JP2000173084A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an optical pickup by which the focus position on the recording medium of every laser beam can be adjusted without using an acromatic lens and without adjusting the position of a laser light source when two laser beams at different wavelengths are emitted simulteneously so as to perform the recording operation of a CD-R. SOLUTION: Out of a first laser beam L1 which is radiated from a first laser diode 3 and a second laser beam L2 which is radiated from a second laser diode 4, the first laser beam L1 on the side of a long wavelength is diffracted by a diffraction grating 22 which is formed on the light incident face 71 of an objective lens 7. As a result, the first laser beam L1 which is guided to a CD-R via a common optical system is focused in the same position as the second laser beam L2, on the side of a short wavelength, which is not subjected to a diffraction action by the diffraction grating 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device that performs a recording operation on an optical recording medium such as a CD-R by simultaneously turning on two laser light sources that emit laser beams of different wavelengths. .

[0002]

2. Description of the Related Art As an optical pickup device for recording and reproducing data on and from a CD-R, a recording operation is performed by simultaneously emitting two laser beams having different wavelengths as disclosed in Japanese Patent Application Laid-Open No. 9-306609. What you do is known. In the optical pickup device disclosed in the publication, during the recording operation of the CD-R, both laser light sources are simultaneously turned on, the laser light having the wavelength of 635 nm is mainly used as the recording laser light, and the laser light having the wavelength of 780 nm is used as the objective lens. As a laser beam for detecting a tracking error and a focusing error.

A laser beam having a wavelength of 635 nm has a high absorptance on the recording surface of the CD-R, so that a reliable recording operation on the CD-R is compensated. In addition, since the laser light having a wavelength of 780 nm has a high reflectance on the recording surface of the CD-R, it is necessary to reliably return light of a light amount necessary for controlling the position of the objective lens (focusing servo control and tracking servo control) during recording. Can be obtained.

[0004]

Here, such a 2
In the optical pickup device of the simultaneous emission type with a wavelength laser, in order to simplify the optical system, both laser beams having different wavelengths are guided to the optical recording medium through a common objective lens, and the return light from the optical recording medium is returned. Are also configured to be guided to a photodetector via a common objective lens.

[0005] However, since the refractive index of the objective lens changes according to the wavelength of the light, the focal positions of the laser beams having different wavelengths that have passed through the common objective lens are shifted. Therefore, when the characteristics of the common optical system including the common objective lens are designed according to one wavelength (635 nm laser light), the other wavelength (780 nm) laser light is applied to the recording surface of the optical recording medium. It is impossible to focus upward, and a position farther from the objective lens than the recording surface becomes a focus.

For the same reason, laser beams of different wavelengths also have different amounts of spherical aberration correction. Therefore, if a common optical system is designed in accordance with laser light of one wavelength, laser light of the other wavelength can be used. The spherical aberration correction becomes incomplete, and the spherical aberration becomes chromatic aberration, which causes deterioration of the imaging performance of the spot of the laser beam of the wavelength formed on the recording surface of the optical recording medium.

Here, in order to adjust the focal position of laser light of each wavelength, it is conceivable to use an achromatic lens assembly in which a plurality of concave lenses and convex lenses are combined as an objective lens. However, achromatic lens assemblies are larger in size and weight than when a single objective lens is used. In particular, an increase in the weight of the objective lens is not preferable because the servo tracking ability during the focusing servo control and the tracking servo control of the objective lens is reduced.

As another method for adjusting the focal position of the laser light of each wavelength, a method of arranging a laser light source having a long wavelength at a position farther from the objective lens can be considered. In this case, the long-wavelength laser light that has passed through the collimator for converting the laser light into parallel light enters the objective lens as convergent light instead of parallel light. Therefore, when the objective lens is moved in the tracking direction, the amounts of movement of the light spots on the recording medium by the two laser beams are different from each other, so that the tracking error correction by moving the objective lens is performed accurately. You will not be able to do it.

[0009] The object of the present invention is to solve the above problems.
In a two-wavelength laser light simultaneous lighting type optical pickup device for performing a recording operation of a CD-R or the like, a common objective lens can be used for both laser lights without using an achromatic lens and adjusting a laser light source position. An optical pickup device capable of focusing on the same position on an optical recording medium via an optical recording medium.

