JP2506642B2 - Information recording master recording method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording master recording method for manufacturing an optical disc capable of recording / reproducing video signals, digital audio signals, computer digital signals, etc. or further erasing. Is.

2. Description of the Related Art Write-once optical discs capable of writing information signals or rewritable optical discs are
The track density is close to two digits, and the amount of recordable information is also increasing. Therefore, it is necessary to perform high-speed access to a high-density track with high accuracy, and for that reason, a pre-format signal is required for the optical disc. The pre-formatted signal has a guide track portion on which a user can record information and address information for designating a track or sector address, which are formed in advance. Apply photoresist to the glass master, laser expose,
After development, a nickel mold is prepared from this. A replica disk is made from this mold by various molding methods. A guide track and address information are formed on this replica disc. A recordable disc is formed by forming a recording film on this by a vacuum deposition method or the like. FIG. 6 shows an enlarged view of the pre-format signal of the conventional disc. The width Wa of the guide track 1 and the width Wb of the address information pit 2 are in the same state. Information is recorded on this guide track portion. In order to improve the far field detection efficiency of the tracking error signal, the optical groove depth is usually set to λ / 8 (λ: wavelength of the reproducing light source). This depends on the thickness of the photoresist applied on the glass master. Set the photoresist thickness to λ / 4, which is equivalent to the optical depth on the replica disk, and make the master so that the address information part has a λ / 4 depth and the guide track part has a λ / 8 depth. At times, a method of recording by performing laser power control has also been proposed.

FIG. 7 shows an example of an optical disc having continuous guide tracks 3 and address information pits 4 formed between the tracks.
An information signal is recorded between the guide tracks. This conventional method requires two recording spots, and the number of recording optical systems increases accordingly.

Problems to be Solved by the Invention The guide track is indispensable for high-speed access, but since it has an uneven structure, when it is irradiated with light, the groove width, groove depth, Diffraction loss occurs depending on the groove shape and the like, and becomes a factor that lowers the C / N (signal-to-noise ratio) when reproducing an information signal. The diffraction loss corresponds to the tracking error signal, and in order to eliminate the diffraction loss, the guide track may be eliminated. However, there are various obstacles to access. A sector servo system has been proposed in which the guide track is eliminated and several tens of sectors are provided on the disk for one rotation, and the tracking servo is applied by an intermittent tracking error signal due to the sector. May become unstable. In the conventional method shown in FIG. 6, the width Wa of the guide track 1 and the width of the address information pit 2
Wb is Wa = Wb, and if the address information can be efficiently read out, the diffraction loss due to the guide track 1 also increases and the influence on the recorded information signal also increases. Further, in the conventional method shown in FIG. 7, it is necessary to separately record the guide track 3 and the address information pit 4, so that two recording spots are required, and the optical system for recording the master becomes complicated. Adjustment of the optical axis, positional stability of the two spots, etc. become problems.

Means for Solving the Problems In order to solve the above problems, the information recording master recording method of the present invention includes a recording light source and a light condensing light for condensing a recording light beam from the recording light source on the information recording master. Information recording by a recording device having a lens, focus control means for controlling a focus state, modulation means for modulating a recording light flux according to an information signal, and an optical element located between the recording light source and the condenser lens. When recording an information signal on the master, a plurality of high-order diffracted light beams are generated by the optical element, and the size of the recording spot on the recording master is substantially changed according to the information signal.

Action According to the above method, the optical element changes the intensity distribution of the light incident on the condenser lens according to the information signal to substantially change the recording spot size on the information recording master disc. The width of the address information pit can be made larger than that of the address information pit, and the output of the address signal is not substantially affected. The diffraction loss due to the guide track is reduced and the reproduction C / N of the recorded information signal is improved. You can Therefore, it is possible to obtain an information recording master disc that can be manufactured stably and that has high-quality access preformat information.

