PURPOSE: To impart high linearity to the amplification gain characteristics of an optical fiber amplifier over a wide dynamic range of input signal amplitude by connecting a plurality of Er-doped optical fibers having different doping concentrations to form an optical amplifying element.
CONSTITUTION: In the optical fiber amplifier 11, a plurality of optical fibers 12a, 12b,...12n doped with Er at different concentrations are connected in series through joints 13a, 13b,... between a WDM coupler 3a and an isolator 2b. An optical pumping means 7 is connected with the WDM coupler 3a. The Er-doped optical fibers 12a-12n are arranged sequentially in the increasing order of doping concentration of Er from the input end toward the output end of the amplifier 11. This constitution brings about approximately ideal pumping state of pumping light in the longitudinal direction of optical amplifying element and widens freedom remarkably in the setting of optical fiber.
MIYAMOTO KATSUYUKI
ORITO TOSHIHIRO
