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publié dans ACS photonics 10.1021/acsphotonics.0c01299; International audience; III-V semiconductor mid-infrared photodetectors based on intersubband transitions hold a great potential for ultra-high-speed operation up to several hundreds of GHz. In this work we exploit a ~350nm-thick GaAs/Al0.2Ga0.8As multi-quantum-well heterostructure to demonstrate heterodyne detection at l~10µm with a nearly flat frequency response up to 70GHz at room temperature, solely limited by the measurement system bandwidth. This is the broadest RFbandwidth reported to date for a quantum-well mid-infrared photodetector. Responsivities of 0.15A/W and 1.5A/W are obtained at 300K and 77K respectively. To allow ultrafast operation and illumination at normal incidence, the detector consists of a 50W coplanar waveguide, monolithically integrated with a 2D-array of sub-wavelength patch antennas, electrically interconnected by suspended wires. With this device architecture we obtain a parasitic capacitance of ~30fF, corresponding to the static capacitance of the antennas, yielding a RClimited 3dB cutoff frequency >150GHz at 300K, extracted with a small-signal equivalent circuit model. Using this model, we quantitively reproduce the detector frequency response and find intrinsic roll-off time constants as low as 1ps at room temperature.

Applications relying on mid-infrared radiation (λ ~ 3-30 μm) have progressed at a very rapid pace in recent years, stimulated by scientific and technological breakthroughs like mid-infrared cameras and quantum cascade lasers. On the other side, standalone and broadband devices allowing control of the beam amplitude and/or phase at ultra-fast rates (GHz or more) are still missing. Here we show a free-space amplitude modulator for mid-infrared radiation (λ ~ 10 μm) that can operate at room temperature up to at least 1.5 GHz (−3dB cutoff at ~750 MHz). The device relies on a semiconductor heterostructure enclosed in a judiciously designed metal–metal optical resonator. At zero bias, it operates in the strong light-matter coupling regime up to 300 K. By applying an appropriate bias, the device transitions towards the weak-coupling regime. The large change in reflectance is exploited to modulate the intensity of a mid-infrared continuous-wave laser up to 1.5 GHz., Broadband integrated electrical modulators are key components for photonic systems. Here, the authors present a room temperature mid-IR free-space amplitude modulator based on a semiconductor heterostructure that exploits the change in reflectance occurring at the change between weak and strong coupling.

We have developed a free-space amplitude modulator for mid-IR radiation $(\lambda=10\mu \mathrm{m})$ that can operate up to at least 1.5 GHz (-3dB cut-off at _ 750 MHz) and at room-temperature. The device relies on a semiconductor heterostructure enclosed in a judiciously designed metal-metal optical resonator. At zero bias, it operates in the strong light-matter coupling regime up to 300K. By applying an appropriate bias, the device transitions to the weak coupling regime. The large change in reflectivity due to the disappearance of the polaritonic states is exploited to modulate the intensity of a mid-IR continuous-wave laser up to speeds of more than 1.5 GHz.

III-V semiconductor mid-infrared photodetectors based on intersubband transitions hold a great potential for ultra-high-speed operation up to several hundreds of GHz. In this work we exploit a ~350nm-thick GaAs/Al 0.2 Ga 0.8 As multi-quantum-well heterostructure to demonstrate heterodyne detection at $\lambda\sim 10\mu \mathrm{m}$ with a nearly flat frequency response up to 70GHz at room temperature, solely limited by the measurement system bandwidth. To the best of our knowledge this is the broadest RF-bandwidth reported to date for a quantum-well mid-infrared photodetector. Responsivities of 0.15A/W and 1.5A/W are obtained at 300K and 77K respectively. To allow ultrafast operation and illumination at normal incidence, the detector consists of a $50\Omega$ coplanar waveguide, monolithically integrated with a 2D-array of patch antennas, electrically interconnected by suspended wires. With this device architecture we obtain a parasitic capacitance of $\sim 30\text{fF}$ , corresponding to the static capacitance of the antennas, yielding a RC-limited 3dB cutoff frequency >150GHz at 300K, extracted with a small-signal equivalent circuit model. Using this model, we quantitively reproduce the detector frequency response and find intrinsic roll-off time constants as low as 1ps at room temperature.

