JPH04103035A - Recording system for optical disk - Google Patents

Abstract

PURPOSE:To form the bit/mark in a normal position by setting a bias value of a laser driving pulse current lower than usual, and delaying the light emission timing of a laser light. CONSTITUTION:A recording signal S inputted to an input terminal 1 is inputted to a delaying circuit 2 and a pulse pattern analyzing part 4. It is delayed by a prescribed time in a delaying circuit 2, and thereafter, inputted to a laser driving pulse current generating part 3, and a laser driving pulse current 10 is generated. Accordingly, a bias value of the laser driving pulse current 10, that is, a bias current value IB immediately before a rise of a pulse becomes constant. That is, an output of the laser driving pulse current generating part 3 and an output of a DC bias current generating part 6 are aligned as to the time bases by the delaying circuit 2 and inputted to an adding circuit 7, added and a laser driving pulse current 12 is generated. In such a way, a bit/mark are formed in a normal position irrespective of a pulse train of a recording signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a recording system for a magneto-optical disk, a write-once optical disk, and the like.

[Prior Art] Conventionally, when recording desired information on an optical disk, magneto-optical disk, write-once optical disk, etc. (hereinafter collectively referred to as an optical disk) using a semiconductor laser, a first step is required. 3 Create a laser drive pulse current as shown in FIG. 3(b) in response to the recording signal shown in FIG. 3(a),
By injecting the laser drive pulse current into the semiconductor laser, a laser beam having an output modulated into two values of high level PM and low level PL by a recording signal as shown in Figure (C) is created as a beam spot on the optical disk. It is irradiated as When the optical pulse is at a high level P, a hole called a pit is formed in a write-once optical disk, and a hole called a mark is formed in a magneto-optical disk because the direction of magnetization of the magnetic film is reversed. It is formed. Note that in the following description, pits and marks are collectively referred to as pits/marks.

[Problems to be Solved by the Invention] However, in the conventional optical disc recording system, if the previously recorded pit/mark is sufficiently far away, the positional shift of the newly recorded pit/mark will be Although it is negligible, even when the laser beam is emitted at precise timing as shown in Figure 3, the front end of the formed bit/mark swells and deviates from its normal position, resulting in jitter. There was a case.

In particular, if the interval from the previous bit/mark is short, as shown by bit/mark PM in Figure 4, the previous bit/mark is long, as shown by bit/mark PMz in the same figure. In addition, when the pit/mark PMs to be formed this time are long, as shown by bit/mark PM3 in the same figure, this phenomenon becomes conspicuous, and △1 in Fig. 4
．． △、.

As shown by Δ, the front end of the bit/mark swells, and the deviation from the normal position becomes large. And the swelling of these bits/marks △1. △1. Δ is not constant, but varies depending on the pulse pattern of the laser beam, that is, the pulse train pattern of the recording signal.

The reason for this is that the recording method for optical discs is basically a thermal recording method that heats the recording medium, so the heat generated when forming the previous bit/mark propagates through the recording medium, causing the next bit/mark to be heated. This is because the temperature at the position where the mark is formed will be increased, which will speed up the formation of the bit/mark that is about to be formed.
In the case of a mark, this is because the heat generated during the formation of the bit/mark propagates to the front end of the bit/mark and increases the temperature of the front end of the bit/mark.

By the way, the present applicant previously disclosed in Japanese Patent Application Laid-Open No. 64-43816 that the laser output is increased by ΔP below the normal low level PL during a certain period TI immediately before the rise of the recording signal indicated by the broken line, as shown in FIG. I suggested lowering it.

According to this, it is possible to steepen the temperature rise on the recording medium when it is irradiated with laser light, thereby improving the C/N ratio and the temperature dependence of the laser output necessary for optimal recording. , and an improvement in recording frequency dependence can be achieved. However, in this case, the laser output is weakened just before the rise of the recording signal to eliminate preheating, so the level just before the rise of the laser drive pulse current is
Even if it is lowered to the maximum, it is still below the oscillation threshold of the semiconductor laser.

This is because if the level of the laser drive pulse current is below the threshold level, the laser output is zero, and it is meaningless to reduce the laser drive pulse current below the threshold level. In addition, in this device, the downward convergence ΔP of the laser output is always fixed at a constant value regardless of the pattern of the recording signal. Therefore, in such a device, it is impossible to prevent the front end of the bit/mark from bulging.

The present invention is intended to solve the above-mentioned problems, and it is an object of the present invention to provide an optical disc recording method that can form bits/marks at regular positions regardless of the pulse train of the recording signal, thereby reducing jitter. This is the purpose.

