JP2001189028A - Optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a scoop by mitigating the entering of the light inside a laser in an optical pickup device such that the light reflected from an optical recording medium is returned to the semiconductor laser. SOLUTION: A signal is reproduced in such a manner that the optical recording medium 6 is irradiated with the laser beam ejected by driving a semiconductor laser source 1 with a pulse current and the light reflected by the optical recording medium 6 is received by a photodetector 8. By increasing the reflectance at the ejected surface side of the semiconductor laser 1, the light is hardly entered inside the semiconductor laser even though the light reflected by the optical recording medium 6 is returned to the semiconductor laser 1 during the laser is emitting, then the scoop is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical pickup device for recording information on an optical recording medium such as an optical disk or reproducing the recorded information.

[0002]

2. Description of the Related Art Conventionally, as this kind of optical pickup device, for example, the one shown in FIG. 3 is known. This optical pickup device includes a laser light source 1, a collimating lens 2, a polarizing beam splitter 3, a quarter-wave plate 4, an objective lens 5, a detector lens (condensing lens) 7, and a light receiving element 8. Have.

In this optical pickup device, light emitted from the laser light source 1 (outgoing light 9) is converted into a parallel light by the collimating lens 2, and passes through the polarizing beam splitter 3. Then, the polarization direction is changed by 45 ° by the 波長 wavelength plate 4 and focused on the optical recording medium 6 by the objective lens 5. The polarization direction of the optical signal (return light 10) reflected by the optical recording medium 6 is again changed by 45 ° by the 波長 wavelength plate 4 and changed by 90 ° from the original light. And
The light is reflected by the polarization beam splitter 3 and focused on the light receiving element 8 by the detector lens 7. The light signal is converted into an electric signal by the light receiving element 8, and the recording is reproduced.

[0004] Further, as a prior art, there is also known one as shown in FIG. This optical pickup device includes a laser light source 1, a collimating lens 2, an objective lens 5,
, A light receiving element 8, and diffraction gratings 11 and 12.

In this optical pickup device, a light source 1
Outgoing light (outgoing light 9) from the diffraction grating 12 is a zero-order light for recording and reproduction signals and ± 0 for tracking error detection.
It is separated into primary light. The optical signal (return light 10) reflected from the optical recording medium 6 is focused on the light receiving element 8 by the diffraction grating 11. Then, when the light signal is converted into an electric signal by the light receiving element 8 and the recording is reproduced, the focus error and the tracking error are corrected.

[0006]

In the conventional optical pickup device shown in FIG. 3, in order to make it difficult for reflected light from the optical recording medium 6 to return to the laser light source 1, a quarter-wave plate 4 and a polarized beam are used. Splitter 3 and detector lens 7
Such parts are required. When the number of components increases in this manner, it becomes difficult to assemble and adjust the optical pickup device, and there is a problem that the size and weight of the device cannot be reduced.

Further, the conventional optical pickup device shown in FIG. 4 has a structure in which the optical signal reflected from the optical recording medium 6 returns to the laser light source 1. Therefore,
When a high power laser light source 1 having a low laser end face reflectance is used to record information on the optical recording medium 6, an optical signal reflected from the optical recording medium 6 enters the inside of the laser light source 1 and Therefore, adverse effects such as noise and scoop occur. Note that the scoop changes the light output from the laser light source 1 in a state where there is no return light from the optical recording medium 6 to P.
1. When the light output from the laser light source 1 in a state where there is return light from the optical recording medium 6 is P2, scoop = P2 /
It is represented by P1 (%).

Further, in the conventional optical pickup device shown in FIGS. 3 and 4, the laser light source 1 is driven by a pulse current and the optical recording medium is not illuminated when the laser light source 1 is not illuminated. Since the shape of the superimposed pulse and the optical path length of the optical pickup device are adjusted so that the reflected light from 6 returns, it is difficult to set these.

The present invention has been made to solve such problems of the prior art. In an optical pickup device in which reflected light from an optical recording medium such as an optical disk returns to a semiconductor laser, the light inside the laser is emitted. To provide an optical pickup device that can reduce noise and scoop by reducing the number of components, reduce the number of parts, reduce the size and weight, and easily adjust the superimposed pulse condition and the optical path length. The purpose is to:

[0010]

An optical pickup device according to the present invention drives a semiconductor laser with a pulse current to emit a laser beam to irradiate an optical recording medium, and receives light reflected by the optical recording medium. And an optical pickup device for reproducing a signal, wherein light reflected by the optical recording medium returns to the semiconductor laser while the pulse current continues, and a main emission surface of the semiconductor laser. The reflectivity on the side is set so that the scoop is 200% or less according to the relaxation frequency, the optical path length of the device, the frequency of the pulse current, the width of the pulse current, and the amplitude of the pulse current. Objective is achieved.

