JPS62125549A - Optical head - Google Patents

Abstract

PURPOSE:To facilitate the easy control of collimation and to detect stably a focus error, a tracking error, etc., by separating and extracting the detected luminous flux between a collimator lens and a secondary collimator lens through a separating device. CONSTITUTION:A semiconductor laser 1 radiate the dispersed luminous fluxes 20, i.e., the linear polarized beams having the polarization plane in the vertical direction as shown in the diagram. Then a primary collimator lens 2 turns the luminous fluxes 20 into the non-parallel illumination luminous fluxes 21, i.e., the weak diffused luminous fluxes. The reflecting surfaces 3a and 3b of a beam splitter 3 have large reflection factors against the vertical polarized light. Thus the luminous fluxes 21 are turned into the vertical polarized light against the surface 3a and therefore almost reflected by the surface 3a. The reflected luminous fluxes 21 are turned into the parallel illumination luminous fluxes 22 having extremely high parallelism through a secondary collimator lens 4. The lens 4 has the small power although it turns the luminous fluxes 20 into the luminous fluxes 22. Thus the sensitivity control range is small with the lens 4 and therefore the detected luminous flux can be extracted with easy control.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical head that can be used in an optical disk device that optically records information on a recording medium or optically reproduces information from the recording medium.

BACKGROUND OF THE INVENTION In recent years, devices for optically reproducing information from information recording carriers on which information is recorded at high density have been commercialized, such as video disc players that can reproduce television signals and PCM audio discs that can reproduce digital audio signals. Players are already on sale. Information is recorded with extremely high density in these devices, and highly accurate focus control and tracking control are generally required during recording or reproduction. The optical head reproduces information from a recording medium and also detects error signals necessary for these controls.

An example of the above-mentioned conventional optical head will be described below with reference to the drawings.

FIG. 2 shows a schematic configuration diagram of a conventional optical head. In Figure 2, ■ is a semiconductor laser with a diverging luminous flux 2
Emit 0. A collimator lens 101 converts the diverging light beam 20 into a collimated light beam 22 which is a parallel light beam. 7
A converging lens converges this collimated beam 22 to form a light spot 8 on the recording medium 103. Recording medium 103
The reflected light is condensed by the converging lens 7 and becomes a detection light beam 23 that follows the same optical path as the parallel illumination light beam 22 in the opposite direction. 10
0 is a beam splitter which converts this detection light beam 23 into a diverging light beam 2.
Separate it from 0 and take it out. Reference numeral 102 denotes a detection optical system that reproduces an information signal from the detection light beam 23 and detects a focus error signal and a tracking error signal that change depending on errors in focus control and tracking control.

The operation of the optical head configured as described above will be explained below.

The semiconductor laser 1 can be substantially regarded as a point light source, and the diverging light beam 20 from the semiconductor laser 1 is collimated onto the recording medium 10 by the collimator lens 101 and the light spot 8.
3, the light emitting point of the semiconductor laser 1 and the light spot 8 are in a conjugate relationship. Therefore, if the optical relative positional relationship between the detection optical system 102 and the semiconductor laser 1 is constant, a constant image will be formed in the detection optical system 102 when the optical spot 8 is converged without error. Ru. In this conventional example, the semiconductor laser 1 and the detection optical system 102 have a simple mirror image relationship due to the beam splitter 100, and it is easy to maintain a constant relative positional relationship. Therefore, the image formed in the detection optical system 102 at the time of focusing is constant, and operations such as focus control are stable. (Refer to Japanese Unexamined Patent Publication No. 57-205833.) FIG. 3 is a schematic configuration diagram showing another conventional example of an optical head. In the figure, reference numeral 5 denotes a circular correction prism, which enlarges the collimated light beam 22 whose light intensity has a circular distribution in one direction so that it approaches a circular distribution.

Since the other components are the same as those in FIG. 2, their explanation will be omitted.

