This PDF file contains the front matter associated with SPIE Proceedings Volume 12009, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

Graphene is a promising material for various optical and electrical device applications because of its high carrier mobility, broadband photoresponse, and low manufacturing cost. One such application is for infrared (IR) photodetectors (PDs) because conventional quantum-type IR PDs require complex and toxic materials such as HgCdTe and Type II superlattice structures. We have developed high-performance graphene IR PDs, which operate in the middle-wavelength or long-wavelength IR (MWIR or LWIR) regions, based on field-effect transistors (FETs) that use a photogating effect. This effect is induced by photosensitizers located around the graphene to produce a voltage change under incident light, inducing a change in the electric current of the graphene, which is attributed to its high carrier mobility and single-atom thickness. Si, InSb, and LiNbO₃ were used as the photosensitizers for the visible to near-IR, MWIR, and LWIR, respectively. The photoresponsivity obtained for each wavelength region was more than 10 times greater than that of conventional PDs. However, graphene FET-based structures inevitably produce a large dark current and require three electrical ports, which significantly degenerates the PD performance, inhibiting the use of readout integrated circuits for the IR image sensors. To address this issue, we have developed graphene photogated diodes (GPDs) with graphene/semiconductor heterojunction structures. The GPDs employ Schottky barrier lowering and carrier density modulation by photogating and have recently realized low dark currents and high responsivities because of the graphene/semiconductor Schottky junction and photogating. These results can contribute to the development of high-performance graphene-based IR image sensors.

Resonant cavity-enhanced photodiodes (RCE-PD) have previously been studied for the narrow spectral responses that can be achieved. A narrow response is useful for spectral sensing of a specific absorption line without interference from neighbouring absorption lines. We have designed and fabricated an array of photodiodes that each have a slightly shifted resonance wavelength; so combined photocurrent measurements from all the pixels can be used to not only monitor a single absorption line, but also monitor all absorption lines in a region of the infrared simultaneously. The RCE-PD array concept allows for many substances to be identified and measured, offering much more versatility than a measurement from a single-wavelength RCE-PD. The shift in resonance wavelength is created by inducing a thickness gradient in the epitaxial layers across the wafer. Using this technique, a fabricated 2-inch wafer showed a resonance shift between 1.9 μm and 2.5 μm. A 1D array of pixels was created with a shift in the resonance of 4nm per pixel. Light from a monochromator was used to test the ability of the array to determine the wavelength of the light. For four closely spaced wavelengths, an accuracy of ±2nm was seen.

In this paper, we present an nBn type dual-band InGaAs photodetector design with bias selectable cut-off wavelengths of 1.7 μm and 2.5 μm. InP based epilayer design consists of a compositionally graded quaternery InAlGaAs barrier region sandwiched between lattice matched InGaAs absorber and extended InGaAs absorber. In this study, we also provide a comparison between suggested nBn structure and a relatively usual npn InGaAs structure, using the same computational environment.

Controlling light penetration depth in Avalanche Photodiodes (APDs) and Single Photon Avalanche Diodes (SPADs) play a major role in achieving high multiplication gain by delivering light near the multiplication region where the electric field is the strongest. Such control in the penetration depth for a particular wavelength of light has been previously demonstrated using integrated photon-trapping nanostructures. In this paper, we show that an optimized periodic nanostructure design can control the penetration depth for a wide range of visible and near-infrared wavelengths simultaneously. A conventional silicon APD structure suffers from high photocarrier loss due to recombination for shorter wavelengths as they are absorbed near the surface region, while silicon has low absorption efficiency for longer wavelengths. This optimized nanostructure design allows shorter wavelengths of light to penetrate deeper into the device, circumventing recombination sites while trapping the longer wavelengths in the thin silicon device by bending the vertically propagating light into horizontal modes. This manipulation of penetration depth improves the absorption in the device, increasing light sensitivity while nanostructures reduce the reflectance from the top surface. While delivery of light near the multiplication region reduces the photogenerated carrier loss and shortens transit time, leading to high multiplication gain in APDs and SPADs over a wide spectral range. These high gain APDs and SPADs will find their potential applications in Time-Of-Flight Positron Emission Tomography (TOF-PET), Fluorescence Lifetime Imaging Microscopy (FLIM), and pulse oximetry where high detection efficiency and high gain-bandwidth is required over a multitude of wavelengths.

