JPH0696459A - Light pickup - Google Patents

Abstract

PURPOSE:To obtain high accuracy in outgoing power control by executing stably monitoring without being affected the change in the polarization ration of a laser light source beam with high accuracy, in a light pickup. CONSTITUTION:An optical element of a polarizing plate 8, etc., increasing the polarization ratio of a passing beam is provided on the incident side of a beam splitter 3 distributing a part of an outgoing going from a semiconductor laser element 1 to a photodetector 7 for a monitor. Then, even when the polarization ratio of the light outgoing from the semiconductor laser element 1 is changed, the intensity ratio between the light made incident on the photodetector 7 for monitor and the outgoing light from an objective lens 5 is not changed substantially, and thus, stable and highly accurate monitoring performance is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup used in an optical recording / reproducing device or the like.

[0002]

2. Description of the Related Art Generally, in an optical recording / reproducing apparatus, information is recorded by irradiating an optical recording medium (for example, an optical disc or a magneto-optical disc) with a laser beam to form a minute spot on the medium. Further, the recorded information is reproduced by photoelectrically converting the reflected light or the transmitted light of the spot from the medium by the light receiving element.

A conventional optical pickup in such an optical recording / reproducing apparatus, that is, a portion for irradiating a laser beam and monitoring the irradiation light amount will be described with reference to the drawings. FIG. 5 is a schematic configuration diagram of the conventional optical pickup. Yes,
1A is a front view seen from the direction directly facing the recording surface of the recording medium, and FIG. 1B is a right side view thereof. In FIG. 5, the light emitted from the semiconductor laser device 1 is collimated by the collimator lens 2 and then collimated.
And is reflected by the mirror 4, and the objective lens 5 focuses the light spot on the optical recording medium 6.

At this time, in order to control the power of the light emitted from the objective lens 5 with high accuracy, the light intensity of the laser light from the semiconductor laser element 1 is monitored. Therefore, as shown in FIG. 5, a part of the light from the semiconductor laser device 1 is distributed to the monitor photodetector 7 by the monitor beam splitter 3, and based on the output from the detector 7, The power of the light emitted from the objective lens 5 is controlled.

The monitor beam splitter 3 is a polarization beam splitter, and has a function of distributing the P-polarized component and the S-polarized component of incident light into transmitted light and reflected light by a polarizing film. Generally, this polarizing film is
It exhibits a high transmittance and a low reflectance for the polarized component and, conversely, a low transmittance and a high reflectance for the S polarized component. Therefore, most of the P-polarized component contained in the light emitted from the semiconductor laser device 1 and S
Part of the polarized component is distributed to the objective lens 5 side, and most of the S polarized component and part of the P polarized component are distributed to the photodetector 7 side.

[0006]

In the above-mentioned conventional optical pickup, since the polarizing film as described above is used for the beam splitter 3 for monitoring, the P-polarized component and the S-polarized component of the light from the light source are separated. When the polarization ratio, which is the intensity ratio, changes, the intensity ratio between the light transmitted through the monitor beam splitter 3 and the light reflected on the monitor photodetector 7 side also changes.

Further, in the semiconductor laser device 1 used as a light source, the polarization ratio also changes as the emission power is changed, and the state of this change varies widely among the semiconductor laser devices used. There is.

For this reason, the conventional monitoring method has a problem in that highly accurate monitoring performance cannot be obtained. For example, when a monitor beam splitter 3 having a P-polarized component transmittance of 85% and a reflectance of 15% and an S-polarized component transmittance of 1% and a reflectance of 99% is used, the polarization ratio of the light source is 20%. In the case of (the ratio of the intensity of the P-polarized component and the intensity of the S-polarized component is 20: 1), as shown in Table 1, the intensity ratio of the light transmitted through the monitor beam splitter 3 and the reflected light is shown. Is 4.3.

[0009]

[Table 1]

On the other hand, when the polarization ratio of the light source is 200 (when the ratio of the intensity of the P-polarized component and the intensity of the S-polarized component is 200: 1), the monitor beam as shown in Table 2 is used. The intensity ratio between the light transmitted through the splitter 3 and the reflected light is 5.5.

[0011]

[Table 2]

As described above, conventionally, since the polarization ratio of the light source changes, the intensity ratio between the light incident on the monitor photodetector 7 and the light emitted from the objective lens 5 changes.
There has been a problem that stable and high-performance monitor performance cannot be obtained.

The present invention has been made to solve the above-mentioned conventional drawbacks, and an object thereof is to obtain stable and highly accurate monitor performance without being affected by the change in the polarization ratio of the laser light source light. It is to provide an optical pickup that can control the emission power with high accuracy.

[0014]

In order to achieve the above-mentioned object, the optical pickup according to the present invention has an optical element for increasing the polarization ratio of light from a laser light source, and the polarization ratio is increased by the optical element. A beam splitter that distributes a part of the light and a photodetector that detects the light distributed by the beam splitter are provided.