[Means for Solving the Problems] The reason why the front end of the bit/mark swells is due to the diffusion of heat caused by laser light irradiation as described above. Therefore, it can be seen that when a bulge in the front end is predicted as described above, the rise time of the laser drive pulse current may be delayed a little more than the rise of the normal recording signal. In other words, even if the rise of the laser drive pulse current is slightly delayed, the front end of the bit/mark to be formed this time will swell due to heat diffusion from the previously formed bit/mark. bits/marks can be formed. Incidentally, as shown in Figure 6, semiconductor lasers have the characteristic that the timing of light emission changes depending on the level of the bias current of the laser drive pulse, that is, the current just before the rise of the laser drive pulse. ), (b), if the bias current of the laser drive pulse is TBI and the emission delay time of the laser beam is tb+, then Fig. 8(a),
As shown in (b), when the bias current of the laser drive pulse is lowered to I@x (<I.1), the emission delay time of the laser beam becomes to 2 (> tn +), and the emission delay time becomes longer. This light emission delay time is determined by the bias current value of the pulse, regardless of the peak value (2) of the laser drive pulse current. In fact, it has been confirmed that the timing of laser light emission can be controlled by about 5 n5 ec by changing the bias value of the laser drive pulse current. Note that in FIG. 6, IIk indicates a light emission threshold current for the semiconductor laser to emit light.

The present invention achieves the above object by utilizing the characteristics of the semiconductor laser described above, and provides an optical disc on which recording signals are recorded by irradiating laser light from the semiconductor laser with pulse modulation according to the recording signal. The recording method is characterized by comprising means for controlling the drive current level during a predetermined period of time immediately before the rise of the laser drive pulse in accordance with the pulse train pattern of the recording signal.

[Operation] In the present invention, when the interval with the previous bit/mark is short, the previous bit/mark is long, and the pit/mark to be formed this time is long, etc. If the front end of the bit/mark is predicted to swell, the bias value of the laser drive pulse current for the pit/mark to be formed this time is lowered than usual, and the timing of laser light emission is delayed. It can be formed in the regular position.

Note that the standard deviation of jitter, which is a problem in optical discs, is usually about 1 n5ec, so according to the present invention, jitter can be reduced with a sufficient margin.

[Example] Examples will be described below with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the optical disc recording method according to the present invention, in which l is an input terminal, 2 is a delay circuit, 3 is a laser drive pulse current generator, and 4 is a pulse pattern. The analysis section 5 is a lookup table (hereinafter referred to as LU
6 is a DC bias current generator, 7 is an adder circuit, and 8 is a semiconductor laser.

In the configuration shown in FIG. 1, assume that a recording signal S as shown in FIG. 2(a) is input to the input terminal 1. The interval between recording signal pulses (hereinafter simply referred to as pulses) SI and 82 is narrow, pulse s3 is a long pulse, and pulse S4 is a pulse input following pulse Ss. Recording is performed using the conventional optical disc recording method. Pulse S
2+Ss.

It is assumed that the front end of the bit/mark formed based on S4 swells.

The recording signal S input to the input terminal 1 is input to the delay circuit 2 and the pulse pattern analysis section 4. After being delayed for a predetermined time by the delay circuit 2, it is input to the laser drive pulse current generator 3, and as shown in FIG. 2(b), a laser drive pulse current 10 similar to the conventional one is generated. Therefore, the bias value of the laser drive pulse current 1°, that is, the bias current value 1.0 just before the rise of the pulse. is constant.

The pulse pattern analysis section 4 is constituted by a logic circuit or a computer, detects the length of the "L" level and the length of the "0" level of the recording signal S, analyzes the pulse train pattern, and determines the bias for the pulse example pattern. The bias current value of the laser drive pulse is determined for each pulse by referring to the LUT 5 in which the current value is written.

Specifically, it is as follows. LUT5 contains a bias current value corresponding to the length of the "02 level" immediately before the "1" level of the recording signal, a bias current value corresponding to the length of the previous "1" level, and the current value to be recorded. The bias current value is written according to the length of the “bi level”. Therefore, in the pulse pattern analysis section 4, for every "1 level" of the recording signal S, the length of the "B level, the length of the immediately preceding "0° level, and the length of the immediately preceding "1 level" are calculated in sequence. By measuring the pressure and referring to the LUT 5, the optimum bias current value for each "1" level of the recording signal S can be determined. The procedure for determining the optimum bias current will be explained below with reference to the flowchart of FIG.

In the flowchart of FIG. 9, the procedure for determining the optimum bias current flows as follows.

When the flow starts (START), first step 1
(Sl) reads the data signal every clock.

In step 2 (S2), old data is discarded and new data is stored in the ring buffer. Step 3 (S3)
Now, determine whether the new data is at the "02 level." If YES, proceed to step 4 (S4);
), the process returns to step H3I). Step 4 (S4)
Now, from the contents of the buffer, we can calculate (1) the length of the latest “1” level data (tA), (2) the length of the immediately preceding “O level data (1 key), and f3) f2). “0”
“1 level data length (t
e). In step 5 (S5), 3
The current correction amount (= f (tA, b, tc)) is read from the table (LUT5) consisting of a dimensional array.

