JP2009277292A - Optical information recording device and optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce loads on servo control. <P>SOLUTION: A first optical beam Lb1 and a second optical beam Lb2 sharing an optical axis Lx are emitted via one and the same objective lens 47, and the second optical beam Lb2 is reflected on a reflection layer 104 to superimpose the first optical beam Lb1 and the second optical beam Lb2 on each other from opposite directions. In this case, in the optical pickup 26, the aperture of the second optical beam Lb2 is restricted, for controlling so that a beam west diameter S2 of a second reflected optical beam Lb2r becomes larger than a beam west diameter S1 of the first optical beam Lb1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical information recording apparatus and an optical pickup, and is suitably applied to, for example, an optical disk apparatus that records information on a recording medium using a light beam.

  Conventionally, as an optical information recording / reproducing apparatus, an optical disk apparatus using a disk-shaped optical disk having an information recording layer as an information recording medium has been widely used. As an information recording medium, generally, a CD (Compact Disc), a DVD (Digital Versatile Disc) and Blu-ray Disc (registered trademark, hereinafter referred to as BD) are used.

  By the way, in the optical disc apparatus, various kinds of information such as various contents such as music contents and video contents, or various data for computers are recorded on the optical disc. In particular, in recent years, the amount of information has increased due to higher definition of video and higher sound quality of music, and an increase in the number of contents to be recorded on one optical disc has been demanded. It has been demanded.

  Therefore, as shown in FIG. 1, the first light beam Lb1 and the second light beam are obtained by separating the light beam emitted from one light source into the first light beam Lb1 and the second light beam Lb2 and irradiating them on the same position. There has been proposed an optical disc apparatus in which a small hologram is recorded as a recording mark by causing Lb2 to interfere (see, for example, Patent Document 1).

  In this optical disc apparatus, the first light beam Lb1 and the second light beam Lb2 are condensed by the same objective lens OL, and the second light beam Lb2 is reflected by the reflection layer 104 formed on the optical disc 100. As a result, the second reflected light beam Lb2r formed by reflecting the first light beam Lb1 and the second light beam Lb2 is irradiated to the same position from opposite directions.

In this optical disc apparatus, information corresponding to a plurality of layers is recorded in one recording layer by forming a plurality of layers in the thickness direction (that is, the focus direction) of the optical disc so that the capacity of the optical disc is increased. Has been made.
JP 2007-220206 A (FIGS. 1, 4 and 5)

  By the way, in the optical disc apparatus having such a configuration, when the optical disc 100 is not tilted due to surface blurring or distortion, the optical axis Lx of the light beam Lb when incident on the reflective layer 104 and the reflection reflected by the reflective layer 104. The optical axis Lxr of the light beam can be matched. Therefore, in the optical disc apparatus, as shown in FIG. 1, the optical axis Lx1 of the first light beam Lb1 and the optical axis Lx2r of the second reflected light beam Lb2 can be made substantially coincident.

  That is, in the optical disc apparatus, since the focal points Fb1 and Fb2 coincide with the tracking direction which is the radial direction of the optical disc 100 and the tangential direction perpendicular to the tracking direction and the focusing direction, the focal points Fb1 and Fb2 are adjusted only in the focusing direction. Accordingly, the first light beam Lb1 and the second light beam Lb2 can be irradiated to the same position.

  However, in the optical disc apparatus, as shown in FIG. 2A, when the optical disc 100 has a tilt, the optical axis Lx1 of the first light beam Lb1 and the optical axis Lx2r of the second reflected light beam Lb2r are completely set. Cannot match. For this reason, in the optical disk apparatus, for example, by using a galvano mirror, servo control is performed so as to shift the optical axis Lx2 from the optical axis Lx1 as shown in FIG. Need to adjust.

  At this time, in the optical disc apparatus, a hologram is formed only in a portion where the first light beam Lb1 and the second light beam Lb2 overlap. Therefore, the focus of the first light beam Lb1 and the second light beam Lb2 is adjusted by precise servo control. There is a problem that it is necessary to superimpose accurately and a great load is applied to the servo control.

  The present invention has been made in view of the above points, and an object of the present invention is to propose an optical information recording apparatus and an optical pickup capable of reducing the load of servo control.

  In order to solve this problem, in the optical information recording apparatus of the present invention, a separation unit that separates light emitted from the light source into first and second light, a reflective layer that reflects the first and second light, and Condensing and irradiating the first and second light onto an optical information recording medium having a recording layer for recording a hologram formed by overlapping the first and second light from opposite directions as a recording mark Forming an objective lens, an aperture limiter for limiting the beam diameter of the first or second light to be smaller than the effective diameter of the objective lens, and a recording mark in the depth direction approaching or separating from the optical information recording medium A first focal point moving unit that moves the focal point of the first light to the target depth to be adjusted, and a second focal point of the second reflected light obtained by reflecting the second light by the reflective layer to the target depth. The focal point moving part is provided.

  Thereby, the first light and the second reflected light can be combined with each other even if the focus of the first light and the focus of the second reflected light are not accurately superimposed on the tracking direction and the tangential direction perpendicular to the depth direction. Can be duplicated.

  In order to solve such a problem, in the optical pickup of the present invention, the separation unit that separates the light emitted from the light source into the first and second light, the reflective layer that reflects the first and second light, and the first And an objective for condensing and irradiating the first and second light onto an optical information recording medium having a recording layer that records a hologram formed by overlapping the second light from opposite directions as a recording mark. A lens, an aperture limiting portion that limits the light beam diameter of the first or second light to be smaller than the effective diameter of the objective lens, and a recording mark in the depth direction that is close to or away from the optical information recording medium should be formed A first focus moving unit that moves the focus of the first light to the target depth, and a second focus that adjusts the focus of the second reflected light obtained by reflecting the second light by the reflection layer to the target depth. A moving part is provided.

  Thereby, the first light and the second reflected light can be combined with each other even if the focus of the first light and the focus of the second reflected light are not accurately superimposed on the tracking direction and the tangential direction perpendicular to the depth direction. Can be duplicated.

  According to the present invention, the first light and the second reflection can be obtained without accurately overlapping the focus of the first light and the focus of the second reflected light in the tracking direction and the tangential direction perpendicular to the depth direction. It is possible to realize an optical information recording apparatus and an optical pickup that can overlap light and thus reduce the load of servo control.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

(1) Configuration of Optical Disc First, the optical disc 100 used as an optical recording medium in the present invention will be described. As shown in the external view in FIG. 3A, the optical disc 100 as a whole is formed in a disk shape having a diameter of about 120 [mm], similar to the conventional CD, DVD and BD, and has a hole 100H at the center. Is formed.

  3B, the optical disk 100 includes a recording layer 101 for recording information, a substrate 103, and a reflective layer 104, and the reflective layer 104 is sandwiched between the recording layer 101 and the substrate 103. It is configured.

  Incidentally, the thickness t1 of the recording layer 101 is about 0.25 [mm], and the thickness t2 of the substrate 103 is about 1.0 [mm].

  The substrate 103 is made of a material such as polycarbonate or glass. The substrate 103 has a certain degree of strength and also plays a role of protecting the recording layer 101. The substrate 103 is not limited in terms of light transmission, and either a material that transmits light highly or a material that does not transmit light can be used.

  The recording layer 101 is made of a photopolymer whose refractive index changes depending on the intensity of irradiated light, and responds to a light beam Lb having a wavelength of 405 [nm]. As shown in FIG. 3B, when the first light beam Lb1 and the second light beam Lb2 for recording information having a relatively strong intensity interfere in the recording layer 101, the recording layer 101 is not fixed. Waves are generated, and an interference pattern having properties as a hologram is formed.

  In the following, the surface on the recording layer 101 side of the optical disc 100 is referred to as an incident surface 100A, and the surface on the substrate 103 side of the optical disc 100 is referred to as a back surface 100B.

  The optical disc 100 also has a reflective layer 104 at the boundary surface between the recording layer 101 and the substrate 103. The reflective layer 104 is made of an aluminum film, a dielectric multilayer film, or the like used for a conventional optical disc, and reflects most of the light beam Lb having a wavelength of 405 [nm].

  Further, the reflective layer 104 forms a guide groove for tracking servo. Specifically, a spiral track is formed by lands and grooves similar to a general BD-R (Recordable) disk or the like. . This track is given an address consisting of a series of numbers for each predetermined recording unit, and the track on which information is recorded or reproduced can be specified by the address.

  Note that pits or the like may be formed in the reflective layer 104 (that is, the boundary surface between the recording layer 101 and the substrate 103) instead of the guide grooves, or the guide grooves and pits may be combined.

  When the servo light beam LbS having a wavelength of 405 [nm] is irradiated from the incident surface 100A side, the reflective layer 104 reflects this toward the incident surface 100A side. Hereinafter, the servo light beam LbS reflected at this time is referred to as a servo reflected light beam LbSr.

  The servo reflected light beam LbSr is assumed to be used for position control (that is, focus control and tracking control) of a predetermined objective lens OL1, for example, in an optical disc apparatus. That is, the servo reflected light beam LbSr is adjusted to a target track (hereinafter referred to as a target mark position) for the focal points Fb1 and Fb2 of the first light beam Lb1 and the second light beam Lb2 collected by the objective lens OL1. Used for.

