CN1138264C - Method and apparatus for writing optical recording media - Google Patents

Abstract

A method is described for setting an optimum write power for recording information on an optical recording medium. First a series of test patterns is written on the medium, each test pattern being written with a different write power. On reading the test patterns, the modulation of each read signal is determined. The modulations as a function of write power are curve-fitted to an analytic function. The normalised derivative of this function is determined analytically and is used to determine the value of the optimum write power for the medium.

Description

Method and apparatus for writing optical recording media

technical field

The invention relates to an optical recording device for writing information on an optical recording medium with a light beam, and specifically relates to a method for setting the optimum writing power level of the light beam.

The method includes a first step of writing a series of test patterns on a recording medium, each pattern is written with a different writing power level value, a second step of reading the patterns to form a corresponding read signal, and a third step from each read The value of the read parameter is obtained from the signal, and the fourth step is curve fitting to the value of the read parameter to obtain a function that defines the relationship between the writing power level and the read parameter.

The invention also relates to a device for writing information on an optical recording medium, the device comprising a light source emitting a light beam with a controllable writing power level, a control unit for writing a series of test patterns, each pattern having a different writing power magnitude value, a reading unit that reads the pattern and forms a corresponding reading signal, a first processor that derives the reading parameter value from each reading signal, curve fitting the reading parameter value to obtain a defined inscription Parameters and a second handler that reads relationships between parameters.

Processors may be of the analog or digital type and include programmable processors and firmware-programmed processors. The processor includes a memory device in addition to an arithmetic unit.

Background technique

The recording method according to the opening paragraph is known in US patent 5 185 733. In this method, a series of test patterns are written on the medium, with each subsequent test pattern being written at an increasing writing power level. After reading the written pattern, a curve fitting operation uses a quadratic polynomial to fit the amplitude of the read signal for each pattern of the writing power level. The writing power corresponding to the maximum value of the polynomial is selected as the optimum writing power for the subsequent recording of information on the medium. The problem of reading noise characteristics of the signal is alleviated by curve fitting. A disadvantage of this known method is that the optimum power level determined by this method does not fully take into account the variations in the properties of the recording device and the variations in the properties of the recording medium. Therefore, using such an optimum writing power may make storing information on the recording medium unreliable.

Contents of the invention

It is an object of the present invention to provide a reliable method of setting an optimum writing power based on a read signal from a test pattern written on a medium and which is less susceptible to noise.

According to one aspect of the present invention, there is provided a method for setting the optimum writing power level of a light beam in an optical recording device for writing information on an optical recording medium with a light beam, comprising: a first step of writing an optical recording medium on the recording medium a series of test patterns, each pattern is written with a different write power level value, the second step reads these patterns to form corresponding read signals, and the third step derives the values of the read parameters from the respective read signals, The fourth step is to curve fit the value of the read parameter to obtain a function that defines the relationship between the magnitude of the writing power and the read parameter, and is characterized in that the method also includes: the fifth step is to determine the derivative of the function and multiply it by a value equal to The derivative is normalized by a factor of the ratio of the writing power value and the reading power value, and, in the sixth step, the optimal writing power level is selected according to the normalized derivative of the function.

In the above method, the optimum writing power level is selected according to the preset value of the normalized derivative of the function.

To obtain a stable curve fitting process, the function to be fitted is preferably defined in terms of orthogonal polynomials. The values of the coefficients of the polynomials determined by the process are then no longer dependent on the values of the coefficients determined for other polynomials.

The polynomials are preferably Legendre polynomials because of their mathematical simplicity, which requires less computing power during the curve fitting process.

The read parameter is preferably the magnitude of the read signal obtained from the medium, since this magnitude can easily be derived from a radiation detection system intercepting the radiation from the medium. Furthermore, the amplitude is a satisfactory parameter for determining the quality of the recorded signal.

Wherein, the above method can read a parameter value from the medium and use this value to select the value of the writing power level.

Alternatively, the method above reads the preset value of the normalized derivative of the function from the medium and uses the preset value to select a value of the writing power level.

Therein, the derivative of the function is determined analytically.

The above method may also include selecting the power level based on the derivative of said function and then multiplying the power level by a constant greater than 1 to determine the optimum power level.

