JP4878761B2 - Optical head and optical information device - Google Patents

Description

The present invention is an optical head used in the optical information processing or optical communication, and optical information equipment concerns.

  In recent years, a digital versatile disc (DVD) has been attracting attention as a large-capacity optical recording medium because it can record digital information at a recording density about six times that of a compact disc (CD). However, there is a demand for higher-density optical recording media as information capacity increases. Here, in order to achieve higher density than DVD (wavelength 660 nm, numerical aperture (NA) 0.6), it is necessary to shorten the wavelength of the light source and increase the NA of the objective lens. For example, when a blue laser with a wavelength of 405 nm is used and an objective lens with a NA of 0.85 is used, a recording density five times that of a DVD is achieved.

  However, in the above-described high-density optical disk apparatus using a blue laser, the reproduction margin is very strict, so that the quantum noise of the light source becomes a problem. Therefore, an optical head that can perform high-quality reproduction with low noise by suppressing the quantum noise of the semiconductor laser while preventing deterioration of the optical disk and erasing of data by suppressing the disk surface power of the optical disk low is patented It is proposed in Document 1.

  That is, the optical head proposed in Patent Document 1 can solve the following problems.

  That is, the problem is that the quantum noise becomes conspicuous when the power of the light source is reduced during reproduction. In the case of a high-density optical disc apparatus, the spot diameter of the light collected on the optical disc is also very small. Therefore, if the power of the light source is not reduced during reproduction, the light irradiation power per unit area on the optical disc Becomes very large. Therefore, in such a case, the irradiation power of light per unit area on the optical disk becomes very large, and it may happen that the signal recorded on the optical disk is erased during reproduction. The optical head proposed in Patent Document 1 solves such problems, and can accurately record a signal on an optical disk or reproduce a signal recorded on an optical disk with high precision.

  Here, an example of the above-described conventional optical head will be described with reference to the drawings.

  FIG. 11 is a schematic diagram showing the configuration of a conventional optical head. Here, 51 is a light source, 52 is an intensity filter, 53 is a beam splitter, 54 is a collimator lens, 55 is a mirror, 56 is an objective lens, 57 is an optical disk, and 58. Is a multi-lens, and 59 is a photodiode.

  The light source 51 is a GaN-based blue-emitting semiconductor laser that outputs coherent light for recording / reproduction to the recording layer of the optical disk 57. The strength filter 52 is an element on which an absorption film is formed, and is provided so that it can be taken in and out. The beam splitter 53 is an optical element for separating light. The collimator lens 54 is a lens that converts divergent light emitted from the light source 51 into parallel light. The mirror 55 is an optical element that reflects incident light and directs it in the direction of the optical disk 57. The objective lens 56 is a lens that collects light on the recording layer of the optical disk 57. The multi lens 58 is a lens that focuses light on the photodiode 59. The photodiode 59 receives light reflected by the recording layer of the optical disk and converts the light into an electrical signal.

  Next, the operation of the conventional optical head configured as described above will be described. Here, the intensity filter 52 is inserted into the optical path at the time of reproduction, and is out of the optical path at the time of recording. The light emitted from the light source 51 is attenuated because it passes through the intensity filter 52 during reproduction, and is not attenuated because the intensity filter 52 is emitted out of the optical path during recording.

  Next, the light that has passed through the intensity filter 52 (light emitted from the light source during recording) is reflected by the beam splitter 53 and converted into parallel light by the collimator lens 54. The parallel light is reflected by the mirror 55 and collected on the optical disk 57 by the objective lens 56.

  Next, the light reflected from the optical disk 57 is transmitted through the objective lens 56, reflected by the mirror 55, transmitted through the collimator lens 54, transmitted through the beam splitter 53, and condensed on the photodiode 59 by the multilens 58. .

  The photodiode 59 outputs a focus error signal indicating the focused state of light on the optical disc 57 using an astigmatism method, and outputs a tracking error signal indicating the light irradiation position.

  A focus control means (not shown) controls the position of the objective lens 56 in the optical axis direction so that light is always focused on the optical disc 57 in a focused state based on the focus error signal. A tracking control unit (not shown) controls the position of the objective lens 56 so that the light is focused on a desired track on the optical disk 57 based on the tracking error signal.

  Further, the photodetector 59 reproduces information recorded on the optical disc 57.

With such a configuration, the power of the light source can be set to a power at which the quantum noise is sufficiently low, and reproduction can be performed while suppressing the board power to a low power that does not cause deterioration of the optical disk or data erasure. In recording, recording can be performed using the power of the light source as it is.
JP 2000-195086 A

  However, in the optical head configured as described above, a mechanism is required to insert and remove the intensity filter 52, which increases the size of the optical head, so that the optical head can be reduced in size. Absent.

  That is, the conventional optical head has a problem that the optical head cannot be reduced in size.

The present invention has been made in view of such a conventional problem, and the power of the light source is set to a power at which the quantum noise becomes sufficiently low, and the disk surface power is deteriorated or the data is erased. it is suppressed to be able to reproduce the low power does not occur, at the time of recording, it is an object to provide an optical head capable of recording, and the optical information equipment the power of the light source used as it is .

