JPH0750530B2 - Optical head - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical head of a magneto-optical device for recording / reproducing by utilizing magneto-optical property such as an optical disk device, etc., and particularly for accurately recording / reproducing. An optical head suitable for obtaining the optical head.

[Prior Art] FIG. 3 shows a configuration example of a conventional optical head.

This optical head includes a light source 1, a light source condensing unit 3, a reflected light spectroscopic unit 5, and first and second condensing units 8 and 11 for reflected light.
, A servo system photodetector 15 and an information reproducing system photodetector 16
And is configured.

The light source 1 is composed of a semiconductor laser, and has a collimator lens 2 which converts a laser beam 20 projected from the semiconductor laser into a parallel light flux.

The condensing unit 3 is composed of an objective lens, and when the disk 4 is driven to rotate, the laser light from the collimator lens 2 is emitted.
Is passed through a first beam splitter 6 described later, so that the laser light 20 is focused on the surface of the disk 4. At that time, the light condensing unit 3 includes the disk 4
When the disk 4 vibrates in the direction of arrow c during the rotational driving of No. 3, the control means (not shown) controls the movement so that the focal position A coincides with the surface of the disk 4. Information is magnetically recorded on the disk 4.

The spectroscopic unit 5 has a first beam splitter 6 and a second beam splitter 7, which are arranged at a light beam path position between the collimating lens 2 and the condensing unit 3 of the laser light 20,
When the first beam splitter 6 allows the laser light 20 passing through the collimator lens 2 to pass through the condensing portion 3 as it is, and the reflected light of the laser light 20 generated by the disk 4 surface enters the transmitting portion, the reflected light is reflected. The light is refracted in the direction of the second beam splitter 7, and the reflected light incident on the second beam splitter 7 is split into two directions. In addition,
The reflected light of the laser light 20 generated by the surface of the disk 4 passes through the condensing unit 3 and is converted into a parallel light flux, which is then incident on the first beam splitter 6 as it is.

The first condensing unit 8 for the reflected light has a converging lens 9 and a cylindrical lens 10, and one of the reflected lights dispersed by the spectroscopic unit 5 sequentially passes through both the converging lens 9 and the cylindrical lens 10. One of the reflected lights 21 is focused at a predetermined position by passing therethrough.

The second condensing unit 11 for the reflected light has a half-wave plate 12, a focusing lens 13, and a polarization beam splitter 14, and the other reflected light separated by the spectroscopic unit 5 is By sequentially passing, the other reflected light 22 is further split into two directions and condensed.

The photodetector 15 of the servo system is installed at the focal position of the one reflected light 21, and detects the one reflected light 21 and outputs a detection signal corresponding to the amount of light to a control means (not shown). ing. The control means (not shown) is a photodetector.
Based on the detection signal of 14, the light condensing unit 3 is positionally controlled so as to condense the laser light 20 on the disk 4 surface. Therefore, the photodetector 15 detects one of the reflected lights 21 and outputs a detection signal for positioning the condenser 3.

The photodetector 16 of the information reproducing system has its light-receiving surfaces arranged at the focal points B, B of the reflected light 22 on the other side, and each is recorded on the disk 4 by detecting the reflected light 22. Configured to reproduce the information.

In the conventional optical head, the second condensing section 11 for reflected light further separates the other reflected light into two directions and condenses the condensed reflected lights 22 and 22. Detector 16,16
Although not shown in the figure, when compared with the one in which the other reflected light condensed without being separated is detected by a single photodetector, the luminous flux can be significantly narrowed down by the second condensing unit 11. Each of the photodetectors 16 can be downsized, and its electric capacity can be reduced to improve frequency characteristics in a high frequency range, and further, the entire optical head can be downsized.

A known technique of this kind is shown in "3-4 Optical head" on page 17 of 53 in "Technical Research Report CMP83 of the Institute of Electronics and Communication Engineers".

[Problems to be Solved by the Invention] Generally, in an optical head, when the laser light from the semiconductor laser 1 is focused on the surface of the disk 4,
Since the reflected light is reflected by the surface, most of the reflected light is refracted by the first beam splitter 6 toward the second beam splitter 7, but part of the reflected light passes through the first beam splitter 6 and the semiconductor laser 1 It is known that the laser output changes because the semiconductor laser 1 is affected.

The re-reflected light due to such reflected light also occurs in the conventional technique, but in the conventional technique, the re-reflected light also occurs by the photodetectors 16, 16 for information reproduction. Distortion N is generated in the detection signal v of the photodetector 15 of FIG.

