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.

Optoelectronic oscillator-based interrogation system for Michelson interferometric sensors

“…A comparison of various temperature-sensing schemes and the interrogation approaches is shown in Table 1. Indeed, the interrogation resolution of our work should be improved compared with that in the work of Li et al [4] However, unlike the wavelength interrogation scheme based on an OSA, [4,14,15] our work achieves wavelength-to-frequency mapping in the electrical domain, illustrating a potential method of highspeed interrogation that supports a wide linear interrogation range by avoiding overlapping of the measured spectrum. [18] Note that the interrogation speed reaches the MHz range when a digital signal processor unit is used.…”

“…[20] Such an OEO-based interrogation system with high resolution and high speed would support practical applications such as bridge security monitoring and industrial machinery sensing. Liquid-filled silica capillary tube [4] Wavelength interrogation Slow 5.086 nm/ • C 0.0039 25-55 based on OSA Long period grating [14] Wavelength interrogation Slow 1.316 nm/ • C 0.0152 25-45 based on OSA Thin fiber-based Sagnac interferometer (SI) [15] Wavelength interrogation Slow 1.55 nm/ • C 0.013 30-94.5 based on OSA Fiber surface plasmon resonance [16] Wavelength interrogation Fast 1.765 nm/ • C 0.198 35-95 based on spectrometer SI [13] Frequency interrogation Fast 2.66 MHz/ • C 0.096 16.5-61.5 based on OEO Mach-Zehnder interferometer [17] Frequency interrogation Fast 3.7 MHz/…”