JPS61230635A - Optical pickup - Google Patents

Abstract

PURPOSE:To attain miniaturization of an optical pickup by providing a two-split photodetector which masks partly the light, another two-split photodetector containing a condenser lens unified with a lens which condenses the remaining unmasked reflected light and a photodetector which detects a focus error signal out of the focused light transmitted through the condenser lens at the radiation terminal for reflected light given from an optical recording medium. CONSTITUTION:The light (a) given from a light source reaches an optical disk through a beam splitter 4, and the reflected light (b) of the optical disk is sent again to the splitter 4 to undergo the separation of its optical path and passed through a condenser lens 15. The half of the light (b) is cut by a photodetector 16 which serves as a two-split photodetector. Then the detector 16 detects a tracking error signal. A division line l1 of a condenser lens serving as a protecting cover 15 is orthogonal to an image of an information track on the optical disk formed by the detector 16. While a division line l2 is set parallel with the image of the information track. The focused light passed through the lens 15 is made incident on a two-split photodetector 14 for focus to produce a focus error signal.

Description

[Detailed description of the invention] [Industrial field of application] The present invention focuses light such as a laser into a spot with a minute diameter,
The present invention relates to an optical pickup in a device that records and reproduces signals at high density by illuminating an optical disk or the like.

[Summary of the invention]

The present invention provides an optical pickup for recording and reproducing information on and from an optical recording medium. , a two-split photodetector with a condensing lens created by integrating a lens that condenses the remaining light that was not blocked by this, and a photodetector that detects all focus error signals, By detecting the tracking error signal from the difference signal of the split photodetector and the information signal from the sum signal, the conventionally used reflected light splitting mirror can be eliminated, the number of optical components and mounting space can be reduced, and the number of optical components and mounting space can be reduced. Since the light splitting means is integrated with the condensing lens, the polarity of the focus error signal does not reverse, and the focus pull-in range can be widened.

[Conventional technology]

Figure 4 shows the conventional configuration of an optical recording and reproducing device.
In the figure, 1 is a light source such as a semiconductor laser, and 2 is a condensing lens that condenses the diverging light of the semiconductor laser and converts it into substantially parallel light. Reference numeral 8 denotes a beam shape conversion optical system that converts the cross-sectional shape of an incident beam and outputs light α having a substantially circular beam cross section. Incidentally, in an apparatus that only reproduces signals recorded in advance on a disk, the optical system 8 may be omitted. Reference numeral 4 denotes a polarizing beam sub-objective lens, which condenses the incident light α into a minute beam with a diameter of about 1 μm and irradiates it onto the optical disk. Reference numeral 8 denotes an objective lens drive device that drives the objective lens 7 in a direction perpendicular to the disk for known focus control, and also drives the objective lens 7 perpendicular to an information track on the optical disk to be described later for known tracking control. The driving method is, for example, a well-known 18τ electromagnetic force. Reference numeral 9 indicates a part of the optical disk, which is rotated by a disk drive motor or the like (not shown). 10 shows the information tracks included in the optical disc 9. In discs that only reproduce signals, the tracks are formed by recorded signals, and in discs VC that record and reproduce signals, tracks are formed with an optical recording thin film attached. The reflected light on the information track 1o on the disk formed by the guide groove etc. is reflected by the objective lens 7, the total reflection mirror 6, and the plate 5.
It returns through the polarizing beam splitter 4, where it is separated from the incident optical path and enters an optical system that detects the two reflected signals.

This optical system includes a condenser lens 11, a split mirror 12. Tracking photodetector 13, focusing photodetector 14
It consists of The condensing lens 11 collects substantially parallel reflected light b
The 1-split mirror 12 that converts the convergent light into a single beam totally reflects half of the convergent light, and allows the other half to pass through.

The dividing line S of the dividing mirror 12 is set to be approximately perpendicular to the image of the information track on the disk at the dividing mirror. The tracking photodetector 13 is located on the dividing line!
It is composed of a P/N photodiode etc. divided into two by l, and is placed at a position VC away from the focal length of the condensing lens 11, and changes in the diffraction image of the information track 1o. and detect the tracking error signal. Specifically, the tracking error signal is detected by taking the difference in the outputs of the two divided detectors. On the other hand, the reproduction output of the signal recorded on the information track 1o is obtained from the sum signal of the two tracking photodetectors. The focusing photodetector 14 is
It is placed near the focal length of the condenser lens 11.

