Abstract

Fiber Bragg gratings (FBGs) inscribed by using femtosecond laser point-by-point (PbP) technology typically have high birefringence due to the elliptical cross-sectional pattern of refractive index modulations (RIMs) created in the fiber core. Additionally, a highly reflective type II PbP FBG, which has a large coupling coefficient, also exhibits large insertion loss due to the limited RIM area induced by a single femtosecond laser pulse. Here we demonstrate a slit beam shaping method for femtosecond laser PbP inscription of high-quality FBGs, featuring by high reflectivity, low insertion loss, and low birefringence. The slit beam shaping method could reduce the ellipticity in the cross-sectional pattern of RIMs without reducing the cross-sectional area, leading to low birefringence and low insertion loss. The experimental results agree well with numerical calculations. Hence, a high-quality type II PbP FBG, which has high reflectivity of 99.12% (i.e., Bragg resonance attenuation of 20.52 dB), low insertion loss of 0.30 dB, and low birefringence of 1.86 × 10⁻⁶, was successfully created by use of a slit width of 0.8 mm. Moreover, an enlarged cross-sectional area was created by use of a slit width of 0.2 mm, resulting in a high ratio of 172.46 of the coupling strength coefficient to the scattering loss coefficient in the fabricated PbP FBG, which exhibits very high reflectivity of 99.99% (i.e., a strong Bragg resonance attenuation of 46.65 dB) and low insertion loss of 0.27 dB. Such high-quality FBGs will be promising in many applications, such as optical fiber communications, sensors, and lasers.

High thermal stability of ultra-low insertion loss type II cladding fiber Bragg grating based on femtosecond laser point-by-point technology

Dan Su and Xueguang Qiao
Opt. Express 30(6) 9156-9164 (2022)

Efficient point-by-point Bragg grating inscription in sapphire fiber using femtosecond laser filaments

Xizhen Xu, Jun He, Jia He, Baijie Xu, Runxiao Chen, Ying Wang, Yatao Yang, and Yiping Wang
Opt. Lett. 46(11) 2742-2745 (2021)

Femtosecond laser point-by-point inscription of an ultra-weak fiber Bragg grating array for distributed high-temperature sensing

Baijie Xu, Jun He, Bin Du, Xunzhou Xiao, Xizhen Xu, Cailing Fu, Jia He, Changrui Liao, and Yiping Wang
Opt. Express 29(20) 32615-32626 (2021)

Optimized femtosecond laser direct-written fiber Bragg gratings with high reflectivity and low loss

Jiafeng Wu, Xizhen Xu, Changrui Liao, Xiaoyu Weng, Liwei Liu, Junle Qu, Yiping Wang, and Jun He
Opt. Express 31(3) 3831-3838 (2023)

High-quality fiber Bragg grating inscribed in ZBLAN fiber using femtosecond laser point-by-point technology

Lin Chen, Cailing Fu, Zhihao Cai, Pengsheng Shen, Yu Fan, Huajian Zhong, Chao Du, Yanjie Meng, Yiping Wang, Changrui Liao, Jun He, and Weijia Bao
Opt. Lett. 47(14) 3435-3438 (2022)