| 摘要 |
PURPOSE:To hold an extinction ratio optimum without loss of signal light for variation of the ambient temperature by using the first waveguide output light of a waveguide-type optical modulator is a transmission signal light and detecting variation of the output of the second waveguide output light to control a bias point of the modulator. CONSTITUTION:An output light 2 of a transmission light source 1 is made incident on a waveguide-type optical modulator 3. A waveguide output 4 of the modulator 3 has the amplitude modulated by a modulating signal 5 and is used as the transmission signal. A waveguide output 6 of the modulator 3 is made incident on an optical fiber 7 and is led to a photodetector 8. An average output voltage 9 of the detector 8 is compared with a reference signal 11 by a comparator 10, and an output error signal 12 passes a modulator bias control circuit 13 to become a feedback signal 14, and the bias level of the modulator 3 is set to an optimum value. Thus, an extinction ratio is held optimum without loss of the signal light for variation of the ambient temperature. |
