JPS63273225A - Track tracing device - Google Patents

Abstract

PURPOSE:To eliminate track offset and to facilitate the adjustment of a detector, by setting the width of a photodetecting part in a direction perpendicular to a track almost equal to that of an interaction area on which the diffracted light of a reflected beam of light is superposed in the direction perpendicular to the track. CONSTITUTION:When track deviation detecting beams of light exist on the photodetecting parts 1a and 1b, the displacement of the interaction areas 4a and 4b are generated. Since the photodetecting parts 1a and 1b are arranged in the centers of the areas 4a and 4b in such a way that the width (u) of them are narrowed than the width in which the double of the maximum travel quantity of the displacement is subtracted from the width (x) of the areas 4a and 4b, small amount of unbalance occurs in a photoreceiving quantity due to the inclination of a recording medium or the travel of an objective lens in the direction perpendicular to the track. Therefore, a stable track deviation signal can be obtained. Also, even when deviation in a direction in parallel with the track occurs, since the width (v) on the other sides of the photodetecting parts 1a and 1b are larger the width (y) of the areas 4a and 4b, no unbalancing occurs in the photoreceiving quantity. In such a way, it is possible to obtain a stable deviation signal for the deviation, and to facilitate the adjustment of an optical detector.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a track tracking device, and more specifically, in an optical disk device, a reflected light beam diffracted from an information recording medium is detected and tracked by a push-pull method. This relates to a track tracking device fK that performs tracking.

[Conventional technology]

Conventionally, this type of track tracking device uses an optical means to focus light from a light source such as a semiconductor laser onto a track on an information recording medium, and a photodetector to detect a reflected light beam diffracted from the information recording medium. a detector, means for detecting a displacement of the position of the focused light spot with respect to the track position, and tracking means for reducing the relative distance between the position of the light from the light source and the position of the track by the output of the detecting means. There is.

Many methods have been proposed for detecting the relative position of the focused light spot with respect to the track. One known method is a push-pull method that uses diffracted light from an information recording medium. However, this method has the disadvantage that when the information recording medium is tilted, the light intensity distribution on the photodetector surface shifts in parallel, and the diffracted light also becomes stifled, causing an offset in the tracking error signal. Various photodetector shapes have been proposed as ways to improve this. - As an example, FIG.
a) # (1b) KO next time new party (ri, -1st.

+1st-order diffracted light (3aL (3b)) is incident.

Next, the effect will be explained. For ease of understanding, K.
First, an overview of a track tracking device using a diffraction phenomenon will be explained with reference to FIG. The light beam emitted from the semiconductor laser (6) is made into a parallel light beam by the collimating lens (7),
The light is reflected by a half mirror (8) and guided to an objective lens (9) to form a light spot on an information recording medium (1o). The information recording medium (1o) is provided with tracks (11), and a diffraction phenomenon occurs in the reflected light from the information recording medium (10). That is, the reflected light is separated into 0th-order diffracted light (2), +1st-order diffracted light (3b), -1st-order diffracted light (3a), and is further divided into K parts depending on the deviation between the center of the -track (11) and the center of the optical spot. Therefore, the phases of the +1st-order diffracted light (3b) and the -1st-order diffracted light (3a) are shifted in opposite directions with respect to the phase of the 0th-order diffracted light (2). The above diffracted light is transmitted through the objective lens (9)
The light beam is again made into a parallel beam of light, passes through a half mirror (8), and enters photodetectors (12a) and (12b) which are divided into two symmetrically with respect to the direction of the track (11). The output of the photodetector (12a) (12b) is connected to the differential amplifier (5)
A tracking error signal is obtained by detecting the difference.

