JPS6043234A - Detector for defocus of optical disk head - Google Patents

Abstract

PURPOSE:To detect a focus error with good characteristics only by making a simple adjustment by using a parallel plane mirror which has a half-mirror as the front surface and a mirror as the rear surface, and providing two photodetectors on the same plane. CONSTITUTION:The parallel plane mirror 17 has a half-mirror as the front surface 18 and a mirror as the rear surface 19 and separates reflected luminous flux 9 into luminous flux 14 to be reflected by the front surface half-mirror 18 and luminous flux 15 to be reflected by the rear surface mirror 19, and the photodetectors 11 and 16 in the same shape are arranged on a plane which is closer than the focusing point Q of the reflected luminous flux and farther than the focusing point Q' of the reflected luminous flux 15, constituting four divisions, i.e. sensitive areas I , II, III, and IV. A three-axis adjustment of two photodetectors 11 and 16 should be made conventionally, but a three-axis adjustment of one photodetecting device consisting of the two photodetectors 11 and 16 arranged on the same plane is only made.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a defocus detection device for an optical disk head that outputs or writes information from an information recording medium such as a digital audio disk or a video disk.

[Prior art]

A conventional device of this type is shown in FIG. FIG. 1 is a schematic diagram showing a conventional focus shift detection device for an optical disk head, where tl+ is a light emitting source such as a semiconductor laser, (2I is an emitted light flux emitted from a light source il+, and (3
) is the output beam (2; collimating lens to make the total parallel beam (4), (5: is a quarter-wave plate, (61 is the parallel beam (4),
4) to form a focused spot (8) on the surface of an optical disk (7) which is an information recording medium.

(91 is the condensing slot on the optical disk surface) From +81 to the objective lens (6t, IBM half-wave plate (5), collimating lens (3) M: reflected light flux, Oll is the output light flux (2) and reflected a beam splitter that separates the light beam (9);
flll is the reflected light beam separated by the beam splitter (
9) The photodetector is placed at an optical axis position closer to the condensing point P, and has a circular inner sensitive area.

Next, the focus shift detection operation will be explained.

The laser emitted light beam (21) from the light source tl+ is made into a parallel light beam (4) by the collimating lens +31, and then passed through the quarter-wave plate (5) and is reflected onto the surface of the optical disk (7) by the objective lens (61). 1 forming a focused spot (8)
, the reflected light flux from this spot (8) is the objective lens + (
ilK writing law Incoming light passes through the quarter-wave plate (5j, collimating lens (3)) and returns along the optical path.This reflected reflected light flux +9 is reflected by the beam sinter (2) and is directed in a 90° direction. is changed and reaches the photodetector 0υ.This photodetector all is located close to the condensing point P'1ll) of one reflected beam (9), so the photodetector (
IIIK (reflected light that is focused) Q3 has a size of . Reflected light spot α to the photodetector 0υ when the surface of the optical disc (7) is at the focal point position of the objective lens (6)
2 is as shown in FIG.
The position of U and the size of area I are set. Therefore, the feeling area 1. The output difference (Ill) of If is 0. On the other hand, when the original disk (7) moves away from the focal point position, one reflected light beam (
9) The condensing point P is close to the photodetector aU, and the reflected light spot az becomes small as shown in FIG. 1C,
The incident sight to sensitive area I becomes larger.

The output difference (II-1) is negative. On the contrary, Hikari Tinuku (
7) approaches the focal point position, the reflected light spot aZ becomes thicker as shown in the first figure, and the photodetector output difference (I
L-1) is stop seven. νIJ Chiko detector output difference (II
-1) is a signal corresponding to the focus shift, which will hereinafter be referred to as a focus error signal Bf.

FIG. 2 shows characteristic 1I showing this focus shift detection operation.
In the ll diagram, the @ axis indicates the deviation X of Tinuku (7) from the in-focus position (positive in the direction of moving away), and the vertical axis indicates the focus error signal Kf. It has been confirmed both experimentally and theoretically that the shape of this characteristic curve is unique to the above-described focus shift detection method (referred to as the areal density method). As described above, in the focus shift detection method using the areal density method, as shown in FIG. 2, the characteristics are asymmetrical and the detection sensitivity differs before and after the in-focus position. For this reason, it is difficult to design a focus servo that can cope with the change in focus shift detection sensitivity, and the focus servo also has the disadvantage of poor stability.

FIG. 3 is a schematic diagram showing a conventional device improved in terms of depth, and the same reference numerals as in FIG. 1 in FIG. 1 indicate the same or opposite parts.

In the figure, 113 is a Hartz mirror that separates the reflected light flux 19 into θ-blind and U5, and Oe is a photodetector (the same shape as Ill) installed at a position far from the focal point P' of the reflected light flux f15. When the disk (7) is at the focused position ll'i: the amount of light incident on the sensitive area 1.IV is set to be equal.In other words, the photodetector ovvc is set to
The photodetector output difference (Ill) with the characteristics shown in the figure is obtained (Figure 3B), and the photodetector θe has a photodetector with the characteristics shown in Figure 2 rotated 180 degrees around the origin. Output difference (1-
IV) is obtained (Fig. 3C).

If we add the output difference between these two photodetectors 111 (Le) and make this the focus error signal Fif, then Ef-(II
-1)+ (I-IV) = (II+I) -(1+
TV) C. Shown in FIG. 4 vc) Characteristics of equal detection sensitivity can be obtained even before and after the 9 focal point position with good symmetry.

