JPH04176031A - Optical recording and/or reproducing device - Google Patents

Abstract

PURPOSE:To increase working speed, and to improve accuracy by changing the state of polarized light by an electrical means when a recording layer composed of an optical recording material is irradiated with polarized light and information is recorded or information is reproduced. CONSTITUTION:P waves 11 branched by a first polarization beam splitter 1 are projected to a second polarization beam splitter 2, and S waves 12 are projected to an electro-optic element 4 through a mirror 3. The reflectivity of the electro-optic element 4 is changed by applied voltage, a phase shift is generated in light projected in response to applied voltage, and applied voltage is controlled by a polarization varying signal 18 determining the state of polarization. Consequently, S waves 12 passed through the electro-optic element 4 have a phase shift to P waves 11 in response to applied voltage, and are projected to the second polarization beam splitter 2 through a mirror 5. As a result, P waves 11 and S waves 12 are synthesized by the second polarization beam splitter 2, and light 15 under the state of polarization corresponding to the phase shift is acquired. Accordingly, working speed is increased, and accuracy is improved.

Description

[Detailed description of the invention] (b) Industrial application field The present invention relates to an optical recording and/or reproducing device.

(b) Prior Art Recently, research on the use of 7 otochromic materials in the recording layer of media has been actively conducted. Such 7 otochromic materials have properties such that when irradiated with light of a predetermined wavelength, the molecular structure changes due to a photochemical reaction, and the optical properties for light with a specific wavelength change in accordance with the structural change of the molecule. have. Furthermore, when irradiated with light of another predetermined wavelength, the changed molecular structure returns to its original structure.

When a recording layer in which an otochromic material is dispersed in a non-oriented manner is irradiated with linearly polarized light, only molecules corresponding to the orientation of the polarization plane of the linearly polarized light mainly cause a photochemical reaction. As a result, among the molecules dispersed in the recording layer, only specific molecules exhibit their molecular structure relative to other molecules (occurrence of anisotropy), making it difficult to record information. can. The above anisotropy (
Depending on the type of optical anisotropy, the following information recording or reproducing methods have been proposed. For example, information is recorded by irradiating the recording layer with linearly polarized light having a predetermined wavelength to cause a difference in absorbance, and polarized light having a specific wavelength is applied to the recording layer for recording or non-recording. There is a known recording/reproducing method that takes advantage of the fact that the absorption of different types of data is different. In addition, information is recorded by causing birefringence in the recording layer using linearly polarized light having a predetermined wavelength, and by irradiating polarized light with little absorption by the recording layer, the transmitted or reflected light is used to record information on the recording layer. A recording/reproduction method is known in which the reproduction is performed by detecting the presence or absence of birefringence. Furthermore, in the above-mentioned recording/reproducing method, a method has been proposed in which crosstalk is reduced by recording, reproducing, and recording/reproducing adjacent tracks using mutually orthogonal linearly polarized light.

A conventional example will be described below with reference to the drawings.

FIG. 6 is a diagram showing an optical system of a recording/reproducing apparatus according to a conventional example.

In the figure, (200) is a disk-shaped recording medium. The recording medium q4) has a recording layer (201) on a transparent substrate (201).
203) is formed, and further the recording layer (203) is formed.
A reflective layer (202) made of AI or Au or the like is formed thereon.

In the conventional example, as the photochromic material contained in the recording layer (203), photochromic materials such as flukyto-based, diallylethyne-based, spiropyran-based, etc. can be used. The recording layer (203) contains a photochromic material in a non-oriented state without oriented molecules. When such a medium is irradiated with linearly polarized light of a wavelength that is absorbed by the photochromic material,
Among photochromic materials, there is a high probability that a specific molecule will cause a photochemical reaction depending on the polarization plane of this linearly polarized light. Therefore, when the recording layer (203) is scanned with the linearly polarized light, a recording portion having an optical anisotropy direction corresponding to the polarization plane of the linearly polarized light is formed.

The recording method will be described below.

