This PDF file contains the front matter associated with SPIE Proceedings Volume 11288, including the Title Page, Copyright Information, Table of Contents, Author and Conference Committee lists.

In 1988 DARPA provided funding to NASA’s Goddard Space Flight Center to support the development of GaAs Quantum Well Infrared Photodetectors (QWIP). The goal was to make a single element photodetector that might be expandable to a two-dimensional array format. Ultimately, this led to the development of a 128 x 128 element array in collaboration with AT&T Bell Labs and Rockwell Science Center in 1990. We continued to develop numerous generations of QWIP arrays most recently resulting in the multi-QWIP focal plane for the NASA-US Geological Survey (USGS) Landsat 8 mission launched in 2013 and a similar instrument on the Landsat 9 mission to be launched in 2020. Toward the end of the Landsat 8 QWIP-based Thermal Infrared Sensor (TIRS) instrument the potential of the newly developed Strained Layer Superlattice (SLS) detector array technology became of great interest to NASA for three primary reasons: 1) higher operating temperature; 2) broad spectral response and; 3) higher sensitivity. We have collaborated extensively with QmagiQ, LLC and Northwestern University to further pursue and advance the SLS technology ever since we started back in 2012. In December of 2018 we launched the first SLS-based IR camera system to the International Space Station on board the Robotic Refueling Mission #3 (RRM3). This paper will describe the evolution of QWIP technology leading to the current development of SLS-based imaging systems at the Goddard Space Flight Center over the past 30 years.

Recently, there has been a surge of interest in the wide bandgap semiconductors for solar blind photo detectors (SBPD). This work presents our recent progress in the growth/doping of AlGaN and Ga₂O₃ thin films for solar blind detection applications. Both of these thin films grown are grown by metal organic chemical vapor deposition (MOCVD) in the same Aixtron MOCVD system. Solar-blind metal-semiconductor-metal photodetectors were fabricated with Ga₂O₃. Spectral responsivity studies of the MSM photodetectors revealed a peak at 261 nm and a maximum EQE of 41.7% for a −2.5 V bias. We have also demonstrated AlGaN based solar-blind avalanche photodiodes with a gain in excess of 57,000 at ~100 volts of reverse bias. This gain can be attributed to avalanche multiplication of the photogenerated carriers within the device. Both of these devices show the potential of wide bandgap semiconductors for solar blind photo detectors.

Uncooled focal plane arrays (FPA) with reduced size, weight, and power consumption (SWaP) features and coupled with enhanced characteristics have the potential to significantly benefit a wide range of imaging applications including space surveillance from terrestrial and space-based platforms and planetary composition mapping for space exploration missions. Recently, an innovative, uncooled Photon-Sensing Integrated Circuit (PSIC) hetero-junction phototransistor (HPT) device has been developed. This InGaAs based PSIC HPT device is a room temperature detector and imager that is of 320 x 256 pixel format with 30 micron pixels, and operates in the short-wave infrared (SWIR) spectral region of 0.9 to 1.7 microns. It is a continuously operating (i.e., zero recovery time), zero-excess-noise and linear-mode (i.e., capable of representing photon numbers) photon-sensing detector and imager. Enabled by its hetero-junction phototransistor (HPT) amplification instead of the conventional avalanche multiplication mechanism, this InGaAs HPT simultaneously exhibits signal amplification gain of >1000, namely, >20 x higher gain, and <1/10 lower dark current areal density than InGaAs avalanche photodiode (APD). The photon transfer data (relationship between signal, noise and photon number) for this PSIC imager at FPA mean value and at room temperature is approximately 0.2 noise-equivalent photons per pixel per frame measured using a readout Integrated circuit (ROIC) with 350-700 electron readout noise. The measured uncooled specific detectivity, D* of 3E14 cm.Hz/W appears to be higher than those available commercially. The current HPTs exhibit higher speed, higher gain, lower dark current and noise, and hence achieve highest signal-to-noise ratio (SNR) for photon detection. Recently, the prototype device was selected for space qualification studies on the international space station (ISS). Under NASA’s MISSE-11 (Materials International Space Station Experiment) mission, this device was integrated on to a carrier with various other test components and was launched in April 2019. In this paper, salient features of material processing, device configuration and packaging architecture followed by the pre-flight performance tests carried out will be presented.

LiDAR sensors in applications like autonomous driving, human-robot-collaboration, or logistics have to be robust, lowcost, and reliable. While several LiDAR architectures and methods are currently tested in the field, the improvement of individual system components, including photon detectors and laser sources, are part of ongoing scientific work.
The detector presented here is a CMOS integrated SPAD (single photon avalanche diodes) array device employing a new groundbreaking technology. Backside illuminated SPADs are fabricated and bonded wafer-to-wafer onto a smart ROIC (read-out IC), combining state-of-the-art circuitry and algorithms in a single device.
With 64x48 pixels the novel detector test vehicle paves the way for near-future LiDAR devices. The detector comprises a state-of-the-art time-to-digital converter (TDC) architecture for accurate time-of-flight (ToF) measurements with one TDC shared among 4 pixels. The TDC provides a time resolution of 312.5 ps and has a measurement range up to 192 m. Furthermore, the sensor supports switching of the acquisition modes between timing, counting, and time gating modes. The integrated background-light rejection algorithm, presented earlier in a previous device, allows about 66% higher maximum measurement ranges in environments with a high level of ambient light.
The large pixel pitch of 125 μm is actually limited by the ROIC manufactured in a 350 nm CMOS process. Thus, with smaller CMOS feature sizes for the ROIC, the pixel count can be scaled up drastically in future devices without changing the detection principle or the architecture of the SPAD detector array.

The costs of manufacturing QCL are still a major bottleneck for the adoption of this technology for chemical sensing. The integration of MIR sources on Si substrate based on CMOS technology paves the way for high-volume low-cost fabrication. Furthermore, the use of Si-based fabrication platform open the way to the co-integration of QCL MIR sources with Si-based waveguides, allowing realization optical sensors fully integrated on planar substrate. We report the fabrication of DFB QCL sources operating at 7.4μm on silicon substrate within 200 mm CMOS/MEMS pilot line. To do so, we have developed an appropriate fabrication process flow that fully respects the design and the process rules of a standard CMOS manufacturing line. Moreover, we have developed wafer level electro-optic characterization on prober station. The characterizations done at wafer level on thousands devices have demonstrated average threshold current densities close to between 3 kA/cm² and 2.5 kA/cm² with a relative dispersion around 5%. The optical power can reach 1 mW at ambient temperature, 1.5% duty cycle. This fabrication run achieves performance at the state of the art, that are comparable with those of QCL fabricated on InP substrate. With a yield of 98% on the wafer central fields, this work give perspectives to address application fields needing low cost MIR laser sources.

