Pressure Sensing in High-Refractive-Index Liquids Using Long-Period Gratings Nanocoated with Silicon Nitride

The paper presents a novel pressure sensor based on a silicon nitride (SiNx) nanocoated long-period grating (LPG). The high-temperature, radio-frequency plasma-enhanced chemical-vapor-deposited (RF PECVD) SiNx nanocoating was applied to tune the sensitivity of the LPG to the external refractive index. The technique allows for deposition of good quality, hard and wear-resistant nanofilms as required for optical sensors. Thanks to the SiNx nanocoating it is possible to overcome a limitation of working in the external-refractive-index range, which for a bare fiber cannot be close to that of the cladding. The nanocoated LPG-based sensing structure we developed is functional in high-refractive-index liquids (nd > 1.46) such as oil or gasoline, with pressure sensitivity as high as when water is used as a working liquid. The nanocoating developed for this experiment not only has the highest refractive index ever achieved in LPGs (n > 2.2 at λ = 1,550 nm), but is also the thinnest (<100 nm) able to tune the external-refractive-index sensitivity of the gratings. To the best of our knowledge, this is the first time a nanocoating has been applied on LPGs that is able to simultaneously tune the refractive-index sensitivity and to enable measurements of other parameters.

[1]  Mark Kerr,et al.  Surface passivation of silicon solar cells using plasma-enhanced chemical-vapour-deposited SiN films and thin thermal SiO2/plasma SiN stacks , 2001 .

[2]  Zhengtian Gu,et al.  Design optimization of a long-period fiber grating with sol-gel coating for a gas sensor , 2007 .

[3]  Predrag Mikulic,et al.  A Novel Fiber-Optic Tapered Long-Period Grating Sensor for Pressure Monitoring , 2007, IEEE Transactions on Instrumentation and Measurement.

[4]  Li Yang,et al.  Optimization of Cladding-Structure-Modified Long-Period-Grating Refractive-Index Sensors , 2007, Journal of Lightwave Technology.

[5]  T. Erdogan.  Fiber grating spectra , 1997 .

[6]  Ian Bennion,et al.  Sensitivity characteristics of long-period fiber gratings , 2002 .

[7]  Gaspar Rego,et al.  Two types of resonances in long-period gratings induced by arc discharges in boron/ germanium co-doped fibers. , 2007, Optics letters.

[8]  Ralph P. Tatam,et al.  Fibre optic sensors with nano-structured coatings , 2006 .

[9]  Peter Kroll.  A DFT study of the compressibility of amorphous silicon oxynitride , 2004 .

[10]  Ralph P. Tatam,et al.  A pressure sensor based upon the transverse loading of a sub-section of an optical fibre Bragg grating , 2007 .

[11]  Wojtek J. Bock,et al.  Highly sensitive pressure sensor based on long-period gratings written in a boron co-doped optical fiber , 2010 .

[12]  David J. Webb,et al.  Investigations of the spectral sensitivity of long period gratings fabricated in three-layered optical fiber , 2003 .

[13]  N. Daldosso,et al.  Comparison among various Si/sub 3/N/sub 4/ waveguide geometries grown within a CMOS fabrication pilot line , 2004, Journal of Lightwave Technology.

[14]  Wojtek J. Bock,et al.  Refractive index sensing of fiber optic long-period grating structures coated with a plasma deposited diamond-like carbon thin film , 2008 .

[15]  I. R. Matias,et al.  Deposition of coatings on long-period fiber gratings: tunnel effect analogy , 2006 .

[16]  Ludvik Martinu,et al.  Interface engineering during plasma-enhanced chemical vapor deposition of porous/dense SiN1.3 optical multilayers , 2004 .

[17]  Oleg I. Medvedkov,et al.  Fibre gratings and their applications , 2005 .

[18]  Daniel Poitras,et al.  Plasma deposition of optical films and coatings: A review , 2000 .

[19]  Gorachand Ghosh.  MODEL FOR THE PRESSURE-OPTIC COEFFICIENTS IN OPTICAL MATERIALS , 1998 .

[20]  A. Abd El-Moneim,et al.  Quantitative analysis of elastic moduli and structure of B2O3–SiO2 and Na2O–B2O3–SiO2 glasses , 2003 .

[21]  I. del Villar,et al.  Two-Layer Nanocoatings in Long-Period Fiber Gratings for Improved Sensitivity of Humidity Sensors , 2008, IEEE Transactions on Nanotechnology.

[22]  Hypolito José Kalinowski,et al.  Fiber optic sensors for hydrocarbon detection , 2005 .

[23]  Wojtek J. Bock,et al.  Comparative study of long-period gratings written in a boron co-doped fiber by an electric arc and UV irradiation , 2010 .

[24]  J. Bravo,et al.  Evanescent Field Fiber-Optic Sensors for Humidity Monitoring Based on Nanocoatings , 2007, IEEE Sensors Journal.

[25]  Jan Szmidt,et al.  Influence of RF PACVD process parameters of diamond-like carbon films on optical properties and nano-hardness of the films , 2008 .

[26]  Wojtek J. Bock,et al.  Application of diamond-like carbon films in optical fibre sensors based on long-period gratings , 2007 .

[27]  Ailun Ye,et al.  Applications of acrylate-based polymer and silicone resin on LPFG-based devices , 2003 .

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

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

[30]  J. Judkins,et al.  Long-period fiber gratings as band-rejection filters , 1995 .

[31]  Agostino Iadicicco,et al.  Sensitivity characteristics in nanosized coated long period gratings , 2006 .

[32]  Wojtek J. Bock,et al.  Pressure sensing using periodically tapered long-period gratings written in photonic crystal fibres , 2007 .