JP2000113493A - Optical head device, information recording and reproducing device, and optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical head device in which positioning of an information head device can be stably performed even when distance between images is made short to miniaturize a device. SOLUTION: An optical head device is provided with a semiconductor laser 101 emitting light, a lens 102 collecting light emitted to a disk 104 from the semiconductor laser 101, and a holding means holding a fixed distance between the disk 104 and the lens 102. Then, when it is assumed that a focal distance of the lens 102 is (f), a distance from the semiconductor laser 101 to a first main point being main point of the semiconductor laser 101 side of the lens 102 is L1, and a distance from a second main point being a main point of the disk 104 side of the lens 102 to the disk 104 held by the holding means is (h), the following equation is satisfied. L2=f×L1/(L1-f) h<L2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information head device for recording information on an information storage medium such as a high-density floppy disk or an optical disk or reproducing the information recorded on the information storage medium. Optical head device for positioning, an information recording / reproducing device such as a floppy disk drive and an optical disk drive equipped with the optical head device, and light having a desired wavefront can be obtained, and the optical head device and the information recording device The present invention relates to an optical system useful for a reproducing apparatus.

[0002]

2. Description of the Related Art When recording information on a floppy disk at a high density, it is necessary to position an information head device in a direction orthogonal to a track. In this case, if the positioning of the information head device is performed mechanically, sufficient positioning accuracy cannot be ensured. Therefore, recently, the technology of positioning the information head device using light has become mainstream. FIG. 2 shows a conventional optical head device in which the information head device is positioned using light.
This will be described with reference to FIG.

As shown in FIG. 20, light emitted from a semiconductor laser 101 as a light source is converted into 0-order light and ± 1st-order diffracted light by a diffraction grating 152 provided on the surface of the diffraction element 150 on the light source side. (The ± 1st-order diffracted light is not shown). Hereinafter, the 0th-order light is referred to as “main beam”,
± 1st order diffracted light is called "sub-beam".

[0004] The main beam and the sub beam are
The light passes through the diffraction grating 151 provided on the lens-side surface of the lens 50 and is condensed by the lens 102 as a condensing optical system. The main beam and the sub-beam condensed by the lens 102 are converted into a desired numerical aperture NA by the aperture stop 103.
The opening is restricted so that the light is emitted to the disk 104 as an information storage medium. On the disk 104, a beam train composed of a main beam and two sub beams is arranged so as to form a predetermined angle with respect to a track. Note that the disk 104 is sandwiched from above and below by a magnetic head 201 as an information head device attached to the arm 211, thereby restricting the position of the disk 104 in the z direction. Each part of the optical system and the magnetic head 201 are fixed to the housing 210. For this reason, the distance from the optical system to the disk 104 is always kept constant (here, 20 mm).

The light reflected by the disk 104 passes through the aperture stop 103 and the lens 102 again, is diffracted by the diffraction grating 151 provided on the surface of the diffraction element 150 on the lens side, and is then transmitted to the photodetectors 105R and 105L. Incident.

Each of the photodetectors 105R and 105L has three detection areas, separates and receives three beams of a main beam and two sub beams, and outputs a signal corresponding to the amount of received light.

On the disk 104, the three beam spots irradiate different positions in a direction orthogonal to the track. Therefore, the modulation degrees of the signals obtained from the three detection areas are different from each other, and the modulation degrees of the signals sequentially change as these beam spots cross the track. Therefore, by calculating these signals, the relative positional relationship between the track and the beam irradiation position can be detected.

That is, first, envelope detection of these signals is performed, and the obtained envelope signals are M, S
1, and S2. Then, using these envelope signals M, S1, and S2, A = M-S1, B = S2-M
To generate signals A and B. By multiplying the signals A and B by an appropriate coefficient k1, tracking error signals k1 · A and k1 · B that cross zero at an arbitrary phase are obtained. Then, these tracking error signals k
The relative positional relationship between the track and the beam irradiation position can be detected from 1 · A and k1 · B. here,
The coefficient k1 is first learned so that the magnetic head 201 is on a track where information is to be recorded and reproduced.
Incidentally, both the magnetic head 201 and the optical system are moved in the radial direction of the disk 104 by the transfer means 203 as shown in FIG.

In the above-mentioned conventional optical head device, a lens 102 having a focal length f of 10 mm is used. When an optical system with a magnification of 1 as shown in FIG. 20 is configured, the distance from the semiconductor laser 101 as the light source to the focal point on the disk 104 as the information storage medium (distance between object and image) is about 40 mm, and the distance L2 from the lens 102 to the converging point on geometrical optics is 20 mm. When the numerical aperture NA is 0.04, the aperture stop 103
When the radius a ′ of the opening is projected onto the disk-side main surface, the radius a of the opening radius is 800 μm. When the wavelength λ of the light emitted from the semiconductor laser 101 as the light source is 800 nm, the spot diameter d = λ / NA on the disk 104 is 20 μm, and the Fresnel number N = (a × a) at this time. / (Λ × L2) is 40. Also,
At this time, the difference in position between the converging point on geometrical optics and the point where the intensity of the condensed light is maximum is about 20 μm. Depth of focus Δz, which is the distance from the point where the intensity of the collected light becomes maximum to the point where the intensity of the collected light becomes 80% of the maximum value
Since is approximately 80 μm, there is no problem in ignoring the difference in position between the converging point on geometrical optics and the point where the intensity of the condensed light is maximized.

[0010]

However, in the above-mentioned conventional optical head device, the difference in position between the converging point on geometrical optics and the point where the intensity of the condensed light is maximized is substantially ignored. Therefore, it was necessary to increase the distance between the object and the image so that the size of the apparatus could not be reduced. Also,
When the distance between the object and the image is increased, the light emitted from the light source of the optical head device is easily affected by a change in the external environment such as a change in temperature or vibration, and the information head device cannot be stably positioned. Was.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems in the prior art, and stably handles an information head device even when the distance between objects is reduced in order to reduce the size of the device. An object of the present invention is to provide an optical head device capable of performing positioning of an optical head device, an information recording / reproducing device including the optical head device, and an optical system useful for the optical head device and the information recording / reproducing device.

