JP2506910Y2 - Optical recording medium and optical recording apparatus for performing optical recording on the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an optical recording medium for optical recording and an optical recording device for recording information on the optical recording medium.

[Conventional technology]

Various optical recording media such as a recording master or an erasable and recordable disk for obtaining a conventional CD or optical video disk have been proposed. For example, a master for obtaining a CD has a glass substrate coated with a photosensitizer such as a photoresist, and a spiral fine pit row is formed by performing a development process after irradiation with a modulated laser beam.

A configuration for recording audio or video information on such a master will be described with reference to FIG.

In FIG. 7, the laser light (1a) emitted from the laser light source (1) corresponds to the information signal (2a) of the audio, video, etc. supplied to the input terminal T ₁ by the optical modulator (2), and the “connection / disconnection” is performed. The first beam splitter (10) and the objective lens (3) focus the light on the photoresist surface of the master (4) mounted on the turntable (13). Further, the master (4) on the turntable (13) is rotationally driven by the rotary motor (5). The rotary motor (5) is mounted on the moving table (1
2) The master (4), which is fixed on top and which includes the moving base (12), is moved in the direction of arrow H by the horizontal movement motor (6).

By the way, the spot diameter and the focal depth condensed by the objective lens (3) are approximated by the values λ / NA and λ / (NA) ² (λ: recording laser wavelength, NA: numerical aperture of objective lens), respectively.
For example, when NA is 0.9 and λ is 457.9 nm, the beam spot diameter is about 0.5 μm and the focal depth is 0.57 μm, which are very small dimensions. Therefore, in order to perform stable recording on the master (4), the objective lens (3) needs to have an accurate focal length with respect to the master (4) and be arranged within the depth of focus, which is highly accurate. Focus control is required. Generally, in such focus control, an auxiliary beam such as a He-Ne laser that does not expose the photoresist coated on the master (4) is used. In FIG. 7, the auxiliary laser beam emitted from the auxiliary light source (7) is the first beam. Beam split (10) → The master (4) is irradiated through the objective lens (3), and the master (4)
The auxiliary laser beam is reflected by the reflection mirror (11) and guided to the two-division photodetector (8). An error signal output is obtained by the photodetector (8) with respect to the position change of the master (4), and this error output is amplified by the differential amplifier (9) and supplied to the drive coil (14) to supply the objective lens (3). Is driven up and down to perform focus control.

[Problems to be solved by the device]

By the way, even when the above-mentioned focus control is performed, the recording laser beam (1a) incident on the objective lens (3) is displaced from the optical axis of the objective lens (3), or the optimum focus position is obtained. When the objective lens (3) is not held at, the spot shape focused on the master (4) becomes elliptical, or the recorded pit is deformed due to asymmetry in the intensity distribution. It is impossible to form pits that are faithful to the information signal such as. When performing optical recording in this way, it is essential to monitor the accurate beam spot shape on the master (4).

FIG. 8 is a conceptual diagram of an optical system showing an example of a monitoring method for achieving this kind of purpose.

In FIG. 8, the laser light (1a) emitted from the laser light source (1) is reflected by the first beam splitter (10) through the second beam splitter (15) and is reflected by the objective lens (3) at the master ( Focus on the surface of 4) at focal length f ₁ . The reflected beam reflected by the master (4) is the objective lens (3) → first
The beam splitter (10) is reflected by the second beam splitter (15) and is condensed by the condenser lens (16) having the focal length f ₂ . The focused spot image is observed with a microscope (17) having a magnification of M. Therefore, the size of the spot image observed in the visual field of the microscope (17) is magnified by f ₂ · M / f _{1 with} respect to the spot image on the master. However, even in such a monitoring method, the observed spot intensity distribution changes due to the microscope (17) main body having optical aberrations or the deviation of the condenser lens (16) from the optical axis in the monitor optical path system. However, there is a problem that the shape of the focused spot on the master (4) cannot be accurately monitored.

The present invention was made in view of the above points, and its purpose is to accurately monitor the spot shape on the master.
It is intended to obtain an optical recording medium and an optical recording device that can be measured.

[Means for solving the problem]

An example of the optical recording medium of the present invention is a beam spot (20) irradiated on the surface of a disc-shaped optical recording medium as shown in FIG.
On the other hand, an optical recording medium (4) in which intersecting portions (4c) having different transmittances are provided at an opposite angle of approximately 45 degrees with respect to the tangential direction of the outer periphery of the optical recording medium (4), and the optical recording medium (4). The detection means (18a) (18b) for detecting the amount of light transmitted or reflected through the intersection part (4c) of the, and the measurement means (24) for measuring the detection output of the detection means (18a) (18b), The light intensity distribution of the beam spot (20) focused on the surface of the optical recording medium is measured in a two-dimensional direction by the measuring means (24).

