InGaAsP Laser with Reduced Beam Divergence

The light emitted from the facet of a semiconductor laser diverges due to diffraction, and this limits the coupling efficiency of the light into a single mode fiber. In order to reduce the beam divergence in an InP/GaAsP laser, a section of semi-insulating Fe-doped InP is formed adjacent to the active region. The semi-insulating region has nearly the same refractive index as the InGaAsP active region, and when the emitted light travels through the semi-insulating region it reaches the laser facet with a spot size large enough to reduce diffraction.