JP2001028147A - Optical recording/reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the consumption of power in a spherical aberration correction mechanism for correcting spherical aberration by changing an interval between lenses by electric driving. SOLUTION: For the recording/reproducing of a recording medium having plural recording layers, an interval between lenses (D1) is set and a current to be supplied to a spherical aberration correction mechanism (i1) is set when a light converging spot is formed on a first layer, and an interval between the lenses (d2) is set and a current to be supplied to the spherical aberration correction mechanism (i2) is set when a light converging spot is formed on an N layer (deepest layer from the surface of the recording medium). Then, |i1|=|i2| is set, and the neutral position of the spherical aberration correction mechanism is decided based on a lens interval (d3)=(d1+d2). Thus, the spherical aberration of a light converging spot for convergence on a position having an optical thickness of nearly t13 by an objective lens 27 becomes smallest.

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 provided with a mechanism for correcting a spherical aberration of a light 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 Application Laid-Open No. H10-188
No. 301 is disclosed as an example, and FIG.
It is explained based on.

Here, a combination lens barrel in which the spherical aberration in a condensed spot on a recording medium is changed by changing the combination lens and the distance between the combination lenses is disclosed.

In FIG. 17, a first lens 100 is disposed on a light source side (not shown), and a second lens 101 is disposed on a 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 displaced in the focus and radial directions. The spherical aberration correction actuator 103 drives the second lens 101 in the focus direction, thereby
It has a function of changing the distance between the lens 100 and the second lens 101 and correcting the spherical aberration of the light spot focused on the recording layer 105 of the recording medium 104.

Light emitted from a light source (not shown)
The light is guided to the 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.

If 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, a spherical aberration occurs in the light spot focused on the recording layer 105. Further, since the numerical aperture of the lens is large, the amount of occurrence of spherical aberration with respect to the error of the optical thickness from the surface on the side of the combination lens to the recording layer 105 is large for a lens having a low numerical aperture. Therefore, by changing the lens interval, the occurrence of spherical aberration is suppressed, and further, it is possible to cope with a recording medium having two or more recording layers.

The optical thickness referred to here is a thickness determined by the thickness and the refractive index of a light transmitting body (or light transmitting layer) through which light is transmitted. It is assumed that the optical thicknesses are equal when the magnitude of the spherical aberration of the condensed spots transmitted and condensed through the light transmitting body matches. Also, the error of the optical thickness from the lens side surface of the recording medium to the recording layer means the optical thickness of the light transmitting body (or light transmitting layer) assumed at the time of lens design and the actual recording / reproducing of information on the recording medium. This is the difference in optical thickness from the surface of the recording medium on the side of the combination lens to each recording layer.

As a driving method for changing the lens interval, a positive or negative current is applied to the coil to generate an electromagnetic force, and the thrust generated between the second lens 101 and the magnet causes the second lens 101 to move in the focusing direction. A method called a voice coil motor for displacing the vertical direction is disclosed (for example, disclosed in JP-A-10-255290).

By the spherical aberration correcting mechanism for changing the lens interval, the amount of displacement of the second lens, ie, the first lens
By setting an appropriate distance between the lens and the second lens, it is possible to correct spherical aberration caused by an error in the optical thickness from the surface of the recording medium on the side of the combination lens to the recording layer.

Japanese Patent Application Laid-Open No. Hei 5-266511 discloses a technique for correcting the spherical aberration by changing the distance between lenses other than the objective lens. Figure 1
8 will be described.

In FIG. 18, a combination objective lens 1 is shown.
09 and a light source, a plano-concave lens 107 and a plano-convex lens 108
And the optical thickness of the optical recording medium (Japanese Patent Laid-Open No. 5-266)
The spherical aberration is corrected by driving the plano-concave lens 107 in the optical axis direction in accordance with “the thickness of the protective layer” in JP-A-511-511.