In order to solve the above-described problem, the first aspect of the present invention provides:
A laser light source for emitting laser light;
An objective lens for condensing the laser light emitted from the laser light source onto an optical recording medium;
An optical element disposed between the light source and the optical recording medium, the transmittance of which varies according to an applied voltage ;
A collimator lens that is disposed between the objective lens and the laser light source and converts the laser light emitted from the laser light source into parallel light ;
The voltage applied to the optical element is such that the transmittance of the optical element is lower when the signal is reproduced from the optical recording medium than when the signal is recorded on the optical recording medium. Switching between when recording a signal and when reproducing a signal from the optical recording medium,
And the like toward the center portion of the optical element is the transmittance becomes lower than the peripheral portion of the optical element, the voltage applied to the optical element, the switching et is the region of the optical element,
The optical element is
An electrochromic material layer whose transmittance changes according to the applied voltage;
An electrolyte disposed on one side of the electrochromic material layer;
A first transparent electrode disposed on the other surface of the electrochromic material layer;
A second transparent electrode disposed on a surface of the electrolyte opposite to the electrochromic material layer,
Wherein at least either the first transparent electrode and the second transparent electrode, Ri Oh an optical element having a plurality of electrodes capable of applying a different voltage to the electrochromic material layer,
Wherein the plurality of electrodes, have a second electrode disposed so as to surround the circular first electrode, said first electrode,
The optical element is disposed on the objective lens side with respect to the collimator lens ,
The voltage and the voltage of the second electrode of the first electrode, the transmittance of the portion of the electrochromic material layer corresponding to the first electrode, the electrochromic material layer corresponding to the second electrode in proportions such that lower than the transmittance of the portion of the, which is applied to the electrochromic material layer,
When recording a signal on the optical recording medium, the ratio of the voltage of the first electrode applied to the central portion of the optical element and the voltage of the second electrode applied to the peripheral portion of the optical element;
When reproducing a signal from the optical recording medium, the ratio of the voltage of the first electrode applied to the central part of the optical element and the voltage of the second electrode applied to the peripheral part of the optical element is:
It is an optical head characterized by being equal .
The second aspect of the present invention
In the optical head according to the first aspect of the present invention, the plurality of electrodes further include one or a plurality of concentric electrodes between the first electrode and the second electrode.
The third aspect of the present invention
A laser light source for emitting laser light;
An objective lens for condensing the laser light emitted from the laser light source onto an optical recording medium;
An optical element disposed between the light source and the optical recording medium, the transmittance of which varies according to an applied voltage;
A collimator lens that is disposed between the objective lens and the laser light source and converts the laser light emitted from the laser light source into parallel light;
The voltage applied to the optical element is such that the transmittance of the optical element is lower when the signal is reproduced from the optical recording medium than when the signal is recorded on the optical recording medium. Switching between when recording a signal and when reproducing a signal from the optical recording medium,
And, the voltage applied to the optical element is switched by the region of the optical element so that the transmittance of the central part of the optical element is lower than that of the peripheral part of the optical element,
The optical element is
An electrochromic material layer whose transmittance changes according to the applied voltage;
An electrolyte disposed on one side of the electrochromic material layer;
A first transparent electrode disposed on the other surface of the electrochromic material layer;
A second transparent electrode disposed on a surface of the electrolyte opposite to the electrochromic material layer,
At least one of the first transparent electrode and the second transparent electrode is an optical element having a plurality of electrodes capable of applying different voltages to the electrochromic material layer,
The plurality of electrodes include an elliptical first electrode and a second electrode disposed so as to surround the first electrode,
The optical element is disposed on the laser light source side with respect to the collimator lens ,
The voltage and the voltage of the second electrode of the first electrode, the transmittance of the portion of the electrochromic material layer corresponding to the first electrode, the electrochromic material layer corresponding to the second electrode in proportions such that lower than the transmittance of the portion of the, which is applied to the electrochromic material layer,
When recording a signal on the optical recording medium, the ratio of the voltage of the first electrode applied to the central portion of the optical element and the voltage of the second electrode applied to the peripheral portion of the optical element;
When reproducing a signal from the optical recording medium, the ratio of the voltage of the first electrode applied to the central part of the optical element and the voltage of the second electrode applied to the peripheral part of the optical element is:
It is an optical head characterized by being equal .
The fourth aspect of the present invention is
In the optical head according to the third aspect of the present invention, the plurality of electrodes further include one or a plurality of concentric elliptical electrodes between the first electrode and the second electrode.
The fifth aspect of the present invention provides
The optical head according to the first or third aspect of the present invention, wherein the wavelength of the laser light source is from 390 nm to 420 nm.
The sixth aspect of the present invention provides
An optical information apparatus for recording or reproducing a signal with respect to an optical recording medium,
Rotation driving means for rotating the optical recording medium;
An optical head for recording or reproducing a signal on the optical recording medium,
The optical head is an optical information device in which the optical head of the first or third aspect of the present invention is used .

In the present invention, while the power of the light source is set to a power at which the quantum noise is sufficiently low, the disk surface power can be controlled to a low power that does not cause deterioration of the optical disk or data erasure, and reproduction can be performed. , the optical head can be carried out directly using recording power of a light source, and it is possible to provide an optical information equipment.

  Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1)
In Embodiment 1, an example of the optical head of the present invention will be described.

  FIG. 1 is a configuration diagram of the optical head 17 according to the first embodiment. The optical head 17 of Embodiment 1 is an optical head provided with the optical element of the present invention.

  In FIG. 1, 1 is a light source, 2 is a collimator lens, 3 is an optical element of the present invention, 4 is a polarization beam splitter, 5 is a first condenser lens, and 6 is a first lens. 7 is a quarter wavelength plate, 8 is an objective lens, 9 is an optical recording medium, 10 is a cylindrical lens, and 11 is a second condenser lens. Reference numeral 12 denotes a second photodetector. Here, the condensing optical system includes a collimator lens 2 and an objective lens 8.

  The processing circuit 43 is a circuit that controls the transmittance of the optical element 3 so that the transmittance of the optical element 3 becomes an optimum value at the time of reproduction and recording, and a circuit that controls other optical heads. It is. Details of the processing circuit 43 will be described in detail in a third embodiment to be described later.

  The optical element 3 of the first embodiment is an example of the optical element of the present invention.

  Here, the light source 1 is composed of, for example, a GaN-based semiconductor laser element (wavelength 390 nm to 420 nm), and is a light source that outputs recording / reproducing coherent light to the recording layer of the optical recording medium 9. Since the light source 1 uses a short wavelength from 390 nm to 420 nm, high-density recording can be achieved.

  The collimator lens 2 is a lens that converts divergent light emitted from the light source 1 into parallel light.

  The optical element 3 is an optical element whose transmittance changes according to an external signal, which will be described in detail later.

  The polarization beam splitter 4 has a transmittance of 90% for the linearly polarized light emitted from the light source 1 and a reflectivity of 10%, and also for linearly polarized light in a direction perpendicular to the linearly polarized light emitted from the light source 1. An optical element having a reflectance of 100%.

  The first condenser lens 5 is a lens that condenses the light emitted from the light source 1 and reflected by the polarization beam splitter 4 on the first photodetector 6.

  The quarter-wave plate 7 is an optical element that converts incident linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light.

  The objective lens 8 is a lens that condenses light on the recording layer of the optical recording medium 9.

  The cylindrical lens 10 is a lens that gives astigmatism to the light reflected by the optical recording medium 9 in order to detect the focus error signal by the astigmatism method.

  The second condenser lens 11 is a lens that condenses the light reflected by the optical recording medium 9 onto the second photodetector 12. The first and second photodetectors 6 and 12 receive light and convert the light into electrical signals.

  Next, the operation of this embodiment will be described.

  In FIG. 1, linearly polarized light emitted from a light source 1 enters a collimator lens 2 and is converted from divergent light into parallel light. The converted parallel light is incident on the optical element 3, and the amount of light is attenuated in the case of reproduction, and the amount of light is not attenuated in the case of recording (this will be described in detail later). The light transmitted through the optical element 3 is incident on the polarization beam splitter 4, a part of which is reflected and most of the light is transmitted.

  Here, the reflected light is incident on the first photodetector 6 by the first condenser lens 5, and the first photodetector 6 outputs an electrical signal for controlling the light quantity of the light source 1. To do. The light transmitted through the polarization beam splitter 4 is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 7, and this circularly polarized light is condensed on the optical recording medium 9 by the objective lens 8.

  Next, the light reflected from the optical recording medium 9 passes through the objective lens 8 and is converted by the quarter wavelength plate 7 into linearly polarized light orthogonal to the polarization direction of the linearly polarized light emitted from the light source 1 by the quarter wavelength plate 7, The light is reflected 100% by the polarization beam splitter 4, is given astigmatism by the cylindrical lens 10, and is incident on the second photodetector 12 by the second condenser lens 11.

  The second photodetector 12 outputs a focus error signal indicating the focused state of light on the optical recording medium 9 using the astigmatism method, and outputs a tracking error signal indicating the light irradiation position. In this case, for example, a phase difference method is used for a read-only optical recording medium, and a tracking error signal is obtained by a push-pull method for a recording optical recording medium.

  A focus control unit (not shown) controls the position of the objective lens 8 in the optical axis direction so that the light is always focused on the optical recording medium 9 in a focused state based on the focus error signal. A tracking control unit (not shown) controls the position of the objective lens 8 based on the tracking error signal so that the light is condensed on a desired track on the optical recording medium 9. Information recorded on the optical recording medium 9 is also obtained from the second photodetector 12.

Here, the optical element 3 will be described in detail. FIG. 2 shows a cross-sectional view of the optical element 3. In FIG. 2, 21 is a first glass, 22 is a first ITO film, 23 is a Ni (OH) ₂ film, 24 is a KCl solution, and 25 is a second ITO film. , 26 is a second glass, and 27 is a sealing layer.

On one surface of the Ni (OH) ₂ film 23, a KCl solution 24 is disposed sealed with a sealing layer 27. The first ITO film is disposed on the other surface of the Ni (OH) ₂ film 23. The second ITO film 25 is disposed on the surface of the KCl solution 24 opposite to the Ni (OH) ₂ film 23. A first glass 21 and a second glass 26 are disposed on both sides of the first ITO film and the second ITO film 25.

