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We introduce a framework for the design of photonic integrated laser sources for FMCW LiDAR, evaluating trade-offs in key laser metrics such as linewidth, chirp linearity and rate, based on laser-system co-design metrics. We review the main performance requirements for mid-range applications, with the goal of guiding ongoing research and commercial development.

Reconfigurable detectors with dynamically selectable sensing and readout modes are highly desirable for implementing edge computing as well as enabling advanced imaging techniques such as foveation. The concept of a camera system capable of simultaneous passive imaging and dynamic ranging in different regions of the detector is presented. Such an adaptive-autonomous detector with both spatial and temporal control requires programmable window of exposure (time frames), ability to switch between readout modes such as full-frame imaging and zero-suppressed data, modification of the number of pixel data bits and independent programmability for distinct detector regions. In this work, a method is presented for seamlessly changing time frames and readout modes without data corruption while still ensuring that the data acquisition system (DAQ) does not need to stop and resynchronize at each change of setting, thus avoiding significant dead time. Data throughput is maximized by using a minimum unique data format, rather than lengthy frame headers, to differentiate between consecutive frames. A data control and transmitter (DCT) synchronizes data transfer from the pixel to the periphery, reconfigures the data to transmit it serially off-chip, while providing optimized decision support based on a DAQ definable mode. Measurements on a test structure demonstrate that the DCT can operate at 1 GHz in a 65 nm LP CMOS process.

Adult patients with asthma often access the emergency department (ED) for the management of exacerbations or uncontrolled symptoms. Sometimes the first diagnosis of asthma occurs right in the ED. In the last couple of years, the COVID-19 pandemic spread around the world, causing an acute respiratory syndrome named SARS-CoV-2, characterized mainly by respiratory symptoms, such as cough and shortness of breath, in addition to fever. This clinical pattern partially overlaps with that caused by asthma, thus generating confusion in terms of diagnosis and management. It is also unclear whether asthma may be associated with a worse prognosis in COVID-19 infection. This expert opinion paper provides specific recommendations to ease the challenges related to adult patients with asthma admitted to the ED during the COVID-19 pandemic, with particular reference to diagnosis and treatment. Moreover, it provides well-defined indications to guide decisions on discharge, hospital admission, as well as follow-up. A panel of experts composed of emergency medicine physicians, pulmonologists and allergologists discussed, voted and approved all the recommendations.

Erbium (Er) is an attractive gain medium for amplifiers and lasers due to its long excited-state lifetime, low noise and nonlinearity, and temperature stability. Recently developed ultra-low-loss Si 3 N 4 photonic integrated circuits combined with Er ion implantation have enabled high-performance on-chip Er lasers, but manufacturing scalability has been limited by the high 2 MeV implantation required for tightly confined 700-nm-thick waveguides. Here we demonstrate the first fully wafer-scale, foundry-compatible Er-doped Si 3 N 4 tunable lasers by using 200-nm-thick waveguides, reducing implantation energy to below 500 keV and enabling usage of 300-mm industrial implanters. The low-confinement design also improves laser performance and output power. We achieve 91 nm tuning across the C- and L-bands, 47.6 mW fiber-coupled output power, and a 78.5 Hz intrinsic linewidth. Devices operate up to 125 ∘ C and show less than 15 MHz drift over 6 hours, enabling scalable  high-performance Er-doped lasers for integrated photonics.