In step 6 (S6), a set value (optimum bias current value) is given to the DC bias current generator 6. Step?
(S7) reads the data signal every clock,
Store in ring buffer.

In step 8 (S8), it is determined whether the new data is at the "l" level, and if YES, step 1 (Sl) is determined.
), and if NO, return to step 7 (S7). In this way, the optimum bias current value can be determined in all cases.

FIG. 10 is an example of data in LUT5. Note that the optimum bias current correction amount determined under the conditions of ■, ■, or ■ in the figure is ΔI, respectively.

1.ΔII! Alternatively, it is assumed that ΔI1m.

Note that the LUT 5 can be configured with a ROM or nonvolatile memory, but it is desirable that it can be set or changed from the outside.

The analysis result from the pulse pattern analysis section 4 is input to the DC bias current generation section 6, and a DC bias current 11 as shown in FIG. 2(C) is generated.

In FIG. 2(c), pulses S , , S , and S
As a result of analysis by the pulse pattern analysis unit 4, the bias current values immediately before 4 are Δ118. ΔIs'.

ΔIss. As is clear from the above, Δ1111 is mainly determined by the interval with the previous pulse S1, that is, the length of the "0" level immediately before the pulse, and ΔIsx is mainly determined by the "1" level of the pulse 83 itself.
Δll11 is determined mainly by the length of the "1" level of the previous pulse S3 and the length of the "0° level immediately before the pulse s4."

Therefore, Δ1.1. ΔI12 and ΔIss are generally different.

Note that the time for generating the bias current may be a preset fixed time, or if the length of the "0" level immediately before the pulse of interest is less than a predetermined length, the time of the previous pulse may be The determined bias value may be set from the time of falling, and when the length of the immediately preceding "O" level is longer than a predetermined length, the determined bias current value may be set for a preset required time. In Figure 2, the latter is adopted.

The output of the laser drive pulse current generator 3 and the output of the DC bias current generator 6 are input to the adder circuit 7 with their time axes aligned by the delay circuit 2, where they are added together as shown in FIG. 2(d).
A laser drive pulse current 12 as shown in is generated.

The laser drive pulse current 12 generated by the adder circuit 7 is injected into the semiconductor laser 8, which causes the semiconductor laser 8 to emit light, but as shown in FIG. 2(e), the bias current Δ1.1. Δ1.8. Semiconductor laser 8 according to ΔIll
The light emission of Δt1°Δt1. There will be a delay of Δh. However, as mentioned above, the front end of the bit/mark PM2 corresponding to the pulse S swells due to the diffusion of heat generated during the formation of the bit/mark PM2 corresponding to the pulse S, so that ), the recording signal S! The length is approximately the same as the length of the “V level.Pulse S
The same applies to bits/marks PMs and PM4 corresponding to , ,S.

Although one embodiment of the present invention has been described above, it will be obvious to those skilled in the art that the present invention is not limited to the above embodiment, and that various modifications can be made.

[Effects of the Invention] As described above, according to the present invention, the light emission timing of the semiconductor laser is delayed by controlling the bias value of the laser drive pulse current according to the pulse train pattern of the recording signal, so that the timing of light emission of the semiconductor laser is delayed. It is possible to easily control the heat of the bits/marks and the swelling of the front end of the bit/mark caused by the propagation of heat, and the jitter can be made extremely small no matter what the pattern of the recording signal is.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the optical disc recording system according to the present invention, FIG. 2 is a diagram showing signal waveforms for explaining the operation of each part in FIG. 1, and FIG. 4 is a diagram for explaining the recording method of an optical disc. FIG. 4 is a diagram showing an example of pits/marks formed by a conventional optical disc recording method. FIG. 5 is a diagram for explaining another conventional example. 6
The figure shows the light emission delay time with respect to the bias of the laser drive pulse current of a semiconductor laser. Figure 7 shows the light emission delay time when the bias of the laser drive pulse current is large. Figure 8 shows the bias of the laser drive pulse current. FIG. 9 is an example of a flowchart explaining the operation of the pulse pattern analysis section, and FIG. 10 is an example of numerical values of an LUT (look-up table). [Explanation of symbols of main parts] 1... Input terminal, 2... Delay circuit, 3... Laser drive pulse current generating section, 4... Pulse pattern analysis section, 5... LUT, 6... ...DC bias current generation section,
7...Addition circuit, 8...Semiconductor laser.

Claims (1)

[Claims] In an optical disk recording method in which recording signals are recorded by irradiating laser light from a semiconductor laser with pulse modulation according to the recording signal, the pulse train pattern of the recording signal is the drive current level for a predetermined time immediately before the rise of the laser drive pulse. An optical disc recording method characterized by comprising a means for controlling according to.