JPH0627429A - Condensing device - Google Patents

Abstract

PURPOSE:To provide a condensing device which can make the spot diameter of a light beam smaller than a light condensing device using a refraction body. CONSTITUTION:The condensing device 10 includes a liquid crystal member 20 including first and second liquid crystal areas 24 and 26 in which a crystal characteristic is formed so as to be freely changed. The first and the second areas 24 and 26 are formed between transparent electrodes 16 and 18. When a desired voltage is impressed between the electrodes 16 and 18, desired phase difference is generated between the light beam transmitted through the area 24 and a laser beam transmitted through the area 26. Then, the spot diameter and the intensity of the light beam transmitted through two areas can be changed to a desired value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device used in, for example, an optical filing device or a music CD device, and more particularly, to a condensing device for converting an optical beam into a focused light. Regarding improvement.

[0002]

2. Description of the Related Art In optical disk devices such as optical filing devices and music CD devices, many methods have been proposed for reducing the beam spot diameter of a focused light beam applied to the recording surface of an optical disk. There is.

For example, in a method called super-resolution, a method of shielding the central portion of an area through which an optical beam can pass in an opening, that is, a lens (M. Born and E. Wolf: Princip)
lesof Optics = Optics, Pergamon Press Ltd. Oxf
ord, 1975), and the optical beam is concentrically divided into two,
A method of shifting the phase of an optical beam passing through each region by 180 ° (JEwilkins, Jr .: J. Oct. Soc. Am.,
40 [1950] 22) are known.

However, when the above-mentioned method called super-resolution is used, the peak intensity of the central beam spot, that is, as the beam spot diameter of the focused optical beam becomes smaller, It is known that the light utilization efficiency, which is the ratio of the central intensity of the focused spot to the light emission amount of the light source, is significantly reduced.

[0005]

When the peak intensity is lowered, for example, when writing information on an optical disk, there is a problem that a recording error is likely to occur due to insufficient light quantity. Further, there is a problem that tracking error or focusing error easily occurs when reading information from the optical disc. An object of the present invention is to provide a light collecting device capable of forming a light beam having a small beam spot diameter while ensuring a sufficient light intensity.

[0006]

The present invention has been made on the basis of the above-mentioned problems, and an electrode means having a desired area and an area provided with a desired area ratio with respect to the area of the electrode means are provided. The crystal characteristics are reversible according to the voltage applied between the transparent electrode means and the transparent electrode means that is disposed opposite to the electrode means and between the transparent electrode means and the electrode means. And optical means that are dynamically changed.

Further, according to the present invention, a light source, and means for guiding the light from the light source to the recording medium and for separating the reflected light reflected by the recording medium and the light traveling from the light source toward the recording medium. A first electrode member and a second electrode member which are arranged between the separating means and the recording medium and which are arranged to face each other and are provided with a desired area ratio. An optical head device is provided that includes an optical unit that provides a reversible change to the light traveling from the light source to the recording medium based on the voltage applied between the members.

[0008]

According to the condensing device of the present invention, the incident light beam is wavefront-divided into at least three regions. The optical beams that have passed through at least two regions among the optical beams divided into these three regions have their phases shifted by ½ wavelength.

Therefore, since the two optical beams whose phases are inverted to each other interfere with each other, a sufficient amount of light can be secured at the central beam spot and an optical beam having a small beam spot diameter can be secured. Will be provided.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a light collecting device according to an embodiment of the present invention.

The light-collecting device 10 is formed of a first support plate 12 made of a transparent material, and a transparent material similar to the first support plate 12, and is arranged to face the support plate 12. It includes a second support plate 14 and an outer wall 10a that maintains a constant space between the first and second support plates 12 and 14 and provides a housing as the light collector 10.

Inside the first and second support plates 12 and 14,
A first transparent electrode (electrode means) 16 formed in an area substantially equal to that of the first support plate 12, and at least a part of which faces the first support plate 12, and the first transparent electrode 16 A second transparent electrode (transparent electrode means) 18 having a desired area ratio to the area is arranged. The second transparent electrode 18
The shape of is defined in this example as being generally circular.

