[1] M. Tabib-Azar, B. Sutapun, R. Petrick, and A. Kazemi, “Highly sensitive hydrogen sensors using palladium coated fiber optics with exposed cores and evanescent field interactions,” Sensors and Actuators B: Chemical, 1999, 56(1–2): 158–163.

[2] S. K. Khijwania and B. D. Gupta, “Fiber optic evanescent field absorption sensor: effect of fiber parameters and geometry of the probe,” Optical and Quantum Electronics, 1999, 31(8): 625–636.

[3] S. Sekimoto, H. Nakagawa, S. Okazaki, K. Fukuda, S. Asakura, T. Shigemori, et al., “A fiber-optic evanescent-wave hydrogen gas sensor using palladium-supported tungsten oxide,” Sensors and Actuators B: Chemical, 2000, 66(1–3): 142–145.

[4] J. Villatoro and D. Monzon-Hernandea, “Fast detection of hydrogen with nano fiber tapers coated with ultra thin palladium layers,” Optics Express, 2005, 13(13): 5087–5092.

[5] D. Monzon-Hernandez, D. Luna-Moreno, and D. Martinez-Escobar, “Fast response fiber optic hydrogen sensor based on palladium and gold nano-layers,” Sensors and Actuators B: Chemical, 2009, 136(2): 562–566.

[6] M. Yang, H. Liu, D. Zhang, and X. Tong, “Hydrogen sensing performance comparison of Pd layer and Pd/WO3 thin film coated on side-polished single- and multi-mode fibers,” Sensors and Actuators B: Chemical, 2010, 149(1): 161–164.

[7] M. Yang, Y. Sun, D. Zhang, and D. Jiang, “Using Pd/WO3 composite thin films as sensing materials for optical fiber hydrogen sensors,” Sensors and Actuators B: Chemical, 2010, 143(2): 750–753.

[8] M. A. Butler, “Micromirror optical-fiber hydrogen sensor,” Sensors and Actuators B: Chemical, 1994, 22(2): 155–163.

[9] X. Bevenot, A. Trouillet, C. Veillas, H. Gagnaire, and M. Clement, “Hydrogen leak detection using an optical fibre sensor for aerospace applications,” Sensors and Actuators B: Chemical, 2000, 67(1–2): 57–67.

[10] K. Lin, Y. Lu, J. Chen, R. Zheng, P. Wang, and H. Ming, “Surface plasmon resonance hydrogen sensor based on metallic grating with high sensitivity,” Optics Express, 2008, 16(23): 18599–18604.

[11] C. Ma and A. Wang, “Optical fiber tip acoustic resonator for hydrogen sensing,” Optics Letters, 2010, 35(12): 2043–2045.

[12] M. Buric, T. Chen, M. Maklad, P. R. Swinehart, and K. P. Chen, “Multiplexable low-temperature fiber Bragg grating hydrogen sensors,” IEEE Photonics Technology Letters, 2009, 21(21): 1594–1596.

[13] M. Buric, K. P. Chen, M. Bhattarai, P. R. Swinehart, and M. Maklad, “Active fibre Bragg grating hydrogen sensor for all-temperature operation,” IEEE Photonics Technology Letters, 2007, 19(5): 255–257.

[14] B. Sutapun, M. Tabib-Azar, and A. Kazemi, “Pd-coated elastooptic fiber optic Bragg grating sensors for multiplexed hydrogen sensing,” Sensors and Actuators B: Chemical, 1999, 60(1): 27–34.

[15] C. Caucheteur, M. Debliquy, D. Lahem, and P. Megret, “Hybrid fiber gratings coated with a catalytic sensitive layer for hydrogen sensing in air,” Optics Express, 2008, 16(21): 16854–16859.

[16] J. Dai, M. Yang, Y. Chen, K. Cao, H. Liao, and P. Zhang, “Side-polished fiber Bragg grating sensor with WO3-Pd composite film as sensing materials,” Optics Express, 2011, 19(7): 6141–6148.

