Recently, a wavelength division multi/demultiplexing system has been viewed with keen interest because it is possible to increase the transmission capacity and system flexibility. An arrayed waveguide grating (AWG) type of Multi/demultiplexer which is one of the key components to realize such a system has been developed by using Planar Lightwave Circuits (PLCs). Newly designed optical circuits have been incorporated into the AWG to control the center wavelength and to expand the pass band width. The 3 dB pass band width is 1.4 times that of a conventional AWG. It is confirmed that the newly developed AWG has low polarization dependence, low temperature dependence and high reliability.