Four-Region Diffraction Grating for Stable Tracking Error Detection

The diffraction grating is divided into four distinct regions (first, second, third, and fourth regions) with different phase configurations. This segmentation allows each region to contribute differently to the diffracted beams, enabling the system to handle multiple guide groove pitches effectively while maintaining stable tracking error detection through the balanced asymmetric intensity distribution.

Each of the four regions in the diffraction grating is assigned a specific phase configuration tailored to its position and function. The first and fourth regions have one phase relationship while the second and third regions have another, creating localized phase characteristics that collectively produce symmetric spot shapes with controlled asymmetric intensity distribution, thereby maintaining accurate phase difference detection.

The patent intentionally introduces asymmetric intensity distribution through the four-region phase configuration, but in a controlled manner. The asymmetric distribution is balanced between the four regions, which allows the in-line DPP method to function while preventing the phase shifts that would otherwise degrade tracking error signal accuracy. This controlled asymmetry enables both method simplicity and measurement precision.