Achieving ultranarrow graphene perfect absorbers by exciting guided-mode resonance of one-dimensional photonic crystals

Abstract

Graphene perfect absorbers with ultranarrow bandwidth are numerically proposed by employing a subwavelength dielectric grating to excite the guided-mode resonance of one-dimensional photonic crystals (1DPCs). Critical coupling of the guided-mode resonance of 1DPCs to graphene can produce perfect absorption with a ultranarrow bandwidth of 0.03 nm. The quality factor of the absorption peak reaches a ultrahigh value of 20000. It is also found that the resonant absorption peaks can be tuned by controlling the dispersion line of the guided mode and the period of the grating. When the parameters of the grating and the 1DPCs are suitably set, the perfect absorption peaks can be tuned to any randomly chosen wavelength in the visible wavelength range.

Near-absolute polarization insensitivity in graphene based ultra-narrowband perfect visible light absorber

“…We also observe that the standing wave pattern is created in both the z and x-directions. While the former is because of the waveguiding effect, the latter is due to the refractive index modulation in the x-direction 45 . The electric field profile in Fig.…”

“…We now want to emphasize the key design strategy in achieving the ultra-narrow bandwidth. To achieve critical coupling in a system where the external leakage rate is low, a very high energy storage, or equivalently, a very high-Q GMR in the resonant structure is needed 43 , 45 . Thus, the bandwidth is narrower in devices where graphene is placed far away from the optical field confined by GMR.…”

“…The difference between two methods is the structures where GMRs are excited. The third method is to couple graphene to the GMRs of photonic crystal slabs (PhCs) 43 or 1-dimensional photonic crystals (1DPCs), excited by sub-wavelength grating (SWG) couplers 44 , 45 . The guided-mode leaks out evanescent waves to graphene.…”

“…Critical coupling of the guided-modes to graphene then produces perfect absorption. Notably, the latter can achieve an ultra-narrow absorption bandwidth of 0.03 nm due to placing graphene far away from 1DPC 45 . Although promising in theory, this method enforces extreme fabrication accuracy on not only the SWG, but also on the 1DPCs to achieve the target wavelength and store very high energy in 1DPC to achieve critical coupling.…”

Broadband light-trapping enhancement of graphene absorptivity

“…A PC is another way of achieving strong localization of light [71]. One-dimensional multilayer PCs have been suggested to enhance the graphene absorptivity using a surface defect mode [72], a PClocalized mode [73], and guided modes [74,75]. These schemes target absorptivity enhancement in a small frequency range.…”