JP3527685B2 - Optical recording / reproducing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing apparatus having a mechanism for correcting spherical aberration of a focused spot focused on a recording layer of a recording medium by changing a lens interval. .

[0002]

2. Description of the Related Art As a conventional technique, Japanese Patent Laid-Open No. 10-188
The example disclosed in Japanese Patent Publication No. 301 is shown in FIG.
I will explain based on.

Here, a combination lens barrel is disclosed in which the combination lens and the distance between the combination lenses are changed to change the spherical aberration in the focused spot on the recording medium.

In FIG. 17, the first lens 100 is arranged on the light source side (not shown), and the second lens 101 is arranged on the recording medium side with respect to the first lens 100. The focus radial actuator (FR actuator) 102 includes a first lens 100 and a second lens 101.
Is for displacing the focus and radial directions. The spherical aberration correction actuator 103 drives the second lens 101 in the focus direction to move the first lens 101
It has a function of changing the distance between the lens 100 and the second lens 101 and correcting the spherical aberration of the focused spot focused on the recording layer 105 of the recording medium 104.

The light emitted from a light source (not shown) is
It is guided to a combination lens 106 by an optical component (not shown) and is focused on the recording layer 105 on the recording medium 104.

The reason why the lens is a combination lens composed of a plurality of lenses is that it is difficult to design and manufacture with only one lens because the numerical aperture of the lens is increased.

When there is an error in the optical thickness from the surface of the recording medium 104 on the side of the combination lens to the recording layer 105, spherical aberration occurs in the focused spot focused on the recording layer 105. Further, since the numerical aperture of the lens is large, the amount of spherical aberration generated with respect to the error in the optical thickness from the combined lens side surface to the recording layer 105 is large with respect to the lens having a small numerical aperture. Therefore, by changing the lens interval, the occurrence of spherical aberration is suppressed, and further, it is possible to deal with a recording medium having two or more recording layers.

The optical thickness referred to here is a thickness determined by the thickness of the light-transmitting body (or the light-transmitting layer) through which light is transmitted and the refractive index, and even if the thickness is different (mechanical thickness), It is assumed that the optical thicknesses are the same when the spherical aberrations of the focused spots that are transmitted through the light transmissive body and focused are the same. The error in the optical thickness from the lens side surface of the recording medium to the recording layer is the optical thickness of the light-transmitting body (or the light-transmitting layer) assumed when designing the lens, and information is actually recorded and reproduced on the recording medium. The difference in optical thickness from the surface of the recording medium on the side of the combined lens to each recording layer at the time of recording.

As a driving method for changing the lens interval, an electromagnetic force is generated by applying a positive or negative current to the coil, and the second lens 101 is moved in the focus direction by the thrust generated between the coil and the magnet. A method called a voice coil motor for vertically displacing the above has been proposed (for example, disclosed in Japanese Patent Laid-Open No. 10-255290).

By the spherical aberration correcting mechanism for changing the lens interval, the displacement of the second lens, that is, the first lens
By setting the distance between the lens and the second lens to be appropriate, it is possible to correct spherical aberration that occurs due to an error in the optical thickness from the combined lens side surface of the recording medium to the recording layer.

As a means for correcting spherical aberration, Japanese Patent Laid-Open No. 266511/1993 discloses changing the lens interval other than the objective lens. Figure 1
8 will be described.

In FIG. 18, the combined objective lens 1
09 and the light source, a plano-concave lens 107 and a plano-convex lens 108
The optical thickness of the optical recording medium (Japanese Patent Laid-Open No. 5-266).
According to the "thickness of the protective layer" in Japanese Patent No. 511), the spherical aberration is corrected by driving the plano-concave lens 107 in the optical axis direction.

The light transmitted through the plano-convex lens 108 is a combined objective lens 109 composed of a plurality of lenses.
Are focused on the recording layer of the optical recording medium.

Here, unlike the previous example, the spherical aberration is not corrected in the objective lens 109 composed of a plurality of lenses, but a plurality of other lenses 107 and 108 arranged between the objective lens and the light source. The spherical aberration is corrected by changing the lens interval of.

[0015]

As described above, an electrically driven system is used as the spherical aberration correction mechanism. However, the spherical aberration correction mechanism is not used when a lens with a low numerical aperture is used. Because it needs power consumption to drive,
There is a problem that extra power consumption occurs. further,
In the case of a combination of a spherical aberration correcting actuator such as a voice coil motor as disclosed in Japanese Patent Laid-Open No. 10-255290, which is incorporated in a combination lens barrel,
When a current is applied to the coil, the coil heats up, and each component of the lens barrel thermally expands, resulting in a change in the spacing, tilt, and decenter between the first lens and the second lens.
There is a problem that a good focused spot cannot be obtained.