We present a mid-IR ($\lambda \approx$ 8.3 $\mu$m) quantum well infrared photodetector (QWIP) fabricated on a mid-IR transparent substrate, allowing photodetection with illumination from either the front surface or through the substrate. The device is based on a 400 nm-thick GaAs/AlGaAs semiconductor QWIP heterostructure enclosed in a metal-insulator-metal (MIM) cavity and hosted on a mid-IR transparent ZnSe substrate. Metallic stripes are symmetrically patterned by e-beam lithography on both sides of the active region. The detector spectral coverage spans from $\lambda \approx 7.15$ $\mu$m to $\lambda \approx 8.7$ $\mu$m by changing the stripe width L - from L = 1.0 $\mu$m to L = 1.3 $\mu$m - thus frequency-tuning the optical cavity mode. Both micro-FTIR passive optical characterizations and photocurrent measurements of the two-port system are carried out. They reveal a similar spectral response for the two detector ports, with an experimentally measured T$_{BLIP}$ of $\approx$ 200K., Comment: Copyright 2021 Mario Malerba, Mathieu Jeannin, Stefano Pirotta, Lianhe Li, Alexander Giles Davies, Edmund Linfield, Adel Bousseksou, Jean-Michel Manceau and Raffaele Colombelli. This article is distributed under a Creative Commons Attribution (CC BY) License. The following article has been submitted to APL Photonics. After it is published, it will be found at https://aip.scitation.org/journal/app

We report quantum well mid-infrared photodetectors operating in the strong light-matter coupling regime. It is an ideal system to elucidate the elusive problem of the injection of electrons (single-particles) into polaritonic modes (bosonic excitations). We have obtained experimental information on the transfer function between a polaritonic system and an electronic reservoir. This approach opens promising avenues in view of adding previously unavailable functionalities to quantum well detectors (mid-IR and THz) and improving their performance.

We present the development of a highly sensitive and compact HEB/QCL heterodyne detection system. The HEB mixer is a NbN nano-bridge mounted in an integrated lens-antenna configuration. The local oscillator is a low power consumption and low beam divergence 3rd order distributed feedback quantum cascade laser with single mode emission at the target frequency of 2.7 THz. A new quasi-optical coupling scheme between the mixer and the local oscillator has been developed that allows the removal of the beam splitter and therefore a better transmission of the RF signal and a more compact detection system. The lowest uncorrected double side band receiver noise temperature of this system is about 880 K.

International audience; We present our work on the development of highspeed, GaAs-AlGaAs multi-quantum wells photodetectors at 10.3μm, based on two-dimensional arrays of patch-antenna resonators. First, the results of FDTD simulations will be presented that allowed to optimize the patch array geometry and fabricate a first generation of detectors with microwave coplanar access. Next, we will report on our initial results from dc optical characterization, namely reflectivity and photocurrent measurements.

We report on the first demonstration of quantum cascade detectors based on ZnO/ZnMgO quantum wells grown by molecular beam epitaxy on an m-plane ZnO substrate. The sample is processed in the form of square mesas with special attention paid to the passivation of the side facets. Photocurrent spectroscopy reveals a resonance at 2.8 μm wavelength slightly blue-shifted with respect to the intersubband absorption peak at 3 μm wavelength. The photocurrent persists up to room temperature. The peak responsivity amounts to 0.15 mA/W under irradiation at Brewster’s angle of incidence of the top surface of the mesas.

International audience; We demonstrate a sensitive and compact terahertz heterodyne detection system based on a quantum cascade laser (QCL) as a local oscillator and a hot electron bolometer (HEB) as a mixer. It relies on an original optical coupling scheme where the terahertz (THz) signal to be detected and the local oscillator (LO) signal are coupled to the HEB from both sides of the integrated lens/antenna mixer. The THz signal of interest impinges on the front side through the silicon lens while the LO onto the rear (air) side. This concept allows us to remove the beam splitter usually employed in terahertz heterodyne receivers. The mixer consists of a Niobium Nitride HEB with a log-spiral planar antenna mounted on the flat side of a hyperhemispherical silicon lens. The local oscillator of the heterodyne detector is a low power consumption and low beam divergence 3rd-order distributed feedback laser with single mode emission at the target frequency of 2.7 THz. The coupling between the QCL and the HEB has been further optimized, using a dielectric hollow waveguide that reliably increases the laser beam directivity and permits us to pump the HEB into its most sensitive state through the air side of the planar antenna. We have measured a noncorrected double sideband receiver noise temperature of 880 K at 2.7 THz

We report on a GaN/AlN quantum cascade detector operating in an extended spectral range going from the mid-infrared to visible wavelengths. This broadband detection is achieved thanks to the design of active quantum wells supporting five bound-to-bound intersubband transitions. The photodetector exhibits a broad signal between 4.1 μm and 550 nm. The photocurrent persists up to room temperature. The calibrated responsivity at 77 K under irradiation through a 45° angle polished facet amounts to 7 μA/W at a wavelength of 633 nm and is peaked at 14 μA/W at a wavelength of 720 nm.

