Single-Mode Operation in Flat Fibers Slab Waveguide via Modal Leakage

An approach to obtain single-mode operation on a semirectangular large core area Flat Fiber (FF) slab waveguide is proposed. A new design of FF with two defect eye holes is presented, and its single-mode guiding is analyzed by simulation. To validate the simulation results, a proof of concept FF with a core area >1200 μm
²
was fabricated, and its modal behavior was examined. It was found that higher order propagation modes could be discriminated from the large core area by introducing a high-refractive index region in the FF eye holes. Experimental results confirmed a single Gaussian mode profile (mode field diameter of ≈745 μm) output of this large core FF, thus validating the simulation results.