| 摘要 |
A multiple stage optical amplifier includes a Raman fiber amplifier first stage coupled to a rare earth doped fiber amplifier which provides a second amplifier stage. Pump signals with two wavelengths are injected into the Raman amplifier and propagate in a direction opposite to input signals. Since the Raman amplifier does not completely absorb the pump signals, a separate optical path is provided to apply the excess pump signal to the second stage fiber amplifier to pump it. The gain and banwidth characteristics of the Raman amplifier are determined by the spectral properties of the pump signal and gain bandwidth characteristic of the Raman amplifier can be selected by appropriately selecting the wavelengths of the pump signals. In one embodiment, the pump signals are selected so that the first stage Raman amplifier has a relatively low noise characteristic. The second stage fiber amplifier, on the other hand, is designed to have a relatively high power characteristic. Furthermore, to increase the gain bandwidth of the entire optical amplifier, the gain bandwidth characteristics of the first and second amplifier stages are selected to overlap rather than coincide. |
