JPS63237226A - Optical pickup device - Google Patents

Abstract

PURPOSE:To attain accurate tracking control by providing light-receiving elements in a fixed optical system and providing a roof prism which light- receives the linear transmitted light of a laser beam from the side of the fixed optical system and reflects it to the side of the light-receiving elements in return in a shifting optical system. CONSTITUTION:The fixed optical system 11 which is fixed to a device at a side below an optical disk 10 is provided, and a semiconductor laser 12, a coupling lens 13 and a beam splitter 14 are provided in the optical system 11. The shifting optical system 15 which is separated in the radius direction of the optical system 11 and positioned under the disk is provided. The optical system 15 is provided so that it can be movably displaced in the tracking direction of the disk 10, and an objective lens 16 which focuses the laser beam with respect to the disk 10 is provided. The roof prism 24 receiving the linear transmitting light which is injected from the side of the optical system 11 and transmits a beam splitter 17 as a detection light 23 is provided in the optical system 15. The light-receiving elements 25a and 25b receiving the detection light 23 which is reflected in the mirror in return are provided in the optical system 11, and accurate tracking can be executed.

Description

TECHNICAL FIELD The present invention relates to a separate optical pickup device for writing, recording, or erasing information on an optical information recording medium such as an optical disk, or for reading and reproducing information from an optical information recording medium.

BACKGROUND TECHNOLOGY In general, this type of optical pickup records, erases, and reproduces information by irradiating an optical information recording medium (optical disk) with a laser beam that is narrowed down to a minute spot using an objective lens. It is attracting attention as a large capacity memory. Such optical disk systems are characterized by their large capacity and the fact that the optical disks are removable.

Here, since the size of the information bit of an optical disk is very small, about 1 μm, focusing control, tracking control, and seek control are required to accurately record or reproduce information, as is well known. Generally, focusing control is performed by displacing the objective lens in the optical axis direction, and tracking control is performed by displacing the objective lens in the tracking direction. As for seek control, the mainstream is to once displace the entire optical pickup to the vicinity of the target track by coarse control, and then to perform fine control.

However, compared to conventional magnetic disk drives, optical pickups generally weigh several hundred grams in total. For this reason, in a control method in which the entire optical pickup is displaced in the tracking direction, the inertia of the optical pickup becomes an obstacle when the objective lens performs a seek operation to bring the laser spot position to a position near a desired track. This makes high-speed seek operations difficult and takes a long access time.

Therefore, in recent years, separate type (actuator seek type) optical pickups have been studied in order to realize high-speed access.

FIG. 4 schematically shows such a separate optical pickup. That is, a moving optical system 2 in an optical pickup is provided which faces the surface of an optical disk 1 and seeks in the radial direction of the optical disk 1 as an optical information recording medium, and a fixed optical system 3 optically coupled to this moving optical system 2 serves as an apparatus. (carriage)
It is fixedly installed. Here, the movable optical system 2 is provided with a deflection prism 4 that couples the laser beam horizontally (parallel to the disk) with the fixed optical system 3, and an objective lens 5 that faces the optical disk 1. . On the other hand, in addition to a light source, generally a semiconductor laser, the fixed optical system 3 is also provided with a detection system for obtaining a focusing signal, a tracking signal, and an RF flaw signal for reading and reproducing. The track signal is detected using the well-known far field method.
The focus signal is detected using the astigmatism method, and the information signal (RF scratch signal is detected using the differential output of the light receiving element for these detections.In addition, in Fig. 3, the tracking direction is determined when the optical disc 1 is placed in the device. This refers to the radial direction of the optical disc 1 in the set state, that is, the left-right direction.

In such a configuration, the separation type optical pickup is characterized in that the movable optical system 2 equipped with the objective lens 5 can be displaced in the tracking direction of the optical disk 1 with respect to the fixed optical system 3.

Considering its operation, first, the laser beam emitted from the fixed optical system 3 side enters the deflection prism 4 in the moving optical system 2, and is reflected toward the objective lens 5 side. The objective lens 5 focuses the light onto the optical disk 1 to a predetermined spot diameter. Thereafter, the reflected light from the optical disc 1 returns to the fixed optical system 3 through the opposite optical path. This serves for reading information on the optical disc 1, focusing, tracking control, etc.