[17] J. H. Lee, J. H. Kim, Y. G. Han, S. H. Kim, and S. B. Lee, “Investigation of Raman fiber laser temperature probe based on fiber Bragg gratings for long-distance remote sensing applications,” Optics Express, 2004, 12(8): 1747–1752.

[18] G. T. Kanellos, G. Papaioannou, D. Tsiokos, C. Mitrogiannics, G. Nianios, and N. Pleros, “Two dimensional polymer-embedded quasidistributed FBG pressure sensor for biomedical applications,” Optics Express, 2010, 18(1): 179–186.

[19] D. Lin, X. Jiang, F. Xie, W. Zhang, Z. Lin, and I. Bennion, “High stability multiplexed fibre interferometer and its application on absolute displacement measurement and on-line surface metrology,” Optics Express, 2004, 12(23): 5729–5734.

[20] M. Armgarth and C. Nylander, “Blister formation in Pd gate MIS hydrogen sensors,” IEEE Electron Device Letters, 1982, 3(12): 384–386.

[21] B. McCool, G. Xomeritakis, and Y. S. Lin, “Composition control and hydrogen permeation characteristics of sputter deposited palladium-silver membranes,” Journal of Membrane Science, 1999, 161(1–2): 67–76.

[22] J. Shu, A. Adnot, B. P. A. Grandjean, and S. Kaliaguine, “Structurally stable composite Pd-Ag alloy membranes: introduction of a diffusion barrier,” Thin Solid Films, 1996, 286(1–2): 72–79.

[23] S. Uemiya, T. Matsuda, and E. Kikuchi, “Hydrogen permeable palladium-silver alloy membrane supported on porous ceramics,” Journal of Membrane Science, 1991, 56(3): 315–325.

[24] A. D. Kersey, M. A. Davis, H. J. Patrick, M. LeBlac, K. P. Koo, C. G. Askins, et al., “Fiber grating sensors,” Journal of Lightwave Technology, 1997, 15(8): 1442–1463.

[25] K. O. Hill, B. Malo, F. Bilodeau, D. C. Johnson, and J. Albert, “Bragg gratings using fabricated in monomode photosensitive optical fiber by UV exposure thorough a phase mask,” Applied Physics Letters, 1993, 62(10): 1035–1037.

[26] K. S. Chiang, R. Kancheti, and V. Rastogi, “Temperature-compensated fiber-Bragg-gratings for DC and AC currents,” Optical Engineering, 2003, 42(7): 1906–1909.

[27] M. Yang, J. Dai, C. Zhou, and D. Jiang, “Optical fiber magnetic field sensors with TbDyFe magnetostrictive thin films as sensing materials,” Optics Express, 2009, 17(23): 20777–20782.

[28] Z. Zhao, M. Knight, S. Kumar, E. T. Eisenbraun, and M. A. Carpenter, “Humidity effects on Pd/Au-based all-optical hydrogen sensors,” Sensors and Actuators B: Chemical, 2008, 129(2): 726–733.

[29] M. Wang and Y. Feng, “Palladium-silver thin film for hydrogen sensing,” Sensors and Actuators B: Chemical, 2001, 123(1): 101–106.

[30] Y. K. Gautam, A. K. Chawla, S. A. Khan, R. D. Agrawal, and R. Chandra, “Hydrogen sbsorption and optical propeties of Pd/Mg thin films prapared by DC magnetron sputtering,” International Journal of Hydrogen Energy, 2012, 37(4): 3772–3778.

[31] R. Kumar, D. Varadani, B. R. Mehta, V. N. Singh, Z. Wen, X. Feng, et al., “Fast response and recovery of hydrogen sensing in Pd-Pt nanoparticle-graphene composite layers,” Nanotechnology, 2011, 22(27): 275719-1–275719-7.

[32] Z. Zhao, M. Knight, S. Kumar, E. T. Eisenbraun, and M. A. Carpenter, “Humidity effects on Pd/Au-based all-optical hydrogen sensors,” Sensors and Actuators B: Chemical, 2008, 129(2): 726–733.

