JP2001093183A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup in which the ratio of light quantities to a photodetector for monitoring and to an objective lens can be adjusted so as to be fixed among products regardless of the dispersion of the characteristics at the time of manufacture of a polarized beam splitter to be used. SOLUTION: This optical pickup for recording and reproducing information on an optical disk D is provided with a 1/2 wavelength plate 28 for changing the polarization direction of a laser beam L for read and write emitted from a laser beam source 1 by rotating the plate about an optical axis as a center, the photodetector 22 for monitoring used for detecting the light amount of the laser beams outputted from the 1/2 wavelength plate and controlling the laser beam output of the laser beam source so as to turn the detected result to a fixed value and the polarized beam splitter 8 for dividing the laser beams outputted from the 1/2 wavelength plate to an optical path to the optical disk and the optical path to the photodetector for monitoring. The 1/2 wavelength plate can be rotated and adjusted in the range of at least 0 to 45 degrees with the optical axis as a rotation center. Thus, regardless of the dispersion of the characteristics at the time of the manufacture of the polarized beam splitter to be used, the ratio of the light quantities to the photodetector for monitoring and to the objective lens is adjusted so as to be fixed among the products.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk optical pickup.

[0002]

2. Description of the Related Art Generally, the optical output of a semiconductor laser device is
A part of the light emitted from the semiconductor laser element is monitored by a monitoring photodetector so as not to be affected by a change in ambient temperature or the like, and the light output of the laser light is controlled to be constant, for example. In a read-only optical pickup, a method is often adopted in which a photodiode is provided in a package of a semiconductor laser element and light leaking to the rear of the chip is detected. On the other hand, an optical pickup for recording requires more accurate control of the light output than a read-only optical pickup, so the monitoring photodetector is part of the forward optical system from the semiconductor laser element to the objective lens. A so-called front monitor system is provided in association with the above.

For example, in order to guide light to the monitoring photodetector, it is necessary to divide the optical path toward the objective lens so that a part of the light is directed to the monitoring photodetector.
In this type of optical pickup, an outward optical system for condensing light on a disk recording surface, and a light reflected on the recording surface
For example, a beam splitter, a polarizing prism, or the like is used to divide the optical signal into a return optical system for leading to an optical detector for detecting an F signal or a servo signal. For example, laser light traveling from the semiconductor laser element to the optical disk is transmitted through the beam splitter or the polarizing prism, and light returning from the optical disk is reflected by the beam splitter or the polarizing prism, and the optical path is bent. Guided to the detection system. In the above example, a part of the light from the semiconductor laser element toward the disk is reflected by the beam splitter or the polarizing prism, travels in the direction opposite to the detection system, and uses this light to generate a photodiode or the like. The amount of light is detected.

Here, a conventional optical pickup will be described. FIG. 5 is a configuration diagram showing an example of a conventional optical pickup, and FIG. 6 is a configuration diagram showing another example of a conventional optical pickup. In FIG. 5, the read / write laser beam L emitted from the semiconductor laser element 2 is converted into a parallel light beam by the collimator lens 4, and the beam shaping prism 6 converts the light emission pattern of the semiconductor laser element 2 from an ellipse to a circle. Further, the laser light transmitted through the polarization beam splitter 8 is incident on the objective lens 14 via the rising reflection mirror 10 and the quarter wavelength plate 12. Then, the laser beam becomes convergent light by this objective lens, and a spot is formed on the recording surface on the optical disk D, thereby enabling signal recording and reproduction. The light reflected on the recording surface again enters the objective lens 14, becomes a parallel light beam, and enters the polarization beam splitter 8 via the 波長 wavelength plate 12 and the reflection mirror 10. The light that has entered the polarization beam splitter 8 has passed through the previous quarter-wave plate 12 twice in the forward path and the return path, so that the polarization direction is 90 degrees.
, The light is reflected by the beam splitter 8 and guided to the detection system 16, where the detection of the servo signal and the R
Detection of the F signal is performed. The detection system 16 includes, for example, a cylindrical lens 18 and a photodetector 20.

