JPH0877617A - Optical master disc recorder - Google Patents

Abstract

PURPOSE: To improve a focus control precision by a method wherein a recording beam itself is used for the focus control during a recording period. CONSTITUTION: A light source 1 is a light source such as a Kr ion laser which emitts a laser beam with a short wavelength. The light beam is approximately a parallel light beam. An optical modulator 2 is provided in order to modulate the intensity of the light beam in accordance with information to be recorded. If an AO modulator as shown in the figure is employed, as the frequency of a recorded signal is high, a light beam condensed by a lens is made to enter the AO modulator. The modulated light beam of the AO modulator is a diffracted primary light and a lens which converts the modulated light beam into a parallel light beam again is provided. The light beam from the optical modulator 2 is transmitted through a mirror and a beam splitter and then reflected by a dichroic mirror 15. The reflected light forms a fine spot on a master disc 5 through the object lens of a lens unit 10. On the other hand, the light beam of the light source 1 which is reflected by the master disc 5 is transmitted through the object lens and the dichroic mirror 15 in an opposite direction and reflected by the beam splitter 19. The reflected light beam is introduced into a focus error detection system 9 to detect the focus discrepancy between the object lens and the master disc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk master recording apparatus for recording an optical disk master, and more particularly to a measure for realizing highly reliable recording.

[0002]

[Prior art]

1. Focus control The optical disc master recording apparatus uses a laser having a short wavelength as a light source and a photoresist as a recording medium in order to accurately record minute pits. For this reason, when a light source for recording information for focus error detection is used as in an ordinary optical disc device, the photoresist is a photochemical recording medium, so that the recording state can be reached by the storage effect even if a minute optical output is applied. It is difficult to realize stable control in combination with the fact that the spectral sensitivity of the photodetector that detects the focus error decreases as the wavelength becomes shorter.

For this reason, conventionally, a light source having a long wavelength is separately provided, and this light beam is detected to detect a focus error. 2. Beam monitor The light spot on the master was enlarged and projected on the light receiving surface of the TV camera to observe the change in spot size (circle with changing diameter).

3. The weight of the objective lens that moves the actuator (10 to 15 g) is heavier than that of an ordinary optical disk device (to 0.1 g). Therefore, the position of the objective lens in the optical axis direction is controlled by an actuator that uses a suspension configured to suppress unnecessary vibration with a leaf spring that hardly moves.

[0005]

SUMMARY OF THE INVENTION As described above, in the conventional method: As the recording density of the optical disc becomes higher, the wavelength of the light source of the optical disc master recording device becomes shorter, and the objective lens has a more special lens structure to detect the wavelength of the light source for recording information (for example, 351 nm) and the focus error. It is very difficult to make the same focal length for the two wavelengths of the light source (for example, 633 nm). This is because, as shown in FIG. 3, when the refractive index of the glass material forming the lens has a short wavelength, the increase in the refractive index becomes large. Therefore, even if a focus error is detected by a long-wavelength light source, it is not clear whether the light beam of the light source that actually records information is in focus on the master.

2. Similarly to the above, as the recording density of the optical disc becomes higher, the light spot on the optical disc master is also required to be smaller. When the light spot gets smaller,
The depth of focus becomes even shallower, and even a slight shift in focus will greatly affect the recording state. Since the conventional beam monitor system is configured to simply observe the diameter change of the light beam, it is far insufficient to judge a minute defocus or a focus offset.

3. A conventional lens actuator suspension has a fixed end on the outer peripheral side of a concentric leaf spring,
The inner side was a free end with a lens attached. The inner circumference and the outer circumference have a structure in which radial rims are linearly connected to each other to suppress the unnecessary vibration of the leaf spring, but the movable amount in the optical axis direction is extremely small. Also,
Damping at the main resonance frequency of the leaf spring was also insufficient, which was a factor limiting the accuracy of the focus control system.