The optical head configured in this manner transmits a conjugate image of the light emitting point of the semiconductor laser 1 to the recording medium 103 as in the conventional example described above.
The difference from the conventional example described above is that the parallel illumination beam 22 having a circular distribution is converted into a circular distribution by the circular correction prism 5. By doing so, it is possible to improve the light utilization efficiency when the collimated light beam 22 is converged by the converging lens 7 having a circular entrance pupil. (Unexamined Japanese Patent Publication No. 1986-1060
(See Publication No. 38) Problems to be Solved by the Invention However, in the configuration shown in FIG. Due to the dependence, the amount of light tends to change depending on the location, and this tendency becomes particularly noticeable when polarization characteristics are provided.

Furthermore, in the configuration shown in FIG. 3 as described above, if the collimated light beam 22 incident on the eclipse correction prism 5 deviates from parallelism, astigmatism and coma aberration will occur and the convergence of the light spot 8 will deteriorate. Since it is necessary to precisely adjust the collimator lens 101 back and forth, the adjustment is difficult, and the characteristics tend to deteriorate when the distance between the semiconductor laser l and the collimator lens 101 changes due to thermal expansion or the like. It had a point.

In view of the above-mentioned problems, the present invention allows easy separation of detection light beams,
The object of the present invention is to provide an optical head that has stable error signal detection and convergence performance and is also easy to optically adjust.

Means for Solving the Problems In order to solve the above problems, the optical head of the present invention includes a main collimator lens that converts the diverging light beam emitted from the light source into a non-parallel irradiation light beam that slightly diverges; A sub-collimator lens that converts the non-parallel irradiated light beam into a parallel irradiated light beam that is a parallel light beam, and a converging lens that converges the parallel irradiated light beam onto a recording medium and condenses the reflected light to obtain a detection light beam, The detection light beam is separated and extracted between the main collimator lens and the sub-collimator lens by a light separating means.

According to the present invention, with the above-described configuration, the detection light beam is separated into light beams having a weak divergence angle or convergence angle, so that the detection light beam can be easily separated by a normal light separation means that does not particularly consider the angular dependence of characteristics. becomes.

Furthermore, collimation adjustment to ensure that the parallel irradiation beam becomes an accurate parallel beam can be performed by a sub-collimator lens with insensitive adjustment sensitivity, and even if this sub-collimator lens is moved, the light source and detection optical system will be affected. Since the relative positional relationship does not change, collimation adjustment can be performed while observing the playback signal while performing focus control and tracking control, making adjustment easy. In addition, there is no need to strictly adjust the distance between the main collimator lens and the light source.
Since these can be firmly fixed to a metal with a low expansion coefficient with a simple structure, stable convergence performance can be obtained.

Embodiments Hereinafter, optical heads according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a perspective view of an optical head in an embodiment of the present invention. In FIG. 1, 1 is a semiconductor laser which emits a diverging beam 20. Reference numeral 2 designates a main collimator lens, which converts this diverging light beam 20 into a non-parallel illumination light beam 21 with a weak divergence angle or convergence angle.

Reference numeral 3 denotes a beam splitter constituting a light separating means, which has two reflecting surfaces 3a and 3b. Reference numeral 4 denotes a sub-collimator lens, which converts the non-parallel irradiated light beam 21 reflected by the beam splitter 3 into a parallel irradiated light beam 22, which is a parallel light beam. 5
is an ellipse correction prism, which expands the collimated light beam 22 in one direction so that the parallel illumination light beam 22, which has an elliptical intensity distribution, becomes a circular distribution. 23 is a detection light beam, and the light reflected by the recording medium of the light spot 8 is passed through the converging lens 7.
Obtained by focusing the light. Reference numeral 9 denotes an error detection optical system, which receives a detection light beam 23 that passes through the half mirror surface 3a of the beam splitter 3 and is reflected by the polarizing beam splitter surface 3b, and detects a focus error and a tracking error. A polarizing beam splitter 10 splits the detection light beam 23 passing through the polarizing beam splitter surface 3b into two light beams perpendicular to each other. lla and 11b each receive the two light beams split by the polarizing beam splitter 10 and convert them into electrical signals.