As described above, in the track tracking device using the push-pull method, the tracking error signal is detected as an intensity change due to interference between the 0th-order diffracted light and the ±1st-order diffracted light, so the photodetector (12a) (tzb) , it is only necessary to receive the interference region of the 0th-order diffracted light and the ±1st-order diffracted light. Here, as shown in FIG. 5, the information recording medium (10) is aligned with the optical axis of the objective lens (9) When tilted by α degree in a plane containing a direction vector perpendicular to the track on the recording medium (1o),
Since the directions of the 0th-order diffracted light and the ±1st-order diffracted light are also tilted by about 2α degrees, each diffracted light that has passed through the objective lens (9) also moves in parallel in the lateral direction, as shown. As a result, the interference region between the 0th-order diffracted light and the ±1st-order diffracted light does not match the interference region when the information recording medium (10) is not tilted, as shown by the broken line (lOO) in FIG. 5, and the tracking error signal An offset will occur. Also, as shown in Figure 6,
The same problem occurs when the objective lens (9) is moved to the position indicated by the broken line using an actuator as a tracking means.

In the photodetector shown in Fig. 3, the area narrowed by the maximum movement amount (ε) of the diffracted light from the interference area of the 0th-order diffracted light and the ±1st-order diffracted light is defined as the light-receiving parts '(la) and (Ib). There is something to do. Therefore, this problem occurs when the information recording medium (1o) is tilted in a plane that includes the optical axis of the objective lens (9) and a direction vector perpendicular to the track, or when the objective lens (9) is moved for tracking. There is an advantage that the offset can be made sufficiently smaller than that of the photodetectors (12a) (12b) shown in FIG.

[Problem that the invention seeks to solve]

Conventional track tracking devices use the photodetector described above, so the offset suppression effect does not work on the movement of the reflected light flux in the direction parallel to the track. Since the light receiving section of the sensor is two-dimensionally arranged, there are problems such as difficulty in adjusting the detector.

This invention was made in order to eliminate the above-mentioned error point, and there is almost no offset caused by the misalignment of the reflected light beam or the photodetector with respect to the track, and furthermore, the detector adjustment is facilitated. The purpose is to obtain a track tracking device.

[Means for solving problems]

In the track tracking device according to the present invention, the width of the light receiving section in the direction perpendicular to the track is equal to the width in the direction perpendicular to the track of the interference region of the 0th-order new beam and the ±1st-order diffracted light among the reflected light beams from the information recording medium. It is equipped with a photodetector for detecting an approximately equal tracking error.

[For production]

In this invention, the imbalance in the amount of light received by the light receiving section caused by the inclination of the information recording medium or the movement of the objective lens in a direction perpendicular to the track is reduced, and track offset is eliminated.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. The track tracking technique using the push-pull method is the same as the prior art, and its explanation will be omitted, and the photodetector, which is the essential part of the present invention, will be explained using FIG. 1. The photodetector shown in FIG. 1 has a light receiving section (la).

(lb), 000th order diffracted light track deviation detection light flux from information recording medium (10)) (2), -1st order, +1st order diffracted light (
3a) l (3b), the interference region between the O-th new party and the 11st-order diffracted light, and the interference region between the O-th new party and the +1st-order diffracted light (4a), (
4b).

In addition, in the figure, (phantom is the width in the direction perpendicular to the track (11) of the interference region (4a), (4b) of the 0th-order new party and ±1st-order diffracted light, ke) is the width in the direction parallel to the track, ( ω is the width of the photodetector light receiving parts (xa) and (xb) in the direction perpendicular to the track, (v) is the width in the direction parallel to the track, and K(ε) is the reflection used for detecting track deviation. It shows the maximum amount of movement of the luminous flux.

In this embodiment, the sizes of the light receiving portions (la) and (lb) are trap-formed so that the relationships of u<(x-26) and v>y hold, and the light receiving portions (la) and (lb) are formed so that the light receiving portions m(1a)#(1b) are arranged so as to be located at the center of the interference regions (4a) and (4b), respectively. The other configurations are the same as shown in FIG. 4.

