JPS60234237A - Optical reading device - Google Patents

Abstract

PURPOSE:To detect a focus shift with high accuracy and also to facilitate the easy control of an optical system with miniaturization of an optical reading device, by applying an asymetrical method to each of two luminous fluxes which are divided by a beam splitter in directions opposite or orthogonal to each other. CONSTITUTION:The reflected light sent from a recording medium 5 is made incident on a beam splitter 3, and the reflected luminous fluxes transmitted through a half surfaces and the other half surface separated centering on a plane formed by the optical axis and the track direction are divided in directions opposite to each other and orthogonal to an incident luminous flux. These two reflected luminous fluxes are made incident on two-split photodetecting elements 9 and 9' set at non-image forming points B and B' distant from image forming points A and A' by (x) in rear and front sides. Then a focus shift signal is obtained from the sum component of the output of a photodetecting element including a cut line of the half luminous flux of one or both of elements 9 and 9' and the difference component of one of both elements 9 and 9'. While a tracking signal is obtained from the difference component of both elements 9 and 9'.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to an optical reader that detects f'Lfc information recorded on a recording medium using light, or records information on a recording medium using light. It is related to the device.

[Prior art]

Traditionally, the astigmatism method, critical angle method,
There were asymmetric methods, SSD methods, etc.

The astigmatism method uses an optical element that causes astigmatism in the light reflected from the disk to obtain an out-of-focus signal, but it has drawbacks such as a long optical path and a narrow detection range. Ta. The critical angle method is characterized by obtaining an out-of-focus n signal behind the scenes where changes in the angle of reflected light are identified using a critical angle prism, but the setting of the critical angle prism is delicate and the sensitivity is low. There were drawbacks such as. The asymmetric method is characterized by providing a knife in the reflected optical path to block part of the beam, thereby obtaining an unfocused n signal.However, since part of the beam is blocked, there is a large loss of light quantity, and the RF multiplied signal is S/
There were drawbacks such as a decrease in the N ratio and a nonlinear error detection curve near the time of focusing. In the EISD method, the focal point n
Although there is no need to provide a special optical element for detecting out-of-focus n, the error detection curve near the time of focusing becomes non-linear, and there are two zero-crossing points. There were drawbacks such as the appearance of

A conventional example of an asymmetric method for performing focus control and tracking control of such a laser beam will be described next.

FIG. 1 shows an example of an asymmetrical method of a focus detection device in a conventional optical reading device, but is a microcosm. The light emitted from the optical meter 1 is converted into parallel light by a collimating lens □2, and is focused onto an information recording medium 5'' through a beam splitter 3 and an objective lens 4'. This light beam is reflected by an information track having a concave and convex bit shape, passes through an objective lens 4, and a beam splitter 8, and enters the inside in a direction perpendicular to the incident light beam. A blocking plate (naifetsuji) 6 that blocks about half of this reflected light flux
and a converging lens 7'f: the reflected light beam is converged through the converging lens 7'f.

An appropriate distance t1 from the imaging point A in the single focus state
．． A four-division light-receiving element 8 is placed at the non-image forming point 13. The four-division light-receiving element 8 is arranged so that the output of each light-receiving element of the four-division light-receiving element 8 is the same in a focused state. FIG. 2 shows the trajectory of the light ray and the state of the light flux on the four-split light receiving element with respect to defocus. (α) The figure shows the in-focus state) The figure shows the information recording medium 5
(C) shows a state where the information recording medium 5 is far away. Therefore, (8α+8d)−(8
b+8c), focus n information can be obtained. However, in the asymmetric method of the conventional focus detection device described above, half of the luminous flux is sacrificed due to the shield plate 7, so there is a large loss of light quantity, and the RF multiplied signal El
/ This led to deterioration of the N ratio. Furthermore, since not all of the light beam entering the lens is used, there is a problem in that several small digital bits cannot be read accurately due to a single diffraction phenomenon, similar to when a lens with a small diameter is used.

