Encoders and decoders using 3-chip superstructured fiber Bragg gratings(SSFBGs) are designed, in which every encoder/decoder grating consists of three subgratings. The grating has an uniform amplitude refractive index level along its length, in which discrete (0,π/2,π,3π/2) jumps in phase are written into the grating at the boundaries of adjacent spatial chips. Quaternary encoding and uncoding can provide codes with desirable auto and cross-correlation characteristics with which the three-chip, 240-Gchip/s all optical encoding and decoding is achieved. As much as we know, this is the highest single channel rate obtained from fiber Bragg grating (FBG) based OCDM system. The agreement between experimental and calculated results indicates the feasibility of multi-phase all optical encoding and decoding using SSFBG. And such all optical encoding and decoding is required in optical code division multiplexing (OCDM) systems and packet-switched networks.