Commentaries

Commentary: Arbitrarily polarized long-range surface-plasmon-polariton waves

[+] Author Affiliations
Yi-Jun Jen

National Taipei University of Technology, Department of Electro-Optical Engineering, No. 1, Sec. 3, Chung-Hsiao E. Rd., Taipei, 106 Taiwan

J. Nanophoton. 5(1), 050304 (September 06, 2011). doi:10.1117/1.3634056
History: Received June 17, 2011; Revised August 17, 2011; Accepted August 18, 2011; Published September 06, 2011; Online September 06, 2011
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A short technical commentary on a specific topic.

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Long-range surface-plasmon-polariton (LRSPP) waves are being investigated for optical propagation guided by the planar interface of a metal film and a dielectric material. For a sufficiently thin metal film, surface-plasmon-polariton (SPP) waves excited on both sides are coupled as an LRSPP wave propagating over a few millimeters in the visible regime and several centimeters in the near-infrared regime. Research on LRSPP waves has sought to realize an optical circuit that guides and manipulates light without any cutoff restriction.1 An LRSPP wave propagates near the metal film that is embedded in a dielectric medium propagate with low dissipation of energy in metal. The LRSPP wave can be excited by either prism coupling or the end-fire excitation method.2 Sarid was the first to propose the prism coupling configuration.3

The mechanism of LRSPP-wave propagation has recently been inferred using a normalized admittance diagram (NAD) that presents the distribution of the ratio of the tangential component of the electric field to that of the magnetic field in a multilayer system.4 For many optical filter designs, a NAD can plot the field ratio that is determined by the interference effect in the multilayer.5 A design method that is based on NAD is utilized to design a multilayered system for the propagation of an LRSPP wave with a predetermined angle of incidence θi (tangential component of wave vector) in a prism-coupling configuration. When the LRSPP wave is excited, the locus of the metal film in NAD is characterized as a projected locus that traverses a huge distance to the terminal point and intersects the real axis far from the origin, as shown in Fig. 1. The projected locus is caused by a multilayer under the metal film that can provide a large imaginary part of normalized admittance

ηip(s) LRSPP
as the start of the locus. The analysis of LRSPP in a NAD supports the design of a new configuration for exciting either s- or p-polarized LRSPP waves. Furthermore, a configuration for exciting s- and p-polarized LRSPP waves simultaneously can be realized using multilayers on both sides of the metal film.6

Graphic Jump LocationF1 :

(a) Optical configuration for p- and s-polarized LRSPP waves. (b) The traditional Kretschmann prism/metal film/air configuration. (c) Loci of metal films associated with an LRSPP wave (dashed line) and an SPP wave (dash-dotted line) with initial admittances

ηip(s) LRSPP and ηip SPP , respectively. The refractive index of the medium of incidence is ni.

In the traditional Kretschmann prism/metal film/air configuration, the p-polarized light can be applied to excite the SPP wave with lower initial admittance

ηip SPP
compared with ηip LRSPP and the associated locus of the metal film is plotted in Fig. 1. However, the s-polarized light cannot excite the SPP wave because the s-polarized admittance of air ηis SPP is always negative imaginary when total reflection occurs. The locus of a metal film would never let the locus point go toward the characteristic admittance of a prism to reach a coupling effect. However, the restriction on an s-polarized LRSPP wave can be overcome using a symmetrical cell that is equivalent to a single layer with designed characteristic admittance and phase thickness. The initial admittance can be provided using a periodic multilayer composed of several symmetric cells of the ABA or ABCBA type with designable equivalent characteristic admittance.5 The initial admittances for s- and p-polarization are functions of the angle of incidence θi, the refractive index, and the thickness of each layer in the unit cell. To excite an LRSPP wave on a metal film at a designated angle of incidence θi, both positive imaginary admittances with values larger than the absolute imaginary part of characteristic admittance of metal can be designed by tuning parameters in the unit cell to cause projected s- and p-polarized loci of the metal in the NAD. A coupling multilayer between the prism and the metal film is also designable with the same trick to bring the ends of metal loci to the same terminal, refractive index of prism, to reach a diminished reflectance that is associated with coupling from the light wave to the LRSPP wave.