[Action]

Since the master disk (4) having the above-described structure is directly formed with a crossing portion having a different transmittance, that is, a knife edge pattern, in the outer peripheral area other than the recording area, it does not need a knife edge and accurately monitors the spot shape on the master disk. You can Further, as a recording device, it is possible to detect a change in laser light amount when a beam spot of laser light passes through or is reflected by a knife edge pattern formed on a disk, and to measure a spot intensity distribution in a two-dimensional direction from a differential waveform of the detected output. The spot shape deviation can be accurately monitored.

〔Example〕

An embodiment of an optical recording medium of the present invention and an optical recording device for performing optical recording on the optical recording medium will be described with reference to FIGS.
The figure will be described.

Prior to explaining the optical recording medium and the optical recording apparatus of the present invention, a generally known method of measuring a one-dimensional intensity distribution of a beam spot by a knife edge method is shown in FIGS. 5 and 6A,
Explain by B.

In FIG. 5, when the knife edge (25) is scanned in the x'direction with respect to the beam spot (20) where the laser light (1a) is focused by the objective lens (3), it is arranged so as to face the objective lens. transmitted light output at x position obtained by the photodetector (18) has is expressed by ^{P (x) = ▲ ∫ ∞} x ▼ I (x ') dx'. Here, I (x) represents the intensity distribution of the beam spot (20). Therefore spot intensity distribution Can be obtained as The output obtained by amplifying the output of the photodetector (18) by the amplifier (21) is taken as the light transmission output P (x) on the vertical axis, and the knife edge (25) on the horizontal axis.
An output curve diagram (26) showing the movement distance x'is shown in FIG. 6A. Further, the intensity distribution I of the beam spot (20) is passed through the differentiating circuit (22) through the output curve (26) of FIG. 6A.
FIG. 6B shows an intensity distribution curve (27) in which (x) is plotted on the vertical axis and the moving distance x ′ of the knife edge (25) is plotted on the horizontal axis.
It is shown in.

The present invention basically uses the principle described in FIGS. 5 and 6A and B.

An example of the present invention based on the above principle will be described with reference to FIGS. FIG. 1 shows a glass master disk of this example, a beam spot focused on the master disk, and a knife edge pattern. The master disk (4) has a structure similar to that described in FIG. Photoresist is applied to a portion to be (4d), and areas (4b) and (4c) having different transmission (reflection) rates are provided on the outer peripheral portion of the recording area (4a).
c) constitutes a knife edge pattern (4c), which is a pattern which intersects the tangential direction of the rotating master (4) at an opposite angle of 45 °. There are various possible methods for producing such a knife edge pattern (4c). For example, one area (4b) on the master (4) is masked and a metal such as chromium is vacuumed on the area (4c). It may be attached by a vapor deposition method or the like. Incidentally, O is such that the beam spot (20) is focused on the center of the master (4) from the center O to a point of radius R.

FIG. 2 shows an optical recording device for recording information signals such as audio and video on such a glass master disk (4), and the parts corresponding to those in FIG. 7 are designated by the same reference numerals. First, the movable table (12) is rotated horizontally by the horizontal drive motor (6) as indicated by an arrow H, and the turntable (1).
3), the master (4) is moved in parallel, and the rotary motor (5) rotates the turntable (13) to rotate the master (4).
Is rotated clockwise, for example. The objective lens (3) is arranged to face the upper surface of the master (4), the lower surface shields external light, and the optical filter (19a) that transmits only the laser light (1a) transmitted through the master (4) is transmitted. A photodetector (16a) for detecting the amount of light is arranged opposite to each other. The laser light (1a) emitted from the laser light source (1) is optically modulated by the optical modulator (2) in accordance with the information signal (2a), and the second beam splitter (15) → the first beam splitter ( 10) → The beam spot focused through the optical path of the objective lens (3) on the surface of the master (4) and transmitted through the master (4) is an optical filter (19).
Diffuse through a) onto the photodetector (18a).

The auxiliary laser beam, which is insensitive to the photoresist such as He-Ne, passes through the first beam splitter (10) and is focused by the objective lens (3), and the reflected beam passes through the first beam splitter (10). A coil that is reflected by the reflection mirror (11) and an error signal is obtained by the two-division photodetector (8), and this error signal is amplified by the differential amplifier (9) to drive the objective lens (3) up and down. Supplied to (14). The two-division photodetector (8) is provided with a position adjusting means (30). The second beam splitter (15) arranged between the optical modulator (20) and the first beam splitter (10) is for guiding the reflected beam on the master (4) to the photodetector (18b). The reflected beam reflected by the second beam splitter (15) is guided to a photodetector (18b) that detects the amount of reflected light through an optical filter (19b) that blocks external light and transmits only the reflected beam.

The detection output signals of the photodetectors (18a) and (18b) are supplied to the fixed contacts a and b of the switch (29), and one of the outputs of the photodetectors (18a) and (18b) is output by switching the movable contact c. Is amplified by the amplifier (21), the amplified output signal of the amplifier (21) is differentiated by the differentiating circuit (22), and the beam spot intensity is measured through the absolute value circuit (23) by a measuring means such as a monitor oscilloscope (24). Curve observations are made.

