Coupled Local-Mode Theory For Photonic Crystal Fiber Based Long Period Grating

Compared with traditional single-mode fiber,the photonic crystal fiber has many unique features.The photonic crystal fiber have more advantages.It has been becoming the researching focus for researchers since it was invented.In the paper,we study the photonic crystal fiber long period grating coupling mechanism and the transmission characteristics.And the package of long period fiber grating is also studied.The main contents are as follows:1.We studied two main models of long period fiber grating--traditional the coupled mode theory and the coupled Local-mode theory.And we analyzes the limitations of traditional coupled mode theory--it is suitable for weak coupling of the modes of unperturbed fiber.And details of simulation process of the LPG-PCF was given.2.The model of strong LPG-PCF based on coupled local-mode.Mode profiles and the effective refractive index was numerically modeled after building the collapse model.The changes of different mode can be seen directly.We analyzed the coupling between LP01 and LP02,LP01 and LP11.And the transmission spectrum is numerically calculated after building the collapse model.Compared with transmission spectrum calculated with local coupled-mode theory and coupled mode theory,the local coupled-mode theory is found in good agreement to analyses the strong PCF-LPGs.3.Considering the manufacture of PCF-LPFs,we discussed the changes of resonant wavelength and resonant depth in different grating periods,number of periods and the depths of cladding collapse.The results indicates that:with the increase of grating period,the resonance wavelength shifts to shorter wavelength;with the increase of number of periods,the resonance depth increase;with the increase of depths of cladding,the resonance wavelength shifts to longer wavelength.4.The capillary of package of LPG is used by glass.Measurements of LPG wavelengths vary with temperatures in a free state showed that with increasing temperature,the wavelength will move towards long wavelength,the extent of drift is large,a linear relationship between the wavelength and temperature.Measurements LPG wavelengths with temperature change after the package showed that the wavelength is affected by temperature greatly reduced,and the extent of drift correspondingly small,moreover the wavelength and the temperature is still a linear relationship.It is shows that this experiment which used plexiglass as a sealing material can effectively achieve the effect of keeping filter stability.