JP2001160235A - Optical head and optical recording and reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head which deals with two kinds of optical recording media varying in the thicknesses of light transparent layers and is capable of easily correcting the respective spherical aberrations generated during the recording and reproducing of the respective optical recording media. SOLUTION: In recording and reproducing of the one optical recording medium, the zero order light which is a first laser beam L1 emitted from a light emitting and receiving element 11 and is transmitted as it is through a hologram element 13 is condensed by an objective lens 14 onto the optical recording medium. In recording and reproducing of the other optical recording medium, the first order light which is a second laser beam L2 emitted from the light emitting and receiving element 11 and is diffracted by the hologram element 13 is condensed by the objective lens 14 onto the optical recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head corresponding to two types of optical recording media having different thicknesses of a light transmitting layer from a light incident surface to an information recording surface, and a light having such an optical head. The present invention relates to a recording / reproducing device.

[0002]

2. Description of the Related Art In order to increase the recording density of an optical recording medium, it is advantageous that the thickness of the light transmitting layer from the light incident surface to the information recording surface is thin. Therefore, as the recording density of the optical recording medium increases, the light transmitting layer of the optical recording medium tends to become thinner. Note that in the case of an optical recording medium in which an information recording layer is formed on a substrate and recording and reproduction are performed by irradiating a laser beam from the substrate side, the thickness of the light transmitting layer corresponds to the substrate thickness.

For example, in a CD (compact disk),
Although the substrate thickness corresponding to the thickness of the light transmitting layer was about 1.2 mm, in order to further increase the recording density, the substrate thickness was reduced to about 0.6 mm.
Optical recording media having a diameter of mm have also been developed.

In order to increase the recording density of an optical recording medium, it is advantageous that the wavelength of a laser beam used for recording and reproduction is short. Therefore, as the recording density of the optical recording medium increases, the wavelength of the laser beam used for recording and reproducing on the optical recording medium tends to be shorter.

For example, the wavelength of a laser beam used for recording / reproducing a CD is about 780 nm. In order to further increase the recording density, the wavelength of a laser beam used for recording / reproducing is about 6 nm.
Optical recording media with a thickness of 50 nm have also been developed.

As described above, there are various types of optical recording media, such as those having different light transmission layers and those having different wavelengths of laser light used for recording and reproduction. Therefore, it is desired that an optical recording / reproducing apparatus that performs recording / reproducing of an optical recording medium can be commonly used for a plurality of optical recording media.

In order to allow the optical recording / reproducing apparatus to be commonly used for a plurality of optical recording media, for example, a plurality of optical heads corresponding to the respective optical recording media may be mounted. The mounting of the optical head is disadvantageous in miniaturizing the apparatus and reducing the manufacturing cost. Therefore, it is desired that one optical head can handle a plurality of optical recording media.

However, it is not easy to make one optical head applicable to a plurality of optical recording media. For example, it is assumed that recording and reproduction of two types of optical recording media having different wavelengths and substrate thicknesses of laser light used for recording and reproduction are performed by one optical head. At this time, if the optical head is optimized so that spherical aberration does not occur during recording / reproducing of one optical recording medium, large spherical aberration occurs during recording / reproducing of the other optical recording medium, and normal recording / reproducing is difficult. Become.

In order to correct such spherical aberration, several methods have been devised.

For example, when the numerical aperture of the objective lens required for recording and reproduction on one optical recording medium is different from the numerical aperture of the objective lens required for recording and reproduction on the other optical recording medium, the difference between them is used. A method has been devised in which spherical aberration correction when the numerical aperture is small is adjusted to one optical recording medium, and spherical aberration correction when the numerical aperture is large is adjusted to the other optical recording medium.

However, to realize this method,
Since it is necessary to make the spherical aberration correction of the objective lens special, there is a problem that it is difficult to manufacture the objective lens.

Further, in order to obtain sufficient characteristics, it is necessary to arrange a so-called aperture limiting filter between the objective lens and the light source, and the aperture limiting filter is moved together with the objective lens by an actuator. There is a need.
Therefore, there is a problem that the configuration of the optical head is complicated.

The aperture limiting filter is an optical filter that performs different functions in accordance with the difference in the wavelength of light. The aperture limiting filter is used for recording and reproducing data on one optical recording medium and recording and reproducing data on the other optical recording medium. It is used to change the diameter of the laser light incident on the objective lens.

Further, when an aperture limiting filter is used, high precision is required for the alignment between the aperture limiting filter and the objective lens, so that there is a problem that it is difficult to manufacture an optical head.

As a method of correcting spherical aberration, a plurality of light sources corresponding to each optical recording medium are prepared, and the distance of each light source from the objective lens is changed, so that the thickness of the light transmitting layer of the optical recording medium is reduced. A method for canceling the spherical aberration caused by the difference has also been devised.

However, this technique has a problem that it cannot be applied to an optical head of the type in which the light emitting point positions of the light sources are the same. In addition, in this method, since the distance between each light source and the objective lens is defined, there is a problem that the degree of freedom in design is reduced.

