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We report a highly efficient graphene-based modulator by using an edge plasmonic effect in this paper. The modulation efficiency of the proposed modulator can be as large as 1.58 dB/μm, which is several times larger than that of previous reported modulators. By enhancing the gap plasmon mode and the edge plasmonic effect in a well-designed diagonal waveguide, a wedge-to-wedge SPP mode is strongly confined in both horizontal and vertical directions in terms of a small mode area (Aef /A0

We performed angle-resolved photoemission spectroscopy studies on a series of FeTe$_{1-x}$Se$_{x}$ monolayer films grown on SrTiO$_{3}$. The superconductivity of the films is robust and rather insensitive to the variations of the band position and effective mass caused by the substitution of Se by Te. However, the band gap between the electron- and hole-like bands at the Brillouin zone center decreases towards band inversion and parity exchange, which drive the system to a nontrivial topological state predicted by theoretical calculations. Our results provide a clear experimental indication that the FeTe$_{1-x}$Se$_{x}$ monolayer materials are high-temperature connate topological superconductors in which band topology and superconductivity are integrated intrinsically., 14 pages, 4 figures

An active absorber with nearly zero static power consumption is proposed based on nonvolatile floating-gate graphene structure. Such absorber has almost no static power consumption benefited from the nonvolatile design. In such design, the central graphene can capture the tunneled electrons under the positive applied voltage, but cannot release these electrons after removing the voltage since it is electrically isolated from the external electrodes. Therefore, no extra power is needed to sustain the conductivity of graphene. Moreover, our proposed absorber exhibits an extremely strong absorption capacity. Even taking the strict condition for the bandwidth where all the absorptivity inside the bandwidth are larger than 90% as criterion, the proposed absorber provides more than 60 GHz absorption bandwidth which is twice larger than previous results. Furthermore, the proposed absorber shows high tolerance against large incidence angle ( $60^\circ $ ), different polarizations and nonideal factors of graphene. The results may promote various future nonvolatile absorber designs.

We present an effective scheme to improve the modulation capacity in graphene-based silicon modulator by employing the double slots configuration with hybrid plasmonic effects. Two modulators, i.e., metal-insulator-metal and insulator-metal-insulator configurations have been demonstrated, showing that the double slots design can significantly improve the modulation efficiency. The obtained modulation efficiency is up to 0.525 dB/μm per graphene layer, far exceeding previous studies. It can be found that the light-graphene interaction plays a pivotal role in the modulation efficiency, whereas the height of metal has profound influence on the modulation. Our results may promote various future modulation devices based on graphene.

A broadband and tunable absorber with nearly zero static power consumption is proposed based on non-volatile floating-gate graphene structure. Such absorber has almost no static power consumption benefited from the non-volatile design. In such design, the central graphene can capture the tunneled electrons under the positive applied voltage, but cannot release these electrons after removing the voltage since it is electrically isolated from the external electrodes. Therefore, no extra power is needed to sustain the conductivity of graphene. Moreover, our proposed absorber exhibits an extremely strong absorption capacity. Even taking the strict condition for the bandwidth where all the absorptivity inside the bandwidth are larger than 90% as criterion, the proposed absorber provides more than 60 GHz absorption bandwidth which is twice larger than previous results. Furthermore, the proposed absorber shows high tolerance against large incidence angle (60°), different polarizations. The results may promote various future non-volatile absorber designs.

We propose a high efficient graphene-on-gap modulator (GOGM) by employing the hybrid plasmonic effect, whose modulation efficiency is ∼8-folds larger than that of present graphene-on-silicon modulator (GOSM) (∼0.1 dB / μm). The proposed modulator has the advantage of short modulation length ∼3.6 μm, relatively low insertion loss ∼0.32 dB and larger modulation bandwidth ∼0.48 THz. Moreover, an efficient taper coupler has been designed to convert the quasi-transverse electric (TE) mode of conventional silicon waveguide to the hybrid plasmonic mode of GOGM, with a high coupling efficiency of 91%. This study may promote the design of high-performance on-chip electro-optical modulator.

This publisher’s note contains corrections to Opt. Lett. 44, 2586 (2019)OPLEDP0146-959210.1364/OL.44.002586.

In this Letter, we report a graphene-based hybrid plasmonic modulator (GHPM) realized by employing the electro-absorption effect of graphene. The simulation results show that the modulation efficiency of GHPM, i.e., extinction ratio per length, can be as large as 0.417 dB/μm, which is more than twice as much as that of recently presented graphene-on-silicon modulator. It was found that the improvement in modulation efficiency is mainly due to the enhancement of the overlap between graphene and the mode field in GHPM. A prototype of GHPM was fabricated. The measurement results showed that the GHPM can work in a broadband from 1530 to 1570 nm and an improved modulation efficiency of 1.08 dB (at 30 μm). Finally, we have discussed the factors that influence the modulation efficiency. Our proof-of-concept design may promote the development of on-chip graphene-based plasmonic devices.

