JPH0831001A - Optical head - Google Patents

Abstract

PURPOSE:To provide an optical head formed in such a manner that the distribution (side lobe) of the annular band-shaped light generated on the outside of a light spot is made small by diminishing the NA in the radial direction of an objective lens. CONSTITUTION:This optical head includes a semiconductor laser which supplies a light beam and the objective lens 23 which converges the light beam supplied from this semiconductor laser by passing the light beam through an aperture 51 and supplies the light beam to an optical disk 25. The shape in the opening 51 of the objective lens 23 is made elliptic and its major axis is approximately aligned to the circumferential direction of the optical disk 25 and its minor axis is approximately aligned to the radial direction of the information 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 used in, for example, an optical disk device.

[0002]

2. Description of the Related Art An optical head of this type is equipped with a semiconductor laser, and a laser beam emitted from this semiconductor laser is sent to an objective lens via an optical system. After the laser beam guided to this objective lens is converged,
Information is read by irradiating the optical disc as a spot to write information, or after being reflected from the optical disc, and again received by a photodetector via the optical system and photoelectrically converted. .

By the way, in recent years, for example, an optical disk drive device using an optical head has a tendency to increase its recording capacity. Therefore, the recording pits that generate the information signal are small and are recorded on the optical disc with high density. In order to accurately record such pits and to accurately read the recorded pits, the light spot supplied from the optical head must have a smaller diameter and higher quality. Therefore, as a method of reducing the light spot diameter, a method of increasing the numerical aperture (NA) of the objective lens is well known.

[0004]

However, in the prior art, as shown in FIG. 18, the aperture of the objective lens 101 is simply formed in a circular shape (radius w) to increase the aperture NA. As shown in FIGS. 19 and 20, the annular light distribution (side lobes) generated outside the central light spot becomes larger. this is,
This means that when the light spot follows a track on the disc, this ring zone is largely applied to the adjacent track.

For this reason, although very slight, there arises a disadvantage that an unnecessary signal is written in an adjacent track, or signals written in an adjacent track are simultaneously read (hereinafter, this phenomenon will occur). Called crosstalk between tracks.).

Although the above problem can be solved by increasing the distance between the tracks, recording at a high density becomes difficult. Therefore, an object of the present invention is to provide an optical head capable of reducing the distribution (side lobe) of annular light generated outside the light spot by reducing the NA in the radial direction.

[0007]

In order to solve the above-mentioned problems, a light beam supplying means for supplying a light beam and a light beam supplied from the light beam supplying means are passed through an opening to be converged to record information. An objective lens for supplying the medium is provided, and the shape of the opening of the objective lens is elliptical.

Further, it is provided with a light beam supplying means for supplying a light beam, and an objective lens for allowing the light beam supplied from the light beam supplying means to pass through the opening portion to be converged and to be supplied to the information recording medium. The opening of the objective lens has an elliptical shape, the major axis of which is substantially aligned with the circumferential direction of the information recording medium, and the minor axis of which is substantially aligned with the radial direction of the information recording medium.

Further, a light beam supplying means for supplying a light beam, an objective lens for allowing the light beam supplied from the light beam supplying means to pass through the opening portion and converge to be supplied to the information recording medium, and the objective lens. And a holding member for holding, the shape of the opening of the objective lens is elliptical, the opening is provided in the holding member, the major axis of the holding member substantially coincides with the circumferential direction of the information recording medium, The minor axis is substantially aligned with the radial direction of the information recording medium.

Further, a light beam supplying means for supplying a light beam, an objective lens for allowing the light beam supplied from the light beam supplying means to pass through an opening and converge to be supplied to an information recording medium, and the objective lens. A holding member for holding the holding member, a mounting portion provided on the holding member, and a plate-shaped member mounted on the mounting portion and forming the opening of the objective lens in an elliptical shape, and the length of the opening. The axis is substantially aligned with the circumferential direction of the information recording medium, and the minor axis is substantially aligned with the radial direction of the information recording medium.

