JPH04328331A - Optical recording medium and its detection method - Google Patents

Abstract

PURPOSE:To record a synchronous mark which can surely be identified from a data mark and which can easily be detected at a short mark length. CONSTITUTION:The synchronous mark 26 is constituted by two synchronous pits 26a formed in the direction of a track width and the data mark is constituted by a single data pit 28. The two synchronous pits 26a are arranged so that the shortest distance of the outline of the pit is shorter than the distance in the direction of the track width of a beam spot 24 for setting the beam spot 24 to simultaneously irradiate the both synchronous pits 26a. The diameter of the synchronous pit 26a is formed to be equal to that of the data pit 28.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an optical recording medium having a synchronization mark necessary for performing synchronization operations such as sector synchronization and frame synchronization when reproducing information from an optical recording medium such as an optical disk, and a method for detecting the same. Regarding.

0002

2. Description of the Related Art Conventionally, synchronization techniques necessary for recording and reproducing optical discs include bit synchronization, sector synchronization, and frame synchronization. Before explaining these synchronizations, let's first explain the format of optical discs.

[0003] On an optical disc on which nothing has been recorded yet, a preformatted preamble section, a sector synchronization signal, a sector address, etc. are recorded with an area left for recording additional data. When recording data,
First, pit synchronization is performed in the preamble section, then sector synchronization is performed, and then the sector address is read. After finding the target sector using this sector address, data is recorded in a predetermined format with gaps at regular intervals. Frame synchronization signals are inserted into the data portion at regular intervals.

[0004] When reproducing data, after searching for the target address using the sector address, bit synchronization is performed in the preamble section, and one sector's worth of data is reproduced based on the frame synchronization inserted in the data. Read sequentially.

[0005] The preamble section for bit synchronization is constituted by repeating a bit pattern of, for example, "100100..." from which clock extraction is easy. If the rotation of the disk changes, this code pattern will also change at the same time, so by locking the PLL to this pattern and generating a clock for reading data, data can be reliably reproduced.

[0006] A bit pattern called a sector mark is normally used to perform sector synchronization. A special pattern is selected for the sector mark that can be reliably distinguished from other areas and also allows for easy detection of the sector mark.

[0007] Frame synchronization is performed using a frame synchronization pattern of several bits to several tens of bits. As this synchronization pattern, a pattern with a sharp autocorrelation function or a pattern that does not satisfy the modulation rules is used. As with the sector mark, the synchronization pattern is also selected to be a pattern that can be reliably distinguished from other areas and that can be easily detected.

[0008] In order to perform various types of synchronization as described above, a synchronization pattern that can be reliably distinguished from other areas and that can be easily detected is required.

[0009]

[Problems to be Solved by the Invention] However, in addition to the problem that such a synchronization pattern has a large degree of redundancy, it is difficult to determine the pattern, and if a synchronization pattern whose autocorrelation function is not sharp is used, errors may occur. The drawback is that it takes time to pull in synchronization in order to prevent synchronization. Furthermore, a synchronization pattern with a sharp autocorrelation function has a long pattern length, which adversely affects recording density.

The present invention has been made in view of the above circumstances, and provides an optical recording medium having a synchronization mark that has a shorter mark length than conventional ones, can be reliably distinguished from marks in other areas, and can be easily detected. and its detection method.

[0011]

[Means for Solving the Problems] The optical recording medium of the present invention includes:
The synchronization mark has a data mark in which a plurality of pits of a predetermined depth are arranged corresponding to the information to be recorded, and a synchronization mark that generates a synchronization signal when the information recorded in the data mark is reproduced. is characterized in that it is configured to generate an optical pattern different from the optical pattern obtained from the data mark.

Further, the detection method detects the synchronization mark by irradiating such an optical recording medium with light for reproducing information and detecting an optical pattern different from the optical pattern obtained from the data mark.

[0013]

In the present invention, the synchronization marks are configured to produce a different optical pattern than the data marks when illuminated. This can be done by configuring the synchronization mark with pits with a different depth from the data pits, or by configuring the synchronization mark with pits with a different shape than the data pits, or by making the synchronization mark with pits with a different arrangement than the data marks. This is achieved by configuring. Since the synchronization mark produces an optical pattern different from the data mark when illuminated, the synchronization mark is detected from the difference in the optical pattern obtained by illuminating the mark.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS There are two types of reproduction optical systems to which the present invention is applied: a reflective optical system that reads the intensity of light reflected from an optical recording medium, and a transmission optical system that reads the intensity of transmitted light that has passed through the optical recording medium. Therefore, before describing embodiments of the present invention, the basic configurations of the transmissive optical system and the reflective optical system will be explained.