Inside the first and second support plates 12 and 14 and further inside the first and second transparent electrodes 16 and 18,
A liquid crystal member (optical means) 20 is formed which has at least two crystal regions, that is, first and second liquid crystal regions 24 and 26, which are divided by a separating wall 22 and are formed so as to be able to change their crystal characteristics independently of each other. Has been done. Since the separation wall 22 is specifically formed in an annular shape defined so as to contact the outer circumference of the circle defined as the second transparent electrode 18, the first liquid crystal region 24 includes the light beam. Is formed in a substantially circular shape when viewed from the direction in which is incident. Therefore, the second liquid crystal region 26
Is the same as when viewed from the direction in which the light beam is incident,
The central portion (that is, the circular region defined by the first liquid crystal region 24 and the separation wall 22) has a cutout shape.

In this embodiment, the light collecting device 10 is
The axis defined as the direction in which the light beam should pass, that is, the optical axis is aligned with the Z axis, and the Z axis is arranged so as to penetrate the central portion of the first liquid crystal region 24. Therefore, the support plates 12 and 14 are arranged substantially parallel to a plane orthogonal to the Z axis, that is, a plane including the X axis and the Y axis. On the other hand, the crystal array direction in the liquid crystal member 20 is the transparent electrodes 16 and 18
It is assumed that they are arranged parallel to the X-axis in a state where no voltage is supplied to both of them. Further, a power source (that is, a desired voltage is applied to the first and second electrodes 16 and 18) device 28 for changing the crystal orientation direction of the liquid crystal member 20 is connected to the light-collecting device 10. It goes without saying that it will be done. Here, with respect to the light condensing device 10, a laser beam whose optical axis is parallel to the Z axis and whose polarization direction is parallel to the X axis.
Consider the case where (polarized light) is incident.

When no voltage is applied to both the transparent electrodes 16 and 18, that is, the entire region (first and second liquid crystal regions 24 and 26) of the liquid crystal member 20 which is divided through the separation wall 22, All the laser beams incident on the light condensing device 10 are emitted with substantially the same optical characteristics as those at the time of incidence. On the other hand, when a voltage having a desired magnitude is applied to the first and second transparent electrodes 16 and 18, the crystal orientation direction of the first liquid crystal region 24 is changed. That is, when a voltage is applied to the first and second transparent electrodes 16 and 18, the first liquid crystal region 24 (of the liquid crystal member 20) is defined corresponding to the area of the second transparent electrode 18. (Area inside the separation wall 22)
The light transmittance of is changed.

In detail, the first and second transparent electrodes 16 and 18
On the other hand, when no voltage is applied, as already described, the crystal alignment directions of all the liquid crystal members 20 are maintained parallel to the X axis. In this state, since a laser beam whose polarization direction is parallel to the X axis is incident, the laser beam is emitted.
The beams are emitted with substantially the same optical characteristics as when they were incident. On the other hand, when a desired voltage is applied to the transparent electrodes 16 and 18, the liquid crystal member corresponding to the first liquid crystal region 24 is formed.
The orientation of the 20 arrays is changed to the Z-axis direction.

This may be because the laser beam passing through the first liquid crystal region 24 has a substantially changed refractive index. In this case, a laser beam passing through the first liquid crystal region 24 and a laser beam passing through the second liquid crystal region 26.
A phase difference is provided between the beam and the beam. Here, regarding the first and second liquid crystal regions 24 and 26, by optimizing the area ratio of each region, the above phase difference is reduced to λ / 2 [r
Ad], the beam spot diameter of the laser beam that has passed through the light condensing device 10 is smaller than the beam spot diameter immediately before entering the light condensing device 10. To be converted. This means that the size of the beam spot when the laser beam emitted from the light condensing device 10 is focused on the recording medium can be made smaller than that of a conventionally used lens or the like. Is shown.

By changing the voltage applied to the transparent electrodes 16 and 18, the polarization direction of the laser beam passing through the first liquid crystal region 24 can be changed by 90 °. is there. In this case, an optical member capable of passing only a laser beam having polarized light in a specific direction,
For example, by combining with an analyzer or the like, a part of the beam spot of the laser beam passing through the light condensing device 10 can be shielded. Even when a part of the beam spot is shielded, the size and the light intensity of the beam spot are not changed in the same manner as the method of giving a phase difference to the part of the laser beam. Needless to say. FIG. 2 shows the principle of changing the beam spot diameter and the light intensity of the laser beam through the light condensing device shown in FIG.

Assuming that the beam spot of the laser beam is generally circular, the condensing device 10 shown in FIG.
The beam spots divided through are shown in FIG. 2 (a).

