Polarization insensitive microbend fiber gratings and devices using the same

Apparatus comprising an optical fiber, the optical fiber configured to support polarization insensitive operation of a microbend-induced grating formed in the core thereof, the fiber comprising:

• a central core region defined by a radius rc and a predetermined refractive index, defined as a refractive index difference Δnc as measured with respect to the refractive index of silica;
• a trench area surrounding the central core region, the trench area having a refractive index difference Δnt less than the refractive index of the central core region;
• and
• a ring area surrounding the trench area, wherein the refractive index difference of the ring area (Δnr) is selected to be greater than 0.015, with a transition of no greater than one micron between the refractive index difference of the trench area and the ring area, the core region refractive index difference (Δnc) being maintained to be approximately three-quarters the value of the refractive index of the ring area (i.e., Δnc≈0.75*Δnr).