Abstract: A control method of speeding up light emission of a laser diode includes the following steps. First step is to boost the supply voltage from a first voltage potential to a second voltage potential before an emission period. At the beginning of the emission period, a current path conducts through the laser diode and a current source. One terminal of the laser diode is coupled to the current source, and the other terminal of the laser diode connects the supply voltage. When the current path is being conducted, the current source is in the transient state and provides a transient driving current; and the voltage difference between the two terminals of the laser diode is generated in response to the second voltage potential and is related to the transient driving current. When the transient driving current is larger than a threshold, the laser diode emits light.