JPH0242643A - Optical head structure - Google Patents

Abstract

PURPOSE:To simplify a photometry sensor and to facilitate the position adjustments of respective parts by allowing the photometry sensor to house a half prism arranged in an optical path so as to turn a part of a detected light, first and second photodetectors and a cylindrical lens integrated with a turning means. CONSTITUTION:The photometry sensor 8 has a first 1 photodetector 13 arranged in the optical path of a detected light 7 so as to detect either of both error states of a tracking and a focus, a half prism 10 arranged in the optical path so as to turn a part of the detected light 7 and a second photodetector 14 arranged in the optical path of the detected light 7 turned so as to detect the other side of both error states. The photodetectors, half prism and a cylindrical lens 11 arranged in the optical path of the detected light up to the light-receiving element at a side to detect the error state of the focus so as to detect the error state of the focus with an astigmatism method, and simultaneously, unified with the turning means are built in. Thus, the optical parts to receive the detected light 7 can be miniaturized and reduced in weight, and simultaneously, the position adjustments 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 apparatuses 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. , detects each error in focus and tracking of the optical head and controls its position.

In reality, the error detection light obtained by deflecting the reflected light from the optical disk using a polarizing beam splitter is split into two directions through a half prism, and one of the two is sent through a cylindrical lens to the center of a four-split photodiode for focus error detection. I am trying to focus the light on it. and,
When a focus error occurs, the light is focused in an elliptical shape on photodiodes located diagonally to each other among the four-split photodiodes, so the sum of the outputs of the photodiodes at one diagonal position and the output from the other diagonal position are Errors can be detected by the difference between the sum of the outputs of the photodiodes (astigmatism method), and the other detection light divided by a half prism can be divided into two photodiodes for tracking error detection. The light is focused on a line,
When a tracking error occurs, there is a difference in brightness between the two photodiodes, and the error can be detected based on the output difference.

However, since the detection structure described in -E uses a half prism, a cylindrical lens, two sets of photodiodes, etc., the number of components increases, and the number of parts for each photodiode relative to the optical axis of the detection light divided into two directions increases. Position adjustment of each part, such as position 4JN alignment, tended to be complicated.

<Problems to be Solved by the Invention> In view of the problems of the prior art, the main object of the present invention is to simplify the photometric sensor for detecting errors in focus and tracking of the optical head, and to It is an object of the present invention to provide an optical head structure that allows easy adjustment of the optical axis of optical components.

[Structure of the Invention] Means for Solving the Problems According to the present invention, such an object is achieved by providing 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 first light receiving element disposed within the optical path of the detection light to detect either one of the error states, and a first light receiving element disposed within the optical path to deflect a portion of the detection light. a second light-receiving element arranged in the optical path of the deflected detection light to detect the other of the two error states; The optical system is characterized by incorporating a cylindrical lens disposed in the optical path of the detection light leading to the light receiving element on the side that detects the focus error state and integral with the deflection means. This is achieved by providing a head structure.

Effect> In this way, the optical component that divides the detection light toward each light receiving element for tracking and focus error detection of the photometric sensor can be made smaller and lighter, and its position can be easily adjusted.

<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, a λ/4 plate 3, and a collimator lens 4 are provided, and the emitted light 5 that has passed through these is irradiated onto an optical disc via an objective lens (not shown).

Here, the emitted light 5 from the semiconductor laser 1 has an elliptical cross section as shown in FIG. By disposing it in the optical path, only the circular cross-sectional portion that passes through the collimator lens 4 is used as the emitted light 5 that is irradiated onto the optical disc.

The emitted light 5 irradiated onto the optical disc is reflected by the disc, becomes reflected light 6, passes through the λ/4 plate 3 again, and enters the polarizing beam splitter 2.

Since this reflected light 6 passes through the λ/4 plate 3 twice, the plane of polarization of the reflected light in the polarizing beam splitter 2 differs by 90 degrees from the plane of polarization of the output light 1. .

