JPH07105567A - Optical disk pickup - Google Patents

Abstract

PURPOSE:To unnecessitate a work with which the output of a light receiving means is made constant by adjusting volumes at the time of an assemblage by providing the light receiving means for monitoring a laser beam in the optical path of the laser beam and providing a light quantity limiting means for limiting the quantity of the laser beam entering to the light receiving means. CONSTITUTION:A laser beam L from a laser light source 11 reflects at the plane 14a of a beam splitter 14 and passes a circular aperture 100 and is received by a front photodetector 15 being a light beam monitoring means. The aperture 100 allows only the center part of the beam of the laser beam L to pass to the front photodetector 15 and the peripheral part of the beam of the laser beam L is cut by the peripheral part of the aperture 100 in an optical system supporting part 42. Thus, in a case that the power of the laser beam L is constant, effects of the beam intensity distribution and the shape of the laser beam L are eliminated and a constant output from the front photodetector 15 can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc pickup for recording / reproducing or reproducing information on / from an optical disc such as a CD or MD for music or digital data storage. .

[0002]

2. Description of the Related Art Conventionally, this type of optical disk pickup has a laser light source such as a semiconductor laser diode, a light receiving portion for laser light, and an optical system for guiding the laser light.

FIG. 7 shows a laser diode LD of a conventional optical disk pickup and an optical system around it. In FIG. 7, the laser light L from the laser diode LD is reflected by the deflection beam splitter PBS and received by a photodetector PD (light receiving chip, so-called front photodetector).

[0004]

However, since the laser beam L is entirely focused on the photodetector PD via the lens LS, it is affected by the beam intensity distribution and the beam shape. In order to improve the influence of the beam intensity distribution and the beam shape, the conventional optical disc pickup has an automatic power control (A) for the photodetector PD.
The adjustment volume for PC) is provided. Then, at the time of assembling the pickup, the operator adjusts the adjustment volume and controls the power of the laser light L emitted from the laser diode LD based on the power received by the photodetector PD.

As described above, since the conventional optical disk pickup requires the adjusting volume, the cost cannot be reduced and the miniaturization is hindered. Further, it is troublesome to adjust the amount of light received by the photodetector PD using the adjustment volume.

In view of the above points, an object of the present invention is to provide an optical disk pickup that does not require an adjusting volume and does not require adjustment work, and can reduce cost and size.

[0007]

SUMMARY OF THE INVENTION In the present invention, the above object is to provide an optical pickup for recording / reproducing information on / from an information recording medium by using a laser beam, and This is achieved by an optical disc pickup including a light receiving unit for monitoring the laser beam on the optical path and a light amount limiting unit for limiting the amount of the laser beam entering the light receiving unit.

In the present invention, the light quantity limiting means is preferably a circular aperture. Further, in the present invention, the information recording medium is preferably a magneto-optical disk.

[0009]

According to the above arrangement, the light quantity limiting means limits the light quantity of the laser light in advance, so that the conventionally used adjusting volume becomes unnecessary.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described in detail below 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.

1 to 4 show an example of an optical disk pickup (hereinafter referred to as an optical pickup) according to the present invention. FIG. 1 is its front view, FIG. 2 is a front view with a shield cover attached, and FIG. FIG. 4 is an enlarged view of the optical system, and FIG. 4 is a layout view of the optical system viewed from the side.

1 and 2, the optical pickup 10
Has an optical base 12 formed integrally by, for example, die casting. The optical base 12 supports each optical element forming an optical system. The optical base 12 has a relatively large space inside, and an optical system that accommodates and supports a slide base portion 41 in which a biaxial actuator (not shown) is to be accommodated and optical elements described later. The housing portion 42 and the portion 43 are integrally formed.

The optical pickup 10 includes a laser light source 11 such as a semiconductor laser diode and a grating 13 for separating the laser light emitted from the laser light source 11.
A polarization beam splitter 14 on which the beam from the grating 13 is incident is provided. In this embodiment, a Wollaston prism 16 is preferably fixed to the polarization beam splitter 14.

Further, as shown in FIGS. 3 and 4, the optical pickup 10 includes a front photodetector 15 for monitoring a laser output, a collimator lens 17, a prism mirror 18, an optical base 12 and a magneto-optical disk. Objective lens 19 located between 21 (see FIG. 4)
Is equipped with.

Further, as shown in FIG. 4, the optical pickup 10 includes a Wollaston prism 16 through which return light passes.
And a multi-lens 22 (see FIG. 4) housed in the multi-lens holder 22a, and a signal detecting photodetector 23 as a light receiving portion.

As shown in FIG. 4, in such an optical pickup 10, a light beam L also called laser light emitted from a laser light source 11 enters a polarization beam splitter 14 through a grating 13. The light beam L incident on the polarization beam splitter 14 is separated here, and a part of the light beam L is moved to the left side in FIG.
It is bent once and then enters the front photodetector 15, where the beam output of the light beam emitted from the laser light source 11 is monitored.

As shown in FIGS. 1 and 3, the light receiving surface of the front photodetector 15 is preferably tilted so as not to be perpendicular to the incident optical axis on the optical path. As a result, it is possible to prevent the light reflected by the surface of the front photodetector 15 or the surface of the light receiving element in the cover lens LS from entering the light beam L passing through each of the optical elements, that is, the generation of stray light. That is, the returning light of the light beam L is prevented.

As shown in FIG. 4, the remaining light beam L separated by the polarization beam splitter 14 is incident on a collimator lens 17 and converted into parallel rays, and then, a reflecting surface 18a formed on a prism mirror 18 is formed. It is bent 90 degrees by, and passes through the objective lens 19 to be focused on the surface of an optical disk 21 such as a magneto-optical disk.

