Athermal optical filter with active tuning and simplified control

A substrate including a plurality of optical devices, comprising:

• a first optical device comprising:
• an input port;
• an output port;
• and
• a plurality of waveguides coupled to the input port and the output port, the plurality of waveguides comprising at least one optical waveguide having a first and a second waveguide section, wherein the first waveguide section has an optical wavelength response as a function of an ambient temperature of the system;
• a second optical device comprising:
• an input port;
• an output port;
• and
• a plurality of waveguides coupled to the input port and the output port, the plurality of waveguides comprising at least one optical waveguide having a third and a fourth waveguide section, wherein the third waveguide section has an optical wavelength response as a function of an ambient temperature of the system;
• a region including the second waveguide section of the first optical device and the fourth waveguide section of the second optical device;
• a heating element to heat the region;
• a temperature sensor to measure the temperature of the region;
• and
• a temperature controller to control the heating element based, at least in part, on the temperature sensor so that the temperature of the region is fixed and greater than the ambient temperature of the system.

An apparatus comprising:

• a passively athermal optical device including:
• an input port;
• an output port;
• a plurality of waveguides coupled to the input port and the output port, wherein each of the plurality of waveguides comprises:
• a first waveguide section;
• and
• a second waveguide section having a higher temperature coefficient of refractive index (dn/dT) than the first section;
• a heating element to heat at least a portion of the second waveguide sections of the plurality of waveguides;
• and
• a temperature controller to control the heating element to adjust a frequency spectrum of the optical device.