JPS62283425A - Signal detection device - Google Patents

Abstract

PURPOSE:To relax the accuracy of arrangement of optical components by using a beam splitter so as to divide a reflected luminous flux from an information recording medium into two, luminous fluxes for track deviation detection and out of focus detection. CONSTITUTION:The beam splotter 24 to divide the luminous flux into two is arranged to a signal detector 22 receiving reflected light beams from a polarized beam splitter 3 and a track deviation detector 25 having two photodetection faces 25a, 25b is arranged in the direction of the reflected light beams by the splitter 24. Further, a roof type prism 28 is arranged in the direction of the luminous flux transmitted through the splitter 24. The luminous fluxes 29a, 29b divided by refracting faces 28a, 28b of the prism 28 are collected respectively to photodetection faces 30a, 30b and 30c, 30d of the out of focus photodetector 30. When the information recording medium 6 is focused to the objective lens 5, an out of focus detection signal a+d-b-c obtained from differential amplifiers 31, 32 and an adder 32 is zero and the detector is controlled to make the detection signal zero.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a signal detection device, and more specifically, an information detection device that optically records and reproduces information on an information recording medium provided with a guide groove. The present invention relates to a signal detection device for detecting focus deviation, track deviation, and reproduction signals in a recording/reproduction device.

[Conventional technology]

Figure 5 shows an outline of a conventional general optical information recording and reproducing device. A beam splitter (Jl, //u wavelength plate (ke) and an objective lens (5) are arranged in sequence, and an information recording medium (
The laser beam is focused on the guide @(ri) of 6).

Signal detection device #(g) is for reproducing signals recorded on the information recording medium (6) and detecting signals such as defocus and track misalignment.
) and a photodetector (10). Conventionally, there was a signal detection device (Kl) as shown in FIG.
&/-1, No. 1, pages 37-3g.
A mirror (l) is inserted into the convergent light beam at an angle up to the optical axis (/3), and half of the convergent light beam is reflected by this mirror (l).
It is reflected at right angles by the light beam (Y) and enters the photodetector (/ψ) for detecting track deviation. The photodetector for track deviation detection (/ri) consists of two light-receiving surfaces (/a) and (/sub), and the dividing line between the light-receiving surfaces (/ua) and (iub) is optically It is arranged parallel to the direction in which the information recording medium (610 guide (7)) extends.On the other hand, the convergent light beam that is not reflected by the mirror (/2) passes through the concave lens (
15) and enters the defocus detection photodetector (/6). The defocus detection photodetector (/6) consists of two light receiving surfaces (/Aa) (/6b), and the convergent light beam It is placed at the focal point of the light.

The photodetector for tracking deviation detection (7g) and the photodetector for defocus detection (/6) are equipped with a differential amplifier (/6) that calculates the output.
q) (to t) are fully connected.

The track deviation detection signal (
TS), and a defocus detection signal (FS) is obtained from the output of the differential amplifier (7g).

A reproduced signal (/RF) is obtained from the output of an adder (/9) for adding the outputs of the trunk shift detection detector (/l).

Next, the operation of one or more such signal detection devices will be explained. In Fig. 6, the track deviation detection method is the push-pull method, and the defocus detection method is known as the Knifezi method. Now, we will take out only the parts necessary for explaining the principle and use a mirror (//
2) is inserted vertically to the optical axis (/J). Figure 1 [al shows the case where there is no deviation of the guide groove (71), (b) shows the case where the guide groove (71 shifts in the -Y direction, (C) shows the case where it shifts in the +Y direction, ~
In fcl, the distribution of the seventh-order diffracted light diffracted by both edges of the guide groove (7) is as follows.

The curve (20) (2/) is also shown in the same figure (dl (
et [fl is.

The same figure (al (bl) shows the shape of incident light on the two light receiving surfaces of the photodetector (/l) in fcl,
Since the mirror (/2) is included in the convergent light beam, the external shape of the incident light is semicircular, and the distribution of the /order diffracted light is shown by the hatched area in the figure.

Guidance 1t (q
If there is no + deviation, the ratios of the diffracted light distribution (20) and (U/) by both edges of the guide @(71) provided on the +W information recording medium (6) are equal to each other, and therefore the track shown in fdl in the figure The two light-receiving surfaces (#) of the optical detector (/μ) for detecting deviation
The outputs from a') (/gb) become equal, and the output from the differential amplifier (/ri) becomes equal. Also, Fig. 1 fbl fa
As shown in t.

