JPH042939A - Detecting apparatus of astigmatism of optical disk head part - Google Patents

Abstract

PURPOSE:To shorten the measuring time of astigmatism and to improve the measuring accuracy by so constituting the apparatus as to include a power source part, a controller part, a knife edge part, a photodetector, a differential circuit, a sample hold circuit, two rectifier circuits, two comparators, two memories and a comparator. CONSTITUTION:A power source part 1 drives an optical disk head part 30 and a semiconductor laser included in the head part 30. A controller part 30 drives an actuator. A knife edge part 4 vibrates a laser light converged by the head part 30. A differential circuit 7 differentiates a signal from a photodetector 6 with time, and a sample hold circuit 8 takes out only a signal of a necessary part. Rectifier circuits 9, 10 take out only a positive current signal and a negative current signal from the necessary signal, respectively. A peak value of each current signal is obtained by comparators 11, 12. The position of a convergent lens part at the peak value is obtained by memory circuits 13, 14 from the controller 3. A comparator 15 obtains the astigmatism of an object to be measured from the position of the convergent lens part.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an optical disk head astigmatism detection device, particularly for automatically detecting astigmatism of an optical disk head during assembly and adjustment of the optical disk head. The present invention relates to an optical disk part astigmatism detection device.

[Common technology]

Generally, the configuration of the optical tisf head section is as shown in FIG.

The optical disk head section shown in FIG. 7 is composed of a semiconductor laser 16 as a light source, a collimator lens 17, a focus servo actuator 1-8, and one converging lens.

Since the optical disk head uses a semiconductor laser as a light source, it is necessary to measure and correct the astigmatism of the laser beam emitted diagonally.

[Conventional technology]

A conventional optical disk head astigmatism detection device consists of a power supply unit that drives a semiconductor laser included in the optical head, which is a non-measurable object, a manual stage that moves the optical disk head, and a laser beam focused on the optical disk head. A knife section with 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 section, and a current that receives the semiconductor laser light that has passed through the knife section and is proportional to the amount of light received. It consists of a photodetector that outputs a current, a differentiation circuit that differentiates the current output from the photodetector with respect to time, and an oscilloscope that allows you to view the waveform of the differential signal that is time-differentiated by the differentiation circuit.

FIG. 8 is a block diagram showing an example of a conventional optical disk head astigmatism detection device.

The optical disk head astigmatism detection device shown in FIG. 8 includes a power supply section 20 for driving a semiconductor laser included in an optical disk head section 31- which is an object to be measured, a manual stage 21- for moving the optical disk head section 31-, an oscillator 23 that vibrates the knife section 22, an oscillator 23 that vibrates the knife section 22; A photodetector 24 receives the passed laser light and outputs a current proportional to the amount of received light, a differentiating circuit 25 differentiates the current with respect to time, and the differentiating circuit 25 converts the waveform of the time-differentiated differential signal. Includes an oscilloscope 26 for viewing.

Detection of tombstone aberration in the optical disc head section is performed as follows.

First, the semiconductor laser 16 of the optical disk head section 31 is caused to emit light using the power supply for the optical disk head section, and the laser light is made into nearly parallel light by the collimator lens]7. Next, the laser beam is converged by a converging lens section. The converged laser beam is cut by the knife section 22 perpendicularly to the optical axis direction.

The knife part is composed of a glass plate 27 and a knife pattern part 28 having an angle of 90 degrees (see FIGS. 9 and 10).

When the short and long axis directions of the laser beam are taken as the X and Y axes, respectively, align the four sides of the knife pattern with the X and Y axes, and move the knife pattern in the direction of the arrow I-Ia, 45 Adjust the position of the knife part 22 so that the laser beam is vibrated at an angle of 100 degrees and cuts the laser beam at the lower right corner of the knife pattern.

At this time, the knife pattern section sequentially cuts the laser beam from two directions, ie, 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 22 is received by the photodetector 24, and the waveform of the current output from the photodetector is as shown in FIG. 1-1. The current is differentiated with respect to time by a differentiating circuit 25, and a waveform as shown in FIG. 12 is displayed on the screen of an oscilloscope 26.

