JP2009238268A - Hologram recording system and hologram reproducing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hologram recording system and hologram reproducing system which always coincide position of an entrance pupil surface of an objective lens and an image location of a dot pattern of a spatial light modulator, and the position of the entrance pupil surface of the objective lens and a location for imaging a dot pattern reproduced on a surface of an optical receiver. <P>SOLUTION: The hologram recording and reproducing system includes a plate object which is disposed in front of the entrance pupil surface of the objective lens on the light path of an information laser beam and whose refraction index is different from air, and a light path length changing means for changing the light path length of an information laser beam by inputting at least either of a signal corresponding to a drive amount from a neutral position in the focus direction of the objective lens by a servo means and a signal corresponding to the drive amount from the neutral position on the hologram recording medium in the radial direction of the objective lens by the servo means to drive the plate object based on the input signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a hologram recording apparatus that records data on a hologram recording medium by a shift multiplexing method and a hologram reproducing apparatus that reproduces data from a hologram recording medium on which data is recorded by a shift multiplexing method.

  Conventionally, in order to increase the capacity of data to be recorded on an optical disc, research for performing multiplex recording on a hologram recording medium has been underway. As a method of performing multiplex recording on a hologram recording medium, there are mainly a two-beam interference method and a collinear method. Among these methods, the collinear method focuses on the recording layer of the hologram recording medium after focusing the recording laser beam. In this method, data is recorded on the hologram recording medium by a shift multiplexing method by moving in parallel with the recording layer.

  Normally, in collinear data recording, servo laser light is irradiated separately from the recording laser light, and a servo signal is generated by a signal based on the reflected light from the track formed on the reflection layer of the hologram recording medium. Focus servo control and tracking servo control are performed so that the laser beam is focused on the track groove and then follows the track groove. With these servo controls, the recording laser beam is focused on the hologram recording medium. The hologram recording medium is moved spirally after being matched with the recording layer.

  These servo controls, for example, as disclosed in Patent Document 1, are similar to the servo control in recording / reproducing of an optical disc such as a DVD or CD, and the objective lens is set to the optical axis direction of the laser beam (hereinafter referred to as the focus direction). There is a method of driving by driving in the radial direction of the hologram recording medium (hereinafter referred to as the radial direction), which is perpendicular to this direction. However, with this method, when the objective lens is driven in the optical axis direction of the laser beam, the position of the entrance pupil plane of the objective lens changes, and when the position of the entrance pupil plane of the objective lens changes, data on the hologram recording medium Recording accuracy and reproduction accuracy of data recorded on the hologram recording medium are deteriorated.

  Also, in this method, when the objective lens is driven in the radial direction of the hologram recording medium, the optical axis of the objective lens and the optical axis of the laser beam are shifted, so that the light diffracted around the spatial light modulator is incident on the objective lens. There is a problem that the amount to be recorded is reduced and the recording accuracy is deteriorated. For this reason, there is a method in which the objective lens and the rising mirror are integrated and driven in the radial direction so that the optical axis of the objective lens and the optical axis of the laser light always coincide with each other. In addition, even when driven in the radial direction, the position of the entrance pupil plane of the objective lens fluctuates, and the problem is that the recording accuracy of data on the hologram recording medium and the reproduction accuracy of data recorded on the hologram recording medium deteriorate. is there.

  The reason why data recording accuracy and data reproduction accuracy deteriorate is that when recording data on a hologram recording medium, a spatial light modulator (SLM: Spatial Light Modulator, etc.) is placed on the entrance pupil plane of the objective lens at the neutral position. This is because the dot pattern on the entrance pupil plane is blurred when the entrance pupil plane of the objective lens fluctuates. In addition, when reproducing data recorded on a hologram recording medium, the dot pattern formed on the entrance pupil plane of the objective lens at the neutral position is set to form an image on the surface of the light receiver. This is because when the entrance pupil plane of the lens fluctuates, the dot pattern is imaged at a position different from the plane of the light receiver, so that the dot pattern on the surface of the light receiver becomes blurred.

As a method for solving this problem, for example, as disclosed in Patent Document 2, one of the relay lens (second moving unit) and a pair of reflectors (third moving unit) according to the driving of the objective lens. And the optical path length among the spatial light modulator, the light receiver, the relay lens, and the objective lens is kept constant. According to this method, even if the position of the entrance pupil plane fluctuates due to the drive of the objective lens, a dot pattern is formed on the entrance pupil plane of the objective lens in data recording, and the entrance pupil plane of the objective lens in data reproduction. The above-mentioned problem does not occur because the dot pattern in FIG.
JP-A-11-311937 JP 2007-193874 A

  However, in the apparatus shown in Patent Document 2, data such as a pair of reflectors is heavy, and it becomes difficult to drive a heavy object in accordance with the driving of the objective lens as the recording speed is increased. There is a problem that the recording accuracy and data reproduction accuracy deteriorate, and there is a problem that the cost of the apparatus increases because it is necessary to provide a large drive mechanism in the apparatus.

  The present invention has been made in view of such circumstances, and it is easy to drive in accordance with the driving of the objective lens, does not require a large driving mechanism, and the position of the entrance pupil plane of the objective lens and the spatial light. Hologram recording apparatus and hologram reproduction capable of always matching the image formation position of the dot pattern of the modulator and the position of the entrance pupil plane of the objective lens with the position for image formation of the dot pattern reproduced on the surface of the light receiver To provide an apparatus.

