Editing Laser diode (section)

=== Distributed Bragg reflector lasers ===
A [[distributed Bragg reflector laser]] (DBR) is a type of single-frequency laser diode.<ref name="hecht">{{cite book|last1=Hecht|first1=Jeff|title=The Laser Guidebook|date=1992|publisher=McGraw-Hill, Inc.|location=New York|isbn=0-07-027738-9|page=317|edition=Second}}</ref> It is characterized by an [[optical cavity]] consisting of an electrically or optically pumped gain region between two mirrors to provide feedback. One of the mirrors is a broadband reflector and the other mirror is wavelength selective so that gain is favored on a single longitudinal mode, resulting in lasing at a single resonant frequency. The broadband mirror is usually coated with a low-reflectivity coating to allow emission. The wavelength-selective mirror is a periodically structured [[diffraction grating]] with high reflectivity. The diffraction grating is within a non-pumped, or passive, region of the cavity. A DBR laser is a monolithic single-chip device with the grating etched into the semiconductor. DBR lasers can be edge-emitting lasers or [[vertical-cavity surface-emitting laser|VCSELs]]. Alternative hybrid architectures that share the same topology include extended-cavity diode lasers and volume Bragg grating lasers, but these are not properly called DBR lasers.