  In practice, when information is recorded on the optical disc 100, the servo light beam LbS is condensed by the position-controlled objective lens OL1 as shown in FIG. This is called a desired servo position).

  Also, the first light beam Lb1 that shares the optical axis Lx with the servo light beam LbS and is condensed by the objective lens OL1 is incident from the incident surface 100A and is on the near side of the desired track in the recording layer 101 (that is, It is focused on a position corresponding to the incident surface 100A side). At this time, when the focal point Fb1 of the first light beam Lb1 is based on the objective lens OL1, the degree of divergence or convergence of the first light beam Lb when entering the objective lens OL1 (hereinafter referred to as a convergence state). The position is positioned before the desired servo position on the common optical axis Lx.

  Furthermore, the second light beam Lb2 having the same wavelength as the first light beam Lb1 and sharing the optical axis Lx is condensed by the objective lens OL1 from the same direction as the first light beam Lb1 (that is, the incident surface 100A side). , Is designed to be irradiated. At this time, the second light beam Lb2 is transmitted through the recording layer 101, reflected by the reflective layer 104, and becomes the second reflected light beam Lb2r, and is focused on a position corresponding to the front side of the desired servo position in the recording layer 101. Is done.

  At this time, the focal point Fb1 of the first light beam Lb1 is a focal point on the common optical axis Lx according to the convergence state of the first light beam Lb when entering the objective lens OL1 when the objective lens OL1 is used as a reference. The light is irradiated at substantially the same position as Fb1.

  As a result, on the optical disc 100, a recording mark RM having a relatively small interference pattern is recorded as a minute hologram at the position of the focal point Fb1 and the focal point Fb2 corresponding to the front side of the desired servo position in the recording layer 101.

  At this time, the recording mark RM is formed in the recording layer 101 where the first light beam Lb1 and the second light beam Lb2 both of which are converged light overlap and have a predetermined intensity or more.

  Incidentally, regarding the recording mark RM, with respect to the diameter RMr in the central portion, assuming that the wavelengths of the first light beam Lb1 and the second light beam Lb2 are λ [m] and the numerical aperture of the objective lens OL1 is NA (1) ).

  The height RMh of the recording mark RM can be obtained by the following equation (2), where n is the refractive index of the recording layer 101.

  For example, when the wavelength λ is 405 [nm], the numerical aperture NA is 0.5, and the refractive index n is 1.5, the diameter RMr = 0.97 [μm] from the formula (1) and the height from the formula (2). RMh = 9.72 [μm].

  Further, the optical disc 100 is designed such that the thickness t1 (= 0.25 [mm]) of the recording layer 101 is sufficiently larger than the height RMh of the recording mark RM. Therefore, as shown in FIGS. 4A and 4B, the optical disc 100 is switched while the distance between the focal point Fb1 and the focal point Fb2 from the reflective layer 104 in the recording layer 101 (hereinafter referred to as depth) is switched. By recording the recording mark RM, multilayer recording in which a plurality of mark recording layers are stacked in the thickness direction of the optical disc 100 can be performed.

  In this case, the depth of the recording mark RM is changed by adjusting the depths of the focal point Fb1 and the focal point Fb2 in the recording layer 101 of the optical disc 100. For example, as shown in FIG. 5, when the distance p3 between the mark recording layers is set to about 15 [μm] in consideration of the mutual interference between the recording marks RM, the optical disc 100 has about 16 in the recording layer 101 as shown in FIG. A mark recording layer can be formed. The distance p3 may be set to various values other than about 15 [μm] in consideration of the mutual interference between the recording marks RM.

  On the other hand, when the information is reproduced, the optical disc 100 is focused so that the servo light beam LbS condensed by the objective lens OL1 is focused on the desired servo position of the reflective layer 104 when the information is recorded. The position of the objective lens OL1 is controlled.

  Further, in the optical disc 100, the focal point Fb1 of the first light beam Lb1 through the same objective lens OL1 corresponds to the “front side” of the desired servo track in the recording layer 101 and has a target depth (hereinafter referred to as “below”). This is called a target mark position).

  At this time, the recording mark RM recorded at the position of the focal point Fb1 generates a reproduction light beam LbG from the recording mark RM recorded at the target mark position due to the property as a hologram. The reproduction light beam LbG has the same optical characteristics as the second reflected light beam Lb2r irradiated during recording of the recording mark RM, and as shown in FIG. 6, the same direction as the second reflected light beam Lb2r. In other words, it proceeds while diverging from the recording layer 101 to the incident surface 100A side.

  Thus, when information is recorded on the optical disc 100, the servo light beam LrS for position control, the first light beam Lb1 and the second light beam Lb2 for information recording are used. At this time, in the optical disc 100, a recording mark RM is formed as the information at a position where the focal point Fb1 and the focal point Fb2 overlap in the recording layer 101, that is, a target mark position on the reflective layer 104 that is in front of the desired servo position and has a target depth. It is made to be done.

  Further, when recorded information is reproduced, the optical disc 100 is recorded at the position of the focal point Fb1, that is, the target mark position by using the servo light beam LbS for position control and the first light beam Lb1 for information reproduction. A reproduction light beam LbG is generated from the recorded mark RM.

(2) Configuration of Optical Disc Device Next, the optical disc device 20 corresponding to the optical disc 100 described above will be described. As shown in FIG. 7, the optical disc apparatus 20 is configured to perform overall control by a control unit 21.

  The control unit 21 is mainly configured by a CPU (Central Processing Unit) (not shown), reads various programs such as a basic program and an information recording program from a ROM (Read Only Memory) (not shown), and stores them in a RAM (Random) (not shown). Various processes such as an information recording process and an information reproduction process are executed by developing the data in an “Access Memory”.

  For example, when the control unit 21 receives an information recording command, recording information, and recording address information from an external device (not shown) with the optical disc 100 loaded, the control unit 21 supplies the recording address information and the driving command to the drive control unit 22. The recording information is supplied to the signal processing unit 23. Incidentally, the recording address information is information indicating an address at which the recording information is to be recorded among the addresses given to the recording layer 101 of the optical disc 100.

  The drive control unit 22 drives and controls the spindle motor 24 in accordance with the drive command to rotate the optical disc 100 at a predetermined rotation speed, and controls the sled motor 25 to drive the optical pickup 26 with the moving shafts 25A and 25B. Are moved to a position corresponding to the recording address information in the radial direction of the optical disc 100 (that is, the inner circumferential direction or the outer circumferential direction).

  The signal processing unit 23 generates a recording signal by performing various signal processing such as predetermined encoding processing and modulation processing on the supplied recording information, and supplies the recording signal to the optical pickup 26.

  The optical pickup 26 performs focus control and tracking control based on the control of the drive control unit 22, so that a track indicated by recording address information in the recording layer 101 of the optical disc 100 (hereinafter referred to as a target mark position). The focal positions of the first light beam Lb1 and the second light beam Lb2 are aligned, and a recording mark RM corresponding to the recording signal from the signal processing unit 23 is recorded (details will be described later).

  When the control unit 21 receives, for example, an information reproduction command and reproduction address information indicating the address of the recording information from an external device (not shown), the control unit 21 supplies the drive command to the drive control unit 22 and also reproduces the reproduction processing command. Is supplied to the signal processing unit 23.

  As in the case of recording information, the drive control unit 22 controls the spindle motor 24 to rotate the optical disc 100 at a predetermined rotational speed, and controls the sled motor 25 to control the optical pickup 26 for reproduction addressing. Move to a position corresponding to the information.

  The optical pickup 26 performs focus control and tracking control based on the control of the drive control unit 22, so that the first light beam Lb 1 is applied to the track (that is, the target mark position) indicated by the reproduction address information in the recording layer 101 of the optical disc 100. And a predetermined amount of light beam is irradiated. At this time, the optical pickup 26 detects the reproduction light beam LbG generated from the recording mark RM of the recording layer 101 in the optical disc 100 and supplies a detection signal corresponding to the light amount to the signal processing unit 23 ( Details will be described later).

  The signal processing unit 23 generates reproduction information by performing various signal processing such as predetermined demodulation processing and decoding processing on the supplied detection signal, and supplies the reproduction information to the control unit 21. In response to this, the control unit 21 sends the reproduction information to an external device (not shown).

  As described above, the optical disc apparatus 20 controls the optical pickup 26 by the control unit 21 to record information at the target mark position in the recording layer 101 of the optical disc 100 and reproduce information from the target mark position. ing.

(3) Configuration of Optical Pickup Next, the configuration of the optical pickup 26 will be described. As schematically shown in FIG. 8, the optical pickup 26 is provided with a large number of optical components, and is roughly composed of a servo optical system 40 and an information optical system 60.

  The laser diode 41 emits a light beam Lb having a wavelength of about 405 [nm]. In practice, the laser diode 41 emits a light beam Lb having a predetermined light amount, which is a divergent light, based on the control of the control unit 21 (FIG. 7) and makes it incident on the collimator lens 42. The collimator lens 42 converts the light beam Lb from diverging light into parallel light and makes it incident on the non-polarizing beam splitter 43.

  The non-polarizing beam splitter 43 transmits and reflects the light beam Lb at a predetermined ratio by the reflection / transmission surface 43S. For this reason, the non-polarizing beam splitter 43 transmits a part of the light beam Lb through the reflection / transmission surface 43S, and enters the mirror 44 in the servo optical system 40 as the servo light beam LbS, while reflecting a part of the light beam Lb. Then, the light is incident on the half-wave plate 61 in the information optical system 60.

