KR20080078020A - System and method of reading/writing data on an optical disc by a plurality of spots - Google Patents

Abstract

The present invention relates to a method and system of reading/writing data on an optical disc by a plurality of spots positioned along inner tracks to outer tracks of the optical disc. The method comprises the steps of detecting successively that each spot has reached a data area previously read/written; and moving the spot to a position adjacent to the current outermost spot if the reading/writing is done from inner to outer tracks, or to a position adjacent to the current innermost spot if the reading/writing is done from outer to inner tracks.

Description

TECHNICAL AND METHOD OF READING / WRITING DATA ON AN OPTICAL DISC BY A PLURALITY OF SPOTS

The present invention relates to a method and apparatus for reading / writing data on an optical disc, and more particularly, to a method and apparatus for reading / writing data on an optical disc by a plurality of spots.

In recent years, optical discs have become relatively inexpensive and have a large data storage capacity, making them widely used data storage media for storing multimedia voice / video information. As a result, the increase in the data transfer speed has become an important factor of improvement, since data stored on the optical disc can be read faster, or data to be stored on the optical disc can be written faster.

One way to increase the data transfer speed of an optical disc is to use multiple spots that simultaneously read or record multiple tracks on an optical disc.

Since most optical discs have a spiral structure, as shown in Figs. 1A and 1B, the spots will encounter some tracks previously read or recorded by other spots.

FIG. 1A is a schematic diagram showing a situation in which data is recorded / read on an optical disc by spot A starting at block 1 and spot B starting at block 5. FIG. Simultaneous processing of writing / reading by this spot A and spot B is continued until spot A reaches the start of block 5, as shown in Fig. 1B. In other words, spot A arrives at a block previously written / read by spot B. In order to prevent spot A from writing new data in the area previously recorded / read by spot B, displacement of the spots is necessary at this point.

In general, the displacement involves moving all spots the same distance. This spot displacement technique is advantageous in that it is easy to implement because only the radial displacement of the objective lens is required. European Patent Application No. EP 0 840 294 A2 (published May 6, 1998 and filed by Samsung Electronics) describes a multiple track scanning method for optical pickup using multiple spots, employing this spot displacement technique.

However, in order to read or write all the data, there is a disadvantage in that the displacement must be a (Nb-1) Ng-1 track (for a device with Nb spots and Ng distance between spots). Accordingly, the data transfer rate of this method is limited to the factor (Nb-1) Ng times the data transfer rate for one spot. In practice, since Ng is usually 1, the data rate gain will be limited to Nb-1.

Therefore, it is expected that a new displacement technology of optical disc reading and writing that exceeds the data transfer rate limit will be realized in existing optical drives to meet the high demands for improving the data transfer rate of reading and writing.

It is an object of the present invention to provide a method and apparatus for reading / writing data on an optical disc by a plurality of spots to improve the read and write data transfer speed.

According to one embodiment of the present invention, a method of reading / writing data on an optical disc by a plurality of spots located along an outer track in an inner track of the optical disc is disclosed. The method sequentially detects that each spot has reached a previously read / written data area, and the spot is located adjacent to the current outermost spot if the read / write consists of an inner to outer track. Or, if the read / write consists of an outer to inner track, moving to a position adjacent to the current innermost spot.

According to one embodiment of the present invention, an apparatus for reading / writing data on an optical disc is disclosed by a plurality of spots located along the outer track in the inner track of the optical disc. The apparatus is configured to sequentially detect that each spot has reached a previously read / written data area, and to generate a detection signal, and to operate the spot by operating the detection signal so that the spot is read from the inside. It is provided with an actuating device which moves to a position adjacent to the current outermost spot when the outer track is made, or to a position adjacent to the current innermost spot when the read / write is made from an outer to inner track.

Unlike the prior art in which the increase in data transfer rate is limited to the factor of Nb-1 / Ng, it is possible to increase the data transfer rate of factor Nb in the displacement technique according to the present invention. That is, by the displacement technique of moving the spots individually, it is possible to increase the data transfer speed of reading and writing on the optical disc.

In addition, the above-mentioned technique of moving the spots can be easily carried out because it is not necessary to move all the spots at the same distance at the same time, which is a cost effective measure.

Other objects and effects of the present invention will become apparent from the description and claims of the present invention with reference to the following drawings, through which the present invention may be fully understood.

1A and 1B are schematic diagrams showing a situation where one spot encounters an area recorded or read by another spot.

