This paper introduces the automation measurement software FlexSensor for capturing resonant spectra, an innovative and extensible software program developed explicitly for measuring and evaluating wafer-level Silicon Photonic (SiPh) circuits. Wafer-level Silicon Photonics allows the integration of numerous optical components and structures on a single wafer. However, researchers and engineers need precise and repeatable measurements to characterize them and face significant challenges when dealing with large numbers of complex systems on a single wafer. A toolchain gap hampers the measuring of such highly integrated photonic structures: While the setup necessitates the integration of an optimized hardware and software toolchain, there is neither software nor a standardized way to implement a reproducible measurement routine for a massive set of measurements.FlexSensor allows integration and control of external hardware (tunable lasers, analog–digital converters) and supports measurement data storage and evaluation. The software enables researchers and engineers to efficiently analyze the spectral response of photonic structures and facilitate rapid measuring.

Due to its ability to meet requirements such as e.g. telemetry, millimeter-wave transceiver technology has gained research interest for various sensor applications, including the automotive and consumer sector. This work presents a resonant metamaterial for millimeter-waves that enables telemetric position sensing. The concept is based on a resonant unit cell that can be tuned to enable position encoding. A 2D metamaterial design was developed to parametrize the resonance frequency via a geometric parameter of the structure. The tuneable range of the metamaterial was estimated using a finite element method (FEM) simulation. This allowed for a unique mapping of resonance frequency and the geometric parameter, where a linear range for the sensor effect was selected. The resonance frequency shift encodes the absolute position via the geometry parameter of the metamaterial. A linear position encoded bar was fabricated using well-known PCB manufacturing techniques for position determination. The position encoded metamaterial was successfully tested with a vector network analyser under lab conditions. This telemetric position sensor concept offers a compact and contactless read-out without mechanical interference with the moving object. The metamaterial is completely passive, resulting in low maintenance and failure issues. The overall sensor concept includes a state-of-the-art radar chip as millimeter-wave transceiver which is currently under development.

We present a fully telemetric sensor concept for angle and position measurement. It is based on single-layer millimeter-wave metamaterials that exhibit an anisotropic resonant behavior in interaction with incident electromagnetic waves. The angle of rotation is determined from the reflected millimeter waves of the metamaterial target using a millimeter wave chip transceiver. We use a metamaterial geometry exhibiting anisotropic Fano-type resonant behavior. The Fano-type resonance shows a distinct minimum in the reflection spectrum, even with a single layer of metamaterial. The metamaterial target is manufactured on a printed circuit board (PCB) laminate with low-cost standard manufacturing methods. We present an analytical model estimating the resonance frequency of the metamaterial used. The model allows us to assess whether with the Fano-type metamaterial unit cell structure resonance frequencies in the millimeter wave regime are achievable and compliant with standard PCB manufacturing design rules. We performed proof-of-principle experiments with the metamaterial targets and a vector network analyzer, assisted by a detailed analysis of the sensor effect by means of finite-element method calculations. Finally, we implemented a demonstrator setup containing a state-of-the-art frequency-modulated continuous-wave (FMCW) radar chip and a metamaterial target manufactured with standard PCB manufacturing processes.

Integrated photonic sensors on silicon nitride platforms are at the forefront of developments for decentralized, real-time detection of biological and chemical substances. Their increasingly precise sensitivity enables broad applications in the medical, pharmaceutical, and chemical sectors. However, attention to the adverse effect of optical loss is often inadequately addressed, limiting the available intensity in the transmission spectrum, thereby impinging on the achievable detection limits. In this computational study, we address the optimization of a microring-based resonator system, harnessing a recently formulated semi-analytical model of surface-roughness-induced scattering for waveguide-based loss optimization. Our focus extends beyond considering sensitivity to propose a comprehensive figure of merit for resonator design by including the quality factor influenced by the coupling coefficient. Simultaneously, we outline how strategic adjustments of gap-coupling metrics can result in significant enhancements in resonator performance. We model a central wavelength of 850nm for operation in the therapeutic window and we include both transverse-electric and -magnetic polarization. The dimensions of the waveguides have been established considering previous studies, with a width falling within 300 and 800 nm. Furthermore, the nitride layer thickness will vary between 200 and 400 nm, the ring radius between 20 and 60 mu m and the gap between 200 and 800 nm. These parameters form the resonator's design's foundational geometry and layer properties. This work emphasizes the need for taking also the loss mechanisms additinally to the sensitivity consideration into account in order to define and optimize a figure of merit of the sensing performance.

The propagation and bend excess loss characteristics of silicon nitride strip waveguides at an 850 nm wavelength were explored in this study. The aim was to optimize fabrication processes using machine learning, particularly gradient-boosted forests, to achieve low-loss photonic integrated circuits (PICs) and accurately predict the losses. The impact of waveguide geometry and layer properties on loss was examined using a full factorial design of experiment. These machine learning models’ predictive accuracy and ability to capture complex relationships between fabrication parameters and different loss mechanisms were assessed. Key parameters and interactions were identified, improving PIC efficiency for photonic sensing applications.