[0008]

[Means for Solving the Problems]

1. During recording of information on the master, a light beam for recording information is used to detect the reflected light from the master to generate a focus error signal. It is configured to be controlled by. The detection sensitivity of the focus error detection system is set to be high with respect to the reduction in the sensitivity of the photodetector caused by using the light beam for recording information.

2. With respect to the reflected light from the master of the light beam for recording information, the aberration (non-uniformity) is generated so that the beam shape due to defocusing does not have a symmetrical shape (for example, the shape of the beam when astigmatism is given). The ITV camera receives light with point aberration, mixed aberration, etc.) and monitors the defocus of the light beam for recording information.

3. The outer peripheral side and the inner peripheral side of the leaf spring are connected by a spiral rim, and the entire region sandwiched between the outer peripheral side and the inner peripheral side is sandwiched by the viscoelastic body.

[0011]

[Action]

1. Since the focus control is performed using the light beam for information recording, the aberration of the objective lens is small, so that the focus error can be detected with high accuracy. Further, since the recording light beam is used only during the recording period, the light output is large, which is also a factor that enables highly accurate detection. On the other hand, during the period other than the recording period, the recording optical beam is not applied to the master, but during this period, another light source with a long wavelength is provided as in the conventional case, and the reflected light from the master is detected. By configuring the focus control to be performed, information can be accurately recorded from the start point of recording.

2. Since the shape of the light beam is distorted even with a minute defocus, the defocus can be easily monitored. Further, even if the shape is in focus, the steady defocus, which cannot be determined by the conventional method when the control is stable, is different from that when the shape is in focus, and therefore, the abnormality can be easily distinguished.

3. Since the inner and outer peripheries are connected with a spiral rim, not only can the objective lens be moved a long distance in the optical axis direction, but the entire surface is sandwiched with a viscoelastic body, which can significantly suppress unnecessary vibrations of the rim and enable focus control. Since the control band can be increased, the control accuracy is improved and it is more effective for high density master recording.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an optical disk master recording apparatus according to an embodiment of the present invention, which includes a light source 1, an optical modulator 2, a moving optical system 3, a slider 4, a spindle motor 6, a turntable 7, A beam monitor system 8 and a focus error detection system 9 are provided. On the moving optical system 3, a lens unit 10 attached to an actuator for vertically controlling the objective lens and a focus error detection system using a light source 12 are provided.

The light source 1 is a light source such as a Kr ion laser which emits laser light of a short wavelength (351 nm: ultraviolet ray). The light beam emitted from the light source 1 is substantially parallel light. An optical modulator 2 is provided to modulate the intensity of the light beam according to the information to be recorded. In the figure, the AO modulator is used. Since the frequency of the recording signal is high, the light beam focused by the lens is incident on the AO modulator.
Further, in the AO modulator, the diffracted primary light is a modulated light beam, and a lens for converting this light beam into parallel light again is provided. The light beam from the light modulator 2 is
After passing through a mirror and a beam splitter, it is reflected by the dichroic mirror 15 and forms a minute spot on the master 5 through the objective lens of the lens unit 10. The master 5 is a substrate coated with a photoresist as a recording medium. The master 5 is mounted on a turntable 7 of a spindle motor 6 and rotates. While recording information,
The moving optical system 3 on the slider 4 is controlled to move in the radial direction of the master in synchronization with the rotation of the master, and information is recorded in a spiral shape.

On the other hand, the light beam of the light source 1 reflected by the master 5 passes through the objective lens and the dichroic mirror 15 in the opposite direction to the forward path, and is reflected by the beam splitter 19. This light beam is guided to the focus error detection system 9 and detects the focus shift between the objective lens and the master. The illustrated example shows an example in which a focus error detection system based on astigmatism is configured. Since this detection system is a very general system, there is no need to explain it again, so it is omitted. The main purpose of the present invention is not that the detection method is a feature, but that the light beam used for detecting the focus error is different depending on the situation of the optical disc master recording device. A part of the reflected light from the master passes through the beam splitter 19, is reflected by the beam splitter 20, and is guided to the beam monitor system 8. The beam monitor system 8 has an astigmatism system similarly to the focus error detection system 9. However, unlike the focus error detection system 9, instead of the photodetector 23, means for observing the beam shape such as an ITV camera is provided.
The aberration imparted to the light beam incident on the beam monitor system is not limited to astigmatism, but may be the aberration imparting a mixed aberration as described in JP-A-3-257 “Optical memory device”.

