JPH0636339A - Optical reproducing device - Google Patents

Abstract

PURPOSE:To provide the optical reproducing device which is not affected by the phase depth and efficiently detects the change of the quantity of light of the diffraction and interference pattern formed from a recording medium to reproduce data with a high S/N. CONSTITUTION:The optical reproducing device optically reproduces data from the recording medium on which prescribed data is recorded by the change of intervals of plural marks. A bisected photodiode 23 is provided which receives the diffraction pattern formed by scanning plural marks on the recording medium with laser light. When an average of the shortest interval and the longest interval of marks is defined as the average mark interval, the bisected photodiode 23 is so arranged that its one end is matched to the vicinity of a 0th-order light peak position E of the sample diffraction and interference pattern formed by plural marks having the average mark interval and its division lines 23a and 23b are matched to vicinities of first dark point positions F and G of the sample diffraction pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical reproducing apparatus for optically reproducing data from a recording medium such as an optical disk or an optical card.

[0002]

2. Description of the Related Art Conventionally, as a recording medium applied to this type of apparatus, a read-only (ROM) CD or a laser disk, a write-once (WORM) Te metal thin film or organic dye film, a reversible type ( E-DRAW) magneto-optical type and chalcogenite phase change films, and in each case, for example, 1-bit data is represented by the presence or absence of one mark.

When recording predetermined data on such a recording medium, a recording laser beam focused to a wavelength is irradiated along the track length direction of the recording medium to form a plurality of marks at predetermined intervals. Form. As a result, encoded data corresponding to the interval between these marks is recorded on the recording medium.

When data is optically reproduced from such a recording medium, a reproducing laser beam is scanned along the track length direction of the recording medium. As a result, the interference light that changes depending on the presence or absence of the mark is detected to reproduce the data.

In recent years, in order to improve the recording density, a method of changing the reflectance at each mark stepwise, a method of changing the depth of the mark, a method of changing the size of the mark, or
There has been proposed a method of reducing the track interval, a method of using a multilayer film as a recording medium, and recording data in each layer to improve the recording density. These are straight-forward methods of multi-valued by changing the state of one mark stepwise.

[0006]

However, in the conventional multi-valued recording, it is difficult to adjust the reflectance and the like stepwise so that the signal from the mark can be accurately detected, and the binary value to 4 to 4 values can be obtained. The limit is multivalue. Therefore, in order to improve the recording density, for example, it is conceivable to pattern and record a set of data in a certain area of a recording medium. However, such a method can be used for a simple system without tracking and focusing, but cannot be used for a complicated system.
It is also possible to increase the size of the recording medium. However, along with this, the device also becomes large.

Therefore, a recently developed high-density multi-value recording method (see Japanese Patent Application Laid-Open No. 3-141033) irradiates a recording laser beam in the track width direction of a recording medium, as shown in FIG. A plurality of marks 2 are formed in parallel at intervals of, and data corresponding to the intervals between these marks are recorded in the track width direction. At the same time, mark sets 4 each composed of a plurality of marks 2 are sequentially formed at a predetermined interval in the track length direction, and other data encoded corresponding to the intervals between these mark sets is used as the track length. Record in the vertical direction. According to such a recording method, since different data are recorded in the track length direction and the track width direction, the recording density of the recording medium is improved.

Further, the recorded data is reproduced by scanning the mark set 4 with a reproducing laser beam and detecting the interference light generated from the plurality of marks 2 constituting the mark set 4. Specifically, when the reproducing laser beam is scanned along the track length direction, the plurality of marks 2 constituting the mark set 4 generate interference light whose extreme value changes corresponding to the distance between these marks. Occur.
Then, by detecting a change in the interval between the maximum values or the minimum value of the interference pattern formed by the interference light, the interval information between the marks is reproduced as data in the track width direction.

