Dr. Roger Krähenbühl Profile

Dr. Roger Krähenbühl

at Ctr Suisse d'Electronique et de Microtechnique SA

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Publications (6)

Proceedings Article | 28 August 2024 Poster

Gratings for future spectro-imagers in space and ground-based telescopes: from lithography techniques to metasurfaces

Frédéric Zamkotsian, Simon Ans, Guillaume Demesy, Nicolas Passilly, Andrei Mursa, Myriam Zerrad, Michel Lequime, Patrick Lanzoni, Roger Krähenbühl, Guillaume Basset

Proceedings Volume 13100, 131005M (2024) https://doi.org/10.1117/12.3021416

Proceedings Article | 12 March 2024 Presentation

Scalable and versatile chip to fiber optical interconnects

Guillaume Basset, Roger Krähenbühl, Martina Renggli, Stefan Mohrdiek

Proceedings Volume PC12892, PC1289206 (2024) https://doi.org/10.1117/12.3003107

KEYWORDS: Fiber optics, Semiconducting wafers, Photonic integrated circuits, Design and modelling, Waveguides, Structured optical fibers, Reflection, Optical switching, Optical interconnects, Optical gratings

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Proceedings Article | 12 July 2023 Open Access

Convex blazed gratings for high throughput spectrographs in space missions

Frédéric Zamkotsian, Roger Krähenbühl, Patrick Lanzoni, Guillaume Basset, Michel Lequime, Myriam Zerrad, Claude Amra, Vincent Costes, Jacques Loesel

Proceedings Volume 12777, 127772J (2023) https://doi.org/10.1117/12.2689996

KEYWORDS: Blazed gratings, Optical gratings, Equipment, Spectrographs, Astronomical imaging, Reflection gratings, Optical surfaces, Spectroscopes, Diffraction gratings, Diffraction

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In next generation space and ground-based instrumentation for Earth and Universe Observation, new instrument concepts include often non planar gratings. Their realization is complex and costly. We propose a new technology for designing and realizing convex blazed gratings for high throughput spectrographs. For this purpose, the requirements are driven by a Digital-Micromirror-Device-based (DMD) MOS instrument we are developing, called BATMAN. The two-arm instrument is providing in parallel imaging and spectroscopic capabilities. The objects/field selector is a 2048 x 1080 micromirrors DMD, placed at the focal plane of the telescope; it is used as a programmable multi-slit mask at the entrance of the spectrograph. The compact Offner-type spectrograph design contains a low density convex grating to disperse light. For optimization of the spectrograph efficiency, this convex grating must be blazed. A blazed reflective grating has been designed with a period of 3300 nm and a blaze angle of 5.04°, and fabricated into convex substrates with 225 mm radius of curvature and a footprint diameter of 63.5 mm. The blaze is optimized for the center wavelength of 580 nm within the spectral range of 400 – 800 nm. Such grating has been fabricated by using lithography, angular Ar ion etching, transfer of the blazed grating from a flat surface onto a convex substrate with a flexible stamp, etched into the substrate by RIE etching. and finally coated with a silver-based layer. With a final 7° blaze angle over the whole surface, efficiency close to 90% on the 1st diffraction order at 700nm has been obtained, measured on BATMAN spectroscopic arm. An optimized device with the exact required blaze angle would reach the same efficiency and be centered on the mid of 400-800nm wavelength band: its realization is on-going. The wavefront error of the diffracted beam will also be optimized. The grating brings a significant contribution in the total amount of straylight at instrument level. Their straylight level remains a critical issue, and its reduction by specific and controlled implementation of improvements in manufacturing process is a challenge to tackle. Straylight measurement has been done and shows a BRDF cosθ values of 10^-8 sr^-1 on the optical surface and 10^-7 sr^-1 on the structured features. This new type of non-planar reflective gratings will be the key component for future high throughput spectrographs in space missions

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Proceedings Article | 9 March 2023 Presentation

