A method for generating an optical pulse train includes generating a source optical pulse train having a predetermined pulse period; optically combining a plurality of uniform pitch grating waveguides having a substantially identical Bragg wavelength and /4-phase-shift waveguides in an alternating sequence so as to form a multiple /4-phase-shift grating waveguide; inputting the source optical pulse train from one end of the multiple /4-phase-shifted grating waveguide; and extracting reflected optical pulses by the plurality of uniform pitch grating waveguides from the one end of the multiple /4-phase-shifted grating waveguide.