The semiconductor laser has a double hetero structure,
The cavity length is 500 μm, the optical path length of the device is 20 mm or more,
When the frequency of the pulse current is 150 MHz or more,
The reflectance on the main emission surface side of the semiconductor laser can be 6% or more and 21% or less.

The semiconductor laser has a multiquantum well structure, a cavity length of 800 μm, and an optical path length of the device of 20 m.
When the pulse current is 150 m or more and the frequency of the pulse current is 150 MHz or more, the reflectance on the main emission surface side of the semiconductor laser can be 10% or more and 15% or less.

The semiconductor laser has a multiquantum well structure, a cavity length is 600 μm, and an optical path length of the device is 20 m.
When the pulse current is 150 m or more and the frequency of the pulse current is 150 MHz or more, the reflectance on the main emission surface side of the semiconductor laser can be 10% or more and 15% or less.

The operation of the present invention will be described below.

According to the present invention, there is provided an optical pickup device having a structure in which light emitted from a semiconductor laser is irradiated on an optical recording medium and light reflected on the optical recording medium returns to the semiconductor laser. Side reflectivity,
Light hardly enters the semiconductor laser. Therefore, in a high-power laser used for recording information on an optical recording medium such as an optical disk, the scoop rate is reduced even when the light is returned to the semiconductor laser as in the conventional example shown in FIG. It can be reduced.

The reflectivity of the semiconductor laser on the main emission surface side depends on the relaxation frequency determined by the structure of the laser chip and the resonator length, the optical path length of the optical pickup device, and the frequency, width and amplitude of the superimposed pulse current. , The scoop can be set to be 200% or less. 20 scoops
If it exceeds 0%, the amount of return light upon focusing on the optical storage medium increases, so that laser noise is likely to occur and the LD power also increases, so that problems such as collapse of the signal amplitude ratio of 3T to 11T occur. Because.

As described above, in the configuration in which the light reflected on the optical recording medium returns to the semiconductor laser, components such as a quarter-wave plate, a polarizing beam splitter, and a detector lens are used as in the conventional example shown in FIG. Is unnecessary, so that assembly adjustment is easy and the device can be reduced in size and weight.

Furthermore, even if reflected light returns from the optical recording medium while the pulse current continues and the semiconductor laser is shining, it is possible to make light hard to enter inside. Therefore,
As in the conventional example shown in FIGS. 3 and 4, there is no need to adjust the shape of the superimposed pulse and the optical path length so that the reflected light returns from the optical recording medium when the laser light source is not emitting light. It is easy to adjust the superimposed pulse condition and the optical path length.

For example, if the semiconductor laser has a double heterostructure, the resonator length is 500 μm, the optical path length of the device is 20 mm or more, and the frequency of the pulse current is 150 MHz or more, the reflectivity of the semiconductor laser on the main emission surface side is 6 μm. % Or more 21
% Or less. The reflectivity of the semiconductor laser on the main emission surface side is 6
If the percentage is less than 200%, the scoop exceeds 200%.

The semiconductor laser has a multiquantum well structure, the cavity length is 800 μm, and the optical path length of the device is 20 μm.
mm or more and the frequency of the pulse current is 150 MHz or more, the reflectance on the main emission surface side of the semiconductor laser is 10% or more and 15% or less. This is because the scoop exceeds 200% when the reflectance on the main emission surface side of the semiconductor laser is less than 10%.

Further, the semiconductor laser has a multiquantum well structure, the cavity length is 600 μm, and the optical path length of the device is 2 μm.
0 mm or more, and when the frequency of the pulse current is 150 MHz or more, the reflectivity of the semiconductor laser on the main emission surface side is 10
% To 15% or less. When the reflectance on the main emission surface side of the semiconductor laser device is less than 10%, the scoop is 200
%.

[0022]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an optical pickup device according to an embodiment of the present invention.

