METHOD FOR CONTROL OF SPECTRUM WIDTH OF SEMICONDUCTOR LASER ELEMENT

摘要

PURPOSE:To keep the spectrum width of a semiconductor laser element at a small value steadily by detecting a field distribution in the semiconductor laser element by at least two beam detectors located closely to the semiconductor laser element so as to control the injected current into a phase control region. CONSTITUTION:A field distribution of a distribution feedback DFB region 2 is detected by detecting secondary diffraction beams emitted from the DFB region 2 to the above by first and second beam detectors 9 and 10 which are located closely to the upper part of the DFB region. The light intensity detected the first and second beam detectors 9 and 10 is inputted in a divider 11 where an intensity ratio is detected. The output of this divider 11 is synchronously detected by a lock-in amplifier 12 to obtain a control signal 13 about the injected current into a phase control region 3. According to this control signal 13, the current injected from a second bias circuit 7 to the phase control region 3 is controlled and the spectrum width of an edge plane high reflection type phase control DFB-LD 1 can be kept at the minimum value constantly.