I. INTRODUCTION
Various two-dimensional nanostructures have been
synthesized from different materials. Graphene is the newest
member in two-dimensional (2D) carrier systems, which have
shown a spectrum of fascinating new physics and consequently
draw much attention [1,2]. Graphene is a single layer of
honeycomb carbon lattice, the atomic sheet of graphite that
represents the ultimate 2D material. Graphene was extensively
studied on electrical transport but not much on optical
investigations. Such an optical study is important to understand
the electronic structures and excited-state properties of lowdimensional
materials, as was demonstrated in carbon
nanotubes [3]. Especially, Infrared (IR) spectroscopy was
shown to reveal the Landau Level (LL) spectrum when
combined with a magnetic field [4,5]. We could also envision
new possibilities of graphene based optoelectronic sensors and
their application to nanoelectromechanical systems (NEMS).
Recently, temperature dependence of graphene resistivity was
studied [6-8]. Optical properties of graphene were also studied
for the optoelectronic applications but were limited to the gate
triggered optical transitions [9,10]. However, investigations of
IR optical properties of graphene are still missing and devices
based on these nanostructures have not been created yet.