  A brief review of optical and Raman studies on the Fe-based superconductors
is given, with special emphasis on the competing phenomenon in this system.
Optical investigations on ReFeAsO (Re=rare-earth element) and AFe$_2$As$_2$
(A=alkaline-earth metal) families provide clear evidence for the gap formation
in the broken symmetry states, including the partial gaps in the spin-density
wave states of parent compounds, and the pairing gaps in the superconducting
states for doped compounds. Especially, the superconducting gap has an s-wave
pairing lineshape in hole-doped BaFe$_2$As$_2$. Optical phonons at zone center
detected by Raman and infrared techniques are classified for several Fe-based
compounds. Related issues, such as the electron-phonon coupling and the effect
of spin-density wave and superconducting transitions on phonons, are also
discussed. Meanwhile, open questions including the \emph{T}-dependent
mid-infrared peak at 0.6-0.7 eV, electronic correlation, and the
similarities/differences between high-\Tc cuprates and Fe-based superconductors
are also briefly discussed. Important results from other experimental probes
are compared with optical data to better understand the spin-density wave
properties, the superconductivity, and the multi-band character in Fe-based
compounds.