As shown in FIG. 2A, the cross section of the laser beam passing through the first liquid crystal region 24 in the light converging device 10 is "B". The cross-sectional area of the laser beam passed through the second liquid crystal region 26 is shown as "A". Since the first liquid crystal region 24 is defined according to the area of the second transparent electrode 18 (in FIG. 1), the cross-sectional area “B” is substantially the same as that of the second transparent electrode 18. Needless to say, it is controlled by the area of.
In the light condensing device of the present invention, the cross-sectional areas “B” and “A”
The relationship of A> B is satisfied between the two. Also,
By optimizing the sizes of “B” and “A”,
The composite amplitude distribution shown in Fig. 2 (c) has various characteristics.
(Distribution shape).

FIG. 2 (b) shows a laser beam divided into the area ratios shown in FIG. 2 (a). Each laser beam is independently formed on the recording surface of the optical disc Rm. The beam spot amplitude distribution in the transmitted state is shown.
In this case, the amplitude distribution indicates the energy distribution contained in the laser beam that has passed through the light condensing device 10. Generally, the absolute value of the amplitude distribution is the intensity distribution (a beam spot that can be visually observed. State).

According to FIG. 2 (b), the amplitude distribution of the beam spot of the laser beam passed through the first liquid crystal region 24 is "Si", and the beam spot passed through the second liquid crystal region 26. The amplitude distribution of the beam spot of the laser beam is "So". In this case, there is a phase difference of λ / 2 [rad] between the laser beam passed through the first liquid crystal region 24 and the laser beam passed through the second liquid crystal region 26. Is given as described in FIG.

FIG. 2C shows a state in which the amplitude distributions Si and So shown in FIG. 2B are combined, that is, the beam of the laser beam transmitted to the recording surface of the optical disc Rm. -The composite amplitude distribution of the mu spots is specified as "Sr". Incidentally, Ss in FIG. 2 (c) shows the amplitude distribution of the beam spot of the laser beam on the recording surface of the optical disc Rm when the light converging device 10 is not used. As is apparent from FIG. 2 (c), the beam spot diameter of the laser beam transmitted to the optical disc Rm can be changed to a small value by using the light condensing device of the present invention.

The amplitude distributions Si and So are the first liquid crystal region.
It is easily understood that the value varies depending on the size of 24 (area of the second transparent electrode 18). As an example, FIG.
It is clear that when “B” in (a) is gradually increased and B = A is satisfied, the beam spot amplitude distributions of the respective laser beams have polarities opposite to each other. is there. In this case, the composite amplitude distribution that can be obtained as in FIG. 2C is expected to be approximately “0”. When "B" is further increased and B> A is satisfied, the combined amplitude distribution has a lower peak level and a beam spot as compared with Ss in FIG. 2 (c). It can be expected that the diameter will increase.

A method for changing the size and light intensity of the beam spot by dividing the beam spot of the laser beam into a plurality of regions has already been filed by the applicant of the present application. For details, see Japanese Patent Application No. 3-278400.

In FIG. 3, as an example of a device using the light condensing device shown in FIG. 1, it is incorporated in an optical disc device to record information on the optical disc or reproduce information from the optical disc. An optical head device for is shown.

The optical head device 2 has a divergent laser beam having a beam shape in section, that is, an elliptical beam spot.
Semiconductor laser (light source) 30 that generates light (light), laser 30
The beam spot of the laser beam generated from the laser beam is corrected into a substantially circular shape, the laser beam is guided toward the optical disc (recording medium) Rm, and the laser beam reflected from the optical disc Rm is reflected. A polarizing beam splitter 32 for separating the beam from the laser beam directed to the optical disc.
have.

A collimating lens 34 for converting the laser beam from the laser 30 into a substantially parallel beam is disposed between the polarization beam splitter 32 and the laser 30. Between the polarization beam splitter 32 and the optical disk Rm, there is provided a condenser 10 (shown in FIG. 1) which is an embodiment of the present invention, and an isolation between a light transmitting system and a detecting system. Match (the phase difference between the polarization direction of the laser beam toward the optical disc Rm and the polarization direction of the reflected laser beam from the optical disc Rm is 90
Λ / 4 plate 36 for changing the angle) and the laser beam that has passed through the polarization beam splitter 32 are focused on the recording surface of the optical disk Rm, and reflected by the recording surface of the optical disk Rm. An objective lens 38 for returning the laser beam to parallel light again is inserted in order. Incidentally, the light collecting device 10
May be arranged, for example, between the objective lens 38 and the optical disc Rm or between the laser 30 and the polarization beam splitter 32.

