Control of the Properties of Micro-Structured Waveguides in Lithium Niobate Crystal

Abstract

We study numerically depressed-cladding, buried waveguides that can be formed in a lithium niobate crystal by femtosecond laser writing. We demonstrate that the guiding properties can be controlled by the waveguide structural characteristics

Optimisation of microstructured waveguides in z-cut LiNbO3 crystals

“…Additionally, the direct fs laser inscription always generates losses both within and around the tracks [16-18], whose effect should be properly accounted for. All the fore-mentioned effects become more significant at the long wavelengths, where we observed an unusual variation of the confinement losses in the O and E polarisations [13]. In order to confirm the accuracy of our numerical model we simulated known microstructured optical fibre (MOF) structures [15] using the same material dispersion relations.…”

“…In a previous work [13] we have demonstrated numerically that the guiding properties of mi-crostructured WGs in z-cut LiNbO 3 crystals can be controlled by the WG geometry. Obviously, with virtually an infinite number of structural parameters the design of such structures is not as trivial.…”

“…Clearly, the range of possible structural parameters that can be investigated for further optimisation is far from being fully explored. We have also shown [13] that WG designs with track diameters that differ from one ring to another [14, 15] can extend the spectral region of low-loss operation to longer wavelengths. However, it emerged from our study that a systematic procedure is required to find optimum laws for the variation of WG parameters such as the track size among different rings of tracks.…”

“…For our modeling, we used the COMSOL simulation software based on the finite element method (FEM), which enables an accurate description of both anisotropic materials and materials with absorption (indicated by the imaginary part of the RI). To truncate computational grids for simulating Maxwell's equations and, thus, minimize the effect of boundary reflections, we used a rather wide perfectly matched layer absorber surrounding the cross-section of the WG structure [13]. However, this limits the number of modes that can be followed simultaneously over a wide wavelength range.…”

Ultrafast Laser Microprocessing of Transparent Dielectrics. New Schemes for the Fabrication of Photonic Devices

“…The simulation can also be used to corroborate the measured value of ∆n. Another important point to take into account is the fact that a perfectly matched layer (PML) was used in the simulations in order to truncate the computational domain and minimize the effects of boundary reflections [125]. For this purpose, a circular PML surrounding the cross section of the waveguide structures was always used as it can be clearly seen in Fig.…”