Optical device including three-coupled quantum well structure having asymmetric multi-energy levels

An optical device comprising:

• an active layer comprising two outer barriers and a coupled quantum well between the two outer barriers,
• wherein the coupled quantum well comprises:
• a first quantum well layer;
• a second quantum well layer;
• a third quantum well layer;
• a first coupling barrier between the first quantum well layer and the second quantum well layer;
• and
• a second coupling barrier between the second quantum well layer and the third quantum well layer,
• wherein the second quantum well layer is between the first quantum well layer and the third quantum well layer,
• wherein an energy band gap of the second quantum well layer is less than an energy band gap of the first quantum well layer, an energy band gap of the third quantum well layer is equal to or less than the energy band gap of the second quantum well layer, and the energy band gap of the third quantum well layer is less than the energy band gap of the first quantum well layer, and
• wherein the first, second, and third quantum well layers comprise at least one of In1-xGaxAs and In1-x-yGaxAlyAs, the first and second coupling barriers comprise at least one of In1-x′-yGax′Aly′As (x′<x, y<y′) and In1-x′Gax′AszP1-z (x′<x) and an outer barrier comprises at least one of In1-x″-yGax″Aly″As (x″<x, y<y″) and In1-x′Gax′AszP1-z (x″<x′<x,z<z′), and 0<x,y,z<1, and
• wherein an amount of indium (In) in In1-xGaxAs or In1-x-yGaxAlyAs is smallest in the first quantum well layer among the first, second, and third quantum well layers and the amount of indium (In) In1-xGaxAs or In1-x-yGaxAlyAs is largest in the third quantum well layer among the first, second, and third quantum well layers.