As described above, the power supply device 28 is connected to the light collector 10. Around the objective lens 38, the objective lens 38 is energized by a control signal generated by focusing and tracking described later, and the objective lens 38 is moved in the optical axis direction and in the direction parallel to the recording surface of the optical disc Rm. A lens coil 40 for moving is arranged.

Beside the polarizing beam splitter 32,
A beam traveling toward the optical disc Rm via the beam splitter 32.
In the direction in which the reflected laser beam separated from the beam is transmitted, a photodetector 42 for detecting the laser beam reflected by the optical disk Rm and converting it into an electric signal.
Are arranged. Further, between the polarization beam splitter 32 and the photodetector 42, the laser beam separated via the polarization beam splitter 32 is focused on the detection surface of the photodetector 42. With respect to the focusing lens 44 of FIG. 1 and this laser beam, the laser beam passed through the objective lens 38 is focused at a desired position on the optical disc Rm at a desired beam spot. A refracting body, for example, a cylindrical lens 46 or the like is arranged to generate a control laser beam for enabling a beam spot control called casing and tracking.

The laser beam generated from the laser 30 is
The beam is converted into a parallel beam through the collimating lens 34, the beam spot is corrected into a substantially circular shape through the polarization beam splitter 32, and the beam spot is incident on the condenser 10. In this embodiment, the laser 30 is fixed so that the polarization direction of the laser beam is parallel to the X axis.

The laser beam incident on the condenser 10 is
As already described with reference to FIG. 1, for example, the optical disc is generated from the laser 30 at the time of recording, or the beam spot diameter is changed at the time of reproduction.
It is emitted toward Rm.

That is, at the time of recording information, the power supply device 28 connected to the light collecting device 10 is maintained in the OFF state, so that the crystal array direction in the liquid crystal member 20 is
The state is parallel to the X axis. On the other hand, at the time of reproducing the information, the power supply device 28 is turned on so that the crystal array direction of a partial region of the liquid crystal member 20, that is, the first liquid crystal region 24 is changed to be parallel to the Z axis.

Therefore, at the time of recording information, the laser beam incident on the condenser 10 is emitted with the beam spot diameter and the light intensity substantially the same as those at the time of incidence. In contrast,
When reproducing information, a laser beam having a beam spot diameter smaller than that of the recording beam is emitted. Thus, by reproducing information from the optical disc Rm by using the laser beam having a beam spot smaller than that at the time of recording, the resolution at the time of reproduction can be improved. Regarding the recording laser beam, it has been conventionally observed that an over-level beam is obviously used in consideration of attenuation of light intensity. Since a sufficient light intensity can be obtained even though the beam spot diameter is small, the length of the recording mark and the recording pitch can be reduced.

The laser beam emitted from the condenser 10 is converted into circularly polarized light through the λ / 4 plate 36, and the objective lens
The focusing property is given by 38, and the recording surface of the optical disc Rm is irradiated with the light. The laser beam applied to the recording surface of the optical disc Rm is reflected by the recording surface of the optical disc Rm. At this time, the reflectance is changed depending on the presence / absence of information recorded on the optical disc Rm.

The laser beam reflected by the recording surface of the optical disc Rm is successively passed through the objective lens 38 and the λ / 4 plate 36 again, and returned to the condenser 10. In this case, the polarization direction of the reflected laser beam is shifted by 90 ° with respect to the polarization direction of the laser beam toward the optical disc Rm.
It goes without saying that the direction of deflection is changed to the Y-axis direction. By the way, the crystal array direction in the light condensing device 10 is maintained in a state parallel to the X-axis direction during recording. On the other hand, during reproduction, the crystal orientation direction of the first liquid crystal region 24 is maintained parallel to the Z-axis direction. However, since the polarization direction of the laser beam reflected by the optical disk Rm and passed through the λ / 4 plate 36 is directed to the Y axis as already described, the crystal of the condensing device 10 is It is returned to the polarization beam splitter 32 without being affected by the arrangement direction. The reflected laser beam returned to the polarization beam splitter 32 is reflected toward the photodetector 42 of the λ / 4 plate 36.

