DFB lasers: From Research to Development, and Further

Among various single-mode lasers proposed so far, distributed Bragg reflector (DBR) lasers and distributed feedback (DFB) lasers were spotlighted as the most practical light sources for long-distance and large-capacity optical transmission. Selections of appropriated lasers were made for the applications depending on the intrinsic performances, such as DFB lasers with wavelength stability and DBR lasers with wavelength tunability. As for the applications of undersea cable systems, high reliability was required, and further devised structures were necessary to reach to a λ/4-shifted DFB laser. The unique fabrication method of λ/4-shifted grating was developed to realize quite wavelength-stable single-mode light sources which were actually installed to TPC-4 and other coherent optical systems.