This PDF file contains the front matter associated with SPIE Proceedings Volume 10353, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Colloidal quantum dots (CQD) attract much interest for optoelectronic applications, as potentially low-cost alternatives to epitaxial materials. In particular, in the mid-IR spectral range, CQD based on the zinc-blend mercury chalcogenides, Hg (S, Se, Te), lead efforts to create mid-IR technologies with solutions based materials. HgTe CQD with their tunable bandgap above 3 microns show promise as mid-IR detectors at a lower cost than existing HgCdTe (MCT) detectors. Progress towards the manufacture of mid-infrared cameras, improved sensitivity of PV devices, and new modalities, will be reviewed. HgS and HgSe CQDs also allow photodetection in the mid-IR because they are stably n-doped in ambient conditions, and they show an intense intraband transitions tunable in the mid-IR. Intraband CQDs is therefore another promising approach that broadens the types of materials considered. For both approaches, some of the challenges are similar, as one needs to develop tightly size-controlled colloidal quantum dots, and an interfacial chemistry that maximizes mobility and carrier lifetime, yet allows for controlling the doping.

There has been significant progress on the development of Type II superlattice detectors in the past 15 years. As we have progressed in advanced heterostructure engineering of the devices, it has also provided insight into some of the challenges associated with the superlattices. In this talk, I will discuss some of our recent results on unipolar barrier detectors. I will also discuss some of the fundamental challenges that need to be addressed for the superlattice detectors such as vertical transport and surface passivation. I will also present some interesting problems including superlattice based avalanche photodiodes and the growth of metamorphic InAsSb absorbers.

Although ZnO and its related heterostructures are really attractive for their potential application in optoelectronics, their developments have been limited by the p-type doping issue. Here, we will show why ZnO properties are also very attractive for unipolar structures, only dealing with electrons, and how the material quality has been improved to reach these devices requirements. First, the benefit of homoepitaxy through material quality improvement is presented. We will show that molecular beam epitaxy allows getting defect density, surface roughness, and residual doping, comparable to the state-of-the-art of GaAs. Moreover, (Zn,Mg)O alloy could be used to fabricate heterostructures with very good optical and transport properties. In the second part, we will give a brief overview of the main transport results, especially bidimensional electron gas, reported in the literature. Few examples of possible applications will also be addressed. Then, we will focus on the potentialities of nonpolar ZnO heterostructures for unipolar devices based on intersubband transitions. Once the advantages of using ZnO for TeraHertz quantum cascade laser discussed, we will show that the structural properties of the ZnO/(Zn,Mg)O heterostructures fulfill the requirements of these devices operation. Moreover, we will finish with absorption measurements clearly showing intersubband transitions in agreement with the light polarization selection rule. The strong influence of physical parameters, like doping level, on the energy of these kind of transitions will also be discussed. This work was funded by EU commission under the H2020 FET-OPEN program; project “ZOTERAC” FET-OPEN 6655107.

Nanophotonic integrated circuits are emerging as a promising platform for quantum photonics. A key building block are waveguide integrated detectors with superior performance. Detectors based on superconductor nanowires (SNSPDs) attached to optical waveguides have been shown to provide high efficiency and good timing performance, as well as broad bandwidth. To move towards applications in high bandwidth quantum communication and processing, ultrafast single-photon detectors with high efficiency are needed. The speed of meander type SNSPDs is limited because the required high absorption efficiency necessitates long nanowires deposited on top of the waveguide. This enhances the kinetic inductance and makes the detectors slow. We overcome this problem by aligning the nanowire perpendicular to the waveguide to realize devices with a length below 1 µm. By integrating the nanowire into a photonic crystal cavity, we recover high absorption efficiency, thus enhancing the detection efficiency by more than an order of magnitude. Our cavity enhanced superconducting nanowire detectors are fully embedded in silicon nanophotonic circuits and efficiently detect single photons at telecom wavelengths. The detectors possess sub-nanosecond decay (~ 120 ps) and recovery times (~ 510 ps), and thus show potential for GHz count rates at low timing jitter (~ 32 ps).

