Polarization independent grating coupling in planar wave-guide using photo-induced birefringence.

The effective refractive index of a guided wave depends on its polarization due to the anisotropic phase shift during the total internal reflection. Thus the grating-coup ling angle is in general different for TM and TE polarized light. The compensation of this anisotropy is a difficult task. Some optical materials may present a significant birefringence when exposed to a polarized light. We would like to compensate the optical anisotropy using this photo-induced birefritigence phenomenon, which would allow us to bring back the TM grating-coupling angle to the TE one. During these studies, we have developed an optical material, which allows us the formation of a relief grating via traditional light exposure techniques. At the same time, this material exhibits a significant photo-induced birefringence. This takes place thanks to the molecular reorientation phenomena after that the recording of the grating coupler is over. It is important to note that this last process does not affect significantly the grating-coupler. Furthermore we have observed that photo-induced birefringence present a strong reminiscence after the pump beam deactivation. The grating coupling experiments with and without the photo-induced phenomena were conducted.