On the other hand, on the moving optical system 3, the stage 11
And a mechanism for moving the lens unit 10 up and down to roughly adjust the position of the objective lens with respect to the master 5 and the long wavelength laser 1.
A focus error detection system using 2 as a light source is provided. In the illustrated example, the focus error detection system using the long-wavelength laser 12 as a light source is also based on the astigmatism method. It should be noted that this detection system also has no feature in the detection system like the focus error detection system 9. The focus error detection system using a long-wavelength laser provided on the moving optical system and the focus error detection system 9 that detects the focus error by receiving the reflected light of the recording beam from the master disc are the focus error detection system based on the recording beam. The optical constants are set so that the detection sensitivity is higher in. This is to compensate for the decrease in the light receiving sensitivity of the photodetector with respect to the recording light beam and to improve the control accuracy by increasing the SN ratio of the control system. FIG. 10 shows the spectral sensitivity characteristics of a PIN silicon photodiode, which is generally used as a photodetector. The wavelength of the ultraviolet laser (e.g., 351 nm) is about three times lower than the wavelength of the He-Ne gas laser (633 nm) or the red semiconductor laser (670 nm) that is used when a focus error is detected by providing another light source. When the wavelength of the recording light source becomes shorter as the sensitivity of the photodetector decreases, the sensitivity of the photoresist of the recording medium increases. FIG. 11 shows an example of the spectral sensitivity characteristic of the photoresist. The recording light source used in the master disk recording apparatus for optical disks has changed in order of 458 nm for Ar ion laser, 407 nm for Ar ion laser, and 351 nm for Kr ion laser as the recording density increases. K
At 351 nm of the r-ion laser, there is a sensitivity difference of about 9 times that of 458 nm. For this reason, the light output for irradiating the master becomes low, so that it is important to set the detection sensitivity of the focus error detection system by the recording beam to be high.

Further, as the structure of the optical disk master recording apparatus, an optical system relating to the recording light beam is developed on a surface rotated 90 degrees about the optical axis of the recording light beam incident on the dichroic mirror 15. One is a general configuration. Further, in the optical disk master recording device, the light beam is once condensed in order to reduce the influence of diffraction such as diameter and dust of the light beam incident on the objective lens, and is made into parallel light again through the pinhole. Those not directly related to the present application are omitted.

It should be noted in FIG. 1 that there are two detection systems, a focus error detection system using a recording light beam as a light source and a focus error detection system composed of a long wavelength light source, and the beam monitor system. Is that an aberration imparting means such as astigmatism is provided.

Before explaining the control method of the optical disk master recording apparatus, an objective lens used here and an actuator for controlling the movement of the objective lens in the optical axis direction will be described.

2 shows an optical recording objective lens "wavelength 35 / nm, NAU.90", Optics, Vol. 23, No. 6, June 1994, as an example of the structure of a general objective lens. It consists of seven lenses, and the lens closest to the master is a parallel plate. In this way, the objective lens composed of a large number of surfaces has each surface treated so as to be anti-reflection for the wavelength of the light source for recording, but the anti-reflection condition is satisfied even for other wavelengths. Since it is extremely difficult, reflected light is generated. Not limited to this application, if a light beam having a wavelength different from that of the recording light beam is provided to detect the focus error, the light beam reflected by each surface of the lens group forming these objective lenses becomes stray light.
If this stray light has an incoherent effect on the focus error detection system by merely increasing or decreasing the amount of light, the effect on the focus error detection will not be so great. However, in reality, there is a coherent effect that stray light interferes with each other, and it is necessary to take measures against stray light. While the wavelength of the recording light source was visible light, most of the objective lenses used microscope objective lenses, so antireflection was applied in the visible region, and this problem did not become apparent. However, in the situation where the ultraviolet light is used as the light source like today, the objective lens is specialized, and the fact is that antireflection is not applied in a wide wavelength range. To solve this problem, the present application uses a laser with low coherence as a light source for a long-wavelength light source to prevent stray light from interfering with each other, and achieves incoherent superposition to prevent stray light. The influence on the detection system was reduced. A laser with low coherence is a semiconductor laser that is self-oscillating or a semiconductor laser that is driven by superposing a high frequency.