[33] E. Lee, J. M. Lee, E. Lee, J. S. Noh, J. H. Joe, B. Jung, et al., “Hydrogen gas sensing performance of Pd-Ni alloy thin films,” Thin Solid Films, 2010, 519(2): 880–884.

[34] M. Yang, J. Dai, C. Zhou, and D. Jiang, “Optical fiber magnetic field sensors with TbDyFe magnetostrictive thin film as sensing materials,” Optics Express, 2009, 17(23): 20777–20782.

[35] D. Luna-Moreno, D. Monzon-Hernandez, S. Calixto-Carrera, and R. Espinosa-Luna, “Tailored Pd-Au layer produced by conventional evaporation process for hydrogen sensing,” Optics and Lasers in Engineering, 2011, 49(6): 693–697.

[36] J. Y. Shim, J. D. Lee, J. M. Jin, H. Cheong, and S. Lee, “Pd-Pt alloy as a catalyst in gasochromic thin films for hydrogen sensors,” Solar Energy Materials and Solar Cells, 2009, 93(12): 2133–2137.

[37] J. Dai, M. Yang, X. Yu, K. Cao, and J. Liao, “Greatly etched fiber Bragg grating hydrogen sensor with Pd/Ni composite film as sensing material,” Sensors and Actuators B: Chemical, 2012, 174: 253–257.

[38] A. Iadicicco, A. Cutolo, R. Bernini, and M. Giordano, “Thinned fiber Bragg gratings as high sensitivity refractive index sensor,” IEEE Photonics Technology Letters, 2004, 16(4): 1149–1151.

[39] J. Dai, M. Yang, X. Yu, and H. Lu, “Optical hydrogen sensor based on etched FBG sputtered with Pd/Ag composite film,” Optical Fiber Technology, 2013, 19(1): 26–30.

[40] B. Sutapun, M. Tabib-Azar, and A. Kazemi, “Pd-coated elastooptic fiber optic Bragg grating sensors for multiplexed hydrogen sensing,” Sensors and Actuators B: Chemical, 1999, 60(1,2): 27–34.

[41] Y. Cheng, Y. Li, D. Lisi, and W. M. Wang, “Preparation and characterization of Pd/Ni thin films for hydrogen sensing,” Sensors and Actuators B: Chemical, 1996, 30(1): 11–16.

[42] K. Scharnagl, M. Efiksson, A. Karthigeyan, M. Burgmair, M. Zimmer, and I. Eisele, “Hydrogen detection at high concentrations with stabilished palladium,” Sensors and Actuators B: Chemical, 2001, 78(1–3): 138–142.

[43] D. Luna-Moreno, D. Monzon-Hernandez, S. Calixto-Carrera, and R. Espinosa-Luna, “Tailored Pd-Au layer produced by conventional evaporation process for hydrogen sensing,” Optics and Lasers in Engineering, 2011, 49(6): 693–697.

[44] G. Rajan, M. Y. M. Noor, N. H. Lovell, E. Ambikaizrajah, G. Farrell, and G. D. Peng, “Polymer micro–fiber Bragg grating,” Optics Letters, 2013, 38(17): 3359–3362.

[45] A. Lebon, A. Garcia-Fuente, A. Vega, and F. Aguilera-Granja, “Hydrogen interaction in Pd-Pt alloy nanoparticles,” Journal of Physical Chemistry C, 2012, 116(1): 126–133.

[46] Wei He, Juanying Liu, Xiaogang Zhang, Daniel L. Akins, Hui Yang, “Simple preparation of PdPt nanoalloy catalysts for methanol-tolerant oxygen reduction”, J. Power Sources, 2010, 195 1046–1050.

[47] J. Y. Shim, J. D. Lee, J. M. Jin, H. Cheong, and S. Lee, “Pd-Pt alloy as a catalyst in gasochromic thin films for hydrogen sensors,” Solar Energy Materials and Solar Cells, 2009, 93(12): 2133–2137.

