JPH0554407A - Focus control device - Google Patents

Abstract

(57) [Abstract] [Purpose] When performing recording on a recording medium with a laser or the like, focus adjustment is automated in a focus control device that controls a light beam focused by an objective lens so as to focus on the recording medium. The purpose is to improve the operability by performing the following operation. [Configuration] The focus control circuit A1 in the switching circuit 16
The focus control circuit A13 by the four-division detector 12 that detects the recording beam A2 by selecting 3
The first focus control system of is activated. At this time, the focus error signal obtained by the focus control circuit B15 from the output of the two-divided detector 14 for detecting the focus beam moves the pulse motor 19 by the focus error signal to move the position of the detector 14, and the position is automatically adjusted. Done.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus control device for controlling a light beam focused by an objective lens or the like so as to focus on the recording medium when recording on a recording medium by irradiation of a light beam such as an electron beam or a laser. It is a thing.

[0002]

2. Description of the Related Art In recent years, the progress of fine recording technology using electron beams, lasers, etc. has been remarkable, and optical disks have been put to practical use as applications of lasers. An optical disk master recording apparatus that performs submicron-order recording on a glass master disk as a recording medium in the process of manufacturing an optical disk master requires a stable and highly accurate focus control device for narrowing the laser beam diameter. ..

A conventional focus control device will be described below. FIG. 4 is a block diagram of a conventional focus control device. In FIG. 4, 1 is a glass substrate having a resist coating, 2 is a recording light source including a recording laser and an optical modulator, 7 is a shutter for turning on / off a recording beam A1 emitted from the recording light source 1, and 8
Is a light source for focusing, 9 is a beam splitter, 10 is a beam splitter, 11 is an objective lens, 14 is a two-divided detector for focus, 15 is a focus control circuit, 17 is a focus drive circuit, 18 is a focus actuator, and 19 is a focus 2 Stepping pulse motor to move the position of split detector, 30
Is a pulse motor drive circuit that drives the stepping pulse motor 19 manually (SW input or the like), and 31 is a monitor system that monitors the reflected light A2 of the recording beam A1.

The operation of the focus control device configured as described above will be described below. First, when recording on the glass master, the shutter 7 is opened and the recording beam A1 emitted from the recording light source is focused on the glass master 1 through the objective lens 11. At this time, the focus beam B1 emitted from the focus light source 8 is also focused on the glass master 1 through the beam splitters 9 and 10 and the objective lens 11. Further, when no recording is performed, the shutter 7 is closed and only the focus beam B1 is focused on the glass master 1. The wavelength of the focus beam B1 is longer than the wavelength of the recording beam, and the resist is not exposed.
The focus beam B1 obliquely enters and is reflected by the glass master 1. In accordance with the vertical movement of the objective lens 11, the optical path of the reflected light B2 of the focus beam B1 changes, and the position on the detector 14 changes. Objective lens 1
1 is attached to the focus actuator 18,
It is driven by the focus drive circuit 17. Therefore, the focus error signal is obtained by taking the difference between the two-divided detectors 14, and the focus control circuit 15, the focus drive circuit 17, and the actuator 18 constitute a focus control system, and the focus beam B2 is at the center position of the two-divided detector 14. The focus actuator 18 is controlled so that it always comes. The two-divided detector 14 can be moved in the moving direction of the focus beam B2 by the stepping pulse motor 19. When the focus is controlled by the focus beam B2, the focus state of the recording beam A1 can be monitored by the monitor system 31. If the recording beam A1 is not focused on the glass master disk 1, the position of the two-divided detector 14 is not aligned with the focus of the recording beam A1. In such a case, a good recording state can be obtained by focusing the recording beam A1 by manually adjusting the position of the two-divided detector 14 while monitoring the recording beam A2.

