JPH0680541B2 - Information recording medium - Google Patents

Description

The present invention relates to a high density recording / reproducing disc such as a digital optical disc.

High density recording / reproducing discs such as digital optical discs
In order to protect the recording film provided on the disc from dust, scratches, etc., with the recording film inside, another substrate or a protective member,
It is considered to have a sealed structure in which a spacer is adhered at a constant interval.

However, in such a sealed structure, when the thermal expansion coefficient of the spacer is different from that of the disk, stress is generated in the disk due to temperature change, and the stress causes the disk or the protective member to have birefringence, so that the read / write signal is Have an adverse effect.

If there is a difference in coefficient of thermal expansion between the glass and the spacer, stress will be applied to each of the tempered glass disc, the adhesive, and the spacer with respect to the temperature change after the spacer and the tempered glass disc are bonded to form a sealed structure. Occurs. This stress varies depending on the shape of the spacer and the shape of the tempered glass disc, but when the stress is large, the adhesive is peeled off, the tempered glass disc is destroyed, and even when the stress is small, the tempered glass disc is Since stress causes birefringence, the read / write signal is adversely affected. The relationship between the birefringence and the signal will be described in more detail. The linearly polarized laser light 6 emitted from the semiconductor laser 5 in the recording / reproducing head passes through the cylindrical lens 7, the polarization prism 8 and the λ / 4 plate 9 to become circularly polarized light. Is focused on the recording film 2 through the focus lens 10 and the tempered glass disc 1, and the reflected light passes through the focus lens 10 and the λ / 4 plate 9 to become linearly polarized light, which is reflected by the polarizing prism 8 and The signal is detected by the detector through 11. If birefringence occurs in the strengthened glass disk 1, the polarization state of the laser light 6 is disturbed when the laser light 6 passes through the strengthened glass disk 1, so that the reflected light is reflected by the polarization prism 8.
Is not completely reflected, and a part of the laser light 6 returns to the semiconductor laser 5. When the reflected light returns to the semiconductor laser 5, the semiconductor laser 5 causes a self-oscillation phenomenon, and the S / N of the detection signal
Problems such as poor ratio occur. Therefore, the birefringence of the tempered glass substrate is
ation), 1/40 to 1/8 of the wavelength λ of laser light 6
It should be kept below 0. When the wavelength λ = 830 nm, the retardation should be kept below about 20 to 10 nm.

An object of the present invention is to provide an information recording medium in which the birefringence of a glass substrate caused by a temperature change is prevented and the retardation is suppressed as much as possible.

In order to achieve the above-mentioned object, the present invention maintains a pair of disk-shaped glass substrates provided with recording members on opposite surface sides at regular intervals, and a spacer is provided on the inner and outer peripheral portions thereof. In the information recording medium adhered by means of the above, the spacer is made of a metal member, and at least the spacer at the inner peripheral portion is made of a nickel-iron alloy. In a preferred embodiment, the inner spacer is made of an alloy of nickel and iron and the outer spacer is made of an aluminum alloy.

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing a state in which recording / reproducing is performed on an information recording medium which is an embodiment of the present invention. The substrate 3 provided with the recording member 2 on the disc 1 is adhered to another substrate 3 via a spacer 4. The linearly polarized laser beam 6 emitted from the semiconductor laser 5 has a lens 7, a polarizing prism 8,
Focusing lens 10, circularly polarized light passing through the quarter-wave plate 9,
Focus on the recording member 2 through the disc 1. Recording member 2
The laser light reflected by the disk 1 is the disc 1, the focusing lens 10 and 4
It passes through the half-wave plate 9 and becomes linearly polarized light, which is reflected by the polarizing prism 8 and reaches the detector 11.

The material of the spacer 4 is Fe-Ni, Ni-Cr-Fe, Cr-FeN.
i-Co-Fe, Ni-Cu, Ni-Mo-Fe, Ni-Mn-Fe, Ni-Cr
An alloy such as -Ti-Fe is preferable, and the material of the disc 1 is glass. In particular, when soda glass that is chemically strengthened is used for the disk 1, an alloy of Ni45% to 50% and the remaining Fe or Ni42% Cr
An alloy of 6% and the remaining Fe is particularly good.