When the beam spot (20) is focused on the knife edge (4a) portion of the master (4) shown in FIG. 1 in the above-described configuration at a position of radius R from the master center O, the focused beam spot ( Since the radius R has a very large value with respect to the diameter of 20), the locus A-A 'of the radius R when the master is rotating is approximately as shown in A-A' of FIG. 3 at the position to be monitored. It is considered to be equivalent to moving on a straight line.
The knife edge pattern (4c) formed on the locus is the locus A-A '.
Since the knife edge pattern (4c) is moved in the order of (4c) → (4c ′) → (4c ″) → (4c), dy is caused by the knife edge a part and dx is caused by the knife edge b part. Since they have been scanned, they are 2
The intensity distribution curve of the beam spot in the dimension (see FIG. 4) can be monitored.

A monitoring method for obtaining the best recording state in this example will be described below.

Focus control is performed in the monitor area where the knife edge pattern (4c) is formed on the master (4), and the photodetector (18a) → fixed contact b of the switch (29) → movable contact c → amplifier (21). → Differentiation circuit (22) → Absolute value circuit (23)
When the beam spot (20) in the knife edge pattern portion is observed by the monitor (24) along the path (2), beam spot intensity distribution curves (31), (32) as shown in FIG. 4 are obtained. Similar to FIG. 6B, in this intensity distribution curve, the vertical axis represents the beam spot intensity, the horizontal axis represents the movement distance of the knife edge pattern (4c), and the curve (31) was scanned with the knife edge a. Corresponding to the resulting dy, curve (32) corresponds to the dx resulting from scanning the knife edge b.

If there is no difference between the waveforms of the curves (31) and (32) in Fig. 4, it indicates that the optimum beam focusing is performed, and if there is a difference between the two waveforms, the focused spot is elliptical. Alternatively, the intensity distribution has asymmetry, and it can be detected that the optical axis is deviated in the optical path system. Further, from the waveform change when the focus position is changed by finely adjusting the moving screw (30) which is the position adjusting means for the two-divided photodetector, it is possible to easily realize the setting of the focus position where the maximum intensity is obtained at the minimum spot diameter.

In the above description, the beam spot (20) is detected by the transmissive photodetector (18a), but the beam spot (2
0) is focused on the surface of the master (4), and the reflected beam is reflected by the first and second beam splitters (10) and (15) through the objective lens (3), and the reflected beam is detected. The detector (18b) receives the light, and the detection output signal of the fixed contact a of the switch (29) → moving contact c → amplifier (21) → differential circuit (22) → absolute value circuit (23) → monitor (24) Even if it is observed through the route, the intensity distribution curve similar to that in Fig. 4 can be observed. Therefore, in order to obtain the effect of this example, the detector (18a),
Only one of (18b) may be used.

According to this example, the spot shape change due to the laser beam optical axis shift and the position shift during focusing can be accurately recognized by monitoring the intensity distribution curve in the two-dimensional direction, and the best spot state can be obtained. .

The present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

[Effect of device]

According to the present invention, it is possible to directly monitor the intensity distribution in a two-dimensional direction of a minute beam spot focused on a rotating master disc, and to detect the optical axis deviation of a laser beam incident on an objective lens and the positional deviation during focusing. It is possible to accurately check the accompanying change in spot shape, easily maintain the best spot state, and perform stable optical recording.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a master as an optical recording medium of the present invention, and FIG. 2 is a schematic diagram of an optical system showing an embodiment of an optical recording apparatus of the present invention and a system diagram of a detection system, FIG. 3 is an operation explanatory diagram of the knife edge method of the present invention, FIG. 4 is a beam spot intensity distribution curve diagram of the present invention, FIG. 5 is a schematic diagram for explaining the knife edge method, and FIG. 6 is a knife edge method. FIG. 7 is a conceptual diagram of a conventional optical recording device, and FIG. 8 is a conceptual diagram of an optical system for explaining a conventional beam spot monitoring method. (1) is a laser light source, (2) is a light modulator, (3) is an objective lens, (4) is a master, (18), (18a) and (18b) are photodetectors, and (19a) and (19b). ) Is an optical filter.

Claims (2)

(57) [Scope of utility model registration request] 1. A cross section having different transmittances is provided at an opposite angle of about 45 degrees with respect to a tangential direction of an outer periphery of the optical recording medium with respect to a beam spot irradiated on the surface of the optical recording medium. An optical recording medium characterized by: 2. An optical recording medium having intersecting portions having different transmittances with respect to a beam spot irradiated on the surface of a disk-shaped recording medium at an opposite angle of about 45 degrees with respect to a tangential direction of an outer periphery of the optical recording medium. And a detecting means for detecting the amount of light transmitted or reflected at the intersection of the optical recording medium, and a measuring means for measuring the detection output of the detecting means, the beam spot of the beam spot focused on the surface of the optical recording medium. An optical recording apparatus characterized in that the light intensity distribution is measured in two-dimensional directions by the measuring means.