Semiconductor optical amplifier

A semiconductor optical amplifier comprising:

• a master source of input radiation;
• and
• an amplifying component optically coupled to said master source, said amplifying component comprising
• a semiconductor heterostructure that includes an active layer positioned between two cladding layers;
• an ohmic contact formed to at least one sublayer of said semiconductor heterostructure;
• and
• an input-output region for radiation to which it is transparent comprising at least one additional layer on at least one side of said heterostructure, said additional layer adjacent to said heterostructure comprising one or more sublayers having refractive indices nIORq and optical loss factors αIORq (cm−1), where q=1, 2, . . . , p are integers corresponding to said sublayers of said radiation input-output region sequentially counted from their boundaries with said heterostructure,
• wherein said semiconductor optical amplifier is adapted such that said input-output region receives input radiation at an angle of input, δ, said angle of said input radiation and said net loss factor αOR (cm−1) for said amplified radiation flowing from said active layer are such that 0 < arccos ⁢ ⁢ n eff n IOR1 ≤ arccos ⁢ ⁢ n eff ⁢ - ⁢ min n IOR1 , and ⁢ ⁢ n eff ⁢ - ⁢ min > n min ,
• wherein neff is the effective refractive index neff of said heterostructure in aggregate with said radiation input-output region, and nIOR1 is the refractive index of said radiation input-output region, neff-min is the minimum value of neff out of all possible neff for said multiplicity of heterostructures that are of practical interest, in aggregate with radiation input-output regions, and nmin is the smallest of said refractive indices of said layers of said heterostructure.