JPH03296643A - Apparatus for detecting astigmatism of optical disk head - Google Patents

Abstract

PURPOSE:To enhance measuring accuracy without receiving the effect of the fluctuation of the output of the beam from semiconductor laser by normalizing the output of the transmitted beam cut by a knife edge on the basis of the monitor current of the semiconductor laser being the monitor of the quantity of the emitted beam from the semiconductor laser. CONSTITUTION:The laser beam emitted from an optical disk head part 30 being an object to be measured is vertically cut by a knife edge part 3 to be incident to a photodetector 5 which in turn outputs the current proportional to the quantity of the incident beam. This current is normalized on the basis of the monitor current of semiconductor laser being the monitor of the output of the beam from the semiconductor laser contained in the head part by a divider circuit 6. Since the output of the beam from the laser changes with the elapse of time by the temp. rise of the laser main body, the time differentiated waveform of the output current of the photodetector 5 also changes with the elapse of time but this change is negated and only the change of a shape duct to the cutting of the laser beam by the edge part 3 is fetched. The output current of the divider circuit 6 is subjected to time differentiation by a differentiation circuit 7 and only the signal of a necessary part is fetched by a sample holding circuit 8.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an astigmatism detection device for an optical disc head, and in particular, a device for automatically detecting astigmatism in an optical disc head when assembling or adjusting the optical disc head. The present invention relates to a device for detecting astigmatism in an optical disk head.

[Prior Art] First, a general optical disk head will be described with reference to the drawings.

FIG. 7 is a configuration diagram of the optical disk head section.

In FIG. 7, the optical disk head section is composed of a semiconductor laser 16 as a light source, a collimator lens 17, a focus servo actuator 18, and a converging lens section 19.

A photodetector for monitoring the amount of emitted light is incorporated in the semiconductor laser 16 (not shown).

Since the optical disk head uses a semiconductor laser as a light source, there is astigmatism in the emitted laser light. Even if the laser beam is made into parallel light using a collimator lens and then converged using a single converging lens section, astigmatism still exists in the converging section, so it is necessary to measure and correct the astigmatism.

Next, a conventional optical disk head astigmatism correcting device will be described with reference to the drawings.

Fig. 8 is a diagram showing an example of a conventional optical disk head astigmatism detection device, Fig. 9 is a configuration diagram of the knife section, and Fig. 1
Figure 0 is a diagram explaining the positional relationship between the knife section and the laser beam, Figure 11 is a diagram of the output waveform of the photodetector, Figure 12 is a diagram of the output current waveform of the differentiating circuit shown in Figure 8, and Figure 13 is a diagram of the output current waveform of the differential circuit shown in Figure 8. 9 is a diagram of an output waveform of the sample and hold circuit shown in FIG. 8. FIG.

In FIG. 8, the optical disc head astigmatism detection device includes a power supply unit 21 that drives a semiconductor laser included in an optical disc head that is an object to be measured, and a controller unit 22 that drives a focus servo actuator of the optical disc head. , a knife section 23 having an angle of 9 degrees that vibrates near the beam waist of the laser beam converged by the optical disk head section perpendicular to the optical axis direction; an oscillator 24 that vibrates the knife section 23;
a photodetector 25 that receives the laser beam that has passed through the laser beam and outputs a current proportional to the amount of received light; a differentiating circuit 26 that differentiates the current output from the photodetector 25 with respect to time; Sample and hold circuit 27 that extracts only the necessary part of the signal
and two rectifier circuits ■-28 and ■-29 that respectively extract a positive side only signal waveform and a negative side only signal waveform from the signal taken out by the sample hold circuit 27, and a signal waveform divided into two. Two comparators ■-30 and ■-31 for determining the peak values of the positive and negative sides of
Two memory circuits that determine and store the position of the convergent lens section when taking the peak value from the controller■-32,■
-33 and two memory circuits on the positive and negative sides■-32゜■-
and a comparator (34) for determining the astigmatism of the object to be measured from the value of the position of the convergent lens section (33).

Next, a procedure for detecting astigmatism of an optical disk head using the optical disk head astigmatism detection device shown in FIG. 8 will be described with reference to FIG.

First, the semiconductor laser 16 of the optical disk head section is caused to emit light by the optical disk head section power supply section 21, and the laser beam is brought into parallel light by the collimating lens 17. Then, the laser beam is converged by a converging lens section 19. The converged laser beam is cut by the knife section 23 perpendicularly to the optical axis direction.