(3-1) Configuration of Servo Optical System As shown in FIG. 9, the servo optical system 40 irradiates the reflection layer 104 of the optical disc 100 with a servo light beam LbS, and the reflection layer 104 causes the servo light beam LbS to be irradiated. The servo reflected light beam LSr is reflected.

  The mirror 44 reflects the servo light beam LbS that has passed through the non-polarizing beam splitter 43, changes its traveling direction by 90 °, and enters the non-polarizing beam splitter 45.

  The non-polarization beam splitter 45 transmits and reflects the light beam Lb at a predetermined ratio by the reflection / transmission surface 45S, and causes the transmitted servo light beam LbS to enter the non-polarization beam splitter 46.

  The non-polarizing beam splitter 46 transmits and reflects the light beam at a predetermined ratio by the reflection / transmission surface 46 </ b> S, and causes the transmitted servo light beam LbS to enter the objective lens 47.

  The objective lens 47 condenses the servo light beam LbS and irradiates the incident surface 100 </ b> A of the optical disc 100. At this time, as shown in FIG. 3B, the servo light beam LbS is transmitted through the recording layer 101 and reflected by the reflective layer 104 to become a servo reflected light beam LbSr that goes in the opposite direction to the servo light beam LbS.

  Thereafter, the servo reflected light beam LbSr is converted into parallel light by the objective lens 47, and then sequentially passes through the non-polarizing beam splitters 46 and 45 and the mirror 44 and enters the non-polarizing beam splitter 43.

  The non-polarizing beam splitter 43 causes the servo reflected light beam LbSr reflected on the reflection / transmission surface 43 </ b> S to enter the condenser lens 51.

  The condensing lens 51 converges the servo reflected light beam LbSr, gives astigmatism by the cylindrical lens 52, and irradiates the photodetector 53 with the servo reflected light beam LbSr.

  By the way, in the optical disc apparatus 20, since there is a possibility that surface blurring or the like occurs in the rotating optical disc 100, the relative position of the desired servo position with respect to the servo optical system 40 may vary.

  Therefore, in order for the servo optical system 40 to follow the focal point Fs (FIG. 3B) of the servo light beam LbS to the desired servo position, the focal point Fs is in the proximity direction or the separation direction with respect to the optical disc 100 and the optical disc. It is necessary to move in the tracking direction which is the inner peripheral side direction or the outer peripheral side direction.

  Therefore, the objective lens 47 can be driven in the biaxial direction of the focus direction and the tracking direction by the biaxial actuator 47A.

  In the servo optical system 40 (FIG. 9), the focused state when the servo light beam LbS is collected by the objective lens 47 and applied to the reflective layer 104 of the optical disc 100 is the focused state when the servo reflected light beam LbSr is collected by the condenser lens 51. The optical positions of various optical components are adjusted so as to be reflected in the focused state when the light is condensed and irradiated to the photodetector 53.

  As shown in FIG. 10, the servo photodetector 53 has four detection areas 53A, 53B, 53C, and 53D divided in a lattice pattern on the surface irradiated with the servo reflected light beam LbSr. Incidentally, the direction (vertical direction in the figure) indicated by the arrow a1 corresponds to the traveling direction of the track when the servo reflected light beam LbSr is applied to the reflective layer 104 (FIG. 3).

  The servo photodetector 53 detects a part of the servo reflected light beam LbSr by the detection areas 53A, 53B, 53C, and 53D, and generates detection signals SDAs, SDBs, SDCs, and SDDs according to the amount of light detected at this time. These are sent to the signal processing unit 23 (FIG. 7).

  The signal processing unit 23 performs focus control by a so-called astigmatism method, calculates a focus error signal SFEs according to the following equation (3), and supplies this to the drive control unit 22.

  The focus error signal SFEs represents the amount of deviation between the focal point Fs of the servo light beam LbS and the reflective layer 104 of the optical disc 100.

  The signal processing unit 23 performs tracking control by a so-called push-pull method, calculates a tracking error signal STEs according to the following equation (4), and supplies the tracking error signal STEs to the drive control unit 22.

  The tracking error signal STEs represents the amount of deviation between the focal point Fs of the servo light beam LbS and the desired track on the reflective layer 104 of the optical disc 100.

  The drive control unit 22 generates a focus drive signal SFDs based on the focus error signal SFEs, and supplies the focus drive signal SFDs to the biaxial actuator 47A so that the servo light beam LbS is aligned with the reflective layer 104 of the optical disc 100. The objective lens 47 is feedback-controlled (that is, focus control) to focus.

  Further, the drive control unit 22 generates a tracking drive signal STDs based on the tracking error signal STEs and supplies the tracking drive signal STDs to the biaxial actuator 47A, whereby the servo light beam LbS is reflected on the reflective layer 104 of the optical disc 100. The objective lens 47 is feedback-controlled (that is, tracking control) so as to focus on the desired track.

  As described above, the servo optical system 40 irradiates the reflection layer 104 of the optical disc 100 with the servo light beam LbS, and supplies the light reception result of the servo reflected light beam LbSr that is the reflected light to the signal processing unit 23. . In response to this, the drive control unit 22 performs focus control and tracking control of the objective lens 47 so that the servo light beam LbS is focused on a desired servo position of the reflective layer 104.

(3-2) Configuration of information optical system (3-2-1) Reproduction of information (3-2-1-1) Irradiation of first light beam As shown in FIGS. During the information reproduction process, the optical disc 100 is irradiated with the first light beam Lb1, and the reproduction light beam LbG generated by irradiating the recording mark RM with the first light beam Lb1 is received. Has been made.

  In FIG. 11, when the light beam Lb that is linearly polarized light that has passed through the non-polarizing beam splitter 43 is incident on the half-wave plate 61 in the information optical system 60, P-polarized light and S-polarized light in the incident light beam Lb Is adjusted to a predetermined ratio, and enters the polarization beam splitter 62.

  The polarization beam splitter 62 reflects or transmits the light beam according to the polarization direction of the light beam by the reflection / transmission surface 62S. The polarization beam splitter 62 transmits the light beam Lb made of P-polarized light through the reflection / transmission surface 55S and enters the mirror 63, while reflecting the light beam Lb made of S-polarized light and makes it incident on the half-wave plate 81. . Hereinafter, the light beam Lb transmitted through the reflection / transmission surface 62S is referred to as a first light beam Lb1, and the light beam Lb reflected from the reflection / transmission surface 62S is referred to as a second light beam Lb2.

  The mirror 63 reflects the first light beam Lb1 transmitted through the polarizing beam splitter 62 by the reflecting surface 63S, changes its traveling direction by 90 °, and enters the quarter-wave plate 64.

  The quarter wavelength plate 64 converts the first light beam Lb1 from linearly polarized light to circularly polarized light and makes it incident on the relay lens 65.

  The relay lens 65 converts the first light beam Lb1 from parallel light to convergent light by the movable lens 66, and the convergence state (degree of convergence or divergence) of the first light beam Lb1 that becomes divergent light after convergence is a fixed lens. The light is adjusted by 67 and is incident on the non-polarizing beam splitter 46.

  Here, the movable lens 66 is moved in the optical axis direction of the first light beam Lb1 by the actuator 66A. In practice, the relay lens 65 can change the convergence state of the first light beam Lb1 emitted from the fixed lens 67 by moving the movable lens 61 by the actuator 66A based on the control of the control unit 21 (FIG. 7). It is made like that.

  The non-polarizing beam splitter 46 reflects the first light beam Lb1 by the reflection / transmission surface 46S and makes it incident on the objective lens 47.

  The objective lens 47 condenses the first light beam Lb1 and irradiates the incident surface 100A of the optical disc 100.

  At this time, as shown in FIG. 3B, the first light beam Lb1 enters from the incident surface 100A and is focused in the recording layer 101. Here, the position of the focal point Fb <b> 1 of the first light beam Lb <b> 1 is determined by the convergence state when it is emitted from the fixed lens 67 of the relay lens 65. That is, the focal point Fb1 moves to the incident surface 100A side or the back surface 100B side in the recording layer 101 according to the position of the movable lens 66.

  In practice, in the information optical system 60, the position of the movable lens 66 is controlled by the control unit 21 (FIG. 7), so that the focal point Fb1 (FIG. 4) of the first light beam Lb1 in the recording layer 101 of the optical disc 100 is obtained. The depth d (that is, the distance from the reflective layer 104) is adjusted.

  Incidentally, the information optical system 60 is designed so that the moving distance of the movable lens 66 and the moving distance of the focal point Fb1 of the first light beam Lb1 are substantially proportional to each other. For example, the movable lens 66 is moved by 1 [mm]. The focal point Fb2 of the first light beam Lb1 moves 30 [μm].

  Thus, the information optical system 60 shares the servo light beam LbS with the optical axis Lx via the objective lens 47 controlled by focusing the servo light beam LbS at the desired servo position. Irradiate with Lb1.

  Further, the information optical system 60 irradiates the first light beam Lb1 from the incident surface 100A side of the optical disc 100 to position the focal point Fb1 of the first light beam Lb1 in the recording layer 101, and further moves the movable lens 66 in the relay lens 65. The depth d of the focal point Fb1 is adjusted according to the position.