This is also a dividing line! It consists of two optically divided photodetectors, and a focus error signal is obtained by taking the difference signal between the two. The dividing line No. 1 on the tracking photodetector 13 is set to be parallel to the image of the information track 10 on the tracking photodetector 13. Photodetector 1 for side focus
The dividing line i3 on 4 is the information track 1 on 14.
It is set to be orthogonal to the image of 0.

FIG. 5 is a plan view of the reflective optical system shown to make the above explanation easier to understand. Sails that are the same as those in figure 4 are given the same numbers and symbols.

[Problems and Objectives to be Solved by the Invention] The structure of the optical pickup used in the conventional optical recording/reproducing device has been described above. This conventional configuration has a large number of parts;
Moreover, as optical pickups become smaller, mutual optical elements can be installed.

It had the disadvantage of complicated stability and adjustment.

Specifically, in order to divide one reflected light into two, a two-split mirror 1 is used.
2i is required, and if dust or dirt adheres to this mirror, or if the mirror is displaced due to temperature changes, vibrations, etc., both of the servo signals mentioned above will be disturbed and the control characteristics will be deteriorated. Also in FIG.

When the oxidation point F of the information track on the focusing photodetector 14 comes closer to the focusing L/lens 11 than the split □ mirror 12 before focus control is applied or during operation, the peak of the focus error signal is reversed. death.

It has the disadvantage that the focus pull-in range cannot be widened.

In order to widen the focus pull-in range, it is necessary to bring the five-divided mirror 12 as close to the condenser lens 11 as possible.

Next, the reason why the focus pull-in range is limited will be described. FIG. 6 shows the relationship between the focus error signal obtained in FIGS. 4 and 5 and the distance between the objective lens 7 and the disc 9. When the point J is closer to the lens 7 and 11 (where the point J coincides with the lens 7), the image point F by the lens 7 and 11 K of the 5 points J is formed at a place farther from the photodetector I4, and as the disk 9 becomes farther away from the lens 7, The position of the focusing photodetector 14 is set so that the image point F approaches 14 VC and the differential output of 14 becomes zero at the in-focus position. The point indicated by α in FIG. 6 is the in-focus position. As the disk 9 further moves away from the objective lens 7, the image point F approaches the splitting mirror 12 rather than the photodetector 14, and finally reaches the disk side from the photodetector 12 (point β in FIG. 6).

To explain the situation at this time using FIG. 5, when the image point F enters between the split mirror 12 and the condenser lens 11,
2Vc The incident reflected light image is reversed, and the left half of the reflected light goes to the photodetector 13K, and the right half goes to the photodetector 14.
When point F is between 12 and 14, completely opposite light reaches 14, the polarity of the focus error signal is reversed at point β in FIG. 6, and the distance between objective lens 7 and disk 9 is larger than β. In this case, the focus servo cannot be retracted. In FIG. 6, the range b O<2<β is the retractable range. Ideally, the characteristics shown by the dotted line in FIG. 6 are the best, and in this case, focus servo pull-in is possible over a wide range of X values.

The present invention solves the problems in conventional devices as described above, and its objectives are (1) to reduce the number of parts and reduce the size of the device, and (2) to provide a stable device that is resistant to changes over time. Our objective is to provide an optical pickup with servo customization.

[Failure to solve the problem]

The optical pickup of the present invention includes a light beam splitting means for directing light emitted from a light source toward a photoacoustic optical recording medium and guiding reflected light from the optical recording medium to a reflective optical system, placed close to or glued to the output end of the reflected light.

It was created by integrating the two-split photodetector that partially blocks the light from the output end and the lens that collects the remaining reflected light that was not blocked by the two-split photodetector. It consists of a two-split photodetector with a condenser lens and a photodetector that detects a focus error signal from the convergent light transmitted through the condenser lens.

The special enemy is to detect an information signal from the sum signal of the two-split photodetector and a tracking error signal from the difference signal.

