Compensation of loss in propagating surface plasmon polariton by gain in adjacent dielectric medium.
ABSTRACT We report the suppression of loss of surface plasmon polariton propagating at the interface between silver film and optically pumped polymer with dye. The large magnitude of the effect enables a variety of applications of 'active' nanoplasmonics. The experimental study is accompanied by the analytical description of the phenomenon. In particular, we resolve the controversy regarding the direction of the wavevector of a wave with a strong evanescent component in an active medium.
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ABSTRACT: We propose a mechanism of ultrahigh-Q metallic nanocavity resonances that involves an efficient loss-compensation scheme favorable for room-temperature operation. We theoretically show that surface plasmon-polaritons excited on the entrance and exit interfaces of a metallic nanocavity array efficiently transfer external optical gain to the cavity modes by inducing resonantly-amplified intracavity feedback. Surprisingly, the modal gain in the nanocavity with the externally amplified feedback is inversely proportional to the cavity length as opposed to conventional optical cavity amplifiers requiring longer cavities for higher optical gain. Utilizing this effect, we numerically demonstrate room-temperature nanocavity resonance Q-factor exceeding 10(4) in a 25-nm-wide silver nanoslit array. The proposed mechanism provides a highly efficient plasmonic amplification process particularly for subwavelength plasmonic cavities which are essential components in active nanoplasmonic devices.Scientific reports. 01/2014; 4:7124.
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ABSTRACT: Spontaneous emission noise is an important limit to the performance of active plasmonic devices. Here, we investigate the spontaneous emission noise in the long-range surface plasmon-polariton waveguide based optical gyroscope. A theoretical model of the sensitivity is established to study the incoherent multi-beam interference of spontaneous emission in the gyroscope. Numerical results show that spontaneous emission produces a drift in the transmittance spectra and lowers the signal-to-noise-ratio of the gyroscope. It also strengthens the shot noise to be the main limit to the sensitivity of the gyroscope for high propagation loss. To reduce the negative effects of the spontaneous emission noise on the gyroscope, an external feedback loop is suggested to estimate the drift in the transmittance spectra and therefor enhance the sensitivity. Our work lays a foundation for the improvement of long-range surface plasmon-polariton gyroscope and paves the way to its practical application.Scientific reports. 01/2014; 4:6369.
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ABSTRACT: This chapter discusses a hydrodynamics-inspired approach to trap and manipulate light in plasmonic nanostructures, which is based on steering optical powerflow around nano-obstacles. New insights into plasmonic nanofocusing mechanisms are obtained by invoking an analogy of the 'photon fluid' (PF). By proper nanostructure design, PF kinetic energy can be locally increased via convective acceleration and then converted into 'pressure' energy to generate localized areas of high field intensity. In particular, trapped light can be molded into optical vortices -tornado-like areas of circular motion of power flux - connected into transmission-like sequences. In the electromagnetic theory terms, this approach is based on radiationless electromagnetic interference of evanescent fields rather than on interference of propagating waves radiated by the dipoles induced in nanoparticles. The resulting ability to manipulate optical powerflow well beyond the diffraction limit helps to reduce dissipative losses, to increase the amount of energy accumulated within a nanoscale volume, and to activate magnetic response in non-magnetic nanostructures. It also forms a basis for long-range on-chip energy transfer/routing as well as for active nanoscale field modulation and switching.04/2014;
Compensation of loss in propagating surface plasmon polariton by gain in adjacent
M. A. Noginov1*, V. A. Podolskiy2, G. Zhu1, M. Mayy1, M. Bahoura1, J. A. Adegoke1, B. A.
Ritzo1, K. Reynolds1
1 Center for Materials Research, Norfolk State University, Norfolk, VA 23504
2 Department of Physics, Oregon State University, Corvallis, OR 97331-6507
Abstract: We report the suppression of loss of surface plasmon polariton propagating at the
interface between silver film and optically pumped polymer with dye. Large magnitude of the
effect enables a variety of applications of ‘active’ nanoplasmonics. The experimental study is
accompanied by the development of the analytical description of the phenomenon and the
solution of the controversy regarding the direction of the wavevector of a wave with a strong
evanescent component in an active medium.
Surface plasmon polaritons (SPPs) – special type of electromagnetic waves coupled to
electron density oscillations – allow nanoscale confinement of electromagnetic radiation .
SPPs are broadly used in photonic and optoelectronic devices [1-7], including waveguides,
couplers, splitters, add/drop filters, and quantum cascade lasers. SPP is also the enabling
mechanism for a number of negative refractive index materials (NIMs) [8-12].
Many applications of SPPs suffer from damping caused by absorption in metals. Over the
years, several proposals to compensate loss by incorporating active (gain) media into plasmonic
systems have been made. Theoretically, field-matching approach was employed to calculate the
reflectivity at surface plasmon excitation ; the authors of  proposed that the optical gain
in a dielectric medium can elongate the SPP’s propagation length; gain-assisted excitation of
resonant SPPs was predicted in ; SPP propagation in active waveguides was studied in ;
and the group velocity modulation of SPPs in nano-waveguides was discussed in . Excitation
of localized plasmon fields in active nanosystems using surface plasmon amplification by
stimulated emission of radiation (SPASER) was proposed in . Experimentally, the
possibility to influence SPPs by optical gain was demonstrated in Ref. , where the effect was
as small as 0.001%.