The present invention has been made in view of the above situation, and reduces the power consumption of a spherical aberration correction mechanism for correcting spherical aberration caused by an optical thickness error of a recording medium, and at the time of recording / reproducing. It improves the reliability of. Further, in an optical recording / reproducing apparatus for recording / reproducing a recording medium having a plurality of recording layers and a recording medium having one recording layer, the power consumption is reduced and the recording density of the recording medium is increased.

[0017]

The present invention has been made to achieve the above object, and the first invention of the present invention is to provide a recording medium having N recording layers with at least one lens. An optical recording / reproducing device that records and reproduces information by condensing light from a light source via two lens groups that are configured, and corrects spherical aberration of a condensed spot formed in each recording layer. Therefore, a spherical aberration correction mechanism that changes the lens group spacing by electric driving is provided, and the recording layer is a first recording layer from the lens group side, ..., Nth (N ≧
2) is a recording layer, and the lens group interval at the time of spherical aberration correction of the focused spot formed on the first recording layer is d1,
When the making current is i1, the lens group interval at the time of spherical aberration correction of the focused spot formed on the Nth recording layer is dN, and the making current is iN, | i1 | = | iN |
Moreover, the lens group interval d3 when the making current is 0 is d3
= (D1 + dN) / 2, which is an optical recording / reproducing apparatus.

In a second aspect based on the first aspect, the lens groups have a lens group spacing of d4 and an optical thickness of t.
4 is set so that the spherical aberration of the condensed spot condensed through the light transmitting member of No. 4 is minimized, and an optical thickness capable of correcting the spherical aberration at the lens group interval d3 is set. Assuming t3, t3 and t4 substantially match, and
The optical thickness is t3 + Δt from the lens group side surface of the recording medium.
And an optical recording / reproducing apparatus, which makes the recording densities of the recording layers at the positions of t3-Δt substantially equal to each other.

The third aspect of the present invention, when information is recorded / reproduced on / from a recording medium having a single recording layer (N = 1) using the optical recording / reproducing apparatus of the first or second aspect, Let t5 be the optical thickness from the lens group side surface of the recording medium composed of two recording layers to the recording layer, and t3 be the optical thickness capable of correcting spherical aberration when the lens group spacing is d3.
And t5 substantially coincide with each other, which is an optical recording / reproducing apparatus.

In a fourth aspect of the invention, in the first to third aspects of the invention, the two lens groups include an objective lens for converging light from a light source on the recording medium. It is a playback device.

In a fifth aspect based on the first to third aspects, an objective lens for focusing the light from the light source on the recording medium is further provided, and the two lens groups include the light source and the objective lens. The optical recording / reproducing apparatus is characterized by being arranged between them.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below with reference to the drawings. The present invention is not limited to this.

Here, the first lens constitutes the first lens group, and the second lens constitutes the second lens group. Further, although each lens group is composed of one lens here, it may be composed of a plurality of lenses.

A spherical aberration correction mechanism including a combination lens and a voice coil motor will be described with reference to FIG.

The combination lens 1 is composed of two lenses, a first lens 2 on the light source side and a second lens 3 on the recording medium side. The second lens 3 is fixed to a magnet 4, and the magnet 4 is supported by a leaf spring 6 via a magnet support 5. The coil 7 is supported by the coil supporter 8. A voice coil motor 9 including a magnet 4, a leaf spring 6, and a coil 7 applies a positive or negative current to the coil 7 to displace the second lens 3 in the focus direction. That is, the distance between the first lens 2 and the second lens 3 can be changed.

The combination lens 1, the voice coil motor 9 and other supporting parts are housed inside the combination lens barrel 10. The combination lens barrel 10 is F
The recording medium 1 is recorded by an R actuator (not shown).
It is driven in the No. 1 focus radial direction.

As shown in FIG. 2, the combined lens 1 has a lens interval of d4, and the spherical aberration of the condensed spot condensed through the light transmitting body 12 having the optical thickness t4 is minimized. Is designed to.

The light transmissive body 12 is made of a transparent material that transmits light, and corresponds to a light transmissive layer of a recording medium which is assumed when the lens is designed. Further, these light-transmitting bodies or light-transmitting layers are called cover glass layers or protective layers, and are made of polycarbonate (PC) or glass,
There are various types such as UV curable resins.

