Optical device including three coupled quantum well structure

An optical device comprising:

• a lower reflective layer;
• a first active layer on the lower reflective layer;
• a middle reflective layer on the first active layer;
• a second active layer on the middle reflective layer;
• and
• an upper reflective layer on the second active layer,
• wherein at least one of the first active layer and the second active layer comprises at least two outer barriers and at least one coupled quantum well, each of the at least one coupled quantum well is sandwiched between the at least two outer barriers,
• wherein each of the at least one coupled quantum well comprises at least three quantum well layers and at least two coupling barriers which are interposed between the at least three quantum well layers, and
• wherein the at least two coupling barriers have a potential energy which is higher than a ground level and is lower than energy levels of the at least two outer barriers.

An optical device comprising:

• a first active layer which comprises at least two outer barriers and at least one three quantum well structure;
• and
• a second active layer which comprises at least one single quantum well structure,
• wherein each of the at least one three quantum well structure comprises a first quantum well layer, a first coupling barrier, a second quantum well layer, a second coupling barrier, and a third quantum well layer,
• wherein each of the at least one single quantum well structure comprises a fourth quantum well layer interposed between the at least two outer barriers.