Functionalized Polymers for Electro-Optic Modulation Through Grating-Induced Resonant Excitation of Guided Modes

Abstract

Most optical modulators are built in the channel waveguide configuration. This is so for the Mach-Zehnder interferometer and of the directionnal couplers where the outcoming guided wave can be monitored by applying an external electric field. All these devices imply sophisticated technologies. On another hand it is also interesting to build devices controling laser beam propagation in the free space by means of a corrugated grating (Reinisch 1985). The intensities diffracted in the various orders by a grating made with an electro-optical polymer can be modulated with an applied electric field (Shi 1994). Such devices can find applications in computers for board to board information transmission. We report in this paper a modulator where both the transmitted and reflected intensities of a laser beam can be modulated. The electro-optic material is paranitroaniline (PNA) grafted on a PMMA polymer backbone. A laser beam is coupled into the planar film by means of a grating. When an electric field is applied, the effective index of the guided mode varies which results in a change of the coupling conditions and subsequently in the intensities of the .transmitted and reflected beams. The modulation yield is 40% when a 40 V external voltage is applied.