Fabrication and characterization of a fused silica-based optical waveguide with femtosecond fiber laser pulses

In this paper, we present the fabrication and characterization of a fused silica-based optical waveguide by a femtosecond fiber laser system whose wavelength and repetition rate are 532 nm and 1 MHz, respectively. In order to successfully form an inner layer of waveguide inside the silica substrate, three main laser parameters, laser power, scanning speed, and focus depth, were systematically tuned and studied. Results show that the fused silica can be ablated for scanning speeds between 5 and 7 mm/s under a laser power of 230 mW and a depth of 10 mu m, and the modified width decreases with the increase of scanning speed, regardless of the machining depth used. The analysis of light path and net fluence in the waveguide suggests that the range of the net fluence for fabricating a low propagating loss waveguide should be kept within 0.973-1.438 kJ/cm(2). The propagating loss measured for this type of waveguide is found to be 4.6, 4.8, 6.2 dB/cm for the scanning speeds of 8, 9 and 10 mm/s, respectively. Studies presented here demonstrate the feasibility of fabricating a femtosecond laser-induced optical waveguide on fuse silica, which is quite promising for the development of new devices and systems suited for many applications in optoelectronics, electronics, medicine, biomaterials and energy production.