JPS63302429A - Focus error detector - Google Patents

Abstract

PURPOSE:To stabilize focus servo, by adopting a pair of tri-sected optical detectors as a pair of divisional type optical detectors, and setting the width of a light receiving part being positioned in the center of each tri-sected optical detector at a size equal to or less than the diameter of a light spot projected on the optical detector. CONSTITUTION:The tri-sected optical detector 1 that is the divisional type optical detector consists of the light receiving parts 11, 12, and 30, and the light receiving part 30 is positioned between the light receiving parts 11 and 12, and the width W of the parts 30 is set at the size equal to or less than the diameter L of a focusing spot Z by reflected light. Since the fluctuation of a detecting signal for the displacement of the spot position of the reflected light is comparatively small and the sensitivity of the optical detector 10 at the time of just focusing is small, a disturbance signal appearing in a focus error signal is reduced, and a range in which the focus error signal changes linearly for a focus error quantity can be expanded. In such a way, it is possible to perform the focus servo stably.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a focus error detection device for a recording medium in which information is recorded and reproduced optically. The reflected light is divided into two parts, and the divided reflected light is irradiated onto the central part of each of a pair of split type photodetectors, and the focus error signal and focus error amount are determined by the detection signals from the left and right light receiving parts sandwiching the central part. The present invention relates to a focus error detection device to be obtained.

[Conventional technology]

FIG. 4 shows a conventional focus error detection device called a Foucault type as described in, for example, JP-A-57-18032, JP-A-58-208,946, etc., and a light beam for recording and reproducing. A beam splitter (4) that transmits the irradiated light (fE) from a light emitting source such as a semiconductor laser that emits light, and also converts the irradiated light (E) into parallel light from the recording medium (8), which will be described later. a collimator lens (5) that condenses the reflected light (R);
A 1/4 wavelength plate (6) that rotates the plane of polarization of the parallel irradiated light (odor and reflected light (R), irradiated light < E that has passed through the 1/4 wavelength plate (6)) and condenses the reflected light. (The irradiation light is focused through the objective lens (7) that makes the river parallel light (
E) is irradiated onto a recording medium (8) such as an optical disk, so that information is optically recorded and reproduced.

The light splitter (9) includes an objective lens (7), a ]/4 wavelength plate (
6), splitting the reflected light (R) from the recording medium (8) incident through the collimator lens (5) and beam splitter (4) into two reflected lights R1 and R2. This light splitter (9) is also called a Foucault prism, and has a three-dimensional shape in which two rectangular refractive surfaces (9a) and (9b) are in contact with each other at an obtuse ridgeline (9C), and the ridgeline (9c) is a focal point for the reflected light (
R)'s optical axis (located perpendicularly across Shu).

The split photodetector (10) detects the split reflected lights R1 and R2, and has four light receiving parts (11) to (14) arranged in a plane perpendicular to the optical axis (A).
It consists of In addition, the light receiving surfaces of the light receiving sections (11) to (14) are arranged in a line in the arrow X' (X) direction perpendicular to both the optical axis (A) and the ridge line (9c), and are aligned along the optical axis. It is properly positioned in the figure and in the direction of arrow (3).

One pair of light receiving sections (11) and (12) form a two-split photodetector that detects one reflected light (R1), and the other pair of light receiving sections (13) and (14) form a two-split photodetector that detects the other reflected light (R1). A two-split photodetector is formed to detect light (R2). Usually, these two-split photodetectors each consist of a two-split pin photodiode, as will be described later. (Sl) ~ (S4
) are detection signals obtained by each of the light receiving sections (11) to (14), which are input to an appropriate arithmetic processing circuit and used for a focus sensor, etc.

With the above configuration, when recording and reproducing information, the irradiation light (E) emitted from the light emitting source (3) passes through the beam splitter (4), becomes parallel light at the collimator lens (5), and becomes 1/4 The polarization plane is rotated by the wavelength plate (6), and the light is focused by the objective lens (7) and irradiated onto the recording medium (8).

The reflected light (R) reflected by the recording medium (8) is
The light is focused at a predetermined convergence angle through the objective lens (7), the quarter-wave plate (6), and the collimator lens (5), is reflected by the beam splitter (4), and is further condensed by the beam splitter (9).
) is split into two reflected lights (R1) and (R2) and irradiated onto a split photodetector (10).