International audience; This paper reports on the demonstration of quantum cascade detectors (QCDs) based on ZnO/ ZnMgO quantum wells (QWs) grown by molecular beam epitaxy on an m-plane ZnO substrate. The TM-polarized intersubband absorption is peaked at a 3 lm wavelength. The sample has been processed in the form of square mesas with sizes ranging from 10_10 lm2 up to 100_100 lm2. The I-V characteristics reveal that 86% of the 260 devices are operational and that the surface leakage current is negligible at room temperature, which is not the case at 77 K. The photocurrent spectroscopy of 100_100 lm2 QCDs reveals a photocurrent resonance at a 2.8 lm wavelength, i.e., slightly blue-shifted with respect to the intersubband absorption peak. The photocurrent persists up to room temperature. The calibrated peak responsivity amounts to 0.15mA/W under irradiation at Brewster’s angle of incidence. This value allows us to estimate the transfer efficiency (1.15%) of the photoexcited electrons into the active QW of the next period. Published by AIP Publishing.

We demonstrate sub-wavelength electromagnetic resonators operating in the THz spectral range, whose resonant properties and optical response can be engineered using lumped elements, similarly to what is done in electronic circuits and antennas. We discuss the device concept, and we experimentally study the tuning of the resonant frequency as a function of variable capacitances and inductances. The advantages of this ‘circuit-tunable’ platform to realize novel THz meta-devices featuring an ultra-small semiconductor core are then discussed. As an application, we show that these micro-resonators have a strong potential for ultra-fast THz detection, when combined to a tiny quantum well photodetector active core. © (2017) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

Coherent backscattering of light is observed when electromagnetic waves undergo multiple scattering within a disordered optical medium. So far, coherent backscattering of light has been studied extensively for elastic (or Rayleigh) light scattering. The occurrence of inelastic scattering affects the visibility of the backscattering effect by reducing the degree of optical coherence in the diffusion process. Here, we discuss the first experimental observation of a constructive interference effect in the inelastically backscattered Raman radiation from strongly diffusing silicon nanowire random media. The observed phenomenon originates from the coherent nature of the Raman scattering process, which typically occurs on a scale given by the phonon coherence length. We interpret our results in the context of a theoretical model of mixed Rayleigh-Raman random walks to shed light on the role of phase coherence in multiple scattering phenomena.

We study surface-enhanced Raman scattering (SERS) in fully dielectric periodic structures supporting Bloch surface waves. We demonstrate a lower bound for the SERS enhancement of 50 when the optical pump is resonantly coupled to the Bloch surface wave supported by the structure. A corresponding photoluminescence experiment shows an emission enhancement of more than two orders of magnitude, suggesting that the actual SERS enhancement is ∼200. Analogous conclusions are obtained by means of a semiclassical theoretical model. These results suggest an alternative to plasmonic materials to enhance Raman scattering at a surface and are of interest to those working in the field of Raman as well as fluorescence spectroscopy.

We demonstrate single-pixel and 2D arrays of THz quantum-well photodetectors featuring extremely sub-wavelength, antenna-coupled resonators. Few-micron sized devices show photodetection in the 100–200 μm range, with a consequent dramatic reduction in the device dark current.

We investigate the scattering properties of novel kinds of nano-textured substrates, fabricated in a self-organized fashion by defocused ion beam sputtering. These substrates provide strong and broadband scattering of light and can be useful for applications in thin-film solar cells. In particular, we characterize the transmitted light in terms of haze and angle-resolved scattering, and we compare our results with those obtained for the commonly employed Asahi-U texture. The results indicate that the novel substrate has better scattering properties compared to reference Asahi-U substrates. We observe super-Lambertian light scattering behavior in selected spectral and angular regions due to the peculiar morphology of the nano-textured interface, which combines high aspect ratio pseudo random structures with a one-dimensional periodic pattern. The enhancement of light absorption observed in a prototype thin film semiconductor absorber grown on nano-textured glass with respect to an Asahi-U substrate further confirms the superior light trapping properties of the novel substrate.