Among the four waveforms E, F, and GH on the positive and negative sides of Fig. 12,
The waveforms of E and H, and F and G are the same and have opposite signs.

Of these, focusing on E and F, the converging lens section is moved in the optical axis direction using the adjustment function of the converging lens section. The difference in the position of the converging lens section when the two waveforms E and F take the maximum value (in absolute value) on the positive side and negative side, respectively, becomes the tombstone aberration of the object to be measured.

[Problem to be solved by the invention]

The above-described conventional optical disk head astigmatism detection device has the drawbacks of poor detection accuracy and long detection time due to the following reasons.

Because astigmatism is measured by looking only at the waveform on the screen of the oscilloscope, it is difficult to judge whether the waveform at that point is at its maximum value, and the measurement takes time. Also, the magnitude of the astigmatism at that point was 7 minutes! In order not to
There is no objective judgment standard, and measurement accuracy varies depending on the operator.

[Means to solve the problem]

The optical disc head astigmatism detection device of the present invention includes: a power supply unit that drives a semiconductor laser included in an optical disc head that is an object to be measured; a controller unit that drives a focus servo actuator of the optical disc head;
A knife part with a 90 degree angle that vibrates near the beam waste I of the laser light that is converged by the optical tisf head part, perpendicular to the optical axis direction, an oscillator that vibrates the knife part, and a laser beam that has passed through the knife part. A photodetector that receives light and outputs a current proportional to the amount of light received;
A differentiation circuit that differentiates the current output from the photodetector with respect to time, a sample-hold circuit that extracts only the necessary part of the current signal differentiated by the differentiation circuit, and only the positive side of the signal extracted by the sample-and-hold circuit. two rectifier circuits that take out the signal waveform of , and the signal waveform of only the negative side, two comparators that find the peak values of the positive and negative sides of the divided signal waveforms, and two comparators that take the peak values. It consists of two memories that calculate and store the position of the converging lens part from the controller at the time of the measurement, and a comparator that calculates the astigmatism of the object to be measured from the position of the converging lens part of the two positive and negative memories. .

〔Example〕

FIG. 1 is a block diagram showing an embodiment of the present invention.

The optical disk head astigmatism detection device not shown in FIG.
The optical disk head section is a non-measurement object, a power supply section 1 drives a semiconductor laser included in the optical disk head section, a non-measurement object, a controller section 3 drives a focus servo actuator of the optical disk head section, and an optical disk head section. a knife section 4 having a 90 degree angle that vibrates near the beam waist of the converged laser beam perpendicular to the optical axis direction; an oscillator 5 that vibrates the knife section;
A photodetector 6 receives the laser beam that has passed through the knife section and outputs a current proportional to the amount of received light; a differentiating circuit 7 that differentiates the signal output from the photodetector with respect to time; A sample-and-hold circuit 8 that extracts only the necessary part of the signal, and two rectifier circuits that extract only the positive current signal and only the negative current signal from the current signal sampled by the sample-and-hold circuit, rectifier circuit■ 9 and rectifier circuit■1
-0, two comparators for determining the peak values of the positive and negative sides of the current signal divided into two, comparator ■11, comparator ■1-2, and a converging lens section for taking the peak value. Memory circuit ■13 that obtains and stores the position of from the controller, and memory circuit ■14.
and a comparator 15 for determining the astigmatism of the object to be measured from the position values of the converging lens portions of the two positive and negative memories.

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 collimated by a collimator lens 17, converged by a single converging lens, and emitted from the optical disk head.

The laser beam emitted from the optical disk head section is cut by the knife section 4 perpendicularly to the optical axis direction.

The laser light that has passed through the knife part is incident on the photodetector 6. The photodetector outputs a current proportional to the amount of incident laser light. FIG. 2 is an example of the current signal waveform.

