JPH0540945A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To reduce the phase lag of an entire driving system, to enable the driving system of a light beam to follow up to a high frequency band with a simple structure so as to raise the linear velocity of tracks and to perform information recording and reproduction at high speed. CONSTITUTION:A first light beam BL and a second light beam BM are generated by an optical head 1; and by means of an objective lens 12, a first optical spot L, by which the information recording and reproduction are performed, is formed on a guiding track 3 on a recording medium, and a second optical spot M is formed on a position that is apart from the first optical spot L for a prescribed distance to the travelling direction of the beam. The information of a track position is detected by a track position detector 27, the linear velocity is determined by a linear velocity detector 26, a rotational mirror 21 is rotated in accordance with this linear velocity of the track, and the space between the optical spots L, M is varied. By means of a photodetector 24 and a driving circuit 23, a control signal based on the second optical spot M is generated, and the objective lens 12 is moved by driving the objective lens driving element 20 in order to perform the focusing and tracking of the first and the second light beams.

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 / reproducing apparatus for irradiating an optical recording medium with an optical beam to record / reproduce information, and more particularly to an optical information recording / reproducing apparatus using a plurality of light spots. Regarding

[0002]

2. Description of the Related Art Various optical information recording / reproducing apparatuses have been developed for irradiating an optical recording medium with a light beam to form a light spot on the medium to record / reproduce information. In this optical information recording / reproducing apparatus, an apparatus for recording / reproducing / erasing information by using a plurality of light spots has been proposed.

An optical information recording / reproducing apparatus having a plurality of light spots is disclosed in, for example, Japanese Patent Application Laid-Open No. 63-7527. This is an example of an erasable optical information recording / reproducing apparatus, which uses the thermal energy of laser light to reversibly change the optical reflectance of the recording thin film of an optical disc. It repeatedly uses the transition between a crystalline state and another crystalline state, or between another amorphous state.

The device as described above has a plurality of light spots. An example of the configuration is shown in FIG. FIG. 7 is an enlarged view of a part of a disc-shaped optical recording medium (hereinafter referred to as an optical disc). On the guide track 3 provided on the optical disc, a circular first light spot L and a track direction are formed. A long elliptical second light spot M is irradiated, a signal is recorded / reproduced with the first light spot L having a circular shape, and a signal is erased with a second light spot M having an elliptical shape.

FIG. 9 shows an example of a conventional optical information recording / reproducing apparatus. In FIG. 9, the portion surrounded by the alternate long and short dash line shows an optical head, and 7 is a semiconductor laser that emits light of wavelength .lambda.1 and its output light beam is shown by BL. A condenser lens 8 condenses the expanded semiconductor output light into a substantially parallel light beam. 9 transmits the light of wavelength λ1 and
Is a polarizing beam splitter effective for light having wavelengths λ1 and λ2, 11 is a quarter-wave plate for wavelength λ1, and 12 is an objective lens.

The light beam BL of the semiconductor laser 7 is incident on the objective lens 12 through these optical elements. The objective lens 12 focuses the incident light beam BL to guide the guide track 3
An approximately circular light spot L is formed on the top.

Reference numeral 13 is a semiconductor laser which generates a light beam BM having a wavelength λ2, and 14 is a condenser lens. Reference numeral 22 is a reflection mirror, which is rotatable. Reference numeral 15 is a quarter wavelength plate for the wavelength λ 2, and filter 16 is the wavelength λ 2.
It has the function of transmitting the light of 1 and reflecting the light of wavelength λ 2. Light beam BM emitted from the semiconductor laser 13
Is reflected by the reflection mirror 22 and the polarization beam splitter 10, passes through the quarter wavelength plate 15 again, passes through the polarization beam splitter 10 this time, and enters the objective lens 12 through the quarter wavelength plate 11. The objective lens 12 forms a light spot M on the same guide track 3 as that of the light spot L, the light spot M having an elliptic shape and the major axis direction of which coincides with the guide track direction.

Thus, in order to arrange the light spots L and M on the guide track as shown in FIG. 7, the objective lens 1
This can be realized by making the incident angles of the light beams BL and BM incident on the objective lens 12 on the objective lens 12 different from each other.

