| 摘要 |
PURPOSE:To securely hold a photodetecting element even if a fault occurs to an optical control function by providing an optical variable attenuator with a bias electrode which is applied with a specific voltage from a stable power source supplying a stable voltage at all times irrelevantly to the optical control function. CONSTITUTION:The bias electrode 3 other than a modulation electrode 13 is provided between branch paths of an optical waveguide 12 and ground electrodes 3E are formed on both sides of both the branch paths across the branch paths. Then the stable power source S which supplies the stable voltage Vs at all times irrelevantly to the voltage applied to the electrode of the optical variable attenuator 1 such as a battery is connected between both the electrodes 3 and 3E to supply the specific bias voltage Vs at all times. Namely, each of the branch paths is supplied with a necessary electric field at all times to supply the specific bias voltage Vs. Thus, an increase in light output is evaded even when the optical control function gets out of order by setting the bias point of light output characteristics so that the output is a nearly minimum output when V=0, thereby holding the photodetecting element stable. |
