TUNABLE CHARACTERISTICS OF MECHANICALLY-INDUCED LONG PERIOD FIBER GRATING

Optical fibers are now widely used for telecommunication. However, in recent years, the fibers have been researched for sensors because of its outstanding features, for example, low loss, small size and low weight, immunity to electromagnetic induction, and resistance to corrosion. In this paper, the authors report on mechanically-induced long period fiber grating (LPFG). LPFG is a kind of wavelength filter. Mechanical induction is realized with photoelastic effect. The effect appears when a grating device which has a lot of periodic protrusions is impressed to the fiber. The protrusions’ period is called a grating period. It varies from 10 μm to few hundred μm. The merits of mechanically-induced LPFG are lower cost for fabrication compared to laser-induced LPFG and easy handling for tuning the grating period. As an experimental setup, a tunable laser and an optical power meter are used as a light source and a receiver, respectively. An automatic servo stand is employed to apply pressure to the grating device. Figure 1 shows transmission spectra of the mechanically induced LPFG. The grating period is fixed at 610 μm. When the wavelength is 1500 nm, the decrease of the output power is very small. However, the output power decreases markedly with increasing pressure at a wavelength around 1550 nm. It is confirmed that characteristics of the mechanically-induced LPFG can be optimized by tuning a wavelength of a laser.