JPS6343386A - Method of judging lifetime of laser - Google Patents

Abstract

PURPOSE:To judge the lifetime of a laser exactly by setting the superposition of high-frequency currents to DC bias currents of the laser to a stoppage state, detecting the luminous power of the laser and judging the lifetime of the laser. CONSTITUTION:When a discrimination instruction signal INST is inputted to a CPU 9, the CPU 9 outputs a signal maintaining the operation of the oscillation of an oscillation circuit 8 for high-frequency super-position under a stoppage state. The CPU 9 sets a set value for light emission at a low level to a decoder 28 for setting luminous power, a laser power value data is written to a memory 31 when the comparision output of a comparison circuit 27 reaches zero, and laser driving currents at that time are written to the memory 31 throught the CPU 9. An output from a photodiode 11 for monitor is transmitted as another input to the circuit 27. Consequently, laser driving currents are written to the memory 31 regarding a low-level data at a slightly large value and a data for a high-level light emission. When said writting is completed, the CPU 9 arithmetically operates the data on the basis of the value of the memory 31, thus judging the lifetime of a laser diode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for determining the life of a high frequency superposition laser.

[Prior Art] In recent years, instead of recording or reproducing information using magnetic heads,
2. Description of the Related Art An optical information recording/reproducing device that can perform high-density recording or reproducing by condensing a light beam Q, J has been put into practical use.

As the source of the light beam used for recording or reproducing, a laser diode having excellent cohesin properties is used, and in particular, a semiconductor laser diode (ray diode), which is easy to downsize and modulate, is widely used.

By the way, when performing the above-mentioned reproduction, when performing recording J:
Since the intensity of the laser beam is low, the return light from the recording medium is strong! Good becomes weak. In order to prevent reading errors, it is desirable to improve the signal-to-noise ratio (S/N).

In order to improve the above S/N, for example,
As disclosed in No. 86, the drive current of Rayleigh is
A known method is to make the longitudinal mode of the laser oscillation into a multi-mode by superimposing a high frequency current around GH2, thereby reducing the noise of the laser beam and increasing the S/N of the reproduced signal.

By the way, in the above-mentioned optical recording/reproducing device 1, the laser 1
1 will kill Su, 4? it! When I deteriorates, the operation of writing or reading information onto an information recording medium becomes unstable or impossible. In order to protect the device from rain, some devices are equipped with a separate function for determining the lifespan of the laser.

For example, 1″irA Sho 60-56891 by the present applicant.
In the device proposed in the issue, the lifetime of the laser is determined by the degree of linearity of the mother-child efficiency of the Leb diode.

[Problems to be solved by the invention] By the way, when the above-mentioned high frequency current is superimposed,
As shown by the solid line J in the figure, the linear characteristic section "without high frequency superimposition" changes to the curved characteristic section "with high frequency superposition" shown by the broken line in the same figure.

For this reason, even if the laser is normal, it is difficult to judge whether the laser is good or bad if it emits laser light using the high-frequency m-contact method, and there is a risk of making an incorrect judgment.

The present invention has been made in view of the above-mentioned points-C1
It is an object of the present invention to provide a method for determining the lifespan of a laser that can reliably determine pass/fail.

[Means and effects for solving the problem] In the present invention, the linearity of the suspension efficiency of the Rayleigh is measured and the C no.
When making a life judgment, the superimposition operation of the high-frequency current supplied to the laser diode is stopped, and the DC bias current is turned off.
By performing C, the lifespan can be determined reliably.

[Example] Hereinafter, the present invention will be specifically explained with reference to the drawings.

Figures 1 to 6 relate to the first embodiment of the present invention.
Figure 2 is a block diagram showing the brightness determination device according to the first embodiment, Figure 2 is a block diagram showing the optical disk device in which the determination A is made, and Figure 3 is the principle behind the determination in the first embodiment. Fig. 4 is a characteristic diagram of the driving fh current vs. emission power of the J31 laser diode when it deteriorates, and Fig. 5 shows the driving current and emission power when a high frequency current is applied. FIG. 6 is a flowchart showing the lifespan determination process of the first embodiment.

