A glass chip with laser-written waveguide channels combines eight light signals into one via integrated couplers. The chip forms the central signal combiner in a quantum key distribution source, that creates indistinguishable polarization-encrypted signal and decoy photons. The waveguide chip is actively thermally controlled inside a Kovar frame with temperature probes and thermo-electric elements. It is situated between a stack of precision-machined heatsinks to integrate the chip without voids with the help of a thermally conductive intermediate layer. Optical input is achieved with lithographic microlenses, that couple light into the waveguide channels, whereas the output is attained via a coupled fiber.