JP2009134844A - Optical pickup and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make compatible outgoing light quantity control of a laser diode and highly accurate elimination of laser noise. <P>SOLUTION: In an optical disk device 130, outgoing light quantity control of a laser diode 62 is performed, while light quantity of a light beam L2 irradiated to the optical disk 100 can be kept constant by performing outgoing light quantity control by performing grating position control of a variable diffraction grating 66 by a light quantity control part 140 so that a signal level of a high-order light high frequency band signal VbcH is adjusted to a signal level of a reproduced RF signal SRF during playback of the optical disk 100, while diffraction efficiency of the 0-order light and the high-order light emitted from the variable diffraction grating 66 is changed appropriately, a laser noise component can be eliminated by only that the high-order light high frequency band signal VbcH is subtracted directly from the reproduced RF signal SRF. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup and an optical disc apparatus, and is suitably applied to an optical disc apparatus that removes a laser noise component contained in a light beam emitted from a laser diode, for example.

  In recent years, optical disc apparatuses record information on optical discs conforming to standards such as CD (Compact Disc), DVD (Digital Versatile Disc) or BD (Blu-ray Disc, registered trademark), and reproduce information from the optical disc. Things made to do so are widespread.

  In such an optical disc apparatus, for example, information is recorded by irradiating the optical disc with a light beam emitted from a laser diode mounted on an optical pickup, and the light quantity of the reflected light beam formed by reflecting the light beam from the optical disc. Information is reproduced by detecting.

  By the way, it is desirable for the laser diode to keep the emission intensity of the light beam constant, but due to its characteristics, the laser noise component resulting from the emission intensity of the light beam changing finely in the emitted light beam. It is known to contain.

  For this reason, the optical disk apparatus has a problem that the intensity of the reflected light beam fluctuates due to the influence of the laser noise component, especially during information reproduction, and the accuracy of the reproduction information is reduced.

  Therefore, some optical disk devices receive a part of the light beam emitted from the laser diode, generate a fluctuation detection signal indicating the fluctuation of the light beam, and generate the fluctuation detection signal from the read information signal that detects the reflected light beam. It is conceivable to reduce or remove the laser noise component by subtracting.

  In this case, in the optical disc apparatus, it is necessary to make the levels of the laser noise component included in the read information signal and the laser noise component included in the fluctuation detection signal uniform. For this reason, in an optical disk apparatus, it is necessary to amplify at least one of a read information signal and a fluctuation detection signal by an amplifier circuit or the like, so that a wideband variable gain amplifier is required, and new noise caused by such an amplifier circuit is generated. There was also a fear of letting it go.

Therefore, the optical disk apparatus can reduce or eliminate the laser noise component without using an amplification circuit or the like by optically adjusting the light amount of a part of the light beam emitted from the laser diode and generating a fluctuation detection signal. What has been made in this way has been proposed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 10-124919 (FIG. 6)

  By the way, the laser diode generally has a characteristic that the light quantity of the emitted light beam is likely to vary depending on the temperature or the like. For this reason, in the optical disc apparatus, it is conceivable to perform emission light amount control for feedback control so that a part of the actually emitted light beam is received and the light amount of the light beam is kept constant.

  However, in the optical disk apparatus having the above-described configuration, the light amount of a part of the light beam emitted from the laser diode is optically adjusted, so that the light amount of the actually emitted light beam cannot be detected correctly, and the emitted light amount There was a problem that control could not be performed correctly.

  The present invention has been made in consideration of the above points, and an object of the present invention is to propose an optical pickup and an optical disc apparatus capable of achieving both control of the amount of light emitted from a laser diode and high-accuracy laser noise removal.

  In order to solve such a problem, in the optical pickup of the present invention, a light beam that emits a light beam composed of laser light, and one main light beam and one or more light beams at a ratio based on a predetermined ratio adjustment signal. A first separator that separates the sub-light beam; a sub-light receiving element that receives the sub-light beam and generates a sub-light detection signal; and a second that separates the main light beam into an irradiation light beam and a monitoring light beam at a predetermined ratio. A separator, a monitoring light receiving element that receives the monitoring light beam and generates a monitoring light detection signal, and causes a predetermined control unit to control the amount of the irradiation light beam based on the monitoring light detection signal; and the irradiation light An objective lens for condensing the beam on the optical disc and a reflected light beam formed by reflecting the irradiation light beam by the optical disc to generate a reflected light detection signal, thereby generating a sub-light detection signal for a predetermined control unit. The reflected light reception that controls the ratio adjustment signal so that the laser noise level included in the reproduced RF signal generated based on the reflected light detection signal is aligned and subtracts the sub-light detection signal from the reproduced RF signal. An element was provided.

  In this optical pickup, the laser noise level of the reproduction RF signal and the sub-light detection signal in the low frequency region can be made uniform by adjusting the light quantity of the sub-light beam by the first separator. By subtracting the sub-light detection signal, the laser noise component included in the reproduction RF signal due to the light source can be reduced. In parallel, the light beam emitted from the light source based on the amount of the monitoring light beam The amount of light can be controlled correctly.

  In the optical disc apparatus of the present invention, the light beam is separated into one main light beam and one or more sub light beams at a ratio based on a light source that emits a laser beam and a predetermined ratio adjustment signal. A first separator that receives the secondary light beam and generates a secondary light detection signal, a second separator that separates the main light beam into an irradiation light beam and a monitoring light beam at a predetermined ratio, and monitoring A monitoring light receiving element that receives a light beam and generates a monitoring light detection signal, an irradiation light control unit that controls the amount of irradiation light beam based on the monitoring light detection signal, and an objective lens that focuses the irradiation light beam on an optical disk And a reflected light receiving element that generates a reflected light detection signal by receiving the reflected light beam reflected by the optical disc, and a laser noise level included in the auxiliary light detection signal and the reflected light detection signal. Generated A sub-light control unit that controls the ratio adjustment signal so as to align the laser noise level included in the reproduced RF signal, and a subtraction processing unit that directly subtracts the high-frequency component of the sub-light detection signal from the reproduced RF signal. I made it.

  In this optical disk apparatus, the laser noise level of the reproduction RF signal and the sub-light detection signal in the low frequency region can be made uniform by adjusting the light quantity of the sub-light beam by the first separator. By subtracting the sub-light detection signal, the laser noise component caused by the light source and included in the reproduced RF signal can be reduced. In parallel, the light beam emitted from the light source based on the amount of the monitoring light beam The amount of light can be controlled correctly.

  According to the present invention, the laser noise level of the reproduction RF signal and the sub-light detection signal in the low frequency region can be made uniform by adjusting the light quantity of the sub-light beam by the first separator. By subtracting the sub-light detection signal, the laser noise component caused by the light source and included in the reproduction RF signal can be reduced. In parallel, the light emitted from the light source based on the amount of the monitoring light beam The light quantity of the beam can be controlled correctly, and thus an optical pickup that can achieve both the control of the quantity of emitted light from the laser diode and the removal of high-precision laser noise can be realized.

  According to the present invention, the laser noise level of the reproduction RF signal and the sub-light detection signal in the low frequency region can be made uniform by adjusting the light quantity of the sub-light beam by the first separator. By subtracting the sub-light detection signal from the laser light component, the laser noise component included in the reproduction RF signal due to the light source can be reduced, and in parallel, the light is emitted from the light source based on the amount of the monitoring light beam. It is possible to realize an optical disc apparatus that can correctly control the amount of light of the light beam and thus achieve both the control of the amount of light emitted from the laser diode and the removal of highly accurate laser noise.

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

(1) Configuration of Diffraction Grating (1-1) Basic Principle Before describing the specific configuration of the present invention, the basic principle of the present invention will be described first. As shown in the external view in FIG. 2A, the variable diffraction grating 10 is a grating in which two diffraction gratings 11 and 12 each having a substantially flat plate shape are close to each other in parallel, and each grating is formed. The surfaces 11A and 12A are configured to face each other. For convenience of explanation, the direction parallel to the normal lines of the lattice planes 11A and 12A is defined as the z direction below.

  The diffraction gratings 11 and 12 are each configured similarly to the diffraction grating 1 (FIG. 1) having a general configuration. The diffraction grating 11 is made of a transparent resin material, glass material, or the like, and exhibits a refractive index n1 with respect to a light beam having a predetermined wavelength (for example, 405 [nm]).

  As shown in the sectional view of FIG. 3A, in the diffraction grating 11, a grating g11 having a grating depth d1 and a period c is formed on the grating surface 11A. This lattice g11 is a two-stage so-called binary type in which protruding mountain-like portions and depressed valley-like portions appear alternately along the lattice arrangement direction of the lattice surface 11A (indicated by an arrow x in FIG. 2). It has become. Further, in the lattice g11, the width h in the x direction in the mountain-shaped portion and the valley-shaped portion is about ½ of the period c.

  On the other hand, the diffraction grating 12 is made of a transparent resin material or glass material, like the diffraction grating 11, and exhibits a refractive index n2 with respect to a light beam having a predetermined wavelength (for example, 405 [nm]). Has been made.

  Incidentally, the period c of the grating g12 in the diffraction grating 12 only needs to correspond to the incident width when light emitted from the diffraction grating 11 with the period c is incident, and parallel light is incident on the diffraction gratings 11 and 12. Therefore, the period c is the same as that of the grating g11 of the diffraction grating 11.

  In the diffraction grating 12, a binary grating g12 having a grating depth d2 and the same period c as the grating surface 11A is formed on the grating surface 12A facing the grating surface 11A. The grating g12 is configured such that mountain-shaped portions and valley-shaped portions appear alternately along the same grating arrangement direction (that is, the x direction) as the grating g11 of the grating surface 11A in the diffraction grating 11.

  The diffraction gratings 11 and 12 are provided in air having a refractive index n0 with respect to a light beam having a predetermined wavelength (for example, 405 [nm]), and the distance between the grating surface 11A and the grating surface 12A of the diffraction grating 12 is set. They are arranged so as to be within a predetermined distance.

  As shown in FIG. 3A, the variable diffraction grating 10 is in a state in which the positions of the mountain-shaped portions of the grating g11 and the grating g12 are aligned in the z direction (hereinafter referred to as a first state). The variable diffraction grating 10 as a whole can act as a diffraction grating having a phase depth φ1 shown by the following equation.

  In this case, the phase of the light beam that is parallel light and passes through the variable diffraction grating 10 along the z direction changes as in the case of passing through the diffraction grating having the phase depth φ1, as shown in FIG. Will do.

  Further, the m-th order (m is an integer of 0 or more) diffraction efficiency η1 (m) in the variable diffraction grating 10 can be obtained by the following equation.

  Here, when the diffraction grating 11 is moved from the first state by the distance Δx in the x direction, that is, the grating arrangement direction of the gratings g11 and g12 while the diffraction grating 12 is fixed, for example, FIG. 4A and 4B corresponding to FIGS. 4A and 4B, respectively.

  Incidentally, the variable diffraction grating 10 can move the diffraction grating 11 by using, for example, an actuator or a piezoelectric element formed by a combination of a coil and a magnet.

  When the diffraction grating 11 is further moved in the x-direction and the amount of movement from the first state becomes the width h, the variable diffraction grating 10 corresponds to FIGS. 5 (A) and 3 (B), respectively. As shown in B), the positions of the crest and trough portions of the lattice g11 and the lattice g12 with respect to the z direction correspond to each other (hereinafter referred to as a second state).

  At this time, the variable diffraction grating 10 as a whole can act as a diffraction grating having a phase depth φ2 as shown in the following expression corresponding to the expression (1).

  Further, the m-th order diffraction efficiency η2 (m) in the variable diffraction grating 10 at this time can be obtained by the following equation corresponding to the equation (2).

  Furthermore, the variable diffraction grating 10 acts as a diffraction grating in the intermediate state in addition to the first state and the second state. Specifically, it has been found that the variable diffraction grating 10 continuously changes the diffraction efficiency as shown in FIG. 6 by the simulation of the 0th order light and the ± 1st order light.

  In FIG. 6, the position of the diffraction grating 11 in the x direction relative to the diffraction grating 12 is represented by the phase of the gratings g11 and g12 with respect to the period c (hereinafter referred to as the grating phase), and the first state and the second state. Are set to “0” and “0.5”, respectively. In FIG. 6, the characteristics of the zero-order light are represented by a characteristic curve U10, and the characteristics of the ± first-order light are represented by a characteristic curve U11.

  In FIG. 6, in the characteristic curve U10 representing the 0th-order light, the diffraction efficiency continuously changes from about 35 [%] to about 90 [%] from the first state to the second state. That is, the variable diffraction grating 10 can act as an attenuator (attenuator) that changes the transmittance from about 35 [%] to about 90 [%] for, for example, zero-order light.

  Similarly, the variable diffraction grating 10 can act as an attenuator that changes the transmittance from about 25 [%] to about 5 [%] for ± first-order light.

  As described above, the variable diffraction grating 10 changes the diffraction efficiency by changing the relative position of the diffraction grating 11 with respect to the x direction with respect to the diffraction grating 12 while the parallel of the grating g11 and the grating g12 is maintained. Can do.

  The diffraction gratings 11 and 12 are formed so that the grating g11 on the grating surface 11A and the grating g12 on the grating surface 12A have the same shape in the y direction (FIG. 2), as in the case of a general diffraction grating. Therefore, the diffraction efficiency of the variable diffraction grating 10 does not change depending on the position of the diffraction grating 11 in the y direction with respect to the diffraction grating 12.

(1-2) Configuration Example of Variable Diffraction Grating The variable diffraction grating according to the present invention is not limited to the variable diffraction grating 10 shown in FIGS. Below, the specific structural example is shown. For convenience of explanation, the above-described variable diffraction grating 10 is referred to as a first variable diffraction grating 10.

(1-2-1) Configuration of Second Variable Diffraction Grating As shown in FIG. 7A corresponding to FIG. 3A, the second variable diffraction grating 20 corresponds to the diffraction gratings 11 and 12, respectively. The diffraction gratings 21 and 22 are combined.

  Although the diffraction gratings 21 and 22 are configured in substantially the same manner as the diffraction gratings 11 and 12, respectively, the refractive indexes n1 and n2 and the gratings are set so that the phase depths of the diffraction gratings 21 and 22 coincide with each other, that is, so as to satisfy the following relationship. Depths d1 and d2 are defined.

  Therefore, the light beam passing through the variable diffraction grating 20 along the z-direction (FIG. 2) has a phase depth φ1 in the first state, as shown in FIG. 7B corresponding to FIG. 3B. The phase changes in the same manner as when passing through the diffraction grating.

  On the other hand, when the diffraction grating 21 is moved in the x direction from the first state while the diffraction grating 22 is fixed, the variable diffraction grating 20 passes through the intermediate state shown in FIG. Two states are entered. If equation (5) is substituted into equation (3), the phase depth φ2 = 0.

  That is, the light beam passing through the variable diffraction grating 20 in the second state along the z direction (FIG. 2) is not diffracted but only the 0th order light, as shown in FIG. become.