The reflected light of the light beam BL from the optical disk passes through the objective lens 12, the quarter-wave plate 11, the polarization beam splitter 10, the quarter-wave plate 15 and the filter 16, and is a control signal for focusing and tracking. It is guided to the photodetector 18 via the lens 17 for obtaining. The photodetector 18 is composed of four-divided PIN diodes, and outputs the reproduced signal and the first light spot L by a known method.
To obtain control signals for focusing and tracking.

On the other hand, the reflected light of the light beam BM from the optical disk passes through the objective lens 12 and the quarter-wave plate 11. Here, for example, the wavelength λ1 is 780 nm and the wavelength λ2 is 83
By making the semiconductor laser of 0 nm, most of the light transmitted through the quarter-wave plate 11 is reflected to the semiconductor laser 7 side by the polarization beam splitter 10 and further reflected by the filter 9 to be a two-divided photodetector. Guided to 19. A tracking control signal for the second light spot M is obtained from the differential output of the two-split photodetector 19.

The objective lens 12 is an objective lens driving element 2
At 0, it is held so as to be movable in the biaxial directions of the optical axis direction for focus and the direction perpendicular to the track for tracking. Therefore, the first light spot L and the second light spot M are moved by the objective lens driving element 20 at the same time and in the same direction in the direction perpendicular to the track. The objective lens driving element 20 may have a known voice coil type structure, and can perform focus control corresponding to surface deviation of the first light spot L of the optical disc and tracking control for track eccentricity by a known technique.

At this time, as described above, the second light spot M also moves. However, since the rotatable reflecting mirror 22 is provided in the optical path of the second light spot M, the turning of the reflecting mirror 22 causes the second light spot M to be independent of the first light spot L. It can be moved vertically to the track. This is because the incident angle of the light beam BM incident on the objective lens 12 in the direction perpendicular to the track changes.

As described above, the tracking control signal for the second light spot M is obtained from the two-divided photodetector 19, but the second light spot can be obtained by rotationally driving the reflecting mirror 22 by a known technique. M tracking control can be performed.

The driving means for moving the second light spot M has been described as the rotatable reflecting mirror 22, but
A driving means and the like for moving the semiconductor laser 13 by a piezoelectric element has also been proposed.

As described above, the first driving means for moving the two light spots together in the direction substantially perpendicular to the track,
There has been proposed an optical recording / reproducing apparatus having a plurality of light spots configured to have a second drive means for moving the second light spot independently of the first light spot.

[0016]

To increase the speed of recording / reproducing information, a method of increasing the linear velocity of the track can be considered. In the case of an optical disc, the number of revolutions of the disc will be increased, but the surface runout of the disc
The frequency of disturbance due to eccentricity, waviness of the track, etc. is also increased, and it is required to increase the servo band of the drive means of the light spot.

However, in the above-mentioned conventional example, tracking control of a plurality of light spots is independently performed using the reflected light of each light spot, so that a phase delay occurs with respect to a high frequency disturbance. Further, the three-beam method using the diffracted light of the 0th order and ± 1st order by the diffraction grating, which is a known technique, is the + 1st order light before and after the 0th order light.
The difference in the amount of reflected light of the primary light is controlled to be 0 so that the 0th light at the center of the ± primary light is on the track. This is because the position of the 0th-order light is controlled, so that a phase delay occurs in a high frequency region as in the above-described conventional example. The same applies to focus control.

The beam driving means of the optical head used in the optical information recording / reproducing apparatus generally has an open loop characteristic as shown in FIG. The gain may be increased so that the beam follows the track even when the frequency band of the servo system is increased and the disturbance has a high frequency, but it is necessary to reduce the phase delay in order to maintain the stability of the servo system.

The present invention has been made in view of these circumstances, and it is possible to reduce the phase delay of the entire drive system and to obtain stable phase characteristics without changing the drive means of the light beam. This makes it possible to obtain a light beam drive system that can follow up to a high frequency band with a simple configuration, and to increase the linear velocity of the track to provide an optical information recording / reproducing device capable of recording / reproducing information at high speed. It is intended to be provided.

