A corner of scientific research | Research progress of femtosecond laser micro-nano processing optical fiber functional devices

Author: Li Jinjian, Liu, Song Shiliang



1. Femtosecond laser direct writing technology



1.1 Femtosecond laser direct writing mechanism

Femtosecond laser direct writing technology focuses the output laser on the target area to be processed and scans it to modify or eliminate some areas.



1.2 Femtosecond laser direct writing waveguide

Femtosecond laser direct writing waveguide technology is based on the femtosecond laser-induced changes in the local refractive index of the material. Generally, the femtosecond laser is focused inside the material, and the sample is moved through a computer-controlled three-dimensional platform to write the designed structure inside the material Form an optical waveguide.



1.3 Femtosecond laser direct writing grating

When using femtosecond laser to write gratings directly, the focused laser is usually scanned along the axis of the fiber to induce internal refractive index modulation, the exposure is moved for a certain distance, the laser is blocked and then moved the same distance, repeat the process to complete the periodic refractive index inside the fiber change.



1.4 Femtosecond laser direct writing fiber Fabry-Perot interferometer

The traditional free-space Fabry-Perot (FP) interferometer consists of two parallel glass lenses with high reflectivity on both surfaces. The light beam is reflected multiple times between the two mirrors to form interference. Compared with the traditional spatial FPGA interferometer, the all-fiber structure of the FPGA interferometer is smaller in size, compact in structure and easy to prepare.



2. Femtosecond laser two-photon polymerization preparation of optical fiber functional devices



2.1 Principle of Femtosecond Laser Two-Photon Polymerization

Two-photon polymerization is a polymerization process initiated by the material simultaneously absorbing two photons under the action of strong light. Femtosecond pulsed laser has large pulse energy at very low average power. Therefore, when the focused femtosecond pulsed laser interacts with the material, it is easy to cause two-photon absorption of the material.



2.2 Fabrication of optical fiber interferometer by femtosecond laser polymerization

Optical fiber interferometer has the characteristics of small size, light weight, anti-electromagnetic interference, strong integration, etc., and has been widely used in optical communication, information processing and sensing.



3. Femtosecond laser induced water breakdown

3.1 Principle of femtosecond laser-induced water breakdown

When the femtosecond laser with larger pulse energy is focused into water, the femtosecond laser pulse will induce the water to produce an optical breakdown phenomenon, and the water molecules will be ionized by the femtosecond laser pulse to produce a plasma with high temperature and high pressure, which rapidly adiabatic expansion in the water , Its internal energy can be transmitted to the water, generating shock waves and laser cavitation in the water.



3.2 Femtosecond laser-induced water breakdown processing microchannels

3.3 Femtosecond laser water-assisted processing fiber interferometer



4. Conclusion

The combination of femtosecond laser micro-nano processing technology, optical fiber sensing technology and microfluidic chip technology can broaden the application fields of microfluidic chip systems, making it no longer limited to single functions such as sample separation and detection, but a truly integrated sample A micro total analysis system with functions such as introduction, mixing, separation, and detection. In addition, it is necessary to explore degradable and biocompatible materials that can be used for micro-nano processing, optimize preparation parameters, improve and perfect device performance, and promote faster development of femtosecond laser processing technology.