Integration of MEMS IR detectors with MIR waveguides for sensing applications

Enhanced Infrared Emission from Rare-Earth Double Perovskite Embedded in Fluoride Glass with Different B-Site Cation Structures for N2O Sensing in a Hydrogen Stream

Rare-earth halide perovskites can lead to a distinctive infrared luminescence. However, achieving tunable infrared luminescence presents significant challenges. The leptons of their f-f ubiquitous forbidden ring influence the energy level splitting, and the substitution of atoms in perovskite by rare-earth ions also distorts the crystal structure. The research on achieving tunable mid-infrared emission by altering the crystal structure of rare-earth perovskites is limited. The crystal structure can be modified by changing the matrix B-site cation for a series of Cs2MIn1-xHoxCl6-ZBLAY (M = Na and Ag) rare-earth perovskites coated with a glass matrix that have been prepared. On this basis, we revealed the local electronic structure of Cs2MInCl6 (M = Na and Ag) perovskites and proposed an effective charge transfer strategy to achieve an efficient infrared emission of Ho3+ ions at 1.2 and 2.87 μm. The contribution of Na s and Na p is minor in Cs2NaIn1-xHoxCl6, which leads to poor interactions between Na+ and Cl- and promotes charge transfer of Ho3+-Cl- in the [HoCl6]3- octahedron. The charge transfer mechanism of Cs2NaInCl6:Ho3+-Cl- is validated by executing density functional theory calculations. Furthermore, a device that identifies N2O gas levels in hydrogen energy was built using the Cs2NaIn1-xHoxCl6-ZBLAY sample. These findings provide a new perspective on how to achieve effective infrared emission.

Evaluation of flip-chip bonding electrical connectivity for ultra-large array infrared detector

Flip-chip bonding is a key technology for infrared focal plane array (IRFPA) detectors. Due to the high cost of device preparation, the ultra-large array infrared detector cannot be directly used for the flip-chip bonding experiment, and the connectivity rate cannot be measured. To evaluate the flip-chip bonding process, a test device which has the same interconnecting structure as current IRFPA detectors is proposed. Indium bumps are electrically extracted to test electrodes. Electrical measurements were performed to characterize the connection and adhesion of the indium bumps and to calculate the connectivity rate. The electrical connectivity characteristics of the test devices correspond to the observation results of the indium bump extrusion, effectively detecting the interconnecting anomalies such as disconnection, adhesion, overall misalignment, etc., and verifying the feasibility of the test method. The test device has similar multi-layer components and thermal properties as HgCdTe infrared detector for process evaluation and post-processing experiment. The connectivity rate of the test device is up to 100%, and remains above 99% after thermal recycle experiment. The contact resistance of the interconnecting structure is calculated to be about 31.84 Ω based on the test results.

Artificial intelligence enhanced sensors - enabling technologies to next-generation healthcare and biomedical platform

The fourth industrial revolution has led to the development and application of health monitoring sensors that are characterized by digitalization and intelligence. These sensors have extensive applications in medical care, personal health management, elderly care, sports, and other fields, providing people with more convenient and real-time health services. However, these sensors face limitations such as noise and drift, difficulty in extracting useful information from large amounts of data, and lack of feedback or control signals. The development of artificial intelligence has provided powerful tools and algorithms for data processing and analysis, enabling intelligent health monitoring, and achieving high-precision predictions and decisions. By integrating the Internet of Things, artificial intelligence, and health monitoring sensors, it becomes possible to realize a closed-loop system with the functions of real-time monitoring, data collection, online analysis, diagnosis, and treatment recommendations. This review focuses on the development of healthcare artificial sensors enhanced by intelligent technologies from the aspects of materials, device structure, system integration, and application scenarios. Specifically, this review first introduces the great advances in wearable sensors for monitoring respiration rate, heart rate, pulse, sweat, and tears; implantable sensors for cardiovascular care, nerve signal acquisition, and neurotransmitter monitoring; soft wearable electronics for precise therapy. Then, the recent advances in volatile organic compound detection are highlighted. Next, the current developments of human-machine interfaces, AI-enhanced multimode sensors, and AI-enhanced self-sustainable systems are reviewed. Last, a perspective on future directions for further research development is also provided. In summary, the fusion of artificial intelligence and artificial sensors will provide more intelligent, convenient, and secure services for next-generation healthcare and biomedical applications.

