JP2002237082A - Optical pickup - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive optical pickup capable of making exit light from a laser beam source pass through a beam splitter and making incident or an optical disk without imparting any bad influence to a light beam. SOLUTION: A laser beam exited from the laser beam source (LD) transmits the wedge shaped beam splitter(WBS), while return light reflected by the optical disk(DISK) is reflected on the reflecting surface of the wedge shaped beam splitter(WBS). The wedge shaped beam splitter(WBS) is optimized so that the laser beam diffused from the laser beam source is transmitted without making astigmatic.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical pickup for reproducing an optical recording medium (optical disk), and more particularly to an optical system thereof.

[0002]

2. Description of the Related Art An optical pickup is a device for reproducing an optical disk. As an optical disc, DVD
(Digital versatile disc) and CD (compact disc). As is well known in the art, in an optical pickup, reflected light (return light) reflected on an optical disk is detected by a photodetector such as a photodetector. At that time, immediately before the return light enters the photodetector. Therefore, it is necessary to introduce (given) astigmatism only for the return light. In other words, it is not preferable to introduce (given) astigmatism to light incident on the optical disk.

As a method of giving astigmatism only to such return light, a conventional optical pickup employs the following optical system.

Hereinafter, a first conventional optical pickup will be described with reference to FIG. FIG. 3 is a system configuration diagram of the optical system of the optical pickup.

The illustrated optical pickup includes a laser diode LD, a diffraction grating (grating) GRT, a beam splitter BS, a collimator lens CL, an objective lens OL, and a photodetector PD.

[0006] The laser diode LD emits laser light having a predetermined wavelength. The diffraction grating GRT is
One laser beam emitted from the laser diode LD is converted into three laser beams (a central beam and two beams on both sides thereof).
It is for separating into. Beam splitter BS
Is for reflecting three laser beams from the diffraction grating GRT and transmitting return light (reflected light from the optical disc DISC) as described later. The three laser beams reflected by the beam splitter BS are emitted toward the collimator lens CL.

[0007] The collimator lens CL is for converting three laser beams from the beam splitter BS into parallel beams. The parallel light from the collimator lens CL is guided to the objective lens OL side. The objective lens OL irradiates the parallel light from the collimator lens CL onto the optical disc DISC. The reflected light (return light) reflected by the optical disc DISC is received by the photodetector PD as described later.

Next, the operation of the optical pickup shown in FIG. 3 will be described.

The laser beam emitted from the laser diode LD is split into three laser beams (light beams) by a diffraction grating GRT, and then enters a beam splitter BS. The three laser beams incident on the beam splitter BS are reflected by the reflecting surface, are made parallel by the collimator lens CL, are converged by the objective lens OL, and are converged by the objective lens OL.
The recording surface is irradiated.

The reflected light (return light) from the recording surface of the optical disk DISC passes through the objective lens OL and the collimator lens CL, passes through the beam splitter BS again, and then enters the photodetector PD.

In any case, in the first conventional optical pickup shown in FIG. 3, astigmatism is given only to the return light by utilizing refraction due to the thickness of the beam splitter BS. In other words, astigmatism is introduced into the return light by transmitting the light through the beam splitter BS. An example in which the beam splitter BS is used also as an astigmatism introducing element is disclosed in Japanese Patent Publication No. 2-8379. Here, the beam splitter BS
Is a plane-parallel plate having two parallel surfaces.

Next, a second conventional optical pickup will be described with reference to FIG. FIG. 4 is a system configuration diagram of the optical system of the optical pickup.

The illustrated optical pickup has a configuration similar to that of the optical pickup shown in FIG. 3 except that a polarization beam splitter PBS and a sensor lens SL are used instead of the beam splitter BS. That is, the optical pickup includes a laser diode LD, a diffraction grating (grating) GRT, and a polarizing beam splitter PBS.
, A collimator lens CL, an objective lens OL, a sensor lens SL, and a photodetector PD. In the following, in order to simplify the description, only the components different from those in FIG. 3 will be described.

