JPS63304428A - Optical disk device - Google Patents

Abstract

PURPOSE:To attain wide recording power margin without deteriorating an optical disk by widening a recording/reproduction beam at recording and narrowering the beam at reproduction. CONSTITUTION:A recording/reproduction collimator lens is moved in the optical axis direction at recording to apply defocusing and an elliptic erasure beam 18 is radiated to erase a recording bit 17 and the recording beam 19 modulated by the signal is used for recording. At reproduction, said collimator lens is focused at the reproduction and the stopped reproduction beam 20 is used to sense the difference in reflectance. Thus, the size of the recording bit is over the erased beam width thereby preventing unerased recording or eliminating the need for a large erasure for the erased power. As a result, the recording power margin is increased without deteriorating the optical disk.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical disc device using a photosensitive recording material whose optical properties can be reversibly changed by irradiation with a laser beam.

Correction of conventional technical information: To create a writable optical disc, a photosensitive material is formed in the form of a thin film on a disc substrate of polymeric phase BFj such as acrylic, and this optical disc is irradiated with a laser. Generally used are materials that perform recording and erasing by changing the optical properties, that is, reflectance and transmittance, by heating and rapidly cooling and slow cooling.

Examples of recording materials exhibiting the above characteristics include chalcogen compounds, tellurium, and germanium.

Metal compounds with additives such as antimony are used, and these are used to create records with low reflectance, generally called amorphous, and erase them by heating and keeping them cool to lower the reflectance.
By making it in a high crystalline state, you can record the Kyushu Information Center in real time.
Can be erased.

Conventionally used optical disc devices first irradiate the erase beam, which is substituted with an elliptical beam, in a coupled manner to the track f where the recording bit exists. The recorded bits in the amorphous state are erased, and the recording film is irradiated with a recording beam, typically a circular light modulated according to the signal, to melt and rapidly cool the recording film, thereby creating new recording bits. By creating a record, we achieve so-called simultaneous erasure. During reproduction, the power of the recording beam described above is reduced, the track is continuously irradiated, and the reflectance difference is detected. Conventionally, in order to increase the C7N ratio (carrier/noise ratio) during playback, the laser for recording and playback is narrowed down to a smaller beam diameter, and the same beam diameter is used during recording as during playback. However, it has been difficult to widen the recordable power range (power margin) necessary for countermeasures against manufacturing variations in semiconductor lasers, deterioration due to long-term laser oscillation, etc., and this poses a major practical problem.

Problems to be Solved by the Invention In conventional optical disc devices, the disc is irradiated with a narrowed light beam during recording, so the size of the recorded bits generated, that is, the size of the melted bits, increases as the recording power increases. The increase is significant and exceeds the erasing width by the erasing beam, causing so-called unerased areas and deteriorating the erasing rate.

Therefore, it is necessary to increase the erasing power to widen the erasing performance, but if the erasing power is high, the disadvantage is that when used repeatedly, the optical disk deteriorates due to the excessive heat load caused by erasing.

In view of this, an object of the present invention is to provide an apparatus with a wide recording back margin without deteriorating the optical disc.

Means to Solve the Problem The diameter of the recording beam emitted from the recording/reproducing laser during recording is made larger than that during reproduction.

The size of the recording bit during recording, that is, the melting width, is approximately proportional to the power linear density of the recording beam in the track direction (laser power/beam half-width), and the beam half-width (beam diameter is defined by the beam half-width) ) When increasing the gold, the increase in power linear density per unit laser puff -1 e.g. 1 mW is
Since it is smaller than the case where it is small, the erasing power is not increased excessively and no unerased data is left. However, during reproduction, since the difference in reflectance between recorded bits on the recording track is detected, the light beam is increased in order to increase the C/N ratio.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings. As a recording medium, materials whose optical constants change before and after recording as mentioned above, such as chalcogen compounds or tellurium, which are heated and rapidly cooled to form an amorphous state with low reflectance, and heated and slowly cooled to form a crystalline state with high reflectance. , germanium, antimony, etc. are used.

The crystal-amorphous phase transformation of these recording media differs slightly depending on the composition of the material, but is not directly related to the method of the present invention and does not affect the present invention.