[0011]

The opening of the objective lens is formed into an elliptical shape, the major axis of which is substantially aligned with the circumferential direction of the information recording medium and the minor axis of which is substantially aligned with the radial direction of the information recording medium. The NA in the radial direction is reduced to reduce the annular light distribution (side lobe) generated outside the light spot.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to an embodiment shown in FIGS. In the figure, reference numeral 1 denotes a semiconductor laser, and a collimator lens 2 and a beam splitter 3 are arranged in the optical path of a laser beam R emitted from the semiconductor laser 1. The beam splitter 3 reflects a part of the laser beam R, and a front photodetector 13 for monitoring the amount of light is provided in the optical path of the reflected laser beam R. Further, the beam splitter 3 reflects a part of the laser beam R reflected from the optical disc 25, as will be described later, and in the optical path of the reflected laser beam R, the ½ wavelength plate 7 and the focusing are provided. A lens 8, a polarization beam splitter 9, a front side photodetector 10 and a rear side photodetector 11 are arranged.

The front side photodetector 10 is placed a predetermined distance ahead of the position where the light beam focused by the converging lens 8 reaches the focus, and the rear side photodetector 11 is the same from the position where the light beam reaches the focus. It is placed a certain distance behind.
The front side photodetector 10 and the rear side photodetector 11 are respectively adjusted by an adjusting mechanism (not shown) in the optical axis direction and two directions in a plane orthogonal to the optical axis, that is, three directions in total, and then a fixing mechanism (not shown). Is fixed to the optical base 12.

Since all the above-mentioned optical components are fixed to the optical base 12, this portion is called a fixed optical system 15. On the other hand, a moving optical system 20 in FIG. 3 is provided with a raising mirror 16 for raising the laser beam R, an actuator 21 (shown in FIG. 4), and an objective lens 23. There is.

The objective lens 23 faces an optical disk 25 as an information storage medium. Then, the laser beam R emitted from the semiconductor laser 1 is converted into a parallel light flux by the collimator lens 2, and the beam splitter 3
Reach About 20% of the parallel light flux is reflected by the beam splitter 3 and enters the front photodetector 13 for monitoring the amount of light emitted from the semiconductor laser 1. The amount of light emitted from the semiconductor laser 1 is controlled based on the output of the front photodetector 13.

The laser beam R emitted from the fixed optical system 15 is guided to an optical system constructed on a linear monitor.
That is, the laser beam R has its optical path changed by 90 ° by the raising mirror 16, passes through the circular opening 22 provided in the actuator 21, and is incident on the objective lens 23.

The laser beam R is guided to the objective lens 23 and converged, and then is irradiated onto the optical disk 25 as a spot. The reflected light R ′ from the optical disc 25 travels backward in the above optical path and reaches the beam splitter 3. A part of the light flux is reflected by the beam splitter 3 and guided to the ½ wavelength plate 7. The polarization direction of the light flux is approximately 45 ° with the half-wave plate 7.
It rotates, and the parallel light flux is converted into a convergent light flux by the next converging lens 8. Thereafter, the light beam is split into approximately half by the polarization beam splitter 9, enters the front side photodetector 10 and the rear side photodetector 11, is converted into an electric signal, and is converted into a predetermined information signal by the objective lens 23. A focus error signal indicating the focus shift between the converged light spot and the optical disc 25 and a tracking error signal indicating the shift from the track on the optical disc 25 are obtained.

Next, the actuator 21 will be described. The objective lens 23 is fixed at a position separated from the center of inertia of the movable body 31 by a predetermined distance. An opening 51, which will be described later, is formed below the objective lens 23 and corresponds to an entrance diaphragm for the objective lens 23. The light flux is supplied to the objective lens 23 through the opening 51.
At the center of inertia of the movable body 31, there is provided a hinge 33 made of an elastic body whose rotation center coincides with the optical axis direction of the objective lens 23. One end 34 of the hinge 33 is fixed to the movable body 31 by means such as press fitting or adhesion. The other end 35 of the hinge 33 is fixed to the moving optical base system 38 by being supported by a fixing member 37 by parallel leaf springs 36a and 36b. The moving optical system base 38 is made of a magnetic material.