Optical frequency comb spectroscopy has proven an indispensable tool for high-resolution spectroscopy. QCL frequency combs offer the possibility to explore the mid-infrared spectral range. However, they suffer from large repetition frequencies which make them seemingly unsuitable for high resolution spectroscopy. We present three measurement modes overcoming this limitation. The rapid-sweep technique allows to retrieve the full high-resolution spectrum in 6ms, the step-sweep technique allows for high-resolution spectroscopy with spectral resolution <5e-4 cm-1. As a last technique we present the time-resolved step-sweep approach enabling high-resolution spectra of sub-millisecond-lived samples. It was assessed in a study of cold gases in supersonic beams.

We present the nonlinear coupled-mode theory for anisotropic microcavity lasers, the birefringent spin-lasers in particular. The modeling technique is based on the decomposition of Maxwell-Bloch equations in a properly-chosen vectorial basis, imprinting all the important information about cavity geometry, gain medium and local anisotropies into the coefficients of coupled-mode equations. The formalism is applied to spin-lasers with high-contrast gratings, in which the interplay of spin dynamics and cavity birefringence offers new possibilities for near-future data-transfer technologies. The model can be used to investigate the effects of spin modulation and grating parameters on dynamical performance of realistic grating-based spin-laser. Moreover, it is used to derive the extended spin-flip model. We show, that the currently-used spin-flip model requires the corrections in order to describe the grating-based spin-VCSELs with extremely large frequency splitting.

Highly efficient electrically–driven single photon sources (SPSs) with a narrow far–field emission pattern suitable for coupling to a single mode fiber are critical components for applications in quantum communication. We address modern concepts of the design of SPSs suitable for such applications: (i) Quantum dot (QD) in a micropillar, where a proper reflectivity balance of top and bottom distributed Bragg reflectors (DBRs) and cavity design allows non–resonant highly directional light source. (ii) Dielectric multilayer structure acting as photon extracting microcavity including a passive cavity design and a deeply etched circular Bragg grating enabling a high efficiency of the light extraction and a narrow far field pattern. The light source is not resonant in wavelength and allows narrow far field distribution at a low series resistance. (iii) Resonant light sources based on broadband high–contrast dielectric DBRs optimized for O–band 1300 nm operation with photon–extraction efficiency above 90% and the coupling efficiency to a single mode fiber of 76%. Resonant tuning of the cavity and QD emission allows Purcell effect–enhancement of the QD photon emission rate.

Quantum technologies containing key GaN laser components will enable a new generation of precision sensors, optical atomic clocks and secure communication systems for many applications such as next generation navigation, gravity mapping and timing since the AlGaInN material system allows for laser diodes to be fabricated over a wide range of wavelengths from the U.V. to the visible. We report our latest results on a range of AlGaInN diode-lasers targeted to meet the linewidth, wavelength and power requirements suitable for quantum sensors such as optical clocks and cold-atom interferometry systems. This includes the [5s²S_1/2-5p²P_1/2] cooling transition in strontium⁺ ion optical clocks at 422 nm, the [5s₂ ¹S₀-5p¹P₁] cooling transition in neutral strontium clocks at 461 nm and the [5s² s_1/2 – 6p²P_3/2] transition in rubidium at 420 nm. Several approaches are taken to achieve the required linewidth, wavelength and power, including an extended cavity laser diode (ECLD) system and an on-chip grating, distributed feedback (DFB) GaN laser diode.

