JP2001101694A - Optical head and aberration control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform good information signal writing/reading with respect to an optical recording medium even when aberration is generated by the manufacturing error, the secular change or the temperature change of each optical component or the optical recording medium. SOLUTION: As luminous flux emitting means for emitting plural luminous fluxes different in the amount of aberration to an optical disk 50, a light source 21, a diffraction optical element 23 and an objective lens 25 are included. As signal quality detecting means for detecting the quality of a reproducing signal obtained from the optical disk 50 by each luminous flux, a photodetector 28, and a control circuit are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for writing or reading an information signal to or from an optical recording medium, and an aberration control method for controlling the aberration of a light beam emitted from the optical head or the like.

[0002]

2. Description of the Related Art Hitherto, an optical head for writing or reading an information signal on or from an optical recording medium such as an optical disk has been proposed. The optical head includes a light source such as a semiconductor laser, and irradiates a light beam emitted from the light source to an optical recording medium. Then, an information signal is written to the optical recording medium by a light beam applied to the optical recording medium, or an information signal is read from the optical recording medium by detecting a reflected light beam of the light beam applied to the optical recording medium. .

In such an optical head, a light beam irradiated on an optical recording medium is focused on the optical recording medium to a state close to a so-called diffraction limit. In order to condense the light flux to such a state, it is necessary to sufficiently correct optical aberrations.

In conventional optical heads, even if aberrations occur due to manufacturing errors, changes over time, changes in temperature, etc. of the optical components and optical recording medium constituting the optical head, care must be taken so that no inconvenience occurs as a whole. The system has been designed.

[0005]

By the way, in the above-mentioned optical head, in order to cope with an optical recording medium having a higher recording density, the manufacturing errors of each optical component and the optical recording medium constituting the optical head, and the like. It is necessary to reduce the allowable value of aberration generated due to aging, temperature change, and the like. If the allowable value of the aberration is reduced, it becomes difficult to manufacture each optical component and the optical recording medium, and the possibility that the aberration remains in the optical head increases.

[0006] If aberration remains in the optical head in this way, particularly when an optical recording medium having a high recording density is used, good writing of information signals or
Reading cannot be performed.

Accordingly, the present invention has been proposed in view of the above situation, and aberrations are produced due to manufacturing errors, aging changes, temperature changes, and the like of optical components and optical recording media constituting an optical head. Another object of the present invention is to provide an optical head capable of writing or reading an information signal to or from the optical recording medium.

Further, the present invention relates to an optical head and the like,
It is an object of the present invention to provide an aberration control method for preventing an aberration caused by a manufacturing error, a temporal change, a temperature change, or the like of an optical component from affecting an optical characteristic.

[0009]

In order to solve the above-mentioned problems, an optical head according to the present invention comprises a light beam emitting means for emitting a plurality of light beams having different amounts of aberration to an optical recording medium;
Signal quality detecting means for detecting the quality of a reproduction signal obtained from the optical recording medium by each of the light beams.

An optical head according to the present invention comprises a light source that emits a light beam emitted to an optical recording medium, a liquid crystal element that changes the amount of aberration of the light beam over time, and an optical head obtained from the optical recording medium using the light beam. Signal quality detecting means for detecting the quality of the reproduced signal to be obtained.

In the aberration control method according to the present invention, the optical recording medium is irradiated with a plurality of light beams having different amounts of aberration, a reproduction signal is obtained from the optical recording medium by each of the light beams, and the quality of the obtained reproduction signal is reduced. It is characterized by detecting.

Further, in the aberration control method according to the present invention, the amount of aberration of a light beam emitted to an optical recording medium is changed with time, and the quality of a reproduction signal obtained from the optical recording medium is detected by the light beam. It is characterized by the following.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, a description will be given of a case where the present invention is applied to an optical head of an optical disk device that records and reproduces information on a rewritable optical disk. However, the present invention is not limited to this embodiment. Instead, the present invention can be applied to an optical head of any type of recording / reproducing apparatus using an optical recording medium in which information signals are recorded or reproduced using light, such as a read-only optical disk or a magneto-optical disk. In addition, the aberration control method according to the present invention is implemented by operating the optical head.