If the guide groove (7) is shifted in the -Y direction, the diffracted light distribution (θ) and (λ/) due to both edges of the guide groove (7) will not be equal to each other, and the light receiving surface ( /Hiroa)
Since the intensity distribution is biased at , the output of the differential amplifier (/7) becomes positive.

If the guide groove (71) is shifted in the +Y direction, the polarization of the diffracted light distribution will be in the opposite direction, and the output of the differential amplifier (/7) will be negative.2. In this case, a track deviation detection signal (Ts) corresponding to the direction and magnitude of the deviation of the guide groove (1) is obtained from the output of the differential amplifier (/7).

Next, we will explain the detection of defocus using the Naifetsu method using diagrams. It is inserted perpendicular to the axis (/J).

In Fig. g fal, the information recording medium (6) is the objective lens ISl.
The reflected and convergent light beam from the information recording medium 16) is incident on the center of the two light-receiving surfaces (/6a) and (/bb) of the defocus detection photodetector (/6). Therefore, the output of the differential amplifier (7g) is fbl in the same figure.
When the information recording medium (6) is located farther than the focal point, one reflected beam is incident on the light receiving surface (/6a), so the output of the differential amplifier (7g) is positive. [The figure (cl) is when the information recording medium (61) is located closer to the focal point, and the output of the differential amplifier (7g) is negative. In other words, the mirror (/2) is the knife in the knife method. do.

As described above, when a focus shift occurs, a focus shift detection signal (FS) corresponding to the direction and magnitude of the focus shift can be obtained from the output of the differential amplifier (7g). Problem 1 The conventional signal detection device described above divides the reflected light from the information recording medium into reflected light and transmitted light using a mirror inserted up to the optical axis, and pushes each reflected light. Track misalignment was detected using the pull method, and defocus detection was performed using the knife method for transmitted light, and the mirror was used as the knife in the knife method, so that the track misalignment detection signal and the defocus detection signal were not the same as the predetermined signals. amplitude.

In order to obtain a certain level of error detection sensitivity, it was necessary to insert the mirror in alignment with the optical axis with high precision. In addition, since track deviation detection is performed using a semicircular light beam that is divided into two by a mirror out of one reflected light beam, the straight line part (corresponding to the diameter) of this semicircle is used as the optical sensor for detecting track deviation. Both track deviation detection and defocus detection are performed using a semicircular light beam divided by one reflected light beam fs, resulting in greater stability compared to the case where the entire light beam is used.

There were many problems, including a lack of reliability.

This invention was made in order to solve the above-mentioned problems, and it divides the entire reflected light beam at a predetermined ratio without requiring strict arrangement precision or adjustment of mirrors, and enables stable error signal detection and detection. An object of the present invention is to obtain a signal detection device capable of detecting a reproduced signal.

Means for Solving Problem C] The signal detection device according to the present invention splits a reflected light beam from an information recording medium into reflected light and transmitted light, each of which has a circular cross-sectional shape, using a beam splitter, To detect defocus, the Naro-Foucault method is used with a roof-shaped prism and a photodetector for defocus detection having φ light-receiving surfaces, and the juxtaposed direction of the light-receiving surfaces of the photodetector is projected onto the photodetector surface. The guide grooves are arranged parallel to the direction in which the guide grooves extend.

[For production]

In this invention, since a beam splitter is used to split one reflected beam, the placement precision of one component can be relaxed, the splitting ratio of the beam can be kept constant, and the total beam of one circular cross section is used. Therefore, stable trunk shift detection signals and focus shift detection signals can be obtained.

Furthermore, by arranging the juxtaposition direction of the light-receiving surfaces of the defocus detection photodetector to be orthogonal to the extending direction of the guide groove projected onto the photodetector surface, the light from both edges of the guide groove can be Each light-receiving surface is equally affected by the diffracted light, and the above-mentioned effects are canceled in the calculated defocus detection signal. [Embodiment] Fig. 1 shows an embodiment of the present invention. (71 is the same part as the conventional device shown in Figure 5. However, the arrangement of the collimator lens (21) and polarizing beam splitter (?l) is reversed, but the basic The polarizing beam splitter (J
) The number of signal detection devices (2 pieces) to which the reflected light enters is 1
It is structured as follows. That is, the signal detection device (
Concave lens (x:t'') to expand the optical path of λ2)
A beam splitter (cog) is arranged to divide the luminous flux from the concave lens (23) into λ parts, and in the direction of the reflected light from the beam splitter (2s), there are λ light receiving surfaces (cos 5a) ( A photodetector for detecting track deviation (COS) with a photodetector for detecting track deviation (CORB),
) connected to a differential amplifier (26) and an adder (27
) are placed. There are two refractive surfaces (2ta') (cot) in the direction of the light beam transmitted through the beam splitter (cog).
rb), and the ridgeline (gc) is optically similar to the guide groove (7).
Roof-shaped prisms (cots) are arranged tσ so as to be orthogonal to the extending arrow A1 direction.

