Ultrabroadband single-mode long-period fiber gratings using high-order cladding modes

We demonstrate analytically that long-period fiber gratings operating near the maximum of a cladding mode's phase-matching curve can be designed to exhibit far broader bandwidths (around 800 nm) than reported to date, at any center wavelength and with any peak attenuation. In a given fiber, the center wavelength and attenuation are controlled independently by properly selecting the grating period and length, respectively, Extremely large bandwidths are obtained by increasing the grating index perturbation, by increasing the fiber core radius, and/or optimizing the numerical aperture. Implemented with a mechanically induced grating, this concept produced a 1465 nm filter with a record 10 dB bandwidth of 360 nm. (C) 2004 American Institute of Physics.