As shown in FIG. 1, the optical disk device having the optical head according to the present invention includes a spindle motor 2 for rotating the optical disk 50. The optical head 1 according to the present invention writes a signal on the optical disc 50 that is rotated by the spindle motor 2, or
The signal written on the optical disk 50 is read. The optical disk device also includes a thread motor 4 for moving the optical head 1 to an arbitrary position on the optical disk 50, a signal to be written on the optical disk 50 by the optical head 1, or a signal to be written on the optical disk 50 by the optical head 1.
A recording / reproducing circuit 5 for generating a reproduced signal based on a signal read from the optical disk 1, an address reproducing circuit 12 for reproducing an address signal on the optical disk 50 based on a signal read from the optical disk 50 by the optical head 1, and The entire optical disc apparatus, such as a focus servo signal and a tracking servo signal based on a signal read from the optical disc 50 by the optical head 1, a signal for positioning the optical head 1, a signal for controlling the rotation of the spindle motor 2, and the like. Is provided with a control circuit 6 for generating a control signal for controlling the operation of.

The spindle motor 2 is driven by a spindle driver 7 operated based on a control signal supplied from a control circuit 6, and rotates the optical disk 50 at a predetermined rotation speed.

The sled motor 4 is driven by a sled driver 8 which is operated based on a control signal supplied from a control circuit 6, and drives the optical head 1 to drive the optical disk 5
It is moved to a predetermined position in the radial direction above zero.

The optical head 1 includes a light source such as a semiconductor laser. The laser light emitted from the light source is condensed by an objective lens.
The information signal is written on the optical disk 50 or the information signal written on the optical disk 50 is read out by irradiating the signal recording surface 51 of the optical disk. At this time,
The objective lens is moved by the objective lens driver 9 which is operated based on the focus error signal and the tracking error signal supplied from the control circuit 6 in two directions, ie, the direction in which the objective lens approaches and separates from the optical disk 50 and the radial direction of the optical disk 50. Then, focus servo and tracking servo are performed.

The recording / reproducing circuit 5 temporarily stores a recording signal input from an external device such as a host computer in a memory 10, sequentially reads out the recording signals from the memory 10, and performs interleave and error correction on the recording signals. A signal to be written to the optical disk 50 is generated by adding a code or the like. Then, the recording / reproducing circuit 5 outputs a signal to be written to the optical disk 50 to the laser driver 11.

The recording / reproducing circuit 5 generates a reproduced signal by performing error correction processing, interleaving, and the like on the signal read from the optical disk 50 by the optical head 1. The reproduced signal generated by the recording / reproducing circuit 5 is output to an external circuit such as a host computer.

The address reproducing circuit 12 reproduces an address signal on the optical disk 50 based on the signal read from the optical disk 50 by the optical head 1 and sends the reproduced signal to the control circuit 6. The guide grooves provided along the recording tracks on the optical disk 50 adopt a so-called wobble method meandering with a small amplitude. This meandering method is obtained by frequency-modulating an address uniquely determined on the optical disk. This meandering appears as a wobble signal on a so-called push-pull signal. Therefore, address information on the optical disk can be obtained by frequency-demodulating the wobble signal.

The control circuit 6 generates a focus servo signal and a tracking servo signal from the signal read from the optical disk 50 by the optical head 1, and supplies the focus servo signal and the tracking servo signal to the objective lens driver 11. . The control circuit 6 generates a signal for positioning the optical head 1 from the signal read from the optical disk 50 by the optical head 1 and supplies the signal to the thread driver 8. A signal for performing the rotation control is generated, and this signal is supplied to the spindle driver 7.

When an information signal is recorded on the optical disk 50 by the optical disk device configured as described above, first, the optical disk 50 is rotated by the spindle motor 2 and the recording / reproducing circuit 5 sends the information to the host computer. The recording signal is input from an external device such as.

When a recording signal is input to the recording / reproducing circuit 5, the recording / reproducing circuit 5 outputs a signal to the optical disk 5 based on the recording signal.
A signal to be written to 0 is generated, and this signal is output to the laser driver 11. The laser driver 11 modulates the intensity of the laser light emitted from the light source of the optical head 1 according to this signal.

The optical head 1 is moved by a thread motor 4 to a predetermined position on the optical disk 50 in the radial direction of the optical disk 50. Then, the optical head 1 focuses the laser light intensity-modulated by the laser driver 11 by the objective lens, and irradiates the focused light spot onto the signal recording surface 51 of the optical disk 50. This allows
A predetermined information signal is written at a predetermined position on the signal recording surface 51 of the optical disk 50.