Regarding the optical head configured as described above, the first
The operation will be explained using figures.

First, in FIG. 1, a semiconductor laser 1 emits a diverging light beam 20 which is linearly polarized light having a polarization plane in the direction perpendicular to the figure. At this time, the diverging light beam 20 has a wide elliptical distribution in the horizontal direction. The main collimator lens 2 converts this diverging light beam 20 into a non-parallel illumination light beam 21 which is a weak diverging light beam. The reflective surfaces 3a and 3b of the beam splitter 3 have a large reflectance (for example, 70 to 80%) for vertically polarized light.
Since the non-parallel irradiation light beam 21 becomes vertically polarized light with respect to the reflecting surface 3a, most of it is reflected thereby. The reflected non-parallel irradiation light beam 21 is turned into a parallel irradiation light beam 22 with extremely high parallelism by the sub-collimator lens 4.

In order to make the collimated beam 22 as parallel as possible, adjustment is made by moving the sub-collimator lens 4 back and forth along the optical axis. At this time, the power of the sub-collimator lens 4 is smaller than that in the case where one collimator lens converts the divergent light beam 20 into the parallel illumination light beam 22, so the adjustment sensitivity is low and adjustment can be easily performed. Since the intensity distribution of the diverging light beam 20 has an elliptical distribution, the parallel irradiation light beam 22 also has an elliptical distribution that is long in the horizontal direction. The ellipse correction prism 5 functions to expand this collimated light beam 22 in the vertical direction of the figure to approximate a circular distribution. The collimated light beam 22, which has been made to have a circular distribution in this manner, is reflected by the reflecting mirror 6 and then converged by the converging lens 7 to form a light spot 8 on the recording medium. Although the recording medium is not shown in the figure, it is assumed that it is a magneto-optical recording medium. The reflected light from the recording medium is focused by a converging lens 7 and becomes a detection light beam 23,
It follows the same optical path as the parallel illumination light beam 22 in the opposite direction. Most of the vertically polarized component of the detection light beam 23 that does not carry a signal is reflected by the reflecting surface 3a. Most of the vertically polarized light components that have passed through the reflective surface 3a are also reflected by the reflective surface 3b and enter the error detection optical system 9. The error detection optical system 9 detects a focus error and a tracking error from a portion of the incident detection light beam 23. The detection means is not particularly limited, and any detection means may be used. Regarding the specific method, for example, JP-A-50-995
61, Japanese Patent Application Laid-open No. 53-28 = 104, Japanese Patent Application Laid-open No. 49-50954, and Japanese Patent Application Laid-Open No. 51-61730, etc., so the explanation thereof will be omitted here. Generally, when the light spot 8 is correctly focused on the recording medium, the light emitting point of the semiconductor laser 1 and the light spot 8 are in a conjugate relationship, and the semiconductor laser 1
and the error detection optical system 9 are in a mirror image relationship with respect to the reflecting surfaces 3a and 3b. Therefore, if the positional relationship between the semiconductor laser 1 and the error detection optical system 9 is constant, a constant luminous flux will be incident on the error detection optical system 9 when the optical spot 8 is correctly focused. Therefore, even if the sub-collimator lens 4 is moved back and forth for adjustment, the focus error signal and tracking error signal are hardly affected. It is also possible to adjust the collimator lens 4 back and forth.

On the other hand, the detection light beam 2 carries the signal reproduced from the recording medium.
Most of the horizontally polarized light component and some of the vertically polarized light components of 3 are transmitted through the reflective surfaces 3a and 3b and are incident on the polarizing beam splitter 10. The polarizing beam splinter 10 has a reflective surface rotated by 45 degrees with respect to the plane of polarization of the horizontally polarized light component, and separates the incident light into two directions to be incident on the photoelectric detectors 11a and 11b, respectively. The information recorded on the recording medium is transmitted to the photoelectric detectors 11a and llb.
is detected as a differential output. The reproduction principle has already been disclosed in, for example, Japanese Patent Application Laid-Open No. 56-98728, and since it is not the gist of the present invention, a description thereof will be omitted.

