JPH0944865A - Optical pickup - Google Patents

Abstract

(57) An object of the present invention is to provide an optical pickup in which spot vibration in a light receiving portion of a photodetector due to vibration of an optical base is not detected as a focus error. SOLUTION: A light source 11 that emits a light beam, an objective lens 15 that irradiates the light beam emitted from the light source so that the recording surface of an optical signal recording medium is focused, and light that passes through the objective lens Cylindrical lens 1 for imparting astigmatism to a return light beam from a signal recording surface of a signal recording medium
7, a photodetector 18 divided by a dividing line that receives the return light beam that has passed through the cylindrical lens, and a base portion 19 that supports at least the photodetector, and detects a focus error of the photodetector 18. Dividing line 1
8b is arranged to be in a direction that coincides with the spot vibration direction generated by the vibration of the base portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for recording and / or reproducing on an optical signal recording medium such as an optical disc and a magneto-optical disc.

[0002]

2. Description of the Related Art Conventionally, for example, recording / recording on a magneto-optical disk
The optical pickup for reproducing is configured as shown in FIG. In FIG. 4, the optical pickup 1 is composed of a semiconductor laser element 2, a grating 3, a collimator lens 4, a beam splitter 5, an objective lens 6, a Wollaston prism 7, a cylindrical lens 8 and a photodetector 9.

The beam splitter 5 is arranged with its reflecting surface 5a inclined by 45 degrees with respect to the optical axis of the objective lens 6, and records the light beam emitted from the semiconductor laser element 2 and the magneto-optical disk MO. Separate the return light from the surface. That is, the light beam from the semiconductor laser element 2 passes through the beam splitter 5, and the return light is reflected by the reflecting surface 5a.

The objective lens 6 is a convex lens and forms an image of the parallel light beam transmitted through the beam splitter 5 on a desired track on the recording surface of the magneto-optical disk MO which is rotationally driven. Further, the objective lens 6 is, as shown by an arrow in FIG.
It is supported so as to be movable in two axial directions.

The photodetector 9 is configured to have a light receiving portion for each of the three light beams polarized and separated by the Wollaston prism 7. That is, as shown in FIG. 5, the photodetector 9 receives the beams separated by the Wollaston prism 7 from the central light receiving portion 9a and the upper and lower light receiving portions I and J, and the light receiving portions E and J from both sides. Have F and. Further, the light receiving portion 9a at the center is divided into four vertically and horizontally by the dividing line, so that the light receiving portions A, B, C, and
Make up D.

According to the optical pickup 1 having such a configuration, the P-polarized light beam emitted from the semiconductor laser element 2 is transmitted through the grating 3 and converted into parallel light by the collimator lens 4, and then the beam is converted into parallel light. The light is transmitted through the splitter 5, and further, via the objective lens 6, an image is formed at a certain point on the signal recording surface of the magneto-optical disc MO.

The return light beam containing the MO signal (magneto-optical signal) of the S-polarized component, which is reflected by the signal recording surface of the magneto-optical disk MO and whose polarization plane is rotated by the Kerr effect,
It again enters the beam splitter 5 via the objective lens 6. Here, the return light beam P
The S-polarized component is reflected while the polarized component is transmitted.

The S-polarized light component reflected by the reflecting surface 5a of the beam splitter 5 is polarized and separated into three light beams by the Wollaston prism 7, and each light beam passes through a cylindrical lens 8 and a photodetector 9 Is incident on the corresponding light receiving portion of. As a result, based on the detection signal from each light receiving unit of the photodetector 9, by the differential method or the like,
The magneto-optical signal is detected, and the servo signal for adjusting the objective lens position, that is, the focus error signal and the tracking error signal are detected.

[0009]

However, in the optical pickup 1 configured as described above, each optical component, that is, the semiconductor laser element 2, the grating 3, the collimator lens 4, the beam splitter 5, the Wollaston prism 7, the cylindrical lens is used. 8 and the photodetector 9
As shown in FIG. 6, the objective lens 6 is mounted on one optical base 1a, and the objective lens 6 is driven by a biaxial actuator (not shown) so as to be driven biaxially. It is attached to the base 1a. On the other hand, the optical base 1a has, for example, 300 Hz to 3
It produces an inherent resonance of the order of kHz. Therefore, this vibration affects the optical components of the optical base 1a, and the spot of the return light formed on the light receiving portion of the photodetector 9 also vibrates.

By the way, the optical base 1a is attached to a mechanical deck, a chassis, etc., but at this time, it is not attached symmetrically. As a result, the spot vibration at the light receiving portion of the photodetector 9 described above is shifted by about 5 to 10 degrees with respect to the vibration direction of the optical base 1a. As a result, the spot vibration on the photodetector 9 is detected as a vibration in the focusing direction, that is, a focus error, and the biaxial actuator is servo-controlled based on this focus error signal. Therefore, there is a problem that a so-called focus squeal or focus loss occurs.