FIG. 4 schematically shows the structural requirements of the lens unit 10. The objective lens 33 is supported by suspensions 34 arranged vertically, and is configured to be vertically movable by electromagnetic action of a magnetic circuit composed of a permanent magnet 35 and a coil 36. If there is a factor that the objective lens moves in the direction orthogonal to the optical axis, the arrangement of the recorded information pits in the radial direction (track pitch) is disturbed. When recording a master disc of an optical disc having a high recording density, the track pitch must be more accurate. In the present application, in order to suppress the movement of the objective lens other than in the optical axis direction, the suspension 34 is devised.

FIG. 5 shows the configuration of the suspension of this apparatus. In FIG. 5 (a), the outer peripheral side and the inner peripheral side of the leaf spring 37 are connected by a spiral rim, and the entire region sandwiched between the outer peripheral side and the inner peripheral side is viscoelastic body 3.
The leaf spring 37 is sandwiched at 8. Note that rubber is used as the viscoelastic body 38, for example. According to this structure, unnecessary vibration generated at the rim portion is suppressed, and a damping action is exhibited also with respect to the vibration response at the main resonance point of the leaf spring, so that a preferable characteristic as an actuator can be obtained. An actuator having good vibration characteristics in this way exhibits a synergistic effect such as achieving a higher bandwidth of the control system for further improving control accuracy.

5 (b) and 5 (c) show the leaf spring 3
A viscoelastic body 38 having the same circular shape as that of No. 7 is attached to the upper and lower sides of a leaf spring 37 punched and formed in a spiral shape. Even with such a configuration, the above effects can be obtained.

The structure of the control system will be described below.
FIG. 6 is a configuration block diagram of the focus control system. The control of the recording light beam for recording information on the master is not shown. However, it is self-evident that when the recording optical beam is applied to the master 5, the reflected light from the master enters the photodetector 23. Here, the operation of the focus control system will be described with reference to FIGS. 6 and 7 in accordance with the operation procedure of the optical disk master recording apparatus. First, on the turntable 7,
Master 5 is set. Stage 11 when mounting the master
The lens unit 10, which is located above, moves slowly so as to approach the master 5. Then, the light beam reflected by the laser 12 on the master 5 is received by the photodetector 18. The actual photodetector 18 has a plurality of light receiving surfaces. The output of the photodetector 18 including the plurality of light receiving surfaces passes through the arithmetic processing unit 41, and the focus error signal difference (FS
1) and the sum (FA1) are output. This difference signal FS1
Is shown in FIG. The horizontal axis is the distance between the lens unit 10 and the master 5, and the detection system is adjusted so that when the output is zero, it corresponds approximately to the focus position of the recording beam. Focus lock detection output “H level” shown in FIG.
That is, when the lens unit 10 reaches the retractable area, the movement of the lens unit 10 itself is stopped. These determinations are performed by the lock determination / pull-in processing circuit 4 of FIG.
Done in 1. Then, this judgment output is sent to the system controller controlling the entire optical disc master recording apparatus. In response to this signal, the system controller outputs a control signal “ON” command to the lock determination / pull-in processing circuit 43. When the lock determination / pull-in processing circuit 43 receives this signal, the lock control / pull-in processing circuit 43 sends A
An instruction is issued to output FS1 that has passed through the GC circuit 42.
Then, the switch 45, the compensation filter 46, and the drive circuit 4
A current corresponding to the output of the control signal FS1 flows through the coil 36 via 7, and the position of the objective lens is controlled. FS1
When the focus lock detection output indicates the "H level" during the control state in 1, the objective lens is controlled at a position where the signal of FS1 becomes zero level. By this control, the master is positioned at the focal position of the recording beam. However, due to chromatic aberration of the objective lens (focal length varies depending on wavelength) and the like, the control signal detected at a wavelength different from that of recording contains an error due to the influence of the thickness and warpage of the master. On the other hand, in the present application, when the actual recording is started, the recording light beam reflected by the master is received by the photodetector 23, and the control is switched to the control based on the control signal. The state of this operation will be described with reference to FIGS. 6 and 7.