At the same time, the presence or absence of the mark set 4 is detected by the reproducing laser beam scanned in the track length direction, and the information on the intervals between the mark sets detected at this time is reproduced as data in the track length direction. It

In such reproduction, in particular, as a method for discriminating the interval between marks, for example, the entire interference pattern or the light around the ± first-order diffracted light is received by a linear array, and the magnitude of the light amount is successively compared and calculated. By ± 1
A method for detecting the position of the next-order diffracted light (hereinafter, referred to as a first method) or a position as shown in FIG. 9 (specifically, the first dark point C and the longest mark of the interference pattern P at the shortest mark interval) A two-divided photodiode 6 is arranged between the second dark point D of the interference pattern S at the time of spacing, and a light amount change signal output via the respective portions 6a and 6b of these photodiodes 6 is used as a signal processing system. There has been proposed a method (hereinafter, referred to as a second method) for detecting the mark interval by performing the calculation in 8.

However, the first method requires a large detection circuit and is difficult to process at high speed. In the second method, the detection light is only 10 to 20% of the entire pattern, and most of the light is discarded. A reproducing laser beam having an excessive beam output is required to give a detectable light amount to the two-divided photodiode 6, but in reality, the SN ratio is lowered due to the insufficient light amount, and highly accurate data reproduction is possible. Can not. Further, according to the second method, when the mark 2 is constituted by the phase type, the intensity distribution of the interference pattern changes under the influence of the phase depth, unlike the case of the transmission type. The positions of the first dark point C and the second dark point D also change. That is, when the phase depth is added as a disturbance factor, the output of each of the two-divided photodiodes 6 changes due to the dislocation of the two-divided photodiodes 6 from the optimum position, making it difficult to reproduce data with high accuracy. Will result in.

The present invention has been made in order to eliminate such an adverse effect, and its purpose is not to be influenced by the phase depth and to efficiently change the light quantity of the diffraction / interference pattern formed from the recording medium. An object of the present invention is to provide an optical reproducing device that can detect and reproduce data with a high SN ratio.

[0013]

In order to achieve such an object, the present invention provides an optical system for optically reproducing data from a recording medium on which predetermined data is recorded by changing a distance between a plurality of marks. In the reproducing apparatus, a two-divided photodiode that receives an interference pattern formed by scanning a plurality of marks on the recording medium with a laser beam is provided, and the average of the shortest distance and the longest distance between the marks is an average mark distance. Then, in the two-division photodiode, the division line is aligned and arranged at a predetermined position of the sample diffraction / interference pattern intensity distribution formed from a plurality of marks at the average mark interval, depending on the type of the recording medium. .

[0014]

When a plurality of marks formed on the recording medium are scanned with laser light, an interference pattern that changes corresponding to the distance between the marks is generated from the recording medium. This interference pattern is received by a two-division photodiode whose division line is aligned and arranged at a predetermined position of the sample diffraction / interference pattern intensity distribution, and is converted into an electric signal corresponding to the received light amount. A predetermined operation is performed on the electric signal output from the two-divided photodiode to reproduce the data.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical reproducing apparatus according to a first embodiment of the present invention will be described below with reference to FIGS.
The recording medium 13 of the transmission type and the reflection amplitude type (the type in which a mark is recorded on the recording medium 13 by the difference in reflectance) is applied to the apparatus of this embodiment. Prescribed data is recorded in the track by a change in the mutual distance between a pair of marks 2 formed in parallel in the track width direction, and a predetermined data is recorded in the track length direction by combining the pair of marks 2 as a set. Other data is recorded by the change in the mutual distance between the mark sets 4 formed at the intervals (see FIG. 8). The track pitch of the recording medium 13 is regulated to 4 μm, and the mark diameter is 1 μm and the distance between the marks is 1.5 μm in the track.
The mark 2 is formed in the range of μm to 3 μm. Figure 3
1 schematically shows the configuration of the optical reproducing apparatus according to the present embodiment.

As shown in FIG. 3, a reproducing laser beam (wavelength λ = 670 to 830) emitted from the semiconductor laser 1 is used.
(nm) is regulated into a parallel light flux through the collimator lens 3, and then is irradiated on the shaping prism 5.