Here, the monitoring photodetector 22 is disposed on the opposite side of the detection system 16 of the polarization beam splitter 8, and a part of the light of the forward light beam toward the disk D is reflected by the polarizing film 8A. Incident on the monitoring photodetector 22. Here, the polarizing film 8A is composed of, for example, a dielectric multilayer film designed to transmit P-polarized light and reflect S-polarized light. Then, the light control unit 24
Performs light amount control of the semiconductor laser element 2 based on the output value of the monitoring photodetector 22. Also in the optical pickup shown in FIG. 6, the laser light L emitted from the semiconductor laser element 2 is converted into a parallel light beam by the collimator lens 4 and enters the polarization beam splitter 8. The light transmitted through the beam splitter 8 is incident on the objective lens 14 by changing the optical path by the rising reflection mirror 10, and is converged to form a light spot on the recording surface on the optical disk D.
The light reflected by the optical disk D is converted again into a parallel light beam by the objective lens 14 and enters the beam splitter 8 via the rising reflection mirror 10. Then, the light reflected by the splitter 8 is guided to the detection system 16, where the detection of the servo signal and the detection of the RF signal are performed. On the other hand, a part of the laser light L emitted from the semiconductor laser element 2 is reflected by the beam splitter 8, and the light reflected by the beam splitter 8 is detected by a monitor photodetector 22 to detect the amount of light, and is controlled by a light control unit. Reference numeral 24 controls the light amount of the semiconductor laser element 2 based on the detected value.

[0006]

When an optical path is divided by a beam splitter or a polarizing beam splitter 8 as shown in FIG. 5, the ratio of the light quantity is determined by the film design such as a polarizing film 8A made of a dielectric multilayer film. Depends on Also,
The optical pickup for recording requires a higher optical power at the time of recording as compared with the read-only optical pickup. Therefore, the amount of light emitted from the semiconductor laser element 2 is reduced by the objective lens 14 to be focused on the optical disk D. Since it is necessary to make the coupling efficiency, which is the ratio, as large as possible, it is desirable to minimize the amount of light to the front monitor photodetector 22 as necessary. However, when designing the polarization beam splitter 8, the light amount toward the disk should be 98% or more,
Normally, the light amount on the front monitor photodetector 22 side is designed to be 1% or less, but in this case,
There is a problem that it is very difficult to control the amount of light incident on the front monitor photodetector 22. In other words, there is a problem that the amount of light incident on the monitoring photodetector 22 is different for each optical pickup, and it is difficult to make the amount constant, because of the influence of manufacturing characteristics of the polarization beam splitter 8. Was.

In the optical pickup shown in FIG. 6, the beam splitter 8 and the polarizing prism have the polarizing film 8A made of a dielectric multilayer film as described above.
This has a structure in which a number of layers of materials having different refractive indices are stacked with a thickness of a wavelength unit. These dielectric multilayer films
The division ratio of the light amount may fluctuate due to a change in thickness due to expansion, a change in refractive index, or the like due to a change in ambient temperature.
Further, the characteristics also differ depending on the polarization direction of the incident light. The laser light L emitted from the semiconductor laser element 2 is P
It is aligned with either the polarization component or the S polarization component, but the opposite component, that is, the S component in the case of P polarization
Some polarization and vice versa are also included. The ratio is also called an extinction ratio or a polarization ratio. Then, the polarization ratio slightly changes due to a change in the temperature or a change in the output power of the semiconductor laser device 2. Therefore, the ratio of the P-polarized light component and the S-polarized light component of the light incident on the beam splitter 8 and the polarizing prism also changes.

For this reason, as in the optical pickup shown in FIG. 6, a beam splitter 8 and a polarizing prism are inserted in the optical path from the semiconductor laser device 2 to the disk D.
The transmitted (or reflected) light is guided to the disk, and the monitor photodetector 2 is used by using the reflected (or transmitted) light.
In the optical pickup of the type that obtains light incident on the optical disk 2, the ratio of the amount of light toward the disk to the amount of light toward the monitor photodetector fluctuates when the ambient temperature changes, when the output power of the semiconductor laser element 2 is switched, or the like. Problem. In particular, in an optical pickup for recording a signal on a disk, since the control of the light amount during recording greatly affects the recording characteristics, a light amount detection method for precisely controlling the light amount is required.