The photodetector 23, like the photodetector 18, has a plurality of light receiving surfaces. The output of the photodetector 23 including the plurality of light receiving surfaces is passed through the arithmetic processing unit 48, and the difference (FS2) and the sum (FA2) of the focus error signals are output. This difference signal FS2 is shown in FIG. 7B, and the sum signal FA2 is shown in FIG.
It is shown in (c). The horizontal axis is the distance between the objective lens 33 and the master 5, and the detection system is adjusted so that the focus position of the recording beam corresponds when the output of FS2 is zero. FS2 is A
The FA2 signal is input to the automatic switching circuit 50 via the GC circuit 49. The automatic switching circuit 50 determines whether the output level of FA2 is a predetermined value (Vref) or higher, and outputs a signal SP for switching the switch 45 as shown in FIG. 7D. When the switch 45 is connected to the lower part of the drawing, the control signal to the focus control system becomes the FS2 signal that has passed through the gain adjusting circuit 51. That is, the control signal is switched to the control signal generated by the light beam for recording on the master. And
Similar to the case of the control signal of FS1, the position control of the objective lens 33 with respect to the master 5 is performed based on the control signal of FS2. The control system configured as shown in FIG.
FS0 in which FS1 and FS2 are combined as shown in (e)
It will be controlled by.

8 and 9 show a switching signal generating circuit for automatically switching the control signal. Figure 8
This is an example of generating a switching signal using the sum signal FA2. The signal of FA2 is passed through a filter 61 (generally a low frequency pass filter) having the same frequency characteristic as the new dynamic characteristic of the actuator that controls the movement of the objective lens in order to stabilize the operation after switching. Input to the comparator 62. The comparator 62 compares with Vref indicating a predetermined level, and compares the Vref with the filter 61.
When FA2 input via is larger, it becomes "H level". The control signal switching signal SP is set to "H level" when this condition and the focus lock detection output indicating that the focus signal is controlled by the control signal of FA1 are set to "H level". Has been done. The states of these signals are shown in FIGS. 7C and 7D.

FIG. 9 shows an embodiment in which a switching signal is generated in order to realize more reliable switching. The output condition of the switching signal SP of the control signal of FIG.
When 2 is within the range of V + and V-, the control signal is FS.
I am trying to switch to 2.

[0029]

According to the present invention, since the recording beam itself is used for the focus control during the recording period, the focus control accuracy is improved. In addition, since the semiconductor laser with low coherence is used as the light source for pro-focusing before the start of recording, and the focus error detection system is configured so that stray light generated by the objective lens does not interfere, pre-focus accuracy is also improved. did. In addition, the beam monitor system, which is provided to monitor abnormal situations during recording, adds aberration to the reflected light beam so that changes in the beam shape can be clearly determined even with slight defocusing. The accuracy of system quality determination has been improved. Furthermore, it was possible to improve the recording accuracy of the optical disc master recording device as a whole by taking measures to suppress unnecessary vibrations even for the actuator of the controlled objective lens.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a main part of an optical disc master recording device according to an embodiment of the invention.

2 is a diagram showing a configuration example of an objective lens used in the apparatus of FIG.

FIG. 3 is a diagram showing a refractive index change depending on wavelength of a glass material used in the objective lens shown in FIG.