  As a result, the information optical system 60 is present in front of the desired track indicated by the desired servo position in the recording layer 101, and can focus the first light beam Lb1 on the target mark position having the target depth. Yes.

  In the information reproducing process, the information optical system 60 causes the second light beam Lb2 reflected by the polarization beam splitter 62 to enter the shutter 83 via the half-wave plate 81 and the aperture 82. At this time, the shutter 83 blocks the second light beam Lb2 so that the second light beam Lb2 does not enter the previous optical path.

(3-2-1-2) Receiving Reproduction Light Beam When the recording mark RM is formed at the target mark position, the optical disc 100 corresponds to the first light beam Lb according to the first light beam Lb as shown in FIG. The reproduction light beam LbG traveling in the direction opposite to the one light beam Lb1 is generated. The reproduction light beam LbG passes through the recording layer 101 and the substrate 103 and enters the objective lens 47.

  At this time, in the information optical system 60, the reproduction light beam LbG is converged to some extent by the objective lens 47, reflected by the non-polarizing beam splitter 46, and incident on the relay lens 65.

  Subsequently, the reproduction light beam LbG is converted into substantially parallel light by the fixed lens 67 and the movable lens 66 of the relay lens 65, and further converted from circularly polarized light to linearly polarized light (S polarized light) by the quarter wavelength plate 64. Further, the reproduction light beam Lb1t is reflected by the mirror 63 and enters the polarization beam splitter 62.

  The polarization beam splitter 62 reflects the reproduction light beam LbG according to the polarization direction of the reproduction light beam LbG and makes it incident on the condenser lens 70. The condensing lens 70 condenses the reproduction light beam LbG and irradiates the photodetector 72 via the pinhole plate 71.

  Here, as shown in FIG. 13, the pinhole plate 71 is disposed so that the focus of the reproduction light beam LbG collected by the condenser lens 70 (FIG. 12) is located in the hole 71H. The reproduction light beam LbG is passed as it is.

  On the other hand, as shown in FIG. 13, the pinhole plate 71 has a focal point that is reflected from, for example, the surface of the substrate 103 in the optical disc 100, the recording mark RM that exists at a position different from the target mark position, the reflective layer 104, and the like. Different light (hereinafter referred to as stray light LN) is substantially blocked. As a result, the photodetector 71 hardly detects the amount of stray light LN.

  As a result, the photodetector 72 generates the detection signal SDb corresponding to the light quantity of the reproduction light beam LbG without being affected by the stray light LN, and supplies the detection signal SDb to the signal processing unit 23 (FIG. 7). .

  In this case, the reproduction detection signal SDb accurately represents information recorded on the optical disc 100 as the recording mark RM. For this reason, the signal processing unit 23 generates reproduction information by performing predetermined demodulation processing, decoding processing, and the like on the reproduction detection signal SDb, and supplies the reproduction information to the control unit 21.

(3-2-2) Recording Information During the information recording process, the information optical system 60 of the optical pickup 26 applies the first light beam Lb1 and the second light beam Lb2 to the recording layer 101 via the same objective lens 47. It is designed to irradiate.

(3-2-2-1) Irradiation of First Light Beam As shown in FIG. 11, the information optical system 60 moves the position of the focal point Fb1 in the depth direction by the relay lens 65 in the same manner as in the information reproduction process. By irradiating the first light beam Lb1 through the objective lens 47 while adjusting, the first light beam Lb1 is irradiated to the target mark position.

  In the information recording process, the information optical system 60 receives the return light beam Lb1t by the photodetector 72, but does not use the light reception result.

(3-2-2-2) Irradiation of Second Light Beam In FIG. 14, as described above, the polarization beam splitter 62 of the information optical system 60 reflects the light beam Lb composed of S-polarized light on the reflection / transmission surface 62S, and This is incident on the half-wave plate 81 as the second light beam Lb2.

  The half-wave plate 81 converts the second light beam Lb made of S-polarized light into P-polarized light and makes it incident on the shutter 83 through an aperture 82 (described in detail later).

  The shutter 83 is configured to block or transmit the second light beam Lb2 based on the control of the control unit 21 (FIG. 7). In the information recording process, the shutter 83 transmits the second light beam Lb2 and makes it incident on the polarization beam splitter 84.

  Incidentally, as the shutter 83, for example, a mechanical shutter that blocks or transmits the second light beam Lb2 by mechanically moving a blocking plate that blocks the second light beam Lb2, or a voltage applied to the liquid crystal panel is changed. A liquid crystal shutter or the like that blocks or transmits the second light beam Lb2 can be used.

  The reflection / transmission surface 84S of the polarization beam splitter 84 transmits, for example, a P-polarized light beam at a rate of about 100% and reflects an S-polarized light beam at a rate of about 100%. In practice, the polarizing beam splitter 84 transmits the second light beam Lb2 made of P-polarized light as it is and makes it incident on the quarter-wave plate 85.

  The quarter-wave plate 85 converts the second light beam Lb2 made of linearly polarized light (P-polarized light) into circularly polarized light (left-handed circularly polarized light), and then makes the second light beam Lb2 incident on the relay lens 86.

  The relay lens 86 is configured similarly to the relay lens 65, and includes a movable lens 87, an actuator 87A, and a fixed lens 88 corresponding to the movable lens 66, the actuator 66A, and the fixed lens 67, respectively.

  The relay lens 86 converts the second light beam Lb2 from parallel light to convergent light by the movable lens 87, adjusts the convergence state of the second light beam Lb2 that has become divergent light after convergence by the fixed lens 88, and is not polarized. The light enters the beam splitter 45.

  Incidentally, like the relay lens 65, the relay lens 86 moves the movable lens 87 by the actuator 87A based on the control of the control unit 21 (FIG. 7), so that the second light beam Lb2 emitted from the fixed lens 88 is converged. Can be changed.

  The second light beam Lb <b> 2 is reflected by the reflection / transmission surface 45 </ b> S of the non-polarizing beam splitter 45, deflects its traveling direction by 90 °, passes through the non-polarizing beam splitter 46, and enters the objective lens 47.

  The objective lens 47 condenses the second light beam Lb2 and irradiates the recording layer 101 of the optical disc 100.

  At this time, as shown in FIG. 3B, the second light beam Lb2 is once transmitted through the recording layer 101, reflected by the reflective layer 104, and then focused in the recording layer 101. Here, the position of the focal point Fb <b> 2 of the second light beam Lb <b> 2 is determined by the convergence state when it is emitted from the fixed lens 88 of the relay lens 86. That is, the focal point Fb2 moves to the incident surface 100A side or the rear surface 100B side in the recording layer 101 according to the position of the movable lens 87, like the focal point Fb1 of the first light beam Lb1.

  In practice, in the information optical system 60, the position of the movable lens 87 in the relay lens 86 is controlled by the control unit 21 (FIG. 7), so that the focal point Fb2 of the second light beam Lb2 in the recording layer 101 of the optical disc 100 ( The depth d in FIG. 3B is adjusted.

  Incidentally, the information optical system 60 is designed so that the moving distance of the movable lens 87 and the moving distance of the focal point Fb2 of the second light beam Lb2 are substantially proportional to each other. For example, the movable lens 87 is moved by 1 [mm]. The focal point Fb2 of the second light beam Lb2 is moved by 30 [μm].

  The control unit 21 focuses the focal point Fb1 of the first light beam Lb1 to a position short by the depth d from the reflective layer 104, and places the focal point Fb2 of the second light beam Lb2 long from the reflective layer 104 by the depth d. The relay lenses 65 and 86 are controlled to focus.

  At this time, in the optical disc apparatus 20, the objective lens 47 in the recording layer 101 when the control unit 21 (FIG. 7) assumes that no surface blur or the like has occurred in the optical disc 100 (that is, in an ideal state). The focal point Fb2 of the second light beam Lb2 is aligned with the focal point Fb1 of the first light beam Lb1 at the reference position.

  That is, the control unit 21 displaces the movable lenses 66 and 87 by the same distance in opposite directions according to the target mark position, thereby increasing the focal length of the first light beam Lb1 and the focal point of the second light beam Lb2. The distance is shortened by the same distance as the focal length of the first light beam Lb1.

  As described above, the information optical system 60 positions the focal point Fb2 of the second light beam Lb2 in the recording layer 101 in the same manner as the first light beam Lb1, and further, according to the position of the movable lens 87 in the relay lens 86, The depth d of the focal point Fb2 is adjusted.

  As a result, the information optical system 60 can irradiate the first light beam Lb1 and the second light beam Lb2 so that the focal points Fb1 and Fb2 are positioned at the target mark position having the same depth d.

(3-2-2-3) Reception of First Light Beam By the way, the first light beam Lb1 irradiated from the objective lens 47 of the information optical system 60 is once in the recording layer 101 of the optical disc 100 as described above. After convergence, the light becomes divergent light, is reflected by the reflective layer 104, and becomes the first reflected light beam Lb1r.

  As shown in FIG. 15, the first reflected light beam Lb1r enters the objective lens 47 while diverging, converges to some extent by the objective lens 47, passes through the non-polarizing beam splitter 46, and then passes through the non-polarizing beam splitter. The light is reflected by 45 and is incident on the relay lens 86.