[0010]

In order to solve the above-mentioned problems, the present invention provides a first laser light source for emitting a first laser light and a second laser light having a different wavelength from the first laser light. A second laser light source for emitting laser light, a common optical system for guiding the first and second laser lights as parallel light to an optical recording medium via a common objective lens, and return light from the optical recording medium Has a photodetector guided through the common optical system, and simultaneously turns on the first and second laser light sources, thereby performing recording on a recording medium mainly by the second laser light. An optical pickup device for controlling the position of the objective lens mainly based on the return light of the first laser light, wherein a focal position of the first and second laser lights on an optical recording medium by the common optical system; It is characterized by having a diffraction grating so that the same position to correct the.

By using a diffraction grating, both laser beams having different wavelengths can be applied to the same position on an optical recording medium without using an achromatic lens assembly as an objective lens and without adjusting the position of a laser light source. Can be focused.

Here, it is desirable to form the diffraction grating on the surface of the objective lens instead of using a diffraction grating as a single optical element from the viewpoint of miniaturization and compactness of the optical system. In this case, a plurality of concentric annular groove grooves may be formed on the surface of the objective lens, and these lattice grooves may be formed at irregular intervals.

Next, if the return light from the optical recording medium is focused on the same position on the photodetector,
It is not necessary to dispose two photodetectors at different positions as the photodetector, and the return light of the laser light of each wavelength can be detected by a common photodetector, which is desirable. In order to do so, a return light diffraction grating for correcting the focal position of the return light by the common optical system on the photodetector so as to be at the same position may be added.

This diffraction grating for return light is also desirably formed on the surface of an optical element constituting the optical system from the viewpoint of making the optical system compact and compact. In a typical example, since the common optical system includes a collimator lens for collimating the first and second laser beams, the return light diffraction grating is provided on the surface of the collimator lens. What is necessary is just to make the formed several concentric ring-shaped lattice groove | channels.

Next, the optical pickup device of the present invention
It can be applied for DR recording / reproduction. In this case, the first laser light may have a wavelength of 780 nm, and the second laser light may have a wavelength of 635 nm or 650 nm.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical pickup device to which the present invention is applied will be described below with reference to the drawings.

FIG. 1 is a schematic structural view of an optical pickup device to which the present invention is applied. Optical pickup device 1 of this example
In this method, the 635 nm and 780 nm laser beams are simultaneously turned on to perform the CD-R recording operation, and the CD-R reproducing operation is performed using only the 780 nm laser beam.

More specifically, the optical pickup device 1 of this embodiment includes a first laser diode 3 for emitting a first laser beam L1 having a wavelength of 780 nm, and a wavelength of 650 nm.
And a second laser diode 4 for emitting the second laser light L2. The first and second laser beams L1 and L2 emitted from these laser diodes 3 and 4 are guided to a CD-R2 as an optical recording medium via a common optical system. The return light from the CD-R 2 is also guided to the common photodetector 8 via the common optical system. The common optical system is
It includes a light guide element 5 on which the laser beams L1 and L2 are incident, a collimator lens 6, and an objective lens 7 mounted on an objective lens driving device 10.

First and second laser diodes 3, 4
Are arranged on the left and right sides of the light guide element 5 in such a manner that each optical axis is orthogonal to the optical axis of the common optical system, and are located at optically conjugate positions. The light guide element 5 is a composite prism in which three triangular prisms 51, 52, and 53 are adhered to each other to form a quadrangular prism as a whole.

A partial reflection surface 54 inclined at 45 degrees with respect to the optical axis of the common optical system is formed on the surface where the prisms 51 and 52 are bonded. 4 with respect to the optical axis of the optical system
A partial reflection surface 55 inclined by 5 degrees is formed. The partial reflection surface 54 partially reflects the second laser light L2 and transmits the first laser light L1. Partial reflection surface 55
Partially reflects the first laser light L1 and transmits the second laser light L2.

The first laser beam L 1 emitted from the first laser diode 3 is incident on the collimator lens 6 after its traveling direction is bent by 90 degrees by the partial reflection surface 55 of the light guide element 5. The second laser light L2 emitted from the second laser diode 4 is transmitted through the partial reflection surface 55 as it is after being bent by 90 degrees by the partial reflection surface 54 of the light guide element 5 and then passes through the collimator lens 6. Incident on.

