By Amit Malewar Published: September 20, 2025
Collected at: https://www.techexplorist.com/new-fiber-grating-trick-unlocks-powerful-optical-signal-filtering/101048/
To improve how light signals travel through optical fibers, scientists use a clever trick: limit the wavelengths being transmitted. One popular method is Fiber Bragg Grating (FBG), a technology that acts like an intelligent filter, blocking specific light wavelengths while letting others pass. This helps boost signal quality, reduce loss, and make sensing more precise.
There are different types of FBGs:
- Uniform (UFBG) and Chirped (CFBG): suitable for narrow signals, but not great for wide ones.
- Tilted (TFBG) and Long-Period (LPFG) filters are better suited for broad signals, but each has its drawbacks. TFBGs filter slowly and imprecisely, while LPFGs are easily affected by environmental factors.
Researchers from Shenzhen University have introduced a powerful new type of optical filter for managing light signals: chirped and tilted fiber Bragg gratings (CTFBG) created using ultra-fast femtosecond lasers. This method allows for precise and flexible filtering of broadband optical signals, something older techniques struggled with.
Published in the Journal of Lightwave Technology, their results show that CTFBGs can act as precise band-rejection filters, offering better control, customization, and performance across various optical applications, from communications to sensing.
Dr. Yu Fan said, “The CTFBGs have the advantages of large filtering bandwidth (up to more than 100 nm), high filtering slope efficiency, and exceptional broadband tunability, which makes them increasingly used in high-quality band-rejection filtering, edge filtering, and gain equalizers.”
Researchers used a special laser technique called femtosecond line-by-line writing to create chirped and tilted fiber Bragg gratings (CTFBGs). This method lets them fine-tune key features like tilt angle, chirp rate, and spacing, which control how light is filtered.
Their study showed that: Longer CTFBGs can efficiently filter wide bandwidth signals. These filters can be customized to target specific wavelengths between 51 and 112 nanometers.
Dr. Fan notes, “The experimental results show that CTFBGs combine the characteristics of wide bandwidth, high transmission loss, and smooth spectral envelope. The spectral characteristics, such as wavelength, bandwidth, and transmission loss, can be customized by CTFBG fabrication parameters such as initial pitches, tilt angles, and chirp rates. By increasing the grating lengths of CTFBGs, large bandwidth and ultra-high filtering efficiency could be simultaneously realized at selected wavelengths.”
Researchers found that CTFBGs offer significant advantages for filtering broadband optical signals. Beyond being flexible and precise, these filters have low insertion loss (minimal signal weakening), deliver high filtering efficiency, cause negligible back-reflection, and stay stable under environmental changes and physical stress.
Dr. Fan highlights that CTFBGs made with line-by-line laser technology show substantial improvements in how light is shaped and managed, making them ideal for band-rejection filtering, edge filters, and gain equalizers in advanced optical systems.
Journal 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,” in Journal of Lightwave Technology, vol. 43, no. 16, pp. 7847-7853, 15 Aug.15, 2025, DOI: 10.1109/JLT.2025.3577737
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