[0020]

An optical information recording / reproducing apparatus according to the present invention comprises a first light beam for recording and / or reproducing information by forming a spot on a track on a recording medium by an objective optical system. Light beam generating means for generating a second light beam that forms a spot at a position separated from the first light beam by a predetermined distance in the beam scanning direction; and the first and second light beams. When the linear velocity of the track is large, the interval between the linear velocity detecting means for detecting the linear velocity of the track following and the first light beam and the second light beam on the recording medium is widened. A beam spacing changing means for changing the linear velocity to be narrow when the linear velocity is small; a signal converting means for converting the reflected light of the second light beam into an electric signal; and focusing from the output of the signal converting means. A control signal generating means for generating a control signal for racking, and a driving means for moving the objective optical system for focusing and tracking the first and second light beams on a track on the recording medium. Then, the drive means of the objective optical system is driven based on the control signal from the control signal generation means,
And at least one of focusing and tracking of the second light beam.

The light beam generating means is not limited to the number and configuration of the light source, the optical system, etc., and is for generating a plurality of light beams.

[0022]

The light beam generating means forms the spot on the track on the recording medium by the objective optical system to perform at least one of recording and reproducing information, and the first light beam.
A second light beam that forms a spot at a position apart from the light beam in the beam scanning direction by a predetermined distance is generated. The linear velocity detecting means detects the linear velocity of the track followed by the first and second light beams. The beam interval changing means changes the beam width so that it is wide when the linear velocity of the track is high and narrow when the linear velocity of the track is low. The signal conversion means converts the reflected light of the second light beam into an electrical signal, and the control signal generation means generates a control signal for focusing tracking from the output of the signal conversion means. The driving means moves the objective optical system in order to focus and track the first and second light beams on a track on the recording medium. At this time, the driving means of the objective optical system is driven based on the control signal from the control signal generating means to perform at least one of focusing and tracking of the first and second light beams.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 relate to a first embodiment of the present invention, and FIG. 1 is a structural explanatory view showing a structure of an optical information recording / reproducing apparatus,
2 is an explanatory diagram showing the arrangement of light spots on the tracks of the optical disk, FIG. 3 is an explanatory diagram showing the phase of the error signal by the sub beam and the main beam, and FIG. 4 is a characteristic showing the phase advance of the servo system according to this embodiment. 5 and 5 are characteristic diagrams showing gain and phase characteristics when the present embodiment is applied to the drive system having the open loop characteristic shown in FIG.

In FIG. 1, a portion surrounded by a chain double-dashed line shows an optical head 1 as a light beam generating means. The same parts as those in the conventional example are designated by the same reference numerals.
A semiconductor laser 7 for generating light of wavelength .lambda.1 is provided and outputs a light beam BL. The condenser lens 8 condenses the output light of the semiconductor laser 7 into a substantially parallel light beam.
The light beam BL of the semiconductor laser 7 includes a condenser lens 8, a filter 9 which transmits light of wavelength λ1 and reflects light of wavelength λ2 described later, a polarization beam splitter 10 which is effective for light of wavelengths λ1 and λ2, and wavelength λ1. To the objective lens 12 through the quarter-wave plate 11. The objective lens 12 focuses the incident light beam BL to form a substantially circular first light spot L on the guide track 3 of the optical disk.

A semiconductor laser 13 for generating a light beam BM having a wavelength λ2, a condenser lens 14 for condensing the output light of the semiconductor laser 13, and a rotating mirror for guiding the beam from the semiconductor laser 13 to the polarization beam splitter 10. 21 is provided. The light beam BM emitted from the semiconductor laser 13 is a rotating mirror 21 and a polarization beam splitter 10.
Is reflected by the filter 16 which passes through the quarter-wave plate 15 for the wavelength λ2, transmits the light of the wavelength λ1 and reflects the light of the wavelength λ2. And again the quarter wave plate 1
5 and then through the polarizing beam splitter 10,
It enters the objective lens 12 through the quarter-wave plate 11. The objective lens 12 forms a substantially circular second light spot M preceding the first light spot L on the same guide track 3 as the light spot L.