The first ITO film 22 and the second ITO film 25 of the present embodiment are examples of the first and second transparent electrodes of the present invention, respectively, and the Ni (OH) ₂ film 23 of the present embodiment. Is an example of the electrochromic material layer of the present invention, and the KCl solution of the present embodiment is an example of the electrolyte of the present invention.

  Next, the operation of such an optical element 3 will be described.

Ni (OH) ₂ has electrochromic properties. When electric energy is applied from the outside, Ni (OH) ₂ undergoes a reduction reaction by electrons supplied from the electrolyte, changes from colorless to brown, and absorbs blue light. Further, if no electric energy is applied from the outside, an oxidation reaction occurs between the electrolyte and the color changes from brown to colorless.

Therefore, when a voltage (V1) is applied between the first ITO film 22 and the second ITO film 25, a reduction reaction occurs in the Ni (OH) ₂ film 23, and the optical element 3 absorbs blue light, thereby transmitting the light. When the voltage application is stopped between the first ITO film 22 and the second ITO film 25, an oxidation reaction occurs in the Ni (OH) ₂ film 23, and the optical element 3 has a transmittance of 100%. That is, the transmittance of the optical element 3 changes according to the voltage applied from the outside, and the amount of light transmitted through the optical element 3 changes.

Thereby, the optical element 3 can reduce the transmittance during reproduction and can increase the transmittance during recording. In other words, the optical head according to the first embodiment uses the optical element 3 at the time of reproduction, even though it does not have a mechanism for inserting and removing the intensity filter, unlike the conventional optical head described in the background art. reduces the transmittance, the transmittance can be above the gel at the time of recording. Therefore, the optical head according to the first embodiment can be made smaller than the conventional optical head described in the background art.

  Further, since the liquid KCl solution 24 is used as the electrolyte layer, the optical element 3 can be colored more quickly when a voltage is applied to the optical element 3 than when a solid electrolyte is used.

  Here, changing the transmittance by an external voltage can also be realized by changing the polarization characteristics of incident light. For example, if a certain voltage is applied if the optical element 3 is formed using liquid crystal, the direction of the linearly polarized light of the incident light is maintained, and if a different voltage is applied, the direction of the linearly polarized light of the incident light is different. Using an optical element that can emit linearly polarized light and whose transmittance varies depending on the polarization direction, such as a polarizing beam splitter, it is possible to change the light transmittance. However, since the polarization direction of the light emitted from the light source 1 is rotated depending on the external temperature and the emission power, the transmittance variation using the polarization characteristics is not stable. However, the optical element 3 of the present invention is very stable because it changes the transmittance of the film itself regardless of the polarization characteristics.

When the light source 1 is controlled so that the polarization direction of the light emitted from the light source 1 is stabilized, the polarization characteristic of incident light such as liquid crystal is used as the optical element 3 used in the optical head of the first embodiment. You may use elements, such as a liquid crystal which changes the transmittance | permeability by changing. In short, the optical element used in the optical head of the present invention, transmittance need only be varying Waru element by controlling the voltage to be applied.

  As described above, by using the optical element 3 of the first embodiment for the optical head, the transmittance of the optical element 3 is lowered while setting the power of the light source 1 to a power that sufficiently reduces the quantum noise. Thus, reproduction can be performed with the disc surface power kept at a low power that does not cause deterioration of the optical recording medium or data erasure, and the power of the light source 1 can be achieved by setting the transmittance of the optical element 3 to 100% during recording. It is possible to perform recording using as it is. In addition, since the transmittance is switched by an external electric signal, it is easy to reduce the size of the optical head. Furthermore, when the optical element 3 is configured using a film of an electrochromic material, the transmittance of the film itself is changed, so that it is very stable.

  In the first embodiment, the ITO film 22 and the ITO film 25 have a uniform structure that is not patterned. However, the present invention is not limited to this, and the ITO film 22 and the ITO film 25 are not limited thereto. One of them may be a patterned one having a non-uniform structure.

  By using an ITO film that is patterned and has a non-uniform structure for the optical element 3, in addition to the effect of the first embodiment, the spot diameter of the light to be condensed on the optical recording medium 9 is further reduced. It is possible to obtain a further effect that the recording density of signals to the optical recording medium 9 can be improved.

  FIG. 3 shows an example of an ITO film that is patterned and has a non-uniform structure as an ITO film 60.

  The ITO film 60 includes a first electrode 61, a second electrode 62, and an insulating layer 63. The shape of the first electrode 61 is circular. The insulating layer 63 has a circular shape having a center in common with the first electrode 61, and is disposed so as to surround the first electrode 61. Further, the second electrode 62 is disposed so as to surround the insulating layer 63. That is, the ITO film 60 has a structure in which the insulating layer 63 is disposed around the circular first electrode 61 and the second electrode 62 is disposed so as to surround the insulating layer 63.

