JP2001184707A - Optical pickup and optical disk drive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup with which recording operation by a light source of one wavelength is made possible by making the utilization efficiency of another optical system higher than the utilization efficiency of an optical system which is the basis of design with the optical system designed to make a condenser lens and an objective lens common for two wavelengths by using two light sources varying in the wavelengths and an optical disk drive. SOLUTION: The optical system commonly using the objective lens 4 and the condenser lens 2 by using a hologram unit 1 for a DVD of 650 nm in wavelength and a hologram unit 20 for a CD of 780 nm in wavelength is mounted with a means 6 for separating and synthesizing the diversion light of the DVD and the diversion light of the CD and is inserted with a lens means 10 between the separating and synthesizing means 6 and the hologram unit 1 for the DVD, by which the utilization efficiency of the CD side optical system of 780 nm in wavelength may be made higher than the utilization efficiency of the DVD side optical system of 650 nm in wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup and an optical disk drive used in an optical disk apparatus for optically recording or reproducing information on an information recording medium such as an optical disk.

[0002]

2. Description of the Related Art In recent years, optical discs are capable of recording a large amount of information signals at high density, and have been used in many fields such as audio, video, and computers.

At present, compact disks (CDs), video disks, mini disks (MD), magneto-optical disks for computers, etc., which are widely commercially available, also have a thickness of 1.
A 2 mm substrate is used.

The objective lens of the optical pickup also has a thickness of 1.2.
It is designed to correct aberrations caused by mm substrates.

On the other hand, various studies have been made to increase the recording capacity. Among them, there are a method of improving the optical resolution by increasing the numerical aperture (NA) of the objective lens, and a method of shortening the wavelength used.

When the focused beam diameter φ is represented by the objective lens NA and the laser wavelength λ, φ = K × λ / NA K: constant.

Here, when the objective lens NA is increased, the condensed beam diameter φ decreases proportionally, but the allowable error of the disk tilt decreases in proportion to the cube of NA. It is necessary to reduce the thickness of the substrate of the disk in order to keep it to the extent.

However, if the substrate thickness of the disk is reduced in order to achieve higher density, one objective lens cannot maintain compatibility with an optical disk having a conventional substrate thickness.
It becomes necessary to change the objective lens NA.

In addition, the specified wavelength is 780 nm to 830 nm.
When the conventional optical disk designed in the above is reproduced with light having a shorter wavelength, there arises a problem that a sufficient reproduction signal cannot be obtained due to a difference in reflectance and absorptivity of the recording surface.

Therefore, as described in JP-A-8-55363, one objective lens and two light sources are used.
An optical pickup that can reproduce two types of optical disks having different substrate thicknesses has been proposed.

In the above publication, two types of light sources, a semiconductor laser having a wavelength of 650 nm and a semiconductor laser having a wavelength of 780 nm, are provided.
An optical pickup capable of reproducing a high-density optical disk having a thickness of 1.2 m and an optical disk having a substrate thickness of 1.2 mm has been disclosed.

According to this disclosure, the number of objective lenses is one, and when parallel light having a wavelength of 650 nm enters this objective lens and converges on the information recording surface of a high-density optical disk having a substrate thickness of 0.6 mm. It is designed to minimize aberration.

On the other hand, when reproducing an optical disk having a substrate thickness of 1.2 mm with light having a wavelength of 780 nm, spherical aberration corresponding to a substrate thickness difference of 0.6 mm is generated. By causing the light to enter as light, spherical aberration having a sign opposite to that of the above-mentioned spherical aberration is generated.
The aberration is reduced on the information recording surface of a 2 mm optical disk.

According to the technology disclosed in the above-mentioned publication, by adopting such a pickup structure, two substrates having different substrate thicknesses can be obtained.
It is intended to reproduce even an objective lens with no problem on optical discs of various types.

[0015]

However, recently,
Recordable discs such as CD-Rs and CD-RWs are rapidly becoming widespread, and it is natural for these discs to be reproduced, and also for pickups to be recordable.

In general, recording information requires 10 times or more the optical power required to reproduce information, and more than 20 times the optical power is required to satisfy the requirement for high-speed recording.

However, the light output of the semiconductor laser is limited, and it is necessary to use the light emitted from the semiconductor laser as effectively as possible to achieve the above power.

Since the utilization efficiency of light emitted from a semiconductor laser is determined by the optical system, the CD-R and the CD-R are used.
In the case of a pickup for RW, it is necessary to set the use efficiency of the optical system large so that a necessary recording power can be secured.

However, when one objective lens corresponds to the optical system of both light sources, for example, an objective lens designed to record and reproduce information on an optical disk having a substrate thickness of 0.6 mm using light having a wavelength of 650 nm is used. When recording or reproducing information on or from an optical disk with a substrate thickness of 1.2 mm using light having a wavelength of 780 nm, the position of the light source is advanced to suppress the occurrence of aberration.
The utilization efficiency of the optical system was unilaterally determined to be a low value by the design of the optical system having a wavelength of 650 nm, and there was no degree of freedom, so that it was impossible to obtain the optical power required for recording.

In consideration of the above-mentioned problems of the conventional optical pickup, the present invention uses two light sources having different wavelengths,
In an optical system in which a condensing lens and an objective lens are shared by two wavelengths, the recording operation can be performed by making the utilization efficiency of the other optical system larger than the utilization efficiency of the optical system that is the basis of design. An optical pickup and an optical disk drive that are characterized.

[0021]

According to a first aspect of the present invention, there is provided a method comprising:
A light source and a second light source, reflecting divergent light from the first light source, transmitting divergent light from the second light source, and combining two light paths, In the optical pickup including the objective lens for condensing the light on the optical disc and the photodetector for receiving the reflected light from the disc, the optical system light utilization efficiency in the optical path on the first light source side is more than the second. A lens unit is mounted between the transmission / reflection unit and one of the light sources so that the optical system light use efficiency in the optical path on the light source side is increased.