The magnitude of the spherical aberration of the focused spot focused by the combination lens 1 varies depending on the thickness and refractive index of the light transmitting body (or the light transmitting layer) and the lens spacing of the combination lens. Therefore, when the lens spacing of the combination lens is fixed and the spherical aberrations in the condensing spots that are condensed by passing through different light transmitting bodies are the same, the optical thicknesses of the light transmitting bodies are the same. Suppose

Although the recording medium has a light transmitting layer, a recording layer, and a light transmitting layer between the recording layers, the light from the surface of the recording medium on the side of the combination lens to the position where the focused spot is formed on the recording medium. The transmission layer, the recording layer, and the light transmission layer between the recording layers may be collectively referred to as a light transmission layer, which will be used in the following description.

Next, a recording medium having two recording layers will be described.

FIG. 3 shows the recording medium 11 of the two recording layers.
2 shows a state in which a focused spot is formed on the first layer 13 near the combined lens side.

The recording medium 11 includes a light transmitting layer 20, a first layer 13, and a recording layer 11 in order from the combination lens side.
It is composed of a light transmission layer 21, a second layer 14, and a substrate layer 22 which are arranged between the recording layers.

Here, by changing the lens interval of the combination lens 1 described with reference to FIG. 2 to d1, the optical thickness t1 from the surface of the recording medium 11 on the combination lens side to the first layer 13 is transmitted, The spherical aberration that occurs in the focused spot due to the focusing is corrected. The operation of positioning the focused spot on the recording layer is performed by the FR actuator, and the spherical aberration at the focused spot is corrected by the spherical aberration correction mechanism.

Here, in order to change the lens interval,
A current is applied to the voice coil motor 9, and the applied current is + i1 (or -i1).

FIG. 4 shows the recording medium 11 of the two recording layers.
3 shows a state in which a focused spot is formed on the second layer 14 far from the combined lens side.

Here, by changing the lens interval of the combination lens described with reference to FIG. 2 to d2, the optical thickness t2 from the surface of the recording medium 11 on the combination lens side to the second layer 14 is transmitted and collected. The spherical aberration generated at the focused spot due to the light is corrected.

Here, in order to change the lens interval,
A current is applied to the voice coil motor 9, and the applied current is -i2 (or + i2).

FIG. 5 shows a case where the lens interval of the combination lens described in FIG. 2 is d3.

Here, d3 = (d1 + d2) / 2 (1) Is.

Further, the spherical aberration correction mechanism is constructed so that the current applied to the voice coil motor 7 at that time is approximately zero.

Further, correction can be performed when the lens interval d3 is set,
The optical thickness of the light transmissive body (or the light transmissive layer) is t3, and FIG. 5 shows a state in which a condensed spot is formed at the position where the optical thickness is t3 from the surface of the recording medium 11 on the combined lens side.

In the voice coil motor 7, the relationship between the applied current and the amount of displacement of the driven body (the second lens 3 in this case) can be made substantially linear. Here, the voice coil motor 7 also has that relationship. It is designed like this.

The relationship between the optical thickness of the light transmitting layer (here, the optical thickness from the surface of the recording medium to the combined lens side to the position where the focused spot is formed) and the spherical aberration, and the correction amount of the spherical aberration, Since the relationship with the lens spacing in the combined lens is almost linear, the spherical aberration correction mechanism is configured so that the input current at the neutral point of the spherical aberration correction mechanism (the state where the lens spacing is d3) is zero. As a result, the relationship of the current supplied to the voice coil motor 7 in the states shown in FIGS. 3 and 4 can be set to | i1 | = | i2 | (2).

Here, it is possible to arbitrarily set whether the making current is positive or negative.

With this structure, the following effects can be obtained.

For example, when the spherical aberration correction mechanism is configured so that the input current in the state of FIG. 3 is approximately 0, the input current i in the state of FIG. 4 is | i | = 2 × | i1 | = 2 × | i2 | (3) Therefore, if the spherical aberration correction mechanism is configured so that the input current in the state of FIG. 5 is approximately 0, the maximum input current to be input to the spherical aberration correction mechanism. Can be reduced.

Considering that information is recorded / reproduced on / from the first layer 13 and the second layer 14 of the recording medium 11 at the same rate, the spherical aberration is set so that the input current in the state of FIG. If the spherical aberration correction mechanism is configured so that the input current in the state of FIG. 5 is approximately 0, rather than the correction mechanism, the power consumption is halved and the power consumption can be reduced.

Further, in the case of the spherical aberration correction mechanism comprising the voice coil motor 9 and the combination lens 1, since the voice coil motor 9 is housed inside the combination lens barrel 10, a current is passed through the coil 7. In this case, there is a problem that the coil 7 generates heat, and it is desirable that the power consumption is lower and the maximum input current is smaller.
The effect can be obtained by configuring the spherical aberration correction mechanism so that the input current in the state is approximately zero. The reason for this is as follows.

