electromagnetic and capillary waves, we bridge interfacial-tension phenomena at the liquid phase boundary to optics, and might impact optofluidics by allowing optical control, interrogation and cooling of water waves.

Strong coupling between excitons and photons inside a microcavity leads to the formation of cavity polaritons, hybrid light-matter particles. Under suitable conditions, polaritons can emit coherent light without population inversion, whereby polariton lasing can exhibit a threshold at least an order of magnitude less than that of conventional photon lasing in the same material. Polaritons in organic semiconductors are stable at room temperature, due to their large exciton binding energy. This renders organic materials interesting for light-mater interaction experiments at ambient conditions. In this paper, we report on polariton-lasing using fluorescent proteins embedded in a planar microcavity. The typical laser-like threshold-behavior, manifesting in an intensity nonlinearity, coherence build-up with a linewidth drop and an interactioninduced blueshift stemming from the part-matter nature of polaritons are presented. Additionally, we show the possibility to confine photonic modes inside deterministically created traps by presenting discretized mode spectra.

In this work, we analyze the possibility of exploiting the recently demonstrated super-resonant intracavity coherent absorption effect for quantitative sensing applications. The method relies on a system of two nested resonators (ring and Fabry-Perot) which allows to increase the radiation-matter interaction pathlength by a factor proportional to the product of the two resonator’s individual finesse coefficients. In this way, it is possible to dramatically increase the interaction of intracavity radiation with a weakly absorbing sample without need of an ultra-high finesse optical cavity. Here, we propose a measurement strategy that allows to exploit the super-resonant enhancement provided by the nested-resonators system and cancel out the noise connected with the radiation source at the same time, and compare it to a conventional cavity-enhanced absorption measurement.

The terahertz (THz) region of the electromagnetic spectrum, broadly defined as between 300 GHz and 30 THz, is of growing importance in fields as diverse as communications, medicine, astronomy, security, biology and materials science. Despite this, the technologies for detection of THz radiation are still comparatively immature. The most sensitive THz detectors are typically slow and require cryogenic cooling, and conversely the fastest detectors lack the sensitivity to measure weak signals. We describe here recent work to employ new two-dimensional (2D) materials for the detection of THz waves.

Wavelength shifting is an important process in fiber-optical communications, and is implicated for example, for transferring information between low-loss transmission windows, typically between 1.3 µm and 1.55 µm. This is normally achieved using optical-electrical-optical (OEO) switches that results in speed bottlenecks. Here, we demonstrate an all-optical wavelength shifting scheme using quantum cascade lasers (QCLs)1 for the generation of sidebands on an optical telecom carrier at room temperature, potentially being considerably faster than OEOs. The process is based on resonant nonlinearities where phase matching is less critical. This work is the first demonstration of telecom sideband generation at room temperature with QCLs, where previous works with QCLs 2-4 have been limited to optical pumps in the near-infrared range (~800 nm). The wavelength shift in the telecom domain was achieved by nonlinear sideband generation using a modified MIR QCL (lambda=10µm), based on InGaAs/AlInAs quantum wells, and a resonant telecom pump, permitting to shift from 1.3 µm to 1.55 µm and vice-versa. Demonstrations at room temperature are shown. THz sideband generation with InGaAs/AlInAs THz QCLs are also demonstrated, compared to those in the MIR and correlated with nonlinear susceptibility calculations. To conclude, sideband generation in the telecom range has been demonstrated at room temperature. This demonstration in the telecom range will further permit novel approaches for the QCL stabilization/injection locking, and the up-conversion of the MIR emission to the telecom domain. 1. J. Faist, et al., Science 264 (5158), 553-556 (1994). 2. J. Madeo, et al., Nat Photonics 6 (8), 519-524 (2012). 3. P. Cavalie, et al., Appl Phys Lett 102 (22) (2013). 4. S. Houver, et al., J. Tignon and S. S. Dhillon, Opt Express 23 (4), 4012-4020 (2015).

We propose and demonstrate a scattering-type near-field probe, designed to increase the sensitivity of high-resolution scattering probe microscopy at terahertz (THz) frequencies. For efficient scattering of THz radiation, the probe, fabricated from indium, is designed to resonate like a dipole antenna. Efficient excitation is achieved by integrating the probe with a radially-polarized THz source. Using time-domain spectroscopy (TDS), we observe resonant enhancement of the scattered fields, and using aperture-type near-field microscopy, we see high field confinement at the scattering probe apex.

