| 摘要 |
PURPOSE:To obviate the generation of a transmission code error occurring in TM mode oscillation by executing the sufficient optical isolation enough to prevent a semiconductor laser from being affected by the reflected return light from a fiber. CONSTITUTION:This device has the DFB type semiconductor laser 1 of 1.3mum band added with a diffraction grating near the active layer so as to make single axis mode oscillation, a lens 2 which condenses the output light from the semiconductor laser 1 and couples this light to the fiber 4, and an optical isolator 3 for averting the reflection of a part of the output light of the semiconductor laser 1 at the input and output ends, etc., of the optical fiber 4 and the coupling of this light as return light to the semiconductor laser 1. The optical isolator 3 has a polarizing plate as a polarizer 11 on the incident side, has a polarizer plate as an analyzer 12 on the output side as well and is inserted with a Faraday rotating element as a polarized light rotating element 13 between the same. The angle theta formed by the TE polarization direction of the semiconductor laser 1 and the polarization angle of the polarizer 11 on the input side of the optical isolator 3 is specified to 45 deg., by which the generation of the error rate floor occurring in the TM mode oscillation is obviated in this case. |