[0017]

As described above, in order that one optical head can cope with a plurality of optical recording media, each spherical aberration generated at the time of recording and reproduction of each optical recording medium can be corrected. You need to do that. And
It is desired that such spherical aberration can be corrected more easily.

The present invention has been proposed in view of the above-mentioned conventional circumstances, and has been proposed as an optical head corresponding to two types of optical recording media, in which each spherical aberration occurring at the time of recording / reproducing of each optical recording medium is reduced. It is an object of the present invention to provide an optical head that can easily perform correction. Another object of the present invention is to provide an optical recording / reproducing apparatus provided with such an optical head.

[0019]

An optical head according to the present invention is an optical head corresponding to two types of optical recording media having different thicknesses of a light transmitting layer from a light incident surface to an information recording surface.
Then, at the time of recording and / or reproduction of one optical recording medium,
A light source that emits a first laser beam of a predetermined wavelength and emits a second laser beam having a different wavelength from the first laser beam during recording and / or reproduction of the other optical recording medium. In addition, the first laser light does not show a diffractive action, or even if it shows a diffractive action, it is diffracted so that the proportion of the 0th-order light is larger than that of the 1st-order diffracted light. Is provided with a hologram element for diffracting so that the ratio of the first-order diffracted light is larger than that of the zero-order light. Also,
An objective lens for condensing the laser light emitted from the light source and passing through the hologram element on the optical recording medium is provided.

When performing recording and / or reproduction on one of the optical recording media, the first laser light emitted from the light source passes through the hologram element as it is, and the 0th-order light is passed through the optical recording medium by the objective lens. Focus on top. When recording and / or reproducing data on the other optical recording medium, the first-order diffracted light obtained by diffracting the second laser light emitted from the light source by the hologram element is focused on the optical recording medium by the objective lens. I do.

This optical head performs recording and / or reproduction on one of the optical recording media by using the zero-order light, in which the first laser light emitted from the light source passes through the hologram element as it is, and The recording and / or reproduction of the other optical recording medium is performed using the first-order diffracted light obtained by diffracting the second laser light emitted from the hologram element. Therefore, the correction of the spherical aberration corresponding to one optical recording medium and the correction of the spherical aberration corresponding to the other optical recording medium,
Each can be performed independently.

In the above optical head, in the hologram element, for example, when diffracting the second laser light, the virtual light source of the first-order diffracted light incident on the objective lens is located at a certain point on the optical axis of the objective lens. Thus, the second laser light is diffracted. This makes it possible to satisfactorily correct spherical aberration that occurs when recording and / or reproducing data on the optical recording medium using the second laser light.

In the above-mentioned optical head, the hologram element is arranged such that, when diffracting the second laser light, a part of off-axis rays of the first-order diffracted light does not enter the objective lens.
The second laser light may be diffracted. Thus, when performing recording and / or reproduction on the optical recording medium using the second laser light, the diameter of the laser light incident on the objective lens can be limited, and the numerical aperture of the objective lens can be controlled. be able to.

In the above optical head, the hologram element has, for example, a plurality of steps formed on a light-transmitting substrate, and the optical path length of each step is substantially equal to the wavelength of the first laser light. Is done. As a result, the hologram element does not act as an optical diffraction element for the first laser light, but acts as an optical diffraction element only for the second laser light.

In the optical recording / reproducing apparatus according to the present invention, the thickness of the light transmitting layer from the light incident surface to the information recording surface is different.
An optical recording / reproducing apparatus including an optical head corresponding to various types of optical recording media. An optical head provided in this optical recording / reproducing apparatus includes a light source, a hologram element, and an objective lens. The light source emits a first laser beam of a predetermined wavelength during recording and / or reproduction of one of the optical recording media,
At the time of recording and / or reproduction on the other optical recording medium, a second laser beam having a different wavelength from the first laser beam is emitted. The hologram element does not show a diffractive effect on the first laser beam, or diffracts the diffracted light so that the ratio of the 0th-order light is larger than that of the first-order diffracted light even if it shows the diffractive effect. Light is diffracted so that the proportion of the first-order diffracted light is larger than that of the zero-order light. The objective lens focuses the laser light emitted from the light source and passing through the hologram element on the optical recording medium.

The optical head provided in the optical recording / reproducing apparatus is such that when recording and / or reproducing on one optical recording medium, the first laser light emitted from the light source passes through the hologram element as it is. The 0-order light is collected on a recording medium by an objective lens. When performing recording and / or reproduction on the other optical recording medium, first-order diffracted light obtained by diffracting the second laser light emitted from the light source by the hologram element is focused on the recording medium by the objective lens. .

An optical head provided in this optical recording / reproducing apparatus uses a zero-order light, in which a first laser beam emitted from a light source passes through a hologram element as it is, to record and / or write data on one optical recording medium. Alternatively, the recording and / or reproduction of the other optical recording medium is performed by using the first-order diffracted light obtained by diffracting the second laser light emitted from the light source by the hologram element. Therefore, the correction of the spherical aberration corresponding to one optical recording medium and the correction of the spherical aberration corresponding to the other optical recording medium can be performed independently.