The movable body 21 is provided with a focus coil 39 at positions symmetrical to each other with respect to the center of inertia of the movable body 21.
a, 39b and tracking coils 40a, 40b are fixed. Here, the focus coils 39a, 3
9b is wound around the Y-axis direction. Further, two tracking coils 40a, 40b are wound around the X-axis direction as an axis, and focus coils 39a,
It is arranged outside 39b.

On the other hand, the movable optical system base 38 is provided with inner yokes 41a and 41b which are inserted inside the focus coils 39a and 39b with a constant gap maintained. The focus coils 39a and 39b and the tracking coil 4 are provided outside the inner yokes 41a and 41b.
Outer yokes 42a and 42b are provided in a protruding manner at positions facing the inner yokes 41a and 41b with the 0a and 40b interposed therebetween. Then, the inner yoke 4 of the outer yokes 42a and 42b
1a, 41b, the surface facing the permanent magnets 43a, 43
b is fixed. Therefore, the inner yoke 41a,
41b and outer yoke 42a, 42b and permanent magnet 43a,
A magnetic circuit is formed by 43b.

The gap between the permanent magnets 43a and 43b and the tracking coils 40a and 40b, the focus coils 39a and 39b, and the inner yokes 41a and 4b.
Vibration breathing bodies 44a and 44b are wholly disposed in a gap between the vibration breathing body 1b and 1b.

With this structure, the movable body 31 is moved in the Y-axis direction by the electromagnetic force associated with the energization control of the focus coils 39a and 39b, whereby focusing control is performed. In addition, the movable body 31 is moved by the electromagnetic force accompanying the energization control of the tracking coils 40a and 40b.
Is rotated around the Y-axis, and tracking control is thereby performed.

FIG. 5 shows the actuator 2 of the objective lens 23.
6 is a cross-sectional view taken along the line FF in FIG. 2, and FIG. 7 is a cross-sectional view taken along the line GG in FIG. The movable body 31 of the actuator 21 is provided with an opening 51 in the lower portion of the mounting portion of the objective lens 23. The opening 51 has an elliptical shape, and when the length of the major axis is w, the length of the minor axis is 0.8w.

The direction of the minor axis is the radial direction (radial direction) of the surface of the optical disk 25, and the direction of the major axis is the circumferential direction (tangential direction) of the surface of the optical disk 25.

The movable body 31 is formed by injection molding using a liquid crystal polymer resin as a material. Therefore, the opening 51 can be easily formed by processing the forming die into a predetermined elliptical shape in advance.

Next, a specific value of the ratio of the length of the minor axis to the length of the major axis of the elliptical opening 51 will be described. The NA in the radial direction is made smaller than the NA in the tangential direction by setting the elliptical opening 51 narrow in the radial direction with respect to the objective lens 23. Along with this, the spot diameter in the radial direction becomes large for the reason described later.

Therefore, the amplitude of the so-called push-pull signal from the group provided on the optical disk becomes extremely small. Therefore, in order to secure the amplitude of the push-pull signal above a certain level, the lower limit of the ratio of the length of the minor axis to the length of the major axis of the ellipse is about 0.4.

On the other hand, the upper limit of the ratio of the length of the minor axis to the length of the major axis of the elliptical shape can be said to be about 0.8. This is because if it exceeds 0.8, the effect of reducing the side rope, which is the object of the present proposal, is significantly reduced.

Next, the reading of information will be described. The diameter of the light spot narrowed down by the objective lens 23 is expressed by the following equation. φ = k. λ / NA (1) where φ: light spot diameter λ: wavelength of light NA: numerical aperture of objective lens k: constant determined by objective lens aperture condition and incident light intensity distribution , NA, the larger the spot diameter, the smaller the spot diameter, and more stable signal reproduction is possible even if pits are recorded with high density.

