JP2865074B2 - Optical head device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head, and more particularly to an optical head device for reproducing information recorded on optical recording media having different thicknesses such as a digital video disk (DVD) and a compact disk (CD). Things.

[0002]

2. Description of the Related Art One of optical recording media in multimedia.
For example, DVDs have attracted attention. In the optical head device for DVD, not only reproduction of DVD but also reproduction of CD which is a conventional optical recording medium is required. Conventionally, as this type of optical head device capable of reproducing DVDs and CDs, Optical Review, Vol. 1, No. 1, November 1994 (OPTICAL REVIEW, VO
L.1, NO.1, NOVEMBER, 1994). By the way, DVD and CD have a substrate thickness of 0.6 m.
Because of the difference between m and 1.2 mm, this type of optical head device reads recorded information through transparent substrates having different thicknesses. For this reason, it is necessary to switch the focusing position on the optical recording medium by the objective lens of the optical head device and the numerical aperture (NA) between DVD and CD.

FIG. 6A is a cross-sectional view of a surface including an optical axis of an example of a conventional optical head device. Lens 22
Collimates the light beam from the light source 21. The half mirror 23 is an optical element for separating the forward and backward light beams. The hologram optical element 24 has a blaze-type lattice shape as shown in FIG. 6B, and has a function of correcting spherical aberration caused by a difference in substrate thickness, and a function of effectively transmitting transmitted light (zero-order diffracted light) and diffracted light. There is a function to change the NA. The objective lens 25 focuses the transmitted light and the first-order diffracted light on the recording surface of the DVD 28 or CD 29, respectively. The error signal detection / reproduction signal detection optical system 26 is an optical system that detects an error signal and a reproduction signal from a reflected light beam of the DVD 28 or CD 29.

Next, the operation will be described. After the light beam emitted from the light source 21 is collimated by the lens 22, the light beam passes through the half mirror 23 and enters the hologram optical element 24. The light is divided into transmitted light and first-order diffracted light by the hologram optical element 24 and is condensed by the objective lens 25. The focused light of the 0th-order diffraction corrects spherical aberration with a substrate thickness of 0.6 mm, and the first-order diffraction light corrects spherical aberration with a substrate thickness of 1.2 mm. Thus, when reproducing the DVD 28, the transmitted light of the hologram optical element 24 is used, and when reproducing the CD 29, the diffracted light of the hologram optical element 24 is used. Light reflected from each medium passes through the objective lens 25 and the hologram optical element 24, is reflected by the half mirror 23, and enters the error signal detection / reproduction signal detection optical system 26. Then, the optical system 26 detects an error signal and a reproduction signal.

[0005]

In such a conventional optical head device, there is a problem that the optical utilization of the optical head device is low. The reason is that the hologram optical element 24
Are always transmitted light (0th-order diffracted light) and 1st-order diffracted light, and only one of them is used depending on the type of optical recording medium, and the other light not used is wasted. It is. Incidentally, the intensity of the transmitted light and the diffracted light is different from the incident light flux of the hologram optical element 24.
53% (transmitted light) and 29% (first-order diffracted light).

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical head device capable of reproducing DVDs and CDs having substrates of different thicknesses and having improved light utilization.

[0007]

SUMMARY OF THE INVENTION An optical head device according to the present invention has an object having two focal points so that the position of a focal spot on an optical recording medium is different depending on the area where light from a light source is incident. A lens and optical means for selectively causing light from the light source to enter different regions of the objective lens, and configured to form pots for condensing light on optical recording media having different thicknesses, respectively. . For example, as a preferred configuration of the present invention, the objective lens has a configuration in which the focal lengths are different between a concentrically arranged central region and a peripheral region, and the optical means corresponds to the central region of the objective lens. The optical system is configured to selectively form a small-diameter ring-shaped light beam and a large-diameter ring-shaped light beam corresponding to the peripheral region. In particular, the optical means includes a reduction optical system that converts the light from the light source into a reduced parallel light beam, a first optical element that converts the reduced light beam into a ring-shaped divergent light, and the ring-shaped divergent light. A second optical element for converting the light into a ring-shaped parallel light, wherein a diameter of the ring-shaped parallel light is changed by changing an optical axis distance between the first optical element and the second optical element. Configuration.

Here, in the present invention, the first optical element is an axicon lens or a transmission axicon hologram, and the second optical element is an axicon lens or a transmission axicon hologram. Is preferred. Alternatively, it is preferable that the first optical element is a conical mirror or a reflective axicon hologram, and the second optical element is a conical mirror or a reflective axicon hologram.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional configuration diagram including an optical axis showing a first embodiment of the optical head device of the present invention. The light beam (which is linearly polarized light) emitted from the light source 1 is collimated by the lens 2, and the light beam reduction optical system 3 reduces the diameter of the collimated light beam. Thereafter, the light beam is diverged in a ring shape by the first axicon lens 4 and further collimated by the second axicon lens 5 while keeping the ring shape. The light flux 7 passes through the polarization beam splitter 10 and the quarter-wave plate 11 and becomes circularly polarized light and enters the bifocal objective lens 6.