The polarizing beam splitter PBS transmits the three laser beams from the diffraction grating GRT and emits them to the collimator lens CL. In addition, the polarization beam splitter P
The BS transmits the return light (optical disc DISC) as described later.
(Reflected light from the object). Polarizing beam splitter PB
S has a cubic shape as shown in FIG.
The sensor lens SL is for giving astigmatism to the light reflected by the polarization beam splitter PBS and guiding the light to the photodetector PD.

Next, the operation of the optical pickup shown in FIG. 4 will be described.

The laser beam emitted from the laser diode LD is split into three laser beams (light beams) by a diffraction grating GRT, then passes through a polarizing beam splitter PBS, and is made parallel by a collimator lens CL. The light is converged by the lens OL and irradiated onto the recording surface of the optical disc DISC.

The reflected light (return light) from the recording surface of the optical disc DISC passes through the objective lens OL and the collimator lens CL again, is reflected by the polarizing beam splitter PBS, and then is transmitted to the photodetector PD via the sensor lens SL. Incident.

In any case, in the second conventional optical pickup shown in FIG. 4, astigmatism is given only to the return light using the sensor lens SL. In other words,
By transmitting the light through the sensor lens SL, astigmatism is introduced into the return light. Here, it should be noted that even if light passes through the polarizing beam splitter PBS, the transmitted light is not given astigmatism.

[0019]

However, due to the structure of the optical pickup, there is a case where the emitted light from the laser diode must be incident on the optical disk through the beam splitter. In such a case, conventionally, as shown in FIG. 4, a three-dimensional polarizing beam splitter PBS must be used as the beam splitter. This is because, as described above, in a plane-parallel plate type beam splitter BS as shown in FIG. 3, astigmatism is given to light transmitted through the beam splitter BS. However, there is a disadvantage that the three-dimensional polarizing beam splitter PBS is expensive.

Therefore, an expensive polarizing beam splitter PB
It is desired that the light emitted from the laser diode be transmitted through the beam splitter and enter the optical disc without using S.

On the other hand, an optical pickup using a wedge-shaped wedge beam splitter (hereinafter also referred to as a "wedge-shaped beam splitter") as a beam splitter is disclosed in Japanese Patent Publication No. 8-3906. However, in the optical pickup disclosed in this publication, the purpose is to make the elliptical laser light close to a perfect circle by the wedge beam splitter, and the wedge beam splitter is disposed between the collimator lens and the objective lens. It is necessary to bend the light beam at a large angle, which may adversely affect the light beam.

Therefore, an object of the present invention is to provide an inexpensive laser beam (laser light source) that can be emitted from a laser diode (laser light source) through a beam splitter and incident on an optical disk without adversely affecting a light beam. An object of the present invention is to provide an optical pickup.

[0023]

According to the present invention, there is provided a laser light source (LD) for emitting laser light, and a wedge-shaped beam splitter (WBS) for transmitting the laser light and reflecting return light on a reflecting surface. A collimator lens (C) that converts the light beam transmitted through the wedge-shaped beam splitter into a parallel beam.
L) and the parallel beam is transferred to an optical recording medium (DISC).
An objective lens (OL) that converges upward, and the return light reflected on the optical recording medium and transmitted through the objective lens and the collimator lens is reflected on the reflection surface of the wedge-shaped beam splitter into a light beam. A sensor lens (SL) for giving astigmatism thereto, and a photodetector (PD) for receiving a light beam transmitted through the sensor lens, wherein the wedge-shaped beam splitter diffuses from the laser light source. An optical pickup characterized by being optimized to transmit laser light without astigmatism is obtained.

It should be noted that the reference numerals in the parentheses are provided for easy understanding, are merely examples, and are not intended to limit the scope of the present invention.

[0025]

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

With reference to FIG. 1, an optical pickup according to one embodiment of the present invention will be described. The illustrated optical pickup has a configuration similar to that shown in FIG. 4 except that a wedge-shaped beam splitter WSB is used instead of the polarization beam splitter PBS, and the incident angle and the like are selected as described later. Therefore, those having the same functions as those shown in FIG. 4 are denoted by the same reference numerals, and the description thereof will be omitted, and only the differences will be described below. It should be noted that the angles described below are angles based on the light beam on the optical axis.