  It has been found that the diffraction efficiency of the variable diffraction grating 20 exhibits characteristics as shown in FIG. 10 corresponding to FIG. 6 by simulation with respect to 0th order light and ± 1st order light. In FIG. 10, the characteristics of the zero-order light are represented by a characteristic curve U20, and the characteristics of ± first-order light are represented by a characteristic curve U21.

  In FIG. 10, the characteristic curve U20 representing the 0th-order light has the diffraction efficiency continuously changing from about 50% to about 100% from the first state to the second state. In other words, the variable diffraction grating 20 can act as an attenuator that changes the transmittance from about 50 [%] to about 100 [%] for the 0th-order light.

  Similarly, the variable diffraction grating 20 can act as an attenuator that changes the transmittance from about 20 [%] to about 0 [%] for ± first-order light.

  The variable diffraction grating 20 exhibits the same property not only when the expression (5) is satisfied but also when the relationship of the following expression is satisfied.

  As described above, the second variable diffraction grating 20 can change the diffraction efficiency by changing the position of the diffraction grating 21 in the x direction with respect to the diffraction grating 22, similarly to the first variable diffraction grating 10. In the second state in particular, only the 0th-order light can be transmitted at a rate of about 100 [%] as in the case where the diffraction grating is not provided.

(1-2-2) Configuration of Third Variable Diffraction Grating As shown in FIG. 11A corresponding to FIG. 3A, the third variable diffraction grating 30 corresponds to the diffraction gratings 11 and 12, respectively. The diffraction gratings 31 and 32 are combined.

  The diffraction gratings 31 and 32 are partly different from the diffraction gratings 11 and 12, respectively, and are so-called blazed diffraction gratings having a sawtooth cross section.

  The gratings g31 and g32 of the diffraction gratings 31 and 32 both have a period c, and the inclined surfaces of the gratings g31 and g32 are opposed to each other.

  In the first state shown in FIG. 11A, the variable diffraction grating 30 is positioned so that one mountain-shaped portion corresponds to the other valley-shaped portion, and satisfies the above-described equation (5). , Refractive indices n1 and n2 and grating depths d1 and d2.

  Therefore, the variable diffraction grating 30 has the same optical characteristics in the first state as in the second state (FIG. 9) of the variable diffraction grating 20. That is, the light beam that is parallel light and passes through the variable diffraction grating 30 in the first state along the z direction (FIG. 2) is not diffracted as shown in FIG. Will pass by. The variable diffraction grating 30 in the first state can also be regarded as a diffraction grating having a duty ratio of 0 [%].

  Here, when the diffraction grating 31 is moved from the first state by the distance Δx in the x direction while the diffraction grating 32 is fixed, for example, the variable diffraction grating 30 is shown in FIG. 12A corresponding to FIG. It becomes an intermediate state.

  In this intermediate state, as shown in FIG. 12B, the light beam that passes through the variable diffraction grating 30 along the z direction has a phase of a portion corresponding to the distance Δx in the period c as shown in the following equation. It changes in the same manner as when passing through a diffraction grating having a depth of φ3.

  At this time, the variable diffraction grating 30 can be regarded as a diffraction grating having a duty ratio of (distance Δx / period c).

  When the diffraction grating 31 is further moved in the x direction and the amount of movement from the first state reaches the width h, the variable diffraction grating 30 has the grating g31 and the grating g31 as shown in FIG. 13A corresponding to FIG. The mountain-shaped portion and the valley-shaped portion of the lattice g32 are in a state where they are shifted from each other by half a period in the x direction (hereinafter referred to as a second state).

  In this second state, as shown in FIG. 13B, the third variable diffraction grating 30 can be regarded as a diffraction grating having a phase depth of φ3 and a duty ratio of 50%.

  That is, as shown in FIGS. 11B, 12B, and 13B, the third variable diffraction grating 30 is changed from the first state to the second state with respect to the phase depth φ3. The duty ratio in the diffraction grating can be changed from 0 [%] to 50 [%].

  It has been found that the diffraction efficiency of the variable diffraction grating 30 exhibits characteristics as shown in FIG. 14 corresponding to FIGS. 6 and 10 through simulations of the 0th order light and ± 1st order light. Incidentally, in FIG. 14, the characteristics of the zero-order light are represented by the characteristic curve U30, and the characteristics of the ± first-order light are represented by the characteristic curve U31.

  In FIG. 14, the characteristic curve U30 representing the 0th order light continuously changes from about 100 [%] to about 50 [%] from the first state to the second state. That is, the variable diffraction grating 30 can act as an attenuator that changes the transmittance from about 100 [%] to about 50 [%] for the 0th-order light.

  Similarly, the variable diffraction grating 30 can act as an attenuator that changes the transmittance from about 0 [%] to about 20 [%] for ± first-order light.

  As described above, the third variable diffraction grating 30 can change the diffraction efficiency by changing the position of the diffraction grating 31 with respect to the diffraction grating 32 in the x direction, similarly to the first variable diffraction grating 10. In the first state in particular, only the 0th-order light can be passed at a rate of approximately 100 [%] as in the case where the diffraction grating is not provided.

  The gratings g31 and g32 of the diffraction gratings 31 and 32 are not limited to the sawtooth shape, and may be configured in a stepped pseudo sawtooth shape.

(1-2-3) Configuration of Fourth Variable Diffraction Grating As shown in FIG. 15A corresponding to FIG. 3A, the fourth variable diffraction grating 40 corresponds to the diffraction gratings 11 and 12, respectively. The diffraction gratings 41 and 42 are combined.

  Unlike the above-described variable diffraction gratings 10, 20, and 30, the variable diffraction grating 40 is premised on the incidence of a divergent light beam.

  For this reason, although the diffraction gratings 41 and 42 basically have a configuration similar to that of the diffraction gratings 11 and 12, respectively, the periods of the gratings g41 and g42 are different from each other according to the divergence of the light beam. Has been made.

  That is, the variable diffraction grating 40 has a relationship as shown in the following equation, where the distances from the light source Q of the light beam to the gratings g41 and g42 are distances f1 and f2, respectively, and the periods of the gratings g41 and g42 are periods c1 and c2, respectively. Have

  In the first state shown in FIG. 15A, the positions of the diffraction gratings 41 and 42 are determined so that the light beam that has passed through the peak portion of the grating g41 passes through the peak portion of the grating g42. .

  For this reason, the light beam that diverges with the point Q as a point light source passes through the variable diffraction grating 40, and as shown in FIG. 15B corresponding to FIG. The phase changes in the same manner as when passing.

  In the variable diffraction grating 40 as well, as in the case of the first variable diffraction grating 10 (FIG. 3), the relationship of the expressions (1) and (2) is established.

  In addition, when the diffraction grating 41 is moved in the x direction by a distance h1 (that is, a distance that is ½ of the period c1), the variable diffraction grating 40 corresponds to FIGS. 16A and 15B. And as shown to (B), it will be in a 2nd state.

  In this second state, the variable diffraction grating 40 can be regarded as a diffraction grating having the phase depth φ2 shown in the equation (3), as in the case of the first variable diffraction grating 10 (FIG. 5). ) To calculate the diffraction efficiency η2 (m).

  The variable diffraction grating 40 has a light beam source on the second diffraction grating side, and can also change the diffraction efficiency in the same manner for a light beam that is collected with a focusing lens or the like as a focal point. it can.

  As described above, the fourth variable diffraction grating 40 can change the diffraction efficiency by changing the position of the diffraction grating 41 in the x direction with respect to the diffraction grating 42, similarly to the first variable diffraction grating 10. Accordingly, the fourth variable diffraction grating 40 can also act as an attenuator for a light beam composed of diverging light or convergent light.

(1-3) Operation and Effect In the above configuration, the variable diffraction grating 10 includes the grating surface 11A of the diffraction grating 11 on which the grating g11 with the period c is formed and the diffraction grating 12 on which the grating g12 with the period c is formed. By making the grating surface 12A face each other, one diffraction grating is formed as a whole.

  In the first state (FIG. 3) in which the positions of the crest portions of the grating g11 and the grating g12 are aligned with respect to the z direction, the variable diffraction grating 10 is expressed by the equation (1) with respect to the light beam incident from the z direction. It acts as a diffraction grating having a phase depth φ1.

  On the other hand, in the variable diffraction grating 10, the diffraction grating 11 is moved in the x direction by a width h that is half of the period c with respect to the diffraction grating 12, and the positions of the crest and trough portions of the grating g 11 and the grating g 12 are mutually aligned. In the corresponding second state (FIG. 5), it acts as a diffraction grating having a phase depth φ2 expressed by equation (3).

  Therefore, the variable diffraction grating 10 can act as a diffraction grating having different diffraction efficiencies by moving the position of the diffraction grating 11 with respect to the diffraction grating 12 and switching to the first state or the second state.

  At this time, since the variable diffraction grating 10 is combined with diffraction gratings 11 and 12 each having the same material configuration as that of a general diffraction grating, for example, the diffraction efficiency is changed by controlling the voltage applied to the liquid crystal element. Compared with the case, light resistance can be improved.

  Further, the variable diffraction grating 10 can move the diffraction grating 11 to a desired position in a very short time by using, for example, an actuator or a piezoelectric element. It can be expected to respond at high speed without being influenced by.

  At this time, since the variable diffraction grating 10 only needs to move the diffraction grating 11 by a width h at the maximum with respect to the diffraction grating 12, for example, compared with the case where the entire diffraction grating is moved and switched to be inserted into the optical path. Thus, the movement time of the diffraction grating 11 can be greatly shortened, and the space required for the movement can be greatly reduced.

  Furthermore, since the diffraction efficiency of the variable diffraction grating 10 continuously changes in the intermediate state (FIG. 4) in addition to the first state and the second state (FIG. 6), when used as an attenuator, The amount of light beam such as ± primary light can be finely adjusted.

  Furthermore, the variable diffraction grating 20 diffracts the light beam in the second state by selecting and designing the refractive indexes n1 and n2 and the grating depths d1 and d2 so as to satisfy the expression (5) or (6). It is also possible to pass through without any change (FIG. 9B).

  Further, the variable diffraction grating 30 can change the duty ratio of the diffraction grating by combining the blazed diffraction gratings 31 and 32 and changing to the first state or the second state (FIG. 11B). 12 (B) and FIG. 13 (B)), thereby making it possible to continuously change the diffraction efficiency.

  Further, in the variable diffraction grating 40, the periods c1 and c2 in the gratings g41 and g42 of the diffraction gratings 41 and 42 are proportional to the distances f1 and f2 from the point Q that is the light source of the light beam based on the relationship of the equation (8). By designing, similarly to the case where the variable diffraction grating 10 acts on a light beam made of parallel light, the diffraction efficiency can be appropriately adjusted for the light beam made of divergent light or convergent light.

  According to the above configuration, the variable diffraction grating 10 causes the grating surface 11A of the diffraction grating 11 on which the grating g11 having the period c is formed to face the grating surface 12A of the diffraction grating 12 on which the grating g12 having the period c is formed. In the first state where the positions of the crest portions of the grating g11 and the grating g12 are aligned with respect to the z direction, the light beam incident from the z direction acts as a diffraction grating having a phase depth φ1 expressed by the equation (1). On the other hand, the diffraction grating 11 is moved in the x direction by a width h that is half the period c with respect to the diffraction grating 12, and the second state in which the positions of the ridges and valleys of the grating g11 and the grating g12 correspond to each other. Then, by acting as a diffraction grating having a phase depth φ2 represented by the expression (3), it is possible to act as diffraction gratings having different diffraction efficiencies.

(2) First Embodiment (2-1) Configuration of Optical Disc Device In FIG. 17, an optical disc device 50 is mainly configured by a control unit 51, and is based on a BD (Blu-ray Disc, registered trademark) system. Information is recorded on the optical disc 100, and the information can be reproduced from the optical disc 100.

  Incidentally, the optical disk device 50 is adapted to correspond to various types of optical disks 100, that is, different in rewritable type or read-only type, and in the number of recording layers.

  The control unit 51 includes a CPU (Central Processing Unit) (not shown), a ROM (Read Only Memory) in which various programs are stored, and a RAM (Random Access Memory) used as a work memory of the CPU. The optical disc device 50 is controlled in an integrated manner.

  That is, the control unit 51 rotates the spindle motor 55 via the drive unit 52 to rotate the optical disc 100 placed on a turntable (not shown) at a desired speed. Further, the control unit 51 drives the sled motor 56 via the drive unit 52, thereby moving the optical pickup 57 along the movement axes G1 and G2 in the tracking direction, that is, the direction toward the inner peripheral side or the outer peripheral side of the optical disc 100. Move it a lot.

  The optical pickup 57 has a plurality of optical components such as an objective lens 58 attached thereto. The optical pickup 57 irradiates the optical disc 100 with a light beam based on the control of the control unit 51. At this time, the reflected light beam is reflected from the light beam. Has been made to detect.

  For example, when the control unit 51 receives a reproduction command for reproducing information recorded on the optical disc 100 from the external device (not shown) in a state where the optical disc 100 is loaded, the control unit 51 receives a predetermined instruction via the drive unit 52. Is supplied to the optical pickup 57.

  In response to this, the optical pickup 57 condenses the light beam on the recording layer of the optical disc 100 by the objective lens 58, and the position of the objective lens 58 by the biaxial actuator 59 based on the focus control and tracking control by the drive unit 52. Adjust.

  Specifically, the optical pickup 57 emits a light beam from an internal laser diode (details will be described later), and irradiates the recording layer of the optical disc 100 through the objective lens 58. The optical pickup 57 receives a reflected light beam formed by reflecting the light beam by the recording layer by an internal photodetector (details will be described later), and generates a plurality of received light signals corresponding to the received light amount at that time. Supply to the processing unit 53.

  In response to this, the signal processing unit 53 performs a predetermined calculation process using the supplied light reception signal, so that the focus direction and tracking between the focal point of the light beam and a desired track in the signal recording layer of the optical disc 100 are detected. A focus error signal and a tracking error signal representing the amount of deviation with respect to the direction are generated and supplied to the drive unit 52.

  The drive unit 52 generates a drive signal for driving the objective lens 58 based on the supplied focus error signal and tracking error signal, and supplies this to the biaxial actuator 59.

  The optical pickup 57 drives the biaxial actuator 59 based on this drive signal, thereby performing focus control and tracking control of the objective lens 58, and focuses the light beam condensed by the objective lens 58 to a desired track. It is made to follow.

  At this time, the control unit 51 can record the information on a desired track by modulating the intensity of the light beam emitted from the laser diode by the signal processing unit 53 based on the information supplied from the outside. ing.

  The control unit 51 can reproduce information recorded on a desired track on the optical disc 100 by performing predetermined arithmetic processing, demodulation processing, decoding processing, and the like on the detection signal by the signal processing unit 53. Has been made.