The role of metal-organic precursors specifically gadolinium precursors on the resulting magnetic properties of gadolinium-doped gallium nitride (GaGdN) is investigated. Gadolinium-doping is expected to render spin-related magnetic properties in GaN for spintronic applications. To achieve and understand this, GaGdN was grown using metalorganic chemical vapor deposition using two types of gadolinium precursors - tris (2,2,6,6-tetramethyl-3,5- heptanedionate) gadolinium ((TMHD)₃Gd) and tris(cyclopentadienyl) gadolinium (Cp₃Gd). GaGdN grown using (TMHD)₃Gd showed Anomalous Hall Effect and ferromagnetism at room temperature (RT). GaGdN grown using Cp₃Gd showed ordinary Hall Effect with no signs of ferromagnetism or any spin polarization. Oxygen from (TMHD)₃Gd incorporated in GaGdN during the MOCVD growth could be responsible for the differences in magnetic properties. GaGdN shows properties at RT that are conducive for spintronic applications. However, metal-organic precursors and corresponding presence of oxygen significantly influence the spin-related capabilities of GaGdN. This work contributes towards understanding the mechanisms for spin-related properties of GaGdN that can enable its RT spintronic applications.

Band structure, strain, and polarization engineering of nitride heterostructures open unparalleled opportunities for quantum sensing in the infrared. Intersubband absorption and photoluminescence are employed to correlate structure with optical properties of nonpolar strain-balanced InGaN/AlGaN nanostructures grown by molecular-beam epitaxy. Mid-infrared intersubband transitions in m-plane (In)Al_xGa_1-xN/In_0.16Ga_0.84N (0.19≤x≤0.3) multi-quantum wells were observed for the first time in the range of 3.4-5.1 μm (244-360 meV). Direct and attenuated total-reflection infrared absorption measurements are interpreted using structural information revealed by high-resolution x-ray diffraction and transmission electron microanalysis. The experimental intersubband energies are better reproduced by calculations using the local-density approximation than the Hartree-Fock approximation for the exchange-correlation correction. The effect of charge density, quantum well width, and barrier alloy composition on the intersubband transition energy was examined to evaluate the potential of this material for practical infrared applications.

Temperature-dependent continuous-wave and time-resolved photoluminescence (TRPL) measurements are also investigated to probe carrier localization and recombination in m-plane InGaN/AlGaN quantum wells. Average localization depths of 21 meV and 40 meV were estimated for the undoped and doped structures, respectively. Using TRPL, dual localization centers were identified in undoped structures, while a single type of localization centers was found in doped structures. At 2 K, a fast decay time of approximately 0.3ns was measured for both undoped and doped structures, while a longer decay time of 2.2 ns was found only for the undoped sample. TRPL in magnetic field was explored to examine the effect of doping sheets on carrier dynamics. Keywords: nitride semiconductors, intersubband absorption, photoluminescence

In this work, we present theoretical and experimental data on detecting pulsed radio frequency fields. We focus on pulse arrival time detection accuracy. We measure two-photon Rydberg atom EIT in response to ~μs pulse-modulated radio-frequency signals resonant with a Rydberg-Rydberg transition, using a room temperature cesium vapor cell with the lasers locked on atomic resonances. We study the dependence of the atomic response on optical and radio-frequency Rabi frequencies as well as effects such as atomic collisions, ionization, and transit time broadening. We find good agreement with time-dependent simulations performed using a density matrix approach, with a dark state added to account for Rydberg atom decay. We present factors that can influence the sensitivity and timing precision of radio frequency pulses detected under these conditions. Such a system demonstrates potential for the detection of weak radio-frequency pulses in communications and radar applications.

Tip-based nanoscopy techniques have emerged as powerful tools for probing the exceptional optoelectronic properties of van der Waals crystals (vdW) on deeply sub-wavelength scales. Based on two sets of experiments, we demonstrate how bound electron–hole pairs – so-called excitons – can be interrogated with near-field microscopy. First, we build on terahertz nanoscopy with subcycle temporal resolution to access the separation of photo-carriers via interlayer tunneling and their subsequent recombination in transition metal dichalcogenide bilayers. By tracing the local polarizability of electron–hole pairs with evanescent terahertz fields, we reveal pronounced variations of the exciton dynamics on the nanoscale. This approach is uniquely suitable to reveal how ultrafast charge transfer processes shape functionalities in a variety of solid-state systems. Second, we image waveguide modes (WMs) in thin flakes of the biaxial vdW crystal ReS₂ across a wide range of near-infrared frequencies. Resolving the dependence of the WM dispersion on the crystallographic direction, polarization of the electric field and sample thickness, enables us to quantify the anisotropic dielectric tensor of ReS₂ including the elusive out-of-plane response. The excitonic absorption at ~1.5 eV induces a backbending of the dispersion and increased losses of the WMs as fully supported by numerical calculations. Thus, we provide crucial insights into the optical properties of ReS₂ and explore light-matter coupling in layered, anisotropic waveguides. Our findings set the stage for probing ultrafast dynamics in biaxial vdW crystals on the nanoscale.

