A polarization insensitive semiconductor optical amplifier (SOA) is provided. The SOA includes an active waveguide, a passive waveguide, and a taper coupler for coupling optical energy from the passive waveguide into the active waveguide, wherein the taper coupler has width W varying relative to position along a main axis z of propagation of the SOA in proportion to the minimum value of 1/C.sub.TE 01(z) 1/C.sub.TM 01(z), where C.sub.TE 01(z) represents the coefficient of energy coupling between a fundamental mode and a first order mode for the transverse electric polarization as a function of the position z, and C.sub.TM 01(z) represents the coefficient of energy coupling between a fundamental mode and a first order mode for the transverse magnetic polarization as a function of the position z.