  Incidentally, the control unit 51 performs a discrimination process for discriminating the type of the optical disc 100 based on the information obtained at this time, the light reception result of the reflected light beam in the optical pickup 57, and the like. As a result, the control unit 51 can correctly cope with different recording methods and reproduction methods depending on the type of the optical disc 100.

  As described above, the optical disc apparatus 50 records information on the optical disc 100 using the light beam and reproduces information from the optical disc 100 using the light beam.

(2-2) Configuration of Optical Pickup As shown in FIG. 18, the optical pickup 57 is configured around an optical integrated element 60 in which a laser diode, a photodetector, a prism, and the like are integrally configured.

  As shown in FIG. 19, the optical integrated device 60 is provided with a laser diode 62 on one surface of a plate-like base plate 61. Based on the laser drive signal DL supplied from the signal processing unit 53 (FIG. 17), The laser diode 62 emits a light beam L1 having a wavelength of about 405 [nm] corresponding to the BD system.

  The light beam L1 is reflected by a rising mirror 63 provided on one surface of the base plate 61, travels to the opposite surface side through a hole 61H provided in the base plate 61, and passes through a pedestal portion 64A having an opening. Then, it enters the half-wave plate 65.

  Incidentally, the optical integrated device 60 is configured to protect the laser diode 62 from deterioration due to oxidation or the like by sealing the periphery of the laser diode 62 with a base plate 61, a member 64C, a lid 64D, a pedestal 64A, and the like.

  The half-wave plate 65 adjusts the polarization direction of the light beam L 1 and makes it incident on the variable diffraction grating 66. As shown in FIGS. 20A and 20B, the variable diffraction grating 66 includes a movable diffraction grating 81 and a fixed diffraction grating 82 inside a chassis 80 that has a hollow rectangular parallelepiped shape as a whole.

  The chassis 80 has a configuration in which a side plate 80B having a quadrangular prism side surface is sandwiched between a plate-like bottom plate 80A and a top plate 80C. Each of the bottom plate 80A and the top plate 80C is configured to allow the light beam to pass through a through hole provided in the center.

  The movable diffraction grating 81 and the fixed diffraction grating 82 are configured in the same manner as the diffraction gratings 41 and 42 in the variable diffraction grating 40 (FIGS. 15 and 16), respectively. 62), the periods c1 and c2 of the gratings g81 and g82 are respectively determined according to the ratio of the optical path lengths from 62).

  Incidentally, since the variable diffraction grating 66 receives the light beam L1 made of diverging light from the fixed diffraction grating 82 side (that is, the lower side in the figure), the period c1 of the grating g81 is opposite to the case of the variable diffraction grating 40. It is made to become larger than the period c2.

  The fixed diffraction grating 82 is attached and fixed to the bottom plate 80A. On the other hand, the movable diffraction grating 81 is attached and fixed to the top plate 80C via a movable support portion 83 formed of a leaf spring, an elastic body, or the like. As a result, the movable diffraction grating 81 can freely move in the x direction in which the grating g81 is arranged or in the opposite direction (hereinafter referred to as -x direction).

  Furthermore, the movable diffraction grating 81 and the fixed diffraction grating 82 are substantially parallel to each other, and the positions of the gratings g81 and g82 are also substantially parallel to each other.

  Thin film coils 84 are attached to the side surfaces 81E and 81F of the movable diffraction grating 81, respectively. Magnets 85 are attached to the inner surfaces of the side plates 80B1 and 80B2 that face the thin film coil 84, respectively. That is, the variable diffraction grating 66 constitutes a grating actuator 86 by a combination of the thin film coil 84 and the magnet 85.

  When the lattice driving signal DG is supplied from the driving unit 52 (FIG. 17) to the thin film coil 84, the lattice actuator 86 generates an electromagnetic force based on the lattice driving signal DG, and the electromagnetic force and the magnetic force of the magnet 85. As a result, the movable diffraction grating 81 is moved in the x direction or the opposite direction by a distance corresponding to the grating driving signal DG.

  In this way, the variable diffraction grating 66 moves the movable diffraction grating 81 by the grating actuator 86 in accordance with the grating drive signal DG supplied from the drive unit 52, and similarly to the variable diffraction grating 40 described above, the zero-order light and ±± It is possible to change the diffraction efficiency of first-order or higher-order diffracted light.

  In practice, the variable diffraction grating 66 divides the light beam L1 into a plurality of light beams composed of higher-order diffracted light of 0th order and ± 1st order or higher (hereinafter referred to as high-order diffracted light). Then, the light is incident on the laminated prism 68 through the mold composite element 67 (FIG. 19) made of a transparent resin material.

  The polarization reflecting film 68A of the laminated prism 68 transmits the light beam L1 at a predetermined ratio according to the relationship with the polarization direction of the light beam L1, thereby forming the light beam L2, which is incident on the collimator lens 71 (FIG. 18). Let At the same time, the polarization reflection film 68A reflects the remaining portion of the light beam L1 to form a light beam L3, which is incident on the condenser lens 73 (FIG. 18). That is, the polarization reflection film 68A distributes the light beam L1 to the light beams L2 and L3.

  The collimator lens 71 converts the light beam L2 from divergent light to parallel light, converts this from linearly polarized light to circularly polarized light by the quarter wavelength plate 72, and then enters the objective lens 58. The objective lens 58 collects the light beam L2 and irradiates the recording layer of the optical disc 100 with it.

  At this time, the light beam L2 is reflected by the recording layer of the optical disc 100, and becomes a reflected light beam L4 in which the rotational direction of the circularly polarized light is reversed, and enters the objective lens 58. The objective lens 58 converts the reflected light beam L4 from diverging light to parallel light, converts this from circularly polarized light to linearly polarized light by the quarter wavelength plate 72, and then enters the collimator lens 71.

  Incidentally, since the direction of rotation of the reflected light beam L4 in the circularly polarized light is opposite to that of the light beam L2, the polarization direction after being converted into linearly polarized light by the quarter wavelength plate 72 is orthogonal to the polarization direction of the light beam L2. Will do.

  The collimator lens 71 converts the reflected light beam L4 into convergent light and makes it incident on the laminated prism 68 (FIG. 19) of the optical integrated device 60. The polarization reflecting film 68A of the laminated prism 68 reflects most of the reflected light beam L4 according to the polarization direction of the reflected light beam L4 and makes it incident on the half mirror 68B.

  The half mirror 68B reflects the reflected light beam L4 at a rate of about 20% to obtain a reflected light beam L5, which is separated into a plurality of light beams by a hologram 67A formed on the mold composite element 67. The reproduction signal detecting photo detector 69 is irradiated.

  Further, the half mirror 68B transmits the reflected light beam L4 at a rate of about 80% to form a reflected light beam L6, which is reflected by the mirror 68C and applied to the reproduction signal detecting photo detector 69.

  The reproduction signal detection photodetector 69 has a plurality of detection areas corresponding to the reflected light beams L5 and L6 (details will be described later), and detects the light amounts of the reflected light beams L5 and L6 by the respective detection areas. A plurality of received light signals corresponding to the amount of light are generated and supplied to the signal processing unit 53 (FIG. 17).

  The signal processing unit 53 generates the above-described focus error signal and tracking error signal by performing predetermined calculation processing based on a plurality of light reception signals.

  On the other hand, the light beam L3 obtained by reflecting the divergent light beam L1 by the polarization reflecting film 68A of the laminated prism 68 (FIG. 19) is converted from divergent light into convergent light by the condenser lens 73 (FIG. 18). The light is incident on a photodetector 74 for APC (Automatic Power Control).

  Here, as shown in FIGS. 21A and 21B, the APC photodetector 74 has detection areas 74A, 74B, and 74C in accordance with the positions of the light beam L3 irradiated with the 0th order light and the ± first order light. Are provided.

  Further, the APC photodetector 74 is provided with a mirror 74M at a position where the ± 3rd order light of the light beam L3 is irradiated, and reflects the ± 3rd order light and guides it to the detection regions 74B and 74C. Yes.

  As a result, the APC photodetector 74 receives the zero-order light of the light beam L3 through the detection region 74A, and receives the ± first-order light and ± third-order light of the light beam L3 as high-order light through the detection regions 74B and 74C. Detection signals SDA, SDB and SDC corresponding to the respective light amounts are generated by the conversion and supplied to the signal processing unit 53 (FIG. 17).

  The signal processing unit 53 generates a laser drive signal DL based on the detection signals SDA, SDB, and SDC, and supplies the laser drive signal DL to the laser diode 62 (FIG. 19) of the optical pickup 57 to emit from the laser diode 62. The light quantity of the light beam L1 is adjusted.

  As described above, the optical pickup 57 moves the movable diffraction grating 81 of the variable diffraction grating 66 based on the grating drive signal DG supplied from the driving unit 52, thereby allowing the zero-order light and the high-order diffraction light in the light beams L2 and L3, respectively. Then, the light beam L2 is guided to the optical disc 100 and the light beam L3 is guided to the APC photo detector 74.

(2-3) Control of light quantity by laser diode and variable diffraction grating (2-3-1) Configuration of light quantity control circuit By the way, in the optical pickup 57, the emitted light quantity of the laser diode 62 (FIG. 19) is directly used as the light beam L1 (FIG. 18), and the light beams L2 and L3 (FIG. 18) in the light beams L1 and the diffraction efficiency of the zero-order light in the variable diffraction grating 66 (FIGS. 19, 20A and 20B). The amount of zero-order light is determined.

  For this reason, as shown in FIG. 22, the optical disc apparatus 50 controls the light amount of the light beam L1 and the light beams L2 and L3 in an integrated manner by the light amount control unit 90 that combines the APC photodetector 74 and the signal processing unit 53. Has been made.

  That is, the detection area 74A of the APC photodetector 74 receives the 0th-order light of the light beam L3, and supplies the detection signal SDA whose current value changes according to the amount of received light to the differential amplifier 91A of the current-voltage conversion circuit 91. .

  As described above, the light beam L3 is reflected at a rate at which the light beam L1 is fixed by the polarization reflection film 68A of the laminated prism 68. For this reason, the detection signal SDA not only directly represents a change in the light amount of the 0th-order light of the light beam L3, but also indirectly represents a change in the light amount of the 0th-order light of the light beam L2 applied to the optical disc 100.

  A current-voltage conversion circuit 91 incorporated in the APC photodetector 74 generates a zero-order optical signal Va by converting a change in current in the detection signal SDA into a change in voltage, and this is generated as a negative input terminal of the differential amplifier 92. And to amplifiers 96 and 97, respectively.

  In the differential amplifier 92, the control unit 51 (FIG. 17) supplies a signal representing the target light amount in the 0th order light of the light beam L3 (hereinafter referred to as the 0th order light reference signal Var) to the positive input terminal. Has been made.

  Incidentally, the 0th-order light reference signal Var is set to a relatively large value when the optical disk device 50 records information on the optical disk 100, while the optical disk device 50 is relatively relatively small when reproducing information from the optical disk 100. A small value is set.

  The differential amplifier 92 calculates the difference between the 0th-order optical signal Va and the 0th-order optical reference signal Var, and supplies the calculated result to the laser diode drive circuit 93 as the 0th-order optical difference signal Vad. This zero-order light difference signal represents the adjustment amount of the light amount of the light beam L1 in the laser diode 62 when the zero-order light of the light beam L3 is brought close to the zero-order light reference signal Var.

  The laser diode drive circuit 93 generates a laser drive signal DL based on the supplied zero-order light difference signal Vad and supplies it to the laser diode 62. As a result, the laser diode 62 emits a light beam L1 having a light quantity that brings the 0th-order light signal Va indicating the 0th-order light of the light beam L3 closer to the 0th-order light reference signal Var. Incidentally, the laser diode driving circuit 93 modulates the laser driving signal DL in accordance with information to be recorded at the time of recording.

  Thus, the light quantity control unit 90 is configured to feedback control the light quantity of the light beam L1 emitted from the laser diode 62 (hereinafter referred to as emission light quantity control).

  On the other hand, the detection areas 74B and 74C of the APC photodetector 74 receive the ± first-order light and ± third-order light (that is, higher-order light) of the light beam L3, and add detection signals corresponding to the respective received light amounts. The SDBC is supplied to the differential amplifier 94A of the current-voltage conversion circuit 94.

  A current-voltage conversion circuit 94 incorporated in the APC photodetector 74 generates a high-order optical signal Vbc by converting a change in current in the detection signal SDBC into a change in voltage, and supplies this to the negative input terminal of the differential amplifier 95. To do.

  The amplifier 96 generates the first comparison signal Va1 by multiplying the 0th-order optical signal Va by 0.05, and supplies this to the switch 98. Similarly, the amplifier 97 generates the second comparison signal Va2 by multiplying the 0th-order optical signal Va by 1.5 and supplies it to the switch 98.

  Based on the control of the control unit 51 (FIG. 17), the switch 98 selects the second comparison signal Va2 at the time of reproducing the optical disc 100, and selects the first comparison signal Va1 at the time of recording on the optical disc 100 (hereinafter referred to as “the first comparison signal Va1”). The selected signal is called a selective comparison signal Vas), and the selective comparison signal Vas is supplied to the positive input terminal of the differential amplifier 95.

  The differential amplifier 95 calculates the difference between the high-order optical signal Vbc and the selection comparison signal Vas, and supplies the calculation result to the phase compensation circuit 99 as the high-order optical differential signal Vbcd.

  Based on the high-order optical difference signal Vbcd, the phase compensation circuit 99 generates a lattice control signal CG that can prevent oscillation and stabilize the control, and supplies this to the drive unit 52. The drive unit 52 generates a grating drive signal DG based on the grating control signal CG and supplies it to the grating actuator 86 of the variable diffraction grating 66, thereby moving the movable diffraction grating 81 (FIG. 20) in the x direction or vice versa. The diffraction efficiency of 0th order light and higher order light is changed by moving in the direction.

  That is, the light quantity control unit 90 performs feedback control (hereinafter referred to as “lattice position control”) so that the high-order optical signal Vbc is made to follow the selection comparison signal Vas.

  Here, since the second comparison signal Va2 obtained by multiplying the 0th-order optical signal Va by 1.5 is the selective comparison signal Vas when the optical disc 100 is reproduced, the light quantity control unit 90 and the 0th-order optical signal Va and the higher-order light are used. The diffraction efficiency of the variable diffraction grating 66 is adjusted so that the ratio to the signal Vbc is about 1: 1.5.

  That is, the light amount control unit 90 reduces the light amount of the zero-order optical signal Va by increasing the ratio of the high-order optical signal Vbc by the variable diffraction grating 66.

  As a result, the light quantity control unit 90 performs optical efficiency in the forward path from when the light beam is emitted from the laser diode 62 to the optical disk 100 (that is, the light with respect to the original emission power when the light beam L1 is emitted from the laser diode 62). The ratio of the objective lens emission power when the beam L2 is emitted from the objective lens 58 can be reduced. Thus, the light quantity control unit 90 can relatively reduce the laser noise as the original emission power is increased.