In this thesis I present the development of high-sensitivity infrared photodetectors with internal gain based on a phototransistor architecture. This class of devices finds use in a plethora of applications ranging from imaging to coherent detection and data links. The internal amplification of these phototransistors is crucial for both low-light and high-density applications, since it enables to amplify a faint signal without the need for bulky low-noise amplification stages. Nonetheless, designing for optimal performance is not as simple as maximizing the gain, and it requires a comprehensive system-aware approach that takes into account the trade-offs between all the design parameters in the desired operating conditions. While most of the results presented in this work are from short-wave infrared phototransistors based on III-V semiconductors, the physical insight and design approach developed are applicable to a wide range of photodetectors, including, for example those based on low-dimensional materials.We employed phototransistors based on different type-I InGaAs/InP epitaxial structures for fabricating highly sensitive imagers in the short-wave infrared. By leveraging a 3D-engineered phototransistor architecture called Electron Injector, we achieved a significant performance improvement with respect to planar structures. Specifically, we experimentally and analytically demonstrated that shrinking the size of the base junctions in order to reduce its capacitance enables to improve the sensitivity of the phototransistors, which can theoretically achieve single-photon sensitivity at room temperature with nanoscale injector diameters. A few dozens of 320 X 256-pixel focal planar arrays were successfully fabricated, allowing the testing of over a million photodetectors to explore the effects of different geometrical and epitaxial designs, as well as fabrication and passivation techniques, with good statistical relevance. This continuous feedback between design and testing enabled a constant improvement of both the performance and the physical understanding of the devices, culminating in the demonstration of an imager operating at 500 fps, with a large number of pixels exhibiting an internal sensitivity below 10 photons.However, the requirements for an attractive imager are not limited to its internal sensitivity, but also include a high quantum efficiency and a good pixel uniformity. Because reducing the size of the pixel photodetector structure detrimentally affects both of these, we concomitantly developed strategies to mitigate this effect. Specifically, we implemented a process for the monolithic integration of immersion lens array on the imager substrate, which enabled to focus the incident light in a 6μm spot, improving the quantum efficiency by a factor of 7. In parallel, we developed a technique for the fabrication and hybridization of multiple parallel injectors within the same pixel, improving the fill factor and the pixel uniformity and operability without excessive increase in the total device capacitance.With appropriate device design, the Electron Injector architecture can be leveraged to fabricate high-speed photodetectors for optical interconnects and coherent detection applications. For this purpose, we designed a series of phototransistor epitaxial structures that employ a type-II band alignment in an Sb-based layer to reduce the total junction capacitance and thereby improve the gain-bandwidth product. In addition, this type-II band alignment helps contrast the onset of base pushout at high current densities (Kirk effect), allowing to decrease the size of the detectors without sacrificing the gain. This phototransistor design enabled the demonstration of an optical receiver with record-high gain-bandwidth product over 270 GHz and energy consumption of 11 fJ/bit, fully-CMOS-compatible and integrated with waveguides and grating couplers. This device reaches data bit rate comparable with the highest reported for integrated receivers, while providing a significantly better energy efficiency and spatial footprint.Finally, I show that these design strategies can be readily extended to photodetectors that employ the same transistor gain mechanisms, such as most photodetectors based on low-dimensional materials. Similarly to phototransistors, the sensitivity of this class of novel detectors is ultimately related to their capacitance. Here, low-dimensional materials have a clear advantage over bulk semiconductors, since small sizes and low-dimensional charge screening enable extremely small junction capacitances. Moreover, this capacitance can be estimated from external photoresponse measurements, providing a straightforward approach to extract the device sensitivity. This approach can guide the design of low-dimensional photodetectors to effectively leverage their unique structural advantage and achieve sensitivities that can exceed, in principle, that of the best existing photodetectors.

We studied the predictive value of the PaO2/FiO2 ratio for classifying COVID-19-positive patients who will develop severe clinical outcomes. One hundred fifty patients were recruited and categorized into two distinct populations (“A” and “B”), according to the indications given by the World Health Organization. Patients belonging the population “A” presented with mild disease not requiring oxygen support, whereas population “B” presented with a severe disease needing oxygen support. The AUC curve of PaO2/FiO2 in the discovery cohort was 0.838 (95% CI 0.771–0.908). The optimal cut-off value for distinguishing population “A” from the “B” one, calculated by Youden’s index, with sensitivity of 71.79% and specificity 85.25%, LR+4.866, LR−0.339, was < 274 mmHg. The AUC in the validation cohort of 170 patients overlapped the previous one, i.e., 0.826 (95% CI 0.760–0.891). PaO2/FiO2 ratio < 274 mmHg was a good predictive index test to forecast the development of a severe respiratory failure in SARS-CoV-2-infected patients. Moreover, our work highlights that PaO2/FiO2 ratio, compared to inflammatory scores (hs-CRP, NLR, PLR and LDH) indicated to be useful in clinical managements, results to be the most reliable parameter to identify patients who require closer respiratory monitoring and more aggressive supportive therapies. Clinical trial registration: Prognostic Score in COVID-19, prot. NCT04780373 https://clinicaltrials.gov/ct2/show/NCT04780373 (retrospectively registered).

