| 摘要 |
PURPOSE: To increase capacity, to accelerate speed and to extend a distance by minimizing the light intensity of a duobinary signal corresponding to a central value and modulating the light intensity while inverting a phase corresponding to the other two values with the same light intensity. CONSTITUTION: A binary digital data signal is converted into the duobinary signal by a code converting circuit 80. The duobinary signal of three values (0, 1 and 2) is branched into two parts, one part is inputted to an inverter circuit 11 so as to generate a duobinary signal (-1, 0 and 1) without two DC components of the same, amplitude and mutually inverted phases, and a voltage proportional to that signal is respectively impressed to electrodes 74a and 74b of an MZ type light intensity modulator 70. The light intensity of output light from a semiconductor laser 76 is modulated corresponding to these two duobinary signals of the mutually inverted phases, and that light intensity converted signal is transmitted to an optical fiber transmission line 77. When modulating the light intensity while using the duobinary signal of three values (0, 1 and 2), a bias voltage is adjusted so that the intensity of output light can be minimized in comparison with its central value (1). |
