Abstract

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 index-modulating fiber devices and high-performance index/thickness-sensing LPG-based fiber sensors for detecting optical property variations of the thin-film coating.

© 2005 Optical Society of America

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References

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Appl. Phys. Lett.

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)
[CrossRef]

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)

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)
[CrossRef]

J. Lightwave Technol.

Opt. Express

Opt. Lett.

Proc. CLEO???04

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)

Proc. IOOC??? Nineteen Nifty-five

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).

Science

Decher, �??Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites,�?? Science 277, 1232-1235 (1997)
[CrossRef]

Other

D. Marcuse, "Theory of Dielectric Optical Waveguides" (New York: Academic, 1991)

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Figures (5)

Fig. 1.
Fig. 1.

(a) Illustrative schematic of LPG with an nm-thick thin-film coating (b) Index profile of the thin-film coated LPG, n 1 is index of fiber core, n 2 is index of fiber cladding, n 3 is index of the thin-film, nair is index of air, and n 3>n 1>n 2>nair . Thickness d of the film is denoted d=b-a.

Fig. 2.
Fig. 2.

Phase Matching Curves (PMC) shifts as functions of index n 3 and thickness d of nm-thick thin-film (a) PMC of LP0,4 mode shifts with d (0, 20, 40, 60, 80, 100nm) at n 3=1.8, (b) PMC of LP0,12 mode shifts with d (0, 20, 40, 60, 80, 100nm) at n 3=1.8, (c) PMC of LP0,4 mode shifts with n 3 (1.5, 1.6, 1.7, 1.8) at d=40nm and d=100nm, (d) PMC of LP0,12 mode shifts with n 3 (1.5, 1.6, 1.7, 1.8) at d=40nm and d=100nm.

Fig. 3.
Fig. 3.

LPG spectra shifts as functions of index n 3 and thickness d of nm-thick thin-film (a) spectra of LP0,4 mode shifts with d (0, 20, 40, 60, 80, 100nm) at n 3=1.8, (b) spectra of LP0,12 mode shifts with d (0, 20, 40, 60, 80, 100nm) at n 3=1.8, (c) spectra of LP0,4 mode shifts with n 3 (1.5, 1.6, 1.7, 1.8) at d=40nm and d=100nm, (d) spectra of LP0,12 mode shifts with n 3 (1.5, 1.6, 1.7, 1.8) at d=40nm and d=100nm.

Fig. 4.
Fig. 4.

(a) Comparison between experimental and simulated LPG spectrum without ISAM coating (b) Experimental LPG spectra with 0, 5, 10, 15 and 20 PAH/PCBS bilayers of ISAM films for PAH at pH=7.5 and PCBS at pH=8.0. One bilayers≈1.3 nm in thickness.

Fig. 5.
Fig. 5.

Experimental results of Δλres of ISAM–coated LPG as a function of thickness d of ISAM films (different pH combinations of PAH and PCBS [(7.5,6), (7.5,8), (9,6), (9,8)] offer corresponding index n 3 [1.7107, 1.6912, 1.6887, 1.6715], respectively).

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