JPH04362538A - Optical type reproduction device - Google Patents

Abstract

PURPOSE:To supply an optical type reproduction device which highly precisely reproduces encoded data in accordance with the intervals of marks by scanning reproduction laser beams whose phases are different and whose beam diameters are small on marks formed on a recording medium and detecting the diffracted light beams diffracted from the marks. CONSTITUTION:The reproduction laser beams are scanned on the plural marks arranged along the track of the recording medium 21. Data encoded in accordance with the intervals of the plural marks is reproduced. The device is provided with a semiconductor laser 11, a phase plate 15 giving a phase difference by pi to a part of the reproduction laser beams emitted from the semiconductor laser 11 and a transmission element 17 which gives an optical characteristic to the reproduction laser beams to which the phase difference is given and makes the beam diameters at the time of scanning by the track of the recording medium 21 small.

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 on which predetermined data is recorded.

0002

Conventionally, recording media used in this type of method include read-only (ROM) CDs and laser discs, write-once (WORM) Te metal thin films, organic dye films, etc.
As the reversible type (E-DRAW), there are a magneto-optical type and a chalcogenite phase change film. When recording predetermined data on such a recording medium, a recording laser beam converged to about the wavelength is irradiated along the track length direction of the recording medium.
A plurality of marks are formed at predetermined intervals. Then, encoded data corresponding to the intervals between these marks is recorded on the recording medium. When reproducing predetermined data from such a recording medium, a reproducing laser beam is scanned along the track length direction of the recording medium, and diffracted light that changes depending on the presence or absence of marks is detected.

In recent years, the following various methods have been proposed for the purpose of improving recording density. A method of changing the reflectance of each mark stepwise, a method of changing the depth of the mark, a method of changing the size of the mark, a method of changing the mark interval, a method of decreasing the track interval, a method of changing the recording medium. There is a method of recording data in each layer of the constituent multilayer film to improve the recording density. These are straightforward methods for creating multiple values by changing the state of one mark step by step.

0004

[Problems to be Solved by the Invention] However, in conventional multi-value recording, it is difficult to make step-by-step adjustments so that signals from marks can be detected accurately. is the limit. In order to further improve the recording density, for example, it is conceivable to record a set of data in a pattern in a certain area of the recording medium. However, such a method can be used for a simple system without tracking or focusing, but cannot be used for a complex system. It is also conceivable to increase the size of the recording medium. However, this also increases the size of the device. Therefore, the following recording method has been proposed.

A recording laser beam is irradiated in the track width direction of the recording medium to form a plurality of marks in parallel at predetermined intervals. These plural marks constitute a mark set. Then, predetermined data encoded by the intervals between the plurality of marks constituting this mark set is recorded in the track width direction. According to such a recording method, different data is recorded not only in the track length direction but also in the track width direction, so that the recording density of the recording medium is improved.

[0006] Recorded data is reproduced by scanning a mark set with a reproduction laser beam and detecting diffracted light diffracted from a plurality of marks. Specifically, for example, this is performed by detecting changes in the distance between the maximum position and minimum value of an optical interference pattern caused by mutual interference of diffracted lights diffracted from each of a plurality of marks.

Here, ± diffracted from a plurality of marks constituting a mark set formed on a track of a recording medium.
The diffraction angle (θ) of the first-order diffracted light is determined by the distance between the marks (d)
stipulated by. In other words, the ±1st order diffracted light is dsi
n θ=λ λ; coherent light wavelength

It is diffracted in the direction defined by . Therefore, it can be seen that the diffraction angle (θ) increases as the distance between the plurality of marks constituting the mark set decreases. That is, since the diffracted light exceeding the acceptance angle determined by the NA of the objective lens is not received by the objective lens, there is a problem that data cannot be reproduced. This causes a problem in that the distance between marks that can be formed on the recording medium cannot be reduced below a predetermined value, and that an improvement in recording density cannot be achieved.

[0009] Furthermore, the beam diameter of the reproducing laser beam when scanning a mark set must be regulated within a range that does not overlap mark sets adjacent in the track length direction. If the beam diameter overlaps with an adjacent mark set, a problem arises in that diffracted light diffracted from multiple marks constituting the adjacent mark set mixes, causing a change in the optical interference pattern (crosstalk). .

The present invention was made to solve these problems, and its purpose is to scan marks formed on a recording medium with reproducing laser beams having different phases and having a small beam diameter. An object of the present invention is to provide an optical reproducing device that reproduces encoded data with high precision in accordance with the spacing between marks by detecting diffracted light diffracted from these marks.