In view of the above points, an object of the present invention is to provide an optical pickup in which the spot vibration in the light receiving portion of the photodetector due to the vibration of the optical base cannot be detected as a focus error.

[0012]

According to the present invention, there is provided a light source for emitting a light beam, and a light beam emitted from the light source for focusing on a recording surface of an optical signal recording medium. An objective lens that irradiates, an optical element that imparts astigmatism to the return light beam from the signal recording surface of the optical signal recording medium through this objective lens, and a dividing line that receives the return light beam that passes through this optical element A photodetector divided by
At least the base portion supporting the photodetector is included, and the dividing line for focus error detection of the photodetector is set in a direction that matches the vibration direction of the spot generated by the vibration of the base portion, This is achieved with an optical pickup.

According to the above construction, the dividing line for detecting the focus error of the photodetector extends in the direction coinciding with the spot vibration direction generated by the vibration of the base portion.
Spot vibration in the light receiving portion of the photodetector caused by the natural vibration of the base portion occurs along the direction of the dividing line for detecting the focus error of the photodetector. Therefore, this spot vibration does not cause the photodetector to detect a focus error.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below with reference to FIGS. The embodiment described below is a preferred specific example of the present invention, and thus various technically preferable limitations are added. However, the scope of the present invention particularly limits the present invention in the following description. The embodiment is not limited to these embodiments unless otherwise stated.

FIG. 1 shows an embodiment of an optical pickup according to the present invention. The optical pickup 10 includes a semiconductor laser element 11, a grating 12, a collimator lens 13, a beam splitter 14, an objective lens 15,
Wollaston prism 16, Cylindrical lens 17
And a photodetector 18.

The semiconductor laser device 11 is a light emitting device utilizing recombination light emission of a semiconductor and is used as a light source. The light beam emitted from the semiconductor laser device 11 is
Guided by the grating 12.

The grating 12 is also called a diffraction grating and splits the light beam from the semiconductor laser element 11 into 0th-order light and plus / minus 1st-order light.

The collimator lens 13 is a convex lens and converts a light beam incident from the semiconductor laser element 11 through the grating 12 into a parallel light beam.

The beam splitter 14 has its reflecting surface 14
a is arranged in a state of being inclined by 45 degrees with respect to the optical axis of the objective lens 15, and separates the light beam emitted from the semiconductor laser element 11 and the return light from the recording surface of the magneto-optical disk MO. That is, the light beam from the semiconductor laser device 11 is transmitted through the beam splitter, and the return light is reflected by the reflecting surface 14.
It is reflected by a.

The objective lens 15 is a convex lens and forms an image of the parallel light beam transmitted through the beam splitter 14 on a desired track on the recording surface of the rotatively driven magneto-optical disk MO. Further, the objective lens 15 is supported by a biaxial actuator (not shown) so as to be movable in biaxial directions as indicated by an arrow in FIG.

The light beam applied to the recording surface of the magneto-optical disk MO is returned to the objective lens 15 as a return light beam.
Is guided to the beam splitter 14 via. Then, the return light beam reflected by the reflecting surface 14 a of the beam splitter 14 passes through the Wollaston prism 16 and the cylindrical lens 17, and then enters the light receiving portion of the photodetector 18.

The Wollaston prism 16 emits a plurality of light beams, in the illustrated case, three light beams, by performing polarization separation on the basis of the return light beam reflected by the beam splitter 14.

The cylindrical lens 17 is an example of an optical element that imparts astigmatism to a transmitted light beam, is a cylindrical lens, and has a converging property only in a direction having a curvature. As a result, the cylindrical lens 17 imparts astigmatism to the incident light beam to facilitate focus servo. Therefore,
In this optical pickup 10, in addition to the cylindrical lens 17, an optical element such as a glass flat plate is used,
Astigmatism may be given to the transmitted light beam.

The photodetector 18 is the Wollaston prism 1.
Each of the three light beams polarized and separated by 6 has a light receiving portion.

Further, in the optical pickup 10, as shown in FIG. 2, the photodetector 18 is arranged so that for each beam separated by the Wollaston prism 16, the central light receiving portion 18a and the upper and lower light receiving portions I, J and light receiving portions E and F on both sides. Further, the central light receiving portion 18a
In this case, the light receiving parts A, B, C, and D are configured by being divided into four vertically and horizontally by the dividing line. Here, the dividing line for focus detection, that is, the dividing line 18b for dividing the light receiving portions A, B and C, D is each optical component, that is, the semiconductor laser element 11, the grating 12, the collimator lens 13, the beam splitter 14, the Wollaston. Prism 16, Cylindrical lens 17 and photodetector 18
However, the optical base 19 to which the objective lens 15 is attached directly or via a biaxial actuator is a mechanical deck,
It is formed so that the spot formed on the light receiving portion of the photodetector 18 extends along the vibrating direction based on the focusing vibration when it is attached to the chassis or the like. Specifically, the dividing line 18a is set in the direction of 45 degrees with respect to the dividing line of the conventional light receiving portion 9a of FIG.

