Design Of ?2?m Broadband Near Zero Flattened Dispersion Fluorotellurite Glass Fibers For Optical Frequency Comb

Mid infrared optical frequency comb has important applications in many fields,such as medical breath analysis,gas detection,spectroscopy,microwave generation and optical communication.Spectrum bandwidth and flatness are the core technical indexes of optical frequency comb.In the current development of optical frequency comb technology,the nonlinear optical process based on the cascade four-wave mixing effect in fiber is an effective way to obtain broadband optical frequency comb.Limited by the window of matrix material,the traditional quartz fiber is not suitable for the development of mid infrared optical frequency comb.Compared with quartz fiber,fluorotellurite glass fiber has a wide optical transmission window and high nonlinear coefficient,and it is a potential medium for optical frequency comb of mid infrared fiber.Before the work of this paper,our research group designed a flattened dispersion fluorotellurite glass fiber,but its dispersion with flattened spectrum range is narrow,so it is difficult to achieve the optical frequency comb with a wide band and flattened spectrum.In view of the above problems,the author has carried out research work on the design of?2?m broadband near zero flattened dispersion fluorotellurite glass fiber and its application in the generation of mid infrared optical frequency comb during the master's study.The main innovation results are as follows:(1)A new kind of all solid-state fluorotellurite glass fiber with near zero ultra flattened dispersion is designed.The dispersion value of the fiber is between 0±1ps/nm/km and covers 1884?2747 nm.70Te O₂-20Ba F₂-10Y₂O₃(TBY)is selected as the core material of the fiber,33Al F₃-9Ba F₂-17Ca F₂-12YF₃-8Sr F₂-11Mg F₂-15Te O₂(ABCYSMT)is selected as the cladding material of the fiber.Two layers of ring structure are introduced,and three zero dispersion points(located at 1958 nm,2249nm and 2587 nm,respectively)are designed by optimizing the size of the core and ring layers.The dispersion value of the fiber is between 0±1 ps/nm/km and its nonlinear coefficient is 306/W/km in the range of 1884?2747 nm.(2)The spectrum range of 1400?4500 nm is realized by using the fiber as the nonlinear medium.The ultra short pulse with center wavelength of 1990 nm,repetition frequency of 45 GHz,average power of 3 W and pulse width of 780 fs is selected as pump.The influence of dispersion and length of fluorotellurite glass fiber on the spectrum of optical frequency comb is studied by numerical solution of nonlinear Schr(?)dinger equation.When the fiber length is 4 m,the optical frequency comb covering 1400?4500 nm is obtained.The spectrum range of 20 d B covers 1833?2276nm.In addition,we study the influence of the pump light frequency change on the performance parameters of the optical frequency comb.The results show that?2?m broadband near zero flattened dispersion fluorotellurite glass fiber can be used for the development of broadband mid infrared optical frequency comb.