JPH04339320A - Optical disc tracking thereof and reader therefor - Google Patents

Abstract

PURPOSE: To provide a device for performing the tracking and reading/writing operations of information to an optical disk memory system having a disk medium having a lot of information tracks provided alternately with a single guide track. CONSTITUTION: The optical disk medium has a surface provided with plural guide tracks 12a and 12b at intervals when observing it along the radius, information tracks 14-1a and 14-2a are parallelly provided on both the sides of these guide tracks 12a and 12b, and these information tracks are not information tracks placed parallelly with the other guide tracks when observing them along the radius of the disk. This device is provided with a means 20 for turning two convergent light beams toward the surface and positioning the respective beams so as to illuminate any different one of information tracks and the intermediate guide track and a means 50 for positioning the light beams on the guide track in response to light reflected from the surface and reading information from two parallelly arranged information tracks 14-1a and 14-2a.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk memory system having a disk medium having a number of information tracks alternating with a single guide track, and to tracking and reading information on the disk. /Related to a device that performs a write operation.

0002

BACKGROUND OF THE INVENTION There are many known systems for reading and tracking information on optical disks or other optical media. In relatively complex systems, such disks or other media typically have information tracks alternating with guide tracks when viewed along the radial direction. Each "track," or information and guide track, is actually a single track within an optical disc, which runs from near the center of the disc to off-center, much like the grooves on a traditional audio record. It is formed in a spiral shape within the disk to the position where it is located. In relatively simple optical media systems,
The information track and the guide track are the same.

All such systems include means for servoing or tracking along the guide track so that the information is correctly read from the information track. The guide track in an optical medium is generally λ/
It is raised above or recessed into the surface of the medium by a value between 8n and λ/4n. here,
λ is the wavelength of the incident light beam and n is the refractive index of the propagation medium. Typical tracking systems use one tracking beam or two tracking beams output from one beam source. The illumination beam is typically focused to a spot size by a lens, and when the beam is centered on a track, 50% of the beam's power impinges on the track. Because of the approximately λ/4n wavelength step between the track and the rest of the media surface, the power of the reflected beam when the center is on the track is substantially lower at the center of the pattern compared to the power of the beam impinging on the media. , and the power focused by the illumination lens is similarly reduced.

One or two detectors are suitably positioned to receive the reflected power and applied to servo means to move the center of the tracking beam onto the guide track. The reading means are coupled to means for generating an illumination beam and position the illumination beam on an information track provided at a predetermined distance in the vicinity of the guide track. In a conventional two-spot tracking system (which actually has a third spot for reading information), two illumination beams are provided, but in reality only one illumination source is provided. It is provided. In a two-spot tracking system, the two beams or spots are generally offset by a certain amount;
% power level touches an imaginary line parallel to the track. As each of the beams passes over the guide track, the signal is significantly reduced due to signal cancellation caused by the depression or rise of about 1/4n wavelength in the guide track. The return signal from one beam is then subtracted from the return signal from the other beam to produce a single sine with the center of the S-curve mark when the two beams are at equal distances on either side of the guide track centerline. An electrical circuit is provided that generates a wave or S-curve signal.

[0005]

SUMMARY OF THE INVENTION In accordance with the present invention, an optical disc medium has a surface provided with a plurality of radially spaced guide tracks, each guide track having a is juxtaposed with an information track that is not an information track that is juxtaposed with another guide track when viewed along the radius of the disc. The apparatus includes means for directing two focused beams of light toward the surface and positioning each beam to illuminate a different one of the information tracks and a portion of the intermediate guide track, and responsive to reflected light from the surface; means for positioning the light beam relative to the guide track and for reading information from two juxtaposed information tracks.

[0006]

DETAILED DESCRIPTION First, referring to FIG. 1, a portion of a conventional optical disc 6 is shown. The cutaway part closest to you is along the radius. Many different shapes of optical discs 6 are known. There are read-only optical discs, optical discs that can be written to once and read many times, and optical discs that can be erased. Retrieval of information from the disk by reflections from formations, magneto-optical processing, etc. are all taken into account. The disk 6 has a reflective top surface 6a provided with preformatted guide tracks 12 (three guide tracks 12a, 12b and 12c are shown) machined or otherwise formed into its substrate 6b. are doing. Guide track 1
2 are alternated with information tracks 14 (two information tracks 14a and 14b are shown). The information tracks are imaginary areas in the layer 6c on the substrate 6b and under the top surface 6a in which magneto-optic areas are formed (written), recognized (read) and rewritten (erased). ), but other formats are also available. In reality, the guide track 12 and the information track 14 are each one continuous track, and FIG.
As shown in the figure, it is formed in a spiral shape outward from a central axis (not shown) on the right side of the disk 6. Although the guide track 12 is shown recessed in FIG. 1, it may actually be raised or, in other words, the information track 14 may be recessed into the surface 6a of the disc.

