Design Of Astrology Transmission Optical Fibers In Large Astronomical Telescope

In recent years, the large sample spectroscopic sky survey has gradually become a hot trend in the astronomy field, which results in the multi-object fiber spectroscopic observation being a hot research topic. In this paper, a five-core special astrology transmission optical fiber,which can realize the low transmission loss at 370?900 nm and provide a feedback signal of the offset was designed to improve the spectral acquirement efficiency of LAMOST(Large Sky Area Multi-Object Fiber Spectroscopic Telescope).The energy crosstalk between the transmitting energy core and the aligning core was analyzed by using mode coupling theory. The maximum energy coupling efficiency between the fundamental mode in the transmitting energy core and the fundamental mode in the alignning core is 4.6×10-14%. The maximum energy coupling efficiency between LP15 2 mode in the transmitting energy core and LP11 mode in the aligning core is 1.4×10-8%. Such a low energy crosstalk will not affect the signal transmission in the astronomy field.According to the mode coupling theory, the excitation characteristics were studied when an aligning core of the five-core optical fiber was connected with a step index fiber and a graded index fiber, respectively. The relationship between the excitation coefficient and the offset of the two fibers is analysed. The maximum excitation coefficient is 0.9094 when the aligning core spliced a step index fiber.The excitation characteristics when a light spot is shone on the end of the five-core optical fiber were investigated numerically. The relationship curves between the excitation coefficient of each core and the offset of the light spot along the radial direction show that the fiber can provide a feedback signal of the offset of the light spot when the offset is in the range of 100?349 pm.We fabricated the five-core astrology transmission optical fiber probe, and tested its characteristics of the alignment by using He-Ne laser. The relationship between the exitted gray value of light intensity and the offest of light spot along the radial direction show that the five-core astrology transmission optical fiber probe can provide a feedback signal of the offset of the light spot when the offset is in the range of -305?-155 ?m or 105?270 ?m. The experiment results basically agree with the theoretical calculations.