Abstract: An energy level due to isoelectronic impurity is provided in the forbidden band of one portion of an optical waveguide in a semiconductor material by doping said portion with an isoelectronic impurity. Upon excitation, a population inversion of electrons and holes is produced in the energy level and the valence band of said portion. When a light having a wavelength corresponding to the energy difference between the level of the isoelectronic impurity and the valence band is impinged on the portion, the incident light is amplified thereby. Since the optical energy of the output is smaller than the forbidden band gap, the attenuation in the waveguide is very small.

Abstract: Molecular beams of elements constituting a crystal and ion beams prepared by ionizing dopant atoms and/or dopant molecules are simultaneously and uniformly directed to a surface of a substrate and a region of the surface which is not required to be doped is simultaneously irradiated with electron beams. The ion beams directed to the regions not to be doped are coupled with the electron beam prior to and on arrival at the region and electrically neutralized. Thus, the crystal grows in some regions without the dopant and the crystal also grows in other regions with the dopant.