The present invention provides an optical fiber suitable for the manufacture
of optical fiber couplers and having low macrobending loss, low cutoff wavelength,
low attenuation, and low sensitivity to variations in overclad mass. One aspect
of the present invention provides an optical fiber having a core having an index
profile, the index profile of the core having a value of of between about
1.7 and about 3.0; and a cladding region surrounding and in contact with the core,
the cladding region having an outer radius of at least about 40 m, wherein
the optical fiber has a cutoff wavelength of between about 870 nm and about 970
nm, and a macrobending loss of below about 1 dB at a wavelength of 1550 nm when
wrapped one turn around a 32 mm mandrel.