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

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

[0015]

As described above, an electrically driven type is used as the spherical aberration correcting mechanism. However, the spherical aberration correcting mechanism is not used when a lens having a low numerical aperture is used. Because driving requires power consumption,
There is a problem that extra power consumption occurs. further,
As disclosed in Japanese Patent Application Laid-Open No. H10-255290, in the case of incorporating a spherical aberration correcting actuator in a combination lens barrel, such as a voice coil motor,
As a result of a change in the distance, tilt, and decenter between the first lens and the second lens due to heat generation of the coil when current flows through the coil and thermal expansion of each component of the lens barrel,
There was a problem that a good condensing spot could not be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and reduces the power consumption of a spherical aberration correction mechanism for correcting a spherical aberration caused by an optical thickness error of a recording medium, and reduces the power consumption during recording and reproduction. It is intended to improve reliability. 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]

Means for Solving the Problems The present invention has been made to achieve the above object, and a first invention of the present invention is to provide a recording medium having N recording layers by using at least one lens. An optical recording / reproducing apparatus for recording / reproducing information by condensing light from a light source through two lens groups configured, and corrects spherical aberration of a converged spot formed on each recording layer. For this purpose, there is provided a spherical aberration correcting mechanism for changing the lens group interval by electric driving, and the recording layers are arranged from the lens group side to the first recording layer,.
2) The distance between the lens groups at the time of spherical aberration correction of the condensed spot formed on the first recording layer is d1,
Assuming that the input current is i1, the distance between the lens groups at the time of spherical aberration correction of the condensed spot formed on the N-th recording layer is dN, and the input current is iN, | i1 | = | iN |
Further, the lens group interval d3 when the input current is 0 is d3
= (D1 + dN) / 2.

According to a second aspect of the present invention, in the first aspect, the lens group has a lens group interval d4 and an optical thickness t.
4 is set so that the spherical aberration of the condensed spot transmitted and condensed through the light transmitting body 4 is minimized, and the optical thickness capable of correcting the spherical aberration at the lens group interval d3 is set. Assuming that t3, t3 and t4 substantially coincide with each other, and
The optical thickness from the lens group side surface of the recording medium is t3 + Δt
An optical recording / reproducing apparatus characterized in that the recording densities of the recording layers located at positions of t3 and t3-Δt are made substantially equal.

According to a third aspect of the present invention, there is provided the optical recording / reproducing apparatus according to the first or second aspect, wherein information is recorded / reproduced on / from a recording medium having a single recording layer (N = 1). Assuming that the optical thickness from the lens group side surface of the recording medium including the two recording layers to the recording layer is t5, and the optical thickness capable of correcting the spherical aberration at the lens group interval d3 is t3, t3
And t5 substantially coincide with each other.

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

According to a fifth aspect of the present invention, in the first to third aspects, an objective lens for condensing light from a light source on the recording medium is further provided, and the two lens groups include the light source and the objective lens. An optical recording / reproducing device, which is disposed between the optical recording / reproducing devices.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. Note that the present invention is not limited by this.

Here, the first lens constitutes a first lens group, and the second lens constitutes a second lens group. Further, here, each lens group is configured by one lens, but may be configured by a plurality of lenses.

Referring to FIG. 1, a spherical aberration correcting mechanism including a combination lens and a voice coil motor will be described.

The combination lens 1 comprises two lenses, a first lens 2 on the light source side and a second lens 3 on the recording medium side, respectively. 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 a coil support 8. By passing a positive or negative current through the coil 7 by the voice coil motor 9 including the magnet 4, the leaf spring 6, and the coil 7, the second lens 3 is displaced 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 a combination lens barrel 10. The combined lens barrel 10 is F
The recording medium 1 is controlled by an R actuator (not shown).
1 is driven in the focus / radial direction.