The coefficient of thermal expansion of the spacer 4 and the coefficient of thermal expansion of the disc 1 are matched, and since birefringence does not occur in the disc 1 due to a temperature change, the polarization state of the laser light 6 passing through the disc 1 is not disturbed,
Good recording and reproducing signals were obtained.

FIG. 2 shows another embodiment of the present invention, in which the same reference numerals indicate the same parts as the above-mentioned embodiments.

The structural difference from the above-described embodiment is that the spacer 3 is provided on the substrate 3.
That is, the protective member 12 is adhered via. The laser beam 6 that has passed through the focusing lens 10 passes through the protective member 12 and reaches the recording film 2.

The protective member 12 is made of the same material as the disc 1, and since the spacer 4 and the protective member 12 have the same thermal expansion coefficient, the temperature change does not adversely affect the recording / reproducing signal.

FIG. 3 shows a state in which the information recording medium of the embodiment shown in FIG. 2 is used in another recording / reproducing optical system, and the same reference numerals are the same as those in the previous embodiment.

The laser light 14 emitted from the semiconductor laser 13 is the focus lens 1
5. Focusing on the recording member 2 through the protective member 12, the transmitted light passes through the lens 16 and the analyzer 17, and the detector 18 detects the polarization state of the transmitted light as a signal. When birefringence occurs in the disc 1 or the protective member 12, the polarization state of the laser light 14 is disturbed when passing through the disc 1 or the protective member 12,
The recording / reproducing signal is adversely affected.

FIG. 4 shows a state in which the information recording medium of the embodiment shown in FIG. 1 is used in another recording / reproducing optical system, and the same reference numerals indicate the same as those in the above-mentioned embodiment.

Laser light 20 emitted from the semiconductor laser 19 is a focus lens 21,
It passes through the disc 1 and is focused on the recording member 2. The laser light reflected by the recording member 2 passes through the disc 1 and the focusing lens 21 and returns to the semiconductor laser 19. When the laser light 20 returns to the semiconductor laser 19, the semiconductor laser 19 causes a self-oscillation phenomenon and its output changes. The change in the output of the semiconductor laser 19 can be detected by using the monitor laser light 22 and the detector 23 to record and reproduce the signal of the recording member 2. If birefringence occurs in the disc 1, the polarization state is disturbed when the laser light 20 passes through the disc 1, and the change in the output of the semiconductor laser 19 becomes small, which makes recording and reproduction difficult.

The material of the spacer 4 is not limited to the alloy, and other combinations may be used.

Although the spacers must be provided on the inner and outer circumferences as shown above, FIG. 5a shows the retardation when only one spacer of aluminum alloy under the conditions shown in FIG. 5b is used. At this time, the tempered glass disc had an inner diameter of 35 mm, an outer diameter of 300 mm, a thickness of 1.1 mm, and a temperature change of 40 mm.
℃. As can be seen, when there is a spacer on the outer circumference, the retardation is small, but it increases as the spacer is arranged near the inner circumference, and in each case, it increases as it gets closer to the inner circumference of the glass.

Fig. 6 shows a glass disk with an inner diameter of 35 mm, an outer diameter of 300 mm, and a thickness of 1.1 mm, and the outer peripheral spacer has an inner diameter of 290 mm and an outer diameter of 300 m.
m, thickness 1mm, inner spacer is 35mm inside diameter, 100m outside diameter
The retardation when both m and 1 mm in thickness are aluminum alloys is shown. Thus, in the case of FIG. 6, the allowable range is exceeded.

