Toward Bloch Surface Wave-Assisted Spectroscopy in the Mid-Infrared Region

We present the first observation of Bloch surface waves in the mid-infrared spectral range. Bloch surface waves are electromagnetic states that can propagate at the interface between a continuous dielectric medium and a periodic stack of materials. We designed a mid-infrared multilayer optical element specifically for this purpose. The structure is made of successive layers of ZnSe and YbF3 deposited on a CaF2 substrate. Surface waves can be coupled into this structure from 6.6 to 10.6 μm. We characterized the optical properties of the fabricated element using a tunable quantum cascade laser centered around 7.85 μm. We believe that Bloch surface wave based platforms are very promising components for surface sensing and spectroscopic applications in the mid-infrared.

Advanced optical components for mid-infrared applications

Grégoire Maxime Smolik

The mid-infrared wavelength range, defined from 2.5 um to 25 um is of a high scientific and technological interest. One of its main application field is in spectroscopy, since these wavelengths coincidewith the fundamental rotational-vibrational modes of many molecules. While the typical optical sensing setup is composed of active elements - detectors and radiation sources- it also requires critical passive components such as lenses, filters and an interface with the medium to be probed. To this day, most of the scientific work in mid-infrared has been mostly focused on active elements such as the quantum cascade laser. While very modern detectors and lasers are now available, the experimental setups still rely on classical and bulky passive optics. The work presented in this thesis explores modern optical technologies for the realization of novel passive mid-infrared optical components. The fabrication of an external cavity tunable quantum cascade laser emitting from 7.6 um to 8.1 um is presented. This thesis describes the fundamentals of sub-wavelength structures for optical phase generation. Such structures allow local modifications of the effective refractive index of a dielectric material. Using these concepts, original designs of polarizers, anti-reflective and diffractive micro-optical elements are proposed for high-index dielectrics such as silicon or germanium. In particular, the fabrication and characterization of a novel binary grating in silicon that combines anti-reflective and diffractive functions around 7.85 um is presented. This component is characterized using the developed tunable light source setup. Another type of optical component is presented, based one dimensional photonic crystals. It consists of a ZnSe-YbF3 multi-layer deposited on top of a CaF2 substrate. This element allows to observe the first occurrence of Bloch surface waves in the mid-infrared, using the same tunable laser setup. The evanescent field of a surface-propagating wave can be used to probe the surrounding medium. Such structures are promising novel types of substrates for surface-based sensing applications. In addition, a quantum cascade laser-based setup for the detection of cocaine in liquid is presented. This experiment illustrates the great potential of quantum cascade lasers for compact chemical sensing setups.

EPFL2017

Vertically moving micromirror for detectors in the mid infrared

Niels Quack

This paper presents continuative results on the design, fabrication and measurements of a vertically moving, electrostatically actuated micromirror, first shown at the IEEE MEMS 2007 [N. Quack, I. Züst, S. Blunier, J. Dual, M. Arnold, F. Felder, M. Rahim, H. Zogg, Electrostatically actuated micromirror for resonant cavity enhanced detectors, 20th IEEE Conference on Micro Electro Mechanical Systems, Kobe, Japan, 2007]. The micromirror is being developed for the use in a tunable resonant cavity enhanced detector (RCED) for the mid-infrared [M. Arnold, D. Zimin, H. Zogg, Resonant-cavity-enhanced photodetectors for the mid-infrared, Appl. Phys. Lett. 87 (2005) 141103]. RCEDs make use of a standing wave formed in an optical cavity and are sensitive at the resonances. The wavelengths of the resonances are hereby depending on the distance of the two cavity mirrors [M.S. Unlu, S. Strite, Resonant cavity enhanced photonic devices, J. Appl. Phys. 78 (1995) 608]. Moving one of the mirrors allows thus selecting the wavelengths which the device is sensitive at. The presented micromirror is actuated electrostatically and fabricated in a single crystalline silicon substrate. With actuation voltages below 25 V, displacements of 3 µm of a 300 µm x 300 µm mirror could be achieved. These displacements are expected to result in a tuning range over several microns wavelength in the infrared of the detector system. Such narrowband detector systems are sought after in multispectral infrared (IR) thermography or infrared spectroscopy [C.A. Musca, J. Antoszewski, K.J.Winchester, A.J. Keating, T. Nguyen, K.K.M.B.D. Silva, J.M. Dell, L. Faraone, P. Mitra, J.D. Beck, M.R. Skokan, J.E. Robinson, Monolithic integration of an Infrared Photon Detector with a MEMS-based tunable filter, IEEE Electron Dev. Lett. 26, (December (12)) (2005)].

2008

Advanced optical components for mid-infrared applications

Grégoire Maxime Smolik

EPFL2017