  On the other hand, when the optical disk 100 is recorded, the light quantity control unit 90 uses the first comparison signal Va1 obtained by multiplying the 0th order light signal Va by 0.05 times as the selection comparison signal Vas. The diffraction efficiency of the variable diffraction grating 66 is adjusted so that the ratio to the signal Vbc is about 1: 0.05.

  That is, the light quantity control unit 90 can increase the light quantity of the 0th-order optical signal Va by greatly reducing the ratio of the high-order optical signal Vbc by the variable diffraction grating 66. As a result, the light quantity control unit 90 can increase the optical efficiency of the forward path as much as possible, so that the objective lens emission power can be increased to a level suitable for recording with a small laser driving current.

  Incidentally, in the light quantity control unit 90, the ratio of the 0th-order light beam should be close to 100% in order to increase the light quantity of the 0th-order light as much as possible. However, from the viewpoint of performing feedback control in the grating position control at high speed, the amplifier 97 The magnification is 0.05, and the ratio of the 0th-order light beam (that is, the diffraction efficiency) is about 95%.

  In this way, the light quantity control unit 90 adjusts the ratio of the high-order light signal Vbc to the zero-order light signal Va, that is, the ratio of the light quantity of the high-order light to the zero-order light to a preset desired value (1.5, 0.05, etc.). By doing so, the diffraction efficiency of the variable diffraction grating 66 is adjusted. Thereby, the light quantity control unit 90 can adjust the amount of attenuation when the variable diffraction grating 66 functions as an attenuator, and can greatly change the optical efficiency of the forward path between reproduction and recording.

(2-3-2) Start of lattice position control By the way, the light quantity control unit 90 reduces the time required for convergence of the feedback loop by starting at the timing satisfying a specific condition when starting the above-described lattice position control. It is made to do.

  When starting recording or reproduction with respect to the optical disc 100, the optical disc device 50 first performs a focus pull-in operation so that feedback control can be started by roughly focusing the light beam L2 on the signal recording layer of the optical disc 100.

  When performing the focus pull-in operation, the light quantity control unit 90 prepares in advance with a waveform as shown in FIG. 23A by the drive unit 52 based on the control from the control unit 51 as preparation before starting the lattice position control. A grating driving signal DG 0 is generated and supplied to the variable diffraction grating 66.

  The pre-lattice drive signal DG0 has a sawtooth waveform and is repeated at a predetermined period. Further, when the prior lattice driving signal DG0 is differentiated, a differential signal ΔDG0 as shown in FIG. 23B is obtained. The pre-lattice drive signal DG0 is not limited to a sawtooth shape, and may be a sine wave shape or a triangular wave shape.

  The variable diffraction grating 66 periodically moves the movable diffraction grating 81 (FIG. 20A) in the x direction or the opposite direction based on the pre-grating drive signal DG0, so that the diffraction efficiency of the zero-order light beam and the high-order light beam is increased. Are continuously changed.

  As a result, the high-order optical signal Vbc (FIG. 22) changes as shown in FIG. 23C in correspondence with the pre-lattice drive signal DG0. If the selective comparison signal Vas is superimposed on FIG. 23C, it can be seen that the high-order optical signal Vbc matches the selective comparison signal Vas at times t1, t2, t3, t4, t5, and t6. When the higher order optical signal Vbc is differentiated, a differentiated signal ΔVbc as shown in FIG. 23D is obtained.

  By the way, the light quantity control unit 90 performs feedback control so that the high-order optical signal Vbc approaches the selective comparison signal Vas by the lattice position control described above. Accordingly, the light quantity controller 90 determines the lattice position at or before and after the time t1, t2, t3, t4, t5 or t6 (FIG. 23C) when the value of the high-order optical signal Vbc matches the value of the selective comparison signal Vas. It can be considered that the feedback loop can be immediately converged if the control is started.

  However, the light quantity control unit 90 finally generates the lattice driving signal DG by supplying the high-order optical signal Vbc to the negative input terminal of the differential amplifier 95 in the signal processing unit 53. That is, in the light quantity control unit 90, if the high-order optical signal Vbc increases, the grating drive signal DG decreases.

  For this reason, the light amount control unit 90 diverges the feedback loop unless the grating position control is started at a timing at which the higher-order optical signal Vbc also increases when the grating driving signal DG tends to increase.

  That is, when the increase or decrease in the high-order optical signal Vbc coincides with the increase or decrease in the grating drive signal DG, that is, the light quantity control unit 90, that is, the sign of the differential value ΔDG0 of the prior grating drive signal and the sign of the derivative value ΔVbc of the high-order optical signal. It can be considered that the feedback loop can be converged in a short time if the lattice position control is started when the polarities coincide with each other.

  Therefore, the light quantity control unit 90 can first calculate the differential value ΔDG0 of the prior grating drive signal and the differential value ΔVbc of the high-order optical signal by the signal processing unit 53, and the difference between the high-order optical signal Vbc and the selection comparison signal Vas is a predetermined value. It is determined whether it is less than the threshold value Vth.

  Next, the light quantity control unit 90 has a difference between the value of the high-order optical signal Vbc and the value of the selective comparison signal Vas less than the threshold value Vth, and the product of the differential value ΔDG0 of the prior grating drive signal and the differential value ΔVbc of the high-order optical signal. Is positive, that is, at the time t1, t2, t5, or t6 where the sign of the differential value ΔDG0 and the sign of the differential value ΔVbc match, or the vicinity thereof.

  As described above, the light amount control unit 90 is based on the relationship between the difference between the value of the high-order optical signal Vbc and the value of the selective comparison signal Vas, the sign of the differential value ΔDG0 of the prior grating drive signal, and the sign of the differential value ΔVbc of the high-order optical signal. By determining the start timing of the lattice position control, the feedback loop can be stably converged in a short time.

(2-3-3) Diffraction Grating Design Example Next, the period c2 of the gratings g81 and g82 in the movable diffraction grating 81 and the fixed diffraction grating 82 of the variable diffraction grating 66 (FIG. 20) will be described. Incidentally, in the variable diffraction grating 66, as in the case of the variable diffraction grating 40 (FIGS. 15 and 16), the period c1 of the grating g81 and the period c2 of the grating g82 are different, but attention is paid to the period c1 of the grating g81 here. .

  When the optical pickup 57 (FIG. 18), for example, records a high-order light beam separated by the variable diffraction grating 66 (that is, a diffracted light beam of ± 1st order or higher) into the objective lens 58 at the time of recording, the original information in the optical disc 100 is obtained. The higher-order light beam is condensed by the objective lens 58 at a location other than the desired track on which recording is desired. In this case, the optical pickup 57 may unintentionally erase information that has already been recorded in the other part.

  Therefore, in the optical pickup 57, a condition for irradiating the optical disk 100 with only the zero-order light beam and not irradiating the optical disk 100 with the higher-order light beam will be examined.

  First, assume an optical pickup 104 in which a variable diffraction grating 105 is arranged in parallel light, as shown in FIG.

  The optical pickup 104 converts a light beam formed by diverging light emitted from the laser diode 62 into parallel light by a collimator lens 71 and makes it incident on the variable diffraction grating 105 through a half-wave plate 65.

  The variable diffraction grating 105 is provided with a movable diffraction grating and a fixed diffraction grating similar to the variable diffraction grating 10, 20, or 30 instead of the movable diffraction grating 81 and the fixed diffraction grating 82 in the variable diffraction grating 66. The light beam can be diffracted and its diffraction efficiency can be changed.

  The variable diffraction grating 105 diffracts the light beam to separate it into 0th-order light and ± 1st-order or higher-order light, and makes the light incident on the polarization beam splitter 106 corresponding to the portion of the laminated prism 68 including the polarization reflection film 68A.

  The polarization reflection film 106A of the polarization beam splitter 106, similar to the polarization reflection film 68A of the laminated prism 68, reflects the light beam at a predetermined ratio and causes the light beam to enter the APC photodetector 74 through the condenser lens 73. The remaining light is transmitted and irradiated onto the optical disc 100 through the quarter-wave plate 72 and the objective lens 58.

  The light beam reflected by the optical disc 100 (that is, the reflected light beam) is incident on the polarization beam splitter 106 via the objective lens 58 and the quarter wavelength plate 72. The polarization beam splitter 106 reflects most of the reflected light beam, converts it into convergent light by the condenser lens 107, and then enters the half mirror 68B and the laminated prism 108 corresponding to the mirror 68C of the laminated prism 68.

  Similar to the laminated prism 68, the laminated prism 108 reflects the reflected light beam at a rate of about 20% by the half mirror 108B, and divides it into a plurality of light beams by the hologram 109, and then irradiates the photodetector 69 for detecting the reproduction signal. . The laminated prism 108 transmits the reflected light beam at a rate of about 80% by the half mirror 108B, reflects the reflected light beam by the mirror 108C, and irradiates the photodetector 69 for detecting the reproduction signal.

  In this optical pickup 104, the distance from the variable diffraction grating 105 to the polarization reflection film 106A of the polarization beam splitter 106 is Y1, the distance from the polarization reflection film 106A to the condenser lens 73 is Y2, and the condenser lens 73 to the APC The distance to the photo detector 74 is Y3, and the distance from the polarizing reflection film 106A to the objective lens 58 is Y6.

  If the wavelength of the light beam is λ [nm], the distance u1 between the zero-order light beam and the first-order light beam at the position of the objective lens 58 uses the grating period c (FIG. 3) in the variable diffraction grating 105, and It can be expressed as:

  Here, assuming that the optical disc 100 is a BD system, it is assumed that the wavelength λ of the light beam is 405 [nm], the distance Y1 + Y6 = 200 [mm], and the effective radius rv of the objective lens 58 is 0.5 [mm]. To do. In this case, in the optical pickup 104, the high-order light beam reaches outside the effective radius of the objective lens 58 when the grating period c = 80 [μm] from the relationship of the equation (9).

  In practice, since the optical pickup 104 has a distance Y1 + Y6 <200 [mm] and an effective radius rv> 0.5 [mm] of the objective lens 58, each diffraction grating has a period c <80 [μm]. There is a need.

  When the period c = 1 [μm], Y2 + Y3 is substituted for Y6 in the equation (9) and the distance Y1 + Y2 + Y3 = 5 [mm] is set, and the zero-order light beam on the light receiving surface of the APC photodetector 74 and The distance between the primary light beams becomes 2 [mm] or more. In this case, it becomes difficult for the APC photodetector 74 to receive both the 0th-order light beam and the first-order light beam by one light-receiving element due to restrictions on the size of the light-receiving element.

  Next, attention is focused on the optical pickup 57 (FIGS. 18 and 19) in which the variable diffraction grating 66 is disposed in the divergent light. In this optical pickup 57, the distance from the laser diode 62 to the variable diffraction grating 66 is Y0, and the distance from the movable diffraction grating 81 of the variable diffraction grating 66 to the polarizing reflection film 68A of the laminated prism 68 is Y1.

  Further, the distance from the polarizing reflection film 68A to the condenser lens 73 is Y2, and the distance from the condenser lens 73 to the APC photo detector 74 is Y3. Further, the distance from the polarization reflection film 68A to the collimator lens 71 is Y4, and the distance from the collimator lens 74 to the objective lens 58 is Y5.

  Here, if the wavelength of the light beam L1 is λ [nm], the distance u2 between the zeroth-order light beam and the first-order light beam at the position of the objective lens 58 can be expressed by the following equation.

  Here, assuming that the optical disc 100 is a BD system, the wavelength λ of the light beam L1 = 405 [nm], the distance Y0 = 3 [mm], the distance Y1 = 2.5 [mm], the distance Y2 = 2. Assume that 5 [mm], distance Y3 = 5.3 [mm], distance Y4 = 10 [mm], distance Y5 = 200 [mm], and effective radius rv = 0.5 [mm] of the objective lens 58.

  In this case, in the optical pickup 57, from the relationship of the expression (10), the higher-order light beam reaches outside the effective radius of the objective lens 58 if the period c1 = 15 [μm] of the grating g81.

  In practice, since the optical pickup 57 has the distance Y5 <200 [mm] and the effective radius rv> 0.5 [mm] of the objective lens 58, the grating g81 of the movable diffraction grating 81 has a period c1 <15 [ μm].

  Further, when Y4 in equation (10) is replaced with Y2, Y5 is replaced with Y3, and the period c1 = 0.5 [μm], even if the distance Y3 = 5 [mm], even on the light receiving surface of the APC photodetector 74 The distance between the zero-order light beam and the primary light beam is 2 [mm] or more. In this case, it becomes difficult for the APC photodetector 74 to receive both the zero-order light beam and the primary light beam with a single light-receiving element.

  Summarizing the above conditions, the period c (or period c1) of the grating in the variable diffraction grating is such that the high-order light beam out of the light beam reaching the objective lens 58 does not enter the effective radius, and ± 1st order of the light beam. In order for the light beam to be received by the APC photodetector 74 formed of one light receiving element, it is desirable that the range is 0.5 [μm] <c (or c1) <80 [μm].

  Incidentally, in the case of the optical pickup 57 in which the variable diffraction grating 66 is arranged in the diverging light, the period c2 of the grating g82 may be determined by the above-described equation (8).

(2-4) Operation and Effect In the above configuration, the optical disc apparatus 50 is provided with the variable diffraction grating 66 on the optical path of the light beam L1 emitted from the laser diode 62 of the optical pickup 57, so that the optical disc 100 can be reproduced or recorded. The diffraction efficiency of the 0th-order light beam in the light beam L1 is adjusted by controlling the position of the movable diffraction grating 81 by the light amount control unit 90 according to which one is performed.

  Therefore, since the optical disk device 50 can appropriately change the attenuation amount of the zero-order light beam emitted from the variable diffraction grating 66, it is emitted from the laser diode 62 when reproducing or recording information. The optical beam 100 can be irradiated with the light beam L2 having an appropriate light amount while the laser noise in the light beam L1 is kept relatively low.

  At this time, the variable diffraction grating 66 includes the movable diffraction grating 81 and the fixed diffraction grating 82 through which the light beam L1 passes are made of a glass material or a resin material similar to a general diffraction grating, and thus a conventional liquid crystal element is used. Compared with the case where it uses, the light resistance with respect to the light beam L1 can be improved.

  The variable diffraction grating 66 can change the diffraction efficiency of the zero-order light beam greatly by moving the movable diffraction grating 81 in the x direction by a width h (FIG. 3) at most by the actuator 86. Compared with the case of using an element, the time required to obtain a desired diffraction efficiency can be extremely shortened.

  Further, as shown in FIG. 4 and FIG. 8 of Patent Document 1, in a configuration in which whether or not an optical component such as an ND filter is largely moved and positioned on the optical path is switched, the switching time is long (for example, 0). For over a second). For this reason, in such a conventional optical component, for example, the recording layer of the optical disc 100 can be applied to the switching of the light amount when the recording layer is a single layer or when it is a multilayer. It is difficult to apply the light quantity switching between the time and the size of the driving actuator.