When the coil 7 generates heat, the coil support 8
And other parts thermally expand and the lens spacing changes. In the case where a method of correcting the spherical aberration of the focused spot focused on each recording layer of the recording medium 11 by applying an input current of a predetermined magnitude to the voice coil motor 7 is used, Since the initial value of the lens interval changes from the design value due to the influence of expansion, the spherical aberration of the focused spot becomes large, which affects the recording and reproduction of information. Especially, in the case of a combination lens having a high numerical aperture, the influence becomes large. Further, when the influence of thermal expansion is non-uniform in the combined lens barrel 10, tilts and decenters between combined lenses occur,
It causes coma and affects the recording and reproduction of information as well as spherical aberration.

More preferably, the optical thickness t3 in FIG.
And the optical thickness t4 of the light transmitting body in FIG. That is, the lens distance d3 and the lens distance d4 are substantially the same, and the recording densities of the recording layers at the positions of the optical thicknesses t3 + Δt and t3−Δt are made equal.

This effect will be described with reference to FIGS.

6A and 7A, the relationship between the optical thickness (corresponding to the optical thickness from the surface of the recording medium on the combined lens side) and the spherical aberration (before spherical aberration correction,
(After correction) is shown. FIGS. 6B and 7B show the optical thickness (corresponding to the optical thickness from the surface of the recording medium on the combined lens side) and the distance between the first lens and the second lens when correcting spherical aberration. Shows the relationship with. 6 (c) and 7 (c), the optical thickness (corresponding to the optical thickness from the surface of the recording medium on the combined lens side) and the making current applied to the voice coil motor when correcting the spherical aberration are shown. Shows the relationship.

The combination lens having the characteristics shown in FIG. 6 is combined so that the spherical aberration of the condensed spot condensed through the light transmitting body having an optical thickness of 80 μm and a refractive index of 1.53 is minimized. It is explanatory drawing about the case where a lens is designed, the lens space | interval in that case was 1.572 mm, and the numerical aperture was 0.85.

FIG. 6 shows the case where the first layer is located at a position of 80 μm and the second layer is located at a position of 120 μm from the surface of the recording medium on the combined lens side, and the refractive index between them is assumed to be constant at 1.53.

As shown in FIG. 6 (a), the spherical aberration remaining after the correction of the spherical aberration is minimum at the position where the recording medium thickness is 80 μm and maximum at the position where 120 μm. Further, as shown in FIG. 6B, the distance between the lenses when correcting the spherical aberration when the recording medium thickness is 120 μm is 1.4.
It is 77 mm.

Therefore, when the making current applied to the voice coil motor is 0, the lens interval is 1.523 mm = (1.572 mm + 1.477 mm).
The spherical aberration correction mechanism is configured so that it becomes / 2.

With this configuration, FIG.
As shown in (c), when the spherical aberration of the focused spots focused on the first layer and the second layer is corrected, the values of the applied currents applied to the voice coil motor can be made substantially the same.

The combination lens having the characteristics shown in FIG. 7 is combined so that the spherical aberration of the condensed spot condensed through the light transmitting body having an optical thickness of 100 μm and a refractive index of 1.53 is minimized. It is explanatory drawing about the case where a lens is designed, and the lens interval in that case was 1.512 mm and the numerical aperture was 0.85.

FIG. 7 shows the case where the first layer is located at a position of 80 μm and the second layer is located at 120 μm from the surface of the recording medium on the combined lens side, and the refractive index between them is 1.53 and is constant.

As shown in FIG. 7A, the recording medium thickness t3 that can be corrected by the lens interval d3 in FIG. 5 and the optical thickness t4 (100 μm in this case) of the light transmitting body determined in lens design shown in FIG. Generally, they match (that is, d3 and d4 also substantially match). Therefore, the value of the spherical aberration remaining after the spherical aberration correction is 100
It is the smallest in the vicinity of μm, and the magnitudes of the spherical aberrations at the positions of 80 μm and 120 μm are almost the same.

As compared with the case of FIG. 6, the optical thickness t3 of FIG. 5 and the optical thickness t4 of the light transmitting body of FIG. 2 are substantially matched, and the positions of the optical thicknesses t3 + Δt and t3-Δt (in this case). Δt is 20 μm), and the relationship between the optical thickness of the light transmission layer (here, the optical thickness from the surface of the recording medium on the combination lens side to the position where the focused spot is formed) and the spherical aberration. Is a linear relationship, the maximum value of spherical aberration (after correction) generated at the focused spots focused on each recording layer is reduced, and
Can be roughly equal. That is, the sizes of the focused spots on the two recording layers can also be made substantially the same. Therefore, it is possible to make the recording densities of the respective recording layers equal, and by doing so, when recording / reproducing information to / from two recording layers, when changing the recording layer for recording / reproducing information. It is not necessary to change the number of rotations for rotating the recording medium. That is, there is no dead time for waiting the settling time of the spindle servo.