The present invention focuses on the above problems,
It was created to solve this effectively. A first object of the present invention is to adjust the ratio of the amount of light directed to the monitor photodetector and the objective lens so as to be constant between products irrespective of variations in the characteristics of the polarizing beam splitter used during manufacture. It is an object of the present invention to provide an optical pickup that can perform the above operations. A second object of the present invention is to control the amount of light incident on an objective lens (optical disk) to be always constant without being affected by a change in a light amount division ratio of a polarizing beam splitter or a polarizing prism due to a temperature change. It is an object of the present invention to provide an optical pickup that can perform the above-described operations.

[0010]

A first aspect of the present invention is defined by the first aspect.
The invention provides an optical pickup for recording / reproducing information on / from an optical disk, a half-wave plate that changes the polarization direction of a read / write laser beam emitted from a laser light source by rotating the optical axis around an optical axis, A monitor light detector used to control the laser light output of the laser light source so as to detect a light amount of the laser light output from the wave plate and to make the detection result a constant value; A polarizing beam splitter for splitting the laser light output from the wave plate into an optical path toward the optical disk and an optical path toward the monitor photodetector, wherein the half-wave plate is rotated at least 0 around its optical axis. The rotation can be adjusted within a range of 45 degrees to 45 degrees. Thus, by fixing the half-wave plate in a state where the rotation angle is adjusted at the stage of assembling the optical pickup, the monitor photodetector can be used regardless of the variation in the characteristics of the polarizing beam splitter to be used at the time of manufacture. And the ratio of the amount of light toward the objective lens can be adjusted to be constant between products.

According to a second aspect of the present invention, there is provided an optical pickup for recording / reproducing information on / from an optical disk, comprising: a laser light source for converging a laser beam onto the optical disk via a rising mirror; An optical system having an objective lens is provided, and the amount of the laser light transmitted from a portion other than the reflection portion of the rising reflection mirror is detected,
A monitoring light detector used to control the laser light output of the laser light source is provided so that the detection result becomes a constant value. As described above, since the monitoring photodetector is provided in association with the optical system on the outward path after the polarizing beam splitter or the polarizing prism, fluctuations in the light amount splitting ratio of the polarizing beam splitter or the polarizing prism due to temperature changes are provided. Objective lens (optical disk) without being affected
Can be controlled so that the amount of light incident on the surface is always constant.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical pickup according to the present invention will be described below in detail with reference to the accompanying drawings. First,
The first invention will be described. FIG. 1 is a configuration diagram showing an optical pickup according to the first invention, and FIG. 2 is a perspective view showing a half-wave plate. In FIG. 1, parts that are the same as the parts shown in FIG. 5 are given the same reference numerals and described. The optical pickup 26 of the present invention shown in FIG. 1 is different from the conventional optical pickup shown in FIG. 5 in that an optical path between the semiconductor laser element 2 and the polarization beam splitter 8 is rotatably 1 /.
The point is that the two-wavelength plate 28 is inserted.

That is, in the figure, reference numeral 2 denotes a semiconductor laser element as a laser light source for outputting a laser beam L, 4 denotes a collimator lens for converting the laser beam L into parallel light, and 6 denotes a cross-sectional pattern of the laser beam L from elliptical to circular. 8 is a polarizing beam splitter having a polarizing film 8A inside, 10 is a rising reflection mirror, 12 is a 波長 wavelength plate, 14 is an objective lens for condensing light on the optical disc D, 16 Are the cylindrical lens 18 and the servo signal or R
A detection system including a photodetector 20 for detecting an F signal;
Is a monitoring photodetector for detecting light partially reflected by the polarization beam splitter 8, and 24 is a light controller for controlling the output of the semiconductor laser element 2 so that the detection value of the detector 22 becomes a constant value. is there. In this embodiment, the half-wave plate 28 is interposed between the beam shaping prism 6 and the polarization beam splitter 8 as described above.

Here, the polarization direction of the laser light L emitted from the semiconductor laser element 2 is, for example, S-polarized light. In order to transmit this laser light L to the polarization beam splitter 8, the laser beam The polarization direction of light L is 9
What is necessary is just to rotate by 0 degree and to make it P-polarized light. Therefore, this 1 /
The two-wavelength plate 28 is an optical element utilizing birefringence,
By arranging this optical axis at 45 degrees with respect to the polarization direction, the polarization direction of the laser light L can be rotated by 90 degrees. As a result, the polarization direction of the laser beam incident on the polarization beam splitter 8 becomes P-polarized light and transmits through the polarization beam splitter 8. The design of the polarizing beam splitter 8
The design is performed under the conditions of 100% transmission of P polarized light, 0% transmission of S polarized light, 0% reflection of P polarized light, and 100% reflection of S polarized light. The characteristics of the polarization beam splitter 8 actually manufactured include a dielectric film constituting the polarization film 8A and reflection loss due to the glass of the prism.
And S-polarized light reflection is not 100%, but each is about 99%. However, P-polarized light reflection and S-polarized light transmission are approximately 0%.

