JPH10199001A - Optical information recorder, optical information recording method, and optical information recording carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to form good groove width and length for information recording signals on an optical information recording carrier, by switching the incident laser beam flux diameter and condensing it on an objective lens in correspondence to the polarization direction where the laser beam flux is switched by a polarization switching device. SOLUTION: The emitted laser beam flux 2 subjected to intensity modulation in accordance with an electric modulation signal 3a by an optical modulator 3 passes the polarization switching device 4, for which an electrooptic effect element, such as, for example, unaxially anisotropic crystal lithium niobate material or the like is used. An element impression voltage 4a is applied on the polarization switching device 4 and a half wavelength voltage of V(λ/2) is added to this voltage, thereby, the deflection direction of the laser beam flux passed the device described above is rotated 90 deg. and the diffraction at diffraction gratings is induced. The transmittance is thereby lowered and the use of only the part of the aperture of the objective lens 11 is made possible. The deflection direction of the laser exit beam flux is switched and the effective NA is changed by this polarization direction at the time of forming a master disk for the optical information recording carrier, by which the regenerative signal quality is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording apparatus and method, and more particularly to an apparatus for recording a signal on an optical information recording carrier master required for manufacturing an optical information recording carrier.

[0002]

2. Description of the Related Art In recent years, an information recording apparatus that modulates the intensity of a laser beam based on an electric signal, condenses the laser beam, and records a signal on a rotating optical information recording carrier has been partially commercialized. Also, development research for further densification has been widely performed.

On the other hand, the optical information recording carrier is prepared by forming a mold by plating based on a groove shape produced on a photosensitive resist applied on an optical information recording carrier master, and then molding the mold. It is manufactured based on a resin substrate.

[0004] On the resin substrate, there is provided an information recording groove portion comprising an address groove portion on which information such as a recording position transferred from the optical information recording carrier master is recorded and a continuous groove.
Optical information recording carriers (hereinafter, referred to as recording carriers) are widely mass-produced by depositing an optical recording material, for example, a magneto-optical material, an amorphous material, or the like on the substrate by vapor deposition or a sputter.

FIG. 6 shows the appearance of the recording carrier. On the recording carrier substrate, as shown in 14b, there are an address portion composed of a series of short pits and a continuous groove portion 14a, and an information recording portion composed of a continuous groove and a land portion 14c surrounded by the continuous groove.

In the conventional optical information recording carrier, only the groove 14a has been used as an information recording section as shown in, for example, Japanese Patent Publication No. Hei 5-12776 proposed by the present inventors. In order to increase the density of optical information recording, information is also recorded on the land part 14c surrounded by the grooves (land and land).
Group recording) to reduce the recording density to about 2
And double. Recently, the distance between grooves is 1.4 μm.
Therefore, the distance between the land and the groove is very small, 0.7 μm.

On the other hand, the information recording apparatus using the present record carrier is much thinner than the conventional one in order to reduce the influence of signals recorded on adjacent tracks and to stably record / reproduce signals on grooves or lands. It is necessary to form a focused spot. For this reason, the conventional information recording apparatus has a recording objective lens of NA 0.5 and a light source wavelength of about 800 nm, but a recent information recording apparatus has an NA of 0.6 and a light source wavelength of 6 nm.
50 nm is applied, which is approximately 1.
It is necessary to condense the light spot thinly to about 1/5.

Accordingly, the groove width ratio (line width of the address portion / line width of the continuous groove portion) shown in the above-mentioned publication proposed by the present inventors needs to be further reduced (in this publication, the optimum line width of the address portion is required). 0.5μm, optimal continuous groove line width 0.8
It is stated that a groove width ratio of about 0.625 is appropriate for μm.

However, in order to achieve a recording density higher than the double density as described above, the information recording apparatus uses a high NA objective lens such as 0.6, a short wavelength laser light source of 650 nm, and a recording carrier. It was obtained from computer simulations by the inventors that the line width ratio between the address portion and the continuous groove portion is desirably about 0.4. That is,
Since the groove pitch is 1.4 μm, the line width of the address portion is preferably about 0.3 μm.

