light limiter 31 the experiments were carried out to confirm the operation and effects for the light limiter 31 21 of these embodiments by use this experimental system in this experiment it is confirmed that the optical spectral band width is increased by the parametric amplification in the dispersion shifted optical fiber 32 by exchanging the optical surge peak power the inhibiting effect for the optical surge peak was examined by varying the fiber length of dispersion shifted optical fiber 32 and then the most suitable length thereof was examined in addition in order to quantitatively confirm the inhibiting effect the efficiency of the light limiter 31 21 of these embodiments was examined by measuring the attenuation characteristics and input output characteristics of the optical surge peak power these experimental results are shown in fig4 to 14 fig4 to 8 show that the optical spectral band width is increased by the parametric amplification in addition fig4 shows that the optical waveform output from the optical amplifier 44 before transmission in a dispersion shifted optical fiber 32 the light having a peak wavelength at 1556 nm is the amplified signal light and the optical spectra having a wide band excepting the peak wavelength of 1556 nm are the ase light fig5 to 7 show the optical spectrum after a transmission of 16 km.