Welcome to YODA – Open Digital Archive for CSEM
The YODA archive gives access to CSEM's publications, such as its annual reports and brochures. For technical papers such as scientific publications, bibliographic information is provided, along with the full paper where this is possible.
This comprehensive database is part of CSEM's Open Access Publishing policy. For further information refer to the YODA support guide or contact repository@csem.ch.
Recent Submissions
Item Optimization And Upscaling Of Microlens Arrays For Advanced Photon Detectors(2026-04-15)Microlens arrays (MLAs) enhance light collection in photon detectors by redirecting incident light to active pixel areas, improving the pixel fill factor and thus the external quantum efficiency. We present recent advancements in MLA optimization and integration for SPADs, SiPMs, and even PICs, addressing diverse substrates and broad optical ranges. A key innovation is the upscaling of MLA fabrication to 200 mm wafers and support for multi-project wafers (MPW), enabling cost-efficient prototyping and industrial compatibility. These capabilities are offered through CSEM’s MLA foundry services, providing design, mastering, and wafer-level replication for next-generation detectors in applications from life sciences to high-energy physics.Item Microlens arrays for advanced silicon photon & radiation detectors(2026-02-19)Microlens arrays (MLAs) are widely employed for beam homogenisation and shaping, either as stand-alone optics or integrated with active components such as wafer-level optics (WLO). In image sensors, each microlens—commonly called an on-chip lens (OCL)—directs incoming light toward the active area of the pixel, improving photo detection efficiency (PDE) by boosting the effective fill factor. This is especially advantageous for front-illuminated sensors with inherently low fill factors. We present recent progress in optimizing and integrating MLAs on high-performance single-photon avalanche diodes (SPADs) and silicon photomultipliers (SiPMs). In particular, the development of the latter is conducted in the context of CERN’s next-generation Large Hadron Collider beauty (LHCb) scintillating fiber tracker (SciFi Tracker) located in a high radiation environment. Improvements of the PDE, external crosstalk and single photon time resolution are reported thanks to the MLA. Our work tackles major challenges such as substrate variability (bare dies, packaged chips, full wafers up to 200mm), wide optical transmission (NUV to NIR), lens geometries spanning micrometers to millimeters, as well as radiation tolerance of the MLAs and operation at cryogenic temperatures. Furthermore, our approach supports multi-project wafers (MPW), allowing multiple designs to be prototyped on a single wafer. This strategy significantly lowers development costs and accelerates time-to-market for research and industry partners. These capabilities are offered through CSEM’s MLA foundry services, providing end-to-end support from optical design and simulation to mastering, tooling, and UV replication. Our thermal reflow and UV-curing techniques guarantee ultra-smooth surfaces and precise alignment, even for complex detector architectures. This scalable and flexible integration approach boosts next-generation photon detector performance for applications ranging from life sciences to advanced detectors for the CERN Large Hadron Collider.Item Integrated micro-optics: an enabler for integrated photonics(2026-04-15)Advanced integrated photonics components deliver and promises unprecedented functions with very compact format, mass manufacturability and lower power consumption than legacy systems. The components being developed for photon generation, manipulation, emission, reception and detection have complex geometries and very small dimensions, making their optical interfacing and overall assembly and packaging very demanding. Micro-optics improves dramatically these optical interfaces by improving the photon emission efficiency, detection efficiency and coupling efficiencies between integrated photonic devices as will be discussed in various cases. Stand-alone micro-optics components allowed dramatic cost reduction in various industries such as for light to fiber coupling, consumer electronics devices or automotive. A few examples of such stand alone micro-optics are presented, such as to miniaturize compact optical atomic clocks. However, integrating micro-optics together with integrated photonic devices offers further miniaturization, ease of assembly and unmatched performance and allow to address emerging needs in a variety of cases. Single‑photon detectors and imagers such as single‑photon avalanche diode (SPAD) arrays, silicon photomultipliers (SiPMs), and advanced CMOS image sensors are intrinsically limited by pixel fill factor, dead areas, and optical losses at the detector surface. However, they allow unmatched low light detection sensitivity, up to single photon detection capability, at room temperature. These limitations are particularly critical under photon‑starved conditions relevant to scientific instrumentation, quantum sensing, time‑resolved imaging, and super-resolution microscopy. Monolithically integrated microlens arrays provide an effective means to increase the effective photon collection area by concentrating incident light onto the active regions of the detector, boosting the quantum efficiency of these photon detectors. CSEM has developed a UV‑replication‑based microlens technology enabling the fabrication of a wide variety of microlens arrays with diameters ranging from a few micrometers to the millimeter scale. Microlenses can be fabricated from a variety of materials, including inorganic sol‑gels and organic polymers such as PMMA and polyurethane, allowing optimization with respect to optical transmission, mechanical stability, environmental robustness, and application‑specific constraints. The technology is compatible with wafers up to 8″ but as well down to individual chips down to 2 × 2 mm². The technology is compatible with aggressive environment such as space and cryostats. The impact of UV‑replicated microlenses has been evaluated on several classes of quantum photonic devices. For front‑illuminated SPAD imagers, cylindrical and square microlenses