Recent development on CO 2 -laser written long-period fiber gratings

Abstract

The paper reviews the recent progress on CO 2 -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 CO 2 -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 CO 2 -laser written LPFGs, especially for the realization of broadband optical couplers, are also discussed.

Fabrication of long-period fiber gratings by CO2 laser in fiber under tension

“…This has been confirmed based on analyses of writing dynamics [3,11] . However, for SMFs with small residual stress, the grating contrast of LPFG written through the mechanism of residual stress relaxation is quite low.…”

“…Owing to the lower fictive temperature of the core material through high boron doping, a high contrast LPFG can be written based on the glass densification in the fiber core using a lower laser energy density so that the transmission spectrum of the grating only consists of the axially symmetric cladding modes [11] . It can be seen that the writing mechanism and the corresponding grating characteristics are dependent on the type of the SMFs used, complicating fabrication of LPFGs using CO 2 laser [3] .…”

“…Different techniques have been developed to fabricate LPFGs since the first demonstration of writing of LPFGs using ultraviolet (UV) light through an amplitude mask in 1996 [2] . Among the reported LPFG fabrication methods, the CO 2 laser writing method [3][4][5][6][7][8][9][10][11] is particularly flexible as it can be practically applied to any fibers and computer-controlled to generate complicated grating profiles without using any masks [3,7,[10][11] . The residual stress relaxation and glass densification are usually considered to be the main mechanisms accounting for the formation of LPFGs using CO 2 laser [3] .…”

“…Among the reported LPFG fabrication methods, the CO 2 laser writing method [3][4][5][6][7][8][9][10][11] is particularly flexible as it can be practically applied to any fibers and computer-controlled to generate complicated grating profiles without using any masks [3,7,[10][11] . The residual stress relaxation and glass densification are usually considered to be the main mechanisms accounting for the formation of LPFGs using CO 2 laser [3] . To study the mechanism of CO 2 laser written LPFGs, we analyze the writing dynamics of laser writing process, which has been adopted in researches on the grating writing in different fibers [10][11] .…”

Chemical sensor for nitrate in water using long period optical fiber grating fabricated by point by point method

“…There are several methods available for the fabrication of LPGs -which include the conventional ultra-violet (UV) writing method using amplitude mask; point by point method using femtosecond-pulse irradiation or electric-discharge or CO 2 laser; diffusion of dopants into the core, relaxation of mechanical stress [16,20]. Of all above, point by point method using CO 2 laser is easiest method because this method can be employed to any type of fiber.…”