Photonic integrated circuit incorporating a bandgap temperature sensor
View Patent ↗An optical device that includes means for thermal stabilization and control is described. The optical device can be a ring resonator, or another device that requires accurate control of the phase of the optical signal. In an example involving an optical resonator, a thermal stabilization system includes a temperature sensor, a control circuit, and a heater local to the resonator. The temperature sensor can be a bandgap temperature sensor formed of a pair of matched p/n junctions biased in operation at different junction currents.
1. A device comprising:
a semiconductor photonic integrated circuit (PIC) comprising:
at least one integrated optical device comprising an optical resonator;
a temperature sensor comprising first and second p/n junctions integrated with the optical resonator, wherein the first and second p/n junctions are operable to produce one or more electrical signals that are indicative of a temperature of the optical resonator; and
a temperature control element integrated with the optical resonator, the temperature control element operable to adjust the temperature of the optical resonator responsive to an electrical temperature control signal,
wherein the first and second p/n junctions are spaced from the temperature control element by at least 10 microns so as to lessen effects of local thermal gradients near the temperature control element on said p/n junctions.
2. The device of claim 1 wherein the first and second p/n junctions are disposed away from the temperature control element at a device location wherein the local temperature is within 0.1 C of a local temperature at a location in the optical resonator that is farthest from the temperature control element over an operating temperature range specified for the PIC.
3. The device of claim 1 , wherein the optical resonator comprises a micro-ring resonator.
4. The device of claim 1 , wherein the optical resonator comprises a micro-disk resonator.
5. The device of claim 1 comprising a substrate including a dielectric layer, wherein:
the optical resonator comprises a patterned semiconductor layer disposed over the dielectric layer, and
the first and second p/n junctions are planar p/n junctions each comprising a p-doped region of the patterned semiconductor layer abutting an n-doped region thereof.
6. The device of claim 5 , comprising a direct electrical connection between either the p-doped regions of the first and second p/n junctions or the n-doped region of the first and second p/n junctions.
7. The device of claim 5 , wherein the first and second p/n junctions are configured to have matching current density vs. voltage characteristics.
8. The device of claim 5 , wherein the optical resonator comprises at least one optical waveguide, and wherein first and second p/n junctions are integrated with the at least one optical waveguide.
9. The device of claim 5 , wherein the first and second p/n junctions are spaced apart from the at least one integrated optical device.
10. The device of claim 2 , wherein the temperature control element comprises a resistive heater integrated with the at least one integrated optical device.
11. The device of claim 10 , wherein the resistive heater comprises a metal element disposed over the at least one integrated optical device.
12. The device of claim 10 , wherein the at least one integrated optical device comprises at least one optical waveguide, and the resistive heater comprises a doped portion of the at least one optical waveguide that is configured to heat the at least one optical waveguide by passing electrical current therethrough.
13. The device of claim 1 , wherein the first p/n junction is matched in size with the second p/n junction.
14. The device of claim 1 wherein the at least one integrated optical device comprises an optical waveguide, further comprising a third p/n junction that is integrated with the optical waveguide and configured for modulating the refractive index of said optical waveguide.
15. The device of claim 2 , further comprising a control circuit in electrical communication with each of the temperature sensor and the temperature control element, the control circuit configured to drive the temperature control element in dependence upon the one or more electrical signals obtained from the temperature sensor.
16. The device of claim 15 , wherein the control circuit includes a comparator comprising first and second input ports electrically coupled to the first and second p/n junctions and configured to produce a differential electrical signal proportional to a difference in voltages across the first and second p/n junctions.