The laser beam guided to the photodetector 42 is converted into an electric signal via the photodetector 42, and a signal processing circuit 48 is provided.
And is reproduced as information recorded on the optical disc Rm. The signal processing circuit 48 also simultaneously generates an objective lens control signal for controlling the beam spot called focusing and tracking. The lens coil 40 is energized according to the objective lens control signal, and the laser beam directed to the optical disc Rm is the optical disc.
It is focused at a desired beam spot at a desired position on Rm.

FIG. 4 shows a modification of the embodiment shown in FIG. The same members as those shown in FIG. 1 are designated by the same reference numerals and detailed description thereof will be omitted.

The condensing device 50 includes a first support plate 12, a second support plate 14 arranged to face the first support plate 12, and a space between the first and second support plates 12 and 14. An outer wall that maintains a constant space and provides a housing as the light concentrating device 50.
Includes 50a.

Inside the first and second support plates 12 and 14,
A first transparent electrode (electrode means) 16 formed in an area substantially equal to that of the first support plate 12, and at least a part of which faces the first support plate 12, and the first transparent electrode 16 A desired area ratio is given to the area, and a second transparent electrode (transparent electrode means) 52 formed in an annular shape is arranged. That is, in the light collecting device 50, the second transparent electrode 18 in the light collecting device 10 shown in FIG. 1 is formed in a hollow circular shape.

Inside the first and second support plates 12 and 14, and further inside the first and second transparent electrodes 16 and 52,
A liquid crystal region having at least three crystal regions, that is, first to third liquid crystal regions 60, 62 and 64, which are divided by two separating walls 54 and 56 and each of which is capable of independently changing the crystal characteristic ( Optical means) 58 is formed. In detail, the two separating walls 54 and 56 are formed in an annular shape defined so as to contact the inner circumference and the outer circumference of the hollow circle defined as the second transparent electrode 52, respectively. Therefore, the first liquid crystal region 60 has a substantially circular shape when viewed from the direction in which the light beam enters, and the second liquid crystal region 62 similarly receives the light beam. It is formed in a concentric annular shape when viewed from the direction. Needless to say, the third liquid crystal region 64
Is the same as when viewed from the direction in which the light beam is incident,
The central portion (ie, the first and second liquid crystal regions 60 and 62 and 2
A circular area defined by two separating walls 54 and 56) has a cutout shape.

It goes without saying that the first and third liquid crystal regions 60 and 64 function substantially the same. In other words, the second transparent electrode arranged to face the first transparent electrode 16
Only the second liquid crystal region 62 defined by 52 can provide a different crystal alignment as compared to the first and third liquid crystal regions 60 and 64. Hereinafter, regarding the light concentrating device 50, a case where a laser beam (polarized light) is incident under the same conditions as those of the light concentrating device 10 shown in FIG. 1 will be considered.

When a laser beam having a polarization direction parallel to the X-axis is incident on the condenser 50 along the optical axis, that is, the Z-axis, voltage is applied to both transparent electrodes 16 and 52. When the laser beam is not applied, all the laser beams incident on the light condensing device 50 are emitted with substantially the same optical characteristics as those at the time of incidence. On the other hand, by applying a desired voltage to the transparent electrodes 16 and 52, the alignment direction of the crystals of the second liquid crystal region 62 is changed. That is, when a voltage is applied to the transparent electrodes 16 and 52, the second liquid crystal region 62 (with respect to the liquid crystal member 58, the separation walls 54 and 56, which are defined corresponding to the shape of the second transparent electrode 52). The light transmittance of the annular region (which is restricted by) is changed.

In the light concentrating device 50, as in the light concentrating device 10, in the liquid crystal region (that is, the second liquid crystal region 62) located between the electrodes to which a voltage is applied, the crystal alignment direction is (X axis direction). (From the direction parallel to the direction) to the direction parallel to the Z-axis direction. Therefore, the laser beam passing through the first liquid crystal region 60 and the laser beam passing through the second liquid crystal region 62 near the center of the light converging device 50 is provided along the Z axis. Between, and
Between the laser beam passing through the second liquid crystal region 62 and the laser beam passing through the third liquid crystal region 64 outside the second liquid crystal region 62, desired positions are respectively provided. The phase difference is provided. In this case, by optimizing the area of the second transparent electrode 52, the phase difference between the laser beams can be set to λ / 2 [rad]. It goes without saying that the phase difference between the laser beam passed through the first liquid crystal region 60 and the laser beam passed through the third liquid crystal region 64 is the same phase. .

