JPS6341618Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention uses a single photodetector to control the output of a semiconductor laser, which is a light source of a pickup device that reproduces optical information, and to detect an optical signal.

As shown in FIG. 1, a conventional pickup for reproducing optical information receives the output of a semiconductor laser 2 attached to a support member 1 with an output monitoring photodetector 3 attached to this support member 1. The semiconductor laser 2 is controlled by an automatic output power control circuit 4, and
The output of the semiconductor laser 1 is focused on a recording material 7 by a condensing lens 6 via a half prism 5, and the reflected light is guided by the half prism 5 to a photodetector 8 for signal detection, and an electric signal is converted by an amplifier 9. is extracted as.

Therefore, two photodetectors are required, 8 for signal detection and 3 for monitoring the output of the semiconductor laser 2, and these need to be adjusted separately. , etc., the error rate in reading the recording material 7 with reduced reflectance increases, and the structure becomes expensive.

In order to eliminate such drawbacks, the present invention uses a single photodetector to monitor the output of the semiconductor laser and detect the signal, and separates these using a circuit to obtain the signal output and detect the output of the semiconductor laser. The object of the present invention is to obtain an inexpensive pickup device that can obtain stable signal output by controlling a laser.

An embodiment of the present invention will be described with reference to FIGS. 2 to 8. A semiconductor laser 12 is mounted on a support member 11.
and a photodetector 13 are attached, and an attenuating material 14 is applied to the support member 11 so that the amount of incident light from the semiconductor laser 12 is appropriate.

On the other hand, the output of the semiconductor laser 12 is bent by a predetermined angle by an optical deflection splitting element 15, and focused onto the recording material 7 by a condensing lens 16. The optical deflection splitting element 15 is connected to the semiconductor laser 12.
The laser beam is deflected by a predetermined angle in the opposite direction to the direction of deflection when it is directly emitted, and is guided to the photodetector 13, and the focal point of the image at this time is shifted by the positional deviation between the semiconductor laser 12 and the photodetector 13. It is spreading.

Therefore, as for the shape of the photodetector 13, when performing one-beam tracking, for example, a concentric circle detector is used for focus detection, and a push-pull method is used for tracking detection.

That is, a photodetector as shown in FIG.
Attached to the rear of the photodetector 2, it receives light whose focal point is widened by the difference in distance between the semiconductor laser 12 and this photodetector 13, balances the intensity on the concentric circle of the photodetector 13, and calculates the amount of deviation from that value. The focus error signal is obtained as follows. That is, when the focus is close, the amount of light incident on the center increases, and when the focus is far, the amount of light incident on the outer periphery increases.

Furthermore, tracking obtains the error amount by push-pull on the right and left of the concentric circle. For example, by lowering the bias signal for the right and left detectors in the inner core, the frequency characteristics of these detectors are lowered in the high range, which is necessary for controlling the semiconductor laser. value can be obtained.

Alternatively, by using a concentric circle with a large outer diameter, the frequency characteristics can be lowered in the high range and a value necessary for controlling the semiconductor laser can be obtained.

The output of the photodetector 13 obtained in this way is amplified by the first stage amplifier 17, and separated by the frequency filter 18 into a signal frequency band, a servo frequency band, and a low frequency band for laser driving, which are connected to a signal demodulation circuit. 19. Focus and tracking servo circuit 2
0, sent to the laser drive circuit 21.

This frequency filter can be made even simpler by appropriately selecting the shape of the detector and the bias current.

The low frequency band sent to the laser drive circuit 21 is
This is a low band that is not affected by the recorded signal band, and therefore the driving current of the semiconductor laser is not modulated by the recorded signal. Although the driving current changes, this relationship is set as shown in FIG. 7, for example.

In FIG. 7, P is an amount of light that does not exceed the maximum rating of the semiconductor laser 12, and Q is an amount that is greater than the minimum amount of light that can obtain the required signal-to-noise ratio.

In this case, the total amount of light incident on the photodetector 13 is:
As shown in FIG. 8, the amount R of light directly incident from the semiconductor laser 12 and the amount S of light reflected from the recording material 7 are always constant.

In addition, when using the three-beam method for tracking detection, the photodetector becomes as shown in Figure 5, and in this case, the tracking error is (output of A) - (output of B)
Since (output of A)+(output of B) is not significantly modulated, the desired result can be obtained by controlling the drive current of the semiconductor laser to keep it constant.

In FIG. 5, C indicates a tracking error output, D indicates a semiconductor laser output setting circuit, and E indicates a semiconductor laser drive output.

Further, in the above embodiment, the semiconductor laser 12 and the photodetector 13 are placed directly opposite each other, but this is changed to an oblique position, and the amount of light from the semiconductor laser 12 is changed depending on the position and angle. It is also possible to determine the ratio of the amount of light from the recording material 7.

Furthermore, the ratio of the amount of light incident on the photodetector 13 to the amount of reflected light from the recording material 7 can be determined by changing the amount of light incident on the photodetector 13 depending on the angle of this portion with respect to the semiconductor laser 12 without using the attenuation material 14.

As mentioned above, according to the present invention, since a single photodetector is used to control the output of the semiconductor laser and detect the signal current, the photodetector is If the amount of input signal decreases, the output of the semiconductor laser is increased accordingly, making it possible to always obtain a high-quality signal and preventing damage to the semiconductor laser due to excessive output. It is possible.

Furthermore, by placing the photodetector near the semiconductor laser and sharing the support member, adjustment becomes easier, and if a sufficiently large signal is obtained, it acts to lower the output of the semiconductor laser.
This improves the reliability of the laser element, and since only one photodetector is required, the cost is low.

[Brief description of the drawings]

Figure 1 is a diagram of the principle of a conventional optical pickup device.
Fig. 2 is a principle diagram of one embodiment of the present invention, Fig. 3 is an enlarged view of the semiconductor laser and photodetector portion, Fig. 4 is a front view showing an example of the photodetector, and Fig. 5 is another one. 6 is a conceptual diagram of the electric circuit of the embodiment shown in FIG. 2, FIG. 7 shows the relationship between the amount of reflected light from the recording material and the amount of oscillated light from the semiconductor laser, and FIG.
The figure shows the relationship between the reflectance of the recording material and the incident light on the detector. 7... Recording material, 12... Semiconductor laser, 13
...Photodetector, 15...Light deflection splitting element, 17...
...First stage amplifier, 18...Frequency filter.

Claims (1)

[Scope of utility model registration request] In an optical pickup device that reproduces information by irradiating light emitted from a semiconductor laser onto an information recording medium and detecting the reflected light with a photodetector, the information recording medium is sent to the photodetector together with the reflected light. An optical system is provided that allows direct light from the semiconductor laser to enter without passing through a medium, and at least a low frequency component of the output of the photodetector is driven so that the amount of light incident on the photodetector is constant. 1. A pick-up device characterized by being provided with a frequency filter for transmitting data to a laser drive circuit.