| 摘要 |
PURPOSE:To suppress the deterioration of SN ratio in a reception section after long- range transmission by wavelength-shaping a light source, in which the spectral width of a LD signal longitudinal-mode oscillating is widened, using some means or other. CONSTITUTION:A laser diode (LD)2 is optical-intensity modulated by a LD driving circuit 1 by an electric signal from a terminal A, and output beams from the laser diode are introduced to an optical filter 3. The passing wavelength of the optical filter 3 coincides with the oscillation wavelength of the laser diode (LD)2, and the same band as the spectral width of a light source required at a necessary transmission length is used as the passband of the filter 3. LD output beams inputted to the optical filter 3 are shaped (wavelength-shaped) on spectra, and outputted to a transmission line from a terminal B. The DC bias currents of the laser diode 2 are controlled by an automatic optical power control system and fed from a DC power supply circuit 4 by monitoring the back optical power of the laser diode 2. Accordingly, since even a light source single longitudinal-mode oscillating is difficult to transmit beams at a long range when oscillation spectra spreads, spread spectra are cut out by wavelength-shaping an output from the light source by the optical filter, thus propagating beams at the long range. |