The current output from the photodetector is time-differentiated by the differentiating circuit 7, and the waveform at that time is as shown in FIG. In FIG. 3, among the waveforms A, B, C, and D, the current signal waveforms A and B, and 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 extracted by the sample and hold circuit is input to both rectifier circuit (2)9 and rectifier circuit (2)10. Of the input signal waveforms, the rectifier circuit (2) 9 outputs only the positive side signal waveform, and the rectifier circuit (2) 10 conversely outputs only the negative side signal waveform.

Rectifier circuit■9. The signal waveforms output from the rectifier circuit 0 are shown in FIGS. 5 and 6, respectively.

The signal waveform output from the rectifier circuit ■9 is the comparator ■
1] and compared with the maximum value up to that point.

If it is larger than the maximum value, the value becomes the comparison reference voltage level of the comparator (2)], and the position of the focus servo actuator (8) at that time is determined from the controller and stored in the memory circuit (11).

Similarly, the signal waveform output from the rectifier circuit [1]0 is input to the comparator [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 (12), and the position of the focus servo actuator at that time is determined from the controller and stored in the memory circuit (2).

Next, the focus servo actuator 18 of the optical disk head section is moved a certain distance in the optical axis direction by the controller 3, and the above procedure is repeated.

Finally, the difference between the position of the focus servo actuator stored in the memory (2) and the memory (2) when the movement of the focus servo actuator] 8 is completed becomes the astigmatism of the object to be measured.

〔Effect of the invention〕

In the optical disk head astigmatism detection device of the present invention, the focus servo actuator is controlled by the controller section.
To detect astigmatism, the output current of the photodetector is differentiated with respect to time to extract only the necessary part of the signal, which is divided into positive and negative sides and the maximum absolute value of each is determined. Aberration measurement time is shortened and measurement accuracy is improved. Furthermore, since the focus servo actuator of the optical tilt head, which is a non-measurable object, is used to move the converging lens, the structure of the apparatus is simplified.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram of the output current of a photodetector not shown in FIG. 1, and FIG. 3 is an output current waveform diagram of the differential circuit shown in FIG. Fig. 4 is an output signal waveform diagram of the sample and hold circuit shown in Fig. 1, Fig. 5 is an output signal waveform diagram of the positive rectifier circuit ■, Fig. 6 is an output signal waveform diagram of the negative rectifier circuit ■, Fig. 7 is a block diagram of the optical disk head section, Fig. 8 is a block diagram without showing a conventional example, Fig. 9 is a block diagram of the knife section, and Fig. 10 explains the positional relationship between the knife section and the laser beam. Figure 11 is the photodetector output waveform diagram, Figure 12 is the output waveform diagram of the photodetector.
The figure is a waveform diagram on the screen of the oscilloscope in FIG. DESCRIPTION OF SYMBOLS 1... Power supply part, 3... Controller part, 4... Knifetsu part, 5... Oscillator, 6... Photodetector, 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 ■, 30... Optical tisf head section. Diagram X Dice

Claims (1)

[Claims] A power supply section that drives the semiconductor laser included in the optical disk head section that is the object to be measured, a controller section that drives the focus servo actuator of the optical disk head section, and a light source near the beam waist of the laser light converged in the optical disk head section. A knife edge section with a 90 degree angle that vibrates perpendicular to the axial direction, an oscillator that vibrates the knife edge section, and a photodetector that receives the laser beam that has passed through the knife edge section and outputs a current proportional to the amount of received light. , a differentiation circuit that differentiates the current output from the photodetector with respect to time, a sample-and-hold circuit that extracts only a predetermined portion of the current signal differentiated by the differentiation circuit, and a positive side of the signal extracted by the sample-and-hold circuit. two rectifier circuits that take out only the negative side signal and only the negative side signal, two comparators to find the peak values of the positive and negative sides of the two divided signals, and a It is characterized by including two memories for determining and storing the position of the converging lens section from the controller, and a comparator for determining the astigmatism of the object to be measured from the position values of the converging lens section in the two positive and negative memories. Optical disk head astigmatism detection device.