Femtosecond Laser Induced Integrated Optical Microstructures

Femtosecond laser has ultrashort pulse and ultrahigh peak power. The extremeconditions of high temperature and high pressure can be generated when femtosecond laserprocesses materials. Under such extreme environment, materials can form some uniquestructure changes. Femtosecond laser can accurately and space-selectively fabricate variousfunctional microstructures in transparent materials, and it has a lot of applicable value in thefield of three-dimensional integrated photonic devices.In this paper, we studied the characterization and functionalization of micro-andnano-structures induced by femtosecond laser. Two kinds of laser were used:500kHz highrepetition rate femtosecond laser and1kHz low repetition rate femtosecond laser. Thecontents of the research mainly includes: space-selective precipitation of Te semiconductornanoparticles and LiTaO3frequency doubling crystal, femtosecond laser direct writingwaveguide. The main research results and conclusion are as follow:1. Nonlinear optical nanoparticles Te have been induced space-selectively by1kHzrepetition frequency femtosecond laser. The morphology and size distribution of the Tenanoparticles were investigated. We investigated the optical properties of the glass doped withTe nanoparticles, and demonstrated its application in the field of micro-nano grating.Regarding the mechanism of Te nanoparticles induced by low frequency femtosecond laser,we suggest that the tellurite glass network structure of Te-O bonds are easy to be broken underthe high temperature and pressure conditions generated by femtosecond laser. Elementsmigration at different rate and concentration at different space resulted in precipitation of Tenanoparticles. Te nanoparticles doped glass materials prepared with femtosecond laserirradiation can be applied in optical components, such as optical switches with ultrafastresponse rate andmicro-nano grating with high diffraction efficiency.2. Frequency doubling crystals LiTaO3were induced by500kHz repetition frequencyfemtosecond lasers. The precipitated crystals shows excellent optical frequency doublingperformance. We found that the frequency doubling crystal precipitated after the laserirradiation for some durations, and the content of the frequency doubling crystals increased gradually with increasing irradiation time and finally reached a dynamic balance. Wecharacterized the distribution of LiTaO3crystals by Raman intensity mapping and the crystalsformation mechanism was analyzed.We also observed the birefringence phenomenon inducedby femtosecond laser, and we analyzed the mechanism by the Raman peak position mapping.The space-selective precipitation of LiTaO3in glass may find some applications in integratedphotonic devices.3. We wrote optical waveguides in phosphate glass and Gd3Ga5O12crystal by1kHzfemtosecond laser. We found that micro cracks and defects generated by the high laser energywill reduce the performance of optical waveguide, but if laser energy was too low, waveguidestructurecannot be effectively formed. Using Raman mapping, the mechanism of glass andcrystal refractive index change were explained. Phase change and residual stress were themain reason for refractive index change.Femtosecond laser micromachine as a new micro processing technology will open up anew way to fabricate integrated optical device.