1,254 research outputs found
Toward an active CMOS electronics-photonics platform based on subwavelength structured devices
The scaling trend of microelectronics over the past 50 years, quantified by Moore’s Law, has faced insurmountable bottlenecks, necessitating the use of optical communication with its high bandwidth and energy efficiency to further improve computing performance.
Silicon photonics, compatible with CMOS platform manufacturing, presents a promising means to achieve on-chip optical links, employing highly sensitive microring resonator devices that demand electronic feedback and control due to fabrication variations. Achieving the full potential of both technologies requires tight integration to realize the ultimate benefits of both realms of technology, leading to the convergence of microelectronics and photonics.
A promising approach for achieving this convergence is the monolithic integration of electronics and photonics on CMOS platforms. A critical milestone was reached in 2015 with the demonstration of the first microprocessor featuring photonic I/O (Chen et al, Nature 2015), accomplished by integrating transistors and photonic devices on a single chip using a monolithic CMOS silicon-on-insulator (SOI) platform (GlobalFoundries 45RFSOI, 45 nm SOI process) without process modifications, thus known as the "zero-change" approach. This dissertation focuses on leveraging the fabrication capabilities of advanced monolithic electronic-photonic 45 nm CMOS platforms, specifically high-resolution lithography and small feature size doping implants, to realize photonic devices with subwavelength features that could potentially provide the next leap in integrated optical links performance, beyond microring resonator based links.
Photonic crystal (PhC) nanobeam cavities can support high-quality resonance modes while confining light in a small volume, enhancing light-matter interactions and potentially enabling ultimate efficiencies in active devices such as modulators and photodetectors. However, PhC cavities have been overshadowed by microring resonators due to two challenges. First, their fabrication demands high lithography resolution, which excludes most standard SOI photonic platforms as viable options for creating these devices. Secondly, the standing-wave nature of PhC nanobeam cavities complicates their integration into wavelength-division multiplexing (WDM) optical links, causing unwanted reflections when coupled evanescently to a bus waveguide.
In this work, we present PhC nanobeam cavities with the smallest footprint, largest intrinsic quality factor, and smallest mode volume to be demonstrated to date in a monolithic CMOS platform. The devices were fabricated in a 45 nm monolithic electronics–photonics CMOS platform optimized for silicon photonics, GlobalFoundries 45CLO, exhibiting a quality factor in excess of 100,000 the highest among fully cladded PhC nanobeam cavities in any SOI platform. Furthermore to eliminate reflections, we demonstrate an approach using pairs of PhC nanobeam cavities with opposite spatial mode symmetries to mimic traveling-wave-like ring behavior, enabling efficient and seamless WDM link integration. This concept was extended to realize a reflectionless microring resonator unit with two microrings operating as standing-wave cavities. Using this scheme with standing-wave microring resonators could lead to an optimum geometry for microring modulators with interdigitated p-n junctions in terms of modulation efficiency in a manner that allows for straightforward WDM cascading.
This work also presents the first demonstration of resonant-structure-based modulators in the GlobalFoundries 45CLO platform. We report the first-ever demonstration of a PhC modulator in a CMOS platform, featuring a novel design with sub-wavelength contacts on one side allowing it to benefit from the "reflection-less"' architecture. Additionally, we also report the first demonstration of microring modulators. The most efficient devices exhibited electro-optical bandwidths up to 30 GHz, and 25 Gbps non-return-to-zero (NRZ) on-off-keyed (OOK) modulation with 1 dB insertion loss and 3.1 dB extinction ratio.
Finally, as the complexity of silicon photonic systems-on-a-chip (SoC) increases to enable new applications such as low-energy data links, quantum optics, and neuromorphic computing, the need for in-situ characterization of individual components becomes increasingly important. By combining Near-field scanning optical microscopy (NSOM) with a flip-chip post-processing technique, this dissertation demonstrates a method to non-invasively perform NSOM scans of a photonic device within a large-scale CMOS-photonic circuit, without interfering with the performance and packaging of the photonics and electronics, making it a valuable tool for future development of high performance photonic circuits and systems
Pulsed Free Space Photonic Vector Network Analyzers
Terahertz (THz) radiation (0.1–10 THz) has demonstrated great significance in a wide range of interdisciplinary applications due to its unique properties such as the capacity to penetrate optically opaque materials without ionizing effect, superior spatial resolution as compared to the microwave domain for imaging or ability to identify a vast array of molecules using THz fingerprinting. Advancements in generation and detection techniques, as well as the necessities of application-driven research and industry, have created a substantial demand for THz-range
devices and components. However, progress in the development of THz components is hampered by a lack of efficient and affordable characterization systems, resulting in limited development in THz science and technology.
Vector Network Analyzers (VNAs) are highly sophisticated well-established characterization instruments in the microwave bands, which are now employed in the lower end of the THz spectrum (up to 1.5 THz) using frequency extender modules. These modules are extremely expensive, and due to the implementation of hollow metallic waveguides for their configuration, they are narrowband, requiring at least six modules to achieve a frequency coverage of 0.2–1.5 THz. Moreover, they are susceptible to problems like material losses, manufacturing and alignment tolerances etc., making them less than ideal for fast, broadband investigation.