According to a second aspect of the present invention, in an optical pickup corresponding to two types of optical discs having different substrate thicknesses, a first light source having a first wavelength, a second light source having a second wavelength, The divergent light from the first light source passes through the lens means, reflects the transmitted light, and transmits the divergent light from the second light source to combine two optical paths, and light of both wavelengths. And a condensing lens having the function of converging the divergent light, and condensing the light of the first wavelength on the optical disc when the substrate is thin, and the second light when the substrate is thick. An objective lens for condensing the light of the wavelength on the optical disk, and the reflected light of the light of the first wavelength from the disk is transmitted through the objective lens, reflected by the transmission / reflection means, and transmitted and received by the lens means. A first photodetector and a second wavelength light The reflected light from passing through the objective lens, a second photodetector for transmitting to receiving a transmission reflecting means,
Wherein the lens means is an optical element having a concave lens function, and the light of the first wavelength is transmitted through the lens means, reflected by the transmission / reflection means, and transmitted through the condenser lens. Lens means designed to be parallel light.

According to a third aspect of the present invention, in an optical pickup corresponding to two types of optical disks having different substrate thicknesses, a first light source having a first wavelength, a second light source having a second wavelength, The divergent light from the first light source passes through the lens means, transmits the transmitted light, reflects the divergent light from the second light source, and combines the two light paths, and the light of both wavelengths. And a condensing lens having the function of converging the divergent light, and condensing the light of the first wavelength on the optical disc when the substrate is thin, and the second light when the substrate is thick. An objective lens for condensing the light of the wavelength on the optical disk, and the reflected light of the light of the first wavelength from the disk is transmitted through the objective lens, transmitted by the transmission / reflection means, transmitted through the lens means, and received. A first photodetector and a second wavelength light Transmitted through the objective lens the reflected light from the second light detector for reflected and received by the transmission reflecting means,
Wherein the lens means is an optical element having a concave lens function, and the light of the first wavelength is transmitted through the lens means, transmitted through the transmission / reflection means, and transmitted through the condenser lens. Lens means designed to be parallel light.

According to a fourth aspect of the present invention, in an optical pickup corresponding to two types of optical disks having different substrate thicknesses, a first light source having a first wavelength, a second light source having a second wavelength, While reflecting the divergent light from the first light source, the divergent light from the second light source passes through the lens means,
A transmitting / reflecting means for transmitting the transmitted light to combine two optical paths, a condensing lens which transmits light of both wavelengths and has an action of converging divergent light, and An objective lens for condensing the light of the wavelength on the optical disc and condensing the light of the second wavelength on the optical disc when the thickness of the substrate is large, and reflecting the light of the first wavelength from the disc; The light passes through the objective lens and is reflected by the transmission / reflection means,
A first photodetector for transmitting and receiving light through the lens means;
A second photodetector that transmits reflected light from the disc of light having a wavelength of
In the optical pickup constituted by the above, the lens means is an optical element having a convex lens function.

According to a fifth aspect of the present invention, in an optical pickup corresponding to two types of optical disks having different substrate thicknesses, a first light source having a first wavelength, a second light source having a second wavelength, While transmitting divergent light from the first light source, divergent light from the second light source transmits through the lens means,
A transmitting / reflecting means for reflecting the transmitted light to combine two optical paths, a condensing lens having a function of transmitting light of both wavelengths and converging divergent light, and a first condensing lens having a thin substrate. An objective lens for condensing the light of the wavelength on the optical disc and condensing the light of the second wavelength on the optical disc when the thickness of the substrate is large, and reflecting the light of the first wavelength from the disc; A first photodetector for transmitting light through the objective lens and transmitting and receiving the light by the transmission / reflection means, and a reflected light of the light of the second wavelength from the disk transmitted through the objective lens and transmitted through the lens means. And a second photodetector that receives light reflected by the transmitting / reflecting means, wherein the lens means is an optical element having a convex lens function.

In the sixth aspect of the present invention, a wavelength selective aperture limiting means for limiting an aperture only for light of the second wavelength is mounted.

In the seventh aspect of the present invention, the wavelength-selecting aperture means restricts the aperture of only the second wavelength light so that the numerical aperture is 0.5.

In the eighth aspect of the present invention, the wavelength selection aperture means is driven integrally with the objective lens.

In the ninth aspect of the present invention, the wavelength selecting aperture means limits the aperture of the light of the first wavelength so that the numerical aperture becomes 0.6, and controls the light of the second wavelength. Thus, the numerical aperture is limited so that the numerical aperture becomes 0.5.

In a tenth aspect of the present invention, the objective lens is
For a disk having a small substrate thickness, the first wavelength light is designed so that aberration is reduced when the light is focused on the information recording surface on the disk. In the case of the second wavelength light, A second light source is arranged at a position where aberration is reduced when light is focused on an information recording surface on a disk with a thick substrate.

In the eleventh aspect of the present invention, the substrate thickness of the optical disk is about 0.6 mm and about 1.2 mm, respectively.

In the twelfth invention, the first wavelength is 6
20 nm to 680 nm, and the second wavelength is 750 nm.
nm to 810 nm.

According to a thirteenth aspect of the present invention, there is provided an optical disk drive equipped with any one of the above optical pickups.

[0034]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a schematic configuration of an optical system of an optical disk pickup.

Light emitted from a hologram unit 1 having a semiconductor laser and a photodetector built therein passes through a concave lens (lens means) 10 and is reflected by a transmission / reflection means 6 to cause a collimator lens (condensing lens) 2 to pass through. After the light path is changed by the rising mirror 3, the light enters the objective lens 4 and is focused on the optical disk 5.

