Patent ID: 7382957

Claim:
An optical fiber comprising: (i). a silica based, single mode rare earth doped core having a radius of at least 7 μm and, an effective area of at least 153 μm 2 , and a first index of refraction n 1 ; (ii). at least one silica based cladding surrounding the core and having a second index of refraction n 2 , such that n 1 >n 2 , said cladding having: (A) a only two stress rods, and (B) a only two air holes extending longitudinally through the length of said optical fiber, and said air holes are circular with a diameter of 5 μm to 50 μm; wherein said optical fiber supports a single polarization mode within a single polarization band or poses polarization maintaining properties within the operating wavelength range and said core has a refractive index delta relative to said cladding of no more than 0.2%.