The return light reflected on the surface of the optical disk 21 passes through the objective lens 19 again and the prism mirror 1
The beam passes through the beam path 8, passes through the collimator lens 17, and enters the beam splitter 14. Here, the light beam L of the returning light is bent 90 degrees to the right in FIG. 1 by the reflection surface 14 a of the polarization 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 a photodetector 23 for signal detection through a multilens 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.

FIG. 5 is a perspective view showing a preferred embodiment of the optical base 12 for accommodating and supporting the above optical elements of the optical pickup 10. The optical base 12 is integrally formed as a whole by die casting or the like as described above.

A biaxial actuator can be accommodated in a relatively large space 45 provided inside the slide base portion 41 of the optical base 12. The slide base portion 41 is integrally provided with a portion 43,
The portion 43 is supported by the guide shaft on the device body side via the bearing 43a.

FIG. 6 shows a laser diode 11 as a laser light source and a polarization beam splitter 14 shown in FIG.
And the front photodetector 15 and the aperture 100. As shown in FIG. 5, this aperture 100 is preferably formed in the optical system support portion 42.

The laser light L from the laser light source 11 is reflected by the surface 14a of the beam splitter 14, passes through the circular aperture 100, and is received by the front photodetector 15 via the condenser lens LS. There is.

The aperture 100 allows only the central part of the beam of the laser light L to pass through the front photodetector 15.
The peripheral portion of the beam of the laser light L is cut at the peripheral portion of the aperture 100 of the optical system supporting portion 42.

The diameter of the aperture 100 is 1.2 mm, for example. Thereby, only the central portion of the beam of the laser light L can be passed through the front photodetector 15, and if the power of the laser light L is constant, a stable output of the front photodetector 15 can be obtained. That is, the influence of the beam intensity distribution and the beam shape of the light beam L is eliminated, and the complicated work of providing the adjustment volume and adjusting the volume at the time of assembly to make the output of the front photodetector 15 constant as in the prior art is unnecessary. Become.

In order to eliminate the conventional adjusting volume, the output current of the front photodetector 15 required from the IC on the set side is, for example, 0.5 mA or less at the time of writing (at the time of writing), and the variation is within ± 25%. Is. The size of the aperture 100 for satisfying these is obtained by the following method, for example.

(1) The amount of light incident on the front photodetector 15 is calculated from the sensitivity of the front photodetector 15 (0.5 mA / 0.5 A / W = 1 as an example).
mW). (2) Assuming that the laser emission has a Gaussian distribution,
The transmittance (or reflectance) of each optical component and the aperture 10
From 0, when the diameter of the circular aperture 100 immediately in front of the front photodetector 15 is X, the incident light amount / objective emission light amount (Cp) of the front photodetector 15 is calculated (program creation).

(3) From (1), the incident light quantity is, for example, 1 m.
If it is W, the Cp required when the amount of light emitted from the objective is 6.8 mW is calculated (for example, 1 mW / 6.8 mW = 0.
1471). (4) The diameter X of the aperture 100 is calculated from (2) and (3). As a result, in the optical system of this example, the diameter of the aperture 100 was X = 1.2 mm, and the tolerance was plus or minus 0.01 mm (corresponding to about 4% variation in Cp).

It should be noted that this tolerance is preferably set strictly in consideration of variations in performance of optical components.

The present invention is not limited to the above embodiment. In the above-described embodiments, the optical pickup used in the optical disc device for recording / reproducing a magneto-optical disc as the optical disc has been described. However, not limited to this,
INDUSTRIAL APPLICABILITY The present invention can be applied to an optical disc device that records or reproduces a compact disc (CD) or another type of disc, or reproduces only.

In the present invention, the light receiving surface of the front photodetector 15 may of course be inclined with respect to the optical axis of the laser light as shown in FIG.

[0033]

As described above, according to the present invention, the adjustment volume is unnecessary and the adjustment work is not required, so that the cost and the size can be reduced.

[Brief description of drawings]

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

FIG. 2 is a front view showing a state in which a shield cover is attached to the optical disk pickup of FIG.

3 is a cross-sectional view of a main part of the optical pickup of FIG.

FIG. 4 is a configuration diagram of an optical system of the optical pickup of FIG. 1 viewed from a side surface.

5 is an overall perspective view of the optical base shown in FIG. 1. FIG.

FIG. 6 is a diagram showing the laser diode of FIG. 1 and its peripheral elements.

FIG. 7 is a diagram showing a conventional laser diode and its peripheral elements.

[Explanation of symbols]

 10 Optical Disk Pickup (Optical Pickup) 11 Laser Light Source 12 Optical Base 14 Polarizing Beam Splitter 15 Front Photodetector (Light Receiving Means) 17 Collimator Lens 18 Prism 19 Objective Lens 21 Optical Disk (Information Recording Medium) 22 Multilens 23 Signal Detection Photodetector 42 Aperture (Light quantity limiting means) L laser light (light beam)

Claims (3)

[Claims] 1. An optical pickup for recording / reproducing information on / from an information recording medium by using laser light, or a light receiving means for monitoring the laser light in the optical path of the laser light, An optical disc pickup comprising: a light amount limiting unit for limiting an amount of the laser light entering the light receiving unit. 2. The optical disc pickup according to claim 1, wherein the light amount limiting means is a circular aperture. 3. The optical disc pickup according to claim 1, wherein the information recording medium is a magneto-optical disc.