  On the other hand, the variable diffraction grating 66 only needs to move the movable diffraction grating 81 in the x direction by the width h (FIG. 3) at most by the actuator 86, that is, the moving distance of the movable diffraction grating 81 is short. The diffraction efficiency can be switched over time, which can be applied to light quantity switching between recording and reproduction, and can contribute to miniaturization and weight reduction of the optical pickup 57 and the optical integrated device 60.

  The light quantity control unit 90 (FIG. 22) switches the selection comparison signal Vas to the first comparison signal Va1 suitable for reproduction or the second comparison signal Va2 suitable for recording, so that both the recording and reproduction can be performed. Therefore, appropriate feedback control can be performed, so that the diffraction efficiency in the variable diffraction grating 66 can be reliably set to a desired value.

  Furthermore, when starting the grating position control, the light quantity control unit 90 periodically moves the movable diffraction grating 81 based on the prior grating driving signal DG0, and the difference between the value of the high-order optical signal Vbc and the value of the selection comparison signal Vas is determined. By starting the lattice position control at a timing when the sign of the differential value ΔDG0 of the prior grating drive signal and the sign of the differential value ΔVbc of the high-order optical signal coincide with each other, the feedback loop is converged in a very short time. Can do.

  According to the above configuration, the optical disc apparatus 50 is provided with the variable diffraction grating 66 on the optical path of the light beam L1 in the optical pickup 57, and the light amount control unit 90 is selected depending on whether the optical disc 100 is reproduced or recorded. By performing feedback control of the position of the movable diffraction grating 81 in the variable diffraction grating 66, the diffraction efficiency of the zero-order light beam emitted from the variable diffraction grating 66 can be appropriately changed, and the laser noise component of the light beam L1 The optical beam 100 can be irradiated with the light beam L2 having a light amount suitable for information reproduction or recording while keeping the value at a relatively low level.

(3) Second Embodiment (3-1) Configuration of Optical Disc Device and Optical Pickup In the second embodiment, the optical disc device 110 is compared with the optical disc device 50 (FIG. 17) in the first embodiment. Although the control unit 111, the drive unit 112, the signal processing unit 113, and the optical pickup 114 are provided instead of the control unit 51, the drive unit 52, the signal processing unit 53, and the optical pickup 57, the difference is that Others are similarly configured.

  The optical pickup 114 is configured in substantially the same manner as the optical pickup 57 (FIG. 18) in the first embodiment, except that an optical integrated element 115 is provided in place of the optical integrated element 60.

  The optical integrated element 115 is configured in substantially the same manner as the optical integrated element 60 (FIG. 19) in the first embodiment, except that a variable diffraction grating 116 is provided instead of the variable diffraction grating 66. ing.

  The variable diffraction grating 116 has a piezoelectric element 117 instead of the actuator 86 (that is, the thin film coil 84 and the magnet 85) in the variable diffraction grating 66, as shown in FIG. And the spring 118 is provided.

  The piezoelectric element 117 is attached between one side plate 80B3 of the chassis 80 of the variable diffraction grating 116 and the side surface 81J of the movable diffraction grating 81, and the piezoelectric element drive signal supplied from the drive unit 112 (FIG. 17). The total length in the x direction can be changed based on DP.

  The spring 118 is attached between the other side plate 80B4 of the chassis 80 of the variable diffraction grating 116 and the side surface 81K of the movable diffraction grating 81 in a state where the spring 118 is slightly compressed from the natural length. For this reason, the spring 118 always presses the movable diffraction grating 81 in the −x direction (that is, the direction opposite to the x direction) against the side plate 80B4.

  With this configuration, the variable diffraction grating 116 moves in the x direction or the −x direction as the piezoelectric element drive signal DP is applied to the piezoelectric element 117 and the total length of the piezoelectric element 117 in the x direction changes. Yes.

(3-2) Start of Grating Position Control In this second embodiment, the optical disk apparatus 110 is driven by the light quantity control unit 120 corresponding to the light quantity control unit 90 and the drive unit 112 in the same manner as the actuator 86 of the variable diffraction grating 66. The grating position is controlled by supplying the piezoelectric element drive signal DP to the piezoelectric element 117 via the.

  At this time, the light amount control unit 120 performs lattice position control by a method different from that of the light amount control unit 90 of the first embodiment. That is, as a preparation before starting the lattice position control, the light amount control unit 120 is similar to that in the first embodiment, based on the control from the control unit 111, the drive unit 112 corresponds to FIG. A pre-grating drive signal DG1 having a waveform as shown in (A) is generated and supplied to the variable diffraction grating 116.

  In response to this, the light amount control unit 120 performs emission light amount control similar to that of the light amount control unit 90 in the first embodiment, and outputs a laser drive signal DL as shown in FIG. While supplying to the laser diode 62, the value is monitored.

  The light quantity control unit 120 detects a local maximum value DLmax (indicated by a circle in the figure) and a local minimum value DLmin (indicated by a triangular mark in the figure) of the laser drive signal DL and at the same time a prior lattice driving signal when the local maximum value DLmax is reached. Pre-lattice drive signal DG1min when DG1max and the minimum value DLmin are obtained is stored in a RAM or the like in control unit 111.

  Here, in the variable diffraction grating 116, it is estimated that the optical coupling efficiency is minimum when the laser driving signal DL is maximum, and the optical coupling efficiency is maximum when the laser driving signal DL is minimum. .

  Therefore, the light amount control unit 120 performs the lattice position control so that the laser drive signal DL becomes the minimum value DLmin, that is, the optical efficiency in the forward path is maximized, at the time of recording that requires a large amount of light. During accurate reproduction, the lattice position control is performed so that the laser drive signal DL becomes the maximum value DLmax.

  Incidentally, in the second embodiment, it is desirable that the diffraction grating drive signal DG and the position of the movable diffraction grating 81 correspond to each other when performing the grating position control. Therefore, in the second embodiment, as shown in FIG. 25, a variable diffraction grating 116 that changes the position of the movable diffraction grating 81 by the piezoelectric element 117 is used.

  As described above, the light amount control unit 120 in the second embodiment performs lattice position control by using the maximum value DLmax and the minimum value DLmin of the laser drive signal DL.

(3-3) Operation and Effect In the above configuration, the optical disc apparatus 110 according to the second embodiment is provided with the variable diffraction grating 116 on the optical path of the light beam L1 emitted from the laser diode 62 of the optical pickup 114, The light efficiency control unit 120 controls the position of the movable diffraction grating 81 in accordance with whether the optical disc 100 is reproduced or recorded, thereby adjusting the diffraction efficiency of the zero-order light beam in the light beam L1.

  Therefore, the optical disc apparatus 110 according to the second embodiment can appropriately change the attenuation amount of the zeroth-order light beam emitted from the variable diffraction grating 116 as in the first embodiment, so that information can be reproduced. In either case of recording, the optical beam 100 can be irradiated with the light beam L2 having an appropriate amount of light.

  At this time, when starting the grating position control, the light quantity control unit 120 periodically moves the movable diffraction grating 81 based on the prior grating drive signal DG1, and at the time of recording, the movable light grating control unit 120 moves the movable diffraction grating 81 so that the laser drive signal DL becomes the minimum value DLmin. By positioning the diffraction grating 81, the optical efficiency of the forward path can be kept high.

  Further, the light quantity control unit 120 can keep the optical efficiency of the forward path low by positioning the movable diffraction grating 81 so that the laser drive signal DL becomes the maximum value DLmax at the time of reproduction. Laser noise can be relatively reduced.

  The variable diffraction grating 116 moves the movable diffraction grating 81 in the x direction or the −x direction using the piezoelectric element 117 based on the piezoelectric element drive signal DP supplied from the light quantity control unit 120, thereby moving the movable diffraction grating 81. A certain degree of correspondence can be provided between the position of and the diffraction grating drive signal DG.

  In addition, the optical disk device 110 according to the second embodiment can obtain the same operational effects as the optical disk device 50 according to the first embodiment.

  According to the above configuration, the optical disc apparatus 110 according to the second embodiment is provided with the variable diffraction grating 116 on the optical path of the light beam L1 in the optical pickup 114, as in the first embodiment. The position of the movable diffraction grating 81 in the variable diffraction grating 116 is controlled by the light quantity control unit 120 depending on whether reproduction or recording is performed. As a result, the optical disc apparatus 110 can appropriately change the diffraction efficiency of the zero-order light beam emitted from the variable diffraction grating 116, and the optical beam 100 has a light beam L 2 having a light amount suitable for information reproduction or recording. Can be irradiated.

(4) Third Embodiment (4-1) Configuration of Optical Disk Device and Optical Pickup In the third embodiment, the optical disk device 130 is a control unit as compared with the optical disk device 50 in the first embodiment. 51, except that a control unit 131, a drive unit 132, a signal processing unit 133, and an optical pickup 134 are provided in place of the drive unit 52, the signal processing unit 53, and the optical pickup 57, but the other configurations are the same. Has been.

  Although the optical pickup 134 is configured in substantially the same manner as the optical pickup 57 (FIG. 18) in the first embodiment, an optical integrated element 135 and an APC photo detector 137 in place of the optical integrated element 60 and the APC photo detector 74 are provided. Different points are provided.

  The APC photodetector 137 is configured in the same manner as the APC photodetector 74 (FIG. 21) in the first embodiment in appearance, and receives the zero-order light of the light beam L3 by the detection region 74A and also detects the detection region. 74B and 74C receive ± 1st order light beam and ± 3rd order light beam.

  The optical integrated element 135 is configured in substantially the same manner as the optical integrated element 60 in the first embodiment, except that a reproduction signal detection photo detector 138 is provided instead of the reproduction signal detection photo detector 69. ing.

(4-2) Configuration of Light Amount Control Unit As shown in FIG. 27, the optical disk device 130 has the same reference numerals as those in FIG. 21, and an APC photo detector 137, a reproduction signal detection photo detector 138, and a signal processing unit. The light amount control unit 140 combined with 133 controls the light amount of the light beam L1 and the light beams L2 and L3.

  The detection area 74A of the APC photodetector 137 receives the 0th-order light of the light beam L3, and performs a current-voltage conversion process on the detection signal SDA corresponding to the received light amount by the current-voltage conversion circuit 91, so that the 0th-order light signal Va. These are supplied to the negative input terminal of the differential amplifier 92 and the amplifier 96, respectively.

  The differential amplifier 92 calculates the difference of the 0th-order optical signal Va with respect to the 0th-order optical reference signal Var supplied from the control unit 131, and supplies the calculated result to the laser diode drive circuit 93 as a 0th-order optical difference signal.

  The laser diode drive circuit 93 generates a laser drive signal DL based on the supplied 0th-order light difference signal, and supplies this to the laser diode 62, thereby converting the 0th-order light of the light beam L3 into the 0th-order light reference signal. A light beam L1 having a light quantity that is close to Var is emitted.

  Thus, like the light amount control unit 90, the light amount control unit 140 keeps the light amount of the 0th order light in the light beam L3 constant, that is, keeps the light amount of the 0th order light of the light beam L2 irradiated to the optical disc 100 constant. The light amount of the light beam L1 emitted from the laser diode 62 is feedback-controlled (emitted light amount control).

  The light beam L1 emitted from the laser diode 62 may contain a noise component (so-called laser noise). In this case, the light beam L1 is generated based on the light beam L3 separated from the light beam L1. The higher-order optical signal Vbc and the reproduction RF signal SRF also contain similar laser noise components.

  The detection areas 74B and 74C of the APC photodetector 74 receive the ± first-order light and ± third-order light of the light beam L3 containing the laser noise component, and add detection signals corresponding to the respective received light amounts. The signal SDBC is supplied to the differential amplifier 94A of the current-voltage conversion circuit 94.

  The current-voltage conversion circuit 94 generates a high-order optical signal Vbc by converting a change in current in the detection signal SDBC into a change in voltage, which is generated as a low-pass filter (LPF, Low Pass Filter) 141 and a high-pass filter (HPF, High Pass). Filter) 143.

  The low-pass filter 141 generates a high-order optical low-frequency signal VbcL composed of low-frequency components such as a DC component by removing a high-frequency component (that is, a laser noise component) unnecessary for the subsequent control from the high-order optical signal Vbc. This is supplied to the negative input terminal of the dynamic amplifier 95.

  On the other hand, the amplifier 96 multiplies the 0th-order optical signal Va by 0.05 to generate the first comparison signal Va1, and supplies this to the switch 142.

  At the time of focus pull-in and at the beginning of focus servo and tracking servo, the switch 142 selects the first comparison signal Va1 based on the control of the control unit 131 (FIG. 16), and the first comparison signal Va1 selected at this time is selected. The comparison low-frequency signal Vas2 is supplied to the positive input terminal of the differential amplifier 95.

  The differential amplifier 95 calculates a difference between the comparison low-frequency signal Vas2 formed of the first comparison signal Va1 and the high-order optical low-frequency signal VbcL, and supplies this to the phase compensation circuit 99 as the high-order optical differential signal Vbcd.

  Based on the high-order optical difference signal Vbcd, the phase compensation circuit 99 generates a lattice control signal CG that can prevent oscillation and stabilize the control, and supplies this to the drive unit 132. The drive unit 132 generates a grating drive signal DG based on the grating control signal CG and supplies it to the grating actuator 86 of the variable diffraction grating 66, thereby moving the movable diffraction grating 81 (FIG. 20) in the x direction or vice versa. Move in the direction to change the diffraction efficiency.

  In other words, the light amount control unit 140 performs feedback control (grating position control) of diffraction efficiency in the variable diffraction grating 66 so that the high-order light low-frequency signal VbcL approaches the comparative low-frequency signal Vas2.

  At the time of focus pull-in and at the time of recording on the optical disc 100, the light amount control unit 140, like the light amount control unit 90, the first comparison signal Va1 obtained by multiplying the 0th-order optical signal Va by 0.05 becomes the selection comparison signal Vas2. Therefore, the diffraction efficiency of the variable diffraction grating 66 is adjusted so that the ratio of the 0th-order optical signal Va and the high-order optical low-frequency signal VbcL is about 1: 0.05.

  In other words, the light quantity control unit 140 increases and increases the light quantity ratio of the zero-order light by reducing the ratio of the high-order light by the variable diffraction grating 66, whereby the optical beam 100 irradiated to the optical disc 100 is focused and recorded. The amount of light can be adjusted to a suitable level.

  On the other hand, the reproduction signal detection photodetector 138 detects the amount of light of the reflected light beam L6 using a detection region (not shown), and supplies a received light signal corresponding to the amount of light to the reproduction RF signal generation circuit 144. The reproduction RF signal generation circuit 144 generates a reproduction RF signal SRF based on the received light signal, and supplies this to the positive input terminals of the low-pass filter 145 and the differential amplifier 146.