  The hologram recording apparatus according to claim 1, wherein a plate-like object having a refractive index different from that of air is disposed on the optical path of the information laser light and in front of the entrance pupil surface of the objective lens, and the focus of the objective lens by the servo means. Input at least one signal corresponding to the driving amount from the neutral position in the direction or the driving amount from the neutral position in the radial direction of the hologram recording medium of the objective lens by the servo means, based on the input signal And an optical path length varying means for driving the plate-like object to vary the optical path length of the information laser beam.

  3. The hologram reproducing apparatus according to claim 2, wherein a plate-like object having a refractive index different from that of air is disposed on the optical path of the information laser light and in front of the entrance pupil surface of the objective lens, and the focus of the objective lens by the servo means. Input at least one signal corresponding to the driving amount from the neutral position in the direction or the driving amount from the neutral position in the radial direction of the hologram recording medium of the objective lens by the servo means, based on the input signal And an optical path length varying means for driving the plate-like object to vary the optical path length of the information laser beam.

  The hologram recording apparatus and hologram reproducing apparatus according to claim 3 are characterized in that the drive of the plate-like object in the optical path length varying means is a rotation drive in which the plate-like object is rotated by a rotation axis perpendicular to the optical path of the information laser light. And

  5. The hologram recording apparatus and the hologram reproducing apparatus according to claim 4, wherein the plate-like object is composed of two pieces of the same material and the same thickness, and is arranged in parallel on the optical path, and the plate-like object in the optical path length varying means. The rotational drive is characterized in that the axial directions of the rotary shafts are the same, and each plate-like object is rotated by an equal amount in the opposite direction.

  In the hologram recording apparatus and the hologram reproducing apparatus according to claim 5, the tracking servo in the servo means drives the optical component including the objective lens, and the optical path length varying means adjusts the drive amount from the neutral position in the focus direction of the objective lens. A corresponding signal and a signal corresponding to the driving amount of the objective lens from the neutral position in the radial direction of the hologram recording medium are input, and the plate-like object is driven based on the two input signals.

  The hologram recording device and the hologram reproducing device according to claim 6 are characterized in that the material of the plate-like object is glass.

  According to the first and second aspects of the present invention, by driving the plate-like object provided in front of the entrance pupil plane of the objective lens based on the drive amount of the objective lens, the movement of the objective lens moves the entrance pupil plane. Even if the position changes, by changing the optical path length by driving the plate-like object, the dot pattern imaging position or the position for imaging the dot pattern on the surface of the light receiver is changed, The position of the entrance pupil plane of the objective lens and the image formation position of the dot pattern, and the position of the entrance pupil plane of the objective lens and the position for imaging the dot pattern on the surface of the light receiver can always coincide.

  According to the third aspect of the present invention, the driving of the plate-like object in the optical path length varying means is the rotation driving that rotates the plate-like object with the rotation axis perpendicular to the optical path of the information laser light, so that it is driven by a simple drive mechanism. Therefore, it is easy to drive in accordance with the driving of the objective lens, and a large drive mechanism is not required.

  According to the invention of claim 4, since the two plate-like objects are rotated by the same amount in the opposite directions, even if the rotation of one plate-like object changes to the optical path position together with the optical path length, the other plate By rotating the object, the optical path position can be returned to the original position, and only the optical path length can be changed.

  According to the fifth aspect of the invention, since the plate-like object is driven based on the two drive amounts of the objective lens in the focus direction and the radial direction, the focus servo and the tracking servo in which the objective lens and the upright mirror are integrated. Even if the two are performed, the position of the entrance pupil plane of the objective lens and the pattern imaging position, and the position of the entrance pupil plane of the objective lens and the position for imaging the pattern on the surface of the light receiver are always matched. be able to.

  According to invention of Claim 6, since the raw material of a plate-shaped object is glass, it is possible to hold down the cost of a plate-shaped object.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. A hologram recording / reproducing apparatus according to an embodiment of the present invention is an apparatus that records data on a hologram recording medium by a shift multiplexing method and reproduces data from a hologram recording medium on which data has been recorded by a shift multiplexing method.

  FIG. 1 is a block diagram showing a first embodiment of a hologram recording / reproducing apparatus according to the present invention. FIG. 2 is an explanatory diagram showing arrangement intervals of a spatial light modulator, a light receiver, a relay lens, an objective lens, and the like in the hologram recording / reproducing apparatus. FIG. 3 is an explanatory diagram showing the rotation of the rotating glass plate accompanying the movement of the objective lens in the focus direction. FIG. 4 is an explanatory diagram showing changes in the optical path length due to rotation of the rotating glass plate.

  In FIG. 1, a hologram recording / reproducing apparatus 1 includes a pickup device 200, a controller 300 having a display device 302 and an input device 304, a recording laser drive circuit 202, a recording signal generation circuit 204, a servo laser drive circuit 210, and a reproduction. Data generation circuit 212, rotation drive circuit 216, turntable 130, spindle motor 132, feed motor 134, spindle motor control circuit 102, feed motor control circuit 108, radial position detection circuit 106, signal amplification circuit 110, tracking error signal generation circuit 112, a tracking servo circuit 114, a thread servo circuit 118, a focus error signal generation circuit 120, a focus servo circuit 122, drive circuits 116 and 124, and the like. In this embodiment, since the objective lens 40 is driven alone in the focus direction and the radial direction, only the change in the position of the entrance pupil plane of the objective lens 40 due to the drive in the focus direction is considered.

  The pickup device 200 includes laser light sources 10 and 30, collimating lenses 12 and 32, mirrors 14 and 28, a spatial light modulator (SLM) 16, relay lenses 18 and 22, as in a conventional hologram recording / reproducing device. 24, polarization beam splitter 20, dichroic prism 38, condenser lens 48, photodetectors 26 and 52, objective lens 40, beam splitter 34, quarter wavelength plate 36, cylindrical lens 50, tracking actuator 46, focus actuator 44, and the like. In addition, rotating glass plates 60 and 62 are provided on the optical path between the relay lens 22 and the objective lens 40.