Here we report conquering the loss of propagating SPPs at the interface between silver film
and optically pumped polymer with dye. The achieved value of gain, ≈ 420 cm-1, is sufficient to
fully compensate the intrinsic SPP loss in high-quality silver films. This, together with the
compensation of loss in localized surface plasmons, predicted in  and recently demonstrated
in , enables practical applications of a broad range of low-loss and no-loss photonic
The experimental attenuated total reflection (ATR) setup consisted of a glass prism with the
real dielectric permittivity e0=n02, a layer of metal with the complex dielectric constant e1 and
thickness d1, and a layer of dielectric medium characterized by the permittivity e2, Fig. 1a.
The wave vector of the SPP propagating at the boundary between media 1 and 2, is given by
where w is the oscillation frequency and c is the speed of light. SPP can be excited by a p
polarized light falling on the metallic film at the critical angle q0, such that the projection of the
wave vector of the light wave to the axis x,
kxq ( )= (w/c)n0sinq0, (2)
is equal to
0). At this resonant condition, the energy of incident light is transferred to the
SPP, yielding a minimum (dip) in the angular dependence of the reflectivity R(q) :
R q ( )=
r01+ r12exp 2ikz1d1
1+ r01r12exp 2ikz1d1
rik= kziek- kzkei
() kziek+ kzkei
kzi= ± ei
- kxq ( )
2, i =0,1,2. (4)
kzc/w defines the field distribution along the z direction. Its real part can be
associated with a tilt of phase-fronts of the waves propagating in the media , and is often
discussed in the content of positive vs. negative refractive index materials (see also Refs. [8-12,
22-24]), while its imaginary part defines the wave attenuation or growth. The sign of the square
root in Eq. (4) is selected to enforce the causal energy propagation. For dielectrics excited in total
internal reflection geometry, as well as for metals and other media with
2]< 0, which do not
support propagating waves, the imaginary part of the square root should be always positive
regardless of the sign of e”. For other systems, the selection should enforce the wave decay in
systems with loss (e”>0) and the wave growth in materials with gain (e”<0) . This selection
of the sign can be achieved by the cut of the complex plane along the negative imaginary axis.
Although such cut of the complex plane is different from the commonly accepted cuts along
the positive  or negative [8-12,23] real axes, our simulations (Fig.1b) show that this is the
only solution guaranteeing the continuity of measurable parameters (such as reflectivity) under
the transition from a weak loss regime to a weak gain regime. Our sign selection is the only one
consistent with previous results on gain-assisted reflection enhancement, predictions of gain-
assisted SPP behavior [13-15,25], and the experimental data presented below. The implications
of selecting different signs of kz2 are shown in Fig.1b.
Note that active media excited above the angle of total internal reflection, as well as the
materials with e’<0 and e”<0 formally fall under negative index materials category. However,
|kz"| in this case is greater than
|kz'|, the “left handed” wave experiences very large
attenuation (in the presence of gain!!!), which in contrast to claims of Ref. , makes the
material unsuitable for superlenses and other proposed applications of NIMs [8-12].
In the limit of small plasmonic loss/gain, when the decay length of SPP, L, is much greater
than 2p/kx0’, and in the vicinity of q0, Eq. (3) can be simplified, revealing the physics behind the
gain-assisted plasmonic loss compensation:
R q ( )ª r01
0)2+ gi+ gr
x =c e2
0= r01(q0), and
d(q) = 4(kx- kx
The shape of R(q) is dominated by the Lorentzian term in Eq. (5). Its width is determined by the
propagation length of SPP,
L = 2 gi+ gr
which, in turn, is defined by the sum of the internal (or propagation) loss
and the radiation loss caused by SPP leakage into the prism,
gr= Im r01ei2kz
()/x . (8)
The radiation loss also leads to the shift of the extremum of the Lorentzian profile from its
resonant position kx0 ,
0= Re r01ei2kz
The term d in Eq. (5) results in the asymmetry of R(q).
The excellent agreement between exact Eq. (3), solutions of Maxwell equations using transfer
matrix method  and approximate Eqs. (5,6) for the 60 nm silver film are shown in Figs. 1,3.
The gain in the medium reduces internal loss gi of SPP, Eq. 7. In reasonably thick metallic
films (where gi>gr in the absence of gain) the “dip” in the reflectivity profile Rmin is reduced when
gain is first added to the system, reaching Rmin=0 at gi≈gr (Fig. 2a). With further increase of gain,
gi becomes smaller than gp, leading to an increase of Rmin. The resonant value of R is equal to
unity when internal loss is completely compensated by gain (gi=0) at
In the vicinity of gi=0, the reflectivity profile is dominated by the asymmetric term d. When gain
is increased to even higher values, gi becomes negative and the dip in the reflectivity profile
converts into a peak, consistent with predictions of Refs. [13,14]. The peak has a singularity
when the gain compensates total SPP loss (gi+gr=0). Past the singularity point, the system