The process of selecting an optimum writing power can be improved by reading a parameter value from the medium and using that value to select a value for a writing parameter. The parameter value may be characteristic of the particular medium on which it is recorded. This parameter adapts the selection process to the characteristics of the media being scanned. The parameter can be an initial value or a range of the optimum writing power level, so as to reduce the range of the power level for writing the test pattern. This parameter can also be a preset value of the normalized derivative, so that the optimal writing power can be selected according to the properties of the medium. In contrast, the preset values fixed by the device do not allow such a choice.

The analog signal is preferably converted into a digital signal by an analog-to-digital converter before the signal value is calculated. Derivatives can be determined by taking the difference of the fitted functions. Thus, the value of the function must be represented by a relatively large number of significant figures, and the calculation must be performed on these large numbers in order not to be affected by the additional noise introduced by this method of determining the derivative. The derivative of the function is preferably determined analytically, since this determination hardly introduces any additional noise. The number of significant figures can then be reduced, which reduces the computing power required by the second processor and allows a reduction in the quality of the analog-to-digital converter.

Generally speaking, the writing power level of the test pattern is selected to be within a range around the desired value of the optimum writing power level. However, the optimum writing power level is often close to the maximum power that the beam can produce. The range is then limited by the maximum laser power. This problem can be avoided by choosing the power level from the function derivative and then multiplying the power level by a constant greater than one. The test pattern is then written in a power range which is subtracted from the maximum laser power. This has the added advantage that the measurements are made over a power range in which the function and its derivatives are at their saturation values removed, which allows for greater precision in determining the function and its derivatives.

Another aspect of the present invention provides a device for writing information on an optical recording medium, including a light source emitting a light beam with a controllable writing power level, and a control unit for writing a series of test patterns, each Patterns with different write power magnitude values, a read unit for reading said pattern and forming corresponding read signals, a first processor for deriving read parameter values from the respective read signals, a curve fitting The value of the read parameter to obtain a second processor defining the relationship between the write power level and the read parameter, characterized in that the second processor is operationally connected in order to obtain the derivative of the function by multiplying it by The derivative is normalized by a factor equal to the ratio of the write power value to the read parameter value, and the value of the write power level is selected according to the normalized derivative.

Preferably in the above device, the read parameter is the amplitude of the read signal.

The objects, features and advantages of this invention will be apparent from the following more particular description of preferred embodiments of the invention, as shown in the accompanying drawings.

Description of drawings

Figure 1 is a schematic diagram of an optical recording apparatus according to the present invention,

Figure 2 shows read signals from two test patterns,

Figure 3 is a graph showing the measured modulation and its derivative as a function of writing power,

Fig. 4 is a plan view of a recording medium, and

Figure 5 is a plan view of a marking pattern in a medium.

Detailed ways

Figure 1 shows a device and an optical recording medium 1 according to the invention. The medium 1 has a transparent substrate 2 and a recording layer 3 distributed thereon. The recording layer includes a material suitable for writing information with light beams. The recording material can be, for example, magneto-optical, phase change, dye or any other suitable material. Information can be recorded on the recording layer 3 in the form of optically detectable areas, also called marks. The device comprises a light source 4 , such as a semiconductor laser, for emitting a light beam 5 . The light beam is focused on the recording layer 3 using the beam splitter 6 , the objective lens 7 and the substrate 2 . The medium can also be air incident, and the light beam is directly incident on the recording layer 3 without passing through the substrate. The light reflected from the medium 1 is converged by the objective lens 7, and after passing through the beam splitter 6, it falls on the detection system 8, and the detection system converts the incident light into a signal of an electronic detector. The detector signal is input to circuit 9 . The circuit derives several signals from the detector signal, such as the read signal _SR representing the information read from the medium 1 . The light source, beam splitter 6, objective lens 7, detection system 8 and circuit 9 together constitute a reading unit 10'. The read signal from the circuit 9 is processed in a first processor 10 in order to derive from the read signal the necessary signals representing the read parameters and controlling the laser power level. The resulting signal is fed to a second processor 11 which processes a series of read parameter values and derives therefrom the optimum write power control signal value. The writing power control signal is connected to the control unit 12 . A signal 13 representing information to be written on the medium 1 is also fed to the control unit 12 . The output of the control unit 12 is connected to the light source 4 . A mark can be written on the recording layer 3 with a single light pulse, the power of which is determined by the processor 11 to determine the optimum writing power level. It can also be written with a series of light pulses of equal or unequal length, and its power is determined by the optimal writing power level.

