Optical signal recording medium and information recording/reproducing apparatus

An optical signal recording medium includes at least one signal recoding plane in which an optical signal is to be recorded, and a control information region which is a portion other than the signal recoding plane, and in which a diffraction grating is disposed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2007-117599 filed on Apr. 26, 2007.

BACKGROUND

1. Technical Field

The present invention relates to an optical signal recording medium and an information recording/reproducing apparatus.

2. Related Art

A recording medium in which an optical signal is recorded as a hologram is known. In order to improve the S/N ratio (signal/noise ratio) of a reproduced image of a hologram recorded in such a recording medium, relative positions in the optical axis direction and an translational direction of the recording medium and a light beam irradiating the recording medium to obtain the reproduced image, the intersection angle between the recording medium and the light beam, and the like are made coincident with predetermined conditions.

SUMMARY

According to an aspect of the invention, there is provided an optical signal recording medium has: at least one signal recoding plane in which an optical signal is to be recorded; and a control information region which is a portion other than the signal recoding plane, and in which a diffraction grating is disposed.

DESCRIPTION OF REFERENCE NUMERALS AND SIGNS

DETAILED DESCRIPTION

An embodiment of the invention will be described with reference to the accompanying drawings. As exemplarily shown inFIG. 1, an information recording/reproducing apparatus using an optical signal recording medium of the embodiment includes the optical signal recording medium1, a supporting portion11, a driving portion12, an information recording/reproducing portion13, a medium posture detecting portion14, and a controlling portion15.

The optical signal recording medium1is a plate-like medium having a disk-like shape or the like, and includes a circular surface2, a circular rear face3, and a side face4which extends along the circumference. In the embodiment, at least the surface2is set as a plane on which an optical signal is incident, and information is recorded in the volume of the medium including the surface2. Hereinafter, a plane in which information is recorded, such as the surface2is referred to as an information recording plane.

As shown inFIG. 2, the side face4may have a semicircular section shape, and configure a curved face which is outward convex.FIG. 2is a section view of the optical signal recording medium1taken along a plane perpendicular to a signal recording plane. A diffraction grating P configured by pits is disposed in the side face4. The diffraction grating is used as a so-called control signal. As described later, a result of reading of the diffraction grating is used in tracking and focusing controls. In the embodiment, namely, the side face of the optical signal recording medium1functions as a control information region.

The supporting portion11supports the optical signal recording medium1. When the optical signal recording medium1has a disk-like shape, for example, the optical signal recording medium1is rotatably supported at a center portion of the medium. In the case where the optical signal recording medium1has a rectangular shape, the optical signal recording medium1is supported so as to be movable in a direction parallel to the information recording plane. In accordance with instructions supplied from the controlling portion15, the supporting portion11inclines the rotation axis of the optical signal recording medium1by an instructed angle, to change the intersection angle between the optical axis of a light beam which is emitted for recording or reproducing a signal by the information recording/reproducing portion13, and the information recording plane of the optical signal recording medium1.

The driving portion12includes an actuator, and rotarily or translationally drives the optical signal recording medium1which is supported by the supporting portion11. In accordance with instructions supplied from the controlling portion15, the driving portion12controls the position of intersection of the optical signal recording medium1and the light beam which is emitted for recording or reproducing information by the information recording/reproducing portion13.

The medium posture detecting portion14detects wobbling (translational wobbling) in a direction parallel to the signal recording plane of the optical signal recording medium1, and wobbling (planar wobbling) in a direction perpendicular to the signal recording plane, with using information recorded on the side face of the optical signal recording medium1. Information of results of the detections of the translational wobbling and the planar wobbling is supplied to the controlling portion15, and used by the controlling portion15in controls (tracking and focusing controls) of relative positions of the information recording/reproducing portion13and the optical signal recording medium1. An example of the configuration of the medium posture detecting portion14will be described later.

As exemplarily shown inFIG. 3, the information recording/reproducing portion13includes a light source21, a beam splitter22, a spatial light modulator23, a first objective optical system24, a second objective optical system25, a light receiving portion26, and a stage27.

In the information recording/reproducing portion13, light emitted from the light source21which is configured by a laser diode or the like is introduced into the beam splitter22. The beam splitter guides the light introduced from the light source21, to the spatial light modulator23. Also, the beam splitter22guides light reflected from the spatial light modulator23, to the first objective optical system24. The first objective optical system24includes an objective lens Lo, and a head case H which covers the lens.FIG. 3shows a state where a part of the head case H is cut away and the objective lens Lo is exposed.

The second objective optical system25causes an optical signal which is transmitted through the optical signal recording medium1and arrives the system, to be imaged onto a light receiving surface of the light receiving portion26. The light receiving portion26supplies image data indicative of the received optical signal, to the controlling portion15.

