RU2425429C2 - Method and device for extracting information from optical recording medium at different read rates - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: invention discloses a method and a reading device (1) for extracting information from an optical recording medium (10). In the method, the power level of reading the radiation beam (3) for scanning the optical recording medium depending on the read rate is established. The power level is determined using the formula

, where α is the extracted predetermined parameter in the range 0.2<α<0.8, P_N is the reading power level at nominal read rate, and n is the actual read rate divided by the nominal read rate.

EFFECT: high signal-to-noise ratio at high read rates.

7 cl, 3 dwg

Description

Technical field

This invention relates to a method for extracting information from an optical recording medium, comprising the steps of setting the power level of the radiation beam at a predetermined reading power level, scanning the recording medium with the radiation beam, detecting the reflected radiation beam reflected from the recording medium, and extracting information from the reflected radiation beam.

This invention further relates to a reader for performing such a method, comprising a radiation source for generating a radiation beam, installation means for setting a radiation beam power level at a predetermined read power level, scanning means for scanning a recording medium with a radiation beam, a detector for transmitting a reflected radiation beam where said reflected radiation beam is reflected from the recording medium into an electrical signal and decoding means for extracting reading information from said electrical signal.

State of the art

In optical recording media, information is encoded in the form of optically detectable marks and the gaps between the marks in the information layer of the optical recording medium. These marks may be in the form of extruded depressions, such as, for example, on read-only-type recording media, in the form of altered optical properties of a dye layer, such as, for example, in recording-type recording media, or in the form of amorphous regions on a crystalline layer, such as, for example, in rewritable media. Typically, these marks are stored along a spiral-shaped or concentric-shaped track on the information layer of a disc such as an optical recording medium. An optical recording medium may comprise one information layer or several information layers separated by intermediate layers, for example, a two-layer disc consisting of two information layers.

In the reader, information is extracted from such an optical recording medium by irradiating the information layer of the optical recording medium with a radiation beam, such as, for example, a laser beam, and detecting a radiation beam reflected from the optical recording medium. When a radiation beam scans the information layer along a track, the reflected radiation beam is modulated according to the pattern of marks and spaces stored on the information layer. This modulated reflected radiation beam is transferred to the modulated electrical signal by the detector. By decoding this modulated electrical signal, information stored on the optical recording medium is extracted.

The signal-to-noise ratio (SNR) of a modulated electrical signal representing information read from an optical recording medium depends on the optics and electronics of the reader. Typically, the SNR of a modulated electrical signal decreases with increasing read speed. Since with increasing read speeds, the throughput of the detecting electronics in the reader must be increased, thus, all kinds of introduced noise, such as the noise of the radiation source, electronic noise, shot noise, etc. are increased.

When reading optical recording media, a more optimal SNR is obtained in the case of high radiation levels. The signal level of the modulated reflected radiation beam, and thus the signal level of the modulated electrical signal, is proportional

P _r · M · R,

where P _r is the power of the radiation beam (often called read power), M is the modulation of marks and spaces, and R is the reflectivity of the information layer.

Currently, the problem with optical systems, especially when using optical recording media having low reflectivity, such as, for example, dual-layer DVD-rewritable systems and systems with a writable and rewritable BluRay disc, is that the signal-to-noise ratio of the modulated electrical signal, representing information read from an optical recording medium, often referred to as a read signal, becomes too low at higher read speeds when used traditional reading power, thereby causing errors in the retrieved information. Especially in the case of low-cost systems, where, as a rule, the efficiency of the light flux from the recording medium to the detector is low.

In future optical systems, where the number of information layers on an optical recording medium increases to three or more, the signal-to-noise ratio of the read signal may even decrease further due to a decrease in the reflectivity of individual information layers with an increase in the number of superimposed information layers on the recording medium.

Purpose of the invention

An object of the present invention is to provide a method and a reader that provides a modulated electrical signal having a sufficiently high signal to noise ratio at higher read speeds, thereby making it easy to extract information even at these high read speeds.