[0007] If the guide track is recessed, which is generally the case, the guide track is formed on the top surface 6 at the time of manufacture of the disk.
processed or reproduced within a. Since the forming process is not perfect, the edges and bottom 12-3, such as guide tracks 12-1 and 12-2, tend to be rough. To this end, conventionally a small guard zone is provided between the guide track 12 and the information track 14, as shown by dotted lines 16-1 and 16-2, to reduce the spot intensity before it hits the edge of the guide track, and to reduce the spot intensity before hitting the edge of the guide track. is known to reduce crosstalk.

Although not limiting the dimensions of the disk 6, typical guide tracks are about 0.6 micrometers (μm) and information tracks are about 0.8 micrometers (μm). , the spacing between the guide track and the information track is approximately 0.1 μm. Therefore, the information tracks are 0.8 μm apart, i.e. as far apart as the maximum width of the information tracks, and the spacing between tracks (information track to information track or guide track to guide track) is 1.6 μm. That will be understood.

For reasons that will become clear as the description progresses, the depth of the guide track 12 below the top surface 6a is of some importance. For tracking purposes, the depth of the track 12 is preferably λ/8n. Here, λ is the wavelength of the incident light source, which will be explained below, and n is the refractive index of the propagation medium. A typical value for λ is 830 nm and a typical value for n is 1.5. For information reading, the depth is preferably λ/4n. Typically, the depth will be λ/6n as an intermediate value.

A typical conventional so-called "two-spot" tracking device will now be described with reference to FIG. In fact, there are three focused illumination spots, designated A, B and C, all of which are illuminated perpendicularly to the top surface 6a from a light source (not shown). Spots A and B are used for tracking. Spot C
is used only for reading, writing, or erasing information in such systems. It should be understood that each spot A, B, and C is not shown at full power diameter, but at half power diameter. The half power dimensions of spots A and B are generally equal to the width of the information track. The illumination spots are mechanically coupled to each other so as to move in a direction perpendicular to the direction of the tracks (12 and 14), as indicated by arrow 7. 5 shown
At a power level of 0%, spots A and B touch a common line 8 parallel to the track, and spot C is centered on that line.

When a spot like A is half on the information track 14 and half on the guide track 12,
The reflected light, measured by a detector (not shown) functionally positioned in line with spot A along a line perpendicular to the top surface 6a, is minimized by the diffraction caused by the width of the guide track λ/6n. become. This is shown as waveform A in FIG. In FIG. 3, the horizontal axis is distance and the vertical axis is the response signal (R). If spot A moves to the left or right from its central position, which is half above the guide track 12 and half above the information track 14 as shown, the reflected light will increase. Same thing with spot B
This also applies to spot B, and the reflected light of spot B has the same shape as spot A, which is simply displaced. The lower waveform in FIG. 3 is the sum of waveform A and waveform B inverted. For spots A and B as shown in Figure 2, Figure 3
A zero crossing occurs at point 9 of the lower waveform. Spots A and B can be positioned so that the center of spot C is located above the information track 14 using well-known thermotechniques.

Referring now to FIG. 4, a portion of an optical disc 11 according to the present invention is shown. As in the case of the disk 6 in FIG. 1, the front cross-sectional part is along a radius. As in the case of the disk 6 of FIG. 1, there is a top surface 11a similar to 6a and a substrate 11b similar to substrate 6b. There are guide tracks 12, two guide tracks 12a and 12b are shown by way of example, and an information track 14.
There is. However, in FIG. 4 there are actually two information tracks between successive guide tracks 12. In other words, an information track 14 is juxtaposed on each side of each guide track 12, and this information track 14 is not common with an information track juxtaposed to another guide track 12 when viewed along the radius of the disc. . To give a specific example, the information tracks 14-1a and 14-2a are juxtaposed on both sides of the guide track 12a, and the information track 1
4-1b and 14-2b are juxtaposed on both sides of the guide track 12b. As in the case of the disk in Figure 1, (
A single guide track 12 (not shown but provided on the right side of FIG. 4) is spirally formed outward from the disk central axis and two information tracks 14 juxtaposed on both sides thereof. be.

As explained in connection with FIG. 1, it is advantageous to provide a guard band between successive information tracks. In FIG. 1, the guard zone was formed by both guide tracks and small spaces on either side of each guide track. However, in FIG. 4, since there are two information tracks between each successive pair of guide tracks,
Requires additional space. Between successive information tracks there are 18-1, 18-2 and 18 as protective strips.
There is a guard track 18 such as -3 or a section consisting of a guide track 12 and its adjacent area 16.