The light from which information has been read on the disk returns to the objective lens 4, the rising mirror 3, the collimator lens 2, the transmission / reflection means 6, the concave lens 10, and the hologram unit 1, and is diffracted by the hologram 11 to be refracted in the unit. The light enters the detector 12 and detects an information signal.

The light beam 31 is a light beam having a numerical aperture (hereinafter, referred to as a numerical aperture A) necessary for recording and reproducing the optical disk substrate 5, and the light beam 31 is regulated by the aperture 30 provided below the objective lens 4. Is the outermost light beam.

The light emitted from the hologram unit 20 having a semiconductor laser and a photodetector built therein passes through the transmission / reflection means 6, passes through the collimator lens 2, passes through the mirror 3, and changes the optical path. Incident on the lens 4,
The light is focused on the optical disk 5 '.

The light from which information has been read on the disk returns to the objective lens 4, the rising mirror 3, the collimator lens 2, the transmission / reflection means 6, and the hologram unit 20, and is diffracted by the hologram 21 to be detected by the light detector 22 in the unit. To detect an information signal.

The light beam 36 has a numerical aperture (hereinafter referred to as a numerical aperture B) necessary for recording and reproducing the optical disc substrate 5 'having a different thickness.
), And the light beam 36 is the objective lens 4
Is the outermost light beam regulated by the wavelength-selecting aperture limiting element 35 installed at the lower part.

Here, as the optical system specifications, the light source wavelength of the hologram unit 1 is 650 nm, the NA of the objective lens 4 defined by the aperture 30 is 0.6, and the focal length is 2.33 m.
m, the thickness of the substrate 5 is 0.6 mm, the light source wavelength of the hologram unit 20 is 780 nm, the NA of the objective lens 4 defined by the aperture 35 is 0.5, and the thickness of the substrate 5 is 1.2 mm.

The objective lens is designed such that parallel light having a wavelength of 650 nm is incident thereon and converges without aberration when condensed on a substrate having a thickness of 0.6 mm.

The focal length of the collimator lens 2 is set to 1
0.5 mm. The concave lens 10 is a plano-concave lens with a radius of curvature of 10 mm. The focal length of the composite lens system of the collimator lens 2 and the concave lens 10 is 14 mm.

Here, it is the numerical aperture on the collimator side that determines the light utilization efficiency of the optical system in question. The larger the numerical aperture, the more light emitted from the LD can be guided to the optical system. it can.

Table 1 shows the output power of the objective lens based on the specific numerical aperture (NA of CL) of the collimator lens.

[0046]

[Table 1] The OL emission efficiency is an efficiency that includes transmission loss of an actual optical component in addition to the light use efficiency determined by the lens specification.

Assuming that, for example, an output power of the objective lens of about 20 mW is required to realize high-speed recording, from the results shown in Table 1, the LD output is 80 at NA 0.11.
It can be seen that the OL output power is too small even with mW. At least 0.13 to 0.14 or more of NA is required.

On the contrary, if the size is too large, the objective lens 6 cannot sufficiently stop down. For example, the beam diameter required for reproducing a DVD having a substrate thickness of 0.6 mm is said to be about 0.9 μm, but in order to achieve this beam diameter, the numerical aperture of the collimator lens 2 is about 0.1. It is known that it needs to be about one.

In other words, when it is desired to sufficiently narrow the beam diameter as in the case of reproducing a DVD, it is desired to reduce the numerical aperture. However, as in the case of recording a CD disc, it is desired to increase the light use efficiency. In such a case, it is desirable to increase the numerical aperture.

However, when a common collimator lens is adopted and the optical system is designed on the premise of DVD, the numerical aperture of the collimator lens is determined to be about 0.1.

Here, the following relationship is established between the numerical aperture NA of the objective lens and the collimator lens and the focal length f.

Objective lens NA / collimator lens NA =
Collimator lens f / Objective lens f When the above optical system specifications are substituted into this relational expression, collimator lens NA = 0.6 × 2.33 / 14 = 0.
1 (at the time of DVD), which indicates that the NA is designed to be suitable for DVD.

On the other hand, considering the case of a CD-type disc, as in the conventional example shown in FIG. 7, in the case of an optical system that does not include the concave lens 10, the focal length of the collimator lens is the same, and the difference in the numerical aperture of the objective lens is different. The numerical aperture of the collimator lens is reduced accordingly.

Collimator lens NA = 0.5 × 2.33
/14=0.083 However, in order to correct the spherical aberration caused by the difference in substrate thickness, the light source position is advanced, so that the actual numerical aperture is larger than the above numerical aperture, and is about 0.11.

It can be seen from this that the power required for recording cannot be secured.

On the other hand, as shown in the above embodiment of the present invention, one of the light sources, specifically, a concave lens is provided on the side of the DVD light source having a smaller numerical aperture to narrow the beam system than the light use efficiency. Is inserted, it is possible to shorten the focal length of the collimator lens itself.

The plano-concave lens having a radius of curvature of 10 mm is
In an optical system inserted between the hologram unit 1 as a VD light source and the transmission / reflection means 6 (midway of the DVD-side optical system), the numerical aperture of the collimator + plano-concave complex lens is set to about 0.
1, the numerical aperture of the collimator lens on the hologram unit 20 side, which is a light source for a CD-type disc without a plano-concave lens, can be increased to about 0.13. 80mW
In this case, it becomes possible to secure an output power of the objective lens of 20 mW or more.

That is, in an optical pickup that uses light of two wavelengths, it is possible to record information by reducing the aberration for one light and increasing the light use efficiency for the light of the other wavelength. A design that simultaneously achieves the two conditions of achieving light output can be performed independently for each wavelength.

The light of the first wavelength is a DV having a small substrate thickness.
If the second wavelength light is used for a D-type disc and the second wavelength light is used for a CD-type disc having a large substrate thickness, the former disc having a high recording density can be more accurately and precisely adjusted according to the density. At the same time as generating a focused light beam spot, the latter is recordable CD-R or CD-RW.
It is possible to achieve the optical power required for recording, which is compatible with such discs.