Next, a recording medium suitable for the optical recording / reproducing apparatus of the present invention will be described.

The recording medium shown in FIG. 8 has one recording layer 15
The optical thickness from the surface of the recording medium 16 on the combined lens side to the recording layer 15 is t5. Here, the optical thickness t3 shown in FIG. That is, both the lens distance d5 for correcting the spherical aberration of the focused spot focused on the recording layer 15 and the lens distance d3 shown in FIG.

With such a configuration, when recording / reproducing information on / from the recording medium 16 having one recording layer 15, the making current applied to the spherical aberration compensating mechanism, that is, the voice coil motor 9 can be made almost zero. Therefore, power consumption can be reduced. Also, due to the heat generation of the coil,
The influence on the optical characteristics can be reduced.

More preferably, in addition to the above configuration,
The optical thickness t4 of the light transmitting body shown in FIG. 2 and the optical thickness (optical thickness from the combined lens side surface of the recording medium 16 to the recording layer 15) t5 shown in FIG. 6 are configured to substantially match. With this configuration, the optical recording / reproducing apparatus for recording / reproducing information on / from the recording medium 11 having two recording layers (shown in FIG. 3) has the recording medium 15 having one recording layer (shown in FIG. 8). When recording and reproducing information,
The spherical aberration of the focused spot focused on the recording layer 15 of the recording medium 16 having one recording layer can be minimized, and the size of the focused spot can be reduced. Therefore, 1
The recording density of the recording medium 16 having the one recording layer 15 can be improved, and by adopting such a recording medium configuration, the recording medium is suitable for the optical recording / reproducing apparatus of the present invention.

As described above, as the spherical aberration correction mechanism,
The case where the combination lens that collects the light flux from the light source is used for the optical recording medium has been described, but the spherical aberration correction mechanism is provided separately from the combination lens (objective lens) that collects the light flux from the light source on the recording medium. May be. For example, it is possible to correct spherical aberration with a plurality of lenses arranged between the light source and the objective lens.

Next, an example in which spherical aberration is corrected by a plurality of lenses arranged between the light source and the objective lens will be described with reference to FIGS.

In this case, various kinds of objective lenses can be used. First, in FIG. 9, when a light beam having no spherical aberration is incident, an optical thickness optically equivalent to the optical thickness t13-Δt. A case will be described in which an objective lens designed to minimize the spherical aberration of the condensed spot condensed through the light transmitting body having a thickness, that is, the condensed spot on the first layer 13 is described. To do. The optical thickness at the position between the first layer and the second layer is t1.
3 and the second layer was t13 + Δt.

In FIG. 9, the divergent light emitted from the light source 23 is collimated by the collimator lens 24 and enters the first lens 25 which is a plano-concave lens. First lens 25
The divergent light thus enters the second lens 26, which is a plano-convex lens. The light emitted from the second lens 26 is reflected by the objective lens group 27 on the first layer 13 of the recording medium 11.
Alternatively, the light is focused on the second layer 14. The objective lens is driven by an FR actuator (not shown).
The first layer 13 and the second layer 14 have optical thicknesses t13−Δt and t13 + Δ from the surface of the recording medium 11 on the objective lens side.
It is at the position of t.

Next, correction of spherical aberration will be described.

The first lens 25 and the second lens 26 are driven by a voice coil motor. When recording / reproducing information on the first layer 13, + i11 (or -i11) is applied as a make-up current, The interval is set to d11 (FIG. 10), and when recording / reproducing information to / from the second layer 14, an input current of −i12 (or + i12) is added,
The lens interval is d12 (FIG. 11).

Here, | I11 | = | i12 | (4) Is.

Further, the lens interval d when the making current is 0
13 is d13 = (d11 + d12) / 2 (5).

Since the objective lens 27 is designed so that when a light beam having no spherical aberration is incident on it, the spherical aberration of the focused spot transmitted through the light transmitting layer having the optical thickness t13-Δt and condensed is minimized. In the first lens 25 and the second lens 26 for correcting spherical aberration, when the lens interval is d11, the spherical aberration of the light flux transmitted through the two lenses is the smallest, and when the lens interval is d12. , The spherical aberration of the focused spot which is emitted from the second lens 26 and is focused by the objective lens 27 after passing through the light transmission layer having the optical thickness t13 + Δt, that is, the focused spot focused on the second layer 14. It may be designed to be small.

In the case of such a structure, the first lens and the second lens are formed in the same manner as the structure using the combination lens (objective lens) described above.
With respect to the change of the lens interval, the second lens is emitted, and the spherical aberration amount in the focused spot focused by the objective lens is changed linearly, and the error of the optical thickness of the light transmitting layer and the spherical aberration It is possible to design the first lens, the second lens, and the objective lens so that the relationship changes in a substantially linear manner. At that time, when the lens interval is d13, the spherical aberration of the focused spot focused by the objective lens 27 at the position where the optical thickness is approximately t13 is the smallest.

