Methods of determining the optimal erase and write power,...

Details Methods of determining the optimal erase and write power,... Methods of determining the optimal erase and write power,...

2000-09-08

2003-06-24

Hindi, Nabil (Department: 2653)

Dynamic information storage or retrieval

Control of storage or retrieval operation by a control...

Mechanism control by the control signal

C369S116000, C369S047530

Reexamination Certificate

active

06584051

ABSTRACT:

The invention relates to a method of determining the optimal erase power for erasing marks provided in an optical record carrier of the type in which marks are provided by locally heating the record carrier with radiation pulses having a sufficiently high power so as to cause changes in optical properties of the record carrier, which changes become manifest by a reduced reflection of the radiation pulses.
The invention also relates to a method of determining the optimal write power for providing marks in an optical record carrier, which marks are provided by locally heating the record carrier with radiation pulses having a sufficiently high power so as to cause changes in optical properties of the record carrier, which changes become manifest by a reduced reflection of the radiation pulses.
The invention further relates to an optical record carrier for use in one of the methods according to the invention, inscribable by a radiation beam, containing an area comprising information about properties of the optical record carrier.
The invention further relates to a recording apparatus comprising a calibration device for determining the optimal erase power required for erasing marks provided in an optical record carrier of the type in which marks are provided by locally heating the record carrier with radiation pulses having a sufficiently high power so as to cause changes in optical properties of the record carrier, which changes become manifest by a reduced reflection of the radiation pulses.
The invention further relates to a recording apparatus comprising a calibration device for determining the optimal write power required for providing marks in an optical record carrier, which marks are provided by locally heating the record carrier with radiation pulses having a sufficiently high power so as to cause changes in optical properties of the record carrier, which changes become manifest by a reduced reflection of the radiation pulses.
The invention also relates to a calibration device for use in a recording apparatus.
The optimal erase power and the optimal write power are dependent on properties of the record carrier used and on the properties of the recording apparatus. These powers should therefore be determined whenever a given record carrier is used in a recording apparatus.
Methods and apparatuses for determining these powers are known, inter alia, from EP 0 737 962 (Ricoh Company Ltd). This application describes a method in which the optimal write power is determined with reference to a modulation power curve to be fixed for each combination of record carrier and recording apparatus. The modulation power curve is fixed by providing marks in the record carrier through a large range of write powers (P
w
) and by subsequently measuring the modulation (m) of the associated marks for each write power, i.e. the reflected power coming from a mark relative to the reflected power coming from an area without marks. The modulation values thus obtained are plotted versus the associated write powers in the modulation power curve (m(P
w
)). Subsequently, a curve (the &ggr; curve) is determined which represents the normalized first-order derivative (y=(dm/dP
w
)·(P
w
/m)) of the modulation power curve (m(P
w
)) described hereinbefore. This &ggr; curve has an asymptotic variation, with only a slight decrease of the y occurring at higher write powers. The optimal write power is found by selecting the power which is associated with a predetermined value of the derivative &ggr;. The optimal erase power is subsequently linearly dependent on the optimal write power found.
The determination of an unambiguous value from an asymptotically varying curve, such as the &ggr; curve, is not very well possible. Small variations of the input value, the predetermined value of &ggr;, may result in large variations of the output value, the optimal write power. Moreover, when determining the modulation power curve, write powers are used which lie above the optimal write power so that unnecessarily high temperatures are caused in the record carrier.
It is an object of the invention to provide a method of unambiguously determining the optimal erase power and to provide a method of unambiguously determining the optimal write power, avoiding unnecessarily high temperatures in the record carrier.
According to the invention, this object is achieved by means of a method of determining the optimal erase power, which is characterized in that the method comprises a preparatory step of providing marks on the record carrier by locally heating the record carrier with radiation pulses having a first power, followed by a first measuring step of determining a second power (P
min
) of the radiation pulses, at which power the optical properties of the record carrier at the location of the marks provided in the preparatory step do not substantially change when the record carrier is irradiated at a power which is lower than said second power, and the optical properties of the record carrier at the location of the provided marks change when the record carrier is irradiated at a power which is higher than said second power, such that the normalized reflected power increases, and a second measuring step of determining a third power (P
max
) of the radiation pulses, at which power the optical properties of the record carrier change to such an extent that the normalized reflected power becomes maximal, when the record carrier is irradiated at said third power at the location of the marks provided in the preparatory step, followed by a comparison step of determining the optimal erase power (P
EO
) from the equation
P
EO
=
β
·
(
P
min
+
P
max
)
α
in which &agr; is a constant known in advance and &bgr; is a variable which is dependent on properties of the record carrier. The normalized reflected power (R) is understood to mean the reflected power relative to the power at which the record carrier is irradiated.
An advantage of this method is that the powers P
min
and P
max
to be determined, from which the optimal erase power follows via an equation, can be unambiguously determined because they are located at points of inflection in a curve in which the normalized reflected power (R) is plotted versus the power (P) at which the record carrier is irradiated at the location of the marks provided in the preparatory step. This means that the first-order derivative dR/dP exhibits an abrupt variation in value or sign at the powers P
min
and P
max
so that these powers can be determined in a simple and unambiguous manner. A further advantage of the method appears to be that the determined powers, P
min
and P
max
, are hardly dependent on the write method with which the marks are provided on the record carrier in the preparatory step. Also the number of times of consecutively performing the method, in which marks are each time provided at the same position on the record carrier, has no significant influence on the determined powers P
min
and P
max
.
According to the invention, this object is further achieved by means of a method of determining the optimal write power, which is characterized in that the method comprises a preparatory step of providing marks on the record carrier by locally heating the record carrier with radiation pulses having a first power, followed by a first measuring step of determining a second power (P
min
) of the radiation pulses, at which power the optical properties of the record carrier at the location of the marks provided in the preparatory step do not substantially change when the record carrier is irradiated at a power which is lower than said second power, and the optical properties of the record carrier at the location of the provided marks change to such an extent that the normalized reflected power increases, when the record carrier is irradiated at a power which is higher than said second power, and a second measuring step of determining a third power (P
max
) of the radiation pulses, at which power the optical properties of the record carrier change when the record carrier i

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