[0012]

In order to achieve the above object, an optical head device according to the present invention comprises a light source for emitting light and an information storage medium for recording or reproducing information. An optical head device comprising: a condensing optical system for condensing the collected light; and holding means for maintaining a constant distance between the information storage medium and the condensing optical system, wherein the focus of the condensing optical system is The distance is f, and the distance from the light source to a first principal point on the light source side of the condensing optical system is L.
1. The second point, which is the main point of the condensing optical system on the information storage medium side
When the distance from the principal point to the information storage medium held by the holding unit is h, the following (Equation 9) and (Equation 10) are satisfied.

[0013]

L2 = f × L1 / (L1-f)

[0014]

H <L2

According to the configuration of the optical head device, even when the point at which the intensity of the condensed light is maximum is shifted from the converging point on geometrical optics, the information is stored at the point at which the intensity of the light is maximum. Media can be placed. Therefore, the distance between the object and the image can be reduced in order to reduce the size of the apparatus. In addition, since the distance between the object and the image can be reduced in this manner, the light emitted from the light source is less likely to be affected by a change in the external world such as a change in temperature or vibration. That is, according to the configuration of the optical head device, the size of the device can be reduced, and the signal for positioning the information head device can be stably obtained.

In the configuration of the optical head device of the present invention, when the wavelength of the light emitted from the light source is λ and the numerical aperture of the condensing optical system on the information storage medium side is NA, It is preferable to satisfy (Equation 11) and (Equation 12).

[0017]

## EQU11 ## Δz = λ / (2π × NA × NA)

[0018]

H <L2-Δz

According to this preferred example, a sufficient signal for positioning the information head device can be obtained.

In the configuration of the optical head device according to the present invention, it is preferable that the condensing optical system includes an aperture stop for determining a numerical aperture, and the aperture stop has a circular aperture. According to this preferred example, since the positional shift between the focal point on the geometrical optics and the point where the intensity of the focused light is maximum is constant regardless of the direction, a focused spot without astigmatism is formed. Obtainable. In this case, a plane including the second principal point and perpendicular to the optical axis is defined as a principal plane on the information storage medium side, and an aperture when the aperture stop is projected on the principal plane on the information storage medium side is used. It is preferable that the Fresnel number N defined by the following (Equation 13) is 10 or less, where a is a radius, and λ is a wavelength of light emitted from the light source.

[0021]

N = (a × a) / (λ × L2)

According to this preferred example, it is possible to reduce the object-image distance of the optical system by using lenses having the same focal length. For this reason, the size of the device can be further reduced. Conversely, if the object-image distance is the same, the focal length of the lens can be increased, so that the radius of curvature of the lens can be increased. As a result, the manufacture of the lens becomes easy.

In the configuration of the optical head device according to the present invention, it is preferable that the condensing optical system includes an aperture stop for determining a numerical aperture, and the aperture stop has a square aperture. According to this preferred example, by using an aperture stop having a simple shape, the displacement between the focal point on geometrical optics and the point at which the intensity of the focused light is maximized is made substantially constant regardless of the direction. Therefore, a focused spot without astigmatism can be obtained.

In the configuration of the optical head device according to the present invention, it is preferable that the condensing optical system includes an aperture stop for determining a numerical aperture, and the aperture stop has an aperture having a different aperture width depending on a direction. According to this preferable example, astigmatism can be generated because the positional shift between the converging point on geometrical optics and the point where the intensity of the condensed light is maximum differs depending on the direction. Then, the astigmatism inherent in the light source or the optical system is canceled by the astigmatism, and a condensed spot without astigmatism can be obtained. In addition, since the astigmatism of the light source or the like can be removed with such a simple configuration, an inexpensive and high-performance optical head device can be realized. Further, in this case, a plane including the second principal point and perpendicular to the optical axis is defined as a principal plane on the information storage medium side, and the minimum aperture when projecting the aperture stop onto the principal plane on the information storage medium side is minimized. It is preferable that the minimum Fresnel number N _min defined by the following (Equation 6) is 10 or less, where a1 is a value of half of the opening width of a and a is a wavelength of light emitted from the light source.

[0025]

N _min = (a1 · a1) / (λ · L2)

According to this preferred embodiment, the object-image distance of the optical system can be reduced by using lenses having the same focal length. For this reason, the size of the device can be further reduced. Conversely, if the object-image distance is the same, the focal length of the lens can be increased, so that the radius of curvature of the lens can be increased. As a result, the manufacture of the lens becomes easy.

[0027] Further, the configuration of the information recording / reproducing apparatus according to the present invention comprises an information head device for recording information on an information storage medium or reproducing information recorded on the information storage medium; An information recording / reproducing apparatus comprising: an optical head device for performing positioning; and a moving unit that relatively moves a position between the information head device and the information storage medium, wherein the optical head device is an optical head device according to the present invention. A head device is used. According to the configuration of the information recording / reproducing device, the entire information recording / reproducing device can be reduced in size. In addition, since it is hardly affected by external changes such as temperature change and vibration, stable recording and reproduction of information can be performed. In the configuration of the information recording / reproducing apparatus of the present invention, it is preferable that the optical head device also functions as the information head device. According to this preferred example, a magnetic head or the like is not required, and an information recording / reproducing apparatus having a simpler configuration can be realized.

The optical system according to the present invention comprises a light source for emitting light, a condensing optical system for condensing light emitted from the light source, and an aperture for determining a numerical aperture of the condensing optical system. An aperture stop having an aperture whose aperture width varies depending on the direction, the focal length of the light-collecting optical system being f, the light-source side of the light-collecting optical system from the light source. The distance to the first principal point, which is the principal point, is L1, and the plane including the second principal point, which is the principal point on the information storage medium side of the condensing optical system, is perpendicular to the optical axis on the information storage medium side. Where a1 is a value of a half of the minimum aperture width when the aperture stop is projected onto the main surface on the information storage medium side, and λ is the wavelength of light emitted from the light source. minimum Fresnel number N _min is defined by the number 16) is not less than 10, an opening width due to the direction of the aperture stop Wherein the resulting astigmatism by difference.

