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Microwave sensing technology has become increasingly widely applied in the biomedical field, playing a significant role in medical diagnosis, biological monitoring, and environmental warning. In recent years, the introduction of metamaterials has brought new possibilities and opportunities to microwave biosensors. This paper aims to explore the applications of microwave sensors in biosensing, with a particular emphasis on analyzing the crucial role of metamaterials in enhancing sensor performance and sensitivity. It provides a thorough examination of the fundamental principles, design strategies, fabrication techniques, and applications of microwave biosensors leveraging metamaterial enhancement. Moreover, it meticulously explores the latest applications spanning biomedical diagnostics, environmental monitoring, and food safety, shedding light on their transformative potential in healthcare, environmental sustainability, and food quality assurance. By delving into future research directions and confronting present challenges such as standardization and validation protocols, cost-effectiveness and scalability considerations and exploration of emerging applications, the paper provides a roadmap for advancing microwave biosensors with metamaterial enhancement, promising breakthroughs in multifaceted bioanalytical realms. ARTICLE HIGHLIGHTS: • Utilizing metamaterials for electromagnetic tuning at subwavelength scales at microwave frequencies enables unprecedented sensitivity, specificity, and resolution for biological sensing. • Microwave sensors, owing to their compact size, direct integration capabilities with integrated circuits and radio circuits, and potential for mass production, hold significant promise for advancing the development of portable miniaturization in biological analysis. • Metamaterial-enhanced microwave biosensors offer the potential for label-free, noncontact, real-time monitoring, paving the way for continuous surveillance in biological molecule analysis, medical diagnostics, and ongoing monitoring of food and environmental safety. [ABSTRACT FROM AUTHOR]

In this paper, we compare the characteristics of several waveguide Bragg gratings (WBGs) with sinusoidal and rectangular corrugated sidewalls in high confinement integrated optics. Our measurements confirm the performance of both the rectangular and sinusoidal grating as band-rejection filters for TE-polarized signals in the telecom C-band. These measurements demonstrate record high extinction ratios of 35 and 28.91 dB for sinusoidal and rectangular WBGs with a rejection bandwidth as narrow as 4.42 and 6.165 nm. The simulation results and measurements show that the filter bandwidth and coupling coefficient can be changed by altering the corrugation width (Δ W), allowing us to control the filter's quality factor precisely. The bandwidth of rectangular WBGs drops for Δ W > --> 80 nm, constraining the design of devices requiring broadband WBGs. In contrast, the bandwidth of sinusoidal WBG continues to increase for Δ W > --> 80 nm, providing a wider bandwidth for designers. These findings demonstrate the potential for effective integration of new photonic functionalities into low-footprint electro-optical waveguide tools for sensing, communicating, and computing applications. [ABSTRACT FROM AUTHOR]

The precise quantification of a dielectric waveguide core thickness, core width, core refractive index, and cladding refractive index across a wafer is critical for greater consistency and accuracy in photonic circuit fabrication. However, accurate wafer-scale measurements of these parameters have not yet been demonstrated. We have previously described a method for extracting these four parameters simultaneously from silicon nitride waveguides using unbalanced Mach–Zehnder interferometers on a single die. In this work, we show that this technique can be scaled to characterize these photonic parameters across an entire 300 mm wafer. The refractive indices of the core and cladding materials are found with relative standard deviations of the mean of 0.07% and 0.03%, respectively. The core width offset (bias) and thickness are found with relative standard deviations of 0.3% (2.6 nm) and 0.5% (1.1 nm), respectively. The extracted parameter maps suggest a radial variation of material indices and a planar variation of geometric parameters. We verify the extracted parameters by accurately predicting the performance of an unbalanced Mach–Zehnder interferometer and the degeneracy between different modes in straight waveguides. [ABSTRACT FROM AUTHOR]