Therefore, the reflected light 6 is deflected by the polarized light reflecting films disposed diagonally within the polarized beam splitter 2, and the detected light 7 is
The light is emitted from the right side of the polarizing beam splitter 2 in FIG. Here, the polarizing beam splitter 2 and λ
Since the /4 plate 3 is placed in the optical path of the emitted light 5 consisting of diverging light from the semiconductor laser 1 and the reflected light 6 consisting of convergent light, compared to the conventional case where parallel light passes through, Therefore, the polarizing beam splitter 2 and the λ/4 plate 3 can be downsized.

A photometric sensor 8 is disposed in the optical path of the detection light 7 to detect errors in focus and tracking of the optical head. In this embodiment, each of the above-mentioned elements is arranged in the optical path of the emitted light 1 that is a straight line from the semiconductor laser to the optical disk, but in reality, this optical path can be freely changed by arranging a mirror or the like. The arrangement is not limited.

FIG. 3 is a cross-sectional view of the photometric sensor 8 along the axial direction.
FIG. 4 is a sectional view taken along line IV--IV in FIG. 3. The substrate 9 of the photometric sensor 8 includes a photodiode 13 as a light-receiving element for detecting a tracking error in the center thereof, and a photodiode 14 as a light-receiving element for detecting a focus error at a predetermined distance from the photodiode. are integrally fixed so that they are located on the same plane.

As shown in FIG. 4, each of these photodiodes 13 and 14 is constituted by a photodiode element divided into four by mutually orthogonal dividing lines. One dividing line of the tracking photodiode 13 is perpendicular to the direction in which the optical axis of the detection light 7 shifts when a tracking error occurs. Further, one dividing line of the focusing photodiode 14, which is slightly wider than the photodiode 13, is located on an extension of the dividing line of the frame 1 to the diode 13.

As shown in FIG. 3G, the photodiode 13 on the substrate 9
A cubic half prism 10 that reflects half of the detection light 7 at right angles is in close contact with the light receiving surface 13a. A surface 1 from which the reflected detection light 7a of the half prism 10 is emitted
As shown in FIG. 5, a cylindrical lens 11 is integrally fixed to Oa in an inclined state. Also,
A triangular prism-shaped reflective member 12 having a reflective surface 12a that deflects the detection light 7a that has passed through the cylindrical lens 11 toward the photodiode 14 is in close contact with the light receiving surface 14a of the photodiode 14.

Then, the lower portions of the half prism 10 and the reflective member 12 are fixed to the substrate 9 by, for example, filling the concave portion 9a of the substrate 9 with a resin mold.

In this way, half of the detection light 7 is focused directly on the photodiode 13, and the remaining half is focused on the half prism 10.
The light passes through the cylindrical lens 11, is reflected by the reflective surface 12a of the reflective member 12, and is focused on the center of the photodiode 14 divided into four parts.

Note that each of the photodiodes 13 and 14 is electrically connected to a control circuit (not shown) via a lead wire (not shown) extending from the substrate 9.

Next, the procedure for detecting each error in tracking and focus by each photo I diode 13 and 14 will be explained.

As shown in FIG. 6, detection signals E to H corresponding to each irradiation pattern are sent from each photodiode element of the photodiode 13 to each amplifier 19, 20 so as to be divided into (E+F) and (G+H). input, and each amplifier 19
．． The output value from 20 is input to amplifier 21. Then, at amplifier 21, from (E1F) to (
G + H) is subtracted and the calculated value is output to the control circuit.

Here, half of the detection light 7 is focused on each photodiode element of the photodiode 13 in a circular shape as shown in the imaginary line, and if a tracking error occurs, the optical axis will change as shown in the figure. Since the tracking error is shifted in either the left or right direction, the direction of the tracking error and the amount of the error can be easily detected using the above-mentioned calculated values.

On the other hand, as shown in FIG. 7, in the photodiode 14, the output values of the diagonal photodiode elements are divided into the sum (A+C) and (B+D) of each amplifier 22, 23. and each amplifier 22.
The output value from 23 is input to an amplifier 24. Then, the amplifier 24 subtracts (B+D> from (A+C)) and outputs the calculated value to the control circuit.

