JPH06230222A - Phase compensation plate and optical pickup for magneto-optical disk system using the phase compensation plate - Google Patents

Abstract

PURPOSE:To provide the phase compensation plate capable of offsetting a phase difference or setting an arbitrary value with a simple constitution at a low cost and slight space. CONSTITUTION:This phase compensation plate H is formed by sticking two sheets of quartz plates H1, H1 having a prescribed thickness difference to each other in such a manner that their optical axes H1a, H2a are perpendicular to each other. This phase compensation plate H is provided with an axis H3 of rotation for changing an angle of inclination with incident light. The phase difference of P polarized light and S polarized light is about 12 deg. if the thickness difference between the quartz plates H1 and H2 is set at, for example, about 2.5mum. The phase difference changes from about 12 deg. to -24 deg. when the angle with the incident light is changed from 0 deg. to 10 deg. by rotating around the rotary shaft H3. Namely, the phase compensation plate H capable of changing the phase difference in such a manner that 0 phase difference is included in the range of the change is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase compensating plate and an optical pickup for a magneto-optical disk system (hereinafter simply referred to as an optical pickup) for writing and reading in a magneto-optical disk device using the phase compensating plate. In particular, it is particularly effective for an optical pickup mounted in an evaluation device for inspecting a magneto-optical disk, because high accuracy is required for the phase difference of the optical system.

[0002]

2. Description of the Related Art A conventional optical pickup manages a phase difference between P-polarized light and S-polarized light (hereinafter, simply referred to as PS phase difference or phase difference) at a component level, and a component having a small phase difference is used. It has been selected and used. In addition, when trying to compensate for the generated phase difference, select and insert a fixed phase difference element having an opposite sign and a close value,
We have dealt with it by offsetting the phase difference. For the purpose of positively varying the phase difference, a Babinet-Soleil phase difference compensator was used, but it was large and expensive.

As a general device for performing phase compensation, there is an Allinghouse compensator (two quartz plates of the same thickness bonded with their crystal axes perpendicular to each other). Considering that the plate is used for compensating the PS phase difference of the optical pickup, the phase difference can be compensated only in one plus or minus direction depending on the inserting direction.

[0004]

The demand for minimizing the PS phase difference of an optical pickup at a low cost has been increasing day by day as the performance of not only the magneto-optical disk evaluation apparatus but also the general apparatus has been improved. . The method of pressing down at the component level results in a poor yield and eventually costs. For example, even if one optical element called a beam splitter is taken, it is difficult to assure manufacture with a phase difference of 3 degrees or less. However, the performance required as an optical pickup may be within a phase difference of 2.5 degrees. Also, it is necessary to prepare many types of methods for inserting a phase compensation plate with a fixed phase difference for compensation.
Not very realistic. Moreover, the Babinet-Soleil phase compensator is out of the question not only in cost but also in size.

Further, if the Aeringhaus compensator is used for compensating the phase difference in the optical pickup, it can be compensated in only one direction depending on the inserting direction. In order to change the phase difference, the direction in which the inserting direction is further changed is used. It is necessary to change the angle in the vertical plane. For this reason, in order to perform the compensation quickly, it is necessary to prepare at least two positive and negative phase difference compensating alling house compensators. There is.

The present invention uses a phase compensator and a phase compensator capable of canceling the phase difference or setting an arbitrary value with a simple structure, at low cost and in a small space, as compared with the above method. An optical pickup is provided.

[0007]

In order to achieve the above object, the present invention changes the phase difference between P-polarized light and S-polarized light and changes the phase difference 0 according to the tilt angle with respect to incident light. The phase compensating plate is made by laminating two crystal plates having different thicknesses so as to have optical characteristics such that the crystal axes are perpendicular to each other.

Further, according to the present invention, a phase compensating plate capable of changing an inclination angle with respect to incident light is provided between a light receiving portion for receiving reflected light from a magneto-optical disk and a reproducing system for converting the reflected light into an electric signal and outputting the electric signal. And the phase compensator has optical characteristics that change the phase difference between the P-polarized light and the S-polarized light according to the tilt angle and include the phase difference 0 within the range of change. An optical pickup for a magneto-optical disk system is adopted.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described with reference to the drawings. 1 is an exploded perspective view and an assembled perspective view of a phase compensating plate of the present invention, FIG. 2 is a graph showing optical characteristics of the phase compensating plate, and FIG. 3 is a block diagram of an optical pickup using the phase compensating plate. It is a figure.

First, the structure of the phase compensating plate of the present invention will be described with reference to FIG. 1. The phase compensating plate H includes, for example, two crystal plates H1 and H2 having a thickness difference (about 2.5 μm). Are laminated so that their optical axes H1a and H2a are perpendicular to each other. The phase compensation plate H is provided with a rotation axis H3 for changing the inclination angle of the phase compensation plate with respect to the incident light.

Next, referring to FIG. 2, the optical characteristics of the phase compensation plate are shown. In the figure, the vertical axis represents the phase difference and the horizontal axis represents the tilt angle with respect to the incident light. If the thickness is set to 2.5 μm as described above, at an angle of 0,
The initial phase difference is about 12 degrees, and the rotation axis H3 (see Fig. 1)
When the angle with respect to the incident light is changed by rotating about, the phase difference can be changed from about 12 degrees to −24 degrees, that is, the phase difference 0 can be changed. A phase compensator capable of changing the phase difference so as to fall within the range of change can be obtained.

