The most widely available commercial diode is based on the Fabry Perot design. In this design, mirrors are placed at either end of the diode facets and provide the means for standing wave formation. The design tends to produce a wide bandwidth. Tuning to a specific wavelength is done by varying the diode temperature and the current going to it. The performance of the basic Fabry Perot laser diode can be improved in various ways.
The Distributed Bragg Reflector (DBR) design replaces one of the mirrors on one end of the diode with a Bragg reflector. The Bragg reflector provides wavelength-selective feedback and lases on a single longitudinal mode. However, the mode is subject to change with changing temperature and current.
The distributed feedback (DFB) diode design, replaces one of the mirrors with a diffractive feedback grating. The grating spacing determines the wavelength that is reflected back into the active area. This is one of the most widely used designs.
Another variation of the Fabry Perot design are lasers that use an external cavity with grating and reflecting mirrors. There are two generally used configurations for the external-cavity diode laser grating and mirrors. They are the Littrow and Littman-Metcalf designs.