Patent ID: 8159742

Claim:
A fiber comprising: a first cladding region comprising a first cladding material having a first index of refraction, n1; cladding features disposed in said first cladding region, said cladding features comprising a second cladding material having a second index of refraction, n2, wherein n2 is less than n1, and a relative refractive index difference characterized by (n1−n2)/n1 is less than about 4.5×10 −3 ; and a core region at least partially surrounded by said cladding features, said first cladding region and said cladding features configured such that said core region propagates at least one lower order mode having a wavelength, while limiting propagation of at least one higher order mode having the wavelength by providing said at least one higher order mode with a higher loss than the at least one lower order mode at the wavelength, the loss of said at least one higher order mode at least about 1 dB/m.