Coupling coefficient of fiber optic grating
The coupling efficiency is highly sensitive to the grating's pitch p p, etch length le l e and etch depth he h e as well as to the fiber's position x x and tilting angle θ θ. These five parameters are usually optimized together to maximize the coupling efficiency at the. Surface grating coupler is a preferred candidate that provides flexibility for circuit design and reduces effort for both fabrication and alignment. In the past decades, considerable research efforts have been made on in-plane grating couplers to address their insufficiency in coupling efficiency. We attribute the coupling bandwidth to the mismatch of effective indices between the diffracted beam and the actual grating structure around the operation wavelength for fiber to waveguide excitation.
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