Tuning of a cavity in a silicon photonic crystal by thermal expansion of an elastomeric infill

We use an elastomer as infill material for a photonic crystal. As a result of the thermal-expansion-induced strongly negative thermal optical coefficient, this material is highly suitable for thermal tuning of the transmission of a cavity. This is demonstrated by global infilling of a hole-type silicon photonic crystal slab and global thermal tuning. In the temperature range 20-60°C the cavity peak shows a pronounced elastomer-induced blue shift of 2.7 nm, which amply overcompensates the red shift arising from the thermo-optic property of the silicon. These results qualify the elastomer for tuning by local optical heating.