SUMMARY OF THE INVENTION

This problem is solved by providing a method according to the introductory paragraph, which is characterized in that the power level of the radiation beam is set depending on the read speed at a read power level equal to

,

,

where α is a predefined parameter with 0.2 <α <0.8, P _N is the read power level at the nominal read speed, often called the reference read speed, and n is the actual read speed divided by the nominal read speed. P _{N is} usually expressed in mW. This task is further solved by providing a reader according to the introductory paragraph, which is characterized in that the installation means is configured to set the power level of the radiation beam depending on the read speed at the read power level equal to

,

,

where α is a predefined parameter with 0.2 <α <0.8, P _N is the read power level at the nominal read speed, and n is the actual read speed divided by the nominal read speed.

According to the present invention, it is intended to increase the reading power level of the radiation beam as a function of the reading speed, thereby compensating for the negative effect of the electronic bandwidth and / or reduced reflectivity of the information layer on the signal-to-noise ratio. Typically, an increase in the read power level of the radiation beam at a certain power level will result in a deterioration in read stability, i.e. the number of times that the recording medium can be read repeatedly without significant deterioration of the recording medium. Therefore, the maximum read power level is determined for various optical systems. However, the inventors realized that this maximum read power level increases with an increase in read speed, thereby allowing the use of higher read power levels at higher read speeds without compromising read stability.

, будет номинальным. Однако изобретатели, кроме того, поняли, что такая зависимость между уровнем мощности считывания и скоростью считывания может закончиться деструктивными уровнями мощности считывания при высоких скоростях считывания, заканчивающихся в результате постоянной потери информации на считываемом носителе записи. Согласно настоящему изобретению уровень мощности считывания увеличивается менее чем пропорционально

, т.е. имеет значение, меньшее чем один. Это разрешает достаточно высокие уровни мощности считывания при всех скоростях считывания без разрушения информации на носителе записи.Note that, from a theoretical point of view, the reading power level, which increases proportionally

will be nominal. However, the inventors further realized that such a relationship between the read power level and the read speed may result in destructive read power levels at high read speeds resulting in a permanent loss of information on the read recording medium. According to the present invention, the read power level is increased less than proportionally

, i.e. matters less than one. This permits sufficiently high read power levels at all read speeds without destroying the information on the recording medium.

Note that the objective of the present invention is solved without the need for expensive and / or complex electronic or optical components.

The values of the parameters α and P _N , as a rule, depend on the properties of the recording medium. Note that when reading various information layers of a multilayer recording medium, each individual information layer can have its own parameter values associated with it. It is further noted that the nominal read speed at which the read power level P _N is determined is generally selected as the so-called 1X read speed corresponding to n = 1. This 1X speed is the slowest read speed defined in the optical system.

The optical disc manufacturer can determine these parameter values during the manufacturing process. Subsequently, these values must be transmitted to the reader. This can be achieved by providing these values in the area for storing information associated with the recording medium on the recording medium itself, for example, in the so-called ADIP, and this area can be read by a reader. Alternatively, the values of the parameters α and P _{N are} defined in the specification of the optical system. The optical disc manufacturer must now adhere to these specifications during the production of the recording medium.

In preferred embodiments of the invention, the value of α is in the range between 0.33 and 0.5.

мВт или, альтернативно, α=0,385, дающее в результате уровень мощности в

мВт.In embodiments of the invention for use with Dual Layer DVD Rewritable optical record carriers (DVD + RW DL) the most optimal values for the parameters α and P _N are α = 0.462 and P _N = 1.3 mW, giving a result of the read power level in

mW or, alternatively, α = 0.385, resulting in a power level of

MW

It should be noted that the reading power level is equal to

,

,

in fact, it is the optimum value of the read power level, which is the optimal choice between increasing the signal-to-noise ratio by increasing the read power level and maintaining read stability by preventing destructively high read power levels. Therefore, the read power level equal to

,

,

can also be considered as a read speed, depending on the upper limit of the safe working area of the read power levels; the fixed estimated lower bound is at the read power level for the slowest read speed. Now, any level of read power below the upper limit and above the lower limit can be selected from this safe work area, resulting in an improved, but not necessarily optimal, read performance.

Brief Description of the Drawings

These and other objects of the invention will become apparent and further elucidated with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which:

Figure 1 shows an embodiment of a reader according to the invention,

Figure 2 is a graph showing the dependence of the read power level of the radiation beam on the read speed, and

Figure 3 are graphs of experimental data with approximated curves according to the claims.