Silicon micro-ring resonators have been demonstrated to be potential “on- chip” efficient sources of time-energy entangled photons. In these devices, photon pairs are generated by spontaneous four-wave-mixing (SFWM), an elastic scattering event involving two pump photons that results in the generation of an idler and a signal photon. The mass production of such integrated devices for quantum optic experiment requires the implementation of fast and reliable techniques to monitor the emitted two-photon state as well as the device performances. In this work we show that the joint spectral density of photon pairs that would be generated by SFWM in a silicon ring resonator can be measured with unprecedented resolution and speed, improving of several orders of magnitudes the results of traditional approaches based on coincidence measurements.

Sputtered aluminum on titanium double layers are widely used in conventional interconnection schemes of integrated circuits (IC); one known phenomenon is the formation of intermetallic compounds. In this work, the kinetic of the TiAl3 reaction is studied by collecting the sheet resistance increase of 400 nm AlCu0.5% on 10 nm titanium sputtered samples, in situ annealed at three different temperatures (450, 480 and 500 °C). The observed resistance drift is correlated to the expected aluminum consumption and the TEM observed TiAl3 grain morphology; by adopting an exponential fit of observed resistance curves, the activation energy of the TiAl3 formation is found out to be 1.75±0.25 eV.

International audience; Terahertz (THz) and sub-THz frequency emitter and detector technologies are receiving increasing attention, underpinned by emerging applications in ultra-fast THz physics, frequency-combs technology and pulsed laser development in this relatively unexplored region of the electromagnetic spectrum. In particular, semiconductor-based ultrafast THz receivers are required for compact, ultrafast spectroscopy and communication systems, and to date, quantum-well infrared photodetectors (QWIPs) have proved to be an excellent technology to address this, given their intrinsic picosecond-range response. However, with research focused on diffraction-limited QWIP structures (λ∕2), RC constants cannot be reduced indefinitely, and detection speeds are bound to eventually meet an upper limit. The key to an ultra-fast response with no intrinsic upper limit even at tens of gigahertz (GHz) is an aggressive reduction in device size, below the diffraction limit. Here we demonstrate sub-wavelength (λ∕10) THz QWIP detectors based on a 3D split-ring geometry, yielding ultra-fast operation at a wavelength of around 100 μm. Each sensing meta-atom pixel features a suspended loop antenna that feeds THz radiation in the ∼20 μm 3 active volume (V eff ∼3 × 10 −4 λ∕2 3). Arrays of detectors as well as single-pixel detectors have been implemented with this new architecture, with the latter exhibiting ultra-low dark currents below the nA level. This extremely small resonator architecture leads to measured optical response speeds-on arrays of 300 devices-of up to ∼3 GHz and an expected device operation of up to tens of GHz, based on the measured S parameters on single devices and arrays.

With unprecedented resolution we measure the joint spectral density of photon pairs that would be generated by spontaneous four wave mixing in a silicon ring resonator and show how the quantum correlations can be tailored. © 2015 OSA.

We report on the strong coupling between the Bloch surface wave supported by an inorganic multilayer structure and J-aggregate excitons in an organic semiconductor. The dispersion curves of the resulting polariton modes are investigated by means of angle-resolved attenuated total reflectance, as well as photoluminescence experiments. The measured Rabi splitting is 290 meV. These results are in good agreement with those obtained from our theoretical model.

In this work we study the Surface Enhanced Raman Scattering (SERS) via Bloch Surface Waves (BSWs) in a dielectric multi-layered structure. When the pump beam is resonantly coupled to the BSW, our results demonstrate a lower bound for the SERS-enhancement of about 50. A photo-luminescence (PL) experiment performed on the same structure shows an emission enhancement in excess of two orders of magnitude, suggesting an actual SERS-enhancement of 200, in agreement with theoretical calculations. These findings suggest that purely dielectric BSW-based structures can be a valid alternative to plasmonic substrates for enhanced Raman and photo-luminescence spectroscopy.