In FIG. 4, the "7-Co method" is used as a focus error detection method, and the light spot irradiated on the photodetector (10) in response to the occurrence of a focus error is
1) Alternatively, the light receiving section (12) is irradiated with a sharp intensity.

At this time, the light receiving sections (11) to (14) that have received each of the reflected lights (R1) and (R2) send continuous signals corresponding to the respective received light amounts, that is, detection signals (Sl) to (S4). occurs. The arithmetic processing circuit processes these detection signals (Sl) to (S
4), the sum of the detection signals (Sl) and (S4) of the outer light receiving sections (11) and (14), and the detection signals (S2) and (S3) of the inner light receiving section (12LNa). The formula for calculating the difference between the sum of F=(S1+S4')-(S2+S3) (1)
Find the focus error signal (Fl).

As shown in FIG. 5, the light-receiving surface of the conventional split-type photodetector (10) used in the focus error detection device shown in FIG. 4 has an appropriate distance between the recording medium (8) and the objective lens (7). This shows a state in which the reflected light (R1) is irradiated as a focused spot (Pl).

In FIG. 5, a pair of light receiving sections (11) and (12)
The two-split pin photodiode (1) forming the split-pin photodiode (1) forms a split-type photodetector (lO) together with the two-split pin photodiode forming another pair of light receiving sections (13) and (14). The separation strip (2) is connected to the light receiving section (11) and (1
2), which divides each light-receiving surface, and its width (d) is about 10 μm. In addition, FIG. 5 shows a photodetector (10)
The light receiving part (11
), (12) to ■detection signal (Sl).

(S2) shows how it changes.

FIG. 7 shows an optical disk (8) which is a recording medium, and is composed of a substrate (8a), a guide groove (8b), and a recording layer (8C). In order to realize recording, reproduction, and erasing of an optical disk (8), a drum-shaped track called a guide groove (8b) is usually formed on the information recording medium in advance, and a recording material is coated or Optical disk structures formed by vapor deposition have been considered.

[Problem that the invention seeks to solve]

Since the conventional focus error detection device is configured as described above, each light receiving section (xB, (tz) [and (13
), (14)] the deviation (d) of the separation zone (2) is 10 μm
Since the focus error signal ('F'') is
It fluctuates sensitively to the displacement of the spot position of each reflected light (R1) and (R2), and the range in which the focus error signal (Fl) changes linearly with the focus error amount becomes narrower.
There was a problem with the focus error signal (initial off in the spine).

Also, the light spot is located at the guide groove (8b) of the optical disc (8).
When moving across K, the reflected light from the optical disk (8) is affected by diffraction because the guide groove (8b) is a concave and convex phase groove, and is particularly affected by the focus error signal (F
Unnecessary disturbances occur during the process. For this reason, the second problem is that the focus servo becomes unstable during random access.
There were also problems.

This invention was made to solve the above-mentioned problems, and it widens the range in which the focus error signal changes linearly with respect to the amount of focus error, and also increases the range in which the light spot on the optical disk crosses the guide groove. Reduce the generated disturbance signal,
It is an object of the present invention to provide a focus error detection device that facilitates focus servo pull-in and follow-up control and can stably perform focus servo.

[Means for solving problems]

In the focus error detection device according to the present invention, the pair of split-type photodetectors is a pair of three-split photodetectors, and the width of the light-receiving part located at the center of each three-split photodetector is determined by the width of the photodetector. The diameter of the light spot is equal to or smaller than the diameter of the light spot irradiated on the surface.

[For production]

In this invention, the fluctuation of the detection signal with respect to the displacement of the spot position of the reflected light is relatively small, and the sensitivity of the photodetector is small at the time of just 7 orcus, so the disturbance signal that is included in the focus error signal is reduced. The range in which the focus error signal changes linearly with respect to the focus error amount is expanded.

〔Example〕

FIG. 1 shows an embodiment of the present invention, in which a three-split photodetector (1) forming a split type photodetector has a light receiving section (11).

(12) and (30), and the light receiving part (3o) is
It is located between the light receiving parts (11) and (12), and its width (
5) is set to be no larger than the diameter of the focusing lens (Z) by the reflected light (R1).

