Investigation On Femtosecond Laser Direct Writing Optical Waveguide In Chalcogenide Glass

Femtosecond-laser microprocessing technology is a frontier research field which is paid close attention to by scholars all over the world.Different from long pulse laser,its pulse duration is of fs(1 fs=10^-15 s)magnitude and possiblely peak power is of PW(1 PW=10¹⁵W)magnitude.So people developed by femtosecond laser micro machining system based on Ti sapphire laser,carry out research on the femtosecond laser micro fabrication.Using femtosecond laser micro processing technology,the energy can be injected into the interior of a transparent material.When interacting with the material,it can directly put its energies into a very small area,high energy density deposition generated by the absorption and movement of electrons'dramatic changes in femtosecond,thus avoiding the influence of laser linear absorption,energy transfer and diffusion,which makes the interaction between femtosecond laser and material become a kind of the“cold”process obtaining ultra-high precision,non-melting,ultra-high spatial resolution.It is three-dimensional manufacturing high precision machining that many type of materials can be applied to.In this paper,we use femtosecond laser processing technology inscribing waveguide in chalcogenide glass.Processing parameters and properties of chalcogenide glass were studied,and try to apply it to waveguide lasers.The main contents are as follows:1.Using femtosecond laser pulse of width 50fs,wavelength 800nm,repetition frequency1kHz to inscribe single or double line waveguides in chalcogenide glass which has large nonlinear coefficient.We roughly find out refractive index change threshold and ablation threshold range,single pulse energy varies from 0.2?J to 8.2?J.This processing power should between these two thresholds in order to inscribe waveguides with micron level,rather than cause ablation phenomenon;at the same time we find that the self focusing effect appears obviously on the internal glass.2.Optical properties of chalcogenide glass?GGSI?have been measured such as transmission spectra from the visible to the near infrared band.Then we set a variety of processing parameters to inscribe many different optical waveguides.Their transmission mode of single optical waveguide are in the observation,a few of them have good single-mode characteristics and the cross section of the mode field distribution is similar to the Gauss distribution.We analyzes the influence of different parameters on the processing quality of the optical waveguide.The transmission loss of the optical waveguide on different parameters have been measured,acquire the best single wave guide with the parameter:single pulse energy 0.8?J,scanning speed of 120?m/s.3.In chalcogenide glass?GSS?we fabricated diffraction gratings with different grating constants,including composite grating,then collect their the grating diffraction image.We measure transmission rate of the glass in 1550 nm,and find that the grating structure can reduce the transmission rate.4.We verify the possibility of chalcogenide glass application in waveguide laser.My sample is Tm?Er co-doped GGSI glass,we measure its emission spectra,it turns out that the fluorescence of Tm ion emission peak is 1750 nm.compared with the theoretical value it is slightly smaller,and the fluorescence of Er ion emission peak is still 1550 nm constant.The cavity is a cavity with a flat concave cavity,and the optical waveguide in the chalcogenide glass is the region where the gain medium is located.We find the threshold of the laser beam is very high,which is not under 500 mW.5.The absorption rate of chalcogenide glass under different power conditions at 793nm is tested,and the average absorption rate was 13%.The damage threshold of the glass has been measured.When the focal spot size is 45?m,a small hole is made on the sample by using 760mW continuous laser.and the damage threshold is estimated to be 4.78×10⁵mW/mm².Therefore,we increase the pumping power of the waveguide laser to 500 mW,and it still doesn't work.We find that the light output threshold value of the glass is larger than the damage threshold,and emitting laser with this sample is not possible.At the same time,we tested the glass transmittance with mode-locked pulse laser of 10 ps,wavelength1030 nm.The transmittance become small with the power increasing,and finally tends to be constant,during the test,the glass emits strong green light,which shows the frequency doubling phenomenon obviously.