As in the case of the disk of FIG. 1, each guide track 12 is typically, but not limited to, 0.6 μm, with small guard tracks 16 of 0.1 μm on each side. Yes, each information track 14
is 0.8μm, and each guard track 18 is 0.8μm.
It is m. A typical guide track-to-guide spacing is approximately 3.2 μm. As in the case of the disk of FIG. 1, the depth of the guide track is ideally λ/8n for tracking and λ/4n for reading and writing information. Moreover, a preferable intermediate value is depth λ/6n.

Referring now to FIG. 5, spots A and B for tracking are similar to spots A and B in FIG. 2 and have the same shape as each other, but their spacing is perpendicular to the track direction. two information tracks 14 which, when properly positioned, are associated with a line (not shown) and are juxtaposed on either side of the guide track 12.
They differ in that their centers are aligned at the top. Both spots are mechanically coupled to each other for movement in the direction indicated by arrow 7 perpendicular to tracks 12 and 14. In Figure 5, the innermost circle is 5
Illumination is shown at a power level of 0%, with the next two largest circles showing a power level of 25% and a power level somewhat greater than 0%, respectively. Note that at 25%, which is somewhat greater than the 0% power level, the light beam falls into the intermediate guide track 12.

Next, referring to FIG. 6, waveforms A and B
corresponds to the response signal received back from the disk when the spot moves across the disk in the direction indicated by arrow 7. The waveform shown as -B+A is the sum of waveform A and the inverted version of waveform B,
This differs from the similar waveform in FIG. 3 because the spacing between spots A and B is further apart than spots A and B in FIG. Nevertheless, in waveform -B+A of FIG. 6, there is a clear zero point at point 9. This point 9 is connected to the guide track 12 as in the conventional case.
can be used to position the centers of spots A and B with respect to the center of . However, unlike before, spots A and B are appropriately positioned to read, write, or erase information from the information track 14. And the third spot C
Unlike the conventional method, which requires a third spot, the present invention does not require a third spot.

Referring now to FIG. 7, a tracking and read/write/erase system 10 according to the present invention is shown. Disk 11 is disk 1 in Figure 4.
Same as 1. System 10 closest to disk 11
2 is a tracking and focus assembly 20 which includes a first lens means 22 . This first lens means 22 is supported by a mechanically movable member 24 and is movable in the direction of arrow F for focusing towards and away from the surface of the disc. . The member 24 is movable relative to the other member 26 by well-known means not shown. The member 26 is oriented radially relative to the disc, i.e. in the direction of the transverse arrow T.
As shown, it is possible to move in a direction perpendicular to the focusing direction of arrow F. The member 26 has further lens means 28 and means 30 for changing the direction of the light beam impinging on or reflected from the disk 11.

As is well known in the art, this type of optical assembly is used to move radially from track to track on a disk, focusing and changing the direction of each light beam. can be used. A group of generally parallel light beams, indicated generally at 36 and symmetrical about a central axis 36a, are provided by an illumination source array 34, such as a laser diode or the like, which includes a beam symmetrical about a central axis portion 36a. 36b and 36
generate c.

Substantially parallel collimated beam 36b
and 36c pass through beam expanding means 40, equal in number to input beams 36b and 36c, and central axis portion 42a.
a set of output beams 4 with a small angular spacing S to
2b and 42c are generated around central axis portion 42a. Focused beam 42b measured along the radius of the disk
and 42c is determined by the rotation of laser array 34 about the line of travel of beams 36b and 36c. Axis 42a is coextensive with axis 36a. Beams 42b and 42c are 1.
They impinge on the surface of the disk 11 as spots 43b and 43c at a spacing equal to the spacing between the information tracks, which is 6 μm. The spot is reflected from the surface of the disk, passes through lenses 22 and 28, is redirected by means 30, enters beam splitting means 44 and is reflected back into reading means 50.

When reading a magneto-optical disk (M-O), the beam splitter 44 must be polarized and the light source 34 must produce linearly polarized light, with a small amplitude of the linearly polarized light. A portion is fed through a beam splitter 44 to reading means 50 . This reading means 5
0 includes a quarter-wave plate 52, lens means 54, Wollaston polarizing prism 56, etc., and includes two pairs of spaced reading beams 57a1/57b1 and 57a2/57.
b2 respectively to the detection element 58- of the solid-state optical detection means 58.
1 and 58-2 onto a first pair 58a1/58b1 and a second pair 58a2/58b2. Each of the sensing elements generates a separate electrical output signal. For example, sensing element 58a1 generates an output signal Vr1 and another detector 58a1 generates an output signal Vr1.
8a2 generates another output signal Vr2, both signals 14-
1a, and the sensing elements 58b1/58b2 generate further output signals Vl1 and Vl2, which signals are for the right information track, such as 14-2a. be.