[0029]

L2 = f × L1 / (L1-f)

[0030]

N _min = (a1 · a1) / (λ · L2)

According to the configuration of this optical system, astigmatism can be given to the condensing optical system or astigmatism of the condensing optical system by using only small and simple parts without adding new glass parts and the like. Can be removed. In addition, coma aberration that occurs when the parallel flat glass is used at an angle is not generated.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described more specifically with reference to embodiments. <First Embodiment> First, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a schematic sectional view showing the structure of the optical head device according to the first embodiment of the present invention. In the following drawings, the same members are denoted by the same reference numerals. The directions of the coordinate axes shown at the lower left of each drawing represent the relationship between the directions of each drawing.

As shown in FIG. 1, light emitted from a semiconductor laser 101 as a light source is converted into 0-order light and ± 1st-order light by a three-beam diffraction grating 152 provided on the surface of the diffraction element 150 on the light source side. (± 1st-order diffracted light is not shown). Hereinafter, the zero-order light is referred to as a “main beam” and the ± first-order diffracted lights are referred to as a “sub-beam”.

The main beam and the two sub beams pass through a detection diffraction grating 151 provided on the lens-side surface of the diffraction element 150 and are condensed by a lens 102 as a condensing optical system. Although diffracted light is generated when the light passes through the detection diffraction grating 151, it is not shown here because it is unnecessary diffracted light. The aperture of the main beam and the two sub-beams condensed by the lens 102 is limited by the aperture stop 103 so as to have a desired numerical aperture NA1, and the beam is irradiated on the disk 104 as an information storage medium. On the disk 104, a beam train composed of a main beam and two sub beams is arranged so as to form a predetermined angle with respect to a track. Note that the disk 104 is sandwiched from above and below by a magnetic head 201 as an information head device attached to the arm 211, thereby restricting the position of the disk 104 in the z direction. Each part of the optical system (the semiconductor laser 101, the diffraction element 15
0, lens 102, aperture stop 103, photodetector 105)
And the magnetic head 201 are fixed to the housing 210. For this reason, the distance from the optical system to the disk 104 is always kept constant. Here, the magnetic head 201, the housing 210, and the arm 211 play a role as a holding unit having a predetermined length.

The light reflected by the disk 104 passes through the aperture stop 103 and the lens 102 again and passes through the detection diffraction grating 15.
The light is diffracted by 1 and enters the photodetectors 105R and 105L.

Each of the photodetectors 105L and 105R has three detection areas, separates and receives three beams of a main beam and two sub-beams, and outputs a signal corresponding to the received light amount. The three beams entering the disk 104 become three spots on the disk 104, and irradiate different positions in a direction orthogonal to the track. Therefore, the modulation degrees of the signals obtained from the three detection areas are different from each other. Therefore, by calculating these signals, the relative positional relationship between the track and the beam irradiation position can be detected.
The recording of information on the disk 104 or the reproduction of information on the disk 104 is performed by a magnetic head 201 as an information head device.

FIG. 2 is a diagram of the aperture stop 103 of FIG. 1 viewed from the optical axis direction. As shown in FIG. 2, the aperture stop 103 is provided with a circular aperture having a radius a ′ centered on the optical axis.

FIG. 3 is a diagram showing the positional relationship among the members constituting the optical system of the optical head device according to the present embodiment.
As shown in FIG. 3, the light emitting point of the semiconductor laser 101 as the light source is P, the first main point on the light source side of the lens 102 as the condensing optical system is H1, and the main point on the disk side of the lens 102 is the main point. The second principal point, which is a point, is H2, the focal length of the lens 102 is f, and the distance from the point P to the point H is L1. The point Q2, which is a condensing point on geometrical optics, is a point separated by a distance L2 from the point H2. Here, the distance L2 can be obtained by the following (Equation 17).

[0040]

L2 = f × L1 / (L1-f)

The focal length f of the lens 102 is shown in FIG.
As shown in (b), this is the distance from the second principal point H2 to the focal point F on geometrical optics when parallel light is incident on the lens 102. When the lens 102 is a plano-convex lens shown in FIG. 3B, the focal length f of the lens 102 is represented by the following (Equation 18).

[0042]

F = R / (n-1)

In the above (Equation 18), R is the lens 10
The radius of curvature of 2 and n is the refractive index of the lens 102.

The point Q1 is a point at which the intensity of the condensed light becomes maximum. In the present embodiment, the disc 104
It is positioned at a point Q1 separated by a distance h (<L2) from the point H2 by a magnetic head 201 or the like (see FIG. 1) as holding means.

In the present embodiment, when a plano-convex lens having a focal length f of 1 mm is used as the lens 102 and the value of L1 is set to 2.0 mm, an optical system having an object-image distance of about 4 mm is obtained. At this time, the value of L2 is 2.0 mm. When the numerical aperture NA is 0.04, the radius a ′ of the aperture of the aperture stop 103 when projected on the main surface on the disk side is a
Is 80 μm, and the spot diameter d of the beam spot on the disk 104 is 20 μm. Here, the main surface on the disk side is a plane that includes the second main point H2 and is perpendicular to the optical axis.
In this case, the Fresnel number N expressed by the following (Equation 19) is 4
Becomes

[0046]

N = (a × a) / (λ × L2)

At this time, the distance z1 between the converging point Q2 on the geometrical optics and the point Q1 where the intensity of the condensed light is maximum is about 1
30 μm. On the other hand, the depth of focus Δz, which is the distance from the point where the intensity of the condensed light becomes maximum to the point where the intensity of the condensed light becomes 80% of the maximum value, is about 80 μm. In the case of designing using optics, light is defocused on the disk 104 as an information storage medium, and desired characteristics cannot be obtained.

When the Fresnel number N is small, the difference between the converging point on geometrical optics and the point where the intensity of the condensed light is maximum differs from that in Y. Li and E. Wolf: Opt. .Am.A (1984)
vol.1, p801-p808, the explanation of the principle is omitted.

