A vertical cavity surface emitting laser (VCSEL) is a specialized laser diode that promises to revolutionize fiber optic communications by improving efficiency and increasing data speed. The acronym VCSEL is pronounced 'vixel.'
Older laser diodes, called edge-emitting diodes, emit coherent light or infrared (IR) energy parallel to the boundaries between the semiconductor layers. The VCSEL emits its coherent energy perpendicular to the boundaries between the layers. The vertical in VCSEL arises from the fact that laser diodes are typically diagrammed showing the boundaries as horizontal planes, so the output of the VCSEL appears to emerge vertically in these drawings.
VCSELs have been constructed that emit energy at 850 nanometers (nm) and 1300 nm. These wavelengths correspond to energy in the near infrared (IR) portion of the electromagnetic spectrum. (The longest visible red is at approximately 770 nm.) Optical fibers transmit energy most efficiently at wavelengths around 1550 nm. Materials used to manufacture VCSELs include gallium arsenide (GaAs), aluminum gallium arsenide (AlGaAs), and indium gallium arsenide nitride (InGaAsN).
The VCSEL has several advantages over edge-emitting diodes. The VCSEL is cheaper to manufacture in quantity, is easier to test, and is more efficient. In addition, the VCSEL requires less electrical current to produce a given coherent energy output. The VCSEL emits a narrow, more nearly circular beam than traditional edge emitters; this makes it easier to get the energy from the device into an optical fiber. The main challenge facing engineers today is the development of a high-power VCSEL device with an emission wavelength of 1550 nm.