FIG. 1 shows an example of a transmission type optical system to which the present invention is applied. Light emitted by a laser diode (LD) 12 is converted into a parallel beam by a collimating lens 14 and then focused onto the surface of a recording medium 18 by an objective lens 16 . The light that has passed through the recording medium 18 is passed through the condensing lens 2
After being made into a parallel beam by 0, the beam enters the detector 22.

FIG. 2 shows an example of a reflective optical system to which the present invention is applied. Light emitted by a laser diode (LD) 12 is made into a parallel beam by a collimating lens 14, passes through a polarizing beam splitter 15 and a λ/4 plate 17, and is focused onto a recording medium 18 by an objective lens 16. The reflected light from the recording medium 18 enters the objective lens 16, is made into parallel light, passes through the λ/4 plate 17, and enters the polarizing beam splitter 15. The linearly polarized light emitted by LD12 is λ
It passes through the /4 plate 17, is reflected by the recording medium 18, and then becomes λ/4 again.
By passing through the four plates 17, the polarization direction is rotated by 90 degrees and reflected by the polarization beam splitter 15. The reflected light enters the detector 22, and its intensity is detected.

A synchronization mark according to the first embodiment of the present invention is shown in FIG. In the figure, the track direction is the x-axis direction, the track width direction is the y-axis direction, and the intersection of both axes is the optical axis center of the reproduction optical system. A large number of marks are formed along the track direction. Hereinafter, in this specification, marks for synchronization detection will be referred to as synchronization marks, and other marks will be referred to as data marks. In this embodiment, a reflective optical system as shown in FIG. 2 is used as the reproduction optical system, the synchronization mark is composed of a single synchronization pit 26, and the data mark is also composed of a single data pit 28. Synchronous pit 2
6 and the data pit 28 have the same diameter but different depths. With respect to the wavelength λ of the light emitted by the LD 12, the synchronization pit 26 is formed at a depth of λ/4, and the data pit 28 is formed at a depth of λ/8.

When reproducing data, the beam spot 24 formed on the optical recording medium moves in the direction of the arrow in the figure, that is, in the track direction, and traces a large number of pits 26 and 28 formed along the track. , the intensity of reflected light from each pit is observed by a detector 22. Synchronous pit 2
Figure 4A shows the light intensity distribution when the data pit 28 is illuminated with the beam spot 24 in an envelope manner.
FIG. 4B shows the light intensity distribution when envelope illumination is performed. The vertical axis shows the light intensity, and the horizontal axis shows the position on the detector 22. Note that the positional relationship between the beam spot and the pit at this time is illustrated above the graph. As can be seen from the figure, in the synchronization pit 26, the light intensity on the center of the optical axis is almost zero, but in the data pit 28, the light intensity on the center of the optical axis shows a high value. Therefore, the synchronization pit 26 can be identified by detecting the light intensity at the center of the optical axis. That is, synchronization can be performed when the reflected light on the center of the optical axis drops to almost zero. Note that a conventional method may be used for synchronization.

A synchronization mark according to a second embodiment of the present invention is shown in FIG. In this embodiment, the synchronization mark 26 is composed of two synchronization pits 26a formed in the track width direction, and the data mark is composed of a single data pit 28. The two synchronous pits 26a are the beam spots 24
is arranged so that the shortest distance of the pit outline is shorter than the distance of the beam spot 24 in the track width direction so that both synchronous pits 26a are irradiated simultaneously. The synchronization pit 26a and the data pit 28 are formed to have the same diameter. Furthermore, if the reproduction optical system is of a reflective type, these pits 26a and 28 are formed at the same depth.

