LAUSR

Abstract In this paper, the relationship between the coupling efficiency and transmission distance of different fiber optic probes is compared for further studying the focusing performance of ultra-small GRIN fiber probes. Taking an example of five typical ultra-small GRIN fiber probes such as single mode fiber (SMF), "SMF + 0.31mm 50/125 GRIN", "SMF + 0.36mm NCF + 0.12mm 50/125 GRIN", "SMF + 0.48mm 100/140 GRIN", "SMF + 0.48mm NCF + 0.14mm 50/125 GRIN", the relationships between the theoretical coupling efficiency and transmission distance are compared with experimental data. The obtained results show that an increase in the working distance of a probe causes increase of the transmission distance to maintain a higher coupling efficiency, and leads to gain of the waist diameter. Therefore, the comprehensive effects of the working distance, waist diameter and coupling efficiency must be taken into consideration in the process of optimizing the design parameters of ultra-small GRIN fiber probes.