JPH0326456B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical recording and reproducing method, and more particularly to an optical recording and reproducing method suitable for use in an optical information recording and reproducing apparatus that optically detects information recorded on a recording medium.

For example, an optical disk device is well known as an optical information recording/reproducing device as described above. This optical disk device generally has a configuration as shown in FIG. 1a. Here, the recording medium 6 is formed by forming a recording layer made of, for example, TeOx on a substrate, and when irradiated with a light beam or the like, a portion (recording bit) 9 whose reflectance has changed as shown in FIG. are formed concentrically or spirally to record information.
At a, the colored laser beam emitted from the laser oscillator 1 passes through a collimator lens 2, a beam splitter 3, a galvano mirror 4, and an objective lens 5, and is focused on a recording medium 8, and is focused on a spot 1 as shown at b.
Connect 0. Here, the laser beam irradiated onto the recording medium 8 is intensity-modulated and reflected according to the recorded information due to the difference in the reflectance of the recording bits 9. This reflected light passes through the objective lens 5, the galvanometer mirror 4, the beam splitter 3, and the condenser lens 7, and is detected by the light receiving element 8, thereby reading recorded information. Such a recording/reproducing function allows a huge amount of information to be stored on a recording medium and reproduced as needed.

However, the optical recording/reproducing method of the optical disk device described above detects only minute changes in the reflectance of the recording medium, and therefore has the disadvantage that the information signal component is small and the reproduction S/N ratio is poor.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical recording/reproducing method that eliminates the drawbacks of the conventional method and allows signal reproduction with a large S/N value.

The present invention records information on a recording medium by irradiating a recording medium with a linearly polarized light beam and detecting changes in the reflectance or transmittance of the recording medium as well as changes in the polarization state of the light beam caused by the recording medium. The above object is achieved by an optical recording and reproducing method for reading recorded information.

Hereinafter, the present invention will be explained in more detail using the drawings.

FIG. 2 is a schematic diagram showing an example of an optical disk device to which the optical recording/reproducing method of the present invention is applied. Here, information is recorded on the recording medium 18 by forming recording bits whose reflectance has changed by irradiation with a light beam, etc., as in the conventional example shown in FIG. 1B. A laser beam oscillated by a laser oscillator 11 passes through a polarizer 12 and becomes linearly polarized light, and then passes through a collimator lens 13, a beam splitter 14, and a galvano mirror 1.
5. Pass through the objective lens 16 and connect a spot on the recording medium 17. The light reflected by the recording medium 17 undergoes intensity modulation due to a change in the reflectance of the recorded bits, and the polarization state changes between the recorded portion and the unrecorded portion. Objective lens 1
6, Galvano mirror 15, beam splitter 1
4. By guiding the light to the light receiving element 20 through the condenser lens 18 and the analyzer 19, the change in the polarization state as well as the change in the reflectance of the recording medium is detected. Detect recorded information.

Next, an example of a recording medium that provides such a change in polarization state will be described.

Bismuth fluoride (BiF ₃ ) and tellurium (Te) powder are used as raw materials. In a vacuum of 5×10 ^-5 Torr, bismuth fluoride and tellurium were placed in aluminum crucibles set in two sets of tungsten spiral heaters, and each film was made to a thickness of 700 Å.
They are vapor-deposited at the same time, one by one. A glass substrate with a thickness of 2 mm and a diameter of 300 mm is used as the deposition substrate. In this case, in order to obtain a uniform deposited film, the substrate should be
Rotate at a rotation speed of 360 rpm. The deposition rate is 1
~40 Å/sec. The following experiment was conducted to check whether the prepared medium had the above-mentioned characteristics that give a difference in the polarization state. In order to create the state of the part written as a bit, the medium created under the above conditions was heated at 50°C for 30 minutes in a nitrogen atmosphere.
Treatments were carried out at temperatures of 100°C, 150°C, 250°C, and 400°C. Next, in the optical disk device shown in Fig. 2,
This medium is set, and the rotating position of the analyzer 19 is fixed while autofocusing on the medium surface.
The magnitudes of reproduced signals detected by the light receiving element 20 while rotating the polarizer 12 were compared. The results are shown in FIG. In Figure 3, the horizontal axis is the polarizer 1
At the rotation angle of 2, the 0 position is the analyzer 19 and polarizer 1.
2 is the position where it becomes a crossed nicol. For convenience, we decided that the plus direction was clockwise toward the laser oscillator, and the minus direction was counterclockwise. The vertical axis is the light receiving element 20
is the voltage expressed in arbitrary units. 21 in graph
22 is 50℃, 23 is the medium without heat treatment.
is 100℃, 24 is 150℃, 25 is 250℃, 26 is 400℃
The media heat-treated at each temperature are shown. At a position deviated by 3 to 4 degrees or more from the crossed Nicols position, a voltage approximately proportional to the reflectance of the medium can be obtained, but if a position deviated by around 1 degree is selected, there will be a large difference in the detected value of the medium before and after heat treatment. Can be done. Therefore, by setting the polarizer 12 and analyzer 19 in such a positional relationship, when reproducing information, the difference between the reproduced signals of the recorded part and the unrecorded part can be made large (up to about 5 times). I understand that. On the other hand, a simple change in the reflectance of the recording medium is at most 1.5 times.

