JPS63298725A - Split type optical pickup - Google Patents

Abstract

PURPOSE:To obtain a detection signal having no effect of optical axis deviation by arranging a couple of mirrors of optical axis capable of splitting symmetrically a light from a stationary optical system side in a direction orthogonal to a track to a movable optical system, synthesizing the light with a reflected light from a recording medium and allowing a 2-split photodetector to receive the resulting light. CONSTITUTION:A couple of mirrors 16, 17 are provided on the rear side of a beam splitter 14 and the mirrors 16, 17 are arranged while being parted in vertical symmetry around the optical axis of a laser beam radiated horizontally from the stationary optical system 12. Moreover, a 2-split photodetector 13 is provided on the stationary optical system 12 in opposition to the beam splitter 14. Thus, an optical path synthesizing the reflected light from the face of the optical disk 10 and the reflected light from the mirrors 16, 17 and leading the result to photodetectors 13a, 13b of the 2-split photodetector 13 in the stationary optical system 12 is formed. Thus, the deterioration in the detection signal is compensated optically even in the presence of an optical axis deviation.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a separate optical pickup in an optical disk device, a magneto-optical disk device, a compact disk device, etc.

BACKGROUND ART Generally, in this type of device, information is recorded and reproduced using an optical pickup, but in order to achieve high-speed access, the movable part thereof is required to be lightweight. For this reason, only the minimum necessary components such as the objective lens and deflection prism in the optical pickup optical system are housed in the movable part to form a movable optical system, and the remaining components such as the laser light source and various detection systems are placed in a fixed optical system. A separate optical pickup is being considered. That is, as shown in FIG.
The light is deflected by 90 degrees by a deflection prism 4 inside, and focused by an objective lens 5 onto a recording medium 6 such as an optical disk. Then, the reflected light 7 from the recording medium 6 is again guided into the fixed optical system 1 via the objective lens 5 and the deflection prism 4. Here, the movable optical system 3 is mounted on a carriage or the like and linearly reciprocated in the radial direction (theta direction) of the recording medium 6 by a linear motor or the like to access a desired track position. Further, the objective lens 5 is supported by an actuator for displacing its attitude so as to follow the track of the recording medium 6 in a focused state. Furthermore, in addition to the semiconductor laser, the fixed optical system 1 includes, as is well known, a coupling lens, a beam shaping prism, etc., as well as optical signals (RF multiplied signal detection means, tracking/focusing for controlling the objective lens actuator). It is equipped with tracking error detection means, focusing detection means, etc. that constitute a servo mechanism.

However, in the case of such a separate optical pickup method, the detection signal deteriorates due to optical axis deviation due to movement of the movable optical system 3, tilt of the movable optical system 3, angular deviation between the optical axis and the movable optical system 3, etc. It gives rise to FIG. 4 shows various causes of such optical axis deviation. First, Figure 4 (a
) shows a case where the optical axis of the reflected light 7 is shifted by Δ with respect to the optical axis of the laser beam 2 from the fixed optical system 1 due to the vertical shift of the movable optical system 3. FIG. 5B shows a case where an optical axis deviation Δ is caused by the tilt of the movable optical system 3, and FIG.

Track detection is particularly affected by such optical axis misalignment, and minimizing optical axis misalignment in the track direction is a major challenge for separate optical pickups.

For this reason, various methods have been proposed for detecting the amount of optical axis deviation and correcting it electrically or mechanically. For example, one type of incident beam monitor (which uses a detector installed near the objective lens to control the incident beam to prevent optical axis deviation)
JP-A-61-214235). Furthermore, there is a method (Japanese Patent Application Laid-Open No. 194647/1983) in which a shift in the optical axis is detected using a mirror tracking method and corrected using one mirror. Another method is to provide a polarizing beam splitter, a λ/4 plate, a mirror, etc. in the objective lens actuator, and to reflect a part of the incident light by these to detect optical axis deviation on the fixed optical system side (Japanese Patent Application Laid-Open No. 1983-1999). Publication No. 148630)
There is also. Furthermore, a method of detecting the position of a moving part (movable optical system) and correcting it by moving a mirror (Japanese Patent Laid-Open No. 61-1826
Publication No. 40).

