Study Of Micro/Nano Multicore Optical Fiber Modal Characteristics

Fiber lasers exhibit a series of interesting properties, such as high conversion efficiency, low threshold, good beam quality and so on. It has been widely used in laser weapons, materials processing, spatial optical communication, remote sensing, electrooptical countermeasures and other fields. In recent years, more and more attentions have been paid to fiber lasers. However, output power of single fiber is difficult to improve because of the nonlinear effects and optical damage. Coherent combination of optical fiber lasers is one of the most effective technical approch to obtain the high power and high beam fiber laser. The multicore fiber beam is the simplest way in all of the coherent combination. However, conventional optical fiber can not be coherent effectively because the evanescent field of conventional optical fiber is very weak. External structures taken to achieve the combination are sophisticated and unstable.In this paper, the modal field characteristics of micro/nano optical fiber array have been studied detailedly by using finite difference time domain (FDTD) method. The results are useful to certain academic value and practical significance.Our work in the thesis includes the following parts:The far field characteristics of micro/nano fiber array have been studied theoretically. Based on analytical method, the far field of coherent beam combining of the micro/nano fiber array have been simulated using matlab when all array elements work in the same frequency and phase locked. Results indicate that all the elements play an effective role of improving the peak power in micro/nano fiber array. In order to obtain higher power and better beam quality of micro/nano fiber array, reducing the space between adjacent elements and increasing the number of fiber array are helpful to micro/nano fiber combining.The article numerically simulates the modal field characteristics of multicore fiber with different optical fiber parameters using finite difference time domain (FDTD) method, including multiple micro/nano fibers and muItiple conventional fibers. The result shows the modal field characteristics of multicore fiber, including the modal field characteristics ofmultiple micro/nano and conventional fibers could be better by adjusting the space between adjacent elements and the diameter of fiber. Based on the large evanescent field of single micro/nano optical fibers, the coupling of micro/nano fiber array could be improved obviously. It is better than nulticore conventional fiber. Micro/nano fiber array may have potential applications in the field of large mode area optical fibers. It is useful to further development of coherent beam combination.