Patent ID: 8223612

Claim:
A grating comprising: a first diffraction grating having patterns formed for dividing a sub-beam with respect to a first optical recording medium having a first track pitch; and a second diffraction grating having patterns formed for dividing the sub-beam divided by the first diffraction grating into sub-beams with respect to a second optical recording medium having a second track pitch, wherein the second diffraction grating again diffracts light diffracted by the first diffraction grating to allow the diffracted light to be incident onto the second optical recording medium, wherein the sub-beam generated by the first diffraction grating is illuminated onto a land portion of the first optical recording medium having the first track pitch and a light reflected by the first optical recording medium is incident to a light detector, wherein the sub-beam generated by the second diffraction grating is illuminated onto a land portion of the second optical recording medium having the second track pitch and a light reflected by the second optical recording medium is incident to the light detector, and wherein diffraction patterns of the first and second gratings are formed on opposite sides of the grating and are substantially perpendicular to each other.