By:Tie Jun Cui and Xiaopeng Shen, State Key Laboratory of Millimeter Waves,

Southeast University, Nanjing 210096, China. Email: tjcui@seu.edu.cn

Forum for Electromagnetic Research Methods and Application Technologies (FERMAT)

Spoof Surface Plasmons and Applications in Microwave Frequencies

Keyword: Surface plasmon polaritons (SPPs), conformal surface plasmons, localized surface plasmons, SPP waveguide, passive SPP components, active SPP components.

Abstract:We present several spoof surface plasmon structures in the microwave and terahertz frequencies, including surface plasmon polariton (SPP) waveguides and the relevant devices, and localized surface plasmons (LSPs). In details, we will introduce our recent work on ultrathin and flexible SPP waveguides with subwavelength width, which can sustain highly localized SPPs along two orthogonal directions in broadband by keeping good modal shapes and propagating long distance with low bending loss, and the resulting compact plasmonic filters, bends, beam spillters, polarizers, and resonantors. We also demonstrate spoof LSPs on planar ultrathin textured metallic disks with subwavelength scales, which have potential applications as plasmonic sensors in the microwave and terahertz frequencies.

References 1. X. Shen, T. J. Cui, D. Martin-Canob, and F. J. Garcia-Vidal, “Conformal

surface plasmons propagating on ultrathin and flexible films,” Proceedings of the National Academy of Science, PNAS, vol. 110, no. 1, pp. 40-45 (2013)

2. X. Shen and T. J. Cui, “Planar plasmonic metamaterial on a thin film with nearly zero thickness,” Applied Physics Letters, vol. 102, 211909 (2013)

3. X. Gao, J. H. Shi, X. Shen, H. F. Ma, W. X. Jiang, L. Li, and T. J. Cui, “Ultrathin dual-band SPP waveguide and frequency splitter in microwave frequencies,” Applied Physics Letters, vol. 102, 151912 (2013)

4. H. F. Ma, X. Shen, Q. Cheng, W. X. Jiang, and T. J. Cui, “Broadband and high-efficiency conversion from guided waves to spoof surface plasmon polaritons,” Laser and Photonics Review, vol. 8, no. 1, pp. 146-151 (2014)

5. X. Gao, L. Zhou, Z. Liao, H. F. Ma, and T. J. Cui, “An ultra-wideband surface plasmonic filter in microwave frequencies,” Applied Physics Letters, vol. 104, 191603 (2014)

6. B. C. Pan, Z. Liao, J. Zhao, and T. J. Cui, “Controlling rejections of spoof surface plasmon polaritons using metamaterial particles,” Optics Express, vol. 22, pp. 13940-13950 (2014)

References

7. H. C. Zhang, S. Liu, X. Shen, L. H. Chen, L. Li, and T. J. Cui, “Broadband amplification of spoof surface plasmon polaritons in the microwave frequency,” Laser and Photonics Review, DOI 10.1002/lpor.201400131, (2014)

8. X. Shen and T. J. Cui, “Ultrathin plasmonic metamaterial for spoof localized surface plasmons,” Laser and Photonics Review, vol. 8, no. 1, pp. 137-145 (2014)

9. P. A. Huidobro, X. Shen, J. Cuerda, E. Moreno, L. Martin-Moreno, F. J. Garcia-Vidal, T. J. Cui, and J. B. Pendry, “Magnetic localized surface plasmons,” Physical Review X, vol. 4, 021003 (2014).

10. J. J. Xu, H. C. Zhang, Q. Zhang, and T. J. Cui, “Efficient conversion of surface-plasmon-like modes to spatial radiated modes,” Applied Physics Letters, vol. 105, accepted for publication, 2015.

◆ Prof. Francisco J. Garcia-Vidal

Universidad Autonoma de Madrid, Spain

◆ Sir John Pendry

Imperial College London, UK

Collaboration Acknowledgments

Outline

◆ Background and Motivations

◆ Conformal Spoof SPPs and Devices

◆ Conversion from SPPs to Guided Waves

◆ Spoof Localized SPs

◆ Conclusions

Spoof (or Mimicking, Designer) SPPs

Natural SPPs only exist at optical frequencies.

To realize SPPs at lower frequencies (GHz, THz), spoof SPPs have been proposed.

The concept of “designer” surface modes opens opportunities to control and direct the radiations at surfaces within a subwavelength region.

Pendry et al. , Science 305, 847 (2004). Garcia-Vidal et al., J. Opt. A: Pure Appl. Opt. 7, S94 (2005).

A theoretical study on localized surface plasmons (LSPs)

Spoof LSPs

F. J. Garcia-Vidal, PRL 108, 223905, 2012

The Motivation of Our Study The existing spoof SP structures are all 3D

(corrugated structures on metal surface, drilling holes on metal surface, Domino structures).