Here, the principle of tracking signal detection will be explained with reference to FIG. First, FIG. 5(a) shows a case where a laser spot 6 focused by an objective lens 5 is irradiated onto the center of a track 7 of an optical disc 1. In FIG. In this case, since the laser spot 6 is focused on the center of the track 7, it is diffracted by the track 7 symmetrically. As a result, each of the light receiving elements 8a and 8b of the two-divided light receiving element 8 for tracking signal detection disposed in the fixed optical system 3
As shown above, the diffraction pattern 9 is bilaterally symmetrical.

As a result, the output A of each of the two light receiving elements 8a and 8b,
B becomes A=B, which means that B is the correct tracking position. However, the irradiation position of laser spot 6 is
As shown in Figure (b), if the track 7 deviates from the center position, the diffraction pattern 9 becomes asymmetrical, and the light receiving element 8a
, 8b produces a difference in magnitude between the outputs A and B of the outputs A and B. Therefore, tracking control is performed so that the difference between the outputs A and B disappears.

In this type of operation, a separate optical pickup
Tracking control is performed by displacing and moving only the moving optical system 2, which has a small mass, so the energy required for these displacement operations is small, and high-speed access (for example, access within 100 m5ec) is possible. becomes.

However, such a separate optical pickup has the following drawbacks. That is, the movable optical system 2 is displaced up and down while the carriage is moving, or the angle (parallelism) between the moving axis of the carriage and the optical axis of the parallel light beam emitted from the fixed optical system 3 side does not match. As the moving optical system 2 moves on the carriage, an offset occurs in the tracking signal. Furthermore, if the moving optical system 2 is displaced during the access operation due to rattling of the carriage, adhesion of dust, etc., an offset will occur in the tracking signal.

This point will now be explained with reference to FIGS. 6 and 7. First, when the deflection prism 4 is at the initial position as shown by the solid line in FIG. 6, the diffraction pattern 9 on the light receiving element 8 for tracking detection also becomes a solid line state. At this time, the offset value of the detection signal obtained from the light receiving element 8 is set to O by initial adjustment as shown in FIG. 7(a). When the deflection prism 4 is displaced upward by a dimension d, for example, as shown by the imaginary line in FIG. The optical axis of the laser beam that goes to the light receiving element 8 in the fixed optical system 3 through
will be displaced upward. As a result, the diffraction pattern 9 on the light receiving element 8 is also displaced as shown by the virtual line. As a result, the detection signal obtained from the light receiving element 8 is
As shown in Figure (b), an offset occurs compared to the initial state. According to the tracking detection signal that is offset in this way, the laser spot 6 is tracked to a position shifted from the center position of the track 7,
In the end, an error of Δ is produced.

As a result, accurate recording and reproduction cannot be performed.

In any case, if an offset occurs in the tracking signal, the spot will not be irradiated onto the center of the track, making the tracking operation unstable.

This also deteriorates information recording, reproducing, or erasing characteristics. Furthermore, assembly and adjustment accuracy may be improved in order to reduce deviations in optical axis parallelism and play, but this increases cost.

Purpose The present invention was made in view of the above points, and is a separable optical pickup capable of high-speed access, which uses a moving optical system. It is an object of the present invention to provide an optical pickup device capable of accurate tracking control without causing an offset in a tracking error signal even if there is a vertical shift.

Structure In order to achieve the above object, the present invention includes an optical information recording medium, a semiconductor laser that emits a laser beam, and an objective lens that focuses the laser beam onto the optical information recording medium. In an optical pickup device for recording, reproducing, or erasing information on an information recording medium, a fixed optical system including at least the semiconductor laser and a fixed position in the device is provided, and the objective lens and the light emitted from the semiconductor laser are provided. a deflection member that guides the laser beam to the objective lens side; and a roof mirror that returns and reflects the laser light emitted from the semiconductor laser toward the deflection member and transmitted straight through the deflection member toward the fixed optical system side. The present invention is characterized in that a moving optical system is provided that is mounted and moves with respect to the optical information recording medium, and a light receiving element is provided that is disposed within the fixed optical system and receives light reflected by the roof mirror.