The actual radiant power emitted by the light source 4 can be measured by means of a detector, not shown, which is placed in an unused side lobe of the beam or in the light reflected by an element in the beam's path. The signal of the detector can be directly connected to the processor 11 . Alternatively, this signal can be connected to the control unit 12 where it can be combined with the peak value of the read signal to form a measure of the optical power received at the recording layer 3 and then fed to the processor 11 .

Before writing information on the medium 1, the apparatus sets its writing power to an optimum value by performing the following procedure. The device first writes a series of test patterns on the medium 1 . The test pattern should be chosen to give the desired read signal. If the read parameter derived from the read signal is the maximum modulation of the read signal, the test pattern should include marks of sufficient length to obtain the maximum modulation of the read signal portion. When encoding information according to so-called EFM modulation, the test pattern preferably comprises long I ₁₁ marks. The test patterns were each recorded at different writing powers. Subsequent patterns can be written with gradually increasing writing power under the control of the processor 11 . These patterns can be written anywhere on the media, or they can be written on specially provided test areas on the media.

Figure 2 shows read signals 18, 19 from patterns written at two different writing power levels. The pattern comprises a short mark, a long mark and a short mark, shown as signal portions 15, 16, 17, in read signal portion 18 and read signal portion 19, respectively. Actual patterns may include hundreds of marks of varying or equal length.

The processor 10 derives a read parameter from the read signal _SR for finding an optimal writing power. One possible read parameter is the ratio of the lowest amplitude of the signal portion of a read signal (indicated by 'a' in Figure 2) to the largest amplitude 'b' of the read signal. A preferred read parameter is the normalized modulation, ie the ratio of the maximum peak-to-peak value 'c' of the read signal to the maximum value 'b' of the read signal.

After reading the test pattern on the medium 1, the processor 11 forms a series of pairs of values for pattern modulation and writing power belonging to the pattern. The writing power can be obtained from the value of the writing power control signal during the recording of the test pattern, or from the measurement result of the optical power. Figure 3 schematically shows the results of the reading; the crossings are measurements of the modulation m as a function of the writing power P, these crossings together constitute the modulation m as a function of the writing power. The processor 11 fits a curve with the measured modulation values to obtain an analytical expression for the modulation variable as a function of writing power. This curve is shown in dashed lines in FIG. 3 . Fitting can utilize the well-known least squares fitting algorithm.

In a next step, the processor 11 analytically calculates the normalized derivative 'g' with respect to the modulated writing power. The normalized derivative g(P) is equal to the function (dm/dP)P/m. The curve plotted in Figure 3 represents the function g derived from the fitted modulation m.

The processor derives the intermediate writing power P _i from the normalized derivative by extracting the value P of the writing power belonging to the preset value g ₀ , as shown by the dotted line in FIG. 3 . The value g ₀ can be set by the manufacturer of the recording device and stored on a memory of the device, or on the medium to be read and written before or during setting of the optimum writing power. In the next step, the value of the intermediate power P _i is multiplied by a constant h greater than 1, so as to obtain the optimum writing power level P ₀ .

The value of the preset value g ₀ and the multiplication constant h are determined by the manufacturer or user of the medium when the medium is initialized and stored on the medium. The setting range for the value g ₀ is 0.2 to 5.0. After this value is higher than 5.0, the normalized derivative loses its predictive value, since the vicinity of the asymptote may cause the P value related to _g0 to be close to the writing power axis. The increased measurement error of the derivative is another reason to avoid g values greater than _5.0 . If the value is less than 0.2, the normalized derivative has a small slope, where a small error in the value of the derivative will lead to a large probability dispersion of the value Pi with respect to _g0 . Tests on rewritable re-recordable media in CD format gave g ₀ values of 0.2 to 2.0 and 2.0 to 4.0 on higher density media. The multiplication constant h is preferably set in the range of 1.00 to 1.35. The optimum writing power P ₀ equal to (hP _i ) is usually set to a value close to the writing power at which modulation m starts to saturate. In a preferred method of setting g ₀ and h, the optimum writing power for a particular medium is by finding the writing power that gives the lowest jitter of the read signal from information written on that medium. This information is preferably random information. Next, the normalized derivative dm/dP(P/m) is determined from the series of test patterns written above. The values of P _i are chosen such that the corresponding values of g ₀ lie within the above range, where the normalized derivative is neither too flat nor too steep. Now, the relevant values of h and g ₀ equal to P ₀ /P _i can be used in all media of this type and in all recording devices.