In the illustrated example, the wedge-shaped beam splitter WS
As B, the thickness is 1.2 mm, preferably 1.0 mm
And a wedge angle γ of 1 °, preferably between 1 ° and 2 °. The incident angle α of the laser beam emitted from the laser diode LD with respect to the reflection surface of the wedge-shaped beam splitter WSB is 35 °, but is preferably in an angle range between 30 ° and 35 °.

Thus, the wedge beam splitter WSB
By optimizing the thickness and the wedge angle γ, the laser light from the incident angle α can be suppressed to astigmatism that is small enough to have no effect, so that optical characteristics that do not affect the laser light can be obtained.

On the other hand, the included angle β between the return light reflected by the optical disk DISK and the reflected light reflected by the reflection surface of the wedge beam splitter WBS is substantially in an angle range between 60 ° and 70 °.

As described above, by transmitting through the wedge-shaped beam splitter WBS whose incident angle α is appropriately selected,
Optical aberrations can be reduced. Thus, the optical characteristics of the optical pickup can be satisfied without using a cubic polarizing beam splitter PBS as shown in FIG. Further, since the flat wedge-shaped beam splitter WBS is used instead of the expensive polarizing beam splitter PBS, there is an advantage that the optical pickup can be manufactured at low cost. Further, since the light emitted from the laser diode LD is made incident on the wedge-shaped beam splitter WSB before passing through the collimator lens CL, it is not necessary to bend the light beam at a large angle, thereby reducing the adverse effect on the light beam. it can.

On the other hand, even if the polarization direction of the laser beam is the same, the transmission and reflection of the laser beam can be easily controlled by using the wedge-shaped beam splitter by changing the wavelength of the laser beam. For example, as is well known, some DVD (digital versatile disk) players are equipped with a special optical pickup to enable reproduction of both DVDs and CDs (compact disks). Such special optical pickups include a short wavelength laser light for DVD (wavelength about 650 nm) and a long wavelength laser light for CD (wavelength about 7 nm).
80 nm) for performing reproduction by properly using two types of laser light, and is called a two-wavelength compatible optical pickup.

Hereinafter, a two-wavelength compatible optical pickup using a wedge-shaped beam splitter will be described with reference to FIG.

The two-wavelength compatible optical pickup shown in FIG.
DVD laser diode DVD-LD that emits DVD laser light having a wavelength of about 650 nm for VD reproduction
And a hologram laser diode CD-HO for emitting a laser beam for CD having a wavelength of about 780 nm for CD reproduction
E and first and second wedge-shaped beam splitters WBS1
And WBS2, a collimator lens LD, an objective lens OL, a sensor lens SL, and a photodetector PD
And However, in FIG. 2, the illustration of the diffraction grating (grating) is omitted. Also, as shown in FIG. 1, although the light actually has a spread, in FIG.
Only the light on the optical axis is shown as a representative.

Hologram laser diode CD-HOE
Has a function of internally giving astigmatism to the return light and a function of detecting the return light. In addition, the first wedge-shaped beam splitter WBS1 has a characteristic of having a reflectance and a transmittance of about 50% for light having a wavelength of about 650 nm. On the other hand, the second wedge-shaped beam splitter WBS2 has a characteristic of a reflectance of 100% for light having a wavelength of about 650 nm, but has a characteristic of a transmittance of 100% for light having a wavelength of about 780 nm. have. Therefore, DVD
About 25% of the amount of laser light emitted from the laser diode DVD-LD for photodetector PD
Will be incident. However, even if the light intensity is 2
Even if it is reduced to 5%, the photodetector PD operates sufficiently and can exhibit its function.

Next, the operation of the optical pickup for two wavelengths shown in FIG. 2 will be described. First, the optical disk D
The operation when the DVD is used as the ISC will be described, and then the operation when the CD is used as the optical disc DISC will be described.

