JPH01296440A - Optical pick-up device - Google Patents

Abstract

PURPOSE:To obtain a stable optical pick-up device at a low cost by providing an optical conducting path, which has a branching optical path, and an optical path selecting means between a laser and a polarizing beam splitter, providing an electro- optical crystal between the splitter and a recording medium and impressing an electric field to an electrode. CONSTITUTION:It is independently executed in the respective optical paths that an incoming light is divided into the optical paths in a right side and a left side by a branching optical path 15 of an optical conducting path 14 and polarization is executed concerning respective right and left lights by an electro-optical crystal 16. During this operation, in correspondence to the dislocation quantity of a spot position to be caused by a track error signal, the electric field is impressed to an electrode part 17 of the crystal 16. Thus, the incoming light of one side part is polarized and the adjustment of the spot position is executed. Since the selection of the branching optical path and the control of the impressing electric field to the electrode part is simultaneously processed, the polarization of the light can be executed independently by each optical path and spot moving quantity for tracking servo can be widely decreased. Then, driving can be executed at a low voltage and an actuator for objective lens drive is eliminated. Thus, the compact device can be obtained at the low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical pink-up device that records, reproduces, etc. information by irradiating an optical information recording medium with light emitted from a semiconductor laser.

2. Description of the Related Art An example of a conventional optical pickup device will be described with reference to FIG. The light emitted from the semiconductor laser 1 is collimated by a collimator lens 2, passes through a polarizing beam splitter 3, passes through an objective lens 4, and is irradiated onto a magneto-optical disk 5 as an optical information recording medium. Information is thereby recorded. Further, the return light reflected by the magneto-optical disk 5 passes through the objective lens 4, is reflected by the polarizing beam splitter 3, and then passes through the 1/2 wavelength plate 6.2 lenses 7.8. The beam is split into two by a polarizing beam splitter 9 and guided to a servo optical system 1o.

In this servo optical system]O, the light transmitted through the polarizing beam splitter 9 is detected as a track error signal by the track light receiving element 11, and tracking servo is performed thereby. The reflected light passes through the cylindrical lens 12,
The light is guided to the focus light receiving element 13 and detected as a focus error signal using an astigmatism method or the like, and focus servo is performed based on this signal. In addition, by taking the difference between these two error signals, a playback signal for the magneto-optical disk 5 is obtained, and by taking the sum of both error signals, a playback signal for the optical disk (not shown) is obtained. It has gained.

Problems to be Solved by the Invention In this way, when recording and reproducing on the magneto-optical disk 5 as an optical information recording medium, the focus position shifts due to surface runout of the magneto-optical disk 5 and the track position shifts due to eccentricity. The error signal detected by
Control is performed by attaching it to an actuator (not shown) and driving it two-dimensionally. That is, to perform focus servo, the objective lens 4 is independently displaced in the optical axis direction, and to perform tracking servo, the objective lens 4 is independently displaced in a direction perpendicular to the optical axis.

However, when displacing the objective lens 4 in this way, it is important to ensure that it is hardly displaced in the tangential direction of the track of the magneto-optical disk 5 (direction perpendicular to the optical axis and perpendicular to the tracking direction). Furthermore, it is important that the objective lens 4 is not tilted or tilted during such displacement, that is, that it is moved almost completely in parallel. The reason is that since the objective lens 4 is designed to ensure only axial performance, the occurrence of such inclinations will lead to the occurrence of coma aberration. Therefore, in the conventional device, in order to accurately displace the objective lens 4, it is necessary to create an actuator (not shown) that drives the objective lens 4 with great precision, and it is also necessary to considerably increase the mass of the optical head (not shown). Therefore, there is a problem that the device itself becomes very expensive and large.

Means for Solving the Problems Therefore, in order to solve such problems, the present invention provides an optical waveguide having a branched optical path on the optical path between the semiconductor laser and the polarizing beam splitter. An optical path selection means for selecting one is provided, an electro-optic crystal having an electrode portion is provided on the optical path between the polarizing beam splitter and the optical information recording medium, and an electric field is applied to the electrode portion of the electro-optic crystal to cause the beam to enter the optical information recording medium. A deflection means for changing the direction of deflection of light is provided.