As shown in FIG. 2, the lens interval of the combination lens 1 is d4, and the spherical aberration of the condensed spot transmitted through the light transmitting body 12 having the optical thickness t4 and condensed is minimized. Designed for

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

The magnitude of the spherical aberration of the condensed spot condensed by the combination lens 1 varies depending on the thickness and refractive index of the light transmitting body (or light transmitting layer) and the lens spacing of the combination lens. Therefore, when the lens spacing of the combination lens is fixed and the magnitude of the spherical aberration in the condensed spot transmitted through different light transmitting bodies is the same, the optical thickness of those light transmitting bodies is the same. And

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 condensed spot is formed on the recording medium is formed. 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, and 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.
3 shows a state in which a converging spot is formed on the first layer 13 near the combination lens side.

The recording medium 11 includes a light transmitting layer 20, a first layer 13, and a
It comprises a light transmitting layer 21, a second layer 14, and a substrate layer 22 arranged between 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 combination lens side surface of the recording medium 11 to the first layer 13 is transmitted. The spherical aberration generated in the condensed spot due to the condensing is corrected. The operation of positioning the focused spot on the recording layer is performed by an FR actuator, and the spherical aberration in the focused spot is corrected by a spherical aberration correcting 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 converging spot is formed on the second layer 14 far from the combination lens side.

Here, by changing the lens distance of the combination lens described in FIG. 2 to d2, the optical thickness t2 from the combination lens side surface of the recording medium 11 to the second layer 14 is transmitted and collected. The spherical aberration generated in the condensed 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).

Further, the spherical aberration correcting mechanism is configured so that the applied current applied to the voice coil motor 7 at that time is substantially zero.

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

In the voice coil motor 7, the relationship between the applied current and the displacement of the driven body (in this case, the second lens 3) can be substantially linear. It has such a design.

The relationship between the optical thickness of the light transmitting layer (here, the optical thickness from the combined lens side surface of the recording medium to the position where the condensing spot is formed) and the spherical aberration, and the amount of correction of the spherical aberration Since the relationship between the combination lens and the lens interval is substantially linear, the spherical aberration correction mechanism is configured so that the input current at the neutral point of the spherical aberration correction mechanism (state where the lens interval is d3) becomes zero. Accordingly, the relationship between the currents applied to the voice coil motor 7 in the states shown in FIGS. 3 and 4 can be expressed as | i1 | = | i2 | (2).

Here, whether the applied current is positive or negative can be arbitrarily set.

With such a configuration, the following effects can be obtained.

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

Further, assuming that information is recorded / reproduced by the same ratio to the first layer 13 and the second layer 14 of the recording medium 11, the spherical aberration is set so that the applied current in the state of FIG. If the spherical aberration correction mechanism is configured so that the applied current in the state of FIG. 5 is substantially zero, rather than configuring the correction mechanism, the power consumption is reduced to 、, and the power consumption can be reduced.

In the case of the spherical aberration correcting mechanism including 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 applied to the coil 7. In this case, there is a problem that the coil 7 generates heat, and it is desirable that the power consumption be lower and the maximum input current be small.
The effect can be obtained by configuring the spherical aberration correction mechanism so that the applied current in the state of (1) becomes substantially zero. The reason is as follows.

When the coil 7 generates heat, the coil support 8
And other parts thermally expand, and the lens interval changes. When a method is used in which a spherical current of a condensed spot condensed on each recording layer of the recording medium 11 is corrected by passing a predetermined input current to the voice coil motor 7, Since the initial value of the lens interval changes from the design value due to the effect of expansion, the spherical aberration of the condensed spot increases, which affects information recording and reproduction. In particular, in the case of a combination lens having a high numerical aperture, the effect becomes large. If the influence of thermal expansion is not uniform in the combined lens barrel 10, tilt and decenter between the combined lenses will occur,
This causes coma aberration and affects recording and reproduction of information similarly to spherical aberration.

More preferably, the optical thickness t3 of FIG.
And the optical thickness t4 of the light transmitting body in FIG. That is, the lens interval d3 and the lens interval d4 substantially match, 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.