In addition, as shown in Fig. 8, the difference output of the light receiving element (8a + 8
d) -(8b +86), the slope of the error detection curve near the time of focus changes continuously with the amount of movement of the disk, and the error detection curve becomes nonlinear. For this reason, the gain of the focus servo changes with the distance traveled by the disk, making it impossible to achieve highly accurate focus servo using electrical servo. Further, the tracking Zn signal is detected from the change in direction of the first-order diffracted light due to the uneven bit string on the track of the information recording medium 6. Conventionally, as shown in FIGS. 1 and 2, a shield plate 6 is placed in a plane perpendicular to the plane -5^ formed by the tracking servo direction and the optical axis so as to divide the light beam into two. In addition, the dividing line of the four-part light receiving element had to be precisely aligned with the track direction and the tracking servo direction. The trackless n signal is (8a+8b)-(
8g +86) However, as mentioned above, it was very difficult to adjust the shield plate 7.4-divided light-receiving element 8.

[Purpose of the invention]

It is an object of the present invention to provide an optical information reading device that eliminates these drawbacks, allows an extremely compact optical system, enables highly accurate out-of-focus detection, and allows easy adjustment of the optical system. All that is offered.

[Structure of the Invention] The optical information reading device of the present invention converges light emitted from a light source to read optical information from tracks recorded on a recording medium, or when reading out optical information from tracks recorded on a recording medium, or when reading out optical information from tracks recorded on a recording medium. In focus control when recording information, the reflective point 1 is
Splitting the reflected light beam that has been filtered by the objective lens into two light beams with equal light intensity using substantially two beam splitters 6-- with the plane formed by the optical axis and the track direction as the boundary surface; The dividing line ′ (i: has A first difference obtained by subtracting the output of the light receiving element that does not include the half-luminous flux line from the output of the light-receiving element that includes the half-luminous flux line of one of the two-split light-receiving elements, which is received by a light-receiving element that is divided into at least two parts. and a second difference component obtained by subtracting the output of the light-receiving element that includes the half-luminous flux truncated line from the output of the other one of the two-split light-receiving elements that does not include the half-luminous flux truncated line, the focal point is determined. The present invention is characterized in that a tracking Zn signal is obtained from the difference components of the two or more divided light receiving elements.

〔Example〕

The present invention will be described in detail below with reference to the drawings. In FIG. 4, a light beam emitted from a light source 1 is collimated by a beam splitter 8 and a collimator lens 2, and is incident on an information recording medium 5 via an objective lens 4. The reflected light from the recording medium 6 is transmitted through the objective lens 5 and the collimator lens 2.
f, and enters the beam splitter 8 via. At this time, the reflected light flux that has passed through one half of the plane bordering the plane formed by the optical axis and the track direction, and the reflected light flux that has passed through the other half are separated by the beam splitter 8 in a direction perpendicular to the incident light flux, so that they are opposite to each other. Divided into directions. The reflected light flux that has passed through one half surface is at a non-image forming point B, which is located π behind the image forming point A.
The light enters the two-split light-receiving element 9 placed at n. The reflected light flux that has passed through the other half surface enters a two-split light receiving element 91 located at a non-imaging point B1 located a distance n in front of the imaging point A and a distance n away. Beam splitter 8 is an element that deflects a beam of light. Therefore, the optical path of the reflected light beam is folded around the interference film multilayer filter of the beam splitter 8 and divided into left and right sides.
If the half luminous flux is shown on the same diagram, it becomes Figure 5. In Fig. 5, n
The state of the light flux on the light-receiving cables 9 and 91 and the ray trajectory diagram are shown. The figure (α) shows a state in focus, the figure (α) shows a state in which the information recording medium 5 is close, and the figure 0 shows a state in which the information recording medium 5 is far away. The two-split light-receiving element is arranged so that the amount of light is equal when the focus is focused.

Only one difference component, for example, (9α-9b) or (9
'c-9'd) If f focus is n signal, the error detection curve near the time of focus becomes non-linear, as shown in Figure 8.
This is not suitable for out-of-focus n signals. Therefore, (9α-gb
) and (9'd-9'a), that is, (9α-96)
+(9'd gl,) is the unfocused n signal. For example, when the information recording medium 5 is far away, 2 in FIG. 2(C)
The state of the divided light receiving element 8 becomes the state of the two divided light receiving element 9' in FIG. 5(C), and the state of the two divided light receiving element 8 in FIG. 2Cb).
This state corresponds to the state of the two-split light-receiving element 9 shown in FIG. 5(c), so the nonlinearity of the error detection curve near the time of focusing disappears by taking complementary signals, as shown in FIG. 6. Similarly, the error detection curve is a curve with very good linearity. Moreover,
Since the error detection range is very wide, the focusing servo can be pulled in very well.