Hereinafter, one embodiment of the present invention will be described based on FIGS. 1 and 2. First, an optical disc 1 as an optical information recording medium
0 is set. And such optical disc 1
A fixed optical system 11 fixed to the apparatus is provided on the lower surface side of the optical system 1. This fixed optical system 11 includes a semiconductor laser 12 that emits a laser beam, a coupling lens 13 that converts the emitted laser beam into a parallel beam, and a fixed optical system that converts the parallel beam in parallel to the optical disk 10. ll
A beam splitter 14 is provided with a reflective film 14a that reflects the light to the outside.

On the other hand, such a fixed optical system 11 is different from a movable optical system 1 located on the lower surface of the optical disk 10 at a position separated in the radial direction.
5 is provided. This moving optical system 15 is movably provided so that it can be displaced in the tracking direction of the optical disc 10, and first, it faces the lower surface of the optical disc 10 and emits a laser beam onto the optical disc 10 as a minute laser spot. An objective lens 16 for condensing light is provided. Also, the beam splitter 1 of the fixed optical system 11
A beam splitter 17 is provided as a deflecting member that guides the laser beam reflected by the laser beam to the objective lens 16 side. That is, this beam splitter 17 includes a 45° reflective film 17a that transmits a part of the light from the beam splitter 14 and reflects most of it.

Further, the reflected light from the optical disc 10 is reflected by an objective lens 16.
After passing through the beam, some light beams are reflected by the reflective film 17a of the beam splitter 17 and head toward the fixed optical system 11 again. Such a light beam is separated from the incident light by the beam splitter 14, and the optical path after passing through the reflective film 14a includes the beam splitter 18 and the detection lens 19.
, a cylindrical lens 20 and a light receiving element 21 for detecting focusing using an astigmatism method are provided. Further, a light receiving element 22 consisting of two divided light receiving elements 22a and 22b for tracking is provided, which receives the light reflected by the reflective film 18a of the beam splitter 18 by a far field method. Note that the original signal reading and reproduction is obtained by the differential outputs of these light receiving elements 21 and 22.

Therefore, the light emitted from the fixed optical system 11 side enters the moving optical system 15, and the reflection film 1 of the beam splitter 17 enters the moving optical system 15.
A roof mirror 24 is provided which receives, as detection light 23, the light that passes straight through 7a (appropriately, the amount of light is 10% or less of the light reflected by the reflective film 17a). This roof mirror 24 is located on the movable optical system 15 side when viewed from the side.
It is provided with two 45'' reflective surfaces 24a and 24b that diverge to 0', and is arranged so that the detection light 23 transmitted through the beam splitter 17 is received by the upper reflective surface 23a.Therefore, the detection The light 23 is reflected downward by the reflective surface 23a, and further reflected again toward the fixed optical system 11 by the reflective surface 23b.In other words, the roof mirror 2
4, the light is reflected in a folded state so that the optical axis is shifted in the vertical direction.

Furthermore, a two-part light receiving element 25 as a light receiving element is also mounted within the fixed optical system 11 at a position to receive the detection light 23 reflected by the reflecting surface 23b of the roof mirror 24. This two-split light receiving element 25 has two light receiving elements 25 a and 25 b divided into two in the vertical direction, and when there is no optical axis deviation, the optical axis center of the detected light 23 from the reflective surface 24 b of the roof mirror 24 is aligned. Light receiving element 25
The position is set to be the center position between a and 25b.

That is, in the state shown in B, the amounts of light received by the light receiving elements 25a and 25b are set to match each other. Tracking control is performed by comparing the detection outputs of these light receiving elements 25a and 25b.

In such a configuration, the detection operation according to the configuration of this embodiment will be explained with reference to FIG. In FIG. 2, a normal initial state in which the moving optical system 15 has no positional deviation is indicated by a solid line. In such a state, the laser beam emitted from the fixed optical system 11 side passes straight through the beam splitter 17 and the detection beam 2
3 is reflected back by the roof mirror 24 and returns to the fixed optical system 11 again. This detection light 23 is received by a light receiving element 25a.

25b, the light is received and detected equally, and it is determined that there is no track deviation due to optical axis deviation.

For example, consider a case where the moving optical system 15 is displaced by d as shown by the imaginary line in FIG.