Larger-Than-Unity External Optical Field Confinement Enabled by Metamaterial-Assisted Comb Waveguide for Ultrasensitive Long-Wave Infrared Gas Spectroscopy

Nanophotonic waveguides that implement long optical pathlengths on chips are promising to enable chip-scale gas sensors. Nevertheless, current absorption-based waveguide sensors suffer from weak interactions with analytes, limiting their adoptions in most demanding applications such as exhaled breath analysis and trace-gas monitoring. Here, we propose an all-dielectric metamaterial-assisted comb (ADMAC) waveguide to greatly boost the sensing capability. By leveraging large longitudinal electric field discontinuity at periodic high-index-contrast interfaces in the subwavelength grating metamaterial and its unique features in refractive index engineering, the ADMAC waveguide features strong field delocalization into the air, pushing the external optical field confinement factor up to 113% with low propagation loss. Our sensor operates in the important but underdeveloped long-wave infrared spectral region, where absorption fingerprints of plentiful chemical bonds are located. Acetone absorption spectroscopy is demonstrated using our sensor around 7.33 μm, showing a detection limit of 2.5 ppm with a waveguide length of only 10 mm.

Advanced Waveguide Based LOC Biosensors: A Minireview

This mini review features contemporary advances in mid-infrared (MIR) thin-film waveguide technology and on-chip photonics, promoting high-performance biosensing platforms. Supported by recent developments in MIR thin-film waveguides, it is expected that label-free assimilated MIR sensing platforms will soon supplement the current sensing technologies for biomedical diagnostics. The state-of-the-art shows that various types of waveguide material can be utilized for waveguide spectroscopic measurements in MIR. However, there are challenges to integrating these waveguide platforms with microfluidic/Lab-on-a-Chip (LOC) devices, due to poor light-material interactions. Graphene and its analogs have found many applications in microfluidic-based LOC devices, to address to this issue. Graphene-based materials possess a high conductivity, a large surface-to-volume ratio, a smaller and tunable bandgap, and allow easier sample loading; which is essential for acquiring precise electrochemical information. This work discusses advanced waveguide materials, their advantages, and disease diagnostics with MIR thin-film based waveguides. The incorporation of graphene into waveguides improves the light-graphene interaction, and photonic devices greatly benefit from graphene's strong field-controlled optical response.

Integrated Nanophotonic Waveguide-Based Devices for IR and Raman Gas Spectroscopy

On-chip devices for absorption spectroscopy and Raman spectroscopy have been developing rapidly in the last few years, triggered by the growing availability of compact and affordable tunable lasers, detectors, and on-chip spectrometers. Material processing that is compatible with mass production has been proven to be capable of long low-loss waveguides of sophisticated designs, which are indispensable for high-light-analyte interactions. Sensitivity and selectivity have been further improved by the development of sorbent cladding. In this review, we discuss the latest advances and challenges in the field of waveguide-enhanced Raman spectroscopy (WERS) and waveguide infrared absorption spectroscopy (WIRAS). The development of integrated light sources and detectors toward miniaturization will be presented, together with the recent advances on waveguides and cladding to improve sensitivity. The latest reports on gas-sensing applications and main configurations for WERS and WIRAS will be described, and the most relevant figures of merit and limitations of different sensor realizations summarized.

Heterogeneous Wafer Bonding Technology and Thin-Film Transfer Technology-Enabling Platform for the Next Generation Applications beyond 5G

Wafer bonding technology is one of the most effective methods for high-quality thin-film transfer onto different substrates combined with ion implantation processes, laser irradiation, and the removal of the sacrificial layers. In this review, we systematically summarize and introduce applications of the thin films obtained by wafer bonding technology in the fields of electronics, optical devices, on-chip integrated mid-infrared sensors, and wearable sensors. The fabrication of silicon-on-insulator (SOI) wafers based on the Smart CutTM process, heterogeneous integrations of wide-bandgap semiconductors, infrared materials, and electro-optical crystals via wafer bonding technology for thin-film transfer are orderly presented. Furthermore, device design and fabrication progress based on the platforms mentioned above is highlighted in this work. They demonstrate that the transferred films can satisfy high-performance power electronics, molecular sensors, and high-speed modulators for the next generation applications beyond 5G. Moreover, flexible composite structures prepared by the wafer bonding and de-bonding methods towards wearable electronics are reported. Finally, the outlooks and conclusions about the further development of heterogeneous structures that need to be achieved by the wafer bonding technology are discussed.