We present a new fab-in-the-loop reinforcement learning algorithm for the design of nano-photonic components that accounts for the imperfections present in nanofabrication processes. As a demonstration of the potential of this technique, we apply it to the design of photonic crystal grating couplers fabricated on an air clad 220 nm silicon on insulator single etch platform. This fab-in-the-loop algorithm improves the insertion loss from 8.8 to 3.24 dB. The widest bandwidth designs produced using our fab-in-the-loop algorithm can cover a 150 nm bandwidth with less than 10.2 dB of loss at their lowest point. [ABSTRACT FROM AUTHOR]

Universal quantum computing holds the promise to fundamentally change today's information-based society, yet a hardware platform that will provide a clear path to fault-tolerant quantum computing remains elusive. One recently proposed platform involves the use of circuit-bound photons to build cluster states and perform one-way measurement-based quantum computations on arrays of long-coherence-time solid-state spin qubits. Herein, we discuss the challenges that are faced during any practical implementation of this architecture by itemizing the key physical building blocks and the constraints imposed on the spin qubits and the photonic circuit components by the requirements of fault-tolerant performance. These considerations point to silicon as a leading candidate to host such a platform, and a roadmap for developing a silicon photonic circuit-based platform for measurement-based, fault-tolerant universal quantum computing is offered. [ABSTRACT FROM AUTHOR]

The magnitudes of the challenges facing electron-based metrology for post-CMOS technology are reviewed. Directed self-assembly, nanophotonics/plasmonics, and resistive switches and selectors are examined as exemplars of important post-CMOS technologies. Materials, devices, and architectures emerging from these technologies pose new metrology requirements: defect detection, possibly subsurface, in soft materials, accurate measurement of size, shape, and roughness of structures for nanophotonic devices, contamination-free measurement of surface-sensitive structures, and identification of subtle structural, chemical, or electronic changes of state associated with switching in non-volatile memory elements. Electron-beam techniques are examined in the light of these emerging requirements. The strong electron-matter interaction provides measurable signals from small sample features, rendering electron-beam methods more suitable than most for nanometer-scale metrology, but as is to be expected, solutions to many of the measurement challenges are yet to be demonstrated. The seeds of possible solutions are identified when they are available. [ABSTRACT FROM AUTHOR]

In the maturing field of silicon photonics, advances continue in both design and process improvements. Waveguide propagation loss is strongly affected by sidewall roughness, and so for fabrication using e-beam lithography, loss is influenced by e-beam writing parameters. Here, the authors look specifically at fracturing strategies in data preparation for e-beam lithography, and find significant reduction in waveguide loss by utilizing advanced fracturing options. For our evaluation, the authors fabricate optical waveguides using a well-characterized, highly stable baseline fabrication process with hydrogen silsesquioxane resist exposed by a 100 kV electron beam, a high-contrast tetramethyl-ammonium hydroxide develop, and a Cl2 inductively coupled plasma etch. Using surface grating couplers for input and output, automated optical measurements are made by scanning input light in the region of the design wavelength of 1550 nm and measuring optical output power. The authors use a design cell containing grating couplers and both straight and curved waveguides with a range of lengths. The authors find a significant reduction in grating coupler insertion loss and waveguide loss along with increased uniformity by leveraging a new fracturing strategy implemented in the beamer pattern data processing software from GenISys, GmbH. Single line edge smoothing is an exposure strategy in which all feature edges are traced using a single-line shape (sometimes referred to as a single-pass line) while the bulk of the shape is then exposed with trapezoidal beam filling. The insertion loss for grating couplers written using single line edge smoothing shows a significant loss reduction of 1.2 dB as well as greatly improved uniformity. Both straight and curved waveguide losses were also reduced by use of single line edge smoothing, by 0.7 and 1.1 dB/cm, respectively. Here, the authors will discuss the likely mechanisms of this improvement as well as present additional device data using these new fracturing methods which represent a significant, incremental improvement in performance of optical waveguides written by e-beam lithography. [ABSTRACT FROM AUTHOR]