Mode number Effective refractive index Modelled refractive index 1 1.9351 1.9354 2 1.9341 1.9345 3 1.9318 1.9320 4 1.9294 1.9298 5 1.9262 1.9266 6 1.9224 1.9227 7 1.918 1.9181 8 1.9128 1.9126 9 1.9069 1.9066 10 1.9002 1.8998 11 1.8926 1.8924 12 1.8842 1.8841 13 1.8754 1.8751 14 1.866 1.8655 15 1.8554 1.8551 16 1.8439 1.8440 17 1.8327 1.8325