significantly increase the photon concentration factor, with measured values of approximately 2 to 9 in agreement with optical simulations. In low‑photon‑flux regimes, these microlenses enhance signal‑to‑noise ratio by increasing the number of detected photons without introducing additional electronic noise. Various optimization techniques are presented to further improve the imagers and detectors. In the context of high‑energy physics, round microlenses integrated on silicon photomultipliers developed for the upgrade of the Large Hadron Collider b detector at CERN achieve pixel fill factors exceeding 80% and enable approximately 15% more detected photons at room temperature as well as in cryostats. In a different direction, the rapid growth of data communications, cloud computing, and AI infrastructure is driving an increasing demand for high‑density optical interconnects capable of supporting large fiber counts while maintaining reliability in demanding environments. Conventional physical‑contact fiber connectors face significant challenges in such applications, including stringent sub‑micron alignment tolerances, high sensitivity to contamination, and reduced mechanical robustness as the number of fibers per connector increases. These limitations become particularly critical in telecom, datacom, defense, and industrial networks, where connectors must operate reliably over wide temperature ranges and under harsh environmental conditions. Expanded beam (EB) fiber connector technology offers an attractive alternative by eliminating direct fiber‑to‑fiber contact. By expanding, collimating, and refocusing the optical beam between mating fibers, EB connectors significantly relax alignment and cleanliness requirements. However, traditional EB implementations often rely on glass or polymer lenses that suffer from either high cost or strong thermal and environmental sensitivity, limiting scalability and stability. We have been developing a next‑generation multi‑fiber optical connector based on expanded beam technology using thermally compensated polymer microlens arrays fabricated and assembled at wafer level. The connector is developed by Zoharay in collaboration with CSEM, VTT, and TH‑Wildau, combining optical system design, advanced micro‑optical fabrication, material characterization, and precision bonding technologies. The core innovation lies in the use of polymer microlens doublets with matched thermo‑optic and thermo‑mechanical properties, enabling stable optical performance across a wide temperature range while retaining the cost and scalability advantages of polymer optics. The connector architecture consists of three main elements: a commercially available MT/MPO multi‑fiber ferrule, an optical insert incorporating the microlens arrays, and a mating interface ensuring repeatable alignment. The ferrule provides accurate fiber positioning through standard guiding holes and alignment pins, enabling compatibility with existing datacom ecosystems. Within the optical insert, paired polymer microlenses expand and collimate the beam, significantly reducing sensitivity to dust particles and lateral misalignment. Optical simulations and ray‑tracing optimization demonstrate a numerical aperture of approximately 0.22 and a coupling loss sensitivity below 0.3 dB for lateral misalignments of ±5 µm, while showing strongly reduced temperature dependence compared to conventional single‑lens EB designs. The resulting connector system targets multimode fiber arrays operating at 850 nm and supports high fiber densities while maintaining low insertion loss, high return loss, and robust environmental performance. Its compatibility with existing MPO‑based infrastructure makes it particularly attractive for large‑scale deployment in data centers, telecom networks, and harsh‑environment applications where conventional physical‑contact connectors reach their limits. In a third direction, micro-optics assembly on photonic integrated circuits (PIC) for waveguide array to fiber array unit (FAU) coupling is today a key enabler for advanced electronic and photonic packages, so called co-package optics. Co-package optics is widely evaluated as being key to reduce the energy consumption of datacenters while providing higher bandwidth inside each rack unit. Examples of implementation in the industry of micro.optics for PIC to FAU coupling are presented to review the current state of the art. Current limitations and expected future development in this strategic field are presented as well as the challenges to enable mass manufacturing of this micro-optics-enabled co-package optics systems.Item Single-cell real-time analysis modules(2025)This report focuses on single-cell real-time analysis modules (SCREAM) integrating fluorescence readout and sorting, microlens arrays for improved imaging and high-throughput viable RNA extraction. Results: (1) software enabling full real-time signal analysis on a field-programmable gate array (FPGA), user-friendly via a python-based graphical user interface (GUI) and implemented sorting capabilities; (2) microlens arrays (MLAs) produced on glass substrates, and integrated on multi-well plates, or micro-stereolithography (µSLA) printed microfluidic chips, unifying novelty in both application and technology; (3) workflow for high-throughput, viable RNA extraction via cell squeezing. Bulk measurements indicate the presence of extracted RNA from viable cells. Overall, SCREAM offers modular components for fluorescent detection and analysis, micro-optics, and viable, high-throughput single-cell RNA sequencing (SCRNA-seq), adaptable to diverse life sciences applications. Results and discussionItem Bioimpedance and biopotential monitoring with cooperative-sensor integrated circuit(2025)This work introduces a cooperative sensor platform based on a custom integrated circuit that enables combined bioimpedance and biopotential monitoring for applications such as cardiac, neurological, and respiratory assessment. The system integrates multiple electrodes connected to the same 2-wire parallel bus with low interference with the measured signals. Initial results demonstrate correct operation, low noise, and strong potential for future clinical and wearable use.
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