The main objective of this thesis is to design a robust but cost-effective characterization system based on a photonic method that can characterize THz components up to several THz in a single configuration. To achieve this, we design architectures for the Photonic Vector Network Analyzer (PVNA) concept, incorporating ErAs:In(Al)GaAs-based photoconductive sources and ErAs:InGaAs-based photoconductive receivers, driven with a femtosecond pulsed laser operating at 1550 nm. The broadband photonic devices replace narrowband electronic ones in order to record the Scattering (S)-parameters in a free space configuration. Corresponding calibration and data evaluation methods are also developed. Then the PVNAs are configured, and their capabilities are validated by characterizing various THz components, including a THz isolator, a
distributed Bragg Reflector, a Split-Ring Resonator array and a Crossed-Dipole Resonator (CDR) array, in terms of their S-parameters. The PVNAs are also implemented to determine the complex refractive index or dielectric permittivity and physical thickness of several materials in the THz range. Finally, we develop an ErAs:In(Al)GaAs-based THz transceiver and implement it in a PVNA configuration, resulting in a more compact setup that is useful for industrial applications. The feasibility of such systems is also verified by characterizing several THz components.
The configured systems achieve a bandwidth of more than 2.5 THz, exceeding the maximum attainable frequency of the commercial Electronic Vector Network Analyzer (EVNA) extender modules. For the 1.1-1.5 THz band, the dynamic range of 47-35 dB (Equivalent Noise Bandwidth (ENBW) = 9.196 Hz) achieved with the PVNA is comparable to the dynamic range of 45-25 dB (ENBW = 10 Hz) of the EVNA. Both amplitude and phase of the S-parameters, determined by the configured PVNAs, are compared with simulations or theoretical models and showed excellent agreement. The PVNA could discern multi-peak and narrow resonance characteristics despite its lower spectral resolution (∼3-7 GHz) compared to the EVNA. By accurately determining the S-parameters of multiple THz components, the transceiver-based PVNA also demonstrated its exceptional competence.
With huge bandwidth and simpler calibration techniques, the PVNA provides a potential solution to bridge the existing technological gap in THz-range characterization systems and offers a solid platform for THz component development, paving the way for more widespread application of THz technologies in research and industry
The 2023 wearable photoplethysmography roadmap
Photoplethysmography is a key sensing technology which is used in wearable devices such as smartwatches and fitness trackers. Currently, photoplethysmography sensors are used to monitor physiological parameters including heart rate and heart rhythm, and to track activities like sleep and exercise. Yet, wearable photoplethysmography has potential to provide much more information on health and wellbeing, which could inform clinical decision making. This Roadmap outlines directions for research and development to realise the full potential of wearable photoplethysmography. Experts discuss key topics within the areas of sensor design, signal processing, clinical applications, and research directions. Their perspectives provide valuable guidance to researchers developing wearable photoplethysmography technology
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
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Extraordinary acoustic transmission via supercoupling and self-interference cancellation
Supercoupling is a widely researched topic in wave engineering, which has been used to build coupling channels that can, in principle, support total transmission and complete phase uniformity, independent of the length of the channel. This has generally been accomplished by employing dispersion in media that display a near-zero index. In the field of acoustics, prior works have required the presence of periodic embedded resonators, such as membranes or Helmholtz resonators, in order to observe near-zero properties. Here it is shown, theoretically and experimentally, that supercoupling can occur in an acoustic channel without the presence of embedded resonators. A compressibility-near-zero (CNZ) acoustic channel was observed to show remarkable properties analogous to those found in electromagnetics. Furthermore, these principles are employed to develop an acoustic power divider, which takes advantage of the CNZ properties of the channel to also exhibit phase invariance at the output. In the next section, another extraordinary acoustic transmission phenomenon is explored, regarding the potential for sending and receiving from a single acoustic transducer at the same time and at the same frequency. This is made possible through an electrical circuit that is designed to cancel self-interfering signals in acoustic measurement systems. Systems that employ self-interference cancellation (SIC) are often referred to as simultaneous transmit and receive (STAR) or in-band full duplex (IBFD) systems, which have recently enabled sending and receiving of Radio Frequency (RF) signals at the same time and at the same frequency. This has led to commercialization efforts with the promise of doubling the throughput of traditional radio systems including Wi-Fi and 5G cellular communications. Prior to these advances, researchers in vibration control explored self-sensing actuator systems, also referred to as sensoriactuators or sensorless control systems. Inspired by these developments, these approaches are combined and extended to explore STAR functionality in an acoustic measurement system. First, self-interference cancellation (SIC) is applied to time-domain measurements to demonstrate the potential for a practical, single-transducer ultrasonic nondestructive evaluation (NDE) system to measure echo returns while it is actively transmitting at the same frequency. Theoretical models and experimental results are presented and discussed.Electrical and Computer Engineerin
Studies of Molecular Precursors Used in FEBID Fabrication of Nanostructures
