According to an example aspect, there is provided an apparatus comprising a first optical converter coupled to a fiber interface and to two waveguides, a dual rail encoder configured to encode dual rail form light from the two waveguides with payload information, and wherein the dual rail encoder is coupled to the first optical converter or to a second optical converter disposed between the dual rail encoder and the fiber interface, and wherein the first optical converter or the second optical converter is coupled so as to provide polarization encoded light into the fiber interface.