This optical pickup device comprises a laser light source 1
A diffraction grating 12 for generating a tracking error detection signal from the laser light source 1, a collimating lens 2 for converting the light 9 emitted from the laser light source 1 into parallel light,
An objective lens 5 for converging the parallel light on an optical recording medium 6 such as an optical disk, a diffraction grating 11 for diffracting an optical signal reflected by the optical recording medium 6 to a light receiving element 8,
A light receiving element 8 for converting an optical signal diffracted by the diffraction grating 11 into an electric signal is provided. In this configuration, the light reflected by the optical recording medium 6 returns to the laser light source 1 as in the conventional optical pickup device shown in FIG.

This optical pickup device can measure a scoop as shown in FIG.

Here, a diffraction grating 15 for diffracting light emitted from the laser light source 1, a reflecting mirror 14 for reflecting the light 13 diffracted by the diffraction grating 15 to a light receiving element 16, and a light of the diffracted light 13 A light receiving element 16 for converting a signal into an electric signal is provided.

The light output P1 from the laser light source 1 when there is no return light from the optical recording medium 6 and the light output P2 from the laser light source 1 when there is return light from the optical recording medium 6 are scooped. = P2 / P1 (%) to obtain the scoop.

In the optical pickup device of this embodiment, the optical path length is set to 20 mm or more, and the frequency
50 MHz, Duty 50% or less, and amplitude 60 mA
The scoop can be reduced to 200% or less by setting the structure of the laser light source 1, the cavity length L and the reflectance Rf of the main emission surface as shown in Table 1 below using the above superimposed pulses. is there.

[0029]

[Table 1]

[0030]

As described in detail above, according to the present invention,
In an optical pickup configured to irradiate an optical recording medium with laser light emitted by driving a semiconductor laser with a pulse current, and the light reflected by the optical recording medium to return to the semiconductor laser, the main emission surface side of the semiconductor laser By increasing the reflectance of the laser beam, it is possible to reduce the penetration of the return light into the laser, so that the laser noise and the scoop phenomenon can be reduced. Further, since the number of parts can be reduced as compared with the conventional optical pickup device, assembly adjustment is easy, cost can be reduced, and furthermore, the optical pickup device can be reduced in size and weight. Further, since the light may return to the semiconductor laser while the pulse current continues, the condition of the superimposed pulse and the optical path length can be easily adjusted as compared with the conventional optical pickup device.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an optical pickup device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a configuration for measuring a scoop in the optical pickup device according to one embodiment of the present invention.

FIG. 3 is a cross-sectional view illustrating a configuration of a conventional optical pickup device.

FIG. 4 is a cross-sectional view illustrating a configuration of another conventional optical pickup device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser light source 2 Collimating lens 3 Polarization beam splitter 4 1/4 wavelength plate 5 Objective lens 6 Optical recording medium 7 Condensing lens 8, 16 Light detecting element for signal detection 9 Outgoing light 10 Return light 11 Diffraction grating 12 Diffraction grating (3 beams 13) Diffracted light 14 Reflector 15 Diffraction grating (for scoop measurement)

Claims (4)

[Claims] 1. An optical pickup device for driving a semiconductor laser with a pulse current to emit a laser beam, irradiate the optical recording medium, receive light reflected by the optical recording medium, and reproduce a signal. Light reflected by the optical recording medium is returned to the semiconductor laser while the pulse current is continued, and the reflectance of the semiconductor laser on the main emission surface side is changed to a relaxation frequency,
An optical pickup device in which a scoop is set to be 200% or less according to an optical path length of the device, a pulse current frequency, a pulse current width, and a pulse current amplitude. 2. When the semiconductor laser has a double hetero structure, the cavity length is 500 μm, the optical path length of the device is 20 mm or more, and the frequency of the pulse current is 150 MHz or more, the reflectance of the semiconductor laser on the main emission surface side. 6% or more 21
%. 3. The semiconductor laser has a multiquantum well structure, a cavity length of 800 μm, and a device optical path length of 20 μm.
mm or more and the pulse current frequency is 150 MHz or more, the reflectivity of the semiconductor laser on the main emission surface side is 10%.
2. The optical pickup device according to claim 1, wherein the content is not less than 15%. 4. The semiconductor laser has a multiquantum well structure, a cavity length of 600 μm, and an optical path length of the device of 20 μm.
mm or more and the pulse current frequency is 150 MHz or more, the reflectivity of the semiconductor laser on the main emission surface side is 10%.
2. The optical pickup device according to claim 1, wherein the content is not less than 15%.