JPS60171647A - Optical head - Google Patents

Abstract

PURPOSE:To enable easy detection and exclusion of recording errors by making erasing, recording and reproducing of a light disk device in the order simultaneously by single head and making simultaneous reading immediately after erasing and recording respectively. CONSTITUTION:The surface 30a of recording medium of a light disk 30 is made to crystalline state by irradiating large output luminous flux 23 for erasing, and information recording points are formed successively on the surface 30a by irradiating luminous flux 22 for recording modulated corresponding to record information. Finally, the surface 30a is irradiated by small output luminous flux 21 for regeneration to read the information. Presence or absence of errors in inputted record is detected, and rewriting is made if there is any error, or, recording is made again changing tracks and sectors of the disk 30. Thus, checking of errors and rewriting immediately after erasing and recording can be made by independent and simultaneous operation of reproducing and erasing.

Description

DETAILED DESCRIPTION OF THE INVENTION (al) Technical Field of the Invention The present invention relates to an optical disk storage device, and more specifically, recording, reproduction, and erasing are possible in the same disk, and reproduction is possible immediately after recording or immediately after erasing. The so-called D RAW (Direct Read After) operation can check for recording or erasing errors.
The present invention relates to an optical head of an optical disk storage device having a function of ``rWrite''.

fb) Background of the Technology As electronic computers become faster and have larger capacities, storage devices, which are the main part of computers, are also required to have higher density and larger capacity. Currently, magnetic recording and reproducing methods such as magnetic disks, which are easy to record and reproduce, are the mainstream, but optical disks that record and reproduce information optically have many advantages in principle over current magnetic disks. , is being actively researched.

Optical discs are characterized by their high recording density.

A laser beam focused to a diameter of around 1 μm is used to achieve high density (for example, a single 30 cm diameter disk has 1010
In addition to recording information on a recording medium (some devices with a storage capacity of 1000 yen have been reported), it also uses reversible changes in the recording medium's properties due to light or heat to create a rewritable storage device. It is developing.

It has a much higher recording density than magnetic disks.

This rewritable optical disk device, which has the potential to achieve access times comparable to magnetic disks and low bit costs comparable to magnetic tape, is particularly suitable for large-capacity storage sections of information processing equipment that require frequent rewriting. It is attracting attention as

(C1 Prior Art and Problems Currently known recording media for rewritable optical disks include magneto-optical materials 3 thermoplastics, amorphous thin films,
There are liquid crystals, etc., but as a conventional example, let's talk about an optical disk that uses crystal/amorphous phase transition.

For example, recording media mainly made of tellurium oxide, etc.

By heat treatment, it is easy to change the state between amorphous state and crystalline state.
Information can be transmitted by utilizing the fact that there is a reversible phase transition between the phases, and the reflectance of the recording medium of one and both phases is different, so that the amount of reflection of the incident light beam changes.

To write information, a crystalline (erased state) recording medium is rapidly heated and rapidly cooled with a laser beam to cause a phase transition to an amorphous state (recorded state), and to erase information, heat is removed and slowly cooled with a laser beam. This is done by causing a phase transition and returning it to crystalline state.

Figure 1fa) shows the shape of the spot of the laser beam for recording (writing) and reproduction (reading), and Figure 1(b)
shows an example of the shape of the spot for erasing.

FIG. 1 (el is a line diagram showing the temperature change of the recording medium surface within the spot when the laser beam is irradiated, and after being irradiated and heated with the laser beam.

In the process of extinguishing the laser beam at point p and cooling it.

It shows the progress of temperature change within the spot. 1st
It can be seen that curve a in Figure (C) shows the temperature characteristics of the recording spot, which is rapidly heated and cooled by laser beam irradiation. The curved line shows that heat is removed and cooled gradually due to the temperature characteristics of the spot for erasing.

The shape of the erasing spot is an oblong ellipse, and several recording points are heated and erased at the same time, but the recording spot is circular, and one recording spot is heated.

Despite the many advantages of current optical disk devices, the bit loss rate is considerably higher than that of magnetic disks and floppy disks, and this is due to the optical disk itself, laser light source, optical system, circuit system, Or there are various types such as dust. Therefore, it is desirable to perform reproduction immediately after recording or erasing to detect and correct these errors.

Conventional optical disk devices use two laser beams, one for recording/reproducing and one for erasing, as shown in Figure 1, but with this, reproduction after erasing is possible;
Since reproduction immediately after recording is impossible, it is not possible to detect and efficiently eliminate the above-mentioned recording errors after recording. Therefore, compared to magnetic disk devices, optical disk devices currently have the drawback of being inferior in reliability as external storage devices for electronic computers.

It has been long awaited for a long time to develop an optical disk device that can detect bit errors and is rewritable to improve this point.