Design and Simulation Investigation of Si3N4 Photonics Circuits for Wideband On-Chip Optical Gas Sensing around 2 µm Optical Wavelength

We theoretically explore the potential of Si₃N₄ on SiO₂ waveguide platform toward a wideband spectroscopic detection around the optical wavelength of 2 μm. The design of Si₃N₄ on SiO₂ waveguide architectures consisting of a Si₃N₄ slot waveguide for a wideband on-chip spectroscopic sensing around 2 μm, and a Si₃N₄ multi-mode interferometer (MMI)-based coupler for light coupling from classical strip waveguide into the identified Si₃N₄ slot waveguides over a wide spectral range are investigated. We found that a Si₃N₄ on SiO₂ slot waveguide structure can be designed for using as optical interaction part over a spectral range of interest, and the MMI structure can be used to enable broadband optical coupling from a strip to the slot waveguide for wideband multi-gas on-chip spectroscopic sensing. Reasons for the operating spectral range of the system are discussed.

Figures of merit for mid-IR evanescent-wave absorption sensors and their simulation by FEM methods

Proper optimization of a photonic structure for sensing applications is of extreme importance for integrated sensor design. Here we discuss on the definition of suitable parameters to determine the impact of photonic structure designs for evanescent-wave absorption sensors on the achievable resolution and sensitivity. In particular, we analyze the most widespread quantities used to classify photonic structures in the context of sensing, namely the evanescent-field ratio (or evanescent power factor) and the confinement factor Γ. We show that, somewhat counterintuitively, the confinement factor is the only parameter that can reliably describe the absorption of the evanescent-field in the surrounding medium, and, by quantifying the discrepancy between the two parameters for a set of realistic photonic structures, we demonstrate that using the evanescent-field ratio can lead to a wrong classification of the performance of different structures for absorption sensing. We finally discuss the most convenient simulation strategies to retrieve the confinement factor by FEM simulations.

Interband Cascade Photonic Integrated Circuits on Native III-V Chip

We describe how a midwave infrared photonic integrated circuit (PIC) that combines lasers, detectors, passive waveguides, and other optical elements may be constructed on the native GaSb substrate of an interband cascade laser (ICL) structure. The active and passive building blocks may be used, for example, to fabricate an on-chip chemical detection system with a passive sensing waveguide that evanescently couples to an ambient sample gas. A variety of highly compact architectures are described, some of which incorporate both the sensing waveguide and detector into a laser cavity defined by two high-reflectivity cleaved facets. We also describe an edge-emitting laser configuration that optimizes stability by minimizing parasitic feedback from external optical elements, and which can potentially operate with lower drive power than any mid-IR laser now available. While ICL-based PICs processed on GaSb serve to illustrate the various configurations, many of the proposed concepts apply equally to quantum-cascade-laser (QCL)-based PICs processed on InP, and PICs that integrate III-V lasers and detectors on silicon. With mature processing, it should become possible to mass-produce hundreds of individual PICs on the same chip which, when singulated, will realize chemical sensing by an extremely compact and inexpensive package.

Multifunctional mid-infrared photonic switch using a MEMS-based tunable waveguide coupler

We demonstrate a multifunctional photonic switch on silicon-on-insulator platform operating at the mid-infrared wavelength range (3.85-4.05 µm) using suspended waveguides with sub-wavelength cladding and a micro-electro-mechanical systems (MEMS) tunable waveguide coupler. Leveraging the flip-chip bonding technology, a top wafer acting as the electrode is assembled above the silicon-on-insular wafer to enable the electrostatic actuation. Experimental characterizations for the functions of the proposed device include (1) an optical attenuator with 25 dB depth using DC voltage actuation, (2) a 1×2 optical switch with response time of 8.9 µs and -3dB bandwidth up to 127 kHz using AC voltage actuation, and (3) an on-chip integrated light chopper with the comparable performance of a commercial rotating disc light chopper.