As shown in FIG. 2, an optical disk device 1 equipped with the method of the first embodiment rotates an optical disk 2 as a recording medium with a spindle Tanabata (disposed in a direction perpendicular to the plane of the paper, not shown). An optical head (pickup) 3 is placed on one side of the disc 2 to face the disc 2, and a light beam is focused on the disc 2 to illuminate it. The second head 3 is mounted on the carriage 4 (-1) and is moved by a head feeding mechanism such as a voice coil Tanabata or a feed screw mechanism.
This allows the disk 2 to move in the radial direction.

When a laser diode 5 is housed in the optical head 3 as a light emitting source, a one-segment light detector 6, for example, for receiving the return light from the disk 2 is housed.

The light emitting output of the laser diode 5 is automatically controlled to an appropriate level by the output current of the laser power controller 1-roll ΔPC circuit 7. Further, this diode 5 is also supplied with a high frequency current from a high frequency superimposition oscillation circuit (also referred to as a high frequency oscillation circuit) 8. In other words, Ray E Agui A-do 5 is APC
A DC-like (however, in the light mode, the emission intensity is changed in a pulsed manner, but it is partially lower than the oscillation frequency of the high-frequency oscillation circuit 8) bias driving current is supplied from the circuit 7, and the ΔPC circuit 7 and A high frequency current is supplied in parallel to this drive current from a parallel high frequency oscillation circuit 8.

The high-frequency oscillation circuit 8 is supplied with a power supply voltage for the high-frequency oscillation circuit slowly raised through an integrating circuit 10 in response to an oscillation start command 2) from the CPU 9.

Based on the current flowing through the seven-two Pinnot Ato diode 11 (reference 1 in Figure 1) that is integrally enclosed in the Sea 11 diode 5, the high frequency oscillation circuit 8 +J +
3 and 5 light emission output is automatically set to the set value power.

An operation panel 12 is provided with operation switches and display LEDs, and by operating this operation panel 12, the CPU 9 controls each part so that the corresponding operation can be performed.

By the way, the outputs of the four optical detector elements that have been received by the F light distribution detector 6 and subjected to photoelectric conversion are sent to the information reproducing circuit 1.
When the information signal is input to the servo circuit 14, the information signal is input to the servo circuit 14, and a focusing and tracking control signal is generated.

lRi of the optical head 3 is as follows. The laser beam from the 1F diode 5 is collimated by a collimator lens 15, and is incident on a polarizing beam splitter 16 as, for example, P-polarized light, where almost 100% of the laser beam is transmitted. This transmitted beam is made into a polarized beam of λ/4 plate 1 sheet metal 7, and is incident on an objective lens that is movable in the focusing direction and in the tracking direction T (perpendicular to the plane of the paper in FIG. 2) by an actuator 18. The light is focused by this single objective lens and illuminated onto the disk 2.

The Ray+J' beam focused and irradiated onto the disk 2 is
It is reflected to the objective lens 19 side, and the objective lens 19, λ/4
From the plate 1 and the metal plate 7, the S leakage light in the polarization direction perpendicular to the outgoing path enters the polarizing beam splitter 16 l31-! I will. Therefore, almost 100% of the light is reflected by the polarizing beam splitter 16 and enters the critical angle beam l\20. The beam whose dimension is q on the slope of the critical angle prism 20 is output as Q=
The light is received by a light γ taker 6'C'' disposed opposite to the J side end surface.

By the way, when performing the 10,000 determination method of RA, in one embodiment, the oscillation operation of the high frequency oscillation circuit E3 is stopped at F':( and fj is performed.

``When the oscillation of the 11゛b frequency oscillation circuit 8 is stopped, driving a laser diode in which the 1Ji property has not deteriorated, the relationship between the 'li current I and the ray IJ' output W (quantization efficiency) is shown in Fig. 3.From J0, three drive currents II
.

12.13 J value a output Pt, P2,
If P3 is measured and the following ratio W is calculated, this ratio W
3. It can be seen that the deterioration of the characteristics (linearity of the hanging efficiency) and the loss of life can be determined based on t.

((P3-PI)/(I3-It))/((P2
−P+)/(12-It))=Rn÷1
/Rn = W...(1) Then, set a certain range for this ratio W, and let the upper limit be Wυ[, the lower limit Wl, L, and if the ratio W satisfies the following relationship, the life has come to an end. No, if the following relationship is not satisfied, it can be determined that the person is alive.