2A-2D illustrate different stages of multi-spot readout of an optical disc using the spot displacement technique in accordance with one embodiment of the present invention.

3 is a schematic diagram showing that a mirror array is used to displace each spot from the laser array.

4 is a schematic diagram showing a spot arrangement on an optical disc.

5 shows the angular displacement of the mirror along the sawtooth pattern over time.

6 is a schematic block diagram showing the structure of a closed loop control system for controlling spots on an optical disc.

7 is a schematic flowchart illustrating a method of reading data on an optical disc in open loop control according to an embodiment of the present invention.

In the drawings, like reference numerals denote like, similar, or corresponding elements or functions.

The technical measures of the present invention will be described below in detail with reference to the accompanying drawings.

Herein, the present invention can be used for both reading and writing of an optical disc. In this embodiment, "read" is used for simplicity. Those skilled in the art will naturally understand that "read" may be replaced with "write" in this specification.

2A-2D show another stage of multi-spot readout of an optical disc using a spot displacement technique in accordance with one embodiment of the present invention. The technique is shown using three spots A, B, and C separated by one track. The three spots, Spot A, Spot B, and Spot C, are located along the outer tracks on the inner tracks on the optical disc, such as tracks T1, T2, and T3, respectively, and the areas shown in Fig. 2A (read in Figs. 2B-2D are grayed out). The tracks are read simultaneously in the direction of the arrow, and the distance between all spots remains constant along the radial direction by at least one track. The detection device sequentially detects the position of each spot and generates a detection signal.

As shown in Fig. 2A, as soon as spot A reaches a part of the track read by another spot, spot A becomes unnecessary and a detection signal is generated indicating that spot A must move to continue reading data. In the present embodiment, spot A is caused by an actuation device in accordance with the detection signal, adjacent to the current outermost spot (i.e., next to the current outermost spot) when the read / write is made from the inner to outer track. ), Or if the read / write consists of an outer to inner track, move to a position adjacent to the current innermost spot (ie, next to the current innermost spot). In this embodiment, as shown in Fig. 2B, spot A moves to track T4, which is next to spot C.

The term " adjacent " here means that the moving spot is located next to the current outermost / innermost spot, and one track (as in the example shown in FIG. 2) or a plurality of tracks from the current outermost / innermost spot. This means that the tracks are separated by the tracks (for example, when the spots are separated from each other by more than one track).

The same technique applied to spot A applies to other spots. For example, as shown in Fig. 2C, spot B also encounters a portion of the previously read track. Like spot A, spot B also moves to track T5 as shown in FIG. 2D.

In connection with the implementation of the technique, there are other methods that can be used to implement this jump technique. However, it is important that each spot be controlled individually.

3 is a schematic diagram illustrating the realization of a jump technique that improves the data transfer speed of a drive by displacing individual spots in a dual laser device by a mirror array. The apparatus has a laser array with two laser sources 4, 5. For the laser beam emitted from the laser array (see dashed line in FIG. 3), there is a mirror array used to deflect the laser beam. The mirror array includes two mirrors 1 and 2. The mirror 1 deflects the laser beam A from the laser source 5, and the mirror 2 deflects the laser beam B from the laser source 4. Each mirror 1, 2 can rotate by a small angle α 1, α 2, and the rotation axis 3 lies approximately in the plane passing through the optical axis of the laser beam.

By rotating one of the mirrors 1, 2, the laser beam after deflection by the mirror is changed so that the corresponding spot on the optical disc is controlled. For example, if the mirror rotates clockwise about the axis 3, the spot will move towards the edge of the optical disc. Conversely, the spot will move towards the center. In this way, a mirror array is employed to realize the displacement of the individual spots from the laser array. A preferred embodiment of the present invention is to place the spots in a nearly tangential direction. This is advantageous to simplify the operation by minimizing the mechanical movement of the component upon displacement of the spots.

This displacement cannot be as short as possible to jump from the previous track to the next, but the difference is so small that it actually causes little trouble. In other words, the structure of the mirror array is simplified because the rotation axis may not be aligned very precisely.

In order to deflect only the laser beam from one laser source per mirror, the mirrors should be placed close to the laser array and at such a distance that the beams do not overlap. Small mirrors, for example, having a width and height of about 50 to 100 microns, are advantageous in that they can be displaced very quickly and can be formed in one component by including them in the same housing together with the laser array. Do. Accordingly, it is possible to provide a simplified application in the optical path for practicing the present invention.

