Femtosecond Pulse Laser Lithography Waveguide Technology

Optical waveguide is the basic element of integrated optics,and it plays an important role in the applications of optical communications.In compared with some traditional waveguide fabrication techniques,such as ion exchange,ion implanting and etching,femtosecond laser optical waveguide writing in transparent material has attracted a lot of attention in recent years.Femtosecond laser inscription waveguide in fused silica has been discussed,in special,I focused on the issue of realization of circular cross-section waveguide in two dimensions,properties of femtosecond laser inscription waveguide,and nonlinear propagation in the waveguide arrays.The main work has been achieved as follows:1) The two schemes of femtosecond laser inscription waveguide,as called longitudinal and transverse writing geometries,and the resulting advantage and disadvantage has been discussed.To meet the requirement of large area of planar light-wave circuit(PLC),it is investigated that the use of beam shaping techniques compensate asymmetry in the waveguide cross-section of transverse writing geometries.The waveguide with circular cross-section has been fabricated with beam shaping by silt in the experiment,and realize fabrication of circular cross-section arc waveguide in two dimensions by rotating the silt.It provides important base to realization of complex planer light-wave circuit.2) Femtosecond laser inscription waveguide contributes typeⅠand typeⅡwaveguide which distinguish with the writing conditions.The dependence of waveguide type on pulse width,focusing optics and polarization of laser has been investigated.Also it is depicted how to obtain characteristic parameters of waveguide such as near field mode,far field mode,refractive index distribution,and waveguide loss,repsectively.3) Nonlinear effect of waveguide arrays prepared by femtosecond laser photoinscription has been studied.Nonlinear refractive index of ultrashort pulse laser propagating in the waveguide array leads to nonlinear localization and delocalization, which are decided by the relationship between initiate refractive index change of waveguide array(Δn₀),nonlinear refractive index change(Δn_non),and optimum refractive index change(Δn_s) which corresponds to optimal coupling constant.Also nonlinear localization and delocalization are observed in experiment with help of high repetition-rate femtosecond laser inscription waveguide array injected by low repetition rate femtosecond laser.