  Optical technologies call for waveguide networks featuring high integration
densities, low losses, and simple operation. Here, we present polymer
waveguides fabricated from a negative tone photoresist via
two-photon-lithography in direct laser writing, and show a detailed parameter
study of their performance. Specifically, we produce waveguides featuring bend
radii down to 40 {\mu}m, insertion losses of the order of 10 dB, and loss
coefficients smaller than 0.81 dB/mm, facilitating high integration densities
in writing fields of 300 {\mu}m x 300 {\mu}m. A novel three-dimensional coupler
design allows for coupling control as well as direct observation of outputs in
a single field of view through a microscope objective. Finally, we present
beam-splitting devices to construct larger optical networks, and we show that
the waveguide material is compatible with the integration of quantum emitters.
