**5. Conclusion and outlook**

Significant progress has been demonstrated for POF grating devices fabrication during the last years, such as to allow fast fabrication of POF grating devices under 248 nm and 266 nm wavelength UV, one 15 ns pulse for POF FBG fabrication. Besides the benefit as potential grating fabrication technology in the optical fiber drawing process, special grating structures such as Chirped FBG also take advantage of the short irradiation time, such as the benefit to reduce the stability requirements for the irradiation setup.

Besides strain and temperature sensitive devices as the main applications of POF FBG, special grating devices open new perspectives. As the main relevant examples, chirped POF FBGs used for high-resolution thermal detection in the biomedical area with a higher sensitivity and bio-compatibility than silica ones, special grating in POF are attractive for future biomedical applications, which also make special POF grating fabrication technology have room to improve.

To conclude, grating devices in POF show attractive performance for sensing applications. However, most of the POF for grating devices fabrication are still homemade, which need time and research to make this technology mature for real applications. From this point of view, grating devices fabrication in commercial CYTOP POF are promising, also the investigated for low cost single-mode commercial CYTOP POF and grating on such fiber.
