Principle and characteristic of super-structured fiber Bragg grating (SSFBG) en/decoder based on equivalent phase shift (EPS) are analyzed, and double band en/decoder is proposed. The +1st and +3rd spectra are successfully linked by designing grating structure with unchanging grating length. The new en/decoder well inherits the advantage of traditional equivalent phase shift, such as flexible design, low manufacture precision and strong wavelength-division-multiplex (WDM) compatible ability. The theoretical and experimental data indicate that double band en/decoder meliorates the en/decoder performance of coherent optical code division multiplex access (OCDMA) system by 3 dB. The essence is the improvement of phase information in unit grating length.