Although this embodiment can be applied to either a reflective reproducing optical system or a transmissive reproducing optical system, in order to simplify the explanation, the explanation will be limited to the transmissive reproducing optical system as shown in FIG. proceed. In the transmission type reproduction optical system, the pits 26a and 28 act as openings. When reproducing data, the beam spot 24 is moved in the direction of the arrow in the figure, that is, in the direction of the track, and traces a large number of pits 26a and 28 formed along the track. When the light intensity distribution of the beam spot 24 is a square wave, two synchronous pits 26
FIG. 6A shows the transmitted light intensity distribution immediately after passing through a (that is, the synchronization mark 26), and FIG. 6B shows the transmitted light intensity distribution immediately after passing through the data pit 28. The vertical axis shows the light intensity, and the horizontal axis shows the position on the recording medium. Pit (or opening) 26a
As shown in FIG. Place the two synchronization pits 26a (that is, the synchronization marks 26) in spot 2.
7A shows the light intensity distribution on the detector 22 when the data pit 28 is illuminated with the spot 24, and FIG.
Shown in B. The vertical axis shows the light intensity, and the horizontal axis shows the position on the detector 22.

The detector 22 of this embodiment includes three photodiodes (PD) 22a and 22b as shown in FIG.
PD22a is located at the zero-order lobe position (range A in the figure), and PD22a is located at the ±1st-order lobe position (range B1 in the figure).
PDs 22b and 22c are arranged in the ranges B2 and B2, respectively. In the figure, the x-axis indicates the track direction, and the y-axis indicates the track width direction. PD22a outputs a signal when a pit is illuminated regardless of the synchronization mark or data mark, and PD22b
and 22c output a signal only when the synchronization mark is illuminated. Therefore, synchronous detection can be performed using the output signals of PD22b and PD22c.

A synchronization mark according to a third embodiment of the present invention is shown in FIG. In this embodiment, the synchronization mark 26 is composed of two synchronization pits 26a formed on both sides of the track (x-axis), and the lines connecting the two synchronization pits 26a are oriented diagonally to the track width direction. is formed. On the other hand, the data mark 28 is composed of two data pits 28a formed along the track width direction, and data is recorded as the distance between these pits. Furthermore, the beam spot 24 is shaped into an ellipse in order to increase the recording density.

When reproducing data, these marks 26
and 28 are traced by the beam spot 24, and the transmitted light intensity is observed. Sync mark 26 to beam spot 24
FIG. 10A shows the interference fringe intensity distribution and the central cross-sectional profile of the distribution when the data mark is envelope-illuminated with the spot 24, and FIG. 10B shows the interference-fringe intensity distribution and the central cross-sectional profile of the distribution when the data mark is envelope-illuminated with the spot 24. This profile shows II-I in FIG. 10A and II-II in FIG. 10B.
is the central cross section. The vertical axis of the profile is light intensity;
The horizontal axis indicates the position on the detector 22. Here, the arrangement direction of the synchronization pits 26a constituting the synchronization mark 26 is the same as that of the data pits 28a constituting the data mark 28.
Since the detector 22 is tilted with respect to the arrangement direction of
The interference fringes observed above also tilt in the same direction. Therefore, Figure 1
By using the two line sensors 22a and 22b arranged as shown in FIG. 1, the synchronization mark 26 can be detected as a difference in the inclination of interference fringes. When observing the data mark 28, as shown in FIG. 11B, the number of interference fringe peaks observed by each of the line sensors 22a and 22b is equal to three. However, when observing the synchronization mark 26, as shown in FIG. 11A,
The number of interference fringe peaks observed by each of the line sensors 22a and 22b is different. In other words, line sensor 22b
observes three peaks, but the line sensor 22a observes only two peaks. In this way, by checking the number of peaks observed by the line sensors 22a and 22b, the inclination of the interference fringes can be determined and the synchronization mark 26 can be detected.

A synchronization mark according to a fourth embodiment of the present invention is shown in FIG. In this embodiment, the synchronization mark is a single synchronization pit 26, and the data mark is also a single data pit 28.
Each is composed of The synchronization pit 26 and the data pit 28 have different diameters, and the beam spot 24
When the diameter of the synchronous pit 26 is "5", the diameter of the synchronous pit 26 is "4".
, the diameter of the data pit 28 is set to "3".

