Patent ID: 6538247
Filing Date: 2003-03-25
Classification: G02B

Abstract:
A method of detecting a positional relationship of a plurality of beam spots for a multi-beam imaging apparatus, the imaging apparatus including a light source emitting a beam, a beam splitter that receives the beam emitted by the light source and divides the beam into a plurality of beams, a deflecting system that deflects the plurality of beams to scan, and an imaging optical system that converges the plurality of scanning beams on a surface to form the plurality of beam spots, said method comprising:providing a phase filter between the light source and the beam splitter, the phase filter being configured to divide a cross section of the beam directed from the light source to the beam splitter into a plurality of areas, light fluxes passed through adjoining two of the plurality of areas of the phase filter having an optical path difference of half a wavelength, at least a dark line being formed in each beam spot due to the phase difference of said adjoining two; and detecting positional relationship of dark lines respectively formed on the plurality of beam spots to determine a positional relationship between the plurality of beam spots.