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Low threshold optical bistability at terahertz frequencies with graphene surface plasmons.

Dai X, Jiang L, Xiang Y - Sci Rep (2015)

Bottom Line: It is found that the switching-up and switching-down intensities required to observe the optical bistable behavior are lowered markedly due to the excitation of the graphene surface plasmons, thus making this configuration a prime candidate for experimental investigation at the terahertz range.And the switching threshold value can be further reduced by decreasing the Fermi-level or increasing the thickness of sandwich structure, hence providing a new way for realizing tunable optical bistable devices.Finally, the optical bistability at higher terahertz frequency and the influence of relaxation time under the actual experimental condition on Fermi-level are discussed.

View Article: PubMed Central - PubMed

Affiliation: SZU-NUS Collaborative Innovation Center for Optoelectronic Science &Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.

ABSTRACT
We propose a modified Kretschmann-Raether configuration to realize the low threshold optical bistable devices at the terahertz frequencies. The metal layer is replaced by the dielectric sandwich structure with the insertion of graphene, and this configuration can support TM-polarization surface electromagnetic wave. The surface plasmon resonance is strongly dependent on the Fermi-level of graphene and the thickness of the sandwich structure. It is found that the switching-up and switching-down intensities required to observe the optical bistable behavior are lowered markedly due to the excitation of the graphene surface plasmons, thus making this configuration a prime candidate for experimental investigation at the terahertz range. And the switching threshold value can be further reduced by decreasing the Fermi-level or increasing the thickness of sandwich structure, hence providing a new way for realizing tunable optical bistable devices. Finally, the optical bistability at higher terahertz frequency and the influence of relaxation time under the actual experimental condition on Fermi-level are discussed.

No MeSH data available.


Related in: MedlinePlus

Dependences of transmitted electric field (a) and transmittance (b) on the incident electric field; (c) Influence of the incident angle on the switching-up and switching-down threshold values. Where λ = 300 um, np = ns = 4, n1 = n2 = 1.5, EF = 0.25 eV and d = 30 um.
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f4: Dependences of transmitted electric field (a) and transmittance (b) on the incident electric field; (c) Influence of the incident angle on the switching-up and switching-down threshold values. Where λ = 300 um, np = ns = 4, n1 = n2 = 1.5, EF = 0.25 eV and d = 30 um.

Mentions: The results of the typical calculation for optical bistability are illustrated in Fig. 4, in which we plot transmitted electric field and transmittance versus incident electric field in Fig. 4(a,b), respectively. Here the magnetic field in Eq. (1) has been converted to the electric field according to the relationship of magnetic and electric fields in dielectric, Ei = η0Hi/np, where η0 = 377Ω is the impedance in a vacuum. We set the incident angle θi = 52°, 54° and 56°, respectively. The resonant angle for EF = 0.25 eV and d = 30 um is θR = 50.9°. Hence the initial angle offsets Δφ = 1.1°, 3.1°, and 5.1°, respectively. In the zero incident power the system is in the total internal reflection (TIR) mode for an enough large initial angle offsets, such as θi = 54° and 56°. However, for θi = 52° the initial angle offset Δφ = 1.1° is not large enough to excite the optical bistability. For larger initial angle offset Δφ, it is clear that the hysterical loop occurs. It is indicated that as the input electric field increases, the resonant evanescent electric field in nonlinear graphene increases, and the surface conductivity of graphene decreases resulting in the shifts of the resonant angle to a larger angle θR. Hence the SPPs mode is approached, and the transmitted electric field increases. When the incident electric field reaches the switching-up threshold, Eup = 5.17 × 104 V/m for θi = 54° and Eup = 1.107 × 105 V/m for θi = 56°, the transmittance jumps from a very small value to a higher value. This jump leads to the resonant angle θR move from below θi to slight above θi. Further increases in electric field move the resonant angle farther from the incident angle θi and hence decrease the transmittance. But now as the input electric field is decreased, the resonant angle θR decreases and which is gradually approaching to the incident angle and hence gradually approaches to the SPPs condition. When the incident electric field reduces to the switching-down threshold, Edown = 2.42 × 104 V/m for θi = 54° and Edown = 2.77 × 104 V/m for θi = 56°, the transmittance resonance is realized due to the excitation of SPPs. However, as the input electric field is further decreased, SPPs cannot be maintained and the transmittance point now jumps from the resonant state of SPPs to TIR off resonant state.