With the above-described structure, the maximum input current and power consumption of the spherical aberration correction mechanism can be reduced as in the case of the combination lens (objective lens) consisting of a plurality of lenses, and the heat generated by the coil or the like can be reduced. This makes it possible to prevent the operation of the spherical aberration correction mechanism from becoming unstable. Further, since the spherical aberration correction mechanism is provided separately from the objective lens, the FR actuator can drive the objective lens at a higher speed.

Next, when a light beam having substantially no spherical aberration is incident, an optical thickness t optically equivalent to the optical thickness t13.
14 (FIG. 12) is a condensed spot that is condensed by being transmitted through the light transmitting member, that is, the first layer 13 and the second layer in the optical recording medium.
A case where an objective lens designed to minimize the spherical aberration of the focused spot at the middle position of the layer 14 is used will be described with reference to FIGS.

When using such an objective lens, the first lens 25 and the second lens are the first lens and the second lens.
When the lens interval of the lens 26 is set to d23, the spherical aberration of the light flux transmitted through the two lenses becomes the smallest (see FIG. 1).
3) and when the lens interval is d21, the light is emitted from the second lens 26 and is condensed by the objective lens 27 after passing through the light transmission layer having the optical thickness t23−Δt, that is, the condensing spot. The spherical aberration of the focused spot focused on the first layer 13 becomes small (FIG. 14), and the lens interval is set to d.
22, the light is emitted from the second lens 26 and is condensed by the objective lens 27 after passing through the light transmitting layer having the optical thickness t23 + Δt, that is, the light is condensed on the second layer 14. Spherical aberration is reduced (Fig. 1
Use the one designed as 5).

Also in this case, as in the case of the combination lens (objective lens) composed of a plurality of lenses, the light collected by the objective lens is changed with respect to the change in the distance between the first lens and the second lens. The amount of spherical aberration of the spot changes linearly, and the relationship of the amount of spherical aberration to the optical thickness error in the optical recording medium also changes linearly. Therefore, a lens configuration that satisfies the above conditions can be obtained by a general design. be able to.

With the above structure, the first
Since the amount of spherical aberration in the converging spots when recording / reproducing on the layer 13 and the second layer 14 can be made substantially the same, the converging spots can also be made to have substantially the same size. When recording and reproducing information for
It is not necessary to change the number of rotations of the recording medium when changing the layer for recording and reproducing information. That is, the dead time for waiting for the settling time of the spindle servo can be reduced.

The recording medium shown in FIG. 16 has one recording layer 15
And the optical thickness from the surface of the recording medium 16 on the objective lens side to the recording layer 15 is t15. Here, the optical thicknesses t13 and t23 shown in FIG. 9 or 13 and the optical thickness t15 shown in FIG. 16 are configured to substantially match. That is, the lens spacing d15 for correcting the spherical aberration of the focused spot focused on the recording layer 15 is also the lens spacing d1 shown in FIG. 9 or FIG.
3, almost coincides with d23. That is, FIG. 9 or FIG.
In the configuration of 3, when the lens interval is d15,
The objective lens corrects the spherical aberration of the focused spot focused at the optical thickness t15, and the current applied to the spherical aberration correction mechanism at that time is approximately zero.

With this configuration, when information is recorded / reproduced on / from a recording medium having one recording layer, the making current applied to the spherical aberration correcting mechanism, that is, the voice coil motor can be made almost zero, and the consumption is reduced. Electric power can be reduced. Further, it is possible to reduce the influence of the heat generation of the coil on the optical characteristics.

Furthermore, preferably, information is recorded / recorded on a recording medium having one recording layer by the structure shown in FIG.
Good to play.

The objective lens shown in FIG. 13 is designed so that, when a light beam having substantially no spherical aberration is incident, the spherical aberration of the focused spot focused at the position of the optical thickness t23 is minimized. The first lens and the second lens are designed so that the spherical aberration of the light beam emitted from the second lens is minimized when the lens interval is d23.

Here, in a recording medium having one recording layer, the optical thickness t15 is set to be substantially equal to the optical thickness t23, whereby optical recording for recording / reproducing information on / from the recording medium having two recording layers. When information is recorded / reproduced on / from a recording medium having one recording layer in the reproducing apparatus, the spherical aberration of the focused spot condensed on the recording layer of the recording medium having one recording layer can be minimized. . That is, since the size of the focused spot can be reduced,
It is possible to improve the recording density of the recording medium having one recording layer and reduce the power consumption during recording and reproduction.

