JPH025235A - Optical pickup device - Google Patents

Abstract

PURPOSE:To obtain the accurate reproduction and error signals by applying the reflection preventing treatment to a diffraction element so as not to reflect the laser light radiated from a laser light source. CONSTITUTION:A diffraction element 2 forms the reflection preventing films 2a and 2b on its both surface sides and therefore does not reflect virtually the laser light radiated from a semiconductor laser 1. Then the offset of the output signal of a light detecting element 6 is extremely suppressed even though the element 6 receives the reflected light from the element 2 since the quantity of said reflected light is extremely small compared with the quantity of reflected light received from a recording carrier. Thus the accurate reproduction and error signals are obtained and no reflecting light preventing treatment is required to the laser light source 1 and the element 6. As a result, the structure of an optical pickup device is simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup device used, for example, in a compact disc player or an optical video disc player.

[Conventional technology]

2. Description of the Related Art In optical pickup devices used in compact disc players and the like, techniques have been developed to reduce the number of parts in an optical system by using a diffraction element.

Such conventional optical pickup devices, for example,
As shown in the figure, in order to reproduce the impressions from the record carrier 15, a semiconductor laser 11 serving as a laser light source, a diffraction element 12, a collimating lens 13, an objective lens 14, and a light receiving element 16 are provided.

The diffraction element 12 has the function of not only deflecting the laser beam but also deforming and dividing the laser beam.

Laser light emitted from the semiconductor laser 11 and transmitted through the diffraction element 12 passes through the collimator lens 13 and is focused onto the record carrier 15 by the objective lens 14 . The reflected light from the record carrier 15 passes through the objective lens 14 and the collimating lens 13, is diffracted by the diffraction element 12, and the first-order diffracted light is guided to a predetermined position of the light receiving element 16, which has a plurality of light receiving parts. He is focused. The focused light is photoelectrically converted into electric signals by each light receiving section of the light receiving element 16, and a focus error signal, a tracking error signal, and a reproduction signal are obtained.

[Problem to be solved by the invention]

However, while the laser light emitted from the semiconductor laser 11 passes through the diffraction element 12 and travels in the direction of arrow A4, a portion of it is reflected by the surface of the diffraction element 12 and is reflected by arrow At and arrow A. A part of the reflected light then enters the light receiving element 16.

In this way, in the conventional optical pickup device, the reflected light from the record carrier 15 (hereinafter referred to as record carrier reflected light)
In addition, since the reflected light from the diffraction element 12 (hereinafter referred to as diffraction element reflected light) also enters the light receiving element 16, an offset occurs in the output signal of the light receiving element 16.

If the amount of light reflected by the diffraction element is extremely small compared to the amount of light reflected from the record carrier, the amount of offset generated in the output signal of the light-receiving element 16 remains within an allowable amount. Because it is reflected from two surfaces of 12,
The amount of light is not negligible compared to the amount of light reflected from the record carrier. Therefore, the offset generated in the output signal of the light-receiving element 16 exceeds the permissible amount, making it difficult to accurately detect errors for information reading, focus control, and tracking control. Was.

[Means to solve the problem]

In order to solve the above problems, an optical pickup device according to the present invention includes a laser light source that emits laser light, a lens system that focuses the laser light emitted from the laser light source onto a record carrier, and a recording medium. In an optical pink-up device that includes a light receiving element that detects reflected light from the carrier and a diffraction element provided in the optical path from the laser light source to the record carrier, the laser light emitted from the laser light source is applied to the diffraction element. It features an anti-reflection treatment to prevent reflections.

[Operation type] With the above configuration, the laser light emitted from the laser light source enters the diffraction element, but since the diffraction element is anti-reflection treated, a small amount of it is reflected by the diffraction element. It's just that.

Therefore, even if the light receiving element receives reflected light from the diffraction element, the amount of light is extremely small compared to the amount of reflected light from the record carrier, so it is possible to significantly suppress the offset that occurs in the output signal of the light receiving element. It is possible to obtain accurate reproduction signals and error signals. Further, there is no need to take measures to prevent reflected light from being applied to the laser light source or the light receiving element, making it possible to simplify the structure of the optical pickup device and to reduce costs.