  The low-pass filter 145 removes a high-frequency component mainly including a laser noise component from the reproduction RF signal SRF, thereby generating a reproduction RF low-frequency signal SRFL composed of a low-frequency component such as a direct current component, which is supplied to the switch 142. To supply.

  During reproduction of the optical disc 100, the switch 142 selects the reproduction RF low-frequency signal SRFL as the comparative low-frequency signal Vas2 based on the control of the control unit 131 (FIG. 16), and supplies it to the positive input terminal of the differential amplifier 95. .

  Thus, the light quantity control unit 140 performs feedback control (that is, grating position control) of the diffraction efficiency of the high-order light in the variable diffraction grating 66 so that the high-order light low-frequency signal VbcL is aligned with the comparative low-frequency signal Vas2.

  Thereby, the light quantity control unit 140 can align the DC component level of the high-order optical signal Vbc with the DC component level of the reproduction RF signal SRF.

  The high-pass filter 143 removes low-frequency components such as a DC component from the high-order optical signal Vbc, thereby forming a high-order component that is composed of high-frequency components (that is, laser noise components) and whose DC component level is equal to that of the reproduction RF signal SRF. An optical high frequency signal VbcH is generated and supplied to the negative input terminal of the differential amplifier 146.

  The differential amplifier 146 subtracts a high-frequency component of the high-order optical signal Vbc whose DC component level is adjusted, that is, a high-order optical high-frequency signal VbcH, which is a laser noise component, from the reproduced RF signal SRF, thereby obtaining the reproduced RF signal SRF. A reproduction RF difference signal SRFd in which the included laser noise component is canceled is generated and supplied to the waveform equivalent circuit 147 of the signal processing unit 133.

  The signal processing unit 133 shapes the signal waveform with respect to the reproduction RF difference signal SRFd by the waveform equivalent circuit 147, digitizes it by the A / D (Analog / Digital) conversion circuit 148, and generates a PRML (Partial Response Maximum Likelihood) reproduction signal. A reproduction signal is generated by performing PRML calculation processing by the processing circuit 149.

  As described above, the light amount control unit 140 adjusts the diffraction efficiency of the variable diffraction grating 66 to change the light amount ratio between the 0th-order light beam and the higher-order light beam in the light beams L2 and L3, and thereby the light irradiated on the optical disc 100. By changing the light quantity ratio of the beam L2 greatly between reproduction and recording, the variable diffraction grating 66 can function as an attenuator.

  In particular, the light quantity control unit 140 adjusts the diffraction efficiency of the variable diffraction grating 66 at the time of reproduction in which the intensity of the zero-order light of the light beam L2 is to be suppressed, so that the DC component level between the high-order optical signal Vbc and the reproduction RF signal SRF Align. Next, the light quantity control unit 140 reproduces the noise component included when the light beam L1 is emitted from the laser diode 62 by subtracting the high-order light high-frequency signal VbcH corresponding to the laser noise component from the reproduction RF signal SRF. It can be removed from the RF signal SRF.

(4-3) Operation and Effect In the configuration described above, the optical disc apparatus 130 according to the third embodiment has the light beam L1 emitted from the laser diode 62 of the optical pickup 134 as in the first embodiment. A variable diffraction grating 66 was provided on the road. Then, the optical disk device 130 controls the position of the movable diffraction grating 81 by the light quantity control unit 140 according to whether the optical disk 100 is reproduced or recorded, thereby improving the diffraction efficiency of the zero-order light beam in the light beam L1. adjust.

  The light amount control unit 140 performs feedback control of the variable diffraction grating 66 so that the ratio of the 0th-order optical signal Va and the high-order optical low-frequency signal VbcL is about 1: 0.05 during the focus pull-in operation and recording on the optical disc 100. By doing so, similarly to the light quantity control unit 90, the ratio of the high-order optical signal Vbc is reduced and the light quantity of the zero-order optical signal Va is increased.

  On the other hand, the light amount control unit 140 performs feedback control of the variable diffraction grating 66 so that the high-order optical low-frequency signal VbcL matches the level equivalent to the reproduction RF low-frequency signal SRFL during reproduction of the optical disc 100, and also reproduces the reproduction RF signal SRF. A reproduction signal is generated after subtracting the high-order optical high-frequency signal VbcH from.

  Accordingly, the optical disc apparatus 130 according to the third embodiment can appropriately change the attenuation amount of the zero-order light beam emitted from the variable diffraction grating 66 as in the first embodiment. In either case of recording, the optical beam 100 can be irradiated with the light beam L2 having an appropriate amount of light.

  At this time, the light quantity control unit 140 can keep the light quantity of the light beam L2 irradiated to the optical disc 100 constant by receiving the 0th order light of the light beam L3 by the APC photodetector 74 and performing the emitted light quantity control.

  Further, the light amount control unit 140 controls the grating position of the variable diffraction grating 66 during reproduction of the optical disc 100 to align the levels of the reproduction RF low-frequency signal SRFL and the high-order optical low-frequency signal VbcL, and from the reproduction RF signal SRF. By directly subtracting the high-order optical high-frequency signal VbcH, the laser noise component contained in the light beam L1 can be removed, so that the quality of the reproduction signal can be improved.

  In other words, the optical disk device 130 separates the light beam L1 into 0th-order light and higher-order light by the variable diffraction grating 66, and controls the light quantity ratio of the 0th-order light and higher-order light by the light quantity control unit 140, based on the 0th-order light. The emitted light quantity control and the lattice position control based on the higher order light can be performed in parallel.

  In addition, since the light quantity control unit 140 can adjust the levels of the reproduction RF low-frequency signal SRFL and the high-order optical low-frequency signal VbcL by the variable diffraction grating 66, it is necessary to use a broadband variable gain amplifier or the like when configuring a laser noise canceller. In addition, the circuit scale can be reduced as compared with the case where such a wide-band variable gain amplifier or the like is used, and the generation of noise due to the amplifier can also be suppressed.

  Further, the light quantity control unit 140 does not need to separately provide an electronic component for removing the noise component contained in the light beam L1 by incorporating the differential amplifier 143 into the reproduction signal detection photo detector 138. Incidentally, even when the light quantity control unit 140 is configured to incorporate the differential amplifier 143 into the APC photo detector 137 instead of the reproduction signal detection photo detector 138, the same operation and effect can be obtained.

  In addition, the optical disk device 130 according to the third embodiment can obtain the same functions and effects as those of the optical disk device 50 according to the first embodiment.

  According to the above configuration, the optical disk apparatus 130 according to the third embodiment performs the same control of the amount of emitted light as in the first embodiment, and at the time of reproducing the optical disk 100, the laser of the high-order light high-frequency signal VbcH. The light quantity controller 140 controls the grating position of the variable diffraction grating 66 so as to adjust the noise level to the laser noise level of the reproduction RF signal SRF, and adjusts the light quantity ratio between the 0th order light and the higher order light. As a result, the optical disk device 130 can control the amount of emitted light and keep the amount of light of the light beam L2 applied to the optical disk 100 constant, and in parallel with this, the zero-order light and the high-order light emitted from the variable diffraction grating 66. Thus, the laser noise component can be removed simply by subtracting the high-order optical high-frequency signal VbcH directly from the reproduction RF signal SRF.

(5) Fourth Embodiment (5-1) Configuration of Optical Disc Device and Optical Pickup In the fourth embodiment, the optical disc device 150 is compared with the optical disc device 130 in the third embodiment, and the control unit 131, the drive unit 132, the signal processing unit 133, and the optical pickup 134 are replaced by a control unit 151, a drive unit 152, a signal processing unit 153, and an optical pickup 154, but the other configurations are the same. Has been.

  As shown in FIG. 28 in which parts corresponding to those in FIGS. 18 and 19 are denoted by the same reference numerals, the optical pickup 154 is an optical pickup in place of the optical integrated device 60 as compared with the optical pickup 134 in the third embodiment. The difference is that an integrated element 155 is provided.

  The optical integrated element 155 differs from the optical integrated element 115 in the third embodiment in that a liquid crystal variable diffractive element 156 is provided in place of the variable diffractive element 66, but the other configuration is the same. Has been.

  The liquid crystal variable diffraction element 156 has a configuration in which liquid crystal molecules 163 are sealed between two glass substrates 161 and 162 as shown in a cross-sectional view in FIG. The liquid crystal variable diffractive element 156 aligns liquid crystal molecules 163 in a predetermined direction by alignment films 164 and 165 provided on the inner surfaces of the glass substrates 161 and 162, respectively.

  Further, transparent electrode films 166 and 167 are provided between the glass substrate 161 and the alignment film 164 and between the glass substrate 162 and the alignment film 165, respectively. On the transparent electrode films 166 and 167, electrode portions 166A and 167A each having a width h in the direction of the arrow x are arranged so as to face each other at every period c.

  Incidentally, the transparent electrode film 166 can apply a voltage to the electrode portion 166A, but cannot apply a voltage to a portion where the electrode portion 166A is not provided. The same applies to the transparent electrode film 167.

  The liquid crystal variable diffractive element 156 has no effect on the light beam passing through the liquid crystal variable diffractive element 156 in the z direction as shown in FIG. 29B when no voltage is applied to the transparent electrode films 166 and 167. Does not give a phase difference.

  In other words, the liquid crystal variable diffraction element 156 is similar to the second variable diffraction grating 20 (FIG. 9) in the second state and the fourth variable diffraction grating (FIG. 16) in the second state. Only the next light is allowed to pass.

  On the other hand, the liquid crystal variable diffraction element 156 forms an electric field between the electrode portion 166A and the electrode portion 167A in a state where a voltage is applied to the transparent electrode films 166 and 167, as shown in FIG. The orientation direction of the liquid crystal molecules 163 is changed.

  Here, regarding the light beam passing in the z-direction through the portion where the electrode portions 166A and 167A are provided in the liquid crystal variable diffraction element 156, the refractive index and phase characteristics when the applied voltage is changed are shown in FIG. It changes as shown in (A) and (B).

  Therefore, the liquid crystal variable diffractive element 156 includes a portion where the electrode portions 166A and 167A are not provided (hereinafter referred to as a phase fixing portion 156B) and the electrode portions 166A and 167A according to the voltage applied to the electrode portions 166A and 167A. Can be changed as shown in FIG. 31 (C).

  As a result, the liquid crystal variable diffractive element 156 partially changes the phase of the light beam passing through the liquid crystal variable diffractive element 156 in the z direction, as shown in FIG. 30B, and diffracts the light beam. it can. That is, the liquid crystal variable diffraction element 156 can act as a diffraction grating.

  Further, as shown in FIG. 31C, the liquid crystal variable diffractive element 156 has a phase depth Φ5 (FIG. 5B) that is a phase difference between the light beam that has passed through the phase changing unit 156A and the light beam that has passed through the phase fixing unit 156B. 30 (B)) can be changed according to the applied voltage.

  As described above, the liquid crystal variable diffractive element 156 diffracts the light beam incident in the z direction as well as the variable diffraction gratings 10, 20, 30, and 40, and 66 and 116, and increases the diffraction efficiency of the 0th order light and the higher order light. It can be changed continuously.

  For this reason, the optical pickup 154 changes the liquid crystal drive signal DL1 supplied to the liquid crystal variable diffraction element 156, and similarly to the optical pickup 134 in the third embodiment, the light amounts of the light beam L1 and the light beams L2 and L3. Can be changed.

  In addition, the optical disk device 150 controls the light amounts of the light beam L1 and the light beams L2 and L3 by the light amount control unit 170 (FIG. 27) configured substantially the same as the light amount control unit 140 in the third embodiment. Has been made.

  Compared with the light amount control unit 140, the light amount control unit 170 includes a drive unit 152 and a signal processing unit 153 instead of the drive unit 132 and the signal processing unit 133, and the drive unit 152 replaces the grid drive signal DG. The difference is that the liquid crystal drive signal DL1 is supplied to the liquid crystal variable diffraction element 156, but the other configuration is the same.

  Therefore, similarly to the light amount control unit 140, the light amount control unit 170 keeps the light amount of the 0th order light in the light beam L3 constant, that is, keeps the light amount of the 0th order light of the light beam L2 irradiated to the optical disc 100 constant. As described above, the light amount of the light beam L1 emitted from the laser diode 62 is feedback-controlled (emitted light amount control).

  In parallel with this, the light amount control unit 170 adjusts the diffraction efficiency of the liquid crystal variable diffraction element 156 to change the light amount ratio between the 0th-order light beam and the higher-order light beam in the light beams L2 and L3, thereby irradiating the optical disc 100. By changing the light quantity ratio of the light beam L2 greatly during reproduction and during recording, the liquid crystal variable diffraction element 156 can function as an attenuator.

  Further, the light amount control unit 170 adjusts the diffraction efficiency of the liquid crystal variable diffraction element 156 in the same way as the light amount control unit 140 at the time of reproduction in which the intensity of the zero-order light of the light beam L2 is to be suppressed. By aligning the DC component level with the signal SRF and subtracting the high-order optical high-frequency signal VbcH from the reproduction RF signal SRF, the noise component contained at the time when the light beam L1 is emitted from the laser diode 62 is reproduced as the reproduction RF signal SRF. Can be removed.

(5-2) Operation and Effect In the above configuration, the optical disc apparatus 150 according to the fourth embodiment is a liquid crystal that replaces the variable diffraction grating 66 on the optical path of the light beam L1 emitted from the laser diode 62 of the optical pickup 154. A variable diffraction element 156 is provided. As in the third embodiment, the optical disk device 150 controls the liquid crystal drive signal DL1 by the light amount control unit 170 according to whether the optical disk 100 is reproduced or recorded, and the liquid crystal in the liquid crystal variable diffraction element 156 is controlled. By changing the orientation direction of the molecules 163, the diffraction efficiency of the zero-order light beam in the light beam L1 is adjusted.

  Similar to the light amount control unit 140, the light amount control unit 170 performs liquid crystal so that the ratio of the 0th-order optical signal Va to the high-order optical low-frequency signal VbcL is about 1: 0.05 during the focus pull-in operation and recording on the optical disc 100. By performing feedback control of the variable diffraction element 156, the ratio of the high-order optical signal Vbc is reduced and the light quantity of the zero-order optical signal Va is increased, as in the light quantity control unit 90.

  Further, the light amount control unit 170 performs feedback control of the liquid crystal variable diffractive element 156 so that the high-order light low-frequency signal VbcL matches the level equivalent to the reproduction RF low-frequency signal SRFL during reproduction of the optical disc 100, and from the reproduction RF signal SRF. A reproduction signal is generated after subtracting the high-order optical high-frequency signal VbcH.

  Accordingly, the optical disc apparatus 150 according to the fourth embodiment can appropriately change the attenuation amount of the zero-order light beam emitted from the liquid crystal variable diffraction element 156, as in the third embodiment. When performing either reproduction or recording, the optical beam 100 can be irradiated with the light beam L2 having an appropriate amount of light.