[48] C. Caucheteur, M. Debliquy, D. Lahem, and P. Megret, “Hybrid fiber gratings coated with a catalytic sensitive layer for hydrogen sensing in air,” Optics Express, 2008, 16(21): 16854–16859.

[49] M. Zhao and C. W. Ong, “Improved H2-sensing performance of nanocluster-based highly porous tungsten oxide films operating at moderate temperature,” Sensors and Actuators B: Chemical, 2012, 174: 65–73.

[50] A. Boudiba, C. Zhang, P. Umek, C. Bittencourt, R. Snyders, M. G. Olivier, et al., “Sensitive and rapid hydrogen sensors based on Pd-WO3 thick films with different morphologies,” International Journal of Hydrogen Energy, 2013, 38(5): 2565–2577.

[51] C. Caucheteur, M. Debliquy, D. Lahem, and P. Megret, “Hydrogen sensor using fiber gratings covered by a catalytic sensitive layer,” in Proc. SPIE, vol. 6593, pp. 65930U, 2007.

[52] M. Yang, Z. Li, J. Dai, Z. Yang, Y. Zhang, and Z. Zhuang, “Comparison of optical fiber Bragg grating hydrogen sensors with Pd-based thin films and sol-gel WO3 coatings,” Measurement Science and Technology, 2013, 24(9): 094009.

[53] C. Caucheteur, M. Debliquy, D. Lahem, and P. Megret, “Catalytic fiber Bragg grating sensor for hydrogen leak detection in air,” IEEE Photonics Technology Letters, 2008, 20: 96–98.

[54] M. Yang, Z. Yang, J. Dai, and D. Zhang, “Fiber optic hydrogen sensors with sol-gel WO3 coatings,” Sensors and Actuators B: Chemical, 2012, 166–167: 632–636.

[55] M. Buric, K. P. Chen, M. Bhattarai, P. R. Swinehart, and M. Maklad, “Active fiber Bragg grating hydrogen sensors for all-temperature operation,” IEEE Photonics Technology Letters, 2007, 19(5): 255–257.

[56] M. Buric, T. Chen, M. Maklad, P. R. Swinehart, and K. P. Chen, “Multiplexable low-temperature fiber Bragg grating hydrogen sensors,” IEEE Photonics Technology Letters, 2009, 21(21): 1594–1596.

[57] J. Z. Ou, M. H. Yaacob, J. L. Campbell, M. Breedon, K. Kalantar-zadeh, and W. Wlodarski, “H2 sensing performance of optical fiber coated with nano-platelet WO3 film,” Sensors and Actuators B: Chemical, 2012, 166–167: 1–6.

[58] Z. Zhao, M. Knight, S. Kumar, E. T. Eisenbraun, and M. A. Carpenter, “Humidity effects on Pd/Au-based all-optical hydrogen sensors,” Sensors and Actuators B: Chemical, 2008, 129(2): 726–733.

[59] R. J. Westerwaal, J. S. A. Rooijmans, L. Leclercq, D. G. Gheorghe, T. Radeva, L. Mooij, et al., “Nanostructured Pd-Au based fiber optic sensors for probing hydrogen concentrations in gas mixtures,” International Journal of Hydrogen Energy, 2013, 38(10): 4201–4212.

[60] S. Silva, L. Coelho, J. M. Almeida, O. Frazao, J. L. Santos, F. X. Malcata, et al., “H2 sensing based on a Pd-coated tapered-FBG fabricated by DUV femtosecond laser technique,” IEEE Photonics Technology Letters, 2013, 25(4): 401–403.

[61] M. Aleixandre, P. Corredera, M. L. Hernanz, and J. Gutierrez-Monreal, “Development of fiber optic hydrogen sensors for testing nuclear waste repositories,” Sensors and Actuators B: Chemical, 2005, 107(1): 113–120.

[62] S. F. Silva, L. Coelho, O. Frazao, J. L. Santos, and F. X. Malcata, “A review of palladium-based fiberoptic sensors for molecular hydrogen detection,” IEEE Sensors Journal, 2012, 12(1): 93–102.

