JPH0793802A - Optical disc pickup - Google Patents

Abstract

(57) [Summary] [Object] To provide an optical disk pickup in which a part of a light beam is reflected on the surface of a monitor photodetector to become stray light and the signal detection accuracy is improved. A light source 11 for emitting a light beam, and an objective lens 1 for irradiating an optical disk 21 with the light beam from the light source and receiving a reflected light beam reflected by the disk 1
9, a light splitting optical system 14 that is inserted between the light source and the objective lens and splits the reflected light beam, and a photodetector 23 that receives the split light beam split by the light splitting optical system. In the optical disc pickup, a monitor photodetector 25 for monitoring the light from the light source is provided on the optical path through which the light beam passes through the plurality of optical elements. It is arranged so as to be inclined with respect to the incident optical axis.

Description

Detailed Description of the Invention

[0001]

The present invention relates to, for example, CD, LD, M
The present invention relates to an optical disc pickup for recording and / or reproducing information on the surface of an optical disc in D, data storage, or the like.

[0002]

2. Description of the Related Art Conventionally, an optical disk pickup of this type has a laser light source such as a semiconductor laser device,
It has optical elements such as a prism mirror, an objective lens, a grating, a beam splitter, a monitor photodetector, a collimator lens, and a signal detection photodetector, which are sequentially arranged on the optical path of the laser light emitted from the laser light source.

In the optical disc pickup thus constructed, the light beam emitted from the laser light source is incident on the surface of the optical disc as an information recording medium via each optical element, and the reflected light reflected on the disc surface is reflected. The recorded information is read out by being guided to a signal processing photodetector through each optical element. In an optical disc pickup, laser light is irradiated onto the surface of the optical disc through an optical system having such an optical element, a predetermined magnetic field is applied, and information is written by a magneto-optical recording method.

[0004]

However, in the optical disk pickup having such a structure, a part of the light beam is reflected by the surface of the monitor photodetector in the plurality of optical elements constituting the optical disk pickup, and this reflection is reflected. The light can be stray.

That is, the surface of such a monitor photodetector is covered with a resin cover,
The cover surface may reflect part of the incident light.
In this case, the monitor photodetector is arranged in any one of the optical paths where the light beam emitted from the laser light source is guided to the surface of the optical disc, reflected on the surface and returned to the signal detection photodetector. Therefore, there is a problem that the above-mentioned stray light affects a variable element of the detection signal of the signal detecting photodetector and reduces the detection accuracy.

In view of the above points, the present invention provides a pickup for an optical disk, which prevents a part of the light beam from being reflected on the surface of the monitor photodetector to become stray light and enhances signal detection accuracy. It is intended to be provided.

[0007]

According to the present invention, there is provided a light source which emits a light beam, and a reflected light beam which irradiates an optical disk with the light beam from the light source and is reflected by the disk. An objective lens for receiving light, a light separating optical system inserted between the light source and the objective lens for separating the reflected light beam, and a photodetector for receiving the separated light beam separated by the light separating optical system. In the optical disc pickup including, on the optical path where the light beam passes through the plurality of optical elements, a monitor photodetector for monitoring the light from the light source is provided, and the monitor photodetector is provided for monitoring the light beam. This is achieved by an optical disc pickup that is arranged at an angle with respect to the incident optical axis.

[0008] Preferably, the monitor photodetector is provided with a light condensing means having a curved surface on the light receiving element.

[0009]

According to the above construction, the monitor photodetector is arranged inclining with respect to the incident optical axis on the optical path of the optical system constituting the pickup. Therefore, the reflection of the light beam on the surface of the monitor photodetector can be prevented, and stray light can be removed.

Further, the monitor photodetector is
When the light receiving element is provided with a light condensing unit having a curved surface, the reflected light on the monitor photodetector surface is less likely to be diffused and become stray light. Moreover, since the light beam is condensed and guided to the light receiving element, the light receiving element can be made smaller accordingly.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that the examples described below are suitable specific examples of the present invention, and therefore, various technically preferable limitations are given, but the scope of the present invention particularly limits the present invention in the following description. Unless otherwise stated, the present invention is not limited to these modes.

FIGS. 1 to 3 are block diagrams mainly showing an optical system of an embodiment of a pickup for an optical disk device according to the present invention. FIG. 1 is a front view thereof, and FIG. FIG. 3 is a cross-sectional view and FIG. 3 is a layout view of the optical system viewed from the side.