In the information recording/reproducing portion13, when information is to be recorded, an image indicative of the information to be recorded is displayed on the spatial light modulator23. For example, the spatial light modulator23is a liquid crystal panel, and, in accordance with instructions supplied from the controlling portion15, displays an instructed image. According to the configuration, the signal recording plane of the optical signal recording medium1is irradiated with the image indicative of the information to be recorded, and the information is fixed to the signal recording plane.

By contrast, when information is to be reproduced, the information recording/reproducing portion13irradiates the optical signal recording medium1with reference light (read light). When the light is transmitted through the optical signal recording medium1, the light is modulated by an image recorded in the portion irradiated with the light on the signal recording plane of the optical signal recording medium1. The modulated light is guided through the second objective optical system25to the light receiving portion26, and the image indicative of information is formed on the light receiving surface of the light receiving portion26. The image is optically read, and then supplied to the controlling portion15. In the controlling portion15, the information is decoded to be reproduced, and the information is reproduced.

The stage27supports the first objective optical system24of the information recording/reproducing portion13, and the medium posture detecting portion14. The stage27includes an actuator AC. In accordance with instructions supplied from the controlling portion15, the stage27drives the actuator AC to integrally move the first objective optical system24and the medium posture detecting portion14in a direction perpendicular to the signal recording plane of the optical signal recording medium1, thereby controlling the distance between the objective lens Lo of the first objective optical system24and the signal recording plane of the optical signal recording medium1(focusing). Furthermore, the position of intersection of the optical signal recording medium1and a light beam which is emitted toward the side face of the optical signal recording medium1by the medium posture detecting portion14is controlled.

The example of the configuration of the medium posture detecting portion14will be described. As exemplarily shown inFIG. 4, the medium posture detecting portion14includes a light source31, a beam splitter32, an optical system33, and an optical detecting portion34.

For example, the light source31is a laser diode, and irradiates the beam splitter32with light. The beam splitter32guides the light emitted from the light source31to the side face of the optical signal recording medium1, and guides light reflected from the side face of the optical signal recording medium1to the optical system33.

For example, the optical system33is a cylindrical lens which causes astigmatism, or a an optical system (astigmatic optical system) configured by a prism, and makes the light which is received through the beam splitter32, to be imaged onto optical detectors of the optical detecting portion34.

For example, the optical detecting portion34is a so-called four-split optical detector including four optical detectors which are arranged in a 2×2 matrix. The optical detectors may be, for example, photodiodes. The optical detecting portion34detects a signal of light reflected from the side face of the optical signal recording medium1, and supplies a result of the detection to the controlling portion15.

In the embodiment, on the basis of an image formed on the four-split optical detector, the controlling portion15detects the distance between the optical signal recording medium1and the first objective optical system24. In this detection, a well known method such as the push-pull method or the three-beam method can be employed. On the basis of the image formed on the four-split optical detector, furthermore, the controlling portion15detects translational wobbling of the optical signal recording medium1. In this detection, a well known method such as the astigmatism method, the Foucault method, or the knife-edge method can be used.

For example, the controlling portion15includes a microcomputer, and the like. The controlling portion15receives information of the reflected light pattern which is produced by the diffraction grating disposed on the side face of the optical signal recording medium1, and which is then detected by the medium posture detecting portion14. Then, the controlling portion15receives a result of imaging on the optical detecting portion34from the medium posture detecting portion14, and detects the distance (planar wobbling) between the optical signal recording medium1and the first objective optical system24, and translational wobbling of the optical signal recording medium1. On the basis of the amount of the detected planar wobbling, the controlling portion15controls the supporting portion11to adjust the inclination angle of the optical signal recording medium1. Namely, the controlling portion15operates as an optical information processing portion and a positioning controlling portion.

In the case where the optical detecting portion34of the medium posture detecting portion14is a four-split photodiode (photodiodes are indicated by A, B, C, and D, respectively) shown inFIG. 5A, for example, the controlling portion15controls the inclination angle of the supporting portion11so as to attain
IA+ID=IB+IC
where IX is the intensity of light incident on a photodiode X.

Moreover, the controlling portion15controls the actuator AC of the stage27so as to attain IA+IB=IC+ID, whereby performing the focusing controls.

On the basis of the amount of the detected translational wobbling of the optical signal recording medium1, furthermore, the controlling portion15controls the driving portion12. Following the amount of the translational wobbling of the optical signal recording medium1, the controlling portion controls relative positions of the first objective optical system24and the optical signal recording medium1.

In the embodiment, the side face of the optical signal recording medium1which is the control information region may include a portion which is parallel to the optical axis of the light beam for recording a signal into the signal recoding plane, or reproducing a signal from the signal recoding plane, and the diffraction grating may be formed in the parallel portion. According to the configuration, light for recording or reproducing information is less affected by scattered light due to the light beam emitted by the medium posture detecting portion14.

Alternatively, the side face of the optical signal recording medium1which is the control information region may be configured by a curved surface. For example, the curved surface may be outward convex. As one example, the curved surface may be a curved face having a section shape which is substantially semicircular.

