Transmission Characteristics of Long-Period Fiber Gratings Using Periodically Corroded Single-Mode Fibers

Abstract

Department of Physics and Research Institute for Convergence of Basic Science,Hanyang University, Seoul 133-791, Korea(Received March 25, 2015 : revised June 1, 2015 : accepted June 26, 2015)Transmission characteristics of long-period fiber gratings (LPFGs) fabricated by periodically etching a conventional single-mode fiber (SMF) are investigated. After coating the SMF with photoresist, the cladding of the SMF is symmetrically and periodically removed by using a wet etching technique resulting in the formation of the LPFG. Tensile strain reinforces the coupling strength between the core and the cladding mode based on the photoelastic effect. The extinction ratio of the SMF-based LPFG at a wavelength of 1550.8 nm is measured to be -15.1 dB when the applied strain is 600 µe. The ascent of ambient index shifts the resonant wavelength to shorter wavelength because of the increase of the effective refractive index of the cladding mode. The extinction ratio is diminished by increase in the ambient index because of the induction of the optical attenuation of the cladding mode. The transmission characteristics of the proposed LPFG with variations in torsion are also measured. The photoelastic effect based on torsion changes the extinction ratio and the resonant wavelength of the proposed SMF-based LPFG. The polarization-dependent loss of the LPFG is also increased by torsion because of the torsion-induced birefringence. The polarization-dependent loss of the LPFG at torsion of 8.5 rad/m is measured to be 3.9 dB.Keywords : Long-period fiber gratings, Fiber-optic sensors, Photoelastic effectOCIS codes : (060.0060) Fiber optics and optical communications; (060.2370) Fiber optics sensors; (050.2770) Gratings