Light emitting element and optical device

A near-infrared light-emitting element on a III-V group compound semiconductor substrate, comprising:

• an active layer having a multi-quantum well (MQW) structure, the multi-quantum well structure including layered type 2 pairs;
• and
• an upper cladding layer and a lower cladding layer disposed on opposite sides of the active layer, the upper cladding layer being more distant from the substrate than the lower cladding layer,
• wherein the type 2 pairs include a plurality of pair thickness groups having different thicknesses, including a first pair thickness group and a second pair thickness group,
• the first pair thickness group includes 10 pairs or more and 100 pairs or less, each monolayer of the pairs having a thickness of 1.5 nm or more and less than 3.5 nm,
• the second pair thickness group includes 10 pairs or more and 100 pairs or less, each monolayer of the pairs having a thickness of the minimum thickness (a second group minimum thickness) or more and 7 nm or less, the minimum thickness being larger than the maximum monolayer thickness 3.5 nm of the first pair thickness group, and
• the light-emitting element has an oscillation peak wavelength of 1.7 μm or more and 3.0 μm or less.