Abstract
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.
Highlights
Relevant theoretical and experimental research on fiber applications in the 2-μm band of the optical spectrum is developing rapidly
When the 2-μm band laser is transmitted through optical fibers or based endoscopes, surgery becomes more precise and controllable if a sensor provided for temperature and the strain or surrounding refractive index (SRI) is available
This paper proposes and experimentally tests a simple tilted fiber Bragg grating (TFBG) fiber sensor operating in the 2-μm band that can realize simultaneous measurement of temperature, axial strain, and a certain SRI range
Summary
Relevant theoretical and experimental research on fiber applications in the 2-μm band of the optical spectrum is developing rapidly. Fiber devices in this band range are suitable for CO2 detection[2] and other sensing measurements Lasers operating in this band are absorbed by biological tissue and can be used in superficial surgery.[3] When the 2-μm band laser is transmitted through optical fibers or based endoscopes, surgery becomes more precise and controllable if a sensor provided for temperature and the strain or surrounding refractive index (SRI) is available. This type of sensing device can be used in many other medical disciplines. By reversely solving the sensitivity coefficients matrix constructed using these three parameters, changes in SRI, temperature, and axial strain can be determined by observing the spectral shifts of different independent resonance peaks
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