Sensitivity enhancement of RI sensor based on SMS fiber structure with high refractive index overlay

We propose a novel way to enhance the sensitivity of single-mode-multimode-single-mode (SMS) fiber structure in the measurement of surrounding refractive index (RI), which is realized by depositing the multimode fiber section with a high RI overlay. First, as an essential basis of the analysis of the novel structure, characteristics of mode reorganizations in the deposited multimode fiber are discussed. Second, based on full-vector mode expansion, a theoretical analysis of transmission characteristics of the deposited SMS fiber structure is presented. Third, aimed at RI measurement ranges which are of common interest in liquid and gas sensing, the transmission spectra of the structure in response to the surrounding RI are investigated by simulations. To well utilize the collective effect of multiple interference modes in mode reorganizations, the monitoring based on wavelength shifts of valleys and the optimization of the overlay are analyzed for various application requirements. Lastly, largely enhanced sensitivities for RI measurements are demonstrated with properly designed overlay. For RI ranges from 1.31 to 1.35 and 1.0 to 1.03, average sensitivities of 900 and 206 nm/RIU are achieved with overlay thicknesses of 340 and 470 nm, respectively.

[1]  Xijia Gu,et al.  All-fiber multimode interference bandpass filter. , 2006, Optics letters.

[2]  Yuliya Semenova,et al.  Investigation of single-mode–multimode–single-mode and single-mode–tapered-multimode–single-mode fiber structures and their application for refractive index sensing , 2011 .

[3]  Philippe Lalanne,et al.  Optimization of sensitivity in Long Period Fiber Gratings with overlay deposition. , 2005, Optics Express.

[4]  Yongxing Jin,et al.  Investigation on Single-Mode-Multimode-Single-Mode Fiber Structure , 2011, 2011 Symposium on Photonics and Optoelectronics (SOPO).

[5]  A. Cusano,et al.  Optical chemo-sensor based on long period gratings coated with /spl delta/ form syndiotactic polystyrene , 2005, IEEE Photonics Technology Letters.

[6]  G. Farrell,et al.  All-fiber multimode-interference-based refractometer sensor: proposal and design. , 2006, Optics letters.

[7]  N. Peyghambarian,et al.  Multimode interference in circular step-index fibers studied with the mode expansion approach , 2007 .

[8]  Qiang Wu,et al.  High sensitivity SMS fiber structure based refractometer--analysis and experiment. , 2011, Optics express.

[9]  Li Yang,et al.  Long-period grating refractive index sensor with a modified cladding structure for large operational range and high sensitivity. , 2006, Applied optics.

[10]  Stephen W James,et al.  Optical fiber long-period gratings with Langmuir-Blodgett thin-film overlays. , 2002, Optics letters.

[11]  S. Campopiano,et al.  Mode transition in high refractive index coated long period gratings. , 2006, Optics express.

[12]  Shuisheng Jian,et al.  Improved Full-Vector Finite-Difference Complex Mode Solver for Optical Waveguides of Circular Symmetry , 2008 .

[13]  Xinyong Dong,et al.  Refractive index measurement by using multimode interference , 2011, International Conference on Optical Fibre Sensors.