A recording incident light beam having linearly polarized light emitted from a first light source (21) such as an Ar ion laser (for example, λ=3
60 nm) is converted into a pulse beam by a beam modulator (22) that modulates the intensity of the recording incident light beam according to the information signal, and then rotates the direction of the polarization plane of the linearly polarized light of the recording incident light beam. The light is incident on the 1/2 wavelength plate (23). The half-wave plate (23) rotates the polarization direction of the linearly polarized light of the recording incident light beam by 90 degrees by rotating the direction of its neutral axis by 45 degrees. Thereafter, the objective lens (2) is passed through the dichroic mirror (24).
5) and is focused by the objective lens (25) onto the recording layer (203) of the recording medium (ZEN!2). While the first light source (21) is being driven in this manner, the recording medium (200) is relatively moved in a predetermined direction by the disk drive device (301), and the beam modulator (22) is used to adjust the recording incidence to the recording medium (200). By modulating the light beam according to the information, a recording track having an optical anisotropy direction corresponding to the polarization plane of the linearly polarized light of the incident recording light beam is formed on the recording layer (203). The recording tracks are arranged concentrically. The recording track is formed mainly by a photochemical reaction of molecules in the recording layer (203) that are arranged in a specific direction according to the polarization direction of the linearly polarized light of the recording incident light beam.

The direction of the neutral axis of the half-wave plate (23) is rotated by mechanical means, so that the polarization direction of the linearly polarized light of the recording incident light beam converged on the recording layer (203) is aligned with the adjacent track. perpendicular to each other.

As shown in FIG. 7, the recording track formed in this way has a specific optical anisotropy direction (indicated by the diagonal line in the figure) using the polarization plane path of the linearly polarized incident recording light beam. have That is, adjacent recording tracks (A) (B) (
C) have mutually orthogonal optical anisotropy directions. At this time, the optical anisotropy direction is generally defined as the direction in which the difference in absorbance is large for recording and reproducing light. In addition, when birefringence is large, it is desirable that the optical anisotropy direction coincides with the polarization direction (polarization plane) of the incident recording light beam.

As shown in FIG. 8, information is reproduced in a recording layer (203) made of a non-oriented photochromic material. ), and the absorbance of linearly polarized light having an angle θ with the polarization plane of the linearly polarized light is at the angle θ with respect to the recording layer (203) irradiated with linearly polarized light. It is done using different things depending on. That is, when the optical anisotropy direction of the recorded track and the polarization direction of the linearly polarized light match, a large reproduction output can be obtained; This method takes advantage of the fact that when the polarization directions of the beams do not match, the reproduction output decreases.

The information reproduction method will be described in detail below.

A second light source (26) such as a He-Ne laser shown in FIG.
) (for example, λ=633 nm). Reproduction is performed by scanning each recording track with an incident light beam emitted from a wavelength of λ=633 nm. The intensity of the incident light beam emitted from the second light source (26) is set to be sufficiently small so that each recording layer (203) does not react with the incident light beam, and the new incident light beam has linear polarization. are doing. The emitted incident light beam is sent to a beam splitter (27)
The light passes through and enters the 1/2 wavelength plate (28). Said 1
The /2 wavelength plate (28) is rotated for each recording track so that its optical anisotropy direction coincides with the polarization plane of the linearly polarized incident light beam. After that, Daikuro, Tsukumira (2
4) and the recording medium (≦
4) The recording layer (203) is irradiated. The incident light beam is then reflected onto the reflective layer (202). The reflected incident light beam passes through the objective lens (25), dichroic mirror (24), half-wave plate (28), beam splitter (27) and lens (29) to the sensor (30).
The light is received by Thus, the sensor (30) outputs an electrical signal modulated according to the information held in each recording track.

The above-mentioned 1/2 wavelength plates (23) and (28) are connected to a disk rotation synchronization circuit (300) that generates a disk rotation synchronization signal, and rotate their neutral axes for each track.

Note that a method similar to the above is also used for recording and reproducing depending on the presence or absence of birefringence.

(c) Problems to be Solved by the Invention However, in the above-mentioned optical recording and reproducing method, rotation of the polarization plane of linearly polarized light was achieved by mechanically rotating a 1/2 wavelength plate. Therefore, recording and playback can be performed at high speed.
Moreover, it was difficult to realize this with high precision.

