## 1 Introduction  
Generation of optical supercontinua (SC) is a fundamental topic that has stimulated tremendous interest since the early works of [PERSON] et al. in the 1970s [1]. The development of practical applications, as well as the physical understanding of the various processes involved in this nonlinear spectral broadening, have strongly benefited from the progress in optical fibre technologies. More especially, the emergence of photonic crystal fibres, combining tailored dispersion properties and enhanced nonlinearity, has led to record spectral expansion [2; 3]. Moreover, advances in soft-glass materials such as fluoride, tellurite or chalcogenide fibres have also contributed to the extension of SC bandwidth far beyond the silica transmission window breaking the short wavelength limit by reaching the deep UV region [4] but also the high wavelength limit paving the way toward mid-infrared SC sources [5; 6; 7; 8]. The next exciting stage is to reduce the footprint of the component and generate octave spanning supercontinua on an optical chip. To this aim, various platforms have been successfully investigated: Si [9; 10; 11], SiGe [12; 13; 14], SiN [15; 16; 17; 18], diamond-on-insulator [19], chalcogenide waveguides [20] or III-V material based waveguides (InGaP [21]) and AlGaAs [22]. Each material provides specific advantages but also strong potential limitations including two photon absorption (TPA) and associated free carrier absorption, high level of losses, limiting transparency window, low refractive index, low handling power as well as high cost or complex manufacturing processes. In this context, we consider here Titanium dioxide (TiO\({}_{2}\)) as an alternative platform that remained until now relatively unexplored. TiO\({}_{2}\) is a promising material thanks to a transparency window spanning from the visible to the mid-infrared wavelengths [23], high linear and nonlinear refractive indices (of >2.3 and 30 times, respectively, larger than silica [24; 25]) and a wide bandgap (3.4 eV) allowing a negligible TPA beyond 800 nm. Its thermo-optic properties can also be of great interest for thermal stability [26; 27; 28]. Moreover, thin films can be prepared by several techniques such as e-beam evaporation, atomic layer deposition (ALD), plasma-enhanced chemical vapour deposition (PE-CVD)or sol-gel process [29]. Therefore, it has become increasingly desirable to consider this cost-efficient material in different scenarios such as subwavelength optical waveguides [30], integrated optical resonators [25; 27; 31; 32], infrared high speed transmissions [33] or sensing applications [34; 35]. Quite recently, several studies aimed at taking advantage of the Kerr nonlinearity of TiO\({}_{2}\) and have reported the observation of self-phase modulation induced spectral broadening of a femtosecond pulse [24], the parametric wavelength conversion of a continuous wave [25] as well as the efficient generation of photon triplet [36]. In the present contribution, to the best of our knowledge, we report on the first experimental generation of a supercontinuum covering an octave in a TiO\({}_{2}\)-based on-chip waveguide. The manuscript is organized as follows. We first describe the properties of the cm-long on-chip waveguides in which SC generation is demonstrated. Next, we detail the experimental set-up based on a femtosecond fibre laser at 1.64 \(\upmu\)m and finally we analyse the main features of the generated supercontinua. **2. TiO\({}_{2}\) Waveguide Design and Fabrication**  
The fabrication process starts with the deposition of a 450 nm-thick layer of TiO\({}_{2}\) onto a 2\({}^{\prime}\) thermally oxidized Si wafer (SiO\({}_{2}\) thickness = 2.0 \(\upmu\)m). TiO\({}_{2}\) deposition is performed by DC magnetron sputtering of a 99.9% pure titanium under an argon oxygen controlled atmosphere. It is well known that different TiO\({}_{2}\) phases can be obtained: rutile [37; 38], anatase [39; 40] or amorphous [25; 40].