The publication also discloses how to fabricate a conventional master for an optical information recording carrier for producing a recording carrier having a line width ratio of about 0.625 between a conventional address portion and a continuous groove portion. Although various descriptions have been made, recently, it has been manufactured by simply changing the output intensity of a laser light source using an optical system as shown in FIG. A conventional recording device for an optical information recording carrier master will be described with reference to FIG.

A laser beam 2 emitted from a recording laser light source 1 (usually a large laser such as Ar, Kr, Xe, HeCd or the like is used as an output of about 100 mW)
The light passes through the optical modulator 3. The types of the modulator include an AO modulator and an EO modulator, and an EO modulator (Electric Optical Modulator) having good frequency characteristics of a normal signal is used.

The modulator performs intensity modulation of the laser beam 2 based on the modulated electric signal 3a. The modulated light beam is spread by the beam expander 6 to fill the opening of the objective lens 11. In this way, the recording objective lens 1
It is possible to form the focused spot 13 narrowed down to the full performance of 1.

The condensed spot 13 is condensed on a photosensitive resist 12a applied on the optical information recording carrier master 12. Usually, a positive resist is used as the photosensitive resist, so that the resist in the portion irradiated with the condensed spot is removed after the development processing. Therefore, in order to produce the master of the optical information recording carrier shown in FIG. 6, continuous light is applied to the continuous groove portion 14a, and intermittent light is applied to the address portion 14b. The groove line width can be changed by changing the peak intensity of the irradiation focused spot at the time of manufacturing the master. This principle will be described with reference to FIG.

FIGS. 7 (a) and 7 (b) respectively show two types of irradiation focused spot peak intensity profiles. The dotted line in the figure indicates the light intensity of the recording threshold of the photosensitive resist. Therefore, if the intensity of the condensed spot is higher than that, the portion is recorded. FIGS. 9C and 9D show grooves recorded on the photosensitive resist at the respective focused spot intensities. As can be seen, when the focused spot peak intensity is strong (b), the groove width wb2 is recorded wider than wb1.

[0015]

In the method of changing the groove width by such a method, since the groove width can be changed very easily, such a method has been widely used in the past. In order to change the light amount, an element 3b (usually an AO modulator is used) that changes the amplitude of the electric modulation signal 3a applied to the optical modulator 3 or changes the light amount is inserted.

The method of changing the groove width by this method is extremely simple and widely used. However, in the method of changing the groove width by the light intensity, the groove cross-sectional shape changes greatly. This is because the recording is performed while irradiating the condensed spot on the rotating master, so that the light irradiation intensity is given by an integral value of the light spot peak intensity between irradiations.

Therefore, the actual way of recording greatly changes depending on the peak intensity of the irradiation focused spot. In particular, since the recording of the address portion is performed with the focused spot peak intensity lowered, the cross-sectional shape of the narrow groove perpendicular to the track is shown in FIG. Holes are less likely to be formed up to the bottom of the groove as compared to FIG. (F), and FIG. It is easy to have a broken groove shape.

Therefore, when a signal is recorded and reproduced by an information recording apparatus using a recording carrier produced from such a master, the signal quality (jitter quality) of a reproduced signal, in particular, the address portion transcribed from the master and produced. ) Becomes significantly worse. The quality of the reproduced signal greatly depends on the condition of the edge of the groove in the track direction. Accordingly, it is not preferable to reduce the peak intensity of the converging spot and record the master of the optical information recording carrier in which the address portion is formed as a narrow groove because a groove having the above-described groove cross section is produced.

In particular, as described above, since it is desired to increase the density of the optical information recording carrier, it is necessary to further reduce the groove width ratio as compared with the conventional one. Therefore, it is necessary to lower the focused spot peak intensity. Therefore, when a record carrier produced from this master is reproduced by an information recording device, the reproduction signal quality of the address portion is increasingly deteriorated.

Therefore, when a master for a high-density information recording carrier is produced by a conventional method, and then a recording carrier is produced,
Reproduction signal (address signal) of the address section in the information recording device
Since the quality deteriorated, a practical optical information recording carrier could not be manufactured.

