| Optical fiber devices based on the optical fiber micro/nano-structures are vital support for the development of information technology. D-shape optical fiber has been made to various all-fiber devices for its simple structure, high sensitivity, good mechanical properties, etc. Improving machining precision and efficiency of D-shape optical fiber has a very important significance for the development of integrated optics and optical fiber sensing. Based on an advanced technology——femtosecond laser micro/nano-machining, the machining and transmission characteristics of D-shape optical fiber were studied.1. Due to the low efficiency and other drawbacks when fabricating D-shape optical fiber by point-by-point ablation near the threshold, a profile-line method based on high-energy femtosecond laser was proposed, the feasibility of which has been verified in both theory and experiment.2. A reliable femtosecond laser micromachining system for optical fiber was built. Based on this system, it was studied that how this several process parameters (defocus, single pulse energy, scanning speed, processing path depth) affected the machining surface quality and the machining depth of D-shape optical fiber, which was fabricated by femtosecond laser profile-line method. Under optimum process parameters, the surface roughness the D-shape optical fiber can be up to about170nm. Furthermore, Several repeated experiments indicate that this method is able to improve the machining efficiency, guarantee the machining precision and have a high repeatability.3. After establishing the three-dimension optical model of D-shape optical fiber, the transmission characteristics of D-shape optical fiber with different structural parameters were calculated based on the finite-difference beam propagation method (FD-BPM). The results show that: when the refractive index of the filler is1.466or less, transmission loss of all D-shape optical fiber is almost0; when beyond1.466, with increasing of the refractive index, the transmission loss of every D-shape optical fiber rises at first and then decreases. The maximum loss all occurred at the refractive index of1.472. In addition, at the same refractive index, with decreasing of the thickness of the remained cladding and increasing of the machining length, the transmission loss of the D-shape optical fiber would increase.4. Finally, research on the transmission characteristics of the D-shape optical fiber fabricated by femtosecond laser profile-line method was done experimentally. Results show that the experimental results and simulation results are very similar. This also indicates that the proposed femtosecond laser profile-line method provides a newly efficient way for the machining of high-performance D-shape optical fiber.54figures,8tables,67references. |
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