As described above, if a plano-concave lens is inserted only into the optical system on the DVD side and its radius of curvature is set to an appropriate numerical value, when a CD-based disc is used (hereinafter abbreviated as “CD time”). The collimator lens numerical aperture can be made larger than the collimator lens numerical aperture when using a DVD-based disc (hereinafter abbreviated as “DVD”).

FIG. 1 shows an embodiment of the present invention.
In the optical system described above, it is necessary to change not only the numerical aperture of the collimator lens but also the numerical aperture of the objective lens when using a DVD-based disc and when using a CD-based disc.

More specifically, D is higher when the recording density is higher.
For a VD disc, the numerical aperture of the objective lens is large (usually 0.6) so that the diameter of the light beam spot is smaller, while for a CD disc, the same objective is used. In order to suppress aberrations while using a lens, it is necessary to somehow limit the numerical aperture of the lens somewhat.

That is, it is necessary to switch the numerical aperture of the objective lens between a DVD and a CD. However, a method of mechanically switching between two types of apertures requires a switching mechanism, which leads to an increase in the size of the pickup. As a result, the mass productivity is reduced and the cost is increased due to the assembly of the mechanism.

Further, since the center of the aperture is easily shifted from the center of the objective lens, the optical characteristics are deteriorated.

In the present embodiment, as described above with reference to FIG. 1, the above-mentioned problem is solved by the wavelength selecting aperture means 35.

FIG. 2 shows the structure of the wavelength selecting aperture means 35. The aperture 46 has a size corresponding to a numerical aperture (for example, 0.5) suitable for using a CD disc. This is the outline of the opening.

In the region outside the opening 46, only light of a short wavelength (for example, light of 650 nm) is transmitted, and light of a long wavelength, which is the second wavelength (for example, light of 780 nm), is not transmitted (reflection / reflection). The optical multilayer 40 is coated.

On the other hand, the area inside the opening 46 is coated with the optical multilayer film 45 that transmits both the short-wavelength light and the long-wavelength light. When the light passes through the selective opening means 35, the optical multilayer film 4
It has a function of controlling the phase of the transmitted light so that the phase of the light transmitted through 0 and the phase of the light transmitted through the optical multilayer film 45 do not shift.

According to this, since the numerical aperture is limited only to the light of the second wavelength, a DVD recorded at high density
For the light of the first wavelength used for the system disk, a light beam spot converged with higher precision can be formed while keeping the numerical aperture of the objective lens large, while C
The light of the second wavelength used for the D-system disc has a limited numerical aperture, and it is possible to suppress the aberration of the light beam spot to be formed to be small while using the same objective lens and optical system. .

In the wavelength selecting aperture means 35, the second
It is desirable to set the numerical aperture for the wavelength of about 0.5. According to this setting, the light of the second wavelength is converted to a CD.
When used for a system disk, both securing of the optical power and reduction of the aberration of the light beam spot are satisfied.

Further, by integrating the wavelength selecting aperture means 35 and the objective lens 4, even if the objective lens moves following the track eccentricity of the disk, the deviation between the objective lens center and the wavelength selecting aperture center can be prevented. Since it does not occur, the optical characteristics do not deteriorate.

FIG. 3 shows another structure of the wavelength selecting aperture means 35. The opening 41 has a size corresponding to, for example, a numerical aperture of 0.6 in a DVD or an outer shape of an opening having a slightly larger diameter. An optical multilayer film 40 that transmits only short-wavelength light (for example, 650 nm light) and does not transmit long-wavelength light (for example, 780 nm light) is coated inside the opening 41 and outside the opening 46. I have.

On the other hand, the area inside the opening 46 is coated with the optical multilayer film 45 that transmits both the short-wavelength light and the long-wavelength light. It has a function of controlling the phase of the transmitted light so that the phase of the light transmitted through the optical multilayer film 40 and the phase of the light transmitted through the optical multilayer film 45 do not deviate when transmitted through the selection opening means 35. .

The reason why the coating region of the optical multilayer film 40 is formed in a ring shape is as follows.

When light having a long wavelength, for example, light having a wavelength of 780 nm, is incident, the light incident on the optical multilayer film 40 is transmitted. In the case of the wavelength selection opening means shown in FIG. Is large, so much light is reflected and enters the photodetector as stray light (noise).
Signal detection and servo control are likely to be hindered.

As shown in FIG. 3, by forming a ring, only a minimum amount of light is reflected, so that stray light components (noise) entering the photodetector can be suppressed.

Therefore, the structure of the wavelength selecting aperture means 35 is as follows.
3 is more preferable than that shown in FIG. 2 earlier.

In the optical system shown in FIG.
Is designed such that no aberration occurs when the substrate 5 is reproduced using the hologram unit 1.

For example, 0.6 mm light with a wavelength of 650 nm is used.
It is designed so that a thick DVD can be recorded and reproduced. Using the objective lens 4 designed in this way, recording and reproduction of substrates 5 'having different substrate thicknesses with light of different wavelengths, that is, recording / reproducing a CD-based disc with a substrate thickness of 1.2mm with light of a wavelength of 780nm. When reproducing, naturally, a spherical aberration is generated by the difference between the substrate thickness and the wavelength difference, and the light beam cannot be sufficiently focused on the information surface of the CD-based disc by only the method described so far, and the information recording / reproducing is performed. May cause problems.

Therefore, a technique of canceling the total wavefront aberration by generating a spherical aberration having a sign opposite to that of the generated spherical aberration may be used as a countermeasure.

More specifically, for example, when the objective lens 4 is designed to enter parallel light, a DVD → C
When the thickness of the substrate is large as in D, the objective lens 4
When a diffused light is made incident on the lens, spherical aberration having a desired reverse sign is generated.

