JPS5911541A - Focus detector of optical information reproducer - Google Patents

Abstract

PURPOSE:To simplify the adjustment of an image rotating prism in locating a track and a boundary line of a 4-segment photodetector in parallel, by providing the image rotating prism to a condenser lens system. CONSTITUTION:A prism in which reflecting light rotates twice incident light is inserted between a cylindrical lens 8 and the 4-segment element 9. Thus, the image of the track is produced in parallel with the boundary line of the 4-segment element 9, while the direction of a generating line of the cylindrical lens 8 is placed coincidently with the direction of the track or orthogonaly thereto. The prism is usable in any case and better to be placed between the condenser lens 7 and the cylindrical lens 8 from the standpoint of the arrangement of the optical system. In using a reflecting prism 14, when the generating line of the cylindrical lens 8 is in parallel with or orthogonal to the track and an angle theta between the ridge line of the reflecting plane and the generating line is a half of 45 deg., i.e., 22.5 deg., the light image irradiated from the prism forms an angle of 45 deg., and one of the boundary lines of the 4-segment photo detector is placed in parallel with the track, the same as the case of the arrangement of the cylindrical lens at 45 deg. to the track. A focus detecting signal is obtained through the combination (SA+SB)-(SC+SD) of the photodetector elements split into four, and track detecting signal is obtained through the combination of (SA+SB)-(SC+SD).

Description

[Detailed Description of the Invention] The present invention is an optical fW sensor reader), in which an astigmatism method is used to detect the focus of the objective lens. The present invention relates to a focus effect device that prevents IF.

In order to read the tW gills recorded optically with a video disc or the like, a laser beam is directed onto the recorded body by an objective lens, and the reflected light is again focused onto a detector by the objective lens. At this time, in order to always focus the laser beam on one spot on the surface of the recording medium due to the difference between the rotation axis and the recording medium, the in-focus state is always detected and the detection signal is used to determine the focus. It is necessary to incorporate a so-called focusing lens, which performs focusing by moving the objective lens in the entire optical axis direction in accordance with this.

FIGS. 1 and 2 are explanatory diagrams of the astigmatism method, which is a conventionally known focus detection method. A beam of υ from a laser beam 1 is converted into parallel light by a coupling lens 2, and a spot of about 1.6 μφ is formed into a disk by an objective lens 5 with a 3.2/4 plate 4 as an axis. Dye the soil.

(The sit light becomes parallel light from the inverted one-piece objective lens 5, and becomes a straight light that follows the incident light and the recitation surface that is a piece of the 2/4 plate.It passes through the three beam splinters and becomes a strip of light. Large astigmatism due to lens 7 and cylindrical lens 8
“Old ゛-4-ru fruit A;
, make a direct-mounted υ beam waist on 11.

I) A light-receiving element 9 whose light-receiving surface is divided into four as shown in FIG. 2 is placed in the mouse pupil where the beam cross section is circular in the two υ beam waists υ 1i1.

In such an optical system, the objective lens 5 and the recording medium 6
If the interval changes and the ejected light beam becomes convergent light or diverging light,
Direct 1i! Since the beam waist lO% LL'7) position is shifted with respect to the four-split element 9, the original incident cross section υ changes to an elliptical shape as shown in FIGS. 2(b) and 2(e).

2 that faces the 4-divided element 9 detection No. 16 output S directly on the top
The PA is summed up, and the difference between the two sets a = total is used as the focusing signal, that is, (SA + SC) - (Sa + SI
If J l is used as the focus signal, this 7) indicates that the signal output is in focus when it is zero, and if it is out of focus, the output signal will be (+) or U (-1,?). (Focus control is performed by moving the objective lens 5 closer to or further away from the recording medium 6.

This 7) Focusing 1ro issue 7) Since the light intensity 1 distribution is measured, even if the cross section of the light beam is circular, diffraction and other causes (
Therefore, if there is a strongly variable distribution O bias in the cross section of the light beam, a sunspot off signal will be output.

The strongly variable distribution υ bias that causes such false detections occurs in the recording medium υ track direction or in the direction perpendicular to the trunk. Instead of arranging the border line 12v of the four-part confectionery at 45 with respect to the trunk, it has been proposed to arrange the border line 12v of the four-part confectionery with one side aligned with the direction of the truck 13, as shown in FIG.

(Unexamined Japanese Patent Publication No. 53-198 (J6)) However.

For this purpose, the cylindrical lens 8 is arranged at a distance of 45+Iji from the trunk 1, which has the disadvantage that the assembly process becomes difficult.

In this ninth invention, by inserting a mirror in which the reflected light rotates by a factor of υ of the incident light into the cylindrical lens 8 and the 4-split elements 9 and 71t, the cylindrical lens 87) is arranged in the generatrix direction coincident with or at right angles to the trunk υ direction. When folded, ridges are formed on the 4-split cord 97) boundary line and the 1li-line of the trunk z).

A trapezoidal prism as shown in FIGS. 5 and 6 and a reflecting prism having mutually orthogonal reflecting surfaces are known as prisms that produce such a strong optical 1v@I.

Any of these prisms can be used, and it is preferable to place them between the condenser lens 7 and the cylindrical lenses 8 and 7) from the optical system arrangement 4. Figure 7 shows reflective prism 1.
When using 4.■ An example is shown below. When the generatrix of the cylindrical lens 80 crosses the track in the F line or perpendicularly, the thickness θ between the reflective surface υ ridgeline and the generatrix is 4521) '/2
, that is, if it is 22.5, the prism is 0 cm out (elephant is 45 without DMffi, and the 7 lindrical lens is placed 45 points apart from the trunk), just like the il! Placing it in the trunk and 1,000 rows will be 4 pieces.So, on top of that, Figure 7 υ) and the reflecting prism 14? The optical system used is compact; it can be rubbed easily. Furthermore, instead of using the prism υ for internal reflection, it is possible to make the system even lighter by using a rough version of two orthogonal υ mirrors.

Also, from the above υ, (this is the focus adjustment code, the combination of the four divided light receiving elements (S,, -1-8c) -(SB+5
Ll), but (SA+8,1- (Sc
+S) 7) At the intersection (therefore, the truck image is on the boundary line of the nine light-receiving elements), it is possible to determine whether the LE is properly riding, that is, to obtain a trunk detection signal.

This υ invention incorporates a 1 x 1 quadruple prism in the υ optical system for focus detection7) as described above, and arranges it between the track and the 4-division light receiving element υ boundary line. 7) It is extremely easy to adjust by adjusting the rotation angle of the prism by half the rotation angle of the 7) degree by I@9dl.

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams of the conventional υ astigmatism method 7), and Figures 3 and 4 are 4-division light-receiving element υ apparatus g! Figures 5 and 6 are diagrams showing the analysis of the rotating prism, Figure 7 is the optical path diagram of the invention 7) Example 1: Light source 2: Coupling lens 3: Beam splitter 4: λ /4 Loss 5: Objective lens 6: 1 bluish d self-recording surface 7: Dyeing lens 8 Nijilintorical lens
9:4 split light receiving element l3 Nidrakku 14:1 elephant rotating prism Patent applicant Legal company Rico m m1 person agent Masu Sotoshi Fumi Sato (t”k
or 1 person) De I M 3I No. 1 Figure 4

Claims (1)

[Claims] An information reproducing device (information reproducing device) in which a light beam from a light source is focused onto a recording medium by an objective lens, and the reflected light is focused onto a light receiving element by a condensing lens system including an objective lens and a cylindrical lens to detect a focus. , upper tic!
A focus detection device with a special feature of a Toko lens system with a rotating prism.