  The reason why the first electrode 61 is circular is that the optical element 3 is disposed on the side opposite to the light source 1 of the collimator lens 2 as shown in FIG. That is, the light beam from the light source 1 becomes a circular beam after passing through the collimator lens 2. In order to match this circular beam, the first electrode 61 has a circular shape.

Since the insulating layer 63 is disposed between the first electrode 61 and the second electrode 62, the first electrode 61 and the second electrode 62 are electrically insulated. Therefore, if different voltages are applied to the first electrode 61 and the second electrode 62, the Ni (OH) ₂ film 23 corresponds to the portion corresponding to the first electrode 61 and the second electrode 62. Different voltages are applied to the portions to be applied. As described above, the ITO film 60 includes a plurality of electrodes that can apply different voltages to the Ni (OH) ₂ film 23.

Then, by applying different voltages to the Ni (OH) ₂ film 23 between the first electrode 61 and the second electrode 62, the transmittance when the Ni (OH) ₂ film 23 is colored is spatially changed. It can be distributed so that it is not uniform.

  In FIG. 4, the first electrode 61, the second electrode 62, the ITO film 22, the case where the signal is recorded on the optical recording medium 9 and the case where the signal recorded on the optical recording medium 9 is reproduced. It shows what voltage is applied to the ITO film in which the first electrode 61 and the second electrode 62 of the ITO film 25 are not formed. In the following description, of the ITO film 22 and the ITO film 25, the ITO film on which the first electrode 61 and the second electrode 62 are not formed is referred to as another ITO film.

  Also, each voltage value shown in FIG. 4 is based on another ITO film, and is described as an absolute value of a difference from the potential of the other ITO film.

  At the time of recording, as shown in FIG. 4, a voltage of C volts is applied to the first electrode 61, a voltage of D volts is applied to the second electrode 62, and a voltage of 0 volts is applied to the other ITO films. Apply. During reproduction, as shown in FIG. 4, a voltage of A volt is applied to the first electrode 61, a voltage of B volt is applied to the second electrode 62, and 0 volt is applied to the other ITO films. Apply a voltage of.

  Here, voltages are applied to the first electrode 61 and the second electrode 62 so that A, B, C, and D shown in FIG. 4 satisfy the following relationship.

(Equation 1)
C> D
A> B
C <A
D <B
That is, at the time of recording, since the relationship of C> D is established from Equation 1, the portion of the Ni (OH) ₂ film 23 corresponding to the first electrode 61 is Ni (OH) corresponding to the second electrode 62. ) The applied voltage is larger than the portion of the _two films 23. Accordingly, the portion of the Ni (OH) ₂ film 23 corresponding to the first electrode 61 has a higher degree of coloring than the portion of the Ni (OH) ₂ film 23 corresponding to the second electrode 62, that is, , The transmittance is low.

During reproduction, the number 1 from the A> B holds, towards the portion of the Ni _{(OH) 2} film 23 corresponding to the first electrode 61, Ni _{(OH) 2} film 23 corresponding to the second electrode 62 The applied voltage is larger than that of the portion. Therefore, as in the recording, the portion of the Ni (OH) ₂ film 23 corresponding to the first electrode 61 is colored more than the portion of the Ni (OH) ₂ film 23 corresponding to the second electrode 62. The degree becomes higher, that is, the transmittance becomes lower.

However, since the relationship of C <A is established from Equation 1, the voltage applied to the portion of the Ni (OH) ₂ film 23 corresponding to the first electrode 61 is larger during reproduction than during recording. Therefore, the portion of the Ni (OH) ₂ film 23 corresponding to the first electrode 61 has a higher degree of coloring at the time of reproduction than at the time of recording, that is, the transmittance is lowered. Further, since the relationship of D <B is established from Equation 1, the voltage applied to the portion of the Ni (OH) ₂ film 23 corresponding to the second electrode 62 is larger during reproduction than during recording. Accordingly, the portion of the Ni (OH) ₂ film 23 corresponding to the second electrode 62 is more colored during reproduction than that during recording, that is, the transmittance is low.

Since the first electrode 61, the second electrode 62, and the other ITO film apply a voltage to the Ni (OH) ₂ film 23 during recording and during reproduction as described above, the optical element 3 is used for reproduction. In both time and recording, the transmittance of the central portion is lower than that of the peripheral portion, and the transmittance of each portion of the optical element 3 is lower during reproduction than during recording.

  In FIG. 5A, when voltage is applied to the first electrode 61, the second electrode 62, and another ITO film as shown in FIG. FIG. 5B shows the power distribution of light from the light source 1, and voltage is applied to the first electrode 61, the second electrode 62, and other ITO films as shown in FIG. In this case, the power distribution of the light from the light source 1 after passing through the optical element 3 is shown. 5A and 5B, the horizontal axis indicates the position in the cross section of the light beam from the light source, and the vertical axis indicates the light power. However, FIG. 5A and FIG. 5B are obtained by measuring light during recording.

  Further, the cross section of the light beam from the light source 1 in the optical element 3 has its center coincident with the center of the first electrode 61, and the diameter of the cross section in the optical element 3 of the light beam from the light source 1 is The light source 1 and the collimator lens shown in FIG. 2 etc. have been adjusted.

