Patent ID: 7583877

Claim:
An optical fiber, comprising: a core; a clad comprising a plurality of air holes at a periphery of the core; and a hardening resin filled in a sealed portion at an end of the plurality of air holes, wherein the hardening resin after a hardening comprises a fill length in a range of 7 mm to 8 mm, wherein the core has a refractive index that is greater than a refractive index of the clad, wherein the sealed portion has a refractive index that is less than the refractive index of the core and greater than the refractive index of the clad, and wherein a relative refractive-index difference between the refractive index of the sealed portion and the refractive index of the clad is greater than zero and less than or equal to 0.4% in a temperature range of −40° C. to 70° C.