Ultra-low loss ridge waveguides on lithium niobate via argon ion milling and gas clustered ion beam smoothening

Abstract

Lithium niobate's use in integrated optics is somewhat hampered by the lack of a capability to create low loss waveguides with strong lateral index confinement. Thin film single crystal lithium niobate is a promising platform for future applications in integrated optics due to the availability of a strong electro-optic effect in this material coupled with the possibility of strong vertical index confinement. However, sidewalls of etched waveguides are typically rough in most etching procedures, exacerbating propagation losses. In this paper, we propose a fabrication method that creates significantly smoother ridge waveguides. This involves argon ion milling and subsequent gas clustered ion beam smoothening. We have fabricated and characterized ultra-low loss waveguides with this technique, with propagation losses as low as 0.3 dB/cm at 1.55 µm.

Analysis of perovskite oxide etching using argon inductively coupled plasmas for photonics applications

“…It's worth noting that there is no post process or added cladding of the measured waveguide. The loss can thus be reduced by optimizing such processing, as is the case with addition of thermal oxidation in silicon waveguides [20,21], or with use of gas cluster ion beam smoothening [22]. In the BTO case reduced index contrast between the DSO substrate and the top BTO layer (the refractive index of BTO and DSO are, respectively, 2.38 and 2.13, as determined by the prism coupling method) would result in poorer light confinement even though the etch is deeper; the loss cannot be directly compared to that in LN.…”

Analysis of perovskite oxides etching using argon inductively coupled plasmas for photonics applications

“…It's worth noting that there is no post process or added cladding of the measured waveguide. The loss can thus be reduced by optimizing such processing, as is the case with addition of thermal oxidation in silicon waveguides [20,21], or with use of gas cluster ion beam smoothening [22]. In the BTO case reduced index contrast between the DSO substrate and the top BTO layer (the refractive index of BTO and DSO are respectively 2.38 and 2.13, as determined by the prism coupling method) would result in poorer light con nement even though the etch is deeper; the loss cannot be directly compared to that in LN.…”

High-Q Lithium Niobate Microcavities and Their Applications

“…7(c)] [36,47], further demonstrating the versatility of the LNOI platform. Besides microcavities, low-loss optical waveguides based on dry etching LN have also been reported by many groups and used for various applications [48][49][50][51][52][53].…”