FIG. 13A shows the transmitted light intensity distribution when the synchronization pit 26 is illuminated using the transmission type optical system of FIG. 1, and FIG. 1 shows the transmitted light intensity distribution when the data pit 28 is illuminated.
Shown in 3B. In this embodiment, since the pits 26 and 28 are single circular pits, the diffracted light distribution is the same in both the track direction (x-axis) and the track width direction (y-axis). As can be seen from the figure, the first zero cross width of the diffracted light distribution due to the synchronization pit 26 is narrower than that due to the data pit 28. Therefore, by detecting the zero cross width, the synchronization pit 26 can be detected, and synchronization detection can be performed. As a method of detecting the zero cross width, for example, detector 2
2. This can be achieved by detecting the diffracted light distribution using a line sensor and observing the zero cross points on the left and right of the maximum value of the light intensity. In this manner, synchronous detection can be performed by detecting the zero cross width of the diffracted light distribution.

A synchronization mark according to a fifth embodiment of the present invention is shown in FIG. In this embodiment, the synchronization mark is composed of a single elliptical synchronization pit 26 long in the track width direction, while the data mark is composed of a single circular data pit 28. The synchronization pit 26 has a major axis approximately equal to the diameter of the circular beam spot 24 and a minor axis approximately equal to the diameter of the data pit 28 .

Although this embodiment can be applied to either a transmission type or a reflection type reproduction optical system, the case where the transmission type optical system shown in FIG. 1 is used will be explained below. FIG. 15A shows the transmitted light intensity distribution when the synchronization pit 26 is illuminated, and FIG. 15B shows the transmitted light intensity distribution when the data pit 28 is illuminated. This figure shows the profile of the central cross section of the diffracted light distribution on the detector 22. Since the synchronization pit 26 has different dimensions in the track (x-axis) direction and in the track width (y-axis) direction, the diffracted light distribution also differs in the x-axis direction and the y-axis direction. on the other hand,
Since the data pit 28 is circular, the diffracted light distribution is the same in both the x-axis direction and the y-axis direction. As a result, synchronous pit 26
The diffraction light distribution in the y-axis direction is different between the data pit 28 and the data pit 28 . In order to detect the difference in the diffraction light distribution in the x-axis direction and the y-axis direction, in the synchronization pit 26 and the data pit 28,
The cross-correlation of the diffracted light distributions in the x-axis direction and the y-axis direction is taken. When the value of this cross-correlation is small, the beam spot 24 is located on the synchronization pit 26, and when the value of this cross-correlation is large,
This means that the beam spot 24 is located on the data pit 28. For example, the method shown in FIG. 16 can be used to obtain this cross-correlation. In the figure, the line sensor 22a is on the x-axis, and the line sensor 22b is on the y-axis.
They are arranged on the axis so that they are orthogonal to each other. In addition, the line sensors 22a and 22b are arranged so that the intersection of the line sensors 22a and 22b is at the center of the optical axis. The data of the diffraction light distribution sampled simultaneously by these two line sensors 22a and 22b is read out serially at the same time. This data is multiplied pixel by pixel by the multiplier 30 and read out serially at the same time. This data is added together using an adder 32. Then, when data reading for one line is completed, the output of the adder 32 becomes a cross-correlation value and is input to the comparator 34. The other input terminal of the comparator 34 receives the cross-correlation value in the synchronization pit 26 and the data pit 2.
The intermediate value of the cross-correlation values in 8 is the reference (r
ef). As a result, it can be determined that when the output of the comparator 34 is positive, the output of the adder 32 is the cross-correlation value of the data pit 28, and when it is negative, it is the cross-correlation value of the synchronization pit 26. Therefore, it can be determined from the output of the comparator 34 whether it is the synchronization pit 26 or the data pit 28 that is currently illuminated by the beam spot 24. In this way, the synchronization pit 26 can be detected and synchronization detection can be performed.