The cylindrical lens 17 is shown in FIG.
As shown in FIG. 7, the photodetector 18 is arranged so that its axial direction E is displaced by 45 degrees with respect to the focus detection division line 18b.

The optical pickup 10 is configured as described above, and the P-polarized light beam emitted from the semiconductor laser element 11 passes through the grating 12 and is converted into parallel light by the collimator lens 13. After that, the light is transmitted through the beam splitter 14, and further, via the objective lens 15, an image is formed at a certain point on the signal recording surface of the magneto-optical disk MO.

The return light beam including the MO signal (magneto-optical signal) of the S-polarized component, which is reflected on the signal recording surface of the magneto-optical disk MO and whose polarization plane is rotated by the Kerr effect, is
It again enters the beam splitter 14 via the objective lens 15. Here, in the return light beam, the P-polarized component is transmitted and the S-polarized component is reflected by the reflecting surface 14a.

The S-polarized component reflected by the reflecting surface 14a of the beam splitter 14 is transferred to the Wollaston prism 16
Thus, the light beams are polarized and separated into three light beams, and the respective light beams enter the corresponding light receiving portions of the photodetector 18 via the cylindrical lenses 17, respectively.

As a result, the light receiving portion 18a of the photodetector 18
The 0th-order light from the grating 13 is incident on, and the plus / minus 1st-order light from the grating 13 is incident on the light receiving portions E and F.

Thus, in the light receiving section 18a, each of the light receiving sections A, B, C, D divided by the dividing line outputs the detection signals Sa, Sb, Sc, Sd, and the light receiving sections E, F,
I and J respectively output detection signals Se, Sf, Si and Sj.

Therefore, the light receiving portions A, B, and
The detection signals from C, D, E, F, I, and J are subjected to appropriate calculation by a signal processing circuit (not shown), and signals such as a read signal of the magneto-optical disk MO and a focus error signal and a tracking error signal are obtained. Is generated.

In this case, the dividing line 18b for focus detection of the photodetector 18 extends along the vibration direction of the spot in the light receiving portion of the photodetector 18 based on the natural vibration of the optical base, as described above. , Because it is formed
The spot vibration in the light receiving portion of the photodetector generated when the optical base vibrates does not change the amount of light on both sides of the dividing line 18b. Therefore, when the focus error signal is detected based on the detection signal of each light receiving portion of the photodetector 18, the focus error signal is accurately detected without being affected by the spot vibration. Thus, since spot vibration is not detected as a focus error, so-called focus squeal and focus drop are prevented.

Although the optical pickup 10 for the magneto-optical disk has been described in the above embodiment, the present invention is not limited to this, and the photodetector is divided along the dividing line, and the light receiving divided by the dividing line is performed. If the optical pickup has a configuration in which a focus error is detected based on the difference between the detection signals of the optical disc and the compact disc (C
It is obvious that the present invention can be applied to optical pickups for other optical discs such as D).

[0035]

As described above, according to the optical pickup of the present invention, the spot vibration in the light receiving portion of the photodetector due to the vibration of the optical base is not detected as a focus error.

[Brief description of drawings]

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

FIG. 2 is a plan view showing a photodetector in the optical pickup of FIG.

3 is a partial perspective view showing the relationship between a photodetector and a cylindrical lens in the optical pickup of FIG.

FIG. 4 is a schematic diagram showing a configuration of an example of a conventional optical pickup.

5 is a plan view showing a photodetector in the optical pickup of FIG.

6 is a schematic perspective view showing an optical base in the optical pickup of FIG.

[Explanation of symbols]

 10 Optical Pickup 11 Semiconductor Laser Element (Light Source) 12 Grating 13 Collimator Lens 14 Beam Splitter 15 Objective Lens 16 Wollaston Prism 17 Cylindrical Lens 18 Photodetector 18a Photoreceptor 18b Dividing Line for Focus Detection 19 Optical Base (Base)

Claims (2)

[Claims] 1. A light source for emitting a light beam, an objective lens for irradiating the light beam emitted from the light source so as to focus on a recording surface of an optical signal recording medium, and an optical signal via the objective lens. An optical element for imparting astigmatism to the return light beam from the signal recording surface of the recording medium, a photodetector divided by a dividing line for receiving the return light beam passing through the optical element, and the photodetector. An optical system including a supporting base portion, wherein the dividing line for detecting a focus error of the photodetector is set in a direction coinciding with a vibration direction of a spot generated by vibration of the base portion. pick up. 2. The optical pickup according to claim 1, wherein the optical element is arranged such that its axial direction is displaced by 45 degrees with respect to the dividing line of the photodetector.