JPH0242641A - Optical head structure - Google Patents

Abstract

PURPOSE:To simplify a detecting means for detecting respective errors by allowing a photometry sensor to house a photodiode for detecting a focus error, a photodiode for detecting a tracking error and a means to reflect a part of an incident light towards the photodiode for detecting the tracking error. CONSTITUTION:On the optical axis of a detected light 8, a converging lens 6 and a photometry sensor 7 are coaxially arranged, respectively. To a substrate 9 of the photometry sensor 7, a photodiode 13 for detecting a focus error positioned in the optical path of the detected light 8 and a photodiode 14 for detecting a tracking error at a prescribed distance from it are integrally fixed so that respective light-receiving surfaces can be positioned on the same plane surface. To a prism body 15, the half of the detected light 8, whose direction is changed by a reflecting film 16, is converged to the central part of the photodiode 14 for detecting the tracking error. Thus, since the detection can be directly executed not through a reflecting means, the position adjustment of the reflecting means can be facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] <Industrial Application Field> The present invention relates to an optical head structure, and particularly to an optical head structure that can be made smaller and lighter.

<Prior Art> Conventionally, there have been high-density recording and reproducing devices that record and reproduce information by detecting reflected light of convergent light irradiated onto the recording surface of an optical disk as an optical head type recording medium.

The optical discs used in this device generally have some warpage and distortion, as well as eccentricity due to installation errors on the optical disc's rotating shaft. ,
Each error in focus and tracking of the optical head is detected and its position is controlled.

In reality, the error detection light obtained by deflecting the reflected light from the optical disk using a polarizing beam splitter is further divided into two directions through a half prism, and half of the detected light is blocked by a knife to detect focus errors. For example, the focus is placed on the dividing line of a two-part photodiode. If a focus error occurs, the focus position shifts to the front or back of the photodiode, and the error can be detected because the light is focused on one of the two divided photodiodes. On the other hand, the other detection light separated by the half prism is focused on, for example, a dividing line of a two-split photodiode for tracking error detection. When a tracking error occurs, there is a difference in brightness between the two photodiodes, so the error can be detected based on the output difference.

However, since the above-mentioned detection structure uses a half prism, a knife lens, two sets of photodiodes, etc., the number of parts increases and the optical head tends to be large and heavy. The position adjustment of each component, such as the position adjustment of each photodiode with respect to the optical axis of the detection light, tends to be complicated. Furthermore, since the photodiodes are provided in different directions, there is also the problem that the wiring tends to become complicated.

Therefore, as described in the specification of Japanese Patent Application No. 62-297136 by the same applicant, a tracking error detection photodiode located on the optical axis of the detection light and a photodiode for tracking error detection located on the optical axis of the detection light and the photodiode are arranged in parallel on the same substrate. Focus and tracking errors are detected using a photometric sensor that includes a photodiode for detecting focus errors and a pair of reflection means for directing a part of the detected light to the photodiode for detecting focus errors. By doing so, it becomes relatively easy to adjust the position of each component, and the optical head becomes smaller and lighter. However, in the above structure, the detection light enters the focus error detection photodiode through at least two reflecting means such as mirrors, but the optical head has relatively high accuracy in the focusing direction. Since it is necessary to adjust the optical axis, there is a problem in that the position adjustment of the reflecting means becomes complicated.

<Problems to be Solved by the Invention> In view of the problems of the prior art, the main purpose of the present invention is to simplify and miniaturize the detection means for detecting errors in focusing and tracking of an optical head. The object of the present invention is to provide a lightweight optical head.

[Structure of the Invention] Means for Solving the Problems According to the present invention, the present invention provides an optical head structure having a photometric sensor that optically detects each error state of tracking and focusing of the optical head. The photometric sensor includes a light receiving element for detecting a focus error located on the optical axis of the incident light, a light receiving element for detecting a tracking error arranged in parallel on the same substrate as the light receiving element, and a light receiving element for detecting a tracking error located on the optical axis of the incident light. This is achieved by providing an optical head structure characterized in that it includes a built-in means for reflecting a portion of the tracking error toward the tracking error detection light receiving element.

<Function> In this way, by arranging the focus error detection photodiode of the photometric sensor on the optical axis of the incident light of the sensor, focus errors can be directly detected without using a reflecting means.

<Embodiments> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram showing the main parts of an optical head to which the present invention is applied. A polarizing beam splitter 2 and a λ/4 plate 3 are disposed on the optical axis of the emitted light 1 irradiated toward the optical disk from a semiconductor laser as a light source (not shown).

The output light 1 that has passed through the polarizing beam splitter 2 has a wavelength of λ/4
After passing through the plate 3, it is reflected by the optical disk and becomes reflected light 4, which passes through the λ/4 plate 3 again and enters the polarizing beam splitter 2. The polarization plane of the light 4 becomes 90 degrees opposite to the polarization plane of the output light 1. Therefore, the polarized light components 'f11rIA5 disposed diagonally within the polarizing beam splitter 2
As a result, the direction of the reflected light 4 is changed, and the reflected light 4 is emitted as a detection light 8 from the right side surface of the polarizing beam splitter 2 in FIG.

A condenser lens 6 and a photometric sensor 7 are each coaxially disposed on the optical axis of the detection light 8, and the detection light 8 is passed through the condenser lens 6 in order to detect errors in focus and tracking. The light is focused on the photometric sensor 7 as convergent light. In reality, each of the above components from the semiconductor laser to the optical disk was arranged on the optical axis of the emitted light 1, but since the direction of the optical axis can be freely changed by providing a mirror etc., the arrangement is It is not limited.

