| 摘要 |
PURPOSE:To easily superimpose a monitor signal onto a signal light by injecting a current including a modulation signal independently to part of an electrode onto which an electric field of an optical resonator of a multi-electrode distribu tion feedback type semiconductor laser is concentrated and part of the electrode onto which the electric field is not concentrated. CONSTITUTION:When a signal via a main modulation circuit 28 is superimposed onto a current injected to a center electrode 12 to which an electric field of an optical resonator of a three electrode distribution feedback type semiconductor laser (DFB-LD) 20 is most concentrated, an optical output is subject to angular modulation in response to a main signal. On the other hand, when the monitor signal is superimposed to an injection current to side electrodes 10, 14 onto which the electric field is not concentrated, the optical output is subject to intensity modulation and a monitor light is easily superimposed on the signal light. |
