JPH04324130A - Optical head - Google Patents

Abstract

PURPOSE:To obtain an appropriate optical head constitution to optimize the light utilization efficienty of each spot in the optical head for which plural light sources having different wavelength are used. CONSTITUTION:A wavelength plate 8 is arranged in the convergence optical system of the optical head composed of plural light sources having different wavelength. The phase difference of light by the wavelength plate 8 is almost integral multiple of the wavelength of a light source of the light sources and is defined almost quarter of the wavelength of the other light source.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for an optical disk using a plurality of light sources having different wavelengths.

0002

[Background Art] Research and development has been carried out in various places with the aim of increasing the speed and performance of optical disc devices. Methods are being considered to realize a /playback/erase function or a parallel processing function that performs recording/playback on multiple tracks at the same time. As a means to realize the above functions, the 32nd Applied Physics Related Conference Proceedings 1a-P-
6, p. 108 (1985), or Proceedings of the 47th Japan Society of Applied Physics Academic Conference 27p-T-10, p. 159
(1986), a method using a semiconductor laser array, and the Proceedings of the 47th Japan Society of Applied Physics Academic Conference 30p-ZE-3, p. 228 (1986
), a method using two separate semiconductor lasers has been proposed in the past.

0003

[Problems to be Solved by the Invention] However, in the prior art, especially when using multiple light sources with different wavelengths, since independent optical systems are used for light of different wavelengths, the axes of the optical systems may be misaligned. The role of each light spot and the efficiency of light use have not been adequately considered, as the position of the spot may be misaligned due to factors such as this, and the number of optical components increases, resulting in a larger configuration.

An object of the present invention is to obtain a configuration of an optical head suitable for optimizing the light utilization efficiency of each spot when a plurality of light sources having different wavelengths are used.

[0005]

[Means for Solving the Problems] The above object is to provide a plurality of light sources having different wavelengths from each other, a focusing optical system that focuses light emitted from the light sources onto a recording medium to form a plurality of light spots, and a focusing optical system that forms a plurality of light spots on a recording medium. An optical head for an optical disk, comprising at least a signal detection optical system for detecting a light spot control signal or a recording information signal by reflected light or transmitted light of the optical disc, and a wavelength plate disposed in the light beam of the focusing optical system, The phase difference of light generated by the wavelength plate is approximately an integral multiple of the wavelength of at least one light source among the plurality of light sources, and is approximately a quarter wavelength of the wavelength of at least one other light source. achieved.

[0006]

[Operation] In the present invention, a wavelength plate is installed in the parallel light beam of the focusing optical system from the light source to the focusing lens, and the phase difference of the light generated by the wavelength plate is applied to the light source of a specific wavelength among the plurality of light sources. is set to approximately an integer multiple of that wavelength,
Furthermore, for light sources of other wavelengths, the wavelength is set to approximately 1/4 wavelength. Even if a wavelength plate is present as described above, if the phase difference of the light caused by it is zero or an integral multiple of the wavelength of the incident light, it does not act as a wavelength plate for light of that wavelength. Moreover, if the above phase difference is approximately 1/4 wavelength,
It can act as a quarter wavelength plate for light of that wavelength.

Normally, when recording with 780 nm light and reading out magneto-optical signals with 680 nm light, the system is mainly configured for the above-mentioned magneto-optical signals, so the 680 nm light is the center and the 780 nm light is not used. Due to the reduced efficiency, it was difficult to obtain sufficient light intensity. However, in the present invention, a wavelength plate is used with light of two wavelengths, 780 nm and 680 nm, and when the 780 nm light passes through the wavelength plate, a phase difference of 1/4 wavelength is generated,
Information is recorded using the above 780 nm spot, and the 680 nm spot
Since recording and reproducing and error checking are performed using nm spots, the configuration of the optical system is simplified and the light utilization efficiency of each spot can be improved.

