JPS6247835A - light pick up - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates particularly to an optical pickup for recording signals on an optical information recording medium (hereinafter referred to as an optical disk) or for reproducing recorded signals. This invention relates to an optical pickup using an optical waveguide.

[Background of the invention]

Conventional optical pickups are assembled using individual parts such as an objective lens, a prism, a semiconductor laser, and a photodetector. In this method, the lower limit of the size of each component is determined from the viewpoint of operability during assembly, positioning accuracy, etc., and a mechanism for mutual position adjustment is also required, making it possible to reduce the size of the optical pickup. Can not. In order to solve this drawback, we have developed an optical waveguide and a focusing grating coupler that acts as a lens.
An optical pickup using FGC (FGC) has been proposed. For example, IEICE Technical Research Report V6L, 84, A 259p.
Reported on p97-104. In order to reproduce the signals recorded on the optical disc using optical pickup, focus control is required to make the optical spot follow the vertical movement of the optical disc, and tracking control is required to make the optical spot follow the eccentricity of the optical disc. is necessary. For this reason, it is customary to configure the optical pickup so that a focus error signal and a tracking error signal can be obtained, but in the conventional example described above, no consideration is given to the specific configuration for obtaining these error signals. In the optical pickup using the optical waveguide shown in the conventional example described above, the tracking error signal can be detected, for example, in
As shown in Japanese Patent No. 12146, a so-called push-pull method is used in which the reflected light from an optical disk is divided into two parts with respect to a straight line corresponding to the center line of the signal track of the optical disk, and a tracking error signal is obtained from the output difference. Especially possible.

On the other hand, the focus error signal can be detected, for example, by
As shown in Japanese Patent No. 110300, approximately half of the reflected light is focused, a photodetector having two light-receiving areas bordering each other is placed at the focus point, and the output signals of the two light-receiving areas are This can be done using the so-called Knifezi method, which obtains a focus error signal from the difference between the two. In this case, the photodetector that detects the focus error signal is placed at the focal point of the reflected light, so it must be placed with high precision with respect to the focal point, which requires conventional measurement components such as lenses and prisms. In an optical pickup that combines the following, it is essential to adjust the position of the photodetector. By the way, in an optical pickup using an optical waveguide, since a semiconductor laser, a photodetector, an FGC, etc. are integrated, it is extremely difficult to adjust the position of the photodetector. As described above, the focus error signal detection method of an optical pickup using an optical waveguide is a method that does not require positional accuracy of the photodetector with respect to the incident light, for example,
The so-called wobbling method disclosed in Publication No. 88306 is suitable, but the above publication does not consider an optical pickup using an optical waveguide.

[Purpose of the invention]

An object of the present invention is to provide an optical pickup using an optical waveguide that employs a focus error signal detection method that does not require high positional accuracy for a photodetector.

[Summary of the invention]

In order to achieve the above object, the present invention disposes an electro-optic element whose refractive index changes by applying an electric field in the optical path between the semiconductor laser and the optical path separating means, and A focus error signal is obtained by applying an alternating current electric field to slightly vibrate a light spot on an optical disk.

[Embodiments of the invention]

Hereinafter, details of the present invention will be explained with reference to embodiments shown in the drawings.

FIG. 1 is a perspective view showing an embodiment of an optical pickup according to the present invention. Laser light emitted by a semiconductor laser 2 mounted on a base 1 is guided to an optical waveguide 3 on the base 1, passes through an electro-optical element 4, is converted into a parallel beam by a collimator lens 5, and passes through a beam splitter 6. After that, FC;C
7, the light is focused onto an optical disk 8. The reflected light from the optical disk 8 is converted into a parallel beam by the FGC 7, reflected by the beam splitter 6, which is a means for separating the reflected light, and is incident on the photodetector 9. The photodetector 9 is composed of two light receiving areas 9h and 9c divided into two by a boundary line 9α that optically corresponds to the center line of the signal trunk 8α of the optical disc 8. In the above configuration, the information signal 11 recorded on the disk 8 is obtained from the sum of the output signals of the light receiving areas 9b and 90, and tracking is performed using the push-pull method described above from the difference between the output signals of the light receiving areas 9b and 9c. An error signal 10 is obtained. Next, detection of the focus error signal will be explained.

The oscillator 15 outputs a sinusoidal AC signal. The AC signal is amplified by the amplifier 14 and supplied to the electro-optical element 4, and an AC electric field is applied to the electro-optical element 4. Here, the electro-optical element 4 is LiNbO2゜LiTaJ, Ea2Na
Ferroelectric material such as Nh5J5 or GaAs + (?
It is a semiconductor such as dS, and its refractive index changes by applying an electric field. The electro-optical element 4 is a semiconductor laser 2
Since it is placed in the divergent optical path between the electro-optical element 4 and the collimator lens 5, when the refractive index of the electro-optical element 4 changes, the FGC 7
The position of the focused light spot in the optical axis direction changes. This situation will be explained with reference to FIG. In FIG. 2, the equal optical path length between the semiconductor laser 2 and the collimator lens 5 (
Optical path length in air) l is here, l, two optical waveguides 3
refractive index t: refractive index lI of the electro-optical element 4: distance between the semiconductor laser 2 and the collimator lens 5! , : is the length of the electro-optical element 4. When an electric field is applied to the electro-optical element 4 and its refractive index becomes 42', the above-mentioned isolateral optical path length becomes l'.