The present invention has been made in view of such a situation, and has been made on a master recording apparatus for producing a high-density information recording carrier.

[0022]

According to the present invention, there is provided an optical information recording apparatus having a laser light source, a device for driving intensity modulation of a laser beam of the laser light source, and an objective lens for condensing the laser beam. After passing through a polarization switching device that switches the polarization direction of the laser light beam, it passes through a light beam diameter switching device in which the laser light beam diameter is changed according to the polarization direction, and thereafter is condensed by the objective lens. In the information recording device, by switching the polarization direction by the polarization switching device, the laser beam diameter incident on the objective lens is switched by the light beam diameter conversion device, and the objective lens has a good thick groove and a narrow groove on the optical information recording carrier. A groove is formed.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to FIGS. In the present embodiment described below, a case where a polarization switching device using an electro-optic effect is used as a polarization switching device and a polarization hologram is used as a light beam diameter switching device will be described.

The intensity of the laser beam emitted from the laser light source 1 is modulated by a light modulator 3 based on an electric modulation signal 3a. The intensity-modulated laser beam then passes through a polarization switching device 4 which is one of the components of the present invention. FIG. 8 shows a principle diagram of a polarization switching device using an electro-optic effect element. The laser beam propagates in the y direction in FIG.

A typical example of the electro-optic effect element is a uniaxially anisotropic crystalline lithium niobate material. In FIG. 8, the width of the element is represented by w, thickness d, and length l. Assuming that an electric field E _z is applied in the anisotropic optical axis z direction, the polarization direction of light is E _i , and the propagation direction is y, the phase shift ψ _z , が of the polarization component of the propagating light received in the z direction and y direction in the crystal. _x is

[0026]

(Equation 1)

(Where r ₃₃ and r ₁₃ in (Equation 1) are photoelastic coefficients). Therefore, the electric field strength E _z
Can take various values depending on the external voltage V, so that when V (λ / 2), ψ _z −ψ _x = π is possible.
When the element application voltage 4a is V (λ / 2), it is called a half-wave voltage. When such a voltage V is applied to the crystal, the polarization direction of the output light from the crystal can be 90 degrees different from the polarization direction of the incident light. As described above, the method of switching polarization using the electro-optic effect is simple and can be performed at high speed.

After the polarization is switched at a high speed in this manner, the laser beam is spread through the beam expander 6 to fill the opening of the recording objective lens 11. A feature of the present invention is that a laser beam diameter switching device 7 (in the case of the present embodiment, which is composed of an element whose light passage area changes according to the polarization direction) is connected to a recording objective after passing through the polarization switching device 4. It is to be installed before the lens 11.
In the case of the present embodiment, it is installed before the objective lens 11 after passing through the beam expander 6.

As the present embodiment, a case will be described in which a polarization hologram is used for an element whose light transmission region changes depending on the polarization direction. FIG. 9 shows an example of the configuration and characteristics of a polarization hologram. As shown in FIG. 9 (a), this element performs proton exchange in the form of a diffraction grating on a lithium niobate substrate to form a phase-type diffraction grating, and the refractive index due to the proton exchange becomes extraordinary light / ordinary light. Since both change, the optical path length correction is applied so that either one becomes zero in phase. Therefore, the present diffraction grating acts only on polarized light in one direction, either ordinary light or extraordinary light, and diffracts only light having that polarized direction. In the case of this element, the proton exchange diffraction grating surface is chemically etched so as not to diffract the extraordinary light, and a phase compensation groove is produced for the extraordinary light. Further, since the diffraction grating of this element can be manufactured using a photomask as in the case of an IC, various elements can be formed by changing the pattern of the photomask in various ways. The detailed description of the present element is described in JP-A-6-77839.

The aperture switching element shown in FIG. 2 has no diffraction grating at the center and has a diffraction grating at the periphery. Therefore, the operation is reversed depending on whether the polarization direction of the present element before rotating the polarization is set in the extraordinary light direction or the ordinary light direction of the present element.

When the polarization direction of the laser beam that has not been rotated is matched with the extraordinary light direction (z direction) in FIG. 9A, the diffraction grating of this device is shown in FIG. 9B. As described above, the laser beam simply passes without performing the function of the diffraction grating. Therefore, since this is equivalent to the case where this element is not installed, the beam expander 6 acts as it is, and a condensed spot is formed with the performance of the recording objective lens 11 full. For example, the recording objective lens of an optical information recording carrier master recording machine usually has an NA of 0.90 and a laser wavelength of 45.
Since it is 79 nm, the diameter of the focused spot 13 narrowed down to the diffraction limit is about 0.51 μm.

On the other hand, a polarization direction switching device, for example, FIG.
When a half-wave voltage is applied to the electro-optic effect element, the polarization direction of the passing laser beam is rotated by 90 degrees. In this case, for the polarization hologram element, the ordinary light direction (y
Direction), and in this case, as can be seen from FIG. 11B, diffraction occurs by the diffraction grating, and the transmission efficiency decreases to several percent. Therefore, in this case, the laser beam when passing through this element passes only through the portion without the diffraction grating 7b in FIG. 2, so that the diameter of the laser beam is 8a in FIG.
Therefore, in this case, the laser beam is
Is not full, only a part of the aperture of the objective lens is used.

Therefore, by appropriately designing the dimensions of the hologram-free region 7b in FIG. 2, it is possible to reduce the effective NA of the objective lens to a value much smaller than 0.9. For example, when the NA is reduced to about 0.35, the focused spot can be increased to 1.31 μm.

When the NA of the objective lens is switched as in the present method, the above-mentioned problem of the deterioration of the reproduction signal quality in the narrow groove portion is solved. This will be described with reference to FIG.
FIG. 3A is a focused spot profile when the aperture is narrowed down by an objective lens having an NA of 0.9, and FIG.
The focused spot profile when the aperture is stopped down at 0.35 is shown, and the dotted lines in both figures show the light intensity of the recording threshold of the photosensitive resist.

A comparison between FIG. 3 according to the present invention and the conventional case shown in FIG. 7 in which a narrow groove is manufactured by reducing the amount of light shows that the method of switching NA is stable and the shape of the groove cross section is small. You can judge whether it will be better.

In other words, when a narrow groove is formed at a high NA as shown in FIG. 3A, a sufficient amount of light required for exposure is irradiated in a region above the threshold value of the resist recording, so that it is perpendicular to the track. FIG. 3 (e) of the cross-sectional shape of the narrow groove of FIG.
A hole is reliably formed up to the bottom of the groove, as in FIG. 6F, which is a cross-sectional shape of a large groove in a direction perpendicular to the track. (H) of the cross-sectional shape of the thick groove of FIG. On the other hand, when the narrow groove is formed by narrowing the light quantity as shown in FIG. 6A, the irradiation light quantity in the resist recording area cannot be given a sufficiently stable light quantity. Therefore, FIG. 6 (e) of the cross-sectional shape of the narrow groove in the direction perpendicular to the track shows
Unlike the figure (f) of the cross-sectional shape of the thick groove in the direction perpendicular to the track, it is difficult to form a hole up to the groove bottom, and at the same time, the cross-sectional shape of the narrow groove in the track direction is as shown in the figure (g). ,
The cross-sectional shape of the thick groove in the track direction has a distorted shape as compared to the same figure (h), and when reproduced by an information recording device using a recording carrier created from such a recording master, the signal quality of the address portion is And the address signal cannot be read stably. Also, when trying to record a signal on such a recording carrier with an information recording device, the address cannot be read or the clock for recording / reproduction cannot be reproduced, and this recording carrier is a very unstable recording carrier. Be a body.

As described above, when the information recording carrier master is prepared, the recording method in which the effective NA is switched to change the line width is much more than the recording method in which the recording power is changed to change the groove width. desirable. As a method of switching the effective NA, a method of switching the polarization direction of the laser beam emitted from the laser and inserting an element whose effective NA changes according to the polarization direction into the front part of the objective lens as in the present invention is preferable. Further, when the polarization hologram is used, the use of the diffracted light makes it possible to easily obtain the polarization switching device stabilizing servo light.

This is because when the electro-optic effect element is used as the polarization switching device, the photoelastic coefficient r ₁₃ ,
Since the value of r ₃₃ changes sensitively, half-wave voltage also varies considerably with temperature. Therefore, in order to stably switch the polarization even when the ambient temperature changes, some control is required. Therefore, when a polarization hologram is used as the light beam diameter conversion element, as shown in FIG. 1, ± 1st-order diffracted light from the polarization hologram can be easily obtained by the photodetector, and this control can be easily performed.

FIG. 4 shows a principle diagram of the stabilization control of the polarization switching device using the amount of diffracted light of the present invention. The polarization rotation ratio in the figure indicates (intensity of a 90-degree rotation component of the laser beam emitted from the laser beam) / (intensity of the laser beam at an element application voltage V (λ / 2)). When the polarization is not switched, a voltage of 0 V is running through the polarization switching device. To switch polarization, a half-wave voltage V (λ / 2) is applied to the device.

When the temperature changes from C0 to C1, the curve of the applied voltage of the element versus the rotation ratio of the polarization is K as shown in FIG.
It changes from C0 to KC1. The polarization rotation ratio in FIG.
Since the incident light polarization angle in FIG. 9B is related to SIN (incident light polarization angle), the output of the photodetector 9 is almost proportional to the polarization rotation ratio. Now, the element application voltage is V (λ /
2), and when the voltage is changed as shown in FIG. 4B, the output voltage from the photodetector 9 becomes
(b) changes from (c-1) to (c-2).

Therefore, it is possible to determine whether or not it is necessary to increase the half-wavelength voltage from the output of the positive and negative periods of the applied voltage waveform of FIG. 4B. In the case of the temperature (c-2), since the detection voltage increases with the positive polarity, it is understood that the half-wave voltage needs to be further increased. Therefore, in this case, the element application voltage becomes a voltage of v ′ because a voltage higher than V (λ / 2) is applied. In this case, since the detection voltage of the output decreases in both the + cycle and the − cycle, it can be seen that the half-wavelength voltage v ′ for this temperature (c−1) is given accurately.

By monitoring the ± first-order diffracted light 10 of the polarization hologram by the photodetector 9 using this principle, the temperature change characteristics of the polarization switching device can be accurately controlled.

Although a polarization switching device using a field-effect optical element has been mainly described as an embodiment of the present invention, a liquid crystal or the like can be considered as an equivalent element. 1/6 to switch polarization
In the case where the switching time is about 0 seconds and the switching speed needs to be further increased, the field optical effect element is more preferable.

Another object of the present invention is to change the width of a signal groove to be recorded by actively changing the NA of a recording objective lens when recording a signal on an information recording carrier. Therefore, no matter how the NA of the objective lens of the present invention is changed, it is important that the laser beam is converted before entering the objective lens.

Further, recently, in order to make the disc carrier thickness compatible with, for example, 1.2 mm and 0.6 mm in the optical information reading apparatus, the aperture is restricted by some means as a method of changing the NA of the objective lens.

In this case, it is also used to reduce the reading NA by restricting the light beam emitted from the laser, but more importantly, in this case, the reflected light from the information recording carrier passes through the objective lens, and This is also an effect that the NA is limited when the signal is detected after entering. Therefore, in this case, the aperture of the return optical path is mainly limited. In this case, the ratio of NA is, for example, 0.6 and 0.1.
It is about 35.

[0047]

【Example】

(Example 1) In a recording apparatus having a recording objective lens NA of 0.9 and a laser light source of 4579 nm using an argon laser, the diameter of a portion without a hologram is 1.4 mm, the extinction ratio by switching the polarization direction is about 1/20, and the pitch is An aperture limiting polarization hologram of 35 μm was installed. At this time, the transmitted wavefront accuracy of the hologram was 10 mλ or less.

To switch the polarization direction, the analyzer was removed.
A servo circuit was configured using an O modulator and + 1st-order light of a hologram to ensure temperature stability. The recording objective lens NA when the polarization direction was switched was reduced to 0.36 by the aperture limiting polarization hologram.

Using this recording apparatus, recording is performed on a photosensitive resist applied on a glass master, and this is used as a master, a resin substrate is formed by molding, and a recording film is deposited thereon by vapor deposition to form an information recording carrier. Created.

Using the record carrier thus created,
The camera was mounted on an information recording apparatus having an objective recording lens with a recording lens NA of 0.6, and signals were recorded and reproduced. As a result, a sufficient quality signal was obtained as the address signal, and stable signal recording / reproduction was possible.

[0051]

As described above, by using the optical information recording apparatus having the means described in the present invention, it is possible to accurately control the groove width and length of the information recording signal recorded on the information recording carrier. become.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical information recording apparatus according to an embodiment of the present invention.

FIG. 2 is a plan view of a light beam diameter conversion element using a polarization hologram according to an embodiment of the present invention.

FIGS. 3A and 3B are principle diagrams of recording of a thick groove and a narrow groove by switching the recording objective lens NA of the present invention. FIG. 3A is a laser beam intensity distribution diagram for a narrow groove, and FIG. (C) is a top view of the narrow groove, (d) is a top view of the thick groove, (e) is a cross-sectional view of the groove perpendicular to the track, and (f) is a thick view. (G) is a cross-sectional view of the narrow groove in the track direction. (H) is a cross-sectional view of the narrow groove in the track direction.

FIG. 4 is a diagram illustrating a relationship between a polarization rotation ratio and an element applied voltage, and a relationship between an output of a photodetector and time in the polarization switching device according to one embodiment of the present invention.

FIG. 5 is a schematic configuration diagram of a conventional recording apparatus for an optical information recording carrier master.

FIG. 6 is a schematic diagram of an optical information recording carrier.

7 (a) and 7 (b) are diagrams showing the principle of conventional recording of a thick groove and a narrow groove by varying the amount of light. FIG. 7 (a) is a laser beam intensity distribution diagram for a narrow groove, and FIG. The distribution diagram (c) is a top view of the narrow groove. (D) is a top view of the thick groove. (E) is a cross-sectional view in a direction perpendicular to the track of the narrow groove. (G) is a cross-sectional view of the narrow groove in the track direction. (H) is a cross-sectional view of the thick groove in the track direction.

FIG. 8 is a diagram illustrating the principle of laser light beam polarization plane conversion by an electro-optic effect element.

9A and 9B are diagrams illustrating the principle of a polarization hologram. FIG. 9A is a perspective view of an embodiment of the polarization hologram of the present invention. FIG. Figure

[Explanation of symbols]

REFERENCE SIGNS LIST 1 laser light source 2 laser output light beam 3 optical modulator 4 polarization switching device 5 mirror 6 beam expander 7 laser beam diameter switching device 8 laser light beam expanded by beam expander 9 photodetector 10 polarization hologram ± primary light 11 recording Objective lens 12 Master for optical information recording carrier 13 Focusing spot 15 Center hole for optical information recording carrier 16 Outer periphery of optical information recording carrier

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Terumasa Sano 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd.

Claims (3)

[Claims] 1. An optical information recording apparatus comprising: a laser light source; a device for driving intensity modulation of a laser light beam of the laser light source according to an information signal; and an optical information recording device having an objective lens for condensing the laser light beam. Is passed through a polarization switching device that switches the polarization direction of the laser beam, passes through a beam diameter switching device that changes the laser beam diameter according to the switched polarization direction, and is then condensed by the objective lens. Recording device. 2. A laser beam emitted from a laser light source passes through intensity modulation means for performing intensity modulation in accordance with an information signal.
The laser beam passes through a polarization switching unit that switches the polarization direction of the laser beam, passes through the beam diameter switching unit that changes the laser beam diameter in the switched polarization direction, and is then condensed by an objective lens. Optical information recording method. 3. The optical information recording method according to claim 2, wherein the optical information recording carrier has an address signal groove and a recording continuous groove, and the address signal groove width is smaller than the recording continuous groove width. An optical information recording carrier characterized by being manufactured using an optical information recording master recorded by the above method.