Analysis of optical response of long period fiber gratings to nm-thick thin-film coatings

We have theoretically and experimentally demonstrated that the resonant wavelength of long period fiber gratings (LPG) can be shifted by a large magnitude by coating with only a nm-thick thin-film that has a refractive index higher than that of the glass cladding. The resonant wavelength shift can result from either the variation of the thickness of the film and/or the variation of its refractive index. These results demonstrate the sensitivity of LPG-based sensors can be enhanced by using a film of nm-thickness and refractive index greater than silica. This coating schematic offers an efficient platform for achieving high-performance indexmodulating fiber devices and high-performance index/thickness-sensing LPG-based fiber sensors for detecting optical property variations of the thinfilm coating. ©2005 Optical Society of America OCIS codes: (060.2370) Fiber optics sensors; (060.2340) Fiber optics components; (350.2770) Gratings; (310.0310) Thin films References and links 1. M. Vengsarkar, P. J. Lemaire, G. Jacobovitz-Veselka, V. Bhatia, and J. B. Judkins, “Long-period fiber gratings as gain-flattening and laser stabilizing devices,” Proc. IOOC’95, PD1–2 (1995). 2. S. Ramachandran, S. Ghalmi, Z. Wang, and M. Yan, “Band-Selection Filters using Concatenated Long-Period Gratings in Few-mode Fibers,” Opt. Lett. 27, 1678-1680 (2002). 3. S. Ramachandran, Z. Wang, M. Yan, “Bandwidth control of long-period grating-based mode converters in fewmode fibers,” Opt. Lett. 27, 698-700 (2002). 4. H. J. Patrick, A. D. Kersey, and F. Bucholtz, “Analysis of the response of long period fiber gratings to the external index of refraction,” J. Lightwave Technol. 16, 1606-1612 (1998). 5. B. Acharya, T. Krupenkin, S. Ramachandran, Z. Wang, C. Huang, and J. Rogers, “Tunable optical fiber devices based on broadband long-period gratings and pumped microfluidics,” Appl. Phys. Lett. 83, 4912-4914 (2003). 6. Z. Wang and S. Ramachandran, “Ultra-Sensitive Long Period Fiber Gratings for Broadband Modulators and Sensors,” Opt. Lett. 28, 2458-2460 (2003). 7. N. Rees, S. James, R. Tatam, G. Ashwell, “Optical fiber long-period gratings with Langmuir-Blodgett thin-film overlays,” Opt. Lett. 27, 686-688 (2002). 8. Z. Wang, J. R. Heflin, R. H. Stolen, N. Goel and S. Ramachandran, “Sensitive optical response of long period fiber gratings to nm-thick ionic self-assembled multilayers,” Proc. CLEO’04, CWD2, (2004). 9. Z. Wang, J. R. Heflin, R. H. Stolen, and S. Ramachandran, “Highly sensitive optical response of optical fiber long period gratings to nm-thick ionic self-assembled multilayers,” Appl. Phys. Lett. (to be published). (C) 2005 OSA 18 April 2005 / Vol. 13, No. 8 / OPTICS EXPRESS 2808 #6675 $15.00 US Received 28 February 2005; revised 25 March 2005; accepted 28 March 2005 10. Decher, “Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites,”,Science 277, 1232-1235 (1997). 11. J.R. Heflin, C. Figura, D. Marciu, Y. Liu, R. Claus, “Thickness dependence of second-harmonic generation in thin films fabricated from ionically self-assembled monolayers,” Appl. Phys. Lett. 74, 495-497 (1999). 12. I. Del Villar, I. R. Matías, F. J. Arregui, and P. Lalanne, “Optimization of sensitivity in Long Period Fiber Gratings with overlay deposition,” Opt. Express 13, 56-69 (2005) 13. D. Marcuse, Theory of Dielectric Optical Waveguides (New York: Academic, 1991). 14. Turan Erdogan, “Fiber grating spectra,” J. Lightwave Technol. 15, 1277-1294 (1997).