Photonic integrated circuit

A photonic integrated circuit disposed on a substrate, comprising:

• first and second light sources to transmit a first light beam and a second light beam via first and second waveguides;
• an interferometer to combine the first and second light beams from the first and second waveguides and transmit a combined signal light beam from an output port of a combined waveguide, wherein the interferometer includes a first coupler, a second coupler and first and second signal waveguides connecting between the first and second couplers;
• a contact layer formed on a backside of the substrate;
• and
• a submount to contact the contact layer, wherein the submount includes a first thermal conductor corresponding to regions of the first and second light sources, a second thermal conductor corresponding to a region of the interferometer and a third thermal conductor corresponding to a part of the combined waveguide, wherein a temperature gradient of the substrate is defined by a heat flow from a region of the first and second light sources to the third thermal conductor, wherein the first signal waveguide and the second signal waveguide are substantially aligned along the temperature gradient.