## 1 Introduction  
Materials offering refractive index tunability and low absorption are extremely useful for realizing optical integrated devices. In silicon nitride (SiN) compounds, like silicon oxynitride and silicon rich nitride, the refractive index can be tuned over a wide range, potentially from 1.45 to about 2, yet at the expense of higher losses [1,2]. Silicon oxycarbide (SiOC) is a versatile material that has been used in a variety of applications including Li-ion batteries [3], photoluminescence [4], electroluminescence [5], and low-k interlayer dielectric [6,7]. It has been demonstrated that the change in composition of SiOC compound can lead to a change in the refractive index n over a wide range from \(\sim\)1.45 to \(\sim\)3.0 under pre- and post-deposition conditions [8,9]. Structural and chemical properties of SiOC films have been extensively reported in the literature [10, 11, 12, 13]. Recently, we have demonstrated the synthesis of SiOC films with reactive RF magnetron sputtering and showed that, under different deposition conditions, the refractive index n can be varied from 1.41 to 1.85 at wavelength \(\lambda\) = 1550 nm, while the extinction coefficient k is below 10\({}^{-4}\) above \(\lambda\) = 1000 nm [14]. The low extinction coefficient k of SiOC films indicates the suitability of this material for fabrication of optical waveguides. However, to the best of our knowledge, SiOC has never been exploited as a core material for guided wave applications.  
In this paper, we demonstrate the fabrication of silicon oxycarbide optical waveguides with reactive RF magnetron sputtering. Reactive sputtering is a well-established technique, relatively simple and cost effective to set up compared to conventional chemical vapor deposition (CVD). First,SiOC films are deposited by sputtering the SiC target in the presence of argon (Ar) and oxygen (O\({}_{2}\)) gases in a controlled process at room temperature. The prepared films are characterized with variable angle spectroscopic ellipsometry over near-infrared wavelength range. The deposited SiOC film exhibits anisotropy on the order of 10\({}^{-2}\) between in-plane and out-of-plane refractive indices as acquired from the ellipsometric data. To quantify the root mean square (RMS) roughness of the deposited SiOC film on SiO\({}_{2}\)/Si wafer, atomic force microscopy is used. RMS roughness is an important parameter that affects the performance of optical waveguides and contributes to the scattering of light. The sputtered SiOC films are then used as core layer to fabricate channel waveguides using UV photolithography and reactive ion etching (RIE) techniques. The SiOC channel waveguides are buried between two layers of SiO\({}_{2}\) (n = 1.444). The optical waveguides with different widths are characterized at an optical communication wavelength (1550 nm) with different lengths. Propagation losses of about 4 dB/cm for both TE and TM polarizations have been achieved indicating the suitability of sputtered SiOC for integrated optics applications.  
The paper is organized as follows: Section 2 explains deposition and characterization techniques used to grow and study the properties of SiOC films (Section 2.1), and the fabrication process and the measurement setup for SiOC optical waveguides (Section 2.2). Section 3 discusses results on the characterization of SiOC films (Section 3.1) and optical waveguides (Section 3.2). Finally, conclusions are presented in Section 4.