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Optical fiber devices and applications in the 2-μm band have been investigated extensively due to its unique advantages, such as eye safety. A fiber sensor based on tilted fiber Bragg grating with a grating plane angle of 2 deg is fabricated and experimentally tested. To the best of the authors’ knowledge, this is the first tilted fiber Bragg grating sensor to realize simultaneous measurements of temperature, axial strain, and a certain range of surrounding refractive index (SRI) at the 2-μm band. This paper uses the wavelength detection method and selects three independent resonant wavelengths as the investigated parameters. Results show that perturbations of temperature, axial strain, and SRI can shift the wavelengths of the core mode resonance and cladding mode resonance to some degree. The temperature sensitivities of the core mode and cladding mode are nearly the same, but their axial-strain sensitivities are different. Furthermore, the core mode is insensitive to the change in SRI. The sensitivities of SRI, temperature, and strain can thus be obtained by experimentally determining the wavelength shifts of the three independent resonance peaks. A 3 × 3 matrix containing the relationship coefficients between the disturbances of temperature, axial strain, and SRI and wavelength shifts is constructed. By reversely solving the matrix equation, variations in temperature, strain, and SRI can be obtained using the experimental determination of wavelength drifts.

The linewidth performance of all-fiber, linear-cavity Fabry–Perot structures based on fiber Bragggratings operating at 2-μm band has been investigated numerically. The output linewidth performance oftwo symmetrical and asymmetrical cavities has been theoretically studied and comprehensively compared.The numerical analysis is based on the transmission matrix method with the simplified parameters. The sim-ulationresultsshowthatcavitylengths,cavitylengthsratio,gratinglengths,gratinglengthsratio,aswellasindexmodulationdepths, affectthe outputlinewidthperformance. Thetoleranceability ofthe asymmetricalstructure isfirst proposed and investigated under 1 mm accuracy, and single-frequency output can be realized by properlyadjusting the properties of the proposed composite linear cavity structure. © 2017 Society of Photo-Optical InstrumentationEngineers (SPIE) [DOI: 10.1117/1.OE.56.5.056107] Keywords: 2-μm band; fiber Bragg grating; linear cavity; narrow linewidth.Paper 170162 received Feb. 4, 2017; accepted for publication May 8, 2017; published online May 23, 2017.