Embodiment An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is an explanatory diagram of recording pits recorded by using the information recording master recording method in one embodiment of the present invention, 11 is a guide track, 12 is an address information pit, and 13 is a recording bit. Width W of the guide track 11 ₁ and the width W ₂ of the address information pit 12
The relation with is W ₁ > W ₂ . The reproduction signal output from the address information section is maximized, and the reproduction signal output from the guide track section is structured to maximize the reproduction signal output by the recording bit 13. The distance between tracks, that is, the track pitch P is usually 1.
A value of about 6 to 2.5 μm is used. At the time of recording the information signal, the recording bit 13 is usually not recorded in the address information portion but is recorded only in the guide track portion. The optimum pit width (or groove width) for efficiently reproducing the address information is 30% to 40% of the diameter at the 1 / e ² intensity of the reproduction light spot (13.5% of the center intensity). For example, if the wavelength of the playback light source is λ = 830 nm and the recording / playback lens NA = 0.53, the spot size is Becomes Therefore, the pit width (groove width) suitable for the address signal
Is about 0.4 to 0.5 μm. Further, with respect to the track pitch P, the width W ₁ of the guide track 11 must be W ₂ <W ₁ <P.

The recording spot for obtaining the pit width of W ₂ <W ₁ <P and the guide track width in this way will be described with reference to FIG. Reference numerals 14a to 14c show intensity distributions of recording spots formed on the recording master by a recording lens, 14a is due to zero-order light, and 14b and 14c are optical elements arranged between the light source and the recording lens. This is due to the ± first-order diffracted light generated by the element. Reference numeral 14 shows the intensity distribution obtained by combining these. When recording the address information pit 12, 14
Only the recording spot of a is generated, and the recording spots of 14a to 14c are generated at the time of recording on the guide track 11, and the recording spot size on the recording master is substantially changed to change the recording width.

As a method of realizing this intensity distribution variable recording spot, an acousto-optic modulator as shown in FIG. 3 is used. In FIG. 3, reference numeral 15 is an acousto-optic modulator made of LiNbO ₃ , tellurite glass, TeO _2, etc. When an ultrasonic wave o is applied to this transparent solid by a high-frequency source 16, a traveling compression wave is generated in the solid. A certain signal ultrasonic wave 17 is generated and becomes a transparent diffraction grating. As a result, the incident light I which is vertically incident on the acousto-optic modulator 15 passes through the acousto-optic modulator 15 and is then separated into luminous fluxes I ₀ and I ± ₁ . The ± 1st-order luminous flux undergoes the Doppler shift due to the ultrasonic wave o, and the frequency of the light changes from ν to ν ±
change to o. Since the frequencies are different in this way, there is no interference unlike when the same wavefront is divided and overlapped. The diffraction angle θm of the Raman nurse diffraction when the light flux is vertically incident on the acousto-optic modulator 15 is m: diffracted light order, λ: incident light wavelength, Λ: acousto-optic modulator, wavelength of traveling ultrasonic wave 17 in 15. The intensity Im of the diffracted light is Im / I = J ² m (K · δn · L) Jm: m-th order Bessel function of the first kind, K: wavelength of light, δn: change in refractive index generated by ultrasonic waves, L: It can be expressed as the length in the traveling direction of the light that acts on the light flux of ultrasonic waves. The diffracted light intensity can be freely changed by the applied ultrasonic intensity.

FIG. 4A shows the 0th order and ± 1 on the entrance pupil of the recording lens.
The distribution of the incident light by the secondary diffracted light is shown, 18a shows the entrance pupil diameter or the 0th-order light, and 18b and 18c show the distributions of the + 1st-order and -1st-order luminous fluxes, respectively. Due to this distribution, the converged light spots generated on the recording master become like 19a to 19c. The intensity distribution is as shown in FIG. 4 (c). By changing the intensity and position of each spot, the intensity distribution of the combined light spot can be changed quite freely. The distance between spots can be changed by changing the ultrasonic frequency, and the intensity ratio can be changed by changing the ultrasonic intensity.