  The laser light emitted from the laser light source 10 is converted into parallel light by the collimator lens 12, the traveling direction is changed by the mirror 14, and then the spatial light modulator 16 is transmitted. The spatial light modulator 16 is made of a transmissive TFT liquid crystal display (LCD) panel or the like, and is a two-dimensional two-dimensional output from a recording signal generation circuit 204 described later when data is recorded on the hologram recording medium HK. The digitized data is input, and a bright and dark dot pattern is formed on the plane. The spatial light modulator 16 forms a bright and dark dot pattern in the central region, and the light transmitted through this portion is diffracted and has information based on two-dimensional binarized data (hereinafter referred to as information laser light). become. Then, the spatial light modulator 16 forms only bright dots in the peripheral region, and the light transmitted through this portion remains unchanged from that before incidence and remains as light having no information (hereinafter referred to as reference laser light). Become. When reproducing the data recorded on the hologram recording medium HK, the spatial light modulator 16 forms only bright dots in the entire area and transmits the incident laser light as it is.

  The laser light passes through the spatial light modulator 16, and information laser light and reference laser light are generated at the time of data recording, and laser light that is only the reference laser light is reproduced by the relay lenses 18 and 22 at the time of data reproduction. The beam diameter is changed, the traveling direction is changed by the mirror 28, the light passes through the rotating glass plates 60 and 62, and enters the dichroic prism 38.

  The rotating glass plates 60 and 62 are composed of glass plates 60a and 62a having the same thickness T and motors 60b and 62b for driving the glass plates 60a and 62a. The thickness T of the glass plate is set to an appropriate value from the driving range of the objective lens 40 in the focus direction and the rotational driving range of the rotating glass plates 60 and 62. This point will be described later. The motors 60b and 62b are configured to rotate by the same amount of rotation in opposite directions based on a drive signal supplied from a rotation drive circuit 216 described later. The optical path length from the relay lens 22 to the objective lens 40 is changed by the rotation of the glass plates 60a and 62a. By making this change equal to the driving amount from the neutral position in the focus direction of the objective lens 40, the position of the entrance pupil plane of the objective lens 40, the image formation position of the dot pattern, and the entrance pupil plane of the objective lens 40 The position at which the dot pattern is formed on the surface of the photodetector 26 always coincides with the position of. The relationship between the drive amount of the objective lens 40 and the rotation amounts of the rotating glass plates 60 and 62 will be described later.

  Between the relay lenses 18 and 22, there is a polarizing beam splitter 20, and most of the information laser light and the reference laser light are transmitted because the polarization direction coincides with the transmission axis of the polarizing beam splitter 20, and a hologram as will be described later. Most of the reproduction light from the recording medium HK side is reflected and changes the traveling direction because the polarization direction is 90 degrees from the transmission axis of the polarization beam splitter 20. The polarization beam splitter 20 is disposed so that the reproduction light from the hologram recording medium HK enters the photodetector 26 via the relay lens 24 when reproducing the data recorded on the hologram recording medium HK.

  The dichroic prism 38 has a characteristic in which transmission and reflection change depending on the wavelength of the laser light. Since the laser light emitted from the laser light source 10 is light having a wavelength that passes through the dichroic prism 38, the information laser light and the reference The laser light passes through the dichroic prism 38 and is focused on the recording layer of the hologram recording medium HK by the objective lens 40. Then, at the time of data recording, the information laser beam and the reference laser beam interfere with each other at the condensing position, data is recorded on the recording layer by interference fringes, and at the time of data reproduction, the reference laser beam to the data recording position is recorded. Reproduction light is generated by condensing light.

  The quarter-wave plate 36 changes linearly polarized light into circularly polarized light and changes circularly polarized light into linearly polarized light in the laser light having the wavelength of the laser light emitted from the laser light source 10. For this reason, the reference laser beam is changed from linearly polarized light to circularly polarized light and irradiated to the hologram recording medium HK, and reproduction light generated at the data recording location is also generated by circularly polarized light. When the reproduction light passes through the quarter wavelength plate 36, it becomes linearly polarized light having a polarization direction different from the polarization direction of the reference laser light by 90 degrees. For this reason, the polarization direction of the reproduction light is 90 degrees from the transmission axis of the polarization beam splitter 20.

  The laser light source 30 is provided for focus servo control and tracking servo control described later. The laser light emitted from the laser light source 30 becomes parallel light by the collimator lens 32, and about half of the light is reflected by the beam splitter 34 and enters the dichroic prism 38. Since the laser light emitted from the laser light source 30 is light having a wavelength reflected by the dichroic prism 38, the laser light incident from the beam splitter 34 side is reflected by the dichroic prism 38 and passes through the quarter wavelength plate 36. Then, the light is condensed on a track formed on the reflection layer of the hologram recording medium HK by the objective lens 40. Then, the reflected light from the condensing position becomes parallel light by the objective lens 40, passes through the quarter-wave plate 36, is reflected by the dichroic prism 38, and about half is transmitted by the beam splitter 34, and the condensing lens 48. The light is condensed on the quadrant photodetector 52 by the cylindrical lens 50.

  The quarter-wave plate 36 is a birefringent material set so as to change linearly polarized light into circularly polarized light in the laser light having the wavelength of the laser light emitted from the laser light source 10, so that the laser light from the laser light source 30 is transmitted. Then, the linearly polarized light is changed to elliptically polarized light, and when reflected again by the hologram recording medium HK and then transmitted again, the elliptically polarized light is changed to another elliptically polarized light. Therefore, the amount of light received by the quadrant photodetector 52 is not affected.