(dl Purpose of the invention The present invention has been made in view of the above-mentioned points.

It is an object of the present invention to provide an optical head for an optical disk device which is capable of independently and simultaneously performing reproduction and erasing operations, is capable of checking errors immediately after erasing and recording, and is rewritable.

(Ql.Structure of the Invention The object of the above invention is to provide an optical head of an optical disk storage device in which a recording light source and a reproducing light source have the same wavelength, and an erasing light source has a wavelength that is different from that of the recording light source. A recording light source, a reproduction light source, and an erasing light source, which can operate independently with wavelengths different from those of the reproduction light source, and a reproduction light beam, a recording light beam, and an erasure light beam are directed onto the surface of the recording medium through a common objective lens. This can be easily achieved by providing an optical system that performs convergent irradiation and a wavelength-selective optical element that introduces only the reproducing light beam into the reproducing optical system.

ffl　Embodiments of the invention An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the structure of an optical recording/reproducing/erasing system of an optical head of an optical disk device according to the present invention.

The laser light source is a reproduction light source 1. There are three sets of recording light source 2 and erasing light source 3, and the wavelength λ1 of reproduction light source 1 is different from that of the other two.
The wavelength λ2 of the recording light source 2 and erasing light source 3 of the set is different. For example, the wavelength of the reproduction light source 10 is 780nrn,
The recording light source 2 and the erasing light source 3 both have a wavelength of 830n.
Let it be m. In both cases, a semiconductor laser is used as a light source.

A laser beam having an elliptical cross section emitted from each light source is made into parallel light beams by coupling lenses 5, 6.7 each having a numerical aperture of 0.2 to 0.5.

Each of them is a reproducing light beam 21. They become a recording light beam 22 and an erasing light beam 23. The reproducing light beam 21 and the recording light beam 22 have their cross sections corrected for roundness by the respective cambling lenses 5 and 6, and the erasing beam 23 is corrected by cambling.
After passing through the lens 7, it is converted into an oblong cross section by the cylindrical lens 7a.

Of course, these three sets of light beams are spatially separated.

These light beams enter the prism 8 at Brewster's angle, are totally reflected by the surface 8a of the prism 8, and exit the prism 8.

Before explaining the optical paths of each of the above-mentioned light beams, let us describe the optical system shown in Figure 1. 9 is a dichroic mirror with wavelength λ1
(reproduction light flux 21) is transmitted.

This is a wavelength selective mirror that reflects light of wavelength λ2.

Dichroic mirrors have a reflectance close to 100% for specific wavelengths, so they can reflect the incident light beam (recording light beam 22) with less loss1 than the normally used half mirror. It's advantageous. However, the transmittance of light of different wavelengths is about 50%.

10 is a composite optical element with a polarizing beam splitter ■1.

Two-wavelength plates 12 and 13. and a filter 1 that transmits light of wavelength λ1 (reproduction light flux) and reflects light of wavelength λ2.
It consists of 4.

Among the laser beams exiting the prism 8, the erasing beam 23
(wavelength λ2) enters the composite optical element 10 as P-polarized light and passes through the polarization beam splinter 11, but after passing through the A-wave plate 13, it is reflected by the filter 14 and passes through the A-wave plate 13 again. It becomes S-polarized light. Thereafter, the polarizing beam splitter 11 changes the direction of the beam by 90 degrees and the beam enters the objective lens 16 . During this time, there is almost no attenuation of the amount of light due to the composite optical element 10.

The erasing light beam 23 is focused by the objective lens 16.

A long elliptical spot 23 is formed on the medium surface 30a of the optical disc 30.
S enters the recording medium, and the recording medium is gradually cooled down to undergo a phase transition to a crystalline state, thereby erasing the signal. At this time, a part of the erasing laser beam 23 reflected on the recording medium surface travels backward along the optical path, but since its wavelength is λ2, it is reflected by the filter 14, the dichroic ink, and the mirror 9, and is used in the reproduction optical system described later. Do not enter the optical path. Recording light beam 22 (wavelength λ
2) enters the dichroic mirror 9 from the prism 8, is reflected by 1, passes through the % wavelength plate 12, and then enters the objective lens 16.
is incident on the recording medium 30a of the optical disc 30 with a diameter of 1
Connect small circular spots 22s on the order of μm. As mentioned above, the dichroic mirror 9 and the composite optical element 1
Since there is almost no loss for the light beam of wavelength λ2, the recording light beam 22 is irradiated onto the optical disk 30 without attenuation.

The recording medium 30a is rapidly heated and cooled for 22 seconds to change the crystalline state of the recording medium 30a in the spot to an amorphous state, and a signal is recorded.

