Fiber Bragg gratings（ FBG） are successfully fabricated in few mode fiber using femtosecond laser and phase mask technique

its reflection spectrum

high temperature and strain sensing characteristics are studied.The results show that there are three main reflection peaks in the reflection spectrum of few modes FBG

which correspond to the self-coupling and the mutual coupling between different modes. This FBG has very good temperature response characteristics under 800 ℃

and the temperature sensitivity is 14. 27 pm/℃. It also has very good strain response characteristics at 500 ℃

and the strain sensitivity is 1. 77 pm/10

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. It can be potentially used in strain sensing under high temperature and multiwavelength fiber laser.