  At this time, the light amount control unit 170 can keep the light amount of the light beam L2 irradiated to the optical disc 100 constant by receiving the 0th-order light of the light beam L3 by the APC photodetector 74 and controlling the emitted light amount.

  Further, the light amount control unit 170 changes the orientation direction of the liquid crystal molecules 163 in the liquid crystal variable diffraction element 156 when reproducing the optical disc 100, and aligns the levels of the reproduction RF low-frequency signal SRFL and the high-order optical low-frequency signal VbcL. By directly subtracting the high-order optical high-frequency signal VbcH from the reproduction RF signal SRF, the laser noise component contained in the light beam L1 can be removed, so that the quality of the reproduction signal can be improved.

  In other words, the optical disc device 150 separates the light beam L1 into the 0th order light and the higher order light by the liquid crystal variable diffraction element 156, and controls the light quantity ratio of the 0th order light and the higher order light by the light quantity control unit 170, thereby changing the light beam L1 to the 0th order light. Based on the emitted light amount control and the lattice position control based on the higher order light can be performed in parallel.

  In addition, the optical disk device 150 according to the fourth embodiment can obtain the same functions and effects as those of the optical disk device 130 according to the third embodiment.

  According to the above configuration, the optical disc apparatus 150 according to the fourth embodiment controls the amount of emitted light as in the third embodiment, and at the time of reproducing the optical disc 100, the laser of the high-order optical high-frequency signal VbcH. The light quantity control unit 170 controls the alignment direction of the liquid crystal molecules 163 in the liquid crystal variable diffraction element 156 so that the noise level is matched with the laser noise level of the reproduction RF signal SRF. As a result, the optical disc device 150 can control the amount of emitted light and keep the amount of light of the light beam L2 applied to the optical disc 100 constant. In parallel with this, the zero-order light emitted from the liquid crystal variable diffraction element 156 and By appropriately changing the diffraction efficiency of the high-order light and subtracting the high-order light high-frequency signal VbcH directly from the reproduction RF signal SRF, the laser noise component can be removed.

(6) Fifth Embodiment (6-1) Configuration of Optical Disc Device and Optical Pickup In the fifth embodiment, the optical disc device 180 is controlled as compared with the optical disc device 130 in the third embodiment. The control unit 181, the drive unit 182, the signal processing unit 183, and the optical pickup 184 are provided in place of the unit 131, the drive unit 132, the signal processing unit 133, and the optical pickup 134. It is configured.

  As shown in FIG. 32 in which parts corresponding to those in FIGS. 18 and 19 are given the same reference numerals, the optical pickup 184 has an optical integrated device 115 and an APC photodetector as compared with the optical pickup 134 in the third embodiment. An optical integrated device 185 and an LNC (Laser Noise Canceller) photo detector 187 are provided in place of 74, and a beam splitter 188, a condensing lens 189, and an APC photo detector 190 are further provided.

  The optical integrated element 185 differs from the optical integrated element 135 in the third embodiment in that a liquid crystal element 186 that replaces the variable diffraction element 66 is provided, but the other configuration is the same. Yes.

  The liquid crystal element 186 has a configuration partially similar to the liquid crystal variable diffraction element 156 (FIG. 29), and the alignment direction of the liquid crystal molecules is uniform according to the voltage of the liquid crystal drive signal DL2 supplied from the drive unit 182. Thus, the polarization direction of the entire light beam L1 can be adjusted.

  As a result, the liquid crystal element 186 changes the light quantity ratio when the light beam L1 is transmitted or reflected by the polarization reflecting film 68A of the laminated prism 68, that is, the light quantity ratio between the light beams L2 and L3, based on the liquid crystal drive signal DL2. It is made to let you.

  At this time, the optical disk apparatus 180 can adjust the light quantity of the light beam L3 irradiated to the LNC photodetector 187 in accordance with the voltage of the liquid crystal drive signal DL2, as shown in the characteristic curve of FIG.

  The beam splitter 188 reflects the light beam L2 at a predetermined ratio (for example, about 20%) by the reflective film 188A to form the light beam L22, and makes this incident on the condenser lens 189. The condensing lens 189 condenses the light beam L22 and irradiates it to the APC photodetector 190.

  The LNC photodetector 187 and the APC photodetector 190 receive the light beams L3 and L22, respectively, and generate detection signals corresponding to the respective light amounts.

  Further, the beam splitter 188 transmits the remaining portion of the light beam L2 through the reflection film 188A to form the light beam L21A, which is incident on the objective lens 58 via the collimator lens 71 and the quarter-wave plate 72 sequentially. The objective lens 58 condenses the light beam L21 on the recording layer of the optical disc 100.

  As described above, the optical disk apparatus 180 according to the fifth embodiment adjusts the light quantity ratio of the light beams L2 and L3 by adjusting the polarization direction of the light beam L1 by using the liquid crystal element 186, and also adjusts one of the light beams L2. The APC photodetector 190 is irradiated with the portion.

(6-2) Configuration of Light Amount Control Unit By the way, in the optical disc apparatus 180, as shown in FIG. 34 in which parts corresponding to those in FIG. 27 are given the same reference numerals, an LNC photodetector 187, an APC photodetector 190, a reproduction signal detection photodetector. The light quantity control unit 200 that combines 138 and the signal processing unit 183 controls the light quantity of the light beams L1, L2 and L3, and the light beams L21 and L22.

  The detection area 190A of the APC photo detector 190 corresponds to the detection area 74A of the APC photo detector 137 in the light amount control unit 140 (FIG. 27). That is, the detection area 190A of the APC photodetector 190 receives the light beam L22 having a predetermined ratio in the light beam L2, generates a detection signal SDA corresponding to the received light amount, and generates a detection signal SDA by the current-voltage conversion circuit 91. The signal Va is converted.

  Similar to the light amount control unit 140, the light amount control unit 200 performs feedback control so that the light amount signal Va approaches the predetermined reference signal Var. Thereby, the light quantity control unit 200 emits the light beam L1 emitted from the laser diode 62 so that the light quantity of the light beam L22 approaches the predetermined light quantity, that is, the light quantity of the light beam L21 irradiated on the optical disc 100 approaches the predetermined light quantity. Perform light control.

  On the other hand, the detection region 187A of the LNC photodetector 187 corresponds to the detection regions 74B and 74C of the APC photodetector 137 in the light amount controller 140 (FIG. 27). That is, the detection region 187A of the LNC photodetector 187 receives the light beam L3 (FIG. 32) containing the laser noise component, and outputs the detection signal SDN corresponding to the received light amount to the differential amplifier 94A of the current-voltage conversion circuit 94. To supply.

  The current-voltage conversion circuit 94 generates an LNC signal Vn by converting a current change in the detection signal SDN into a voltage change, and supplies the LNC signal Vn to the low-pass filter 141 and the high-pass filter 143.

  The light quantity control unit 200 uses the LNC signal Vn instead of the high-order light signal Vbc in the light quantity control unit 140 and performs the same arithmetic processing as the light quantity control unit 140. The drive unit 182 generates a liquid crystal drive signal DL2 instead of the lattice drive signal DG (FIG. 27), and supplies the generated liquid crystal drive signal DL2 to the liquid crystal element 186, thereby adjusting the polarization direction of the light beam L1 and the light beams L2 and L3. Change the light intensity ratio.

  That is, the light amount control unit 200 changes the polarization direction of the light beam L1 so that the low-frequency LNC signal VnL, which is a low-frequency component of the LNC signal Vn, approaches the first comparison signal Va1 (comparison low-frequency signal Vas2). Feedback control is performed (hereinafter referred to as polarization direction control).

  When the focus is pulled in and when the optical disc 100 is recorded, the light amount control unit 200, like the light amount control unit 140, uses the first comparison signal Va1 obtained by multiplying the 0th-order light signal Va by 0.05 as the selection comparison signal Vas2. Therefore, the light quantity ratio between the light beams L2 and L3 is adjusted so that the ratio between the 0th-order optical signal Va and the low-frequency LNC signal VnL is about 1: 0.05.

  That is, the light amount control unit 200 increases the light beam L2 light amount ratio by reducing the ratio of the light beam L3 by the liquid crystal element 186, and thus the light beam L21 irradiated to the optical disc 100 is suitable for focus pull-in and recording. The light intensity can be adjusted.

  On the other hand, at the time of reproduction of the optical disc 100, the light amount control unit 200, like the light amount control unit 140, aligns the low-frequency LNC signal VbcL with the reproduction RF low-frequency signal SRFL (comparison low-frequency signal Vas2). The polarization direction is feedback-controlled (that is, polarization direction control).

  As a result, the light quantity control unit 200 can adjust the light quantity of the light beam L3 to align the DC component level of the LNC signal Vn with the DC component level of the reproduction RF signal SRF. Incidentally, the light quantity of the light beam L2 is kept constant by the above-described emission light quantity control.

  The light amount control unit 200 is similar to the light amount control unit 140 by subtracting the high frequency component of the LNC signal Vn whose DC component level is adjusted, that is, the high frequency LNC signal VnH, which is a laser noise component, from the reproduction RF signal SRF. Then, a reproduction RF difference signal SRFd in which the laser noise component included in the reproduction RF signal SRF is canceled is generated.

  In this way, the light quantity control unit 200 controls the emitted light quantity and adjusts the polarization direction of the light beam L1 to change the light quantity ratio between the light beams L2 and L3, thereby irradiating the optical beam 100 with the light beam L21. The light quantity ratio can be changed greatly between reproduction and recording.

  In particular, the light amount control unit 200 first adjusts the polarization direction of the light beam L1 by the liquid crystal element 186 at the time of reproduction in which the intensity of the 0th-order light of the light beam L2 is to be suppressed, whereby the LNC signal Vn and the reproduction RF signal SRF are obtained. Align the DC component level. Next, the light amount control unit 200 subtracts the high frequency LNC signal VnH corresponding to the laser noise component from the reproduction RF signal SRF, thereby reproducing the noise component included when the light beam L1 is emitted from the laser diode 62. It can be removed from the signal SRF.

(6-3) Operation and Effect In the above configuration, the optical disc apparatus 180 according to the fifth embodiment is provided with the liquid crystal element 186 on the optical path of the light beam L1 emitted from the laser diode 62 of the optical pickup 184, and the optical disc The light amount control unit 200 controls the polarization direction of the light beam L1 depending on whether playback or recording of 100 is performed, whereby the light beams L2 and L3 separated from the light beam L1 by the polarization reflection film 68A. Adjust the light intensity ratio.

  The light amount control unit 200 performs the feedback control of the liquid crystal drive signal DL2 so as to reduce the LNC signal Vn during the focus pull-in operation and the recording on the optical disc 100, and similarly to the light amount control unit 140, the light amount of the light beam L2 Increase the ratio.

  On the other hand, the light amount control unit 200 feedback-controls the light amount of the light beam L3 so that the low-frequency LNC signal VnL matches the level equivalent to the reproduction RF low-frequency signal SRFL during reproduction of the optical disc 100, and from the reproduction RF signal SRF. A reproduction signal is generated after directly subtracting the high frequency LNC signal VnH corresponding to the laser noise component.

  Accordingly, the optical disk apparatus 180 according to the fifth embodiment can perform the emission light quantity control by appropriately changing the light quantity ratio between the light beams L2 and L3, so that either reproduction or recording of information is performed. In addition, the optical beam 100 can be irradiated with the light beam L2 having an appropriate amount of light.

  In parallel with this, the light amount control unit 200 aligns the levels of the reproduction RF low-frequency signal SRFL and the low-frequency LNC signal VnL with the liquid crystal element 186 during reproduction of the optical disc 100, and then generates a high frequency from the reproduction RF signal SRF. By directly subtracting the light amount signal VnH, the laser noise component contained in the light beam L1 can be removed as in the third embodiment, so that the quality of the reproduction signal can be improved.

  At this time, the light quantity control unit 200 can adjust the light quantity of the light beam L3 by the liquid crystal element 186 to make the levels of the reproduction RF low-frequency signal SRFL and the low-frequency LNC signal VnL uniform. It is not necessary to use a broadband variable gain amplifier or the like, and the circuit scale can be reduced as compared with the case of using such a broadband variable gain amplifier or the like.

  In addition, the optical disk device 180 according to the fifth embodiment can obtain the same functions and effects as those of the optical disk device 130 according to the third embodiment.

  According to the above configuration, the optical disc device 180 according to the fifth embodiment performs the control of the emitted light amount by the light amount control unit 200 and changes the polarization direction of the light beam L1 by the liquid crystal element 186, thereby polarizing the reflection film. The light amount ratio when the light beam L1 is distributed to the light beams L2 and L3 is changed by 68A. As a result, the optical disc apparatus 180 can irradiate the optical beam 100 with the light beam L21 having an appropriate amount of light, and removes the laser noise component only by subtracting the high frequency LNC signal VnH from the reproduction RF signal SRF. Can do.

(7) Other Embodiments In the third embodiment, the amount of high-order light in the light beam L1 (that is, the light beam L3) is adjusted by the variable diffraction grating 66, and in the fourth embodiment, a variable liquid crystal is used. In the fifth embodiment, the light quantity of the light beam L3 (or its higher order light) is adjusted after adjusting the light quantity of the light beam L3 by the combination of the liquid crystal element 186 and the polarization reflection film 68A in the fifth embodiment. The high frequency component in the light reception result is directly subtracted from the reproduction RF signal to cancel the laser noise component. However, the present invention is not limited to this, and various optical components may be used as means for adjusting the light amount. .

  In the third and fourth embodiments described above, the light amount control units 140 and 170 perform feedback control of the light amount of the high-order light of the light beam L3 irradiated to the APC photodetector 137, and in the fifth embodiment, The case where the light amount of the light beam L3 irradiated to the LNC photodetector 187 is feedback controlled by the light amount control unit 200 has been described. However, the present invention is not limited to this, and a method other than the feedback control, for example, the optical disc 100 is used. The amount of light beam L3 or its higher-order light may be adjusted by setting the diffraction efficiency or transmittance to a predetermined value depending on whether it is a rewritable type or a read-only type.

  Further, in the above-described third embodiment, the reproduction signal detection photo detector 138 subtracts the high-order optical high-frequency signal VbcH, which is the high-frequency optical component of the high-order optical signal Vbc, from the reproduction RF signal SRF. However, the present invention is not limited to this. For example, when it has been found that the low-frequency component of the high-order optical signal Vbc does not adversely affect the reproduction RF signal SRF, The laser noise component may be canceled by subtracting the higher-order optical signal Vbc from the reproduction RF signal. The same applies to the fourth to fifth embodiments.

  Furthermore, in the third embodiment described above, the light amount control unit 140 adjusts the diffraction efficiency of the variable diffraction grating 66 so that the low-frequency components of the high-order optical signal Vbc and the reproduction RF signal SRF are aligned during reproduction. Although the case where laser noise cancellation is performed has been described, the present invention is not limited to this. For example, DC when a high-order optical signal Vbc including a low frequency component is subtracted from a reproduction RF signal including a low frequency component is used. Even if laser noise cancellation is performed after controlling the high-order light quantity so that the component becomes zero, the same effect can be obtained.