The optical head 1 is mounted on the optical disk 5.
The return light reflected by the 0 signal recording surface 51 is received by the photodetector. The return light received by the photodetector is converted into an electric signal and supplied to the control circuit 6.
The control circuit 6 generates a focus error signal and a tracking error signal based on the signal supplied from the photodetector of the optical head 1 and supplies the generated signal to the objective lens driver 9. Then, based on the focus error signal and the tracking error signal supplied from the control circuit 6, the objective lens driver 9 moves the objective lens of the optical head 1 toward and away from the optical disk 50 and two axes in the radial direction of the optical disk 50. The focus servo and the tracking servo are performed by moving in the directions.

When an information signal is reproduced from the optical disk 50 by the optical disk device, first, the optical disk 50 is rotated by the spindle motor 2 and the optical head 1 is moved to a predetermined position on the optical disk 50 by the thread motor 4. Is moved to the position.

When the optical head 1 is moved to a predetermined position on the optical disk 50, a laser beam having a predetermined intensity is emitted from the light source of the optical head 1. The laser light emitted from the light source of the optical head 1 is condensed by an objective lens and is irradiated to a predetermined position on the signal recording surface 51 of the optical disk 50.

The laser light applied to a predetermined position on the signal recording surface 51 of the optical disk 50 is modulated according to the information signal written at this position, and contains a signal component. The light is reflected by the recording surface 51. The return light reflected by the signal recording surface 51 of the optical disk 50 is received by the photodetector of the optical head 1,
The signal is converted into an electric signal and supplied to the recording / reproducing circuit 5.

The recording / reproducing circuit 5 generates a reproduced signal based on the signal supplied from the photodetector of the optical head 1.
Then, the reproduced signal generated by the recording / reproducing circuit 5 is
It is output to an external circuit such as a host computer.

The signal received by the photodetector of the optical head 1 and converted into an electric signal is supplied to the control circuit 6. The control circuit 6 generates a focus servo signal or a tracking servo signal based on the signal supplied from the photodetector of the optical head 1 and supplies the generated signal to the objective lens driver 9. Then, the objective lens driver 9 controls the control circuit 6
The objective lens of the optical head 1 based on the focus error signal and the tracking error signal supplied from
The focus servo and the tracking servo are performed by moving the optical disk 50 in two axial directions, that is, the direction in which the optical disk 50 comes into contact with the optical disk 50 and the radial direction of the optical disk 50.

As described above, the optical disk apparatus records and reproduces a signal on and from the optical disk 50 while performing focus servo and tracking servo. Is always connected to the signal recording surface 51 of the optical disk 50, and the light spot is made to appropriately follow the recording track of the optical disk 50 so that the signal can be recorded and reproduced appropriately.

As shown in FIG. 2, in the focus servo portion of the optical disk device, that is, in the focus servo system circuit, first, in the focus error signal generation circuit 15 of the control circuit 6, the photodetector of the optical head 1 is detected. A focus error signal is generated based on the signal supplied from the CPU. Then, the focus error signal is supplied to the arithmetic unit 16, and the arithmetic unit 16
The amount of deviation from the target value supplied from the target value control circuit 17 is calculated. The signal indicating the amount of deviation between the focus error signal calculated by the calculator 16 and the target value is supplied to the objective lens driver 9 via the phase compensation circuit 18.

Then, based on the signal indicating the amount of deviation between the focus error signal and the target value, the objective lens driver 9 moves the focus error signal generated by the focus error signal generation circuit 15 in a direction approaching the target value. The objective lens of the optical head 1 is moved.

As described above, the focus servo system of the optical disc apparatus is a closed loop in which the focus error signal generated based on the signal received by the photodetector of the optical head 1 is controlled to be equal to the target value. It has become. That is, the focus servo system feeds back a signal indicating the amount of deviation between the focus error signal and the target value to the optical head 1 to move the objective lens,
The focus error signal is controlled to be equal to the target value.

In this focus servo system, the target value supplied from the target value control circuit 17 is normally set to zero. Therefore, in this case, the focus error signal generated by the focus error signal generation circuit 15 is supplied to the objective lens driver 9 via the phase compensation circuit 18 as it is.

However, when the optical disk 50 is a so-called land / groove type optical disk which is configured to record a signal on both a land portion and a groove portion, a signal is recorded on a land. Different target values may be set depending on whether a signal is recorded in a groove. In this case, a signal indicating the amount of deviation between the focus error signal and each of the target values is supplied to the objective lens driver 9 via the phase compensation circuit 18.

