Patent ID: 7110647

Claim:
A polarization maintaining optical fiber, comprising: a core extending along a longitudinal axis, said core including a rare earth and a first index of refraction; a cladding disposed about said core and having a second index of refraction that is less than said first index of refraction, said cladding having a first thermal coefficient of expansion (TCE); a pair of longitudinally extending members, each of said members having a TCE that differs from said first TCE of said cladding, said pair being spaced apart by a distance d i ; a second cladding disposed about said cladding, said second cladding having a third index of refraction that is less than said second index of refraction; said fiber having a fundamental mode having a mode field diameter (MFD), and wherein said core is a multimode core having a diameter d c that is greater than or equal to 15 microns; the numerical aperture of said core relative to said first cladding is less than or equal to 0.12; the ratio d i /MFD is greater than 2; and said fiber provides a beat length of less than 3.5 mm at a wavelength of 633 nm.