[0008]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the optical head according to the present invention, FIG. 2 is a diagram showing the state of a focused spot on a disk, and FIG. 3 is a diagram showing the shape of the light-receiving surface of the photodetector of the optical head. 4 is a block diagram showing another embodiment of the optical head according to the present invention, and FIG. 5 is a diagram showing the shape of the light-receiving surface of the photodetector in the other embodiment. The embodiment shown in FIG. 1 shows an optical head equipped with two laser light sources having different wavelengths. The light emitted from the laser light source 1a with the wavelength λ1 becomes a parallel beam by the collimating lens 2a, passes through the beam shaping optical system 3a, the wavelength filter 4, the polarizing beam splitter 7, the wavelength plate 8, and the focusing lens 9, and is focused onto the disk 10. It will be done. On the other hand, the light emitted from the laser light source 1b with the wavelength λ2 becomes a parallel beam by the collimating lens 2b, passes through the beam shaping optical system 3b, has its traveling direction changed by the rotary mirror 5, passes through the diffraction grating 6, and then passes through the wavelength λ2. The filter 4 combines the laser beam with the wavelength λ1. Thereafter, the light passes through a polarizing beam splitter 7 , a wavelength plate 8 , and a focusing lens 9 and is focused onto a disk 10 . Note that the beam shaping optical systems 3a and 3b shown above may be omitted.

The wavelength plate 8 causes a phase difference of light that is approximately an integral multiple of the wavelength of one of the two light sources, and approximately a quarter wavelength of the wavelength of the other light source. It is set as follows. For example, the wavelength of the light source is around 780 nm as wavelength λ1, and approximately 6 nm as wavelength λ2.
Let us consider a case where information is recorded using the former and error checking after recording is performed using the latter using a wavelength around 80 nm. At this time, the phase difference of the wave plate is set to 2 wavelengths with respect to the wavelength of 680 nm (2λ plate with λ=680 nm). Since the phase difference is an integral multiple of the wavelength, light with a wavelength of 680 nm does not produce a substantial phase difference even when it passes through the wavelength plate. On the other hand, wavelength 780n
When light of m passes through this wave plate, a phase difference occurs as shown below.

[0010]2×(780−680)/780=0.256λ In other words, for light with a wavelength of 780 nm, it almost acts as a 1/4 wavelength plate.

In this embodiment, information is recorded using a spot with a wavelength of 780 nm, and reproduction of the recorded information and error checking are performed using a spot with a wavelength of 680 nm. (Information etc. will be played at both spots). In this case, since the light beam with a wavelength of 780 nm records information, it is preferable that the light utilization efficiency is as high as possible. Therefore, wavelength 7
For a light beam of 80 nm, the configuration of a conventional optical head for a write-once optical disk is preferable. On the other hand, since a spot with a wavelength of 680 nm reproduces a magneto-optical signal, the configuration of a conventional optical head for a magneto-optical disk is preferable. In order to realize the above-mentioned write-once optical system, it is sufficient to insert a quarter-wave plate into the focused light beam, but since the disk is irradiated with circularly polarized light,
Conventional methods cannot reproduce magneto-optical signals.

Now, according to the present invention, a wavelength plate is inserted into the focused light beam, and a component satisfying the following characteristics is used as the polarizing beam splitter 7, and the p-polarized light beam is made incident thereon. If the optical system is set, p
Polarized light transmittance Tp: ~70% (λ=680nm)
>90% (λ=780
nm) s-polarized light reflectance Rs: >95% (λ=680,
780nm) For a light flux with a wavelength of 780nm, a conventional optical head for a write-once type optical disk, and for a light flux of a wavelength of 680nm, a conventional optical head for a magneto-optical disk.
This can be accomplished at the same time. A polarizing beam splitter having the above optical characteristics is possible. In this way, in an optical head for optical disks equipped with multiple light sources with different wavelengths, the optical characteristics (reflectance, transmittance, etc.) of the mounted optical components can be adjusted to each spot according to the role of the light spot. Another feature of the present invention is that different values are set for different wavelengths.

