| CPC G02B 6/136 (2013.01) [G02B 6/122 (2013.01); G02B 6/132 (2013.01)] | 20 Claims |

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1. A device comprising:
a substrate;
a dielectric layer on the substrate;
a waveguide within the dielectric layer;
a heater disposed in the dielectric layer;
a thermal isolation structure including a trench in the dielectric layer and an undercut in the substrate; and
a photodetector disposed above the waveguide and monolithically integrated with the substrate, the photodetector optically coupled to the waveguide and configured to operate at temperatures below 50 K.
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