Theoretical and experimental study of 37-core waveguides with large mode area

The evanescently coupled multicore waveguide lattice composed of 37 linear type I cores hexagonally arranged has been theoretically studied and fabricated by low-repetition-rate femtosecond laser inscription of bulk fused silica. The effects of the single corés numerical apertures (NAs) and spacing on the mode characteristics of the 37-core waveguide were calculated by the finite-element method. It was found that the mode field areas of the fundamental mode LP₀₁ with 5 μm spacing of different NAs were all larger than 577 μm², which was confirmed by the experiments. The measured near-field mode profiles for different writing conditions and different spacing also showed that the waveguide supported both a single mode (LP ₀₁) and two modes (LP₀₁ and LP₁₁). The multicore waveguide, according to our study, is particularly interesting for mode converters.