The luminous flux (29) that is split as a result of passing through the roof-shaped prism (cot) and being refracted is a luminous flux (2qtl) refracted by the refracting surface (2ra) and a luminous flux refracted by the refracting surface (yugb). It consists of (ko?b). The defocus detection photodetector (JO) is arranged to receive the light beam (29) f.
The light-receiving surfaces (30a) (30b) are divided into two parts, respectively.
) and (JOc) (JOd'), and is arranged so that the light flux (2qa) is received by the light receiving surface (, yoa) (Job) and the light flux (sqb) is received by the light receiving surface (JOC) (30d),
Furthermore, the direction in which these light-receiving surfaces (:toa) to (30eL") are arranged parallel to the direction in which the guide groove (7) projected on the surface of the sunspot shift detection photodetector (30) extends. , and the focal point of the luminous flux (ko?a) (2?b).

7 defocus detection photodetectors (30
) is connected to differential amplifiers (3/) (3),
The differential amplifier (3/) outputs the output (al
and the output of the light receiving surface (fb) (differential output of bl (a-b)
The differential amplifiers (3) have a light receiving surface rxr.
Obtain the differential output (d-c') of the output icl of the light-receiving surface (d) and the output (di) of the light-receiving surface (d).
The adder (3J) connected to the differential amplifier (3x)
)(Jλ) Add the respective outputs.

The beam splitter (cog) used to split the light beam, whose operation will be described next, has the effect of splitting the amount of light at a predetermined ratio without changing the shape of the light beam. Track deviation detection for a beam reflected by a beam splitter (2≠) is performed using the same push-pull method as in the prior art, and defocus detection for a beam transmitted through a beam splitter (2≠) is known as the Foucault method. The principle of track deviation detection is the same as that of the prior art, but in this embodiment, since detection is performed using a circular light beam, a stable track deviation detection signal can be obtained.

Next, defocus detection using the Foucault method will be explained using FIG. 2. Fig. fal shows a case where the information recording medium (6) is in focus with respect to the objective lens Isl, and the luminous flux (λ9a) divided by the refractive surface (:2ta'3 (21b)) of the roof-shaped prism (Fig. (29b'), the light receiving surface (30a) of the defocus detection photodetector (JO) and (
The light is focused at the center of 3θb), (JOc), and (, yod). In this case, the differential amplifier (3
/) (32) and the adder (Jyu) and the defocus detection signal (ald-b-c') becomes zero. %, the luminous fluxes (9a) and (2db) are incident on the outer light-receiving surfaces (30a) and (30d), respectively, so the defocus detection signal [ald-b-c') has a positive value. Become. Figure 2 (cl is the information recording medium (6)
, tl, and the light beams (29a') and (9b) are incident on the inner light-receiving surfaces (30b) and (30c), respectively, so the defocus detection signal is negative.Therefore, the defocus detection signal is negative. The direction and magnitude of the defocus detection signal (ald
-b-c).

As is clear from the above explanation, defocus detection using the Foucault method uses a circular light beam in combination with the Naifetsu method using a semicircular light beam. ) has the effect of compensating for the influence of placement error in the X direction of the guide groove (7), and a stable defocus detection signal can be obtained. Photodetector (3
0) is important in relation to the direction in which the light-receiving surfaces are juxtaposed. FIG. 3 is a diagram showing the relationship between the direction of the guide @ (71) and the direction of juxtaposition of the light-receiving surfaces in the above embodiment. In the figure, the diffracted light distribution (2o) (2/) received from both edges of the guide @ (71) spreads in the Y-Z plane direction, so as shown in the figure (bl), In the defocus detection photodetector (30), the diffracted light distribution shown by the shaded area may be in the Y-axis direction.If there is a track deviation here, the distribution of this diffracted light will be, for example, as shown in the same figure (cl. However, the light receiving surface (Joa) and (JO
b'), and the light-receiving surface (,yoc) and (JO
The intensity distribution of the first diffracted light is symmetrical with respect to the dividing line in d). Therefore, in the differentially amplified defocus detection signal, the influence of the diffracted light is canceled out, and the influence of the diffracted light due to track misalignment is canceled out. is not mixed in as a disturbance, and stable defocus detection can be performed regardless of track misalignment. Note that in the above embodiment, track misalignment detection and transmission are performed using reflected light from the beam splitter (2q). Although a configuration is shown in which defocus detection is performed using light, the opposite configuration may be used, that is, defocus detection may be performed using reflected light, and track deviation detection may be performed using transmitted light.

