Stefan M. Koepfli


Last Name

Koepfli

First Name

Stefan M.

ORCID

0000-0003-0291-2065

Organisational unit

03974 - Leuthold, Juerg / Leuthold, Juerg

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2020 - 202651
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Publications1 - 10 of 51
  • All-Plasmonic sub-Terahertz Wireless Link
    Item type: Conference Paper
    Kulmer, Laurenz; Blatter, Tobias; Zuerrer, Amane; et al. (2025)
    Technical Digest Series ~ Optical Fiber Communication Conference (OFC) 2025
    We offer a highest bandwidth, low-footprint, scalable and low-cost solution for sub-THz wireless communication links. We employ a plasmonic-graphene approach. The solution is tested for transmission of 120 Gbit/s at a carrier-frequency of 285 GHz.
  • Engineering Graphene Phototransistors for High Dynamic Range Applications
    Item type: Journal Article
    Nashashibi, Shadi; Koepfli, Stefan M.; Schwanninger, Raphael; et al. (2024)
    ACS Nano
    Phototransistors are light-sensitive devices featuring a high dynamic range, low-light detection, and mechanisms to adapt to different ambient light conditions. These features are of interest for bioinspired applications such as artificial and restored vision. In this work, we report on a graphene-based phototransistor exploiting the photogating effect that features picowatt- to microwatt-level photodetection, a dynamic range covering six orders of magnitude from 7 to 10(7) lux, and a responsivity of up to 4.7 x 10(3) A/W. The proposed device offers the highest dynamic range and lowest optical power detected compared to the state of the art in interfacial photogating and further operates air stably. These results have been achieved by a combination of multiple developments. For example, by optimizing the geometry of our devices with respect to the graphene channel aspect ratio and by introducing a semitransparent top-gate electrode, we report a factor 20-30 improvement in responsivity over unoptimized reference devices. Furthermore, we use a built-in dynamic range compression based on a partial logarithmic optical power dependence in combination with control of responsivity. These features enable adaptation to changing lighting conditions and support high dynamic range operation, similar to what is known in human visual perception. The enhanced performance of our devices therefore holds potential for bioinspired applications, such as retinal implants.
  • Graphene Plasmonics – A Beyond 100 GHz Technology
    Item type: Other Conference Item
    Leuthold, Juerg; Koepfli, Stefan M.; Ma, Ping; et al. (2023)
    2023 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)
    Novel approaches towards new generations of graphene plasmonic modulators and detectors with responses of 500 GHz and beyond are introduced. Important performance parameters such as losses, efficiency or responsivity are addressed by combining the technologies.
  • Der schnellste Detektor der Welt
    Item type: Other Journal Item
    Homs, Marina; Koepfli, Stefan M. (2023)
    Physik in unserer Zeit
    Die optische Datenübertragung ermöglicht einen immer schnelleren Datenaustausch, wird aber auch immer mehr an ihre Grenzen getrieben. Um die großen Datenmengen effizient auslesen zu können, hat ein Forschungsteam der ETH Zürich den bisher schnellsten Lichtsensor der Welt entwickelt, mit einer Bandbreite von über 500 GHz. Dieser Erfolg stellt einen wichtigen Schritt für die nächste Generation der optischen Datenübertragung dar.
  • High-Speed Graphene Photodetection: 300 GHz is not the Limit
    Item type: Other Conference Item
    Koepfli, Stefan M.; Baumann, Michael; Giger, Sascha; et al. (2021)
    2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)
    Graphene’s unique band structure leading to high carrier mobility and broad spectral absorption have successfully been exploited in high-speed photodetectors (PD) [1] . Several demonstrated graphene devices did not show any decline in performance over the tested frequency response even above 100 GHz [1] , [2] leading to speculations on how fast these graphene-based devices can actually be. Some reports indicate thermal- and carrier-based effects in graphene should offer device responses above 300-500GHz [3] , [4] , making graphene a promising material for next generation high-speed optoelectronics integrated into the silicon (Si) photonics platform.
  • Metasurface Colloidal Quantum Dot Photodetectors
    Item type: Journal Article
    Dordevic, Nikola; Schwanninger, Raphael; Yarema, Maksym; et al. (2022)
    ACS Photonics