Although Quantum cascade lasers (QCLs) are frequently used in sensing, spectroscopy, and free space communication applications, their poor thermal properties lead to high temperature gradients in the devices. To diagnose failure mechanisms of mid-wave infrared (MWIR) QCLs, it is critical to understand their thermal generation and transport characteristics. In this work, we use 3D anisotropic steady state heat transfer analysis to investigate the thermal behavior in lattice matched InP/InAlAs/InGaAs buried heterostructure (Bh) mounted epi-layer side down QCLs. We introduce anisotropic thermal conductivities in the in-plane and cross-plane directions in QCL’s superlattice active region, and study the temperature distribution inside the laser. We consider several configurations, including the overhanging of the laser chip on the submount by different amounts, the choice of front facet dielectric coating materials and their thicknesses, and the width of the active region. Combining these effects, we optimize QCL’s thermal performance. This work aims to provide guidelines for the design of durable QCLs as well as to help diagnose QCL failure mechanisms.

For some applications, a reliable detection of the distance of objects is necessary, even under strong environmental conditions. Commonly this includes sunlight, but fog, rain and snow cause interferences as well. For fast and reliable threedimensional monitoring of the environment, LiDAR is a key sensor technology. A light source, often in the near-infrared, emits a short light pulse and the time-of-flight of the photons reflected by an object is measured. This allows to calculate the distance by using the speed of light. In order to be able to ensure reliable detection despite possible interferences, we have set up a new measurement concept based on the existing time-gating. Thus, an area is covered by step-wise shifting of the measuring window. By accumulating different delays, the true distance to the object can be determined. An advantage of the method is that no information about the approximate position of the object has to be known in advance. In this paper we present measurement results with this method, which were taken in different environmental conditions. The method can be implemented in addition to already existing concepts and can therefore supplement them

Quantum cascade lasers (QCLs) are optical sources exploiting radiative intersubband transitions within the conduction band of semiconductor heterostructures.¹ Mid-infrared QCLs have been thoroughly considered for applications such as spectroscopy,² free-space communications³ and countermeasure systems.⁴ Under conventional optical feedback, QCLs have been proven to operate in several non-linear dynamic regimes, including deterministic chaos,⁵ entrainment of low-frequency fluctuations⁶ and square wave all-optical modulation.⁷ We extend the understanding of non-linear phenomena in QCLs with the experimental study of rogue waves. Rogue waves represent random isolated events with amplitudes well above that of neighboring ones, occurring more often than expected from the distribution of lower amplitude events.⁸ In the optical domain, rogue waves were first demonstrated experimentally in 2007 in the context of super-continuum generation in optical fibers⁹ and have since been observed in a wide variety of configurations such as semiconductor lasers.¹⁰ In QCLs, the extra power from these sudden bursts can be used in order to improve the efficiency of mid-infrared remote sensing or countermeasure systems. It can also be a helpful tool for neurophotonics clusters aiming to reproduce synaptic transmissions in an all-optical system. As a step toward a reliable control over these rare spikes, we carry out a statistical analysis of the interval between rogue events and show that precursors always occur before these events. The advantage of these precursors is to have a characteristic time longer than that found in other semiconductor lasers exhibiting the same non-linear phenomena. Birth of giant pulses like dragon-kings events are also discussed and analyzed.

This Conference Presentation, "Quantum devices: QWIPs/QDIPs, QCLs/ ICLs, and topological excitations," was recorded at Photonics West 2020 held in San Francisco, California, United States.

Efficient light generation from inelastic electron tunneling (IET) using self-assembled edge-to-edge (EE) single-crystalline silver nanoparticles has been demonstrated with an efficiency up to ~2%. Various nanostructures including nanocube, nanobar, and square prism, have been explored, where the emission wavelengths covering from the visible to the near infrared. The excellent performance is attributed to the use of high-quality atomic level plasmonic cavities created within ultra-small gaps (~1.5 nm) as well as of optical nano-antenna formed by the EE nanoparticles. The realization of 2% efficiency based on IET brings on-chip ultrafast optical sources one step closer to reality.

We are developing a semi-classical model to explain the physical processes behind the origin of the statistical variations in the photoelectron current pulses that we register for different kinds of light. They are: super-Poissonian thermal light, Poissonian laser light and sub-Poissonian nonlinearly generated light. Einstein’s photoelectron equation is an energy balancing equation. It does not incorporate the E-vector stimulation process before the quantum mechanically bound electrons can be released, which constitutes a key objective of physics. To introduce physics, we postulate that the photons are hybrid entities. They are discrete packets of energy hν_mn at the moment of emission. Then they immediately evolve into spatially spreading diffractive wave packets to accommodate Huygens-Fresnel principle. HF principle has been behind the sustained progress in classical optics and photonics engineering. Thus a spatially spread out single wave-packet cannot any more deliver the necessary quantum cupful of energy hν_mn to Angstrom-size detecting atoms. We need simultaneous stimulation of the same quantum entity by multiple wave packets. This model of physical interaction process naturally brings into play the significance of the degree of mutual coherence between different photon wave packets, along with their time varying amplitudes that are simultaneously stimulating the detecting quantum entities during any time-interval selected for the detection system. The superposition effects on the detector due to these phase and amplitude fluctuations are the physics-reasons behind the generation of different statistical variations in the photoelectron counts due to different kinds of sources even though the original photons are released randomly by all quantum sources.

In this work we review the reported results as well as the analytical and 3D numerical modeling tools we used to analyze dark current and quantum efficiency data from lattice matched InP/In_0.53Ga_0.47/InP double layer planar 15 μm pixel pitch focal plane arrays (FPAs). These imaging sensors are designed to operate in the near infrared under overcast “Night-Glow” illumination conditions. A notable finding is that the diffusion dark current component is the dominant current component near and above 300 K and is limited by band-to-band radiative recombination processes. The Shockley-Read-Hall (SRH) recombination through band gap states situated at the intrinsic Fermi level is the dominant component for temperatures below 300 K. 3D numerical simulations consisting of both bulk area and perimeter dependent components explains the dark current component of origin in the space charge region (SCR) with an SRH lifetime of τ_SRH = 107 μs. Image sensors with extended cut-off wavelength of 2.5 μm at room temperature built on InP/InGaAs are not lattice matched and needed are reductions in the mismatch throughout the InP/InGaAs multilayer epitaxial structure. We analyzed devices with a buffer layer introduced between the InP and the In_0.81Ga_0.10As absorber and showed that the measured dark current consisted of a diffusion current limited by a back surface interface recombination velocity and a shunt current component expected to be dominant at T ≤ 200 K. At 293 K we calculated a factor of 10 increase in the diffusion current caused by lattice mismatch. Recommended are hole minority carrier lifetime measurements and variable junction diode geometries to assess suspected perimeter/area dependency.

