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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

KY(WO4)2 is a promising material for on-chip laser sources. Deep etching of small KY(WO4)2 samples in combination with various thin film deposition techniques is desirable for the manufacturing of such devices. There are, however, several difficulties that need to be overcome before deep etching of KY(WO4)2 can be realized in small samples in a reproducible manner. In this paper, we address the problems of (i) edge bead formation when using thick resist on small samples, (ii) sample damage during lithography mask touchdown, (iii) resist reticulation during prolonged argon-based inductively coupled plasma reactive ion etching (ICP-RIE), and (iv) redeposited material on the feature sidewalls. We demonstrate the etching of 6.5 &micro, m deep features and the removal of redeposited material using a wet etch procedure. This process will enable the realization of waveguides both in ion-irradiated KY(WO4)2 as well as thin KY(WO4)2 membranes transferred onto glass substrate by bonding and subsequent polishing.

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.

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)).