Timing resolution (or timing jitter) and time walk are separate parameters associated with a detector’s response time. Studies have been done mostly on the time resolution of various single photon detectors ^[1]. As the designer and manufacturer of the ultra-low noise (ƙ-factor) silicon avalanche photodiode the SLiK SPAD, which is used in many single photon counting applications, we often get inquiries from customers to better understand how this detector behaves under different operating conditions. Hence, here we will be focusing on the study of these time related parameters specifically for the SLiK SPAD, as a way to provide the most direct information for users of this detector to help with its use more efficiently and effectively. We will be providing the study data on how these parameters can be affected by temperature (both intrinsic to the detector chip and environmental input based on operating conditions), operating voltage, photon wavelength, as well as light spot size. How these parameters can be optimized and the trade-offs from optimization from the desired performance will be presented.

We realize fast, efficient and small footprint niobium nitride superconducting nanowire single photon detectors atop of photonic waveguides. By reducing the bias current of the nanowire, in order to break the superconductivity and trigger a detection event, more than one photon needs to be absorbed in a localized section of the wire within a very short time delay (hot-spot relaxation time), making such devices promising also for multiphoton sensing applications. We adopt a near-infrared pump-probe technique in a cryogenic environment to investigate the bias current dependence of the hot-spot relaxation time. A minimum relaxation time of (22 ± 1) ps is obtained when applying a bias current of 50% of the switching current at a bath temperature of 1.7K. Our study reveals a strong increase of the picosecond relaxation time with increasing bias current. We further adopt the same technique for determining the multi-photon detection regimes of the detector, which are in agreement with standard quantum detector tomography. In this context, we introduce a practical model and reconstruction method for determining the detector sensitivity regimes. Our work provides a complete description of the detector working operation in both number photon threshold sensitivity and time-delay sensitivity. The results allow for implementing on-chip measurement architectures for the characterization of weak classical light emitters and fast single photon sources with only one detector, driven at different biasing currents, with a drastic reduction of the time uncertainty limitations of typical correlation measurement systems.

GaAs nanowires (NWs) are promising advanced materials for the development of high performance photodetectors in the visible and infrared range. In this work, we optimize the epitaxial growth of GaAs NWs compared to conventional procedures, by introducing a novel two-steps growth method that exhibits an improvement of the resulting NW aspectratio and an enhancement of the NW growth rate. Moreover, we investigate the contactless manipulation of NWs using non-uniform electric fields to assemble a single GaAs NW on conductive electrodes, resulting in assembly yields above 90%/site and an alignment yields of around 95%. The electrical characteristics of the dielectrophoretic contact formed between the NW and the electrode have been measured, observing that the use of n-type Al-doped ZnO (AZO) as electrode material for NW alignment produces Schottky barrier contacts with the GaAs NW body. Moreover, our results show the fast fabrication of diodes with rectifying characteristics due to the formation of a low-resistance contact between the Ga catalytic droplet at the tip of the NW and the AZO electrode. The current-voltage measurements of a single GaAs NW diode under different illumination conditions show a strong light responsivity of the forward bias characteristic mainly produced by a change on the series resistance.

We report the development of terahertz intersubband photodetectors based on GaN/AlGaN quantum wells, covering the frequency range that is fundamentally inaccessible to existing III-V semiconductor devices due to Reststrahlen absorption. Two different approaches have been employed to mitigate the deleterious effects of the intrinsic polarization fields of nitride heterostructures: the use of suitably designed double-step quantum wells, and epitaxial growth on semipolar GaN substrates. Promising results are obtained with both approaches, which could be extended to other device applications as a way to utilize the intrinsic advantages of nitride semiconductors for THz intersubband optoelectronics.

Efficiency of photoconductive detectors is limited by the bulk optical properties of photoconductive materials. The absorption length is on the order of several hundred nanometers, which limits the device thickness. Optical absorption however in the photoconductive layer can be modified substantially by using the concept of hybrid cavity, which consists of nanoantennas and a Distributed Bragg Reflector. A hybrid cavity containing a GaAs photoconductive layer of just 50 nm can be used to absorb >75% of incident photons by trapping the light within the cavity. We will discuss an intuitive model, which describes the dependence of the optimum operation wavelength on the cavity thickness. We will also show that the nanoantenna size is a critical parameter, small variations of which lead to both wavelength shifting and reduced absorption in the cavity. This behavior suggests that impedance matching is key for achieving efficient absorption in the hybrid cavities.