Here, in order to understand the characteristics of the optical characteristics of the phase compensating plate of the present invention, the optical characteristics of the above-mentioned conventional Aering house compensating plate will be described. In the case where the rotation axis H3 is rotated to change the phase difference, the optical characteristic does not change the phase difference from plus to minus or vice versa, and only the plus side or the minus side does not occur. Only one of the two phase differences changes. Therefore, when used to compensate for the phase difference on either side with a single Allinghouse compensator, for example, from the change in the phase difference only on the plus side to the change in the phase difference only on the minus side. In order to change it, the insertion direction of the optical pickup into the device must be inserted by rotating the compensating plate 90 degrees clockwise or counterclockwise as viewed from the compensating plate on the right side of FIG. 1, for example. This means that if one conventional Allinghouse compensator is used for compensating the phase difference on either the plus side or the minus side, it is necessary to provide two rotary shafts, and the Allinghouse compensation is also required. This means that the structure of the optical pickup on which the plate is set will be quite complicated.

Instead of this, when a quick compensation is to be performed with a simple structure, an plus-side phase difference compensation Allinghouse compensation plate and a minus-side phase difference compensation Allinghouse compensation are provided. At least two of the plates need to be prepared.

Next, an example of an optical pickup using a phase compensation plate will be described with reference to FIG. The present invention can be applied to any appropriate optical pickup, and is not particularly limited to the configuration of the optical pickup. In the figure, A is a laser, B is a collimating lens, C is a beam shaping pyrism, D, E, and J are beam splitters, F is a rising mirror, and G is an objective lens. In the figure, H represents the above-mentioned phase compensator, I represents a half-wave plate, K1 and K2 represent RF signal detectors, K3 represents servo signal detectors, and L represents a differential signal amplifier. , M are magneto-optical disks.

Next, the operation of this optical pickup will be outlined. The light from the laser A, which is a light source, is collimated lens B, beam shaping prism C, beam splice AD, beam splitter E, rising mirror F, objective lens G. And is applied to the magneto-optical disk M through the. The light reflected by the magneto-optical disk M is incident on the beam splitter E through the objective lens G and the raising mirror F. The light incident on the beam splitter E is split into two light beams, and one light beam from the beam splitter D is detected by the servo signal detector K3.
Then, a servo signal is obtained by the servo signal detector K3.

The other light split by the beam splitter E is made incident on the phase compensator H, is phase-compensated by the phase compensator H as will be described later, and is then made incident on the half-wave plate I of the reproducing system. Then, it is incident on a beam splitter J, and is split into two lights by this beam splitter J.
It is incident on the F signal detectors K1 and K2. The respective signals obtained from the RF signal detectors K1 and K2 are input to the differential signal amplifier L and compared to obtain an RF output.

Now, in the above-mentioned optical pickup, if the phase difference is 10 degrees before inserting the phase compensating plate H, the phase is canceled if the phase compensating plate H gives a phase difference of -10 degrees. I can compensate. From the graph of FIG.
It can be seen that the phase difference of degrees can be achieved by setting the tilt angle to about 7.8 degrees. Therefore, the tilt angle of the phase compensator with respect to the incident light is set to about 7.
Set to 8 degrees. If the same optical pickup is used and the phase difference is to be set to 5 degrees, the compensation amount may be set to -5 degrees. Therefore, if the tilt is adjusted to be about 6.9 degrees and fixed, Good.

Next, the experimental example will be described. Data of the phase difference compensation effect was examined using the optical pickup having the above-mentioned configuration. As a result, the phase difference before compensation was 5.6 degrees, but the phase difference after compensation was 1.1 degrees. The phase difference before compensation was 5.9 degrees, but the phase difference after compensation was 1.2 degrees.

In the optical pickup of the evaluation apparatus, the phase difference must be suppressed within 2.5 degrees in the standard, but these values sufficiently satisfy this standard.

[0020]

As described above, according to the present invention,
By changing the tilt angle with respect to the incident light, the phase difference becomes 0
It is possible to obtain a phase compensating plate having optical characteristics in which the phase difference changes so as to include in the range of change. Further, by using the phase compensating plate, an optical pickup having a simple structure and a highly accurate phase compensation with a simple operation can be obtained.

[Brief description of drawings]

FIG. 1 is an exploded perspective view and an assembled perspective view of a phase compensation plate of the present invention.

FIG. 2 is a graph showing optical characteristics of a phase compensation plate.

FIG. 3 is a block diagram of an optical pickup using a phase compensation plate.

[Explanation of Codes] A laser H phase compensation plate M magneto-optical disk

Claims (3)

[Claims] 1. A thickness difference is provided so as to have optical characteristics that change the phase difference between P-polarized light and S-polarized light according to the tilt angle with respect to incident light and include a phase difference of 0 within the range of change. A phase compensator made by laminating two crystal plates so that their crystal axes are perpendicular to each other. 2. A phase compensating plate capable of changing an inclination angle with respect to incident light is arranged between a light receiving portion for receiving reflected light from the magneto-optical disk and a reproducing system for converting the reflected light into an electric signal and outputting the electric signal, The phase compensator has P polarization and S polarization depending on the tilt angle.
An optical pickup for a magneto-optical disk system, which has optical characteristics such that a phase difference with polarized light is changed and a phase difference of 0 is included in a change range. 3. The optical pickup for a magneto-optical disk system according to claim 2, wherein the phase compensating plate is made by bonding two crystal plates having different thicknesses so that their crystal axes are perpendicular to each other. An optical pickup for a magneto-optical disk system.