WLL<W<WtlL (2) When the ratio W does not satisfy the relationship of equation (2), the Rade output becomes as shown in FIG. 4, and the hanging efficiency of the semiconductor relay 11 deteriorates. Indicates that the product has reached the end of its lifespan. still,
l th indicates a threshold current for laser emission.

A device 30 for determining whether a laser is white or not having a lifespan determination function that performs the laser lifespan determination method of the first embodiment using this principle.
is the fM configuration shown in FIG.

A laser drive current is supplied to the laser diode (main body) 5 via a current control circuit 22 and a sea 1F drive circuit 23 that form the APC circuit 7 . The laser drive current of this laser IJ' drive circuit 23 is converted into digital fiiI via the A/D converter 24, and can be taken into the CPLJ9.

From the laser diode 5 to the high frequency oscillation circuit 8,
The high frequency current can be supplied via the capacitor C to be superimposed on the laser drive current from the laser laser drive circuit 23 side.

On the other hand, the light emitting output of the LED IJ' diode A-5;
The optical output of the F diode 5 is received, and the photocurrent that is charged and converted changes the current flowing through the resistor R in series with the bin photodiode 11 in accordance with the optical output. This current is connected to the resistance R
This voltage is converted into a voltage by - of the comparator circuit 27.
is applied to the other input terminal. Further, to the other input terminal of the comparison circuit 27, the light emission power setting value (7?digital value) of the light emission power setting decoder 28 is applied after being converted into an absolute value by the D/A converter 2. Incidentally, the light emission power setting value data of the decoder 28 can be variably set by the CPU 9.

The comparison circuit 27 takes the light emission power set value as the base If+, compares it with the output value received by the bin photodiode 11, and inputs the comparison output to the current 1i control circuit 22,
The laser drive current supplied to the laser diode 5 is controlled so that the comparison output becomes zero. In this way, the current flowing through the laser diode 5 is controlled so as to be maintained at the light emission power setting value.

By the way, the output of the comparison circuit 27 is (Δ/
The data can be taken into the CPU 9 via the D converter. For example, in a state where the oscillation operation of the high frequency oscillation circuit 8 is stopped, it is determined whether or not the output current of the sea 1f diode A-5 has fallen to the set value using the output current of the rake drive circuit 23. C.

Thus, while the comparison output is maintained at the set value where it is almost zero, the CPU 9 inputs a voltage corresponding to the laser emission power value input to the comparison circuit 27 into the memory 31 external to or internal to the CPU 9. ] is stored via the converter 32.

In addition, this menu 31 shows the laser drive current supplied to the laser diode 5 via the radar drive circuit 23 and connected to the CP card 9 via the A/D converter 24, as well as the laser emission power value (data). The loaded drive current value data is also stored via the data bus.

Both of the above data, that is, the drive current value data and the "IJ" light emitting power storage data, are stored on the operation panel 12.
Discrimination instructions (g,
It operates by inputting 01NsT to the CPU 9. When this discrimination instruction (ii Sj I N ST is input), the CPU 9 outputs a signal to keep the oscillation operation of the high frequency oscillation circuit 8 in a stopped state.

Further, the CPU 9 sets setting value data for low-level light emission in the decoder 28, and when the comparison output of the comparison circuit 27 settles to zero, the laser mediated light power 1i+° is stored in the memory 31.
When the f data is written to iq, the CPU outputs the sea 1F drive current at the time of q to the CPU via the A/D:1 inverter 24.
9, and output the data to the computer 31. When the writing of both data is completed, low level data with a value slightly larger than the above set value data is set in the decoder 28, and in that state, the laser emission power value data and the laser drive current are set in the same manner as in the above case. (“1 disk in memory 31
get old. When this writing is completed, the decoder 28
The data for high level light emission is set in , and the radar light emission power data and the sea 1f drive current data are inputted into the memory 31 in the same way as in the case of the low level.

When the writing of both data in the low level state and the high level state is completed, the CPU 9 calculates based on the above equation (1), performs the J judgment shown in the equation (2), and the judgment result is is displayed on the display 333. As a result, it is possible to reliably detect deterioration in the hanging efficiency, and to detect the leakage of the diode 5 in the sea 11.
ω can be determined.

