| Summary: | The effect of employing a midway isolator in a two-stage short-wavelength-band erbium-doped fiber amplifier (S-band EDFA) is demonstrated. The gain and the noise figure are improved for the system with a midway isolator as compared to the system without a midway isolator. These improvements are attributed to the suppression of the backward-propagating ASE. For an amplifier with a midway isolator, the small signal gain can reach approximately 30 dB, which is about 15 dB higher than in the system without the midway isolator, and the saturated power can be up to 12 dBm for an input power of 0 dBm. Noise figure reductions of about 1.2 to 2.8 dB are obtained in the input signal power region from -40 to -8 dBm with the midway isolator.
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