High sensitive and efficient photorefractive tunable optical wavelengthfilter with applied external field

摘要

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