JP2003217165A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To change the polarization direction of a laser beam emitted from a semiconductor laser so as to be matched with the optical characteristics of a beam splitter. <P>SOLUTION: The optical pickup device which reflects the laser beam having the prescribed polarization direction emitted from the semiconductor laser (LD) by a beam splitter (BS), condenses the laser beam to a signal recording surface of an optical disk (Disc) by an objective lens (OL), and transmits the return light from this signal recording surface through the beam splitter and detects the light with a photodetector (PD) is provided with a polarization direction changing element (PDP) for changing the polarization direction of the laser beam emitted from the semiconductor laser so as to be matched with the optical characteristics of the beam splitter between the semiconductor laser and the beam splitter. A half wavelength plate is used as the PDP. <P>COPYRIGHT: (C)2003,JPO

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 incorporated in an optical disc device for reproducing an optical recording medium (optical disc).

[0002]

As is well known, an optical pickup device focuses laser light emitted from a semiconductor laser, which is a light source, on a signal recording surface of an optical disc by an objective lens,
This is an apparatus for detecting the returning light from the signal recording surface by a photodetector which is a photodetecting means.

A conventional optical pickup device will be described below with reference to the drawings. 1 and 2 are a plan view and a front view showing an optical system of a conventional optical pickup device, respectively.

The optical pickup device includes a semiconductor laser (laser diode) LD, a diffraction grating GRT, a beam splitter BS, a collimating lens CL, a raising mirror MIR, an objective lens OL, and a concave lens (magnifying lens) EL. , A photodetector (light receiving element) PD and a forward sensor FS. The Disk is an optical disk.

In the illustrated optical pickup device, the rising angle θ of the reflecting surface of the rising mirror MIR with respect to the lower surface of the pickup is smaller than 45 °. Then, as shown in FIG. 2, the semiconductor laser LD and the photodetector P
The optical components of D, the diffraction grating GRT, the collimator lens CL, the concave lens EL, and the forward sensor FS are arranged in a state of being inclined with respect to the optical base (not shown) so as not to protrude downward from the lower surface of the pickup. is doing.

FIG. 3 shows the relationship between the rising angle θ of the reflecting surface of the rising mirror MIR. Since the rising angle θ of the reflecting surface of the rising mirror MIR is smaller than 45 °, the laser beam incident on the rising mirror MIR and the rising mirror MIR are incident on the rising surface.
The optical axis of the return light reflected from R is inclined upward by an angle α with respect to the lower surface of the pickup. This angle α is α =
It is represented by 90 ° -2θ.

Next, the operation of the conventional optical pickup device shown in FIGS. 1 and 2 will be described.

A single laser beam emitted from the semiconductor laser LD arranged in the foreground in the forward direction in a state of being inclined downward at an angle α with respect to the horizontal plane (the lower surface of the pickup) is a diffraction grating GRT (see FIG. In 1), it is split into three laser beams, bent at a right angle by the beam splitter BS, and proceeds leftward while being inclined downward by an angle α with respect to the horizontal plane. The beam splitter BS splits the incident laser light into reflected light and transmitted light at a fixed ratio. For example, the beam splitter BS is configured to reflect 80% of the incident laser light and transmit 20% thereof. The forward sensor FS (FIG. 1) monitors the amount of laser light that has passed through this beam splitter BS. Laser light that inclines downward by an angle α with respect to this horizontal plane and travels to the left is
After being collimated by the collimator lens CL, it is reflected by the reflecting surface of the rising mirror MIR and travels vertically upward, and is focused (irradiated) onto the signal recording surface of the optical disc Disk through the objective lens OL.

Reflected light (returned light) from the signal recording surface of the optical disc Disc travels vertically downward and reaches the objective lens OL.
And is reflected by the reflecting surface of the rising mirror MIR,
Inclined upward by an angle α with respect to the horizontal plane (Fig. 3)
It proceeds rightward and is detected by the photodetector PD through the collimator lens CL, the beam splitter BS, and the concave lens EL.

A semiconductor laser LD, a diffraction grating GRT,
Optical components such as the beam splitter BS, the collimator lens CL, the rising mirror MIR, the concave lens EL, the photodetector PD, and the forward sensor FD are held by an optical base (not shown). The objective lens OL is held by a lens holder (not shown), and the lens holder is supported so as to be finely movable with respect to the optical base.
The lower surface of the pickup is the lower surface of the optical base.

[0011]

The laser light emitted from the semiconductor laser LD has a polarization direction, as shown in FIG. 4A is a perspective view of the semiconductor laser LD, and FIG. 4B is a front view of the semiconductor laser LD.