[0015]

In the optical pickup of the present invention, a polarizing plate can be used as an optical element for increasing the polarization ratio of the light from the laser light source. By providing this polarizing plate between the laser light source and the beam splitter, the polarization ratio of the light from the laser light source is increased and then the light is distributed by the beam splitter for monitoring.

For example, as the optical element, an extinction ratio, that is, a value obtained by dividing the amount of transmitted light in open Nicols (parallel Nicols) by the amount of transmitted light in crossed Nicols (orthogonal Nicols) is 10.
If the polarizing plate of No. 00 is used, even if the polarization ratio of the light itself from the laser light source is about 20, the polarization ratio of the light after passing through the polarizing plate can be improved to about 20000.

In this case, similarly to the above, the transmittance of the P-polarized component is 85%, the reflectance is 15%, and the transmittance of the S-polarized component is 1.
%, A monitor beam splitter with a reflectance of 99% is used, and an extinction ratio of 1000 is provided on the incident side of the beam splitter.
When the polarization ratio of the laser light source itself is 20 when the polarizing plate of No. 2 is interposed, the intensity ratio between the light transmitted through the monitor beam splitter and the reflected light is 5 as shown in Table 3. It becomes 7.

[0018]

[Table 3]

The polarization ratio of the laser light source itself is 2
Even when the value changes to 00, the intensity ratio between the light transmitted through the monitor beam splitter and the reflected light is 5.7, as shown in Table 4.

[0020]

[Table 4]

In this way, by interposing an optical element such as a polarizing plate on the incident side of the beam splitter and increasing the polarization ratio of the light from the laser light source, the polarization ratio of the emitted light from the laser light source changes. However, the intensity ratio between the light incident on the monitor photodetector and the light emitted from the objective lens 5 does not substantially change, and thus stable and highly accurate monitor performance can be obtained. Power control is also highly accurate.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Several embodiments of the present invention will be described with reference to the drawings. First, FIG. 1 is a layout diagram of an optical system showing a schematic configuration of an optical pickup according to a first embodiment of the present invention.
1A is a front view seen from the direction directly facing the recording surface of the recording medium, and FIG. 1B is a right side view thereof. In FIG. 1, the same parts as those in FIG. 5 are designated by the same reference numerals.

In FIG. 1, the optical pickup according to the first embodiment of the present invention records or reproduces information on or from an optical recording medium 6, and includes a semiconductor laser element 1, a collimator lens 2, a beam splitter 3, and a mirror. 4, an objective lens 5, and a light receiving element 7. The functions and arrangements of these constituent elements are the same as those of the conventional example shown in FIG. The optical pickup according to this embodiment is different from the conventional one in that a polarizing plate 8 is arranged between the semiconductor laser device 1 and the beam splitter 3.

By passing through this polarizing plate 8, the polarization ratio of the light emitted from the semiconductor laser device 1 is improved. For example, as described above, if the extinction ratio of 1000 is used for the polarizing plate 8, even if the polarization ratio of the light itself from the semiconductor laser device 1 is about 20, the polarization ratio of the light after passing through the polarizing plate 8 is 20000. Can be improved to a certain degree.

Thus, the polarization ratio of the light from the semiconductor laser device 1 is set to 1000 by using the polarizing plate 8 having the extinction ratio of 1000.
If it is doubled, as shown in Tables 3 and 4 above, even if the polarization ratio of the emitted light of the semiconductor laser device 1 changes, the beam splitter 3 distributes the incident light to the monitor photodetector 7 and makes it incident. The intensity ratio between the light and the light emitted from the objective lens 5 does not substantially change, so that stable and highly accurate monitor performance can be obtained.

FIG. 2 is a layout diagram of an optical system showing a schematic configuration of an optical pickup according to a second embodiment of the present invention. FIG. 2A is a front view seen from a direction directly facing a recording surface of a recording medium. FIG. 3B is a right side view thereof. In FIG. 2, the same parts as those in FIG. 1 are designated by the same reference numerals.

In FIG. 2, the optical pickup according to the second embodiment of the present invention has a configuration in which a polarizing beam splitter 9 is arranged instead of the polarizing plate 8 in the first embodiment shown in FIG.

The polarization beam splitter 9 is an optical element that transmits almost 100% of P-polarized light and reflects almost 100% of S-polarized light, and has the same function as the polarizing plate 8.
Therefore, the polarization ratio can be increased by making the light from the semiconductor laser device 1 incident on the polarization beam splitter 9 and transmitting the light. As a result, similarly to the first embodiment, even if the polarization ratio of the emitted light of the semiconductor laser device 1 changes, the intensity ratio between the light incident on the monitoring photodetector 7 and the light emitted from the objective lens 5 is There is substantially no change, and therefore stable and highly accurate monitor performance can be obtained.

FIG. 3 is a layout view of an optical system showing a schematic configuration of an optical pickup according to a third embodiment of the present invention. FIG. 3A is a front view seen from the direction directly facing the recording surface of the recording medium. FIG. 3B is a right side view thereof. In FIG. 3, the same parts as those in FIG. 1 are designated by the same reference numerals.

