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6 pags., 5 figs., KY(WO4)2 crystal has a lot of potential as an on-chip waveguide material for lanthanide ion-doped, Raman active lasers and on-chip amplifiers. One method of fabricating these waveguides is by using swift carbon ion irradiation, which produces a step-like, damage-induced refractive index contrast of up to Δn ≈ 0.2. The irradiation is followed by an annealing step to reduce color centers that cause high optical absorption, leading to an optical slab waveguide with optical transmission losses as low as 1.5 dB/cm at 1550 nm. In this article, we report an upper limit of ∼ 450 ° C to the annealing temperature, above which stresses and recrystallization induce additional scattering detrimental to waveguide performance. The effects are characterized using transmission electron microscopy and Raman microscopy., We would like to thank the operators of the MESA+ Institute for Nanotechnology of the University of Twente for their indispensable help in obtaining the transmission electron microscope images and their general support. We also thank the Technical Staff of the CMAM-UAM center for their support with the irradiations. This research was not possible without the funding from the Horizon 2020 European Research Council programme through Grant No. 648978 and the Comunidad de Madrid through the grant TECHNOFUSION(III)-CM (No. S2018/EMT-4437).

Rare-earth ion doped potassium yttrium double tungstate, RE: KY(WO4)(2), is a promising candidate for small, power-efficient, on-chip lasers and amplifiers. There are two major bottlenecks that complicate the realization of such devices. Firstly, the anisotropic thermal expansion coefficient of KY(WO4)(2) makes it challenging to integrate the crystal on glass substrates. Secondly, the crystal layer has to be, for example, < 1 mu m to obtain single mode, high refractive index contrast waveguides operating at 1550 nm. In this work, different adhesives and bonding techniques in combination with several types of glass substrates are investigated. An optimal bonding process will enable further processing towards the manufacturing of integrated active optical KY(WO4)(2) devices. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Rare earth ion doped potassium double tungstates (e.g. KY(WO4)2, KYb(WO 4 ) 2 , and KGd(WO 4 ) 2 ) have long been used as laser and amplifier materials thanks to the high achievable gain provided by the rare-earth ions. This family of host materials is also very attractive for nonlinear optics due to their high nonlinear refractive index and Raman gain. Very efficient on-chip solid state lasers, frequency combs, supercontinuum sources and Raman lasers could be realized if high refractive index waveguides with the correct dispersion were developed. To date, the demonstrated integrated devices in rare-earth ion doped potassium double tungstates have shown very promising results, including high gain in on-chip amplifiers and high efficiency and output power in on-chip lasers. These devices, however, were fabricated using low refractive index contrast waveguides, which are not suitable for ring resonators or to achieve anomalous dispersion. High refractive index contrast KY(WO 4 ) 2 waveguides with high confinement are therefore needed as building blocks for active devices. In this work, pedestal disk resonators are proposed, based on a combination of swift ion irradiation, focused ion beam milling and a novel wet etching process. In-coupling of light into the first fabricated pedestal disks will be presented.

KY(WO4)2 and other materials of the double tungstate crystal family have been used for decades in active optical applications because of their relatively high refractive index (n≈2-2.04 @ 1550 nm), high transparency window (0.3- 5 μm), excellent gain characteristics when doped with rare-earth ions and reasonably high thermal conductivity (~3.3 Wm-1K-1). Low-contrast (Δn

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.

A method for determining the spatially resolved acoustic field inside a water-filled microchannel is presented. The acoustic field, both amplitude and phase, is determined by measuring the change of the index of refraction of the water due to local pressure using stroboscopic illumination. Pressure distributions are measured for the fundamental pressure resonance in the water and two higher harmonic modes. By combining measurement at a range of excitation frequencies, a frequency map of modes is made, from which the spectral line width and Q-factor of individual resonances can be obtained.

15 pags. 10 figs., Rare-earth ion doped KY(WO) is a well-known active laser crystal, due to its excellent gain characteristics and its relatively high nonlinear refractive index. As these properties are of great benefit to applications in integrated photonics, a study has been done into the fabrication of high refractive index contrast slab waveguides in KY(WO) as a first step towards the fabrication of channel waveguides. When properly choosing the fluence and annealing parameters, ion irradiation with 12 MeV carbon ions produces a step-like damage profile. Confocal Raman microscopy, X-ray diffraction and transmission electron microscopy are used in this work to study the structural damage induced by ion irradiation. The characterization indicates damage to the crystal structure due to the ion irradiation that increases as a function of both depth and ion fluence till the threshold for amorphization is achieved. Successive annealing steps of the irradiated crystals at different temperatures show partial repair of the crystalline structure when the irradiation did not fully amorphize the material. When the threshold of amorphization was reached, annealing further increases the damage induced by the irradiation. By tuning the irradiation fluence, a high-refractive index contrast slab waveguide in KY(WO) produced by ion irradiation was demonstrated., H2020 European Research Council (648978); Comunidad de Madrid (TECHNOFUSION(III)- CM(S2018/EMT-4437)).