Furthermore, the method of detecting the synchronization mark is not realized only by the above-mentioned embodiment; for example, the method shown in FIG.
This can also be realized by a reproduction optical system including a matched filter 38 such as the one shown in FIG. In this optical system, the light collected by the condenser lens 20 is divided into two parts by the half mirror 36, one of which is directly incident on the detector 22, and the other is incident on the detector 40 via the matched filter 38. The matched filter 38 is an optical filter made to match the light intensity distribution of the diffraction interference pattern during synchronization mark reproduction, and the intensity of transmitted light to the detector 40 is greater during synchronization mark reproduction than during data mark reproduction. It is made like this. Thereby, synchronous detection can be performed based on the light intensity detected by the detector 40. Data marks are reproduced by the intensity of light that passes straight through the half mirror 36 and reaches the detector 22. Although FIG. 18 is an example related to a transmission type optical system, similarly in a reflection type optical system, a half mirror 36 is arranged in front of the detector 22 to divide the optical path into two, and each has a matched filter 38 and a detector 4.
0 and the detector 22 may be placed. This detection method using a matched filter can be used to detect synchronization marks in the first to fifth embodiments described above. This method allows the reproduction optical system to be simplified.

Furthermore, the synchronization mark is not realized only in the above embodiment; for example, the synchronization mark is realized by the synchronization pit 2 in FIG.
This can also be achieved by not arranging 6 on the track center line but slightly shifting it in the track width direction (y-axis direction). In this way, the synchronization mark may be any mark that produces a characteristic reflection or transmission diffraction interference pattern when the data pit 28 is illuminated with the beam spot 24.

The synchronization mark described above can be used for sector synchronization and frame synchronization. The synchronization mark in the present invention can also be used for bit synchronization. In this case, a plurality of synchronization marks may be arranged at equal intervals as shown in FIGS. 17A and 17B. By arranging it in this way, it is possible to extract the clock, and the PL
Bit synchronization can be performed by detecting the phase difference with the sample clock in the circuit using L and controlling the clock so that they match.

[0031]

[Effects of the Invention] According to the present invention, synchronization marks that can be reliably distinguished from marks in other areas and are easily detected can be recorded with a short mark length, which is effective in improving recording density. There is.

[Brief explanation of drawings]

FIG. 1 shows an example of a transmission type reproduction optical system to which the present invention is applied.

FIG. 2 shows an example of a reflective reproduction optical system to which the present invention is applied.

FIG. 3 shows synchronization marks for the first embodiment of the invention.

FIG. 4 shows a light intensity distribution when the pit shown in FIG. 3 is illuminated.

FIG. 5 shows synchronization marks for a second embodiment of the invention.

6 shows the transmitted light intensity distribution immediately after passing through the pit shown in FIG. 5. FIG.

FIG. 7 shows a light intensity distribution on a detector when the pit shown in FIG. 5 is illuminated.

FIG. 8 shows the configuration of a detector used in this example.

FIG. 9 shows synchronization marks for a third embodiment of the invention.

10 shows an interference fringe intensity distribution and a central cross-sectional profile of the distribution when the pit shown in FIG. 9 is illuminated; FIG.

FIG. 11 shows the configuration of a detector according to this embodiment.

FIG. 12 shows synchronization marks for a fourth embodiment of the invention.

FIG. 13 shows a transmitted light intensity distribution when the pit shown in FIG. 12 is illuminated.

FIG. 14 shows synchronization marks for a fifth embodiment of the invention.

FIG. 15 shows a transmitted light intensity distribution when the pit shown in FIG. 14 is illuminated.

FIG. 16 shows a configuration for taking cross-correlation in the x-axis direction and the y-axis direction.

FIG. 17 shows the configuration of synchronization marks according to the present invention for bit synchronization.

FIG. 18 shows another reproduction optical system for detecting synchronization marks.

[Explanation of symbols]

24... Beam spot, 26... Synchronization mark, 28... Data mark.

Claims (5)

[Claims] Claim 1: A data mark having a plurality of pits arranged at a predetermined depth corresponding to the information to be recorded, and a synchronization mark that generates a synchronization signal when reproducing the information recorded in the data mark. An optical recording medium characterized in that the synchronization mark is configured to generate an optical pattern different from an optical pattern obtained from the data mark. 2. The optical recording medium according to claim 1, wherein the synchronization mark is composed of pits having a different depth from the data mark. 3. The optical recording medium according to claim 1, wherein the synchronization mark is composed of a plurality of pits having a different arrangement from the arrangement of the data marks. 4. The optical recording medium according to claim 1, wherein the synchronization mark is composed of pits having a shape different from that of the data mark. 5. A method of detecting a synchronization mark by irradiating the optical recording medium according to claim 1 with light for reproducing information and detecting an optical pattern different from the optical pattern obtained from the data mark. How to detect recording media.