FIGS. 6A and 7A show the relationship between the optical thickness (corresponding to the optical thickness from the combined lens surface of the recording medium) and the spherical aberration (before the spherical aberration is corrected).
(After correction). FIGS. 6B and 7B show the optical thickness (corresponding to the optical thickness from the combined lens side surface of the recording medium) and the distance between the first lens and the second lens when correcting spherical aberration. The relationship is shown below. FIGS. 6C and 7C show the optical thickness (corresponding to the optical thickness from the combined lens side surface of the recording medium) and the input current to be applied to the voice coil motor when correcting spherical aberration. Shows the relationship.

The combination lens having the characteristics shown in FIG. 6 is combined so that the spherical aberration of the condensed spot transmitted through a light transmitting body having an optical thickness of 80 μm and a refractive index of 1.53 is minimized. FIG. 3 is an explanatory diagram of a case where a lens is designed, in which case the lens interval is 1.572 mm, and the numerical aperture is 0.85.

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

As shown in FIG. 6A, 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 is maximum at the position where the recording medium thickness is 120 μm. Further, as shown in FIG. 6B, when correcting the spherical aberration when the recording medium thickness is 120 μm, the distance between the lenses is 1.4.
77 mm.

Therefore, when the input current applied to the voice coil motor is 0, the lens interval is 1.523 mm = (1.572 mm + 1.477 mm)
/ 2 was set for the spherical aberration correction mechanism.

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

The combination lens having the characteristics shown in FIG. 7 is combined so that the spherical aberration of the condensed spot transmitted through a light transmitting body having an optical thickness of 100 μm and a refractive index of 1.53 is minimized. FIG. 3 is an explanatory diagram of a case where a lens is designed, in which case the lens interval is 1.512 mm and the numerical aperture is 0.85.

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

As shown in FIG. 7A, the recording medium thickness t3 which 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 when designing the lens shown in FIG. They are almost matched (that is, d3 and d4 are also almost matched). Therefore, the value of the spherical aberration remaining after the spherical aberration correction is 100
It is the smallest around μm, and the magnitudes of the spherical aberration at the positions of 80 μm and 120 μm also substantially match.

Compared to the case of FIG. 6, the optical thickness t3 of FIG. 5 is substantially equal to the optical thickness t4 of the light transmitting body of FIG. 2, and the positions of the optical thicknesses t3 + Δt and t3-Δt (in this case, Relationship between the presence of the recording layer at Δt of 20 μm, the optical thickness of the light transmitting layer (here, the optical thickness from the combined lens side surface of the recording medium to the position where the condensing spot is formed) and the spherical aberration Is a linear relationship, the maximum value of the spherical aberration (after correction) occurring at the condensed spot condensed on each recording layer is reduced, and
Can be almost equal. That is, the size of the condensed spots in the two recording layers can also be made substantially equal. Therefore, it is possible to make the recording densities of the respective recording layers equal, and by doing so, when recording and reproducing information on the two recording layers, when the recording layer for recording and reproducing information is changed, Therefore, there is no need to change the number of rotations for rotating the recording medium. That is, there is no dead time for waiting for the spindle servo to settle.

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

The recording medium shown in FIG.
The optical thickness from the combination lens side surface of the recording medium 16 to the recording layer 15 is t5. In this case, the optical thickness t3 shown in FIG. That is, both the lens interval for correcting the spherical aberration of the condensed spot focused on the recording layer 15 and d5 approximately match the lens interval d3 shown in FIG.

