JP2008071447A - High frequency superimposing level setup method, and disk player - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a superimpose effect without spoiling its stability by suppressing the superimpose effect variations when making high frequency superimposed driving of a large output and large current drive laser diode close to 400 nm. <P>SOLUTION: By obtaining the current difference between the Ith electric current of the laser diode LD to use and the Ith of a reference laser diode after adjusting the superimposing high frequency current to the setup ΔIop (value where the superimposed light emitting peak power becomes 3.5 times) of a reference laser diode, the controller 8 adjusts the superimposing high frequency level from a high frequency oscillator circuit 4 to the output circuit 1 by subtracting or adding the superimposing high frequency current which is obtained by multiplying this current difference by a correction factor from or to the above adjusted superimposing high frequency current. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a disk reproducing apparatus for reproducing data by irradiating a disk with laser light, and more particularly to a method for setting a high-frequency current level to be superimposed on a current for driving a laser diode during reproduction.

  The disk recording / reproducing apparatus records and reproduces data by irradiating the disk with laser light emitted from a laser diode (LD). Normally, the laser diode is DC driven at the time of writing, but high frequency superposition driving is performed at the time of reproduction to suppress an increase in noise due to return light and wavelength jump due to LD temperature change (see, for example, Patent Document 1).

The setting of the conventional high frequency superposition level of the LD used at the time of reproduction of the disk reproducing device is not the observation adjustment by the optical transmitter (OSC), but the LD drive current of the IL characteristic that changes by high frequency superposition on / off as shown in FIG. The indirect adjustment method using the differential current of the DC component is used. This differential current is called ΔIop at the operating point of the LD and ΔIth near Ith. High frequency superposition diffuses the emission spectrum and suppresses return light and wavelength skipping. The higher the level, the greater the effect. However, since the energy of light is high in a Blu-ray disc apparatus using a 400 nm laser, if the peak power is increased, data recorded at the time of reproduction is deteriorated and stability is deteriorated. In the Blu-ray Disc (400 nm disc) standard, the peak power is 7 times or less of the average reproduction power.
JP 2000-149302 A

  By the way, while the output of the 400 nm LD was as small as 50 mW (pulse), Ith was small and its variation was small, so that the design specification was satisfied by the fixed adjustment of ΔIop. Here, recording on a double-layer disc is required, the output of the LD is 150 mW (pulse), and as shown in FIG. 11, the Ith is larger and the variation is larger in the 150 mW LD than in the 50 mW LD. ing. As a result, in the fixed adjustment, the superposition effect varies, and the multiple of the peak power is 2 to 5 times as shown in FIG. .

  The present invention has been devised in view of the above circumstances, and an object of the present invention is to suppress variation in superposition effect during high-frequency superposition drive of a large current drive laser diode having a large output near 400 nm and impair stability. It is an object of the present invention to provide a high frequency superimposition level setting method capable of reliably obtaining a superimposing effect without any problem and a disc reproducing apparatus using this setting method.

  In order to achieve the above object, the present invention provides a method for setting a high-frequency superposition level when high-frequency superimposition is performed on a current for driving a laser diode during reproduction by an optical disk reproducing apparatus, and a light emission peak at the time of high-frequency superposition of a standard laser diode After adjusting the high-frequency superimposed current level so that ΔIop is obtained such that the power becomes a predetermined multiple, Ith of the laser diode to be used and Ith of the standard laser diode are measured, and a difference current value between the two Ith current values is obtained. The current obtained by multiplying the difference current value by the correction coefficient is added to or subtracted from the high frequency superimposed current level obtained by the adjustment to obtain the high frequency superimposed current level of the laser diode to be used.

  Thereby, read stability can be ensured by suppressing variations in the emission peak power magnification of high frequency superposition, eliminating the influence of return light, and minimizing the pea peak power.