Therefore, when the Fresnel number N is small (N ≦
10) The design and optical arrangement of the lens must be performed in consideration of the above. That is, when the point Q1 at which the Fresnel number N is small and the intensity of the condensed light is maximum deviates from the convergent point Q2 on geometrical optics, the two points are separated from each other, particularly exceeding the actual focal depth Δz. In this case, the disk 10 is located at the point Q1 where the light intensity actually becomes maximum.
4 or the focal length f of the lens 102 is designed to be longer, and the focal point Q2 on the geometrical optics is
It is necessary to set the position farther than 4.

The wave number of light is k, the radius of the aperture a ′ of the aperture stop 103 projected on the disk-side main surface is a, and the second principal point H2 of the lens 102 is a geometrical optical collection. Let L2 be the distance to the light point Q2, and let z1 be the distance from the converging point Q2 on geometrical optics to the point Q1 where the intensity of the condensed light is maximum. Note that z1 has a negative sign when the point Q1 is closer to the lens 102 than the point Q2.

Z satisfying the following (Equation 20) and (Equation 21) becomes z1 (-L2 <z1 <0), the point Q1 at which the intensity of the condensed light becomes maximum, and the converging point Q2 on geometrical optics. Is | z1 |.

[0052]

A = k × a × a / (4 × L2)

[0053]

(Equation 21)

In FIG. 19, when the value of L2 is 0.5 mm, the Fresnel number N, the deviation z1 between the point Q1 at which the intensity of the condensed light is maximum and the converging point Q2 on geometrical optics, And the depth of focus Δz. Here, the depth of focus Δz is
It is represented by the following (Equation 22).

[0055]

Δz = λ / (2π × NA × NA)

As shown in FIG. 19, when the Fresnel number N is about 10 or less, the deviation z1 between the point Q1 at which the intensity of the condensed light is maximum and the converging point Q2 on geometrical optics is larger. It becomes larger than the depth of focus Δz. If the Fresnel number N is 5
In the following cases, the difference becomes remarkable, and a great effect due to the different light converging points can be reliably obtained.

As described above, by using the structure of this embodiment, the disk 104 is irradiated with the beam spot as expected, and the magnetic head 201 as the information head device is positioned. It is possible to read a track, read a signal for recording / reproducing information, and write information to the disk 104. Also, near the point Q1 where the intensity of the condensed light is maximum, the wavefront of the light approaches a plane, so that the light reflected here is condensed on a point conjugate with the light emitting point. As described above, according to the present embodiment, it is possible to stably read a track for positioning the magnetic head 201 as an information head device using an optical system that is small and has a small Fresnel number N. It becomes possible. As a result, a small and highly reliable optical head device can be realized at low cost.

The Fresnel number N as in this embodiment
If an optical system having a small focal length is used, the object-image distance of the optical system can be reduced by using lenses having the same focal length. For this reason, the size of the device can be further reduced. vice versa,
If the object-image distance is the same, the focal length of the lens can be increased, so that the radius of curvature of the lens can be increased. As a result, the manufacture of the lens becomes easy.

When the width of the aperture of the aperture stop differs depending on the direction, the Fresnel number N changes depending on the direction, and the position of the condensing point also changes accordingly. When the Fresnel number N is small, the difference between the positions of the condensing points increases.

Accordingly, in order to generate a spot free of astigmatism, especially in an optical system in which the Fresnel number N in the direction in which the opening width is narrow is about 10 or less, the opening width is made substantially the same in all directions. There is a need.

When the Fresnel number N is about 10, an aperture stop 1 having a square aperture as shown in FIG.
Even when the aperture stop 10 is used, it is possible to obtain substantially the same effect as when the aperture stop 103 having a circular aperture as shown in FIG. 2 is used.

Incidentally, in the optical head device shown in FIG.
Diffraction element 1 provided with diffraction gratings 151 and 152 on both sides
Although the generation of three beams and the generation of the light beam for detection are performed using the reference numeral 50, the same effects as described above can be obtained even with the configuration shown in FIGS. . That is, in the optical head device shown in FIGS. 5 and 6, when the Fresnel number N is small and the point at which the intensity of the condensed light is maximum is different from the converging point on geometrical optics, the light intensity Is arranged at the position of the point where the maximum value is obtained, the disk 104 is irradiated with the beam spot that is actually expected, and the track reading for positioning the magnetic head 201 as the information head device is performed. In addition, it becomes possible to read a signal for recording and reproducing information, and to write information to the disk 104. Less than,
These optical head devices will be described.

First, the optical head device shown in FIG. 5 will be described. In the optical head device shown in FIG. 5, a polarizing beam splitter 121 and a quarter-wave plate 122 are used. As shown in FIG. 5, light emitted from the semiconductor laser 101 serving as a light source is split into a main beam and two sub beams when passing through a diffraction grating 162 provided on a surface of the diffraction element 160 on the light source side. The sub-beam is not shown). These beams pass through the polarizing beam splitter 121. The light emitted from the semiconductor laser 101 is linearly polarized light, and its polarization direction is the direction that transmits the polarization beam splitter 121. The light transmitted through the polarizing beam splitter 121 is transmitted through the quarter-wave plate 122 and becomes circularly polarized light. These beams are focused by a lens 102 as a focusing optical system, and
4 is illuminated. The aperture of the lens 102 is an aperture stop 10
Three. When the light reflected and diffracted by the disk 104 passes through the aperture stop 103 and the lens 102 again and passes through the quarter-wave plate 122, the light travels by 90%.
It becomes linearly polarized light having different polarization directions. This light is reflected by the polarization beam splitter 121 and enters the photodetector 106.

The photodetector 106 includes three detection areas, separates and receives the three beams of the main beam and the two sub-beams, and outputs a signal corresponding to the amount of the received light.

When the optical system as shown in FIG. 5 is used, the semiconductor laser 1 is operated by the action of the polarizing beam splitter 121.
01 to the disk 104 and the disk 104
Can be separated from the light that has returned after being reflected by the semiconductor laser 101, so that no light returns to the semiconductor laser 101. For this reason, even when the distance between object images is reduced, fluctuations in the light amount of the semiconductor laser 101 and noise do not occur. Therefore, the effect of reducing the size of the device using this embodiment is greater.