FIG. 1 is a partial configuration diagram of an optical disc device of the present invention,
During recording and erasing, the light beam emitted from the erasing semiconductor laser 1 passes through the erasing collimator lens 2, is collimated, and passes through the erasing prism 3, which is an oval shaped iron, a polarizing beam splitter 4. The beam is focused by a two-wavelength plate 5 and an objective lens 6 to form an erasing beam spot on the optical disk γ.

On the other hand, the light beam emitted from the recording/reproducing semiconductor laser 8 passes through the recording/reproducing collimator lens 9, the beam splitter 10. be done.

The light reflected from the optical disc 7 passes through the knife 12,
The shift is detected by the detector 14 through the detection lens 13, and the collimator lens 9 for recording/reproduction is driven to the position a to focus. During recording, the collimator lens 9 is moved from the position a to the optical axis. The spot on the optical disc 7 is defocused by displacing it by ΔZ to position b. During playback, the power of the semiconductor laser for recording and playback is completely destroyed, the collimator lens 9 is set to position a, the spot f on the optical disc T is focused, the aperture is stopped, and the detector 1
5 to obtain the reflectance signal.

,,AfJ21KyoA is a diagram showing beam formation on a disk during recording and erasing by Honjiki Kiyo], in which an amorphous recording bit 17 formed on a recording track 16 is moved by an oblong erasing beam 18. The continuous irradiation erases the recorded bits 17, followed by melting and melting of the recording tracks 16 by the recording beam 19 modulated by the signal.
It is rapidly cooled to form new amorphous recording bits 19. During playback shown in Figure 2B, focus on
The focused reproduction beam 2o detects the difference in reflectance between the recorded bit 19 on the recording track and the non-recorded portion, and reproduces it. At this time, it is better for the reproducing beam to have a small beam diameter, and a diameter of approximately 0.8 μm is possible.

FIG. 3 is a diagram explaining the present invention in detail, with a linear velocity of approximately 3 m.
/sec on a track rotating at a frequency of 2MH
The recording bit diameter in the case of recording with z is shown against the recording power using the recording beam half width φ0.8 μm to φ2.0 μm as a parameter. The recording bit diameter required to obtain a sufficient reproduction signal is 0.5 μm to 1.0 μm, and as the recording beam diameter increases, the recording start power increases. Regarding the diameter range, the bit diameter variation with respect to power variation becomes smaller and the operating power range can be expanded. Bee 4 table A, E
where O is the usable power range where the C/N ratio is 50 dB or more and the erasure rate is 40 dB or more when recording 1 and erasing is repeated 10,000 times, X is the unusable power range, and the recording beam diameter φO, a μm 〜φ2.0μm,
If a range of φ1.0 to φ1.5 μm is used, the usable power range can be reliably expanded without causing a large decrease in sensitivity.

(Fu°person) /1(-s)$<A Recording beam diameter φ0.8μm Erasing power (mW) Recording beam diameter φ1.0μm Erasing power (mW) (0) Recording beam diameter φ1.25μm Erasing power ( mW) Recording beam diameter φ1.5 μm Erasing power (mW) −t, t (En Recording beam diameter φ2.0 μm Erasing power (mW) As can be seen from the effects of the invention, according to the present invention, during recording, the recording and
By expanding the beam for reproduction and narrowing down the beam during reproduction, it is possible to provide an optical disk device that can be used repeatedly without leaving a wide power range unerased.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an optical disk device according to an embodiment of the present invention, Fig. 2A is a beam arrangement diagram during recording/erasing, and Fig. 2B
3 is a beam arrangement diagram during reproduction, and FIG. 3 is a recording characteristic diagram during recording. 1... Semiconductor laser for erasing, 6... Objective lens, 7... Optical disk, 8...
Semiconductor laser for recording and reproduction, 9...Collimator lens for recording and reproduction, 17.20...-Amorphous recording pit, 18...Erasing beam, 19.
...Recording beam, 21...Reproduction beam. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 (A) (B)

Claims (2)

[Claims] (1) A first light beam is irradiated to erase information recording pits formed on an optical disk whose recording material is a substance whose optical properties change depending on the light irradiation state, and then a second light beam is irradiated to erase the information recording pits. An optical disc device characterized in that, after recording, when irradiating the second light beam for reproduction, the diameter of the second light beam during recording is made larger than the beam diameter during reproduction. (2) The optical disc device according to claim 1, wherein the recording/reproducing collimator lens is moved in the optical axis direction to defocus during recording and focus during reproducing.