That is, the position of the light emitting point = the hologram unit 20 may be advanced beyond the focal length of the collimator lens 2.

When the thickness of the substrate is reduced, convergent light is incident on the objective lens 4, that is, the hologram laser unit 20 is retracted.

With such a configuration, it is possible to improve the performance when recording and reproducing optical disks having different wavelengths and different substrate thicknesses using a common objective lens.

However, when diffusing light or converging light is made incident on the objective lens 4 as described above, if the incident optical axis is inclined, remarkable coma aberration is generated. That is, it is preferable to provide a mechanism for adjusting the hologram unit 20 in a direction perpendicular to the optical axis.

In the present optical system, an example of an infinite optical system using a collimator lens has been described, but a finite optical system without the collimator lens may be used.

Although the optical path from the rising mirror 3 to the disk 5 is actually located in a direction perpendicular to the plane of the drawing, it is described in the same plane as the plane of the drawing for easy understanding of the drawings. I have.

Further, in FIG. 1, a hologram unit in which the light source and the photodetector are integrated and the optical system can be simplified is employed. However, separate optical systems may be used.

Next, a second embodiment according to the present invention will be described with reference to FIG. FIG. 4 is a diagram showing a configuration of an optical system of an optical pickup according to the second embodiment.

Light emitted from a hologram unit 1 having a semiconductor laser and a photodetector built therein passes through a concave lens 10, then passes through a transmission / reflection means 6, passes through a collimator lens 2, and passes through an optical path by a rising mirror 3. After the conversion, the light enters the objective lens 4 and is focused on the optical disk 5.

The light from which information has been read on the disk returns to the objective lens 4, the rising mirror 3, the collimator lens 2, the transmission / reflection means 6, the concave lens 10, and the hologram unit 1, and is diffracted by the hologram 11 to be refracted in the unit. The light enters the detector 12 and detects an information signal.

The light beam 31 is a light beam having a numerical aperture (hereinafter, referred to as a numerical aperture A) necessary for recording and reproducing the optical disk substrate 5, and the light beam 31 is regulated by the aperture 30 provided below the objective lens 4. Is the outermost light beam.

The light emitted from the hologram unit 20 having a semiconductor laser and a photodetector built therein is reflected by the transmission / reflection means 6, passes through the collimator lens 2, changes the optical path by the rising mirror 3, and then passes through the objective. Incident on the lens 4,
The light is focused on the optical disk 5 '.

The light from which information has been read on the disk returns to the objective lens 4, the rising mirror 3, the collimator lens 2, the transmission / reflection means 6, and the hologram unit 20, and is diffracted by the hologram 21 to be detected by the light detector 22 in the unit. To detect an information signal.

The light beam 36 is a light beam having a numerical aperture (hereinafter, referred to as a numerical aperture B) necessary for recording and reproducing information on and from the optical disk substrate 5 ′. This is the outermost light beam regulated by the restricting element 35.

In the second embodiment, as in the first embodiment, the first light source side (more specifically, the D
A plano-concave lens is inserted only into the optical system (VD side) and its radius of curvature is set to an appropriate value. The arrangement of the hologram units 1 and 20 and the concave lens 10 with respect to the transmission / reflection means 6 is different.

Therefore, first, a concave lens 1 is provided between the hologram unit 1 and the transmission / reflection means 6 which is an optical system on the DVD side.
Since 0 is provided, the collimator lens numerical aperture for a CD can be made larger than the collimator lens numerical aperture for a DVD in the same manner as in the first embodiment.
The features and the like described in the first embodiment can be similarly enjoyed.

In the optical system shown in FIG. 4 according to this embodiment, the light emitted from the first light source is transmitted without being reflected by the transmission / reflection means 6, so that the optical system shown in FIG. Is not reflected by the transmission / reflection means 6 and directed toward the condenser lens (collimator lens) 2 as in the optical system of (1).

Generally, in an optical system, when light is transmitted through an optical component and reflected, light is more likely to cause wavefront aberration. When the light reflecting surface is tilted from a desired angle, the reflected light has a tilt angle of 2 of the reflecting surface.
Since the direction and the direction are shifted, transmission is more advantageous than reflection in terms of parts and assembly tolerance.

Therefore, in the optical system shown in FIG. 4, the light emitted from the first light source can converge on the information recording surface of the optical disk with higher accuracy. As has been frequently described in the above description, the hologram unit 1 as the first light source is
A light beam spot suitable for a high-density recording optical disc with higher precision than the optical system shown in FIG. 1 in the first embodiment is intended because it is intended for a DVD in which higher-density recording is performed. Can be generated.

The mounting positions of the wavelength selection opening means 35 and the hologram unit 20 are the same as in the first embodiment.

FIG. 5 shows a third embodiment. So far, a first light source, for example, an optical system having a lens unit mounted in an optical path with a wavelength of 650 nm has been described, but a second light source, for example, an optical system having a lens unit mounted in an optical path with a wavelength of 780 nm, may also be used. Similar effects can be expected.

Light emitted from the hologram unit 1 having a semiconductor laser and a photodetector built therein is reflected by the transmission / reflection means 6, passes through the collimator lens 2, and rises in the mirror 3.
After the optical path is changed by the above, the light enters the objective lens 4 and is focused on the optical disk 5.

The light from which information has been read on the disk returns to the objective lens 4, the rising mirror 3, the collimator lens 2, the transmission / reflection means 6, and the hologram unit 1, and is diffracted by the hologram 11 to be detected by the photodetector 12 in the unit. To detect an information signal.

The light beam 31 is a light beam having a numerical aperture (hereinafter, referred to as a numerical aperture A) necessary for recording and reproducing the optical disk substrate 5, and the light beam 31 is regulated by the aperture 30 provided below the objective lens 4. Is the outermost light beam.

