Low-repetition rate femtosecond laser writing of optical waveguides in KTP crystals: analysis of anisotropic refractive index changes

Abstract

We report on the direct low-repetition rate femtosecond pulse laser microfabrication of optical waveguides in KTP crystals and the characterization of refractive index changes after the thermal annealing of the sample, with the focus on studying the potential for direct laser fabricating Mach-Zehnder optical modulators. We have fabricated square cladding waveguides by means of stacking damage tracks, and found that the refractive index decrease is large for vertically polarized light (c-axis; TM polarized) but rather weak for horizontally polarized light (a-axis; TE polarized), this leading to good near-infrared light confinement for TM modes but poor for TE modes. However, after performing a sample thermal annealing we have found that the thermal process enables a refractive index increment of around 1.5x10(-3) for TE polarized light, while maintaining the negative index change of around -1x10(-2) for TM polarized light. In order to evaluate the local refractive index changes we have followed a multistep procedure: We have first characterized the waveguide cross-sections by means of Raman micro-mapping to access the lattice micro-modifications and their spatial extent. Secondly we have modeled the waveguides following the modified region sizes obtained by micro-Raman with finite element method software to obtain a best match between the experimental propagation modes and the simulated ones. Furthermore we also report the fabrication of Mach-Zehnder structures and the evaluation of propagation losses.

Modelling of the optical planar waveguide based on (Yb,Nb):RTP/RTP(001) system for cell counting

“…First exploratory research to obtain optimum conditions for RIE in (Yb,Nb):RTP epitaxial layer to obtain a channel waveguide with a height around 1 microns was demonstrated [3]. Recently, some work related to RTP waveguides based on ion exchange, RIE and direct laser writing were demonstrated [4,5,6]. We believe that, this report is the first demonstration of the waveguide sensor to count cells based on RTP waveguides.…”

OPTICAL PLANAR WAVEGUIDE SENSOR BASED ON (Yb,Nb):RTP/RTP(001) SYSTEM FOR THE ESTIMATION OF METAL COATED CELLS

“…First exploratory research to obtain optimum conditions for RIE in (Yb,Nb):RTP epitaxial layer to obtain a channel waveguide with a height around 1 microns was demonstrated [5]. Recently, some work related to RTP waveguides based on ion exchange, RIE and direct laser writing were demonstrated [5][6][7]. We believe that, this report is the first demonstration of the waveguide sensor to count cells based on RTP waveguides.…”

Fabrication of optical waveguides in RbTiOPO4single crystals by using different techniques

“…Secondly we have modeled the waveguides following the modified region sizes obtained by micro-Raman with finite element method software to obtain a best match between the experimental propagation modes and the simulated ones. Furthermore we also report the fabrication of MZ structures and the evaluation of propagation losses [9]. In order to evaluate how the cladding waveguide split the modes in two, Y-splitters were also characterized in its output.…”