Increasing the efficiency and reducing the footprint of on-chip photodetectors enables dense optical interconnects for emerging computational and sensing applications. Avalanche photodetectors (APD) are currently the dominating on-chip photodetectors. However, the physics of avalanche multiplication leads to low energy efficiencies and prevents device operation at a high gain, due to a high excess noise, resulting in the need for electrical amplifiers. These properties significantly increase power consumption and footprint of current optical receivers. In contrast, heterojunction phototransistors (HPT) exhibit high efficiency and very small excess noise at high gain. However, HPT's gain-bandwidth product (GBP) is currently inferior to that of APDs at low optical powers. Here, we demonstrate that the type-II energy band alignment in an antimony-based HPT results in a significantly smaller junction capacitance and higher GBP at low optical powers. We used a CMOS-compatible heterogeneous integration method to create compact optical receivers on silicon with an energy efficiency that is about one order of magnitude higher than that of the best reported integrated APDs on silicon at a similar GBP of 270 GHz. Bitrate measurements show data rate spatial density above 800 Tbps per mm2, and an energy-per-bit consumption of only 6 fJ/bit at 3 Gbps. These unique features suggest new opportunities for creating highly efficient and compact on-chip optical receivers based on devices with type-II band alignment.

Frequency-agile lasers operating in the ultraviolet-to-blue spectral range (360-480 nm) are critical enablers for a wide range of technologies, including free-space and underwater optical communications, optical atomic clocks, and Rydberg-atom-based quantum computing platforms. Integrated photonic lasers offer a compelling platform for these applications by combining low-noise performance with fast frequency tuning in a compact, robust form factor through monolithic integration. However, realizing such lasers in the blue spectral range remains challenging due to limitations in current semiconductor materials and photonic integration techniques. Here, we report the first demonstration of a photonic integrated blue laser at around 461 nm, which simultaneously achieves frequency agility and low phase noise. This implementation is based on the hybrid integration of a gallium nitride-based laser diode, which is self-injection locked to a high-Q microresonator fabricated on a low-loss silicon nitride photonic platform with 0.4 dB/cm propagation loss. The laser exhibits a sub-30 kHz linewidth and delivers over 1 mW of optical output power. In addition, aluminum nitride piezoelectric actuators are monolithically integrated onto the photonic circuitry to enable high-speed modulation of the refractive index, and thus tuning the laser frequency. This enables mode-hop-free laser linear frequency chirps with excursions up to 900 MHz at repetition rates up to 1 MHz, with tuning nonlinearity below 2%. We showcase the potential applications of this integrated laser in underwater communication and coherent aerosol sensing experiments.

Frequency-agile lasers that can simultaneously feature low noise characteristics as well as fast mode hop-free frequency tuning are keystone components for applications ranging from frequency modulated continuous wave (FMCW) LiDAR, to coherent optical communication and gas sensing. The hybrid integration of III-V gain media with low-loss photonic integrated circuits (PICs) has recently enabled integrated lasers with faster tuning and lower phase noise than the best legacy systems, including fiber lasers. In addition, lithium niobate on insulator (LNOI) PICs have enabled to exploit the Pockels effect to demonstrate self-injection locked hybrid lasers with tuning rates reaching peta-hertz per second. However, Pockels-tunable laser archetypes relying on high-Q optical microresonators have thus far only achieved limited output powers, are difficult to operate and stabilize due to the dynamics of self-injection locking, and require many analog control parameters. Here, we overcome this challenge by leveraging an extended distributed Bragg reflector (E-DBR) architecture to demonstrate a simple and turn-key operable frequency-agile Pockels laser that can be controlled with single analog operation and modulation inputs. Our laser supports a continuous mode hop-free tuning range of over 10 GHz with good linearity and flat actuation bandwidth up to 10 MHz, while achieving over 15 mW in-fiber output power at 1545 nm and kHz-level intrinsic linewidth, a combination unmet by legacy bulk lasers. This hybrid laser design combines an inexpensive reflective semiconductor optical amplifier (RSOA) with an electro-optic DBR PIC manufactured at wafer-scale on a LNOI platform. We showcase the performance and flexibility of this laser in proof-of-concept coherent optical ranging (FMCW LiDAR) demonstration, achieving a 4 cm distance resolution and in a hydrogen cyanide spectroscopy experiment.