  Further, for example, the noise components of the high-order optical signal Vbc and the reproduction RF signal SRF are directly compared to adjust the diffraction efficiency of the variable diffraction grating 66 so as to align the two, and laser noise cancellation is performed, or after laser noise cancellation. The diffraction efficiency of the variable diffraction grating 66 may be adjusted by various methods such as adjusting the diffraction efficiency of the variable diffraction grating 66 so that the error rate in the reproduction signal generated from the reproduction RF signal is minimized. The same applies to the fourth to fifth embodiments.

  Further, in the third embodiment described above, the case where the differential amplifier 146 is incorporated in the reproduction signal detection photo detector 138 and the reproduction RF differential signal SRFd is generated by the reproduction signal detection photo detector 138 has been described. The present invention is not limited to this. For example, the differential amplifier 146 may be incorporated in the APC photodetector 137 and the reproduction signal SRF may be supplied to the APC photodetector 137 to generate the reproduction RF difference signal SRFd. The same applies to the fourth to fifth embodiments. Furthermore, in the fifth embodiment, a differential amplifier 146 may be incorporated in the LNC photodetector 187.

  In the above-described embodiment, the case where the gratings g11 and g12 are provided on the mutually opposing surfaces of the diffraction gratings 11 and 12 of the variable diffraction grating 10 has been described (FIG. 2), but the present invention is not limited thereto. First, the grating g11 may be provided on any surface of the diffraction grating 11, and the grating g12 may be provided on any surface of the diffraction grating 12.

  That is, in the variable diffraction grating 10, for example, the grating g12 is provided on a surface that does not face the grating plate 11 as shown in FIG. 35A, or the grating g11 faces the grating plate 12 as shown in FIG. The grating 12g may be provided on a surface that does not face the grating plate 11 while being provided on the surface that is not provided. However, in the case of the present invention, it is desirable that the distance between the gratings g11 and g12 is as close as possible in consideration of the operation principle of the diffraction grating. From this viewpoint, the state in which the gratings g11 and g12 face each other is the best (FIG. 2). Presumed to exhibit characteristics. The same applies to the variable diffraction gratings 20, 30, 40, 66 and 116.

  In the embodiment described above, in the fourth variable diffraction grating, the entire diffraction grating 40 is moved by moving the diffraction grating 41, which is the diffraction grating closer to the point light source Q, in the x direction (FIG. 15A). However, the present invention is not limited to this. For example, the diffraction grating 42 far from the point light source Q is moved in the x direction, or the variable gratings 41 and 42 are used. The diffraction efficiency of the diffraction grating 40 as a whole may be changed by moving each in the x direction and the opposite direction.

  Further, in the first to third embodiments described above, the case where the variable diffraction grating 66 or 116 configured similarly to the variable diffraction grating 40 is provided in the diverging light or the convergent light has been described. The invention is not limited to this, and a variable diffraction grating configured similarly to the variable diffraction grating 10, 20 or 30 may be provided in the parallel light.

  Furthermore, in the variable diffraction grating 10 described above, the case where the diffraction grating plates 11 and 12 are provided in the air having a refractive index n0 with respect to light having a wavelength of 405 [nm] has been described, but the present invention is not limited to this. Instead, for example, the diffraction grating plates 11 and 12 may be provided in a solvent having a refractive index nx. In this case, the refractive index n0 in the above formulas (1), (3), (5), (6), and (7) may be replaced with the refractive index nx. The same applies to the variable diffraction gratings 20, 30, 40, 66 and 116.

  Further, in the above-described first embodiment, the case where the amplifier 96 multiplies the 0th-order optical signal Va by 0.05 and the amplifier 97 multiplies the 0th-order optical signal Va by 1.5 is described. The present invention is not limited to this, and each amplifier may amplify the 0th-order optical signal Va at an arbitrary magnification. The point is that it is determined according to a desired ratio between the 0th-order optical signal Va and the higher-order optical signal Vbc. good. The same applies to the second to fifth embodiments.

  Furthermore, in the first embodiment described above, the optical disk device 50 corresponds to the BD system, and the case where the light beam L1 having a wavelength of about 405 [nm] is emitted from the laser diode 62 has been described. However, the present invention is not limited to this, and the optical disk device 50 is compatible with the CD method and the DVD method, and the laser diode 62 may emit a light beam L1 having a wavelength corresponding to each method. The wavelength of the beam L1 may be switched. The same applies to the second to fifth embodiments.

  Furthermore, in the third embodiment described above, the laser diode 62 as the light source, the variable diffraction grating 66 as the first separator, the APC photodetector 137 as the auxiliary light receiving element and the monitoring light receiving element, A polarizing reflection film 68A as a two-separator, an objective lens 58 as an objective lens, a reproduction signal detection photo detector 138 as a reflected light receiving element, and an amount of light as an irradiation light control unit, sub-light control unit, and subtraction processing unit Although the case where the optical disc device 130 as the optical disc device is configured by the control unit 140 has been described, the present invention is not limited to this, and a light source having various other configurations, a first separator, a secondary light receiving element, The second separator, the monitoring light receiving element, the irradiation light control unit, the objective lens, the reflected light receiving element, the auxiliary light control unit, and the subtraction processing unit It may be configured disk device.

  The present invention can also be used in an optical pickup and an optical disc apparatus compatible with various systems.

It is a rough-line perspective view which shows the structure of a general diffraction grating. It is a rough-line perspective view which shows the structure (1) of a 1st variable diffraction grating. It is an approximate line sectional view showing composition (2) of the 1st variable diffraction grating. It is an approximate line sectional view showing composition (3) of the 1st variable diffraction grating. It is an approximate line sectional view showing composition (4) of the 1st variable diffraction grating. It is a basic diagram which shows the relationship between the grating position in a 1st variable diffraction grating, and diffraction efficiency. It is an approximate line sectional view showing composition (1) of the 2nd variable diffraction grating. It is an approximate line sectional view showing composition (2) of the 2nd variable diffraction grating. It is an approximate line sectional view showing composition (3) of the 2nd variable diffraction grating. It is a basic diagram which shows the relationship between the grating position in the 2nd variable diffraction grating, and diffraction efficiency. It is an approximate line sectional view showing composition (1) of the 3rd variable diffraction grating. It is an approximate line sectional view showing composition (2) of the 3rd variable diffraction grating. It is an approximate line sectional view showing composition (3) of the 3rd variable diffraction grating. It is a basic diagram which shows the relationship between the grating position in the 3rd variable diffraction grating, and diffraction efficiency. It is an approximate line sectional view showing composition (1) of the 4th variable diffraction grating. It is an approximate line sectional view showing composition (2) of the 4th variable diffraction grating. 1 is a schematic diagram illustrating an overall configuration of an optical disc device. It is a basic diagram which shows the structure of the optical pick-up by 1st Embodiment. It is a basic diagram which shows the structure of the optical integrated element by 1st Embodiment. It is a basic diagram which shows the structure of the variable diffraction grating by 1st Embodiment. It is a basic diagram which shows the structure of the photodetector for APC. It is a rough-line circuit diagram which shows the structure of the light quantity control part by 1st Embodiment. It is a basic diagram which shows the control start timing of the variable diffraction grating by 1st Embodiment. It is a basic diagram which shows the structure of the optical pick-up which has arrange | positioned the variable diffraction grating in parallel light. It is a basic diagram which shows the structure of the variable diffraction grating by 2nd Embodiment. It is a basic diagram which shows the control start timing of the variable diffraction grating by 2nd Embodiment. It is a basic circuit diagram which shows the structure of the light quantity control part by 3rd Embodiment. It is a basic diagram which shows the structure of the optical pick-up by 4th Embodiment. It is a basic diagram which shows the structure (1) of a liquid-crystal variable diffraction element. It is a basic diagram which shows the structure (2) of a liquid crystal variable diffraction element. It is a basic diagram which shows the characteristic change with respect to the applied voltage of a liquid crystal element. It is a basic diagram which shows the structure of the optical pick-up by 5th Embodiment. It is a basic diagram which shows the ratio of the detected light quantity with respect to the applied voltage of a liquid crystal element. It is a basic circuit diagram which shows the structure of the light quantity control part by 5th Embodiment. It is a rough-line perspective view which shows the structure of the variable diffraction grating by other embodiment.

Explanation of symbols

1, 11, 12, 21, 22, 31, 32, 41, 42 ... Diffraction gratings 10, 20, 30, 40, 66, 116 ... Variable diffraction gratings, 50, 110, 130, 150, 180 ... Optical disk device, 51, 111, 131, 151, 181 ... Control unit, 52, 112, 132, 152, 182 ... Drive unit, 53, 113, 133, 153, 183 ... Signal processing unit, 57, 114, 134, 154, 184... Optical pickup, 58... Objective lens, 62... Laser diode, 69, 138... Reproduction signal detection photo detector, 74, 137, 190 .. APC photo detector, 74A, 74B, 74C 156A, 187A, 190A ... detection area, 74M ... mirror surface, 80 ... chassis, 80A ... bottom plate, 80B ... side plate, 80C ... Top plate 81... Movable diffraction grating 82... Fixed diffraction grating 83. Movable support 84. Thin film coil 85. Magnet 86 86 Grating actuator 90, 120, 140, 170, 200 ... Light quantity control unit, 91, 92, 94, 95, 143... Differential amplifier, 93... LD drive circuit, 99.

Claims (15)

A light source that emits a light beam of laser light;
A first separator for separating the light beam into one main light beam and one or more sub light beams at a ratio based on a predetermined ratio adjustment signal;
A secondary light receiving element that receives the secondary light beam and generates a secondary light detection signal;
A second separator for separating the main light beam into an irradiation light beam and a monitoring light beam at a predetermined ratio;
A monitoring light receiving element that receives the monitoring light beam and generates a monitoring light detection signal to cause a predetermined control unit to control the amount of the irradiation light beam based on the monitoring light detection signal;
An objective lens for condensing the irradiation light beam on an optical disc;
The reflected light beam formed by reflecting the irradiated light beam by the optical disc is received to generate a reflected light detection signal, so that the laser noise level included in the auxiliary light detection signal and the reflection are transmitted to a predetermined control unit. A reflected light receiving element that controls the ratio adjustment signal so as to match the laser noise level included in the reproduced RF signal generated based on the photodetection signal and subtracts the sub-light detection signal from the reproduced RF signal. An optical pickup characterized by The first separator is
A first grating plate having a first grating provided on one surface for each predetermined first period;
The light emitted from the first grating plate with the first period width is incident on the opposite surface facing the first grating plate or opposite to the first grating plate. A second grating plate provided with a second grating substantially parallel to each grating constituting the first grating for each second period corresponding to the incident width at the time of
The light beam is diffracted by changing the position of the first grating plate or the second grating plate in the grating arrangement direction of the first grating based on the control signal, so that the zero-order light and the sub-light as the main light beam are diffracted. 2. The optical pickup according to claim 1, wherein the optical pickup comprises a variable diffraction grating including a position changing unit that changes a light quantity ratio when the light beam is separated into first-order or higher-order light as a light beam. The second lattice is
The ratio between the distance from the predetermined reference point to the one surface and the first period is equal to the ratio between the distance from the reference point to the surface on which the second grating is provided and the second period. The optical pickup according to claim 2. The second period is
The optical pickup according to claim 2, wherein the optical pickup is equivalent to the first period. The second lattice is
3. The optical pickup according to claim 2, wherein a phase depth that is a product of a depth of the grating and a refractive index of the medium is equal to a phase depth of the first grating portion. The optical pickup according to claim 2, wherein the first grating and the second grating are binary gratings. The first lattice and the second lattice are:
The optical pickup according to claim 5, wherein the optical pickup is formed in a sawtooth shape or a stepped pseudo sawtooth shape. The first lattice is
Provided on the surface of the first grid plate facing the second grid plate;
The second lattice is
The optical pickup according to claim 2, wherein the optical pickup is provided on the facing surface. The first separator is
The liquid crystal molecules are sealed between two substantially parallel glass substrates, and a transparent electrode film in which rectangular plate-like electrodes are arranged at predetermined intervals so as to sandwich the liquid crystal molecules on the inner surface of each glass substrate, By applying the control signal between the electrodes to change the alignment direction of the liquid crystal molecules, the light beam is diffracted into zero-order light as the main light beam and first-order or higher-order light as the sub light beam. The optical pickup according to claim 1, wherein the optical pickup is a liquid crystal variable diffraction element that changes a light amount ratio at the time of separation. The first separator is
A liquid crystal element that changes the orientation direction of liquid crystal molecules based on the control signal to change the polarization direction of the light beam;
A polarized light reflection film having a reflectance that differs depending on the polarization direction of the incident light beam reflects the light beam with a reflectance corresponding to the changed polarization direction, so that the main light beam and the sub light beam are reflected. The optical pickup according to claim 1, further comprising a polarizing beam splitter for separating the optical pickup. The secondary light receiving element is
The optical pickup according to claim 1, further comprising a subtraction processing circuit that subtracts the sub-light detection signal from the reflected light detection signal. The reflected light receiving element is
The optical pickup according to claim 1, further comprising a subtraction processing circuit that subtracts the sub-light detection signal from the reflected light detection signal. A light source that emits a light beam of laser light;
A first separator for separating the light beam into one main light beam and one or more sub light beams at a ratio based on a predetermined ratio adjustment signal;
A secondary light receiving element that receives the secondary light beam and generates a secondary light detection signal;
A second separator for separating the main light beam into an irradiation light beam and a monitoring light beam at a predetermined ratio;
A monitoring light receiving element that receives the monitoring light beam and generates a monitoring light detection signal;
An irradiation light control unit for controlling the amount of the irradiation light beam based on the monitoring light detection signal;
An objective lens for condensing the irradiation light beam on an optical disc;
A reflected light receiving element for receiving a reflected light beam formed by reflecting the irradiated light beam by the optical disc and generating a reflected light detection signal;
A sub-light control unit that controls the ratio adjustment signal so as to align the laser noise level included in the sub-light detection signal and the laser noise level included in the reproduction RF signal generated based on the reflected light detection signal;
An optical disk apparatus comprising: a subtraction processing unit that subtracts the sub-light detection signal from the reproduction RF signal to cancel a laser noise component included in the reproduction RF signal. The secondary light control unit is
The ratio adjustment signal is controlled by controlling the ratio adjustment signal so that the signal level of the low frequency region component in the sub-light detection signal and the signal level of the low frequency region component in the reproduction RF signal generated based on the reflected light detection signal are aligned. The optical disk apparatus according to claim 13, wherein a laser noise level is adjusted. The subtraction processing unit
The optical disk apparatus according to claim 13, wherein the laser noise component is canceled by directly subtracting a high frequency region component of the auxiliary light detection signal from the reproduction RF signal.

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