The phase of the laser beam passing through the first liquid crystal region 60 and the third liquid crystal region 64 is set to the same phase, and the phase of the laser beam passing through the second liquid crystal region 62 is set to the same phase. By shifting the laser beam passing through the first and third liquid crystal regions 32 and 36 by λ / 2 [rad], the light concentrating device 10 according to the first embodiment is sufficiently operated. The light intensity of the side lobe, which cannot be reduced, can be reduced. FIG. 5 shows a modification of the light collecting device shown in FIGS. 1 and 4. In the light collecting device 70, an example is shown in which members that function similarly to the first liquid crystal region 24 and the separation wall 22 in the light collecting device 10 shown in FIG.

That is, the condensing device 70 provides an aspect ratio which is substantially matched to the aspect ratio (ratio of the major axis and the minor axis in the ellipse) in the beam spot of the incident laser beam. A second transparent electrode 72 defined in an elliptical shape, a separation wall 74 defined in contact with the outer periphery of the transparent electrode 72, a first liquid crystal region 76 formed via the separation wall 74, and , And has a second liquid crystal region 78 defined outside the first liquid crystal region 76. The second transparent electrode 72
It goes without saying that, like the condensing device 50 shown in FIG. 4, may be formed in a hollow circular shape.

When this condensing device 70 is used, for example, in the optical head device 2 shown in FIG. 3, the incident surface facing the laser 30 side of the polarization beam splitter 32 is normally used. It is possible to omit the combined ellipse correction function. Figure 6
Shows an embodiment different from the light collecting device shown in FIGS. 1, 4 and 5.

The condensing device 90 comprises a plate-shaped support 92, and a common electrode formed on the support 92 and having an area equal to that of the support 92.
The piezoelectric element (piezo element) 96 having a substantially uniform thickness is provided on the common electrode 94a. A portion of the piezoelectric element 96, which is the common electrode 94
A counter electrode 94b having a desired area ratio with respect to the common electrode 94a is arranged at a position facing a.
Further, a light reflecting layer 98 for reflecting a light beam supplied from the outside is formed on the surface of the piezoelectric element 96 including the counter electrode 94b facing the support body 92. A power supply device (not shown) is connected to the common electrode 94a and the counter electrode 94b. Further, the piezoelectric element 96 is the above-mentioned counter electrode.
What was divided beforehand according to the area of 94b may be used.

The piezoelectric element 96 is known as a member in which, when a voltage is applied between electrodes sandwiching the piezoelectric element, the thickness of the element itself changes according to the applied voltage. From this, the light condensing device 90 can define all the regions of the light reflecting surface 98 in substantially the same plane when a voltage is not applied between the electrodes 94a and 94b. On the other hand, when a voltage is applied between the electrodes 94a and 94b, the electrodes
Based on the magnitude of the voltage applied between 94a and 94b,
The thickness of the region corresponding to the area of the counter electrode 94b in the piezoelectric element 96 is changed. Therefore, the light reflecting surface 98 is defined as a reflecting surface that does not have the same height at least in part.

In this case, the light condensing device 90 can provide a desired phase difference to the light beam incident on the light reflecting surface 98, as in the other embodiments described above. The light concentrator 90 is
Obviously, it will only function as a reflective concentrator. Therefore, it goes without saying that the optical path design must be taken into consideration when it is used as an optical head device, for example.

FIG. 7 shows a modification of the optical head device shown in FIG. The same members as those shown in FIG. 3 are designated by the same reference numerals, and detailed description thereof will be omitted.

According to FIG. 7, the optical head device 100 is constructed substantially similar to the embodiment shown in FIG. That is, between the semiconductor laser 30 and the optical disc Rm,
Optical members such as a polarization beam splitter 32, a collimator lens 34, a condenser device 10, a λ / 4 plate 36, and an objective lens 38 are arranged in order.

By the way, in the optical head device 100,
The condensing device 10 and the objective lens 38 are incorporated in a lens housing 110 that integrally accommodates them. Also,
The lens coil 40 is fixed around the lens housing 110.

