| Much effort has been taken to investigate waveguides fabricated with femtosecond laser around the world since 1990s when Miura K and his cooperators first found that permanent refractive index modification can be achieved within the volume of multi kinds of glasses.Many kinds of on-chip integrated optical devices such as beam splitters,coupler,sensors,modulators and especially quantum optical components have been made.It is widely accepted that fabricating waveguides with low loss,small bending radius and deep written depth is essential to enhance the integration of device and improve the design freedom.In order to get the best performance of waveguides,we focused femtosecond laser pulses into the volume of alumino-borosilicate glass and silica glass using long working distance microscope objective lenses to optimize waveguides in series of fabrication conditions.Because of the discrepancy in band gap,element composition,thermal diffusion rate and working point between the two glasses,waveguides fabricated in these two glasses are quite different.Plasma formation,element migration and thermal ionization play different role in the structure reengineering and refractive index change in these two kinds of glasses.Varying average laser power from 100mW to 1200mW,scan speed from 50μm/s to 2000μm/s and scan times from 1 to 20,we found that the more times a single waveguide was scanned,the smoother morphology and the higher refractive index change(average core refractive index change Δn≈0.0023)can be acquired.Waveguides with low propagation loss(0.1dB/cm),low coupling loss(less than 0.3dB/facet)and focal dqpth of 900μm beneath the surface were successfully fabricated.The bending radius can be as small as 30mm and the bending loss can be compressed to 1.8dB/90°at the same time.The mode field diameter of the single mode waveguide at wavelength of 1550nm can be modulated from 15.84μm to 7.76μm by changing the scan speed and scan times.Finally low-loss 7-core fiber Fan-out optical interconnection component with was successfully fabricated. |
