2D Layered Materials: Synthesis, Nonlinear Optical Properties, and Device Applications

A nanoscale sensor which comprises dielectric-metal-dielectric waveguide and plasmonic metasurface resonators is proposed to realize plasmon-induced transparency responses. The properties of the device are numerically and analytically investigated with different physical parameters. The effect of the incident polarization, geometrical parameters, plasmonic metasurface materials, prism dielectric constant, and the shape of metasurface in near infrared region are then studied to enhance the performance parameters of the structure including the sensitivity, figure-of-merit, and tunability. Our calculations show that the proposed devices are able to operate as a high-sensitivity and tunable sensor with maximum figure-of-merit of 480, and sensitivity of 497.8 nm/refractive index unit for slight change of $\Delta n = 0.24$ , in the refractive index, which stems from its ultra-narrow transparency window and long coupling length between resonators. Furthermore, the structure can be utilized for harnessing light propagation. It is shown that by using silver plasmonic metasurface and appropriate dielectric, a slow up factor as high as 800 is achievable in the proposed structure. We believe that the proposed sensor can be used as a promising platform for future sensing applications such as nanostructure biosensors.

High Sensitivity and Tunable Nanoscale Sensor Based on Plasmon-Induced Transparency in Plasmonic Metasurface

Slow light in photonic crystal waveguides

Graphene biosensors have received more and more attention over the past two decades in the modern fields including labeled, and label-free sensing owing to their ability to harness of electromagnetic fields in a fantastic way. Among these, label-free graphene plasmonic biosensors have been received significant attention for nano-scale applications. The main aim of this work is to study the detection capacity of the biomaterial-based graphene plasmonic biosensor using three-dimensional finite difference time domain (3D-FDTD) method. Herein, taking the advantages of the strong light–matter interaction of graphene layer and its highly tunable optical properties, a new smart biosensor for colorless biomaterial detection is developed. To evaluate the performance parameters of the proposed bio-nanochip sensor, the effects of different biomaterial are considered. Compared to the previous works, the footprint of the proposed biosensor is too small, i.e. λ /10 where λ is the incident wavelength. Also, the sensitivity and figure of merit (FoM) as main parameters of the biosensor are calculated. Numerical results show that the maximum shift of resonance wavelength is around of 100 nm as the variation of refractive index of biomaterials is 0.3. Through the above result, the maximum sensitivity and FoM of the biosensor are respectively 333.3 nm/RIU and 16.665 RIU.

A label-free graphene-based nanosensor using surface plasmon resonance for biomaterials detection

In this paper, a perfect metamaterial (MTM) absorber with simple design has been proposed and investigated in terahertz (THz) region. The suggested absorber has the controllability of the resonance frequency to have a perfect absorption at different frequencies by tuning the graphene chemical potential. The structure has near-unity absorption for the incident angles up to 70°. Strong coupling of the graphene surface plasmon resonance (GSPR) and the resonance of the structure result in a narrow and sensitive absorption peak. Therefore, the suggested absorber can be used as a sensor to detect sensing media with different refractive indices. The simulation results show the capability of the proposed structure to detect glucose with an ultra-high sensitivity of 22.72 THz per refractive index unit (THz/RIU) and diagnose malaria with high sensitivities of 4.7 and 10.58 THz/RIU and good figure of merits (FOM) of 13.84 and 36.51 1/RIU, at the frequencies of 5.71 and 9.88 THz, respectively. Moreover, the equivalent circuit model of the structure has been derived to verify the FDTD simulation results. The proposed plasmonic sensor is a good candidate for biomedical applications in diagnosis of cancer, malaria, anemia and bacterial infection.

Ultrasensitive THz Refractive Index Sensor Based on a Controllable Perfect MTM Absorber

A high-performance electro-optical cross-bar switch based on a vertical graphene plasmonic directional coupler is proposed. The structure consists of two pattern-free graphene plasmonic waveguides which have major advantages over their previous counterparts. An ultrashort switching length of just 223 nm is obtained at the frequency of 37.5 THz. To the best of our knowledge, this switching length is remarkably shorter than those in the recently reported structures. Our designed structure is simulated using a three-dimensional finite-difference time-domain method. According to the illustrated results, extinction ratios of 10.5 and 9.52 dB are obtained at the cross and bar ports, respectively, and a wide spectral width of more than 1 μ m is presented. The required switching voltage is also calculated as 6 V and a very high 3 dB bandwidth of more than 60 GHz is obtained. An extremely low switching energy of 3.8 fJ/bit is also estimated.

Three-Dimensional Analysis of an Ultrashort Optical Cross-Bar Switch Based on a Graphene Plasmonic Coupler

Design and analysis of low loss plasmonic waveguide and directional coupler based on pattern-free suspended graphene sheets

In this paper, two graphene-based all-optical terahertz (THz) modulators are proposed. The operations of the structures are based on high quality factor (Q-factor) resonances in graphene–dielectric metasurfaces. The first modulator is a polarization-dependent metasurface where a sharp resonance is originated from the effect of electromagnetically induced transparency. The structure is analyzed using the finite element method. The modulation is performed by photoexcitation of carriers in graphene by infrared optical pumping. Interestingly, owing to the stimulated emission of THz photons, a high transmission change of more than 120% and a high modulation depth of 93% at the frequency of 5 THz are obtained. The second structure is a polarization-independent modulator that operates based on a high Q-factor Fano resonance in asymmetric dielectric disks. It is presented that a high modulation depth of 98% is achieved. The required optical intensity for both structures is calculated to be as low as 7.35 W/cm2. As the proposed graphene-based metasurfaces are optically tunable, they are promising for the realization of fast and efficient spatial THz modulation.

Tunable graphene–dielectric metasurfaces for terahertz all-optical modulation

In this paper, two double-layer graphene optical modulators based on all-dielectric metasurfaces are proposed. The double-layer graphene modulators remove the requirement of doped silicon back gates which would cause excessive loss and limit the modulation speed. The first structure is based on the electromagnetically induced transparency phenomenon, and the second one is a polarization-independent modulator that is based on the Fano resonance. The structures are simulated and analyzed using the finite element method. According to the simulation results, large modulation depth of about 95% at the wavelength of 1.55 μm can be obtained. The required voltages of 4.95 V are obtained for both of the modulators. By assuming the device of 50 × 50 unit cells, the 3 dB bandwidth of the first (second) structure is calculated as 630 MHz (482 MHz). It is estimated that by improving the quality of graphene, the 3 dB bandwidth of more than 2 GHz could be attained. The achieved modulation performances are much better than the previously reported free-space modulators with the same device area. The proposed high-performance optical modulators are promising for free-space optics technology especially free-space optical communication networks.

Double-layer graphene optical modulators based on Fano resonance in all-dielectric metasurfaces

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Shahram Bahadori-Haghighi

Papers

Three-Dimensional Analysis of an Ultrashort Optical Cross-Bar Switch Based on a Graphene Plasmonic Coupler

Design and analysis of low loss plasmonic waveguide and directional coupler based on pattern-free suspended graphene sheets

Tunable graphene–dielectric metasurfaces for terahertz all-optical modulation

Double-layer graphene optical modulators based on Fano resonance in all-dielectric metasurfaces

A high-performance TE modulator/TM-pass polarizer using selective mode shaping in a VO2-based side-polished fiber