Temperature insensitive lower-index-mode photonic crystal nanobeam cavity.

We present the design, fabrication, and characterization of a temperature insensitive lower-index-mode photonic crystal (PhC) nanobeam (NB) cavity by overlaying SU-8 cladding. The lower-index-mode is utilized to control the amount of light confined in the SU-8 cladding to compensate for the thermo-optic effect of silicon. The temperature sensitivity of the PhC NB cavity can be tuned by changing the radius of the air holes. The temperature dependence of the PhC NB cavity with SU-8 cladding is demonstrated to be 5.1  pm/°C over 50°C temperature range. The measured quality factor of the temperature insensitive lower-index-mode PhC NB cavity is ∼1×10(4).