Study On Long-period Fiber Gratings With Rotary Refractive Index Modulation Fabricated By CO₂ Laser

In recent years, on the basis of long period fiber grating fabricated by high frequency CO₂ laser pulses invented by Prof. Rao , the ordinary and a variety of special structured long period fiber grating has been researched in many aspects and good results has been achieved. On this basis, the mechanism of high-frequency CO₂ laser pulses on the fiber is further studied, and long-period fiber gratings with rotary refractive index modulation rotating (R-LPFG) has been researched systematic and deeper in this paper. The major work and results are as follows:1. The mechanism and the role of it played in the fabricating process of the high-frequency CO₂ laser pulses on the fiber is further studied. The results show that the forming mechanism of grating is different from the energy side-hated. The study provides the theoretical foundation and a more perfect process approach for the fabricating of different all-optical devices with high-frequency CO₂ laser pulses.2. Long-period fiber gratings with rotary refractive index modulation rotating(R-LPFG) is been researched systematic and deeper. The transmission spectra and some basic characteristics of the R-LPFGs in the ordinary single-mode fiber (Corning SMF28e), boron doped, erbium-doped fibers are researched and analyzed respectively. Their prelimary applications are being offered. The results show that: (1) The energy needed to be grating is different between the doped and non-doped fiber. The R-LPFG fabricated in different fiber has different characteristics, and it can meet different needs in optical fiber communication and sensing. (2) These different R-LPFGs will have great potential applications in temperature-sensitive devices, high-sensitivity trefractive index sensor, EDFA gain equalizer, tunable filter and so on.3. A all-fiber band-stop tunable filter based on the composition of R-LPFG and LPFG is proposed. When different torsion applied to the R-LPFG, its two separated resonance peaks get faraway or closer, and the resonance peaks of the LPFG compensates the drop between the two resonance peaks of the R-LPFG. So this composed LPFG could be a tunable filter when different torsion applied. The experimental results show that this tunable filter has a flat-bottom rejection and a large tunable range. It has low insertion loss and low polarization dependent loss, and will be greatly useful as a dynamic gain equalizer in the broadband light source.