The extremely sharp dip in the attenuated total reflections in the angular spectrum indicates the ultralong propagation of an LRSPP wave. Such a sharp dip also appears in the wavelength spectrum at the resonant angle. Besides the application of light guiding, the prism coupling configuration of an LRSPP wave can be adopted as a narrow bandpass filter by placing a polarizer and a crossed analyzer in the incident and reflected optical paths, respectively. As shown in a previous work,7 when the prism coupling configuration of an SPP wave is illuminated with light at a fixed angle, the wavelength at which resonance occurs presents a reflection maximum. It is expected that configuration of an LRSPP wave can achieve narrower bandpass reflection.

The large propagation length enables the guided light to be experimentally detected. Generally, longer propagation requires more accurate fabrication. Although the arbitrarily polarized LRSPP wave has not been experimentally realized so far, the effect of film thickness and refractive index on the LRSPP wave must be examined to estimate the feasibility of realizing the design. Depositing a uniform ultrathin metal film using a general coating technique is difficult; the reduced ratio of the extinction coefficient to the index of refraction of a porous metal film yields a low propagation length of an LRSPP wave in the traditional configuration of Sarid. However, a multilayer can be designed and arranged underneath the metal film to increase the imaginary part of the initial admittance. Accordingly, a projected locus of metal locus in NAD can be estimated and this configuration increases the propagation length of the LRSPP wave.

Instead of a uniform metal thin film, a nanostructured metal film has been experimentally demonstrated as a thin film with single negative or double negative optical property for permittivity and permeability.89 The double negative property for normal incidence is interpreted by a magnetic reversal effect between the metal rods; it can be estimated that the magnetic reversal effect still exists even for oblique incidence. A double negative thin film has been theoretically proposed to support both s- and p-polarized SPP waves.10 The recent reported fabrication of a metamaterial film based on glancing angle deposition simplifies the fabrication of a thin film with double negative property over the visible regime. The polarization-independent SPP waves will be observed in the near future. Let us realize the simultaneous excitations from NAD, the p- and s-polarized loci will follow clockwise and counter clockwise from positive and negative imaginary points (initial admittances) to approach the same termination, respectively. It can be expected that a suitable arrangement of medium or multilayer on either side of the nanostructured metal film would achieve polarization-independent LRSPP waves.

In conclusion, the breakthroughs in design method and metamaterial lead to various LRSPP waves in the future. Increasing the number of tunable parameters in the design increases the diversity of the LRSPP waves. For example, the unit-cell ABCDEDCBA can support more LRSPP waves than can the unit-cell ABA. Beyond the simultaneous excitation of s- and p-polarized LRSPP waves, a configuration in which LRSPP waves can exist at multiple wavelengths or multiple angles can be designed and observed in the near future.

Acknowledgments

The author would like to thank the National Science Council of the Republic of China, Taiwan, for financially supporting this research under Contract Nos. NSCT NSC 99-2221-E-027-043-MY3 and NSCT NSC 99-2120-M-002-012 .

