Tracking control method and apparatus and image capture method and apparatus for holographic information recording medium

An apparatus for controlling tracking of an information recording medium including an area for storing a holographic image and an area for storing servo spots formed discretely and at a predetermined interval, the apparatus comprising:

• a photodetection unit obtaining an RF-SUM signal by adding all detection signals of a quadrant photodetection devices for detecting the servo spots;
• and
• a servo control unit monitoring whether the RF-SUM signal exceeds a predetermined level and performing tracking control during a section wherein the RF-SUM signal exceeds the predetermined level.

An apparatus for controlling tracking of an information recording medium including an area for storing a holographic image and an area for storing servo spots formed discretely and at a predetermined interval, the apparatus comprising:

• a photodetection unit obtaining a shuttering signal by subtracting a sum of values of signals of third and fourth photodetection devices from a sum of values of signals of first and second photodetection devices, in a direction in which the information recording medium rotates, from detection signals of a quadrant photodetector for detecting the servo spots;
• and
• a servo control unit monitoring whether the shuttering signal belongs to a predetermined section and performing tracking control during a period when the shuttering signal belongs to the predetermined section.

An apparatus for capturing a holographic image from an information recording medium including an area for storing a holographic image and an area for storing servo spots formed discretely and at a predetermined interval, the apparatus comprising:

• a photodetection unit obtaining a shuttering signal by subtracting a sum of values of signals of third and fourth photodetection devices from a sum of values of signals of first and second photodetection devices, in a direction in which the information recording medium rotates, from detection signals of a quadrant photodetector for detecting the servo spots;
• and
• a shuttering control unit monitoring whether the shuttering signal reaches a zero level and instructing to capture the image stored in the information recording medium at a time point when the shuttering signal reaches the zero level.