Research On Femtosecond Laser Fabrication Of Optical Fiber Micro-hole Structures

Sensing technology is one of the three pillars of modern information technology. Along with the development of optical fiber communication technology, the optical fiber sensing technology is also developing rapidly with great advantages such as simple structure, anti-electromagnetic interference, corrosion resistance, ease of real-time monitoring and remote measurements, etc. While using long pulse laser to fabricate microstructures, there are problems of large focal spot and strong thermal effects, which are very bad for the manufacturing of optical fiber microstructures. Femtosecond laser can achieve manufacturing with high precision, high quality, high resolution and little thermal effect with the characteristics of extremely short pulse width and high peak power. In this article, the ablation threshold of optical fiber is calculated. Based on the characteristics analyzation of focused femtosecond laser beam, experimental research about manufacturing a kind of V-shaped microstructures on optical fiber is conducted. The theoretical analyzation and experimental research about fabrication of micro-holes on single mode optical fiber are also carried out. The main contents of this article are as followed:1. Focused beam characteristic of femtosecond laser is analyzed. And calculation about the relationship of beam waist radius and Rayleigh length with the diaphragm aperture size is conducted.2. According to the main interaction mechanism of femtosecond laser beam with transparent materials, the ablation threshold of optical fiber is calculated, the result isFth=2.67J/cm2. And an verification experiment is also conducted, the experimental result is F’th=2.59J/cm2, which meet very well with the calculated result.3. Experiments about fabricating V-shaped microstructures on optical fiber and then testing their sensitivity performance to liquid refractive index are carried out. According to the experiment results, for the V-shaped microstructures with different optical power attenuation under the same processing path, it is found that the greater of the optical power attenuation, the better of sensitivity performance to liquid refractive index.4. As to the relationship of the diameter and depth of the optical fiber micro-holes with parameters such as laser fluence, laser power and numerical aperture, theoretical simulation is carried out. And experiments about analyzing the effect of laser power and pulse duration time on hole depth and diameter are also conducted. Based on previous research, a series of micro-holes were manufactured under different parameters, and the sensitivity performance to liquid refractive index of those micro-holes is also tested respectively.