Next, the optical head device shown in FIG. 6 will be described. As shown in FIG. 6, the light emitted from the semiconductor laser 101 as a light source is split into a main beam and two sub-beams when passing through a diffraction grating 132 of a wedge lens 130 as a condensing optical system ( The sub-beam is not shown). These beams are collected by the lens surface of the wedge lens 130, and
04. The aperture of the wedge lens 130 is formed by an aperture stop 13 provided around the diffraction grating 132.
Three. The light reflected / refracted by the disk 104 is transmitted to the wedge surface 131 of the wedge lens 130.
And is incident on the photodetector 105R provided at a position different from the light emitting point.

In the case of the optical system shown in FIG. 6, as in the case of the optical system shown in FIG. 5, no light returns to the semiconductor laser 101. That is, by the action of the wedge lens 130, the light traveling from the semiconductor laser 101 to the disk 104 and the light reflected back from the disk 104 can be separated. For this reason, even when the object-image distance is reduced, the semiconductor laser 101
There is no fluctuation of light amount and no noise. Therefore,
Also in this case, the effect of reducing the size of the device using the present embodiment is enhanced.

In the present embodiment, the case where a single plano-convex lens is used as the condensing optical system has been described as an example, but the condensing optical system is constituted by using a plurality of lenses. In this case, or even when the condensing optical system is configured by using a lens other than the plano-convex lens, the effect of reducing the size of the apparatus using the present embodiment is not impaired.

The aperture stop may be arranged on the disk side with respect to the lens as the light collecting optical system (FIGS. 1 and 5), or may be arranged on the light source side (FIG. 6). When the position of the aperture stop changes, the Fresnel number N = (a × a) / (λ ×
The radius a of the aperture at the time of calculating L2) is the radius when the aperture of the aperture stop is projected onto the main surface of the lens on the disk side.

FIG. 7 shows an outline of a magnetic disk drive as an information recording / reproducing apparatus. As shown in FIG. 7, in this magnetic disk drive, the optical head device 202 of the present embodiment having the above-described configuration is used. The disk 104 is sandwiched from above and below by a magnetic head 201 as an information head device attached to the arm 211, thereby restricting the position of the disk 104 in the z direction. Each part of the optical system of the optical head device 202 and the magnetic head 201 are fixed to the housing 210. The housing 210 is provided with the transfer means 20 as a moving device.
3 so that the optical head device 20
2 and the magnetic head 201 can move from the inner peripheral side to the outer peripheral side in the radial direction of the disk 104. The disk 104 is rotated by a motor 204 as a rotating unit. With these mechanisms, information is recorded and reproduced over the entire surface of the disk 104.

In the magnetic disk drive as the information recording / reproducing apparatus, since the optical head device 202 having the configuration of the present embodiment is used, the entire information recording / reproducing apparatus can be downsized. In addition, since it is hardly affected by external changes such as temperature change and vibration, stable recording and reproduction of information can be performed.

<Second Embodiment> Next, a second embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS. 1, 3, and 8 to 13. FIG. In the present embodiment, astigmatism caused by the difference in the position of the light-convergent point due to the difference in the number N of Fresnel is used.

In the optical head device shown in FIG. 1, instead of the aperture stop 103 having a circular aperture, an aperture stop 111 having a rectangular aperture shown in FIG. 8 or an aperture stop having an oblong aperture shown in FIG. By using 112,
Astigmatism can be generated in the beam spot irradiated on the disk 104.

In the aperture stop 111 having a rectangular opening shown in FIG. 8, the width in the x direction when projected onto the main surface on the disk side is 160 μm, and the width in the y direction is 320 μm. The distance L2 between the converging point Q2 on the geometrical optics and the second principal point H2 of the lens 102 is 2 mm, and the semiconductor laser 10
If the wavelength of light emitted from 1 is 800 nm, the number of Fresnel Nx in the x direction is 4 and the number of Fresnel Ny in the y direction is 1
It becomes 6. Therefore, the light is collected by the lens 102,
The beam spot applied to the disk 104 is
Astigmatism as shown in FIG. Here, the point where the spot half-value width becomes minimum in the x direction where the Fresnel number is small is on the side closer to the lens 102, and the point where the spot half-value width becomes minimum in the y direction where the Fresnel number is large is on the side farther from the lens 102. . In this case, the difference (astigmatic difference) between the position of the point where the spot half-value width in the x direction is minimum and the point where the spot half-value width in the y direction is minimum is about 120 μm.

When an aperture stop 112 having an oblong aperture shown in FIG. 9 is used, similarly to the case where an aperture stop 111 having a rectangular aperture shown in FIG. 8 is used, a beam having astigmatism is used. Spots can be generated.

FIG. 11 shows an example in which a beam spot having such astigmatism is used for focus detection.
This will be described with reference to FIG. As shown in FIG. 11, linearly-polarized light emitted from a semiconductor laser 101 as a light source passes through a polarizing beam splitter 121, and then becomes １ ／.
The light becomes circularly polarized light by the wave plate 122. This light is condensed by a lens 102 as a condensing optical system, and is irradiated on an optical disk 120 as an information storage medium. The light reflected and diffracted by the optical disk 120 is condensed again by the lens 102, and when transmitted again through the quarter-wave plate 122, the light emitted from the semiconductor laser 101 differs from the light emitted from the semiconductor laser 101 by 9 times.
It becomes linearly polarized light having a different polarization direction by 0 degrees. This light is reflected by the polarization beam splitter 121, passes through the aperture stop 113, and then enters the photodetector 107. Photodetector 107
Comprises a plurality of light receiving areas and outputs a signal corresponding to the amount of light received.

FIG. 12 shows the shape of the aperture stop 113.
As shown in FIG. 12, the aperture stop 113 is provided with a rectangular opening inclined at 45 degrees with respect to the −y direction.
The aperture stop 113 realizes an optical system having a small Fresnel number in the u direction and a large Fresnel number in the v direction.
As a result, in the light incident on the photodetector 107, the point where the spot half-value width becomes minimum in the u direction where the Fresnel number is small is closer to the aperture stop 113, and the spot half-value width becomes minimum in the v direction where the Fresnel number is large. An astigmatism such that a given point is on the far side from the aperture stop 113 can be given. The photodetector 107 is disposed between these two points, and when the light transmitted through the lens 102 is condensed on the information surface of the optical disc 120, the shape of the condensed spot on the photodetector 107 becomes circular. Has been adjusted as follows.