On the other hand, when the NA is increased, the strength of the ring zone is increased as shown in FIG. 20, which is disadvantageous in reducing the cross stroke between the tracks. On the other hand, when a circular aperture is set, the numerical aperture NA of the objective lens has a relationship of 2a = 2f · NA (2), where 2a is the aperture diameter on the incident side and f is the focal length of the objective lens.

Therefore, as described above, by adopting a configuration in which the shape of the opening 51 is an elliptical shape narrow in the radial direction, the NA peculiar to the objective lens is maintained in the tangential direction, so that high density recording is performed. It becomes possible to stably reproduce.

On the other hand, when viewed in the radial direction, since the NA is small, it is possible to reduce the unnecessary inter-track stroke by reducing the strength of the ring zone. Further, by adopting the above-mentioned configuration, it is possible to more stably perform high-density recording at the time of recording, and it is possible to avoid the disadvantage that a signal is erroneously recorded on an adjacent track.

The present invention is not limited to the above-mentioned embodiment, but may be constructed as shown in FIGS. In the figure, reference numeral 1 denotes a semiconductor laser, and a collimator lens 2 and a beam splitter 3 are arranged in the optical path of a laser beam R emitted from the semiconductor laser 1. The beam splitter 3 reflects a part of the laser beam R, and a front photodetector 13 for monitoring the amount of light is provided in the optical path of the reflected laser beam R. Further, the beam splitter 3 reflects a part of the laser beam R reflected from the optical disc 25, as will be described later, and in the optical path of the reflected laser beam R, the ½ wavelength plate 7 and the focusing are provided. A lens 8, a polarization beam splitter 9, a front side photodetector 10 and a rear side photodetector 11 are arranged.

The front side photodetector 10 is placed in front of the position where the light flux narrowed down by the converging lens 8 reaches the focal point by a predetermined distance, and the rear side photodetector 11 is the same from the position where the light flux reaches the focal point. It is placed a certain distance behind.
The front side photodetector 10 and the rear side photodetector 11 are respectively adjusted by an adjusting mechanism (not shown) in the optical axis direction and two directions in a plane orthogonal to the optical axis, that is, three directions in total, and then a fixing mechanism (not shown). Is fixed to the optical base 12.

Since all the above-mentioned optical components are fixed to the optical base 12, this portion is called a fixed optical system 15. On the other hand, a moving optical system 20 in FIG. 3 is provided with a raising mirror 16 for raising the laser beam R, an actuator 21, and an objective lens 23.

The objective lens 23 faces an optical disk 25 as an information storage medium. Then, the laser beam R emitted from the semiconductor laser 1 is converted into a parallel light flux by the collimator lens 2, and the beam splitter 3
Reach About 20% of the parallel light flux is reflected by the beam splitter 3 and enters the front photodetector 13 for monitoring the amount of light emitted from the semiconductor laser 1. The amount of light emitted from the semiconductor laser 1 is controlled based on the output of the front photodetector 13.

The laser beam R emitted from the fixed optical system 15 is guided to an optical system constructed on a linear monitor.
That is, the laser beam R has its optical path changed by 90 ° by the rising mirror 16, passes through an elliptic opening 62, which will be described later, provided in the actuator 21, and enters the objective lens 23.

The laser beam R is guided to the objective lens 23 and converged, and then is irradiated onto the optical disk 25 as a spot. The reflected light R ′ from the optical disc 25 travels backward in the above optical path and reaches the beam splitter 3. A part of the light flux is reflected by the beam splitter 3 and guided to the ½ wavelength plate 7. The polarization direction of the light flux is approximately 45 ° with the half-wave plate 7.
It rotates, and the parallel light flux is converted into a convergent light flux by the next converging lens 8. Thereafter, the light beam is split into approximately half by the polarization beam splitter 9, enters the front side photodetector 10 and the rear side photodetector 11, is converted into an electric signal, and is converted into a predetermined information signal by the objective lens 23. A focus error signal indicating the focus shift between the converged light spot and the optical disc 25 and a tracking error signal indicating the shift from the track on the optical disc 25 are obtained.