The reproducing laser beam, which is irradiated onto the shaping prism 5 and converted into an elliptical beam (axial ratio 1: 4),
After passing through the polarization beam splitter 7 and the quarter-wave plate 9, it is focused on the recording medium 13 by the objective lens 11.

Here, the recording medium 1 having the above-mentioned structure
The beam spot (ie,
When the irradiation area) overlaps another mark 2 adjacent in the track length direction, the overlapped portion becomes noise during reproduction, and the recorded data may not be read correctly.

Therefore, in the optical reproducing apparatus of this embodiment,
The beam spot (that is, the irradiation area) 33 has an elliptical shape (1 that is short in the track length direction and long in the track width direction).
The focus / tracking servo system is provided so as to be (μm × 4 μm) (see FIG. 8).

In focus / tracking control, the reflected diffracted light reflected from the recording medium 13 is converted into the objective lenses 11 and 1.
Via the quarter wave plate 9 and the polarization beam splitter 7
The light is guided to the servo detector 15 and the actuator 17 is controlled based on the detected change in the amount of received light.
On the other hand, the transmitted diffracted light that has passed through the recording medium 13 is regulated into a parallel light flux via the condenser lens 19, is irradiated onto the beam splitter 21, and is split into two directions.

One of the transmitted diffracted light beams is applied to a pair of two-divided photodiodes 23 connected in series and converted into electric signals corresponding to the received light amounts, respectively, and a predetermined calculation is performed on these electric signals. It is applied and the data is reproduced.

The other transmitted diffracted light is applied to the second servo detector 25 so that the transmitted diffracted light from the recording medium 13 is accurately applied to the two-divided photodiode 23 during data reproduction. The actuator 27 is controlled based on the detected change in the amount of received light.

In the optical reproducing apparatus of the present embodiment, in order to increase the amount of light received by the two-divided photodiode 23 and efficiently reproduce the data having a high SN ratio, the installation positions of the pair of two-divided photodiodes 23 are as follows. (See FIG. 1).

As shown in FIG. 1, the pair of two-divided photodiodes 23 applied to this embodiment are arranged symmetrically with respect to the zero-order light peak position E of the transmitted diffracted light.
Both have the same effects. Therefore, in the following description, one of the two-divided photodiodes 23 (see FIG.
Only the center, right side) will be described.

As shown in FIG. 1, the two-divided photodiode 23 has its left end portion aligned with the 0th-order optical peak position E of the diffraction pattern as viewed in the drawing, and the division line 23a of the two-divided photodiode 23 is aligned. It is aligned with the first dark spot position F of the diffraction pattern.

Specifically, the two-divided photodiode 23
The alignment of the dividing line 23a is performed on the basis of an interference pattern corresponding to the average mark interval (hereinafter, temporarily referred to as a sample diffraction / interference pattern). In this embodiment, the mark interval is 1.5 to 3 μm. Since there is, the average mark spacing D
Is D = (1.5 + 3) /2=2.25 μm. In FIG. 1, the average mark interval (D = 2.2
A sample diffraction / interference pattern formed from a pair of marks 2 (see FIG. 8) at 5 μm) is illustrated.

Further, the size (X) of the sample diffraction / interference pattern when the light is received by the two-divided photodiode 23.
Is defined by the numerical aperture (NA) and focal length (f) of the condenser lens 19 (see FIG. 3) as X = 2 · NA · f (1).

Therefore, the first dark spot position F of the sample diffraction / interference pattern having the size calculated by the above equation (1) is expressed by the following equation F = (f · λ) / (2 · D). ) F; focal length λ; wavelength D; average mark interval (= 2.25 μm). That is, the calculated value corresponds to the matching position of the dividing line 23a of the two-divided photodiode 23. Hereinafter, the two-divided photodiode 23
The specific position of the dividing line 23a is calculated by substituting specific numerical values into the equations (1) and (2).

