| 摘要 |
PURPOSE:To attain stable and high quality optical transmission by using a cross type optical modulator to modulate a laser diode optical output, detecting one optical output of the modulator output and using the optical output so as to control the optical modulator. CONSTITUTION:The optical output from the laser diode LD1 is led to an input terminal (a) of the cross type optical modulator 3 through a lens 2. When a signal is fed to control electrodes e1, e2 of the modulator 3, the modulated light is outputted to output terminals (b, c). A transmission optical output is extracted from an optical fiber 4 by using a photodetector 5 for the output light from the terminal (b). On the other hand, the output of the terminal (c) is inputted to a control circuit 6, from which the bias current of the diode LD1 is controlled. The modulator 3 consists of LiNbO3 or the like, the distribution factor of the light two waveguides by varying the coupling constant of the waveguide while applying the signal input and the sum of the optical outputs of the two waveguides is made almost constant. Thus, the transmission characteristic is made stable. |