  As is clear from FIG. 5 (a), the power is maximum at the position c which is the center of the cross section of the light beam from the light source 1 in the optical element 3, and the power decreases as the distance from the position c increases. Yes.

  On the other hand, as is apparent from FIG. 5B, the portion corresponding to the first electrode 61 including the position c that is the center of the cross section in the optical element 3 of the light beam from the light source 1 is shown in FIG. Compared with a), the power is reduced. That is, the power of the light beam that has passed through the optical element 3 has a lower power in the central portion than in the peripheral portion.

  Thus, by reducing the power of the central portion of the light beam that has passed through the optical element 3, the light spot diameter when the light from the light source 1 is condensed on the optical recording medium 9 can be made smaller. I can do it. That is, by using the optical element 3 using the ITO film 60 shown in FIG. 3, the light from the light source 1 can be condensed on the optical recording medium 9 in a narrower range.

  At the time of reproduction, the power of the light that has passed through the optical element 3 as a whole is attenuated to a greater extent than that at the time of recording. The power is greatly attenuated compared to.

  Accordingly, at the time of reproduction, as in recording, the power of the light beam 1 when the light from the light source 1 is condensed on the optical recording medium 9 by reducing the power of the central portion of the light beam that has passed through the optical element 3. The spot diameter can be made smaller. That is, by using the optical element 3 using the ITO film 60 shown in FIG. 3, the light from the light source 1 can be condensed on the optical recording medium 9 in a narrower range.

  As described above, the ITO film 60 shown in FIG. 3 is used for any one of the ITO film 22 and the ITO film 25 shown in FIG. 2, and as shown in FIG. By applying a voltage, in addition to the effect of the above-described embodiment, the effect of condensing the light from the light source 1 in a narrower region of the optical recording medium 9 can be obtained. The resolution of the head can be improved, and therefore recording and reproduction of high-density signals can be realized by the optical recording medium 9.

  When the ITO film 60 of FIG. 3 is used for the optical element 3, the center of the light beam from the light source 1 passes through the center of the first electrode 61 of the ITO film 60 when passing through the optical element 3. It is necessary to position the optical element 3 when the optical element 3 is arranged in the optical head of FIG. However, as long as the optical element 3 and the like are positioned and sufficiently fixed when the optical head of FIG. 1 is manufactured, it is not necessary to adjust the position where the optical element 3 is disposed again during recording or reproduction.

  On the other hand, when an intensity filter 52 having a transmittance near the center lower than that of the peripheral portion is temporarily used as the intensity filter 52 of the conventional optical head, the intensity filter 52 is used for the light from the light source 1 during recording or reproduction. When inserting in the middle of the beam, it is necessary to accurately align the center of the intensity filter 52 and the center of the light beam from the light source 1 one by one.

  Therefore, a mechanism for aligning the intensity filter 52 and the light beam from the light source 1 is required in addition to a mechanism for taking in and out the intensity filter 52. Accordingly, in order to realize a function equivalent to that of the optical element 30 using the ITO film 60 of FIG. 3 with the conventional optical head, a positioning mechanism is further required. It becomes increasingly difficult. As described above, when the ITO film 60 of FIG. 3 is used for the optical element 3, the optical head of this embodiment is much more advantageous from the viewpoint of miniaturization than the conventional optical head.

  In the above description, the ITO film 60 shown in FIG. 3 has been described as an example of an ITO film that is patterned and has a non-uniform structure. However, the present invention is not limited thereto. Even if the ITO film 70 shown in FIG. 6 is used as the ITO film that is patterned and has a non-uniform structure, the same effect as that in the case of using the ITO film 60 shown in FIG. 3 can be obtained.

  In FIG. 6, the ITO film 70 includes a first electrode 61, a second electrode 62, a third electrode 65, and a fourth electrode 66, a first insulating layer 67, a second insulating layer 68, and And a third insulating layer 69.

  The shape of the first electrode 61 is circular. The first insulating layer 67 has a circular shape having a center in common with the first electrode 61 and is disposed so as to surround the first electrode 61. The third electrode 65 has a circular shape having a common center with the first electrode 61 and is disposed so as to surround the first insulating layer 67. The second insulating layer 68 has a circular shape having a common center with the first electrode 61 and is disposed so as to surround the third electrode 65. The fourth electrode 66 has a circular shape having a common center with the first electrode 61 and is disposed so as to surround the second insulating layer 68. The third insulating layer 69 has a circular shape having a common center with the first electrode 61 and is disposed so as to surround the fourth electrode 66. The second electrode 62 is disposed so as to surround the third insulating layer 69.

That is, the ITO film 70 in FIG. 6 further includes one or a plurality of concentric electrodes between the first electrode 61 and the second electrode 62. That is, the ITO film 70 of FIG. 6 has a plurality of electrodes that can apply different voltages to the Ni (OH) ₂ film 23 because each electrode is electrically insulated by each insulating layer. Yes.

Therefore, the ITO film 70 of FIG. 6 is used for either the ITO film 22 or the ITO film 25 of the optical element 3 and at the time of recording and reproduction, Ni (OH) is applied from each electrode in the same manner as the ITO film 60 of FIG. 4) By applying a voltage to the _two films 23, the power of the central portion of the light beam that has passed through the optical element 3 can be reduced, so that it is equivalent to the case where the ITO film 60 of FIG. The effect of can be obtained.