In addition, as shown in FIG. 4, the track shift signal can be obtained by simply adjusting the intersection line of the multilayer films of the beam splitter 8 in the track direction. d)
You can get more. This is because when a track zn occurs, the first-order diffracted light generated by the track hits 9 and 91 with different intensities. Also, the RF multiplied signal, the sum of the signals from each light receiving element, that is, C9a+9b)+(9' c
+9' d) gives you tails.

In the above embodiment, the light beam incident on the beam splitter is a diverging light beam, but the same effect can be obtained by inserting a collimator lens between the light source and the beam splitter and inserting convex lenses on both sides of the beam splitter 9. You can get it.

Note that the beam splitter used in the above embodiment may be a half mirror, or a polarizing beam splitter and a 1/4 beam splitter.
A combination of wave plates may also be used. In addition, a beam splitter is a device that distributes the reflected light flux in an equal amount in a direction perpendicular to the incident light flux, in opposite directions, or in directions orthogonal to each other.
-n, any &10^ deflected electrons may be used. For example, as shown in FIG. 7, the luminous flux e [2 pollution 1] may be set in the intersecting direction with the track direction as the boundary.

〔Effect of the invention〕

As described above, according to the present invention, the beam splitter 8
It is possible to carry out the asymmetric method without using a shield plate for each of the two luminous fluxes that are separated by By taking this method, it is possible to obtain a focus error signal with no nonlinearity in the error detection curve. In addition, the detection range for defocus n can be widened, and at the same time, there is no loss of light quantity, and the S/N ratio of the RF signal can be greatly improved. Furthermore, the optical system is very easy to adjust, is very small, and has a simple optical system.

[Brief explanation of the drawing]

FIG. 1 is a diagram of an optical system in a conventional asymmetric focal pointless 7L detection method. Figure 2 shows (a) the trajectory of the ray when in focus and the state of the light flux on the 4-split light-receiving element in the conventional asymmetric defocus detection method. Light flux state (6) A diagram showing the light ray locus and the light flux state on the 4-split light receiving element when the information recording medium moves away. FIG. 8 is a diagram showing the relationship between the amount of movement of the information recording medium and the amount of error signal in the conventional asymmetric method. FIG. 4 is a diagram of the optical system according to the present invention. FIG. α) Ray trajectory when in focus and respective luminous flux states on the two-split light-receiving element (b) Ray trajectory and 2 minutes when the information recording medium approaches. (C) A diagram showing the trajectory of the light beam when the information recording medium moves away from the side light receiving element and the state of the light flux on the two-split light receiving element. Fig. 6 is a diagram showing the relationship between the amount of movement of the information recording medium and the amount of error signal in the defocus n detection method according to the present invention. Yes. Applicant: Seiko Electronic Industries Co., Ltd. Agent, Patent Attorney: Mogami, 13- Figure 5, Figure 6, 99' Figure 7

Claims (1)

[Scope of Claims] (1) In an optical reading device that detects recorded information on a disc using light or records information on a disc using light, from a light source on an optical path connecting the light source and the disc surface,
At least, the objective lens of the beam splitter 1 is arranged, and on the optical path connecting the disk surface and the light receiving element, at least the plane formed by the objective lens, the optical axis, and the track direction is set as a boundary surface from the disk surface. A beam splitter that divides the light beam into two half-beams of equal light intensity is placed equidistantly from the imaging point of each of the two half-beams of n1, one at a position close to the disk and the other at a position farther from the disk. , at least two having weight lines parallel to the truncation line of the half-luminous flux
An optical reading device characterized by an arrangement of light-receiving elements that are more than divided! . (2) The focus n signal is a first difference component obtained by subtracting the output of the light receiving element that does not include the half-luminous flux tangent from the output of one of the two-split light receiving elements that includes the half-luminous flux tangent; It is characterized in that it is obtained from the sum component of a second difference component obtained by subtracting the output of the light receiving element that includes the half luminous flux tangent from the output of the other of the two-split light receiving elements that does not include the half luminous flux tangent. An optical reading device according to claim α). (8) The optical reading device according to claim (1), wherein the tracking deviation signal is obtained from a difference component between the two or more divided light receiving elements.