Detailed Description of Drawings

1 shows a reader 1 according to an embodiment of the invention for extracting information from an optical recording medium 10. In this example, the optical recording medium 10 is shown as a two-layer recording medium containing two information layers (L0, L1). However, it is noted that the invention works equally well with single-layer information carriers and with multi-layer information carriers containing more than two information layers.

The reader 1 comprises a radiation source 2, such as, for example, a diode laser, for forming a radiation beam 3, such as, for example, a laser beam. This radiation beam 3 scans the optical recording medium 10 using well-known scanning means. These scanning means include, for example, an engine (not shown) for rotating the recording medium around its center and a lens system 5 comprising a beam splitter 51 and an objective lens 52 for generating a radiation beam at a focus point 15 on the information layer of the recording medium. 1, a radiation beam 3 is shown focused on a first information layer of a recording medium located closest to the input surface of a radiation beam, often referred to as an L0 layer. However, under the control of the focusing and tracing means 7, which is also considered to be part of the scanning means, the radiation beam can also be focused on another information layer, often referred to as the L1 layer.

When the recording medium rotates, the focusing and tracing means 7 ensures that the focal spot 15 scans the track on the information layer on which the information to be extracted is stored. The reflected radiation beam 9 reflected by the information layer L0 is directed by the lens system 5 to the detector 4. This reflected radiation beam 9 is modulated according to the pattern of marks and the gaps between the marks along the track being scanned. The detector 4 converts the incident reflected beam of radiation 9 into one or more electrical signals. At least one of these electrical signals, i.e. modulated electrical signal 13, has a modulation that relates to the read information. This modulated electrical signal 13 is supplied to decoding means 8 for extracting the actual information itself.

The reading device 1 further comprises installation means 6 connected to a radiation source 2 for controlling the power level of the radiation beam 3 generated by the radiation source. In readers of the prior art, this installation means 6 sets the power level of the radiation beam at a predetermined read power level when extracting information from the optical recording medium 10.

It should be noted that when the reader is combined with a recording device for recording information on the recordable optical recording medium, the radiation source 2 can also be used to form a radiation beam for recording information on the recordable recording medium. In such a combination device, the installation means 6 is typically also used to set the radiation beam power level, typically at a higher recording power level or according to a pattern of recording power levels.

In the reader according to the present invention, the installation means 6 is configured to set the power level of the radiation beam depending on the read speed, also referred to as linear speed. It should be noted that the installation tool 6 can be implemented by means of several separate hardware elements and / or by means of an appropriately programmed controller.

In general, a faster read speed enables faster retrieval of information from an optical recording medium. In constant angular velocity (CAV) devices, the angular velocity of the disk-shaped recording medium remains constant as long as the read speed (i.e. linear velocity) changes from the inner diameter of the disc to the outer diameter of the disc.

According to the present invention, the installation means 6 sets the power level of the radiation beam 3 at a read power level equal to

,

,

where α is a predefined parameter with 0.2 <α <0.8, P _N is the read power level at the nominal read speed, and n is the actual read speed divided by the nominal read speed. The nominal read speed is typically selected to be the so-called 1X speed, or a reference speed corresponding to n = 1.

мВт, в то время как начерченная кривая 22 представляет α=0,385, дающее в результате кривую уровня мощности считывания, равную

мВт.In embodiments of the invention for use with dual-layer DVD rewritable optical recording media (DVD + RW DL), the most optimal values for α and P _N are α = 0.462 and P _N = 1.3 mW, or alternatively α = 0.385 and P _N = 1.3 mW. This is shown in the graphs of FIG. 2, where the vertical axis represents the read power level (mW) and the horizontal axis represents n, which is the actual read speed divided by the nominal read speed. Intermittent curve 21 represents α = 0.462, resulting in a read power level curve equal to

mW, while the plotted curve 22 represents α = 0.385, resulting in a read power level curve equal to

MW

The dashed line 24 represents a fixed read power level of 1.2 mW, which is defined in the prior art as a nominal read power level for testing purposes. This dashed line 24 can be considered as the lower limit of the safe working area of the read power levels. The upper limit of this safe working area of read power levels is a drawn curve 22 or, alternatively, discontinuous curve 21. Any read power level can now be selected from this safe working area, resulting in, on the one hand, improved reading performance, and with on the other hand, to maintain read stability.

