A laser module for transmitting/receiving digital signals using a laser diode as an optical source is disclosed. The input end of the laser module is provided with a low pass filter, such that the low pass filter makes a 3 dB bandwidth of frequency response transferred from the input pins to the laser diode to be equal or less than the on-state relaxation oscillation frequency of the laser diode, wherein the overshoot is minimized by adjusting a relative amount of the frequency component input to the laser diode.