Interdigitated photoconductive (iPC) switches [1] are powerful and convenient devices for time-resolved spectroscopy, with the ability to operate both as sources and detectors of terahertz (THz) frequency pulses. However, reflection of the emitted or detected radiation within the device substrate itself can lead to echoes that inherently limits the spectroscopic resolution achievable from their use in time-domain spectroscopy (TDS) systems. In this work, we demonstrate a design of low-temperature-grown-GaAs (LT-GaAs) iPC switches for THz pulse detection that suppresses such unwanted echoes [2]. This is realized through the growth of a buried multilayer LT-GaAs structure that retains its ultrafast properties, which after wafer bonding to a metal-coated host substrate, results in an iPC switch with a metal plane buried at a subwavelength depth below the LT-GaAs surface. Using this device as a detector, and coupling it to an echo-less iPC source [3], enables echo-free THz-TDS and high-resolution spectroscopy, with a resolution limited only by the temporal length of the measurement governed by the mechanical delay line used. As a proof-of-principle, the 2(12)-2(21) and the 1(01)-2(12) rotational lines of water vapor have been spectrally resolved, demonstrating a spectral resolution below 10 GHz. [1] A. Dreyhaupt, S. Winnerl, T. Dekorsy, M. Helm, Appl. Phys. Lett. 86, 121114 (2005) [2] K. Maussang, J. Palomo, J.-M. Manceau, R. Colombelli, I. Sagnes, L. H. Li, E. H. Linfield, A. G. Davies, J. Mangeney, J. Tignon, and S. S. Dhillon, Appl. Phys. Lett. 110, 141102 (2017). [3] K. Maussang, A. Brewer, J. Palomo, J.-M. Manceau, R. Colombelli, I. Sagnes, J. Mangeney, J. Tignon, S.S. Dhillon, IEEE Trans. Terahertz Sci. Technol. 6, 20 (2016)

Multi-mode optical microcavities have enabled the emergence of compact optical sources such as parametric oscillators and nonlinear combs for quantum information and metrology. Efficient nonlinear interactions take place, owing to a combination of large Q factor, small modal volume and large material index. The control of the frequency spacing of the resonances is also a critical aspect. Here we demonstrate an effective harmonic potential for photons owning to the concept of bichromatic lattice in a photonic crystal structure. Wide gap semiconductor material, i.e. GaInP, is used here to prevent any detrimental non-linear absorption such as two photons. The experimental evidence is given through the statistical analysis of the frequency spacing of high-Q resonances over 68 cavities. For each structure, the complex reflection spectra is measured using Optical Coherent Tomography (OCT) with a resolution of 20 MHz. The dispersion of the resonator is extracted through a polynomial fit. It appears to be small and more importantly crosses zero as the radius of the holes is changed. Moreover, each of these resonators have many modes, typically four, with loaded Q factor in the 10^5 to 7x10^5 range and intrinsic Q factor well above one million. Equi-spaced resonances in a very compact structure should lead to ultra-strong nonlinear interactions, particularly resonantly enhanced Four Wave Mixing and parametric oscillation.

We present a scheme for generation and characterization of entangled spatial qubits based on type-II spontaneous parametric down-conversion (SPDC) in a periodically poled titanyl phosphate (PPKTP) multimode nonlinear waveguide [1]. Our scheme exploits intermodal dispersion which has been hitherto successfully employed to produce spatially pure SPDC photon pairs from a multimode waveguide without spatial filtering [2]. Production of discrete entanglement relies on driving simultaneously two SPDC processes that involve different combinations of transverse spatial modes for which phase matching bandwidths significantly overlap. We propose a procedure for experimental identification of the spatial qubit subspace based on a scan of the spatial Wigner function via the displaced parity measurement using an inverting Sagnac interferometer and photon counting. We numerically verified the robustness of the mode reconstruction procedure against experimental imperfections. We also propose an experimental method for detecting spatial entanglement in the position-wave vector phase space. Numerical simulations indicate that waveguide parameters required for experimental demonstrations are compatible with current manufacturing capabilities. Using simulated mode profiles we calculate the maximum attainable Clauser-Horne- Shimony-Holt combination value reaching 2.12, which clearly violates the classical limit and confirms the feasibility of observing non-classical features of the generated state. [1] M. Jachura et al. Physical Review A, 95, 032322 (2017). [2] M. Jachura, M. Karpiński, C. Radzewicz, K. Banaszek, Optics Express, 22, 8624-8632 (2014).

