PHOTO : Devices - Nanostructured optical filters

The use of periodic structures to make devices for free space optics has led to a proliferation of work in recent years on structures known as "High Contrast Gratings" (HCG), "Zero Contrast Gratings" (ZCG) or "Flat Optics"... The applications are numerous, ranging from simple spectral or spatial filtering to the creation of 3D imaging systems. This is an extremely open field of research, in which many conceptual and technological obstacles still need to be overcome. In this very rich field, and in particular to meet the growing needs for space observation processed by the CNES in Toulouse, we have focused our studies on a new generation of nanostructured spectral filters, which should ideally be ultra-selective, wavelength-tunable and independent of polarization.

Guided mode resonant filters (GMRFs)

Resonant filters are of great interest because they make ultra-selective filters from a relatively simple structure. This structure consists of a dielectric guide corrugated with a shallow sub-wavelength grating. Out of resonance, the structure reflects and transmits light with reflectivity and transmission properties very close to those of the stack of dielectric layers. We were able to propose and demonstrate an innovative concept of resonant grating filters combining two simple optical waveguides and two crossed 1D gratings. In the near infrared range, we have thus demonstrated an operation in reflection under oblique incidence, with tunability over a wide spectral band (> 100 nm), a selectivity of less than 1 nm (quality factor ~ 2300), and an independence to polarization better than 97%. Recent works focus on the study and demonstration of devices operating in transmission, exploiting several simultaneous resonances (ZCG filters). This work was the subject of a PhD thesis in collaboration with Safran-REOSC, defended in 2018 (thesis by Léopold Macé).

Related publications:

L. Macé, O. Gauthier-Lafaye, A. Monmayrant, S. Calvez, H. Camon, and H. Leplan, “Highly-resonant two-polarization transmission guided-mode resonance filter,” AIP Advances 8, no. 11, 115228, 2018.

A.-L. Fehrembach, K. Sharshavina, F. Lemarchand, E. Popov, A. Monmayrant, P. Arguel, and O. Gauthier-Lafaye, "2 × 1D crossed strongly modulated gratings for polarization independent tunable narrowband transmission filters," JOSA A 34 (2), 234-240, 2017.
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Léopold Macé, O. Gauthier-Lafaye, A. Monmayrant, H. Camon, "Design of angularly tolerant zero-contrast grating filters for pixelated filtering in the mid-IR range," J. Opt. Soc. Am. A 34, 657-665, 2017.

A. Monmayrant, S. Aouba, K. Chan Shin Yu, P. Arguel, A.-L. Fehrembach, A. Sentenac, O. Gauthier-Lafaye, "Experimental demonstration of 1D crossed gratings for polarization-independent high-Q filtering," Opt. Lett. 39 (20), 6038-6041, 2014. 

CRIGFs filters

Resonant grating filters demonstrate an angular tunability that is particularly interesting for tunable filtering applications. However, this tunability is the source of their greatest weakness: their lack of angular tolerance, especially for fine spectral filters. Therefore we have been interested in a new generation of nanostructured filters, proposed by Professor Ura's team at the Kyoto Institute of Technology. After initial experimental demonstrations of fabrication and characterization of the high angular tolerance of these new devices, we started to work on the physics behind these filters and their modelling, in collaboration with the Institut Fresnel. We were thus able to show some insight on the specific operating regime of these filters based on the coupling between propagative modes in air with confined modes trapped in a planar cavity. Our work now focuses on the possibility of using these confined modes to give birth to a new family of devices providing non-linear optical functions, in the framework of a thesis co-supervised with the Institut Fresnel.

Related publications:

S. Augé, S. Gluchko, A. L. Fehrembach, E. Popov, T. Antoni, S. Pelloquin, A. Arnoult, A. Monmayrant, and O. Gauthier-Lafaye, "Mid-infrared cavity resonator integrated grating filters," Opt. Express 26, 27014-27020, 2018.

Sylvain Augé, A. Monmayrant, S. Pelloquin, J. B. Doucet, and O. Gauthier-Lafaye, "Tunable graded cavity resonator integrated grating filters," Opt. Express 25, 12415-12420, 2017.

P. C. Chaumet, G. Demésy, O. Gauthier-Lafaye, A. Sentenac, E. Popov, and A.-L. Fehrembach, "Electromagnetic modeling of large subwavelength-patterned highly resonant structures," Opt. Lett. 41, 2358-2361, 2016.

R. Laberdesque, O. Gauthier-Lafaye, H. Camon, A. Monmayrant, M. Petit, O. Demichel, and B. Cluzel, "High-order modes in cavity-resonator-integrated guided-mode resonance filters (CRIGFs)," JOSA A 32, 1972-1981, 2015.