  Since the cylindrical lens 50 is provided before the laser beam is incident on the quadrant photodetector 52, when the focus of the laser beam is deviated from the position of the reflection layer of the hologram recording medium HK, a circular shape formed on the quadrant photodetector 52. The spot becomes an elliptical light having a long axis on the diagonal line of the four-divided photodetector 52, and a laser beam from the position of the opposite layer is calculated by calculating a signal output from each photodetector of the four-divided photodetector 52 as described later. Can be detected as a signal. Focus servo control is performed so that this deviation is eliminated. In this embodiment, focus servo control by the astigmatism method is used.

  Further, when the focus of the laser beam is deviated from the track groove position of the hologram recording medium HK, the light quantity on one side of the circular spot formed on the quadrant photo detector 52 is decreased, and each of the quadrant photo detectors 52 will be described later. By calculating the signal output from the photodetector, the deviation of the focal point of the laser beam from the track groove position can be detected as a signal. Tracking servo control is performed so that this deviation is eliminated. In this embodiment, focus servo control by the push-pull method is used.

  The focus actuator 44 drives the objective lens 40 in the focus direction by a drive signal from a drive circuit 124 described later in focus servo control. The tracking actuator 46 drives the objective lens 40 in the radial direction by a drive signal from a drive circuit 116 described later in tracking servo control.

As shown in FIG. 2, the system including the spatial light modulator 16, the photodetector 26, the relay lenses 18, 22, 24, the objective lens 40, etc.
The optical path length from the spatial light modulator 16 to the relay lens 18 The optical path length from the relay lens 18 and the relay lens 22 to the intermediate position between the relay lenses 18 and 22 The optical path from the relay lens 22 to the entrance pupil plane of the objective lens 40 The optical path length from the intermediate position of the relay lenses 18 and 22 to the relay lens 24 is arranged such that the optical path length from the relay lens 24 to the photodetector 26 becomes Fl which is the focal length of the relay lenses 18 and 22.
However, the optical path length from the relay lens 22 to the entrance pupil plane of the objective lens 40 is F1 when the objective lens 40 is in the neutral position (that is, when ΔX is 0). At this time, at the time of data recording, the dot pattern formed on the spatial light modulator 16 is imaged on the entrance pupil plane of the objective lens 40 and is Fourier-transformed by the objective lens 40 to record data on the hologram recording medium HK. Is done. At the time of data reproduction, the reproduction light from the hologram recording medium HK is subjected to inverse Fourier transform, and a dot pattern is formed on the entrance pupil plane of the objective lens 40, and this dot pattern is formed on the photodetector 26.

  However, the optical path length from the relay lens 22 to the entrance pupil plane of the objective lens 40 changes from F1 when the objective lens 40 fluctuates from the neutral position. That is, the optical path length is F1 + ΔX. More specifically, the distance from the objective lens 40 to the entrance pupil plane of the objective lens 40 is the focal length F2 of the objective lens 40, which is constant. The objective lens 40 is driven in the focus direction by driving the focus actuator 44 by focus servo control, and is controlled so that the distance from the objective lens 40 to the recording surface of the hologram recording medium HK is always the focal length F2. As a result, the position of the entrance pupil plane of the objective lens 40 varies.

  As described in the background section, if the position of the entrance pupil plane of the objective lens 40 fluctuates, the dot pattern on the entrance pupil plane of the objective lens 40 blurs during data recording, and the photo detector during data playback. Since the dot pattern on the surface No. 26 is blurred, the data recording accuracy and the data reproduction accuracy are deteriorated. Therefore, by rotating the rotating glass plates 60 and 62 as described above, the spectral path length equal to the amount of movement of the objective lens 40 from the neutral position in the focus direction is changed, thereby changing the image position of the dot pattern to the objective. The dot pattern is imaged on the position of the entrance pupil plane of the objective lens 40 and the imaging position of the dot pattern, the position of the entrance pupil plane of the objective lens 40 and the surface of the photodetector 26 by moving the lens 40 by an amount equal to the movement amount of the lens 40. To match the position for.

  Specifically, as shown in FIG. 3A, when the hologram recording medium HK moves ΔX to the left in the figure, the objective lens 40 is controlled to keep the distance to the recording surface of the hologram recording medium HK constant by focus servo control. Therefore, it moves ΔX to the left in the figure. Similarly, the entrance pupil plane of the objective lens 40 also moves ΔX to the left side in the figure. As a result, the distance from the relay lens 22 to the entrance pupil plane of the objective lens 40 is reduced by ΔX, but the optical path length decreases when the rotating glass plates 60 and 62 are rotated from the dotted line state to the solid line state as shown in the figure. . If the decrease in the optical path length is ΔX, the image position of the dot pattern is also moved ΔX to the left in the figure, and coincides with the position of the entrance pupil plane of the objective lens 40.

  On the contrary, when the hologram recording medium HK moves ΔX to the right in the figure as shown in FIG. 3B, the objective lens 40 also moves ΔX to the right in the figure. Similarly, the entrance pupil plane of the objective lens 40 moves ΔX to the right side in the figure. As a result, the distance from the relay lens 22 to the entrance pupil plane of the objective lens 40 increases by ΔX, but the optical path length increases when the rotating glass plates 60 and 62 are rotated from the dotted line state to the solid line state as shown in the figure. To do. If the increase in the optical path length is ΔX, the image position of the dot pattern is also moved ΔX to the right in the figure, and coincides with the position of the entrance pupil plane of the objective lens 40.

