Ayman HOBLOS : "Electro-Optical Photonic Crystal Devices for Modulation and Detection of Weak Electric Fields"

Ayman HOBLOS PhD works : "Electro-Optical Photonic Crystal Devices for Modulation and Detection of Weak Electric Fields"

Although the presentation will be public, the sanitary restrictions currently in force limit the number of people allowed tp be in the amphitheatre. Only those invited will be able to attend the presentation, but it is always possible to follow the presentation via Visio (the link will be sent later).

Abstract : In this thesis, we have studied two different devices: an electric field sensor and an electro-optical modulator made of LiNbO3, based on the electro-optical effect of this material. The proposed structures are based on photonic crystals in which a very confined optical mode with a high quality factor (Q) can be excited in LiNbO3. This leads to a strong enhancement of the electro-optical effect which results in a modification of the refractive index of LiNbO3. This index variation induces a spectral shift in the resonance of the optical mode. We used the FDTD method for the calculation of the optical response of the proposed structures. Through its character of spatial discretization (Yee schema), this numerical method allowed us to reveal the excitation of the symmetry protected modes (SPM) through a symmetry break related to the numerical scheme used. By exciting this type of SPM modes, we reach resonances with a very high Q factor up to 10^6. By combining the high Q-factors with the dielectric mode required for an electro-optical device, we have obtained a high local field factor of about 245. We have demonstrated, with the versatile structure we propose, an electric field detection sensitivity of 4 pm.m/V and a temperature detection sensitivity of about 947 nm/^oC. In addition, we have proposed another geometry of an electro-optical modulator based on an enhanced transmission meta-material deposited on LiNbO3. Numerical simulations show that our electro-optical modulator has a value of the half-wave voltage Vpi of only 0.3 V, which is more than 3 times lower than the state of the art. The fabrication of the proposed structure has been started and preliminary results are presented. The optical characterization of the structure allows us to validate the theoretical behavior of its optical response taking into account manufacturing imperfections. The optical bench used for the characterization of the fabricated structures was set up during this thesis.

Jury composition  : 

M. Christophe SAUVAN Chargé de Recherche au Laboratoire Charles Fabry, Reporter
M. Gaëtan LEVEQUE Maitre de conférence à l'Université de Lille 1, Reporter
M. Brahim GUIZAL Professeur à l'Université de Montpellier, Reviewer
M. Abdelkrim KHELIF Directeur de recherche CNRS à l’Institut FEMTO-ST, Reviewer
M. Maria-Pilar BERNAL Directrice de recherche CNRS à l’Institut FEMTO-ST, PhD co-director
M. Fadi I. BAIDA Professeur à l'Université de Bourgogne Franche-Comté, PhD Director

Localization : Amphithéâtre J.J Gagnepain, Institut FEMTO-ST, 15B, Avenue des Montboucons - 25000 Besançon