In this work, we demonstrate that it is possible to use III-V semiconductors for plasmonics from the THz up to the midinfrared spectral range. We have fabricated hyperbolic nano-antenna based on heavily doped semiconductors demonstrating localized plasmon modes. This hyperbolic nano-antenna is 10 times: 10 nm doped InAs / 10 nm undoped GaSb. The free carriers are confined in the 10 nm layer of InAs. The confinement shifts the effective plasma frequency of the metamaterial towards the high frequencies, extending the possibility to probe molecules until 2000 cm^-1 , thus covering the complete fingerprint frequency range for molecular and biosensing applications. The nano-structuration of the hyperbolic material allows to access two main plasmonic resonances at 800 cm^-1 and 2000 cm^-1 . This bimodal property is appealing to detect and identify biomolecules over a large spectral range. With these hyperbolic nanoantennas, we can either enhance the absorption of rovibrational modes of molecules with surface-enhanced infrared absorption (SEIRA) spectroscopy1 or enhance the thermal emission of molecules with surface-enhanced thermal emission spectroscopy (SETES)2

Rapid development in integrated optoelectronic devices and quantum photonic architectures creates a need for optical fiber to chip coupling with low losses. Here we present a fast and generic approach that allows temperature stable self-aligning connections of nanophotonic devices to optical fibers. We show that the attainable precision of our approach is equal to that of DRIE-process based couplings. Specifically, the initial alignment precision is 1.2±0.4 μm, the average shift caused by mating < 0.5 μm, which is in the order of the precision of the concentricity of the employed fiber, and the thermal cycling stability is < 0.2 μm. From these values the expected overall alignment offset is calculated as 1.4 ± 0.4 μm. These results show that our process offers an easy to implement, versatile, robust and DRIE-free method for coupling photonic devices to optical fibers. It can be fully automated and is therefore scalable for coupling to novel devices for quantum photonic systems.

We report on a compact, lightweight, and portable sensor for simultaneous detection of methane, nitrous oxide, and ammonia in atmosphere. The sensor embeds two detection modules based on quartz-enhanced photoacoustic spectroscopy, with two quantum cascade lasers as light sources and two spectrophones with custom-made quartz tuning forks. Dedicated electronic boards were designed to control the laser sources, to stabilize the gas flow and to perform data analysis, with a computer interface for an easy end-user operation. The sensor was calibrated in laboratory environment with certified concentrations. Detection limits well below the natural abundance in standard air were achieved.

In this work, we study the non-radiative energy relaxation rate of methane isotopologues in the mid-infrared spectral range, at about 7.719 µm. We exploited quartz-enhanced photoacoustic spectroscopy to measure the photoacoustic signal at different pressures, exploiting several custom quartz tuning forks operating in the range from 3 to 16 kHz. For each isotopologue the relaxation time in a matrix of water vapor and nitrogen was retrieved, to evaluate the effect of water vapor as an energy relation promoter. Moreover, mixtures composed of 12CH4 and 13CH4, with concentration ratios different from the natural abundance, in a matrix of water vapor and nitrogen were analyzed.

Herein, we are making a step forward by treating cancerous tissues as the highly disordered anisotropic media. The classical Maxwell-Garnett technique is utilized. The former stands for as a perfect tool allowing to evaluate an effective medium of the sample analytically with no needs of human intervention by performing an experimental analysis to measure the parameters of the sample. It should be noted, that laboratory measurements of the effective properties are not needed in this case as well. In this relation, the presented technique allows for the creation of the phantom tissue models for the further usage in clinical applications.