  At this time, the thickness of the glass plates 60a and 62a is made the same, and the laser after passing through the glass plates 60a and 62a by making the angles of the glass plates 60a and 62a with respect to the optical axis of the laser beam the same angle in the opposite direction. The optical axis position of light can be made constant. The change amount ΔX of the optical path length with respect to the rotation amount θ of the rotating glass plates 60 and 62 is set by the refractive index n of the material of the glass plates 60a and 62a, the thickness T of the glass plates 60a and 62a, and the initial rotation position θs. Can be calculated as follows.

  As shown in FIG. 4, when the surface of the glass plate 60a is perpendicular to the optical axis of the laser beam (in the state of a dotted line), the optical path length from the point A to the point B is a numerical value of Formula 1.

  When the surface of the glass plate 60a is rotated by an angle θ with respect to the optical axis of the laser beam (in the state of a solid line), the optical path length from the point A to the point B is a numerical value of Formula 2.

  Equation 2 to Equation 1 become the optical path length change ΔX, and Equation 3 is obtained.

  Substituting n = sin θ / sin φ, which is an expression of the refractive index n, into Equation 3 gives Equation 4.

  Since this is a change in the optical path length due to the glass plate 60a, the change in the optical path length due to the glass plates 60a and 62a becomes twice as many as Equation 4 but as in Equation 5.

  This is the change ΔX in the optical path length from when θ = 0, but the change ΔX in the optical path length from the initial rotational position θs can be subtracted from Equation 5 to Equation 5 where θ = θs. Therefore, the equation of Equation 6 is obtained.

  ΔX is determined when the refractive index n, the thickness T, and the angles θs and θ are determined. Accordingly, if the refractive index n, the thickness T, and the initial rotation angle θs are set, ΔX is determined by the angle θ. Conversely, if ΔX is determined as the amount of movement from the neutral position of the objective lens 40, the angle θ at that time is also determined. Therefore, if the amount of movement ΔX from the neutral position of the objective lens 40 is detected, the angle θ is obtained from this ΔX by the equation (6), and the rotating glass plates 60 and 62 are driven, the entrance pupil plane of the objective lens 40 is detected. The dot pattern imaging position and the position for the dot pattern to form an image on the surface of the photodetector 26 change in accordance with the change in position. The refractive index n of the glass plates 60a and 62a varies slightly depending on the wavelength of the laser light, but is almost fixed at about 1.54. Therefore, the thickness T of the glass plates 60a and 62a is the neutrality of the objective lens 40. This can be obtained by substituting ΔX for the maximum movement amount from the position and the maximum rotation angle θ of the glass plates 60a and 62a into the equation (6).

  The circuit will be described below. The spindle motor control circuit 102 controls the rotation of the spindle motor 132 so that the number of pulses per unit time of the pulse signal input from the encoder in the spindle motor 132 becomes the number of pulses corresponding to the rotation speed input from the controller 300. To do. The controller 300 calculates a rotational speed at which a predetermined linear speed is obtained from a radius value input from a radial position detection circuit 106 described later, and outputs the rotational speed to the spindle motor control circuit 102.

  The radial position detection circuit 106 starts driving when the apparatus is turned on, and when the input of the pulse signal from the encoder built in the feed motor 134 is stopped, the initial radial value is used as a pulse of the pulse signal input thereafter. The moving distance is calculated by counting the number, and the radius value is calculated by adjusting to the initial radius value, and is output to the controller 300 and a feed motor control circuit 108 described later.

The feed motor control circuit 108 functions as follows.
When the apparatus is turned on, the driving is started, and the feed motor 134 is driven to the driving limit position (position that is the initial radius value).
When a radius value is input from the controller 300, the driving direction is determined from the radius value input from the radius value detection circuit 106, the feed motor 134 is driven, and the radius value input from the radius position detection circuit 106 is input from the controller 300. When the radius value is reached, the drive of the feed motor 134 is stopped.
When a thread servo start command is input from the controller 300, the number of pulses per unit time of the pulse signal input from the encoder in the feed motor 134 becomes the number of pulses corresponding to the feed speed input from the thread servo circuit 118 described later. Thus, the rotation of the feed motor 134 is controlled.

  When an operation start command is input from the controller 300, the recording laser drive circuit 202 supplies the laser light source 10 with a voltage and a current for emitting laser light with a predetermined intensity from the laser light source 10. When an operation start command is input from the controller 300, the servo laser drive circuit 210 supplies the laser light source 30 with a voltage and a current for emitting laser light with a predetermined intensity from the laser light source 30.

  The signal amplifying circuit 110 receives the signals output from the respective photodetectors of the four-divided photodetector 52, amplifies them at a predetermined amplification factor, and outputs them to the tracking error signal generation circuit 112 and the focus error signal generation circuit 120, respectively.

  The tracking error signal generation circuit 112 generates a signal output from each of the photodetectors of the four-divided photodetector 52 and amplified by the signal amplification circuit 110 using (a + b) − (c + d), which is an arithmetic expression in the push-pull method. A tracking error signal is output to the tracking servo circuit 114. a, b, c and d are a, b, c and d clockwise from the upper right photodetector when the quadrant photodetector 52 is applied in the groove direction of the track.

  The tracking servo circuit 114 receives the tracking error signal from the tracking error signal generation circuit 112, creates a tracking servo signal corresponding to the driving amount of the objective lens 40 so that the input tracking error signal becomes zero, and the drive circuit 116. Output to. The drive circuit 116 receives a tracking servo signal from the tracking servo circuit 114 and supplies a signal for driving the objective lens 40 in the radial direction to the tracking actuator 46 based on this signal.

  Tracking servo control is performed by the quadrant photodetector 52, tracking error signal generation circuit 112, tracking servo circuit 114, drive circuit 116, and tracking actuator 46.

