CSEM Scientific and Technical Report 2008

Plasmon Based All Optical Switch
R. Eckert, J. Dintinger • , T. Ebbesen • , R. P. Stanley
Surface plasmons can strongly confine electric fields to metal-dielectric interfaces. Nano-structuring the metal can result in extraordinary optical
transmission. J-aggregates are an efficient non-linear optical material. An optical switch with just a monolayer of J-aggregates on a nano-structured
metal which can be pumped using a CW laser has been developed.
Surface plasmons are electromagnetic surface waves which
strongly confine the light at a metal dielectric interface. They
play a key role in the extraordinary optical transmission (EOT)
seen by Ebbesen in 1998. Ebbesen and co-workers showed
that an array of subwavelength holes drilled in a metal film
makes the otherwise opaque film transparent [1] . The concept
of an ultrafast all–optical switch, which exploits EOT, has been
recently demonstrated [2] .
The all-optical switch consists of a metal film with a hole array
covered with J-aggregates (Figure 1). J-aggregates (JA) are
formed from cyanine molecules and have well-defined
absorption bands. The strong non-linearity of the J-aggregates
means that when they are optically pumped the refractive
index changes. This causes a shift in the peak transmission
wavelength at which the EOT occurs. Therefore one beam of
light (the probe beam) can be switched on and off by exciting
the JA with a second beam of light (pump beam). The JA
response time is 10 -12 seconds allowing very fast switching. As
surface plasmons are tightly confined to the surface they are
extremely sensitive to refractive index changes so switching
could be achieved at very low powers.
Figure 1: Concept of an all optical switch based on EOT
In the work by Ditinger et al. JA were randomly dispersed in a
thick polymer film [2] . Here CSEM achieves the same effect but
by using only a monolayer. The monolayer consists of a highly
ordered JA formed by a process developed at CSEM using a
template of self-assembled dendrimers. The remarkable
absorption efficiency of these monolayers and the fact that the
monolayer is very close to the metal allows optical switching
at lower intensities.
Figure 2: (a) Side profile of the optical switch – not to scale;
(b) Scanning electron microscope (SEM) image of the holes in the Au
on glass.
A side profile of a typical switch is shown in Figure 2a. It
consists of the following stack: a monolayer of the JA (