Light emitted from the hologram unit 20 having a semiconductor laser and a photodetector built therein is reflected by the convex lens 4.
After passing through 0, the light passes through the transmission / reflection means 6, passes through the collimator lens 2, changes the optical path by the rising mirror 3, enters the objective lens 4, and is focused on the optical disk 5 ′.

The light from which information has been read on the disk is reflected by the objective lens 4, the rising mirror 3, the collimator lens 2, the transmission / reflection means 6, the convex lens 40, and the hologram unit 20.
Then, the light is diffracted by the hologram 21 and enters the photodetector 22 in the unit to detect an information signal.

The light ray 36 is a light ray having a numerical aperture (hereinafter, referred to as a numerical aperture B) necessary for recording and reproducing the optical disk substrate 5 ′, and the light ray 36 is a wavelength selecting aperture provided below the objective lens 4. This is the outermost light beam regulated by the restricting element 35.

In the third embodiment, the first,
Unlike the case of the second embodiment, the second light source (CD) is not the first light source (more specifically, the DVD).
Insert a plano-convex lens only into the optical system (disc side of the system)
The radius of curvature is set to an appropriate value.

Also in this embodiment, by setting the radius of curvature of the plano-convex lens inserted only into the optical system on the CD-system disk side to an appropriate value, a CD-type disk can be used similarly to the first embodiment. The collimator lens numerical aperture is D
It is possible to make the numerical aperture larger than the collimator lens numerical aperture for the VD system disk.

In other words, inserting the convex lens on the CD side increases the light use efficiency as compared with the DVD side, so that even if the DVD side is designed with emphasis on the beam system, optical power can be obtained on the CD side. Thus, a result similar to that of inserting a concave lens on the DVD side can be obtained.

By the way, in general, any optical parts are subject to processing and assembly tolerances, or non-uniform physical properties.
When light is transmitted or reflected, optical performance is somewhat degraded due to, for example, generation of aberration.

However, in the third embodiment, FIG.
In the configuration of the optical system described above, the light emitted from the hologram unit 1 as the first light source does not pass through other optical components before reaching the transmission / reflection means 6.

Therefore, in the optical system shown in FIG. 5, the light emitted from the first light source can converge on the information recording surface of the optical disk with higher accuracy.

As has been frequently described in the foregoing description, the hologram unit 1 as the first light source is intended for a DVD on which higher-density recording is performed. Than the optical system shown in FIG.
It is possible to generate a light beam spot suitable for a high-density recording optical disc with higher accuracy.

The mounting positions of the wavelength selection opening means 35 and the hologram unit 20 are the same as in the first embodiment.

FIG. 6 shows a fourth embodiment. Hologram unit 1 with built-in semiconductor laser and photodetector
The emitted light passes through the transmission / reflection means 6, passes through the collimator lens 2, changes the optical path by the rising mirror 3, enters the objective lens 4, and is focused on the optical disk 5. The light from which information has been read on the disk returns to the objective lens 4, the rising mirror 3, the collimator lens 2, the transmission / reflection means 6, and the hologram unit 1, is diffracted by the hologram 11, and enters the photodetector 12 in the unit. Then, an information signal is detected.

The light beam 31 is a light beam having a numerical aperture (hereinafter, referred to as a numerical aperture A) necessary for recording and reproducing the optical disk substrate 5, and the light beam 31 is regulated by the aperture 30 provided below the objective lens 4. Is the outermost light beam.

Light emitted from the hologram unit 20 having a semiconductor laser and a photodetector built therein is reflected by the convex lens 4.
After passing through 0, the light is reflected by the transmission / reflection means 6, passes through the collimator lens 2, changes the optical path by the rising mirror 3, enters the objective lens 4, and is focused on the optical disk 5 ′.

The light from which information has been read on the disk is reflected by the objective lens 4, the rising mirror 3, the collimator lens 2, the transmission / reflection means 6, the convex lens 40, and the hologram unit 20.
Then, the light is diffracted by the hologram 21 and enters the photodetector 22 in the unit to detect an information signal. Ray 36
Is a light beam having a numerical aperture (hereinafter, referred to as a numerical aperture B) necessary for recording and reproducing the optical disk substrate 5 ′, and a light beam 36 is regulated by a wavelength-selective aperture limiting element 35 installed below the objective lens 4. Is the outermost light beam.

In the fourth embodiment, as in the third embodiment, the second light source (CD-system disc) is not the first light source (more specifically, the DVD). A plano-convex lens is inserted only into the optical system, and its radius of curvature is set to an appropriate value.

Also in this embodiment, by setting the radius of curvature of the plano-convex lens inserted only into the optical system on the CD-system disk side to an appropriate value, the same applies to the CD-system disk as in the first embodiment. The collimator lens numerical aperture is D
It is possible to make the numerical aperture larger than the collimator lens numerical aperture for the VD system disk.

Therefore, the advantages and features described in the first embodiment can be similarly enjoyed.

In the configuration of the optical system shown in FIG. 6 according to the fourth embodiment, the light emitted from the hologram unit 1 as the first light source is transmitted to another optical part, specifically, the light source before reaching the transmission / reflection means 6. Does not pass through the convex lens 40 and is not affected by the tolerance or the like.

Therefore, the optical system shown in FIG. 6 can more accurately generate a light beam spot suitable for a high-density recording optical disk, similarly to the optical system shown in FIG. 5 in the third embodiment. Become.

Further, in the optical system of FIG. 6 according to the fourth embodiment, the light emitted from the first light source is reflected by the transmission / reflection means 6 similarly to the optical system of FIG. 4 according to the second embodiment. Since the light is transmitted without being transmitted, the transmission and reflection means 6 are less susceptible to tolerances and aberrations.

Therefore, it is possible to generate a light beam spot suitable for a high-density recording optical disk with higher accuracy.

The mounting positions of the wavelength selection opening means 35 and the hologram unit 20 are the same as in the first embodiment.