In this case, the roof mirror 24 is also displaced by the same amount d together with the moving optical system 15, as indicated by 24'.

As a result, the straight transmission position of the detection light 23 is also shifted by d toward the reflection surface 23a of the roof mirror 24.

What should be noted here is that due to the characteristics of the roof mirror 24, if the incident position of the detection light 23 with respect to the reflective surface 24a is shifted by d, it will be reflected toward the reflective surface 24b, and further
The optical axis of the detection light 23 reflected toward the fixed optical system 11 by b is displaced by 2Xd with respect to the initial normal state. As a result, the light receiving elements 25a and 25b detect the detected light 23
It is detected that the optical axis has shifted by 2Xd. In other words, optical axis deviation can be detected with twice the sensitivity of the displacement amount d of the moving optical system 15 itself, and even a slight optical axis deviation can be detected. As a correction method, the offset of the track signal may be canceled by amplifying the detection signal of the light receiving element 25 and adding it to the original track detection signal from the light receiving element 22.

As shown in FIG. 3, an aperture 26 having a minute opening 26a is interposed between the beam splitter 17 and the roof mirror 24, so that only a part of the straight transmitted light of the beam splitter 17 is used as detection light 23. By doing so, the beam may be made smaller and the light receiving element 25 may be made smaller.

Further, in this embodiment, the two-split light receiving element 25 is used as the light receiving element, but in addition to this, for example, a PSD (position sensor diode) or a COD that can specify the beam receiving position may be used.

Further, in this embodiment, the roof mirror 24 is mounted in the moving optical system 15, but this does not increase the weight so much and the high-speed access operation by the moving optical system 15 is not impaired.

Note that in this embodiment, the light receiving element 20 and the like for detecting the focusing signal are arranged on the fixed optical system 11 side.
These members do not increase the weight of the moving optical system 15.

This is because there is no problem even if the focus system is disposed on the fixed optical system 11 side. That is, the focus detection by the light receiving element 2o is to detect whether a focusing error has occurred depending on whether the reflected light from the optical disk 10 changes from a parallel light state to a convergent light or a diverging light. This is because even if there is an optical axis tilt, no offset occurs in the focusing signal.

Effects As described above, the present invention provides a light receiving element in a fixed optical system, and a roof mirror in a movable optical system that receives straight transmitted laser light from the fixed optical system side and reflects it back to the light receiving element side. Therefore, when a displacement such as a shift occurs in the moving optical system, it is possible to reliably detect the optical axis displacement with twice the sensitivity of the amount of displacement, and the track signal is not affected by offset due to the optical axis displacement. This makes it possible to perform correction control, provide accurate tracking control, and maintain high-speed access operation by the moving optical system.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an embodiment of the present invention, FIG. 2 is a side view showing the front axis deviation detection operation, FIG. 3 is a side view showing a modified example, and FIG. 4 is a side view showing a conventional example. Schematic side view shown, fifth
FIG. 6 is an explanatory diagram showing the principle of tracking signal detection, FIG. 6 is a side view showing the operation that produces an offset, and FIG. 7 is a signal waveform diagram. 10... optical disc (optical information recording medium), 11...
Fixed optical system, 12... Semiconductor laser, 15... Moving optical system, 16... Objective lens, 17... Beam splitter (deflection member), 23... Detection light, 24... Roof mirror, 25...2-split light receiving element (light receiving element) output
Applicant Rico Co., Ltd. Masato Kazuyo
Aiki Meisha (Mij is Sue-35

Claims (1)

[Claims] An optical information recording medium, a semiconductor laser that emits a laser beam, and an objective lens that focuses the laser beam onto the optical information recording medium, the recording, reproduction, or erasing of information on the optical information recording medium. In an optical pickup device, a fixed optical system including at least the semiconductor laser and fixed in position within the device is provided, the objective lens, and a deflection member that guides the laser beam emitted from the semiconductor laser toward the objective lens. , mounted with a roof mirror that returns and reflects laser light emitted from the semiconductor laser toward the deflection member and transmitted straight through the deflection member toward the fixed optical system, and moves with respect to the optical information recording medium; 1. An optical pickup device comprising: a moving optical system, and a light receiving element disposed within the fixed optical system to receive light reflected by the roof mirror.