Scanning near-field optical microscopy as a tool for the characterization of multimode interference devices.
We report the scanning near-field optical microscopy (SNOM) characterization of a 4 x 4 multimode interference (MMI) device working at a wavelength of 1.55 microm and designed for astronomical signal recombination. A comprehensive analysis of the mapped propagating field is presented. We compare SNOM measurements with beam-propagation-method simulations and thus are able to determine the MMI structure's refractive-index contrast and show that the measured value is higher than the expected value. Further investigation allows us to demonstrate that good care must be taken with the refractive-index profile used in simulation when one deals with low-index contrast structures. We show evidence that a step-index contrast is not suitable for adequate simulation of our structure and present a model that permits good agreement between measured and simulated propagating fields.
Martin
Matthieu J
MJ
Laboratoire de Physique de la Matière, Unité Mixte de Recherche-Centre National de la Recherche Scientifique 5511, Institut National des Sciences Apliqués de Lyon, Villeurbanne, France. matthieu.martin@insa-lyon.fr
Benyattou
Taha
T
Orobtchouk
Régis
R
Rooms
Frédéric
F
Morand
Alain
A
Schanen
Isabelle
I
Benech
Pierre
P