Degiron  A., , Berini  P., , and Smith  D. R., “ Guiding light with long-range plasmons. ,” Opt. Photon. News. 19, , 28–34  ((2008)).
Stegeman  G. I., , Wallis  R. F., , and Maradudin  A. A., “ Excitation of surface polaritons by end-fire coupling. ,” Opt. Lett.. 8, , 386–388  ((1983)).
Sarid  D., “ Long-range surface-plasma waves on very thin metal films. ,” Phys. Rev. Lett.. 47, , 1927–1930  ((1981)).
Jen  Y.-J., , Lakhtakia  A., , Yu  C.-W., , and Chan  T.-Y., “ Multilayered structures for p- and s-polarized long-range surface-plasmon-polariton propagation. ,” J. Opt. Soc. Am. A. 26, , 2600–2606  ((2009)).
Macleod  H. A.,  Thin-Film Optical Filters. ,  Taylor & Francis ,  United Kingdom  ((2000)).
Jen  Y.-J., and Yu  C.-W., “ Optical configuration for unpolarized ultra-long-range surface-plasmon-polariton waves. ,” Appl. Opt.. 50, , C154–C158  ((2011)).
Kajenski  P. J., “ Surface plasmon resonance based wavelength selector: Design considerations. ,” Opt. Eng.. 36, , 263–267  ((1997)).
Jen  Y.-J., , Lakhtakia  A., , Yu  C.-W., , and Lin  C.-T., “ Vapor-deposited thin films with negative real refractive index in the visible regime. ,” Opt. Express. 17, , 7784–7789  ((2009)).
Jen  Y.-J., , Chen  C.-H., , and Yu  C.-W., “ Deposited metamaterial thin film with negative refractive index and permeability in visible regime. ,” Opt. Lett.. 36, , 1014–1016  ((2011)).
Ruppin  R., “ Surface polaritons of a left-handed medium. ,” Phys. Lett. A. 277, , 61–64  ((2000)).
© 2011 Society of Photo-Optical Instrumentation Engineers (SPIE)

Citation

Yi-Jun Jen
"Commentary: Arbitrarily polarized long-range surface-plasmon-polariton waves", J. Nanophoton. 5(1), 050304 (September 06, 2011). ; http://dx.doi.org/10.1117/1.3634056


Figures

Graphic Jump LocationF1 :

(a) Optical configuration for p- and s-polarized LRSPP waves. (b) The traditional Kretschmann prism/metal film/air configuration. (c) Loci of metal films associated with an LRSPP wave (dashed line) and an SPP wave (dash-dotted line) with initial admittances

ηip(s) LRSPP and ηip SPP , respectively. The refractive index of the medium of incidence is ni.

Tables

References

Degiron  A., , Berini  P., , and Smith  D. R., “ Guiding light with long-range plasmons. ,” Opt. Photon. News. 19, , 28–34  ((2008)).
Stegeman  G. I., , Wallis  R. F., , and Maradudin  A. A., “ Excitation of surface polaritons by end-fire coupling. ,” Opt. Lett.. 8, , 386–388  ((1983)).
Sarid  D., “ Long-range surface-plasma waves on very thin metal films. ,” Phys. Rev. Lett.. 47, , 1927–1930  ((1981)).
Jen  Y.-J., , Lakhtakia  A., , Yu  C.-W., , and Chan  T.-Y., “ Multilayered structures for p- and s-polarized long-range surface-plasmon-polariton propagation. ,” J. Opt. Soc. Am. A. 26, , 2600–2606  ((2009)).
Macleod  H. A.,  Thin-Film Optical Filters. ,  Taylor & Francis ,  United Kingdom  ((2000)).
Jen  Y.-J., and Yu  C.-W., “ Optical configuration for unpolarized ultra-long-range surface-plasmon-polariton waves. ,” Appl. Opt.. 50, , C154–C158  ((2011)).
Kajenski  P. J., “ Surface plasmon resonance based wavelength selector: Design considerations. ,” Opt. Eng.. 36, , 263–267  ((1997)).
Jen  Y.-J., , Lakhtakia  A., , Yu  C.-W., , and Lin  C.-T., “ Vapor-deposited thin films with negative real refractive index in the visible regime. ,” Opt. Express. 17, , 7784–7789  ((2009)).
Jen  Y.-J., , Chen  C.-H., , and Yu  C.-W., “ Deposited metamaterial thin film with negative refractive index and permeability in visible regime. ,” Opt. Lett.. 36, , 1014–1016  ((2011)).
Ruppin  R., “ Surface polaritons of a left-handed medium. ,” Phys. Lett. A. 277, , 61–64  ((2000)).

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