| 摘要 |
PURPOSE:To obtain a direct light amplifier compensating the lowering of the gain for a low frequency signal. CONSTITUTION:An optical signal is branched in an optical branching device 17 and the one of these branched signal is converted into current by a pin photo diode 18. This current is converted into a voltage signal in a current voltage conversion circuit 19 and the signal component of a low frequency area is extracted by a low-pass filter 21. The output of this low-pass filter is inputted in an exciting light source driving circuit 15 after the output is amplified in an amplifier 22. At this place, exciting current where current amount is increased corresponding to the amplitude of the component of the low frequency signal extracted in the low-pass filter is generated and an exciting light source 16 is driven. The exciting light source 16 supplies exciting light where light intensity is increased according to the amplitude of the component of the low frequency signal to an erbium doped fiber 12 via a wavelength division multiple coupler 13. The other optical signal branched in the optical branching device 17 is amplified by this exciting light in the erbium doped fiber 12. Thus, a light direct amplifier where the lowering of the amplifier gain in the low-pass of the erbium dope fiber is compensated by appearances can be realized. |
