JPH0229928A - Optical disk device - Google Patents

Abstract

PURPOSE:To record accurately shaped pits by reducing laser power for forming the pits in the middle part of each pit. CONSTITUTION:An EFM signal (b) is delayed by delay circuits 1 and 2 by time T respectively, and a shortened pulse (h) is obtained by an AND circuit 3 by shortening the latter half part of each pulse of the delayed pulses (g) by a length of 1T. The shortened pulse (h) is further delayed by T in a delay circuit 5, and from its inversion output, a pulse (j) is obtained. The pulses (j) and (h) are inputted to an AND circuit 4 to obtain a leading edge pulse (k). Then, an output by inverting the EFM signal (b) with an inverter 12 and the pulse (h) are inputted to an AND circuit 6 to obtain a trailing edge pulse (m). An edge pulse (n) is obtained by an OR circuit 7 from the pulse (k) and the pulse (m). An intermediate pulse (p) is obtained by logically multiplying the pulse (n) by the pulse (h), and the pulse (n) and the pulse (p) are added together in an appropriate ratio to obtain a recording waveform (d) through an amplifier 10. By this method, the laser power is controlled, and hence the accurately shaped pits are recorded.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical disc device with improved recording characteristics.

[Conventional technology]

Conventionally, in recordable optical disk devices, modulation methods such as group coding that use differences in recording pit length as information have been known in order to improve recording density.For example, compact discs use a type of modulation method such as group coding. A certain EFM or the like is used.

[Problem that the invention seeks to solve]

In this case, correct pit length and constant pit width are required, but short pits require relatively more light energy, while longer pits require relatively less energy. That is, there is no linear relationship between the length of the pit and the length of the recording waveform.

For this reason, in the past, long pits were recorded by making the pulse length shorter than a predetermined value, but the pit width was not constant, which caused a problem.

This point will be explained in more detail using FIG. 3.

FIG. 3 is an explanatory diagram of the writing state.

In FIG. 3, for example, an EFM signal that is modulated with the period T of clock a as one unit length has various pulse widths, such as a relatively long pulse b, and the shortest pulse b2 (3T pulse bz) with a length of 3T. It is necessary to form pits by making each of these lengths correspond to the recording waveform.

For high-density recording, for example, a 3T pulse b2 requires a length of about 0.8 μm, but the spot diameter of a semiconductor laser is as large as 780 nm, and the NA is 0.8 μm.
Even if a lens system of No. 5 is used, the diameter of 1/eZ is about 1.9 μm.

When this spot is modulated with a waveform and irradiated onto the rotating disk surface, the light amount distribution in which this light energy is accumulated on the disk surface becomes as shown by waveform C. That is, waveform b
At the point S2 on the disk surface corresponding to the light emission starting point SI of the waveform C4 corresponding to 1, irradiation starts from the center point of the light spot and this spot passes, and the light energy is integrated. On the other hand, in the center M of waveform C1, point M2
Since the entire spot passes through, the energy stored at the light emission starting point S2 is half of the energy stored at the central point M2. On the other hand, in the case of a short pulse like waveform b2, not all spots pass through even at the center of the pulse, and the energy does not reach its maximum value. Therefore, the pits recorded by such spots are d,,d.

, the maximum track widths are different as Wl and W2, respectively.

When reproducing such a pit, a 3T pulse b is generated.

This is equivalent to the pulse width being shortened because the reproduction level is lowered.

Therefore, conventionally, pit d2 corresponding to 3T pulse b2
EF corresponds to a predetermined 3T pulse.
The recording energy was increased by increasing the wave height of the M signal. However, if you do this, the longer pit d1
becomes longer than necessary. For this reason, although the recording pulse was shortened, it was not possible to narrow the pit width.

There is a drawback that the change in the focus width due to the difference in recording time becomes even more significant as the recording linear velocity becomes smaller as the influence of thermal diffusion increases.

The present invention has been made with the object of solving these drawbacks and providing an optical disc device that can obtain pits having the correct length and width.

[Means for solving problems]

An optical disc device according to the present invention is an optical disc device that records information by variable focus length, and is characterized in that the laser power for forming pits is reduced at the center of each pit.

[Effect]

Therefore, according to the present invention, a short pit has a relatively short length at a low intermediate level, and the recording energy is high, so that pits with a good shape can be formed.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of a waveform shaping circuit that can be used in a zero-start system.

In the figure, the EFM signal applied to the input terminal 15 is
Delay circuit using one shot multi etc. 1. 2.
5. AND circuit 3. 4. 6. 9. Processed by a logic circuit consisting of an OR circuit 7 and inverting circuits 8 and 12,
Output terminal + via variable resistor 13, 14 and amplifier 10
16.

The operation of the waveform shaping circuit with the above configuration will be explained using the operation explanatory diagram of FIG. 2.

Each symbol in the figure a+ b+ C+ d+ g+
h+ j+ k+m, n, p show the waveform diagrams of the parts shown in FIG. 1 with the same reference numerals. In the figure EF
The timing of the M signal is determined by the clock pulse a, and the EFM signal is sent to the delay circuit 1.
2, delay pulses C2 and g are obtained, and AND circuit 3 takes the AND of the delayed pulses C and g.
A shortened pulse h can be obtained by shortening the last half of each pulse of the delayed pulse g by IT. The shortened pulse h is further delayed by T by delay 5, the pulse j is obtained from the inverted output Q, and the AND of pulse j and pulse h is AND4.
to obtain the leading edge pulse k. Also, 5. , HMi
The output obtained by inverting t5b by the inverter 5 and the pulse h
By performing an AND operation with AND6, each pulse of the trailing edge pulse m and this edge pulse n has a shape obtained by extracting IT of the leading edge and trailing edge of the shortened pulse h. This edge pulse n is inverted and logically ANDed with the shortened pulse h to obtain an intermediate pulse p. These edge pulse n
and intermediate pulse p are added at an appropriate ratio using a variable resistor 14.13 to obtain a recording waveform d at the output terminal 16 of the amplifier 10.
This allows the laser power to be controlled and recorded. Here, adjust the resistor 14 so that the 3T pit has the desired shape, and then adjust the resistor 13 to change the mixing ratio of the intermediate pulse p so that it has the same width as the 3T focal point, 4T or more. Adjust the length of the pit. If the delay amount of each delay circuit 1, 2.5 is changed here, even more precise adjustment is possible.

As explained above, according to this embodiment, there is little change in pulse width, pits with the correct shape can be formed, and recording with a low error rate is possible. Furthermore, the efficiency of laser power is also better than in normal pulse recording. If the front and rear parts of the pit do not have the same shape, the amount of delay of each delay circuit may be adjusted so as to change the pulse width of the front and rear parts of each edge pulse n.

〔Effect of the invention〕

As described above, according to the present invention, the wave height of the recording pulse becomes higher in the front and rear edges of the pit where recording energy tends to be insufficient, so that pits with accurate shapes can be recorded.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a diagram for explaining its operation, and FIG. 3 is a diagram for explaining problems of the prior art. 1, 2. 5...Delay circuit 13.14...Variable resistor patent applicant Nippon Columbia Co., Ltd.1!2 mountains? (-Sen L'L)

Claims (2)

[Claims] (1) An optical disc device that records information by variable pit length, in which the laser power for forming pits is reduced at the center of each pit. (2) comprising means for generating first pulses corresponding to the leading edge portion and trailing edge portion of each recording waveform; and means generating a second pulse corresponding to the central portion of each of the recording waveforms; An optical disc device characterized in that the recording waveform is obtained by adjusting the level of at least one of the first and second pulses and adding these pulses.