Since the wavelength of the recording light beam 22 is λ2, similarly to the above-mentioned erasing light beam 23, the reflected light from the optical disk does not enter the reproduction optical system.

Finally, the reproducing light beam 2I having a wavelength of λ1 different from other laser beams will be described. In Fig. 2.

For ease of understanding, only the optical path of the reproducing light beam 21 is shown by a dotted line.

After the reproducing light beam 21 exits the prism 8, its optical path is changed to a right angle by a reflecting mirror 15 and is transmitted through a dichroic mirror 9. At this time, since the wavelength of the reproducing light beam 21 is λ1, the transmittance of the dichroic ink mirror 9 is approximately 50.
%, the reproduction light flux 21 is halved. However, since the output level of the reproducing light beam 21 may be low, there is no practical problem.

Thereafter, the reproduction light beam 21 passes through the composite optical element 10 as it is, is focused by the objective lens 16, and is focused on the optical disk recording medium 3.
A circular spot 21S is connected on 0a. The laser beam 21 incident on the optical disc recording medium 30a is reflected. The amount of the reflected recording light beam 21a is proportional to the reflectance of the surface of the recording medium 30a. Therefore, in advance.

The recording medium 30a, which is in a crystalline state with high reflectance, is irradiated with a recording laser beam 22, and the irradiated point is changed to a spot-like amorphous state with low reflectance to be in a recording state, and then 5 reflections of the recording laser beam 22 are applied. 21a and recording medium 30
When irradiated with a, the amount of reflected light from the spot-shaped area in the amorphous state decreases rapidly, so that it can be read out as an information signal.

The respective light beams reflected by the recording medium 30a are reflected together and travel backward along the input optical path to the objective lens 16. After passing through the V4 wavelength plate 12, it is reflected by the beam splitter 11, changes its optical path at right angles, and enters the ++A wavelength plate 13 and filter 14. Filter 14 transmits light of wavelength λ1.

Since the light having the wavelength λ2 is reflected, as described above, the reflected light of the erasing light beam 23 and the recording light beam 22 is reflected by the filter 14, but the one-reflected reproduction light beam 21a passes through the filter 14 and is reflected by the prism 24. changed the optical path.

The light enters a reproduction optical system 17, 19, 20 which detects a reproduction signal and also detects a focus deviation signal and a track deviation signal. 17 is a convex lens, 19 is a band/pass filter that transmits only light of wavelength λ1, and 20 is a 4-split photodetector. The method and principle for detecting the reproduced signal and signal-po signal by the reproduction optical system 25 described above are well-known facts that are not directly related to the present invention, and therefore a description thereof will be omitted.

By the servo signal obtained by the 4-split photodetector 20,
The objective lens 16 is driven in the focus direction and the track direction by a voice coil motor (νCM) 26 to perform focusing and tracking as is well known in the art.

Now, each spot of the laser beam on the recording medium surface 30a is not concentrated at the same point, but is focused for reproduction, recording, and erasing along the rotational direction of the optical disk 30 (as shown by the arrow mark). Arrange at intervals in this order. This method can be easily achieved by slightly tilting the optical axis of the optical path of each light beam. Therefore, when looking at the surface of the optical disc 30, data is first erased using the erasing spot, and then recorded and reproduced sequentially. Using this arrangement, we will describe how to use the optical disk device according to this embodiment.

The information recording method can be summarized as follows.

First, the erasing light beam 23 with strong output (for example, about 10 mw)
By irradiating the recording medium surface 30a of the optical disc 30, heat is removed and the irradiated point is slowly cooled to a crystalline state.

Next, a recording light beam 22 modulated in accordance with the recording information is irradiated to sequentially form information recording points in a spot shape that has undergone a phase transition to an amorphous state on the surface 30a of the recording medium in a crystalline state.

Finally, the medium surface 30 of the optical disc 30 on which information is recorded
A is always used as a reproducing light beam 2 with a weak output (for example, 1 mw)
1 to read out the information and detect the presence or absence of errors in the input recording. In other words, the recorded signal and playback signal are compared, and if there is an error, the data is rewritten.

Alternatively, take measures such as changing the track/sector of the optical disc 30 and re-recording.

In this way, what is called a magnetic disk.

Information can be recorded on a highly reliable, high-speed optical disc that has both a so-called override function and a DRAM function.

Furthermore, when erasing information on the optical disk, the recording light source 2 is turned off, and the erasing light beam 23 and the reproduction light beam 21
If you perform the above operations on the optical disc, immediately after erasing the information records existing on the optical disc, the playback signal will check to see if there are any remaining information records that have not been erased properly, and if there are any remaining information records that have been erased, repeat the erasing process again. Therefore, information on the optical disc can be erased reliably.

