ABSTRACT
A laser consisting of a distributed-Bragg-reflector (DBR) having a strong wavelength selection mechanism in its reflectivity due to periodicity in the refractive index of the waveguide or the resonator, is called as a DBR laser. A laser consisting of a periodic structure on an active region is called a distributed feedback (DFB) laser, in which periodicities in both refractive index and optical gain are the areas of concern. Semiconductor-based DBR lasers as well as DFB lasers have been investigated especially for light sources in wideband optical communications because of their superior single-mode operation characteristics. Simple DBR laser with relatively long cavity is not in practical use in present day; however, the concept of DBR laser is widely used in vertical cavity surface emitting lasers and wavelength tunable lasers. The DBR regions consist of low-loss optical waveguides with corrugations on or beneath the waveguides, which are made of compound crystals with an energy gap wider than that of the active layer.