As a result, the light spot focused by the FGC 7 moves a in the optical axis direction.

δ= (I!-/') X (-L!-)"
f31f weight Here, C: Focal length of collimator lens 5 fx: FG
Since an alternating current electric field is applied to the focal length electro-optical element 4 of c7, FGC
The position of the light spot υ focused by 7 in the optical axis direction also changes in an alternating current manner. Here, in FIG. 1, the sum of the output signals of the photodetector 9 is input to the envelope detector 15. The output signal of the envelope detector 15 and the output signal of the oscillator 13 are synchronously detected by a synchronous detector 16, and the output signal and the output signal of the oscillator 13 are added together by an adder 17 to obtain the output signal. The high-frequency component is removed by a low-pass filter 18, and a focus error signal 12 can be obtained as a result.

Here, since the optical detector and output device 9 are arranged in the parallel beam of reflected light, it is clear that the positional accuracy thereof does not require higher precision than the above-mentioned Knifezi method.

Next, focus control using the focus error signal 12 obtained as shown in FIG. 1 and tracking control using the tracking error signal 10 will be explained using FIGS. 1 and 3. FIG. 3 shows focus control of an optical pick amplifier according to the present invention.

This is an example of a drive device suitable for performing tracking control. The optical pickup shown in FIG. 1 is fixed to a heat sink 21. The heat sink 21 radiates heat from the semiconductor laser 2.

The heat sink 21 has a drive coil 22 in the X direction, which is perpendicular to the optical disk surface, and a Y direction drive coil, which is in the radial direction of the optical disk.
Directional drive coils 25,24 are fixed. Furthermore, the heat sink 21 has a parallel plate spring 25 that can be displaced in the Y direction.
One end of α, 25b is fixed, and the other end is connected to one end of parallel plate springs 26α, 26b which are movable in the X direction. The other ends of the parallel plate springs 26a and 261r are fixed to the base 27. Permanent magnets 28 and 29 are yokes 30 and 3, respectively.
1 and constitutes a magnetic circuit together with the yoke 32. X direction drive coil 22 and Y direction drive coil 23.2
A portion of each of 4 is disposed in the magnetic air gap of the above-described magnetic circuit. Here, the focus error signal 12 obtained as shown in FIG. 1 is input to the focus control circuit 33, and its output current is supplied to the X-direction drive coil 22, thereby moving the optical pickup 20 in the X-direction and performing focus control. It will be done. Further, by inputting the tracking error signal 10 to the tracking control circuit 34 and supplying its output current to the Y-direction drive coils 23 and 24, the optical pickup 20 moves in the Y-direction and tracking control is performed.

〔Effect of the invention〕

As explained above, in the optical pickup according to the present invention, an electro-optical element whose refractive index is changed by an electric field is arranged in the optical path between the semiconductor laser and the FGC, and an alternating current electric field is applied to the electro-optical element to generate the FCC. In order to obtain a shift focus error signal using the so-called wobbling method, which changes the position of the focused light spot in the optical axis direction, the photodetector can be placed in the parallel optical path of the reflected light. High precision is not required for placement.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing the configuration of an optical pickup according to the present invention, FIG. 2 is a diagram for explaining that a light spot moves in the optical axis direction, and FIG. 5 shows an example of an optical pickup driving device. FIG. 2... Semiconductor laser 3...
...... Optical waveguide 4 ...... Electro-optical element 7 ...
...Condensing grating coupler 9...
・・・・・・To the photodetector Otsu′, ゝ. Representative Patent Attorney Masaru Ogawa (1 son) Pa (2 figures)

Claims (1)

[Claims] In an optical pickup for reproducing an information signal recorded on an optical information recording medium, or recording an information signal on an optical information recording medium and reproducing the recorded information signal,
At least a semiconductor laser, an optical waveguide that guides the light emitted from the semiconductor laser, a condensing grating coupler that is provided on the optical waveguide and condenses the laser light in the waveguide to the outside, and a condensing grating coupler that condenses the laser light from the optical disk to the semiconductor. A separating means for separating the laser from the optical path connecting the condensing grating coupler, a photodetector for detecting the reflected light from the separated optical disk, and a photodetector disposed in the optical path between the semiconductor laser and the separating means to apply an applied light. It is characterized by comprising an electro-optical element whose refractive index changes according to the alternating electric field and causes the spot of the laser beam focused on the optical information recording to vibrate slightly in the optical axis direction. optical pickup.