The reflected light of the light beam BL from the optical disk passes through the objective lens 12, the quarter-wave plate 11, the polarization beam splitter 10, the quarter-wave plate 15 and the filter 16, and passes through the lens 17 to the photodetector. Guided to 18. A reproduction signal or the like is generated from the output of the photodetector 18 by a known method.

On the other hand, the reflected light of the light beam BM from the optical disk passes through the objective lens 12 and the quarter-wave plate 11. Most of the light transmitted through the quarter-wave plate 11 is reflected to the semiconductor laser 7 side by the polarization beam splitter 10 and further reflected by the filter 9 to obtain a lens 17 for obtaining control signals for focusing and tracking. And is guided to the photodetector 24 divided into four. The photodetector 24 is connected to the drive circuit 23, and drives the objective lens drive element 20 with a difference signal of the output from the photodetector 24.

The objective lens 12 is held by an objective lens driving element 20 so as to be movable in two axial directions, that is, an optical axis direction for focusing and a direction perpendicular to a track for tracking. Therefore, the first light spot L and the second light spot M are moved by the objective lens driving element 20 at the same time and in the same direction in the direction perpendicular to the track. That is, the objective lens drive element 20 and the drive circuit 23 perform focus control corresponding to surface deflection of the optical disc in the second light spot M and tracking control for track eccentricity. Thus, in this embodiment, the first light spot L
Information is recorded / reproduced / erased by the second optical spot M
The objective lens is driven by the tracking / focusing signal from (1) to track the first light spot L.

Further, the photodetector 24 is connected to the track position detector 27, and the track position information of the guide track 3 is detected by an electric signal from the photodetector 24. This detected track position information is
It is transmitted to the linear velocity detector 26 of the truck. CA
In a V or ZCAV type optical information recording / reproducing apparatus, the linear velocity at the inner circumference and that at the outer circumference differ depending on the position of the track. In this case, the track linear velocity detector 26
The linear velocity is calculated from the track position information of the guide track 3 on the disc, and a signal corresponding to the linear velocity is transmitted to the stepping motor 25. The stepping motor 25 is connected to the rotating mirror 21, and changes the incident angle of the light beam BM from the semiconductor laser 13 on the polarization beam splitter 10 according to the linear velocity of the track, so that the light on the guide track 3 is emitted. The distance between the spots L and M can be changed.

Next, the operation of this embodiment will be described.
FIG. 2 shows a light spot formed on the guide track 3 of the optical disk with the above-described configuration. In this embodiment, the first
The second light spot M (hereinafter, sub beam) is arranged in front of the light spot L (hereinafter, main beam) in the beam scanning direction. Therefore, as for the tracking (focusing) error signal, the phase of the signal by the sub-beam M is advanced as shown in FIG. Therefore, when tracking / focusing control is performed by the reflected light of the sub-beam M, there is no difference from the conventional servo characteristics for the sub-beam M, and the band of the servo system cannot be increased, but the phase of the track waviness is With respect to the main beam L at the delayed position, the delay of the phase can be reduced by controlling based on the error signal at the advanced position of the phase.

When the phase delay reduction is θ, the disturbance frequency is f, the track linear velocity is V, and the distance between the main beam and the sub beam is D, the relationship of θ = 2πfD / V [rad] (1) is established. Therefore, the higher the frequency disturbance in which the phase delay of the servo system becomes a problem, the greater the effect of reducing the phase delay becomes. When the optical disc is used at a constant rotation, the linear velocity V changes depending on the radial position of the track, but the beam interval D
And the D / V is kept constant by changing
Depends only on the disturbance frequency.

FIG. 4 shows an example of phase advance with frequency when D / V is kept constant in the equation (1). As described above, the higher the frequency, the greater the phase advance. FIG. 5 shows an example of open loop gain and phase characteristics when this phase advance is applied to the drive system having the open loop characteristics shown in FIG. In FIG. 5, the broken line shows the conventional open loop characteristic, and the solid line shows the open loop characteristic according to the present embodiment. In the high frequency band, since the phase advance is added, the phase delay stops at a certain value and rotation does not continue any further, and in the higher frequency band, the phase advances in the opposite direction. Therefore, the phase margin (margin value up to -180 degrees in the phase when the gain is 0 dB) increases as compared with the conventional example. Generally, the phase margin is 40
Since it suffices to obtain a phase margin of about 40 degrees, if θ is set so that a phase margin of 40 degrees can be taken, a stable servo system can be configured without oscillation even if the gain is increased.