However, in the case of these methods, the optical system becomes complicated to detect optical axis misalignment, a dedicated detector is required, and a correction mechanism is required after detecting optical axis misalignment. There are drawbacks.

Purpose The present invention has been made in view of the above points, and has a simple configuration that does not require a detection mechanism for detecting the amount of deviation of the optical axis and also does not require a positional correction mechanism corresponding to the detection mechanism. An object of the present invention is to obtain a separate optical pickup capable of optically compensating for a decrease in a detection signal even if there is an optical axis misalignment.

Structure In order to achieve the above object, the present invention includes an optical system including a laser light source, a coupling lens, a beam shaping prism, etc., as well as a fixed optical system including an optical signal detection means, a tracking error detection means, a focusing detection means, etc. Separated into a movable optical system equipped with a deflection prism and an objective lens,
The laser beam emitted from the fixed optical system is deflected by the deflection prism and focused on the recording medium surface by the objective lens, and the reflected light from the recording medium surface is returned to the fixed optical system via the objective lens and the deflection prism. In a separate type optical pickup that is guided into an optical system and subjected to various detection operations, a part of the movable optical system is arranged symmetrically with the optical axis so that a part of the light from the fixed optical system is separated in a direction perpendicular to the track. A pair of mirrors are provided, and the reflected light from the recording medium surface and the reflected light from these mirrors are combined to form an optical path that leads to the two-split light receiving element in the fixed optical system. It is.

Hereinafter, a first embodiment of the present invention will be described based on FIGS. 1 and 2. First, FIG. 1 shows the basic configuration of this embodiment, in which an optical system for an optical pickup can move the lower surface of an optical disk 10 as a recording medium in the radial direction (theta direction; direction perpendicular to the track indicated by the arrow). Movable optical system 11
and a fixed optical system 12 fixed to the device.

22. The fixed optical system 12 is equipped with a laser light source such as a semiconductor laser, a coupling lens, a beam shaping prism, etc., as well as an optical signal (RF multiplication signal detection means, tracking error detection means, focusing detection means, etc.). However, these are well-known configurations, and the two-split light receiving element 13
Illustrations and explanations are omitted except for. Such a fixed optical system 12 emits a laser beam toward the movable optical system 11. Further, the movable optical system 11 includes at least a beam splitter 14 as a deflection prism that deflects the laser beam from the fixed optical system 12 by 90', and an objective lens 1 that focuses the deflected light on the surface of the optical disk 10.
5 is built-in. This is the basic structure of a separate optical pickup, and the reflected light from the optical disk 10 also goes through the opposite path, that is, to the objective lens 15 and the beam splitter 14.
The light passes through again and returns to the fixed optical system 12, where it is used for signal reading, tracking/focusing servo control detection, etc.

Therefore, in this embodiment, the reflective surface 14a of the beam splitter 14 has predetermined reflectivity and translucency, and is set to transmit a part of the laser beam 13 emitted from the fixed optical system 12. ing. The reflectance (transmittance) of the reflective surface 14a of the beam splitter 14 is set as described below.

A pair of mirrors 16 are arranged behind such a beam splitter 14 (on the opposite side from the fixed optical system 12).
．． 17 are provided. Here, these mirrors 16
．． 17 are vertically symmetrically spaced apart (shape and position) with respect to the optical axis of the laser beam emitted horizontally from the fixed optical system 12. Also, these mirrors 16.1
7 may have a reflective surface structure formed by vapor deposition.

Further, the two-split light receiving element 13 is provided in the fixed optical system 12 so as to face the beam splitter 14 (more practically, the two-split light receiving element 13 is disposed in the fixed optical system 12 after the beam splitter, etc.). ). This two-part light receiving element 13 consists of two light receiving elements 13 a and l 3 b that are divided into two around the optical axis of the laser beam emitted by the fixed optical system 12 .