For making a high-performance thermopile, which is a kind of cooling-free infrared sensor and composed of thermoelectric materials and capable of detecting infrared rays without electric power, we developed Si-Ge thin film thermoelectric materials. The thermal conductivity of the Si-Ge thermoelectric material was successfully reduced to 1 Wm^-1K^-1 by making use of nano-structuring. Besides, its Seebeck coefficient was effectively increased by a multi element doping technique. The thermopile constructed using the developed nanostructured Si-Ge was confirmed to sensitively detect infrared rays.We constructed gases detection system using the thermopile and an infrared laser and demonstrated its superior function.

In this presentation, we will report our recent efforts in achieving high performance in Antimonides type-II superlattice (T2SL) based infrared photodetectors using the barrier infrared detector (BIRD) architecture. The initial BIRD devices (such as the nBn and the XBn) used either InAs absorber grown on InAs substrate, or lattice-matched InAsSb alloy grown on GaSb substrate, with cutoff wavelengths of ~3.2μm and ~4μm, respectively. While these detectors could operate at much higher temperatures than existing MWIR detectors based on InSb, their spectral responses do not cover the full (3 – 5.5μm) MWIR atmospheric transmission window. The T2SL BIRD devices not only covers the full MWIR atmospheric transmission window, but the full LWIR atmospheric transmission window and beyond. The LWIR detectors based on the BIRD architecture has also demonstrated significant operating temperature advantages over those based on traditional p-n junction designs. Two 6U SmalSat missions CIRAS (Cubesat Infrared Atmospheric Sounder) and HyTI (Hyperspectral Thermal Imager) are based on JPL’s T2SL BIRD focal plane arrays (FPAs). Based on III-V compound semiconductors, the BIRD FPAs offer a breakthrough solution for the realization of low cost (high yield), high-performance FPAs with excellent uniformity and pixel-to-pixel operability.

The Time Correlated Single Photon Counting (TCSPC) technique is a powerful tool to analyze extremely fast and faint optical signals; however, its main drawback relies in its intrinsic slowness which is due to the necessity to acquire a large number of events to make an accurate reconstruction of the analog waveform in the time domain. In recent years, a significant research effort has been put in the design of multichannel systems: indeed, parallelization could in principle increase the overall speed of the acquisition system. In this scenario, we focused on the investigation of both singlechannel and multichannel systems potentiality to push the speed of TCSPC acquisition towards its ultimate limits. In this paper we report a solution to increase the speed of a single-channel system by almost an order of magnitude with respect to the state of the art and a smart routing architecture to provide a true increment of the acquisition speed based on the exploitation of a single photon detector array.

Based on the requirements on high resolution and high signal-to–ratio for infrared thermal imaging technology and infrared nondestructive detection, the paper firstly introduces their research significance and basic concept, and compares their differences and advantages in basic theory, research scale and instruments design. Then the paper elaborates the author and his team, after three periods of researches that focusing on the theory, experiments and technology, have completed the production of infrared quantum spectral detection principle prototype in December 2014. All tests and experiments show that every technical indicators meets the requirements, the resolution is 2-3 times higher than that of coherent light detection imaging, which provides significant technical basis for the production of infrared quantum spectral imaging engineering prototype. Finally, the paper summarizes the key technical problems to be solved and application outlook for the infrared quantum spectral detection imaging technology research.

We report lateral-type, GaAs/AlGaAs double hetero-structure (DH) spin-LEDs with stripe Fe spin injectors that exhibit nearly pure circular polarization (CP) electroluminescence (EL) with current densities of J ~ 10 A/cm² or less. Experiments with such spin-LEDs have made it possible to obtain experimental data that were not accessible in the first report [1,2]: namely, clear experimental proof for the presence of a threshold J value at which the annihilation of minority-helicity CPEL component takes place.

Band-edge exciton states in bulk lead chalcogenides are 64-fold degenerate. In quantum dots (QDs), the degeneracy is lifted by the valley mixing and the electron-hole exchange interaction. To investigate their interplay we calculate excitonic states in PbS QDs within the tight-binding method. This allows one to trace the genesis of the bright excitonic states from the valley-degenerate states of the direct exciton which may be described within the effective mass model. We compute optical absorption spectra fully accounting for the exciton fine structure within the tight-binding method and extend the effective-mass model to include description of the inter-valley coupling.

C-AFM and KPFM techniques have been applied to investigate advanced junctions that are currently involved in highly efficient silicon solar cells. Our first study focuses on silicon heterojunctions and notably hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) P/n or N/p heterostructures which band bending at the interface forms a 2D channel. This conductive channel was indeed evidenced for the first time by cross-sectional investigations by C-AFM confirming the analysis of macroscopic planar conductance measurements. A second example of nanoscale characterization concerns the passivating selective contacts consisting in a thin silicon oxide (SiOx) layer between the c-Si and a highly doped polysilicon (poly-Si) layer. The electrical carrier transport is here not limited by the oxide layer and it is assumed that tunnelling through the oxide and/or the presence of pinholes are the main competitive mechanisms. For this specific heterostructure KPFM reveals local surface potential drops of 15- 30 mV, which do not exist on samples without SiOx. These potential drops suggest the presence of pinholes that are formed during the poly-Si annealing process performed in the range of 700-900°C. Finally, in a third study, we concentrate on p-i-n radial junction (RJ) silicon nanowire (SiNW) devices that are investigated under illumination by KPFM, in the so-called surface photovoltage (SPV) technique. This work focuses on the possibility of extracting the open-circuit voltage (VOC) on single isolated SiNW RJ by local SPV measurements using different AFM tip shapes and illumination directions in order to minimize shadowing effects.

Microwave detectors based on the spin-torque diode effect are among the key emerging spintronic devices. By utilizing the spin of electrons in addition to their charge, they have the potential to overcome the theoretical performance limits of their semiconductor (Schottky) counterparts. In the first part of the talk, I will discuss our recent results in the field of microwave detectors based on spin diodes.1 Those devices realized with magnetic tunnel junctions exhibit high-detection sensitivity >200kV/W at room temperature, without any external bias fields, and for low-input power (micro-Watts or lower).2 This sensitivity, achieved taking advantage of the injection locking, is significantly larger than both biased state-of-the-art-Schottky diode detectors and other existing spintronic diodes.

