A low optical feedback noise self-pulsating semiconductor laser is provided to improve operation reliability by suppressing optical feedback nose over whole temperature range. A self-pulsating semiconductor laser includes a bottom coating layer(103) formed on a semiconductor substrate(101). An active layer(105) is formed on the bottom coating layer. A first top coating layer(107) is formed on the active layer. The thickness of the first coating layer is equal to or larger than 220nm and is equal to or smaller than 450nm. A second top coating layer(109) is formed on the first top coating layer and has a mesa structure. A block layer includes layers formed on both sides of the mesa structure. The band-gap of the layers is larger than band-gap of the active layer.
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