Hydrogen (H₂) is considered as a very clean energy, with the very high heat of combustion. However, due to the explosive concentration range of hydrogen is very large for 4% to 75%, requiring very low ignition energy (0.02mg), and spreading very fast; at the same time, the tiny molecular scale also led to its storage and transportation very difficult. Therefore, the development of high sensitive hydrogen optical fiber sensor which can accurately and quickly apply to detect a variety of hydrogen concentration for kinds of environment have become a hot research topic. Currently, the market presence of hydrogen gas sensor is mainly based on precious metals multimode silica fibers, however, these sensors have lower sensitivity, high cost, short life, easy to polluted from environment and other shortcomings.

 

Tungsten trioxide (WO₃) is a transition metal oxide, belonging to the n-type semiconductor, as a semiconductor gas sensor, tungsten trioxide has been considered to be one of the most promising new oxide sensitive materials to detected NO_x, SO_x, NH₃, CO, hydrogen, hydrogen sulfide, etc.. A lot of researches are based on the tungsten trioxide hydrogen gas sensor films, in which mostly are combined with noble metal palladium, platinum, etc., in 1975, Lund-strom proposed research of hydrogen gas sensor Pd-MOSFET structure which opened up the field of film; in 2012, a scholar has inducted the research about thermal response of palladium-catalyzed tungsten trioxide film for hydrogen.
 

 

One study indicated a standards-based multi-mode silica hydrogen optical fiber sensor with fiber core of 62.5-micron diameter and cladding of diameter of 125 microns. Its tungsten film is deposited by RF sputtering to the head of fiber, and then corroded to tungstic acid film, followed by calcination under the controlled temperature to obtain tungsten trioxide optical fiber sensor. Follow-up experiments showed that tungsten trioxide optical fiber sensor is based near-infrared light as a light source; at hydrogen concentration of 0.06%, the reaction intensity is 6% reflectance change, and when the concentration of hydrogen is increased to 1%, it increased to 12%, thus to exhibit the high sensitivity of tungsten trioxide sensor to hydrogen.