Coherent control of magneto-optical Faraday rotation at terahertz frequencies in graphene-based metasurfaces via electromagnetically induced transparency
Hazrat Ali, Muhammad Imtiaz Khan, Rafi Ud Din, Muhammad Zubair, Irfan Mahmood, Pervaiz Ahmad, Guo-Qin Ge
Abstract We investigate theoretically the controlled magneto-optical Faraday rotation (MO-FR) through graphene-based metasurfaces placed on electromagnetically induced transparency (EIT) substrate at terahertz (THz) frequencies. MO-FR and transmission of the probe light are studied by changing the electric field that manipulates the group index of the substrate. The MO-FR can be controlled and enhanced by varying the periodic width of graphene ribbons. The polarization plane of MO-FR changes with 180 degrees while increasing the probe field detuning through the EIT substrate. The zero-crossing of MO-FR shifts to higher THz frequencies with increasing the magnetic field. The transmission of the probe light pulse at THz frequencies is investigated with the probe detuning and the applied magnetic field.
Abstract We investigate theoretically the controlled magneto-optical Faraday rotation (MO-FR) through graphene-based metasurfaces placed on electromagnetically induced transparency (EIT) substrate at terahertz (THz) frequencies. MO-FR and transmission of the probe light are studied by changing the electric field that manipulates the group index of the substrate. The MO-FR can be controlled and enhanced by varying the periodic width of graphene ribbons. The polarization plane of MO-FR changes with 180 degrees while increasing the probe field detuning through the EIT substrate. The zero-crossing of MO-FR shifts to higher THz frequencies with increasing the magnetic field. The transmission of the probe light pulse at THz frequencies is investigated with the probe detuning and the applied magnetic field.
Abstract We investigate theoretically the control over Faraday rotation via an electromagnetically induced transparency medium (EIT) and graphene metasurfaces. The Faraday rotation of the light pulse is enhanced with increased probe field detuning. The increasing strength of the magnetic field enhances the rotation of the polarization plane and shifts its zero crossing at a higher frequency. The increase in the chemical potential rotates the polarization plane of the light pulse propagating through the system at low frequency. The periodic arrangement of disks on a graphene metasurface enhances the Faraday rotation of the light pulse and shifts the zero crossing relatively at a low frequency. The chemical potential, magnetic field and periodic length of disks can be used to control the Faraday rotation of light pulses at the desired frequency.
Landau-quantized graphene (LQG) offers a magnetically controlled platform for manipulating coherent inter-Landau-level transitions of Dirac fermions. Such a platform provides compact control of terahertz and infrared photonic signals. Here, a closed-form susceptibility expression is derived using the density-matrix approach, where the real part of the susceptibility describes dispersion and the imaginary part describes absorption or gain. The numerical results show that tuning the control field modifies the probe response from a dispersive resonance regime to a transparency window and a gain-assisted response. The calculated group-index variation, approximately from 0.6 to 1.7, enables broad modulation of the probe group velocity, ranging from about 1.8 × 10 8 m/s to 5.2 × 10 8 m/s . The reduced-absorption region indicates an electromagnetically induced transparency response suitable for controlled probe-field transmission. Distinct spectral features are also observed in the absorption coefficient and electron energy-loss spectrum (ELS), indicating selective energy transfer near the LQG resonance and potential relevance for THz/IR modulation. In addition, the frequency-selective and sign-reversible photon-drag response suggests detuning-controlled optical momentum transfer. These tunable responses within the linear regime support LQG as a reconfigurable medium for quantum optical transport, synchronization, pulse routing, buffering, and chip-scale THz photonic interfaces.
Abstract Tunable slow light systems have gained much interests recently due to their efficient control of strong light–matter interactions as well as their huge potential for realizing tunable device applications. Here, a dynamically tunable polarization independent slow light system is experimentally demonstrated via electromagnetically induced transparency (EIT) in a terahertz (THz) metasurface constituted by plus and dimer-shaped resonators. Optical pump-power dependent THz transmissions through the metasurface samples are studied using the optical pump THz probe technique. Under various photoexcitations, the EIT spectra undergo significant modulations in terms of its resonance line shapes (amplitude and intensity contrast) leading to dynamic tailoring of the slow light characteristics. Group delay and delay bandwidth product values are modulated from 0.915 ps to 0.42 ps and 0.059 to 0.025 as the pump fluence increases from 0 to 62.5 nJ cm−2. This results in tunable slow THz light with group velocities ranging from 2.18 × 105 m s−1 to 4.76 × 105 m s−1, almost 54% change in group velocity. The observed tuning is attributed to the photo-induced modifications of the optoelectronic properties of the substrate layer. The demonstrated slow light scheme can provide opportunities for realizing dynamically tunable slow light devices, delay lines, and other ultrafast devices for THz domain.
This article presents an exclusive study of the linear and higher-order susceptibilities, as well as the reduction in group index of a weak probe pulse in a three-level Landau-quantized graphene (LQG) system, under the influence of a strong control field, utilizing the phenomenon of electromagnetically induced transparency. The influence of the magnetic field on the higher-order nonlinearities (Kerr, quintic, and septic) leads to observable changes in amplitudes and shifts in probe frequencies. The LQG system exhibits giant values for these nonlinear susceptibilities with χ(3), χ(5), χ(7) reaching magnitudes approximately ∼10−18m3/V2, ∼10−30m5/V4, and ∼10−42m7/V6, respectively, in the mid-infrared range. The magnetic field also induces asymmetric absorption peaks and modifies dispersion profiles. The study also demonstrates a reduction in the group velocity of the probe, under the effect of the magnetic field, by 1000-fold compared to the speed of light in free space. These giant higher-order nonlinearities, coupled with significantly reduced group velocity, suggest that the LQG system is a quick responder, revealing it as an excellent candidate for terahertz modulation. This also highlights the potential of the system as a promising material for generating and detecting coherent nonlinear signals in the mid-infrared range.
Graphene nanomaterials exhibit excellent optical properties when interacting with electromagnetical fields, which plays an important role in a wide range of applications such as optical communications, optical storage and other fields. Based on the electromagnetically induced transparency (EIT) effect, we investigate control of slow light in the Landau quantized graphene system with different three-level and four-level coupling schemes. Utilizing the EIT effect, group velocity of the probe fields can be significantly reduced and well controlled by manipulating Rabi frequencies and detunings of the coupling lasers as well as probe detuning. Furthermore, probe light with different frequencies can even be controlled in different EIT windows in the graphene system with the four-level scheme, which may find applications in signal selection and discrimination. This work can provide reference for the design of graphene-based quantum devices and have potential applications in optical communications and optical quantum information processing, etc.
We investigate theoretically the optical bistability from a Fabry-Perot cavity with graphene in the terahertz (THz) frequency. It is demonstrated that the optical bistablility in this cavity can be realized due to the electric field enhancement and the giant third-order nonlinear conductivity of graphene. The optical bistable behavior is strongly dependent on the transmission amplitude of the mirror and the position of the graphene in the cavity. It is especially important that the hysterical behaviors of the transmitted light rely on the optical conductivity of graphene, making the Fabry-Perot cavity to be a good candidate for dynamic tunable optical bistable device in the THz frequencies, owing to the possibility of high tunability of graphene conductivity by means of external electrostatic or magnetostatic field.