An optical packet header identifier having a simplified configuration and being superior in reliability, stability, and economical efficiency, an optical router incorporating the identifier therein, and a routing method using the optical router are provided. The optical packet header identifier includes an optical waveguide, optical focusing elements, and a photo receiver. Tilted gratings for diffracting an incident optical beam and emitting the beams as diffracted optical beams to the outside of the waveguide are formed within the optical waveguide. The tilted gratings are not formed uniformly in a longitudinal direction of a core of the optical waveguide, but are arranged at intervals. The length of a portion containing a set of gratings and the length of a portion containing no gratings can be defined in increments of length "L". "L" equals to the spatial length which 1 bit in an optical signal occupies.