Codoping $\mathrm{K}\mathrm{Y}{\left(\mathrm{W}{\mathrm{O}}_4\right)}_2:\mathrm{Yb}$ layers with optically inert Lu and Gd ions allows a large increase of the refractive index contrast with respect to $\mathrm{K}\mathrm{Y}{\left(\mathrm{W}{\mathrm{O}}_4\right)}_2$ substrates. This paves the way for the realization of integrated optical circuits based on this very promising material. First riblike waveguide structures have been fabricated and propagation losses below $1\mathrm{dB}∕\mathrm{cm}$ have been evaluated. A Y-junction with a splitting ratio close to 1:1 and additional losses of $1.4\mathrm{dB}$ has also been demonstrated.