Chirped Bragg Gratings in PMMA Step-Index Polymer Optical Fiber

In this letter, we report for the first time, a chirped fiber Bragg grating photo-inscribed in undoped PMMA polymer optical fibre (POF). The chirped polymer optical fiber Bragg gratings (CPOFBGs) were inscribed using an UV KrF excimer laser operating at 248 nm and a 25-mm long chirped phase mask customized for 1550-nm grating inscription. The used laser pulsing frequency was 1 Hz with an energy of 5 mJ per exposure and only few shots for each grating inscription were employed. The reflection amplitude spectrum evolution of a CPOFBG is investigated as a function of the applied strain, temperature, and pressure. These results can potentiate further developments in different sensing fields, such as liquid level monitoring, splits, and transverse cracks in structural health monitoring by local pressure analysis or even biomedical field. Furthermore, CPOFBGs could present some critical advantages preferably replacing their silica counterparts as well as the uniform polymer FBGs.