Patent ID: 7623147

Claim:
An optical scanning device, comprising: light emitting means; a resonance-type optical deflector configured to scan a scan surface reciprocally in a main-scan direction and configured to scanningly deflect a light beam emitted from said light emitting means; an imaging optical system configured to image the light beam scanningly deflected by a deflecting surface of said resonance-type optical deflector, upon a scan surface to be scanned; a synchronism detecting element configured to detect the light beam scanningly deflected by the deflecting surface of said resonance-type optical deflector, to determine an image-writing start position of the light beam on the scan surface in the main-scan direction; and first and second synchronism detecting optical elements configured to direct the light beam scanningly deflected by the deflecting surface of said resonance-type optical deflector to said synchronism detecting element, wherein each said synchronism detecting optical element is comprised of a prism having a plurality of reflecting surfaces being unified and having a power in a sub-scan direction, wherein, in a sub-scan section, said prism is configured to place the deflecting surface of said resonance-type optical deflector and a light-receiving surface of said synchronism detecting element in an optically conjugate relationship with each other, wherein said optical synchronism detecting optical elements are provided respectively at each of an image-writing starting side and an image-writing ending side, outside an effective image region within a main-scan section, wherein a first synchronous signal is generated based on a light beam passed through said first synchronism detecting optical element disposed at the image-writing starting side outside the effective image region, in the main-scan section scanned by the deflecting surface of said resonance-type optical deflector, wherein a second synchronous signal is generated based on a light beam passed through said second synchronism detecting optical element disposed at the image-writing ending side outside the effective image region, in the main-scan section scanned by the deflecting surface of said resonance-type optical deflector, and wherein the light beam passed through said first synchronism detecting optical element and the light beam passed through said second synchronism detecting optical element are incident on the same synchronism detecting element.