[0011]

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention scans a plurality of marks arranged along a track of a recording medium with a reproduction laser beam to remove these marks. This is an optical reproducing device that reproduces encoded data corresponding to mutual intervals, and includes means for emitting the reproduction laser beam, and means for imparting a predetermined phase difference to a part of the reproduction laser beam. , a means for giving optical characteristics to the reproducing laser beam given a phase difference to reduce the beam diameter when scanning the track, and detecting the light intensity of the diffracted light diffracted from the plurality of marks. and means for reproducing the data.

0012

[Operation] The reproduction laser beam emitted from the light source is
A phase difference is given to a part of the beam, and then an optical characteristic is given so that the beam diameter becomes small when the recording medium is scanned. Such a reproducing laser beam is scanned over a plurality of marks arranged on a track of a recording medium. Then, the light intensity of the diffracted light diffracted from these marks is detected, and the data is reproduced.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical reproducing apparatus according to an embodiment of the present invention will be described below with reference to FIGS. 1 to 6. Note that in this embodiment, a transmission type reproducing device is used. In Figure 1,
The configuration of the optical reproducing device of this embodiment is schematically shown.

As shown in FIG. 1, the reproducing laser beam (wavelength 830 nm) emitted from the semiconductor laser 11 is
The collimator lens 13 regulates the beam into a parallel beam, and the phase plate 1
5. This phase plate 15 has a function of imparting a phase difference to a portion of the irradiated reproduction laser beam. The reproduction laser beam given the phase difference is irradiated onto the transmission element 17. This transmitting element 17 is configured such that its transmittance increases as it moves away from the optical axis Z in the radial direction, and has the function of reducing the beam diameter when focused on the recording medium 21. The reproducing laser beam transmitted through the transmission element 17 is focused on the recording medium 21 via the objective lens 19. A pair of marks (not shown) are formed on the recording medium 21 in the track width direction (direction indicated by x in the figure), and encoded data is recorded in correspondence with the intervals between these marks. There is. The transmitted diffracted light diffracted from these marks is regulated into a parallel beam by a condenser lens 23 and sent to a detector 25 (for example, CC
D camera). This detector 25 detects an optical interference pattern formed by the transmitted diffracted light diffracted from the pair of marks, and measures, for example, the distance between the maximum values of the 0th order and ±1st order diffracted light. As a result, the distance between the marks is calculated and the data is reproduced. Note that data can be similarly reproduced by measuring the interval between local minimum values or the interval between other parts. Note that even when the laser beam passes through the transmission element 17, no displacement occurs in the phase difference of the reproduction laser beam. Next, the phase plate 15 and the transmission element 17 provided in the optical reproducing device of this embodiment
will be explained in detail.

The phase plate 15 is formed by vapor-depositing ZnS on a glass substrate, and the phase plate 15 is formed by depositing ZnS on a glass substrate. It has the characteristic of giving a phase difference of π. Therefore, in the reproducing laser beam transmitted through such a phase plate 15, half of the light beam in the track width direction is given a phase difference of π with respect to the remaining light beam.

When the reproducing laser beam given the phase difference in this manner is focused on the recording medium 21, the intensity distribution has characteristics as shown in FIG. That is, it has an intensity distribution with peaks (Imax) at symmetrical positions with respect to the optical axis. In terms of phase, an intensity distribution with one peak has a phase shift of π with respect to the other. These peaks are then focused on a pair of marks formed on the recording medium 21 via the objective lens 19. In other words, the pair of marks are illuminated with beams whose phases are shifted by π from each other. Transmitted diffracted light beams having mutually different phases are generated from these marks, and are irradiated onto the detector 25 via the condenser lens 23. At this time, the optical interference pattern detected by the detector 25 has characteristics as shown in FIG. 3(a). Note that FIG. 3 shows an optical interference pattern when the distance between marks is 1.4 μm and the diameter of the marks is 1 μm. Note that FIG. 3B shows an interference pattern without the phase plate 15.

As is clear from comparing FIGS. 3(a) and 3(b), when the phase plate 15 is not provided (see FIG. 3(b)), the NA of the condenser lens 23 (0.55 ), the peak position of the diffracted light that occurs in the undetectable range is
By using the phase plate 15, the N of the condenser lens 23
High light intensity can be concentrated within the range A (see (a) in FIG. 3). In other words, it is possible to detect mark intervals with high precision, which could not be detected conventionally. This means that the recording density of the recording medium 21 is improved.

Such a phase plate 15 has a characteristic of increasing the beam diameter of the reproducing laser beam when it is focused on a track of the recording medium 21. Therefore, the reproducing laser beam may overlap other tracks, causing crosstalk.

