In an advancement that could improve the way that optical distribution networks are maintained, researchers at Shenzhen University have demonstrated an encrypted fiber optic tag for all-optical labeling and the recognition of optical transmission channels, such as access networks. Unlike traditional optical link labeling methods, the fiber optic tag makes full use of the optical link to achieve all-optical reading, recognition, and restoration of link information. The fiber optic tag is based on an encoded fiber Bragg grating (FBG) array that is fabricated using a point-by-point femtosecond laser pulse chain inscription method. The encrypted, all-optical labeling method uses the feature information and spatial distribution of the FBG array to flexibly store different coding sequences. According to its developers, optical channel recognition and data encryption using FBGs — with specially designed spatial distributions, reflection wavelengths, and reflectivities — establishes a technology that is reliable both for data encryption applications as well as for data storage within optical fiber access networks. It could be used for applications in port identification, encrypted data storage, and transmission in fiber networks, the researchers said. Specifically, the fiber optic tag carries a binary data sequence. This sequence is written into the fiber core in the form of the FBGs, with different spatial locations, different resonant wavelengths, and different reflectivity strengths. By controlling the femtosecond laser fabrication parameters, the researchers control the characteristics of the different grating fragments. The tag carries rich information due to the way it uses the spatial distribution, reflectivity, and reflection wavelength of the gratings. To improve the storage capacity of the fiber tag, the researchers used the reflected signal of the grating to increase the number of switch states that the tag can represent. To restore the encrypted information contained in the fiber tag, the researchers measured the backscattering signal with an optical backscatter reflectometer. Recovery of the featured grating information, as well as the spatial distribution of the FBGs and the information carried in their specific channels, is based on a code rule. When an optical time-domain reflectometer is used for reading, a specific administrator can be assigned to perform a complete and error-free information recovery. The correct optical link information can only be obtained by designated personnel. After the fiber tag is connected to the network, it can be used as a channel marking and detection tool. In experiments, the researchers showed that a binary data sequence carried by a fiber tag can be inscribed into the fiber core in the form of an FBG array. They further showed that the tag data can be encrypted by providing the spatial distributions of the FBGs with the appropriate reflection wavelengths and reflectivity strengths. The team also demonstrated that the information carried by the optical fiber tag can only be decoded when the predefined code rule is known. The flexible preparation of encoded fiber Bragg grating arrays using femtosecond laser, multipulse exposure for optical link labeling. The optical fiber tags use the spatial distribution and reflected signal characteristics of the grating to carry rich information and achieve encryption functions. Courtesy of Z. Cai et al. “Faced with the increasing number of optical transmission links, traditional physical labels have high labor costs and are prone to waste port resources, making it difficult to meet efficient and stable link labeling requirements,” researcher Changrui Liao said. “All of these indicate that this fiber optic tag will have broad market application prospects.” The research was published in International Journal of Extreme Manufacturing (www.doi.org/10.1088/2631-7990/acd825#artAbst2).