[0005]

However, the above conventional configuration has the following problems. Since the focus is indirectly controlled by the focus beam B2, first, the position of the two-divided detector must be adjusted manually while monitoring the condensed state of the recording beam A1. Therefore, there is a problem that a series of operations for recording on the glass master cannot be automated. Also,
When the focus is directly controlled by the recording beam A2 (such as the astigmatism method), the above adjustment is not necessary, but there are the following problems. Since the unrecorded area of the glass master is exposed by irradiating the glass master with the recording beam A1, it cannot be irradiated and reflected light A2 cannot be detected and focus control cannot be performed. For this reason, the focus control is first performed at the recording start position, and there is a problem that the recording start is delayed due to the focus pulling operation, and the recording is performed in the defocus state in which the focus is not completely taken.

The present invention is to solve the above-mentioned conventional problems, and provides a focus control device for automating focus adjustment to improve operability.

[0007]

In order to solve this problem, the focus control apparatus of the present invention comprises the following means. In the first invention, the first control means for keeping the focal position of the first light flux constant, the second control means for keeping the focal position of the second light flux constant, and the positions of the second detecting means are Moving means for moving, and movement control means for moving the position of the second detecting means in the detection direction of the second light flux by the output of the second detecting means and the moving means when the first controlling means operates. And have. In the second invention,
During the operation of the first control means, instead of moving the position of the second detection means, the holding circuit that samples and holds the error signal of the second detection means and the output of the holding circuit when holding the holding circuit It has an adding means for adding to the control means.

[0008]

With this configuration, in the first invention, the position of the second detection means is adjusted by the movement control means and the movement means during the operation of the first control means, and the position is fixed. The focus position of the first light flux is kept constant even during the operation of the control means. In the second invention, the second control means,
By adding the error signal of the second detection means detected during the operation of the first control means, the focal position of the first light flux can be kept constant even during the operation of the second control means.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a glass master, 2 is a recording light source including a recording laser for emitting recording light A1 and an optical modulator, 3 is a polarization beam splitter, 4 is a quarter wavelength plate, and 5 is a lens. , 6 is a cylindrical lens, 7 is ON-OFF of the recording beam A1 emitted from the recording light source 1.
Shutter, 8 is a focusing light source that emits the focus beam B1, 9 is a beam splitter, 10 is a beam splitter, 11 is an objective lens, 12 is a four-division detector, 13 is a focus control circuit A for recording light A2, and 14 is a focus Two-divided detector, 15 is a focus control circuit B, 16 for a focus beam B2
Is a switching circuit for switching between the focus control circuit A and the focus control circuit B, 17 is a focus drive circuit, and 18
Is a focus actuator, 19 is a stepping pulse motor that moves the position of the focus splitting detector, 20 is a pulse motor drive circuit that drives the stepping pulse motor 19 by the output of the focus control circuit 15, and 21 is a pulse motor drive circuit 20.
It is an ON-OFF circuit that turns the output of ON-OFF.

The operation of the focus control device configured as described above will be described. First, shutter 7
When is open, the recording beam A1 emitted from the recording light source 2 passes through the objective lens 11 and is reflected by the glass master 1. The reflected light A2 is guided to the lens 5 and the cylindrical lens 6 by the quarter-wave plate 4 and the polarization beam splitter 3, and is detected by the four-division detector 12. The focus error signal is obtained by taking the difference of the diagonal sums of the quadrant detector 12. The objective lens 11 is attached to the focus actuator 18, and is driven by the focus drive circuit 17. When the focus control circuit A13 is selected by the switching circuit 16, the focus drive circuit 1
7. Focusing actuator 18 for recording beam A1
Is controlled so that it is always in focus on the glass master 1.
Further, when the shutter 7 is closed, the focus is controlled by the focus beam B2. The focus beam B1 emitted from the focus light source 8 passes through the beam splitters 9 and 10 and the objective lens 11 and is focused on the glass master 1. The focus beam B1 obliquely enters the glass master disk 1, and a part B2 of the reflected light is guided to the two-divided detector 14 by the beam splitter 9. The focus control circuit B is selected by the switching circuit 16, the focus control system is configured by the two-divided detector 14, the focus control circuit B15, the focus drive circuit 17, and the actuator 18, and the focus beam B2 is always located at the center position of the two-divided detector 14. The focus actuator 18 is controlled to come. The position of the two-divided detector 14 is movable by the stepping pulse motor 19, and the two-divided detector 14 is movable in the direction in which the focus beam B2 moves in response to the vertical movement of the objective lens 11. When the focus control circuit A13 is selected by the switching circuit 16, the ON-OFF circuit 21 is turned on in cooperation with the switching circuit 16. At this time, the position of the detector 14 is controlled by the pulse motor drive circuit 20 and the stepping pulse motor 19 by the output of the focus control circuit B15. ON-OFF circuit 2
When 1 is turned off and the position of the detector 14 is fixed at this position, the recording beam A1 is focused on the glass plate by controlling the focus beam B2.

