||In integrated optics and communications, a coupler is the important devices to divide signal light into different channels. Unfortunately, the most common coupler, directional coupler nowadays, has the worst fabricated tolerance and wavelength dependent of optical property. However, the three waveguides adiabatic coupler is able to solve these problems including the disadvantage of directional coupler. Lithium Niobate is an attractive substrate material with high electro-optics and nonlinearity, which benefits the studies and usage related to active devices to build up a more compact and multi-functional device.|
In this work, a three-Ti-diffused-waveguide adiabatic coupler was design and fabricated by stimulated Raman adiabatic passage (STIRAP) method on lithium niobate crystal. In the experiment, the tolerance from the fabrication error of the middle waveguide could reach to 0.6 μm. In addition, the deviation of the crossover-state division ratio was less than 7.5 % for TM polarization as well as 4 % for TE polarization in the operating wavelength range of 1495 nm to 1600 nm.
However, the prior experimental result, the complete energy coupling/ transferring, didn’t follow the design properly, which could be caused by some issues, such as a initially excited and unexpected mode and unwanted coupling effect between two sides waveguides are also discussed. In order to deal with and analysis different waveguide parameters in a three-waveguide adiabatic coupler, a commercial software, BeamPROP, is utilized to simulate and develop the designed parameters, and prove that the design is comparable with others research works. In the future, the new design will be kept improving and fabricating.
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