Oxygen Implantation Allows Fabrication of Optical Channel Waveguides in Nd:YAG Transparent Ceramics
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Oxygen Implantation Allows Fabrication of Optical Channel Waveguides in Nd:YAG Transparent Ceramics Transparent polycrystalline ceramics doped with rare-earth ions, among them Nd:YAG ceramics, have been revealed as excellent gain media for high-power continuous-wave or pulsed solid-state lasers. The combination of the excellent laser performance of Nd:YAG ceramics and waveguide technology may drive the realization of high-power integrated lasers with stable output. F. Chen and Y. Tan from Shandong University, China, and D. Jaque from the Autonomous University of Madrid, Spain, reported in the January 1 issue of Optics Letters (DOI: 10.1364/OL.34.000028; p. 28) the fabrication of channel waveguides in Nd:YAG ceramic by selective implantation of O3+ ions using a photoresist stripe template. The researchers patterned on the surface of a 1 at.% Nd3+-doped YAG transparent ceramic sample (8 × 10 × 2 mm3) with an average grain size of 15 µm, a series of open stripes 10 μm in width and separated by 40 µm. A 5-μm-thick photoresist layer was used as the implantation mask, through which O3+ ions were implanted at an energy of 6 MeV and a dose of 1.0 × 1015 cm-2. After implantation, the researchers annealed the sample at 260ºC for 1 h in air to reduce color centers and defects created during the implantation process. The index profile of these channel waveguides, that the researchers reconstructed according to the index profile of the planar waveguide and calculated from the dark-mode spectrum, was formed by an enhanced index well (Δnw = +0.001) in the waveguide region and an optical barrier wall with negative index changes (Δnb = -0.006) at the boundary between the waveguide and the substrate. Experimental characterization of the near-field intensity distribution of the light carried in the quasi-TM00 mode matched well with simulations performed by the researchers using the finite-difference beam propagation method. The researchers also measured the waveguide’s losses (which were ~1.5 dB/cm) using the Fabry–Perot resonance method. The researchers said that this was approximately three times lower loss than similar waveguides produced by carbon implantation. The researchers performed spectroscopic characterization of Nd3+ in both the implanted and unimplanted regions, which showed that the spectrum of the 4F3/2 metastable state was only slightly modified during the fabrication procedure, and its lifetime was reduced by less than 3% when compared with that of the bulk. The researchers
observed that ion implantation induced a slight broadening of the emission line at ~936 nm and a shift to shorter wavelengths. The researchers attributed this to a slight increment in the lattice disorder
and a slight change in the crystal field around the Nd 3+ ions, due to slight changes in the unit cell volume. However, the researchers concluded that the luminescence properties of Nd3+ ions were
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