When the rake guide 5 is determined to be normal according to the above determination method, the CI) U 9 sets the high frequency oscillation circuit 8 to the oscillation state via the integrating circuit 10.In this case, the decoder Step 28 may be performed after the low-level light emission data is set.

Since the integration time constant of the integrating circuit 10 is larger than the response time of the eight PC loops, the high-frequency light (membrane circuit 8
The power supply voltage supplied to the integrator circuit 10 slowly rises and rises, and at each time when this slow rise rises,
The radar emission power is maintained at the power value set by the decoder 28 by the PC loop of the APC circuit 7.

Therefore, even when the high frequency oscillation circuit 8 starts the oscillation operation, a large light emission power state that transiently deviates from the set value to be maintained at ΔP C does not occur at the time of the start. In other words, the ray+J' beam with a large emission power is irradiated onto the recording medium at the superimposed port of the high-frequency oscillation circuit 8), which may destroy the data written on the recording medium or destroy the data recorded on the recording medium. This prevents the creation of defective parts that cannot be used.

The operation of high frequency superposition by this integrating circuit will be explained below with reference to FIG.

The characteristics of the light emission power P of the sheet 11 with respect to the laser drive current IF are as shown in Fig. 1, the threshold lightning current fth
When exceeding i1. ．． .

By the way, with respect to the DC bias current IAV supplied to the laser diode 5 in the case of "P" without high frequency superimposition, the laser emission power P is expressed by the symbol PAV by using the 1F-P characteristic (directly expressed as Become.

On the other hand, when a high frequency current II-IF is suddenly superimposed on the DC bias current I A V, the laser drive 'kh current IF
The average value of J does not change, but the instantaneous value changes in a sinusoidal manner. Because of this sinusoidal change/J, when calculating the light emitting power P of the sea 11 using the IF-P characteristic, the sign f'3PH'("1) is obtained in the right part of Fig. 5, and the average light emitting power is It is indicated by the symbol PHAV.

In other words, for a 1f drive 1FIJ current IF with the same average value, the Rake light emission power P becomes more impressive in the case of ``with high frequency superposition'' than in the case of ``no high frequency superposition''. Assume that the above case of "high frequency, no kidney" is the equilibrium value of white 1h output control, and in that state suddenly "high frequency superimposition"
, the average value of the light emitting power P of the sea 11 increases from PAV to PHu v, so the pin photodiode 11
Through the 7 to PC function, the laser emission power P decreases to the value of PAV, and the laser drive current IF decreases in the direction indicated by the arrow.

On the other hand, since the power supply voltage supplied to the high frequency oscillation circuit 8 by the integrator circuit 10 gradually rises, the sinusoidal high frequency current shown in FIG. /E I Hi (directly to 51")
Rir□. When the light emitting power of the sea 11 increases due to the superposition of this high frequency current, the DC bias current decreases by J in the ΔPC loop, and the light emitting power of the sea 11 (in the case of no high frequency superimposition, It will be held at a value of '31.

In addition, when making a Q judgment for "Rake", the previous one is 1.
It is desirable that the focusing servo system of the navigation circuit 14 performs day focus control to maintain one objective lens within a predetermined eye focus area.

In order to perform this day focus control, it is sufficient to determine whether or not the sum total of the optical daylight signals; i signal is within a predetermined differential A-casun 1 range. In addition, in the state of the objective lens in this predetermined day focus area, pits etc. are not formed on the disk by the light beam focused by the objective lens, and therefore, there is no possibility of any inconvenient serious situation such as destruction of recorded data. This can be prevented from occurring.

The process of the above-described laser life determination method is, for example, as shown in FIG.

Here, the code n is 51 of the counter register in CPIJ9.
Express numbers. As mentioned above, after memorizing the light emitting powers P+, P2, and P3 corresponding to the three 5° currents (f: &I+, I2.13), the process moves to the precharging efficiency calculation routine. This shows a process of calculating efficiency, determining whether it is within a range that can be considered normal, and displaying the determination result.

FIG. 7 is a diagram showing the principle of life determination in the second embodiment.

In the second embodiment, three or more measurement points for the drive current I are prepared. In this case as well, it is determined that the semiconducting laser is not dead only when all of the ratios Wi of the following sections satisfy the relationship of equation (2) above.