As shown in FIG. 9, the knife portion 23 is connected to the glass plate 4.
5 and a knife pattern portion 46 having a 90 degree angle.

The short axis direction and long axis direction of the laser beam are the Y axis and Y axis, respectively.
When used as an axis, align the four sides of the knife pattern with the X@Y axis, vibrate the knife pattern at an angle of 45 degrees in the direction of the arrow I-1', and Adjust the position of the knife part 23 so that the corner cuts the laser beam. At this time, the knife pattern section 46 sequentially cuts the laser beam from two directions, the short axis direction and the long axis direction, during one stroke. At this time, the laser beam that has passed through the knife section 23 is received by the photodetector 24. The waveform of the current output from the photodetector 24 is as shown in FIG.

Then, the current is differentiated with respect to time by the differentiating circuit 26, and the waveform at that time becomes as shown in FIG.

In Fig. 12, E and F of the E, F, G, and H waveforms are shown.
, G and H current waveforms are the same and have opposite signs. From the signal differentiated by the differentiating circuit, only the necessary part of the signal (in the waveform of FIG. 12, the F and G waveforms) is extracted by the sample and hold circuit 27, and the extracted signal waveform is sent to the rectifier circuit -28 and the rectifier circuit. ■Input to both -29. Among the input signal waveforms, the rectifier circuit ■−
28 outputs only the positive side signal waveform, and the rectifier circuit ■-29
Conversely, outputs only the negative side signal waveform.

The signal waveform output from the rectifier circuit ■-28 is input to the comparator ■-30 and compared with the maximum value up to that point, and if it is larger than the maximum value, the signal waveform is input to the comparator ■-30.
The comparison reference voltage level is reached, and the position of the focus servo actuator 18 at that time is obtained from the controller 2 and stored in the memory circuit 1-32.

Similarly, the signal waveform output from the rectifier circuit ■-29 is input to the comparator ■-31 and compared with the minimum value up to that point. The position of the focus servo actuator 18 at that time is determined from the controller 2 and stored in the memory circuit 1-33.

Then, the controller 2 moves the focus servo actuator 18 of the optical disk head section a certain distance in the optical axis direction, repeats the above steps, and finally the memory ■-32 , the difference in the position of the focus servo actuator 18 stored in the memory 1-33 becomes astigmatism of the object to be measured.

[Problem to be solved by the invention]

The above-described conventional optical disk head astigmatism detection device is affected by fluctuations in the optical output of the semiconductor laser as described below, and has the drawbacks of poor detection accuracy and long detection time.

Astigmatism is measured by measuring the maximum value of the differential waveform of the output current of the photodetector, but the optical output of the semiconductor laser included in the optical disk head, which is the object to be measured, is determined by the temperature rise of the semiconductor laser itself. etc., and the output current of the photodetector also varies accordingly.

Therefore, the output current of the photodetector is likely to be affected not only by changes in shape due to the knife cutting the semiconductor laser beam, but also by fluctuations in the output of the semiconductor laser. The aberration value is also affected by fluctuations in the optical output of the semiconductor laser.

[Means to solve the problem]

The optical disk head astigmatism detection device of the present invention includes a power supply unit that drives a semiconductor laser included in an optical disk head that is a non-measurable object, a controller unit that drives a focus servo actuator of the optical disk head, and an optical disk head. There is a knife part with a 90 degree angle that vibrates near the beam waist of the laser beam focused in the head part perpendicular to the optical axis direction, an oscillator that vibrates the knife part, and a knife part that receives the laser light that does not pass through the knife part. A photodetector that outputs a current proportional to the amount of light it receives;
There is a division circuit that normalizes the current output from the photodetector with the monitor current of the semiconductor laser, a differentiation circuit that differentiates the eight currents of the division circuit with respect to time, and a differentiation circuit that differentiates the current signal of the current signal differentiated by the differentiation circuit. A sample hold circuit takes out only the signal, two rectifier circuits take out only the positive side signal and only the negative side signal from the signal taken out by the sample hold circuit, and the positive side and negative side of the signal divided into two. Two comparators for determining the peak value for each side, two memories for determining and storing the position of the converging lens section when taking the peak value, and two memories for positive and negative sides for determining the position of the converging lens section. and a comparator that determines the astigmatism of the object to be measured from the value.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
Figure 3 is a diagram of the output waveform of the photodetector shown in Figure 1, Figure 3 is a diagram of the output waveform of the differentiating circuit shown in Figure 1, Figure 4 is a diagram of the output waveform of the sample hold circuit shown in Figure 1, and Figure 5 is a diagram of the output waveform of the sample and hold circuit shown in Figure 1. FIG. 6 is a diagram of the output waveform of the rectifier circuit on the positive side, and FIG. 6 is a diagram of the output waveform of the rectifier circuit on the negative side.