The mirror array may be disposed at a place other than the optical path. For example, to produce non-overlapping beams, a telescope for generating focus is needed. The mirror array is then placed near these focal points.

In this embodiment a mirror array is used to displace each spot. Alternatively, the displacement of each spot may be performed by other means, such as a group of lenses used to change the direction of the laser beam. Another possible way is to make the displacement of individual spots by controlling the deflection angle of each other parallel and non-overlapping beams with a liquid crystal module in a plane perpendicular to the optical axis. In addition, the liquid crystal module has a constant refractive index slope. Therefore, the beam angle can also be changed by changing the refractive index slope by changing the voltage of the module.

The light source corresponds to a laser array. Other light sources, for example a single beam laser source divided by a grating or paralleled by a lens, can also be used in embodiments of the present invention. In particular, mirror arrays used to deflect parallelized laser beams are suitable for read-only systems. Alternatively, the light source can be formed using an ultrasonic optical modulator, which can split the incoming beam into different (various) angled modulated beams, or make the individual lasers with the beams the same optical path.

According to one embodiment of the present invention, it is preferable to slowly return each mirror to its starting position after each jump since another jump is required if the spot meets another previously read area. Otherwise, the mirror displacement becomes excessive due to repeated displacement of one spot. The normal radial tracking system with the objective lens actuator keeps all spots on each track while the mirror is returned to its initial position.

Figure 4 shows the general arrangement of the spots on the disc to explain the result of holding the axis of rotation near the plane of the laser beam. For example, the distance between spots is 10 μm (for example according to the Blu-ray Disc standard) and the track pitch is 320 nm. Thus the spots are on a line that forms a small angle to the track. The displacement of the spot after rotating one mirror with the axis of rotation in the plane of the optical axis of the laser array is perpendicular to this line (as indicated by the arrow).

5 shows the angular displacement of the mirrors along the saw blade pattern over time, where α1 and α2 represent the angles of rotation of the mirrors as indicated by the solid and dashed lines. The mirrors are individually controlled as shown in FIG. The decreasing line also represents the time it takes for the mirror to return to its starting point, while the rapidly rising line represents the time it takes to displace. In another example, the mirrors return to the starting position faster and then remain constant for a short time. Depending on the change in the disk rotation time (eg depending on the mode of operation of the drive at constant angular velocity or constant linear velocity), one of the two methods is easier to implement.

Objective lens actuators, part of a typical radial feedback loop control system, are used to focus spots on a track.

6 is a schematic block diagram showing the structure of a closed loop control system for controlling spots on an optical disc. The system includes an optical system 601 including an optical path, a disk, a return optical path, and other electronic devices, together with a photodetector element. The optical system 601 transmits the measurement result to the radial tracking error generator 602 to produce an electronic signal called a radial error signal, which is more or less proportional to the distance of the spot on the disc relative to the center of the data track. This distance can be adjusted by the radial actuator 603 (that is, the objective lens actuator) for moving the objective lens in the radial direction. The force (magnitude and sign) that the radial actuator 603 moves to keep the spot at the center of the track to reduce the radial error to zero is defined by the radial controller 604, which is a controller module. The radial controller 604 receives a radial error signal as an input and calculates an output signal to reduce the input to zero.

The radial controller 604 is an electronic filter having different characteristics in different frequency domains. A typical and often applied example of such a controller is a Proportional-Integrator-Differentiator (PID) controller, which has an integrator function that dominates the controller output at low frequencies, a proportional gain that dominates the output at intermediate frequencies, and high It has a differential that dominates the output at frequency.

Or the average of the tracking errors of all spots can be fed back. As the feedback loop includes an upper pass low pass (LPF) 605, the movement of the spot is adjusted only to a certain band width. The tracking error portion above that band width is eliminated by another feedback loop (bottom) that controls the rotatable mirrors. Since the mirrors are small and light, very high band widths can be realized.

The wide arrow here represents the collection of signals for each spot. The signal starts in the optics and then a radial tracking error is generated for all spots. These radial tracking errors are filtered by high pass paltor (LPF) 606 so that only high frequency components are processed. Clearly the cutoff frequencies of LPF 605 and LPF 606 have similar values. With respect to the error signal passing through this high pass filter, the jump signal from the jump signal generator 607 is added to the signal mixer 608 as shown in FIG. For example, through N controllers 609, PID type, each controlling a spot or mirror, signals are fed to the actuated mirrors 610, which in turn deflect the individual beams to the correct position on the disc track.

