Heterogeneous integration of KY(WO₄)₂-on-glass: a bonding study

Abstract

Rare-earth ion doped potassium yttrium double tungstate, RE:KY(WO 4 ) 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(WO 4 ) 2 makes it challenging to integrate the crystal on glass substrates. Secondly, the crystal layer has to be, for example, <1 µm 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(WO 4 ) 2 devices.

High-temperature recrystallization effects in swift heavy ion irradiated KY(WO4)2

“…Figure 5 shows an overview of the cracks that have formed in the irradiated sample upon annealing at 550 C. Vertical cracks occur every few micrometers through the entire crystal and generally run parallel to the a axis. This effect has been documented before as a result of significant differences in the thermal expansion coefficient between the crystalline axes of KY(WO 4 ) 2 22 or stress between layers of different compositions or crystalline structures due to lattice mismatch. 7 In the high-temperature annealed irradiated crystals, the cracking is most likely the result of a mix of both effects because recrystallization happens at a high temperature and the resulting crystallites exhibit a different structure than the original crystal lattice.…”

Lapping and Polishing of Crystalline KY(WO4)2: Toward High Refractive Index Contrast Slab Waveguides

“…Details about the integration methods of KY(WO 4 ) 2 on glass substrates, using an ultraviolet (UV) curable adhesive, were described in our previous work [21]. The height of the individual assemblies was measured with a precision thickness measurement system (Milimar C1208, Mahr, GmbH, Göttingen, Germany), including an inductive probe (Milimar P1300, Mahr, GmbH), before mounting on an ultra-parallel plate (Ø 83 mm, thickness 6 mm, 0CON-166, Logitech, Glasgow, UK).…”

“…Lapping of KY(WO 4 ) 2 samples bonded on flat glass substrates was tested. The samples were bonded using an optical curable adhesive and a flip-chip bonder, as described in our previous work [21].…”

Redeposition-Free Deep Etching in Small KY(WO4)2 Samples

“…Deep etching capabilities are also necessary for the fabrication of high refractive index contrast waveguides on KY(WO 4 ) 2 membranes obtained by bonding followed by mechanical lapping and polishing [22][23][24]. Lapping and polishing very thin layers carries great risk of sample damage, while thicker layers are less fragile.…”