Laser diodes are often used in optical communications, acting as the signal source or optical source. They are used in other laser type sources such as laser pointers and basic laser sources. They are also found in the Blu-ray players and barcode readers. 

Laser diodes are simply a p-n junction, just like a typical diode. They are made from a p-doped semiconductor crystal and an n-doped semiconductor crystal. They work on the concept of electron-hole recombination. Electron-hole recombination is the process where an electron and a hole are recombined. As they are recombined, they emit a photon with energy equal to the band gap energy level.

Laser diodes can have different colors, which also implies the wavelength of the light emitted from the diode is different. In order to get different wavelengths, the energy of the emitted photon needs to be different. The way the energy can be different is to vary the bandgap energy. By varying the band gap energy, it is feasible to change the color of the emitted photons or light because the energy of the emitted photons cannot exceed that of the bandgap.

When laser diodes were originally developed, they were homojunction devices. They required a lot of power to be able to lase. With such high power demands, it was necessary to pulse the power supplied to the device. If pulsing were not done, the semiconductor device would otherwise melt. Today they are built more efficiently such that lasing can occur with much less power required and have made practical for continuous use in different industries.