[63] J. Dai, M. Yang, Y. Chen, K. Cao, H. Liao, and P. Zhang, “Side-polished fiber Bragg grating hydrogen sensor with WO3-Pd composite film as sensing materials,” Optics Express, 2011, 19(7): 6141–6148.

[64] C. Chan, W. C. Hsu, C. C. Chang, and C. S. Hsu, “Hydrogen incorporation in gasochromic coloration of sol-gel WO3 thin films,” Sensors and Actuators B: Chemical, 2011, 157(2): 504–509.

[65] L. F. Zhu, J. C. She, J. Y. Luo, S. Z. Deng, J. Chen, X. W. Ji, et al., “Self-heated hydrogen gas sensors based on Pt-coated W18O49 nanowire networks with high sensitivity, good selectivity and low power consumption,” Sensors and Actuators B: Chemical, 2011, 153(2): 354–360.

[66] Y. Liu,Y. Chen, H. Song, and G. Zhang, “Modeling analysis and experimental study on the optical fiber hydrogen sensor based on Pd-Y alloy thin film,” Review of Scientific Instruments, 2012, 83(7): 075001.

[67] R. Ghosh, M. B. Baker, and R. Lopez., “Optical properties and aging of gasochromic WO3,” Thin Solid Films, 2010, 518(8): 2247–2249.

[68] C. Chan, W. Hsu, C. Chang, and C. Hsu, “Hydrogen incorporation in gasochromic coloration of sol-gel WO3 thin films,” Sensors and Actuators B: Chemical, 2011, 157(2): 504–509.

[69] A. Boudiba, C. Zhang, and P. Umek, “Sensitive and rapid hydrogen sensors based on Pd/WO3 thick films with different morphologies,” International Journal of Hydrogen Energy, 2013, 38(5): 2565–2577.

[70] M. H. Yaacob, M. Breedon, K. Kalantar-Zadeh, and W. Wlodarski, “Absorption spectral response of nanotextured WO3 thin films with Pt catalyst towards H2,” Sensors and Actuators B: Chemical, 2009, 137(1): 115–120.

[71] M. H. Yaacob, M. Z. Ahmad, A. Z. Sadek, J. Z. Oub, J. Campbell, K. Kalantar-zadeh, et al., “Optical response of WO3 nanostructured thin films sputtered on different transparent substrates towards hydrogen of low concentration,” Sensors and Actuators B: Chemical, 2013, 177: 981–988.

[72] M. Shibuya and M. Miyauchi, “Efficient electrochemical reaction in hexagonal WO3 forests with a hierarchical nanostructure,” Chemical Physics Letters, 2009, 473(1–3): 126–130.

[73] E. Lee, J. Lee, J. Noh, W. Kim, T. Lee, S. Maeng, et al., “Pd-Ni hydrogen sponge for highly sensitive nanogap-based hydrogen sensors,” International Journal of Hydrogen Energy, 2012, 37(19): 14702–4706.

[74] D. Luna-Moreno, D. Monzon-Hernandez, J. Villatoro, and G. Badenes, “Optical fiber hydrogen sensor based on core diameter mismatch and annealed Pd-Au thin films,” Sensors and Actuators B: Chemical, 2007, 125(1): 66–71.

[75] H. Shanak, H. Schmitt, J. Nowoczin, and C. Ziebert, “Effect of Pt-catalyst on gasochromic WO3 films: optical, electrical and AFM investigations,” Solid State Ionics, 2004, 171(1–2): 99–106.

[76] H. Zheng, J. Z. Ou, M. S. Strano, R. B. Kaner, A. Mitchell, and K. Kalantar-zadeh, “Nanostructured tungsten oxide-properties, synthesis, and applications,” Advanced Functional Material, 2011, 21(12): 2175–2196.

[77] Y. Baek and K. Yong, “Controlled growth and characterization of tungsten oxide nanowires using thermal evaporation of WO3 powder,” The Journal of Physical Chemistry C, 2007, 111(3): 1213–1218.