Next, the optical head 1 provided in the optical disk device has an irradiation optical system for emitting a plurality of light beams having different aberration amounts. That is, as shown in FIG. 3, the irradiation optical system includes a light source 21 for emitting laser light, a collimator lens 22 for converting the laser light emitted from the light source 21 into parallel light, And a diffractive optical element 23 for generating a plurality of light beams having different aberration amounts from the laser light converted into light. The irradiation optical system further includes a beam splitter 24 that bends the optical path of the laser light transmitted through the diffractive optical element 23, and condenses the laser light whose optical path is bent by the beam splitter 24 to form a condensed light spot. Lens 25 for irradiating the light onto the signal recording surface 51 of the optical disc 50.

The optical head 1 serves as a light receiving optical system, and a condensing lens 26 for converting reflected light reflected by the signal recording surface 51 of the optical disk 50 and transmitted through the objective lens 25 and the beam splitter 24 into convergent light. And a cylindrical lens 27 that causes astigmatism in the return light converged by the condenser lens 26, and a photodetector 2 that receives the return light transmitted through the cylindrical lens 27.
8 is provided.

The optical head 1 allows the optical disk 50
When reading the information signal recorded in the
Emits a laser beam having a predetermined intensity. The laser light emitted from the light source 21 is collimated by the collimator lens 22 and then enters the diffractive optical element 23.

As the diffractive optical element 23, a hologram can be used. This hologram is formed by using a plane wave as a reference light and using convergent light by an astigmatic convex lens or divergent light by an astigmatic concave lens as object light. Therefore, when a plane wave that has passed through the collimator lens 22 is incident on this hologram, the incident light is divided into 0-order light, which is the same plane wave as the incident wave, and convergent light by the convex lens used for forming the hologram, or divergent light by the concave lens The + 1st-order light and the + 1st-order light having the same wavefront are divided into three luminous fluxes: divergent light having a complex conjugate relationship or -1st-order light which is convergent light.

The 3 divided by the hologram in this way
When the light beam of the book enters the objective lens 25, the optical disk 5
On the 0 signal recording surface 51, three beam spots are formed. The +1 order light and the −1 order light are as shown in FIG.
The zero-order light is defocused in opposite directions. This defocus can be considered as a kind of aberration.

By the way, as shown in FIG. 5, as typical characteristics of the aberration of the light beam and the amplitude of the wobble signal, the amplitude of the wobble signal does not change even if the aberration increases in the positive direction or the negative direction. There is a property to decrease. The wobble signal amplitude due to the + 1st-order light having a positive defocus aberration with respect to the 0th-order light is I +, and the wobble signal amplitude due to the -1st-order light having a negative defocus aberration with respect to the 0th-order light is I. -
Assuming that ΔI = I + −I−, when ΔI is positive, FIG.
As shown in the figure, the zero-order light is negatively defocused and Δ
When I is negative, as shown in FIG. 7, the zero-order light is positively defocused. That is, ΔI is an error signal indicating the direction and amount of defocus of the zero-order light.

In this manner, highly accurate defocus detection that cannot be performed only by detecting the amplitude of the wobble signal due to the zero-order light can be performed by defocusing in opposite directions.
This is made possible by detecting the amplitude of the wobble signal using the primary light and the −1st light.

The amplitude of the 0th-order light wobble signal is I0, ΔI ′ = I0−I−−k (Ｉk is a constant), and ΔI ′ becomes 0 when the defocus amount of the 0th-order light is 0. If k is appropriately set as described above, when ΔI ′ is positive, the zero-order light is defocused negatively as shown in FIG.
When I 'is negative, as shown in FIG. 7, the zero-order light is positively defocused. That is, ΔI ′ is
The error signal indicates the direction and amount of defocus of the zero-order light.

Thus, in this optical head,
If at least two of the light beams split by the diffractive optical element are used, it is possible to detect the amount of aberration such as the amount of defocus for the zero-order light.

As the diffractive optical element 23, as shown in FIG. 8, an off-axis Fresnel zone plate (FZP) whose center is shifted from the optical axis can be used.

The Fresnel zone plate has a plurality of regions, as shown in FIG. 9, and, like a grating (diffraction grating), has a constant optical phase difference between transmitted lights in adjacent regions. I have. In the Fresnel zone plate, the divided shape of each region is concentric. The Fresnel zone plate has the same function as a lens, and outputs conjugate positive and negative diffracted light, like a grating. An off-axis Fresnel zone plate is obtained by cutting a part of the Fresnel zone plate off the center.