Effect: Therefore, the light emitted from the semiconductor laser, which enters the branched optical path of the optical waveguide, is emitted only from one branched optical path selected by the optical path selection means, so that the optical path is changed. The light is guided to the electro-optic crystal, and the deflection direction of the light is changed according to the magnitude of the electric field applied to the electrode portion by the deflection means, and the light is irradiated onto the optical information recording medium.

In this way, by simultaneously processing the selection of the branched optical path and the control of the electric field applied to the electrode section, it is possible to independently deflect the light for each optical path, thereby making it possible to record optical information for tracking servo. The amount of light spot movement on the medium can be significantly reduced, making it possible to drive at a lower voltage than before, and also to drive the objective lens like before to perform tracking servo. Since there is no need for an actuator for this purpose, an inexpensive and compact device can be obtained.

Embodiment First, an embodiment of the present invention will be described based on FIGS. 1 to 4. Note that the overall configuration of the optical pickup device has been described in the prior art, so it will be omitted here, and the same parts will be denoted by the same reference numerals.

The optical waveguide 14 has two branch optical paths 15, left and right, which branch light.
It is located on the optical path between the semiconductor laser 1 and the polarizing beam splitter 3. Further, an optical path selection means (not shown) is provided for selecting one of the branch optical paths 15 based on the track error signal.

The electro-optic crystal 16 has a thin crystal structure, and comb-shaped electrode portions 17 are provided on the front and back sides thereof. The electro-optic crystal 16 is provided on an optical path between the polarizing beam splitter 3 and the magneto-optical disk 5 as an optical information recording medium. Further, a deflection means (not shown) is provided which applies an electric field to the electrode section 17 and changes the direction of deflection of incident light.

In such a configuration, a method of performing 1 to racking servo will be described. Now, the trunk error signal detected in the two-divided track light receiving element 11 (see FIG. 7) of the servo optical system]
It is assumed that the spot position of the light beam irradiated onto the track (not shown) is shifted to the left from the normal position.

The light emitted from the semiconductor laser 1 passes through the collimator lens 2
After the light is made into parallel light, it enters the optical waveguide 14 and is guided to the branch optical path 15. At this time, since it is known in advance that the position of the spora I~ has shifted to the left based on the track error signal described later, the right branch optical path 15 is selected by the optical path selection means, so that the light is transferred to the right branch optical path. 15
It comes out of the chisel. The light emerging only from this right branched optical path 15 is irradiated onto the right side of the electro-optic crystal 16 via the polarizing beam splitter 3.

The electro-optic crystal 16 has the following characteristics: the Pockels effect, in which the refractive index change is proportional to the first power of the applied electric field strength, and the Kerr effect, in which the refractive index change is proportional to the square of the applied electric field strength. The relationship between intensity and deflection angle is calculated in advance.

Therefore, depending on the amount of deviation of the spot position obtained from the track error signal, the electro-optic crystal 16 is
By applying an electric field to the electrode section 17, the light incident from the right side is deflected, and the spot position is adjusted. Thereafter, the deflected light obliquely enters the objective lens 4 and is irradiated onto the magneto-optical disk 5, so that the spot is irradiated at the original normal position without deviation.

Tracking servo is performed in this way, and the principle of detecting the tracking error signal will be explained below. The 1-rank error signal is detected by the well-known bush-pull method using a track light receiving element 18 as shown in FIG. 3, but the light is deflected by the electro-optic effect of the electro-optic crystal 16. In this case, the return light reflected by the magneto-optical disk 5 does not pass through the same path as the going path, and as a result, in the case of the bush-pull method in which the optical axis is aligned assuming the case where the light is not deflected as described above. will result in an error.

Therefore, as an initial setting, after applying a voltage to the electro-optic crystal 16 to deflect the light, (S,
-32) is stored in advance in a memory (not shown) for each applied voltage. Then, a tracking error signal is detected by comparing this initial setting value with the actually detected value of (Sl-S2), and tracking servo is performed based on this.