Here, if the gain is increased too much, on the contrary, the phase advances when the gain is 0 dB, and the phase may advance to +180 degrees and oscillate. Therefore,
When the phase is +180 degrees, the gain is set so that the gain margin is set to be -3 to 6 dB or less. In other words, if the minimum phase margin that can obtain stable characteristics is secured, it is desirable to prevent θ from increasing beyond that. By doing so, it is possible to prevent the phase from advancing too much in the high frequency region, and it is possible to set the gain higher.

As described above, in this embodiment, since the objective lens is driven by the control signal from the light spot M of the preceding sub-beam, the light spot M has some phase with respect to the undulation of the track of high frequency. Attempt to follow up with a delay Φ. At this time, the light spot L of the main beam, which is at a position delayed in phase with respect to the waviness of the track, follows the track in a state in which the phase delay is reduced by θ as compared with the light spot M of the sub beam. Therefore, the gain can be increased as much as the phase delay is reduced, and it is possible to follow the disturbance in a higher frequency band.

At this time, when a constant rotation optical disk is used, since the linear velocity of the track is different between the inner and outer circumferences as described above, θ changes and the open loop characteristic also changes. That is, if the linear velocity becomes larger than the state when the gain is set, the phase of the drive system may be delayed and the phase margin may not be secured, or if the linear velocity becomes smaller, the phase may advance too much and oscillate in a high frequency region. is there. Therefore, depending on the linear velocity of the track, when the linear velocity V is high, the interval D between the main beam and the sub beam is widened, and when the linear velocity V is small, the interval D between the beams is narrowed to keep D / V constant. Try to keep it. That is, the stepping motor 25 is operated according to the linear velocity detected by the linear velocity detector 26 of the track to rotate the rotating mirror 21 to change the beam interval D. As a result, it is possible to obtain a constant phase lead that does not depend on the linear velocity but only on the disturbance frequency, and thus it is possible to always maintain a state in which the optimum tracking performance according to the characteristics of the drive system is obtained. ..

Although it is desirable to keep D / V constant, a means for finely adjusting the beam interval D is required, and the construction may not be easy in some cases. In this case, the distance D between the main beam and the sub-beams is changed in such a way that it widens when the linear velocity V is high and narrows when the linear velocity V is low so that the open loop characteristic does not change so much and the servo system is stabilized. The gain or the like may be set within a range in which the degree can be maintained.

As described above, according to this embodiment,
By performing tracking focusing control with the reflected light of the beam preceding the reproduction beam, the phase delay in the high frequency range can be mechanically reduced. As a result, the phase delay of the servo system is reduced and a sufficient phase margin can be secured, so that the gain can be increased and the frequency band can be extended to the high frequency band. Therefore, it is possible to follow a high-frequency disturbance with a simple configuration without changing the driving means of the light beam.
Since the linear velocity of the track can be increased, high speed information recording / reproducing becomes possible.

Even when the optical disc is used at a constant rotation and the linear velocities of the inner and outer circumferences are different, the reduction of the phase delay θ changes only with respect to the frequency of the disturbance and the open loop characteristic does not change, so that the stable phase delay is obtained. A reduction effect can be obtained.

FIG. 6 is a perspective view showing the structure of a track position information detecting device according to the second embodiment of the present invention.

The second embodiment shows a modification of the track position detector 27 in the first embodiment. Recording medium 28
A carriage 32 is provided which is movable in the radial direction of the guide rail 30. The carriage 32 is provided with a raising mirror 31 for raising the beam from the polarization beam splitter 10. A drive coil 29 placed in a magnetic field (not shown) is connected to the carriage 32. Further, a glass scale 34 for detecting the track position is attached to the carriage 32. And this glass scale 34
An optical sensor 33 for reading the bright and dark pattern 34a is provided. Others are the same as those in the first embodiment.

