Patent ID: 7148468

Claim:
A mirror angle measurement apparatus for a Holographic Digital Data Storage (HDDS) system, the HDDS system causing a reference beam to be incident on a holographic medium to reproduce digital data recorded on the holographic medium, the mirror angle measurement apparatus comprising: a first mirror having a first reflecting surface on a front surface thereof by which the reference beam is reflected toward the holographic medium and a second reflecting surface on a back surface thereof by which a control beam is reflected to adjust an incident angle of the reference beam while the reference beam is incident on the holographic medium; a transmission unit for providing the control beam to the second reflecting surface; a second mirror, in case the control beam provided from the transmission unit is reflected by the second reflecting surface toward the second mirror, for returning the control beam to the second reflecting surface by reflecting the control beam; and a photo detector unit for detecting the amounts of the control beam that is reflected twice by the second reflecting surface, wherein an angle of the first mirror is adjusted based on data on the amounts of the control beam detected by the photo detector unit.