Discrimination of bending and temperature by using a multiwavelength raman fiber laser incorporating a sampled fiber Bragg grating

A simple and practical scheme for simultaneous measurement of bending and temperature based on a multiwavelength Raman fiber laser incorporating a single sampled fiber Bragg grating (FBG) is investigated. By using a sampled FBG and a Raman gain medium, we generated a multiwavelength Raman fiber laser and then applied it to discriminate between bending and temperature. Because the bending-induced tension strain gradient changes the chirp ratio of the sampled FBG, the wavelength spacing of the multiwavelength Raman fiber laser is changed as the bending curvature increases. The wavelength spacing, however, is not changed by the applied temperature change, but only multiple lasing wavelengths are shifted to longer wavelengths because of the positive thermal properties of the sampled FBG. Because the proposed sensing configuration combines a signal source with a sensing probe, no additional light sources for sensing signals are required. Accordingly, the proposed sensing technique allows for distinguishing between the bending and the temperature sensitivities.