In FIG. 3, an optical pickup according to the third embodiment of the present invention has a structure in which a Glan-Thompson prism 10 is arranged instead of the polarizing plate 8 in the first embodiment shown in FIG.

The Glan-Thompson prism 10 is an optical element that can utilize the birefringence of light and have a function equivalent to that of the polarizing plate 8. In this case, the extinction ratio of the Gran-Thomson prism 10 can be 10,000 or more. By making the light from the semiconductor laser device 1 incident on the Glan-Thompson prism 10 and transmitting the light, the polarization ratio of the transmitted light can be increased to about 10,000 times. As a result, similar to the first and second embodiments, stable and highly accurate monitor performance can be obtained.

FIG. 4 is a layout diagram of an optical system showing a schematic configuration of an optical pickup according to a fourth embodiment of the present invention. FIG. 4A is a front view seen from the direction directly facing the recording surface of the recording medium. FIG. 3B is a right side view thereof. In FIG. 4, the same parts as those in FIG. 1 are designated by the same reference numerals.

In FIG. 4, an optical pickup according to a fourth embodiment of the present invention has an incident surface with respect to an incident optical axis from the semiconductor laser element 1 instead of the polarizing plate 8 in the first embodiment shown in FIG. The beam shaping prism 11 that is tilted is disposed, and a film that reflects only S-polarized light is provided on the incident surface of the prism 11.

In general, the intensity distribution shape of the emitted light of the semiconductor laser device 1 is an ellipse, and therefore when using this, it is necessary to shape the light intensity distribution into a substantially circular shape.
Therefore, in the present embodiment, the shape of this light intensity distribution is shaped by using the beam shaping prism 11 as shown in FIG. As is apparent from FIG. 4A, the light from the semiconductor laser device 1 is collimated by the collimator lens 2 and then incident on the beam shaping prism 11 at an incident angle of about 60 degrees. The incident surface of the beam shaping prism 11 is coated with a polarizing film that reflects only S-polarized light, thereby increasing the polarization ratio of the light transmitted through the beam shaping prism 11.

For example, when BK7 is used as the glass of the beam shaping prism 11 and the incident angle of light is about 65 degrees, a two-layer film called a so-called V coat is formed on the prism 11.
By coating the incident surface of the
% Can be removed. In this way, the polarization ratio of the light incident on the monitor beam splitter 3 can be increased, and stable and highly accurate monitor performance can be obtained, as in the above-described embodiments. .

[0036]

As described above, according to the present invention,
By inserting an optical element that increases the polarization ratio of the light from the laser light source on the incident side of the beam splitter, even if the beam splitter that distributes the light to the photodetector has a characteristic that depends on the polarization ratio, the polarization ratio in the laser light source It is possible to constantly monitor with high accuracy regardless of changes in
It is possible to obtain the effect that it is effective in improving the accuracy of the power control of the light emitted from the optical pickup.

[Brief description of drawings]

1A and 1B are layout diagrams of an optical system showing a schematic configuration of an optical pickup according to a first embodiment of the present invention, FIG. 1A is a front view seen from a direction directly facing a recording surface of a recording medium, and FIG. Is a right side view thereof.

2A and 2B are arrangement diagrams of an optical system showing a schematic configuration of an optical pickup according to a second embodiment of the present invention, FIG. 2A is a front view seen from a direction directly facing a recording surface of a recording medium, and FIG. Is a right side view thereof.

3A and 3B are layout diagrams of an optical system showing a schematic configuration of an optical pickup according to a third embodiment of the present invention, FIG. 3A is a front view seen from a direction directly facing a recording surface of a recording medium, and FIG. Is a right side view thereof.

4A and 4B are arrangement diagrams of an optical system showing a schematic configuration of an optical pickup according to a fourth embodiment of the present invention, FIG. 4A is a front view seen from a direction directly facing a recording surface of a recording medium, and FIG. Is a right side view thereof.

5A and 5B are arrangement diagrams of an optical system showing a schematic configuration of a conventional optical pickup, FIG. 5A is a front view seen from a direction directly facing a recording surface of a recording medium, and FIG. 5B is a right side view thereof. is there.

[Explanation of symbols]

 1 Semiconductor Laser Element 2 Collimator Lens 3 Beam Splitter 4 Mirror 5 Objective Lens 6 Optical Recording Medium 7 Photodetector 8 Polarizing Plate 9 Polarizing Beam Splitter 10 Condensing Lens 11 Gran-Thomson Prism 12 Beam Shaping Prism

Claims (1)

[Claims] 1. An optical pickup for irradiating a recording medium with light from a laser light source, comprising: an optical element for increasing the polarization ratio of the light from the laser light source; and a part of the light with the polarization ratio increased by the optical element. An optical pickup comprising: a beam splitter for distributing the light; and a photodetector for detecting the light distributed by the beam splitter.