Research On Process Parameters Of Fused Silica Optical Waveguide Directly Written By Femtosecond Laser

Abstract:The fast development of optical communication in recent year has facilitated the advancement of integrated optics. Optical waveguide devices, being the main components of integrated optics, have found broad applications in obtaining, transferring, and processing signals. On the one hand, the fabrication of optical waveguide usually requires micro-nano-scale manipulation. Thus, compared to the traditional technics such as vapor deposition, ion exchange, and ion implantation, femtosecond laser processing, which is the most important technics in micro-nano-units fabrication, has been widely used to fabricate optical waveguide devices. On the other hand, integrated optical circuits have received less attention compared to optical fibers; hence, they restrain the development of optical waveguide devices. Therefore, to advance the development of integrated optical devices, it is desirable to investigate the integration of optical waveguide devices as well as the optimization of waveguide processing parameters using femtosecond laser processing for improved transmission performances.In this study, we first theoretically analyzed the relationships between the laser beam radius, the Rayleigh length, and the optical lens aperture. Based on the analysis, an experimental system was built to realize accurate control of the focused laser spot and the working depth employing CCD, in which300-350μm slits were used to shape the laser spot after it being focused by the lens. The types and mechanisms of optical waveguide loss were studied, and several measuring methods were summarized with respective pros and cons. Then, a MATLAB program was written to process the light scattering images of the focused optical waveguide, and calculate the transmission loss.We then measured the waist radius of the femtosecond laser coming out of the focal lens and the peak intensity at the laser focal spot, and analyzed their relations. The peak energy densities of the laser corresponding to different numerical apertures, processing energies, and processing speeds were calculated to obtain its effect on the Optical waveguide devices and on the losses. The results show that the optimal transmission performance of the optical waveguide with a loss of less than-0.2dB/cm can be obtained using a0.25laser beam radius, a6mW laser power, and45-60μm/s processing speed.