  Polarized far-infrared (FIR) spectroscopic measurements and FIR
magneto-optical studies were performed on the inorganic spin-Peierls compound
CuGeO_3. An absorption line, which was found at 98 cm$^{-1}$ in the dimerized
phase (D phase), was assigned to a folded phonon mode of B$_{3u}$ symmetry. The
splitting of the folded mode into two components in the incommensurate phase
(IC phase) has been observed for the first time. A new broad absorption
centered at 63 cm$^{-1}$ was observed only in the ${\bf E}\parallel b$ axis
polarization, which was assigned to a magnetic excitation from singlet ground
state to a continuum state.