Strain engineering in single-layer semiconducting transition metal dichalcogenides aims to tune their bandgap energy and to modify their optoelectronic properties by the application of external strain. In this paper we study transition metal dichalcogenides monolayers deposited on polymeric substrates under the application of biaxial strain, both tensile and compressive. We can control the amount of biaxial strain applied by letting the substrate thermally expand or compress by changing the substrate temperature. After modelling the substrate-dependent strain transfer process with a finite elements simulation, we performed micro-differential spectroscopy of four transition metal dichalcogenides monolayers (MoS₂, MoSe₂, WS₂, WSe₂) under the application of biaxial strain and measured their optical properties. For tensile strain we observe a redshift of the bandgap that reaches a value as large as 94 meV/% in the case of single-layer WS₂ deposited on polypropylene. The observed bandgap shifts as a function of substrate extension/ compression follow the order WS₂ < WSe₂ < MoS₂ < MoSe₂.

The ability to integrate electronics with Nanocrystals (NCs) allows utilizing their unique properties for a future optoelectronic device. Combing top down approach using self-assembled hybrid organic-NCs systems, with bottom up components can revolutionize devices in future. In my talk I will present an ultra-high light sensing device based on InAs NCs acting as an optical gate to high electron mobility transistor (HEMT) device. Using a very narrow channel the device quantum efficiency is high as 106V/W, while the single to noise ratio (SNR) enables high sensitivity photon detection. In addition a side gate detector will be present showing enhancement in the sensitivity for light and gas detection. The same concept can be used to develop tunable, simple and flexible detector for the IR range printing semiconducting/conducting carbon nanotubes layer mixed with doped semiconductor nanocrystals.

Optically measuring temperature fields around plasmonic structures is of great importance for their thermal management considering the strong energy dissipations along with the extraordinary abilities of light coupling. Among all the available methods, ratiometric studies are particularly desirable since they suppress the influence of trivial factors, such as temporal fluctuations in excitation and spatial non-uniform distributions of fluorescent species, and thus gives reliable temperature dependence. Here we report a new ratiometric thermometry that simultaneously captures the fluorescence images of different numerical apertures (NAs) to resolve the temperature-dependent orientations of emission dipoles. This thermometry measures fluorescent anisotropy based on the directionality of emission. We show that this thermometry can be used to measure temperature near metallic surfaces. We foresee it to trigger interests of a large community who desire simultaneous thermal characterization along with the optical imaging. Moreover, it brings out a general idea to simplify ratiometric setups if inequalities exist on the excitation side, which may reach for a larger number of researchers.

Integrated optical biosensors based on Mach-Zehnder Interferometers and Microring Resonators are widely used for food/drug monitoring and protein studies thank to their high intrinsic sensitivity, easy integration and miniaturization, and low cost.^{1, 2} In this study, we present a system to perform antibody interaction analysis using a photonic chip made of an array of six microring resonators (MRRs) based on the TriPleX platform. A compact system is presented where the input light is provided by a Vertical Cavity Surface Emitting Laser (VCSEL) pigtailed to a single mode fiber and operating at a ≈ 850nm wavelength. The output signal is detected by PIN photodetectors placed in the optical signal read-out module (the so-called OSROM) and processed by an easy-to-use Fourier Transform algorithm. Bulk sensitivity (S_b=98±2.1 nm/RIU) and Limit of Detection (LOD=(7.5± 0.5) x10^-6 RIU) are measured and appeared to be very similar for the six MRRs on the same chip,³ which is an important property for multianalyte detection. An analysis of the anti-biotin interaction with immobilized biotin is performed by using different concentrations of anti-biotin antibody. The dependence of the resonance wavelength shift from the antibody concentration, as well as the association and the dissociation rate constants are calculated. For the average dissociation constant (K_D) of anti-biotin antibody toward immobilized biotin, a value of (1.9±0.5) x10^-7M is estimated, which is of the same order of magnitude of other published data.⁴ Furthermore, the specificity of the interaction is confirmed by using negative control antibodies and by performing competition with free, i.e., dissolved, biotin. In addition, the functional surface of the sensors could be regenerated for repeated measurements up to eight times by using 10 mM glycine/HCl pH 1.5.