The values of the normalized derivatives proved to be hardly affected by variations in the parameters of the recording device and recording medium. If the optimum writing power level is selected according to the normalized derivative, the selected level is suitable for reliable recording on various recording media with different recording devices. This magnitude can be selected by taking a power magnitude corresponding to a preset value of the normalized derivative. The advantage of using normalized derivatives can also be realized without curve fitting. In this case, the derivative can be determined from a comparison of the read parameter with the write power level data, eg by calculating the difference between the measured values. However, omitting the curve fitting step will add noise in the derivative value, making it impossible for some media to use the derivative to set the optimum writing power.

The values g ₀ and h can be stored in the device, thereby providing medium-independent parameter values. Preferably, the g ₀ value is stored in a medium, making the value medium dependent. FIG. 4 shows an optically readable recording medium 1 with a track 30 . The track may be helical and in the shape of a groove or embossment. The area of the medium is divided into an information recording area 31 for writing user information and a control area 32 for storing information related to writing, reading and erasing the medium and generally not used for recording user information. For some types of media, the information in the control area is embossed. The control area 32 is marked with a dotted line track 32 in the figure. The information recording area 31 is of the type that changes its optical detection properties when exposed to writing power levels above a certain level. The value of g ₀ may be stored as a pattern of control information in the media control area 32 . The media manufacturer should document this value when embossing the control area. Alternatively, the user can record the value for a specific disc by recording this value in the media when it is initialized. The value h can also be recorded like g ₀ . FIG. 5 shows a portion of track 33 comprising a pattern of markings 34 in a substantially enlarged manner.

The curve fitted using pairs of values (m, P) may be one or more polynomials, preferably orthogonal polynomials. This curve can be written as: $\left(1\right).......m\left(P\right)=\underset{i}{\mathrm{\Σ}}{a}_i{f}_i\left(P\right)$

The normalized derivative given in analytical form is $\left(2\right).....g\left(P\right)=\frac{P\underset{i}{\mathrm{\Σ}}{a}_i{f}_i^{\′}\left(P\right)}{\underset{i}{\mathrm{\Σ}}{a}_i{f}_i\left(P\right)}$

Here f'(P) is the derivative of the function with respect to the parameter P. The value of P _i can be obtained from the equation

(3) g(P _i )=g ₀

Depending on the curve to be chosen to fit, the value _Pi can be obtained in analytical form or as the result of a numerical successive root approximation method such as the trial position method or Newton's method. Where possible, the advantage of using an analytical formula is that it provides the correct roots, whereas successive approximations may lead to undesired roots. If equation (3) can be obtained in analytical form, it is no longer necessary to determine the normalized derivative g, but the preset value g ₀ can be directly inserted into equation (3) to determine the relevant value P _i .

A suitable set of orthogonal polynomials f _i are Legendre polynomials. The three lowest order Legendre polynomials are:

(4)

f ₀ (P)=1

f ₁ (P)=P $f_2\left(P\right)=\frac{3}{2}{P}^2-\frac{1}{2}$

Since these polynomials are defined on the interval of -1<P<+1, the writing power value to be fitted should be converted as follows $\left(5\right)P_{\mathrm{the\; s}}=\frac{2P-(P_{\max }+P_{\min })}{P_{\max }-P_{\min }}$

The scaled writing power level P _s must now be used in the formula of equation (4). The value P _i obtained from equation (3) must be converted back to the ranges P _min and P _max .

When using a digital processor, an analog-to-digital converter must be used to convert the input values of m and P from analog to digital. The number of bits of the digital output value can be set to correspond to the noise in the measured value. If, for example, the noise in the parameter value is 1% of the maximum value of the parameter, the converter should be at least 8 bits, thus introducing additional 1/2 ⁸ =1/256 quantization noise.