Next, the state of reproduction when information is actually recorded will be explained. A recording bit was formed by irradiating a laser beam modulated at 5 MHz at 50% duty with a spot size of about 1 μm onto the medium, which was not subjected to the heat treatment described above, while rotating at 1800 r.p.m. . The laser beam is emitted from a semiconductor laser, and the output at the medium surface is approximately 9.0mV.
And so. This recording medium is installed in the device shown in Fig. 2,
Signal reproduction was performed with the laser beam output on the medium surface being approximately 1.5 mW. Here, at a playback frequency of 5MHz,
Analyzer 19 measures the carrier to noise ratio (C/N).
The measurement was carried out while fixing the polarizer 12 and rotating the polarizer 12. Here again, the C/N value is about 45 dB at the position where the polarizer 12 and analyzer 19 are shifted by 3 to 4 degrees or more from the orthogonal Nicols position, with the same tendency as the result in Fig. 3. 1 to 2 from the orthogonal nicol position
When set at a position with a degree deviation, a maximum C/N value of approximately 60 dB was obtained.

Similar experiments were conducted by changing the media material. The created recording medium was a combination similar to that of the previous example, and a semiconductor laser with a wavelength of 820 nm was used.
A film deposited on a substrate with two sources: a matrix material such as bismuth fluoride, which has low absorption and low thermal conductivity, and a material such as tellurium, which absorbs 820 nm light well. It is. Specifically, the materials are as shown below.

Matrix material oxide TeO ₂ , SiO ₂ , In ₂ O ₃ , Bi ₂ O ₃ , Sb ₂ O ₃ ,
V ₂ O ₅ , PbO, Al ₂ O ₃ etc Fluoride BiF ₃ , PbF ₂ , MgF ₂ etc Iodide CuI TlI CsI SnI ₂ AgI PbI ₂ etc Sulfide Sb ₂ S ₃ SnS GeS As ₂ S ₃ MoS Cu ₂ S
Bi ₂ S ₃ etc Selenium compounds As ₂ Se ₃ etc Light absorbing materials Metals, metalloids Te, Bi, Au, Pb, As, Sb,
Ti, Ag, In, Si, Ge, Fe, Cu, Sn etc. As a result of this experiment, it was found that the S/N ratio of the above-mentioned recording medium was improved by the optical recording/reproducing method of the present invention, as in the previous embodiment. It was found that it is possible to reproduce signals with large values. In addition, the trend in recording media is to use materials such as Te that have optical anisotropy themselves,
It has been found that materials with a high refractive index or materials under conditions where stress tends to remain in the film during vapor deposition have a strong effect of changing the polarization state. In addition to the materials listed above, any recording medium can be used in the present invention as long as it changes the polarization state of the light beam between the recorded portion and the final recorded portion.

The optical recording and reproducing method of the present invention is not limited to the above-mentioned embodiments, but can be applied in various ways. For example, signal reproduction may be performed by detecting light transmitted through a recording medium.

As explained above, the present invention irradiates a recording medium with a linearly polarized light beam and detects changes in the reflectance or transmittance of the recording medium as well as changes in the polarization state of the light beam due to the recording medium. Since the information recorded on the recording medium is read using the recording medium, the S/N value of the reproduced signal is improved.

[Brief explanation of the drawing]

1A and 1B are schematic diagrams illustrating an optical recording and reproducing method in a conventional optical disc device, FIG. 2 is a schematic diagram showing an example of an optical disc device used in the optical recording and reproducing method of the present invention, and FIG. FIG. 3 is a diagram illustrating changes in the polarization state of a light beam due to the recording medium of the example. 11... Laser oscillator, 12... Polarizer, 13
... Collimator lens, 14 ... Beam splitter, 15 ... Galvano mirror, 16 ... Objective lens, 17 ... Recording medium, 18 ... Condensing lens, 1
9... Analyzer, 20... Light receiving element.

Claims (1)

[Claims] 1. Information is recorded as recording bits with changed transmittance or reflectance by partially irradiating a recording medium with a light beam, and the medium is also exposed to light polarized in a predetermined direction. An optical recording and reproducing method in which recorded information is read by irradiating a beam and detecting reflected light or transmitted light of the light beam by a medium through an analyzer with a light receiving element, wherein the medium is TeO ₂ , _SiO2 , _{In2O3 , Bi2O3 ,}
Sb ₂ O ₃ , V ₂ O ₅ , PbO, Al ₂ O ₃ , BiF ₃ , PbF ₂ ,
_MgF2 , CuI, TlI, CsI, _SnI2 , AgI, _PbI2 ,
_{Sb2S3 ,} SnS, GeS, _As2S3 , _MoS , _Cu2S ,
A matrix material selected from Bi ₂ S ₃ , As ₂ Se ₃ and Te, Bi, Au, Pb, As, Sb, Ti, Ag,
The analyzer is made of a mixture with a light-absorbing material selected from In, Si, Ge, Fe, Cu, and Sn, and when reading information, the analyzer is rotated from a perpendicular Nicol to the predetermined polarization direction. An optical recording and reproducing method characterized in that the arrangement is rotated by ~2 degrees.