Next, the actuator 21 will be described. The objective lens 23 is fixed at a position separated from the center of inertia of the movable body 31 by a predetermined distance. Below the objective lens 23, an opening 62 corresponding to an entrance diaphragm for the objective lens 23 is formed. The light flux is supplied to the objective lens 23 through the opening 62. At the center of inertia of the movable body 31, there is provided a hinge 33 made of an elastic body whose rotation center coincides with the optical axis direction of the objective lens 23. One end 34 of the hinge 33 is fixed to the movable body 31 by means such as press fitting or adhesion. The other end 35 of the hinge 33 is fixed to the moving optical base system 38 by being supported by a fixing member 37 by parallel leaf springs 36a and 36b. The moving optical system base 38 is made of a magnetic material.

The movable body 21 has a focus coil 39 at a position symmetrical to the center of inertia of the movable body 21.
a, 39b and tracking coils 40a, 40b are fixed. Here, the focus coils 39a, 3
9b is wound around the Y-axis direction. Further, two tracking coils 40a, 40b are wound around the X-axis direction as an axis, and focus coils 39a,
It is arranged outside 39b.

On the other hand, the movable optical system base 38 is provided with inner yokes 41a and 41b which are inserted inside the focus coils 39a and 39b with a constant gap maintained. The focus coils 39a and 39b and the tracking coil 4 are provided outside the inner yokes 41a and 41b.
Outer yokes 42a and 42b are provided in a protruding manner at positions facing the inner yokes 41a and 41b with the 0a and 40b interposed therebetween. Then, the inner yoke 4 of the outer yokes 42a and 42b
1a, 41b, the surface facing the permanent magnets 43a, 43
b is fixed. Therefore, the inner yoke 41a,
41b and outer yoke 42a, 42b and permanent magnet 43a,
A magnetic circuit is formed by 43b.

The gap between the permanent magnets 43a and 43b and the tracking coils 40a and 40b, the focus coils 39a and 39b, and the inner yokes 41a and 4b.
Vibration breathing bodies 44a and 44b are wholly disposed in a gap between the vibration breathing body 1b and 1b.

With this structure, the movable body 31 is moved in the Y-axis direction by the electromagnetic force associated with the energization control of the focus coils 39a and 39b, whereby focusing control is performed. In addition, the movable body 31 is moved by the electromagnetic force accompanying the energization control of the tracking coils 40a and 40b.
Is rotated around the Y-axis, and tracking control is thereby performed.

12 is a perspective view showing the actuator 21 of the objective lens 23, FIG. 13 is a plan view thereof, FIG. 14 is a sectional view taken along line FF in FIG. 13, and FIG. 15 is G- in FIG. It is sectional drawing shown along the G line.

As shown in FIGS. 14 and 15, the movable body 31 of the actuator 21 is provided with a groove portion 61 as a mounting portion. The groove 61 has a plurality of types of elliptical shapes, for example, a plate as shown in FIG. 17 having an opening 62 in which the ratio of the length of the short axis to the length of the long axis is 0.9, 0.8 or 0.7. The member 63 is adapted to be selectively attached.

Next, a specific value of the ratio of the length of the minor axis to the length of the major axis of the elliptical opening 62 will be described. The NA in the radial direction is made smaller than the NA in the tangential direction by setting the elliptical opening 62 narrow in the radial direction with respect to the objective lens 23. Along with this, the spot diameter in the radial direction becomes large for the reason described later.

Therefore, the amplitude of the so-called push-pull signal from the group provided on the optical disk becomes extremely small. Therefore, in order to secure the amplitude of the push-pull signal above a certain level, the lower limit of the ratio of the length of the minor axis to the length of the major axis of the ellipse is about 0.4.