If, for cost reasons, the processor 11 performing the above calculations is a small processor, it is preferable to perform the calculations in integer format. Therefore the values m and P should be converted from real numbers to integers. The multiplication constant for this conversion should be large enough not to introduce additional noise and small enough not to require too much computing power. A good practice is to choose such that the noise present in the values m and P (determined by the integer representation of the values) is slightly larger than the value in the least significant bit of the integer representation. The noise in this value includes the quantization noise described above. If, for example, the noise in the value m is 0.5% of the maximum value of m, then a reasonable multiplication factor is 1000 divided by the maximum value of this parameter.

Instead of using a series of polynomials to fit the values m and P, a single function can also be used. The function preferably has an asymptote for large values of P, a zero value for indeterminate values P > 0, and an indefinite value for the derivative of the function for the value P where the function is zero. A suitable function is $\left(6\right).......f\left(P\right)=a_0-\frac{a_1}{P-a_2}$

The normalized derivative can be given in analytical form. Equation (4) then reduces to a quadratic equation, allowing the roots of the equation to be found without successive approximations.

Other suitable functions are the tangent of a circular arc and the tangent of a hyperbola.

(7) f(P)＝a ₀ arctan(a ₁ Pa ₂ )

(8) f(P)＝a ₀ tanh(a ₁ Pa ₂ )

The tangent of arcs and tangent of hyperbolas can be stored in lookup tables to speed up calculations.

Claims (12)

1. inscribe on an optical recording media in the optical recording apparatus of information with light beam a kind of, a kind of the best that light beam is set is inscribed the method for power magnitude, comprising:

The first step is inscribed a series of test patterns on recording medium, each pattern is inscribed with different inscription power magnitude value,

Second step was read these patterns forming the corresponding signal that reads, and

The 3rd step read from each and draws the value that reads parameter signal,

The value that parameter is read in the match of four step line has obtained defining inscription power magnitude and has read the function that concerns between the parameter,

It is characterized in that this method comprises

The 5th step determined function derivative and made derivative normalization by the factor that it be multiply by the ratio that equals to inscribe performance number and readout power value, and

The 6th step was selected best inscription power magnitude according to the normalization derivative of function.

2. according to the process of claim 1 wherein that the described best power magnitude of inscribing selects according to the preset value of the normalization derivative of described function.

3. according to the method for claim 1 or 2, wherein this function defines with orthogonal polynomial.

4. according to the method for claim 3, wherein this polynomial expression is Legendre (Legendre) polynomial expression.

5. according to the method for claim 1 or 2, wherein reading parameter is to read the amplitude of signal.

6. from medium, read a parameter value and utilize this value to select to inscribe the value of power magnitude according to the process of claim 1 wherein that the 6th step comprised.

7. according to the method for claim 2, wherein said the 6th step comprises the described preset value of the normalization derivative that reads described function from medium and uses described preset value to select the value of inscription power magnitude to inscribe the value of power magnitude.

8. according to the process of claim 1 wherein that described function derivative is to determine with the method for resolving.

9. select a power magnitude and determine the best power magnitude by this quantity of power level being multiply by a constant subsequently according to the normalization derivative of described function according to the process of claim 1 wherein greater than 1.

10. according to the method for claim 2, wherein the 5th step comprised that also subsequently this quantity of power level being multiply by a constant greater than 1 determined the best power magnitude according to described function derivative selection power magnitude.

11. device that is used for the information of on optical recording media, inscribing, comprise the light source that sends light beam with controlled inscription power magnitude, one inscribes the control module of a series of test patterns, each pattern has different inscription power magnitude value, one reads described pattern and forms the reading unit that reads signal accordingly, one reads signal from each draws the first processor that reads parameter value, one curve fitting reads the value of parameter and inscribes the power magnitude and read second processor that concerns between the parameter to obtain having defined, it is characterized in that second processor is that computing links to each other, so that draw function derivative, come this derivative of normalization by it being multiply by the factor that equals to inscribe performance number and read the ratio of parameter value, and select to inscribe the value of power magnitude according to normalized derivative.

12. according to the device of claim 11, the wherein said parameter that reads is to read the amplitude of signal.

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