When the optical disc DISC is a DVD,
Only the DVD laser diode DVD-LD is put into operation, and the hologram laser diode CD-HOE is put into non-operation. Therefore, only the DVD laser diode DVD-LD emits laser light having a wavelength of about 650 nm.

The laser light emitted from the DVD laser diode DVD-LD passes through the first wedge beam splitter WBS1 and then passes through the second wedge beam splitter WBS.
It is incident on BS2. This second wedge-shaped beam splitter W
The laser light incident on BS2 is reflected on its reflection surface,
The light is collimated by the collimator lens CL and the objective lens OL
And irradiates the recording surface of the optical disc DISC (DVD).

The reflected light (return light) from the recording surface of the DVD is again transmitted to the objective lens OL and the collimator lens CL.
After being reflected by the second wedge-shaped beam splitter WBS2 and the first wedge-shaped beam splitter WBS1, the light is incident on the photodetector PD via the sensor lens SL.

Next, the operation when the optical disk DISC is a CD will be described. In this case, only the hologram laser diode CD-HOE is put into operation and D
The VD laser diode DVD-LD is in a non-operation state. Therefore, the hologram laser diode CD
Only -HOE emits a laser beam having a wavelength of about 780 nm.

Hologram laser diode CD-HOE
Is transmitted through the second wedge-shaped beam splitter WBS2, is collimated by the collimator lens CL, is converged by the objective lens OL, and is converged by the objective lens OL.
Irradiated on the recording surface of ISC (CD).

Light reflected from the recording surface of this CD (return light)
Again passes through the objective lens OL and the collimator lens CL, passes through the second wedge-shaped beam splitter WBS2, and then enters the hologram laser diode CD-HOE.

The present invention is not limited to the above embodiment,
It goes without saying that various changes and modifications can be made without departing from the spirit of the present invention.

[0043]

As is apparent from the above description, according to the present invention, since the wedge-shaped beam splitter is used as the beam splitter, the light emitted from the laser light source is reduced in a wedge-shaped manner with the optical aberration reduced. The light can pass through the beam splitter and enter the optical disc. Thus, the optical characteristics of the optical pickup can be satisfied without using a cubic polarizing beam splitter. In addition, there is no expensive polarizing beam splitter, and a flat wedge beam splitter is used.
There is also an advantage that the optical pickup can be made inexpensive. Furthermore, since the light emitted from the laser light source is made incident on the wedge beam splitter before passing through the collimator lens, it is not necessary to bend the light beam at a large angle, and the adverse effect on the light beam can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an optical system of an optical pickup according to an embodiment of the present invention.

FIG. 2 is a diagram showing an optical system of a two-wavelength compatible optical pickup using a wedge-shaped beam splitter.

FIG. 3 is a diagram showing an optical system of a first conventional optical pickup.

FIG. 4 is a diagram showing an optical system of a second conventional optical pickup.

[Explanation of symbols]

 LD Laser diode (laser light source) GRT Diffraction grating WBS, WBS1, WBS2 Wedge beam splitter CL Collimator lens OL Objective lens DISC Optical disk SL Sensor lens PD Photodetector (photodetector) α Incident angle β Inclusion angle γ Wedge angle CD-HOE Hologram laser diode DVD-LD Laser diode for DVD

Claims (1)

[Claims] 1. A laser light source that emits laser light, a wedge-shaped beam splitter that transmits the laser light and reflects a return light on a reflection surface, and a collimator that converts the light beam transmitted through the wedge-shaped beam splitter into a parallel beam. A lens; an objective lens for converging the parallel beam on an optical recording medium; and a reflection of the return light, which is reflected on the optical recording medium and transmitted through the objective lens and the collimator lens, to the reflection of the wedge-shaped beam splitter. A sensor lens that gives astigmatism to the light beam reflected by the surface, and a photodetector that receives the light beam transmitted through the sensor lens, wherein the wedge-shaped beam splitter is An optical pickup characterized in that it is optimized to transmit a diffused laser beam without causing astigmatism.