Characteristics
Because VCSELs emit from the top surface of the chip, they can be tested on-wafer, before they are cleaved into individual devices. This reduces the fabrication cost of the devices. It also allows VCSELs to be built not only in one-dimensional, but also in two-dimensional arrays.
The larger output aperture of VCSELs, compared to most edge-emitting lasers, produces a lower divergence angle of the output beam, and makes possible high coupling efficiency with optical fibers.
The high reflectivity mirrors, compared to most edge-emitting lasers, reduce the threshold current of VCSELs, resulting in low power consumption. However, as yet, VCSELs have lower emission power compared to edge-emitting lasers. The low threshold current also permits high intrinsic modulation bandwidths in VCSELs.
The wavelength of VCSELs may be tuned, within the gain band of the active region, by adjusting the thickness of the reflector layers.
While early VCSELs emitted in multiple longitudinal modes or in filament modes, single-mode VCSELs are now common.
Read more about this topic: Vertical-cavity Surface-emitting Laser