Broadband and polarization insensitive design of terahertz absorber with high-index contrast grating on SOI chip

Simple design of a broadband terahertz absorber consisting of a high-index contrast grating (HCG) on a silicon-on-insulator chip is proposed. Large absorption (98.4 %) over a wavelength range of 66–84 \(\upmu \hbox {m}\) is obtained for normal incidence with large fabrication tolerance (\(14\,\upmu \hbox {m}\) grating period tolerance for grating height of \(2.6\,\upmu \hbox {m}\)). The absorption remains high (\(\sim \)98 %) for wide range of angle of incidence from \(0^{\circ }\) (normal incidence) to \(60^{\circ }\). The bandwidth of high absorption (\(\sim \)98 %) is also large i.e. \(40\,\upmu \hbox {m}\) over a wide range of angle of incidence from \(0^{\circ }\) to \(60^{\circ }\). The proposed broadband terahertz absorber also exhibits the design flexibility for the realization of polarization insensitivity with respect to the incident light of arbitrary polarizations. The proposed structure is easy-to-fabricate with a large fabrication tolerance which may provide a desirable broadband absorption for practical applications in terahertz devices. The proposed absorber is designed using rigorous coupled wave analysis and the results are in good agreement (with a maximum difference of 0.6 % in absorption) with those obtained with finite difference time domain method. The proposed characteristics of the device arise from the wavelength scalability and broadband nature of the HCG.