[OPTICAL REVIEW Vol. 6, No. 4 (1999) 321-329]
Modulation Frequency Characteristics of Erbium-Doped Fiber Amplifier
Nobuaki TAKAHASHI, Haruaki AKASHI and Tai SASAKI
Department of Applied Physics, National Defense Academy, 1-10-20, Hashirimizu, Yokosuka, Kanagawa, 239-8686 Japan
(Received September 4, 1998; Accepted February 24, 1999)
The modulation frequency characteristics of an erbium-doped fiber amplifier are analyzed theoretically and experimentally for various values of modulation frequency. The theoretical predictions by the approximate equations in the low and high frequency modulation and that by the Runge-Kutta method for all modulation frequencies are in good agreement with the experimental results. In the low frequency modulation, the population inversion is depleted because of the saturation effect due to the instantaneous power of the incident light, and a distorted output is obtained without phase delay. In the high frequency modulation, the linear amplification is obtained with the gain depletion determined by the time averaged power of the incident signal. In the intermediate frequency modulation, the highly distorted output is obtained with phase delay.
Key words : optical fiber, fiber amplifier, erbium-doped fiber, modulation-frequency characteristics, gain saturation