Furthermore, the present invention has advantages and disadvantages as shown below depending on the installation position of the diffraction grating. In this embodiment, as shown in FIG. 1, a diffraction grating 6 is arranged between a wavelength filter 4 and a rotating mirror 5. In this configuration, the distance between the diffraction grating 6 and the aperture lens 9 is long, so if the so-called 3-spot method, which will be described later, is used as a track deviation detection method, the track deviation detection signal will be affected due to sub-spot vignetting. The disadvantage is that a slight offset occurs. However, since the wavelength filter 4 and the polarizing beam splitter 7 can be integrated, it also has the advantage that the optical system can be made smaller.

Next, it is also possible to arrange the diffraction grating 6 between the wavelength filter 4 and the polarizing beam splitter 7. In this case, as the diffraction grating 6, an element may be used in which the depth of the grating is set so that the phase difference caused by passing through the grating is an integral multiple of one wavelength. For example, if the grating structure is set so that the above-mentioned phase difference is an integer multiple for a light beam with a wavelength of 780 nm, the diffraction grating will act as a diffraction grating for a light beam with a wavelength of 680 nm, but for a light beam with a wavelength of 780 nm, It does not act as a diffraction grating. Thereby, it is possible to suppress the occurrence of unnecessary narrowing spots on the disc 10. With the above configuration, the diffraction grating 6 and the diaphragm lens 9
This embodiment is preferable to the embodiment shown in FIG. 1 from the viewpoint of offset generation in the above-mentioned track deviation detection signal, since the distance between the embodiments can be made relatively close. but,
Since the wavelength filter 4 and the polarizing beam splitter 7 need to be arranged separately, this is not necessarily preferable from the viewpoint of downsizing the optical system and reducing the number of parts.

Furthermore, if the diffraction grating 6 is placed between the polarizing beam splitter 7 and the diaphragm lens 9, the distance between the diffraction grating 6 and the diaphragm lens 9 will be minimized, so that the offset in the track deviation detection signal will be reduced. From the viewpoint of occurrence, this is more preferable than the above two examples. However, with such a configuration, since the reflected light from the disk 10 passes through the diffraction grating 6 again, a plurality of unnecessary light beams enter the detection optical system, making it difficult to separate the light beams in the detection optical system. There are disadvantages.

Three examples have been described above regarding the position of the diffraction grating 6, and these include miniaturization of the optical system, offset generation in the track deviation detection signal,
It is necessary to select one of them from the viewpoint of light beam separation in the detection optical system.

FIG. 2 shows an example of the arrangement of narrowed-down spots on the disk in this embodiment. A guide groove is formed on this disk to guide the light spot.
Each spot is focused on the land between the grooves. Information is recorded on the land portions along the center line between the grooves. Since the light beam of wavelength λ1 does not pass through the diffraction grating 6, there is only one spot SPa on the disk. On the other hand, since the light beam of wavelength λ2 passes through the diffraction grating 6, ±1st-order diffracted lights SPb+1 and SPb-1 are narrowed down in addition to 0-dimensional SPb0. The light reflected from the disc 10 is filtered through the aperture lens 9.
, passes through the wavelength plate 8, is reflected by the polarizing beam splitter 7, and is guided to the signal detection optical system 11. The signal detection optical system 11 detects a defocus signal, a track deviation signal, a recording information signal, etc. First, the wavelength filter 12 performs wavelength separation. The light beam with wavelength λ2 passes through wavelength filter 12 and lens 13, and has its polarization direction rotated by approximately 45 degrees by half-wave plate 14. Thereafter, the light beam is polarized into two beams by a Wollaston prism 15 and enters a photodetector 16 . On the other hand, the light beam having the wavelength λ1 is reflected by the wavelength filter 12 and passes through the lens 17. Thereafter, the beam splitter 18 separates the beam, and the beam is incident on photodetectors 19a and 19b which detect a defocus signal or a track deviation signal. In the configuration shown in FIG. 1, the number of parts can be reduced by integrating the polarizing beam splitter 7 and the wavelength filter 12. Further, by arranging a lens between the polarizing beam splitter 7 and the wavelength filter 12, it is also possible to replace both lenses 13 and 17 with one lens.