In this way, the light reflected from the surface of the optical disk 10 and the light reflected from these mirrors 16 and 17 are combined and transmitted to each of the light receiving elements 13a and 13 of the two-split light receiving element 13 in the fixed optical system 12. An optical path is formed that leads to b.

In such a configuration, the operation of the system of this embodiment will be explained. First, FIG. 1 shows a normal case in which the movable optical system 11 has no vertical positional deviation. That is, both the reflected light from the optical disk 10 as shown by halftone dots in FIG. 1 and the reflected light from the mirrors 18 and 17 as shown by diagonal lines are in a state of optical axis symmetry when viewed in the direction perpendicular to the track. It is. Therefore,
Each light receiving element 13a, 1 in the two-divided light receiving element 13
3b receives the same amount of light. In other words, the light receiving element 13
If the amounts of light received by a and 13 b are A and B, respectively, then A
-B=O.

Consider a case where a positional shift occurs in the movable optical system 11. In this case, the reflected light from the optical disc 1o causes an optical axis shift as shown in FIG. 2(a). That is, if the movable optical system 11 is shifted upward, the reflection optical axis is also shifted upward. As a result, the amount of reflected light received by the light receiving elements 13a and 13b from the optical disc 10 is A D + B D
Then, AD>BD.

If the movable optical system 11 shifts downward, AD<BD.

In other words, the AD-B
This results in a difference in the amount of received light of D. This corresponds to an offset due to positional deviation of the movable optical system 11 in the prior art.

On the other hand, when a positional shift occurs in the movable optical system 11, considering the behavior of the reflected light from the mirrors 16 and 17, the behavior shown in Fig. 2 (b
)become that way. That is, although the reflected light from the mirrors 16 and 17 does not cause an optical axis shift, the reflection position changes because the movable optical system 11 is shifted from the normal position shown by the imaginary line. Therefore, if the movable optical system 11 is shifted upward, the amount of reflected light received from the mirrors 16 and 17 of the light receiving elements 13a and 13b AM+BM will be different from the magnitude of the reflected light from the optical disc 10. <Becomes BM. Movable optical system 1
If 1 shifts downward, AM>BM. That is, in the light receiving elements 13a and 13b, there is also a difference 1 in the amount of received light between AM and BM due to the mirrors 16 and 17.

That is, the amount of light received by the light receiving element 13a is AD+AM, and the amount of light received by the light receiving element 13b is BD+BM. Therefore, if the transmittance (or reflectance) of the beam splitter 14 is set so as to satisfy the relationship: A D B D "; B M - A M, the light receiving elements 13a, 13b
The difference in the amount of received light A-B between them is A-B-(AD+AM) (BD+BM)#0. In this way, there is no difference in the amount of light received by the two light receiving elements 13a and 13b, and the optical axis shift does not affect the detection signal. That is, due to the optical axis misalignment, each light receiving element 13 for the reflected light from the optical disk 10
Even if there is a difference in the magnitude of the received light amounts AD and BD of a and 13 b, the effect of optical axis deviation is reduced due to the combined reception of the light transmitted through the reflective surface 14a of the beam splitter 14 and reflected by the mirrors 16 and 17. This will compensate for the detected light amount state that is not affected. In other words, in this embodiment, the optical axis (movable optical system 11
By forming a positional deviation compensating optical system that optically gives a deviation of -α when the position of This prevents the detection signal from deteriorating without electrically or mechanically correcting the axis misalignment. or,
In order to configure such an adaptive optical system, mirror 16.
17 is added, but the structure is simple and the weight burden on the movable optical system 11 is light.