The III-V semiconductor AlGaAs is an ideal material for nonlinear optics. It has large second and third order nonlinearities, a low two-photon absorption coefficient at the half band gap and allows for the easy fabrication of integrated optical devices. In addition, AlGaAs can be used to directly integrate photodiodes, modulators and passive optical elements on the same chip as the nonlinear elements.  This talk will highlight the benefits of this nonlinear material for the generation of entangled photon states using both spontaneous down conversion and spontaneous four wave mixing.

Photonics nanomaterials are considered to be a major source of innovation for advanced optical systems, since their electromagnetic properties can be engineered by implementing a suitable geometry of their nano-sized elementary unit cells. While for many applications mainly their far field properties, i.e. the influence on the reflected, transmitted, and scattered fields measurable in a distance large compared to the exciting wavelength, are of interest, they provide many degrees of freedom to influence also the nearfields surrounding the unit cells. This becomes important particularly if nonlinear light matter interaction is exploited, where the far field response depends critically on the local field strength. Hence nanomaterials offer a conceptually new way to tailor the nonlinear material properties to the needs of particular applications. Furthermore new types of nonlinearities, by e.g. surface effects, become important, due to the increased surface to volume ratio of nanomaterials. In this presentation we will present our recent results on nonlinear optical investigations of photonic nanomaterials, which derive from the hybridization of resonant photonic nanostructures, which provide highly dispersive field enhancement. The hybridization of such metallic or dielectric nanoresonators with highly nonlinear materials, as e.g. atomically thin semiconducting membranes, "classical" semiconductors, or ferroelectrics, provides a route towards even more efficient nonlinear processes. Furthermore we will show examples of how the combined control of dispersive and nonlinear properties can be exploited to address applications in frequency conversion, quantum light sources and sensing.

We overview recent advances in the research on spatiotemporal beam shaping in nonlinear multimode optical fibers. An intense light beam coupled to a graded index (GRIN) highly multimode fiber undergoes a series of complex nonlinear processes when its power grows larger. Among them, the lowest threshold effect is the Kerr-induced beam self-cleaning, that redistributes most of the beam energy into a robust bell-shaped beam close to the fundamental mode. At higher powers a series of spectral sidebands is generated, thanks to the phase matching induced by the long period grating due to the periodic self-imaging of the beam and the Kerr effect. Subsequently a broadband and spectrally flat supercontinuum is generated, extending from the visible to the mid-infrared.

Boosting nonlinear frequency conversion in extremely confined volumes remains a crucial task in nano-optics, all-optical signal processing and nanomedicine. Photon-photon interactions at the nanoscale are intrinsically weak and can only be excited using very high light intensities. Optical materials featuring large nonlinearities and low absorption losses offer a valuable solution to circumvent this limitation and effectively generate nonlinear effects in nanoscale volumes. Metal-less nanophotonics has recently raised an increasing interest because the optical response of high-permittivity dielectric nanoparticles exhibits negligible dissipative losses and strong magnetic multipole resonances in the visible and near-IR. We have recently proposed all-dielectric AlGaAs-on-AlOx nanodisks and coupled dimers featuring an intense second harmonic generation (SHG) with conversion efficiency up to 10-^5 upon pumping with an ultrafast Erbium-doped fiber laser centered at 1554 nm (150 fs pulses, 80 MHz repetition rate) at 1.6 GW/cm^2 fluency, which is in excellent agreement with our numerical simulations. To further enhance the SHG efficiency, we propose a metal-dielectric hybrid nanostructure based on a nanodisk surrounded by a gold plasmonic nanoring. The role of the plasmonic nanoantenna is to efficiently collect the illumination light and convert it to match the anapole mode supported by the AlGaAs nanodisk, to significantly amplify the electric field inside the disk. We theoretically predict and experimentally demonstrate that the SHG conversion efficiency in this nanostructure can be boosted by one order of magnitude with respect to the isolated nanodisk.

SHG is used in many practical applications such as a substance diagnostics, and imaging of various processes as well as for a frequency conversion of an optical pulse. As a rule, the frequency doubling is used also for a generation of the optical wave with tripled frequency by using the mixing of optical radiation with the basic and doubled frequencies. Nevertheless, THG can occur in a medium with cubic nonlinear response and in a medium with quadratic nonlinear response if the incident laser pulse intensity of the basic wave is enough high or if the intensities of the interacting waves increase until such values which are sufficient for occurring the cubic nonlinearity of a crystal. As a consequence, THG may occur. We investigate an efficiency of comb frequency generation if an intensity of the incident femtosecond pulse is sufficiently high .

