Abstract
We propose the narrowband perfect absorbers with enormously high fabrication tolerance, which consists of a low-contrast grating and a finite distributed Bragg reflector (DBR) layer with an ultrathin absorbing medium (graphene). It is numerically shown that the proposed perfect absorber outperforms the previously proposed schemes in fabrication tolerance. According to the rigorous coupled wave analysis (RCWA) and coupled mode theory (CMT) fitting, over a considerably wide range of grating width and thickness, the proposed absorber provides a proper ratio of leakage rate to loss rate while preserving resonant condition, so that almost perfect absorption (>99.9%) can be obtained. This result is attributed to the strong electric field confinement in the DBR region rather than the grating layer owing to lower index of grating compared to DBR. In addition, without degrading the fabrication tolerance, the bandwidth of the proposed absorber can be controlled by the DBR thickness (the number of pairs) and a narrow absorbing bandwidth of sub-nanometer is achieved with 8.5 Si/SiO2 pair stacked DBR.
Highlights
Due to high conductivity, atomically unltrathin graphene of ~0.34 nm has attracted strong interests in developing high-speed graphene-based photodetectors[1,2,3,4]
In the scheme reported in refs[5,11], the distributed Bragg reflector (DBR) works as just a mirror and the high-contrast grating (HCG) is mainly responsible for the guided-mode resonance (GMR)
The fabrication tolerance of our proposed perfect absorber scheme based on the ‘DBR-guiding’ mode resonance has been investigated in comparison to the previously suggested similar schemes
Summary
Atomically unltrathin graphene of ~0.34 nm has attracted strong interests in developing high-speed graphene-based photodetectors[1,2,3,4]. The application of their ‘DBR-guiding’ mode-based resonance to perfect absorption or the resonance performance dependence on the structural parameters of the gold grating was not considered at all If their structure is used to enhance to the absorption of thin layer like the monolayer graphene, the ohmic loss of the gold grating limits a minimum achievable bandwidth of the resonance and a maximum achievable absorption in the thin layer. Another type of DBR-based perfect absorber has been suggested, in which graphene is located in the high-Q one-dimensional cavity formed by two DBR mirrors[14]. The mechanism of the greatly enhanced fabrication tolerance of our proposed scheme is analyzed by using the coupled mode theory (CMT)[5,18]
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