Low-noise properties of squeezed light in transmission chains formed from nonlinear alternating attenuators and amplifiers.

An idealized model of an optical communication link in which identical sections of nonlinear attenuating 6ber alternate with identical amplifiers is considered. Signal-to-noise ratios of chains of these elements for input squeezed and coherent light have been numerically evaluated. It is found that input squeezed light and nonlinear attenuators improve the signal-to-noise ratios with respect to coherent inputs and linear chains. In the case of three-photon attenuators, the noise and signalto-noise ratio remain practically constant from certain elements of the chain. Moreover, the inhuence of the attenuation coelicient and the input mean photon number on the signal-to-noise ratios was considered, as well as chains with nonlinear ampli6ers and chains in which the amplifier gain does not exactly compensate for the Sber attenuation.