Research On The Spectrum Characteristics And Applications Of Brewster Tilted Fiber Gratings

Polarization is an important parameter in the field of wave science,such as optics,seismology,radio and microwave.It has a decisive influence on the performance of laser,radar,wireless and optical fiber communication technologies.Polarized light can be thought as a kind of electromagnetic wave with pure vibration that oscillates only in a fixed plane.Most of light in nature is non-polarized.In order to realize or manipulate polarized light,polarizer is needed in optical system.At present,in the field of optical fiber communication and optical fiber sensing,most polarizers are hybrid optical fiber input and output devices with the structure of optical fiber-bulk polarization devices-optical fiber,which have the disadvantages of high insertion loss and low coupling efficiency.Currently reported all-fiber polarization devices,such as high birefringence fiber,chiral fiber grating,broadband graphene polarizer,and polarizer based on micro-nano fiber coupler,have good polarization performance,but still have defects such as complex structure,difficult fabrication,high cost,narrow bandwidth and low mechanical strength.This paper presents a Brewster tilted fiber grating,which makes use of the principle that the light incident with Brewster angle causes partially polarization and the structure characteristics of fiber grating to realize all-fiber linear polarizer.The research on the theoretical simulation and polarization spectrum detection of tilted fiber grating and all-fiber device application based on the Brewster tilted fiber grating is carried out.The main research contents of this paper are as follows:1.Based on volume current method,the theoretical model of polarization related transmission of tilted fiber grating is established,and the influence of the parameters such as the tilt angle,period and length of the grating on the polarization spectral characteristics of tilted fiber grating is systematically studied.2.The UV exposure method is used to fabricate the Brewster tilted fiber grating,and the polarization spectrum test platform is built.The full bandwidth polarization dependent loss of the Brewster tilted fiber grating is mainly studied.The experimental results show that the Brewster tilted fiber grating has the polarizing bandwidth of > 350 nm.At the same time,the high temperature annealing characteristics of Brewster tilted fiber grating are studied in detail.The test results show that the structure of Brewster tilted fiber grating begins to erase when the temperature exceeds 300 ℃,and thus Brewster tilted fiber grating is proved to be Type I grating.3.The all-fiber device research based on the Brewster tilted fiber grating linear polarization filtering characteristics is carried out,mainly including:(1)all-fiber polarization interference filter.Through the transfer matrix method simulation and experimental validation,this paper systematically studies the bandwidth,free spectral range and temperature tuning features of the all fiber polarization interference filter which is based on the Brewster tilted fiber grating.The results show that the filter with any bandwidth can be designed by controlling the length of polarization-maintaining fiber cavity.The 23 m long polarization-maintaining fiber can achieve 0.08 nm single channel bandwidth near 1550 nm.(2)the all-fiber twist sensor.In this paper,by virtue of birefringent effect of twisting fiber,the all-fiber twist sensor with single-ended structure has been realized through the integration of reflective chirp grating and Brewster tilted fiber grating.The proposed sensor is not sensitive to temperature and strain.The twisting sensitivity is 15.037 d B/rad and not affected by the space between two gratings.