In this work, we investigate the current-induced switching in micrometer-scale circular memory bits based on the metallic antiferromagnet PtMn, which is already widely used as part of the pinned layer in in-plane magnetic tunnel junctions manufactured on CMOS. The device shows reversible switching in response to currents applied to the Pt layer, with opposite current polarities achieving opposite switching directions in the PtMn. The switching current density is ~2 MA/cm2. We show that the switching process is essentially unaffected by external fields up to 16 T, and is robust over a wide temperature range. We also investigate the switching process by micromagnetic simulations, which shed light on the current-controlled domain structure of the device and the role of different torque terms in the switching process. Our results pave the way towards practical antiferromagnetic memories integrated on silicon.

A two terminal short wavelength infrared heterojunction phototransistors based on type-II InAs/AlSb/GaSb on GaSb substrate are designed fabricated and presented. With the base thickness of 40 nm, the device exhibited 100% cut-off wavelengths of ~2.3 μm at 300K. The saturated peak responsivity value is of 325.5 A/W at 300K, under front-side illumination without any anti-reflection coating. A saturated optical gain at 300K was 215 a saturated dark current shot noise limited specific detectivity of 4.9×10¹¹ cm·Hz^1/2/W at 300 K was measured. Similar heterojunction phototransistor structure was grown and fabricated with different method of processing for high speed testing. For 80μm diameter circular diode size under 20 V applied reverse bias, a -3 dB cut-off frequency of 1.0 GHz was achieved, which showed the potential of type-II superlattice based heterojunction phototransistors to be used for high speed detection.

Free-space optical communications (FSOC) is a promising avenue for point-to-point, high-bandwidth, and high-security communication links. It has the potential to solve the “last mile” problem modern communication systems face, allowing for high-speed communication links without the expensive and expansive infrastructure required by fiber optic and wireless technologies ¹ . Although commercial FSOC systems currently exist, due to their operation in the near infrared and short infrared ranges, they are necessarily limited by atmospheric absorption and scattering losses ² . Mid-infrared (MWIR) wavelengths are desirable for free space communications systems because they have lower atmospheric scattering losses compared to near-infrared communication links. This leads to increased range and link uptimes. Since this portion of the EM spectrum is unlicensed, link establishment can be implemented quickly. Quantum cascade lasers (QCL) are ideal FSOC transmitters because their emission wavelength is adjustable to MWIR ³ . Compared to the typical VCSEL and laser diodes used in commercial NIR and SWIR FSOC systems, however, they require increased threshold and modulation currents ⁴ . Receivers based on type-II superlattice (T2SL) detectors are desired in FSOC for their low dark current, high temperature operation, and band gap tunable to MWIR ⁵ . In this paper, we demonstrate the implementation of a high-speed FSOC system using a QCL and a T2SL detector.

Gas spectroscopy is a tool that can be used in a variety of applications. One example is in the medical field, where it can diagnose patients by detecting biomarkers in breath, and another is in the security field, where it can safely alert personnel about ambient concentrations of dangerous gas. In this paper, we document the design and construction of a system compact enough to be easily deployable in defense, healthcare, and chemical safety environments. Current gas sensing systems use basic quantum cascade lasers (QCLs) or distributed feedback quantum cascade lasers (DFB QCLs) with large benchtop signal recovery systems to determine gas concentrations. There are significant issues with these setups, namely the lack of laser tunability and the lack of practicality outside of a very clean lab setting. QCLs are advantageous for gas sensing purposes because they are the most efficient lasers at the mid infrared region (MIR). This is necessary since gases tend to have stronger absorption lines in the MIR range than in the near-infrared (NIR) region. To incorporate the efficiency of a QCL with wide tuning capabilities in the MIR region, sampled grating distributed feedback (SGDFB) QCLs are the answer as they have produced systems that are widely tunable, which is advantageous for scanning a robust and complete absorption spectrum. The system employs a SGDFB QCL array emitter, a Type II InAsSb Superlattice detector receiver, a gas cell, and a cooling system.

Excitation of localized surface plasmon resonance in noble metal nanoparticles leads to enhancement and localization of electromagnetic fields in the immediate vicinity of nanoparticles. These properties may be employed to amplify the lightmatter interaction in the near-infrared range where the overtone molecular vibrations are situated. Since the overtone vibration bands are much weaker than the fundamental bands, the amplification is essential. Here we explored SENIRA in the framework of molecular overtones sensing, particularly, those overtones that correspond to the C-H (1676 nm) and NH (1494 nm) stretching modes overtones. The gold nanorods (GNRs) are placed on the dielectric substrate and embedded into a thin layer of organic probe molecules (N-Methylaniline). The dispersion characteristics of N-Methylaniline, namely, its wavelength-dependent absorption and refractive indices in the spectral vicinity of the overtone transitions were fully taken into account. To find out the enhancement of overtone transitions provided by the GNR, we numerically calculated the differential transmission (DT) as a function of the gold nanoantenna’s size and grating periods. The computational results evidence that in sparse arrays of GNRs when the near fields of the neighbor GNRs do not overlap with each other, the differential transmission of stretching overtone modes shows the resonance at the right spectral position which is around 8.8 times larger as compared to the absorption of the bare molecular film of the same thickness. Thus, the obtained results substantiate a new sensing spectroscopy concept for identification of versatile “fingerprints” in the near-IR range based on plasmon-overtones interactions.

Despite comparatively poor interlayer conductivity photosensors of few-layer semiconducting 2D transition metal dichalcogenides (TMDCs) can be both fast (<70 ps) and highly efficient (IQE>50%). To understand the unexpected result, we use tunable E-fields to isolate the dynamics of interlayer electron-hole dissociation using time-space resolved photocurrent microscopy on semiconducting TMDCs and thin-film transistors. We show how this novel scanning microscopy approach, combines ultrafast photocurrent and transient absorption to identify new long-lived and metastable interlayer electronic states in emerging twisted and stacked 2D and thin-film devices.

In this talk I will discuss the design and engineering of novel diffractive devices for light focusing and directional control with applications to light emission, imaging spectroscopy, and photodetection from the visible to the infrared spectral range.

This Conference Presentation, "Crystalline InGaZnO quaternary nanowires with superlattice structure for high-performance thin-film transistors and UV photodetectors," was recorded at Photonics West 2020 held in San Francisco, California, United States.

Half-harmonic generation is the inverse of second-harmonic generation. This talk overviews the concept, and how it is used for mid-IR frequency combs for molecular spectroscopy, and optical Ising machines, which can enable special-purpose nonclassical computing.

