OPTICAL TRANSMISSION SYSTEM OPERATING METHOD, LASER OUTPUT POWER CONTROL METHOD, AND LASER CONTROL CIRCUIT

摘要

PROBLEM TO BE SOLVED: To provide an optical link control method and equipment by controlling a bias current which prevents errors caused by clipping at the time of a low temperature. SOLUTION: A control circuit to an injection laser supplies a pre-bias current for preventing errors in a laser output caused by clipping. An analog modulation signal is applied directly to a laser diode 10, and laser receives the sum of a feedback current Ifb and a current source Io as a pre-bias current Ipd. A monitor photodiode 14 detects the laser light output, and supplies a current Idet. The feedback current corresponds to the change of Idet, adjusts the laser pre-bias current in order to maintain Idet equal to a present value, and keeps effectively the average output power of laser constant. By preventing Ipb from becoming less than Imin, the errors and the distortions which are caused by clipping can be avoided.