With the above configuration, when the track deviation detection light beam is located on the light receiving section (1aL (lb)), the information recording medium (1
0) and displacement of the interference area (4a)-(4b) occurs when the track of the objective lens (9) moves in the vertical direction, but the width of the light receiving parts (la) and (lb) (ω is twice the maximum movement amount (ε) of the displacement as the interference area (4a
), (4-b) (which is narrower than the width subtracted from the phantom) and placed in the center of the interference areas (4a'), (4b), so the inclination of the information recording medium (10), The light receiving area (
The imbalance in the amount of light received by la) and (lb) is relatively small. In other words, the track deviation signal is transmitted to the light receiving section (
Since it is obtained as a differential signal from 1a)+(1b), a stable track deviation signal can be obtained. Furthermore, when a shift of the photodetector or a shift of the reflected light beam used for track shift detection occurs in the direction parallel to the track (11), the interference region (4a) # (4b
) occurs in the direction perpendicular to the direction of the deviation, but
The other width (v) of the light receiving portions (1a) e (1b) is the interference region (4a).

Since the width of (4b) is set sufficiently larger than yl,
There is no imbalance in the amount of light received by the light receiving section (1aL (lb)).

Note that the condition u<(x-zg) in the above embodiment may be replaced by u=x, and the same effect can be obtained.

In addition, in the above embodiment, a photodetector was shown in which the light receiving part was arranged focusing on the interference region between the 0th order new party (2) and the ±1st order diffracted light (3aL (3b)). As shown in the figure, there are five light receiving sections (1aL (lb)) on the photodetector.
, (lc), (,rd), and (le) are arranged, and it is possible to detect the total amount of the track deviation detection light beam in addition to the track deviation signal. In such a configuration, the light receiving sections (la) and (1b) are arranged under the same conditions as in the embodiment described above, and it goes without saying that the same effects can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, the width of the light-receiving part of the photodetector in the direction perpendicular to the track (ω is approximately equal to the width in the same direction of the interference region of the 0th-order diffracted light and the ±1st-order diffracted light). Since they are made equal, a stable track deviation signal can be obtained even when the information recording medium is moved, the objective lens is moved, and the photodetector is misaligned.
This has the effect of making it easier to adjust the photodetector.

[Brief explanation of the drawing]

FIG. 1 is a front view of a main part of one embodiment of the present invention, FIG. 2 is a front view of a main part of another embodiment, and FIG. 3 is a main part of a photodetector used in a conventional track tracking system [K]. FIG. 4 is an optical diagram of a conventional track tracking device, and FIGS. 5 and 6 are explanatory diagrams of the operation of the device shown in FIG. 4, respectively. (6) Light source such as Φ semiconductor laser, (1) Collimating lens, (8) Half mirror 1 (9) Fist/objective lens, (It)) Information recording medium, (12a), (
12b)...Photodetector, (1a), (lb)...Light receiving part of photodetector, (4a), (4b)...0th order new party and 11th order new party, 0th order diffracted light and +1st order diffracted light, respectively. interference area. In each figure, the same reference numerals indicate the same or similar parts. 4b: 0th order light, 111st order light and interference region Figure 3 Figure 4 Figure 5 Figure 6 Procedure amendment October 20, 1988

Claims (3)

[Claims] (1) a light source, an optical means for focusing the light emitted from the light source onto a track provided on an information recording medium, a photodetector for detecting the reflected light beam diffracted from the information recording medium, and the above-mentioned Track tracking of an optical disk device, comprising a detection means for detecting a displacement of a convergence position of focused light with respect to the position of the track, and a tracking means for reducing a relative interval between the position of the light and the position of the track by the output of the detection means. The device has at least two light receiving sections arranged symmetrically with respect to the direction of the track, and the width of the light receiving section in the direction perpendicular to the track is equal to the 0th order diffracted light of the reflected light beam. 1
A track tracking device comprising: the photodetector having a width approximately equal to the width in the direction perpendicular to the track of the interference region where the second-order diffracted light overlaps. (2) The above-mentioned track is an area in which the width in the direction perpendicular to the track of the light-receiving section is such that the interference region where the 0th-order diffracted light and the 1st-order diffracted light of the reflected light beam overlap is narrowed by twice the maximum movement amount of the reflected light beam. A track tracking device according to claim 1, wherein the track tracking device has a width in a direction perpendicular to the track width. (3) A patent in which the width of the light receiving section in the direction parallel to the track is sufficiently larger than the width in the direction parallel to the track of the interference region where the 0th-order diffracted light and the 1st-order diffracted light of the reflected light beam overlap. A track tracking device according to claim 1.