In the above optical recording / reproducing apparatus, the hologram element is such that, for example, when diffracting the second laser beam, the virtual light source of the first-order diffracted light incident on the objective lens is located at a certain point on the optical axis of the objective lens. The second laser light is diffracted so as to be located. This makes it possible to satisfactorily correct spherical aberration that occurs when recording and / or reproducing data on the optical recording medium using the second laser light.

In the above-mentioned optical recording / reproducing apparatus, the hologram element is arranged so that, when diffracting the second laser beam, a part of the off-axis ray of the first-order diffracted light does not enter the objective lens. Light may be diffracted. Thus, when performing recording and / or reproduction on the optical recording medium using the second laser light, the diameter of the laser light incident on the objective lens can be limited, and the numerical aperture of the objective lens can be controlled. be able to.

In the above-mentioned optical recording / reproducing apparatus, the hologram element has, for example, a plurality of steps formed on a substrate that transmits light, and the optical path length of each step is the first.
Is substantially equal to the wavelength of the laser light. As a result, the hologram element does not act as an optical diffraction element for the first laser light, but acts as an optical diffraction element only for the second laser light.

[0031]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows an example of an optical head to which the present invention is applied.
Shown in The optical head 1 includes two types of optical recording media 2
An optical head corresponding to No. 3. Here, the thickness t1 of the light transmitting layer 2c from the light incident surface 2a of the one optical recording medium 2 to the information recording surface 2b and the light incident surface 3 of the other optical recording medium 3
The thickness is different from the thickness t2 of the light transmitting layer 3c from a to the information recording surface 3b.

In the following description, the thin light transmitting layer 2c will be described.
Is referred to as a first optical recording medium 2,
The optical recording medium 3 having the thick light transmitting layer 3c is referred to as a second optical recording medium 3. However, the first optical recording medium 2 and the second
When it is not necessary to distinguish the optical recording medium 3 from the optical recording medium 3, these are simply referred to as an optical recording medium.

The optical head 1 shown in FIG.
1, a collimator lens 12, and a hologram element 13
And an objective lens 14. Although not shown, the objective lens 14 is mounted on a two-axis actuator. The optical head 1 drives the biaxial actuator during recording / reproduction on the optical recording medium to drive the objective lens 14.
The focusing servo and the tracking servo are performed by moving the.

The light emitting / receiving element 11 is a so-called laser coupler, and emits a first laser beam having a wavelength of 650 nm at the time of recording / reproducing on the first optical recording medium 2. Then, the first laser light is reflected by the first optical recording medium 2 to detect return light returned, and a signal necessary for recording and reproduction is detected from the return light.

The light emitting / receiving element 11 emits a second laser beam having a wavelength of 780 nm when recording / reproducing on / from the second optical recording medium 3. Then, the return light reflected by the second optical recording medium 3 and returned is detected, and a signal necessary for recording and reproduction is detected from the return light.

Here, the optical axis of the first laser light emitted from the light emitting / receiving element 11 and the optical axis of the second laser light may coincide with each other or may be slightly shifted. . Specifically, for example, when the laser light source that emits the first laser light and the laser light source that emits the second laser light are separately provided inside the light receiving and emitting element 11, the light of the first laser light The laser light sources are arranged close to each other so that the axis substantially coincides with the optical axis of the second laser light. Alternatively, the optical axis of the first laser light may be made to coincide with the optical axis of the second laser light using a half mirror or the like.

In the following description, when there is no need to distinguish between the first laser light and the second laser light,
These are collectively referred to simply as laser light. Here, the numerical value of the wavelength of the laser light is specifically described, but it goes without saying that the wavelength of the laser light is not limited to the above example in the present invention.

The collimator lens 12 includes a light receiving / emitting element 11
The laser light emitted from the light emitting / receiving element 11 is disposed on the optical axis of the laser light emitted from the light emitting / receiving element 11 and is made into parallel light. In addition,
In the optical head 1 shown in FIG. 1, the collimator lens 12 is disposed between the light receiving / emitting element 11 and the hologram element 13, but the collimator lens is not essential in the present invention, and the optical head is configured without using a collimator lens. It is also possible.

The hologram element 13 is arranged on the optical axis of the laser light collimated by the collimator lens 12. The hologram element 13 is designed not to exhibit a diffraction effect on the first laser light,
When the first laser light is incident, almost 100% of the first laser light is transmitted as it is. The hologram element 13 may slightly show a diffractive effect on the first laser light, but even in such a case, the proportion of the 0-order light is set to be larger than at least the first-order diffracted light.

The hologram element 13 has a diffractive effect on the second laser light. When the second laser light is incident, the hologram element 13 converts the second laser light to the first-order light from the zero-order light. Diffraction is performed so that the ratio of the folded light is increased.
At this time, the hologram element 13 diffracts the second laser light so that the first-order diffracted light becomes divergent light. That is, the 0th-order light transmitted through the hologram element 13 as it is is parallel light, whereas the 1st-order diffracted light diffracted by the hologram element 13 is divergent light.

