High sensitive and efficient photorefractive tunable optical wavelength filter with applied external field

Abstract

We develop a tunable optical wavelength filter with PR (photorefractive) materials applied the external field for achieving higher sensitivity and efficiency. In the past, the diffraction efficiency of the PR tunable filters with transmission gratings has been much lower than other conventional wavelength filters, such as the array wavelength gratings filter, the thin film filter, and the fiber Bragg gratings filter. By applying the external field to PR materials, we can obtain the refractive index modulation depth of 13 times larger than that without applied field, specifically in lithium niobate with the acceptor density of ~1022 [1/m3] and the voltage of 10 [kV/cm]. Our PR tunable filter provides reconfigurable wavelength routing of the signal beam since the various diffraction gratings can be immediately induced and multiplexed by changing incident conditions of two coherent writing beams viewpoint in comparing experimental results to numerical simulations, and can be rewritten dynamically through the PR effect. These advantages allow us to achieve more flexible optical net work based on the wavelength division multiplexing technique. In this work, we calculate the relationship between the diffraction efficiency and the magnitude of the applied external field by solving coupled wave equations in the case of lithium niobate, respectively.