FIG. 3 shows an example of the shape of the light-receiving surface of each photodetector. 3A shows the shape of the light-receiving surface of the photodetector 16 (the light-receiving surface is indicated by a diagonal line), and a track deviation signal TR (so-called 3-spot method) and a magneto-optical signal MO are obtained by the illustrated calculation. If the half-wave plate 14 is not used, the Wollaston prism 15 can be set by rotating it approximately 45 degrees around the optical axis, but the shape of the light-receiving surface in this case is shown in the same figure (b).
The light-receiving surface may be shifted by 45 degrees to the left and right as shown in FIG. FIG. 4(c) shows the shape of the light receiving surfaces of the photodetectors 19a and 19b (the light receiving surfaces are indicated by diagonal lines). Both detectors are arranged equidistantly before and after the focal point of the lens 17, and a track deviation signal TR (so-called diffracted light differential system) and a focus deviation signal AF are obtained by the illustrated calculation. As mentioned above, the wavelength of the light source is, for example, 78 as the wavelength λ1.
If information is recorded using the former and error checking after recording is performed using the latter using approximately 680 nm as the wavelength λ2, reproduction will be performed with a shorter wavelength than the recording light, and the resolution of reproduction will be improved.

A servo for defocus and track deviation is constructed by a signal obtained from light of wavelength λ1. As a result, it is possible to suppress track misalignment, especially of the recording spot, with high precision, and data destruction due to so-called track misalignment can be suppressed. In order to perform an error check immediately after recording, it is necessary to position the recording spot and the reproduction (check) spot on the same track. To do this, the rotating mirror 5 is rotated around the optical axis. With this rotation, the light flux moves on the photodetector, but
Since the track deviation signal is detected using the so-called three-spot method, an offset is unlikely to occur in the track deviation signal. This is effective when a so-called separated optical system is configured in which only the diaphragm lens 9 moves. The rotation of the rotary mirror 5 is controlled using the track deviation signal from this reproduction spot.

Another embodiment of the optical head according to the present invention is shown in FIG.
Shown below. This embodiment is a configuration in which the diffraction grating 6 of the embodiment shown in FIG. 1 is not used. The configuration of components other than the photodetector 16 is the same as that in FIG. 1, so a description thereof will be omitted. Figure 5(a)
2 shows the configuration of the light receiving surface of the photodetector 16 in the above embodiment. If the diffraction grating 6 is not used,
Track misalignment is detected using the so-called diffracted light differential method, but when the rotating mirror 5 is moved to position the two focused spots on the same track, the light flux moves on the photodetector 16, causing an offset in the track misalignment detection signal. There is a problem that occurs. In order to solve this problem, in this embodiment, a portion of the detector is subdivided. Same figure (b)
indicates one light receiving surface 16a of the photodetector 16. The light-receiving surfaces are Da, Db, and subdivided light-receiving surface groups D1 to D.
It is composed of n. The light beam S is positioned approximately at the center of the light receiving surface, and the relationship between the diffracted light from the track and the light receiving surface is arranged as shown. At this time, as described above, an offset occurs in the diffracted light differential signal due to movement of the rotating mirror 5 or displacement of the detector due to temperature change or vibration. Therefore, the signals DSa and DS from each light receiving surface
b. By comparing DS1 to DSn with the controller 200, the position of the center of the light beam S is detected, and the light-receiving surface division position C for obtaining the diffracted light differential signal is determined. The division positions of the light receiving surfaces are Dk and Dk+1 among the light receiving surface groups D1 to Dn.
When set to , the diffracted light differential signals TRa and TRb are as follows: TRa=DSa+(DS1+...+DSk)TRb=DS
b+(DSk+1+...+DSn), and the track deviation detection signal TR is obtained by TR=TRa-TRb. For example, ISO
Any mirror section, such as the one located between the address information and the data recording area on a standard disk, etc., is used. In the above description, a case has been described in which a track deviation signal is detected from only one light receiving surface of the photodetector 16, but a track deviation signal may be detected from both of the two light beams split by the Wollaston prism 16. Needless to say, it is also possible.

