JPS6035338A - Optical reader - Google Patents

Abstract

PURPOSE:To widen the detection permissible range of focus errors and to realize adjustmentless assembly by constituting a photodetector in a three-dimensional shape, and providing a photodetection surface to its flank. CONSTITUTION:A focus error signal is obtained as SB-(SC1+SC2) by photodetection areas B-C, and focus control is performed on this focus error signal. When a disk D is in an in-focus state, reflected luminous flux is projected upon the photodetection surface of the photodetector P in relation SB-(SC1+SC2). When the disk D is displaced approaching an object lens 4, SB-(SC1+SC2) becomes negative. When the disk D moves away from the objective lens 4, the output difference SB-(SC1+SC2) becomes positive. Then, the objective lens 4, and a laser light source L or the whole optical system are moved on the basis of the positive or negative output difference SB-(SC1+SC2) due to the out-of-phase state of the disk so that the output difference SB-(SC1+SC2) is eliminated, and thus the disk is put in focus, performing focus control.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical reading device, and more particularly to an optical reading device having a focus control function.

BACKGROUND ART AND PROBLEMS Conventionally, in optical reading devices, in order to obtain a focus error signal for focus control, the astigmatism method,
Foucault method, critical angle method, etc. were used.

However, in these methods, the reflected light beam from the optical recording medium is passed through a lens or prism having a special shape, and the focus error is detected by utilizing the specificity of the shape. Therefore, it is extremely difficult to process the lenses and prisms, making the optical system expensive, and the performance of the specificity directly affects the quality of the focus error signal obtained by detection. <Fj! 'I Jl'E!
ie It has the disadvantage of being ugly.

Purpose of the Invention The present invention eliminates such conventional drawbacks and detects focus errors using an inexpensive optical system without using lenses or prisms whose specificity performance is directly linked to the quality of focus error signals. It is an object of the present invention to provide an optical reading device that has a wide tolerance range and allows adjustment-free assembly.

SUMMARY OF THE INVENTION The present invention converges a light beam emitted from a light source onto a signal surface of an optical recording medium using an objective lens, and converges a reflected light beam reflected from the signal surface of the optical recording medium into a spot shape. In an optical reading device in which light enters a light receiving surface of a photodetector through an objective lens, the photodetector is formed into a three-dimensional shape having a light receiving surface on a side surface through which at least a part of the outer circumference of the reflected light beam is incident. first and second light-receiving areas for receiving the outer periphery of the reflected light beam are provided on the side surface so as to be arranged one after another along the direction of the optical axis of the reflected light beam; A focus error signal is obtained from the difference in output corresponding to the amount of light received by each of the light receiving area and the second light receiving area. With this configuration, there is no need to use specially shaped lenses or prisms as in the past (where specificity performance directly affects the quality of the focus error signal), and an inexpensive optical system can be used. can be provided. Furthermore, since the focus error detection range is widened, it becomes possible to assemble the heat control.

Embodiment An embodiment of the optical reading device of the present invention will be described with reference to the drawings.

FIG. 1 is an overall diagram of the optical system.

Laser) "0 source 1" The emitted light beam is an example of a beam splitter, which separates the light beam with different polarization axes and changes the direction of the light beam in the forward and backward paths, making it a polarized beam that does not return the reflected light beam to the laser light source. The light is input to the splitter (1).

This polarized light and a part of the light flux transmitted through the splitter (1) are
The collimator lens (2) converts the light into a parallel beam. The parallel light flux passes through the wavelength plate (3) and the objective lens (
4), the light is focused into a single fine spot on the signal surface of the disk D, which is an example of an optical recording medium.

On the signal surface of the disk D, spiral or concentric tracks are formed. This track is composed of pit rows modulated by video or sound P information, or both information.

The reflected light beam reflected by the signal surface of the disk D and modulated by the pit row is picked up by an objective lens (4) and converted into a parallel light beam. The reflected light flux, which has been converted into a parallel light flux, follows the optical path in the opposite direction and goes back to the polarizing beam splitter (1) via the wavelength plate (3) and collimator lens (2) in sequence
). At this time, since the light beam passes through the wave plate (3) twice in a round trip, the polarization axis is rotated by 90 degrees compared to the light beam from the original laser light source.

Therefore, the reflected light beam is reflected without returning to the laser light source side, and the convergent light is incident on the light receiving surface of the photodetector P and is received.

Note that the arrow a indicates the tangential direction of the track on the signal surface of the disk D, and the arrow a' indicates the tangential direction of the track to be projected.

The photodetector P has a cylindrical shape as shown in an enlarged view in FIG. 2, and has a top surface (5) and a circumferential side surface (6) of its outer surfaces as light-receiving surfaces. The photodetector P is arranged so that its axis coincides with the optical axis of the reflected light beam.

The outer peripheral portion of the converged reflected light beam from the polarizing beam brick (1) is made incident on the circumferential side surface (6) centered on the optical axis. Then, a light receiving area A is provided on the upper surface (5) of C1, and a light receiving area B is provided on the upper side and a light receiving area C is provided on the lower side, arranged in the direction of the optical axis on the circumferential side surface (6). It is being These light receiving areas 13, C have a ring shape centered on the optical axis. Note that the light receiving area C
is composed of a pair of received light amounts +p, C1, and C2, which are divided into two in a direction perpendicular to the tangential direction a' of the projected track. And these light receiving areas A, B, C
1 and C2 each have an output end, and the output 8 corresponds to the amount of received light.
Output A1SB%Sc1, SC2.