The first lens is a plano-concave lens, and the second lens is
An example using a plano-convex lens as the lens has been described, but the configuration of the lens is not particularly limited, and a plano-convex lens as the first lens and a plano-concave lens as the second lens may be used. Alternatively, a configuration in which two plano-convex lenses are combined may be used. That is, a configuration generally called a beam expander or a relay lens can be used, and a configuration in which the amount of spherical aberration is changed by changing the lens interval may be used.

In the above description, the voice coil motor is used as the spherical aberration compensating mechanism for changing the lens interval. However, a mechanism for changing the lens interval by electrically driving a piezoelectric element or the like also has the same effect.

Further, a configuration in which the distance between the collimator lens and the light source is changed by a spherical aberration correction mechanism is also possible,
In that case, the state in which the focal length of the collimator lens and the distance between the collimator lens and the light source are the same may be set as the neutral point of the spherical aberration correction mechanism.

Further, although the combination lens has been described as having two lenses, the same applies to the case where spherical aberration is compensated by changing the lens interval of two lens groups each of which has a plurality of lenses. Produce an effect.

Further, the lens is not limited to a lens having a refraction effect, and may be a lens utilizing a diffraction effect.

Although the recording medium having two recording layers has been described, the same effect can be obtained in a recording medium having a larger number of recording layers.

Further, as the recording medium having a plurality of recording layers, the one in which the light transmitting layer, the plurality of recording layers, the light transmitting layer disposed between the recording layers, and the substrate layer are arranged in this order from the combination lens side has been described. However, the same effect can be obtained even with, for example, what is called a bonded disk in which two such recording media are bonded. However, in that case, it is necessary to record and reproduce from both sides of the recording medium. The same applies to a recording medium having one recording layer.

The same effect can be obtained whether the recording layer is a read-only type, a write-once type, or a recordable type.

The optical thickness from the lens side surface of the recording medium to the recording layer is determined by the refractive index and the thickness from the lens side surface of the recording medium to the recording layer (for example, by focusing an objective lens on each layer). It can be defined by the value of (measured thickness), and those values also have a certain range in the production of the recording medium. That is, the recording layer of the recording medium having one recording layer of the present invention and the first layer of the recording medium having a plurality of recording layers, ..., And the Nth layer also have a certain refractive index and the lens side of the recording medium. It exists within the range of the thickness from the surface to the recording layer. That is, it can be said that the optical thickness is within a certain range.

In the following, such a case will be described. First, the optical thickness of a recording medium having a plurality of recording layers according to the present invention means the refractive index in which the first layer is defined and the recording medium. Assuming a certain refractive index n1 and thickness s1 in the thickness range from the lens side surface to the recording layer, a focused spot by an objective lens or a combination lens other than that is formed on the recording layer having this refractive index n1 and thickness s1. Is assumed to be d1, the refractive index in which the Nth layer is defined, and the refractive index n2 and the thickness s2 in the range of the thickness from the lens side surface of the recording medium to the recording layer are assumed. Refractive index that maximizes the difference between d1 and d2 when the condensing spot formed by the combination lens is formed with the refractive index n2 and the lens spacing is d2 when formed on the recording layer of thickness s2. 1, the thickness s1 and refractive index n2, and an optical thickness of the first layer and the N layer made of a thickness s2.

A light transmission layer is present between the recording layer and the adjacent recording layer.
The optical thickness between the layers and the optical thickness (refractive index, thickness) of the light transmission layer between the recording layers may differ. In that case, the optical thickness from the lens side surface of the recording medium to the first layer Optical thickness and the optical thickness of the light transmission layer between the recording layers,
The lens intervals d1 and d2 may be determined based on the above-mentioned idea.

[0098]

As described above, according to the present invention, it is possible to reduce the power consumption for correcting the spherical aberration in the focused spot.

Further, the power consumption for correcting spherical aberration can be reduced, and the load on the system such as rotation control of the recording medium can be reduced.

Further, when recording / reproducing a recording medium having a plurality of recording layers and one recording layer, the power consumption in the spherical aberration correcting mechanism can be reduced and the recording density can be improved.

Further, the objective lens can be driven at a higher speed.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a spherical aberration correction mechanism of the present invention.

FIG. 2 is an explanatory diagram of a combination lens of the present invention.

FIG. 3 is an explanatory diagram when recording / reproducing on / from a combination lens of the present invention and a plurality of recording layers.

FIG. 4 is an explanatory diagram when recording / reproducing on / from a combination lens of the present invention and a plurality of recording layers.

FIG. 5 is an explanatory diagram for recording / reproducing on / from a combination lens of the present invention and a plurality of recording layers.