  After adjusting the high frequency superimposition level so as to obtain a standard laser diode ΔIop (a value at which the peak power of superimposed light emission is 3.5 times), the difference current between the Ith current value of the laser diode used and the Ith of the standard laser diode Since the high frequency superposition level is adjusted by adding / subtracting the high frequency superposition current obtained by multiplying the difference current by the correction coefficient to the high frequency superposition current level obtained by the adjustment, the output is around 400 nm. Thus, it is possible to suppress the dispersion of the superposition effect during the high-frequency superposition drive of the large current drive laser diode and to obtain the superposition effect reliably without impairing the stability.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(Example 1)
FIG. 1 is a circuit diagram showing a configuration of a laser driving circuit for explaining a method for setting a high-frequency superposition level according to the first embodiment of the present invention. The laser drive circuit includes an output circuit 1 for driving the laser diode LD, a current switch circuit 2 for supplying a drive current to the output circuit 1, a laser power control circuit 3 for controlling the drive current of the current switch circuit 2, and a high-frequency current as a current switch circuit. 2, a high-frequency oscillation circuit 4 that outputs to the laser diode 5, a laser power memory 5 that stores the light emission power of the laser diode LD, and a D / A conversion that converts the power value read from the laser power memory 5 into an analog signal and supplies the analog signal The circuit 6 includes a state holding circuit 7 that holds various values indicating the state of the circuit in accordance with instructions from the control unit 8, and a control unit 8 that performs control during high-frequency superposition level adjustment.

  Next, the operation at the time of adjusting the high frequency superimposition level of this embodiment will be described. When the drive circuit is set to the read mode by the control unit 8, read power data is output from the laser power memory 5, which is converted into an analog value by the D / A conversion circuit 6 as a reference value (REF) of the laser power control circuit 3. Given. The laser power control circuit 3 inputs a monitor signal corresponding to the actual light emission output of the laser diode LD from the front monitor photodiode FFD, and outputs a drive signal such that an error signal between the monitor signal and the REF becomes 0 as a current switch. Output to the output circuit 1 through the circuit 2. The output circuit 1 amplifies the current of the input drive signal and outputs it to the laser diode LD. The light emission output of the laser diode LD is monitored by the FFD and is fed back to the laser power control circuit 3 as the monitor signal. By this feedback loop, the light emission output of the laser diode LD is adjusted so that the monitor signal becomes REF.

  Thereafter, the controller 8 turns on / off the high frequency current while changing the level of the high frequency oscillation circuit 4 and monitors the current of the output circuit 1. The control unit 8 takes in a current value every time the high-frequency oscillation circuit 4 is turned on and off, and sets a current difference (ΔIop) at the time of on / off to set a high-frequency current superposition level to be superimposed on the drive current of the laser diode LD to an optimum value. .

Here, a method for adjusting the high frequency superimposition level will be described. This method takes advantage of the indirect adjustment method to correct the peak power level due to variations in the laser diode LD. Focusing on the correlation between Ith and ΔIop of the laser diode LD, correction of ΔIop with respect to Ith The superimposition level is adjusted by taking over the equation. In the correction formula, ΔIop at which the multiple of the peak power level is 3.5 is measured in a large number of laser diodes having different Iths to be used, and a laser diode superimposition level correction formula is created based on this ΔIop.

  FIG. 2 illustrates the generation of ΔIop due to high frequency superposition. The original high frequency superposition wave is a sine wave but a rectangular wave. In DC light emission, Iop (mA) is given and Rp (read power) is obtained. When light is emitted, the light is emitted at a level slightly more than twice that of DC lighting, and when the light emission is stopped, driving with a 50% rectangular wave smaller than Ith, the average power of light emission is the same as that of DC light emission, and the average current is reduced by ΔIop. That is, a current equal to or less than Ith is an invalid current for light emission, and Iop can be reduced. In other words, ΔIop is generated when the nonlinear part of IL is used.