[Function] According to the above configuration of the present invention, since the focusing photodetector and the tracking photodetector are present on the same optical path, the number of optical components and the mounting space can be reduced. In addition, since the 5-reflection beam splitter is not used, the adverse effect on the servo characteristics due to changes over time can be eliminated. Since the reflected light splitting means is integrated with the condensing lens, the polarity of the focus error signal does not invert, and the focus servo pull-in range can be widened.

〔Example〕

FIG. 1 shows an example of the configuration of an optical pickup according to the present invention, and the same parts as in the conventional example shown in FIG. 4 are given the same numbers and symbols.

In FIG. 1, light a emitted from a light source passes through a beam splitter 4 and reaches an optical disk.

The reflected light from the optical disk is returned to the beam splitter 4.
The optical path is separated here. And passed all 15,
Here, half of the reflected light is blocked by 16. Second
The figure shows a view of the reflected beams 15 and 16 from the traveling direction. 16 is a two-split photodetector that detects all the tracking error signals. 1.5Fi16t - A protective cover made of transparent resin or the like for protection, one side of which is a lens that converges the reflected light bf. If it is essential, then 16
The lens surface is coated with an anti-reflection coating, and the dividing line! 1 is perpendicular to the 1.6 K point of the information track on the optical disk, and the dividing line A of 16 is parallel to the image of the information track. The convergent light that has passed through the lens 15 is incident on a two-split focusing photodetector 14 placed near the focal length of this lens, producing a focus error signal.

On the other hand, the reproduction output of the information signal recorded on the information track is obtained from the Irl-sum signal of the two tracking photodetectors 16.

FIG. 8 shows another example of the structure of the optical pickup according to the present invention, in which the same parts as in FIGS. 1 and 2 are given the same numbers and symbols. Here, 17 is a protective cover made of transparent resin or the like to protect the two-split photodetector 16, and the light emitting surface serves as a lens that converges the light transmitted through 17. And this 17 is the beam splitter 4
It is glued into one piece.

〔Effect of the invention〕

As described above, the present invention has the following effects.

(1) The reflected light splitting error in the conventional example is eliminated, and the track photodetector and focus photodetector are placed on the same optical path, resulting in a reduction in the number of optical components and mounting space.

(2) Since the reflected light splitting means is integrated with the condensing lens, the polarity of the focus difference signal does not reverse as in the conventional example, and the focus pull-in range is wide and the servo operation is stable.

-1] - (8) By integrating the beam splitter 4 and the photodetector 16'lk, it is possible to prevent mounting misalignment between the two, temperature changes, etc.
It is possible to prevent mutual misalignment.

[Brief explanation of the drawing]

Fig. 1 is a detailed view of the reflective optical system according to the present invention, Fig. 2 is a plan view of the main components of Fig. 1, and Fig. 8 is a reflective optical system that integrates a beam splitter and a two-split photodetector with a condensing lens. Detailed diagram of the optical system. Figure 4 is a diagram showing the optical system of a conventional optical pickup. Figure 5 is a diagram showing details of the reflective optical system in Figure 4. Figure 6 is a diagram showing the focus error signal and the disk objective. FIG. 3 is a diagram showing the relationship with the distance between lenses. l: Light source 2: Condensing lens 8: Beam shape conversion λ optical system 4: Polarizing beam splitter 5: 1 plate 6: Total reflection mirror 7: Objective lens 8: Objective lens drive device
9: Optical disc lO: Information track 11: Condensing lens 12: Split tler 13, 14: Photodetector 1
5: Condensing lens and protective cover 16: Hikarito (Hama Junka type medium)

Claims (1)

[Claims] a beam splitting means for directing the light emitted from the light source toward an optical recording medium and guiding the reflected light from the optical recording medium to a reflective optical system; A two-split photodetector that is bonded and arranged and partially blocks light from the output end, and a lens that collects the remainder of the reflected light that is not blocked by the two-split photodetector are integrated. With condensing lens created 2
An optical system comprising a split photodetector and a photodetector that detects a focus error signal, and detects an information signal from a sum signal of the two-split photodetector and a tracking error signal from a difference signal. pick up.