In the case where the control information region is configured by a curved surface, when the side face of the optical signal recording medium1which is the control information region is not a curved surface, the reflection directions from the pits are differentiated by the angle of the planar wobbling. By contrast, when the side face of the optical signal recording medium is a curved surface, planar wobbling of the optical signal recording medium1causes the reflection directions from the pits to be possibly larger than the angle of the planar wobbling. Therefore, the accuracy of detecting planar wobbling is enhanced.

Alternatively, the diffraction grating which is formed in the control information region of the optical signal recording medium1may be a computer generated hologram (CGH) indicating a Fourier pattern, in place of the pits. In the alternative, as exemplarily shown inFIG. 5B, the optical detecting portion34of the medium posture detecting portion14may be configured so that CMOS (Complementary Metal Oxide Semiconductor) cameras are placed in the four corners of a rectangle and a central portion, respectively. The controlling portion15controls the inclination angle of the supporting portion11so as to attain
IA+ID=IB+IC
where IX is the intensity of light incident on the five CMOS cameras (A to D in the four corners and E in the central portion).

Moreover, the controlling portion15controls the actuator AC of the stage27so as to attain IA+IB=IC+ID, whereby performing the focusing controls.

The controlling portion15controls the driving portion12so that the diameter RE of the light beam which is incident on the CMOS camera E placed in the central portion is minimum (or has a specified size), thereby adjusting the position of the optical signal recording medium1. Namely, direct light (zero-order light) which is not diffracted by the diffraction grating is incident on the CMOS camera E placed in the central portion, and the distance between the optical signal recording medium1and the medium posture detecting portion14can be detected based on the size of the light beam. In the embodiment, therefore, the position of the optical signal recording medium1is adjusted on the basis of the detected distance.

Alternatively, the diffraction grating may be a hologram indicating different information depending on a location (FIG. 6). In this case, for example, a hologram in which different information is recorded at each rotation angle H may be formed on the side face of the disk-like optical signal recording medium1. In this case, the controlling portion15observes diffracted light from the hologram to detect the rotation position of the optical signal recording medium1, and, on the basis of a result of the detection, controls the relative positions of the optical signal recording medium1and the information recording/reproducing portion13.

In addition to or in place of the above-mentioned diffraction grating, a light reflecting member (mirror) M which is an identification information recording portion indicating a predetermined position may be disposed on the side face of the optical signal recording medium1(FIG. 7). In this case, the medium posture detecting portion14may detect reflected light from the mirror. At the timing when the reflected light is detected, the controlling portion15determines that the optical signal recording medium1is in the predetermined position. In the case where the optical signal recording medium1has a disk-like shape, for example, a light reflecting member may be adhered at each predetermined rotation angle, and, while setting the rotation angle as a reference position, a process of detecting the rotation angle of the optical signal recording medium1may be performed. When the optical signal recording medium1is rotated at a constant angular velocity a, for example, the elapsed time t after the reference position is detected is measured by a timer which is not shown. The rotation angle θ is calculated as θ=ωt. The reflected light from the light reflecting member may be disposed aside from the optical system for detecting the diffraction grating.

The embodiment may be configured so that a light reflecting member is formed on the outer periphery of the head case H of the information recording/reproducing portion13, the member is irradiated with convergent or divergent light, and the optical detector D fixed to the stage27detects the shape of the reflected light of the diameter of the light beam. Using a result of the detection, the controlling portion15detects the distance from the optical detector D fixed to the stage27, to the head case H. Using the distance (which may be predetermined, or which may be detected with using the medium posture detecting portion14) from the outer circumference of the optical signal recording medium1to the optical detector D, and that from the optical detector D to the head case H, the controlling portion15detects the distance from the rotation axis (center) of the optical signal recording medium1to the position where the light beam emitted from the first objective optical system24incorporated in the head case H intersects with the optical signal recording medium1. Alternatively, the controlling portion may detect the distance from the outer circumference of the optical signal recording medium1to the position where the light beam emitted from the first objective optical system24incorporated in the head case H intersects with the optical signal recording medium1.

According to the configuration, the controlling portion15can detect which position of the signal recording plane is irradiated by the information recording/reproducing portion13.

In the case where the optical signal recording medium1has a rectangular shape, as exemplarily shown inFIG. 8, plural medium posture detecting portions14may be placed so as to be opposed to the side faces of the edges of the rectangle (it is assumed that the edges extend the X and Y axes, respectively). Using signals detected by the medium posture detecting portions14, the controlling portion15detects the X- and Y-axis direction positions of the optical signal recording medium1. Using a result of the detection, the controlling portion controls the driving portion12to control the position of the optical signal recording medium1.

In the embodiment, the example in which a transmissive hologram is coaxially recorded has been described. The invention is not restricted to this. A reflective hologram in which a reflective layer is disposed on the rear face of a medium may be used. Furthermore, the invention is not restricted to coaxial recording. A two-beam type in which a medium is irradiated with signal light and reference light in different directions may be employed. The invention can be similarly applied also to an optical signal recording medium using a system other than the hologram recording.