With this configuration, when recording / reproducing information on / from the recording medium 16 having one recording layer 15, the input current applied to the spherical aberration compensating mechanism, ie, the voice coil motor 9 can be reduced to almost zero. Power consumption can be reduced. Also, due to the heat of the coil,
The effect on 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 is substantially equal to 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. With such a configuration, an optical recording / reproducing apparatus that records / reproduces information on / from a recording medium 11 having two recording layers (shown in FIG. 3) can be used in a recording medium 15 having one recording layer (shown in FIG. 8). When recording and reproducing information,
The spherical aberration of the light spot focused on the recording layer 15 of the recording medium 16 having one recording layer can be minimized, and the size of the light spot can be reduced. Therefore, 1
The recording density of the recording medium 16 having one recording layer 15 can be improved, and such a configuration of the recording medium provides a recording medium suitable for the optical recording / reproducing apparatus of the present invention.

As described above, as a spherical aberration correcting mechanism,
Although the description has been given of the case where the combination lens for condensing the light beam from the light source is used for the optical recording medium, the spherical aberration correction mechanism is provided separately from the combination lens (objective lens) for condensing the light beam from the light source on the recording medium. May be. For example, it is possible to correct spherical aberration by using a plurality of lenses arranged between a light source and an objective lens.

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

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

In FIG. 9, the divergent light emitted from the light source 23 is converted into parallel light by the collimator lens 24 and enters the first lens 25 which is a plano-concave lens. First lens 25
As a result, the divergent light is incident on the second lens 26, which is a plano-convex lens. The light emitted from the second lens 26 is transmitted to the first layer 13 of the recording medium 11 by the objective lens group 27.
Alternatively, the light is focused on the second layer 14. The objective lens is driven by a not-shown FR actuator.
In addition, 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 position 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 information is recorded / reproduced on / from the first layer 13, the input current is increased by + i11 (or −i11). The interval is d11 (FIG. 10), and when recording / reproducing information on / from the second layer 14, the applied current is -i12 (or + i12).
The lens interval is set to d12 (FIG. 11).

Here, | i11 | = | i12 | (4)

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

The objective lens 27 is designed so that when a light beam having no spherical aberration is incident, the spherical aberration of a condensed spot transmitted through the light transmitting layer having an optical thickness of t13-Δt and condensed is minimized. The first lens 25 and the second lens 26 for correcting the spherical aberration have the smallest spherical aberration of the luminous flux transmitted through the two lenses when the distance between the lenses is d11, and when the distance between the lenses is d12. , The condensed spot emitted from the second lens 26 and condensed by the objective lens 27 through the light transmitting layer having the optical thickness t13 + Δt, that is, the spherical aberration of the condensed spot condensed on the second layer 14 is reduced. What is necessary is just to design so that it may become small.

In the case of such a configuration, similarly to the configuration using the combination lens (objective lens), the first lens and the second lens are used.
In response to a change in the distance between the lenses, the second lens is emitted and the amount of spherical aberration at the condensed spot condensed by the objective lens is linearly changed. It is possible to design the first lens, the second lens, and the objective lens such that the relationship also changes substantially linearly. At that time, when the lens interval is d13, the spherical aberration of the condensed spot condensed by the objective lens 27 at a position where the optical thickness is approximately t13 is minimized.

With the above-described configuration, the maximum input current and power consumption in the spherical aberration correction mechanism can be reduced as in the case of the combination lens (objective lens) including a plurality of lenses, and the heat generated by the coil and the like can be reduced. Accordingly, it is possible to prevent the operation of the spherical aberration correction mechanism from becoming unstable. In addition, since the spherical aberration correction mechanism is provided separately from the objective lens, the speed at which the FR lens drives the objective lens can be increased.

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

When such an objective lens is used, the first lens and the second lens are the first lens 25 and the second lens.
When the lens distance between the lenses 26 is d23, the spherical aberration of the light beam transmitted through the two lenses is minimized (see FIG. 1).
3) When the distance between the lenses is d21, the light is emitted from the second lens 26, and is condensed by the objective lens 27 and transmitted through the light transmission layer having an optical thickness of t23-Δt. The spherical aberration of the light spot focused on the first layer 13 is reduced (FIG. 14), and the lens interval is set to d.
22, a condensed spot emitted from the second lens 26 and condensed by the objective lens 27 through the light transmitting layer having an optical thickness of t23 + Δt, that is, a condensed spot collected on the second layer 14 Spherical aberration is reduced (see FIG. 1).
5) Use the one designed as described above.

