Modeling and compensation of backreflection signal in diffuse reflection optical MEMS spectrometersAbozyd, Samir; Erfan, Mazen; Mortada, Bassem; Sabry, Yasser M.
doi: 10.1117/12.3043246pmid: N/A
Near-infrared (NIR) spectrometry, particularly in the diffuse reflection mode, offers significant advantages for measuring material spectral response without specialized sample preparation or destruction. Moreover, it provides both qualitative and quantitative analysis of materials in various applications, including industrial, medical, agriculture, and food. However, the presence of specular reflection from spectrometer and sample holder introduces unwanted signals, leading to non-linear photometric spectral errors. This issue is especially pronounced when measuring highly absorbing materials, limiting the accuracy of determining their maximum absorbance levels. Moreover, it is more significant in miniaturized MEMS spectrometers since the portability necessitates a compact optical head, where the stray light cannot be easily avoided. This work investigates and models the backreflection, considering the reflective index of windows and the refractive index of the material under test. Furthermore, the research proposes an effective method for compensating the backreflection error. To validate our compensation method, experiments were conducted using milk as a test material. Milk is a suitable candidate for this experiment due to its high water content, which gives it strong light absorption properties in the realm of diffuse reflection. Backreflection compensation leads to a substantial reduction in absorbance saturation, increasing maximum measured absorbance of milk from 1.77 AU to 2.5 AU and decreasing variations of different sampling configurations more than 10 times. Furthermore, the backreflection compensation was evaluated using a chemometric model for high-moisture feed material, demonstrating a reduction in prediction error by 29% and an improvement in bias variations by a factor of 11.
Waveguide-coupled, broadband thermal emission enabled by a bulk-micromachined trench undercutPruessner, Marcel W.; Tyndall, Nathan F.; Bouchard, Jacob N.; Holmstrom, Scott A.; Lipkowitz, Steven T.; Stievater, Todd H.
doi: 10.1117/12.3043483pmid: N/A
Waveguide-based broadband light sources in photonic integrated circuits are useful for applications ranging from device characterization to chemical sensing to absorption spectroscopy. This work demonstrates a waveguide-coupled optical source capable of broadband light emission and waveguide propagation from visible-to-infrared wavelengths. A foundryprocessed SiN/SiO2 nanophotonic waveguide has two doped-Si microheater strip lines placed on either side of it. A bulk-micromachining trench undercut etch is performed in which the silicon substrate is isotropically-etched to suspend the Si/SiN/SiO2 structure enabling exceptional thermal isolation. A bias is applied to both doped-Si microheaters resulting in efficient Joule heating, and the resulting hot lattice thermal emission couples to and propagates down the SiN waveguide. Measurements show a broadband spectrum ranging from 875-1680 nm (limited by our instrumentation) consistent with a blackbody emission. This broadband thermal source has the potential for high efficiency via subsequent waveguide optimization.
Holographic photo-morphing of polymer surfaces for reprogrammable diffractive opticsReda, Francesco; Salvatore, Marcella; Januariyasa, I Komang; Borbone, Fabio; Oscurato, Stefano Luigi
doi: 10.1117/12.3041094pmid: N/A
The fabrication of reconfigurable diffractive optics requires lithographic techniques capable of dynamically modifying surface geometries. Traditional methods, such as etching and resist-based processes, impose limitations on post-fabrication modifications, increasing manufacturing complexity and cost. Holographic photomorphing of azopolymer surfaces enables direct, all-optical, and reversible fabrication of diffractive optical elements. In this study, we demonstrate the fabrication of linearly chirped diffraction gratings using computer-generated holography to project structured illumination onto azopolymer films. The digital lithographic setup allows precise control of the intensity patterns, enabling the fabrication of chirped gratings with continuously varying periodicity. Real-time diffraction analysis is performed using a probe beam to capture the evolution of surface modulation and diffraction efficiency during the writing process. Experimental results confirm theoretical predictions, with diffraction efficiencies up to 34%. The ability to fabricate complex diffractive elements without sequential exposures or mechanical alignment enhances the versatility of this method and provides a scalable approach for tunable optical components.