Obviously, one of these generation processes occurs with a big phase mismatching. We investigate comb generation efficiency in a dependence of the phase mismatching between interacting waves and other parameters. As a result, we observe various regimes of comb generation. It should be emphasized that we find out the generation regime with synchronic changing of the maximal intensities of all waves. At the same time, shape of the appearing sub-pulses at these frequencies are similar to Gaussian one.

Our consideration is based on computer simulation with taking into account the SOD, phase mismatching, selfand cross-modulation for interacting waves.

Time and Frequency applications need high accuracy and high stability clocks. Optically pumped compact industrial Cesium atomic clocks are a promising approach that could satisfy these demands. However, the stability of these clocks relies, among others, on the performances of the laser diodes that are used. This issue has led the III-V Lab to commit to the European Euripides-LAMA project that aims to provide competitive compact optical Cesium clocks for ground applications. This work will provide key experience for further space technology qualification. III-V Lab was in charge of the design, fabrication and reliability of Distributed- Feedback diodes (DFB) at 894 nm (D1 line of Cesium) and 852 nm (D2 line). The use of D1 line for pumping will provide simplified clock architecture compared to the D2 line pumping thanks to simpler atomic transitions and a larger spectral separation between lines in the 894 nm case. Also, D1 line pumping overcomes the issue of unpumped “idle states” that occur with D2 line. The modules should provide narrow linewidth (<1 MHz), very good reliability in time and, crucially, be less sensitive to optical feedback. We show here results from Al-free active region with InGaAsP quantum well Ridge DFB lasers. We obtain the D1 Cs line (894.4nm) at 67°C and 165mA (optical power of 40mW) with a high side mode suppression ratio. The D2 Cs line (852.1nm) is obtained at room temperature at 40mW. By a small increase of temperature it is also possible to get Cs lines at 20mW. In order to address the long term reliability of these lasers, long duration ageing tests (more than one year targeted) have been carried out for both wavelengths at 20mW and 25°C The laser diodes have aged during 10 000 hours and 9336 hours for DFB addressing Cesium D2 and D1 lines, respectively. These ageing tests show very low increase of the operating current, almost linear with time. Lasers designed for D1 and D2 Cesium lines show an average increase of operating current of 0.15% and 0.37% per 1000hours, respectively.

LiDAR is a key sensor technology for future driving. For autonomous vehicles a fast and reliable three dimensional monitoring of the environment is essential for managing a wide variety of common traffic situations. Since these kinds of systems use typically light in the near infrared range, ambient light of the sun is a serious problem due to its high intensity compared to the laser source. Therefore, reducing the influence of ambient light on the distance measurement is very important. In this paper we present a 2 × 192 pixel SPAD-based direct time-of-flight line sensor for flash LiDAR applications with high ambient light rejection integrated in standard CMOS technology. Two commercially available 905 nm laser diodes emitting short pulses are employed for scene illumination. For time measurement an in-pixel timeto- digital-converter with a resolution of 312.5 ps and full range of 1.28 μs has been implemented. Each pixel uses four vertically arranged single SPADs for background light rejection based on the detection of temporal correlated photons. This technique allows the discrimination of the received laser pulse buried in the superimposed background light and, hence, to improve the measurement quality. Additionally, different parameters of the coincidence detection circuit, such as coincidence depth and time, can be varied during operation to enable a real time adjustment to the present ambient light condition, which is measured between each laser shot by operating the sensor in photon counting mode. By using this technique the sensor allows a reliable distance measurement at various ambient and target conditions.

The very short life-time of the excited carriers is a very important intrinsic property of quantum well photodetectors (QWIPs), based on III-V semiconductor materials, that have not been exploited for performances yet. Its typical value is in the order of a ps [7], which leads to two important consequences: the detector frequency response can be up to 100 GHz and its saturation intensity is extremely high in the in the order of 10e7 W/cm2. These two figures are ideal for a heterodyne detection scheme, where a powerful local oscillator (LO) can drive a strong photocurrent, higher than the detector dark current, that can coherently mix with a signal shifted in frequency with respect to the LO. Notably, these unique properties are unmatched in infrared interband detectors based on mercury-cadmium-telluride alloys, which have a much longer carrier lifetime and therefore intrinsic low-speed response. Yet, the performances of all photonic detectors are limited by the high dark current which originates from thermal emission of electrons from the wells, rising exponentially with temperature and imposing cryogenic operation (~ 80K) for high sensitivity. In the present work we show that the intrinsic limitation of QWIP detectors can be overcome by the use of a photonic metamaterial made of metallic resonators. The absorbing region of the detector consists of a 5 period GaAs/AlGaAs QWIP operating at a wavelength 8.9µm (139meV) which has been designed according to an optimized bound to continuum structure. The absorbing region is inserted in an array of double-metal patch resonators [ref], which provide sub-wavelength electric field confinement and act as antennas. The resonant wavelength is fixed by the patch size s through the expression lambda = 2 s neff, with neff = 3.3 the effective index. This allows us to tune the cavity mode in resonance with the absorption peak of the bare detector for values of s between 1.3µm-1.4µm. The detectors obtained in this way have high detectivity up at room temperature, in the order of 3-4 10e7 cmHz1/2/W. Given this his high detectivity we could calibrate the detector using a black body emitting only few µW. Up to date high sensitivity at room temperature, with values comparable to those we are reporting, have been demonstrated, only in the 3-5µm wavelength range, using quantum cascade detectors (QCDs) [9-11] and with MCT standard detectors. To the best of our knowledge this is the best results ever reported for a photoconductive detector at 9µm at room temperature. Since the detector has an extremely fast response of several GHz we built an heterodyne setup tp beat two quantum cascade lasers. We obtained heterodyne signal at high frequencies up to 3GHz, with NEP in the pW range at 300K.

