| 摘要 |
We have found that it is possible to make a multistage optical fiber amplifier having a substantially flat gain band of spectral width of 40 nm or more, excellent noise figure (e.g.,<4 dB) and output power. Such amplifiers can advantageously be used, for instance, in multichannel WDM systems and analog CATV systems. A significant aspect of the amplifier is the provision of an optical loss element (exemplarily a multi-grating optical fiber filter) that provides, at least at one wavelength in the gain band, an attenuation of more than +E,ovs G+EE /3 dB, where +E,ovs G+EE is the average amplifier gain (in dB) in the gain band. A further significant aspect of the amplifier is the use of relatively longer amplifier fibers, which facilitates attainment of high output power and low noise figure. Exemplarily, the amplifier is a 2-stage amplifier comprising silica-based Er-doped amplifier fiber, with three-Gaussian filters between the stages. By way of further example, the amplifier has 3 or more stages, with the loss elements selected such that the loss, in absolute value, is greater than +E,ovs G+EE , and the gain bandwidth of the amplifier is 80 nm or more.
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