On the other hand, the beam splitter BS is manufactured by depositing a spectral vapor deposition film on a predetermined base material. The spectral vapor deposition film defines the polarization direction, reflectance, and transmittance of the beam splitter BS. This is called the optical characteristic of the beam splitter BS. Therefore, depending on the specifications of the spectral vapor deposition film, it is necessary to rotate the semiconductor laser LD around its optical axis to change the polarization direction of the laser light emitted from the semiconductor laser LD. In other words, it is necessary to change the polarization direction of the laser light emitted from the semiconductor laser LD so as to match (match) the optical characteristics of the beam splitter BS (specifications of the spectral vapor deposition film).

However, the product height H (FIG. 2) of the thin optical pickup device is limited. For that reason,
In the thin optical pickup device, a D-shaped thin semiconductor laser LD as shown in FIGS. 2 and 4 is used as the semiconductor laser. as a result,
It is almost impossible to rotate the thin semiconductor laser LD around its optical axis.

On the other hand, Japanese Patent Laid-Open No. 11-261171 discloses an optical pickup device which reduces return light noise which is caused by the return light entering a semiconductor laser (laser element). ing. In this publication, an optical element having a polarization rotation function is arranged in the optical path of a laser element, and this optical element makes the polarization direction of return light to the laser element different from the polarization direction of emission light from the laser element. Is being converted to. Specifically, this optical element converts the polarization direction of the return light to the laser element so as to be approximately 90 degrees with respect to the polarization direction of the emission light from the laser element. One such optical element is
A quarter wave plate is used.

However, in this publication, an optical element such as a quarter-wave plate is used to convert the polarization direction of the return light, and the final purpose thereof is to reduce the return light noise. is there. Therefore, in this publication, the optical element is not used in order to match the polarization direction of the light emitted from the laser element with the optical characteristics of the beam splitter.

Therefore, an object of the present invention is to provide an optical pickup device capable of changing the polarization direction of laser light emitted from a semiconductor laser so as to match the optical characteristics of a beam splitter.

[0017]

According to the present invention, a laser beam emitted from a semiconductor laser (LD) and having a predetermined polarization direction is reflected by a beam splitter (BS) and an optical disk (OL) is produced by an objective lens (OL). In the optical pickup device which collects light on the signal recording surface of Disc), transmits the return light from the signal recording surface through the beam splitter and detects it by the photodetector (PD), between the semiconductor laser and the beam splitter. In addition, an optical pickup device is provided which is provided with a polarization direction changing element (PDP) that changes the polarization direction of the laser light emitted from the semiconductor laser so as to match the optical characteristics of the beam splitter.

In the above optical pickup device, a half-wave plate can be used as the polarization direction changing element.

It should be noted that the reference numerals in the above parentheses are given for easy understanding and are merely examples, and it is needless to say that they are not limited to these.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Referring to FIG. 5 in addition to FIGS. 2 and 3,
An optical pickup device according to an embodiment of the present invention will be described.

In the illustrated optical pickup device, a half-wave plate PDP which is a polarization direction changing element is added between the semiconductor laser LD and the beam splitter BS, except that
It has the same structure as the conventional optical pickup device. Therefore, components having the same functions as those of the conventional optical pickup device are designated by the same reference numerals, and the description thereof will be omitted to avoid redundant description.

The half-wave plate PDP has a semiconductor laser LD so as to match the optical characteristics of the beam splitter BS.
This is for changing the polarization direction of the laser light emitted from the.

Therefore, the half-wave plate P according to the present invention
It is obvious that the DP has a different purpose from that of the optical element disclosed in JP-A-11-261171.

In the present embodiment, the half-wave plate PD
P is arranged between the diffraction grating GRT and the beam splitter BS. The other arrangement of the optical components is the same as that of the conventional optical pickup device described above.

As described above, in the present embodiment, the polarization direction of the laser light emitted from the semiconductor laser LD is set between the semiconductor laser LD and the beam splitter BS so as to match the optical characteristics of the beam splitter BS. Since the polarization direction changing element (1/2 wavelength plate) PDP to be changed is provided, the polarization direction of the laser light emitted from the semiconductor laser LD is changed without rotating the semiconductor laser LD around its optical axis. can do. Thereby, even if the height of the semiconductor laser LD is the product control height upper limit H of the optical pickup device, it is possible to change the polarization direction of the laser light emitted from the semiconductor laser LD.
As a result, it is not necessary to manufacture a special package for reducing the size of the semiconductor laser, and a standard package can be adopted, so that an inexpensive optical pickup device can be manufactured.