FIG. 2 is a cross-sectional view of the photometric sensor 7 along the axial direction.
FIG. 3 is a sectional view taken along the line ■--■ in FIG. 2.

The substrate 9 of the photometric sensor 7 includes a photodiode 13 for focus error detection located in the optical path of the detection light 8;
A photodiode 14 for tracking error detection is integrally fixed on the lower side in FIG. 2 at a predetermined distance from the photodiode so that each light receiving surface is located on the same plane. .

Each of these photodiodes 13 and 14 is constituted by a four-division diode, as clearly shown in FIG.

On the photodiodes 13 and 14 of the substrate 9, a prism body 15 formed in a trapezoidal cross-section by bonding together large and small transparent bodies made of the same homogeneous material is placed in close contact with and covering the light receiving surface of each photodiode. It is fixed like that.

The bonding surface of the transparent bodies of the prism body 15 has an inclination of 45 degrees with respect to the surface of the substrate 9, and the bonding surface passes through the glass plate 12 and is placed on the photodiode 13 for focus error detection. A reflective film 16 is attached that blocks half of the detection light 8 focused at the center of the sensor by reflecting it in a direction perpendicular to the incident axis. Further, the prism body 15 has a reflective surface facing into the prism body 15 so that half of the detection light 8 whose direction has been changed by the reflection film 16 is focused on the center portion of the tracking error detection photodiode 14. A reflective surface portion 17 is formed parallel to the reflective film 16.

In this way, half of the detection light 8 that has entered the photometric sensor 7 is focused on the focus error detection photodiode 13 without passing through the reflective surface, and the remaining half is focused on the focus error detection photodiode 13 without passing through the reflective surface. The light is focused on a tracking error detection photodiode 14. Note that each of the photodiodes 13 and 14 is electrically connected to a control unit via a lead wire (not shown).

Next, the method of detecting each error in focus and tracking by each photodiode 13 and 14 will be explained.

As shown in FIG. 4, half of the detection light 8 is incident on the photodiode 13 so as to be substantially focused as shown by the imaginary line, indicating a state where no focus error has occurred. Here, if the focus changes and, for example, the focal position is in front of the photodiode 13, a semicircular When the focal point position is on the back side of the photodiode 13, the light is focused on the upper two portions of the four-part photodiode 13 as shown in FIG. 6. Therefore, the 4-division photodiode 1
Since the sum of the detection signals A and B from the two upper left and right ones and the sum of the detection signals C and D from the lower left and right two signals of 3 change depending on the focus position of the optical head, this detection signal A , B (A+B) by the amplifier 19, and the sum (C+D) of the detection signals C, D by the amplifier 20 and the amplifier 21.
and output the difference (A+B)-(C+D) to the amplifier 21.
The focus error is detected by outputting it to the control unit.

In addition, in FIG. 7, the reflective film 16 and the reflective surface portion 17
The remaining half of the detection light 8 whose direction has been changed is incident on the approximately central portion of the first diode 14 divided into four parts in a semicircular shape as a virtual image, as shown by the imaginary line. If a tracking error occurs, a difference in brightness will occur in either the left or right direction in FIG. Therefore, the sum of the detection signals E and F from the upper and lower two on the left side of the 4-split photodiode 14 and the sum of the detection signals G and H from the two upper and lower right sides of the 4-split photodiode 14 change depending on the tracking position of the optical head. , the sum of the detection signals E and F (E+F) is output by the amplifier 22, and the sum of the detection signals G and H (G+H)
is outputted from the amplifier 23 to the amplifier 24, and the difference (E1F>-(G+H)) is outputted from the amplifier 24 to the control section,
A tracking error amount is detected.

The read signal can be detected by using the sum (E+F+G+H) of the detection signals E, F, G, and H of the tracking error detection photodiode 14.

In this embodiment, the photodiodes 13 and 14 are each divided into four parts, but in reality, the photodiode 13 for focus error detection is divided into two parts vertically, and the photodiode 14 for tracking error detection is divided into two parts on the left and right sides. It may also be divided. Furthermore, in this embodiment, half of the detection light 8 is reflected twice by the reflective film 16 and the reflective surface portion 17 and is incident on the tracking error detection photodiode 14, but in reality, for example, the reflection of the reflective film 16 By changing the angle, the light may be reflected only once by the reflective film and made incident on the photodiode 14.

[Effects of the Invention] As described above, according to the present invention, by arranging the photodiode for detecting focus error of a photometric sensor on the optical axis of the incident light of the sensor, direct detection can be performed without using a reflecting means. The effects of the present invention are extremely significant, not only because the position of the means can be easily adjusted, but also because the position of the optical head in the focus direction can be controlled with high precision.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the main parts of an optical head to which the present invention is applied. FIG. 2 is a cross-sectional view of the photometric sensor along the axial direction. FIG. 3 is a sectional view taken along the line ■--■ in FIG. 2. 4 to 6 are schematic circuit diagrams showing the focus error detection procedure. FIG. 7 is a schematic circuit diagram showing how to detect a tracking error. 1... Emitted light 2... Polarizing beam splitter 3... λ/4 plate 4... Reflected light 5... Polarizing film 6... Condensing lens 7... Photometric sensor 8... Detection light 9...Substrate 13.14...Photodiode

Claims (1)

[Scope of Claims] In an optical head structure having a photometric sensor that optically detects each error state of tracking and focusing of the optical head, the photometric sensor is located on the optical axis of incident light. a light receiving element for tracking error detection, which is arranged in parallel on the same substrate as the light receiving element;
An optical head structure characterized in that it incorporates means for reflecting a part of the incident light toward the tracking error detection light receiving element.