The diffracted light includes not only the first-order diffracted light that becomes divergent light but also a −1st-order diffracted light that becomes convergent light. However, the hologram element 13 used here has a large proportion of the first-order diffracted light. , -1st order diffracted light is reduced. That is, the hologram element is designed so that the ratio of the first-order diffracted light becomes sufficiently large and the ratio of the 0-order light and the -1st-order diffracted light becomes sufficiently small when the second laser light is incident. .

The objective lens 14 emits light from the light receiving / emitting element 11, the collimator lens 12 and the hologram element 13
Is focused on the optical recording medium.
The objective lens 14 is designed to minimize the amount of spherical aberration when the first laser beam passes through the hologram element 13 and condenses the zero-order light on the first optical recording medium 2. Design it.

When recording and reproducing on the first optical recording medium 2 by the optical head 1 as described above, as shown in FIG.
The first laser beam L1 is emitted from the light receiving / emitting element 11. The first laser light L <b> 1 is collimated by the collimator lens 12 and enters the hologram element 13. Here, since the hologram element 13 does not exhibit a diffraction effect on the first laser light L1, the first laser light L1 incident on the hologram element 13 is substantially equal to one.
It is transmitted as it is by 00%. And the hologram element 13
The first laser beam L1 having passed through is incident on the objective lens 14, and is focused on the first optical recording medium 2 (more precisely, on the information recording surface 2b) by the objective lens 14.

The light converged on the first optical recording medium 2 by the objective lens 14 is reflected by the first optical recording medium 2 and returns. Then, the return light reflected by the first optical recording medium 2 and returned is returned to the objective lens 1 again.
4. The light enters the light receiving / emitting element 11 via the hologram element 13 and the collimator lens 12, and is received and detected by the light receiving / emitting element 11. Then, the light emitting and receiving element 11 detects a signal necessary for recording and reproduction from the return light.

When recording / reproducing the second optical recording medium 3 by the optical head 1, the second laser beam L2 is emitted from the light emitting / receiving element 11 as shown in FIG. The second laser light L2 is converted into parallel light by the collimator lens 12 and enters the hologram element 13. here,
The hologram element 13 has a diffraction effect on the second laser light L2, and the second laser light L2
2 is diffracted so that the ratio of the first-order diffracted light is larger than that of the zero-order light. In FIG. 3, only the first-order diffracted light is shown,
Illustration of other diffracted light including the next light is omitted.

Next, the first-order diffracted light is supplied to the objective lens 14.
Incident on. At this time, since the first-order diffracted light is divergent light, the fact that the first-order diffracted light enters the objective lens 14 is equivalent to the case where the divergent light emitted from the virtual light source P enters the objective lens 14. . And the objective lens 1
4 is incident on the second optical recording medium 3 by the objective lens 14 (more precisely, the information recording surface 3b).
Focused on).

The light collected on the second optical recording medium 3 by the objective lens 14 is reflected by the second optical recording medium 3 and returns. Then, the return light reflected back by the second optical recording medium 3 returns to the objective lens 1 again.
4. The light enters the light receiving / emitting element 11 via the hologram element 13 and the collimator lens 12, and is received and detected by the light receiving / emitting element 11. Then, the light emitting and receiving element 11 detects a signal necessary for recording and reproduction from the return light.

Next, the hologram element 13 used in the optical head 1 will be described in more detail with reference to FIGS. FIG. 4 is a plan view of the hologram element 13 viewed from the optical axis direction, and FIG.
FIG. 2 is an enlarged view with a portion cut away.

As shown in FIGS. 4 and 5, the hologram element 13 has a plurality of steps formed on a substrate that transmits light. These steps are formed in steps with approximately 4 to 7 steps as one unit, and are formed on the substrate surface so that they are repeated. In addition, these steps are formed concentrically on the substrate, and by forming these steps on the substrate surface,
The hologram element 13 has a diffraction effect.

In the hologram element 13, the height t3 of each step formed on the substrate surface is such that the optical path length at the step is substantially equal to the wavelength of the first laser beam L1. Specifically, for example, the first laser light L1
Is 650 nm and the refractive index of the substrate constituting the hologram element 13 is 1.6, the height t3 of each step is about 1
050 nm.

As described above, when the optical path length of each step formed on the substrate surface is substantially equal to the wavelength of the first laser beam L1, the hologram element 1 is placed on the optical path of the first laser beam L1.
Even if 3 is inserted, the hologram element 13 does not show a diffractive effect on the first laser beam L1, which is substantially the same as the case where a mere parallel plane plate is inserted. Therefore, when the first laser light L1 is incident on the hologram element 13, the first laser light L1 is transmitted almost 100% without being diffracted.

On the other hand, the optical path length of each step formed on the surface of the substrate is different from the wavelength of the second laser light L2.
When the hologram element 13 is inserted into the optical path of the laser beam L2, the hologram element 13 has a diffraction effect on the second laser beam L2. When the second laser beam L2 is incident, the hologram element 13
The second laser light L2 is diffracted so that the proportion of the first-order diffracted light is larger than that of the zero-order light.

