InGaAs/AlGaAs semiconductor lasers come in three
types: VCSELs and two types of EELs. The VCSEL, as
its name implies, emits vertically, normal to the plane
of the device, owing to cavity mirrors grown within
the epitaxial material itself. The VCSEL’s circular beam
has a numerical aperture (NA) of roughly 0.2, or a full
angle of approximately 25 degrees.
