A laser diode capable of reducing a radiating angle .theta..perp. in the
vertical direction, an optical pickup device, an optical disk apparatus,
and optical communications equipment, all equipped with the laser diode
which increases optical coupling efficiency. It has a first cladding layer
of the first conductive type formed on a substrate, with an active layer
on top of the first cladding layer and a second cladding layer of the
second conductive type on top of the active layer. In at least the first
or second cladding layer, it is formed of at least one optical guide layer
having a higher refractive index than the first or second cladding layer
and operating to expand a beam waist in the waveguide. This operation
contributes to widening a region in which to shut up light, enabling a
radiating angle .theta..perp. in the vertical direction to be reduced.