The first and second laser beams L1 and L2 incident on the collimator lens 6 are converted by the collimator lens 6 into substantially parallel light beams. The first and second laser beams L1 and L2 converted into parallel light beams enter the common objective lens 7, and converge there as a light spot on the recording surface 20 of the CD-R2.

The return light of the first and second laser beams reflected on the recording surface 20 of the CD-R 2 is guided to the photodetector 8 again through the common optical system. That is, the light returns to the light guide element 5 via the objective lens 7 and the collimator lens 6. Of the return light, the light components transmitted through the respective partial reflection surfaces 54 and 55 are condensed on the photodetector 8. The photodetector 8 is provided with, for example, a four-divided light receiving surface, and a light receiving signal detected on the light receiving surface is processed by the control device 15.

Here, the optical characteristics of the common optical system of this embodiment are basically designed in accordance with the second laser beam L2. For this purpose, a laser light diffraction grating 22 is formed on the light incident surface 71 of the objective lens 7 so that the first laser light L1 is focused at the same position as the second laser light L2. Due to the diffraction effect of the laser beam diffraction grating 22, the first and second laser beams L1, L2 having different wavelengths,
L2, via the common objective lens 6, the CD-R2
Will be focused on the same position on the recording surface 20.

Referring to FIGS. 2A and 2B, the laser light diffraction grating 22 formed on the objective lens 7 will be described. As shown in the figure, a laser light diffraction grating 22 for diffracting the first laser light L1 is formed on a convexly curved light incident surface 71 of the objective lens 7. The diffraction grating 22 for laser light includes a plurality of annular grating grooves 22b concentrically cut on the light incident surface 71.

Each grating groove 22b of the diffraction grating 22 is designed to satisfy the following conditions. That is, the diffraction efficiency for the first laser light L1 is set to be maximum, and the diffraction efficiency for the second laser light L2 is set to be minimum. Further, the pitch of each grating groove 22b is unequally spaced, and the + 1-order light L11 of the first laser light L1 diffracted by the diffraction grating pattern 22a cancels out the chromatic aberration generated in the objective lens 7. As described above, chromatic aberration in the opposite direction is provided.

Most of the short-wavelength second laser light L2 incident on the diffraction grating 22 is directly incident on the objective lens 7 as zero-order light without being subjected to diffraction, and is subjected to the refraction of the objective lens 7. Focus on the recording surface 20 of the CD-R2.

On the other hand, most of the first laser light L1 on the long wavelength side incident on the diffraction grating 22 is
The light is diffracted by 2 to become the + -1st order light L11. The + 1-order light L11 is provided with chromatic aberration, and the chromatic aberration occurring in the + 1-order light L11 due to the refraction of the objective lens 7 is cancelled. Further, the focal position in the optical axis direction of the +/− 1 order light L11 of the first laser light L1 on the long wavelength side coincides with the focal position in the optical axis direction of the second laser light L2 on the short wavelength side.

Since most of the first laser light L1 is the + -first order light L11 in the diffraction grating pattern 22a,
The focal position of the primary light L11 is substantially the first laser light L
1, the focal position in the optical axis direction of the first laser light L1 coincides with the focal position in the optical axis direction of the second laser light L2.

Therefore, when the two laser diodes 3 and 4 are simultaneously turned on to perform the recording operation of the CD-R2,
Both the first and second laser beams L1, L2 emitted from the first and second laser diodes 3, 4 are CD-
Focus on the recording surface 20 of R2. The diffraction grating 22
+ 1st-order light L of the first laser light L1
11, the +/− 1 order light L11 is
The spherical aberration in the opposite direction is given so as to cancel the spherical aberration given by Therefore, it is possible to prevent the imaging performance of the first laser light L1 from being reduced.

As described above, in the optical pickup device 1,
Laser light diffraction grating 2 formed on the incident surface of objective lens 7
The focus position of the laser light L1 on the long wavelength side is adjusted to the focus position of the laser light L2 on the short wavelength side by the diffraction action of No. 2. Therefore, laser beams having different wavelengths can be focused at the same position without using a heavy achromatic lens and without adjusting the positions of the laser diodes 3 and 4.