All-dielectric optical metasurfaces consist of 2D arrangements of nanoresonators and are of great importance for shaping polarization, phase and amplitude of both linear and harmonic fields. Here, we demonstrate the generation of second harmonic (SH) with zero-order diffraction from nonlinear AlGaAs metasurfaces with spatial period comparable with a pump wavelength in the near-IR. Upon normal incidence of the pump, we demonstrate paraxial SH light into the zero order. SH polarization is effectively controlled via either the meta-atom shape or the pump polarization, with potential applications for on-axis imaging and free-space communication systems.

The minimum resolvable signal in optical metrology and sensing applications is usually limited by the so-called standard quantum limit. One way to improve the signal-to-noise ratio is to use squeezed states of light. Squeezed light can be generated using different types of nonlinear interactions either in solid-state nonlinear crystals or in atomic systems. One way to generate squeezed light is to use a phase sensitive amplifier that will amplify one quadrature of the considered mode and deamplify the other one. We have recently shown that metastable helium vapor at room temperature can exhibit strong four-wave mixing effects and behave like a perfect phase sensitive amplifier when it is prepared in coherent population trapping situation. In this talk, we will present the application of this phase sensitive amplification to the generation of squeezed vacuum states of light and detail the performances and limitations of the system

Semiconductors are considered as building blocks for electronics and photonics. I will discuss about our efforts in the growth of semiconductor nanowires and demonstrate nanowire lasers, nanowire THz detectors, nanowire solar cells and nanowires for photocatalyis. We have also extended this work to engineer neuronal circuits using nanowire arrays.

On-chip optical communications have experienced great progress lately, gaining in maturity with fast, reliable and efficient optical interconnects. Silicon photonics has demonstrated huge potential to become the dominant technology to support this development. Still, the silicon photonics lacks of a monolithic light source. To overcome this blocking point, hybrid integration of III-V materials on silicon raises as a viable route in the short term. In this work, we will revisit the hybrid III-V on Si platform and put forward our particular vision at the III-V lab, discussing several points that will play a key role in the coming years.

Two-dimensional layered materials like graphene pave the way to advanced (opto-) electronic devices. Their extraordinary properties can be further controlled employing plasmonic nanostructures, e.g., enhancing light focusing, increasing the absorption cross sections, and generating hot-carrier due to the excitation and decay of localized surface plasmons. However, this interplay strongly depends on the particle’s environment and geometry mandating the investigation of individual structures. Raman spectroscopy maps reveal spatially resolved information on charge transfer as well as temperature and strain distributions in graphene sheets in the vicinity of individual spherical gold nanoparticles. Hot-electrons are efficiently injected from single gold nanoparticles into graphene for resonant excitation of the localized surface plasmons of the gold nanoparticle. Additionally, heating of the graphene sheet and its intrinsic strain can be separated and quantified.

Nanowire technology can offer unique opportunities for realization of different 3D device structures, ranging from 1D nanowires for radial LEDs to the formation of c-oriented dislocation-free planar structures for vertical microLEDs, as well as to self-forming dislocation-free and atomically smooth photonic cavity structures. In this talk I will describe nanowire-mediated formation of microLEDs via controlled reshaping of ternary InGaN pyramids yielding c-oriented relaxed and dislocation-free InGaN-platelets that form the basis for vertical InGaN microLEDs emitting all three RGB-colors. I will also describe recent progress in the self-formation of atomically smooth and dislocation-free hexagonal prism structures acting as photonic cavity structures.

III-V superlattice has emerged as an important material in the field of infrared detection. Infrared cameras and systems have been built and demonstrated worldwide. Theoretical modeling plays a significant role in terms of understanding the materials, devices, and associated technical limits. In this talk, temperature dependent empirical tight binding modeling (ETBM) will be discussed for efficient modeling of the bandgap of an alloy and a superlattice incorporating alloy compositions. It was observed that the temperature dependency of superlattice bandgap is independent of the superlattice design for a nominal bandgap at a given temperature. In addition, effect of cross incorporation of elements will be modeled. Its manifestation in xray diffraction will be shown. On the device side, a theory of photo carrier collection mechanism will be proposed for a barrier infrared detector structure. A hypothesis of photonic up/down conversion and photo current gain mechanism without excessive noise will also be discussed.

A novel method of preparing magnetic ink belonging to the class of ferrofluids which contains magnetic particles with a polar surface-active agent is disclosed. The magnetic material belongs to the group known as magnetite (Fe₃O₄), typically to those with γ-Fe₂O₃ and their likes. Ni-Zn ferrite and Mn ferrite inks were prepared using this method. The inks have a PH value and total dissolved solute of about 6.3, 3.78 mS and 5.9, 4.2 mS respectively, and a viscosity of about 7 cPa, 7.4 cPa respectively. The saturation magnetization of Mn ferrite ink at 300K was 62 emu/cm³. This lower value of the saturation magnetization of Mn ferrite compared to the bulk is because of the shell-core structure of the surfactant coated ferrite particles. The inks were used to prepare various thicknesses ranging from 0.5um to 20um of both Ni-Zn ferrite and Mn ferrite thin films. The surface morphology of the thin film was observed using Atomic Force Microscopy (AFM), showing a compact, dense and relatively smooth film. The microstrip transmission line permeameter approach was used to extract the permittivity and permeability of the thin film samples within the frequency range of 10MHz-1GHz. A relative permeability of 2 was measured. The developed ink and thin film are promising for future magneto-optical applications.

A broadband, Cu-Cu THz quantum cascade laser is presented. The device shows an 50% improved dynamical range and doubled peak power in pulsed compared to Au-Au devices. The pulsed maximum lasing temperature was increased from 105 K to 133 K. In CW similar bandwidths for Cu-Cu and Au-Au devices are observed with an increased temperature performance. At 77 K the emitted power of the device is reduced by 57% compared to 30 K. At this temperature a single narrow beatnote is observed, which can be locked to an RF synthesizer. THz comb emission spans roughly 800 GHz.

Reaching high average powers and room temperature operation for THz sources has become the key challenge for the uptake of THz applications that require real-time imaging. In this work, we show that by placing a photoconductive switch within a quasi-resonant cavity based on a metal-insulator-metal geometry, we are able to generate, at room temperature, average THz powers greater than of 200 µW, with the frequency of the THz emission centred at 1.5THz, specifications ideally adapted to NDT. We demonstrate proof-of-principle real-time THz imaging.