As described above, according to this embodiment, the main collimator lens converts the diverging light beam emitted from the light source into a slightly divergent non-parallel irradiation light beam, and the parallel irradiation light beam converts the non-parallel irradiation light beam into a parallel light beam. a sub-collimator lens,
a converging lens that converges the parallel irradiation beam onto a recording medium and condenses the reflected light to obtain a detection beam;
By separating and extracting the detection light beam between the main collimator lens and the sub-collimator lens using the light separation means, collimation adjustment to make the parallel irradiation light beam into a strictly parallel light beam is easy, and the main collimation Since the meter lens does not require as much Igl adjustment as in the conventional case, it can be easily and firmly fixed after adjustment, and error detection such as focus error and tracking error can be stabilized.

In addition, in the above embodiment, the polarizing beam splitter 1
0 and the photoelectric detectors 11a and llb are used to read signals from the magneto-optical recording medium, but this configuration may be changed depending on the principle of recording and reproduction.

Furthermore, the base circle correction prism 5 is not necessarily necessary (although a configuration without it may be used as well).

Alternatively, a plurality of cylindrical lenses may be used instead of the base circle correction prism 5. At this time, the astigmatism may be smaller when the collimated light beam 22 is not a parallel light beam, so in this case, the sub-collimator lens 4 should be adjusted back and forth so that the astigmatism is as small as possible. Bye.

Furthermore, the beam splitter 3 may be of any other type as long as it separates and takes out the detection beam 23 from the non-collimated irradiation beam 21; for example, a beam splitter 100 shown in FIG. 2 may be used. You can also do that.

Effects of the Invention As described above, the present invention provides a main collimator lens that transforms a diverging light beam emitted from a light source into a non-parallel irradiation light beam that slightly diverges, and a parallel irradiation light beam that converts the non-parallel irradiation light beam into a parallel light beam. and a converging lens that converges the collimated light flux onto a recording medium and condenses the reflected light to obtain a detection light flux, and the detection light flux is transmitted to the main collimator by a light separating means. By separating and extracting between the lens and the sub-collimator lens, it is easy to adjust the collimation to make the collimated light beam as parallel as possible, and the main collimator lens does not need to be adjusted in the conventional manner. Therefore, fixing after adjustment is easy and strong, and error detection such as focus error and tracking error can be stabilized.

Moreover, by providing a light amount distribution converting means between the sub-collimator lens and the converging lens to expand or compress the parallel irradiated light beam in one direction and convert the light amount distribution of this parallel light beam, the use of light can be improved. Since it is possible to increase the ratio and to precisely adjust collimation using the sub-collimator lens, it is possible to obtain the effect that aberrations generated by this light amount distribution converting means can be made as small as possible.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an optical head according to an embodiment of the present invention, and FIGS. 2 and 3 are schematic configuration diagrams of a conventional optical head. 1... Semiconductor laser, 2... Main collimator lens, 3... Beam splitter, 4
...Sub-collimator lens, 7...Convergent lens 7゜Name of agent: Patent attorney Toshio Nakao Haka1
Famous confectionery 2 diagram

Claims (2)

[Claims] (1) A light source that emits a diverging light beam, a main collimator lens that converts the diverging light beam emitted from this light source into a non-parallel irradiation beam that slightly diverges or converges, and a main collimator lens that converts the non-parallel irradiation beam into a parallel light beam. a sub-collimator lens for producing a parallel irradiation light beam, a converging lens for converging the parallel irradiation light beam onto a recording medium and condensing its reflected light to obtain a detection light beam, the main collimator lens and the sub-collimator lens. and a detection optical system that detects a reproduction signal, an error signal necessary for control, etc. from the detection light beam separated by the light separation means. An optical head characterized by comprising: (2) A light amount distribution converting means is provided between the sub-collimator lens and the converging lens to expand or compress the parallel irradiated light beam in one direction and convert the light amount distribution of the parallel light beam. An optical head according to claim (1).