(I) When the numerical aperture (NA) = 0.55 and the focal length (f) = 3.9 mm, the size (X) of the sample diffraction pattern is X = 4.29 mm from the equation (1). . At this time, the wavelength (λ) of the reproducing laser beam
Is 830 nm, D = 2.25 μm.
From the formula (2), F = (f · λ) / (2 · D) = 0.7193 mm. As a result, the dividing line 23a may be aligned with a position deviated from the zero-order light peak position E by about 0.7193 mm to the plus (+) side.

(Ii) When the numerical aperture (NA) = 0.5 and the focal length (f) = 4.3 mm, the size (X) of the sample diffraction pattern is X = 4.3 mm from the equation (1). . At this time, the wavelength (λ) of the reproducing laser beam
Is 830 nm, F = (f · λ) / (2 · D) = 0.7931 mm from the formula (2). As a result, the dividing line 23a may be aligned with a position deviated from the zero-order light peak position E by about 0.7931 mm to the plus (+) side.

The positioning of the dividing line 23b of the two-divided photodiode 23 on the left side in FIG. 1 is calculated in the same manner as described above. In this case, the dividing line 23b is minus (-) from the zero-order light peak position E. It suffices to match the position shifted to the side (that is, the minus-side first dark spot position G).

In the optical reproducing apparatus of this embodiment, since the pair of two-divided photodiodes 23 are arranged at the above-mentioned positions, the diffraction pattern (formed through the condenser lens 19 (see FIG. 3)) ( The light utilization efficiency of the diffraction pattern formed by actual scanning instead of the sample diffraction pattern is 55% or more, and the SN ratio thereof is significantly improved as compared with the conventional case (light utilization efficiency of 5 to 10%).

At this time, the output signals A and B output from the light receiving areas A and B of the pair of two-divided photodiodes 23 are (AB) / (A + B) via a signal processing system (not shown). 2), it has been found that the relationship between the calculated value and the mark interval has a one-to-one correspondence which is optimum for data reproduction, as shown in FIG.

When the amount of light received by the pair of two-divided photodiodes 23 applied to this embodiment is detected, it is 1 mW.
When the mark set 4 (see FIG. 8) is irradiated with the laser output of, the two-divided photodiode 6 (see FIG.
However, in the case of the present embodiment (see FIG. 1), the amount of received light is only 20 μW.
A received light amount of 10 μW was detected.

As a result, the SN ratio can be improved by about 9 dB, and erroneous reproduction of data due to disturbance such as eccentricity or inclination of the recording medium 13 (see FIG. 3) can be prevented. Further, since the resolution can be increased by 1.5 bits (bits) as compared with the conventional one, it is possible to reproduce multi-valued information recorded at high density with high accuracy.

The present invention is not limited to the configuration of the above-mentioned embodiment, but can be variously modified within the scope of the claims. For example, the two-divided photodiodes are not necessarily required to be two, and only one of them has the same operational effect. Also, the alignment of the dividing line of the two-divided photodiode and the end on the 0th-order light side,
It is not necessary to match the first dark spot position and the peak position of the 0th-order light with high accuracy, and it is possible to arbitrarily match within the allowable range. Further, a four-division photodiode may be used. Further, in the above-described embodiment, the transmissive reproducing apparatus has been described, but it goes without saying that the reflective type reproducing apparatus also exhibits the same operational effect.

Next, an optical reproducing apparatus according to the second embodiment of the present invention will be described with reference to FIGS. 4 to 7. The apparatus of the present embodiment is of the reflection phase type (a format in which marks are recorded on the recording medium 20 by changing the unevenness).
The recording medium 20 of FIG.
Predetermined data is recorded in the track by a change in the mutual distance between a pair of marks 2 formed in parallel in the track width direction, and these pairs of marks 2 are combined at a predetermined interval in the track length direction. Other data is recorded by changing the mutual spacing of the formed mark sets 4 (FIG. 8).
reference). The recording medium has a track pitch of 4 μm.
In this track, marks 2 are formed with a mark diameter of 1 μm and an interval between marks of 2 μm to 3 μm. Here, a semiconductor laser having a wavelength (λ) of 830 nm is applied as a reproduction light source. FIG. 4 schematically shows the configuration of the optical reproducing device according to the present embodiment.