We report a preliminary investigation of ion bombardment (IB) effects on interband cascade laser (ICL) properties. Under some conditions, IB almost completely suppresses the vertical transport through a broad-area laser, although other times only a partial or negligible suppression is observed. To elucidate the mechanism that induces the suppression and in what part of the structure it occurs, we investigated the effects of IB on samples containing only ICL sub-regions. While IB increased the resistivity of a lightly-n-doped GaSb layer such as that used as a top or bottom separate confinement layer in an ICL, that layer was still much too conductive to strongly suppress the current flowing through a full device. The voltage drop was larger following IB of an InAs-AlSb superlattice such as that used in the top and bottom optical cladding layers in an ICL, although the effect was not large enough to fully account for the strong net suppression. And finally, the resistivity of an interband cascade LED containing the same active stages as an ICL was actually found to decrease following IB. Despite the inconclusive and sometime inconsistent findings of this study, it is nonetheless clear that if the effects can be controlled reproducibly, IB may provide a valuable tool for enhancing such ICL device configurations as weakly-index-guided narrow ridges and interband cascade vertical-cavity surface-emitting laser mesas that inject current and emit light only within a small central aperture.

The generation of short pulses with quantum cascade lasers (QCLs) remains challenging to date due to their ultrafast gain dynamics. Here, we report on active mode-locking of mid-infrared QCLs. For the first time we show, that picosecond pulses can be generated also at room-temperature using high-performance QCL material. Mounted epi-up, the QCLs emit a train of pulses as short as a 7ps with an average power of 100mW. The nonlinear autocorrelation shows reveals the famous 8:1 ratio, which proves unambiguously that the QCL operates in the mode-locked regime. This result is further verified using the beatnote spectroscopy technique SWITS.

Free-space optics constitutes a growing technology offering higher bandwidth with fast and cost-effective deployment compared to fiber technology. Multiple applications are envisioned like private communications. In such a case, the secret message is encoded into a chaotic waveform from which the information is extremely hard for an eavesdropper to extract. For free-space optics applications, the operating wavelength is an important parameter that has to be chosen wisely to reduce the impact of the environmental parameters. In this context, quantum cascade lasers are highly relevant semiconductor lasers because the lasing wavelength can be properly adjusted in the mid-infrared domain, typically at wavelengths for which the atmosphere is highly transparent. The simplest way to generate a chaotic optical carrier from a quantum cascade laser is to feed back part of its emitted light into the device after a certain time delay, beyond which chaos synchronization between the drive and the response lasers occurs. In this paper, we discuss about how quantum cascade laser's chaos can be used to develop private communication lines. We also give realistic perspectives for further developing mid-infrared private communications using chaotic waves.

The fundamental optical diffraction in infrared microscopes limits their spatial resolution to about ~5μm and hinders the detailed observation of heat generation and dissipation behaviors in micrometer-sized optoelectronic and semiconductor devices, thus impeding the understanding of basic material properties, electrical shorts and structural defects at a micron and sub-micron scale. We report the recent development of a scanning near-field optical microscopy (SNOM) method for thermal imaging with subwavelength spatial resolution. The system implements infrared fiber-optic probes with subwavelength apertures at the apex of a tip for coupling to thermal radiation. Topographic imaging and tip-to-sample distance control are enabled by the implementation of a macroscopic aluminum tuning fork of centimeter size to support IR thermal macro-probes. The SNOM-on-a-fork system is developed as a capability primarily for the thermal profiling of MWIR quantum cascade lasers (QCLs) during pulsed and continuous wave (CW) operation, targeting QCL design optimization. Time-resolved thermal measurements with high spatial resolution will enable better understanding of thermal effects that can have a significant impact on a laser's optical performance and reliability, and furthermore, will serve as a tool to diagnose failure mechanisms.

Promising effects such as electrical tunability of the spectral response and broadband optical emission have been demonstrated on tiny 3D resonators, opening the way to substrate-independent electrically-controlled light sources. In this talk we present the interplay between optical and electrical properties of large areas of MIM nanogap antennas. Dedicated design and low-temperature process are presented for Au/SiO2/Au structures. A drastic decrease of the effective index of the gap mode is observed for significant electron-tunneling probability (gap < 1.2nm). Electrically biased antennas show a net tunneling current together with a spectral-shift. Last but not least, light emission is characterized.

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 Secondly, 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. Finally, 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. In this proceeding, we report the concepts of nanostructures and how it influences TPA absorption in a PIN photodiode. Experimental data point out that infrared photons were detected inside our first generation of diodes. However some issues are still to deal with to reach infrared detection with low fluxes thermal sources. The SNR (signal to noise ratio) can be widely improved by reaching higher values of NDTPA photocurrent and limiting the sub-gap absorptions mainly responsible for the structure noise. Consequently a second generation of nanostructured photodiodes has been designed to perform better detection.

Fundamental modelocking to generate short terahertz (THz) pulses and THz frequency combs from semiconductor lasers has become a routine affair using quantum cascade lasers (QCLs) as a gain medium. However, no demonstrations of harmonic modelocking have been shown in THz QCLs, where multiple pulses per round trip are generated when the laser is modulated at harmonics of the cavity’s fundamental round trip frequency. Here, using time resolved THz techniques, we show for the first time harmonic injection, and active and passive mode-locking where THz QCLs are modulated at harmonics of the round-trip frequency. Furthermore, using the unique ultrafast nature of our approach, we show that passive or self-starting harmonic modelocking originates from the QCL self-generating a harmonic microwave modulation. The latter auto-modulates the gain and loss in the system, spontaneously forcing the QCL to operate up to its 15th harmonic and opening up prospects of passive THz short pulse generation.

Quantum technologies containing key GaN laser components will enable a new generation of high precision quantum 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 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 [5s₂¹S₀-5p¹P₁] cooling transition in neutral strontium clocks at 461 nm and the [5s²s_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.

Many applications such as toxic gas detection or H₂S monitoring in natural gas require operation in the THz spectral region, where gas species show distinct spectral “fingerprints” that can be easily discriminated by the gas matrix background absorption features.
So far, continuous-wave THz quantum cascade lasers employed in quartz-enhanced photoacoustic (QEPAS) sensors required liquid helium-cooling systems. In this work, we demonstrated the first liquid nitrogen-cooled THz QEPAS sensor for H₂S detection operated in pulsed mode and mounting a spectrophone based on a quartz tuning fork with 1.5 mm prong spacing. A sensitivity level in the part-per-billion concentration range was achieved.