Next, the operation of the optical pickup device shown in FIG. 5 will be described.

One laser beam emitted from the semiconductor laser LD arranged in the foreground in the forward direction in a state of being inclined downward at an angle α with respect to the horizontal plane (the lower surface of the pickup) is 3 by the diffraction grating GRT. The laser light of the book is divided into 1 /
After being polarized by the two-wave plate PDP so that its polarization direction matches the optical characteristics of the beam splitter BS, it is bent at a right angle by the beam splitter BS and leftward in a state of being inclined downward at an angle α with respect to the horizontal plane. Go to. still,
The beam splitter BS splits the incident laser light into reflected light and transmitted light at a constant ratio. For example, the beam splitter BS reflects 80% of the incident laser light and
Is configured to be transparent. Forward sensor FS
Monitors the amount of laser light transmitted through the beam splitter BS. The laser light which inclines downward by an angle α with respect to the horizontal plane and travels to the left is collimated by the collimator lens CL, is reflected by the reflecting surface of the rising mirror MIR, and travels vertically upward, and the objective lens OL. The light is focused (irradiated) onto the signal recording surface of the optical disc Disk via.

Reflected light (returned light) from the signal recording surface of the optical disc Disc travels vertically downward and reaches the objective lens OL.
And is reflected by the reflecting surface of the rising mirror MIR,
Inclined upward by an angle α with respect to the horizontal plane (Fig. 3)
It proceeds rightward and is detected by the photodetector PD through the collimator lens CL, the beam splitter BS, and the concave lens EL.

The present invention is not limited to the above embodiment,
Of course, various changes and modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiment, one half-wave plate PD is used as the polarization direction changing element.
Although P is used, two quarter-wave plates may be arranged in series. Further, in the above-described embodiment, 1 /
Although the two-wave plate PDP is arranged between the diffraction grating GRT and the beam splitter BS, the same effect can be obtained by attaching the half-wave plate to another optical component. Furthermore, 1 /
The same effect can be obtained by integrating the two-wave plate with another optical component such as a diffraction grating plate.

[0031]

As is apparent from the above description, according to the present invention, between the semiconductor laser and the beam splitter,
To match the optical characteristics of the beam splitter,
Since a polarization direction changing element that changes the polarization direction of the laser light emitted from the semiconductor laser is provided, the polarization direction of the laser light emitted from the semiconductor laser can be adjusted without rotating the semiconductor laser around its optical axis. Can be changed. This makes it possible to change the polarization direction of the laser light emitted from the semiconductor laser even if the height of the semiconductor laser is the upper limit of the product regulation height of the optical pickup device. As a result, it is not necessary to manufacture a special package for reducing the size of the semiconductor laser, and a standard package can be adopted, so that an inexpensive optical pickup device can be manufactured.

[Brief description of drawings]

FIG. 1 is a plan view showing an optical system of a conventional optical pickup device.

FIG. 2 is a front view showing an optical system of the conventional optical pickup device shown in FIG.

FIG. 3 is a diagram showing a relationship between a reflecting surface and a rising angle of a rising mirror used in the conventional optical pickup device shown in FIG.

FIG. 4 is a perspective view (A) and a front view (B) showing a semiconductor laser used in the conventional optical pickup device shown in FIG. 1 together with a polarization direction of the emitted laser light.

FIG. 5 is a plan view showing an optical system of the optical pickup device according to the embodiment of the present invention.

[Explanation of symbols]

LD semiconductor laser (laser diode) GRT diffraction grating BS beam splitter CL collimating lens MIR startup mirror OL objective lens Disc optical disc EL concave lens (magnifying lens) PD photo detector (light receiving element) FS forward sensor PDP Polarization direction changing element (1/2 wavelength plate) θ Rise angle

Claims (2)

[Claims] 1. A laser beam emitted from a semiconductor laser and having a predetermined polarization direction is reflected by a beam splitter and focused on a signal recording surface of an optical disc by an objective lens, and a return light from the signal recording surface is reflected by the beam. In an optical pickup device that transmits light through a splitter and detects with a photodetector, between the semiconductor laser and the beam splitter, the semiconductor laser emitted from the semiconductor laser is matched so as to match the optical characteristics of the beam splitter. An optical pickup device comprising a polarization direction changing element for changing the polarization direction of laser light. 2. The optical pickup device according to claim 1, wherein the polarization direction changing element is a half-wave plate.