  FIG. 3 is a characteristic diagram showing the IL characteristics of the low output portion of the high output laser. As can be seen from the comparison of A, B, and C in the figure, the non-linear portion of the low output portion IL tends to increase as Ith increases. An IL curve is added to the modulation characteristics of the LD of the A part and the C part, and the modulated sine wave is obtained by multiplying such an IL curve. In the LD of the C part, a large ΔIop is generated even in the LD light emitting region.

  FIG. 4 is a characteristic diagram in the case of measuring the high-frequency superimposed current of the LD having a different Ith when ΔIop = 0.4 mA as the high-frequency superimposed current when the high-frequency superimposed level is set by ΔIop. The high-frequency superimposed current that generates the same ΔIop: 0.4 mA decreases as the LD having a larger Ith.

  FIG. 5 is a characteristic diagram when the high-frequency superimposed current is measured when the peak power of light emission is quadrupled. From the viewpoint of the high-frequency superimposed current, although it depends on the output power, it can be understood that a constant current is sufficient because it is almost constant.

  FIG. 6 illustrates a method for setting the superimposition level. The superimposition level that generates the same peak power may be set by adding or subtracting the correction current to or from the set current of ΔIop = 0.4 mA as shown in the figure. I understand.

  From the above examination, when the correction is set to 15 mV / mA (ΔIth), the peak power is approximately 3 to 4.5 times, and the measurement results show that the waveform can sufficiently detect the relaxation oscillation even at Ith = 50 mA. I understand. This ensures read stability without being influenced by the return light. Since the correction is made with Ith = 40 mA as the origin, if it is smaller than Ith = 40 mA, the amplitude is reduced by negative correction, and if it is larger, it is increased by positive correction.

  As described above, in order to manage the peak power at the time of high frequency superposition, it is only necessary to manage the high frequency superposition current flowing in the LD. However, in actual optical pickups, frequency attenuation and variation are impossible, and this is impossible in practice. . The adjustment with ΔIop is an adjustment method based on the result including these factors. If correction can be made in some form, the peak power can be managed. FIGS. 7 and 8 summarize the measurement data corrected by 15 mV (SG correction level) / mA (ΔIth), and the peak power is considerably improved. In particular, in FIG. 8, the high-frequency superimposed current corrected by ΔIop measured at the same time matches the polynomial of ΔIop. Therefore, in order not to overcorrect, Δmop / Ith of 6.5 mW may be set as the set target value. In this way, the adjustment includes the frequency characteristics of the transmission system and LD.

    ΔIop set value = 0.00186X2−0.1217X−2.2813

  Note that the high frequency superposition is deeper and the suppression of the return light is stronger. However, in the case of 400 nm LD, since RIN is as large as -125 dB, superimposition above a certain level is buried in noise and meaningless, and lead stability is improved. It is a cause of damage. Below, it was found that various measurement results of about 3.5 times were sufficient.

According to this embodiment, after adjusting the high frequency superimposition level so as to obtain ΔIop (a value at which the peak power of superimposed light emission is 3.5 times) of the standard laser diode, the Ith current value of the laser diode to be used and the standard laser are adjusted. The high-frequency superimposition level is adjusted by obtaining a differential current from the diode Ith and adding / subtracting the high-frequency superimposed current obtained by multiplying the differential current by the correction coefficient to the high-frequency superimposed current level obtained by the adjustment. Therefore, read stability can be ensured by suppressing variations in the light emission peak power magnification of high frequency superposition, eliminating the influence of return light, and minimizing the peak power.
(Example 2)

  FIG. 9 is a partial schematic block diagram showing the configuration of a disc recording / reproducing apparatus according to the second embodiment of the present invention. The disk recording / reproducing apparatus superimposes the high-frequency current output from the high-frequency oscillator 12 on the laser diode-driven DC current output from the laser drive circuit (LD driver) 11 (only at the time of reproduction). The laser diode LD is driven. At the time of writing, a write signal given separately by the laser drive circuit 11 is amplified and output to the laser diode LD to write on the Blu-ray disc. Part of the laser light emitted from the laser diode LD is received by the photodiode PD, and the received light current is input to the APC error amplifier 13. The APC error amplifier 13 controls the output of the laser drive circuit 11 so that the average received light power of the LD becomes a predetermined set value. The laser diode output from the laser diode LD is irradiated onto a disk (not shown) through an optical system (not shown) to perform data recording / reproducing, but the data recording / reproducing system is a well-known circuit, and is not shown.