Nickel-doped zinc oxide (ZnNiO) was grown on sapphire by metal organic chemical vapor deposition (MOCVD) with varying Ni content under two growth conditions of 400°C/100 Torr and 450°C/30 Torr. Elemental composition indicated that Ni could occupy Zn and O/interstitial sites in ZnNiO. Ni-doping in ZnO resulted in shifts in X-ray diffraction (002) peak, and introduced a (111) phase. Absorption spectrum showed a reduction in near band edge with Ni content in both the samples’ sets. Samples grown at 400°C/100 Torr had a band gap reduction from 3.276 eV to 3.269 eV, while those synthesized at 450°C/30 Torr showed reduction from 3.287 eV to 3.260 eV. The bandgap reduction rate was influenced by growth conditions, and sites activated for Ni incorporation during the growth. Nickel could introduce shallow energy states near the valence band in ZnNiO, and result in a reduction in the bandgap. A potential for bandgap tunability, and controllable introduction of energy states in zinc oxide with transition metal doping by MOCVD, could widen the application range of zinc oxide-based materials for energy harvesting and electronics.

We describe a system that combines isotope ratio analysis via mid-infrared (Mid-IR) laser absorption spectroscopy with fine spatial resolution sampling using a UV pulsed laser. The UV laser ablates a pit in a solid on the order of 10 microns in diameter. The sample-derived particulates resulting from laser ablation pass through a micro-combustor, and the resulting gas is analyzed using Mid-IR laser absorption spectroscopy in a capillary absorption spectrometer (CAS). The CAS uses a hollow fiber optic waveguide with a reflective inner coating and a small internal volume on the order of 1 ml. The hollow fiber both guides the laser light from source to detector and contains the gas sample at reduced pressure. Near unity overlap between the laser beam and sample enables sensitive analysis with ultra-small sample size. A prototype system has been demonstrated to enable stable carbon isotopic analysis (δ¹³C) with 1 per mil precision using < 1 picomole of carbon and is currently being used to study nutrient exchange in soil/root/microbial rhizosphere studies. The smaller sample size of this system is enabling fine spatial resolution analysis (on the order of 10 microns), which is roughly an order of magnitude smaller than was possible with an isotope ratio mass spectrometer (IRMS). In addition to rhizosphere studies, the system can provide a useful tool for fine scale isotope analysis with applications in biological, forensic, and environmental science.

A mid-infrared gas sensor based on intracavity quartz-enhanced photoacoustic spectroscopy (I-QEPAS) and a custom quartz tuning fork is here reported. A 4.59 μm distributed feedback quantum cascade laser was optically coupled into a high-finesse Brewster window linear optical cavity. A power enhancement factor of ~ 250 has been achieved. A spectrophone composed of a custom tuning fork having 1.5 mm prong spacing, acoustically coupled with a pair of micro-resonator tubes, was placed in the focal point of the high-finesse cavity. The sensor was calibrated for humidified carbon monoxide and nitrous oxide detection. Gas concentration sensitivities in the part-per-trillion range were achieved for both gas species.

A compact, single-pass and low-power-consumption methane sensing system is presented and its sensitivity is investigated for a set of reference cells with pressures of 7.4, 74 and 740 Torr and the same methane concentration of 1351 ppm. A single-mode GaSb-based continuous-wave (CW) distributed feedback (DFB) tunable diode laser at 3270 nm and wavelength modulation spectroscopy were employed to collect 2f spectra in the ν₃,R₃ band of ¹²CH₄. A modulated Voigt line profile model was used to fit the collected 2f spectra. The best detectivity of 4 ppbm is obtained for the highest pressure cell using an Allan-Werle variance analysis.

Nano-arrays are an important structure for building chemical filters, photonic crystal waveguides, antireflection, or transmission devices. There are different methods of lithography to produce these nano-arrays, which include contact and projection photolithography, E-beam direct writing, and X-ray lithography. Contact photolithography is the most widely used method due to its simplicity and good for time and cost-saving. However, there are penalties that come with these benefits which include problems of generating Newton rings and difficulties of transferring patterns faithfully for situations at and beyond the diffraction limit.

In this work, we fabricated nano-arrays for high power antireflection applications using contact photolithography. Fortunately for the antireflection application, pattern periodicity is more important than obtaining the exact shape of the nanostructure. The fabricated structure, even though not the same as the original pattern, can still produce promising antireflection results. We have studied how the range of the distance between the mask and the photoresist affects the shapes of the produced patterns including holes, posts, and cones. The experimental results with different shapes and periodic patterns produced by different diffraction distances are explained with simulation results involving Fourier transformation and Fresnel diffraction of the mask patterns.

The quanta image sensor (QIS) is a novel CMOS-based image sensor capable of photon counting without the necessity of avalanche gain. The QIS reported in this work is implemented in a state-of-the-art backside-illuminated (BSI) CMOS image sensor commercial stacking (3D) process. The detector wafer consists of a megapixel array of specialized active pixels known as “jots” and the ASIC readout wafer utilizes cluster-based readout circuitry. This specialized pixel architecture and cluster readout circuits allow for the QIS to achieve accurate photon-counting capabilities with average read noise of 0.23e- rms, average conversion gain of 345μV/e-, and average dark current less than 0.1e-/sec/jot at room temperature without active cooling.

The optical activity of Raman scattering provides insight into the absolute configuration and conformation of chiral molecules. Applications of Raman optical activity (ROA) are limited by long integration times due to a relatively low sensitivity of the scattered light to chirality (typically 10^-3 to 10^-5). We apply ROA techniques to hyper-Raman scattering using incident circularly polarized light and a right-angle scattering geometry. We explore the sensitivity of hyper- Raman scattering to chirality as compared to spontaneous Raman optical activity. Using the excitation wavelength at around 532 nm, the photobleaching is minimized, while the hyper-Raman scattering benefits from the electronic resonant enhancement. For S/R-2-butanol and L/D-tartaric acid, we were unable to detect the hyper-Raman optical activity at the sensitivity level of 1%. We also explored parasitic thermal effects which can be mitigating by varying the repetition rate of the laser source used for excitation of hyper-Raman scattering.

Gas mixtures analysis is a challenging task because of the demand for sensitive and highly selective detection techniques. Partial least squares regression (PLSR) is a statistical method developed as generalization of standard multilinear regression (MLR), widely employed in multivariate analysis for relating two data matrices even with noisy and strongly correlated experimental data. In this work, PLSR is proposed as a novel approach for the analysis of gas mixtures spectra acquired with quartz-enhanced photoacoustic spectroscopy (QEPAS). Results obtained analyzing CO/N₂O and CH₄/C₂H₂/N₂O gas mixtures are presented. A comparison with standard MLR approach highlights a prediction errors reduction up to 5 times.