That is, in the prior art, as shown in the explanatory diagram equivalently modeling the configuration in FIG. 4, when the laser light 20 is focused on the surface of the disk 4, the reflected light is the photodetector of the information reproducing system. 16
Since it is configured to collect light on the light receiving surface of, the reflected light is further reflected by the photodetector 16, and the second light collecting unit
11, passing through the spectroscopic unit 5 and the collimating lens 2, the semiconductor laser 1
Return to.

Therefore, since the laser output changes, the servo system photodetector 15 is distorted in the linear region v ₁ which is the range possible to control the movement of the light converging unit 3 in the detection signal v, as shown in FIG. N is generated.

Further, although the photodetector 16 is originally fixed, the laser output may be significantly changed even when a slight displacement occurs due to an increase in ambient temperature.

That is, when the member fixing the photodetector 16 expands due to a rise in ambient temperature, etc., and the position of the photodetector 16 is slightly displaced from the focal point B of the reflected light 22, as shown in FIG. When the focal position A of the laser light deviates from the surface of the disk 4, the light receiving surface of the photodetector 16 coincides with the focal position B of the reflected light 22, and the re-reflected light due to the reflected light returns to the semiconductor laser 1 as described above. , The laser output changes significantly.

Therefore, as shown in FIG. 7, the servo system photodetector 15
The distortion N is generated in the linear region v ₁ of the detection signal v.

As a result, when the distortion N occurs in the linear region v ₁ of the detection signal v of the photodetector 15, it becomes impossible to accurately position the condensing unit 3 so as to follow the surface of the disk 4, and eventually the disk 4 There is a problem that it is difficult to accurately reproduce the information recorded in the.

In order to solve this problem, the re-reflected light is emitted from the semiconductor laser 1
It is conceivable to arrange the light receiving surface of the photodetector 16 so as not to return to the above position. However, doing so may result in extremely complicated processing and structure.

In view of the above problems of the prior art, an object of the present invention is to have a practical influence on the detection signal of the servo system photodetector with a simple configuration even if re-reflected light is generated by the information reproduction system photodetector. It is an object to provide an optical head which can reproduce information accurately by not applying it.

[Means for Solving Problems] In the present invention, a light source, a light condensing unit that is controlled to move relative to the disk surface, and that can condense the projection light from the light source onto the disk surface, and a disk surface A spectroscopic unit that disperses the reflected light in two directions, and a unit that condenses each of the spectroscopically reflected lights.
1, a second light collecting means, a servo system photodetector for receiving the light collected by the first light collecting means, and outputting a signal for controlling the movement of the light collecting section, And a photodetector of an information reproducing system for receiving the light condensed by the second condensing means. Further, the position of the light receiving surface of the photodetector of the information reproducing system is arranged so as to be deviated by a predetermined distance in the optical axis direction from the focus position condensed by the second condensing means.

[Operation] When the reflected light is re-reflected by the light receiving surface of the photo detector of the information reproducing system, the re-reflected light influences the projected light, so that the detection signal of the photo detector of the servo system is affected.

However, in the present invention, as described above, the position of the light receiving surface of the photodetector of the information reproducing system is arranged so as to be displaced from the focus position focused by the second focusing means in the optical axis direction by a predetermined distance. Therefore, the effect of re-reflected light occurs at a position outside the linear region of the detection signal in the servo system photodetector, and the effect of distortion that occurs in the detection signal of the servo system photodetector can be practically ignored, The lens means for focusing light on the disk surface can be positioned accurately, and accurate reproduction of information can be achieved.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 is an overall view showing an example of an embodiment of the present invention, and FIG.
The figure is an explanatory waveform diagram showing the detection signal of the photodetector of the servo system. In the figure, the same reference numerals as those in FIG. 3 represent the same or corresponding ones.

The optical head of the embodiment includes a semiconductor laser 1 and a disk 4
Focusing unit 3 that is controlled to move relative to the surface and that focuses the laser light 20 from the semiconductor laser 1 on the Dick 4 surface.
And a spectroscopic section 5 for reflected light that disperses the reflected light from the surface of the disk 4 in two directions, a first condensing section 8 for reflected light that condenses one of the spectroscopically reflected light 21, and a spectroscopic section. The second condensing section 11 for reflected light that condenses the other reflected light 22 and the servo system light that detects one reflected light 21 and outputs the detection signal v for condensing section movement control. The detector 15 and the photodetector 16 of the information reproducing system that detects the other reflected light 22 are configured. This point is similar to the conventional example.

The difference between this embodiment and the conventional example is that the second light detection is performed so that the influence of the reflected light 22 occurs at a position deviated from the linear region v ₁ of the detection signal v of the first photodetector 15. The light receiving surface of the container 16 is located at a point displaced from the focal position of the reflected light 22.

