A reflective phase compensator (RPC) based on thin film interference theory is constructed. It can be used to compensate the group delay (GD) of an extra narrow band pass filter that cannot be compatible with the 40 Gb/s system. The group delay for an extra-narrow band filter with bandwidth of 0.2 nm is reduced from about 10 ps to <0.76 ps by means of combination of a 50 GHz narrow band thin film filter and RPC filter.