Light signal converter, light encoder, light decoder and CDMA communication

An optical signal encoder/decoder includes a grating waveguide having an identical number of uniform pitch gratings to the number of code chips of a binary phase optical code, the uniform pitch gratings being formed in a waveguide direction to reflect light of a predetermined wavelength. Here, adjacent gratings corresponding to a position at which the optical code value changes are disposed a spacing apart from each other to give a phase shift of (2m+1)pi/2 to the light, and the remaining adjacent gratings are disposed a spacing apart from each other to give a phase shift of npi to the light (m, n: integer).