Low threshold optical bistability at terahertz frequencies with graphene surface plasmons.

Dai X, Jiang L, Xiang Y - Sci Rep (2015)

Dependences of transmitted electric field (a) and transmittance (b) on the incident electric field; (c) Influence of the incident angle on the switching-up and switching-down threshold values. Where λ = 300 um, np = ns = 4, n1 = n2 = 1.5, EF = 0.25 eV and d = 30 um.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508658&req=5

f4: Dependences of transmitted electric field (a) and transmittance (b) on the incident electric field; (c) Influence of the incident angle on the switching-up and switching-down threshold values. Where λ = 300 um, np = ns = 4, n1 = n2 = 1.5, EF = 0.25 eV and d = 30 um.
Mentions: The results of the typical calculation for optical bistability are illustrated in Fig. 4, in which we plot transmitted electric field and transmittance versus incident electric field in Fig. 4(a,b), respectively. Here the magnetic field in Eq. (1) has been converted to the electric field according to the relationship of magnetic and electric fields in dielectric, Ei = η0Hi/np, where η0 = 377Ω is the impedance in a vacuum. We set the incident angle θi = 52°, 54° and 56°, respectively. The resonant angle for EF = 0.25 eV and d = 30 um is θR = 50.9°. Hence the initial angle offsets Δφ = 1.1°, 3.1°, and 5.1°, respectively. In the zero incident power the system is in the total internal reflection (TIR) mode for an enough large initial angle offsets, such as θi = 54° and 56°. However, for θi = 52° the initial angle offset Δφ = 1.1° is not large enough to excite the optical bistability. For larger initial angle offset Δφ, it is clear that the hysterical loop occurs. It is indicated that as the input electric field increases, the resonant evanescent electric field in nonlinear graphene increases, and the surface conductivity of graphene decreases resulting in the shifts of the resonant angle to a larger angle θR. Hence the SPPs mode is approached, and the transmitted electric field increases. When the incident electric field reaches the switching-up threshold, Eup = 5.17 × 104 V/m for θi = 54° and Eup = 1.107 × 105 V/m for θi = 56°, the transmittance jumps from a very small value to a higher value. This jump leads to the resonant angle θR move from below θi to slight above θi. Further increases in electric field move the resonant angle farther from the incident angle θi and hence decrease the transmittance. But now as the input electric field is decreased, the resonant angle θR decreases and which is gradually approaching to the incident angle and hence gradually approaches to the SPPs condition. When the incident electric field reduces to the switching-down threshold, Edown = 2.42 × 104 V/m for θi = 54° and Edown = 2.77 × 104 V/m for θi = 56°, the transmittance resonance is realized due to the excitation of SPPs. However, as the input electric field is further decreased, SPPs cannot be maintained and the transmittance point now jumps from the resonant state of SPPs to TIR off resonant state.

Bottom Line: It is found that the switching-up and switching-down intensities required to observe the optical bistable behavior are lowered markedly due to the excitation of the graphene surface plasmons, thus making this configuration a prime candidate for experimental investigation at the terahertz range.And the switching threshold value can be further reduced by decreasing the Fermi-level or increasing the thickness of sandwich structure, hence providing a new way for realizing tunable optical bistable devices.Finally, the optical bistability at higher terahertz frequency and the influence of relaxation time under the actual experimental condition on Fermi-level are discussed.

View Article: PubMed Central - PubMed

Affiliation: SZU-NUS Collaborative Innovation Center for Optoelectronic Science &Technology, Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province, College of Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China.

ABSTRACT
We propose a modified Kretschmann-Raether configuration to realize the low threshold optical bistable devices at the terahertz frequencies. The metal layer is replaced by the dielectric sandwich structure with the insertion of graphene, and this configuration can support TM-polarization surface electromagnetic wave. The surface plasmon resonance is strongly dependent on the Fermi-level of graphene and the thickness of the sandwich structure. It is found that the switching-up and switching-down intensities required to observe the optical bistable behavior are lowered markedly due to the excitation of the graphene surface plasmons, thus making this configuration a prime candidate for experimental investigation at the terahertz range. And the switching threshold value can be further reduced by decreasing the Fermi-level or increasing the thickness of sandwich structure, hence providing a new way for realizing tunable optical bistable devices. Finally, the optical bistability at higher terahertz frequency and the influence of relaxation time under the actual experimental condition on Fermi-level are discussed.

No MeSH data available.


Related in: MedlinePlus