FIG. 5 is a block diagram of a recording optical system. As a recording light source,
Short wavelength lasers such as Ar ⁺ ion lasers and He-Cd lasers are used for exposing the photoresist AZ-1350. A
r ⁺ laser wavelength is 4579Å, He-Cd laser is 441
It is 6Å. This is because the photoresist AZ-1350 has higher sensitivity on the shorter wavelength side. The laser light flux 20 that has entered the acousto-optic modulator 15 is diffracted by the traveling ultrasonic wave 17 and enters the lens 21. The light flux from the lens 21 enters the lens 13, becomes a parallel light flux, and enters the recording lens 23. Then, spots for recording are formed on the recording master 24.

Next, the shape of the spot formed on the recording master 24 will be examined. A lens having a large numerical aperture NA is generally used as the recording lens 23 in order to perform accurate master disk recording. Here, we consider the case of NA = 0.9. The spot diameter narrowed down to the diffraction limit is the Airy disk diameter. The diameter at strength is Becomes If NA = 0.9 and λ = 0.4579 μm (Ar ⁺ laser), then φ ₁ / _e ² = 0.42 μm. The diameter of the airy disk is φ _A = 0.62 μm, and the recording of the guide track 11 having a maximum width of 0.6 to 0.7 μm is the limit. According to the diffraction integral, the pit width of the address information section is 30/40% of the diameter of the reproduction spot at 1 / e ² intensity gives the maximum diffraction efficiency.
If the e ² diameter is 1.3 μm, the pit width is preferably 0.4 to 0.5 μm. On the other hand, the guide track width is not a width that gives the maximum diffraction efficiency, but may be a width that gives a necessary and sufficient signal strength for tracking servo. In addition, the micro-roughness of the guide track edge portion caused by the etching of the resist is one factor that deteriorates the C / N. Therefore, if the width W ₁ of the guide track 11 is selected within the range of 1.5W ₂ <W ₁ <3W _{2 with} respect to the width W ₂ of the address information pit 12, C / N can be improved by several dB. If W ₂ = 0.5 μm, 0.75 μm W ₁ <
It becomes 1.5 μm. To get this guide track width,
It is necessary to accurately set the interval between the 0th and ± 1st order light spots on the recording master 24. The 1 / e ² diameter of a lens with NA = 0.9 is φ ₁ / _e ² = 0.42 μm as described above. Assuming that the 0th-order light and the ± 1st-order lights have approximately equal intensities, recording can be performed by selecting the distance between the 0th-order light and the ± 1st-order lights to be 0.54 μm in order to obtain a guide track width of 1.5 μm. 0 on the recording master 24.
It is estimated how much the applied ultrasonic frequency of the acousto-optic modulator 15 should be set in order to obtain the spots separated by 54 μm. The recording lens 23 has a focal length of ₃ , the lens 22 which is a collimator lens has a focal length of ₂ , and the lens 21 for converging and diffusing a light flux has a focal length of _1, and the arrangement is as shown in FIG. The inter-spot distance δ on the focal plane of the lens 22 or the lens 21 is [Δ ': Distance between spots on recording master 24] If δ' = 0.54 μm, ₃ = 2.7 mm, ₂ = 300 mm, then δ = 60 μm. The light flux incident on the recording lens 23 needs to be allowed to be incident on the entrance pupil at least at a position higher than 1 / e ² intensity of the incident light intensity distribution. By doing so, a spot having a shape close to the diffraction limit can be obtained. For that purpose, it is necessary to expand the laser light by the lenses 21 and 22. When the incident laser beam diameter is φ ₁ and the beam on the recording lens 23 surface is φ ₂ , Becomes If φ ₂ = 12 mm, φ ₁ = 12 mm, f ₂ = 300 mm, Becomes At this time, the spot distance δ on the focal plane of the lens 21
= 60 μm was necessary, the diffraction angle θ ₁ of the ± first-order light is Therefore, θ ₁ ≈2 mrad.