That is, the position of the photodetector 16 is, as shown in FIG. 2 in the detection signal v, when the photodetector 15 of the servo system detects when the reflected light is re-reflected by its light receiving surface. Distortion N is generated at a position deviated from the linear region v ₁ which is a range in which the light converging unit 3 can be moved and controlled, for example, the curved portion of the detection signal v is distorted. In this example, the light receiving surface reflects light. Although it is arranged at the light beam position on the incident side of the focal position B of 22, it may be arranged at the light beam path position beyond the focal position B of the reflected light 22.

Then, the shift amount 1 between the light receiving surface position of the photodetector 16 and the focal position B of the reflected light 22 can be easily obtained by the following formula.

Here, f ₁ is the focal length of the condensing unit 3, f ₂ is the focal length of the focusing lens 13 in the second condensing unit, and ε is the distortion N in the detection signal v.
It represents the amount of focus shift on the disk 4 when the occurrence of the.

Therefore, the shift amount is appropriately selected according to the distances f ₁ , f ₂ , and ε according to the above formula.

As described above, when the photodetector 16 is arranged with an appropriate shift amount 1 with respect to the focal position B of the reflected light 22, the light receiving surface of the photodetector 16 causes re-reflection of the other reflected light 22, and the re-reflection Even if the laser output of the semiconductor laser 1 is changed by the light, when the servo system detector 15 detects, the linear region v ₁ which is the range in which the movement of the condensing unit 3 can be controlled in the detection signal v ₁
Distortion N is generated at a position deviated from it, and no distortion N is generated in the linear area v _1. Therefore, the control means (not shown) to which the detection signal v is sent accurately controls the light collecting unit 3 to the disc 4 surface. The movement of the laser output can be controlled so that the influence of the change in the laser output on the detection signal v of the photodetector 15 is practically no problem.

Further, since it suffices to shift the position of the photodetector 16 of the information reproducing system in the front-back direction along the optical axis with respect to the focus position B, the light receiving surface of the photodetector is prevented so that the re-reflected light does not return to the semiconductor laser 1. It is possible to solve the problem that the processing and the structure become complicated as compared with the case where the is arranged in a tilted manner, and it is possible to configure extremely easily.

In the present invention, the specific configuration of each part is not limited to the illustrated embodiment, and the same effect can be obtained as long as it has a desired function.

[Effects of the Invention] As described above, according to the present invention, the position of the light receiving surface of the photodetector of the information reproducing system is set in the optical axis direction from the focus position focused by the second focusing means. It is configured so that the detection signal of the servo system photodetector is not affected in practice even if the distance from the photodetector changes the projection light from the light source due to the re-reflected light from the photodetector. Therefore, there is an effect that the spectroscopic section can be accurately positioned with respect to the disk surface, and therefore information can be accurately reproduced with an extremely simple configuration.

[Brief description of drawings]

FIG. 1 is an overall view showing an embodiment of the present invention, FIG. 2 is an explanatory waveform diagram showing a detection signal of a photodetector of a servo system, and FIG. 3 is an overall view showing a configuration example of a conventional optical head. FIG. 4 is an explanatory diagram equivalently modeling a conventional optical head, FIG. 5 is an explanatory diagram showing detection signals of a servo system photodetector in FIG. 4, and FIG. 6 is a conventional optical head. FIG. 7 is an explanatory diagram showing a state where the disc and the photodetector of the information reproducing system are displaced with respect to an equivalently modeled focus position, and FIG. 7 is an explanatory diagram showing detection signals of the photodetector of the servo system in FIG. . 1 ... Semiconductor laser, 3 ... Focusing unit, 4 ... Disk,
5 ... Spectroscopic unit, 8 ... First condensing unit, 11 ... Second condensing unit, 15 ... Servo system photodetector, 16 ... Information reproducing system photodetector, 20 ... Laser light, 21 …… One reflected light, 22 ……
The other reflected light, B ... The focal position of the other reflected light 22, v ...
… Detection signal, v ₁ …… Line area.

Claims (1)

[Claims] Claim: What is claimed is: 1. A light source, a light condensing section that is controlled to move relative to the disk surface, and that can condense the projection light from the light source onto the disk surface, and the reflected light from the disk surface into two directions. The spectroscopic means and the first to collect the respective reflected light
1, a second light collecting means, a servo system photodetector for receiving the light collected by the first light collecting means, and outputting a signal for controlling the movement of the light collecting section, An information reproducing system photodetector for receiving the light condensed by the second condensing means, and the position of the light receiving surface of the information reproducing system photodetector is condensed by the second condensing means. An optical head, which is arranged so as to be displaced from the focused position by a predetermined distance in the optical axis direction.