A method of performing a write operation in a holographic data storage system, in which schedule schedules at least one write operation across multiple non-contiguous write intervals, the write operation pertaining to a set of data to be stored in a region of a holographic recording medium. In each of the non-contiguous write intervals, the region of the holographic recording medium is exposed to an interference pattern caused by interference between a reference beam and an input beam carrying the set of data. The multiple non-contiguous write intervals have a total aggregate duration of sufficient length to cause a persistent state change in the exposed region, such that the set of data is recoverable from that region by the end of a final write interval of the multiple non-contiguous write intervals.

An improved optical encoder uses an optical pick-up unit that provides for degrees of freedom in the tracking and focus axes that are unavailable in conventional optical encoders thereby improving the encoders' performance. In an embodiment the encoder employs an optical disc marked with pits and lands which may be arranged in a spiral pattern. The optical disc is mounted on the shaft whose motion is to be monitored by the optical encoder. The encoder may be arranged to read the markings on the optical disc using the three-beam pickup method.

A method of performing a write operation in a holographic data storage system, in which schedule schedules at least one write operation across multiple non-contiguous write intervals, the write operation pertaining to a set of data to be stored in a region of a holographic recording medium. In each of the non-contiguous write intervals, the region of the holographic recording medium is exposed to an interference pattern caused by interference between a reference beam and an input beam carrying the set of data. The multiple non-contiguous write intervals have a total aggregate duration of sufficient length to cause a persistent state change in the exposed region, such that the set of data is recoverable from that region by the end of a final write interval of the multiple non-contiguous write intervals.

In relation to recording and reproducing of a hologram, consideration has not thus far been given to crosstalk among adjacent pages Information is recorded by writing onto a holographic medium, an interference pattern formed by signal light and reference light, and the recorded information is reproduced by the reference light being projected on the interference pattern. According to the method, when angle multiplexing recordings in units of pages is carried out in a holographic medium by changing the angle of incidence of reference light, and if a stack is defined as a unit of angle multiplexing recording in the same location in the holographic medium and a book is defined as a set of multiple stacks with shifted recording positions, for adjacent stacks therein, recording is carried out by allotting, between the reference light angles for one of the stacks, reference light angles for the stacks adjacent thereto.

The optical information recording device includes a light source configured to emit a laser beam, an optical element configured to divide the laser beam into the reference beam and the signal beam, an angle control unit configured to control an angle of incidence of the reference beam on the optical information recording medium, and a phase control unit configured to control a phase of at least one of the signal beam and the reference beam in a recording period, wherein the angle control unit controls an angle interval so that a position of a 1st null of an adjacent page of the signal beam is fixed, and wherein the phase control unit controls the phase of the signal beam or the reference beam so that a phase difference between the adjacent pages is a predetermined value.

An optical-information recording/reproducing apparatus of the present invention is capable of carrying out position detection of a reproduction image even if reproduction image data with incomplete alignment marks (markers) is obtained. A relative correlation value is calculated from a first correlation value retained by a first correlation-value retaining unit and a second correlation value retained by a second correlation-value retaining unit, and pass/fail of a position detection result of the marker is judged according to the relative correlation value. The pass/fail of the position detection result is judged by mutually comparing the detection positions of the markers judged as passes by the relative correlation-value judgement, the positions of the markers judged as fail by the relative correlation-value judgement or the mutual position judgement is complemented, and the position of two-dimensional data is detected based on the pass-judged markers and the complemented markers.

The optical information recording device includes a light source configured to emit a laser beam, an optical element configured to divide the laser beam into the reference beam and the signal beam, an angle control unit configured to control an angle of incidence of the reference beam on the optical information recording medium, and a phase control unit configured to control a phase of at least one of the signal beam and the reference beam in a recording period, wherein the angle control unit controls an angle interval so that a position of a 1st null of an adjacent page of the signal beam is fixed, and wherein the phase control unit controls the phase of the signal beam or the reference beam so that a phase difference between the adjacent pages is a predetermined value.

A hologram recording and playback device is provided with: a medium rotation unit which rotates a hologram recording medium around a predetermined rotational axis; a movement unit which is capable of moving the position of the medium rotation unit within a plane that is perpendicular to the rotational axis; an orthogonal incident angle modification unit which is capable of modifying an orthogonal incident angle; a medium rotation control unit which controls the medium rotation unit so as to rotate the hologram recording medium; an eccentricity compensation unit which performs positioning control of the movement unit; an orthogonal incident angle control unit which controls the orthogonal incident angle modification unit; and an orthogonal incident angle calculation unit which calculates the orthogonal incident angle.

An optical-information recording/reproducing apparatus of the present invention is capable of carrying out position detection of a reproduction image even if reproduction image data with incomplete alignment marks (markers) is obtained. A relative correlation value is calculated from a first correlation value retained by a first correlation-value retaining unit and a second correlation value retained by a second correlation-value retaining unit, and pass/fail of a position detection result of the marker is judged according to the relative correlation value. The pass/fail of the position detection result is judged by mutually comparing the detection positions of the markers judged as passes by the relative correlation-value judgement, the positions of the markers judged as fail by the relative correlation-value judgement or the mutual position judgement is complemented, and the position of two-dimensional data is detected based on the pass-judged markers and the complemented markers.

This recording/reproducing apparatus that records or reproduces information by radiating light to a recording medium is provided with: a medium rotating unit that rotates the recording medium; a moving unit having a movable unit that is capable of moving within a predetermined plane; a rotation angle detecting unit that detects a rotating angle of the recording medium using an angle detection mark that is provided on the recording medium; a position detecting unit that detects a position of the recording medium using an eccentricity detection mark that is provided on the recording medium; and a member for fixing the rotation angle detecting unit and the position detecting unit. With respect to the member, the movable unit relatively moves within a plane substantially parallel to the recording surface of the recording medium, and the medium rotating unit is fixed to the movable unit.