A Sensor With High Strain Sensitivity Based on Four-Sided Modulated LPFG

In this letter, a novel strain sensor based on four-sided modulated long period fiber grating (FM-LPFG) is introduced and demonstrated. Due to the asymmetric refractive index modulation of the CO₂ laser, the cladding radius is reduced and the core deviation effect is strengthened. In addition, by simulating the equivalent strain during tension, the strain sensitive area of FM-LPFG is proposed. The measurement results indicate that the strain sensitivity of FM-LPFG is 127.5 pm/ $\mu \varepsilon $ ( $0~\sim ~125~\mu \varepsilon$ ) and 17.7 pm/ $\mu \varepsilon $ ( $125~\sim ~575~\mu \varepsilon$ ). The proposed FM-LPFG can be realistically applied in precision measurement.