The Design Of Linear Phase Masks And Improvement Of Fabrication Efficiency Of Chirp Gratings

Currently,fiber gratings are generally fabricated by phase mask method.In the process,phase masks are needed,but the production technology of phase masks is only controlled by a few companies,which consequently results in the high price of phase masks,and the increase in the production cost of the fiber grating.In the production process of the edge spectrum grating,it needs a relatively special phase mask which is the linear phase mask specially designed.In the design of the edge spectrum chirp fiber grating,it can use the CEO algorithm,which has the advantages of flexible and high precision,and the disadvantage of low production efficiency.In order to reduce the production cost of the edge spectrum chirp fiber grating,design a suitable linear chirp phase mask for edge spectrum chirp fiber gratings,and improve the production efficiency of the edge spectrum chirp fiber grating,the paper proposes a method of designing linear chirp phase mask,and use a double-exposure method to fabricate the edge spectrum fiber grating.The specific work done in the paper is as follows:1)A method of designing a linear chirped phase mask suitable for fabricating broadband edge gratings is proposed.First,in order to meet a certain bandwidth requirement,it is necessary to first determine the specific chirp and length of the chirped phase mask.Then,in order to meet a certain reflection wavelength requirements,it is necessary to determine the periodic distribution of the linear chirp phase mask.In the process of using the phase mask to fabricate the FBG,it is necessary to suppress the 0 order diffraction efficiency.The grating is written by using the interference fringes formed by the first-order and first-order diffracted lights.Therefore,the 0 order diffraction efficiency and the ±1 order diffraction efficiency of the phase mask must satisfy certain requirements.In order to satisfy the requirements of the diffraction efficiency of the phase mask,the specific parameter values of the phase mask plate are determined by the simulation results based on the rigorous coupled wave theory.2)A method for improving the fabrication efficiency of fiber gratings is proposed.In the process of making an edge spectrum fiber grating using the CEO algorithm,it needs multiple exposures to complete the fabrication of a fiber grating.In order to improve the production efficiency of the grating,it is necessary to optimize the fabrication process of the fiber grating,which use the double exposure method to complete the fabrication of the edge spectrum chirp fiber grating.First,the laser beam needs to be collimated and shaped using a telescope system,then it is homogenized with a microlens array.Then it uses double exposure method to inscribe photosensitive fiber.In the first exposure,it need the phase mask overlaid the triangular plate.In the second exposure,the apodization plate is overlaid on the triangular plate to complete the second exposure.The research work of the paper has certain guidance significance for the fabrication of linear germanium phase masks and the improvement of fabrication efficiency of grating.But due to the limitations of time and realistic conditions,this paper only stays in the theoretical research stage and does not enter the actual experimental stage.