| 摘要 |
Distortion in an optical transmission system is significantly reduced by the use of two modulatable optical sources with non-ideal transfer functions of electric signal to light. The output of the first modulator is sampled and then delayed using an optical delay line. The sampled signal is compared with the input signal to generate an electrical error signal. This error signal is then used to modulate the second optical source. The output of this second modulatable optical source is then combined with the delayed output from the first optical source in a four-port optical coupler in such a way that the departures from linearity (which form the error signal) are removed on both outputs of the coupler, giving two optical outputs which possess a linear transfer function of electric signal to light through the entire system. The first optical source is chosen to have high power and low noise. The second source is chosen to be low power, moderate noise. The error signal generator and ratio of optical powers are chosen such that most of the final optical output comes from the first optical source, giving a linear, high power, low noise optical signal at the output of the system. Suitable modulatable sources include diode pumped Nd-YAG lasers with waveguide Mach-Zehnder modulators, and laser diodes. This method may be used in a modulating system and a transmission system for analog signals. |
