LAUSR

A twist sensor based on a few-mode long period grating (LPG) and a tilted fiber Bragg grating (TFBG) is proposed and demonstrated. The LPG, inscribed in a step index few-mode fiber by a CO₂ laser, is utilized to excite the LP₁₁ core mode. The followed TFBG written in graded index a few mode fiber with the LP₁₁ core mode as exciting light is served as sensing element. By analyzing transmitted intensity difference of two dips in transmission spectrum of the TFBG induced by the mode couplings from forward-propagating LP₁₁ core mode to backward-propagating LP₁₁ and LP₂₁ core modes, a twist sensitivity of 1.074 dB/(rad/m) from −5.23 rad/m to 5.23 rad/m is achieved. The proposed sensor has advantages of easy operation and simple structure.