The ± first-order diffraction angle θ ₁ by the acousto-optic modulator 15 is Because it was Becomes If λ = 4579Å, then Λ≈0.23 mm. When the material of the acousto-optic modulator 15 is TeO ₂ , the speed of sound V = 4.2km / se
Since it is c, the frequency f applied to the acousto-optic modulator 15
Is Therefore, it becomes = 18MHz.

Thus, by applying the frequency of 18 MHz, the interval between the 0th order light and the ± 1st order light on the recording master 24 is 0.54μ.
Three spots of m can be obtained. High-order light of the second or higher order is also generated, but by changing the intensity of the applied high frequency, it is possible to make it a size that does not pose a problem. By changing this frequency, the spot interval can be freely selected. That is, at the time of recording on the guide track 11, a high frequency is applied to the acousto-optic modulator 15 to widen the spot on the recording master 24, and at the time of recording the address information pit 2, high frequency is not applied and a single round spot is recorded. It is possible to form a pit having a narrow width. Acousto-optic modulator
Since the ultrasonic wave generated in 15 is the traveling ultrasonic wave 17, the diffracted light intensity fluctuates with time even if the applied frequency is constant.
In this embodiment, since the applied frequency is 18 MHz, this frequency fluctuates with time. In order to avoid this effect, it is necessary to properly select the recording linear velocity. In the case of a disc with a diameter of 300 mm, the effect can be avoided by recording at a rotation speed of 900 rpm.

As described above, according to the present invention, since the size of the recording spot on the information recording master is substantially changed by the optical element, conventionally, the recording width is changed only by power control with one beam. Alternatively, the guide track portion and the address information portion are separately recorded by two beams, but the recording spot diameter can be changed with one beam and according to the signal, and the groove is stable and reproducible. Records of different widths can be made. Since recording can be performed stably with one beam in this way, the optical system becomes simpler,
The optical axis can be adjusted easily and the drift of the optical axis can be reduced. Further, a disc having a guide track wider than the address information pit width can be obtained, and C / N can be improved by recording in a groove having a wide width.

[Brief description of drawings]

FIG. 1 is an explanatory view of a guide track and address information pits obtained by an information recording master recording method according to an embodiment of the present invention, FIG. 2 is an explanatory view of a relationship between a spot shape and a track width, and FIG. Operation explanatory view of acousto-optic modulator, 4th
FIG. 5 is an explanatory diagram of the relationship between the light amount distribution of the recording lens and the spot shape, FIG. 5 is an explanatory diagram of the operation of the recording optical system, and FIGS. 6 and 7 are guide tracks and addresses obtained by the conventional recording method. It is explanatory drawing of an information pit. 11 …… Guide track, 12 …… Address information pit, 15 ……
Acousto-optic modulator, 23 ... Recording lens, 24 ... Recording master

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yoshitaka Watanabe 1006 Kadoma, Kadoma City Matsushita Electric Industrial Co., Ltd. (56) References JP-A-59-177744 (JP, A) JP-A-54-162554 (JP) , A) Actual development Sho 60-132616 (JP, U)

Claims (3)

(57) [Claims] 1. A recording light source, a condenser lens for condensing a recording light beam from this recording light source on an information recording master, a focus control means for controlling a focus state, and a recording light beam according to an information signal. When recording an information signal on an information recording master by a recording device having a modulating means for modulating and an optical element located between the recording light source and the condenser lens,
Generating a plurality of high-order diffracted light beams by the optical element,
An information recording master recording method, which substantially changes the size of a recording spot on the recording master according to an information signal. 2. An information recording master recording method according to claim 1, wherein an acousto-optical element is used as the optical element, and the acousto-optical element has a Raman nurse diffraction arrangement. 3. The relationship between the d ₁ and d ₂ is defined by setting the spot size of the recording spot on the recording master in the radial direction of the disc to be substantially d ₁ during guide track recording and d ₂ during address signal recording. The information recording master recording method according to claim _{1, wherein} 1.5d ₂ <d ₁ <3d ₂ .