Here, astigmatism is caused by the difference in the Fresnel number in the path from the condenser lens 102 to the photodetector 107. When the number of Fresnels in the u direction (the minimum number of Fresnels _Nmin ) is 10 or less, the difference in light condensing position becomes remarkable, and substantially effective astigmatism occurs. Here, the minimum Fresnel number N _min is equal to u of the aperture stop 113.
Assuming that the value of half of the opening width in the direction is a1, the following (Equation 23)
It is represented by

[0079]

N _min = (a1 · a1) / (λ · L2)

FIG. 13 shows the light receiving area 10 of the photodetector 107.
8a to 108d and pattern example 109 of cross section of light beam
f, 109n. The focus error signal is the difference between the sum of the signal detected in the light receiving region 108a and the signal detected in the light receiving region 108c, and the sum of the signal detected in the light receiving region 108b and the signal detected in the light receiving region 108d. Obtained from When the optical disk 120 moves away from the lens 102, the cross section of the light beam on the photodetector 107 becomes 1
09f, and the optical disk 120 is the lens 1
When approaching 02, the cross section of the light beam on the photodetector 107 has a shape like 109n. For this reason, if the focus error signal is generated as described above and servo is performed using the focus error signal, it is possible to keep the focal point on the optical disk 120 following the surface deviation of the optical disk 120 or the like.
The tracking signal can be obtained by a phase difference method.

According to the present embodiment, a beam spot having astigmatism can be easily generated without adding a new glass part or the like. Also, unlike an optical system using a half mirror made of parallel plate glass, transmitted light can be used for light traveling from the semiconductor laser 101 to the optical disk 120, so that the surface accuracy of components can be reduced, and inexpensive components can be used. An optical system can be configured. In addition, coma as in the case where the parallel flat glass is used at an angle does not occur, and only astigmatism can be given.

In this embodiment, the case where a beam spot having astigmatism is used for focus detection has been described as an example. However, in this embodiment, a method of generating astigmatism has been described. The application range is not limited to focus detection only.

<Third Embodiment> Next, a third embodiment of the present invention will be described.
The embodiment will be described with reference to FIG. 14 and FIG. In the present embodiment, an example of an optical system capable of correcting astigmatism of a light beam having astigmatism and obtaining a focused spot with less aberration will be described.

The semiconductor laser differs in the position of the light emitting point in the direction parallel to the active layer and the direction perpendicular to the active layer. That is, the semiconductor laser has an astigmatic difference. This astigmatic difference is compressed by the magnification of the optical system by the magnification of the optical system when the light is condensed again by the lens 102. However, if the tolerance of the aberration with respect to the condensed spot is low, there is a problem.

FIGS. 14A and 14B show the effect of the astigmatic difference. Here, the active layer of the semiconductor laser 101 is
Assume that they lie in the yz plane. FIG. 14A shows y
FIG. 1 is a view of the optical system viewed from a direction perpendicular to a −z plane, and FIG.
FIG. 4B is a diagram of the optical system viewed from a direction perpendicular to the zx plane orthogonal to the yz plane. As shown in FIG. 14A, in the yz plane where the active layer exists, a light emitting point exists inside the active layer with respect to the end surface of the semiconductor laser 101.
On the other hand, as shown in FIG. 14B, in the zx plane,
Since light confinement reaches the end face of the semiconductor laser 101, a light emitting point exists on the end face of the semiconductor laser 101. Therefore, the beam spot condensed by the lens 102 is located closer to the lens 102 in FIG. 14A, and is located farther from the lens 102 in FIG. 14B.

As shown in FIG. 14C, in this embodiment, the aperture stop 114 is inserted for the light condensed by the lens 102. As shown in FIG.
The aperture stop 114 has an elliptical aperture whose aperture width in the x direction is slightly narrower. By using the aperture stop 114, the number of Fresnels in the x direction can be made smaller than the number of Fresnels in the y direction, so that the converging point in the x direction can be closer to the lens 102. As a result, the x direction and y
The converging points in the directions can be matched. in this way,
Aperture stop 1 having an elliptical aperture whose aperture width in the x direction is slightly narrower
By inserting 14 into the light condensed by the lens 102, astigmatism caused by the astigmatic difference of the semiconductor laser 101 can be reduced.

Here, the astigmatism of the light emitted from the semiconductor laser 101 is reduced by the astigmatism caused by the difference in the Fresnel number in the path from the semiconductor laser 101 to the condenser lens 102. Also in this case, when the number of Fresnels in the x direction (the minimum number of Fresnels N _min ) is 10 or less, the difference in the light condensing position becomes significant,
A substantially effective effect of reducing astigmatism is obtained.

In this case, as in the case of the second embodiment, no coma aberration occurs when the parallel flat glass is used in an inclined state, so that the semiconductor laser 101 does not deteriorate the wavefront. And the astigmatism of the optical system can be corrected. Therefore, a high-quality wavefront with less aberration can be obtained.

According to the present embodiment, astigmatism caused by astigmatism of a semiconductor laser can be eliminated with a simple configuration, so that an inexpensive and high-performance optical head device can be realized.

In the present embodiment, the case where astigmatism caused by astigmatism of the semiconductor laser 101 is corrected has been described as an example. However, the present invention is not necessarily limited to this case. For example, with the configuration of the present embodiment, astigmatism and the like caused by optical components can be corrected.

<Fourth Embodiment> Next, a fourth embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS. In this embodiment, an example of an optical system which can correct astigmatism of a ray having astigmatism and obtain light having a wavefront with less aberration will be described.

FIG. 16 shows the structure of a laser pointer as an example. Here, astigmatism caused by the astigmatism difference of the semiconductor laser 101 is also corrected. FIG.
In the figure, reference numeral 302 denotes a battery for causing the semiconductor laser 101 to emit light.
And the lens 102 are housed in a housing 301. A switch 303 is provided on the outer surface of the housing 301, and the switch 303
Can be turned on / off. Further, an aperture stop 114 is arranged on the side of the semiconductor laser 101 of the lens 102.