In this work, we report on the measurement of methane (CH₄) effective non-radiative relaxation rate in a mixture containing 1% of CH4 and 0.15% of water vapor in nitrogen, by using a set of custom quartz tuning forks (QTFs). The dependence of quartz-enhanced photoacoustic spectroscopy (QEPAS) peak signal and QTF quality factor as a function of operating pressure allowed the estimation of the radiation-to-sound conversion efficiency and, consequently, the calculation of the effective relaxation rate of the investigated gas mixture. We measured an effective relaxation rate of 3.2 ms·Torr, in good agreement with values reported in literature.

In oil and gas exploration and environmental monitoring fields is extremely important to rely on versatile and rugged trace gas sensors that can be mounted on remote-controlled unmanned vehicles to monitor dangerous areas inaccessible to a human operator. Thereby, a compact fiber-coupled dual-gas QEPAS sensor employing a custom tuning fork was designed and tested. Two distributed feedback pigtailed diode lasers emitting at 1654 nm and 1684 nm, for methane and ethane detection respectively, were also employed. The gas sensor was calibrated for ethane and methane trace detection and a minimum detection level of 18 parts per million and 570 parts per billion at 1 s integration time were respectively achieved. Methane detection in atmosphere was also performed.

We describe the development and the first characterization of a compact trace-gas sensor based on cantilever photoacoustic spectroscopy (CEPAS). The sensor was characterized in order to find the optimal operating parameters (pressure, molecule absorption line and laser modulated frequency). N₂O was selected as test molecule. A quality factor of 200 at 10 mbar of cell pressure were determined. Furthermore, the first test measurements showed a minimum detection level of hundreds of ppb with integration time of 30 ms.

With the mid-infrared spectral region (3 to 20 µm) home to the fundamental absorption peaks of most molecules, the region has come to be known as the “molecular-fingerprint” region and various technologies have evolved to perform the detection and quantification task. Popular technologies include cavity ring-down spectroscopy, tunable diode laser absorption spectroscopy and Fourier transform infrared spectroscopy; and parts-per-billion sensitivity is commonly achieved. But the size, weight and sensitive optics of these technologies tends to limit their use to the laboratory. Field applications, particularly airborne and handheld ones, demand compact on-chip technologies. Now, with the ability of quantum cascade lasers (QCLs) to provide narrow-band tunable room-temperature emission across the majority of the mid-infrared region, the move to on-chip technologies is enabled. In this work we seek to demonstrate the monolithic integration of QCL, quantum cascade detector (QCD) and passive components for an on-chip gas sensor around λ = 4.6 μm (an absorption peak of carbon monoxide). Since most efficient QCLs have been demonstrated in InP-based material, we use a lattice-matched InGaAs/InP platform to avoid the low-yield lossy costs of bonding, and work with a single-growth epitaxial structure. Light is coupled from the QCL active region downward to the passive InGaAs waveguide structure by a coupling taper; interaction with the analyte occurs on or near the passive structure and is subsequently passed to the QCD. Variations in design are investigated to compare sensitivity.

Gas sensing based on infrared absorption spectroscopy has attracted considerable attention owing to the rovibrational signatures of compounds of interest in the molecular fingerprint region. On-chip spectrometers are promising devices that unlike their on-chip commercially available counterparts offer sensing in portable applications. Carbon monoxide as one of the major air pollutants is dangerous even at very low concentrations. For real-time and precise detection of trace amounts of this gas we need a compact highly sensitive and selective sensor. In this paper, we design a grating array device in the InP/InGaAs platform for trace detection of carbon monoxide. The passive device consists of an InGaAs strip waveguide with InP as cladding, split-cascaded into an equally spaced array of 32 separate optical paths by y-junctions. At the output of each waveguide shallow etched subwavelength emitter gratings couple the light out. Light-analyte interaction occurs on top of the gratings as well as in free space. The device is optimized to operate at mid-IR wavelength of λ=4.6μm where the absorption peak of carbon monoxide is located. Using this structure, gas sensing is experimentally demonstrated down to a concentration of 10ppm. Feasibility of achieving lower limit of detection will be shown by design modifications. This device, can be simply integrated with QCL/QCD and be used for portable high sensitivity gas sensors.

By leveraging a three-dimensional device structure to decouple the optical and electronic areas of the detectors, Electron Injector (EI) technology has proven capable of surpassing the current performance of commercial short-wave infrared (SWIR) cameras. The improvement in sensitivity enabled by a nanoscale electronic area, however, comes at the cost of a decrease in quantum efficiency: the diffusion length of the minority carriers limits the area over which a photo-generated carrier can be collected at the small electron injector junction before recombining. This intrinsic limitation hinders the prospect of further improvements of the EI detector performance.

We here present a novel device architecture consisting of multiple nanoscale electron injectors connected to the same contact and constituting one individual pixel: by appropriate spacing of the injectors within the diffusion length of the photogenerated excess carriers, the fill factor of such multi-injector pixel can be considerably improved. The presented design was successfully implemented into an integrated FPA for SWIR imaging, showing excellent pixel yield, and a sensitivity of ~10 photons. While the high sensitivity is enabled by the small size of the 1μm injectors, the multi-injector design allows to achieve an area fill factor or ~20% of the 30x30μm pixel area, which is considerably higher than that of a single-injector design.

In summary, we demonstrate a highly sensitive SWIR FPA based on 1μm electron multi-injector design, which allows for a substantial improvement of the imager’s quantum efficiency and sensitivity.

Advances in laser diode technology enable the generation of eye-safe laser pulses with short pulse duration and high peak power. This opens up new opportunities for Light Detection and Ranging (LiDAR)-systems based on the direct time-of-flight (dTOF) principle because their range performance is mainly limited by the requirement of eye-safe laser pulse energy. Another limiting factor for dTOF LiDAR is the sensitivity to background noise. Shorter pulse width enables better parasitic light suppression inside the LiDAR system for improved performance in high background flux scenarios. With the improvements caused by using short laser pulses, new challenges emerge. Shorter pulse duration and limited achievable timing resolution of time discrimination circuits inside of dTOF detectors lead to histogram data distributions in which the laser originated time stamps can only fill few time bins. The time stamp histogram of the detected and clocked laser photons shows a sharp exponential decline. The slope is strongly dependent on the occurring laser event rate inside the system. In an extreme case, all laser generated events fall into one time bin. Because of the coarse discrete arrangement of those laser generated events, a need for new algorithmic approaches arises. This work illustrates the dependency between the occurring laser photon rate in the system and its distribution inside the measurement data. Influence of the time discrimination circuit's time bin width is discussed with regards to resulting histogram shapes.