On the other hand, the upper limit of the ratio of the length of the minor axis to the length of the major axis of the elliptical shape can be said to be about 0.8. This is because if it exceeds 0.8, the effect of reducing the side rope, which is the object of the present proposal, is significantly reduced.

Next, the reading of information will be described. The diameter of the light spot narrowed down by the objective lens 23 is expressed by the following equation. φ = k. λ / NA (1) where φ: light spot diameter λ: wavelength of light NA: numerical aperture of objective lens k: constant determined by objective lens aperture condition and incident light intensity distribution , NA, the larger the spot diameter, the smaller the spot diameter, and more stable signal reproduction is possible even if pits are recorded with high density.

On the other hand, when the NA is increased, the strength of the ring zone increases as shown in FIG. 20, which is disadvantageous in reducing the cross stroke between the tracks. On the other hand, when a circular aperture is set, the numerical aperture NA of the objective lens has a relationship of 2a = 2f · NA (2), where 2a is the aperture diameter on the incident side and f is the focal length of the objective lens.

Therefore, as described above, by adopting a configuration in which the shape of the opening 62 is a narrow elliptical shape in the radial direction, the NA peculiar to the objective lens can be maintained in the tangential direction, so that high density recording is possible. It becomes possible to stably reproduce.

On the other hand, when viewed in the radial direction, since the NA is small, it is possible to reduce the unnecessary track-to-track stroke by reducing the strength of the ring zone. Further, by adopting the above-mentioned configuration, it is possible to more stably perform high-density recording at the time of recording, and it is possible to avoid the disadvantage that a signal is erroneously recorded on an adjacent track.

By the way, in the optical head, due to variations in members, variations in assembly, and the like,
Subtle variations occur in various characteristics obtained as an optical head.

Therefore, even if a proper ratio of the length of the major axis to the length of the minor axis is set in design, it may not always be appropriate for each individual case. Therefore, when setting the opening having an elliptical shape, it is configured to be adjustable so that an appropriate ratio of the length of the major axis and the length of the minor axis can be arbitrarily selected for each optical head. There is.

Next, an actual adjustment method will be described.
First, for example, for example, a plate-like member 63 having a ratio of the length of the short axis to the length of the long axis of the elliptical opening is 0.9 is inserted into the groove 61, and a predetermined signal is observed, and When the amount of side lobes generated is large, the plate-shaped member 63 having an opening with a smaller ratio of the length of the minor axis to the length of the major axis of the ellipse is replaced.

After the appropriate plate-shaped member 63 is determined in this way, for example, the ultraviolet curable adhesive 64 is applied to the portion of the plate-shaped member 63 protruding from the tip of the movable body 31, and this is applied. It is fixed by irradiating a predetermined ultraviolet ray.

According to this embodiment, it is possible to absorb variations in the members of the optical head, variations in assembly, etc., and more reliable and stable high-density recording / recording is possible.

[0058]

As described above, according to the present invention, the shape of the opening of the objective lens is elliptical, the major axis of which is substantially coincident with the circumferential direction of the information recording medium, and the minor axis is the information recording medium. The radial direction of N
A becomes smaller, the annular light distribution (side rope) can be made smaller, and information can be stably reproduced and recorded.

Since the opening has an elliptical shape that is wide in the tangential direction, the NA peculiar to the objective lens can be maintained in the tangential direction, and stable reproduction of high-density recording is possible. .

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a fixed optical system of an optical head that is an embodiment of the present invention.

FIG. 2 is a perspective view showing the fixed optical system of FIG.

FIG. 3 is a configuration diagram showing an optical head including the fixed optical system of FIG.

4 is a perspective view showing an actuator of an objective lens of the optical head of FIG.

5 is a plan view showing the actuator of FIG. 4. FIG.

FIG. 6 is a sectional view taken along line FF in FIG.