Accordingly, the optical axis of the half-wave plate 28 is set to 45
In this case, approximately 100% of the amount of light passing through the polarizing beam splitter 8 is guided to the objective lens 14, that is, the optical disk D side, and the amount of light guided to the monitoring photodetector 22 is substantially zero. Here, when the optical axis of the half-wave plate 28 is rotated from 45 degrees as shown in FIG. 2, each of the P-polarized light component and the S-polarized light component becomes Occurs accordingly. That is, here, the polarization beam splitter 8 is reflected by the polarization film 8A and guided to the monitoring photodetector 22. Thus, the half-wave plate 2
By rotating 8, the ratio of the amount of light going to the objective lens 14, that is, the optical disk D, to the amount of light going to the monitoring photodetector 22 can be managed by the rotation of the half-wave plate 28. Therefore, even if there is a variation in the characteristics of the polarizing film 8A of the polarizing beam splitter 8, when the optical pickup 26 is assembled, the half-wave plate 28 is appropriately rotated and adjusted, and The rotation angle of the half-wave plate 28 may be fixed at a point where the detection value becomes a predetermined value, and the plate may be shipped in this state. Thus, even if the polarization film 8A of the polarization beam splitter 8 has a variation in characteristics, the distribution ratio between the amount of light incident on the monitoring photodetector 22 and the amount of light traveling toward the objective lens 14 (optical disk D) is always kept constant. It can be adjusted to be

Next, the second invention will be described. FIG.
FIG. 4 is a configuration diagram showing an optical pickup according to the second invention, FIG.
FIG. 9 is a view showing a modification of the rising reflection mirror. In FIG. 3, the same parts as those shown in FIG. The optical pickup 29 of the present invention shown in FIG. 3 is greatly different from the conventional optical pickup shown in FIG. 6 in that the monitoring photodetector is related to the optical system on the outward path after passing through a beam splitter or a polarizing prism. This is the point provided. That is, in the drawing, reference numeral 2 denotes a semiconductor laser element that outputs laser light L, 4 denotes a collimator lens that converts the laser light L into parallel light, 8 denotes a polarizing beam splitter, and 30 denotes a polarizing beam splitter.
Is a rising reflection mirror, 14 is an objective lens for condensing light on the optical disk D, 16 is a detection system including a cylindrical lens 18 and a photodetector 20 for detecting servo signals and RF signals, and 22 is a rising reflection mirror. A monitoring photodetector for detecting a part of the light that has passed therethrough without being reflected at 30, and controls the output of the semiconductor laser device 2 so that the detection value of the photodetector 22 becomes a constant value. This is a light control unit. Incidentally, a polarizing prism may be used instead of the polarizing beam splitter 8.

Here, the optical system on the outward path of the laser beam L includes a semiconductor laser element 2, a collimator lens 4, a polarizing beam splitter 8, a rising reflection mirror 30, and an objective lens 14.
On the other hand, the optical system on the return path includes the objective lens 1
4. Start-up reflection mirror 30, polarization beam splitter 8,
It comprises a cylindrical lens 18 and a photodetector 20. As described above, in the present embodiment, the monitoring photodetector 22 is provided in association with the optical system on the outward path after passing through the polarization beam splitter 8, specifically, in association with the rising reflection mirror 30. . That is, as shown in FIG. 4 (A), the rising reflection mirror 30 has a circular reflection film 32A formed only at the center portion of the light incident surface 32, and uses the reflection film 32A as a reflection surface. 32B is configured to transmit light without forming a reflective film. Then, the monitor photodetector 22 is provided behind the reflection mirror 30 so that a part of the transmitted light LB can be detected by the monitor photodetector 22.