With this configuration, the reflected light beam from the polarizing beam splitter (1) is directed to the photodetector P in the light receiving area A as shown in FIG.
, C (C1, C2). Then, the pit signal (reproduction information signal) is transmitted to the light receiving areas A and C (C1, C2).
The sum of the respective outputs sA+8B+S. to l+sc2. 1;
That's what you get.

Next, the focus error signal is the light receiving area B - C (C1+
C2) is obtained as ``B (Sc+ + Sc2), and the focus control i!if is performed based on this error signal.If the disc (■) is in the focused state, the photodetector The reflected light flux projected onto the light receiving surface of P is 8B (bcl +Sc2) -Q
``It is projected so that the 1-1 relationship holds true.

However, if the disk D deviates from the in-focus state and the disk D deviates in the direction approaching the objective lens (4), the projection radius of the reflected light beam becomes a dog, and becomes larger than the output SB. The output (ScH+SC2,) becomes larger, and the label -(S(-14-8C2) becomes negative.Also, if the disk 1) moves away from the objective lens (4), In the above case (!: upside down, the output difference Sn (
Sc1+ 5C2) becomes positive.

In this way, the positive or negative output difference 5B (Sc1 + 5C2) due to the deviation from the focused state of the disc D is also realized,
Focus control is performed by cutting the objective lens (4), the laser light source, or the entire optical system so that the output difference SB (8C1+5C2) becomes zero.

Note that the tracking error signal is generated as 5c1-8C2 by the light receiving areas C1 and C2 by the push-pull method. Tracking control is performed based on this signal.

The photodetector P is formed into a cylindrical three-dimensional shape with the outer peripheral part of the reflected light from the disk D incident on the circumferential side surface (6), and the focus is adjusted. Since errors and tracking errors are detected, it is possible to provide an inexpensive optical system that does not require specially shaped lenses or prisms as in the past.

In addition, since the inclination of the circumferential side surface (6) of the photodetector P, which is configured in a cylindrical shape as shown in FIG. i
(m) If the angle of incidence on (6) can be selected appropriately, the detection tolerance range for focus errors and tracking errors becomes wider, and assembly without adjustment becomes possible.

Although a cylindrical photodetector P was used in this embodiment, the present invention is not limited to this.
, other columnar shapes (prismatic etc.) or figures 3 and 4.
It may be configured in the same manner as described above using a cone-shaped object (including a truncated circular truncated or truncated pyramid-shaped one) such as a circular IL or an angle (Mlj) shown in the figure.

Further, in this embodiment, a case has been described in which a convergent light beam that is converged into a conical shape is incident on the light receiving surface of the photodetector P, but the present invention is not limited to this, and the present invention The light receiving surface of the photodetector P can be made into a cube or a rectangular parallelepiped as shown in Fig. 15.Then, the optical system can be constructed. Of course, a 1/lens system or the like can be constructed so as to obtain a pyramid-shaped convergent light beam (reflected light beam).

Furthermore, in this embodiment, a case has been described in which the reflected light beam from the disk D becomes a convergent light beam and is incident on the light receiving surface of the photodetector P. However, the present invention is not limited to this; The light beam may be incident on the light-receiving surface of the photodetector P as a flat fj light beam and a diverging light beam. In this case, the three-dimensional shape of the photodetector P may be, for example, an S body shape (cone, angle 1llft+, circle (11; platform, A truncated pyramid (such as a truncated pyramid) can be considered, and it is sufficient to form the receiving area C as described above.

Effects of the Invention As described above, if the present invention is used, the following advantages can be achieved.

(1) Since the light-receiving surface of the photodetector has a three-dimensional shape, there is no need for specially shaped lenses or prisms as in the past, and an inexpensive optical system can be provided.

(2) Since the photodetector has a three-dimensional shape and has a light-receiving surface on its side, the angle of inclination of the side and the reflection plate C
:If we choose the relationship between the angles of incidence on the sides of the bundle appropriately,
The detection tolerance range for focus errors is widened, and therefore adjustment-free assembly is possible.

[Brief explanation of the drawing]

Fig. 1 is an overall view of the optical system for explaining the assembly of the optical reading device of the present invention, Fig. 2 is an enlarged view of the photodetector shown in Fig. 1, and Figs. 3 to 5 are FIG. 7 is an external view showing another example of a photodetector. In addition, in the symbols used in the drawings, (4)...... Objective lens (6)...
・・・・・・・・・Side P・・・Yuyuki photodetector L・・・・・・・・・Laser light source D・・・・・・
・It is a listening disk. Agent Masaru Doyo〃 Yoshio Tsunekako〃 Toshiki Sugiura

Claims (1)

[Claims] The light beam emitted from the light source is converged into a spot on the signal surface of the optical recording medium by the objective lens, and the reflected light beam reflected from the signal surface of the optical recording medium is directed to the photodetector via the objective lens. In an optical reading device that makes light enter a light-receiving surface, the photodetector is configured in a three-dimensional shape having a light-receiving surface on a side surface into which at least a part of the outer circumference of the reflected light beam is incident, and the light detector receives the outer circumference of the reflected light beam. first and second light-receiving regions are provided on the side surface so as to be arranged one after the other along the direction of the optical axis of the reflected light beam, and the first and second light-receiving regions are respectively provided on the side surface. 1. An optical reading device characterized in that a focus error signal is obtained by a difference in output corresponding to the amount of received light.