〔Example〕

An embodiment of the present invention will be described below based on FIGS. 1 and 2.

As shown in FIG. 1, a diffraction element 2, a collimating lens 3, and an objective lens 4 are arranged in the light irradiation direction of the semiconductor laser 1 in the optical big amplifier device, and the laser beam emitted from the semiconductor laser 1 is recorded. It is designed to lead to the carrier 5.

As shown in FIG. 2, the diffraction element 2 has antireflection films 2a and 2b formed on both surfaces thereof, so that almost no laser light emitted from the semiconductor laser 1 is reflected. In this example, anti-reflection coatings 2 are applied to both surfaces of the diffraction element 2 as an anti-reflection treatment applied to the diffraction element 2.
Although a and 2b were formed, the specific embodiment of the antireflection treatment is not limited.

With the above configuration, the laser light emitted from the semiconductor laser 1 travels in the direction of arrow A, with most of the laser light being transmitted, except for a very small portion being reflected by the diffraction element 2. The laser beam that has passed through the diffraction element 2 passes through a collimating lens 3 and is focused onto a record carrier 5 by an objective lens 4 . At the same time as the light is focused on the record carrier 5, it is reflected from the record carrier 5, passes through the objective lens 4 and the collimating lens 3, is diffracted by the diffraction element 2, and the first-order diffracted light is guided to the light receiving element 6.

In the light receiving element 6, the received light is photoelectrically converted and outputted, and a reproduction signal, a focus error signal, and a tracking error signal can be obtained by performing a predetermined calculation on the output signal.

On the other hand, a part of the reflected light from the diffraction element 2 also enters the light receiving element 6, but the amount of light is extremely small compared to the amount of reflected light from the record carrier 11, so the output signal of the light receiving element 6 is The resulting offset will be very small.

Although the diffraction element 2 in this embodiment has a diffraction grating formed so as to guide the reflected light from the record carrier 5 to the light receiving element 6, the shape of the diffraction grating in the diffraction element 2 is not limited to the above-mentioned shape. For example, the above-described anti-reflection treatment may be applied to a diffraction element for three-beam generation used when tracking error detection is performed by a three-beam method to reduce reflection of laser light.

〔Effect of the invention〕

As described above, the optical pink-up device according to the present invention includes a laser light source that emits laser light, a lens system that focuses the laser light emitted from the laser light source onto a record carrier, and a record carrier. a light receiving element that detects reflected light from the
In an optical pickup device including a diffraction element provided in an optical path from a laser light source to a record carrier, the diffraction element is subjected to anti-reflection treatment so as not to reflect the laser light emitted from the laser light source. It is the composition.

As a result, the light emitted from the laser light source is hardly reflected by the diffraction element, and the amount of light reflected from the diffraction element that enters the light receiving element is significantly reduced. Therefore, the offset that occurs in the output signal of the light receiving element is suppressed, and not only can accurate reproduced signals and error signals be obtained, but also the structure of the optical pickup device can be simplified and costs can be reduced. play.

[Brief explanation of the drawing]

Figures 1 and 2 show an embodiment of the present invention, with Figure 1 being an explanatory diagram showing the configuration of an optical pickup device, and Figure 2 showing a diffraction element subjected to anti-reflection treatment. FIG. FIG. 3 shows a conventional example, and is an explanatory diagram showing the configuration of an optical pickup device. 1 is a semiconductor laser, 2 is a diffraction element, 2a and 2b are antireflection films (antireflection treatment), 3 is a collimating lens, 4 is an objective lens, and 6 is a light receiving element. Figure 3 Diagram b

Claims (1)

[Claims] 1. A laser light source that emits laser light, a lens system that focuses the laser light emitted from the laser light source onto a record carrier, and a light receiving element that detects reflected light from the record carrier. and a diffraction element provided in the optical path from the laser light source to the record carrier, wherein the diffraction element is subjected to anti-reflection treatment so as not to reflect the laser light emitted from the laser light source. An optical pickup device characterized by: