JPS6093649A - Method for removing noise in optical pickup of semiconductor laser - Google Patents

Abstract

PURPOSE:To offset a noise component and to prevent reduction of SN ratio from by detecting a part of light radiated from a semiconductor laser by a detector, extracting a noise signal and applying its phase-reversed signal to an information signal. CONSTITUTION:In an optical system of an optical pickup, laser light reflected by a beam splitter 2 is used to obtain a signal including a noise component, detected by a detector 7 and photoelectrically converted to obtain a noise signal. Information signal light including the same noise component is photoelectrically converted by a detector 6 and the information signal and the noise signal are inputted to a differential amplifier 9 to offset the noise component. If the band of the differential amplifier 9 is expanded, noises from low frequency to an audio/ video band can be sharply reduced. A unit 10 shows an amplifier.

Description

[Detailed description of the invention] Production? 2. Field of Application The present invention relates to a method for removing noise from a semiconductor laser optical pickup used in the field of optical information processing for digital audio disks (DAD), optical disk files, and the like.

Conventional structure and its problems In recent years, semiconductor lasers have established a firm position as light sources for DAD and optical disk pickups due to their small size, light weight, high efficiency, and high reliability. As a laser, it is possible to narrow down to a minute spot, and it is a semiconductor laser with a single transverse mode, and the astigmatism difference of the laser beam is a few microns? A performance of n or less is required.

This (p na 1" - full power") bends in the underwater direction at the P-N junction of the 1'1 electric core laser laser diode 1) i + l
) This can be realized by having a structure in which the active layer has a cloth and makes the active layer an all-optical waveguide. This is usually called a four-wave refractive index semiconductor laser, and in this type of laser, the transverse mode is a single mode, and the longitudinal mode is also a single mode.

Now, regarding all examples of optical pickups for DAD, a typical optical system is shown in FIG. 1, and problems when using a refractive index waveguide type semiconductor laser as a light source will be described.

In Fig. 1, the laser beam emitted from the semiconductor laser 1 is completely transmitted through the beam splitter 2, becomes a parallel beam by the collimator lens 3, and is transmitted to the objective.
'The light is focused on the isk surface 5. The laser beam Fi containing the information reflected by the bits on the disk is again aimed at the object.
The beam is reflected by the beam splitter 2 passing through the collimator lens 3 and enters the detector 6, where it is photoelectrically converted and taken out as an information signal. A part of the information signal light that has entered the beam splitter 2 (usually a half mirror with 5% transmission and 50% reflection) at these points ll and li returns to the semiconductor laser 1 again. The ratio of fil) j'M light to the total emitted light from the semiconductor laser t'2 depends on the beam exit angle, lens NA (open 10), disk reflectance, etc., but is usually between 0.1% and 1. It is about %.

However, the waveguide laser has good spectral unity and its coherent length is considerably longer than the distance between the laser 1 and the disk 5 of the pink amplifier as shown in Figure 1. If such feedback light exists, the noise of the semiconductor laser light will increase significantly due to the interference effect. This is called return optical noise, and when it occurs, the S/N of the information signal decreases, potentially causing a bit error. An example of such noise is shown in FIG. This is done by keeping the optical output of the semiconductor laser 1 constant.
The output of Dichiku 6 was observed using an oscilloscope.

Purpose of the Invention In view of the above-mentioned drawbacks of the conventional art, the present invention has been developed to eliminate the noise component IJ contained in the information signal even if optical noise is generated back in the semiconductor laser.
SUMMARY OF THE INVENTION To achieve this object, the semiconductor laser optical pickup noise removal method of the present invention provides a method for removing noise in a semiconductor laser optical pickup that prevents a reduction in S/N by completely canceling out the noise emitted from a semiconductor laser. The noise signal is received by some of all the detectors, the noise signal is taken out, the phase is reversed, and the signal is added to the information signal to cancel out the noise component.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below.
FIG. 3 is a diagram illustrating a noise removal method according to an embodiment of the present invention. Optical pickup optical system C ↓ Same as Figure 1 (゛[
and use the same number. Combined with the rise of Nagasaki /1/
In order to obtain a signal, a laser beam that is deflected by the beam splitter 2 is used, which is received by all detectors and photoelectrically converted into a noise signal sound (r). The information signal υ and the noise (liυ total I) are photoelectrically converted by the information transmission light rt detector containing the same noise group 13 as this J[, and by manually adding the noise group 13 to 9, the noise group/ J) wo can be offset.