  Subsequently, the first light beam Lb1 is converted into parallel light by the fixed lens 88 and the movable lens 87 of the relay lens 86, and further converted from circularly polarized light to linearly polarized light (S polarized light) by the quarter wavelength plate 85, The light enters the polarizing beam splitter 84.

  The polarization beam splitter 84 reflects the first reflected light beam Lb1 according to the polarization direction of the first light beam Lb1 and makes it incident on the condenser lens 90. The condensing lens 90 converges the first light beam Lb1 and gives astigmatism by the cylindrical lens 91, and then irradiates the focusing light detector 92 with the first light beam Lb1.

  Here, the optical disc 100 may actually cause surface blurring. For this reason, as described above, the objective lens 47 is focus-controlled and tracking-controlled by the servo optical system 40 and the drive control unit 22 (FIG. 7) and is focused on the target mark position in the recording layer 101. Yes.

  Further, in the information optical system 60, the position control of the focus Fb2 is executed so that the positions of the focus Fb1 of the first light beam Lb1 and the focus Fb2 of the second reflected light beam Lb2r coincide.

  In the information optical system 60, the amount of deviation of the focal point Fb2 of the second reflected light beam Lb2r from the focal point Fb1 of the first light beam Lb1 in the recording layer 101 is focused by the first reflected light beam Lb1r by the condenser lens 90. The optical positions of the various optical components are adjusted so as to be reflected in the irradiation state when the light detector 92 is irradiated.

  As shown in FIG. 16, the focus photodetector 92 includes four detection areas 92A, 92B, 92C, and 92D divided in a lattice pattern on the surface irradiated with the first reflected light beam Lb1r, as in the photodetector 72. Have. Incidentally, the direction (lateral direction in the figure) indicated by the arrow a2 corresponds to the traveling direction of the track in the reflective layer 104 (FIG. 3B) when the first light beam Lb1 is irradiated.

  The focus photodetector 92 detects a part of the first reflected light beam Lb1r by the detection areas 92A, 92B, 92C, and 92D, and generates detection signals SDAb, SDBb, SDCb, and SDDb according to the detected light amount, respectively. Then, these are sent to the signal processing unit 23 (FIG. 7).

  The signal processing unit 23 performs focus control by a so-called astigmatism method, calculates a focus error signal SFEb according to the following equation (5), and supplies this to the control unit 21.

  This focus error signal SFEb represents the amount of shift in the focus direction between the focal point Fb1 of the first light beam Lb1 and the focal point Fb2 of the second reflected light beam Lb2r.

  The control unit 21 controls the relay lens 86 at which the depth d of the focus Fb2 from the reflection layer 104 becomes substantially the target depth and the focus error signal SFEb becomes zero, thereby setting the focus Fb2 with respect to the focus Fb1. It is made to match.

  Specifically, the control unit 21 generates a movement signal so as to move the relay lens 65 by the same amount in the opposite direction to the movable lens 66, and generates a drive signal by superimposing the focus error signal SFEb on the movement signal. This is supplied to the movable lens 87 of the relay lens 86.

  As a result, the control unit 21 can drive the movable lens 87 so that the focal point Fb2 follows the focal point Fb1.

  As described above, the information optical system 60 receives the first reflected light beam Lb1r formed by reflecting the first light beam Lb1 by the reflecting layer 104, and controls the relay lens 86 based on the first reflected light beam Lb1r. Thus, the focal point Fb2 is made to coincide with the focal point Fb1.

(4) Second Light Beam Aperture Restriction As described above, the recording mark RM is in the vicinity of the focus Fb1 of the first light beam Lb1 (hereinafter referred to as the focus vicinity region Af1) and in the vicinity of the focus Fb2 of the second light beam Lb2. (Hereinafter, this is referred to as a focal vicinity area Af2), it is formed only in the vicinity overlapping part where it overlaps.

  Here, as shown in FIG. 17A, the focal point Fb (Fb1, Fb2) is collected by the objective lens 47 when it is assumed that the first light beam Lb1 and the second light beam Lb2 have no diffraction phenomenon. An imaging point formed on the optical axis Lx of the emitted first light beam Lb1 and second light beam Lb2.

  The angle formed by the optical axis Lx of the first light beam Lb1 and the second light beam Lb2 and the contour (outermost peripheral portion) Lo (Lo1 and Lo2) of the first light beam Lb1 and the second light beam Lb2 is condensed. It is called an angle α (first light collection angle α1 and second light collection angle α2).

  Actually, as shown in FIG. 17B, due to the diffraction phenomenon, the first light beam Lb1 and the second reflected light beam Lb2r do not become points at the focal points Fb1 and Fb2, but the first light beam Lb1 and the second reflected light. The intersections between the beam waist BW and the optical axis Lx where the light beam diameter of the light beam Lb2r is the smallest are the focal points Fb1 and Fb2.

  For convenience of explanation, the light beam diameters of the first light beam Lb1 and the second light beam Lb2 are shown in FIG. 17B as the same, but in reality, the light beams of the first light beam Lb1 and the second light beam Lb2 are shown. The diameter is not the same.

  As shown in FIG. 18, in the optical disc apparatus 20, the light beam diameter of the second reflected light beam Lb2r at the focal point Fb2 (hereinafter referred to as the beam waist diameter S2) is set as the light beam diameter of the first light beam Lb1 at the focal point Fb1 (hereinafter, referred to as “beam waist diameter S2”). By making this larger than the beam waist diameter S1, the focus vicinity region Af1 and the focus vicinity region Af2 are surely overlapped.

  That is, in the optical disc apparatus 20, the first light beam Lb1 is incident on the objective lens 47 without restricting the opening, whereas the aperture of the second light beam Lb2 is restricted by the aperture 82 (FIG. 14), The two light beams Lb2 are incident on the objective lens 47.

  As a result, the optical disk apparatus 20 causes the objective lens 47 to act on the first light beam Lb1 as a lens having a numerical aperture NA (NA) that the objective lens 47 originally has, whereas the optical disk device 20 acts on the second light beam Lb2. Thus, the objective lens 47 can be operated as a lens having a numerical aperture NA smaller than the numerical aperture NA that the objective lens 47 originally has.

  As a result, in the optical disc apparatus 20, as shown in FIG. 17A, the second light collection angle α2 of the second light beam Lb2 (that is, the second reflected light beam Lb2r) collected by the objective lens 47 is set to The first light beam Lb1 collected by the objective lens 47 can be made smaller than the first collection angle α1.

  For example, in the optical disc apparatus 20, the objective lens 47 is caused to act as a lens having a numerical aperture NA that is approximately half that of the first light beam Lb1 in accordance with the aperture restriction of the second light beam Lb2, thereby changing the beam waist diameter S2 to the beam waist diameter. It can be about twice that of S1.

  In this case, since the beam waist diameter S1 is smaller than the beam waist diameter S2, only the focus vicinity area Af1 where the first light beam Lb1 exists in the light beam diameter direction becomes a neighborhood overlap part, and the recording mark RM is only in the focus vicinity area Af1. Is formed.

  As a result, the optical disc apparatus 20 can form the recording mark RM having a size based on the beam waist diameter S1 of the first light beam Lb1 on the recording layer 101, so that two light beams having the beam waist diameter S1 are overlapped. Thus, it is possible to form a recording mark RM having substantially the same size as that for forming the recording mark, and it is not necessary to reduce the recording density in the optical disc 100.

  As shown in FIG. 19, for example, when tilt occurs, the optical axis Lx of the first light beam Lb1 and the second light beam Lb2 is not incident on the reflection layer 104 perpendicularly. Lx and the optical axis Lxr of the second reflected light beam Lb2r are shifted.

  Even in such a case, in the optical disc apparatus 20, the beam waist diameter S2 is larger than the beam waist diameter S1, and therefore the contour portion Lo2 of the second reflected light beam Lb2r in the focal vicinity region Af2 is the contour of the first light beam Lb1. As long as it is within the range that does not deviate from the portion Lo1, the focus vicinity region Af1 can be set as a neighborhood overlap portion. As a result, the optical disc apparatus 20 can reliably form the recording mark RM having the beam waist diameter S1 without performing highly accurate tracking control and tangential control for matching the focal points Fb1 and Fb2.

  As a result, unlike the conventional optical disc apparatus, the optical disc apparatus 20 does not require tracking control and tangential control for matching the focal points Fb1 and Fb2 with the tracking direction and the tangential direction according to surface blurring of the optical disc 100.

  In practice, the optical disk apparatus 20 is provided with a mirror 63 that is not driven instead of the galvano mirror that the conventional optical disk apparatus has, and the mechanism for tracking control and tangential control can be omitted, and the structure is simple. Become.

  As shown in FIG. 20, the wavefronts of the first light beam Lb1 and the second reflected light beam Lb2r are substantially flat in the focal vicinity regions Af1 and Af2, but the wavefronts are curved as they move away from the focal points Fb1 and Fb2. It becomes. Since this wavefront is reflected in the hologram formed in the adjacent overlapping portion, when the wavefront is a plane, a plane stripe is recorded as the recording mark RM, whereas when the wavefront is a curved surface, a curved stripe is recorded. Is recorded as the recording mark RM. In practice, the first light beam Lb1 and the second light beam Lb2 have different light beam diameters. However, for convenience of explanation, the same light beam diameter is shown in the figure.