In this way, in conventional optical recording and reproducing devices, the polarization state of light is 1/
Changes are made by mechanically rotating a two-wave plate, a quarter-wave plate, etc., and there are problems with high speed and accuracy of operation.

(d) Means for solving the problem In view of the above problem, optical recording is performed in which the state of polarization is switched when recording and/or reproducing information by irradiating a recording layer made of an optical recording material with polarized light. The recording and/or reproducing apparatus for a medium is characterized in that the state of polarization is changed by electrical means.

Furthermore, when recording and/or reproducing information by irradiating a recording layer made of an optical recording material with polarized light, an optical recording medium recording and/or reproducing apparatus that switches the state of polarization may be used. The polarization state is changed by means for splitting the light into two components, means for causing a phase difference between one of the components and the other component, and means for recombining the two components having the phase difference. do.

(e) According to the present invention, the polarization state is changed by:
Since it is an electrical means or a means for generating a phase difference, only a minute change is generated in the optical path difference between the two components, so it is possible to improve the speed ratio and precision of the operation.

(F) Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Linearly polarized light is represented by the electrical combination of two orthogonal electric field vector components having angles of 45 degrees and 145 degrees with respect to the polarization plane of the linearly polarized light. The phase difference between the two orthogonal components is M×π (M: integer). Therefore, by changing the phase difference, the plane of polarization of the linearly polarized light is rotated,
Furthermore, the linearly polarized light can be changed into elliptically polarized light and circularly polarized light.

That is, the phase of at least one of the orthogonal components is shifted by L×π (L: an odd number) to obtain the phase difference (M±L
)Xπ, linearly polarized light orthogonal to the above linearly polarized light can be obtained. FIG. 1 shows a diagram in which the phase of the X component is converted into linearly polarized light by π using a polarization state converter that changes the polarization state. Further, by shifting the phase difference by L×π/2, the linearly polarized light can be changed to circularly polarized light.

Furthermore, circularly polarized light is also represented by two orthogonal electric vector components. Therefore, it is possible to change the polarization state to another one using the same method as for the linearly polarized light described above.

FIG. 2 shows a polarization state conversion device according to a first embodiment of the present invention.

In the figure, (decoy) is a polarization state converter. (1) is the first
It is a polarizing beam splitter that splits the incident linearly polarized or circularly polarized light (10) into a P wave component (11) and an S wave component (11).
2) is set so that the intensities are equally divided.

This setting is possible by the arrangement of the first (Ei optical beam splitter (1)), and if the light incident on the first polarizing beam splitter (1) is linearly polarized light, a half-wave plate ( This can be easily realized by adjusting the plane of polarization using a polarizing beam splitter (not shown).Of the P waves (11) and S waves (12) of equal intensity split by the first polarized beam splitting/Z-splitting (1), The P wave (11) is incident on the second polarizing beam splitter (2), while the S wave (12) is incident on the electro-optical element (4) via the mirror (3).

The refractive index of the electro-optical element (4) changes depending on the applied voltage, causing a phase shift in the incident light depending on the applied voltage. The applied voltage is controlled by a polarization direction changing signal (18) that determines the polarization state. The S wave (12) that has passed through the electro-optical element (4) passes through the electro-optical element (
4) has a phase shift (including a phase difference based on the optical path difference between the P wave and the S wave) with respect to the P wave (11) according to the voltage applied to the second polarized light via the mirror (5). The beam is incident on the beam splitter (2). As a result, P wave (11) and S wave (
12) are combined by the second polarizing beam splitter (2),
Light (15) having a polarization state corresponding to the phase shift is obtained. .

Note that the electro-optical element (4) is located at the mirror (3).
and mirror (5), but also between P wave (11) and 5 (12).
) If the optical path is branched into waves, the same effect as above can be obtained. For example, the polarization state may be changed by causing a phase shift in the P wave (11).

In addition, two electro-optical elements are used to generate P waves (11) and S waves (
12) may be configured to cause a phase shift.

Therefore, in the polarization state conversion device of the first embodiment as described above, in order to cause a change in the polarization state of linearly polarized light or circularly polarized light using electrical means, the change in the polarization state is performed at high speed and This can be done with high precision.

A second embodiment of the present invention will be described below.

FIG. 3 shows a polarization state converter according to a second embodiment.

Incidentally, the same parts as in the first embodiment are given the same reference numerals, and the explanation thereof will be omitted.

In the figure, (palan) is a polarization state conversion device. (4o) is a mirror having reflective surfaces (41) and (42). mirror(
40) is attached with a piezoelectric element (50). The piezoelectric element (50) is displaced by an applied voltage to move the mirror (40) (arrows indicate the direction of movement in the figure).
. Therefore, the optical path length of the S wave (12) generated by being split by the first polarizing beam splitter (1) changes, and a phase shift is generated in accordance with the applied voltage. Note that in the above, the piezoelectric element (5o) is attached to the mirror (4o), but the first piezoelectric element (5o) is attached to the mirror (4o).
The phase shift may be generated by attaching it to the polarizing beam splitter (1) or the second polarizing beam splitter (2).

Therefore, in the polarization state conversion device of the second embodiment as described above, the polarization state can be changed at high speed and with high precision, similarly to the polarization state conversion device of the first embodiment.

Next, a third embodiment of the present invention will be described.

4 and 5 are diagrams showing a recording optical system of a recording/reproducing apparatus according to a third embodiment.

Incidentally, the same parts as in the conventional example, the first embodiment, and the second embodiment are given the same reference numerals, and the explanation thereof will be omitted.

FIG. 4 is a diagram in which the first embodiment of the present invention is applied to a conventional recording optical system.

When the incident light beam of linearly polarized light is irradiated onto the recording layer (203), the polarization state conversion device q4) described in the first embodiment is used to Rotates the direction of linearly polarized light. The polarization direction of the linearly polarized light is rotated based on a polarization direction changing signal (18) that determines the polarization direction. In addition, the optical system in FIG. 4 includes the polarization state converter 1 (
100-) was used, however, the polarization state converter (palette) described in the second embodiment may also be used, as shown in FIG.

In the third embodiment, the polarization state conversion device described in the first and second embodiments was used in the recording optical system of an optical recording and reproducing device, but it is possible to use it in the reproducing optical system. it is obvious.

As mentioned above, the optical recording device of the third embodiment as described above rotates the polarization direction of linearly polarized light by 90 degrees using a polarization state conversion device that uses electrical means, so that the speed and precision of recording can be increased. can be achieved.

Further, a fourth embodiment is shown in FIGS. 9 and 10. In this embodiment, an EO (Electro-Optical) element (such as that disclosed in "New Ceramics J (1990), page 31, page 79" published by Optronics Co., Ltd.) is used.
60) to rotate the plane of polarization by 90°. FIG. 9 shows the configuration and operation of such an EO element (60). In the figure, (61) is a crystal body with a neutral axis orientation of birefringence in the X-axis direction or y-axis direction, and (62) (62) is an electrode plate for applying a voltage in the X-axis direction to this crystal body. It is. Linearly polarized light whose traveling direction is in the Z-axis direction is incident on the crystal (61) so that its polarization plane has an angle of 45° with respect to the neutral axis direction (X-axis direction, y-axis direction). urge

Such light is divided into an electromagnetic component Ex in the X-axis direction and an electromagnetic component Ey in the y-axis direction, but due to the birefringence of the crystal (61), as the light passes through the crystal (61), the electromagnetic component Ex A phase difference occurs between and Ey.

Therefore, the polarization state of the light after it passes through the crystal body (61) can be changed compared to the polarization state before it enters the crystal body (61). Here, the phase difference between Ex and Ey can be adjusted by the biaxial thickness of the crystal (61). In this embodiment, the thickness of the crystal (61) is set so that the light transmitted through the crystal (61) becomes linearly polarized light.

In such a state, when a voltage is applied between the electrode plates (62) (62), the refractive index of the crystal (61) with respect to the electromagnetic component Ex changes. The amount of change in the refractive index changes depending on the applied voltage. When the refractive index changes in this way, the phase difference between Ex and EV changes accordingly, thereby making it possible to change the polarization state of the light after passing through the crystal (61). In this embodiment, the applied voltage is set so that the polarization planes of the light transmitted through the crystal body (61) are orthogonal before and after the voltage is applied.