Miniaturized tuneable light source based on a digital micromirror deviceChalyan, Astghik; Hoving, Willem; Meulebroeck, Wendy; Ottevaere, Heidi
doi: 10.1117/12.3040759pmid: N/A
A miniaturized tuneable light source using a white LED and a Fastie-Ebert configuration of a mini-spectrometer is demonstrated. In this work, the CMOS sensor in the Fastie-Ebert configuration is replaced with a DLP2010 0.2 WVGA Digital Micromirror Device (DMD). Experimentally, 36 wavelengths within the range of 615 nm to 685 nm were tuned by changing the pattern on the DMD and activating 10 columns of mirrors. This resulted in narrow spectral lines with a FWHM between 3.24 nm and 5.85 nm. The demonstrated optical performance experimentally showcases perspectives of developing a programmable miniaturized broadband tuneable light source based on a DMD while going towards miniaturization.
Glass-based micro-opto electromechanical systems manufactured by laser induced deep etchingBertke, Maik; Heinz, Jannis; Schudak, Svenja
doi: 10.1117/12.3042817pmid: N/A
We introduce a novel fabrication process for glass-based Micro Opto Electromechanical Systems (MOEMS) utilizing Laser Induced Deep Etching (LIDE). This method enables the creation of high aspect ratio structures (up to 50:1) with precise, defect-free features (<10 1 µm) in various glass types such as fused silica and borosilicate glass. The fabricated glass-MOEMS include optical components, highly flexible spring structures, integrated actuators, and capacitive or piezoelectric sensing elements, demonstrating their versatility for applications such as tunable optical filters, lenses, and transparent MEMS with integrated diffractive elements. Mechanical testing, including force-displacement measurements, validated the functionality and robustness of these systems, with finite element method (FEM) simulations aligning closely with experimental results. Glass springs with dimensions of 30µm260µm exhibited exceptional mechanical strength, with an estimated maximum breaking strength of ~1GPa, underscoring their potential for durable and high-performance MOEMS. This work highlights the integration of LIDE with established microsystem processes such as wet etching, thin-film deposition, and anodic bonding, showcasing advancements in glass-based MOEMS for next-generation miniaturized optical and mechanical systems.
Piezoelectric MEMS mirror based SPAD LiDAR system enabling real-time monitoring across large covered areas for smart factory applicationsHwang, J.-Y.; Henschke, A.; Wysocki, L.; Raschdorf, P.; Ligges, M.; Kasischke, M.; Mensing, M.; Kapels, H.; Gu-Stoppel, S.
doi: 10.1117/12.3042925pmid: N/A
This paper presents a MEMS mirror based SPAD LiDAR system that monitors the surrounding in smart factories. The proposed LiDAR system enables safety monitoring in real-time by acquiring spatial and depth information of the region of interest in a production scenario where workers and machines coexist. This sensor system features a MEMS mirror using piezoelectric material AlN and wafer-level packaging that steers the diverged laser beam with a wavelength of 915 nm for a large field of view. In addition, a CMOS based SPAD pixel array is deployed to detect the target region and thus the improved detector performance can be achieved. This study includes the lens system design for an effective LiDAR illumination part and the evaluation results of real-time object and human detection with the prototype LiDAR sensor system.
