Wavelength and sensitivity tunable long period gratings fabricated in fluid-cladding microfibers

Abstract

We report the fabrication of long period gratings in fluid-cladding microfibers by directly focusing a femtosecond laser beam on the microfibers surface to induce periodical modification a long one side of the microfibers. A long period grating is fabricated in a water-cladding microfiber with a diameter of ~ 5 μm, which demonstrates a resonant attenuation of 28.53 dB at wavelength of 1588.1 nm with 10 pitches. When water cladding is changed to be refractive index oil of n= 1.33 and alcohol solution with concentration of 5%, the resonance wavelength shifts to 1575.1 nm with resonant attenuation of 24.91 dB and 1594.1 nm with resonant attenuation of 35.9 dB, respectively. The long period grating demonstrates different temperature sensitivities of–0.524 nm/°C,–0.767 nm/°C and–1.316 nm/°C for water, alcohol solution and refractive index oil cladding microfibers, respectively, which means the alterable liquid cladding allows the availability of tunable wavelength and sensitivity. The fluid-cladding protects the microfibers from external disturbance and contamination and allows more flexibility in controlling the transmission property and sensing characteristics of long period gratings, which can be used as fiber devices and sensors for chemical, biological, and environmental applications.