As mentioned frequently in the above description of the embodiments, the substrate thickness of the optical disk assumed in designing the optical system is about 0.6 mm for the thinner one and about 1.2 mm for the thicker one. It is desirable.

According to this, an optical system and an optical pickup suitable for various optical disks widely distributed in the market can be obtained.

Further, the first wavelength is 620 nm to 680 nm.
And the second wavelength is preferably designed between 750 nm and 810 nm. According to this, DVDs, which have a large market size and are widely distributed, among optical discs
Optical pickup suitable for an optical disk of a CD or CD system.

Further, if these optical pickups are used in an optical disk drive, it is possible to configure a drive compatible with various optical disks with a small number of parts and a small size at low cost.

[0133]

As described above, according to the present invention, in an optical system in which two light sources having different wavelengths are used and a condensing lens and an objective lens are commonly used for two wavelengths, the utilization of the optical system which is the basis of design. It is possible to provide an optical pickup and an optical disk drive characterized in that the recording operation can be performed by increasing the utilization efficiency of the other optical system rather than the efficiency.

That is, according to the present invention, a DV having a wavelength of 650 nm is used.
A means for separating and combining the divergent light of DVD and the divergent light of CD is mounted in an optical system that shares an objective lens and a condenser lens by using a hologram unit for D and a hologram unit for CD with a wavelength of 780 nm. By inserting a lens means between the means and one of the hologram units, the light use efficiency of the 780 nm wavelength CD-side optical system is larger than the light use efficiency of the 650 nm wavelength DVD-side optical system. CD-R, CD-
This enables recording on an RW disc.

Therefore, it is possible to cope with the conventional optical system of the read-only pickup by inserting only one lens means, and it is possible to reduce the size, thickness, and cost of the recording pickup.

According to the first aspect of the present invention, in an optical pickup using light of two wavelengths, information is recorded by reducing the aberration for one light and increasing the light use efficiency for the light of the other wavelength. Independent design is possible to achieve the two conditions of achieving the possible light output.

According to the second aspect of the present invention, a narrower high-precision light beam spot is generated on a disk having a thinner substrate and higher density recording than two types of optical disks having different thicknesses. In addition, a pickup that can output the required optical power can be realized for a disk having a large substrate thickness and requiring optical power for recording.

Effect of Claim 3 In addition to the effect of Claim 1 or 2, light from the first light source is hardly affected by its tolerance and aberration, and can generate a light beam suitable for a high-density recording disk. .

Effect of Claim 4: In addition to the effect of Claim 1 or 2, in addition to the small number of optical components through which the light from the first light source passes, it is hardly affected by its tolerance and aberration, and the high-density recording disk Can generate a light beam suitable for

Effect of Claim 5 In addition to the effect of Claim 1 or 2, light from the first light source is transmitted through the transmitting / reflecting means and the number of optical components passing therethrough is small. It is possible to generate a light beam which is hardly affected and is more suitable for a high density recording disk.

According to the sixth aspect of the invention, since the numerical aperture can be kept large for the light of the first wavelength, a narrower light beam spot suitable for a light source for a high density recording optical disk can be generated. By limiting the numerical aperture for light of wavelength 2, it is possible to reduce aberrations while sharing the same objective lens.

Effect of Claim 7 In addition to the effect of Claim 6, the aberration of the light beam spot generated from the light of the second wavelength can be set to an optimum value.

According to the eighth aspect, since the wavelength selection aperture means is driven integrally with the objective lens, a mechanism for selecting or switching the numerical aperture is not required. Therefore, the operation time is not required, the weight is light, and there is no displacement from the objective lens, and the optical characteristics are excellent.

Effect of Claim 9 In addition to the effects of Claims 6 and 7, by limiting the aperture of the first wavelength light, unnecessary light can be suppressed from entering the photodetector. Therefore, the quality of the reproduced signal can be improved.

According to the tenth aspect, while using the light of the first wavelength and sharing most of the optical system designed for an optical disc that requires more strict optical characteristics, the light of the second wavelength is shared. The aberration of the optical beam spot for optical discs that uses AE can be reduced by a simple method.

Effect of Claim 11: It is possible to provide an optical pickup suitable for most optical discs distributed in the market.

Effect of Claim 12: D that is circulating in the market
An optical pickup suitable for VD and CD discs can be provided. Effect of Claim 13: DVDs and CDs circulating in the market
Suitable for various types of optical discs, low cost optical disc drive is possible.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a pickup optical system according to a first embodiment of the present invention.

FIG. 2 is a schematic view of a wavelength selecting aperture unit according to the first embodiment of the present invention.

FIG. 3 is a schematic view of another wavelength selecting aperture means according to the first embodiment of the present invention.

FIG. 4 is a schematic diagram of a pickup optical system according to a second embodiment of the present invention.

FIG. 5 is a schematic diagram of a pickup optical system according to a third embodiment of the present invention.

FIG. 6 is a schematic diagram of a pickup optical system according to a fourth embodiment of the present invention.

FIG. 7 is a schematic diagram of a conventional pickup optical system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 20 Hologram unit 2 Collimator lens 3 Start-up mirror 4 Objective lens 5 Optical disk substrate 6 Transmission / reflection means 10 Concave lens

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Miki Renzaburo 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside (72) Inventor Hiroshige Hirashima 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka F-term (for reference) 2H048 AA12 AA18 AA22 5D119 AA41 AA43 BA01 EC45 EC47 FA08 JA58 JB02

Claims (13)

