Stress-induced buried waveguides in the 0.8CaSiO3–0.2Ca3(PO4)2 eutectic glass doped with Nd3+ ions

Abstract

a b s t r a c tIn this work the fabrication of buried optical waveguides by femtosecond laser inscription in the 0.8CaSiO 3 -0.2Ca 3 (PO 4 ) 2 eutectic glass doped with Nd 3+ ions is reported. The glass samples were prepared by melting the eutectic powder mixture in a Pt-10 wt.% Rh crucible at 1600 • C and pouring it in a preheated brass mould. Afterwards, the glass was annealed to release the inner stresses. Buried waveguides were fabricated by focusing beneath the surface a pulsed Ti:sapphire laser with a pulsewidth of 120 fs working at 1 kHz. Two adjacent parallel tracks were written to define a region where an increase in the refractive index occurs. The effects produced by the variation of the laser pulse energy as well as the lateral separation between tracks, scanning speed and focusing distance were studied. After the laser processing, the near-field intensity distribution at 633 nm of the waveguide's modes was studied demonstrating the confinement of both, the TE as the TM polarizations. In order to diminish the losses induced by colour centres absorption, heat treatments were carried out in the samples. The waveguide's modes were compared with respect to the samples without heat treatments. The spectroscopic properties of the neodymium ions have been characterized to evaluate in what extent their optical properties could be modified by the waveguide fabrication process and to elucidate the potential application of such waveguides as integrated laser sources.

Ultrafast direct laser writing of cladding waveguides in the 0.8CaSiO3-0.2Ca3(PO4)2 eutectic glass doped with Nd3+ ions

“…The guiding properties decay dramatically for index decrease lower than 3 Â 10 À3 , and for Dn max lower than 5 Â 10 À4 the tunnelling losses are too high to properly sustain light propagation in the structure. These values agree with the increase in refractive index modifications reported in this material, 20 as well as the values reported in other materials with similar fabrication process. 2,32 Comparing the experimental results of Figure 4 with the numerical simulations, it is possible to conclude that the index modification induced by the fs-laser processing induced at least an index change of 5 Â 10…”

“…Following the procedure previously reported in doubleline waveguides fabricated in this material with similar fabrication technique, 20 isochronal thermal treatments have been carried out in order to decrease the propagation losses by removing colour centres created in the waveguides during the laser writing process. [27][28][29] In this way, 30-min isochronal annealings have been applied starting from 200 C up to 750 C with steps of 50 C. After each treatment, the propagation losses have been determined by measuring the transmitted power along the waveguide.…”

“…Comparing these waveguides to double track waveguides fabricated in CaSiO 3 -Ca 3 (PO 4 ) 2 as previously reported, 20 it can be noticed that it is possible to achieve higher temperatures during the thermal treatments without losing guiding properties. This point suggest that the tailoring of the waveguide allows to maintain the mode confined with a lower index increase, and thus, it is possible to improve the quality of the waveguides by applying more aggressive thermal treatments that in the case of the double filament waveguides lead to the destruction of the waveguide.…”

“…This point suggest that the tailoring of the waveguide allows to maintain the mode confined with a lower index increase, and thus, it is possible to improve the quality of the waveguides by applying more aggressive thermal treatments that in the case of the double filament waveguides lead to the destruction of the waveguide. 20 It is remarkable that Type II waveguides started to present propagation loses due to tunneling processes at 350 C, while in the case of Type III waveguides, the quality of the waveguides improves continuously reaching the optimum point in de region between 600 and 650 C. Finally, the spectroscopic analysis of the Nd 3þ ion inside the waveguides has been performed. It has been found that the luminescence spectra of the 4 F 3/2 !…”

“…The waveguiding properties have been evaluated for different processing conditions, and compared to the double-line configuration previously reported on this glass. 20 CaSiO 3 -Ca 3 (PO 4 ) 2 eutectic glass presents two interesting properties. First, it is a bioactive material since tricalcium phosphate (TCP), Ca 3 (PO 4 ) 2 , is osteoconductive and bioactive (reasorbable), 21 and wollastonite (W), CaSiO 3 , is bioactive with osteostimulative properties.…”