However, in the device shown in Fig. 3, the photodetector (lυQf
9 positions must be adjusted independently on three axes, which has the disadvantage that the adjustment is complicated and the adjustment cost is high.

[Summary of the Invention 3 This invention was made in order to eliminate all the drawbacks of the conventional ones as described above.The two surfaces are half mirrors and the back surface is a parallel plane mirror that acts as a mirror. The object of the present invention is to provide an optical disc head out-of-focus detection device that can handle a focus error M signal with a good 9% accuracy by providing the two on the same plane.

[Embodiments of the invention]

FIG. 5 is a schematic diagram showing an embodiment of the present invention.

The same symbols as in FIGS. 1 and 3 indicate the same or equivalent parts,
In f+, 71, 9 surface Og acts as a half mirror, 9 back surface Og acts as a mirror, and separates 1 reflected light beam (9) into light beam I reflected by front half mirror (2) and light beam 09 reflected by back surface mirror OJ. The parallel plane mirror ClG1 is a photodetector installed on a surface nearer to the focal point Q of the reflected beam I and farther from the focal point Q° of the 1 reflected beam 09,
The two-split photodetector (photodetector (IIIQ61) having the same shape as the group Oe shown in FIG.

It is configured into four parts: n, m, and iv. That is.

The reflected light flux [91 is reflected by the surface of the parallel plane mirror (18), and the light flux 041 reflected by the back surface f19, whose optical axes are parallel. 171. Therefore, the focal point Q+ of the reflected beam 09 is closer than the focal point Q of the reflected beam 141. Therefore, the focal point Q+ of the reflected beam 09 is closer to the focal point Q of the reflected beam 141. At a certain position between the light points Q and 91, there is a place where the cross-sectional beam diameters of the respective reflected beams 009 are equal i-.At that position, there is a 2-split photodetector (4-split consisting of 1υθυ) that receives each reflected beam. When the optical disc (7) is in focus level 1 after placing the original detection device (to), the output of the light detection device 4, that is, the focus error signal E
f = (ff + I) - (1 + IV) = o If the tonal shift is set, E will be negative if the optical disc (7) moves away from the focal point position, and Ef will be negative if it moves towards it.
is positive. Here, its characteristics are the same as in the case of Fig. 4.
As shown in the figure, it is symmetrical about the focal point position. Furthermore, in the case of Fig. 3, it was necessary to perform three-axis viewing independently for the two photodetectors (IG), but in the device of this invention, two photodetectors are arranged on the same plane. It is only necessary to adjust one photodetector (■) consisting of a detector 0υ0υ along three axes.

In the above embodiment, a four-division light detection device 12I having two circular 41-sensing areas was shown, but it could be as shown in FIG.
A six-divided strip-shaped photodetector (20') consisting of a three-division photodetector (11°) (16°) may be used. θ in the figure
l1 (21°) (I is an adder, (C) (25°) is a subtracter, and the focus error signal Jy in this case is 1f = (1 + II' 1 N) - (1 + IV + IV'). This light detection If the direction of the dividing line of the device (20') is set to be parallel to the direction in which the reflected light spot of the photodetector moves as a result of tracking, there is an advantage that no out-of-focus detection error occurs due to tracking. 0 [Effect of the invention] This invention is configured as described above.

Focus error detection with good characteristics can be performed with simple adjustment, and the adjustment cost is low, making the entire device inexpensive.0

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a conventional focus shift detection device for an optical tilt pickup, FIG. 2 is a diagram showing its operating characteristics, and FIG. 3 is a schematic diagram showing another conventional example. FIG. 4 is a diagram showing its operating characteristics, FIG. 5 is a schematic diagram showing one embodiment of the present invention, and FIG. 6 is a schematic diagram showing a photodetecting device according to another embodiment of the present invention. In the figure, 111 is a light emitting source, (6) is an objective lens, (7) is an optical disk which is an information recording medium, 'tl (I is a beam splitter), αhue is a two-split photodetector, (11') (16°) is 3
The dividing source detector, 03 is a half mirror, [+7] is a parallel plane mirror, and 4 (20') is a photodetector 011 (l[9 and 01°) (16°) arranged on the same plane. This is a split and 6-split photodetector. The same reference numerals in the drawings indicate the same or corresponding parts. Agent Masuo Oiwa (and 2 others) Figure 1 Figure 2 Figure 3 (A) Figure 4 Figure 6 Shiki [(■

Claims (1)

[Scope of Claims] A light emitting source, an objective lens that focuses the emitted light flux from the light emitting source onto an information recording medium, and an emitted light flux from the light emitting source;
A beam splitter that separates a reflected light beam from a focused spot on the recording medium that passes through the objective lens, and is located at a position shifted in the optical axis direction from a focal point position of the separated reflected light beam. The device is equipped with a photodetector configured to obtain different light reception outputs depending on the size of the reflected light beam spot that is focused on the object, and the objective lens uses the output of the photodetector to detect the light that is focused on the recording medium. In a defocus detection device for an optical disk head that extracts a signal corresponding to the defocus of a light spot, one surface is a half mirror and the back surface is a mirror, which separates the reflected light beam separated by the beam splitter into two parallel light beams. A parallel plane mirror is provided which acts as a
Farther than one focal point of the reflected light beam. The other light-converging point is provided with the above-mentioned photodetectors that receive these separated reflected beams on the same plane at a nearby position, and the output of the light-detecting device consisting of these two-party detectors is determined according to the above-mentioned focus shift. What is claimed is: 1. A defocus detection device for an optical disk head, characterized in that the defocus detection device is configured to obtain a signal based on the optical disc head.