As shown in FIG.
After the focal length of the component along the direction formed by 1 (the diagonal direction of the 4-split photodiode 14) is changed, the reflecting member 1
The light is reflected by the reflecting surface 12a of the photodiode 14 and is incident on the intersection of the dividing lines of the four-part photodiode 14 in a substantially circular shape as shown by the imaginary line K, indicating that no focus error has occurred. There is. Here, if a focus error occurs, either the output value (A + C) or (B + D) will become larger, as shown by the imaginary line or imaginary line M in FIG. Accordingly, the direction and amount of focus error can be easily detected using the known astigmatism method.

Note that the read signal is transmitted to the tracking photodiode 1.
It can be detected by using the sum of the three detection signals E to I ((E+F+G+H)).

According to this embodiment, since the photodiodes for detecting errors in focus and tracking are provided on one substrate, wiring to the photodiodes is simplified, and noise resistance can be improved. Since the optical axis adjustment only needs to be performed at one location, the adjustment time can be reduced.

FIG. 8 is a diagram similar to FIG. 2 showing a second embodiment based on the present invention. In this embodiment, the reflecting member 25 has a plate shape. The rest of the configuration is the same as the first embodiment.

Incidentally, in the above embodiment, a four-division photodiode was used as the tracking error detection photodiode 13, but
A two-split photodiode divided into (E1F) and (G1H) may be used. In addition, in this embodiment, half of the detection light 7 is transferred to the half prism 10 and the reflecting member 1.
However, in reality, for example, by changing the reflection angle of the half prism 10, the light is reflected only once by the prism and enters the photodiode 14. It may be made to be incident.

[Effects of the Invention] As described above, according to the present invention, the optical component that separates the detection light toward each light receiving element for tracking and focus error detection of the photometric sensor is miniaturized, and its position adjustment is facilitated. The entire optical head is also smaller and lighter,
Since the responsiveness is also improved, the effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of main parts showing a first embodiment of an optical head to which the present invention is applied. FIG. 2 is a front view of the collimator lens taken along the line ■--■ in FIG. 1. FIG. 3 is a cross-sectional view along the axial direction of the photometric sensor in the optical head shown in FIG. 1. FIG. FIG. 4 is a sectional view taken along line IV--IV in FIG. 3. FIG. 5 is an enlarged perspective view showing only the half prism and cylindrical lens of the photometric sensor shown in FIG. 3. FIG. FIG. 6 is a schematic circuit diagram showing how to detect tracking errors. FIG. 7 is a schematic circuit diagram showing a focus error detection procedure. FIG. 8 is a diagram similar to FIG. 3 showing a second embodiment of the optical head to which the present invention is applied. 1... Semiconductor laser 2... Polarizing beam splitter 3... λ/4 plate 4... Collimator lens 5... Output light 6... Reflected light 7... Detection light 7a... Split Detected light 8... Photometry sensor 9... Substrate 9a... Concave portion 1
0... Half prism 10a... Output surface 11... Cylindrical lens 12... Reflective member 12a... Reflective surface 13.1
4... Photodiode 13a, 14a... Light receiving surface

Claims (3)

[Claims] (1) 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 detects the detection light in order to detect either one of the error states. a first light-receiving element disposed in the optical path; a half prism disposed in the optical path for deflecting a portion of the detected light; and a half prism disposed in the optical path for deflecting a portion of the detected light; a second light-receiving element disposed in the optical path of the detected detection light, and a second light-receiving element disposed in the optical path of the detected focus error state; 1. An optical head structure comprising a cylindrical lens disposed in an optical path and integral with the deflection means. (2) The optical head structure according to claim 1, wherein the half prism is in close contact with the light receiving surface of the first light receiving element. (3) Claim 1 or 2, characterized in that both the light receiving elements are arranged on the same plane.
Optical head structure described in section.