Next, a second embodiment of the present invention will be described with reference to FIG. The principle is the same as that of the previous embodiment, but the optical path for irradiating the optical disc 10 and the optical path for irradiating the mirrors 16 and 17 are separated. First, a semiconductor laser 18 that is a laser light source is provided in the fixed optical system 12, and is configured to convert the light into a parallel light beam using a coupling lens 19, and then split the light using a beam splitter 20. A deflection prism 21 is attached to the casing 22 of the movable optical system 11 for deflecting the light split by the beam splitter 20 toward the movable optical system 11 toward the objective lens 15. This deflection prism 21, unlike the beam splitter 14 of the embodiment described above, has a reflecting surface with a reflectance of 100%, and may have a mirror configuration. On the other hand, the beam splitter 2o is included in the fixed optical system 12.
The light transmitted straight through the mirror 16゜1 of the movable optical system 11
A deflection prism 23 is provided to reflect the light toward the 7 side.

With such a configuration, the light from the semiconductor laser 18 is
On the other hand, the light is irradiated onto the optical disc 10 through the beam splitter 20, the deflection prism 21, and the objective lens 15. Then, the reflected light from the optical disk 10 passes through the objective lens 15 and the deflection prism 21, and then passes straight through the beam splitter 20 and is received by the two-split light receiving element 13. On the other hand,
Emitted from the semiconductor laser 18 and sent to the beam splitter 20
The light that has passed through is reflected by the deflection prism 23 and irradiated onto the mirrors 16 and 17. This is the deflection prism 21
parallel to the light. Then, the reflected light from the mirrors 16 and 17 is reflected by the deflection mirror 23 and then also reflected by the beam splitter 20, and is received by the divided light receiving element 3 in a state where it is combined with the reflected light from the optical disk 10 side. That will happen. By combining the reflected lights from the mirrors 16 and 17, the optical axis shift is optically corrected.

According to this embodiment, the deflection prism 21 with 100% reflection can be used, and the amount of light reaching the optical disk 10 can be increased. Mirror the light 16.1
The light is guided to the 7 side and is used in the adaptive optics system, so that the light utilization efficiency can be made high.

Effects As described above, in the present invention, a pair of optically symmetrical mirrors capable of separating the light from the fixed optical system side in a direction perpendicular to the track is disposed in a part of the movable optical system, and the reflected light from the recording medium and the mirrors are separated. Since the combined light is received by the two-split light receiving element, even if the reflected optical axis of the feedback system deviates from the output optical axis due to positional deviation of the movable optical system, the two-split light receiving element will receive the combined light due to the front axis deviation. The pair of mirrors acts as an adaptive optical system that cancels out fluctuations in the amount of received light, and it is possible to obtain a detection signal that is not affected by optical axis deviation. Does not require correction means,
The configuration is simple, and the weight of the movable optical system is only slightly increased.
It can be a simple separate optical pickup.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing the first embodiment of the present invention in a normal state, FIG. FIG. 3 is an explanatory diagram showing the behavior of mirror reflected light when the optical axis is misaligned, FIG. 3 is a configuration diagram showing two embodiments of the present invention, and FIG. 4 is an explanatory diagram showing the cause of optical axis misalignment. 10... Recording medium, 11... Movable optical system, 12...
・Fixed optical system, 13...2-split light receiving element, 14...
14... Deflection prism, 15... Objective lens, 16
．． 17...Mirror, 18...Semiconductor laser (laser light source), 19...Coupling lens 13"○

Claims (1)

[Claims] The optical system includes a fixed optical system including a laser light source, a coupling lens, a beam shaping prism, etc., an optical signal detection means, a tracking error detection means, a focusing detection means, etc., and a movable optical system including a deflection prism and an objective lens. The laser beam emitted from the fixed optical system is deflected by the deflection prism and focused on the recording medium surface by the objective lens, and the reflected light from the recording medium surface is transmitted again to the objective lens and the deflection prism. In a split-type optical pickup that guides the light into the fixed optical system for various detection operations, the optical axis is arranged so that a part of the light from the fixed optical system is separated in a direction perpendicular to the track. A pair of symmetrically arranged mirrors is provided, and an optical path is formed by combining the reflected light from the recording medium surface and the reflected light from these mirrors to guide the light to the two-split light receiving element in the fixed optical system. Separate optical pickup featuring: