Electro-optic modulator based on X-cut proton-exchanged planar lithium niobate waveguide

Abstract

Conventional electro-optic modulators have been always fabricated based on channel waveguide with complicated electrodes. In this paper, we propose a new type of modulator based on proton-exchanged planar lithium niobate waveguide. After proton exchange and annealing, the refractive index of planar lithium niobate waveguide is gradually changed with the depth. Two-prism coupling method is used to determine the effective index of the planar waveguide by measuring the coupling angle of m-lines. When the transverse electric field is applied along the Z axis of the X-cut proton-exchanged planar lithium niobate waveguide, the index distribution of the waveguide will be changed due to the electro-optic effect, and the coupling angle of the m-lines will be also changed accordingly. Based on this principle, a new type of amplitude modulator is proposed theoretically. The relationship between the driven voltage and position of two electrodes are theoretically investigated. The change of refractive index of the waveguide caused by the applied transverse electric field as a function of waveguide depth is also studied. Compared with other type of amplitude modulators, it shows some advantages such as low fabrication cost and the low driven voltage.