They are inconvenient for integration.

Our motivations: To propose, design, and realize spoof SPPs and

LSPs on ultrathin metal surfaces; To construct planar and conformal SPP waveguides,

SPP devices, and SPP circuits; To propose and construct ultrathin planar LSPs.

Spoof SPPs on Different-Thickness Structured Metal Strip

Shen, et al., PNAS 110, 40-45 (2013)

The proposed ultrathin SPP structure works from microwave to THz frequencies

Spoof SPPs on Ultrathin Metal Film

Experiment results: Wideband (7GHz – 11 GHz)

Excellent propagation properties with low loss and long propagation distance.

Low loss

Good modal

shape

Long distance

Exponential

decay in both

orthogonal

directions

Spoof SPPs Devices

Beam Bending Beam Splitter

(Wideband)

Ring Resonator

Shen and Cui, APL 102, 211909, 2013

Spoof SPPs Devices Gao et al., APL 102, 151912, 2013

Dual-Band SPP Frequency Splitter

Flexible and Conformal SPPs

Flexible Copper Clad Laminate (FCCL)

Shen, et al., PNAS 110, 40-45 (2013)

Flexible and Conformal SPPs

Efficient Polarization Conversion

Sharp Bending

Flexible and Conformal SPPs

Shen, et al., PNAS 110, 40-45 (2013)

Conversion of Guided Modes and SPPs Ma et al., Laser & Photonics Review,

vol. 8, pp. 146-151 (2014)

Conversion of Guided Modes to SPPs

• Very high efficiency • Very broad band • Direct measurements of

reflection & transmission

Advantage: Very Small Cross Talk

SPP Filters Gao et al., APL 104, 191603 (2014)

SPP Filters Pan et al., Opt. Exp. 22, 13940 (2014)

SPP Filters

Spoof Integrated SPP Circuits Shen, Zhang & Cui, unpublished, 2014

• Five-Port Circuit: • Splitter • Ring Resonator • Directional Coupler

Radiation of SPP Waves Xu et al., Efficient conversion of surface-plasmon-like modes to spatial radiated modes, APL, accepted for publication, 2015

A Spoof SPP Emitter, in which the gradient index metasurface will change the SPP modes to radiated modes

Radiation of SPP Waves

Different gradience of the metasurface will result in different radiation performance.

Radiation of SPP Waves

The simulated and measured reflection coefficients, showing good radiation efficiency in wide frequency band.

The measured near-field distributions (phases) and far-field radiation patterns of the proposed spoof SPP emitters, in which the beam deflection angles are -22.5o, -2o, and 16.1o

Amplification of SPP Waves

Amplifier Chip SPP Waveguide

Zhang et al., Laser and Photonics Review, DOI 10.1002/lpor.201400131, (2014)

Amplification of SPP Waves

Measured Near Fields for SPP Amplification

• Hybrid SPP-

Conventional

Integrated Circuits

• Hybrid Passive

and Active SPP

Integrated Circuits

SPP Mixers

Zhang, Liu & Cui, unpublished, 2014

Spoof Localized SPs Shen and Cui, Laser and Photonics Review, vol. 8, pp. 137-145 (2014)

Spoof Localized SPs Monopole Excitation: Simulation Results

quadrupole

dipole

hexapole octopole

decapole dodeca-pole quattuordec-pole

Spoof Localized SPs Monopole Excitation: Measured Results

quadrupole

dipole

hexapole octopole

decapole dodeca-pole quattuordec-pole

Spoof Localized SPs

Shen and Cui, Laser and Photonics Review, vol. 8, pp. 137-145 (2014)

Subwavelength Spoof LSPs

Huidobro, Shen et al., Physical Review X 4, 021003 (2014)

0.5 1.0 1.5 2.0 2.50

1000

2000

3000

4000

ECS RCS ACS

ECS/

RCS/

ACS

Frequency (GHz)

r w

g

x, K

y, E

. H

ED

MD

The spirally curved grooves make the ultrathin LSP structure more compact: with subwavelength scale. The right figure shows the electric and magnetic dipole resonances.

Electric Dipole Magnetic Dipole

Power Flux

Far-Field Patterns

Near Fields

Subwavelength Spoof LSPs

Measurement Results

Summary

With the ultrathin planar or flexible structures, SPs will be practical in the microwave and terahertz frequencies.

We produced compact-size SPP waveguides and various passive devices.

We proposed the first SPP amplifier in the microwave frequencies, which is the basis to realize SPP circuits and systems.

We also produced subwavelength LSP sensors.

Thank you!

tjcui@seu.edu.cn