In FIG. 1, the optical disk head astigmatism measuring device of this embodiment includes an optical disk head as an object to be measured, a power supply section 1 for driving a semiconductor laser included in the optical disk head as an object to be measured, and an optical disk. A controller section 2 that drives the focus servo actuator of the head section, a knife section 3 having a 90 degree angle that vibrates near the beam waist of the laser beam focused in the optical disk head section perpendicular to the optical axis direction, An oscillator 4 that vibrates the laser section 3, a photodetector 5 that receives the laser light that has passed through the knife section 3 and outputs a current proportional to the amount of received light, and an object to be measured that outputs the current output from the photodetector 5. A divider circuit 6 that normalizes with the monitor current of the semiconductor laser included in the optical disk head.
, a differentiation circuit 7 that differentiates the output current of the division circuit 6 with respect to time, a sample hold circuit 8 that extracts only the necessary part of the signal differentiated by the differentiation circuit 7, and two rectifier circuits, rectifier circuits ■-9 and ■-10, which extract a current signal only on the positive side and a current signal only on the negative side, respectively, from the current signal obtained by
Two comparators to find the peak values of the positive and negative sides of the two divided current signals, comparator■
-11, ■-12, two memory circuits that obtain and store the position of the convergent lens section when taking the peak value from the controller 2, memory circuits ■13, ■-14, and two memories on the positive and negative sides. It is comprised of a comparator (1)-15 for determining the to-be-targeted aberration of the object to be measured from the value of the position of the converging lens section.

A semiconductor laser 16 included in an optical disk head section, which is an object to be measured, is driven by a power supply section 1. Laser light emitted from the semiconductor laser 16 is made into parallel light by a collimator lens 17, converged by a converging lens 19, and emitted from the optical disk head section.

The laser beam emitted from the optical disk head section is cut by the knife section 3 perpendicularly to the optical axis direction. The laser beam that has passed through the knife section 3 enters a photodetector 5. The photodetectors output a current proportional to the amount of incident laser light.

In FIG. 2, the current output from the photodetector 5 is normalized by the dividing circuit 6 with the monitor current of the semiconductor laser 16 included in the optical disk head section which is the object to be measured. The optical output of the semiconductor laser 16 is
Since the current changes over time due to a rise in the temperature of the main body, etc., the time differential waveform of the output current of the photodetector 5, which receives the output as it is, changes over time. Therefore, by normalizing the output current of the photodetector 5 to the monitor current of the semiconductor laser 16, which monitors the optical output of the semiconductor laser 16, the fluctuations are canceled out, and only the change in shape due to the cutting of the semiconductor laser beam by the knife is eliminated. Take it out.

The output current of the divider circuit 6 is time-differentiated by the differentiating circuit 7, and the waveform at that time becomes as shown in FIG.

In Fig. 3, among the waveforms A, B, C, and D, A and B,
The current signal waveforms of C and D are the same and have opposite signs. From the signal differentiated by the differentiating circuit, only the necessary portion of the signal (waveforms B and C in the waveform of FIG. 3) is extracted by the sample-and-hold circuit 8, and the signal waveform at that time becomes as shown in FIG. 4.

The signal waveform taken out by the sample and hold circuit 8 is input to both rectifier circuits -9 and -10. Of the input signal waveforms, the rectifier path (1)-9 outputs only the positive side signal waveform, and the rectified waveform (2)-10 conversely outputs only the negative side signal waveform. Rectifier circuit ■-9 and rectifier circuit ■
The signal waveforms output from -10 are shown in FIGS. 5 and 6, respectively.

The signal waveform output from the rectifier circuit (2)-9 is input to the comparator (2)-11 and compared with the maximum value up to that point. If it is larger than the maximum value, the value is the comparator -11
The comparison reference voltage level is reached, and the position of the focus servo actuator 18 at that time is obtained from the controller and stored in the memory circuit 1-13.