  As described above, the optical disc apparatus 20 adjusts the convergence state of the first light beam Lb1 and the second reflected light beam Lb2r by the relay lenses 65 and 86, adjusts the focal point Fb1 to the target depth, and focuses on the focal point Fb1. Fb2 is made to match. As a result, the optical disc apparatus 20 can reliably overlap the focal vicinity regions Af1 and Af2 in the first light beam Lb1 and the second reflected light beam Lb2r, and the recording mark RM having a planar stripe shape on the recording layer 101. Can be formed.

  Thereby, the optical disc apparatus 20 can generate a good reproduction light beam LbG without irregularly reflecting the first light beam Lb1 to the recording mark RM during the reproduction process.

  By the way, it is generally known that when an optical beam is irradiated onto the optical disc 100, spherical aberration and coma aberration occur depending on the distance that the optical beam travels within the optical disc 100. . Hereinafter, these aberrations that occur in the optical disc 100 are collectively referred to as intra-disc aberrations.

  As shown in FIG. 21, when the recording layer 101 is irradiated with the first light beam Lb1 through the objective lens 47, the focal point Fb1 is formed in the recording layer 101. For this reason, the first light beam Lb1 forms the focal point Fb1 after traveling through the optical disc 100 by the disc internal distance tr corresponding to the target depth from the incident surface 100A.

  Assuming that the first light beam Lb1 is irradiated over the entire area of the recording layer 101, the disc internal distance tr is at most approximately the same as the thickness t1 of the recording layer 101 and is at most approximately zero. In other words, the optical disk device 20 needs to sufficiently reduce the in-disk aberration of the first light beam Lb1 within the range from zero to the thickness t1 of the recording layer 101.

  On the other hand, when the second light beam Lb2 is irradiated onto the recording layer 101 via the objective lens 47, the second light beam Lb2 is once transmitted through the recording layer 101 and then reflected by the reflecting layer 104 in the opposite direction to the second light beam Lb2. The second reflected light beam Lb2r travels, and the focal point Fb2 is formed in the recording layer 101.

  Therefore, the second light beam Lb2 is obtained by subtracting the thickness t1 of the recording layer 101 (that is, the distance from the incident surface 100A to the reflective layer 104) and the disc internal distance tr from the thickness t1 (t1-tr). And the focal point Fb2 is formed after traveling through the optical disc 100 by a distance (t1 + t1-tr) obtained by adding together. That is, in the second light beam Lb2, the optical path length to the focal point in the optical disc 100 (hereinafter referred to as the in-disc focal optical path length) is longer than that of the first light beam Lb1.

  Assuming that the second reflected light beam Lb2r is irradiated over the entire area of the recording layer 101, the disc internal distance tr is about twice as large as the thickness t1 of the recording layer 101, and is about t1 at the minimum. Take the same value. That is, the optical disk device 20 needs to sufficiently reduce the in-disk aberration of the first light beam Lb1 within the range from the thickness t1 of the recording layer 101 to twice the thickness t1.

  Here, it is generally known that the in-disk aberration is generated in accordance with the numerical aperture NA of the objective lens 47 and the in-disk focal length.

  For example, generally, the amount of spherical aberration generated is proportional to the fourth power of the numerical aperture NA and the in-disk focal length. The objective lens 47 adds a predetermined spherical aberration to the previously incident light beam, so that the spherical aberration is zero at a predetermined depth inside the optical disc 100 (hereinafter referred to as a spherical aberration reference depth). Designed to be

  Accordingly, the spherical aberration generated in the first light beam Lb1 and the second reflected light beam Lb2r irradiated through the objective lens 47 is the fourth power of the numerical aperture NA of the objective lens 47 and the distance ts from the spherical aberration reference depth. It will be proportional to

  As described above, in the information optical system 60 (FIG. 14) in the optical disc apparatus 20, the aperture limitation is performed on the second light beam Lb2 having a large focal length in the disc, so that the objective is applied to the second light beam Lb2. The lens 47 is made to act as a lens having a low numerical aperture NA. Hereinafter, the actual numerical aperture NA of the objective lens 47 with respect to the first light beam Lb1 is referred to as a first optical numerical aperture NA1, and the numerical aperture NA of the objective lens 47 acting on the second light beam Lb is the second optical numerical aperture. Called NA2.

  In practice, in the information optical system 60, the aperture is limited by limiting the diameter of the second light beam LB2 to be smaller than the effective diameter of the objective lens 47 by the aperture 82.

  For example, in the information optical system 60, by limiting the second optical numerical aperture NA2 to about 84% of the first optical numerical aperture NA1, the amount of spherical aberration per unit distance generated in the second reflected light beam Lb2r is the first. It is about ½ of the light beam Lb1. That is, in the information optical system 60, the spherical surface generated in the second reflected light beam Lb2r is compensated by compensating for the amount of spherical aberration caused by the in-disk focal length of the second reflected light beam Lb2r being longer than the first light beam Lb1. Aberration can be reduced.

  In this case, in the information optical system 60, the spherical aberration generated in the second reflected light beam Lb2r can be reduced by designing the objective lens 47 so that the spherical aberration becomes as small as possible in accordance with the first light beam Lb. It becomes.

  In general, the amount of coma generated is proportional to the cube of the numerical aperture NA and the in-disk focal length.

  Therefore, in the information optical system 60, for example, by limiting the second optical numerical aperture NA2 to about 79% of the first optical numerical aperture NA1, the amount of coma aberration per unit distance generated in the second reflected light beam Lb2r is the first. This is about ½ of one light beam Lb1.

  As a result, for example, coma generated in response to the so-called disc tilt in which the optical disc 100 is tilted can be made equal between the first light beam Lb1 and the second reflected light beam Lb2r, and the overall tolerance for the disc tilt can be increased. It is made like that.

  In other words, in the information optical system 60, the first reflected light is set by setting the second optical numerical aperture NA2 to 70% or more and less than 90%, more preferably 79% or more and 84% or less of the first optical numerical aperture NA1. Both spherical aberration and coma aberration generated in the beam Lb1 and the second reflected light beam Lb2r can be compensated.

Here, in general, the numerical aperture NA of the lens can be expressed by equation (6). Here, n _LENS is the refractive index of the lens, and α is the converging angle α when the light beam is incident as parallel light.

Here, since the first light beam Lb1 and the second light beam Lb2 are condensed by the same objective lens 47 and the refractive index n _LENS is the same, the first light beam Lb1 and the second light beam Lb2 depend on the condensing angle α (α1 or α2). The numerical aperture NA1 and the second optical numerical aperture NA2 are determined.

  That is, the first numerical aperture NA1 and the second numerical aperture are adjusted by adjusting the beam diameter of the second light beam Lb2 so that sin α2 is 70% or more and less than 90% of sin α1, more preferably 79% or more and 84% or less. NA2 can satisfy the above conditions.

By the way, when the beam waist diameter S1 is 80% of the beam waist diameter S2, for example, the light flux area in the focus vicinity area Af1 is [80%] ² of the focus vicinity area Af2, that is, about 64%.

  Here, in the optical disc apparatus 20, the second light beam when the light intensity of the first light beam Lb 1 when incident on the objective lens 47 (hereinafter referred to as the first light incident intensity PW 1) is incident on the objective lens 47. The light intensity of Lb2 (hereinafter referred to as the second light incident intensity PW2) is adjusted to about 64%. Thereby, in the optical disc apparatus 20, the light intensity (that is, the light intensity density) per unit area of the first light beam Lb1 and the second light beam Lb2 in the focal vicinity regions Af1 and Af2 can be made similar, and the interference characteristics can be improved. Thus, the recording mark RM made of a clear hologram can be formed.

  Specifically, the optical disc device 20 adjusts the ratio of P-polarized light and S-polarized light by the half-wave plate 61 and separates the P-polarized light and S-polarized light by the beam splitter 62 to obtain about 39% of the first light beam Lb1. The first light beam Lb1 is incident on the mirror 63 and the remaining 61% is incident on the half-wave plate 81 as the second light beam Lb2.

  As a result, the optical disc apparatus 20 can make the first light incident intensity PW1 about ¼ of the second light incident intensity PW2, and can make the light intensity densities in the focal vicinity regions Af1 and Af2 comparable. The optical disk apparatus 20 may increase the ratio of the second light beam Lb2 in consideration of the fact that the aperture 82 creates the outer peripheral portion of the second light beam Lb2.

  Further, the optical disc apparatus 20 irradiates the optical disc 100 with the first light beam Lb1 having no aperture limitation during the reproduction process on the optical disc 100, and the first light beam Lb1 is reflected by the optical disc 100, thereby reproducing the light beam LbG. Is received by the photodetector 72.

  At this time, since the beam waist diameter S1 is smaller than the beam waist diameter S2, the optical disc apparatus 20 uses the recording mark RM adjacent to the target mark position as compared with the case where the second light beam Lb2 whose aperture is limited is irradiated. It is possible to reduce so-called crosstalk in which one light beam Lb1 is reflected. As a result, the optical disc apparatus 20 can reduce the interval between the recording marks RM during the recording process, and can improve the recording density.