In these figures, the optical disc pickup 10 has optical elements constituting its optical system supported by an integrated optical base 12 formed by, for example, die casting. The pickup 10 includes a laser light source 11 such as a semiconductor laser element, a grating 13 that shapes the beam shape of laser light emitted from the laser light source 31, and the grating 13.
It is equipped with a beam splitter 14 on which the beam from In the case of the present embodiment, a Wollaston prism 16 described later is integrally fixed to the beam splitter 14.

Further, the optical pickup 10 includes a front photodetector 15 for monitoring a laser output,
Objective lens 19 located behind collimator lens 17, prism mirror 18 and optical base 12 in the figure
(See FIG. 3). Also, the optical pickup 10
Includes a Wollaston prism 16 through which return light passes,
It has a multi-lens 22 housed in a multi-lens holder 22a and a photodetector 23 for signal detection as a light receiving section.

Here, as the front photodetector for the monitor, for example, the one shown in FIG. 4 is used. The monitor photodetector 25 is configured by forming a light receiving element 32 on a substrate 31 and covering a transparent cover 33 made of glass or synthetic resin. In this case, the surface 33a of the cover 33 has a flat plate shape, and when light is perpendicularly incident on this surface, reflection is likely to occur.

Therefore, as shown in FIG. 5, the monitor photodetector 25 is tilted at a slight angle with respect to the optical axis of the light incident on the monitor photodetector 25. This effectively prevents the light reflected by the surface 33a of the monitor photodetector 25 from directly entering the light beam as stray light.

Optical disk pickup 10 of the present embodiment
The light beam emitted from the laser light source 11 enters the beam splitter 14 through the grating 13 as described above. The light beam incident on the beam splitter 14 is separated here, and a part of the light beam is bent 90 degrees to the left side in FIG. 1 to enter the front photodetector 15 (25), where the light emitted from the laser light source 11 is emitted. The beam output of the beam is monitored.

Here, the front photo detector 25
Is not perpendicular to the incident optical axis on the optical path,
Since it is arranged so as to be inclined, it is possible to avoid the light reflected by the surface 33a of the front photodetector 25 from entering the light beam passing through the optical elements, that is, the generation of stray light as much as possible. Next, the remaining light beam split by the beam splitter 14 is incident on the collimator lens 17 and converted into parallel rays, which are then reflected by the reflecting surface 18a formed on the prism mirror 18 as shown in FIG.
It is bent once, passes through the objective lens 19, and is focused on the surface of the optical disc 21.

The return light reflected by the surface of the optical disk 21 and returning, passes through the objective lens 19 again, through the prism mirror 18, passes through the collimator lens 17, and enters the beam splitter 34. Here, the light beam of the return light is bent 90 degrees to the right in FIG. 1 by the reflecting surface 14 a of the beam splitter 14 and enters the Wollaston prism 16.

The return light is separated into three beams by the Wollaston prism 16 and is incident on the photodetector 23 for signal detection through the multilens assembly 22. As a result, the photodetector 23 detects the focusing control signal, the tracking control signal, and the reproduction signal based on the received reflected light (return light) beam.

Here, the photodetector 2 for signal detection
The stray light reflected by the surface of the front photodetector 25 hardly enters the return light entering the beam 3 as in the conventional case. Therefore, unlike the conventional case, such a stray light is not affected by the variable components such as the DC component and the AC component in the detection signal, and a highly accurate detection signal can be obtained.

FIG. 6 shows another embodiment of the monitor front photodetector. In the figure, the front photodetector 15 is composed of a substrate 36, a small light receiving element 37 formed on the substrate 36, and a cover 38 formed by resin molding or the like so as to cover the substrate 36 and the light receiving element 37. ing.

The surface 38a of the cover 38 is a spherical or aspherical curved surface. The cover 38 is formed of a transparent synthetic resin, glass, or the like as a condenser lens, and is configured so that the light incident on the surface 38a is condensed on the light receiving element 37. This has an advantage that the substrate 36 and the light receiving element 37 can be formed in a small size.

By the way, even if the front photodetector 15 having such a configuration is arranged in the optical path of the optical system of the optical pickup 10 perpendicularly to the optical axis of the incident light (for example, perpendicular to the plane of the substrate 36), it is covered. Since the surface of 38 is composed of a spherical surface, the light reflected here hardly enters the light beam.