Note that the focus error signal is detected by the well-known Naifezi method using a Naifezi prism 19 as shown in FIG. With no focus error signal or track error signal, the value of (Sl-82) in FIG. 4 is stored in advance for each applied voltage in the memory, and this initial setting value is 87.) to detect a focus error signal. Further, as described above, although the deflected light obliquely enters the objective lens 4, the spot diameter is not disturbed by this. This is because, when the optical axis of the objective lens 4 and the surface of the magneto-optical disk 5 are kept perpendicular, the allowable angle of oblique incidence of the objective lens 4 is larger than the optical deflection angle required to perform tracking servo. It is from.

As described above, the branching optical path 15 of the optical waveguide 14 divides the incident light into the left optical path and the right optical path, and furthermore, the electro-optic crystal 16 deflects the left and right beams independently for each optical path. Spot transfer 1! The amount of ll can be reduced by half compared to the conventional one, thereby making it possible to further reduce the applied voltage.

Next, a modification of the above-mentioned embodiment will be explained based on FIGS. 5 and 6. This embodiment is a modification of the electro-optic crystal 16 in the previous embodiment, and the same reference numerals are used for other identical parts.

The electro-optic crystal 21 has a thin fan-shaped crystal structure, and has comb-shaped electrode portions 2 on its front and back sides.
2 are arranged. This electro-optic crystal 21 is located on the optical path between the deflection beam splitter 3 and the magneto-optical disk 5, and in this case, the objective lens 4 and the electro-optic crystal 21 are always maintained at the same distance. In a relationship.

By arranging it in this way, the tracking servo can obtain the same effect as in the embodiment described above. Note that a description of the configuration of the circuit will be omitted here.

Effects of the Invention The present invention provides an optical waveguide having a branched optical path on the optical path between a semiconductor laser and a polarizing beam splitter, and includes an optical path selection means for selecting one of the branched optical paths, thereby combining the polarizing beam splitter and optical information recording. An electro-optic crystal having an electrode part is provided on the optical path between the medium and the electro-optic crystal, and a deflection means is provided to apply an electric field to the electrode part of the electro-optic crystal to change the direction of deflection of the incident light, so that the light emitted from the semiconductor laser is The light incident on the branched optical path of the optical waveguide is emitted only from one branched optical path selected by the optical path selection means, so that the optical path is changed, and the light is guided to the electro-optic crystal. The light is deflected in a different direction depending on the magnitude of the electric field applied to the electrode section by the light deflecting means, and is irradiated onto the optical information recording medium.

Therefore, by simultaneously processing the selection of the branched optical path and the control of the electric field applied to the electrode section, it is possible to independently deflect the light for each optical path. The amount of light spot movement can be significantly reduced, which makes it possible to drive with a lower voltage than before, and it is also possible to drive the objective lens with a lower voltage than before to perform tracking servo. Since no actuator is required,
An inexpensive and compact device can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a simplified plan view of an embodiment of the present invention, Fig. 2 is a plan view of its electro-optic crystal, Fig. 3 is an explanatory diagram showing the principle of detecting a tracking error signal, and Fig. 4 is a focus diagram. An explanatory diagram showing the principle of error signal detection, FIG. 5 is a simplified plan view of a modification of FIG. 1, FIG. 6 is a plan view of the electro-optic crystal, and FIG. 7 is a plan view of a conventional example. It is. ■...Semiconductor laser, 2...Collimator lens, 3...
...Polarizing beam splitter, 4...Objective lens, 5.
・Pa optical information recording medium, 14... optical waveguide, 15.
... Branch optical path, 16... Electro-optic crystal, 17... Electrode section, 21... Electro-optic crystal, 22... Electrode section

Claims (1)

[Claims] The light emitted from the semiconductor laser is made into parallel light by a collimator lens, this parallel light is incident on a polarizing beam splitter, and the light that passes through this is focused by an objective lens and irradiated onto an optical information recording medium to record information. In an optical pickup device that performs tracking servo or focus servo by reflecting the reflected light from the optical information recording medium by the polarizing beam splitter and guiding it to the servo optical system, An electro-optic device comprising an optical waveguide having branched optical paths on an optical path, an optical path selection means for selecting one of the branched optical paths, and an electrode portion on the optical path between the polarizing beam splitter and the optical information recording medium. An optical pickup device comprising: a crystal; and a deflection means for applying an electric field to the electrode portion of the electro-optic crystal to change the direction of deflection of incident light.