Further, in this optical head, the diffractive optical element can be formed by using liquid crystal as shown in FIG. That is, if a voltage is applied to a liquid crystal having electrodes concentrically divided in the same manner as the above-described Fresnel zone plate so that transmitted light has the same phase difference as transmitted light of the Fresnel zone plate, this liquid crystal becomes Acts the same as a Fresnel zone plate. Assuming that the phase difference of the transmitted light is approximately linear with the voltage, the voltage waveform may be similar to the phase difference shown in FIG. When using a liquid crystal, usually, a voltage is applied so that the phase difference of the transmitted light becomes zero, and the applied voltage is changed only when it is desired to detect the defocus aberration, and the transmitted light from the Fresnel zone plate is changed. A similar phase difference may be generated.

In the above-described embodiment, the diffractive optical element is used for detecting the defocus aberration, but the optical head according to the present invention is not limited to such a configuration. For example, it is possible to detect spherical aberration with high accuracy by generating light beams having different amounts of spherical aberration by the diffractive optical element.

By providing, for example, a diffractive optical element for producing diffracted light having spherical aberration in addition to the diffractive optical element for producing diffracted light having defocus aberration, each aberration can be detected with high accuracy. Alternatively, by providing a single diffractive optical element that forms both diffracted light having defocus aberration and diffracted light having, for example, spherical aberration, each aberration can be detected with high accuracy.

If the division of the liquid crystal area is made to correspond to a plurality of aberrations, it is possible to detect a plurality of aberrations by applying a voltage. That is, as shown in FIG. 11, in step st1, a voltage is applied so that ± first-order light having defocus aberration is formed by the liquid crystal, and defocus is detected. Next, in step st2, spherical aberration is detected. Thus, a plurality of aberrations can be detected in a time-division manner, for example, by applying a voltage so as to form ± first-order light having the above-mentioned shape and detecting spherical aberration.

Further, in the above embodiment, ±
Although the use of first-order diffracted light has been shown, the present invention
The aberration is detected with high accuracy by using not only the next diffracted light but also a plurality of light beams having different aberrations. That is, by applying a voltage to the liquid crystal through an electrode that divides the liquid crystal into an appropriate region, it is possible to form a plurality of arbitrary wavefronts. For example, coma caused by disk skew (tilt) is an aberration in which the wavefront is distorted in a three-dimensional curve. However, voltage must be applied by arranging liquid crystal electrodes so as to approximate a straight line to this curved surface. Accordingly, the transmitted light flux of the liquid crystal has a coma aberration within an approximate range.

By controlling the applied voltage to change the amount of aberration and generating different aberrations in a time-division manner and detecting the reproduced signal quality each time, it is possible to detect the coma aberration with high accuracy. it can.

In this case, the aberration of the transmitted light beam can be minimized by controlling the voltage applied to the liquid crystal itself. That is, as shown in FIGS. 5 to 7, the reproduced signal quality due to the aberration is often an even function with respect to the aberration. Therefore, as shown in FIG.
In step 3 and step st4, different aberrations are generated in a time-division manner, and the reproduced signal quality is detected each time, and step st5
Then, the reproduction signal qualities at different time points of the aberration generation amounts are compared, and if the quality difference becomes the same level, step st6
Thus, by giving an intermediate aberration, the best reproduced signal can be obtained. In this case, a coma aberration that cancels the coma aberration generated by the disk skew can be generated by the liquid crystal so that the influence of the disk skew does not occur.

In the case where the liquid crystal as described above is used, the type and amount of aberration can be changed in a time-division manner. , It is possible to perform highly accurate detection for each type of aberration.

[0056]

As described above, in the optical head and the aberration control method according to the present invention, a plurality of light beams having different amounts of aberration are applied to the optical recording medium, and a reproduction signal is obtained from the optical recording medium by each light beam. , The quality of the obtained reproduction signal is detected.

Alternatively, in the optical head and the aberration control method according to the present invention, the amount of aberration of the light beam applied to the optical recording medium is changed with time, and a reproduction signal is obtained from the optical recording medium by the light beam. The quality of the obtained reproduction signal is detected.

Therefore, in this optical head,
Various aberrations such as defocus, spherical aberration, and coma can be detected with high accuracy, and the aberrations can be corrected based on the detection results.

