| Photonic crystal fiber(PCF for short)is composed of base material and doped holes in various arrangements,so PCF is also called microstructure fiber.The structural arrangement of the cross-section of the PCF fiber is different,and its refractive index changes.It is precisely because of this characteristic of PCF that we can adjust the type of substrate material,the shape,size,number and arrangement of the doping holes.to flexibly adjust its optical properties to be suitable for various types of application scenarios,so the research on PCF has become a hot research topic.For the application scenarios of PCF,it can be divided into two categories according to the optical characteristics,namely the linear field and the nonlinear field.The linear field is mainly used in modern communication systems,requiring signals to achieve ultra-long-distance signal stable transmission when transmitting signals to the destination,while the nonlinear field requires that the frequency of the signal at the output end be converted and controlled to the required frequency range,mainly used in super continuous generation of spectrum.Due to the wide spectrum,high brightness and high spatial coherence of supercontinuum,it has important applications in optical communication,spectroscopy,micromet rics,remote sensing and medical diagnosis.Two PCFs are designed in this paper,corresponding to the linear and nonlinear fields,respectively.The design method is mainly based on the nonlinear Schrodinger equation and the finite element method.The main research contents and innovative achievements of this paper are as follows:1.A near-zero ultra-flat photonic crystal fiber with normal dispersion in the E+S+C+L band is designed,silica is used as the base material,and the cladding is filled with air holes,its structural design method is to add additional small air holes in the innermost and outermost layers of the traditional three-layer hexagonal air holes,so as to achieve more precise control of the dispersion curve.After fine adjustment,an ultrasmall fluctuation amplitude of 0.15085ps/(km·nm)was finally obtained.This ultraflat PCF can increase the bandwidth of the wavelength division multiplexing system,which is beneficial to improve the efficiency of disper sion compensation in the transmission system,reduce the number of dispersion compensation modules,and thus achieve the purpose of reducing costs while realizing ultra-long distance transmission.In order to verify its long-distance transmission performance,the maximum transmission distance without dispersion compensation in linear transmission in a wavelength division multiplexing system is tested.The test results show that the limit transmission distance without dispersion compensation is about 1620 km.If you want to transmit farther,you can use dispersion compensating fiber to compensate for it and continue to transmit.2.A full-band normal dispersion ultra-flat photonic crystal fiber based on arsenic selenide is designed.Arsenic selenide is selected as the base material,and the cladding layer is filled with air holes,its cladding structure follows the structure designed for the above linear transmission.The evolution of femtosecond pulses in the time domain and frequency domain during PCF transmission is analyzed numerically.By analyzing the effects of incident peak power,transmission distance and other factors on the pulse transmission characteristics,an ultra-flat supercontinuum output was finally obtained in the 2700-6000 nm band. |
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