title: Negative-index gratings formed by femtosecond laser overexposure and thermal regeneration.
abstract: We demonstrate a method for the preparation of negative-index fibre Bragg gratings (FBGs) using 800 nm femtosecond laser overexposure and thermal regeneration. A positive-index type I-IR FBG was first inscribed in H2-free single-mode fibre using a femtosecond laser directed through a phase mask, and then a highly polarization dependant phase-shifted FBG (P-PSFBG) was fabricated from the type I-IR FBG by overexposure to the femtosecond laser. Subsequently, the P-PSFBG was thermally annealed at 800 °C for 12 hours. Grating regeneration was observed during thermal annealing, and a negative-index FBG was finally obtained with a high reflectivity of 99.22%, an ultra-low insertion loss of 0.08 dB, a blueshift of 0.83 nm in the Bragg wavelength, and an operating temperature of up to 1000 °C for more than 10 hours. Further annealing tests showed that the thermal stability of the negative-index FBG was lower than that of a type II-IR FBG, but much higher than that of a type I-IR FBG. Moreover, the formation of such a negative-index grating may result from thermally regenerated type IIA photosensitivity.
authors.affiliation: Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Jun
authors.initials: J
authors.lastname: He
authors.affiliation: Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Yiping
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Changrui
authors.initials: C
authors.lastname: Liao
authors.affiliation: Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.|Department of Electrical Engineering, The Hong Kong Polytechnic University, Hong Kong, China.
authors.forename: Chao
authors.initials: C
authors.lastname: Wang
authors.affiliation: Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Shen
authors.initials: S
authors.lastname: Liu
authors.affiliation: Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Kaiming
authors.initials: K
authors.lastname: Yang
authors.affiliation: Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Xiaocong
authors.initials: X
authors.lastname: Yuan
authors.affiliation: College of Electronic Science and Technology, Shenzhen University, Shenzhen 518060, China.
authors.forename: Guo Ping
authors.initials: GP
authors.lastname: Wang
authors.affiliation: Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Zhang