As shown in FIG. 4, the reproducing laser beam (λ = 830 nm) emitted from the semiconductor laser 10 is
Parallel light flux (axis ratio 1: 4) by collimator lens 12
Regulated by. Here, the astigmatic difference of the applied semiconductor laser 10 is used to regulate the elliptical beam with an axial ratio of 1: 4, but it is also possible to adjust the axial ratio using a shaping prism (not shown). .

The reproducing laser beam that has been transmitted through the collimator lens 12 and converted into an elliptical beam (axial ratio 1: 4) passes through the polarization beam splitter 14 and the quarter-wave plate 16 and then the objective lens 18 (NA). = 0.5, f = 4m
m) is focused on the recording medium 20.

Here, the recording medium 2 having the above-mentioned structure
The beam spot formed when focused to 0 (ie,
When the irradiation area) overlaps another mark 2 adjacent in the track length direction, the overlapped portion becomes noise during reproduction, and the recorded data may not be read correctly.

Therefore, in the optical reproducing apparatus of this embodiment,
The beam spot (that is, the irradiation area) 33 has an elliptical shape (1 that is short in the track length direction and long in the track width direction).
The focus / tracking servo system is provided so as to be (μm × 4 μm) (see FIG. 8).

In the focus / tracking control, the reflected interference light reflected from the recording medium 20 is converted into the objective lenses 18 and 1.
The light is guided to the half prism 22 through the quarter wavelength plate 16 and the polarization beam splitter 14, and the half prism 2
The light reflected by 2 is received by the servo detector 24, and the actuator 26 is controlled based on the detected change in the amount of received light.

While such servo control is being performed,
The reflected interference light reflected from the recording medium 20 and guided to the half prism 22 passes through the half prism 22 and is applied to a pair of two-divided photodiodes 28.
Each of the divided photodiodes 28 converts it into an electric signal corresponding to the amount of received light. Then, the electric signal output from the pair of two-divided photodiodes 28 is subjected to a predetermined calculation to reproduce the data.

As shown in FIG. 5, each of the pair of two-divided photodiodes 28 applied to this embodiment has its division line 28c aligned near the peak position of the reflected interference pattern intensity distribution other than the zero-order light. Then, they are arranged symmetrically with respect to the optical axis, and all have the same effect. Therefore, in the following description, one of the two split photodiodes 28 will be described.
Will be described only.

Specifically, the two-division photodiode 28
Positioning of the dividing line 28c is performed on the basis of an interference pattern corresponding to the average mark interval (hereinafter, temporarily referred to as a sample diffraction / interference pattern). In this embodiment, the mark interval is 2 to 3 μm. , The average mark interval D is D = (2 + 3) /2=2.5 μm. Therefore, the average mark interval (D = 2.5 μ
m) at the maximum peak position E of the sample diffraction / interference pattern X formed from the pair of marks 2 (see FIG. 8),
The two-division photodiode 28 is arranged by aligning the division line 28c.

The phase depth of the mark 2 is set to λ / 4, and each light receiving element 28 of the two-divided photodiode 28 is set.
The width of a and 28b is specified to be about 0.5 mm. Further, the symbol Y indicates the intensity distribution of the interference pattern at the mark interval D = 2.0 μm, and the symbol Z indicates the mark interval D = 3.
The intensity distribution of the interference pattern at 0 μm is shown.

After arranging the two-divided photodiodes 28 in this way, when an experiment is performed by changing the mark interval to 2 to 3 μm, light is output from the light receiving regions 28a and 28b of the pair of two-divided photodiodes 28, respectively. Output signals A and B that are output via the signal processing system 30 (AB) /
When the calculation of (A + B) is performed, it has been found that the relationship between the calculated value and the mark interval has a one-to-one correspondence that is optimum for data reproduction, as shown in FIG.

In this state, when the same experiment was performed by changing the phase depth of the mark 2 to λ / 8, 2-3 μ was obtained.
The intensity distributions X, Y, and Z of the interference pattern at m change as shown in FIG. 7, and the amount of light received by the pair of two-divided photodiodes 28 is smaller than that when the phase depth is λ / 4. However, it has been found that the relationship between the calculated value and the mark interval is maintained as shown in FIG.

