Chalcogenide-on-Lithium Niobate Resonator Waveguides and their nonlinear applications
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Chalcegenide glass material, such as amorphous As2S3, is an ideal candidate material to be integrated onto a much lower refractive index substrate and used as an all-optical active device. The As2S3 glass is with wide infrared transparence from near IR to mid IR and refractive index as high as 2.45 at 1.55 ?m. As2S3 glass also shows a good potential as a Kerr medium for ultra-fast all-optical tuning capability because of its high nonlinearity coefficient at infrared wavelength range. In terms of the all-optical nonlinear application, resonant cavity devices are favored for their easily tunable ability as a small change of refractive index in the material would lead to a shift for their resonance. Therefore, it is motivating to combine the As2S3-on-LiNbO3 optical waveguide platform and the resonant cavity structure together for the integrated all-optical circuits. A vertically integrated As2S3 ring resonator side-coupled to a low-index Ti:diffused LiNbO3 straight waveguide was designed and fabricated. At 1.55-?m wavelength, a low 1.2 dB/cm propagation loss and an over 30-dB extinction ratio were demonstrated on the fabricated As2S3-on-LiNbO3 ring resonator waveguide with 400-?m bend radius, which corresponded to an intrinsic Q value as high as 3.5x105. At the same time, an integrated As2S3-on-LiNbO3 optical cavity waveguide based on sidewall grating couplers was designed, fabricated and optically tested. Using the sidewall grating couplers with a coupling strength as high as 14 mm-1, the cavity resonant response with a FSR of 0.5 nm over a 5 nm bandwidth at 1.55 ?m was demonstrated with a cavity propagation loss at 2.5 dB/cm. The waveguide nonlinear efficiency ? of the As2S3-on-LiNbO3 ring waveguide was calculated at 3.85 radian/m?W and a pump-signal measurement platform was setup to observe the nonlinear tuning phenomenon of the ring resonator waveguide. Also, the nonlinear tunability of our hybrid As2S3-on-LiNbO3 grating cavity waveguide is numerically analyzed. The optical energy at the resonant wavelength inside the grating cavity waveguide is 7 times as high as the input energy, which would significantly reduce the pump power for the nonlinear tuning applications.