  The sled servo circuit 118 receives the tracking servo signal from the tracking servo circuit 114, detects the DC component of the signal, and creates a signal corresponding to the feed speed of the feed motor 134 so that the DC component becomes zero, Output to the feed motor control circuit 108. The DC component of the tracking servo signal corresponds to the average of the deviation from the neutral position of the objective lens 40 within a predetermined time. By driving the feed motor 134 so as to eliminate this deviation, the servo laser beam is focused on the hologram recording medium. It follows the groove of the HK track and moves in the radial direction.

  The focus error signal generation circuit 120 outputs the signals output from the respective photodetectors of the four-divided photodetector 52 and amplified by the signal amplification circuit 110 using (a + c) − (b + d), which is an arithmetic expression in the astigmatism method. The focus error signal is output to the focus servo circuit 122. The focus servo circuit 122 receives the focus error signal from the focus error signal generation circuit 120, creates a focus servo signal corresponding to the driving amount of the objective lens 40 for the input focus error signal to be 0, and drives the drive circuit 124. Output to. The drive circuit 124 receives a focus servo signal from the focus servo circuit 122 and supplies a signal for driving the objective lens 40 in the focus direction to the focus actuator 44 based on this signal.

  Focus servo control is performed by the quadrant photodetector 52, the focus error signal generation circuit 120, the focus servo circuit 122, the drive circuit 124, and the focus actuator 44.

  When the original data is input from the controller 300, the recording signal generation circuit 204 converts the input original data into two-dimensional binary data and stores it in a memory in the circuit. When an output command is input from the controller 300, the two-dimensional binarized data stored at a predetermined time interval is output to the spatial light modulator 16. The recording signal generation circuit 204 outputs data in which all dots (pixels) of the spatial light modulator 16 stored in the memory are bright when a data reproduction start command is input from the controller 300.

  The reproduction data generation circuit 212 starts to operate when an operation start command is input from the controller 300. When the hologram recording medium HK is irradiated with only the reference laser beam, the reproduction data generation circuit 212 receives the reproduction light from the hologram recording medium HK, thereby receiving the photodetector 26. A signal based on light and dark dots (corresponding to light and dark dots formed in the spatial light modulator 16 in data recording) formed on (for example, formed by CCD or CMOS) is input, and two-dimensional from this signal The binarized data (corresponding to the signal generated by the recording signal generation circuit 204) is generated, and this data is converted in reverse to the data conversion performed by the recording signal generation circuit 204 to decode the original data. And output to the controller 300.

  The rotation driving circuit 216 starts operating when an operation start command is input from the controller 300, and receives a signal output from the focus servo circuit 122, which is a signal corresponding to the amount of movement from the neutral position of the objective lens 40, A signal corresponding to the rotational drive amount is created by the arithmetic expression of the above-described equation 6 set in the circuit or a correlation table, and is output to the rotating glass plates 60 and 62.

  In the hologram recording / reproducing apparatus 1 configured as described above, when the operator sets the hologram recording medium HK on the turntable 130 and instructs the start of data recording or data reproduction from the input device 304, the controller 300 operates on each circuit. A start command is output, and data recording or data reproduction is performed in the same manner as a normal hologram recording / reproducing apparatus. At this time, since the rotation drive circuit 216 rotates the rotating glass plates 60 and 62 based on the movement amount of the objective lens 40, the position of the entrance pupil plane of the objective lens 40, the image formation position of the dot pattern, and the incidence of the objective lens 40 The position of the pupil plane and the position at which the dot pattern is formed on the surface of the photodetector 26 always coincide with each other, so that accurate data recording and data reproduction can be performed.

  Further, since the driving of the plate-like object in the optical path length varying means is the rotational driving in which the glass plates 60a and 62a, which are plate-like objects, are rotated around the rotation axis perpendicular to the optical path, it can be driven by a simple driving mechanism. Therefore, it is easy to drive in accordance with the driving of the objective lens 40, and a large drive mechanism is not required.

  Further, since two glass plates 60a and 62a rotate by the same amount in the opposite direction, even if one plate-shaped object changes to the optical path position along with the optical path length by rotation, the other plate-shaped object By rotating, the optical path position can be returned to the original position, and only the optical path length can be changed.

  Furthermore, since the material of the plate-like object is glass, the cost of the plate-like object can be suppressed.

  FIG. 5 is a block diagram showing a second embodiment of the hologram recording / reproducing apparatus according to the present invention. FIG. 6 is an explanatory view showing the rotation of the rotating glass plate accompanying the radial movement of the objective lens and the raising mirror. In this embodiment, in order to make the optical axis of the objective lens 40 coincide with the optical axis of the laser beam, the objective lens 40 is driven alone in the focusing direction, and the objective lens 40 and the rising mirror 54 are integrated into a radius. Drive in the direction. For this reason, variation in the position of the entrance pupil plane of the objective lens 40 due to driving in the focus direction and driving in the radial direction is taken into consideration.

  The difference from the first embodiment is that the objective lens 40 and the rising mirror 54 are integrally driven in the radial direction, and the signals of the focus servo circuit 122 and the tracking servo circuit 114 are input to the rotation drive circuit 216. It is only a point. The other configuration is the same as that of the first embodiment.