As shown in FIG. 2, the bifocal objective lens 6 has a central region 6a and a peripheral region 6b which are concentrically distinguished from each other, for example, so that the curvature and the refractive index of the two are different. In the central area 6a, the light beam is condensed on the recording surface of the CD 9 to correct a spherical aberration with a substrate thickness of 1.2 mm. In the peripheral area 6b, the light beam is focused on the recording surface of the DVD 8, and the spherical aberration with a substrate thickness of 0.6 mm is corrected.
The NA of each area is DVD8 and CD9.
It effectively satisfies the standard. The second axicon lens 5 is configured to be movable in the optical axis direction. When the second axicon lens 5 moves in the direction 5a which is the light source side direction, the ring-shaped collimated light beam 7 Is a small diameter 7a and the central area 6 of the bifocal objective lens 6
a. When the second axicon lens 5 moves in the direction 5b which is the direction toward the bifocal objective lens, the ring-shaped collimated light beam has a large diameter 7b and enters the peripheral area 6b of the bifocal objective lens 6. Therefore, the position and NA of the condensed spot on the optical recording medium are changed according to the areas 6a and 6b that are incident on the bifocal objective lens 6.

Therefore, in the optical head device of the first embodiment, when the optical recording medium is a CD 9, the second axicon lens 5 is moved in the direction 5a. As a result, the light beam from the light source 1 has a small diameter, and is incident on the central region 6a of the bifocal objective lens 6. As a result, the light beam forms a focused spot with a small NA at a position corresponding to the thick transparent substrate of CD9. The optical recording medium is DVD8
In the case of (2), the second axicon lens 5 is moved in the direction 5b. As a result, the light beam is brought into a large diameter state, and is incident on the peripheral region 6b of the bifocal objective lens 6. As a result, the light flux forms a focused spot with a large NA at a position corresponding to the thin transparent substrate of the DVD 8. Then, the reflected light from each medium passes through the bifocal objective lens 6 and the quarter-wave plate 11, and becomes a linearly polarized light inclined at 90 degrees from the outward path. Therefore, this reflected light beam is reflected by the polarization beam splitter 1.
0 and is reflected by the error signal detection / reproduction signal detection optical system 12
Led to. The optical system 12 detects a focus and tracking error signal and a reproduction signal by using an existing technology.

As described above, by moving the second axicon lens 5 with respect to the CD and DVD of the optical recording medium to be reproduced, a desired focal position and a focused spot of NA are created, and the CD 9 and DVD 8 are Can be reproduced together. In any case, since all the light beams from the light source are used for reproduction, the light utilization rate is increased, and high-sensitivity reproduction can be realized.

FIG. 3 is a cross-sectional view of a second embodiment of the optical head device according to the present invention, including the optical axis, and the same parts as those in the first embodiment are denoted by the same reference numerals. Here, the axicon lenses 4 and 5 of the first embodiment described above are used.
Are replaced with transmissive axicon holograms 4A and 5A. The first transmissive axicon hologram 4A can diverge incident light in a ring shape, and the second transmissive axicon hologram 5A can emit parallel light having a diameter corresponding to the diameter of the incident light. By moving the transmissive axicon hologram 5A in the directions 5a and 5b, light beams having different diameters can be obtained as in the first embodiment. By selectively entering the peripheral region 6a and the peripheral region 6b, it is possible to obtain a focal position and a focal spot of NA corresponding to CD9 and DVD8. Therefore, also in the second embodiment, it is possible to increase the light use efficiency.

FIG. 4 is a sectional view of an optical head according to a third embodiment of the present invention, including an optical axis, and the same parts as those in the above embodiments are denoted by the same reference numerals. Here, the above-described axicon lens and transmission-type axicon hologram are replaced by first and second conical mirrors 4B and 5B. The light beam (which is linearly polarized light) emitted from the light source 1 is collimated by the lens 2, and the light beam reduction optical system 3 reduces the diameter of the collimated light beam. Thereafter, the light beam is reflected in a ring shape by the first conical mirror 4B,
The light diverges, is reflected again by the second conical mirror 5B, and is collimated in a ring shape. This luminous flux 7
Passes through the polarizing beam splitter 10 and the quarter-wave plate 11 to become circularly polarized light and enter the bifocal objective lens 6.
The bifocal objective lens 6 is the same as in each of the above embodiments.

