An overview on S-band erbium-doped fiber amplifiers

An erbium-doped fiber amplifier (EDFA) for S-band signal amplification is designed by using a depressed cladding erbium-doped fiber (DC-EDF). The fiber's characteristics are described in terms of the effects of the fiber spooling diameter on the amplifier's performance. In this experiment, the spooling diameter required for optimum amplifier gain was around 5–7 cm. By using a typical two-stage configuration (with a 27 m long DC-EDF and a 260 mW pump laser power), the maximum small signal gain obtained was about 32 dB. Yet, by employing a double pass amplifier configuration with a shorter DC-EDF length and a lower pump laser power (15 m and 135 mW, respectively), a similar maximum small signal gain of approximately 30 dB was achieved. This improvement in gain characteristics however, incurred an increased noise figure penalty of about 1 dB in comparison to single-pass amplifier configurations. In order to reduce the amplifier's noise figure while maintaining its high gain, a partial double-pass S-band EDFA configuration was introduced. This configuration provides a high 26.9 dB gain and an improved noise figure comparable to a single pass configuration. Gain clamping in S-band EDFAs are also demonstrated by utilizing a fiber Bragg grating to form an oscillating laser at around 1530 nm. This technique enables good gain clamping with a gain variation of less than 1 dB.