The introduction of the ITU-T G.694.1[3] frequency grid in 2002 has made it easier to integrate WDM with older but more standard SONET/SDH systems. WDM wavelengths are positioned in a grid having exactly 100 GHz (about 0.8 nm) spacing in optical frequency, with a reference frequency fixed at 193.10 THz (1,552.52 nm).[4] The main grid is placed inside the optical fiber amplifier bandwidth, but can be extended to wider bandwidths.