As shown in FIG. 16, light emitted from a semiconductor laser 101 serving as a light source passes through an aperture stop 114, and is converted into parallel light by a lens 102.
1 is emitted outside. As shown in FIG. 15, the aperture stop 114 has an elliptical aperture whose aperture width in the x-direction is slightly narrower. The semiconductor laser 101 is arranged in such a direction that the active layer exists in the yz plane. The astigmatism caused by the astigmatism difference of the semiconductor laser 101 is based on the same principle as that of the third embodiment. The astigmatism caused by the aperture stop 114 (the astigmatism of the path from the semiconductor laser 101 to the condenser lens 102) Astigmatism caused by the difference in the Fresnel number) cancels out and becomes smaller.

Therefore, the light emitted to the outside of the housing 301 becomes a plane wave, and the cross-sectional shape of the light beam can be kept circular even if it travels a long distance. Also, the lens 102
Can be made closer to the semiconductor laser 101, so that the size of the device can be reduced. Further, since the cross-sectional shape of the light beam can be reduced, a bright light beam can be obtained.

<Fifth Embodiment> Next, a fifth embodiment of the present invention will be described.
The embodiment will be described with reference to FIGS. In the present embodiment, a case where focus control is performed by an optical disk device or the like will be described.

FIG. 17 shows an example of the optical head device according to the present embodiment. As shown in FIG. 17, light emitted from a semiconductor laser 101 as a light source is reflected by a half mirror 123, and is reflected by a lens 1 as a condensing optical system.
After being condensed by 02, the light is irradiated onto an optical disk 120 as an information storage medium. Reflected on the optical disc 120
The diffracted light is collected again by the lens 102,
The light passes through the half mirror 123. The light condensed by the lens 102 is given astigmatism when passing through the half mirror 123, and then received by the photodetector 125. The photodetector 125 outputs an electric signal according to the amount of received light.

Although not described in detail here, the photodetector 1
Reference numeral 25 denotes a plurality of detection areas, from which a focus error signal is obtained by an astigmatism method and a tracking error signal is obtained by a phase difference method. The actuator 124 as a lens holding unit moves the lens 102 in the focus direction and the tracking direction according to the focus error signal and the tracking error signal.

Actuator 1 as lens holding means
Normally, the distance between the lens 102 and the optical disk 120 can be arbitrarily changed, but when the focus control is performed, the lens 102 and the optical disk 12
The distance to zero remains virtually constant. In this focus control, the lens 102 is controlled such that the point where the intensity of the condensed light is maximum comes on the optical disc 120. Therefore, also in this case, the optical disc 120 is arranged not at the converging point on geometrical optics but at the point where the light intensity becomes maximum.

When the Fresnel number N is small, the point at which the intensity of the condensed light is maximum exists at a position closer to the lens 102 than the converging point on geometrical optics. Therefore, the distance from the surface of the optical disc 120 to the vertex of the lens 102 (FIG. 1)
7 (WD of working distance)
Is smaller than when the optical system is designed using geometrical optics. If the working distance is small, the optical disk 120
When the optical disc 120 is rotated,
And the lens 102 collide, and the lens 102 and the optical disc 1
20 may be damaged.

In order to secure a predetermined working distance when the Fresnel number N is small (N is 10 or less), the focal length of the lens 102 is designed to be longer than when the Fresnel number N is sufficiently large. There is a need. That is, if the focal length of the lens 102 is designed to be longer, the focal point on geometrical optics can be brought to a position farther than the lens 102, and the point at which the light intensity becomes maximum is determined by design. Can be brought to the position. As a result, a sufficient working distance can be secured.
20 and the lens 102 do not collide, and the lens 10
2 and the optical disk 120 are not likely to be damaged.

If the Fresnel number N is reduced, the distance between the object and the image in the optical system can be reduced by using lenses having the same focal length. For this reason, the size of the device can be reduced. Conversely, if the object-image distance is the same, the focal length of the lens can be increased, so that the radius of curvature of the lens can be increased. As a result, the manufacture of the lens becomes easy.

FIG. 18 shows an outline of an optical disk drive as an information recording / reproducing apparatus using the optical head device according to the present embodiment. In FIG. 18, an optical head device 202 also has a function as an information head device for recording or reproducing information. Therefore, a magnetic head or the like is not required, and recording and reproducing of information can be realized with a simpler configuration. The optical head device 202 is moved from the inner peripheral side to the outer peripheral side in the radial direction of the disk 120 by the transfer means 203 as an optical head device moving device. The disk 120 is rotated by a motor 204 as a rotating unit. With these mechanisms, information is recorded and reproduced over the entire surface of the disk 104.

[0103]

As described above, according to the optical head device of the present invention, even if the point at which the intensity of the condensed light is maximum deviates from the convergent point on geometrical optics, the intensity of the light can be reduced. The information storage medium can be arranged at a point where the maximum value is obtained. Therefore, the distance between the object and the image can be reduced in order to reduce the size of the apparatus. In addition, since the distance between the object and the image can be reduced in this manner, the light emitted from the light source is less likely to be affected by a change in the external world such as a change in temperature or vibration. That is, according to the optical head device of the present invention, it is possible to reduce the size of the device and to stably obtain a signal for positioning the information head device.

Further, according to the information recording / reproducing apparatus of the present invention, the size of the entire apparatus can be reduced. In addition, since it is hardly affected by external changes such as temperature change and vibration, stable recording and reproduction of information can be performed.

Further, according to the optical system of the present invention, astigmatism can be given to the condensing optical system and astigmatism of the condensing optical system can be removed by using only small and simple components.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration of an optical head device according to a first embodiment of the present invention.

FIG. 2 is a plan view showing an example of an aperture stop used in the optical head device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a positional relationship between members constituting an optical system of the optical head device according to the first embodiment of the present invention.

FIG. 4 is a plan view showing another example of the aperture stop used in the optical head device according to the first embodiment of the present invention.

FIG. 5 is a schematic sectional view showing another configuration of the optical head device according to the first embodiment of the present invention.