  The rotation drive circuit 216 corresponds to a signal output from the focus servo circuit 122, which is a signal corresponding to the amount of movement of the objective lens 40 from the neutral position in the focus direction, and the amount of movement of the objective lens 40 from the neutral position in the radial direction. And a signal (a signal corresponding to ΔX + ΔY described later) obtained by amplifying the two signals with an appropriate amplification factor and adding the two signals. A signal corresponding to the rotational drive amount is created by the arithmetic expression of Equation 6 or the correlation table, and is output to the rotating glass plates 60 and 62. ΔX in this case is ΔX + ΔY obtained by adding ΔX, which is the amount of movement from the neutral position in the focus direction shown in FIG. 3, and ΔY, which is the amount of movement from the neutral position in the radial direction shown in FIG.

  That is, FIGS. 6A and 6B show how the rotating glass plates 60 and 62 rotate with respect to the change ΔY of the position of the entrance pupil plane in the movement in the radial direction when there is no movement in the focus direction. Also in this case, the position of the entrance pupil plane of the objective lens 40 and the image of the dot pattern are changed by changing the optical path length by ΔY with respect to the change of the entrance pupil plane position ΔY as in the movement in the focus direction shown in FIG. The position and the position of the entrance pupil plane of the objective lens 40 can coincide with the position where the dot pattern is imaged on the surface of the photodetector 26. When there is a movement amount ΔX in the focus direction in the movement amount ΔY in the radial direction, the change in the position of the entrance pupil plane is ΔX + ΔY, and therefore ΔX in the equation (6) should be ΔX + ΔY.

  The first and second embodiments can be variously modified. In the above embodiment, the signal output from the focus servo circuit 122 (the focus servo circuit 122 and the tracking servo circuit 114) is used as a signal corresponding to the amount of change from the neutral position of the objective lens 40. The apparatus 200 is provided with position sensors 42 and 43 that change the state of a signal output depending on the driving position of the objective lens 40. Based on the signals output by the position sensors 42 and 43, a displacement amount signal generation circuit A214 (displacement amount signal) is provided. A signal corresponding to the displacement amount of the objective lens 40 may be generated by the generation circuit A214 and the displacement amount signal generation circuit B215), and this signal may be used. The parentheses indicate the case of Example 2. As the position sensors 42 and 43, for example, a combination of a light emitting element and a photodetector can be used.

  In the second embodiment, the variation in the position of the entrance pupil plane of the objective lens 40 due to the driving of the objective lens 40 in the focus direction and the radial direction is considered. However, the hologram recording medium HK hardly fluctuates due to rotation. If there is, only a change in the position of the entrance pupil plane of the objective lens 40 due to the radial drive of the objective lens 40 needs to be considered. In this case, only the signal output from the tracking servo circuit 114 may be input to the rotation drive circuit 216.

  Furthermore, in Example 1 and Example 2 described above, the two pairs of rotating glass plates 60 and 62 were rotated in the opposite direction by the same amount. However, if cost is not important, the number of rotating glass plates is one. The rotating direction of the laser light may be changed and transmitted through the rotating glass plate twice from the opposite direction. According to this, the number of optical components such as mirrors increases, but the same effect as in the above embodiment can be obtained. Moreover, in the said Example 1 and Example 2, although the glass plate was used for the plate-shaped object to rotate, as long as a refractive index is moderate, you may use the board | plates of raw materials other than glass.

  Furthermore, in the said Example 1 and Example 2, although the rotating glass plates 60 and 62 which became two pairs were rotated with the motor, as shown in FIG. 7, the supporting member which attached the glass plates 60a and 62a is shown. It may be configured such that it is set on an arc-shaped rail and moves on the rail. In this case, if the support member is attached to the moving direction side from the center line of the glass plate in the vertical direction of the moving direction, even if the glass plate moves, the optical axis of the laser beam overlaps with any part of the glass plate. Good. Also by this, the same effect as the above embodiment can be obtained.

  In the first embodiment, an SLM (Spatial Light Modulator) is used as the spatial light modulator 16, but a DMD (Degital Micro Mirror Device) or a GLV (Grating Light Valve) may be used instead. Also by this, the same effect as the above embodiment can be obtained.

  Further, in the first and second embodiments, the spindle motor 132 and the turntable 130 are moved by the feed motor 134 so that the focal point of the laser beam on the hologram recording medium HK is moved in the radial direction. 200 and 220 may be moved by the feed motor 134. Also by this, the same effect as the above embodiment can be obtained.

  In the first and second embodiments, the astigmatism method is used for focus servo control and the push-pull method is used for tracking servo control. However, other control methods such as the edge knife method and the differential push-pull method are used. It may be used. Also by this, the same effect as the above embodiment can be obtained. As described above, various modifications can be made without departing from the object of the present invention.

  As described above, according to the present invention, it is easy to drive in accordance with the driving of the objective lens, and does not require a large driving mechanism, and the position of the entrance pupil plane of the objective lens and the dot pattern of the spatial light modulator The hologram recording apparatus and hologram reproducing apparatus capable of always matching the image forming position and the position of the entrance pupil plane of the objective lens with the position for imaging the dot pattern reproduced on the surface of the light receiver are provided. Can do.