((Pi+2 −P i )/(Ii+2 −
T i ) )/((Pi+1-P i
)/ (I'i÷1-Ii))=Ri+1/Ri-W i (i=1~m-2) -(
3) Although this embodiment requires a considerable amount of sampling time due to the large number of samplings, it has the advantage that even local changes in the localization efficiency as shown in FIG. 7 can be reliably detected.

FIG. 8 is a dimensional diagram showing the principle of life determination in the third embodiment.

In this example, measurements are taken once at the time of shipment or when the device is used, and then measurements are taken every other time during use to differentially calculate the degree of change over time. In other words, the 8th
As shown in the figure, four drive currents 11. I2.13. I4
．． (Here, !2-[+=jlt, I cow-I3 =, 0
2) Rayleigh output P1. P2, P3, P
4, and the ratio W1=(h2/fJ2)/(h1/fJ
1) (Here, one g r't = h+, P4-
1'3=h2 > wo performance G'JLTJ3. This is me [
Store it in the ROM in the S10 and run it on the J3. During actual use, the laser output P+' for four driving currents 1+ and 12.13°I4 is similarly shown in FIG.
, P2', P3'.

1] Measure 4' and calculate the ratio W2-(h2'7'ka2
)/(h1', 11) (where P2' - Pl' -
h+', P4'-P3' = h2') (
2[1jC7t6° This is stored in the RAM in the memory 10 and a3 <.

Since these satisfy the following relationship, the CPU 9 determines that the semiconductor laser is not vital.

D=l(W2-Wl)/W1+≦K...(
4) Here, K is any just i Pil. [ ] indicates the degree of change in the d-concentration precharge. According to the third embodiment, it is possible to detect a slight change in the pre-charge efficiency, and the life span can also be determined based on this. In addition, to simplify the demonstration, it is sufficient to go to fJt=, o2.

For example, in the first embodiment, it is determined whether or not the life of the laser diode 5 has deteriorated, and if the laser diode 5 is normal, the high frequency oscillation circuit 8 is caused to oscillate and the high frequency current is applied to the DC bias current on the laser drive circuit 23 side. I will have him supervise.

[Effects of the Invention] As described above, according to the present invention, when determining the lifespan of a radar, the quantization efficiency of Since the judgment is made based on the
It is possible to determine whether the character has 1 characteristic, 1 characteristic, or 1 weakness.

[Brief explanation of drawings]

Figures 1 to 6 relate to the first embodiment of the present invention.
The figure shows a rib [ ] tsuku diagram of the lifespan judgment device IT according to the first embodiment, Fig. 2 shows the structure of an optical disk installed in which the lifespan judgment is performed, and Fig. 3 shows the structure of the optical disk in which the lifespan judgment is performed in the first embodiment. An explanatory diagram explaining the principle of the operation, Figure 4 is a characteristic diagram of the upstream emission power of the laser diode when it deteriorates, and Figure 5 shows the driving current that increases by J3t when high frequency current is applied. A 1° characteristic diagram showing the relationship between light emitting power, Fig. 6 is a flowchart showing the processing block for life judgment in the first embodiment, and Fig. 7 shows the principle of the judgment method in the second embodiment of the present invention. FIG. 8 is an explanatory diagram showing the principle of the determination method of the third embodiment of the present invention. FIG. 9 is a characteristic diagram showing the characteristics of a deteriorated laser diode. FIG. 10 is a diagram showing the characteristics of a deteriorated laser diode. It is a characteristic diagram showing the relationship between the drive current and the light emitting power in the case of ``with tatami mat'' and ``without high frequency heavy''. 1... Optical disk device 2... Disk 3...
Optical pickup 5...Raede diode 7...to CP circuit 8...
・High frequency superimposition oscillation surface path 9...CPLJ 10...Integrator circuit 1
1... Bin photodiode 23... Laser drive circuit 28... Decoder 31.
...Memory 32...Δ/D converter Fig. 2 Fig. 3 Fig. 4 I' l2I3r Fig. 5 In-+ Im-+ ( Fig. 6 Fig. 8

Claims (1)

[Claims] In an optical information recording/reproducing device that irradiates a laser beam onto a recording medium by superimposing a high-frequency current on a DC bias current, A method for determining the lifespan of a laser, characterized in that the lifespan or characteristic deterioration of the laser is determined by detecting the emission power of the laser using only current.