In this embodiment, a magneto-optical disk is assumed (however, the magnet for applying an external magnetic field is omitted), and the structure is such that the photodetector 16 reproduces the magneto-optical signal. It is also possible to adopt a configuration in which the magneto-optical signals are reproduced by the devices 19a and 19b. In that case, the beam splitter 18 is set as a polarizing beam splitter that separates p and s polarized light by rotating it approximately 45 degrees around the incident optical axis, or by rotating the polarization direction approximately 45 degrees using a 1/2 plate. What is necessary is to make the light beam incident. Next, as the defocus signal detection method, it is also possible to use a method other than this embodiment, such as a so-called astigmatism method. Further, the method of the present invention may be applied to other than magneto-optical disks, such as phase-change optical disks and write-once optical disks. Further, in this embodiment, various signals are detected using reflected light from the disc, but transmitted light from the disc may also be used. In that case, the signal detection optical system 11 may be placed opposite the aperture lens 9 with the disk 10 in between. Regarding the track deviation signal detection method,
In this embodiment, the so-called diffracted light differential detection method has been mainly explained, but the essence of the present invention is not impaired even if a so-called sample servo method is used.

[0022]

[Effects of the Invention] As described above, the optical head according to the present invention has
A plurality of light sources with different wavelengths, a focusing optical system that focuses the light emitted from the light sources onto a recording medium to form a plurality of light spots, and a light spot control signal or recording using reflected light or transmitted light from the recording medium. An optical head for an optical disk, comprising at least a signal detection optical system for detecting an information signal, and a wavelength plate disposed in a light beam of the focusing optical system, wherein the phase difference of light caused by the wavelength plate is equal to or greater than the plurality of wavelength plates. The wavelength of at least one of the light sources is approximately an integral multiple of the wavelength of at least one other light source, and the wavelength is approximately a quarter of the wavelength of at least one of the other light sources. The wavelength plate does not work for other light source wavelengths, but can act as a quarter-wave plate for other light source wavelengths, so the former can be used to record information and the latter can be used to perform recording/reproduction and error checking. It is possible and
Therefore, despite the simple optical system configuration, it is possible to realize an optical head that can improve the light utilization efficiency of each optical spot.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an optical head according to the present invention.

FIG. 2 is a diagram showing the state of narrowed-down spots on a disc.

FIG. 3 is a diagram showing the shape of a light-receiving surface of a photodetector of the optical head.

FIG. 4 is a configuration diagram showing another embodiment of the optical head according to the present invention.

FIG. 5 is a diagram showing the shape of a light-receiving surface of a photodetector in the other embodiment.

[Explanation of symbols]

1a, 1b Laser light source 8 Wave plate 10 Recording medium (disk) 11 Signal detection optical system

Claims (1)

[Claims] 1. A plurality of light sources having different wavelengths, a focusing optical system that focuses light emitted from the light sources onto a recording medium to form a plurality of light spots, and a focusing optical system that focuses light emitted from the light sources onto a recording medium to form a plurality of light spots; An optical head for an optical disk, comprising at least a signal detection optical system for detecting a point control signal or a recording information signal, and a wavelength plate disposed in the light beam of the focusing optical system, the optical head having a position of light generated by the wavelength plate. An optical head in which the phase difference is approximately an integral multiple of the wavelength of at least one light source among the plurality of light sources and approximately a quarter wavelength of the wavelength of at least one other light source.