A superluminescent diode having emission layers which emit different wavelengths of light disposed side-by-side whereby light emitting in a first direction from an emission layer having a longer wavelength than an adjacent layer in the first direction is not absorbed. Thus, light of the different wavelengths is represented in an output spectra in the first direction at a point beyond the adjacent layer. A semiconductor optical amplifier is formed by creating a symmetrical structure in which the longest wavelength material is grown in the center and the shortest wavelength material is grown near the facets.