The information signal reproduced from the track is the difference between the formation output signals. For example, the track information on the left is (Vl1-Vl2), and the track information on the right is (Vl1-Vl2).
Vr1-Vr2). A more detailed description of the reading process can be found, for example, in the article by Challener and Rinehart, "Jones Matrix Analysis and Reading Systems for Magneto-Optical Media".
of Magneto-Optical Media
and Read-Back Systems)”, Applied Optics, Vol. 26,
No. 12, pp. 3974-3980, (September 1987
on the 15th of the month). archival
The disk includes elements 58a1 and 58b1 (or 58
b2 and 57a2) are used and treated in the same way, except that there is no need to polarize the light beam.

According to the invention, the same output signal is used to center shaft 42a on guide track 12, such as guide track 12a. This is Vr1 and V
This is achieved by subtracting the sum of r2 from the sum of Vl1 and Vl2. The resulting value, if non-zero, is used by feedback means well known in the art to move the assembly 20 in the direction of the arrow, reacquire the central guide track 12, and
Beams 42b and 42c are positioned on the information tracks on either side of the. The system 10 described above using only two light spots is capable of tracking and read/write/erase. The read, write and erase functions are well known to those skilled in the art.
It will be appreciated that this is achieved through a combination of the power output by laser array 34 and the presence or absence of a magnetic field at disk 11.

[Brief explanation of the drawing]

1 is a perspective view of a portion of an optical disc according to the prior art; FIG.

FIG. 2 is an explanatory diagram showing tracking by two light beams used in the disk of FIG. 1 according to the prior art;

3 is a set of waveform diagrams useful for understanding tracking methods on the disk of FIG. 1 according to the prior art; FIG.

FIG. 4 shows an optical disc according to the invention.

5 is an illustration showing tracking with two light beams used with the disk of FIG. 4 according to the present invention; FIG.

6 is a set of waveform diagrams used to explain the tracking method on the disk of FIG. 4; FIG.

FIG. 7 is a block diagram of an optical disc reading and tracking system used for the optical disc of FIG. 4;

[Explanation of symbols]

11 Optical disc 11a Upper surface 11b Substrate 12, 12a, 12b Guide track 14, 14-1
a, 14-2a information track 18-1, 18-2,
18-3 Guard track 20 Tracking and focus assembly section 34 Laser array 40 Beam expander 44 Beam splitter 50 Reading means

Claims (12)

[Claims] 1. A plurality of guide tracks spaced apart when viewed along a radius, each of the guide tracks being juxtaposed on either side with an information track, the information track being adjacent to the other guide tracks. An optical disc that is not juxtaposed to a guide track. 2. Having a central axis and having guide tracks spirally formed outward from a position relatively close to the central axis to a position relatively close to an edge of the disk, each guide track being formed in a spiral shape, An optical disc having two information tracks arranged substantially parallel to each other on either side of a shaped guide track. 3. The optical disc of claim 2, wherein the guide track is recessed below the surface of the disc. 4. The guide track is recessed from the surface of the disk by about λ/4n to λ/8n;
3. Optical disk according to claim 2, where λ is the wavelength of the illumination source used for the disk and n is the refractive index of the propagation medium in which the disk is placed. 5. The guide track is recessed from the surface of the disk by about λ/6n, where λ is the wavelength of the illumination source used for the disk and n is the wavelength at which the disk is positioned. 3. The optical disk according to claim 2, wherein the refractive index of the propagation medium is . 6. The optical disk of claim 2, wherein the disk is a magneto-optic disk. 7. The optical disc of claim 2, further comprising a pair of guard tracks, each adjacent to the guide track and adjacent to each of the information tracks. 8. The width of the two information tracks measured along the radius is the same and the width of the two information tracks measured along the radius is the same.
8. The optical disc of claim 7, wherein the size of the two guard tracks is equal to the size of the track. 9. Directing two focused light beams onto the surface of the disk, each beam respectively targeting a different one of the juxtaposed information tracks and at least a portion of an intermediate guide track of the optical disk of claim 1. means for positioning to illuminate, and in response to reflected light from said surface, generating positional information of a light beam relative to said juxtaposed information track and from said two juxtaposed information tracks; 2. A reading and tracking device for optical discs according to claim 1, comprising means for reading information. 10. The apparatus of claim 9, wherein said means for directing two focused beams of light comprises a laser array. 11. The apparatus of claim 10, wherein said laser array includes two light emitting diodes each generating said beam. 12. The means responsive to the reflected light comprises:
10. The apparatus of claim 9, further comprising detection means responsive to light reflected from said disk for generating signals representative of said read information and position information.