We report on a sensor for methane (C1) and ethane (C2) detection employing a quartz tuning fork as a photodetector for tunable diode laser spectroscopy (TDLAS). In this configuration, the QTF is immersed in the gas mixture under investigation within a vacuum-tight cell. Concentrations of methane and ethane in nitrogen-based mixtures ranged from traces up to percent. An interband cascade laser emitting at 3.345 μm was used as light source. Natural gas-like mixtures were generated in 1:10 nitrogen dilution, and gas mixtures composition was retrieved with an accuracy >98%. Decreasing the target gases concentration, minimum detection limits of 770 ppb and 75 ppb for C1 and C2, respectively, were measured at 10 s integration time.

Upcoming quantum technologies require scalable and cost-efficient technical solutions for widespread functionality. In order to exploit the quantum states of light, single-photon detectors are essential for application. Here, we present a low-footprint plug-and-play multi-channel single-photon detector system featuring integrated photonics that allows for ultra-fast quantum key distribution (QKD). Each channel comprises a superconducting nanowire single-photon detector (SNSPD) patterned from a niobium-titanium nitride (NbTiN) superconducting film atop silicon nitride waveguide structures. Subsequently, the on-chip photonics are interfaced by broadband 3D polymeric fiber-to-chip couplers to the ports of an 8x8 fiber array. The readout electronics allow for individual evaluation of up to 64 channels simultaneously. Integrated to a QKD experiment, a pair of the system's detection channels achieves secret key rates of up to 2.5 Mbit/s employing a coherent one-way protocol.

In this work, we investigate the application of intermodal spontaneous four wave mixing (SFWM) to ghost spectroscopy in the mid-infrared (MIR) spectral region. This technique is of great interest for MIR sensing, being able to overcome the limitations faced by MIR detectors in terms of background noise and dark counts. Through intermodal SFWM in a Silicon-On-Insulator (SOI) waveguide, two temporally correlated photons are generated: using a standard C-band pump, the idler photon is in the near-infrared (NIR) and the signal photon is in the MIR. The integrated source, with a coincidence to accidental ratio (CAR) of 114 ± 4, is used to demonstrate that, in situations of environmental noise, ghost spectroscopy yields advantages with respect to the traditional absorption spectroscopy. The time-energy entanglement of the photon pairs is used to enhance the visibility of the measurement against noisy background conditions and to increase the spectral resolution in the MIR by spectral filtering the NIR photons. Modeling and experimental data support these improvements.

The transition from the conventional concept of “laser in the lab” to that of “lab in the laser”, which implies the presence in a laser with variable output parameters of all the necessary built-in sensors for characterization of the output radiation, is prompted by development of a new generation of devices and/or techniques enabling this function. The potential of speckle-based technologies is discussed in this respect, including the use of special surfaces. It is shown that the recent progress in image acquisition imparts to the speckle-based technologies a new potential both for universal monitoring of radiation parameters and for AI-assisted control.

Semiconductor quantum dots (QDs) are known for their high capacity to nonlinear interaction with light via two-photon absorption (TPA). This allows them to absorb efficiently the infrared photons with energies lower than the bandgap energy. In addition, the TPA can be further enhanced due to interaction of QD excitons with plasmons of metal nanoparticles making it possible to design highly efficient optoelectronic devices with a nonlinear response to irradiation. To achieve this goal, we have fabricated the nonlinear photodetectors based on the QDs and silver nanoplates (SNPs) which combine both mentioned effects and demonstrate a highly efficient nonlinear photocurrent response at the excitation in the nearinfrared region of optical spectrum. In this study, we compared the photodetectors efficiency enhancement in hybrid devices based on the CdSe QDs and SNPs designed by the different ways. In one case, the SNPs were deposited on the top of 10 layers of QDs, and in the other, they were placed between these layers. We have demonstrated that both types of hybrid photodetectors operate in the two-photon regime. At the same time, we have found that the two-photon absorption efficiency was significantly higher in the sample where the SNPs were located between the QD-layers.