As described above, the steps formed in the hologram element 13 are formed in steps with approximately 4 to 7 steps as one unit.
The first-order light diffraction efficiency when the second laser beam L2 is incident on the first laser beam L2 depends on the number of steps. For example, if the number of steps is four, the primary light diffraction efficiency is about 65%. If the number of steps is six, the primary light diffraction efficiency is about 93%.

When the optical head 1 performs recording and reproduction on the second optical recording medium 3, the second laser beam L2 emitted from the light receiving / emitting element 11 is diffracted by the hologram element 13 for the first time. The folded light is converged on the second optical recording medium 3 by the objective lens 14. That is, when recording / reproducing the second optical recording medium 3, the first-order diffracted light obtained by diffracting the second laser light L2 by the hologram element 13 is used.

Therefore, when the second laser beam L 2 is diffracted by the hologram element 13, the light intensity of the first-order diffracted light is set to a sufficient level for recording and reproducing on the second optical recording medium 3. Need to be kept. In particular,
The number of steps of the step formed on the hologram element 13 is adjusted so that when the second laser beam L2 is diffracted by the hologram element 13, at least the proportion of the first-order diffracted light is larger than the zero-order light. deep. More preferably, the first-order light diffraction efficiency is set to be 60% or more.

Then, as described above, the optical head 1 outputs the first laser light L
1 uses the zero-order light transmitted through the hologram element 13 as it is to perform recording / reproduction on the first optical recording medium 2 and the second laser light L2 emitted from the light receiving / emitting element 11
Performs recording and reproduction of the second optical recording medium 3 using the first-order diffracted light diffracted by the hologram element 13. Therefore, in the optical head 1, the correction of the spherical aberration corresponding to the first optical recording medium 2 and the correction of the spherical aberration corresponding to the second optical recording medium 3 can be performed independently.

Therefore, in the optical head 1, as described above, the objective lens 14 transmits the first-order laser light L 1 to the 0-th order light transmitted through the hologram element 13 as it is, as described above.
When the light is condensed on the optical recording medium 2, the amount of spherical aberration is designed to be minimized.

On the other hand, the spherical aberration generated when the first-order diffracted light obtained by diffracting the second laser light L 2 by the hologram element 13 is condensed on the second optical recording medium 3 is obtained by utilizing the diffraction by the hologram element 13. And correct. That is,
When diffracting the second laser light L <b> 2, the hologram element 13 causes the virtual light source P of the first-order diffracted light incident on the objective lens 14 to be located at a certain point on the optical axis of the objective lens 14. Is diffracted. At this time,
The position of the virtual light source P is set to a position where spherical aberration generated when the second laser beam L2 is condensed on the second optical recording medium 3 is corrected. This makes it possible to satisfactorily correct the spherical aberration that occurs when performing recording and reproduction on the second optical recording medium 3 using the second laser beam L2.

That is, in the optical head 1, the spherical aberration caused by the difference in the thickness of the light transmitting layers 2c and 3c of the two types of optical recording media 2 and 3 is canceled by utilizing the function of the hologram element 13. Like that. Thus, the spherical aberration caused by the difference in the thickness of the light transmitting layers 2c and 3c of the two types of optical recording media 2 and 3 can be canceled without using a special objective lens.

When spherical aberration is corrected using a hologram element, if the hologram element is also corrected by having a phase term, the hologram element is also moved when the objective lens is moved by a biaxial actuator. It is necessary to move the lens integrally. Furthermore, it is necessary to align the center of the objective lens and the center of the hologram element with high accuracy.

However, in the hologram element 13 of the optical head 1, the parallel incident light is
Only the function of converting into a light beam diverging from one point on the optical axis of the hologram element 13 is used, and the operation of the hologram element 13 does not include the phase term. In other words, the hologram element 1
In No. 3, the spherical aberration is corrected only by converting the parallel incident light into a light beam diverging from one point on the optical axis of the objective lens 14 without using the phase term.

In such a hologram element 13, even if the relative positional relationship between the hologram element 13 and the objective lens 14 is slightly deviated, an aberration that cannot be used is not generated.
Therefore, there is an advantage that the initial alignment accuracy is greatly relaxed as compared with the case where a hologram element having a phase term is used.

In such a hologram element 13, when the objective lens 14 is moved by a two-axis actuator, the hologram element 13 is
It is not necessary to perform the moving operation together. Therefore, it becomes possible to arrange the hologram element 14 on the fixed part side,
The degree of freedom in design increases. As a result, for example, it is possible to further reduce the thickness of the optical recording / reproducing apparatus on which the optical head 1 is mounted.

Further, the hologram element 13 is connected to the objective lens 1
Since it is not necessary to perform the moving operation together with the hologram element 4, it is not necessary to mount the hologram element 13 on the biaxial actuator. Therefore, the weight of the member moved and operated by the two-axis actuator can be reduced. This is very preferable for operating the two-axis actuator at high speed.

