| 摘要 |
<p>An optical communication link having an overall linear transfer characteristic and high dynamic range suitable for transmitting analog signals. The link includes an optical intensity modulator, such as a Mach-Zehnder modulator, biased to a low-bias point to reduce noise, and a detector that performs optical heterodyning to recover a transmitted modulating signal. Heterodyning produces a beat frequency signal and sidebands that contain the same information as the modulating signal, but without second-harmonic distortion components. Use of the low-bias point is known to reduce noise and increase dynamic range, but only at the expense of second-harmonic distortion because the modulator output is a function of the square of the modulating signal. Although second harmonics can be filtered out, the bandwidth of the modulating signal is then limited to less than an octave. In the communication link of the invention, heterodyning produces sidebands that vary with the square root of the modulator transmission characteristic. Therefore, the overall transfer characteristic is substantially linear, second harmonic distortion is eliminated, and the modulating signal can extend over a multi-octave bandwidth.</p> |