Further, when the same experiment is carried out by changing the phase depth in the range of λ / 16 to λ / 4, the same effect is obtained and the focal length (f) of the objective lens 18 is changed. Accordingly, even if the width of the light receiving element of the two-divided photodiode 28 is appropriately changed, it is possible to reproduce data with high accuracy.

From the above experimental results, the dividing line 28c of the two-divided photodiode 28 is matched with the vicinity of the peak position other than the zero-order light of the interference pattern intensity distribution formed by the pair of marks 2 at the average mark interval (D). It has been found that by arranging them, the data can be reproduced with high accuracy from the interference pattern formed by the marks 2 without being affected by the phase depth of the marks.

[0051]

According to the optical reproducing apparatus of the present invention, the dividing line of the two-division photodiode is arranged in alignment with the predetermined position of the sample diffraction / interference pattern intensity distribution formed by a plurality of marks having an average mark interval. Therefore, it is possible to perform data reproduction with a high S / N ratio without being affected by the phase depth of the mark and by efficiently detecting the change in the light amount of the diffraction / interference pattern formed from the recording medium. .

[Brief description of drawings]

FIG. 1 is a diagram showing an arrangement position of a pair of two-divided photodiodes applied to an optical reproducing apparatus according to a first embodiment of the present invention with respect to a sample diffraction / interference pattern.

FIG. 2 is a diagram showing a relationship between a calculated value of an output signal output from a pair of two-divided photodiodes shown in FIG. 1 and a mark interval.

FIG. 3 is a diagram schematically showing a configuration of an optical reproducing device according to a first embodiment of the present invention.

FIG. 4 is a diagram schematically showing a configuration of an optical reproducing device according to a second embodiment of the present invention.

5 is a diagram showing the arrangement positions of a pair of two-divided photodiodes applied to the device shown in FIG. 4 with respect to a sample diffraction / interference pattern.

6 is a diagram showing a relationship between a calculated value of an output signal output from a pair of two-divided photodiodes shown in FIG. 5 and a mark interval.

FIG. 7 is a diagram showing a layout position of a pair of two-divided photodiodes with respect to an interference pattern when the phase depth is changed.

FIG. 8 is a diagram showing a state in which marks are formed on a recording medium.

FIG. 9 is a diagram showing an arrangement position with respect to an interference pattern of a two-divided photodiode applied to a conventional reproducing device.

[Explanation of symbols]

23 ... 2-division photodiode, 23a ... Dividing line, 23
b ... Dividing line, E ... Zero-order light peak position, F, G ... First dark spot position.

Claims (3)

[Claims] 1. An optical reproducing apparatus for optically reproducing data from a recording medium on which predetermined data is recorded by changing a distance between a plurality of marks, wherein a plurality of marks on the recording medium are scanned with laser light. A two-divided photodiode that receives an interference pattern formed by the two-divided photodiode, and an average of the shortest distance and the longest distance between the marks is an average mark distance, An optical reproducing apparatus, wherein the optical reproducing apparatus is arranged at a predetermined position of a sample diffraction / interference pattern intensity distribution formed from a plurality of marks having the average mark interval according to the type. 2. The recording medium is a transmission type or a reflection amplitude type recording medium, and sample diffraction / interference in which the dividing line of the two-divided photodiode is formed by a plurality of marks at the average mark interval. 2. The aligning arrangement at a predetermined position near the first dark point of the pattern intensity distribution, and the aligning arrangement at one end thereof near the 0th-order optical peak position of the sample diffraction / interference pattern. Optical playback device. 3. The recording medium is a reflective phase type recording medium, and the 0th-order light of a sample diffraction / interference pattern formed by a plurality of marks at the average mark interval on the dividing line of the two-division photodiode. The optical reproducing apparatus according to claim 1, wherein the optical reproducing apparatus is arranged in alignment near the peak position.