[Claims] 1. A transmission / reflection means having a first light source and a second light source, combining divergent light from the first light source and divergent light from the second light source, and transmitting light from both light sources. In an optical pickup comprising an objective lens for condensing light on an optical disc and a photodetector for receiving each reflected light from the disc, when light from a first light source is condensed on an information recording surface on the disc, In order to reduce the aberration, a lens means is mounted between the transmission / reflection means and the first light source, or the light utilization efficiency of the optical system in the optical path on the first light source side (total emission from the light source) The lens means is disposed between the transmission / reflection means and one of the light sources so that the light use efficiency of the optical system in the optical path on the second light source side is greater than the ratio of the light quantity emitted from the objective lens to the light quantity. Optical pick-up Up. 2. An optical pickup corresponding to two types of optical disks having different substrate thicknesses, a first light source having a first wavelength, a second light source having a second wavelength, and a first light source having a second wavelength.
The divergent light from the light source passes through the lens means, reflects the transmitted light, and transmits the divergent light from the second light source to combine the two optical paths. A condensing lens that transmits and converges divergent light, and a light having a first wavelength is condensed on an optical disk when the substrate is thin, and a light having a second wavelength is condensed on the optical disk when the substrate is thick. An objective lens for condensing the light of the first wavelength on the optical disk, and a reflected light of the first wavelength light from the disk transmitted through the objective lens, reflected by the transmission / reflection means, transmitted through the lens means, and received. 1. An optical pickup comprising: a first photodetector; and a second photodetector for transmitting reflected light of the second wavelength light from the disc through an objective lens and transmitting and receiving the reflected light through a transmission / reflection means. Is an optical element having a concave lens function,
An optical pickup having lens means designed to transmit light of the first wavelength through the lens means, reflect the transmission / reflection means, transmit through the condenser lens, and become parallel light. . 3. An optical pickup corresponding to two types of optical disks having different substrate thicknesses, a first light source having a first wavelength, a second light source having a second wavelength, and a first light source having a second wavelength.
The divergent light from the light source passes through the lens means, transmits the transmitted light, reflects the divergent light from the second light source, and transmits and reflects the two optical paths. A condensing lens that transmits and converges divergent light, and a light having a first wavelength is condensed on an optical disk when the substrate is thin, and a light having a second wavelength is condensed on the optical disk when the substrate is thick. An objective lens for condensing the light of the first wavelength on the optical disk, and a reflected light of the light of the first wavelength from the disk transmitted through the objective lens, transmitted by the transmission / reflection means, transmitted through the lens means, and received by the lens means. 1. An optical pickup comprising: a first photodetector; and a second photodetector that receives reflected light of the second wavelength light from the disk through an objective lens and reflects and receives the reflected light with a transmission / reflection unit. Is an optical element having a concave lens function,
An optical pickup characterized by having lens means designed to transmit light of the first wavelength through the lens means, transmit through the transmission / reflection means, transmit through the condenser lens, and become parallel light. . 4. An optical pickup corresponding to two types of optical disks having different substrate thicknesses, a first light source having a first wavelength, a second light source having a second wavelength, and a first light source having a second wavelength.
The divergent light from the light source is reflected, and the divergent light from the second light source is transmitted through the lens means, and the transmitted light is transmitted. A condensing lens that transmits and converges divergent light, and a light of a first wavelength is condensed on an optical disk when the substrate is thin, and a second light is condensed on the optical disk when the substrate is thick.
An objective lens for condensing the light of the wavelength of 1 on the optical disk, and the reflected light of the light of the first wavelength from the disk is transmitted through the objective lens, reflected by the transmission / reflection means, transmitted through the lens means, and received. An optical pickup comprising: a first photodetector; and a second photodetector that transmits reflected light of the second wavelength light from the disc through the objective lens and transmits and receives the reflected light through the transmission / reflection means. An optical pickup wherein the lens means is an optical element having a convex lens function. 5. An optical pickup corresponding to two types of optical discs having different substrate thicknesses, a first light source having a first wavelength, a second light source having a second wavelength, and a first light source having a second wavelength.
The divergent light from the second light source is transmitted while the divergent light from the second light source is transmitted through the lens means, and the transmitted light is reflected to combine the two optical paths. A condensing lens that transmits and converges divergent light, and a light of a first wavelength is condensed on an optical disk when the substrate is thin, and a second light is condensed on the optical disk when the substrate is thick.
A first lens detecting means for converging light having a wavelength of 1 on an optical disc, and transmitting reflected light of the light having a first wavelength from the disc through the objective lens and transmitting and receiving the reflected light with a transmitting / reflecting means. And a second photodetector for transmitting reflected light of the second wavelength light from the disk through the objective lens, passing through the lens means, and reflecting and receiving the reflected light with the transmission / reflection means. An optical pickup, wherein the lens means is an optical element having a convex lens function. 6. An optical pickup according to claim 1, further comprising a wavelength-selecting aperture limiting means for limiting an aperture only for the light of the second wavelength. 7. An optical pickup according to claim 6, wherein said wavelength selecting aperture means limits the aperture of only the second wavelength light so that the numerical aperture becomes 0.5. 8. An optical pickup according to claim 6, wherein said wavelength selecting aperture means is driven integrally with an objective lens. 9. The wavelength selecting aperture means restricts the numerical aperture of the light of the first wavelength so that the numerical aperture becomes 0.6, and the numerical aperture of the light of the second wavelength. 9. The aperture is limited so that the value is 0.5.
Optical pickup as described. 10. The objective lens is designed such that, when a light having a first wavelength is focused on an information recording surface on the disk, aberration is reduced with respect to a disk having a small substrate thickness, In the case of the light of the second wavelength, it is necessary to arrange the second light source at a position where the aberration becomes small when the light is focused on the information recording surface on the disk with respect to the disk having a large substrate thickness. The optical pickup according to claim 2, wherein: 11. The optical pickup according to claim 2, wherein said optical disc has a substrate thickness of about 0.6 mm and about 1.2 mm, respectively. 12. The first wavelength is from 620 nm to 680.
nm and the second wavelength is between 750 nm and 810 nm.
The optical pickup according to any one of claims 2 to 10, wherein 13. An optical disk drive equipped with the optical pickup according to claim 1.