That is, according to the present invention, manufacturing errors, aging, and the like of each optical component and optical recording medium constituting the optical head are provided.
An object of the present invention is to provide an optical head that can write or read an information signal to or from an optical recording medium even when an aberration occurs due to a temperature change or the like.

Further, the present invention relates to an optical head or the like,
An object of the present invention is to provide an aberration control method for preventing an aberration caused by a manufacturing error, a temporal change, a temperature change, or the like of an optical component from affecting an optical characteristic.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical disk device configured using an optical head according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of a focus servo system circuit of the optical disk device.

FIG. 3 is a side view showing a configuration of the optical head.

FIG. 4 is a side view showing a state of aberration generated by a diffractive optical element in the optical head.

FIG. 5 is a graph showing a relationship between an aberration amount and a reproduction signal amplitude in the optical head.

FIG. 6 is a graph showing a state in which zero-order light is negatively defocused in the relationship between the amount of aberration and the reproduction signal amplitude.

FIG. 7 is a graph showing a state in which zero-order light is positively defocused in the relationship between the aberration amount and the reproduction signal amplitude.

FIG. 8 is a front view showing a configuration of a Fresnel zone plate which is a diffractive optical element.

FIG. 9 is a side view showing a configuration of a Fresnel zone plate which is a diffractive optical element.

FIG. 10 is a side view showing a configuration using liquid crystal as a diffractive optical element in the optical head.

FIG. 11 is a flowchart showing an aberration control method for defocus performed in the optical head.

FIG. 12 is a flowchart showing an aberration control method for various aberrations performed in the optical head.

[Explanation of symbols]

1 optical head, 21 light sources, 23 diffractive optical elements, 25
Objective lens, 28 photodetector, 50 optical disk, 51
Signal recording surface

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 7/005 G11B 7/005 Z 7/135 7/135 Z F Term (Reference) 2H049 AA02 AA43 AA51 AA57 AA66 CA01 CA15 CA20 2H087 KA13 NA01 PA01 PB01 RA42 RA46 UA09 2H088 EA48 HA02 HA06 HA22 HA24 HA28 MA20 5D090 AA01 CC04 CC16 DD03 FF11 GG03 HH01 LL02 5D119 AA36 BA01 EA02 EA03 EC01 EC04 JA08 JA09 JA43

Claims (12)

[Claims] 1. A light beam emitting device for emitting a plurality of light beams having different aberration amounts to an optical recording medium, and a signal quality detecting device for detecting the quality of a reproduction signal obtained from the optical recording medium by each of the light beams. An optical head, comprising: 2. An aberration correction control means for comparing a plurality of light beams based on the detected quality of the reproduced signal, and performing aberration correction control of an emitted light beam based on the comparison result. The optical head according to claim 1. 3. The optical head according to claim 1, wherein the light beam emitting means includes a diffractive optical element that generates a plurality of light beams having different amounts of aberration. 4. The optical head according to claim 3, wherein the diffractive optical element is a hologram element. 5. The optical head according to claim 3, wherein the diffractive optical element is a liquid crystal element. 6. The optical head according to claim 5, wherein the type of aberration is sequentially changed by a liquid crystal element. 7. A light source for emitting a light beam emitted to an optical recording medium, a liquid crystal element for changing the amount of aberration of the light beam with time, and detecting a quality of a reproduction signal obtained from the optical recording medium by the light beam. An optical head comprising: 8. An aberration correction control means for comparing the states of the light beams having different aberration amounts at different points in time based on the detected quality of the reproduced signal, and performing the aberration correction control of the emitted light beam based on the comparison result. The optical head according to claim 7, wherein the optical head is provided. 9. An aberration characterized by irradiating an optical recording medium with a plurality of light beams having different amounts of aberration, obtaining a reproduction signal from the optical recording medium with each of the light beams, and detecting the quality of the obtained reproduction signal. Control method. 10. A method for comparing a plurality of light beams based on a detected quality of a reproduced signal, and performing aberration correction control of a light beam irradiated on an optical recording medium based on a result of the comparison. Item 10. An aberration control method according to Item 9. 11. An aberration control method comprising: changing the amount of aberration of a light beam emitted to an optical recording medium with time, and detecting the quality of a reproduction signal obtained from the optical recording medium using the light beam. . 12. Based on the quality of the detected reproduction signal,
12. The aberration control method according to claim 11, wherein a comparison is made between different states of the aberration amount of the light beam at different time points, and the aberration correction control of the emitted light beam is performed based on the comparison result.