This is related to the optical head device 2 shown in FIG. 3, for example, the objective lens 38 and the focusing lens which may occur when only the objective lens 38 is moved during focusing or tracking. The influence of the deviation of the optical axis from the device 10 can be reduced. That is, in the optical head device 2 shown in FIG. 3, since only the objective lens 38 is moved at the time of focusing or tracking, the laser beam passing through the optical axis of the condenser 10 is used. A displacement or inclination occurs between the objective lens 38 and the optical axis.

When the optical axis between the condenser 10 and the objective lens 38 is deviated, the effective beam of the laser beam emitted from the condenser 10 toward the objective lens 38. The spot size may be limited. Further, with respect to the laser beam traveling from the condenser 10 to the objective lens 38 and the laser beam reflected from the optical disc Rm and returned to the objective lens 38, the coma aberration component may be increased. in this case,
Regarding the beam spot guided to the optical disc Rm, there is a possibility that the peak intensity at the beam spot may be reduced.

On the other hand, in the embodiment shown in FIG. 7, the objective lens 38 and the condenser 10 are arranged in the lens housing 1.
Moved through 10 simultaneously. This means that
All the laser beams passed through the objective lens 38 can be made incident on the objective lens 38, and all the laser beams passed through the objective lens 38 can be made incident on the condenser 10.

Therefore, through the lens housing 110,
By holding the objective lens 38 and the condenser 10 together,
With respect to the beam spot guided to the optical disc Rm, the laser beam can be effectively used without reducing the peak intensity.

In this embodiment, the first embodiment shown in FIG. 1 was used as an example of the light concentrating device, but any one shown in FIGS. 4 to 6, for example. It goes without saying that the light concentrator (50, 70 or 90) of the above may be used.

[0059]

As described above, according to the present invention,
The beam spot diameter of the light beam can be made smaller than when the refracting means is used. On the other hand, there is provided a light collecting device that does not attenuate the peak intensity of the beam spot. Therefore, at the time of recording information on the recording medium, a sufficient amount of light of the central beam spot of the optical beam is secured, so that the recording density can be increased. Further, when reproducing information from the recording medium, since an optical beam having a small beam spot diameter can be used, the resolution of the reproduced signal can be improved.

[Brief description of drawings]

FIG. 1 shows a light collecting device according to an embodiment of the present invention,
(a) is a perspective view showing the external appearance of the light collecting device, (b) is (a)
A sectional view of the perspective view of FIG.

FIG. 2 is a characteristic diagram for explaining the principle that the beam spot diameter and the light intensity of an optical beam can be changed by the light concentrating device shown in FIG. Graphs showing examples of division, (b) and (c) are graphs showing the relationship between the divided area ratio and the amplitude distribution of light, respectively.

FIG. 3 is a schematic plan view showing an optical head device in which the light collecting device shown in FIG. 1 is incorporated.

FIG. 4 shows a modification of the light collecting device shown in FIG.
(a) is a perspective view showing the external appearance of the light collecting device, (b) is (a)
FIG. 4 is a sectional view of the perspective view of FIG.

5 shows a modification of the light collecting device shown in FIG.
(a) is a perspective view showing the external appearance of the light collecting device, (b) is (a)
FIG. 5 is a sectional view of the perspective view of FIG.

FIG. 6 is a schematic cross-sectional view showing an embodiment different from the light concentrating device shown in FIG.

7 is a schematic plan view showing a modified example of the optical head device shown in FIG.

[Explanation of symbols]

10 ... Light collector, 12, 14 ... Support plate, 16 ... First transparent electrode
(Electrode means), 18 ... Second transparent electrode (Transparent electrode means), 2
0 ... Liquid crystal member (optical means), 22 ... Separation wall, 24 ... First liquid crystal region, 26 ... Second liquid crystal region, 28 ... Power supply device.

Claims (2)

[Claims] 1. An electrode means having a desired area, a transparent electrode means having an area having a desired area ratio with respect to the area of the electrode means, the transparent electrode means facing the electrode means, and the transparent electrode means. A light-collecting device comprising: an electrode means and an optical means disposed between the electrode means and reversibly changing crystal characteristics in response to a voltage applied between the electrode means. 2. A light source, means for guiding the light from the light source to a recording medium, and separating the reflected light reflected by the recording medium and the light traveling from the light source to the recording medium; A first and a second electrode member which are arranged between the recording medium and facing each other and are provided with a desired area ratio, and are applied between the first and second electrode members. An optical head device, comprising: an optical unit that provides a reversible change to light directed from the light source to the recording medium based on a voltage.