In addition, the direction of the reflected light from the beam splitter (2G) may be arbitrary. In addition, in the above embodiment, the defocus detection photodetector (30)
Fig. 1 shows a configuration in which two sets of two-part photodetectors are arranged in parallel, but a modified example as shown in Fig. ψ may also be used. It is arranged in a figure eight shape rather than parallel, and is a roof-shaped prism (2!; )K
Therefore, the interval between the two divided light condensing points is the same as that of the roof-shaped prism (
This method deals with the deviation from the design value due to processing accuracy or placement error of optical components in 2g), and it is possible to obtain a defocus detection signal when the distance between the focal points is within the range of 1 to 12. In the figure fbl and fcl, the two inner light-receiving surfaces are integrated to form a three-split photodetector, which has the same effect as the above embodiment. vessel(
2s), but the addition output of the defocus detection photodetector (30) or the addition output of both photodetectors (5) and (30) is shown. [Effects of the Invention] As is clear from one or more explanations, this invention may be used.

A beam splitter is used to split the reflected light beam from the information recording medium into two beams, one for track deviation detection and the other for defocus detection, and the direction in which the photodetector for defocus detection is juxtaposed is projected onto the photodetector surface. Since it is parallel to the direction in which the guide groove extends, the placement precision of optical components is relaxed, and the division ratio of the luminous flux can be set accurately to any ratio, and it is stable and reliable. This has the effect of obtaining a high signal.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIGS. 2 and 3 are illustrations of defocus detection in this embodiment, and FIG. 3 is a photodetector for detecting defocus in another embodiment. Figure 5 is a schematic layout of a conventional signal detection device, Figure 6 is a front view of
The figures are also detailed layout diagrams of the main parts, Figure 7 is an explanatory diagram of a method for detecting track deviation in a conventional signal detecting device, and Figure 2 is an explanatory diagram of a method for detecting defocus in a conventional signal detecting device. (/1... Laser light source, M1... Objective lens, (6)...
・Information recording medium, (ri)...Guide groove, (22)...Signal detection device, (2g)...Beam splitter, (2j)φ
- Photodetector for detecting track deviation, (2t)...Roof-shaped prism, (29a) (bump b)...Single divided light beam, (30)...Photodetector for detecting defocus. CJOa)~(30d)+1・Light-receiving surface. In each figure, the same reference numerals indicate the same or equivalent parts. 6. Inquiry 1 Supervisor Kago-sama stop L-J Ko 2 figure Atsushi 4 figure Bo 5 figure leather 6 figure original 7 figure

Claims (4)

[Claims] (1) In a signal detection device for optically recording and reproducing information by irradiating an information recording medium with a guide groove with a beam of light from a laser light source along the guide groove, a beam splitter that splits the reflected light beam into reflected light and transmitted light; a defocus detection means that uses one of the reflected light and transmitted light to detect the defocus of the information recording medium by the Foucault method; and the reflected light and track deviation detection means for detecting track deviation of the information recording medium by a push-pull method using the other of the transmitted light and the transmitted light, and the focus deviation detection means is divided into two parts by a roof-shaped prism. Two sets of each 2 that receive the light flux of the book
The divided defocus detection photodetector is configured such that the juxtaposition direction of the light receiving surfaces is parallel to the extending direction of the guide groove projected on the surface of the defocus detection photodetector, and the two light beams are parallel to each other. A signal detection device characterized in that the signal detection device is arranged to serve as a focal point. (2) The signal detection device according to claim 1, wherein the two dividing lines of the photodetector for detecting defocus are arranged in a figure-eight shape. (3) The signal detection device according to claim 1, wherein the inner two light-receiving surfaces of the light-receiving surfaces of the photodetector for detecting defocus are integrated. (4) The signal detection device according to claim 1, wherein the reproduction signal is detected using at least one of defocus detection means and track deviation detection means.