As described above, according to this embodiment, when the focus control using the recording beam is performed, the position of the two-divided detector for detecting the focus beam is automatically controlled by the position control by the difference output of the two-divided detector. The position of the two-divided detector can be adjusted.

A second embodiment of the present invention will be described below with reference to the drawings. In FIG. 2, 1 is a glass master, 2 is a recording light source including a recording laser for emitting recording light A1 and an optical modulator, 3 is a polarization beam splitter, 4
Is a quarter-wave plate, 5 is a lens, 6 is a cylindrical lens, 7 is a shutter for turning ON / OFF the recording beam A1 emitted from the recording light source 1, and 8 is a focus beam B.
Focusing light source for emitting 1; 9 for beam splitter, 10 for beam splitter, 11 objective lens, 12
Is a four-division detector, 13 is a focus control circuit A for recording light A2, 14 is a two-division focus detector, 15 is a focus control circuit B for focus beam B2, 16 is a switching circuit for switching between the focus control circuit A13 and the focus control circuit B15 , 17 is a focus drive circuit, and 18 is a focus actuator. The above is the same configuration as in FIG. The difference from the configuration of FIG. 1 is that the stepping pulse motor 19 and the pulse motor drive circuit 2 which constitute the position control system of the detector.
0, instead of the ON-OFF circuit 21, a sample hold circuit 22 that holds the output of the focus control circuit B13
And an analog switch 23 for adding the inverted output of the sample hold circuit 22 to the focus control circuit B13.

The operation of the focus control device configured as described above will be described. First, the recording beam A2
When the focus control is performed by the control circuit B
The amount of deviation of the detector position detected by 13 is sampled by the sample hold circuit 22, and the inverted output of the held value is added to the control circuit B13 by the analog switch 23. The analog switch 23 is open at the time of sampling of the sample hold circuit 22, the analog switch 23 is closed at the time of hold, and the inverted output of the sample hold circuit 22 is added to the control circuit B13 at the time of hold. Further, during control by the focus beam B2, the analog switch 23 is closed and the sample hold circuit 22 is always in the hold state.

As described above, the sample hold circuit 22
By giving an offset to the control circuit B13 by means of the analog switch 23, the position shift amount of the detector 12 can be automatically corrected during focus control by the recording beam.

A third embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, 1 is a glass master, 2 is a recording light source, 3 is a polarization beam splitter, 4
Is a quarter-wave plate, 5 is a lens, 6 is a cylindrical lens, 7 is a shutter for turning ON / OFF the recording beam A1 emitted from the recording light source 1, and 8 is a focus beam B.
Focusing light source for emitting 1; 9 for beam splitter, 10 for beam splitter, 11 objective lens, 12
Is a four-division detector, 13 is a focus control circuit A for recording light A2, 14 is a two-division focus detector, 15 is a focus control circuit B for focus beam B2, 16 is a switching circuit for switching between the focus control circuit A13 and the focus control circuit B15 , 17 is a focus drive circuit, 18 is a focus actuator, and the above is the same configuration as in FIGS. The difference from the configuration of FIG. 2 is that the switching circuit 1 is provided by an adder 24 that adds the outputs of the four-division detector 12 and an output of a comparator 25 that determines whether the output of the adder 24 is a certain value or more.
That is, the configuration is such that 6 is switched.