FIG. 1O shows an embodiment using such an EO element. In the figure, (70) is a 2/1 wavelength plate that converts the linearly polarized light from the light source (21) so that its polarization plane is at an angle of 45° with respect to the neutral axis of the crystal (61) of the EO element (60). It is arranged so that it can be made incident so as to have a . The EO element (60) receives the polarization direction conversion signal (18) which is the voltage mentioned above.
is selectively applied. Depending on the presence or absence of such applied voltage,
The polarization planes of the light transmitted through the EOX element (60) can be made orthogonal as described above.

According to this embodiment, the polarization plane of light can be easily changed by 90° without splitting and recombining the optical paths as in the previous embodiment. For this reason, in the previous embodiment, accurate position adjustment of the optical components (optical axis alignment, etc.) was required, but in this embodiment, this is not necessary, and the number of parts can be reduced, so the equipment can be easily adjusted. It is also possible to reduce the size of the device.

In this embodiment, the magnitude of birefringence of the EO element is controlled by the presence or absence of the applied voltage; however, the magnitude of the birefringence of the EO element is not limited to this. ) The magnitude of birefringence of the EO element may be controlled. Further, as another element in which the magnitude of birefringence can be electrically controlled in this way, an element using liquid crystal as a crystal can also be used. In such a case, the liquid crystal molecules are aligned in one direction by applying a voltage, and thus birefringence occurs in this direction.

It should be noted that the polarization state changing device of the present invention is not limited to the above-mentioned optical recording device, but it is clear that it can be used in optical recording devices, magneto-optical recording devices, etc. that utilize a method of changing the polarization state of polarized light. It is. Further, the present invention is not limited to the above example, and any other elements and devices that can electrically convert the polarization state can be used.

(G) Effects of the Invention Therefore, according to the present invention, since the polarization state of light is changed by electrical means or by the means for creating a phase difference, the optical path difference between the two components is changed by a minute amount. Since the polarization state is simply generated, the polarization state can be converted at high speed and with high precision. Therefore, an optical device equipped with the above means can operate at higher speeds, have higher precision, and be smaller in size.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing changes in polarization state according to the present invention,
FIG. 2 shows a polarization state conversion device according to a first embodiment of the present invention,
FIG. 3 shows a polarization state conversion device according to a second embodiment of the present invention,
4 and 5 relate to a third embodiment of the present invention, in which FIG. 4 is a diagram showing a recording optical system in an optical recording/reproducing apparatus, and FIG.
The figure is a diagram showing another recording optical system in the optical recording/reproducing apparatus. 6 to 8 relate to a conventional example; FIG. 6 is a diagram showing an optical system in an optical recording/reproducing apparatus, FIG. 7 is a conceptual diagram of a recording track, and FIG. 8 is a diagram showing absorbance. 9th
10 and 10 are diagrams showing a fourth embodiment of the present invention. (1)...first polarizing beam splitter, (2)...
Second polarizing beam splitter, (4)... Electro-optical element, (50)... Piezoelectric element, (60)... EO element,
(wear) (slow,)...Polarization state conversion device.

Claims (3)

[Claims] (1) When recording and/or reproducing information by irradiating a recording layer made of an optical recording material with polarized light, an optical recording medium recording and/or reproducing apparatus that switches the state of polarization, A recording and/or reproducing device for an optical recording medium, characterized in that the state is changed by electrical means. (2) The optical recording and/or recording device according to claim 1, wherein the electrical means includes an element whose birefringence changes in magnitude by applying a voltage, and means for applying a voltage to this element. playback device. (3) When recording information and/or reproducing information by irradiating a recording layer made of an optical recording material with polarized light, in an optical recording medium recording and/or reproducing device that switches the state of polarized light, the polarized light is The polarization state is changed by means for branching the light into two components, means for creating a phase difference between one of the components and the other component, and means for recombining the two components having the phase difference. A recording and/or reproducing device for optical recording media.