This three-split photodetector (1) replaces the split-type photodetector (1o) in FIG. 4 with its one pair,
The focus error detection device is otherwise constructed in the same manner as shown in FIG.

Separation strip (
Within the width of 100) (101), as shown in FIG. Changes linearly with directional displacement. Also, separation strip (100)
, (IOI), each detection signal (
Sl"l, (S2) and (S3) are each light receiving section (11
), (30), and (12) are set to output approximately 1/2 of the maximum photocurrent.

The 7-occasion error signal is transmitted from the light receiving sections (11) and (12) at both ends.
) is determined as the differential output of

Next, the operation will be explained. The focusing point (Pi') of the reflected light (R1) shown in FIGS. 4 and 5 is
), the width (W) of the light receiving part (3o)
is not larger than the in-focus spot diameter (L), almost no reflected light (R1) is received by each of the light receiving sections (11) and (12). Furthermore, even if a focus error occurs and the spot position is displaced in the direction between the arrows in FIG.
) is relatively small. Hence the focus error! -! Ic # focus error signal (F)
As shown by the solid line in FIG. 3, the characteristic of , as shown by the solid line in FIG. 3, has a gentle slope in the linear portion compared to the characteristic of the conventional device shown by the broken line. Furthermore, even if the light spot crosses the guide groove (8b) on the optical disc (8), the light receiving part (11
) or (12), the disturbance superimposed on the focus error signal is also extremely reduced.

Furthermore, a reproduced signal can also be obtained from the sum signal of the three light receiving sections.

In addition, in the above embodiment, the case where the width of the light receiving part (30) is not larger than the focal spot diameter was explained, but due to various specification changes, the reflected light (wavelength (λ) and convergence angle (α) ) are different, the width (W) of the light receiving part (30) is
Any value satisfying w4z, 44λ/sinα and less than the in-focus spot diameter is sufficient.

Moreover, although the case where the recording medium (8) is an optical disk is taken as an example, it goes without saying that it can also be applied to a focus error detection device such as an autofocus camera, and the same effect can be achieved.

〔Effect of the invention〕

As described above, according to the present invention, the width of the light receiving part located at the center of the three-split photodetector is made equal to or smaller than the diameter of the light spot irradiated to the photodetector, so that the focus error The range in which the signal changes linearly with respect to the focus error amount is expanded, and the disturbance signal that appears on the focus error signal when just focusing is reduced, so the focus servo can be performed stably and easily. .

[Brief explanation of the drawing]

FIG. 1 is a front view of essential parts of an embodiment of the present invention, FIG. 2 is a detection signal diagram in the embodiment, FIG. 3 is a characteristic comparison diagram of focus error signals, and FIG. 4 is a conventional focus 5 is an explanatory diagram showing the light-receiving surface of the 2-split photodetector in FIG. 4; FIG. 6 is a characteristic diagram of the 2-split photodetector in FIG. 4; The X diagram is the same (cross-sectional view of the optical disk).
)...Light splitter, (In, (12), (30)"-Light receiving section, (R1), (R2)-"Reflected light, (81), (S2
), (83)...detection signal. In each figure, the same reference numerals indicate the same or corresponding parts.

Claims (3)

[Claims] (1) Divide the reflected light from the recording medium into two parts, irradiate each of the two divided reflected lights onto the central part of a pair of split-type photodetectors, and In a focus error detection device that obtains a focus error signal and a focus error amount based on detection signals output from left and right light receiving sections sandwiched between each other, the split photodetector is a three-split photodetector, and further,
A focus error detection device characterized in that the width (W) of the light receiving section located at the center is set not larger than the focused spot diameter of the reflected light. (2) The width (W) of the light-receiving part in the center is defined as W, where α is the convergence angle of the reflected light in the direction parallel to the dividing line of the three-split photodetector, and λ is the wavelength of the reflected light. ≦2.44×(λ
The focus error detection device according to claim 1, which satisfies the following: /sin α). (3) In the three-split photodetector, the detector sensitivity changes linearly within the dividing line with respect to a direction perpendicular to the dividing line, and the sensitivity of each light-receiving surface changes at the center of the dividing line. The focus error detection device according to claim 1, wherein the focus error detection device is set to be approximately half the sensitivity on the light receiving surface.