Double Heterostructure Diode Laser
A double heterostructure diode laser is created when low bandgap material is fitted between two layers of high bandgap material. A bandgap is an energy range in a solid object without and electron states. Junctions between bandgap materials are referred to as “heterostructures.” In a double heterostructure diode laser, the active region exists in the thin middle layer, allowing more electron-hole pairs to aid in light amplification.

Quantum Well Lasers
A quantum well is created when the middle layer is extremely thin, quantizing the vertical variation of the electron’s wavefunction. Quantum well diode lasers have a good efficiency because the abrupt edge in the quantum well system concentrates electrons in energy states that contribute to laser action.

Quantum Cascade Diode Lasers
A quantum cascade laser utilizes the difference in quantum energy levels for the laser transition instead of using the bandgap, allowing for long and easily tuned wavelengths.

Separate Confinement Heterostructure Lasers
A separate confinement hetereostructure laser is made when two additional layers are added on the outside of a quantum well laser’s original three layers. The middle layer in a quantum well laser can be too thin to confine light, so additional layers with a low refractive index have to be added in order to effectively confine light.

Distributed Feedback Lasers
A distributed feedback laser has a diffraction grating etched near the p-n junction in the diode to stabilize the wavelength. The grating is essentially an optical filter which causes a single wavelength to bounce back to the gain region and laser. In this system, facet reflection is no longer needed, so at least one facet in a distributed feedback laser is anti-reflection coated. These lasers have stable wavelengths because the wavelength is determined by the pitch of the grating.

For more detailed information on laser diode types, consult the EDU Photonics Overview of Commercial Laser Diode Devices.

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