A recent breakthrough in fiber optics is set to change the way light signals are filtered in optical networks. Scientists have developed chirped and tilted fiber Bragg gratings (CTFBGs) using ultra-fast femtosecond lasers, enabling precise and flexible wavelength filtering for broadband optical signals.

Fiber Bragg gratings (FBGs) have long been used to control the transmission of specific light wavelengths, improving signal quality, reducing loss, and enhancing sensing accuracy. Traditional designs like uniform (UFBG) and chirped (CFBG) gratings perform well for narrow signals but struggle with wider bandwidths. Tilted (TFBG) and long-period gratings (LPFG) help with broad signals, yet they have limitations such as slow filtering or environmental sensitivity.

The new CTFBG method overcomes these challenges by combining chirped and tilted structures created through femtosecond laser line-by-line writing. This technique allows precise adjustment of parameters like tilt angle, chirp rate, and grating spacing, producing filters that offer exceptional control over wavelength, bandwidth, and transmission characteristics.

Dr. Yu Fan from Shenzhen University explains: “CTFBGs provide wide filtering bandwidths over 100 nm, steep filtering slopes, and excellent tunability. These features make them ideal for high-quality band-rejection filtering, edge filtering, and gain equalization in modern optical systems.”

Experimental results show that longer CTFBGs efficiently filter wide-bandwidth signals and can be tailored to target specific wavelengths between 51 and 112 nanometers. These filters maintain low insertion loss, minimal back-reflection, and strong stability under environmental and mechanical stress.

Published in the Journal of Lightwave Technology, this research demonstrates the potential of CTFBGs to improve optical communications, sensing, and advanced photonics applications. By combining femtosecond laser precision with innovative grating design, these next-generation filters offer unmatched flexibility and performance.

Reference: Y. Fan, W. Bao, C. Fu, C. Liao, and Y. Wang, “Broadband and High-Filtering-Efficiency Band-Rejection Filters Fabricated Using Femtosecond Laser Line-by-Line Technology,” Journal of Lightwave Technology, vol. 43, no. 16, pp. 7847-7853, 15 Aug. 2025, DOI: 10.1109/JLT.2025.3577737