In an alternative embodiment of the invention, the manufacturer of the optical disk 10 determines the parameter values during the manufacturing process and provides these values in the storage area related to the recording medium information on the recording medium 10 itself. Such an area for storing information related to the recording medium is, for example, the known ADIP and ATTP. The reader 1 shown in FIG. 1 now reads, for example, with a read speed of 1X, i.e. with a reference speed, and / or using a certain nominal read power in order to test the values of the parameters from the recording medium itself, transmits them via signal 11 to the installation means 6. The setup means 6 subsequently uses these parameter values to set the read power level at higher read speeds.

Figure 3 shows graphs of experimental data with approximated curves according to the claims. All measurement data can be well approximated using this formula showing that it is the best expression to describe the maximum read powers.

A general requirement for re-reading is that the disc can be read a million times, while remaining within the specification, such as the level of mark jitter. In experiments on a rewritable DVD disc, the number of read cycles is determined for different read powers and read speeds. Typically, the read power at which a disk can be read a million times is determined by extrapolating points of experimental data obtained at higher read powers corresponding to fewer read cycles. The measurements in FIG. 3 give read power at which exactly 1 million read cycles can be obtained. In practical applications, a lower maximum read power is selected to obtain limits for

- accuracy of reading power setting

- higher disk temperatures

- lower laser modulation frequency (the lower the modulation frequency, the higher the peak power)

- differences between disk drives (spot size, wavelength, etc.).

The two extreme situations in practice in order to get the limit are to use the multiplication factor or to get the limit by using the bias. Situations between them may also occur. When an additional limit as a function of speed n is provided by a coefficient, in practice the value of Pn will be chosen lower. When an additional limit as a function of speed is specified by the offset in mW, in practice Pn will be chosen lower and higher.

Claims (7)

1. A method of extracting information from an optical recording medium (10), comprising the steps of:
set the power level of the radiation beam at a predetermined reading power level,
scanning the recording medium with a radiation beam (3),
detecting a reflected radiation beam reflected from the recording medium, and
information is extracted from the reflected ray (9) of the radiation, characterized in that
said method further comprises the step of retrieving the value of a predetermined parameter α from the optical recording medium, as well as the fact that
the power level of the radiation beam is set depending on the extracted value of the parameter α and is set depending on the read speed at the read power level equal to

,
where α is the extracted predefined parameter with 0.2 <α <0.8, a P _N is the read power level at the nominal read speed, and n is the actual read speed divided by the nominal read speed. 2. The method according to claim 1, in which the value of α is in the range between 0.33 and 0.50. 3. The method according to claim 1 for extracting information from a multilayer optical recording medium, in which the power level of the radiation beam is set for each information layer individually, and each information layer has a parameter α predefined for it. 4. A reader (1) for extracting information from an optical recording medium (10), comprising
a radiation source (2) for forming a beam (3) of radiation,
installation means (6) for setting a radiation beam power level at a predetermined read power level,
scanning means (5, 7) for scanning the recording medium with a radiation beam,
a detector (4) for transferring the reflected beam (9) of the radiation reflected from the recording medium into an electrical signal (13), and
decoding means (8) for extracting information from said electrical signal, characterized in that
further comprises extraction means (8) for extracting a value of a predetermined parameter α from the optical recording medium, and also that
the installation tool is configured to set the power level of the radiation beam depending on the read speed at a read power level equal to

,
where α is the extracted predefined parameter with 0.2 <α <0.8, a P _N is the read power level at the nominal read speed, and n is the actual read speed divided by the nominal read speed. 5. The reader according to claim 4, in which the value of α is in the range between 0.33 and 0.50. 6. An optical recording medium (10) comprising a region consisting of patterns of optically detectable marks and spaces between marks representing parameter values indicating properties of the recording medium,
characterized in that said region comprises patterns of optically detectable marks and spaces between marks representing a value of a predetermined parameter α for use in the method according to claim 1 or in a reader according to claim 4. 7. The optical recording medium according to claim 6, comprising multiple information layers, wherein said region comprises patterns of optically detectable marks and spaces between marks representing parameter values α for each of the information layers.

Images