The hologram element 13 used in the optical head 1 is used to diffract the second laser light L2.
The second laser light L2 may be diffracted so that a part of the off-axis light of the first-order diffracted light does not enter the objective lens 14.

Thus, the first optical recording medium 2 has the first
It is possible to change the numerical aperture when condensing the laser light L1 by the objective lens 14 and the numerical aperture when condensing the second laser light L2 on the second optical recording medium 3 by the objective lens 14. it can.

For example, when the first laser beam L 1 is focused on the first optical recording medium 2 by the objective lens 14, the numerical aperture is 0.65, and the second laser beam L 1 is focused on the second optical recording medium 3. It is assumed that the numerical aperture when condensing the laser beam L2 by the objective lens 14 is to be 0.45.

In this case, the objective lens 14 is designed so that the numerical aperture NA = 0.65 when the 0th-order light of the first laser beam L1 transmitted through the hologram element 13 is incident as it is. . If the objective lens 14 is designed in this manner, the first laser light L
When 1 is condensed by the objective lens 14, the numerical aperture NA =
0.65.

On the other hand, when diffracting the second laser beam L2, the hologram element 13 diffracts the second laser beam L2 so that a part of off-axis rays of the first-order diffracted beam does not enter the objective lens 14. Let it be done. More specifically,
As shown in FIG. 6, when the second laser light L2 is incident, the hologram element 13 emits only the light beam corresponding to the numerical aperture NA = 0.45 out of the first-order diffracted light into the objective lens 14
The light outside the entrance pupil of the objective lens 14 is diffracted toward the outside of the entrance pupil of the objective lens 14. It is to be noted that the light distribution can be easily realized by adjusting the pattern of the steps formed on the hologram element 13.

Then, as described above, the second laser light L
2 out of the first-order diffracted light diffracted by the hologram element 13, only the light flux corresponding to the numerical aperture NA = 0.45,
When the first-order diffracted light is condensed on the second optical recording medium 3 by the objective lens 14, the numerical aperture NA is set to 0.45 by allowing the light to enter the entrance pupil of the objective lens 14.

As described above, when the second laser beam L 2 is diffracted by the hologram element 13, a part of the off-axis ray of the first-order diffracted light is prevented from entering the objective lens 14, so that the hologram element 13 Can be made to work substantially equivalently to the aperture limiting filter. In other words, by using such a hologram element 13, it is possible to realize switching of the numerical aperture of the objective lens 14 without using an aperture limiting filter.

However, in the optical head according to the present invention, the numerical aperture of the objective lens may be switched using an aperture limiting filter. FIGS. 7 and 8 show examples of an optical head using an aperture limiting filter. In the optical head 20 shown in FIGS. 7 and 8, members having the same configuration as the optical head 1 shown in FIG. 1 are denoted by the same reference numerals as those of the optical head 1 shown in FIG. Description is omitted.

In the optical head 20 shown in FIGS. 7 and 8,
An aperture limiting filter 21 is attached to a surface of the collimator lens 12 on the light receiving / emitting element 11 side. The aperture limiting filter 21 is an optical filter that performs different functions according to the difference in the wavelength of light. The aperture limiting filter 21 transmits almost 100% of the first laser beam L1 as shown in FIG. 7, but does not transmit the second laser beam L2 as shown in FIG. Part of the external light is prevented from entering the objective lens 14.
That is, the aperture limiting filter 21 functions as an aperture that limits the light diameter of the second laser light L2.

Here, for example, when the first laser beam L1 is focused on the first optical recording medium 2 by the objective lens 14, the numerical aperture is 0.65, and the first laser beam L1 is focused on the second optical recording medium 3. Second
It is assumed that the numerical aperture when condensing the laser beam L2 by the objective lens 14 is 0.45.

In this case, as shown in FIG. 7, when the first laser beam L1 that has passed almost 100% through the aperture limiting filter 21 is incident, the objective lens 14 has a numerical aperture NA = 0.65. It is designed to be. If the objective lens 14 is designed in this way, when the first laser beam L1 is converged on the first optical recording medium 2 by the objective lens 14, the numerical aperture NA becomes 0.65.

On the other hand, as shown in FIG. 8, when the second laser beam L 2 is incident, the aperture limiting filter 21 controls the second laser beam L 2 so that a part of the off-axis ray does not enter the objective lens 14.
Part of the laser beam L2 of FIG. More specifically, the aperture limiting filter 21 outputs the second laser light L2
Is incident, only the luminous flux corresponding to the numerical aperture NA = 0.45 of the second laser light L2 is transmitted, and light outside of the second laser light L2 is shielded.

In this way, the second laser light L
2, only the light beam corresponding to the numerical aperture NA = 0.45 enters the entrance pupil of the objective lens 14,
When the second laser beam L2 is focused on the second optical recording medium 3 by the objective lens 14, the numerical aperture NA becomes 0.45.

Next, an optical recording / reproducing apparatus according to the present invention will be described. An optical recording / reproducing apparatus according to the present invention includes an optical head corresponding to two types of optical recording media having different thicknesses of a light transmission layer from a light incident surface to an information recording surface, thereby providing the two types of optical recording media. Recording and reproduction can be performed. FIG. 9 shows a configuration example of such an optical recording / reproducing apparatus according to the present invention.