Enhancing fields is an important task in millimeter-wave applications, such as nondestructive microwave inspection, metamaterial sensing applications, or millimeter-wave imaging. This demand for compact yet high-performance devices for field enhancement operating in the millimeter-wave regime has led to innovative approaches regarding lens design. State-of-the-art lens designs in this wavelength regime tend to be bulky and operate in the far field, making them unsuitable for small form factor applications. In this context, formulating the required functionality and algorithmically looking for the desired material topology is an inversion of the standard approach. This paper presents an inverse-designed field-amplifying metalens operating in the near field of a 60GHz patch antenna. With a size of about three times the wave length, the given structure promises good performance while maintaining a smaller form factor than conventional solutions. It yields an enhancement of the power amplitude by over 7dB.

This study provides an in-depth evaluation of two fundamental techniques for fabricating sensing windows on silicon nitride platforms: a traditional etching strategy using reactive ion etching (RIE) combined with wet etching, and a lift-off-based process in which the top cladding material is deposited onto a suitable resist which is subsequently stripped of the distinct sensing waveguides. The analysis, based on a side-by-side comparison, meticulously examines the effectiveness of these methods. Key evaluation metrics include propagation and bending loss in the sensing windows, process robustness, and uniformity of critical dimensions and heights across the wafer. This will provide a comprehensive understanding of the strengths, weaknesses, and potential application limitations of each technique. An integral part of the study is the careful revision of the waveguide material stack to address specific challenges and applications. This precise tuning and adaptation of the material stack serve as a proxy for the demands likely to be encountered in real-world applications. The conservative etching technique has the advantage that it can be easily combined with subsequent facet etching processes for edge coupling approaches. Conversely, the lift-off resist based approach, despite its relative complexity and sensitivity to high-temperature deposition on the resist, reduces the negative impact of the process on surface roughness and sidewall angles. The knowledge gained from this research provides valuable guidance in the selection of appropriate fabrication techniques for specific silicon nitride sensor applications to increase the robustness of the processing steps for potential mass production stability.

This study introduces an innovative chip-upending technique to enhance the quality of silicon nitride waveguides by minimizing sidewall roughness, which is critical for reducing optical propagation losses. By reflowing the resist after development, we effectively control the resist expansion effect typically observed in standard procedures. Our analysis indicates that this method can decrease line edge roughness (LER). We employ atomic force microscopy (AFM) to measure the LER of the resist and the waveguide sidewalls via a special tilting technique, ensuring precise characterization of the surface topography. The fabrication is carried out by the choice of a suitable DOE for ensuring the statistical robustness in the evaluation process. Additionally, we conduct propagation and bend loss measurements at 850 nm across waveguides of various widths, with thicknesses ranging from 200 to 400 nm. These measurements in correlation with the roughness analysis confirms that sidewall roughness is indeed smoothed, resulting in notable improvements in light propagation efficiency. The versatility of the low-temperature reflow process is further demonstrated by its compatibility with several waveguide geometry alterations . The inclusion of tree-based modeling in optimizing relevant parameters in the fabrication, foremost the reflow parameters, thereby contributing to a more efficient and controlled reflow process. The findings suggest that our approach can be universally adopted for the fabrication of low-loss waveguides in photonic integrated circuits, with necessary wafer-to-wafer stability.

This paper presents a detailed investigation into the propagation loss characteristics of silicon nitride strip waveguides at an 850 nm wavelength, utilizing a random forest model. The primary aim is to optimize low-loss conditions in photonic integrated circuits (PICs). To achieve this, a systematic 2x3 full factorial design of experiments is implemented, focusing on different layers within the PIC framework. The study revolves around a critical examination of how the waveguide width influences propagation loss. Leveraging the random forest model, known for its high precision in complex data analysis, we delve into the correlation between various design elements and their impact on loss. This methodology not only aids in pinpointing the pivotal factors affecting loss but also elucidates their interplay, particularly emphasizing the role of waveguide width. One of the key contributions of this research is the identification of optimal material configurations that significantly reduce loss. This is instrumental in enhancing the efficiency of PICs, a crucial aspect for their performance in applications such as optical communications and photonic computing. Our approach uniquely combines empirical data analysis with machine learning techniques, offering a novel perspective in photonic engineering research. The findings of this study not only shed light on the complex dynamics of waveguide design but also pave the way for the development of more efficient and effective photonic systems. This research stands to make a significant impact in the field, presenting a comprehensive methodology for designing low-loss silicon nitride strip waveguides, thereby contributing to the advancement of photonic technologies.