Propagation in doubly clad single-mode fibers

General propagation properties and universal curves are given for doubly clad single-mode fibers with inner cladding index higher or lower than outer cladding index, using the two parameters: inner cladding/core radii ratio and inner cladding/core index differences ratio. LPO1, LP11, and LPO2 cutoff conditions are examined. It is shown that dispersion properties largely differ from the singly clad single-mode fiber case, leading to large new possibilities for low-loss dispersion-free fibers at any wavelength between 1.3 and 1.7 μm.