FIG. 6 is a schematic sectional view showing still another configuration of the optical head device according to the first embodiment of the present invention.

FIG. 7 is a schematic sectional view showing the configuration of an information recording / reproducing apparatus according to the first embodiment of the present invention.

FIG. 8 is a plan view showing an example of an aperture stop used in an optical head device according to a second embodiment of the present invention.

FIG. 9 is a plan view showing another example of the aperture stop used in the optical head device according to the second embodiment of the present invention.

FIG. 10 is a conceptual diagram showing a light converging point and a light converging spot when astigmatism occurs according to the second embodiment of the present invention.

FIG. 11 is a schematic sectional view showing a configuration of an optical head device according to a second embodiment of the present invention.

FIG. 12 is a plan view showing an example of an aperture stop used in an optical head device according to a second embodiment of the present invention.

FIG. 13 is a front view showing an example of a pattern of a cross section of a light beam and a detection area of a photodetector of an optical head device according to a second embodiment of the present invention.

FIG. 14 is a schematic sectional view showing an example of an optical system of an optical head device according to a third embodiment of the present invention.

FIG. 15 is a plan view showing an example of an aperture stop used in an optical head device according to a third embodiment of the present invention.

FIG. 16 is a schematic sectional view showing an example of an optical system according to a fourth embodiment of the present invention.

FIG. 17 is a schematic sectional view showing an example of an optical system of an optical head device according to a fifth embodiment of the present invention.

FIG. 18 is a schematic sectional view showing an example of an information recording / reproducing device according to a fifth embodiment of the present invention.

FIG. 19 shows the relationship between the Fresnel number, the deviation between the point where the intensity of the condensed light becomes maximum and the converging point on geometrical optics, and the depth of focus in the first embodiment of the present invention. Figure

FIG. 20 is a schematic cross-sectional view showing an example of an optical system of an optical head device according to the related art.

[Explanation of symbols]

Reference Signs List 101 semiconductor laser 102 lens 103, 110, 111, 112, 113, 114, 1
33 Aperture stop 104 Disk 105L, 105R, 106, 107, 125 Photodetector 108a-d Detection area 109f, 109n Light beam pattern 120 Optical disk 121 Polarization beam splitter 122 Quarter wave plate 123 Half mirror 124 Actuator 130 Wedge lens 131 Wedge surface 132, 151, 152, 162 Diffraction grating 150, 160 Diffraction element 201 Magnetic head 202 Optical head device 203 Transport means 204 Motor 210 Housing 211 Arm 301 Housing 302 Battery 303 Switch

Claims (10)

[Claims] 1. A light source for emitting light, a condensing optical system for condensing light emitted from the light source on an information storage medium for recording or reproducing information, the information storage medium and the condensing optical system Holding means for keeping the distance to the system constant, wherein the focal length of the light-collecting optical system is f, and a principal point on the light source side of the light-collecting optical system from the light source. Where L1 is the distance to the principal point 1 and h is the distance from the second principal point, which is the principal point on the information storage medium side of the condensing optical system, to the information storage medium held by the holding means. An optical head device satisfying the following (Equation 1) and (Equation 2). L2 = f × L1 / (L1-f) h <L2 2. The wavelength of light emitted from the light source is λ,
2. The optical head device according to claim 1, wherein when the numerical aperture on the information storage medium side of the condensing optical system is NA, the following (Equation 3) and (Equation 4) are satisfied. 3. Δz = λ / (2π × NA × NA) h <L2-Δz 3. The focusing optical system according to claim 1, further comprising an aperture stop for determining a numerical aperture, wherein the aperture stop has a circular aperture.
Or the optical head device according to 2. 4. A plane including the second principal point and perpendicular to an optical axis is defined as a main surface on the information storage medium side, and an aperture radius when the aperture stop is projected on the main surface on the information storage medium side is defined as: 4. The optical head device according to claim 3, wherein a, the Fresnel number N defined by the following (Equation 5) is 10 or less, where λ is the wavelength of light emitted from the light source. N = (a × a) / (λ × L2) 5. The optical head device according to claim 1, wherein the focusing optical system includes an aperture stop for determining a numerical aperture, and the aperture stop has a square aperture. 6. The optical head device according to claim 1, wherein the condensing optical system includes an aperture stop that determines a numerical aperture, and the aperture stop has an aperture having a different aperture width depending on a direction. 7. A minimum aperture when projecting the aperture stop onto the main surface on the information storage medium side, wherein a plane including the second main point and perpendicular to the optical axis is a main surface on the information storage medium side. the half value width a1, the optical head apparatus according to claim 6 minimum Fresnel number N _min is equal to or less than 10, which is defined by the following equation (6) the wavelength of light emitted as a λ from the light source. N _min = (a1 · a1) / (λ · L2) 8. An information head device for recording information on an information storage medium or reproducing information recorded on the information storage medium, an optical head device for positioning the information head device, and the information head device. An information recording / reproducing apparatus comprising: a moving unit for relatively moving a position of the information recording medium with the information storage medium, wherein the optical head device is used as the optical head device.
7. An information recording / reproducing apparatus using the optical head device according to any one of 7. 9. The information recording / reproducing apparatus according to claim 8, wherein the optical head device also functions as the information head device. 10. An optical system comprising: a light source for emitting light; a condenser optical system for condensing light emitted from the light source; and an aperture stop for determining a numerical aperture of the condenser optical system. , The aperture stop has an opening having a different opening width depending on a direction,
The focal length of the light-collecting optical system is f, the distance from the light source to the first principal point on the light-source side of the light-collecting optical system is L1, and the distance between the light-collecting optical system and the information storage medium is A plane including the second principal point, which is the principal point, and perpendicular to the optical axis is defined as the main surface on the information storage medium side, and is half the minimum aperture width when the aperture stop is projected on the main surface on the information storage medium side. Is the value of a1, the wavelength of light emitted from the light source is λ, the minimum Fresnel number N _min defined by the following (Formula 7) and (Formula 8) is 10 or less, and the aperture in the direction of the aperture stop is An optical system wherein astigmatism is caused by a difference in width. L2 = f × L1 / (L1-f) _Nmin = (a1 · a1) / (λ · L2)