Specialty Optical Fibers Handbook

region and the trench region, the greater is the ability to tailor the group delay

and dispersion of the waveguide. The presence of the third raised index layer

adds an additional guiding layer to the waveguide and as wavelength increases

further, when overall structure is properly designed the energy will spread

across the entire three layer structure and remain confined. As the mode

spreads out over the entire structure, the fraction of energy contained within

the trench region peaks and eventually decreases as the ring layer provides

guidance. With appropriate choices of waveguide dimensions, the waveguide

can be designed so that as the mode grows with wavelength and extends

outward into the trench and ring regions, the group delay and the magnitude ...