FIG. 7 shows the distribution of the retardation generated in the tempered glass disk due to the temperature change of 40 ° C. when the spacer which is one example of the present invention is used. The horizontal axis represents the radius of the tempered glass disk, and the vertical axis represents the retardation. The shape of the disc at this time is shown in Fig. 1. The tempered glass disc 1 has an inner diameter of 35 mm, an outer diameter of 300 mm, and a thickness of 1.1 mm.
Outer peripheral spacer 4 has an inner diameter of φ290 mm, an outer diameter of φ300 mm, and a thickness of 1 m.
m, inner spacer 3 is 35mm inner diameter, 100mm outer diameter, thickness
It is 1 mm. Inner spacer is 50% nickel, 50% iron
Material with a coefficient of thermal expansion of 9.5 × 10 ^-6 / ℃ was used, and an aluminum alloy with a coefficient of thermal expansion of 23 × 10 ^-6 / ℃ was used for the outer peripheral spacer. The coefficient of thermal expansion of a tempered glass disk is 8 ×
It is 10 ^-6 / ° C. In FIG. 7, the retardation of the tempered glass disk is suppressed to 15 nm or less, which is about one-fifth of the value when the aluminum alloy is used for the inner peripheral spacer, and it can be sufficiently used.

FIG. 8 shows the distribution of retardation generated in the tempered glass substrate by the temperature change of 40 ° C. when the spacer which is another embodiment of the present invention is used. The horizontal axis represents the radius of the tempered glass disk, and the vertical axis represents the retardation. The shape of the disk at this time is the same as that of the above-mentioned embodiment. The inner spacer is made of an alloy of nickel 42%, chromium 6%, iron 52% and has a thermal expansion coefficient of 7.2 × 10 ⁻⁶ / ° C., and the thermal expansion coefficients of the outer spacer and the tempered glass disk are the same as those in the above embodiment. It is the same. In FIG. 8, the retardation of the tempered glass disk was suppressed to 10 nm or less, which was about 1/8 of the value when the aluminum alloy was used for the inner peripheral spacer, and a better result than the above-mentioned example was obtained. Has been.

With the spacer shapes shown in FIGS. 7 and 8, a sufficient effect can be obtained by matching the thermal expansion coefficients of the inner diameter spacers, but even better effects can be obtained by matching the thermal expansion coefficient of the outer diameter spacers.

According to the present invention, it is possible to prevent the birefringence of the glass substrate caused by the temperature change and suppress the occurrence of retardation as much as possible.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which recording and reproducing are performed on an information recording medium which is an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a state of recording / reproducing on / from an information recording medium which is another embodiment of the present invention. FIG. 3 is a sectional view showing a state in which the information recording medium shown in FIG. 2 is used in another recording / reproducing optical system. FIG. 4 is a sectional view showing a state in which the information recording medium shown in FIG. 1 is used in another recording / reproducing optical system. FIG. 5a is a diagram showing retardation when a conventional spacer is used under various conditions. FIG. 5b is a diagram showing conditions in FIG. 5a, FIG. 6 is a diagram showing retardation when an aluminum alloy spacer is used, and FIG. 7 is a diagram showing retardation in one embodiment of the present invention. , FIG. 8 is a diagram showing retardation in another embodiment of the present invention. 1 ... Disc, 2 ... Recording member 3 ... Substrate, 4 ... Spacer 5, 13, 19 ... Semiconductor laser 6, 14, 20 ... Laser light, 7, 16 ... Lens 8 ... Polarizing prism , 9 ...... Quarter wave plate 10, 15, 21 ... Focus lens 11, 18, 23 ... Detector 12 ... Protective member, 17 ... Analyzer 22 ... Monitor laser light

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Shigematsu 1-280, Higashi Koigokubo, Kokubunji, Tokyo (56) References JP-A-57-120243 (JP, A) JP-A-52 -156605 (JP, A) JP-A-57-212637 (JP, A) JP-A-54-55445 (JP, A) JP-A-53-1002 (JP, A) JP-A-56-83852 (JP-A) )

Claims (2)

[Claims] 1. Information in which a pair of disk-shaped glass substrates, each having a recording member provided on opposite sides thereof, are adhered to the inner and outer peripheral portions of the substrates with a spacer kept at regular intervals. In the recording medium, the spacer is made of a metal member, and at least the spacer provided on the inner peripheral portion of the substrate is made of a nickel-iron alloy. 2. The information recording member according to claim 1, wherein the inner peripheral side spacer is made of an alloy of nickel and iron, and the outer peripheral side spacer is made of an aluminum alloy.