An optical recording / reproducing apparatus 30 shown in FIG. 9 comprises a spindle motor 32 for rotating and driving an optical recording medium 31, an optical head 33 to which the present invention is applied, a feed motor 34 for moving the optical head 33, and a predetermined motor. , A modulation / demodulation circuit 35 for performing the modulation / demodulation processing, a servo control circuit 36 for performing servo control and the like of the optical head 33, and a system controller 37 for controlling the entire system.

The spindle motor 32 is driven and controlled by a servo control circuit 36, and is driven to rotate at a predetermined rotation speed. That is, the optical recording medium 31 to be recorded and reproduced
The spindle motor 3 is chucked by the spindle motor 32 and driven and controlled by the servo control circuit 36.
2 drives at a predetermined number of rotations.

When recording / reproducing an information signal, the optical head 33 irradiates a laser beam to the optical recording medium 31 which is driven to rotate, and detects the return light. This optical head 3
Reference numeral 3 denotes an optical head (for example, the optical head 1 or the optical head 20) to which the present invention is applied, and is adapted to correspond to two types of optical recording media having different thicknesses of the light transmitting layer. .

The optical head 33 is connected to a modulation / demodulation circuit 35. When the information signal is reproduced, the optical head 33 is rotated by the optical recording medium 31.
Is irradiated with a laser beam, a reproduced signal is detected from the returned light, and the reproduced signal is supplied to the modulation / demodulation circuit 35.

When recording an information signal, a recording signal input from an external circuit 38 and subjected to a predetermined modulation processing by a modulation / demodulation circuit 35 is supplied to an optical head 33. The optical head 33 irradiates the optical recording medium 31 with a laser beam based on the recording signal supplied from the modulation / demodulation circuit 35, and records an information signal on the optical recording medium 31.

The optical head 33 is also connected to a servo control circuit 36. Then, at the time of recording / reproducing the information signal, a focusing servo signal and a tracking servo signal are generated from the return light reflected and returned by the optical recording medium 31 which is driven to rotate, and these servo signals are supplied to the servo control circuit 36. I do.

The modem 35 is connected to a system controller 37 and an external circuit 38. When the information signal is recorded on the optical recording medium 31, the modulation / demodulation circuit 35 receives a recording signal to be recorded on the optical recording medium 31 from the external circuit 38 under the control of the system controller 37. A predetermined modulation process is performed on the signal.
The recording signal modulated by the modulation / demodulation circuit 35 is supplied to the optical head 33.

When the information signal is reproduced from the optical recording medium 31, the modulation / demodulation circuit 35 receives the reproduced signal reproduced from the optical recording medium 31 from the optical head 33 under the control of the system controller 37. The reproduction signal is subjected to a predetermined demodulation process. Then, the reproduced signal demodulated by the modulation / demodulation circuit 35 is output from the modulation / demodulation circuit 35 to the external circuit 38.

The feed motor 34 is for sending the optical head 33 to a predetermined position on the optical recording medium 31 when recording and reproducing information signals, and is driven based on a control signal from a servo control circuit 36. Is done. That is, the feed motor 34 is connected to the servo control circuit 36 and is controlled by the servo control circuit 36.

The servo control circuit 36 controls the feed motor 34 so that the optical head 33 is sent to a predetermined position facing the optical recording medium 31 under the control of the system controller 37. Also, the servo control circuit 36
It is also connected to the spindle motor 32, and controls the operation of the spindle motor 36 under the control of the system controller 37. That is, the servo control circuit 36
The spindle motor 32 drives the optical recording medium 31 to rotate at a predetermined number of revolutions when recording and reproducing information signals.
Control.

The servo control circuit 36 is also connected to the optical head 33, receives a servo signal from the optical head 33 at the time of recording / reproducing an information signal, and controls the focusing servo of the optical head 33 based on the servo signal. And controls the tracking servo. The focusing servo and the tracking servo of the optical head 33 are performed, for example, by mounting the objective lens of the optical head 33 on a two-axis actuator and finely moving the objective lens by the two-axis actuator.

In the optical recording / reproducing apparatus 30 as described above, since the optical head 33 to which the present invention is applied is employed as the optical head 33, the optical recording / reproducing apparatus 30 can cope with two types of optical recording media having different light transmitting layers. Can be.

[0092]

As described in detail above, the optical head according to the present invention can easily correct each spherical aberration occurring at the time of recording / reproducing on each optical recording medium while supporting two types of optical recording media. . Therefore, according to the present invention, it is possible to provide an optical head and an optical recording / reproducing apparatus which can be commonly used for two types of optical recording media and which are easy to manufacture.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an optical head to which the present invention has been applied.