  Note that the number of electrodes disposed between the first electrode 61 and the second electrode 62 is not limited as long as the electrode has a center in common with the first electrode 61.

(Embodiment 2)
Next, a second embodiment of the present invention will be described with reference to the drawings. The difference between the second embodiment and the first embodiment described above is that the arrangement of the optical element 3 is different. Otherwise, the second embodiment is the same as in the first implementation. Therefore, in the second embodiment, those not particularly described are the same as those in the first embodiment, and the description thereof is omitted. In the second embodiment, components having the same reference numerals as those in the first embodiment have the same functions as those in the first embodiment unless otherwise specified.

  FIG. 7 is a configuration diagram of an optical head according to Embodiment 2 of the present invention.

  The optical head of the second embodiment shown in FIG. 7 is different from the optical head of the first embodiment shown in FIG. 1 in that the optical element 3 is disposed between the collimator lens 2 and the light source 1. Yes. Other than that, the optical head of the second embodiment is the same as the optical head of the first embodiment shown in FIG.

  Next, the operation of the second embodiment will be described.

  In FIG. 7, the linearly polarized light emitted from the light source 1 is incident on the optical element 3, and the amount of light is attenuated in the case of reproduction, and the amount of light is not attenuated in the case of recording (this is the first embodiment). ).

  The light transmitted through the optical element 3 enters the collimator lens 2 and is converted from divergent light into parallel light. The converted parallel light is incident on the polarization beam splitter 4, a part of which is reflected and most of the light is transmitted.

  Here, the reflected light is incident on the first photodetector 6 by the first condenser lens 5, and the first photodetector 6 outputs an electrical signal for controlling the light quantity of the light source 1. To do. The light transmitted through the polarizing beam splitter 4 is converted from linearly polarized light to circularly polarized light by the quarter wavelength plate 7, and this circularly polarized light is condensed on the optical recording medium 9 by the objective lens 8.

  Next, the light reflected from the optical recording medium 9 passes through the objective lens 8 and is converted by the quarter wavelength plate 7 into linearly polarized light orthogonal to the polarization direction of the linearly polarized light emitted from the light source 1 by the quarter wavelength plate 7, The light is reflected 100% by the polarization beam splitter 4, is given astigmatism by the cylindrical lens 10, and is incident on the second photodetector 12 by the second condenser lens 11.

  The second photodetector 12 outputs a focus error signal indicating the focused state of light on the optical recording medium 9 using the astigmatism method, and outputs a tracking error signal indicating the light irradiation position. In this case, for example, a phase error method is used for a read-only optical recording medium, and a tracking error signal is obtained by a push-pull method for a recording optical recording medium.

  A focus control unit (not shown) controls the position of the objective lens 8 in the optical axis direction so that the light is always focused on the optical recording medium 9 in a focused state based on the focus error signal. A tracking control unit (not shown) controls the position of the objective lens 8 based on the tracking error signal so that the light is condensed on a desired track on the optical recording medium 9. Information recorded on the optical recording medium 9 is also obtained from the second photodetector 12.

  Here, the difference from the optical head of the first embodiment is that the optical element 3 is disposed between the collimator lens 2 and the light source 1, that is, the optical element 3 is disposed in diverging light. is there. Here, when the thickness of the optical element 3 is t and the average refractive index is n, the optical element 3 is arranged in the divergent light rather than the optical element 3 is arranged in the parallel light. We will describe the possibility of further miniaturization.

  If the optical element 3 is placed in divergent light, the distance from the collimator lens 2 to the objective lens 8 can be shortened by t compared to when the optical element 3 is placed in parallel light. Further, the distance from the light source 1 to the collimator lens 2 is increased by (n−1) t when the optical element 3 is placed in divergent light compared to when the optical element 3 is placed in parallel light. Therefore, the length of the entire optical head can be shortened by (2-n) t. For example, since the optical element 3 is almost made of glass, the refractive index n of the optical element 3 is considered to be about 1.5, and the length of the optical head can be shortened by 0.5 t.

  Next, consider the case of the variable transmittance optical element that changes the solid polarization characteristics in the first embodiment. An optical element capable of converting the polarization characteristics has a birefringence effect itself. Therefore, astigmatism occurs when it is disposed in divergent light due to this birefringence. If this astigmatism does not fluctuate, it is sufficient to include a means for canceling astigmatism when assembling the optical head, but changing the transmittance means changing the birefringence of the optical element. Therefore, the astigmatism generated due to the arrangement in the divergent light changes, which becomes a problem.

  On the other hand, the optical element 3 of the second embodiment does not have polarization characteristics, that is, does not change the polarization characteristics, so astigmatism does not occur even if it is arranged in divergent light. Therefore, the optical element 3 according to the second embodiment is advantageous for being disposed in diverging light. Furthermore, since the optical element 3 according to the second embodiment can be used in a finite optical system, the optical head can be reduced in size and cost.