FIG. 6 is an explanatory diagram in the case where the thickness of the light transmission layer when designing the combined lens of the present invention is the first layer.

FIG. 7 is an explanatory diagram in the case where the thickness of the light transmission layer when designing the combined lens of the present invention is the thickness between the first layer and the second layer.

FIG. 8 is an explanatory diagram of a recording medium having one recording layer of the present invention.

FIG. 9 is an explanatory diagram of a configuration in which spherical aberration is corrected by a plurality of lenses arranged between a light source and an objective lens of the present invention.

FIG. 10 is an explanatory diagram of a configuration in which spherical aberration is corrected by a plurality of lenses arranged between a light source and an objective lens of the present invention.

FIG. 11 is an explanatory diagram of a configuration for correcting spherical aberration by a plurality of lenses arranged between a light source and an objective lens of the present invention.

FIG. 12 is an explanatory diagram of an objective lens of the present invention.

FIG. 13 is an explanatory diagram of a configuration in which spherical aberration is corrected by a plurality of lenses arranged between a light source and an objective lens of the present invention.

FIG. 14 is an explanatory diagram of a configuration in which spherical aberration is corrected by a plurality of lenses arranged between a light source and an objective lens of the present invention.

FIG. 15 is an explanatory diagram of a configuration for correcting spherical aberration by a plurality of lenses arranged between a light source and an objective lens of the present invention.

FIG. 16 is an explanatory diagram of a recording medium having one recording layer of the present invention.

FIG. 17 is an explanatory diagram of a combination lens in the related art.

FIG. 18 is an explanatory diagram of a spherical aberration correction mechanism in a conventional technique.

[Explanation of symbols]

1 combination lens 2 First lens 3 second lens 4 magnets 7 coils 5 magnet support 6 leaf spring 7 First lens support 8 coil support 9 Voice coil motor 10 Combination lens barrel 11 recording media 12 Light Transmitter 13 First layer 14 Second layer 15 recording layer 16 recording media 20 Light transmission layer 21 Light transmission layer 22 Substrate layer 23 Light source 24 Collimating lens 25 First lens 26 Second lens 27 Objective lens 100 first lens 101 Second lens 102 FR actuator 103 Spherical aberration correction actuator 104 recording medium 105 recording layer 106 Combination lens 107 Plano-concave lens 108 Plano-convex lens 109 Objective lens

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-251645 (JP, A) JP-A-9-251662 (JP, A) JP-A-10-134387 (JP, A) JP-A-2000-331362 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 7/135

Claims (5)

(57) [Claims] 1. An optical recording / reproducing method for recording / reproducing information by condensing light from a light source onto a recording medium having N recording layers via two lens groups each including at least one lens. The apparatus is provided with a spherical aberration correction mechanism that changes a lens group interval by electric driving in order to correct spherical aberration of a focused spot formed on each recording layer, and the recording layer is arranged from the lens group side. First recording layer ...
An Nth (N ≧ 2) recording layer, the lens group interval at the time of spherical aberration correction of the focused spot formed on the first recording layer is d1, the input current is i1, the Nth recording layer When the lens group interval at the time of spherical aberration correction of the focused spot formed on is dN and the making current is iN, | i1 | = | iN |, and when the making current is 0, the lens group interval d3 Is an optical recording / reproducing apparatus, wherein d3 = (d1 + dN) / 2. 2. The optical recording / reproducing apparatus according to claim 1, wherein the lens group has a condensing spot condensed through a light transmissive body having a lens group spacing of d4 and an optical thickness of t4. The spherical aberration is set to be minimum, and when the optical thickness capable of correcting the spherical aberration at the lens group interval d3 is t3, t3 and t4 substantially match each other, and the recording medium The optical thickness is t3 from the lens group side surface of
An optical recording / reproducing apparatus, wherein the recording densities of the recording layers at the positions of + Δt and t3-Δt are made substantially equal. 3. When recording and reproducing information on a recording medium having a single-layer (N = 1) recording layer using the optical recording and reproducing apparatus according to claim 1 or 2, the single-layer recording layer The optical thickness from the lens group side surface of the recording medium consisting of to the recording layer is t5, and the lens group interval d
The optical recording / reproducing apparatus is characterized in that, when the optical thickness capable of correcting the spherical aberration at 3 is t3, t3 and t5 substantially match. 4. The optical recording / reproducing apparatus according to claim 1, wherein the two lens groups include an objective lens for condensing light from a light source on the recording medium. Recording / playback device. 5. The optical recording / reproducing apparatus according to claim 1, further comprising an objective lens for condensing light from a light source on the recording medium, wherein the two lens groups include the light source and the objective lens. An optical recording / reproducing apparatus characterized in that it is arranged between.