The light beam from the polarization beam splitter 10 has its optical path bent 90 degrees by the rising mirror 31.
Guide track 3 on recording medium 28 by objective lens 12
Form spots on top. Here, the rough access of the light spot is performed by the carriage 32 to which the driving coil 29 placed in the magnetic field is attached. The carriage 32 is guided by the guide rail 30 in the disk radial direction.
At this time, the optical sensor 33 reads the light and dark pattern 34 a of the glass scale 34 attached to the carriage 32. As a result, the absolute position of the carriage 32 is detected, so that the position of the track on which the light spot is formed can be detected. Optical sensor 33
Transmits an electric pulse signal according to the read light and dark pattern to the stepping motor 25 to rotate the rotating mirror 21.

In this way, by detecting the position of the glass scale 34 attached to the carriage 32,
Absolute track position information can be obtained. By rotating the rotating mirror 21 based on the track position information, the interval between the two light spots can be changed according to the linear velocity of the track. Other functions and effects are similar to those of the first embodiment.

The plurality of light spots are not limited to those formed by the light beams from the plurality of semiconductor lasers, and may be obtained by using a diffraction grating from one semiconductor laser. In addition, the spot of the preceding beam is recorded and
The reproducing beam spot is not limited to the one on the same track as the reproducing beam spot, and each may be located on the adjacent tracks in the front and rear positions in the beam scanning direction.

[0044]

As described above, according to the present invention, the tracking / focusing control is performed by the reflected light of the beam preceding the recording / reproducing beam, so that the driving means of the light beam can be driven without changing. The phase delay of the entire system can be reduced. Further, stable phase characteristics can be obtained by changing the beam interval according to the linear velocity of the track. This makes it possible to obtain a light beam drive system that can follow up to a high frequency band with a simple configuration, and increase the linear velocity of the track to record / record information at high speed.
There is an effect that reproduction becomes possible.

[Brief description of drawings]

FIG. 1 is a structural explanatory view showing the structure of an optical information recording / reproducing apparatus in a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing the arrangement of light spots on a track of an optical disc.

FIG. 3 is an explanatory diagram showing phases of error signals due to a sub beam and a main beam.

FIG. 4 is a characteristic diagram showing an example of phase advance of a servo system according to the present invention.

5 is a characteristic diagram showing an example of gain and phase characteristics when the present invention is applied to a drive system having an open loop characteristic shown in FIG.

FIG. 6 is a perspective view showing the configuration of a track position information detecting device according to a second embodiment of the present invention.

FIG. 7 is a perspective view showing an arrangement of an optical disc and a light spot.

FIG. 8 is a structural explanatory view showing a structure of a conventional optical information recording / reproducing apparatus.

FIG. 9 is a characteristic diagram showing an example of open loop characteristics of a drive system of a light beam.

[Explanation of symbols]

 L, M ... Light spots BL, BM ... Light beam 1 ... Optical head 3 ... Guide track 7, 13 ... Semiconductor laser 12 ... Objective lens 18, 24 ... Photodetector 20 ... Objective lens driving element 21 ... Rotating mirror 23 ... Drive circuit 25 ... Stepping motor 26 ... Linear velocity detector 27 ... Track position detector 28 ... Recording medium 32 ... Carriage 33 ... Optical sensor 34 ... Glass scale

Claims (1)

[Claims] 1. A first light beam for forming a spot on a track on a recording medium by an objective optical system and performing at least one of recording and reproducing information, and a predetermined light beam in a scanning direction of the beam with respect to the first light beam. A light beam generating means for generating a second light beam forming a spot at a position separated by a distance; and a linear velocity detecting means for detecting a linear velocity of a track followed by the first and second light beams. And a beam interval for changing the distance between the first light beam and the second light beam on the recording medium so as to be wide when the linear velocity of the track is high and narrow when the linear velocity of the track is low. Changing means, signal converting means for converting the reflected light of the second light beam into an electrical signal, and control signal generation for generating a control signal for focusing tracking from the output of the signal converting means. And a drive means for moving the objective optical system for focusing and tracking the first and second light beams on a track on the recording medium, and a control signal from the control signal generating means. An optical information recording / reproducing apparatus, characterized in that the driving means of the objective optical system is driven based on this to perform at least one of focusing and tracking of the first and second light beams.