Towards the modeling and control of a quasi-static 2D-MEMS vector scanner with a hybrid-integrated moving magnet driveBirnbaum, Klemens; Mustin, Benjamin; Schneider, Julius; Sandner, Thilo
doi: 10.1117/12.3042702pmid: N/A
Monocrystalline silicon-based quasi-static 2D-MEMS vector scanners are classified as micro-opto-electro-mechanical systems (MOEMS). These controllable micromirrors are primarily utilized for the precise and dynamic deflection of laser beams in applications such as light detection and ranging (LiDAR), optical coherence tomography (OCT), and compact therapeutic laser systems. While system integration can be difficult, the use of hybrid-integrated electromagnetic (EM) drives—including moving magnet types—yields high energy densities and require lower driving voltages than those seen in conventional monolithically integrated electrostatic drives, thus facilitating innovative design options for MOEMS. This work presents an approach for the modeling and control of a quasi-static gimbal-based 2D-MEMS vector scanner with a hybrid-integrated moving magnet drive. A general procedure for the static and dynamic characterization of the system is provided. Furthermore, the performance of the proposed control system is evaluated using a set of non-resonant vectorial scan trajectories. The results demonstrate that the system can be accurately controlled for a 5 mm mirror aperture and large quasi-static tilt angles of 13 on both scan axes, a significant finding that indicates the potential of compact MOEMS scanning systems with hybrid-integrated EM drives for broader application in fields requiring precise vectorial control of laser beams.
Micromechanically bending membrane for curved SERSFeizpour, Mehdi; Abbasi, Sara; Ottevaere, Heidi
doi: 10.1117/12.3043777pmid: N/A
Planar surface-enhanced Raman scattering (SERS) substrates are widely used in sensing due to their ease of fabrication, reproducibility, and compatibility with lab-on-chip systems. However, their utility can be limited by weak interactions with larger analytes such as macromolecules and cells. Here, we demonstrate how micro-scale curvature enhances lightguiding and improves SERS performance. We designed a micromechanical bending structure (“microbender”) that enables a 150 µm-long membrane to be deflected by 30 µm rotating arms. Fabricated via two-photon polymerization, the microbender preserves the membrane’s planar profile during printing and subsequently permits precise curvature for postfabrication modification. Experimental validation with short (0.8 µm) and tall (4 µm and 6 µm) pillars on the microbender membrane confirmed enhanced SERS signals in the curved state. Notably, 6 µm-tall pillars achieved intensities on par with denser 0.8 µm-tall arrays, illustrating the potential for detecting larger analytes (>1 µm). Beyond SERS, the microbender offers a versatile platform for printing other optical components such as metastructures, microlens arrays, or waveguides. Our findings suggest that curving SERS substrates provides a robust strategy to increase hotspot density, improve light collection, and tailor detection capabilities for diverse applications—especially where standard planar substrates fall short.
Integrated, waveguide-based spectrometer for high-performance applicationsWeber-Porter, Z.; Amin, Md.; Dixon, P.; Adams, T.; Yuzvinsky, T. D.; Ramollari, H.; DeMartino, M.; Bundy, K.; Hawkins, A. R.; Schmidt, H.
doi: 10.1117/12.3046000pmid: N/A
Spectral analysis of light is at the heart of countless scientific discoveries, techniques, and instruments. Miniaturized spectrometers have recently seen great advances, but combining low complexity with high performance remains challenging. We have recently introduced a novel integrated photonic spectrometer based on imaging of wavelength-dependent light propagation patterns in multi-mode interference (MMI) waveguides, followed by machine learning analysis with suitable techniques. A spectral resolution of 0.05 nm and resolving power of 16,000 were demonstrated in the near-infrared range, along with broadband operation in the visible spectrum, and the integration of four spectrometers in an array on a single chip. Stable operation of the device over extended periods of time is critical for many applications. Here, we introduce a robust approach for achieving long-term fiber-to-chip coupling by permanent attachment of a single-mode fiber to the input waveguide in a custom-made device holder. A mechanically stable and permanent coupling method, employing a UV-curable adhesive with minimal shrinkage, ensures precise and lasting alignment. This technique significantly enhances spectrometer stability and performance under environmental and mechanical perturbations. Over a week-long evaluation, the permanently coupled spectrometer demonstrated exceptional spectral accuracy and stability, with only a modest ~10% power reduction, in stark contrast to the rapid misalignment observed in free-space coupled systems. Accurate spectral reconstruction using a convolutional neural network was maintained throughout the testing period. Future work will focus on extending operational testing durations, advanced packaging solutions, and adaptations for remote and real-time applications, cementing the practicality of MMI waveguide-based spectrometry in diverse realworld environments.