Recent development on CO₂-laser written long-period fiber gratings

The paper reviews the recent progress on CO₂-laser writing of long-period fiber gratings (LPFGs) in different kinds of fibers, including conventional single-mode fiber (SMF), boron-doped SMF, polarization-maintaining fiber, photonic crystal fiber, and polarization-maintaining photonic crystal fiber. In particular, we report the writing dynamics for the understanding of the physical mechanisms involved in the writing process and show that the CO₂-laser pulses can not only relax the internal stress in the fiber core but also induce a frozen-in stress in the cladding of the fiber under tension. The applications of CO₂-laser written LPFGs, especially for the realization of broadband optical couplers, are also discussed. © 2008 SPIE.