Tunable surface plasmon resonance-based graphene nanoribbon (GNR) terahertz (THz) polarizers with adjustable operating frequency are proposed in this work. While conventional THz polarizers lack robustness and tunability, recently reported graphene-based metastructure polarizers have complex fabrication processes and comparatively smaller extinction ratios (ERs). A comprehensive study using finite-difference time-domain (FDTD) simulation technique reveals high ER, broad tunability, near-perfect degree of polarization (DOP), and low insertion loss for our proposed single and double stage GNR polarizers. The operating frequency of these narrow band polarizers can be tuned by varying GNR width, GNR pitch, chemical potential, and substrate material. Our optimized THz polarizer has an ER of 30 dB which is comparable to the commercially available THz polarizers. The maximum insertion losses within the tunable frequency range were found to be 0.24 dB and 1.87 dB for single and double stage GNR polarizers, respectively, which are substantially low. We compared the performance of the proposed structures with recently demonstrated graphene-based metastructure polarizers. The polarizers are promising for the design of photonic devices, integrated photonic circuits, and optoelectronic systems.

An extensive study on the optical characteristics of vertically aligned single-wall carbon nanotubes (SWCNTs) and engineered multi-wall carbon nanotubes (MWCNTs) using finite-difference time-domain (FDTD) simulation technique is presented in this work. We investigated absorption characteristics for SWCNTs, MWCNTs, dual-diameter MWCNTs, and cone MWCNTs with the changes in the occupation area and incident angle of light in the visible wavelength range. The enhancement of absorption was achieved by changing the geometrical shapes. Our study suggests that 99.569 % of the total light energy is absorbed in SWCNTs and 99.883 % in cone-shaped-top MWCNTs with an occupation area of 20 % and 50 %, respectively, at 450 nm wavelength and 5000 nm tube height. Moreover, for both SWCNTs and MWCNTs, reflectance increases with the increase of the occupation area due to the larger reflecting top surface area. We found that a drastic reduction of absorption occurs as the angle between the tube axis of aligned carbon nanotubes (CNTs) and the incoming light source increases above 30 °. Our study will be valuable for further investigation of the optical properties of shape-engineered CNTs and will promote CNT-based ultra-broadband absorber devices and systems for multifunctional optoelectronic applications.

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