Optimized frequency conversion photonic integrated circuits

A device comprising:

• an input port configured to receive as a device input a fundamental optical mode characterized by an input wavelength and a corresponding fundamental frequency;
• an output port configured to provide as a device output an Nth harmonic mode characterized by a Nth harmonic frequency relative to the fundamental frequency, where N>1;
• and
• first and second resonators, first, second and third coupler structures and first and second tuner elements;
• wherein the first and third coupler structures are optimized for operation at the fundamental frequency, and the second coupler structure is optimized for operation at the Nth harmonic frequency;
• wherein the first tuner element is positioned in relation to the first resonator such that the first tuner element can tune each of the fundamental optical mode and the Nth harmonic mode;
• and
• wherein the third coupler structure and the second tuner element are positioned in relation to the second resonator such that the second tuner element can tune the fundamental optical mode and has no significant tuning effect on the Nth harmonic optical mode.