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

With the above configuration, the first
Since the amount of spherical aberration at the converging spot at the time of recording / reproducing on the layer 13 and the second layer 14 can be made substantially the same, the converging spot can be made almost the same size. When recording and reproducing information for
When the layer for recording and reproducing information is changed, it is not necessary to change the number of rotations for rotating the recording medium. That is, the dead time for waiting for the spindle servo to settle can be reduced.

The recording medium shown in FIG.
And the optical thickness from the objective lens side surface of the recording medium 16 to the recording layer 15 is t15. Here, the optical thicknesses t13 and t23 shown in FIG. 9 or FIG. 13 and the optical thickness t15 in FIG. That is, the lens interval d15 for correcting the spherical aberration of the light spot focused on the recording layer 15 is also the lens interval d1 shown in FIG. 9 or FIG.
3, d23. That is, FIG. 9 or FIG.
In the configuration of 3, when the lens interval is d15,
The spherical aberration of the condensed spot condensed at the position of the optical thickness t15 by the objective lens is corrected, and the current supplied to the spherical aberration correction mechanism at that time is almost zero.

With this configuration, when recording / reproducing information on / from a recording medium having one recording layer, the input current applied to the spherical aberration correction mechanism, ie, the voice coil motor, can be reduced to almost zero, and the power consumption can be reduced. Power can be reduced. Further, the influence on the optical characteristics due to the heat generation of the coil can be reduced.

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

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

Here, in a recording medium having one recording layer, by setting the optical thickness t15 to be substantially equal to the optical thickness t23, the optical recording for recording and reproducing information on the recording medium having two recording layers is performed. When information is recorded / reproduced on / from a recording medium having one recording layer by the reproducing apparatus, the spherical aberration of the light spot focused on the recording layer of the recording medium having one recording layer can be minimized. . That is, since the size of the converging spot can be reduced,
It is possible to improve the recording density of a 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
Although an example in which a plano-convex lens is used as a lens has been described, the configuration of the lens is not particularly limited, and a plano-convex lens may be used as the first lens, and a plano-concave lens may be used as the second lens. Further, 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 any configuration may be used as long as the amount of spherical aberration changes by changing the lens interval.

In the above description, the voice coil motor has been described 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 has the same effect.

It is also possible to adopt a configuration in which the distance between the collimator lens and the light source is changed by a spherical aberration correcting mechanism.
In this case, a state in which the focal length of the collimating lens and the distance between the collimating lens and the light source may be set as the neutral point of the spherical aberration correction mechanism.

Although the combination lens has been described as being composed of two lenses, the same applies to a case where spherical aberration is compensated by changing the lens interval between two lens groups in which each lens is composed of a plurality of lenses. It works.

The lens may be a lens utilizing a diffraction effect as well as a lens utilizing a refraction effect.

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

Further, as a recording medium having a plurality of recording layers, a recording medium in which a light transmitting layer, a plurality of recording layers, a light transmitting layer disposed between the recording layers, and a substrate layer are arranged in order from the combination lens side has been described. However, for example, a so-called bonded disc in which two such recording media are bonded together has the same effect. However, in that case, it is necessary to perform recording and reproduction from both sides of the recording medium. The same applies to a recording medium having one recording layer.

The same effect can be obtained with any of the recording layers that are read-only, write-once, and recordable.