  As described above, the optical disc apparatus 20 makes the optical axis Lx of the first light beam Lb1 the second reflected light by making the beam waist diameter S2 of the second reflected light beam Lb2r larger than the beam waist diameter S1 of the first light beam Lb1. Even in a case where the optical axis Lxr of the beam Lb2r does not completely coincide, the recording mark RM can be formed reliably. As a result, the optical disc apparatus 20 can reduce the load of tracking control and tangential control that makes the focus of the second reflected light beam Lb2r coincide with the tracking direction and the tangential direction with respect to the focus Fb1 of the first light beam Lb1. .

(5) Operation and Effect In the above configuration, the optical pickup 26 of the optical disc apparatus 20 uses the light beam Lb emitted from the laser diode 41 as the light source as the first light beam Lb1 and the second light as the first light. Into the second light beam Lb2. The optical pickup 26 collects and irradiates the first light beam Lb1 and the second light beam Lb2 from the same objective lens 47 to the optical disc 100 as an optical information recording medium.

  This optical disc 100 records a reflection layer 104 that reflects the first light beam Lb1 and the second light beam Lb2 and a hologram formed by overlapping the first light beam Lb1 and the second light beam Lb2 from opposite directions on the recording mark RM. As a recording layer 101.

  The optical pickup 26 changes the convergence state of the first light beam Lb1 by the relay lens 65, so that the first light beam has a target depth at which a recording mark RM in the depth direction close to or away from the optical disc 100 is to be formed. The focal point Fb1 of Lb is moved.

  Further, the optical pickup 26 restricts the beam diameter of the second light beam Lb2 to be smaller than the effective diameter of the objective lens 47 by the aperture 82 and changes the convergence state of the second light beam Lb2 by the relay lens 86 to change the second light beam Lb2. The focal point Fb2 of the second reflected light beam Lb2r formed by reflecting the light beam by the reflecting layer is adjusted to the target depth.

  Accordingly, the optical pickup 26 can make the beam waist diameter S2 that is the light flux diameter of the focus of the second reflected light beam Lb2r larger than the beam waist diameter S1 that is the light flux diameter of the focus of the first light beam Lb1. As a result, the optical pickup 26 has the first tilt even when the disc tilt occurs according to, for example, surface blurring and the optical axis Lx of the first light beam Lb1 and the optical axis Lxr of the second reflected light beam Lb2r shift. The focal point Fb1 of the light beam Lb1 and the focal point Fb2 of the second reflected light beam Lb2 can be reliably overlapped in the tracking direction and the tangential direction parallel to the reflective layer 104.

  For this reason, in the optical pickup 26, the focal points Fb1 and Fb2 can be matched by simply entering the first light beam Lb1 and the second light beam Lb2 while sharing the optical axis Lx, and the configuration can be simplified. it can.

  Further, in the optical pickup 26, a recording mark RM having a relatively small size corresponding to the beam waist diameter S1 of the first light beam Lb1 can be formed, and the recording capacity as the optical disc 100 is not reduced.

  Further, in the optical pickup 26, since the focal point Fb2 is formed after being reflected by the reflective layer 104, the light beam diameter of the second light beam Lb2 having a long in-disk focal path length is limited to be smaller than the effective diameter of the objective lens.

  As a result, the optical pickup 26 can reduce the amount of aberration generated according to the same distance by lowering the numerical aperture NA of the second light beam Lb2, and the length of the optical path length in the disc is long. It is possible to suppress the amount of aberration of the second light beam Lb2 that generates a large amount of internal aberration. As a result, the optical pickup 26 can reduce the aberration amount as the total of the first light beam Lb1 and the second light beam Lb2.

  Further, the optical pickup 26 has a second optical numerical aperture NA when condensing the second light beam Lb2 that is 70% or more and 90% or less of the first optical numerical aperture NA when condensing the first light beam Lb1. The objective lens 47 is caused to act as the numerical aperture NA.

  Here, since the second reflected light beam Lb2r forms the focal point Fb2 after being reflected by the reflective layer 104, the average value of the optical path length in the disc at the focal point Fb2 is approximately twice the optical path length in the disc at the focal point Fb1.

  Accordingly, the optical pickup 26 can make at least one of coma aberration and spherical aberration generated in the second light beam Lb2 equivalent to that of the first light beam Lb1.

  The optical pickup 26 has a second optical numerical aperture NA when condensing the second optical beam Lb2 that is 79% to 84% of the first optical numerical aperture NA when condensing the first optical beam Lb1. The objective lens 47 is caused to act as the numerical aperture NA.

  Accordingly, the optical pickup 26 can make both coma and spherical aberration generated in the second light beam Lb2 equivalent to those of the first light beam Lb1.

  Furthermore, the optical pickup 26 equalizes the light intensity density at the focal point Fb1 of the first light beam Lb1 and the light intensity density at the focal point Fb2 of the second reflected light beam Lb2.

  Thereby, the optical pickup 26 can improve the coherence of the first light beam Lb1 and the second light beam Lb2, and can form a good recording mark RM.

  Further, the optical pickup 26 adjusts the ratio of P-polarized light and S-polarized light in the light beam Lb by the half-wave plate 61, and the light beam Lb is converted into the first light beam Lb1 and the second light by the polarization beam splitter 62 according to the polarization direction. The ratio between the first light beam Lb1 and the second light beam Lb2 is adjusted by separating the beam Lb2.

  Thereby, the optical pickup 26 uses the configuration used in the conventional optical pickup as it is, and calculates the light intensity density at the focal point Fb1 of the first light beam Lb1 and the light intensity density at the focal point Fb2 of the second reflected light beam Lb2. Can be equivalent.

  Further, the optical pickup 26 irradiates the optical disk 100 on which the recording mark RM is recorded with the first light beam Lb1 having a small beam waist diameter S1, and the first light beam is modulated according to the presence or absence of the recording mark. Information recorded on the optical disc 100 is read based on the reproduction light beam LbG.

  As a result, the optical pickup 26 can irradiate the recording mark RM with the first light beam Lb1 having a small beam waist diameter S1 corresponding to the size of the recording mark RM. Can be generated.

  In the optical pickup 26, the light emitted from the laser diode 41 is separated into the first light beam Lb1, the second light beam Lb2, and the servo light beam LS as the third light, and the objective lens 47 is displaced by the actuator 47A. As a result, the servo light beam LS is focused on the reflective layer 104.

  Accordingly, the optical pickup 26 can adjust the focal points Fb1 and Fb2 to the target depth by displacing the focal points Fb1 and Fb2 by an arbitrary depth with reference to the reflective layer 104. Unlike the case where optical beams having different wavelengths are used as servo light beams, the optical pickup 26 only needs to be provided with one laser diode 41, and the configuration can be simplified.

  According to the above configuration, the optical pickup 26 of the optical disc apparatus 20 irradiates the first light beam Lb1 and the second light beam Lb2 sharing the optical axis Lx through the same objective lens 47, and also by the reflective layer 104. By reflecting the second light beam Lb2, the first light beam Lb1 and the second light beam Lb2 are overlapped from opposite directions. At this time, the optical pickup 26 restricts the opening of the second light beam Lb2, thereby making the beam waist diameter S2 of the second reflected light beam Lb2r larger than the beam waist diameter S1 of the first light beam Lb1.

  As a result, the optical pickup 26 moves the first light beam Lb1 and the second light beam Lb2 in the tracking direction and tangential without accurately matching the focus Fb1 of the first light beam Lb1 and the focus Fb2 of the second light beam Lb2. Thus, it is possible to realize an optical information recording apparatus and an optical pickup that can be overlapped in the direction and thus can reduce the load of servo control.

(6) Other Embodiments In the above-described embodiment, the case where the servo light beam LbS is separated from the light beam Lb from which the first light beam Lb1 and the second light beam Lb2 are separated will be described. However, the present invention is not limited to this, and a light beam having a wavelength different from that of the first light beam Lb1 and the second light beam Lb2 may be used as the servo light beam that is the third light. In this case, a laser diode that emits a servo light beam having a wavelength different from that of the first light beam Lb1 and the second light beam Lb2 is installed, and the objective lens 47 is displaced by the actuator 47A so that the servo light beam is reflected on the reflection layer. 104 is in focus.

  In the above-described embodiment, the case where the aperture 82 is provided on the optical path of the second light beam Lb2 to limit the beam diameter of the second light beam Lb2 has been described. For example, the beam diameter of the first light beam Lb1 may be limited. The method for limiting the beam diameter is not limited to the aperture, and for example, a liquid crystal element or the like may be used.

  Further, in the above-described embodiment, the case where the first light beam Lb1 and the second light beam Lb2 are separated by the polarization beam splitter 62 has been described. However, the present invention is not limited to this. The first light beam Lb1 and the second light beam Lb2 may be separated by a splitter.

  Further, in the above-described embodiment, the case where the focal point Fb1 of the first light beam Lb1 is moved by the relay lens 65 that is a combination of the movable lens 66 and the fixed lens 67 has been described. It is not limited. For example, the focus Fb1 may be moved by displacing the movable lens installed in the diverging light or the objective lens 47.

  Further, in the above-described embodiment, the case where the focal point Fb1 of the first light beam Lb1 is moved by the relay lens 86 that is a combination of the movable lens 87 and the fixed lens 88 has been described. It is not limited. For example, the focal point Fb <b> 2 may be moved by displacing the movable lens installed in the diverging light or the objective lens 47.