We report on the experimental realization of ultra-high quality factor (Q) designs of the L3-type photonic crystal nanocavity. Based on genetic optimization of the positions of few nearby holes, our design drastically improves the performance of the conventional L3 as experimentally confirmed by direct measurement of Q similar or equal to 2 x 10(6) in a silicon-based photonic crystal membrane. Our devices rank among the highest Q/V ratios ever reported in photonic crystal cavities, holding great promise for the realization of integrated photonic platforms based on ultra-high-Q resonators. (C) 2014 AIP Publishing LLC.

The authors present a case of bullous dermatosis in a diabetic patient. The lesions were drained and deroofed, and at 1-year follow-up, the patient related no problems. Proper diagnosis and treatment of these lesions will avoid infection and ulceration.

Terahertz (THz) and sub-THz frequency emitter-detector technology is receiving increasing attention because of key apphcations in several fields. In particular, ultrafast THz receivers are desired for compact, ultrafast spectroscopy and communication systems. While most of the available THz detectors (thermal, FET …) are currently limited in response time by slow thermal processes and/or by the read-out electronics, quantum well infrared photodetectors (QWIP) are excellent candidates given their intrinsic ps-range response [1]. The key to true ultrafast response is an aggressive reduction in device size, well below the typical diffraction-limited optical cavities [2].

We experimentally demonstrate surface-enhanc e d Raman scattering in fully dielectric structures supporting Bloch surface waves. These results suggest an alternative to plasmonic materials for enhancing the light-matter interaction at a surface with application in optical sensing.

A recent theoretical proposal suggested strong coupling between excitons and Bloch Surface Waves, which are photonic modes that exist at the interface between a truncated photonic crystal, and an ideally semi-infinite dielectric medium. In this work we report on the observation of strong coupling between the Bloch surface wave supported by an inorganic multilayer structure and J-aggregate excitons in an organic semiconductor. The dispersion curves of the resulting polariton modes are investigated by means of angle-resolved attenuated total reflection as well as photoluminescence experiments. The measured Rabi splitting is 290 meV.

We experimentally demonstrate ultra-high quality factors (Q = 1.96 × 10^6) in genetically designed 2D L3 photonic crystal nanocavities fabricated in Si slabs. Together with ultra-small effective mode volumes ~ 0.96(λ/n)^3, such a nanocavity offers a new platform in future integrated nanophotonics.

Compact silicon integrated devices, such as micro-ring resonators, have recently been demonstrated as efficient sources of quantum correlated photon pairs. The mass production of integrated devices demands the implementation of fast and reliable techniques to monitor the device performances. In the case of time-energy correlations, this is particularly challenging, as it requires high spectral resolution that is not currently achievable in coincidence measurements. Here we reconstruct the joint spectral density of photons pairs generated by spontaneous four-wave mixing in a silicon ring resonator by studying the corresponding stimulated process, namely stimulated four wave mixing. We show that this approach, featuring high spectral resolution and short measurement times, allows one to discriminate between nearly-uncorrelated and highly-correlated photon pairs., Fondazione Cariplo (Project 2010-0523, Nanophotonics for thin-film photovoltaics), Fondazione Alma Mater Ticinensis, Italy. Ministry of Education, Universities and Research (FIRB “Futuro in Ricerca” project RBFR08XMVY)

We experimentally demonstrate ultra high quality factors (Q = 1.45times;10^6) in evolutionary optimized 2D L3 photonic crystal nanocavities fabricated in Si slabs. Together with ultra small effective mode volumes 0.96(lambda;/n)^3 such a nanocavity offers a new platform in future integrated nanophotonics.

We report quantum well mid-infrared photo-detectors operating in the strong light-matter coupling regime. We claim that this is an ideal system to elucidate the elusive problem in intersubband polaritonics of the injection of electrons (single-particle fermionic states) into polaritonic modes (bosonic excitations). By reversing the perspective and focusing on the electron extraction, we have obtained experimental information on the transfer function between a polaritonic system and an electronic reservoir. In addition to its interest for fundamental science, this approach also opens promising avenues in view of adding previously unavailable functionalities to quantum well detectors and improving their performance.

Intervista in forma dialogica a Cristina Negro e Francesco Cappa. Conversazione attorno alla natura formativa e trasformativa del laboratorio teatrale rivolto agli studenti che si stanno formando per divenire educatori a cura di Silvia Luraschi. Contributo tra esperienza corporea e pensiero riflessivo in "Palpitare di Menti. Il laboratorio formativo: stili, metafore, epistemologie" a cura di Beppe Pasini