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 the objective lens on each layer, etc.). (Thickness measured) can be defined, and in the production of a recording medium, those values also have a certain range. That is, the recording layer of the recording medium having one recording layer of the present invention, and the first layer,..., Nth layer of the recording medium having a plurality of recording layers also have a certain refractive index and the lens side of the recording medium. It will be 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 is defined by the refractive index of the first layer and the refractive index of the recording medium. Assuming a certain refractive index n1 and thickness s1 in the range of the thickness from the lens side surface to the recording layer, a condensed spot by the objective lens or another combination lens is formed on the recording layer having this refractive index n1 and thickness s1. The lens interval at this time is d1, the refractive index defining the Nth layer 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, and the objective lens or other The refractive index is such that the difference between d1 and d2 is the largest when the distance between the lenses is d2 when the condensed spot formed by the combination lens is formed on the recording layer having this refractive index n2 and 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 transmitting layer exists between the recording layer and the adjacent recording layer.
The optical thickness between the layers may differ from the optical thickness (refractive index, thickness) of the light transmitting layer between the recording layers. In such a case, the optical thickness from the lens side surface of the recording medium to the first layer may be different. Combined with the optical thickness of the light transmitting layer between the recording layers,
What is necessary is just to determine the lens intervals d1 and d2 based on the above idea.

[0098]

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

Further, the power consumption for correcting the spherical aberration can be reduced, and the load on the system such as the 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 of 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 the 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 in the case where recording and reproduction are performed on a combination lens of the present invention and a plurality of recording layers.

FIG. 4 is an explanatory diagram in a case where recording / reproduction is performed on a combination lens of the present invention and a plurality of recording layers.

FIG. 5 is an explanatory diagram in a case where recording and reproduction are performed on 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 transmitting layer is set to the first layer when the combination lens of the present invention is designed.

FIG. 7 is an explanatory diagram in a case where the thickness of the light transmitting layer at the time of designing the combination lens of the present invention is a thickness between the first layer and the second layer.

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

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

FIG. 10 is an explanatory diagram of a configuration for correcting spherical aberration by using a plurality of lenses disposed between a light source and an objective lens according to the present invention.

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

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

FIG. 13 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 according to the present invention.

FIG. 14 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 according to 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 according to the present invention.

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

FIG. 17 is an explanatory diagram of a combination lens in a conventional technique.

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

[Explanation of symbols]

 Reference Signs List 1 combined lens 2 first lens 3 second lens 4 magnet 7 coil 5 magnet support 6 leaf spring 7 first lens support 8 coil support 9 voice coil motor 10 combination lens barrel 11 recording medium 12 light transmitting body 13th 1 layer 14 second layer 15 recording layer 16 recording medium 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

Claims (5)

[Claims] 1. An optical recording / reproducing apparatus for recording / reproducing information by condensing light from a light source on a recording medium having N recording layers via two lens groups including at least one lens. An apparatus, comprising: a spherical aberration correction mechanism that changes a lens group interval by electrical driving in order to correct a spherical aberration of a condensed spot formed on each recording layer, wherein the recording layer is arranged from a lens group side. A first recording layer,...
An Nth (N ≧ 2) recording layer, wherein the distance between lens groups at the time of spherical aberration correction of the condensed spot formed on the first recording layer is d1, the input current is i1, and the Nth recording layer When the lens group interval at the time of spherical aberration correction of the converged spot formed at the point is dN and the input current is iN, | i1 | = | iN | and the lens group interval d3 when the input current is 0 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 is formed of a condensed spot transmitted through a light transmitting body having a lens group interval of d4 and an optical thickness of t4. The spherical aberration is set so as to be minimized. Assuming that the optical thickness capable of correcting the spherical aberration at the lens group interval d3 is t3, t3 and t4 substantially coincide with each other, and the recording medium The optical thickness is t3 from the lens group side surface of
An optical recording / reproducing apparatus characterized in that the recording densities of the recording layers at 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, the single-layer recording layer. The optical thickness from the lens group side surface to the recording layer of the recording medium composed of
An optical recording / reproducing apparatus characterized in that, when the optical thickness capable of correcting the spherical aberration at t3 is t3, t3 and t5 substantially coincide. 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 and 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 an objective lens. An optical recording / reproducing device, which is arranged between the optical recording and reproducing devices.