  Further, in the above-described embodiment, the case where the objective lens 47 has the second numerical aperture NA2 and acts on 80% of the first numerical aperture NA1 that condenses the first light beam Lb1 has been described. Is not limited to this. For example, the second numerical aperture NA2 may be ½ of the first numerical aperture NA1. Since the size of the second numerical aperture NA2 affects the size of the beam waist diameter S2, for example, the amount of deviation from the focus Fb1 of the focus Fb2 assumed from the disc tilt of the optical disc 100 and the thickness t1 of the recording layer 101 is affected. It is possible to select as appropriate.

  Further, in the above-described embodiment, the ratio of the first light beam Lb1 and the second light beam Lb2 is adjusted by the half-wave plate 61 and the polarization beam splitter 62, and the light intensity density in the vicinity of the focal points Fb1 and Fb2 is adjusted. Although the case where it did in this way was described, this invention is not restricted, For example, various methods, such as what is called ND filter which cuts the 1st light beam Lb1 by a predetermined ratio, can be used.

  Further, in the above-described embodiment, the case where information is reproduced using the first light beam Lb1 has been described. However, the present invention is not limited to this, and the second light beam Lb2 may be used. .

  Further, in the above-described embodiment, the case where a mechanism for controlling the first light beam Lb1 or the second light beam Lb2 in the tracking direction and the tangential direction is not provided, but the present invention is limited to this. It is not a thing. Even in the case where a mechanism for controlling the first light beam Lb1 or the second light beam Lb2 in the tracking direction and the tangential direction is provided, the accuracy of the control system can be lowered. Servo control load can be reduced.

  In this case, for example, a galvanometer mirror is provided instead of the mirror 63, and the optical axis of the first reflected light beam Lb1r received by the focusing photodetector 92 is tilted to follow the focal point Fb2. In this way, the focal point Fb1 can be displaced in the tracking direction and the tangential direction.

  In addition, a galvanometer mirror is provided in place of the mirror 63, and an aperture is provided between the quarter wavelength plate 64 and the relay lens 65 to irradiate the second light beam Lb2, and the second reflected light beam Lb2r is a focus photodetector. It is also possible to control so that the light is received by 92 and the focus Fb2 follows the focus Fb1.

  Further, in the above-described embodiment, the servo light beam Ls is focused on the reflective layer 104, and the target mark position to be irradiated with the first light beam Lb1 and the second reflected light beam Lb2 is determined based on the reflective layer 104. Although the case of determining is described, the present invention is not limited to this. For example, it is possible to determine the target mark position with reference to the already recorded recording mark RM or a pre-formatted servo mark.

  Further, in the above-described embodiment, the case where the thickness t1 of the recording layer 101 is set to about 0.25 [mm] and the thickness t2 of the substrate 103 is set to about 1.0 [mm] has been described. The present invention is not limited to this and can be set to various other values.

  Further, in the above-described embodiment, the case where the recording mark RM is formed on the disc-shaped optical disc 100 has been described. However, the present invention is not limited to this, and the recording is performed on, for example, a rectangular parallelepiped optical information recording medium. The mark RM may be formed.

  Further, in the above-described embodiment, the case where the light beam Lb having a wavelength of 405 [nm] is used for recording and reproduction has been described. However, the present invention is not limited to this, and light having various other wavelengths is used. A beam may be used.

  Further, in the above-described embodiment, the half-wave plate 61 and the polarization beam splitter 62 as the separating unit, the objective lens 47 as the objective lens, the aperture 82 as the aperture limiting unit, and the first focus moving unit. The case where the optical disk device 20 as an optical information recording device is configured by the relay lens 65 as the optical information recording device and the relay lens 86 as the second focal point moving unit has been described. You may make it comprise the optical information recording device of this invention by the separation part which consists of various structures, an objective lens, an aperture restriction | limiting part, a 1st focus movement part, and a 2nd focus movement part.

  The optical information recording apparatus and the optical pickup of the present invention can be used for various electronic devices in which, for example, an optical disc apparatus is mounted.

It is a basic diagram with which it uses for description of formation of the conventional recording mark. It is a basic diagram with which it uses for description of the adjustment of the conventional focus position. It is a basic diagram which shows the structure of an optical disk. It is an approximate line figure used for explanation of formation (1) of a recording mark. It is a basic diagram with which it uses for description of formation (2) of a recording mark. It is an approximate line figure used for explanation of reproduction of information. It is a basic diagram which shows the structure of an optical disk device. It is a basic diagram which shows the structure of an optical pick-up. It is a basic diagram with which it uses for description of the optical path of a servo light beam. It is a basic diagram which shows the structure of the detection area | region in the photodetector for servos. It is a basic diagram with which it uses for description of irradiation of a 1st light beam. It is a basic diagram of light reception of a reproduction light beam. It is a basic diagram with which it uses for description of the selection of the light beam by a pinhole. It is a basic diagram with which it uses for description of irradiation of a 2nd light beam. It is a basic diagram with which it uses for description of light reception of a 1st reflected light beam. It is a basic diagram which shows the structure of the detection area in the photodetector for a focus. It is a basic diagram with which it uses for description of a focus and a beam waist. It is a basic diagram with which it uses for description of formation (1) of a hologram. It is a basic diagram with which it uses for description of formation (2) of a hologram. It is a basic diagram with which it uses for description of the wavefront of a 1st light beam and a 2nd reflected light beam. FIG. 6 is a schematic diagram for explaining an optical path length in an optical disc.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... Optical disk apparatus, 21 ... Control part, 22 ... Drive control part, 23 ... Signal processing part, 26 ... Optical pick-up, 40 ... Servo optical system, 41 ... Laser diode, 43, 45, 46 ... Non-polarizing beam splitter, 47 ... Objective lens, 47A ... Actuator, 62, 84 ... Polarizing beam splitter, 53, 72, 92 ... Photo detector, 60 ... Information optical system, 61, 81 ... 1 / Double wavelength plate, 65, 86 ... Relay lens, 66, 87 ... Movable lens, 67, 88 ... Fixed lens, 100 ... Optical disc, 101 ... Recording layer, 103 ... Substrate, 104 ... Reflective layer, Lb ... light beam, Lb1 ... first light beam, Lb2 ... second light beam, LbS ... servo light beam, Lb1r ... first reflected light beam, Lb2r ... second reflected light beam , Fb1, Fb2 ...... focus, RM ...... record mark.

Claims (10)

A separation unit that separates light emitted from the light source into first and second light;
For an optical information recording medium having a reflective layer for reflecting the first and second light and a recording layer for recording a hologram formed by overlapping the first and second light from opposite directions as a recording mark An objective lens that collects and irradiates the first and second lights,
An aperture limiter that limits the beam diameter of the first or second light to be smaller than the effective diameter of the objective lens;
A first focal point moving unit that moves a focal point of the first light to a target depth at which a recording mark in a depth direction close to or away from the optical information recording medium is to be formed;
An optical information recording apparatus comprising: a second focus moving unit that adjusts a focus of the second reflected light obtained by reflecting the second light by the reflective layer to the target depth. The opening restriction part is
The optical information recording apparatus according to claim 1, wherein a light beam diameter of the second light is limited to be smaller than an effective diameter of the objective lens. The opening restriction part is
The optical information recording apparatus according to claim 2, wherein when the second light is collected, the objective lens is caused to act as a numerical aperture of 70% to 90% when the first light is collected. The opening restriction part is
The optical information recording apparatus according to claim 3, wherein when the second light is collected, the objective lens is caused to act as a numerical aperture of 79% or more and 84% or less when the first light is collected. The objective lens is
The optical information recording apparatus according to claim 1, wherein the light intensity density at the focal point of the second light is made equal to the light intensity density at the focal point of the first light. The light intensity density of the second light at the target position is adjusted by adjusting the ratio of the first and second light when separating the light into the first light and the second light. The optical information recording apparatus according to claim 5, further comprising: a light intensity adjusting unit that equalizes a light intensity density of the first light at the target position. The objective lens is
Irradiating the first light to the optical information recording medium on which the recording mark is recorded,
2. The optical information recording according to claim 1, further comprising: a reading unit that reads information recorded on the optical information recording medium based on a return light beam obtained by modulating the first light according to the presence or absence of the recording mark. apparatus. The separation part is
Separating the light emitted from the light source into the first and second lights and the third light;
The objective lens is
The optical information recording apparatus according to claim 1, wherein the third light is focused on the reflective layer by being displaced. A light source that emits third light having a wavelength different from that of the first and second lights,
The objective lens is
The optical information recording apparatus according to claim 1, wherein the third light is focused on the reflective layer by being displaced. A separation unit that separates light emitted from the light source into first and second light;
An optical information recording medium having a reflective layer for reflecting the first and second lights and a recording layer for recording an interference pattern formed when the first and second lights overlap in opposite directions as a hologram On the other hand, an objective lens that collects and irradiates the first and second lights,
An aperture limiter that limits the beam diameter of the first or second light to be smaller than the effective diameter of the objective lens;
A first focal point moving unit that moves a focal point of the first light to a target depth at which a recording mark in a depth direction close to or away from the optical information recording medium is to be formed;
An optical pickup comprising: a second focal point moving unit that focuses the second reflected light obtained by reflecting the second light by the reflective layer to the target depth.

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