Optical integrated device

An optical integrated device, comprising:

• a GaAs substrate having a first region and a second region, said second region directly contacting said first region, said first and second regions being arranged along a prescribed axis in this order;
• a first cladding layer commonly disposed on said first region and said second region;
• an active layer disposed on said first cladding layer, said active layer including a first quantum well structure disposed in said first region and a second quantum well structure disposed in said second region and having a thickness substantially equal to a thickness of said first quantum well structure, said second quantum well structure including at least one well layer and two barrier layers puffing said well layer therebetween;
• and
• a second cladding layer disposed on said active layer,
• wherein said first quantum well structure has a band-gap energy smaller than 1.3 eV and said second quantum well structure has a band-gap energy greater than said band-gap energy of said first quantum well structure, and
• wherein an interface between said well layer and one of said barrier layers of said second quantum well structure is relaxed.