Here, the second conical mirror 5B is moved in the optical axis direction. When the second conical mirror 5B moves in the direction 5a, the ring-shaped collimated light beam has a large diameter 7a and enters the peripheral area 6b of the objective lens 6. When the second conical mirror 5B moves in the direction 5b, the ring-shaped collimated light beam has a small diameter 7b and enters the central area 6a of the objective lens 6. By moving the conical mirror with respect to the optical recording medium to be reproduced, the DV
A focused spot with a desired focal position and NA is created for each of D8 and CD9. The reflected light from each optical recording medium is transmitted to a bifocal objective lens 6 and a １ ／ wavelength plate 11.
And the outgoing path becomes linearly polarized light inclined at 90 degrees. For this reason, the reflected light beam from the disc is reflected by the polarization beam splitter 10, and the error signal detection / reproduction signal detection optical system 1
It is led to 2. The optical system 12 detects a focus and track error signal and a reproduction signal by using an existing technology.

In the third embodiment, the conical mirror 4
Since the optical axis length of the components B and 5B can be shorter than in the first and second embodiments, the entire optical system can be reduced. The diameter of the light beam can be changed by moving the first conical mirror 4B in the optical axis direction.

FIG. 5 is a sectional view of an optical head device according to a fourth embodiment of the present invention, including an optical axis, and the same parts as those in the above embodiments are denoted by the same reference numerals. Here, the conical mirrors 4B and 5B of the third embodiment are replaced with first and second reflection-type axicon holograms 4C and 5C. By moving the second reflection type axicon hologram 5C in the directions 5a and 5b, the beam diameter can be changed, and the same effect as in the third embodiment can be obtained.
Also in this case, the first reflection type axicon hologram 4C can be moved in the optical axis direction.

In the embodiment described above, the combination of the optical element for converting the collimated light into the ring-shaped divergent light and the optical element for converting the ring-shaped divergent light into the ring-shaped collimated light has been defined. In the present invention, if a combination of different optical elements is possible, a combination of an axicon lens and an axicon hologram, an axicon lens and a conical mirror, an axicon hologram and a conical mirror, and the like are also possible.

[0019]

As described above, the optical head device according to the present invention has an objective lens having two focal lengths so that the condensed spot is different depending on the incident light area, and the incidence of light on the objective lens. Optical means for changing the area, and the optical means switches the incident area to the objective lens according to the type of the optical recording medium, so that the objective lens is positioned at the light-collecting position corresponding to the optical recording medium. Is formed, and information can be reproduced. With this, DVD
It is possible to reproduce optical recording media having different substrate thicknesses, such as CDs and CDs, and to use all of the light from the light source in any case. There is an effect that reproduction of sensitivity can be realized.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of the present invention.

FIG. 2 is a front view of a bifocal objective lens.

FIG. 3 is a configuration diagram of a second embodiment of the present invention.

FIG. 4 is a configuration diagram of a third embodiment of the present invention.

FIG. 5 is a configuration diagram of a fourth embodiment of the present invention.

FIG. 6 is a configuration diagram of a conventional optical head device and a schematic cross-sectional view of a hologram optical element.

[Explanation of symbols]

 Reference Signs List 1 light source 2 lens 3 light flux reduction optical system 4 first axicon lens 4A first transmission type axicon hologram 4B first conical mirror 4C first reflection type axicon hologram 5 second axicon lens 5A 2 transmission type axicon hologram 5B 2nd conical mirror 5C 2nd reflection type axicon hologram 6 bifocal objective lens 7 luminous flux 8 DVD 9 CD 10 polarization beam splitter 11 1/4 wavelength plate 12 error signal detection / reproduction Signal detection optical system

Claims (5)

(57) [Claims] 1. An optical head device for condensing a light beam from a light source as a light spot on an optical recording medium, wherein a position of a focal spot on the optical recording medium differs according to a difference in a region where light from the light source is incident. 1. An optical head device comprising: an objective lens having two focal points so that light from the light source selectively enters different regions of the objective lens. 2. The objective lens according to claim 1, wherein a focal length is different between a concentrically arranged central region and a peripheral region, and said optical means converts the light beam into a small-diameter ring-shaped light beam corresponding to said central region and said peripheral region. 2. The optical head device according to claim 1, wherein said optical head device is an optical system for selectively forming a large-diameter ring-shaped light beam corresponding to (a). 3. An optical system comprising: a reduction optical system that converts light from a light source into a reduced parallel light beam; a first optical element that converts the reduced light beam into a ring-shaped divergent light; A second optical element for converting the divergent light into a ring-shaped parallel light, and changing the optical axis distance between the first optical element and the second optical element to change the diameter of the ring-shaped parallel light. 3. The optical head device according to claim 2, wherein? 4. The light according to claim 3, wherein said first optical element is an axicon lens or a transmission axicon hologram, and said second optical element is an axicon lens or a transmission axicon hologram. Head device. 5. The optical head according to claim 3, wherein the first optical element is a conical mirror or a reflective axicon hologram, and the second optical element is a conical mirror or a reflective axicon hologram. apparatus.