Fig. 1

(a) A quarter cross-section of the multimode W-type GI mPOF. The pitch Λ determines the position of air-holes with diameters d₁, d₂, d₃, d_p and d_q in a triangular lattice, (b) The solid black line represents the RI distribution of W-type GI mPOF, for g = 2.0, at λ = 645 nm.