Abstract
KY(WO4)2 is an attractive material for integrated photonics due to its high refractive index and excellent non-linear and gain characteristics. High refractive index contrast structures increase light-matter interaction, reducing the threshold for lasing and non-linear effects. Furthermore, high refractive index contrast permits dispersion engineering for non-linear optics. In this work, we present a novel fabrication method to realize pedestal microdisk resonators in crystalline KY(WO4)2 material. The fabrication process includes swift heavy ion irradiation of the KY(WO4)2 with 9 MeV carbon ions and sufficient fluence (>2.7·1014 ion/cm2) to create a buried amorphous layer. After annealing at 350° C, microdisks are defined by means of focused ion beam milling. A wet etching step in hydrochloric acid selectively etches the amorphized barrier producing a pedestal structure. The roughness of the bottom surface of the disk is characterized by atomic force microscopy.
Highlights
Potassium yttrium double tungstate (KY(WO4)2) is a member of the potassium double tungstate family of materials
KY(WO4)2 has a high Raman gain value with sharp peaks at 765 cm−1 and 905 cm−1 [11], which has been exploited for the realization of Raman lasers [12]
A cross-section of the structure after focused ion beam (FIB) milling and two cycles of 2 hours etching in 32% HCl at room temperature followed by 1 hour of 25% TMAH is shown in Fig. 5 (b)
Summary
Potassium yttrium double tungstate (KY(WO4)2) is a member of the potassium double tungstate family of materials. The amorphized layer induced by ion irradiation has been reported to exhibit a preferential etching in common wet etching solutions with respect to the undamaged material. We exploit the selective etching of the irradiation-induced amorphous layer with respect to the undamaged crystalline structure of undoped KY(WO4) to further increase the contrast of the KY(WO4) waveguides by producing a pedestal geometry, in which the mode lies inside a thin KY(WO4) layer surrounded by air. The sample was annealed at 350°C for 3 hours in order to repair point defects, reduce propagation losses and sharpen the refractive index boundary by repairing partially amorphized KY(WO4)2 [22] In future devices, this annealing will be performed after milling to repair any potential damage caused by the gallium ions [30]. The pedestal disks were imaged with the SEM in the DualBeam FIB using 2 kV acceleration voltage (Fig. 5)
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