Flat waveguides enabling ultra-compact wafer-based atomic clocks

Benjamin Gallinet, Jacques Haesler, Roger Krähenbühl, Steve Lecomte, Guillaume Basset

Proceedings Volume PC12447, PC124470D (2023) https://doi.org/10.1117/12.2649283

KEYWORDS: Atomic clocks, Waveguides, Wafer-level optics, Satellite navigation systems, Optical fabrication equipment, Networks, Beam shaping, Time metrology, Telecommunications, Semiconducting wafers

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Proceedings Article | 29 August 2022 Presentation + Paper

Blazed gratings on convex substrates for high throughput spectrographs

Frédéric Zamkotsian, Roger Krähenbühl, Patrick Lanzoni, Guillaume Basset, Michel Lequime, Myriam Zerrad, Claude Amra, Vincent Costes, Jacques Loesel

Proceedings Volume 12188, 1218824 (2022) https://doi.org/10.1117/12.2630045

KEYWORDS: Spectrographs, Diffraction gratings, Optical design, Diffraction, Digital micromirror devices, Bidirectional reflectance transmission function, Reflectivity, Imaging spectroscopy

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In next generation space and ground-based instrumentation for Earth and Universe Observation, new instrument concepts include often non planar gratings. Their realization is complex and costly. We propose a new technology for designing and realizing convex blazed gratings for high throughput spectrographs. For this purpose, the requirements are driven by a Digital-Micromirror-Device-based (DMD) MOS instrument we are developing, called BATMAN. The two-arm instrument is providing in parallel imaging and spectroscopic capabilities. The objects/field selector is a 2048 x 1080 micromirrors DMD, placed at the focal plane of the telescope; it is used as a programmable multi-slit mask at the entrance of the spectrograph. The compact Offner-type spectrograph design contains a low density convex grating to disperse light. For optimization of the spectrograph efficiency, this convex grating must be blazed. A blazed reflective grating has been designed with a period of 3300 nm and a blaze angle of 5.04°, and fabricated into convex substrates with 225 mm radius of curvature and a footprint diameter of 63.5 mm. The blaze is optimized for the center wavelength of 580 nm within the spectral range of 400 – 800 nm. Such grating has been fabricated by using lithography, angular Ar ion etching, transfer of the blazed grating from a flat surface onto a convex substrate with a flexible stamp, etched into the substrate by RIE etching. and finally coated with a silver-based layer. With a final 7° blaze angle over the whole surface, efficiency close to 90% on the 1st diffraction order at 700nm has been obtained, measured on BATMAN spectroscopic arm. An optimized device with the exact required blaze angle would reach the same efficiency and be centered on the mid of 400-800nm wavelength band: its realization is on-going. The wavefront error of the diffracted beam will also be optimized. The grating brings a significant contribution in the total amount of straylight at instrument level. Their straylight level remains a critical issue, and its reduction by specific and controlled implementation of improvements in manufacturing process is a challenge to tackle. Straylight measurement has been done and shows a BRDF cosq values of 10-8 sr-1 on the optical surface and 10-7 sr-1 on the structured features. This new type of non-planar reflective gratings will be the key component for future high throughput spectrographs in space missions.

Proceedings Article | 5 March 2021 Presentation

Photonic integration: from wafer level to the module

Christian Bosshard, Rolando Ferrini, Stefan Mohrdiek, Oscar Fernandez, Ton Offermans, Roger Krähenbühl, Angelique Luu-Dinh, Frederic Zanella, Guillaume Basset, Rony Jose James, Mark Fretz, Guido Spinola Durante, Amir Ghadimi

Proceedings Volume 11692, 116920Q (2021) https://doi.org/10.1117/12.2578669

KEYWORDS: Semiconducting wafers, Ultraviolet radiation, Silicon carbide, Microlens, Wafer-level optics, Wafer bonding, Transparency, Thermography, Structured optical fibers, Standards development

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