CO2 laser-induced long-period fiber grating in the dispersion turning point

Abstract

A CO2 laser-induced long-period fiber grating (LPFG) in the dispersion turning point (DTP) has been proposed in this work, which has demonstrated the possibility of fabricating LPFG with a shorter period of 115 μm in a thin single-mode fiber (SMF) without etching cladding. The LPFG working near DTP was also induced in a conventional SMF by CO2 laser after etching cladding, whose grating period was 196 μm. Then, the refractive index (RI) sensitivity of LPFG based on thin SMF was optimized by fully combining DTP and cladding reduction. Considering the sensor probe's mechanical strength comprehensively, the thin SMF cladding was etched to 51.03 μm to ensure cladding mode LP1,6 work near DTP, which can result in an average RI sensitivity of 2117.12 nm/RIU in the RI range of 1.33222 to 1.39018. Based on its excellent RI sensing performance, the proposed LPFG is a prospective sensor that can be applied to significant fields such as environmental, chemical, or biological parameters measurement. At the same time, this study provides a low-cost path to fabricate LPFG worked in DTP for most researchers.