FIG. 2 is a diagram showing an optical path of a first laser beam when recording and reproducing on a first optical recording medium by the optical head shown in FIG. 1;

FIG. 3 is a diagram showing an optical path of a second laser beam when recording and reproducing on a second optical recording medium by the optical head shown in FIG. 1;

FIG. 4 is a diagram illustrating an example of a hologram element used in an optical head to which the present invention is applied, and is a plan view of the hologram element as viewed from an optical axis direction.

FIG. 5 is a diagram illustrating an example of a hologram element used in the optical head to which the present invention is applied, and is a perspective view illustrating a part of the hologram element in a cutaway manner;

FIG. 6 is a diagram showing an optical path of a second laser beam when the second laser beam is diffracted by the hologram element so that a part of the off-axis ray of the first-order diffracted light does not enter the objective lens. .

FIG. 7 is a diagram showing an optical path of a first laser beam when performing recording and reproduction on a first optical recording medium in an example in which an aperture limiting filter is added to an optical head to which the present invention is applied.

FIG. 8 is a diagram showing an optical path of a second laser beam when performing recording and reproduction on a second optical recording medium in an example in which an aperture limiting filter is added to an optical head to which the present invention is applied.

FIG. 9 is a diagram showing a configuration example of an optical recording / reproducing apparatus to which the present invention is applied.

[Explanation of symbols]

Reference Signs List 1 optical head, 2, 3 optical recording medium, 11 light receiving / emitting element, 12 collimator lens, 13 hologram element, 14 objective lens

Claims (8)

[Claims] 1. An optical head corresponding to two types of optical recording media having different thicknesses of a light transmission layer from a light incident surface to an information recording surface, wherein at the time of recording and / or reproduction of one of the optical recording media, A light source that emits a first laser light having a predetermined wavelength and emits a second laser light having a different wavelength from the first laser light during recording and / or reproduction of the other optical recording medium; The laser beam does not show a diffractive action, or even if it shows a diffractive action, it is diffracted so that the proportion of the 0th-order light is larger than the 1st-order diffracted light, while the 0th-order light is emitted for the second laser light. A hologram element for diffracting the light so that the proportion of the first-order diffracted light increases, and an objective lens for condensing the laser light emitted from the light source and passing through the hologram element onto an optical recording medium. Recording and / or playback In this case, the first-order light emitted from the light source and transmitted through the hologram element as it is is focused on the optical recording medium by the objective lens, and the recording and / or reproduction of the other optical recording medium is performed. An optical head for converging a first-order diffracted light obtained by diffracting a second laser beam emitted from a light source by a hologram element onto an optical recording medium by an objective lens. 2. The hologram element according to claim 1, wherein, when diffracting the second laser light, the virtual light source of the first-order diffracted light incident on the objective lens is located at a certain point on the optical axis of the objective lens. 2. The optical head according to claim 1, wherein the second laser beam is diffracted. 3. The hologram element, when diffracting the second laser light, diffracts the second laser light so that a part of off-axis rays of the first-order diffracted light does not enter the objective lens. The optical head according to claim 1, wherein: 4. The hologram element according to claim 1, wherein a plurality of steps are formed on a substrate that transmits light, and an optical path length of each step is substantially equal to a wavelength of the first laser light. Item 7. The optical head according to Item 1. 5. An optical recording / reproducing apparatus comprising an optical head corresponding to two types of optical recording media having different thicknesses of a light transmitting layer from a light incident surface to an information recording surface, wherein the optical head comprises: Emits a first laser beam of a predetermined wavelength at the time of recording and / or reproduction of the optical recording medium, and has a wavelength different from the first laser light at the time of recording and / or reproduction of the other optical recording medium. A light source that emits the second laser light, and diffracts the first laser light so as not to exhibit a diffractive effect, or even if exhibiting a diffractive effect, so that the proportion of the 0th-order light is greater than the 1st-order diffracted light; On the other hand, a hologram element for diffracting the second laser light so that the proportion of the first-order diffracted light is larger than the zero-order light, and the laser light emitted from the light source and passing through the hologram element is focused on the optical recording medium. With objective lens When performing recording and / or reproduction on one optical recording medium, the first-order laser light emitted from the light source and transmitted through the hologram element as it is is focused on the optical recording medium by an objective lens. When performing recording and / or reproduction on the other optical recording medium, the first-order diffracted light obtained by diffracting the second laser light emitted from the light source by the hologram element is focused on the optical recording medium by the objective lens. An optical recording / reproducing apparatus characterized by the above-mentioned. 6. The hologram element according to claim 1, wherein, when diffracting the second laser beam, the virtual light source of the first-order diffracted light incident on the objective lens is located at a certain point on the optical axis of the objective lens. The optical recording / reproducing apparatus according to claim 5, wherein the second laser beam is diffracted. 7. The hologram element, when diffracting the second laser light, diffracts the second laser light so that a part of off-axis rays of the first-order diffracted light does not enter the objective lens. The optical recording / reproducing apparatus according to claim 5, wherein: 8. The hologram element according to claim 1, wherein a plurality of steps are formed on a substrate that transmits light, and an optical path length of each step is substantially equal to a wavelength of the first laser beam. Item 6. The optical recording / reproducing apparatus according to Item 5.