Gain Improvement of $\hbox{Er-Ti:LiNbO}_{3}$ Waveguide Amplifier by an $\hbox{As}_{2}\hbox{S}_{3}$ Overlay Waveguide

A new configuration consisting of an arsenic trisulfide (As
₂
S
₃
) channel waveguide on top of an erbium (Er)-doped titanium-diffused x-cut lithium niobate (Er:Ti:LiNbO
₃
) waveguide has been investigated by simultaneous analytical expressions, numerical simulations, and experimentation. Both simulation and experimental results have shown that this structure can enhance the optical gain, as predicted by the analytical expressions. An As
₂
S
₃
channel waveguide has been fabricated on top of a conventional Er:Ti:LiNbO
₃
waveguide, where the higher refractive index As
₂
S
₃
waveguide is used to pull the optical mode toward the substrate surface where the higher Er concentration yields an improved propagation gain. The relationship between the gain and As
₂
S
₃
layer thickness has been evaluated, and the optimal As
₂
S
₃
thickness was found by simulation and experimentation. Side integration was applied to reduce the extrapropagation loss caused by the titanium diffusion bump. The propagation gain has been improved from 1.1 to 2 dB/cm.