The operation of the focus control device configured as described above will be described. First, when the shutter 7 is open, the reflected light A2 of the recording beam A1 from the glass master is detected by the four-division detector 12, and the adder 2
At 4, the total sum of the reflected light A2 is obtained. Comparator 25
The size of A2 is discriminated by and the switching circuit 16
When 2 is equal to or more than a certain amount of light, focus control is performed by the recording beam A2, and when A2 is less than a certain amount of light, focus control is automatically performed by the focus beam B2.

As described above, by providing the comparator for discriminating the amount of light of the recording beam A2, the focus control system can be automatically switched at the start and end of recording without an external command.

Although the two-divided detector 14 is movable by the stepping pulse motor 19 in the first embodiment, another motor actuator may be used.

In the first, second and third embodiments, 2 is the recording laser for emitting the recording light A1 and 8 is the focusing light source for emitting the focus beam B1. The beam B1 may be incident on the second harmonic generation element to generate a beam having a half wavelength of the focus beam, and this may be used as the recording light 2.

Further, the sample hold circuit 23 can be realized by using a D / A converter, a memory, an A / D converter, or an analog hold circuit for holding an analog signal for a long time.

[0022]

As described above, according to the present invention, the control means for keeping the focal position of the first light flux constant, the moving means for moving the position of the second detecting means, and the operation of the first control means. Sometimes the output of the second detection means and the movement means move the position of the second detection means in the detection direction of the second light flux by the movement control means or the first control means. By providing a means for holding the offset amount of the second detection means and adding it with the polarity for canceling it, it is possible to automatically correct the positional deviation amount of the two-divided detector for detecting the focus beam with respect to the recording beam. The focus control device can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a focus control device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a focus control device according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a focus control device according to a third embodiment of the present invention.

FIG. 4 is a block diagram of a conventional focus control device.

[Explanation of symbols]

 1 Glass Master 2 Laser for Recording 3 Polarization Beam Splitter 4 Quarter Wave Plate 5 Lens 6 Cylindrical Lens 7 Shutter 8 Light Source for Focusing 9 Beam Splitter 10 Beam Splitter 11 Objective Lens 12 Four-Division Detector 13 Focus Control Circuit A 14 Two-Division Detector 15 Focus control circuit A 16 Switching circuit 17 Focus drive circuit 18 Focus actuator 19 Stepping pulse motor 20 Pulse motor drive circuit 21 ON-OFF circuit 22 Sample hold circuit 23 Analog switch 24 Adder 25 Comparator 26 Manual input pulse motor drive Circuit 27 Recording beam monitor

Claims (5)

[Claims] 1. A first detection means for irradiating a recording medium with a first light flux and a second light flux that pass through the same objective lens, and detecting reflection of the first light flux from the recording medium; Second detecting means for detecting the reflection of the light flux of the light, focus position driving means for moving the focus positions of the first and second light fluxes connected on the recording medium, the output of the first detecting means, and the focus The position drive means controls the focus position of the second light flux by the first control means for keeping the focus position of the first light flux constant, and the output of the second detection means and the output of the focus position drive means. Second control means for keeping constant, switching means for switching the first and second control means, moving means for moving the second detection means, and the first control means by the switching means. When selected, the output of the second detection means and the movement Focus control apparatus characterized by having a position of said second detecting means by the step, and the second movement control means for moving the detection direction of the reflected light beams. 2. A second switching means is provided between the moving means and the movement control means, and the moving means and the movement control means are operated by the second switching means when the second control means operates. 2. The focus control device according to claim 1, wherein the focus detection device is cut off, and the position of the second detection means is fixed. 3. A holding means for moving means and movement control means to sample and hold the error signal of the second detecting means when the first controlling means operates and hold it when the second controlling means operates. The focus control device according to claim 1, comprising a circuit and an addition unit that adds the output of the holding circuit to the second control unit when holding the holding circuit. 4. A third detection means for detecting the amount of reflected light of the first light flux, and a control signal for switching to the first control means if the output of the third detection means is a certain value or more. The focus control device according to claim 1, further comprising a determination circuit that outputs the changeover means. 5. The focus control device according to claim 1, 3 or 4, wherein the first light flux and the second light flux have different wavelengths.