The optical reproducing apparatus of this embodiment is provided with a transmission element 17 in order to reduce such crosstalk. The transmitting element 17 is formed of a pattern-printed film such that the transmittance increases as the distance from the optical axis increases in the radial direction. In this embodiment, a transmitting element 17 is used which has a transmittance of 0% on the optical axis and a transmittance of 70% at the farthest point. The transmittance distribution of this transmitting element 17 is shown in FIG. By providing the transmission element 17 having such characteristics, the recording medium 21
The beam diameter of the reproducing laser beam focused on can be reduced (see FIG. 5).

As shown in FIG. 5, it has been found that the beam diameter when the transmission element 17 is used is approximately 20% smaller than when the transmission element 17 is not used. This means that the recording density is improved by about 20%.

[0021] In this way, by combining the phase plate 15 and the transmission element 17, it has become possible to detect mark intervals that were previously undetectable with high precision without causing crosstalk. .

Further, in the optical reproducing apparatus of this embodiment, the distance between the pair of marks formed on the recording medium 21 is set to 1.
Regarding the cases of 3 μm, 1.4 μm, and 1.5 μm,
Optical interference patterns were detected for each. Note that the diameter of the mark is 1 μm.

FIG. 6 shows the results of this detection. As shown in FIG. 6, when the phase plate 15 and the transmission element 17 are not used (see (b) in FIG. 6), the peak of the diffracted light that occurs in the range that cannot be detected due to the NA limitation of the condenser lens 23 is By using the plate 15 and the transmission element 17 in combination, it is possible to regulate the NA within the range of the condenser lens 23 (see (a) in FIG. 6).

Specifically, even when the distance between the marks is narrowed as described above (for example, 1.3 μm),
The peak of the diffracted light can be concentrated within the NA range of the condenser lens 23 with high light intensity.

As described above, the optical reproducing apparatus of this embodiment can detect minute changes in the mark spacing with high precision, which could not be detected conventionally. This means that the recording medium 21
This means that the recording density will improve.

[0026]While such reproduction is being performed,
It goes without saying that the focus/tracking servo works to focus the reproducing laser beam onto the tracks of the recording medium 21 with an optimum beam diameter.

Note that the present invention is not limited to the above-mentioned embodiment. For example, in the above-mentioned embodiment, a transmission type reproducing apparatus was described, but similar results can be obtained with a reflective type reproducing apparatus. Furthermore, the recording medium 21 is not limited to the above-described configuration, and for example, marks may be formed in the track length direction. In addition, the transmission element 17
The structure is not limited to the above-mentioned configuration, and for example, the transmittance on the optical axis may be 0% and the transmittance at the farthest part may be 50% to 100%. Furthermore, in the embodiment described above, the phase difference provided by the phase plate 15 is set to π, but it is not limited to this, and for example, a value near π may be used.

[0028]

Effects of the Invention The optical reproduction device of the present invention focuses reproduction laser beams having different phases and small beam diameters onto a recording medium, and collects diffracted light from marks arranged along a track. By detecting the marks, encoded data corresponding to the intervals between the marks can be reproduced with high precision. As a result, the interval between marks formed on the recording medium can be made narrower than in the past, making it possible to improve the recording density.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the configuration of an optical reproducing device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a light intensity distribution when a reproducing laser beam is focused on a recording medium using the apparatus shown in FIG.

FIG. 3 is a diagram showing an optical interference pattern detected by a detector arranged in the apparatus of FIG. 1, in which (a) shows a case with a phase plate, and (b) shows a case without a phase plate. .

4 is a diagram showing a transmittance distribution of a transmitting element arranged in the apparatus of FIG. 1. FIG.

FIG. 5 is a diagram showing the relationship between the presence or absence of a transmission element arranged in the apparatus of FIG. 1 and the beam diameter.

FIG. 6 is a diagram showing the relationship between the presence or absence of a phase plate and transmission element arranged in the apparatus of FIG. 1 and an optical interference pattern.

[Explanation of symbols]

11... Semiconductor laser, 15... Phase plate, 17... Transmission element,
21... Recording medium, 25... Detector.

Claims (2)

[Claims] Claim 1: Scanning a reproduction laser beam across a plurality of marks arranged along a track of a recording medium,
This is an optical reproducing device that reproduces encoded data corresponding to the intervals between the plurality of marks, and includes means for emitting the reproducing laser beam, and a predetermined phase difference in a part of the reproducing laser beam. means for giving optical characteristics to the reproducing laser beam given a phase difference to reduce the beam diameter when scanning the track; and means for reducing the beam diameter when scanned on the track; An optical reproducing device comprising: means for detecting light intensity and reproducing the data. 2. The optical reproducing apparatus according to claim 1, wherein the means for reducing the beam diameter is a transmission element having a predetermined transmittance distribution.