Linearly thermal-tunable near-infrared ultra-narrowband metamaterial perfect absorber with low power and a large modulation depth based on a four-nanorod-coupled a-silicon resonator.

The bandwidths of thermal-tunable metamaterial perfect absorbers (MPAs) based on the phase change materials such as GeSbTe and VO are usually hundreds of nanometers at near-infrared frequency. Amorphous silicon (a-Si) provides the approach to achieve linearly thermal-tunable ultra-narrowband MPAs, if the absorption band is narrow enough. Four-nanorod-coupled a-Si resonators are proposed in this Letter. An absorption band at 1064 nm is obtained with ultra-narrow bandwidth (FWHM) only 1.4 nm by exciting the coupled magnetic dipole (CMD) mode, which exhibits great linearity to the temperature. In addition, the thermo-optical sensitivity (S=Δλ/ΔT) is about 0.08 nm/°C. The figure of merit of the thermal tunability performance FOM=S/FWHM=0.06. As a modulator, the critical temperature of absorptivity at 1064 nm is only 40°C, which is much lower than the GeSbTe (GST) and VO. In addition, the modulation depth is up to 82% at near-infrared frequency.