Highly doped semiconductors, such as Si-doped InAsSb, are promising alternative materials for plasmonic application in the mid-infrared spectral range because they benefit from compatibility with silicon technology, from low losses and from tunable permittivity. We propose to detail what are the main advantages of InAsSb:Si compared to noble metals and how they can be used for bio-sensing applications. We demonstrate that 1-D InAsSb:Si ribbon arrays outperform 1- D gold ribbon arrays because of the latter uses little the lightning rod effect. In the case of 2-D nano-antenna arrays, it is possible to exploit a strong polarization dependent resonance to cover a large spectral range for sensing. Finally, we demonstrate that the highly doped semiconductor 1-D ribbon arrays and 2-D nano-antenna arrays allow surface plasmon resonance (SPR) sensing and surface-enhanced infrared absorption (SEIRA).

The initial excitement about the use of plasmonic nanostructures for the development of nanophotonic devices operating in the optical regime was later partially eclipsed with the observation that losses could, in some cases, overtake actual radiative properties [1]. In this scenario, dielectric nanoantennas have recently emerged as promising alternative candidates to plasmonic systems in the visible range [2]. When excited above their bandgap energies, high-refractive-index dielectric nanostructures can highly concentrate electric and magnetic fields within subwavelength volumes, while presenting ultra-low absorption compared to metals [3]. In particular, by locally enhancing the incident light intensity, dielectric nanoantennas are expected not only to produce negligible heating, but also boost nonlinear phenomena and surface-enhanced spectroscopies, since their efficiencies increase with the excitation density. In this presentation, Si, Ge, and GaP nanoantennas will be introduced as promising nanosystems for surface-enhanced fluorescence and Raman spectroscopies, as well as for generating efficient second and third harmonic light on the nanoscale at visible wavelengths [2,4-7]. It will be shown that their associated temperature increase at resonance can be over one order of magnitude lower than that corresponding to metals. At the same time, fluorescence enhancement factors of over 3000 and harmonic conversion efficiencies of nearly 0.01% will be demonstrated for suitably engineered dielectric nanostructures. Finally, hybrid dielectric/metallic nanoantennas will also be analyzed, and, in all cases, comparison will be made with reference plasmonic nanosystems. [1] Khurgin, J. B. Nat. Nanotech. 2015, 10, 2-6. [2] Caldarola, M. et al. Nat. Commun. 2015, 6, 7915. [3] Albella, P. et al. ACS Photonics 2014, 1, 524–529. [4] Grinblat, G. et al. Nano Lett. 2016, 16, 4635-4640. [5] Grinblat, G. et al. ACS Nano 2017, DOI: 10.1021/acsnano.6b07568. [6] Cambiasso, J.; Grinblat, G.; et al. Nano Lett 2017, DOI: 10.1021/acs.nanolett.6b05026. [7] Shibanuma, T.; Grinblat, G.; et al. Submitted, 2017.

We demonstrate an increase in Förster Resonance Energy Transfer (FRET) efficiency for paired fluorescent molecules on gold nanogratings for a range of acceptor concentrations. For gratings, the periodicity allows for a broad range of surface plasmon wavelengths that follow a dispersion relationship. The dispersion relationship is determined by the periodicity of the grating and the dielectric function of the metal that makes the grating. Locating a fluorophore near a plasmonic metal structure increases the emission in two ways – an excitation enhancement and an emission modification. The second mechanism occurs when the plasmonic substrate increases the local density of optical states (LDOS). This has the effect of shortening the lifetime of the excited state which increases the quantum yield of the fluorophore. In this work, gold wire nanogratings with a period of 500 nm were fabricated. We used Atto 532 and Atto 633 as the donor and acceptor FRET molecules respectively. A thin layer of PVA containing different concentrations of the donor and acceptor FRET molecules was spun cast onto the gratings. The donor molecules were excited with a 532 nm laser, and the fluorescence emission from both the donor and acceptor molecules were recorded. We found that for all concentrations of acceptors, the FRET efficiency was the largest when the surface plasmon modes overlapped the acceptor emission. Compared to the unenhanced efficiency, the largest gains in efficiency were measured for the lowest concentration of acceptors.