    Efficient photodetectors that can be easily engineered for a specific spectral window are of high interest. Here, we report on the design, fabrication, and characterization of metasurface-enhanced photodetectors and photodiodes using colloidal quantum dots. We fabricate photoconductors optimized for the wavelength range around 1550 nm featuring responsivities of up to 8000 A/W with low noise equivalent powers on the order of tens of pW/Hz. Further, we produce photodiodes with responsivities of ∼5 mA/W that offer faster responses (14 μs rise time). The high responsivities are due to the metasurface, which increases the absorption by a factor of 10 compared to that of a quantum dot thin film of the same thickness and a structure that enables a photo-gain. We introduce a metasurface to detect either of the two orthogonal polarizations. The fabricated photoconductors operate at low voltages (1-5 V), making them compatible with the complementary metal-oxide-semiconductor (CMOS) read-out circuitry.
  • All-plasmonic sub-terahertz wireless communication link
    Item type: Journal Article
    Blatter, Tobias; Koepfli, Stefan M.; Zuerrer, Amane; et al. (2025)
    Nature Communications
    A promising approach to increase wireless capacity is the transition to sub-Terahertz carrier frequencies (0.1–0.3 THz). While traditional high-frequency approaches employ III-V semiconductor technologies, plasmonics is emerging as a potential solution for highest-speed components. In this paper, we introduce an all-plasmonic sub-THz wireless link, utilizing compact (<50 µm²) plasmonic components that exhibit a flat frequency response up to 300 GHz while providing full flexibility in carrier frequency selection. The plasmonic approach offers unprecedented integration potential, compatibility with diverse platforms, and scalable, cost-effective fabrication. To demonstrate its capabilities, we conduct a lab experiment transmitting 120 Gbit/s on a 285 GHz carrier across a 5 m free-space link, validating the system’s linear performance and large power dynamic range. While this first demonstration is constrained in transmission distance, it showcases the transformative potential of plasmonic technology in closing the wireless-optical data-rate bottleneck: The proposed plasmonic converters could provide the capacity expansion needed for future 5G, 6G, and beyond wireless networks, paving the way for high-speed, cost-effective, and scalable sub-THz communications.
  • High-speed graphene-based sub-terahertz receivers enabling wireless communications for 6G and beyond
    Item type: Journal Article
    Soundarapandian, Karuppasamy Pandian; Castilla, Sebastián; Koepfli, Stefan M.; et al. (2026)
    Nature Communications
    Wireless data traffic has grown at an unprecedented rate, creating an urgent need for innovative solutions to overcome current technological limitations. Sub-terahertz (sub-THz) carrier frequencies offer increased capacity and low attenuation for short-range wireless applications. Here, we demonstrate sub-THz receivers based on graphene, which offer several advantages over state-of-the-art sub-THz receivers, such as a direct detection scheme, passive operation, and compactness. We exploit multiple concepts incorporated into a single device, including a high-quality sub-THz cavity placed in the vicinity of a high-mobility graphene channel to overcome its intrinsically low absorption. The graphene receivers achieve a multigigabit-per-second data rate with a maximum distance of similar to 3 m from the transmitter. We demonstrate a trade-off between bandwidth and responsivity: a setup-limited 40 GHz bandwidth in low-responsivity devices, and a maximum responsivity of 0.16 A/W in devices with a 2 GHz bandwidth. Our findings enable applications such as chip-to-chip communication and close-proximity device-to-device communication.
  • Single Carrier net 400 Gbit/s IM/DD over 400 m Fiber enabled by Plasmonic Mach-Zehnder Modulator
    Item type: Conference Paper
    Kulmer, Laurenz; Blatter, Tobias; Kohli, Manuel; et al. (2024)
    Technical Digest Series ~ Optical Fiber Communication Conference (OFC) 2024
    We demonstrate a 437.1Gbit/s IM/DD link by employing a 178GBd PAM8 signal encoded by a plasmonic MZM. Symbol rates of up to 256GBd and transmission over 400m while maintaining net-rates of >400Gbit/s are successfully demonstrated.
  • A 100 W Output Power Coherent Transmission Link for Future High Data Rate Earth-to-Satellite Communication
    Item type: Other Conference Item
    Horst, Yannik Matthias Julius; Kulmer, Laurenz; Blatter, Tobias; et al. (2024)
    Technical Digest Series ~ Optical Fiber Communication Conference (OFC) 2024
    An optical coherent transmission link with 100Watt output power is tested for satellite communications. Modulation formats are tested for transmission of the highest data-rates despite of nonlinear amplifier impairments across a linear, low-SNR free-space link.
Publications1 - 10 of 51