Mid-IR supercontinuum sources are a new type of source for the 2-4.5 μm spectrum, but their weight, size and power consumption has previously made them unsuitable for mobile sensing. We demonstrate a highly compact supercontinuum source with a weight of <1 kg and a power consumption of <15 W emitting a spectral brightness comparable to that of a synchrotron and covering the entire 1.8-4.4 μm spectrum. We will also discuss challenges and opportunities of working with a broadband source instead of a single line or tunable source and touch upon the future potential for supercontinuum reaching further into the mid-IR

Remote leak detection of gases such as the homonuclear molecules (N2, H2, etc.) and noble gases (He, Ar etc.) is still an issue for tunable laser spectroscopy (TLS) because these gases do not have infrared absorption bands. In order to detect a leak in air, the gas displacement of the ambient air is used as an indirect indication of the leak. So, the unique idea is to measure the reduced oxygen concentration by a standoff laser spectrometer at an emission wavelength of 761 nm. The advantage of oxygen as indicator gas is the stable concentration level with respect to low spatial and temporal fluctuations. The challenge of the standoff detection is to analyze the small relative transmission change for weak light intensity scattered by the background. Furthermore, a remote measurement technique for high-level oxygen concentration on ppm level resolution is demonstrated. Here the combination of a high performance distributed feedback laser at 761 nm and high end sophisticated electronics for driver and data acquisition is required and designed. With the direct absorption spectroscopy, the concentration change of 2000 ppm within a 1 cm plume size (10 ml/min flow, ambient room conditions) corresponds to a transmission change in order of 2E-4 has been resolved on a low absolute power level of few micro watts in 1m distance. The detection limit corresponds to a nitrogen leakage rate of 0.1mbar·l/s which is comparable to ordinary remote detection systems for methane leakages.

We report on an investigation of the optical performances of tapered hollow-core waveguides (HCWs) operating in the mid-IR spectral range. The HCW core diameter linearly increases over a fiber length of 50 cm. Five laser sources emitting in the range 3.5-7.8 μm were coupled with the HCWs by using a lens to focus the collimated beam at the waveguide entrance. We demonstrated single-mode circular-symmetric Gaussian-like beam profiles at HCW exit in all investigated spectral range, when operating with an HCW having core diameter varying from 200 μm to 260 μm, with slight variations in the measured propagation losses.

The room temperature detection of terahertz (THz) waves remains a challenging task, especially for detectors operating at room temperature. Among the solutions that have been proposed, thermal detectors based on bilayer membranes combined with metamaterial absorbers provide competitive sensitivity and detection speed in the kHz range. We have recently proposed a new device concept, where the photo-thermal interactions take place in a single meta-atom resonator with subwavelength dimensions. Thanks to the compactness of our device, the thermal diffusion time is reduced down to the µs range and the detector speed is increased beyond 10MHz, with 1GHz at reach. I will discuss experimental measurements and dynamical modelling of the detector performance.

Quartz-enhanced photoacoustic spectroscopy (QEPAS) offers efficient gas detection, compactness, robustness, fast time response and affordability, exploiting quart tuning forks (QTFs) as resonant optoacoustic transducers. Recently, new geometries for the QTFs were proposed and implemented in QEPAS sensors, opening the way to novel sensing configurations providing excellent results in detection sensitivity. Recent results obtained by exploiting custom QTFs in QEPAS trace-gas sensors operating in the near-IR and mid-IR ranges will be reviewed.