FIG. 7 is a sectional view taken along line GG in FIG.

8 shows the objective lens of FIG. 4 and its aperture,
8A is its plan view, FIG. 8B is a sectional view taken along the minor axis direction of the opening, and FIG. 8C is a sectional view taken along the major axis direction of the opening.

FIG. 9 is a configuration diagram showing a fixed optical system of an optical head that is another embodiment of the present invention.

FIG. 10 is a perspective view showing the fixed optical system of FIG.

11 is a configuration diagram showing an optical head including the fixed optical system of FIG.

12 is a perspective view showing an actuator of the objective lens in FIG.

13 is a plan view showing the actuator of FIG.

FIG. 14 is a sectional view taken along line FF in FIG.

FIG. 15 is a sectional view taken along the line GG in FIG.

16 shows a plate-like body attached to the actuator of FIG. 14, FIG. 16 (a) is a plan view thereof, and FIG.
16B is a sectional view taken along line HH in FIG.
16C is a sectional view taken along line I-I in FIG. 16A, and FIG. 16D is a perspective view thereof.

17 shows an actuator to which the plate-like body of FIG. 16 is attached, FIG. 17 (a) is a sectional view taken along the major axis direction of the opening, and FIG. 17 (b) is a short view of the opening. Sectional drawing shown along an axial direction.

18A and 18B show an objective lens and an opening provided in a conventional actuator, FIG. 18A is a plan view thereof, and FIG. 18B is a cross-sectional view taken along the long axis direction of the opening. 18C is a cross-sectional view taken along the minor axis direction of the opening.

FIG. 19 is a graph showing the relationship between the distance from the spot center and the relative intensity when the NA of the objective lens provided in the conventional actuator is 0.5.

FIG. 20 is a graph showing the relationship between the distance from the spot center and the relative intensity when the NA of the objective lens provided in the conventional actuator is 0.5.

[Explanation of symbols]

1 ... Semiconductor laser (light beam supply means), 51, 62 ...
Aperture, 25 ... Optical disc (information recording medium), 23 ... Objective lens.

Claims (6)

[Claims] 1. A light beam supply means for supplying a light beam, and an objective lens for allowing the light beam supplied from the light beam supply means to pass through an opening to be converged and to supply to an information recording medium. An optical head, wherein the opening of the objective lens has an elliptical shape. 2. A light beam supply means for supplying a light beam, and an objective lens for allowing the light beam supplied from the light beam supply means to pass through an opening portion to be converged and to supply the information recording medium. The objective lens has an elliptical shape in its opening, the major axis of which is substantially aligned with the circumferential direction of the information recording medium and the minor axis of which is substantially aligned with the radial direction of the information recording medium. Optical head to do. 3. The optical head according to claim 2, further comprising adjusting means for adjusting the ellipticity of the opening of the objective lens. 4. A light beam supplying means for supplying a light beam, an objective lens for allowing the light beam supplied from the light beam supplying means to pass through an opening and converge to be supplied to an information recording medium, and the objective lens. And a holding member for holding the opening, the opening of the objective lens has an elliptical shape, the opening is provided in the holding member, and its major axis is substantially aligned with the circumferential direction of the information recording medium. An optical head having a minor axis substantially aligned with a radial direction of the information recording medium. 5. A light beam supply means for supplying a light beam, an objective lens for allowing the light beam supplied from the light beam supply means to pass through an opening and converge to be supplied to an information recording medium, and the objective lens. A holding member that holds the holding member, a mounting portion provided on the holding member, and a plate-shaped member that is mounted on the holding member and forms an opening of the objective lens in an elliptical shape. An optical head having a major axis substantially aligned with a circumferential direction of the information recording medium and a minor axis substantially aligned with a radial direction of the information recording medium. 6. The elliptical opening has a ratio of a minor axis to a major axis of 0.4 or more and 0.8 or less, according to any one of claims 1 to 5. Optical head.