In the above embodiment, not only the present invention can be implemented, but also an additional function of compensating for the high frequency tracking error by displacing the spot on the disc is realized. By adding LPF and HPF, high frequency signals are used to adjust the mirrors that are run separately. It is useful for recording and read from the optical disc at high rotational speed.

The displacement of the spot on the disc also causes the displacement of the spot in the photodetecting device from which an electronic signal can be generated and the data signal (high frequency-HF-signal), focus error and radial tracking error signals can be extracted. This causes disturbance in the optical signal. For example, this causes a push-pull radial signal to cancel as conventional beam landings do. This can be avoided by moving the photodetector in accordance with the spot displacement.

In all of the above executions, open loop or closed loop control can be selected to perform the displacement of the spot. One difference between open-loop and closed-loop control is that in open-loop systems, rotation is achieved by supplying a predetermined electronic signal to the actuator, whereas for closed-loop reverse jumps, the electronic signal to the actuator is measured from one of the spots where it is not stopped It depends on the radial error signal.

7 is a schematic flowchart illustrating a method of reading / writing data on a disc by a plurality of spots located along an outer track in an inner track of the optical disc in the open loop control according to an embodiment of the present invention. In step S710, it is sequentially detected whether each spot has reached the previously read / written data area. In step S720, the detected spot is a position adjacent to the outermost spot of each spot present where the read / write is made from the inner side to the outer track, and the current innermost spot if the read / write is made of the outer track from the outer side. Is moved to a position adjacent to. This completes the spot displacement. The method in open loop control is generally easier to implement. In closed loop control, the position of the moving spot is measured during the displacement, and the movement of each spot is controlled based on the measured signal.

The results show that in the dual beam Blu-ray Disc system (Ng = 1, infinitely short jump times) using the present invention, the improvement in data transfer rate is factor 1.9, whereas in the conventional method the data transfer rate factor drops below one. It was. In addition, the present invention can be applied to almost all optical storage systems having a plurality of spots such as CD, DVD, Blu-ray drive.

The above-described embodiments are merely examples, and do not limit the technical approach of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it will be apparent to those skilled in the art that the technical approach of the present invention may be changed or equivalently substituted without departing from the spirit or scope thereof, and that the present invention is also within the protection scope of the claims of the present invention. Will be understood for granted.

Claims (12)

A method of reading / writing data on an optical disc by a plurality of spots located along an outer track in an inner track of the optical disc, Sequentially detecting that each spot has reached a previously read / written data area, The spot to a position adjacent to the current outermost spot if the read / write consists of an inner to outer track, or to a position adjacent to the current innermost spot if the read / write consists of an outer to inner track. And moving / reading data on the optical disc by a plurality of spots, the method comprising moving. The method of claim 1, Moving a photodetector to follow the movement of the spots; And measuring the position of said spots. Read / write data on an optical disc by a plurality of spots. The method of claim 1, And the distance between all the spots is kept constant along the radial direction by at least one track. The method of claim 1, And said moving step comprises rotating a mirror for deflecting one laser beam. An apparatus for reading / writing data on an optical disc by a plurality of spots located along an outer track in an inner track of the optical disc, A detection device for sequentially detecting that each spot has reached a previously read / written data area, and generating a detection signal; Actuated by the detection signal to move the spot to a position adjacent to the current outermost spot if the read / write consists of an inner to outer track, or to a position adjacent to the current outermost spot if the read / write consists of an outer to inner track. And an actuating device which moves to a position adjacent to the innermost spot, wherein the data on the optical disc is read / recorded by a plurality of spots. The method of claim 5, And a rotatable mirror array coupled to the actuation device, the rotatable mirror array for deflecting a laser beam used to generate the plurality of spots. The method of claim 5, And a liquid crystal module, which deflects a laser beam, connected to said actuation device, the apparatus for reading / writing data on an optical disc by a plurality of spots. The method of claim 5, And the distance between all the spots is kept constant along the radial direction by at least one track. The method of claim 6, And an axis of rotation of the mirror array lies approximately in a plane passing through the optical axis of the laser beam. The method of claim 6, And said mirror array is comprised of laser sources emitting said laser beam. The apparatus for reading / writing data on an optical disc by a plurality of spots. The method of claim 6, And said laser beams are formed by dividing one laser source through a grating or an ultrasonic optical modulator. The method of claim 6, And the time for returning each mirror of the rotatable mirror array to its initial position after rotation is dependent on the rotation time of the disk.

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