TY - CHAP A1 - Fünning, Tabea A1 - Peczek, Anna A1 - Kroh, Aleksandra A1 - Mai, Christian A1 - Paul, Martin A1 - Thomsen, Florian A1 - Tannenberg, Robert A1 - Schumann, Christoph A1 - Weller, Michael G. A1 - Mai, Andreas A1 - Steglich, Patrick ED - Baldini, Francesco ED - Homola, Jiri ED - Lieberman, Robert A. T1 - Optimization of local backside released micro-ring resonators for sensing applications using silicon photonic integrated circuits in a SOI technology T2 - Proceedings of SPIE : Optical Sensors 2025 N2 - Photonic micro-ring resonators (MRR) are widely studied for their high sensitivity across applications like environmental monitoring, healthcare, and chemical analysis. Their evanescent field sensing requires partially unembedded waveguides compatible with CMOS processing. Our approach uses local backside etching with an additional buried oxide (BOX) etch to release waveguides while preserving the back-end of line (BEOL) structure, enabling spatial separation of the sensing area and electronics. The BOX etch critically affects sensor performance, as waveguide surface roughness can alter MRR properties and coupling. We analyzed MRR design variations, comparing wet and dry etching techniques for their effects on optical performance across rib and strip waveguides in quasi-TE and quasi-TM modes. Wafer-level measurements show that backside-released MRR achieve high extinction ratios with slightly reduced quality factors, advancing high-sensitivity photonic sensors. KW - photonic sensor KW - micro-ring resonator (MRR) KW - silicon-on-insulator (SOI) KW - local backside etching (LBE) Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-20449 VL - 13527 PB - SPIE ER - TY - JOUR A1 - Fünning, Tabea A1 - Paul, Martin A1 - Manganelli, Costanza Lucia A1 - Wenger, Christian A1 - Mai, Andreas A1 - Steglich, Patrick T1 - Comparative simulation analysis of photonic ultrasound sensors based on silicon waveguides JF - Scientific Reports N2 - Pressure sensors based on photonic integrated circuits (PIC) offer the prospect of outstanding sensitivities, extreme miniaturization and have the potential for highly scalable production using CMOS compatible processing. PIC-based pressure sensors detect the change in optical properties, i.e. the intensity or phase of the optical carrier wave inside miniaturized waveguide structures. The detection of ultrasound is achieved by engineering the waveguide architecture such that a pressure causes a high change in the effective refractive index of the waveguide. A range of PIC-based pressure sensors have been reported, but a comparison of the sensitivity of the different approaches is not straightforward, since different pressure sensitive waveguide architectures as well as photonic layouts and measurement setups impact the performance. Additionally, the used sensitivity unit is not uniform throughout the different studies, further complicating a comparison. In this work, a detailed simulation study is carried out by finite element modeling of different pressure sensitive waveguide architectures for a consistent comparison. We analyze three different sensor architectures: (A) a free standing membrane located within a tiny air gap above the waveguide, (B) a waveguide located on top of a deflectable membrane as well as (C) a waveguide embedded inside a pressure-sensitive polymer cladding. The mechanical response of the structures and the resulting changes in mode propagation, i.e. the change of the effective refractive index, are analyzed. The waveguide sensitivities in RIU/MPa for different waveguide types (strip, slot) and polarization states (TE, TM) are compared. The results reveal inherent limitations of the different waveguide designs and create a basis for the selection of suitable designs for further ultrasound sensor development. Possibilities for enhancing waveguide sensitivity are identified and discussed. Additionally, we have shown that the studied approaches are extensible to SiN waveguides. Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-20560 VL - 15 PB - Springer Nature ER - TY - JOUR A1 - Raju, Ashraful Islam A1 - Dubey, Pawan Kumar A1 - Lukose, Rasuole A1 - Wenger, Christian A1 - Mai, Andreas A1 - Lukosius, Mindaugas T1 - Optimized silicon nitride-spaced graphene electro-optic modulator with high efficiency and bandwidth JF - Optical and Quantum Electronics N2 - Optical modulators with high modulation efficiency, large operational bandwidth, high-speed and low energy consumption is essential for the advancement of on-chip optical signal processing. To overcome the bandwidth-efficiency trade-off in graphene optical modulators, a buried silicon nitride waveguide-coupled double-layer graphene electro-absorption (EA) optical modulator has been proposed. In the proposed design, silicon nitride layer is also embedded between the two graphene layers as a dielectric spacer to enhance the graphene-light interaction. An extensive simulation has been performed to optimize the dielectric spacing layers between the two graphene for optimal device performance including the waveguide dimensions and optical modes profile. The simulated results show a high modulation efficiency of 1.1 dB/V and a modulation depth of 0.16 dB/µm, corresponding to a 15-dB extinction ratio for a 100 µm device at 1550 nm, with a 30 nm spacer and 12 V driving voltage. The proposed modulator achieves a 14 GHz bandwidth and operates over a 1050 nm broadband operation spectral range. The concurrent presence of high modulation bandwidth and efficiency renders these modulator designs highly viable for on-chip optical communication applications. KW - electro-optical modulator KW - graphene modulator KW - modulation efficiency KW - silicon nitride waveguide Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-20597 VL - 57 IS - 7 PB - Springer Nature ER - TY - JOUR A1 - Bauer, Joachim A1 - Heinrich, Friedhelm A1 - Villasmunta, Francesco A1 - Villringer, Claus A1 - Reck, Johanna A1 - Peters, Sven A1 - Treffer, Alexander A1 - Kuhnt, Christian A1 - Marschmeyer, Steffen A1 - Fursenko, Oksana A1 - Stolarek, David A1 - Mai, Andreas A1 - Regehly, Martin T1 - Reflectometric method for measuring residual oxides in through-silicon vias for 3D chip integration JF - Optics Express N2 - A significant aspect of fabricating 3D chip architectures is ensuring proper contact between the different layers of the chip, which often requires removing the underside of isolation layers before filling vias with conductive material. Currently, scanning electron microscopy is the established method for investigating such structures. In this paper, we propose a rapid, non-destructive optical analysis technique for the simultaneous measurement of through-silicon vias (TSV) depths, silicon wafer thickness, and residual oxide thickness. The proposed method utilizes Fourier peak shift analysis (FPSA) of reflectance measurements in the near-infrared (1200 nm—2200 nm) spectral regions. The application of FPSA to representative samples taken from a commercial TSV integration process for MEMS and CMOS fabrication demonstrated good agreement with reference scanning electron microscopy measurements, confirming the feasibility of the method for in-line and in-situ metrology. The results indicate that FPSA has great potential for real-time process monitoring and control during 3D chip manufacturing. KW - effective refractive index KW - Fourier transforms KW - near infrared KW - ray tracing KW - scanning electron microscopy KW - thin film Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:526-opus4-20633 VL - 33 IS - 15 SP - 32175 EP - 32189 PB - Optica ER -