High-refractive-index transparent coatings enhance the optical fiber cladding modes refractometric sensitivity.

The high order cladding modes of standard single mode optical fiber appear in quasi-degenerate pairs corresponding to mostly radially or mostly azimuthally polarized light. In this work, we demonstrate that, in the presence of a high-refractive-index coating surrounding the fiber outer surface, the wavelength spacing between the orthogonally polarized cladding modes families can be drastically enhanced. This behavior can be advantageously exploited for refractometric sensing purposes. For this, we make use of tilted fiber Bragg gratings (TFBGs) as spectral combs to excite the orthogonally polarized cladding modes families separately. TFBGs were coated with a nanometer-scale transparent thin film characterized by a refractive index value close to 1.9, well higher than the one of pure silica. This coating brings two important assets: an ~8-fold increase in refractometric sensitivity is obtained in comparison to bare TFBGs while the sensitivity is extended to surrounding refractive index (SRI) values above 1.45.

[1]  Patrice Mégret,et al.  The sensitivity characteristics of tilted fibre Bragg grating sensors with different cladding thicknesses , 2007 .

[2]  M. Wuilpart,et al.  Tilted Fiber Bragg Grating Refractometer Using Polarization-Dependent Loss Measurement , 2008, IEEE Photonics Technology Letters.

[3]  F. Baldini,et al.  Optical fibre gratings as tools for chemical and biochemical sensing , 2011, Analytical and Bioanalytical Chemistry.

[4]  Marc Wuilpart,et al.  High resolution interrogation of tilted fiber grating SPR sensors from polarization properties measurement. , 2011, Optics express.

[5]  C. Caucheteur,et al.  Demodulation technique for weakly tilted fiber Bragg grating refractometer , 2005, IEEE Photonics Technology Letters.

[6]  Fan Zhang,et al.  Polarization Effects in Tilted Fiber Bragg Grating Refractometers , 2010, Journal of Lightwave Technology.

[7]  Reinhardt Willsch,et al.  A fibre Bragg grating refractometer , 2001 .

[8]  Ignacio Del Villar,et al.  Mode transition in complex refractive index coated single-mode-multimode-single-mode structure. , 2013, Optics express.

[9]  J. Albert,et al.  Tilted fiber Bragg grating sensors , 2013 .

[10]  Qi Jiang,et al.  Thermal independent solution concentration sensing with tilted fiber Bragg grating , 2010, SPIE/COS Photonics Asia.

[11]  G. Laffont,et al.  Tilted short-period fibre-Bragg-grating-induced coupling to cladding modes for accurate refractometry , 2001 .

[12]  D. Paladino,et al.  External Refractive Index Sensitivity of Weakly Tilted Fiber Bragg Gratings With Different Coating Thicknesses , 2008, IEEE Sensors Journal.

[13]  G. Laffont,et al.  Sensitivity of slanted fibre Bragg gratings to external refractive index higher than that of silica , 2001 .

[14]  A. Cusano,et al.  Thinned fiber Bragg gratings as high sensitivity refractive index sensor , 2004, IEEE Photonics Technology Letters.

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

[16]  S. James,et al.  Modification of the refractive index response of long period gratings using thin film overlays , 2005 .

[17]  D. Paladino,et al.  Spectral Behavior in Nano-Coated Tilted Fiber Bragg Gratings: Effect of Thickness and External Refractive Index , 2007, IEEE Photonics Technology Letters.

[18]  I. Del Villar,et al.  Optical fiber refractometers based on indium tin oxide coatings fabricated by sputtering. , 2012, Optics letters.

[19]  Jacques Albert,et al.  Polarized spectral combs probe optical fiber surface plasmons. , 2013, Optics express.

[20]  Y. Shevchenko,et al.  Polarization-selective grating excitation of plasmons in cylindrical optical fibers. , 2010, Optics letters.

[21]  Agostino Iadicicco,et al.  Cladding mode reorganization in high-refractive-index-coated long-period gratings: effects on the refractive-index sensitivity. , 2005, Optics letters.

[22]  J. P. Woerdman,et al.  Observation of Goos-Hänchen shifts in metallic reflection. , 2007, Optics express.

[23]  D. Thomson,et al.  Optical fiber refractometer using narrowband cladding-mode resonance shifts. , 2007, Applied optics.

[24]  Qida Zhao,et al.  Refractive index sensor based on measuring the transmission power of tilted fiber Bragg grating , 2009 .

[25]  Patrice Mégret,et al.  Highly sensitive detection of molecular interactions with plasmonic optical fiber grating sensors. , 2014, Biosensors & bioelectronics.

[26]  A. Vengsarkar,et al.  Optical fiber long-period grating sensors. , 1996, Optics letters.