By widening the band of differential amplification A::9, it is possible to significantly reduce noise from low frequencies to audio/video bands. Note that 1o is the amplification g.

FIG. 4 shows the effect of noise reduction by the method of this implementation ++U.

Here, a mirror device with the same reflectance is used instead of the disk 6, the semiconductor laser 1 is driven with a constant output, and the differential amplifier 9
The output was observed using an oscilloscope.

X with the output of detector 7: The signal output when no movement is performed is the waveform on the left side of Figure 4. There is noise with an amplitude of 2 shades, but differential amplification is performed to completely cancel out the noise. The noise amplitude was 0.1% or less, and the S/N was improved by 26 dB.

Next, an embodiment of a song according to the present invention will be described with reference to drawing f:.

FIG. 5 is a diagram showing a method for removing semiconductor laser optical pickup noise in an embodiment of the candy of the present invention. In FIG. 6, 7 is a detector glued around the window 13 on the top surface of the seal 11-container 12 of the semiconductor laser element, which detects the intensity of the emitted laser light and sends its output to the APC circuit 1.
1, the total power supplied to the semiconductor laser element A P
C (Automatic Power Control
), and the laser light that is reflected from the disk 5 and contains information is reflected by the beam splitter 2 and is input to the differential amplifier 9 together with the output of the incident detector 6, where the above-mentioned implementation is performed. As in the example,
Noise components are canceled out.

As described above, according to this embodiment, the detector 7
Since it also serves as a detector for PC operation failures, noise can be removed with a simple configuration.

Effects of the Invention As described above, the method of the present invention converts a portion of the semiconductor laser light into gold photoelectrically during optical pink-up to produce a noise signal sound.4. H
F, by increasing the differential of this and the information signal, 1
All of the optical noise can be canceled out to a large extent, and its practical effects are excellent.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the operation of a conventional semiconductor laser optical pickup, FIG. 2 is a diagram showing an output signal waveform when the pickup system of FIG. 1 is used, and FIG. 3 is a diagram showing a semiconductor laser in an embodiment of the present invention. A diagram showing a noise removal method for a laser optical pickup, FIG. 4 is a diagram showing an output signal waveform when the pickup barrel shown in FIG. 3 is used, and FIG. FIG. 3 is a diagram showing a noise removal method. 1...Semiconductor laser, 2...Beam splinter, 3...Collinor 1゛lens, 4...River...
・Objective lens, 5... Disk, 6...
Detector, 7...Detector, 8...
・Power supply, 9...Differential amplification g, 10.Amplifier, 11...APC circuit, 12.Seal/Customer base, 1
3...Top window. Name of agent: Patent attorney Toshio Nakao (written by one person)
1 mouth WA3 diagram δ / Figure 4

Claims (2)

[Claims] (1) 10) A part of the emitted light from the 1-digital laser is received by a first photoelectric conversion element, and the electric signal reflected from the disk surface is converted by the first photoelectric conversion element. By adding the reflected light of the semiconductor laser to the electrical signal photoelectrically converted by the second photoelectric conversion element, the noise group /A'4 is canceled out, and the reflected light is ・1 signal A1; υ S/ The noise removal power of the pickup, which is characterized by improving the N ratio. (2) The first photoelectric transformer 15- and J' are bonded to the emitted light on the inner surface of the 1'Noq Laser Moon'I'6 and around the 6 application window. Particularly ii'I Claim 1: A method for removing noise from a single electric core laser optical pickup;