1 is a configuration diagram showing a first embodiment of a hologram recording / reproducing apparatus according to the present invention. It is explanatory drawing which shows arrangement space | intervals, such as a spatial light modulator, a light receiver, a relay lens, an objective lens, in the hologram recording / reproducing apparatus. It is explanatory drawing which showed rotation of the rotation glass plate accompanying the movement of the focus direction of an objective lens. It is explanatory drawing which showed the change of the optical path length by rotation of a rotating glass plate. It is a block diagram which shows 2nd Embodiment of the hologram recording / reproducing apparatus which concerns on this invention. It is explanatory drawing which showed rotation of the rotation glass plate accompanying the movement of the objective lens and a raising mirror to the radial direction. It is explanatory drawing which showed the other drive method of the glass plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Hologram recording / reproducing apparatus 2 ... Hologram recording / reproducing apparatus 10 ... Laser light source 12 ... Collimating lens 14 ... Mirror 16 ... Spatial light modulator 18 Relay lens 20 Polarizing beam splitter 22 Relay lens 24 Relay lens 26 Photo detector 28 Mirror 30 Laser light source 32 ··· Collimating lens 34 ··· Beam splitter 36 ··· 1/4 wavelength plate 38 · · · Dichroic prism 40 · · · Objective lens 42 · · · Position sensor 43 · · · Position sensor 44 .... Focus actuator 46 ... Tracking actuator 48 ... Condensing lens 50 ... Cylindrical lens 52 ... 4 Split photo detector 54 ... Rising mirror 60 ... Rotating glass plate 60a ... Glass plate 60b ... Motor 62 ... Rotating glass plate 62a ... Glass plate 62b ... Motor 102 ... ..Spindle motor control circuit 106 ... radial position detection circuit 108 ... feed motor control circuit 110 ... signal amplification circuit 112 ... tracking error signal generation circuit 114 ... tracking servo circuit 116 ... drive Circuit 118 ... Thread servo circuit 120 ... Focus error signal generation circuit 122 ... Focus servo circuit 124 ... Drive circuit 130 ... Turntable 132 ... Spindle motor 134 ... Feed motor 200 ..Pickup device 202 ... Recording laser drive circuit 204 Recording signal generation circuit 210 ... Servo laser drive circuit 212 ... Reproduction data generation circuit 214 ... Displacement amount signal generation circuit 215 ... Displacement amount signal generation circuit 216 ... Rotation drive circuit 220 ... Pickup device 300 ... Controller 302 ... Display device 304 ... Input device

Claims (6)

A turntable on which the hologram recording medium is mounted, a table rotating means for rotating the turntable, and the original data is converted into two-dimensional binarized data while being rotated by the table rotating means. An information laser beam is generated based on two-dimensional binarized data, and the generated information laser beam is irradiated onto the hologram recording medium through an objective lens together with a reference laser beam having no information, and the hologram recording medium A data recording means for recording data in a shift multiplex manner, and a servo laser beam via the objective lens with respect to the reflection layer formed on the hologram recording medium while being rotated by the table rotating means. , And the focal position of the servo laser beam by the objective lens matches the reflective layer by a signal created based on the reflected light from the reflective layer. A focus servo for driving the objective lens or an optical component including the objective lens, or the objective lens or the servo lens so that a focal position of the servo laser beam by the objective lens is aligned with a groove of a track formed in the reflective layer. In a hologram recording apparatus having servo means for performing at least one of tracking servos for driving an optical component including an objective lens,
A plate-like object having a refractive index different from that of air, which is disposed on the optical path of the information laser light and before the entrance pupil plane of the objective lens;
At least a signal corresponding to the driving amount of the objective lens from the neutral position in the focus direction by the servo means or a signal corresponding to the driving amount of the objective lens from the neutral position in the radial direction of the hologram recording medium by the servo means. A hologram recording apparatus comprising: an optical path length varying unit that inputs one signal, drives the plate-like object based on the input signal, and varies the optical path length of the information laser beam. A turntable on which the hologram recording medium is mounted, a table rotating means for rotating the turntable, and a reference laser beam having no information is shifted and multiplexed on the hologram recording medium while being rotated by the table rotating means. Data reproducing means for irradiating the data recording location recorded by the method, receiving the reproduction light from the data recording location, and reproducing the data recorded in the data recording location based on the received reproduction light; While the rotation by the table rotating means is being performed, the reflection layer formed on the hologram recording medium is irradiated with servo laser light via the objective lens, and based on the reflection light from the reflection layer The objective lens or the light including the objective lens so that the focal position of the servo laser beam by the objective lens matches the reflective layer by the signal generated by Focus servo for driving a component, or tracking servo for driving the objective lens or an optical component including the objective lens so that the focus position of the servo laser beam by the objective lens matches a groove of a track formed in the reflective layer A hologram reproducing apparatus having servo means for performing at least one of the following:
A plate-like object having a refractive index different from that of air, which is disposed on the optical path of the information laser light and before the entrance pupil plane of the objective lens;
At least a signal corresponding to the driving amount of the objective lens from the neutral position in the focus direction by the servo means or a signal corresponding to the driving amount of the objective lens from the neutral position in the radial direction of the hologram recording medium by the servo means. 1. A hologram reproducing apparatus comprising: an optical path length varying unit that inputs one signal, drives the plate-like object based on the input signal, and varies the optical path length of the information laser beam.   3. The drive of the plate-like object in the optical path length varying means is a rotary drive in which the plate-like object is rotated by a rotation axis perpendicular to the optical path of the information laser light. Hologram recording apparatus or hologram reproducing apparatus.   The plate-like object is composed of two pieces of the same material and the same thickness, and is arranged in parallel on the optical path, and the rotational drive of the plate-like object in the optical path length varying means is the axis of the rotation axis. 4. A hologram recording apparatus or a hologram reproducing apparatus according to claim 3, wherein the directions are the same, and the plate-like objects are rotated by an equal amount in the opposite directions. Tracking servo in the servo means drives an optical component including the objective lens,
The optical path length variable means inputs a signal corresponding to the driving amount from the neutral position of the objective lens in the focus direction and a signal corresponding to the driving amount of the objective lens from the neutral position in the radial direction of the hologram recording medium. The hologram recording apparatus or the hologram reproducing apparatus according to claim 1, wherein the plate-like object is driven based on the two input signals.   The hologram recording apparatus or hologram reproduction apparatus according to claim 1, wherein a material of the plate-like object is glass.

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