Quantum cascade laser

A quantum cascade laser comprising:

• a substrate having a principal surface including a first region and a second region arranged along a first axis;
• a stacked semiconductor layer disposed on the principal surface in the second region of the substrate, the stacked semiconductor layer having an end facet located on a boundary between the first region and the second region of the substrate, the stacked semiconductor layer including a core layer and a cladding layer disposed on the core layer, the core layer and the cladding layer being exposed at the end facet of the stacked semiconductor layer;
• and
• a distributed Bragg reflection structure disposed on the principal surface in the first region of the substrate, the distributed Bragg reflection structure including a semiconductor wall and a covering semiconductor wall that covers the end facet of the stacked semiconductor layer, the distributed Bragg reflection structure being optically coupled to the end facet of the stacked semiconductor layer,
• wherein the semiconductor wall and the covering semiconductor wall are made of a single semiconductor material,
• the semiconductor wall has a first side surface and a second side surface opposite to the first side surface,
• the first side surface and the second side surface of the semiconductor wall intersect the first axis and extend along a second axis intersecting the principal surface,
• the covering semiconductor wall provides an end facet that intersects the first axis and extends along the second axis, and
• the end facet provided by the covering semiconductor wall is located away from the first side surface and the second side surface of the semiconductor wall.