Provided are a laser diode generating passive mode locking that does not contain non-linear sector of an SA, and a method of creating an optical pulse using the same diode. The laser diode includes a DFB sector serving as a reflector and a gain sector. The gain sector is connected to the DFB sector and includes an as-cleaved facet formed at the end of the gain sector. When a current less than a threshold current is applied to the DFB sector to allow the DFB sector to operate as a reflector, passive mode locking occurs swiftly and therefore a sector of the SA is not required, which makes manufacturing simple. Also, it is possible to effectively extend a frequency variable region compared to using of the SA.