An apparatus, comprising: a photonic integrated circuit (300a, 300b), including: a substrate; a passive device and an active device formed on the substrate, the passive device comprising a first waveguide (302a, 302b), the active device comprising a second waveguide (304a, 304b); a first region proximate to the first waveguide (302a, 302b), wherein an optical mode associated with the first waveguide (302a, 302b) is to be substantially confined by the first region, and wherein the first region has a first thermal conductivity and is configured to dissipate heat from the passive device at a first rate; a second region proximate to the second waveguide (304a, 304b), wherein an optical mode associated with the second waveguide (304a, 304b) is to be substantially isolated from the second region, and wherein the second region has a second thermal conductivity greater than the first thermal conductivity, the second region configured to dissipate heat from the active device at a second rate greater than the first rate; and a buried oxide layer on the substrate, and wherein: the first region proximate to the first waveguide comprises a first cavity in the substrate and the buried oxide layer, the first region extending at least partially through the buried oxide layer; and the second region proximate to the second waveguide comprises a second cavity in the substrate, the second region extending at least partially through the buried oxide layer; and the buried oxide layer is filled with a second material with the second thermal conductivity. a photonic integrated circuit (300a, 300b), including: a substrate; a passive device and an active device formed on the substrate, the passive device comprising a first waveguide (302a, 302b), the active device comprising a second waveguide (304a, 304b); a first region proximate to the first waveguide (302a, 302b), wherein an optical mode associated with the first waveguide (302a, 302b) is to be substantially confined by the first region, and wherein the first region has a first thermal conductivity and is configured to dissipate heat from the passive device at a first rate; a second region proximate to the second waveguide (304a, 304b), wherein an optical mode associated with the second waveguide (304a, 304b) is to be substantially isolated from the second region, and wherein the second region has a second thermal conductivity greater than the first thermal conductivity, the second region configured to dissipate heat from the active device at a second rate greater than the first rate; and a buried oxide layer on the substrate, and wherein: the first region proximate to the first waveguide comprises a first cavity in the substrate and the buried oxide layer, the first region extending at least partially through the buried oxide layer; and the second region proximate to the second waveguide comprises a second cavity in the substrate, the second region extending at least partially through the buried oxide layer; and a substrate; a passive device and an active device formed on the substrate, the passive device comprising a first waveguide (302a, 302b), the active device comprising a second waveguide (304a, 304b); a first region proximate to the first waveguide (302a, 302b), wherein an optical mode associated with the first waveguide (302a, 302b) is to be substantially confined by the first region, and wherein the first region has a first thermal conductivity and is configured to dissipate heat from the passive device at a first rate; a second region proximate to the second waveguide (304a, 304b), wherein an optical mode associated with the second waveguide (304a, 304b) is to be substantially isolated from the second region, and wherein the second region has a second thermal conductivity greater than the first thermal conductivity, the second region configured to dissipate heat from the active device at a second rate greater than the first rate; and a buried oxide layer on the substrate, and wherein: the first region proximate to the first waveguide comprises a first cavity in the substrate and the buried oxide layer, the first region extending at least partially through the buried oxide layer; and the second region proximate to the second waveguide comprises a second cavity in the substrate, the second region extending at least partially through the buried oxide layer; and the first region proximate to the first waveguide comprises a first cavity in the substrate and the buried oxide layer, the first region extending at least partially through the buried oxide layer; and the second region proximate to the second waveguide comprises a second cavity in the substrate, the second region extending at least partially through the buried oxide layer; and the buried oxide layer is filled with a second material with the second thermal conductivity.