An optical fiber (101, 201, 301, 401, 501, 601, 701, 801, 901, 1001, 1101, 1201, 1301, 1401, 1501, 1601, 1701, 1801, 1901, 2105, 2204, 2301,3001,3101,3201,3301,3401,3501,3601,3701,3801,3901, 4001) adapted for suppression of higher order modes HOM and for guiding light in a narrow spectral wavelength range, said optical fiber comprising an axial direction, a cross section perpendicular to said axial direction, and a core region (103, 203, 303, 403, 503, 603, 703, 803, 903, 1003, 1103, 1203, 1303, 1403, 1503, 1603, 1703, 1803, 1903, 2303, 3003, 3103, 3203, 3303, 3403, 3603, 3703, 3803, 3903, 4003) extending along said axial direction, said core region being adapted to guide an optical signal; a cladding region surrounding said core region, said cladding region comprising an inner cladding region comprising an inner cladding basis material in which inner cladding features extending along said axial direction are defined, said inner cladding features comprising a plurality of first inner cladding features (105, 205, 305, 405, 505, 605, 705, 705, 805, 905, 1005, 1105, 1205, 1305, 1405, 1505, 1605, 1705, 1805, 1905, 2305, 3005, 3105, 3205, 3305, 3405, 3605, 3705, 3805, 3905, 4005) comprising a first material and having a first refractive index profile, a first cross sectional shape and a first normalized frequency parameter relative to said inner cladding basis material, wherein said plurality of first inner cladding features forms a first cross sectional extending optical resonant structure connecting said core region to a first light sink, wherein said inner cladding features further comprises a plurality of second inner cladding features (206, 306, 406, 506, 606, 706, 706, 806, 906, 1006, 1106, 1206, 1306, 1406, 1506, 1606, 1706, 1806, 1906, 2306, 3006, 3106, 3206, 3306, 3406, 3606, 3706, 3806, 3906, 4006) comprising a second material and having a second refractive index profile, a second cross sectional shape and a second normalized frequency parameter relative to said inner cladding basis material, wherein said plurality of second inner cladding features forms a second cross sectional extending optical resonant structure connecting said core region to a second light sink, and wherein • said first refractive index profile differs from said second refractive index profile; and/or • said first cross sectional shape differs from said second cross sectional shape, and/or • said first normalized frequency parameter differs from said second normalized frequency parameter, wherein variations in the cross sectional shape between two inner cladding features is determined by arranging them with a maximal overlap and determine any difference in cross sectional shape as the total area of the sections of one inner cladding feature that is not matched by a section in the other inner cladding feature relative to the total cross sectional area of the one inner cladding feature and variations in the refractive index profile between two inner cladding features is determined by arranging them with a maximal overlap and determine a difference in refractive index profile by integrating over the common area of the respective two inner cladding features to obtain two refractive index profiles and determine any difference between the two refractive index profiles, and wherein said inner cladding features further comprising a plurality of third inner cladding features (104, 204, 304, 404, 504, 604, 704, 704, 804, 904, 1004, 1104, 1204, 1304, 1404, 1504, 2304, 3004, 3104, 3204, 3304, 3404, 3604, 3704, 3804, 3904, 4004) that comprise a third material and have a third refractive index profile and a third cross sectional shape, wherein said third inner cladding feature comprises a low index region, and wherein said low index region comprise a void. • said first refractive index profile differs from said second refractive index profile; and/or • said first cross sectional shape differs from said second cross sectional shape, and/or • said first normalized frequency parameter differs from said second normalized frequency parameter,