In such an apparatus, the semiconductor laser element 2
Is converted into a parallel light beam by the collimator lens 4 and enters the polarization beam splitter 8.
Most of the light transmitted through the beam splitter 8 impinges on the reflecting film 32A of the light incident surface 32 of the rising reflecting mirror 30, changes its optical path and enters the objective lens 14, where it is converged and spotted on the recording surface on the optical disk D. To form Here, an area 3 on the outer periphery of the reflection mirror 30 where no reflection film is provided.
The light incident on 2B is transmitted as it is, and the light LB transmitted through the reflection mirror 30 is incident on the monitoring photodetector 22, and is used as a front monitor of the semiconductor laser device 2. That is, the light control unit 24 controls the output of the semiconductor laser element 2 so that the detection value of the monitoring light detector 22 is always constant. Therefore, even if the light amount splitting ratio in the polarization beam splitter 8 fluctuates due to a temperature change, or the polarization ratio of the laser light emitted from the semiconductor laser element 2 fluctuates, the objective lens 1
4 (optical disc D) can be controlled to always maintain a constant light amount.

In FIG. 4A, the reflecting film 32A is formed at the center of the light incident surface 32 of the rising reflecting mirror 30, but the present invention is not limited to this. Since the laser light need only be directly incident on the detector 22 without being reflected, only the portion corresponding to the monitoring photodetector 22 as shown in FIG. Only the area 32B where the reflective film is not formed may be formed only on the entire surface, and the reflective film 32A may be formed on the entire other portion. Further, as shown in FIG.
Area (B) in which no reflective film (32A) is provided in (B)
May be formed in such a shape that a portion corresponding to the above is deleted in advance. In FIG. 4C, the deleted portion 34 is indicated by a chain line. still,
The configuration of the optical pickup in each of the first and second inventions is merely an example, and it goes without saying that the present invention can be applied to optical pickups other than the configuration described above.

[0020]

As described above, according to the optical pickup of the present invention, the following excellent functions and effects can be exhibited. According to the first aspect of the present invention, at the stage of assembling the optical pickup, the half-wave plate is fixed in a state where the rotation angle is adjusted, so that the polarization beam splitter to be used has a characteristic in manufacturing. Irrespective of the variation in the light amount, it is possible to adjust the ratio of the amount of light directed to the monitor photodetector and the objective lens to be constant between products. According to the second aspect of the present invention, the monitor photodetector is provided so as to detect the laser beam transmitted from a portion other than the reflection portion of the rising reflection mirror. It is possible to control so that the amount of light incident on the objective lens (optical disk) is always constant without being affected by the fluctuation of the light amount division ratio of the beam splitter or the polarizing prism.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical pickup according to a first invention.

FIG. 2 is a perspective view showing a half-wave plate.

FIG. 3 is a configuration diagram showing an optical pickup according to a second invention.

FIG. 4 is a view showing a modification of the rising reflection mirror.

FIG. 5 is a configuration diagram illustrating an example of a conventional optical pickup.

FIG. 6 is a configuration diagram showing another example of a conventional optical pickup.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser element, 8 ... Polarization beam splitter, 8
A: polarizing film, 10: rising reflection mirror, 14: objective lens, 16: detection system, 22: photodetector for monitoring, 24: light control unit, 26: optical pickup, 28: 1/2 wavelength plate,
29: Optical pickup, 30: Start-up reflection mirror, 32
... Light incident surface, 32A ... reflective surface, 32B ... area without reflective film, D ... optical disk, L ... laser light.

Claims (2)

[Claims] An optical pickup for recording / reproducing information on / from an optical disk, comprising: a half-wave plate for changing a polarization direction of a read / write laser beam emitted from a laser light source by rotating about an optical axis; A monitoring light detector used to control the laser light output of the laser light source so as to detect a light amount of the laser light output from the two-wavelength plate so that the detection result becomes a constant value; A polarizing beam splitter that divides the laser light output from the two-wavelength plate into an optical path toward the optical disk and an optical path toward the monitoring photodetector, wherein the half-wavelength plate has at least its optical axis as a rotation center. An optical pickup characterized in that rotation can be adjusted within a range of 0 to 45 degrees. 2. An optical pickup for recording / reproducing information on / from an optical disc, comprising: an optical system having an objective lens for converging laser light on the optical disc via a reflecting mirror which rises from a laser light source; A monitor used to control the laser light output of the laser light source so as to detect the amount of the laser light transmitted from a portion other than the reflection portion of the rising reflection mirror and to make the detection result a constant value. An optical pickup comprising a photodetector.