However, according to experiments by the present inventors, the stray light is generated not only on the surface of the front photodetector 15 but also on the surface of the light receiving element 37. Therefore, the reflection of the incident light on the surface of the light receiving element 37 may enter the light beam as stray light and adversely affect the detection result of the signal detector photodetector 23.

Therefore, even when such a type of front photodetector 15 is used, it is better to arrange the photodetector for signal detection at a predetermined angle with respect to the optical axis of the incident light in the optical path as shown in FIG. The detection accuracy of 23 can be improved. In this case, it has been found that the front photodetector 15 can be prevented from generating stray light by arranging the front photodetector 15 at an angle of, for example, 1 to 45 degrees with respect to the surface of the substrate 36 with respect to the optical axis 35.

Here, the smaller the inclination angle of the front photodetector 15 with respect to the optical axis 35, the more easily stray light is emitted. Further, the larger the inclination angle of the front photodetector 15 with respect to the optical axis 35, the lower the signal sensitivity detected by the signal detecting photodetector 23.

According to an attempt by the present inventors, the inclination angle of the front photodetector 15 which can prevent stray light without lowering the sensitivity of the detection signal more than necessary is 3 to 10 degrees. The best results were obtained when the tilt angle was set to 5 degrees. Note that FIG. 7 shows an example in which the front photodetector 15 is arranged in diffused light without using a collimator lens, unlike FIGS. 1 to 3.

Further, in the front photodetector 15 of the type shown in FIG. 6, since the surface of the cover 38 is curved, it is difficult to position and fix it on the optical base 12 of FIG.

That is, the front photo detector 15
When fixed to the optical base 12, if the positioning of incident light with respect to the optical axis varies, the output current value may fluctuate. Conventionally, since a hole having a constant inner diameter was formed at the location where the front photodetector 15 of the optical base 12 was attached, it was extremely difficult to accurately position the front photodetector 15.

Therefore, in the optical base 12 of this embodiment,
As shown in FIG. 2, a hole having a substantially V-shaped cross section is formed in a portion of the front photodetector 15 that receives the cover 38.
The center of this V-shaped hole is configured to coincide with the optical axis. On the other hand, the cover portion 3 of the front photo detector 15
If the curved surface configuration of 8 is a spherical surface, the spherical surface has few dimensional intersections and does not have burrs.
It becomes easy to position the optical disc with respect to the optical base 12.

The front photodetector 15 thus positioned is arranged from the outside of the substrate 36,
It can be pressed and fixed by a leaf spring provided in a shield case that covers the optical base 12.

[0033]

As described above, according to the present invention, it is possible to prevent a part of the light beam from being reflected on the surface of the monitor photodetector to become stray light, thereby improving the signal detection accuracy. An optical disk pickup can be provided.

[Brief description of drawings]

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

FIG. 2 is a cross-sectional view of essential parts of the optical disc pickup of FIG.

FIG. 3 is a configuration diagram of an optical system of the optical disc pickup of FIG. 1 viewed from a side surface.

FIG. 4 is a schematic configuration diagram of a front photodetector used in the optical disc pickup of FIG.

FIG. 5 is a schematic view showing an arrangement example of the front photo detectors of FIG.

6 is a schematic configuration diagram showing another example of a front photodetector used in the optical disc pickup of FIG. 1. FIG.

FIG. 7 is a schematic view showing an arrangement example of the front photo detectors of FIG.

[Explanation of symbols]

 10 Optical Disk Pickup 11 Laser Light Source 12 Optical Base 13 Grating 14 Beam Splitter 15 and 25 Front Photo Detector 16 Wollaston Prism 17 Collimator Lens 18 Prism Mirror 19 Objective Lens 21 Optical Disc 22 Multi-lens 23 Signal Detection Photo Detector

Claims (2)

[Claims] 1. A light source for emitting a light beam, an objective lens for irradiating the optical beam from the light source onto an optical disc and receiving a reflected light beam reflected by the disc, and between the light source and the objective lens. In a pickup for an optical disc, which includes an optical separation optical system that is inserted and separates the reflected light beam, and a photodetector that receives the separated light beam separated by the optical separation optical system, A monitor photodetector for monitoring the light from the light source is provided on the optical path passing through the plurality of optical elements, and the monitor photodetector is arranged to be inclined with respect to the incident optical axis of the light beam. Characteristic optical disk pickup. 2. The optical disk pickup according to claim 1, wherein the monitor photodetector is provided with a light condensing unit having a curved surface on the light receiving element.