Similarly, the signal waveform output from the rectifier circuit 1-10 is input to the comparator 2-12 and compared with the minimum value up to that point. If it is smaller than the minimum value, the value becomes the comparison reference voltage level of the comparator (1)-12, and the position of the focus servo actuator at that time is determined from the controller and stored in the memory circuit (2)-14.

Then, the controller 2 moves the focus servo actuator 18 of the optical disk head part a certain distance in the optical axis direction, and the above procedure is repeated.

Finally, the difference between the positions of the focus servo actuator 18 stored in the memory circuit ■-13 and the memory circuit ■-14 when the movement of the focus servo actuator 18 is completed is the astigmatism of the object to be measured. become.

〔Effect of the invention〕

As explained above, according to the present invention, by normalizing the transmitted light output cut by the knife with the monitor current of the semiconductor laser, which monitors the amount of light emitted from the semiconductor laser, This has the effect of improving the accuracy of astigmatism measurement without being affected by fluctuations in the optical output of the semiconductor laser.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
Figure 3 is a diagram of the output waveform of the photodetector shown in Figure 1, Figure 3 is a diagram of the output waveform of the differentiating circuit shown in Figure 1, Figure 4 is a diagram of the output waveform of the sample hold circuit shown in Figure 1, and Figure 5 is a diagram of the output waveform of the sample and hold circuit shown in Figure 1. Figure 6 is a diagram of the output waveform of the rectifier circuit on the positive side, Figure 7 is a diagram of the configuration of the optical disk head, Figure 8 is a diagram showing an example of the conventional system, Figure 9 is a diagram of the output waveform of the rectifier circuit on the negative side, The figure shows the configuration of the knife part, Figure 10 shows the positional relationship between the knife part and the laser beam, Figure 11 shows the output waveform of the photodetector, and Figure 12 shows the output of the differentiator circuit shown in Figure 8. A current waveform diagram, FIG. 13, is a diagram of an output waveform of the sample and hold circuit shown in FIG. 8. DESCRIPTION OF SYMBOLS 1... Power supply part, 2... Controller part, 3... Knifetsu part, 4... Oscillator, 5... Photodetector, 6... Division circuit, 7... Differentiation circuit, 8...
・Sample hold circuit, 9... Rectifier circuit■, 10・
... Rectifier circuit ■, 11... Comparator ■, 12...
・Comparator ■, 13...Memory circuit ■, 14・
...Memory circuit ■, 15...Comparator ■, 16
... Semiconductor laser, 17 ... Collimator lens, 1
8...Focus servo actuator, 19...
- Converging lens, 21... Power supply section, 22... Controller, 23... Knifetsu section, 24... Oscillator,
25... Photodetector, 26... Differential circuit, 2
7... Sample hold circuit, 28... Rectifier circuit■
, 29... Rectifier circuit ■, 30... Comparator ■,
31... Comparator ■, 32... Memory circuit ■
, 33...Memory circuit ■, 34...Comparator ■, 35...Glass plate, 36...Knifetsu pattern, 40...Optical disk head section.

Claims (1)

[Scope of Claims] A power supply section that drives a semiconductor laser included in an optical disk head section, which is a non-measurement object; a controller section that drives a focus servo actuator of the optical disk head section; a knife edge section having a 90 degree angle that vibrates near the beam waist of the laser beam perpendicular to the optical axis direction; an oscillator that vibrates the knife edge section; and a receiver that receives the laser beam that has passed through the knife edge section. a photodetector that outputs a current proportional to the amount of current; a division circuit that normalizes the current output from the photodetector with a monitor current of the semiconductor laser; a differentiation circuit that differentiates the output current of the division circuit with respect to time; and the differentiation circuit. a sample-and-hold circuit that extracts only a predetermined portion of the current signal differentiated by the current signal; and two rectifier circuits that extract only the positive side signal and only the negative side signal from the signal extracted by the sample-and-hold circuit. , two comparators for determining the peak values of the positive and negative sides of the two divided signals, and two memories for determining and storing the position of the converging lens section when taking the peak value, and a comparator for determining astigmatism of the object to be measured from the position values of the converging lens sections of the two positive and negative memories, and detects astigmatism of the optical disk head. Astigmatism detection device.