  According to the present embodiment, even when the laser diode LD is for a Blu-ray disc and its light emission power is large, the variation in the superposition effect during the high-frequency superposition drive is suppressed by adopting the high-frequency superposition level adjustment method of the first embodiment. Thus, a reliable high frequency superposition effect can be obtained without impairing stability.

  In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it can implement also with another various form in a concrete structure, a function, an effect | action, and an effect.

It is a circuit diagram showing the composition of the laser drive circuit for explaining the setting method of the high frequency superposition level concerning a 1st embodiment of the present invention. It is a figure explaining generation | occurrence | production of (DELTA) Iop by high frequency superimposition. It is the characteristic view which showed the IL characteristic of the low output part of a high output laser. It is a characteristic view at the time of measuring the superposition current of LD from which Ith differs. It is a characteristic view showing the IL characteristic of the low output portion of the high output laser, which is a characteristic view when measuring the superimposed current of the LD in which the emission peak is 4 times. It is a figure explaining the setting method of a superimposition level. It is the figure which put together the measurement data which corrected 15mV (SG correction level) / mA ((DELTA) Ith). It is the figure which put together the measurement data which corrected 15mV (SG correction level) / mA ((DELTA) Ith). It is the partial schematic block diagram which showed the structure of the disc recording / reproducing apparatus concerning the 2nd Embodiment of this invention. It is a characteristic figure showing high frequency superposition and IL characteristic. It is the figure which showed Ith and the variation tendency example with respect to the output power of laser diode LD. It is the characteristic figure which showed the example (at the time of (DELTA) Iop = 0.4mA) of a high frequency superimposed light emission waveform.

Explanation of symbols

  1 ... Output circuit, 2 ... Current switch circuit, 3 ... Laser power control circuit, 4 ... High frequency oscillation circuit, 5 ... Laser power memory, 6 ... D / A conversion circuit, 7 ... State holding circuit , 8: Control unit.

Claims (4)

A method of setting a high frequency superposition level when superposing a high frequency on a current for driving a laser diode during reproduction of an optical disk reproducing device,
After adjusting the high-frequency superposition current level so that ΔIop is obtained so that the emission peak power when high-frequency superposition of a standard laser diode is superposed is a predetermined factor, Ith of the laser diode used and Ith of the standard laser diode are measured. Then, a differential current value of both Ith current values is obtained, and a current obtained by multiplying the differential current value by a correction coefficient is added to or subtracted from the high frequency superimposed current level obtained by the adjustment to obtain a high frequency superimposed current level of the laser diode to be used. A method for setting a high frequency superimposition level.   2. The high frequency superimposition level setting method according to claim 1, wherein the predetermined multiple is about 3.5 times. A disk reproducing apparatus for recording and reproducing data by irradiating a disk with a laser emitting light from a laser diode,
The setting of the high frequency superposition level when superposing the high frequency on the current for driving the laser diode during reproduction is performed so that ΔIop is obtained such that the peak power of light emission at the time of high frequency superposition of a standard laser diode is a predetermined multiple. After adjusting the level, Ith of the laser diode to be used and Ith of the standard laser diode are measured to obtain a difference current value of both Ith current values, and the current obtained by multiplying the difference current value by a correction coefficient is adjusted as described above. A disk reproducing apparatus characterized in that the high frequency superimposed current level of the laser diode to be used is added to or subtracted from the high frequency superimposed current level obtained in this way.   4. The disk reproducing apparatus according to claim 3, wherein the laser diode is a laser diode for recording / reproducing a Blu-ray disk.

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