The diffraction grating 22 has a plurality of annular grating grooves 22b arranged at unequal intervals so that the condensing by the first-order diffracted light can cancel the chromatic aberration generated in the laser light on the long wavelength side. The groove 22b is employed. For this reason, it is possible to prevent the imaging performance of the first laser beam on the long wavelength side on the recording surface 20 from deteriorating.

Next, in the present embodiment, the surface of the collimator lens 6 on the objective lens side is set so that return light returning from the CD-R 2 via the common optical system is focused on the light receiving surface of the photodetector 8. A diffraction grating 23 for return light is also formed at 61. The return light diffraction grating 23 is composed of grating grooves 22a having the same pattern as that of the laser light diffraction grating 22 described above. This diffraction grating 23 has the following diffraction characteristics.

That is, the first laser light L1 on the long wavelength side
Is set so that the diffraction efficiency of the second laser beam L2 on the short wavelength side with respect to the return light Lr2 is minimized. In addition, the pitch of each grating groove is made unequal, and chromatic aberration in the opposite direction is given to the diffracted return light Lr11 of the first laser light L1 so as to cancel the chromatic aberration generated in the collimator lens 6. It has become.

Therefore, most of the return light Lr11 of the first laser light L1 on the longer wavelength side is the return light diffraction grating 23.
Is diffracted into + -1 order light Lr111. The relevant + -1
The next light Lr111 focuses on the light receiving surface of the photodetector 8. On the other hand, most of the return light Lr2 of the second laser light L2 on the short wavelength side passes through the return light diffraction grating 23 as it is as zero-order light, and then focuses on the light receiving surface of the photodetector 8. In this way, only the return light on the long wavelength side is diffracted by the diffraction grating 23, so that it is focused on the same position as the return light of the second laser light on the short wavelength side.

Therefore, in the optical pickup device 1, since the focal positions in the optical axis direction of the return lights Lr11 and Lr2 of the laser lights L1 and L2 coincide with each other, the light receiving surfaces for receiving the return lights are flush with each other. Can be formed on. That is, both return lights can be detected using the common photodetector 8 in which each light receiving surface is formed on the substrate surface of the semiconductor substrate.

A control device 15 for controlling the position of the objective lens 7 will be described with reference to FIG. The control device 15 may have a generally known configuration, and includes a lighting control circuit 16 for lighting the first and second laser diodes 3 and 4 and a light receiving signal generated by the photodetector 8. A signal processing circuit 17 for processing, and an objective lens driving control circuit 18 for driving and controlling the objective lens driving device 10 based on the signal processed by the signal processing circuit 17
Contains.

The signal processing circuit 17 generates a reproduction signal RF, a focusing error signal FE, and a tracking error signal TE based on the light receiving signal detected by the photodetector 8. For example, the focusing error signal FE can be generated by the astigmatism method, and the tracking error signal TE can be generated by the push-pull method.

The focusing error signal FE and the tracking error signal TE are sent to the objective lens drive control circuit 18. The objective lens drive control circuit 18 generates a drive signal for the objective lens drive device 10 based on these error signals FE and TE, and controls the objective lens drive device 10.

The objective lens driving device 10 is, for example, a sliding type in which a lens holder (not shown) on which the objective lens 7 is mounted is slidably supported on a fixed shaft (not shown). . The objective lens driving device 10 includes a focusing magnetic drive circuit 11 and a tracking magnetic drive circuit 12. The focusing magnetic drive circuit 11 moves the lens holder in the axial direction of the fixed axis based on the focusing error signal FE generated by the objective lens drive control circuit 18. By this movement, it is possible to correct the focusing error of the light spot of the laser light L1, L2 formed on the recording surface 20 on the CD-R / RW2 by the objective lens 7.

The tracking magnetic drive circuit 12 moves the lens holder about the axis of the fixed axis based on the tracking error signal TE generated by the objective lens drive control device 18. With this movement, it is possible to perform tracking error correction of the light spots of the laser beams L1 and L2 formed on the recording surface 20 of the CD-R / RW2 by the objective lens 7.