FIG. 3 is a configuration diagram showing a modification of one embodiment of the present invention. Compared to FIG. 2, the same numbers are used for the same parts.

Although it is essentially the same as the one shown in Figure 2, the arrangement of the optical system is slightly different, and the prism that reflects the light beam from the light source and changes the optical path at right angles is used to separate the recording light beam and the erasing light beam. (prisms 8 and 8a), but for the reproducing light beam, the reproducing light source 1
The prism is omitted because the light beam emitted from the lens travels straight.

Correction of the roundness of the cross section of the light beam emitted from the light source is also omitted for the erasing light beam 23 and the reproduction light beam 21, and is provided only for the recording light beam 22.

As described above, in the optical head according to the present invention, each of the laser beams for erasing, recording, and reproduction is emitted simultaneously from each independent semiconductor laser light source to perform each function, and most of the optical system is shared. Therefore, the optical system is simple and uses filters and dichroic mirrors.

The feature is that only the reproduction laser beam is introduced into the reproduction optical system by utilizing the difference in wavelength.

(gl Effects of the Invention As is clear from the above explanation, when two optical heads based on the present invention are adopted, erasing, recording, and reproduction of an optical disk device can be performed simultaneously in that order with a single head, and Alternatively, since simultaneous reading is possible immediately after recording, recording errors in optical disk devices can be easily detected and eliminated, compared to magnetic disk devices.

High density means that it provides an effective means of compensating for the high bit error rate, which is the weak point of optical disk devices.

This is extremely effective in improving the reliability of large-capacity optical disk devices. Furthermore, by configuring the optical system of the optical head using a common optical element for the three optical paths, the structure can be simplified, which greatly contributes to cost reduction.

Furthermore, as detailed in the previous section, dichroic
Composite optical element 1 including mirror 9 and beam splinter 11
By using 0, there is an advantage that almost no loss occurs in the recording light beam and the erasing light beam, which have large outputs, throughout the entire optical path.

Half mirror instead of dichroic mirror 9,
Alternatively, it is possible to use a dichroic mirror or a half mirror instead of the beam splitter 11, but the half mirror's light reflectance and transmittance are both around 50%, and light of wavelengths other than the dichroic mirror's specific wavelength cannot be used. Considering that the transmittance is also about 50%, it is obvious that the loss of each laser beam is much larger.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the shapes of the reproducing/recording light beam and the erasing light beam of a conventional rewritable optical disk, and the temperature change of the recording medium of the optical disk in the slot when the laser beam is irradiated. be. FIGS. 2 and 3 are configuration diagrams showing the optical configuration of an optical head of an optical disk device based on the present invention. In the figure, 1, 2.3 are semiconductor laser light sources for reproduction, recording, and erasing, respectively, and 5, 6.7 are laser light sources for reproduction, recording, and erasing, respectively.
Lens + 7a is a cylindrical lens, 8 is a prism, 9 is a dichroic mirror, 10 is a compound optical element, 11 is a beam splinter, 12. '13 is a ward wavelength plate. 14 is a filter, 15.24 is a reflecting mirror, and 16 is an objective lens. 25 is a reproduction optical system, 26 is a voice coil motor (VCM)
) are shown respectively. Figure 1 (C1) @ (b3 @ Please see Figure 3 0

Claims (1)

[Claims] (11) An optical head for optically recording, reproducing, and erasing information on a recording medium of an optical disk storage device, wherein a recording light source and an erasing light source have the same wavelength, and A recording light source, an erasing light source, and a reproducing light source, each of which has a wavelength different from that of the recording light source and the erasing light source and can each operate independently, and a recording light beam, an erasing light beam, and a reproduction light beam. an optical system that converges and irradiates the light onto the surface of the recording medium through a common objective lens, and a wavelength-selective optical element that introduces only the reproducing light beam into the reproducing optical system. Head. (2) In the optical head, light spots converged and formed by the respective light beams formed on the recording medium along the rotational direction of the optical disc are a reproduction spot, a recording spot, and an erasing spot, respectively. (3) In the optical system of the optical head, three light sources emitted from the recording light source, the erasing light source, and the reproducing light source are arranged in the following order.
Kampling to make each of the book's light beams into parallel rays
a lens, and a correction prism that corrects the circularity of the cross section of the parallel light beam. Among the three spatially separated light beams, there is a gicroic mirror that mixes the reproduction light beam and the recording light beam to form a mixed light beam, and a gicroic mirror that mixes the mixed light beam and the erasing light beam for total mixing. an optical element that combines a polarized beam splitter and an A wavelength plate to form a light beam, and an A wavelength that converges and irradiates the total mixed light beam onto the optical disk to form a light spot on each of the three light beams. The optical head according to claim 1, characterized in that the optical system includes a plate and an objective lens.