In this work, we use ultraviolet nanoimprint lithography (UV-NIL) to transfer metallic nanostructures from a polymer mold to the facet of the optical fiber with 200 μm core diameter. Once a polymer mold carrying nanopillar array is fabricated by thermal embossing, a thin layer of gold is deposited on it by thermal evaporation. Then the metallic nanostructure is transferred onto fiber facet by the cross-linked UV-cured resist. The transferred metallic nanostructures feature closely spaced double layers of disks and holes. Strong coupling between the metal disk and hole generates resonantly enhanced local electrical field under incident excitation light, as revealed by peaks and dips in the reflection spectra. A layer of hydrogel is coated and cross-linked on fiber facet as a pH-sensing element. Hydrogel shrinks in acid and swells in basic solutions by containing different amount of water and thus has a different refractive index, which can be detected from the resonant reflection peaks/dips of plasmonic fiber probe. Our hydrogel fiber probe shows obvious spectrum response to solutions with pH values ranging from 1 to 8. Under cycling test, the sensor remains stable for three cycles when switching between acid and basic solutions.

Two-photon absorption (TPA) is a third order non-linear process that relies on the quasi-simultaneous absorption of two photons. Therefore, it has been proved to be an interesting tool to measure ultra-fast correlations¹ or to design all-optical switches.² Yet, due to the intrinsically low efficiency of the non-linear processes, these applications rest upon high peak power light sources such as femtosecond and picosecond pulsed laser. However TPA has also been noticed as an appealing new scheme for quantum infrared detection.^{3, 4} Indeed, typical quantum detection of IR radiation is based on small gap semiconductors that need to be cooled down to cryogenic temperature to achieve sufficient detectivity. TPA enables the absorption of IR photons by wide gap semiconductors when pump photons are provided to complete optical transitions across the gap. Still, the low efficiency of TPA represents a difficulty to detect usual infrared photon fluxes. To tackle this issue, we combined three strategies to improve the detection efficiency. First, it has been proved theoretically and experimentally that using different pump and signal photon energies which is known as non degenerate TPA (NDTPA) help increasing the TPA efficiency by several orders of magnitude.⁵ Thus we decided to work with different pump and signal wavelength. Secondly, since TPA is a local quasi-instantaneous process, both pump and signal photons must be temporarily and spatially co-localized inside the active medium. We made sure to maximize the overlap of the fields inside our device. Finally, it is well known that TPA has a quadratic dependence with the signal electric fields modulus, so we designed a specific nanostructure to enhance the signal field inside the active medium of the detector.

A Multimode Fiber Bragg Gratings for refractive index sensing has been demonstrated experimentally. The fabrication of Bragg gratings in the Standard step-index multimode fiber with a core diameter of 50 μm and a numerical aperture of 0.20 is carried out by phase mask method. The period of the phase mask is 1064 nm. The etching of cladding portion of grating region (2 cm) is carried out by Hydrofluoric acid (48%) for 15 minutes. The etching process causes reduction of cladding diameter by 55 μm which further enhances the interaction of light propagating in core mode with higher cladding modes. Solutions of varied concentrations of glycerol were prepared having corresponding refractive index. Shift in wavelength in the reflection peak of high-order mode L1 is observed when glycerol solution is passed over the cladding surface of grating region. The proposed sensor with 1-pm resolution was successfully employed for sensing of different glycerol solutions. The sensitivity of proposed sensor is 15000 pm/RIU and it can be used as potential sensing platform for bio-chemical applications.