We reported a novel terahertz modulator based on graphene-embedded waveguide. Comparing to previous solution, the terahertz wave-matter interaction in the modulator structure is enhanced greatly. In theory, the modulation depth can be nearly 100% as the simulation results show. Experimental characterisations are carried out through continuous terahertz wave system and the terahertz time-domain spectroscopy (TDZ) system respectively. The best experimental modulation depth is 29.53%, which is much larger than state-of-art results.

We have systematically investigated the slow light performances based on two-dimensional material graphene, giving the conclusion that graphene exhibits much larger slow light capability than other materials. A large delay-bandwidth product has been obtained in a simple yet functional graphene-based waveguide with slow down factor c / υ g at 109 and slow light bandwidth Δω at 14.5 nm, which is several orders of magnitude larger than previous results.

A hybrid plasmonic parallel transmission line scheme constructed by a spatial single-mode with time-domain multi-line waveguide is presented in this paper. The proposed configuration enables a nanometer field localization with zero crosstalk between data channels. Furthermore, the proposed plasmonic transmission line shows the advantages of enabling an integrated circuits (IC) with a large number of parallel transmission channels, as well as a good robustness with respect to the fabrication tolerances.

Former study shows that the graphene-embedded modulator can only work in TE mode while cannot achieve enough extinction ratio in TM mode. However, an optical modulator which can work in both TE mode and TM mode is required by the mode multiplexing technology. By simply growing a graphene-aluminum oxide metamaterial layer on the silicon waveguide, an optical-absorption modulator which can achieve a large extinction ratio in both TE mode and TM mode is designed in this letter. In addition, our modulator can achieve a very compact footprint which is only 10 μm.

We have systematically investigated the wideband slow light in two-dimensional material graphene, revealing that graphene exhibits much larger slow light capability than other materials. The slow light performances including material dispersion, bandwidth, dynamic control ability, delay-bandwidth product, propagation loss and group-velocity dispersion are studied, proving graphene exhibits significant advantages in these performances. A large delay-bandwidth product has been obtained in a simple yet functional grating waveguide with slow down factor c/vg at 163 and slow light bandwidth Δω at 94.4 nm centered at 10.38 μm, which is several orders of magnitude larger than previous results. Physical explanation of the enhanced slow light in graphene is given. Our results indicate graphene is an excellent platform for slow light applications, promoting various future slow light devices based on graphene.

The dynamic control of wide band slow surface wave in a graphene-based grating waveguide is proposed here. The extreme large bandwidth and strongly delay has been obtained and the group index can be dynamically tuned.

We report the growth process of FeTe 1−x Sex ( ) monolayer films on SrTiO 3 (STO) substrates through molecular beam epitaxy and discuss the possible ways to improve the film quality. By exploring the parameters of substrate treatment, growth control and post growth annealing, we successfully obtain a series of FeTe 1−x Sex monolayer films. In the whole growth process, we find the significance of the temperature control through surface roughness monitored by the reflection high-energy electron diffraction and scanning tunneling microscopy. We obtain the best quality of FeSe monolayer films with the STO substrate treated at T = 900–950°C before growth, the FeSe deposited at T = 310°C during growth and annealed at T = 380°C after growth. For FeTe 1−x Sex ( ), both the growth temperature and annealing temperature decrease to T = 260°C. According to the angle-resolved photoemission spectroscopy measurements, the superconductivity of the FeTe 1−x Sex film is robust and insensitive to Se concentration. All the above are instructive for further investigations of the superconductivity in FeTe 1−x Sex films.

We propose a highly efficient graphene-on-gap modulator (GOGM) by employing the hybrid plasmonic effect, whose modulation efficiency (up to 1.23 dB/μm after optimization) is ∼12-fold larger than that of the present graphene-on-silicon modulator (∼0.1 dB/μm). The proposed modulator has the advantage of a short modulation length of ∼3.6 μm, a relatively low insertion loss of ∼0.32 dB, and a larger modulation bandwidth of ∼0.48 THz. The physical insight is investigated, showing that both the slow light effect and the overlap between graphene and the mode field contribute. Moreover, an efficient taper coupler has been designed to convert the quasi-transverse electric mode of conventional silicon waveguide to the hybrid plasmonic mode of GOGM, with a high coupling efficiency of 91%. This Letter may promote the design of high-performance on-chip electro-optical modulators.

Enlarged group index has been reported previously when surface plasmons propagate through the graphene sheet, yet a clear slow wave performance in graphene has not been explored. We proposed and numerically analyzed here for the first time to the best of our knowledge an extremely wideband slow surface wave in a graphene-based grating waveguide. The strongly delayed wave (120n(g)167) with extremely large bandwidth (2.7 THzΔf0.7 THz) can be dynamically controlled via the gate-voltage dependent optical properties of graphene. Our results suggest that graphene may be a very promising slow light medium, promoting future slow light devices based on graphene.