| 摘要 |
In optical amplifiers of the kind in which a so-called loop mirror is form ed by connecting the ends of a loop of active optical fiber to a 3 dB coupler, improved signal-to-noise ratios are obtained by coupling pump energy into th e loop without passing through the 3 dB coupler. The input signal and amplifie d 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 ma y 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, whic h reflects part of the amplified signal having a selected wavelength back into the loop, to provide lasing. The amount of energy so reflected may be controlled by an attenuator.
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