The adoption of nanotechnology is increasingly important in many aspects of our daily life influencing the clothes we wear and most of the electronic devices we use while also underpinning the development of drugs and medical techniques that we will need at some point in our lives. The methods by which nanoscale devices are fabricated is changing from a 'top down' etching based procedure to a 'bottom up' molecule by molecule deposition and assembly. The focus of the present research is the development, design, and analysis of new precursors for focused electron beam induced deposition (FEBID) and extreme ultraviolet nanolithography (EUVL) through a large pool of experimental and computational resources. The research is divided into two areas: gas - phase analysis of precursors (largely used for fragment and radicals' analysis, and molecular design) and surface and deposition science (physical deposition of precursors, simulation analysis of surface - molecule interactions and characterization of deposition processes to obtain optimal process parameters for molecular structures). It is necessary to collect data such as cross sections of electron - molecule interactions e.g., dissociative ionization (DI) and dissociative electron attachment (DEA) to provide accurate simulations that can be used to improve the FEBID and EUVL while understanding surface processes such as molecular absorption and diffusion to determine the structure and purity of the nanostructures formed by these methods. The objective of this thesis is to provide a gas - phase and deposition analysis of potential and widely used precursors for FEBID and EUVL at the nanoscale. To achieve this the experimental technique of velocity sliced map imaging (VsMI) was used in conjunction with theoretical tools such as density functional theory (DFT) simulations using Gaussian 16 software and evaluation of cross-section data for molecular dissociation at low electron energies of 0 - 20 eV using Quantemol-N. Results of the gas - phase analysis of negative ionic fragments formed by DEA and DI with their appearance, dissociation and ionization energies, angular distributions and kinetic energies, cross-sections for DEA fragmentation at low energy and excited states calculations at values up to 10 eV are presented. These results are used as the inputs to the models of the FEBID processes. The electronic, structural, and kinetic properties of several FEBID precursors are explored, and FEBID method used to create nanostructures using a Zeiss MeRiT SEM with GEMINI column operated at 20 kV. Analysis of the deposits was performed using EDX and atomic force microscopy (AFM) analysis as well as electron stimulated desorption (ESD) and temperature programmed desorption (TPD). Complementary simulations of the dynamics of processes at the surface were studied using MBN Explorer and surface - molecule interactions with great results in simulating the deposition process of islands and structures (results presented in Chapter 8)
Thermo-Electro-Optical Properties of Disordered Nanowire Networks
Metallic nanowire networks are promising candidates for next-generation transparent conductors, owing to their exceptional electrical and thermal conductivity, high optical transparency, and mechanical flexibility. A nanowire network is a disordered arrangement of nanowires that exhibits no discernible long-range order or periodicity. Previous studies have placed significant emphasis on the individual analysis of electrical resistance, optical transmission, and thermal conduction in diverse network materials. Nonetheless, insufficient focus has been devoted to comprehending the relationship between the multiple extrinsic and intrinsic variables that characterize a disordered nanowire network (or an ensemble of them) and the trade-offs that arise when investigating the system response trio of namely electrical/ optical/thermal natures. This thesis presents a comprehensive computational study that exclusively employs theoretical and numerical models to examine the thermoelectric and optical characteristics of two types of disordered metallic nanowire networks: (i) junction-based random nanowire networks and (ii) seamless random nanowire networks. The raw materials that compose their nanowires are metals namely, silver, gold, copper, and aluminium and we used a variety of computational tools to obtain prominent physical quantities that infer the network’s performance such as sheet (electrical) resistance, optical transmission, and temperature variation. A range of adjustable parameters, including those pertaining to geometrical structure in device design, have been systematically tuned in order to conduct a figure of merit analysis with respect to thermal and electrical conduction, and optical transmission of the network materials. Moreover, we obtained local current and temperature mappings that detail the conduction mechanisms used by the networks to propagate signals through their disordered skeleton. We verified that, under certain conditions, junction-based and seamless nanowire networks fall into the same temperature distribution mechanisms that can be generally described with Weibull probability density functions. This study offers valuable insights into the electrical/optical/thermal performance of disordered nanowire networks prone to transparent conductor applications
Efficient wireless coverage of in-building environments with low electromagnetic impact
The city of tomorrow is a major integrating stake, which crosses a set of major broad spectrum domains. One of these areas is the instrumentation of this city and the ubiquity of the exchange of data, which will give the pulse of this city (sensors) and its breathing in a hyper-connected world within indoor and outdoor dense areas (data exchange, 5G and 6G).
Within this context, the proposed doctorate project has the objective to realize cost- and energy- effective, short-range communication systems for the capillary wireless coverage of in-door environments with low electromagnetic impact and for highly dense outdoor networks.
The result will be reached through the combined use of:
1) Radio over Fiber (RoF) Technology, to bring the Radio Frequency (RF) signal to the different areas to be covered.
2) Beamforming antennas to send in real time the RF power just in the direction(s) where it is really necessary
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