| 摘要 |
In optical amplifiers of the kind in which a so-called loop mirror is formed by connecting the ends of a loop of active optical fiber to a 3 dB coupler, improved signal-to-nois e ratios are obtained by coupling pump energy into the loop without passing through the 3 dB coupler. The input signal and amplified output signal may be conveyed to and from the coupler by way of isolators connected to input and output ports of the amplifier. Alternatively, they may be conveyed by way of a circulator. Automatic gain control may be provided by means of a fiber grating, or other such wavelength- selective device, which reflects part of t:he amplified signal having a selected wavelength back into true loop, to provide lasing. The amount of energy so reflected may be controlled by an attenuator.
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