JPH0816987B2 - Optical recording / reproducing device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention limits a light beam such as a laser beam to a minute spot light,
The present invention relates to an optical recording / reproducing apparatus capable of recording / reproducing signals with high density on an optical recording medium and erasing signals once recorded.

Configuration of Conventional Example and Its Problems A device capable of recording / reproducing a signal at high density by irradiating a rotating optical disc coated with a light-sensitive recording material by squeezing a laser beam into a minute spot light of φ1 μm or less is a recording density. In the future, it is possible to increase the reliability of the optical disk and the device by making it possible to reduce the memory cost per bit, access at high speed, and record / reproduce without contact between the optical head and the optical disk. Has attracted attention as a new recording device and medium for the information society.

As a recording medium used for the above optical recording, a recording thin film,
There have been proposed a method of evaporating with heat energy of a laser to form small holes in the recording thin film, a method of changing optical density of the recording thin film with heat energy of laser light, and the like.

In addition, the recording thin film that changes the optical density described above,
It has also been reported that the optical density can be reversibly changed by using an amorphous recording thin film.

The fact that the optical density can be reversibly changed means that signals can be recorded / reproduced and erased.

Generally, the reversible concentration change of the recording thin film is performed by using the state transition of the recording material, and the transition between the amorphous state and the crystalline state of the thin film, or one amorphous state and the other stable state. It is performed by repeatedly utilizing the transition between various amorphous states.

For the sake of simplicity of description, it is assumed that an optical density change is obtained as a transition between an amorphous state and a crystalline state.

FIG. 1 shows a simplified model of the transition condition between the amorphous state and the crystalline state.

In FIG. 1, the amorphous state is shown as A, and the reflectance of the recording thin film in the amorphous state is small and the light transmittance is large. The crystalline state is indicated by C, and the recording thin film in the crystalline state has high reflectance and low transmittance.

The recording thin film capable of reversibly changing the optical density,
When the temperature of the recording thin film in the amorphous state A in the figure is locally raised to near the melting point and that portion is gradually cooled, the crystalline state C is obtained.
(For example, deletion of information). On the other hand, if the temperature of the recording thin film in the crystalline state is locally raised to near the melting point and the portion is rapidly cooled, it becomes the amorphous state A (for example, information recording).

As a method for realizing the temperature rising / quenching condition and the temperature rising / gradual cooling condition on the recording thin film, a device has been proposed in which the light spot for temperature rising / quenching and the light spot for temperature rising / slow cooling are simultaneously irradiated by the same condenser lens. ing. In this device, the focus control signal is detected by one reflected light from the optical disc. However, since the light spot for temperature rising and rapid cooling and the light spot for temperature rising and slow cooling are arranged close to each other on the optical disk, the reflected light from both of these light spots is controlled until the focus control becomes stable. Since the light is mixed and received on the photodetector for the vehicle, the focus control cannot be pulled in stably.

An object of the present invention is to provide a novel optical recording / reproducing apparatus capable of realizing stable focus control for an apparatus including an optical head having a plurality of light spots.

According to the present invention, a plurality of light sources capable of emitting and not emitting light independently, one condensing lens for narrowing a light beam from the light source onto an optical disc to form a plurality of light spots, and the optical disc and the optical disc are combined. When the distance between the optical lenses is at a desired position, only one reflected light from the optical disc can be received, and a photodetector for detecting a focus control signal from the one received reflected light is provided, and focus control is performed. Until the stable state is reached, only one light source emits light, and the other light sources do not emit light.

Description of Embodiments Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a radial cross-sectional view of an optical recording disk having guide tracks used in the present invention. Here, as an example of the guide track, a groove is provided over the entire signal recording area on the disc. An example of a grooved optical disk is shown.

In FIG. 2, the disc substrate 1 is made of a transparent material, and the groove 2 having a width w, a depth d and a track pitch p is formed on the disc substrate 1 in a spiral shape or a concentric shape. A recording thin film 3 having a thickness t is formed thereon by vapor deposition or another method, and a protective layer 4 is provided thereon.

The width w of the groove 2 is smaller than the diameter of the irradiation beam 5 to be irradiated. The depth d of the groove 2 is selected so that the diffraction effect due to the groove in the far field pattern of the reflected light is asymmetric with respect to the optical axis when the center of the groove is deviated from the optical center. Specifically, if the wavelength of the laser light to be irradiated is λ,
It is set to about λ / 6 to λ / 12.

Such a groove 2 functions as a guide track which can be detected optically with respect to the irradiation beam 5. That is, by detecting the asymmetry of the far field pattern of the reflected light,
A known tracking servo can be applied. Therefore, the irradiation beam of FIG. 2 can record or reproduce a signal along a specific groove.

FIG. 3 shows an embodiment of the configuration of the minute spot light of the present invention for forming the conditions of temperature rising rapid cooling and temperature rising gradual cooling on the groove track.

First, FIG. 3A is a side view showing a state in which a substantially circular minute spot light L _{1 obtained} by narrowing a laser beam is irradiated onto a recording medium traveling in the direction of an arrow, and b is an irradiation spot on the groove track 2. C represents the temperature distribution on the recording thin film when the spot light L ₁ is incident, the horizontal axis is the distance, and the vertical axis is the temperature of the recording thin film.

When the intensity of the minute spot light L ₁ is increased to irradiate a local portion of the recording thin film, the temperature rises while the local portion is irradiated and heated (t ₁ second), but thereafter, the recording thin film and , The heat is absorbed and diffused by the base material and the protective layer which are in contact with each other, and a quenching condition is created.

On the other hand, as shown in FIG. 3, if an ellipse-shaped minute spot light L ₂ narrowed down in the traveling direction of the recording medium is formed and a local portion of the recording thin film is irradiated, the heat distribution in this case is spot light L _1.
In comparison with FIG. 3c, the distribution is elongated in the traveling direction as shown in FIG. 3c, and the time t ₂ during which heat is applied to the local area is longer than t ₁ . Therefore, the local portion is cooled more slowly than the spot light L ₁ . That is, if a substantially circular minute spot light is applied to the advancing recording thin film and the intensity thereof is temporally intensity-modulated according to the information to be written, the temperature rising / quenching condition can be locally obtained and the pit can be written. Further, by irradiating an elongated oval minute spot light in the traveling direction and modulating the intensity, a temperature rising and slow cooling condition is obtained, and the written pit can be erased. It should be noted that the reproduction signal is obtained from the substantially circular minute spot light.

Small circular spot light L ₁ and small circular spot light
L ₂ is made up of a single aperture lens 6. Specifically, a substantially circular laser beam is formed within the effective diameter (aperture) of the diaphragm lens 6.
By irradiating both the a ₁ and the groove 2 with an oval laser beam a ₂ which is long in the vertical direction, and setting the optical axes of the re-laser beams a ₁ and a ₂ so that they are not parallel, Above, minute spot lights L ₁ and L ₂ having a substantially circular shape separated from each other by a distance of ₁ and an oval shape elongated in the groove direction are obtained. The distance 1 is determined by the angle Q of both optical axes in the traveling direction of the recording medium, and Q
The smaller is, the smaller is l, and the minute spot lights of L ₁ and L ₂ are closer to each other.

 FIG. 4 shows an embodiment of the present invention.

In FIG. 4, 7 is a semiconductor laser in which the divergence angles of the light beams are substantially equal to each other in the horizontal and vertical directions to the light emitting surface, and 8 is a condenser lens that collects the light beams from the semiconductor laser 7 and is a substantially circular parallel light beam. a ₁ is formed, 9 is a beam splitter (half mirror), 10 is a polarization beam splitter, and 11 is a λ / 4 plate. The light beam a ₁ of the semiconductor laser 7 is incident on the diaphragm lens 6 through these optical elements. To do. The diaphragm lens 6 narrows the incident substantially circular light beam a ₁ to form a substantially circular minute spot light L ₁ on the groove 2 as a guide track as shown in FIG. 4b.

Reference numeral 12 denotes an actuator for driving the diaphragm lens 6, which drives the diaphragm lens 6 in a direction perpendicular to the optical disc in accordance with the surface wobbling of the optical disc to perform a well-known focus control, and also tracks on an eccentric guide track. For the purpose of control, the diaphragm lens 6 is driven in the direction perpendicular to the guide track. Further, if necessary, the control of the time axis correction for driving in the tangential direction of the guide track is also performed. Reference numeral 13 is a semiconductor laser in which the divergence angle of the light beam in the vertical direction is larger than that in the horizontal direction with respect to the light emitting surface, and 14 is a condenser lens that collects the light beams into a substantially parallel light beam a ₂ . Light beam a ₂
Is reflected by the beam splitter 9, passes through almost the same optical path as the light beam a ₁ , enters the diaphragm lens 6, and is a small spot light.
A minute spot light L ₂ is formed in the same groove 2 as the groove irradiated with L _{1 and} has an elliptical shape and the longitudinal direction thereof matches the direction of the groove.

How to make the substantially circular and oval minute spot light will be described later.

The light beam reflected by the optical disc is
It is incident on the polarization beam splitter 10 via a / 4 plate. Since the light beam has passed through the λ / 4 plate twice at the time of incidence and at the time of reflection, the polarization direction of the light beam is rotated by 90 ° and is reflected by the polarization beam splitter 10 this time. Reference numeral 15 is a single lens that converts the reflected lights b ₁ and b ₂ into aperture light. 16 is placed at a near edge in the vicinity of the image forming position of the reflected lights b ₁ and b ₂ , and is arranged so that only the reflected light beam b ₂ from the semiconductor laser 13 is blocked. Reference numeral 17 denotes, for example, a photodetector divided into four parts, and control signals for focus control and tracking control and reproduction signals can be obtained by a conventionally known means.

Drive circuits 18 and 19 drive the semiconductor lasers 7 and 13, respectively, and are intensity-modulated according to the input signals S ₁ and S ₂ .

In the configuration of FIG. 4, two light spots are arranged close to each other on the same guide track, one light spot is substantially circular and the other light spot is a long light spot along the guide track. These lights can independently realize both conditions of temperature rising and rapid cooling and temperature rising and slow cooling while tracking the guide track on the optical recording disk.

FIG. 5 shows how to make a minute spot light of a substantially circular shape and an oval shape.

FIG. 5 is a view of the diaphragm lens 6 as seen from the light incident direction. The light beam a ₁ making a minute spot light L ₁ is substantially circular, the light beam a ₂ to make a minute spot light L ₂ is a long oval in a direction perpendicular to the grooves 2. This is because the larger the effective diameter of the diaphragm lens is, the smaller the diaphragm can be.

Further, since the light beams a ₁ and a ₂ have an inclination of Q between the two optical axes as shown in FIG. 3, they are irradiated closely on the groove.

Now, in the irradiation procedure of both light beams a ₁ and a ₂ in FIG. 4, the state of FIG. 4 shows the state in which the focus control is pulled in. Therefore, the reflected light b ₁ and b ₂ have an image forming position. Since they are different, they can be separated by knife edge 16. However, until the focus control is pulled in, the single lens 15
The position of the reflected light imaged by is not near the knife edge 16. Therefore, the photodetector 17 is also irradiated with the reflected light b _2, which adversely affects the focus control pull-in and stable pull-in cannot be realized. Even after the focus control is pulled in, the stray light of the reflected light b ₂ is detected by the photodetector 17
May affect the focus control. Therefore, at least until the focus control is pulled in, or while the playback signal is being obtained from the optical disc,
The semiconductor laser 13 that forms the elliptical minute spot light L ₂ is prevented from emitting light.

Next, regarding the distance between the minute spot lights L ₁ and L ₂ , since both of the minute spot lights are formed by one diaphragm lens, they can be brought close to each other until they are thermally influenced by each other. For example, as shown in FIG. Both light spots L ₁ and L ₂ during heating and slow cooling
It is possible to give a longer heat distribution in the groove direction by irradiating with, and it is possible to obtain a more gradual cooling effect.

Similarly, as shown in FIG. 6b, when the temperature of the light is rapidly cooled, the intensity of the light spot of L ₂ is weakened and both minute spot lights L ₁ and L ₂ are irradiated, so that L ₂ is the light of L ₁ required for recording. It has both the effect of preheating that can reduce the strength and the effect of stabilizing the recording condition by L ₁ because it can be completely erased once and made into a completely uniform crystal state. The optimum value of the light intensity of each minute spot light is selected according to each condition.
It is obtained by intensity modulation at 18,19.

Next, regarding the temporal arrangement of both minute spot lights, if L ₂ precedes L ₁ on the groove in time, recording can be performed while erasing, and if L ₁ precedes L _{2 in} time. The section to be erased can be determined by the signal reproduced by the minute spot light L ₁ , and the section minute spot light L ₂ can be emitted.

7 and 8 show other embodiments of the present invention. Both of the embodiments are examples using a laser array having two or more light emitting surfaces shown in 21 to 25 as shown in the laser sectional views of FIGS. 7c and 8c. The same reference numerals are given to the same components.

In FIG. 7, the semiconductor laser 20 is indicated by 21 and 22 in the groove direction.
It has two light emitting surfaces, the shape of which is substantially circular 21 and the shape of ellipse 22 is long in the groove direction. Therefore, on the groove 2, the light beam a ₁ emitted from the light emitting surface 21 is a substantially circular minute spot light.
The light beam a ₂ which forms L _{1 and} which is emitted from the light emitting surface 22 forms an elliptic minute spot light L ₂ . Micro spot light L ₁ heats up and cools down (records) and plays back, and L ₂ heats up gradually cools (erases)
And the reflected light b _{1 of the} light beam a ₁ as in the embodiment of FIG.
Only the light is guided to the photodetector 17, and the control signal and the reproduction signal are taken out.

FIG. 8 shows an embodiment in which a semiconductor laser 26 including a laser array having 23, 24, 25 and three light emitting surfaces is used. 23,2
5 has a substantially circular light emitting surface and 24 has an oval light emitting surface, which are arranged in the groove direction. The light emitting surface 23 forms minute spot light of L ₁ and 24, L ₂ and 25 and L ₃ along the groove 2. Groove is advanced in the direction of the arrow, fine spot light L ₃ is reproduced signal and a focus from the optical disk, in order to obtain a control signal for tracking such, L ₂ in order to obtain a heated annealing (erase) effect , L ₁ are used to obtain the temperature rise and quenching (recording) effect.

B ₃ to obtain a reproduced signal and the control signal of the reflected light b ₁ ~b ₃
The knife edge 16 is placed so that it is only guided to the photodetector 17.

The light output of each light emitting surface is independently modulated by the currents I _{1 to} I ₃ . 27 in FIG. 7c and FIG. 8c respectively shows an electrode.

An elliptical small spot light is used as a light source for heating and cooling.
Although the description has been made using L ₂ , if a long and narrow heat distribution can be obtained in the groove direction, a similar effect occurs even in other shapes.
As shown in the figure, it is also possible to arrange a plurality of minute spot lights L ₂₁ , L ₂₂ , and L ₂₃ .

As means for producing a plurality of minute spot lights as shown in FIG. 9, the structure of the diffraction grating 29 shown in FIG. 10a, the trapezoidal prism 30 shown in b, and the laser array 28 shown in c can be considered. This can be achieved by creating multiple light beams a ₂₁ , a ₂₂ , and a ₂₃ . Reference numeral 29 is a semiconductor laser.

As described above, according to the present invention, of the plurality of light spots, only the light source that produces the focus control signal is made to emit light and the other light sources are not made to emit light until the focus control becomes stable. Therefore, the reflected light from another light source does not enter the photodetector during the focus control pull-in, and stable focus pull-in can be realized.

[Brief description of drawings]

FIG. 1 is an operation explanatory view showing an operation principle of a recording medium capable of reversibly changing optical characteristics, and FIG. 2 is a cutaway perspective view showing an example of a structure of an optical disk having grooves as optical guide tracks used in the present invention. FIG. 3a is a diagram showing a lens system for forming a minute spot light that gives conditions for rapid cooling and a gradually rising temperature, and b is a diagram showing a minute spot light on a guide track,
c is a diagram showing the temperature by the same spot light, FIG. 4a is a block diagram showing an embodiment of the present invention, b is an enlarged plan view of the same main portion, and FIG. 5 is a method of producing a minute spot light of the present invention. 6A and 6B are diagrams for explaining the conditions of temperature rising / gradual cooling and temperature rising / quenching when brought close to each other by the influence of the heat of the minute spot lights, and FIG. FIG. 8 and FIG. 8 show other embodiments of the present invention, in which a is a block diagram, b is an enlarged view of the main part, c is a sectional view of the main part, and FIG. FIGS. 10 (a), 10 (b), 10 (c) and 10 (c) are views for explaining obtaining an elongated heat distribution in the groove direction, and FIGS. 2 ... Guide track consisting of grooves, 3 ... Recording medium consisting of recording thin film, 6 ... Aperture lens, 7,13 ... Light source, 15 ...
Single lens, 16 …… Knife edge, 17 …… Photodetector, 20,2
6 ...... arrayed semiconductor lasers, 21-25 ...... emitting surface (light source), 27 ...... light source, 28 ...... arrayed semiconductor laser, L ₁ ...... substantially circular fine spot light, L ₂ ... … Oval round spot light, L ₃ …… Small round spot light, L ₂₁
~ L ₂₃ ... Multiple small spot lights.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Kenji Koishi, 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor, Yuzuru Kuroki 1006, Kadoma, Kadoma City, Osaka

Claims (1)

[Claims] 1. A plurality of light sources capable of independently emitting and not emitting light, one condenser lens for narrowing a light beam from the light source onto an optical disc to form a plurality of light spots, the optical disc and the condenser lens. When the distance between them is at a desired position, only one reflected light from the optical disc can be received, and a photodetector that detects a focus control signal from the one received reflected light is provided, and the focus control is in a stable state. Until then, only one light source emits light and the other light source does not emit light.