(Other Embodiments) In the above-described optical pickup device 1, the return light diffraction grating 23 can be omitted. In this case, as shown by a dashed line in FIG. 1, the return light Lr11 of the laser light L1
Becomes longer than the focal length of the return light Lr2 of the second laser light L2. Therefore, in addition to the photodetector 8 for detecting the return light Lr2 of the second laser light L2, a dedicated photodetector 8a for detecting the return light Lr11 of the first laser light L1 may be provided. .

In the above example, the diffraction gratings 22 and 23
Are formed on the surface of the objective lens and the surface of the collimator lens, respectively, but it is also possible to use a diffraction grating as a single optical element.

Further, the pattern of the diffraction grating 22 for laser light shown in FIG. 2 is merely an example, and any other diffraction pattern may be used as long as it has the diffraction characteristics described above. Of course.

On the other hand, in the above example, the first laser beam L1 on the long wavelength side is diffracted in order to adjust the focal positions of the first and second laser beams L1 and L2. Instead, the second laser beam L2 on the short wavelength side may be diffracted to adjust the focal positions of both laser beams L1 and L2.

The wavelength of the laser beam L2 emitted from the second laser diode 4 can be 635 nm. The laser light L2 (wavelength 650 nm or 635) on the short wavelength side emitted from the second laser diode 4
nm) can be used to reproduce a DVD.

[0047]

As described above, in the optical pickup device according to the present invention, one of the laser beams on the long wavelength side and the short wavelength side is diffracted by using the diffraction grating, so that both laser beams are diffracted. The focal positions of the light on the recording medium are matched. Therefore, the focal positions of both laser beams can be adjusted without using a heavy achromatic lens or adjusting the position of the laser light source.

In the present invention, since the diffraction grating for laser light is formed on the light incident surface of the objective lens, the optical system can be made small and compact.

On the other hand, in the present invention, the return light from the optical recording medium due to one of the laser light on the long wavelength side and the laser light on the short wavelength side is diffracted, and the return light of both laser lights is converted. The focal positions are set to be the same. Therefore, it is sufficient to dispose a common photodetector at the same position without using a separate photodetector to detect the return light of each laser beam, and the optical system can be made small and compact.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical pickup device for recording and reproducing a CD-R to which the present invention is applied.

2A is an explanatory diagram showing a cross-sectional configuration of a diffraction grating formed on an objective lens in the optical pickup device shown in FIG. 1, and FIG. 2B is an explanatory diagram showing a planar configuration of a diffraction pattern of the diffraction grating. is there.

[Explanation of symbols]

 Reference Signs List 1 optical pickup device 2 CD-R 3 first laser diode 4 second laser diode 5 light guide element 6 collimator lens 7 objective lens 10 objective lens drive device 15 control device 16 lighting control circuit 17 signal processing circuit 20 recording surface 22 Diffraction grating for laser light 22b Grating groove 23 Diffraction grating for return light

Claims (5)

[Claims] A first laser light source that emits a first laser light; a second laser light source that emits a second laser light having a different wavelength from the first laser light; A common optical system that guides the second laser beam as parallel light to the optical recording medium via a common objective lens; and a photodetector to which return light from the optical recording medium is guided via the common optical system. By simultaneously turning on the first and second laser light sources, recording on a recording medium is performed mainly by the second laser light, and the objective lens is mainly driven based on the return light of the first laser light. An optical pickup device for performing position control, comprising: a diffraction grating for correcting the focal positions of the first and second laser beams on the optical recording medium by the common optical system so that the focal positions are the same. Optical pickup device characterized by there. 2. The apparatus according to claim 1, wherein the diffraction grating is formed of a plurality of concentric annular grating grooves formed on a surface of the objective lens, and the grating grooves are unequally spaced. An optical pickup device characterized by the following. 3. The return light diffraction grating according to claim 1, further comprising a return light diffraction grating for correcting a focal position of the return light by the common optical system on the photodetector so that the return light becomes the same position. An optical pickup device comprising: 4. The collimating lens according to claim 3, wherein the common optical system includes a collimating lens for collimating the first and second laser beams, and the return light diffraction grating includes a collimating lens. Consisting of a plurality of concentric annular zonal lattice grooves formed on the surface of
The optical pickup device, wherein the lattice grooves are arranged at irregular intervals. 5. The method according to claim 1, wherein the wavelength of the first laser light is 780 nm, and the wavelength of the second laser light is 635 nm or 650 n.
m, an optical pickup device.