Origins of waveguiding in femtosecond laser-structured LiNbO3

Abstract

Femtosecond laser-induced structural changes in LiNbO3 are studied. Depending on the laser processing parameters two different types of modification are identified and their origin is discussed. Both types of modification can be described within the framework of induced lattice defects. For strong material damage a refractive index increase can be obtained due to the induced stress field. By appropriate tailoring of this stress field thermally stable and highly symmetric waveguides can be obtained well suited for nonlinear integrated-optical applications

Computation of the expansion parameters of femto-waveguides using a two dimensional μ-Raman map and guided modes

“…The most of them are not quantitatively described. So, the result of the whole process from a point of view of the surrounding residual strain field was modeled in literature, 11,15,17 as a pseudoarbitrary mechanical expansion of an ellipse in an "infinite" medium. Consequently, the expansion and geometrical parameters of this model represent, in a first order of approximation, the sum of all the mentioned phenomena.…”

“…[6][7][8][9][10] Following this, knowledge about femtosecond laser written waveguides (herein "femto-waveguides") in LiNbO 3 has been obtained via experimental studies and a numerical model approach. 11,12 This elastic model has played an important role, particularly in the study of the origin of femto-waveguides. The model consists of an ellipse that statically expands within an anisotropic domain, and the mechanical deformation surrounding the ellipse generates a refractive index increment, which allows waveguiding.…”

“…The model consists of an ellipse that statically expands within an anisotropic domain, and the mechanical deformation surrounding the ellipse generates a refractive index increment, which allows waveguiding. Following this initial model, 11,12 various studies aimed to investigate the residual stress in femto-waveguides using numerical models. [13][14][15] Another study retrieved characteristics of the material structure and made a qualitative residual strain analysis in femto-waveguides using micro-Raman measurements.…”

Optical Cladding Waveguides in Dielectric Crystals Produced by Femtosecond Laser Inscription

“…Efficient second harmonic generation (SHG) from 1064 to 532 nm light have been realized through fs-laser written cladding waveguides in KTiOPO 4 and BiB 3 O 6 crystals based on the phase matching mechanisms. Under pulsed laser pump, the SHG conversion reaches a value as high as 45% for KTiOPO 4 waveguide, and 25% for the BiB 3 O 6 waveguide.…”

“…Femtosecond (fs) laser inscription has become a powerful and unique technique to fabricate waveguides in a wide range of optical materials [2], since Davis et al reported their pioneer work in glass [3]. Depending on the diverse parameters of the fs laser pulses and the material properties, the fs-laser inscribed waveguides can be with directly written structures (so-called Type I waveguide with single line writing) [4], stress-induced waveguides (Type II with double line filaments) [5], and depressed cladding waveguides [6]. In the cladding structures, the waveguide are located in the regions surrounded by the fslaser induced tracks with negative refractive-index changes.…”