FIG. 4 is a diagram schematically showing a main part of the lens unit shown in FIG.

FIG. 5 is a sectional view showing a main part of a suspension according to an embodiment of the present invention.

FIG. 6 is a block diagram of a focus control system according to an embodiment of the present invention.

FIG. 7 is a diagram schematically showing each signal of the focus detection system according to the embodiment of the present invention.

FIG. 8 is a block diagram of a focus control signal switching unit according to an embodiment of the present invention.

FIG. 9 is another block diagram of the focus control signal switching unit according to the embodiment of the present invention.

FIG. 10 is a diagram showing an example of a spectral sensitivity characteristic of a light detection unit.

FIG. 11 is a diagram showing an example of a spectral sensitivity characteristic of a photoresist.

[Explanation of symbols]

 1 ... Light source 2 ... Optical modulator 3 ... Moving optical system 4 ... Slider 5 ... Master 6 ... Spindle motor 7 ... Turntable 8 ... Beam monitor system 9 ... Focus error detection system 10 ... Lens unit 12 ... Light source 15 ... Dichroic mirror 18 , 23 ... Photodetector 33 ... Objective lens 34 ... Suspension 35 ... Permanent magnet 36 ... Coil 37 ... Leaf spring 38 ... Viscoelastic body 41, 48 ... Arithmetic processing unit 43 ... Lock determination / pull-in processing circuit 44 ... Pull-in control circuit 50 ... Automatic switching circuit

Claims (10)

[Claims] 1. A first light source for recording a signal on an optical disc master, an objective lens for condensing a light beam from the first light source on the optical disc master, the objective lens and the optical disc. A second light source for detecting a defocus between the master and the master is provided, and a second light source obtained by performing arithmetic processing on the reflected light from the master of the optical source while the signal is recorded on the master of the optical disc. An optical disk master recording apparatus, characterized in that it is configured to control defocusing based on the No. 1 focus error signal. 2. During a period in which no signal is recorded on the optical disc master, defocusing is performed based on a second focus error signal obtained by arithmetically processing reflected light from the optical disc master of the second light source. The optical disk master recording apparatus according to claim 1, wherein the optical disk master recording apparatus is configured to control the optical disk master. 3. The optical disk master recording apparatus according to claim 1, wherein the second light source uses a laser having low coherence as a light source. 4. A detection optical system is set such that a focus error detection range of the first focus error signal is narrower than a focus error detection range of the second focus error detection signal. 4. The optical disk master recording device according to claim 1, 2 or 3. 5. The optical disc master recording apparatus according to any one of claims 1, 2, 3 and 4, wherein the determination of switching between the first focus error signal and the second focus error signal is performed by the second focus error detection. An optical disk master recording device, characterized in that it is configured to perform automatically based on a signal. 6. A light source for recording a signal on an optical disc master, an objective lens for converging a light beam from the light source on the optical disc master, and a focus shift between the objective lens and the optical disc master. In the optical disc master recording device including at least a beam monitor system for monitoring, the beam monitor system monitors a change in a beam shape obtained by adding aberration to reflected light from the optical disc master of the light source, and monitors the focus. An optical disk master recording device, characterized in that it is configured to observe a shift. 7. The optical disc master recording apparatus according to claim 6, wherein the aberration-imparting difference element is astigmatism. 8. The optical disk master recording device according to claim 6, wherein the aberration element that gives the aberration is a mixed aberration. 9. A light source for recording a signal on an optical disc master, an objective lens for condensing a light beam from the light source on the optical disc master, and a relative position shift between the objective lens and the optical disc master. In an optical disc master recording apparatus including at least an actuator for moving the objective lens in the optical axis direction so as to cancel out (focus shift), a suspension for supporting the objective lens in the optical axis direction is a plate. An optical disk master recording device having a structure in which a spring is sandwiched with a viscoelastic body. 10. The optical disk master recording device according to claim 9, wherein the viscoelastic body is rubber.