  By using this optical element 3 for the optical head, the power of the light source 1 is set to a power at which the quantum noise is sufficiently lowered during reproduction, and the surface power of the optical recording medium is reduced by reducing the transmittance of the optical element 3. Reproduction can be performed with low power that does not cause deterioration or data erasure, and recording can be performed using the power of the light source 1 as it is by setting the transmittance of the optical element 3 to 100%. it can. In addition, since the transmittance is switched by an external electric signal, it is easy to reduce the size of the optical head. Further, when the optical element 3 is configured using a film of an electrochromic material, the transmittance of the film itself is changed, so that it can be placed in divergent light and is suitable for further miniaturization of the optical head. . That is, the optical element 3 can be further miniaturized by arranging the optical element 3 in the divergent light of the optical head.

  In the second embodiment, the ITO film 22 and the ITO film 25 have a uniform structure that is not patterned. However, the present invention is not limited to this, and the ITO film 22 and the ITO film 25 are not limited thereto. One of them may be a patterned one having a non-uniform structure.

  FIG. 8 shows an ITO film 80 that is patterned and has a non-uniform structure. The ITO film 80 has an elliptical first electrode 81, an insulating layer 83 having a center common to the first electrode 81, and arranged to surround the first electrode 81, and the insulating layer 83. And a second electrode arranged as described above.

  The reason why the first electrode 81 and the like in the ITO film 80 in FIG. 8 are elliptical is as follows.

  That is, in the second embodiment, as described with reference to FIG. 7, the optical element 3 is arranged on the light source 1 side of the collimator lens 2. The light beam from the light source 1 has an elliptical shape in a cross section orthogonal to the traveling direction until it enters the collimator lens 2. Accordingly, a light beam having an elliptical cross section perpendicular to the traveling direction is incident on the optical element 3. Therefore, the first electrode 81 and the like are formed in an elliptical shape so as to conform to the shape of the beam. Yes. Other than that, it is the same as the ITO film 60 described with reference to FIG.

  Furthermore, an ITO film 100 shown in FIG. 9 may be used instead of the ITO film 80 shown in FIG.

  In FIG. 9, the ITO film 100 includes a first electrode 81, a second electrode 82, a third electrode 95, and a fourth electrode 96, a first insulating layer 97, a second insulating layer 98, and And a third insulating layer 99.

  The shape of the first electrode 81 is an elliptical shape. The first insulating layer 97 has an elliptical shape having a center in common with the first electrode 81 and is disposed so as to surround the first electrode 81. The third electrode 95 has an elliptical shape having a center in common with the first electrode 81 and is disposed so as to surround the first insulating layer 97. The second insulating layer 98 has an elliptical shape having a center in common with the first electrode 81 and is disposed so as to surround the third electrode 95. The third insulating layer 99 has an elliptical shape having a center in common with the first electrode 81 and is disposed so as to surround the fourth electrode 96. The fourth electrode 96 has an elliptical shape having a center in common with the first electrode 81 and is disposed so as to surround the third insulating layer 99. The second electrode 82 is disposed so as to surround the third insulating layer 99.

That is, the ITO film 100 of FIG. 9 further includes one or a plurality of concentric elliptical electrodes between the first electrode 81 and the second electrode 82. That is, the ITO film 100 in FIG. 9 has a plurality of electrodes that can apply different voltages to the Ni (OH) ₂ film 23 because each electrode is electrically insulated by each insulating layer. Yes.

  The reason why the first electrode 81 and the like in the ITO film 100 in FIG. 9 are elliptical is the same as the reason described in the ITO film 80 in FIG.

  Other than that, it is the same as the ITO film 70 described with reference to FIG.

  In the present embodiment, the optical element 3 is described as being disposed between the light source 1 and the collimator lens 2 of the optical head, that is, the optical element 3 is disposed in the divergent light of the optical head. Absent. The optical element 3 may be disposed between the optical recording medium 9 of the optical head and the objective lens 8, that is, the optical element 3 may be disposed in the convergent light of the optical head.

  In the present embodiment, it has been described that the light source 1 has a short wavelength from 390 nm to 420 nm. However, the light source 1 may have a wavelength other than the wavelength from 390 nm to 420 nm.

  Furthermore, in Embodiments 1 and 2, the optical system is a polarization optical system, but there is no problem even if it is a non-polarization optical system.

Furthermore, in the present embodiment, it has been described that the Ni (OH) ₂ film 23 is used. However, the present invention is not limited to this, and instead of the Ni (OH) ₂ film 23 of the present embodiment, the coloration is performed when a voltage is applied. You may use the other electrochromic material which has.

That is, in this embodiment, the Ni (OH) ₂ film 23 is used as the electrochromic material, but this is a material that is colored by a reduction reaction as the electrochromic material. Thereby, by using a material that electrochromic material is colored by a reduction reaction, the transmittance of the electrochromic material is changed according to the voltage applied from the outside, and the amount of light transmitted through the optical element can be changed. . However, the electrochromic material is not limited to a material that is colored by a reduction reaction, and there is no problem even if a material that is colored by an oxidation reaction is used. By using a material that is colored by an oxidation reaction as the electrochromic material, the transmittance of the electrochromic material layer changes according to the voltage applied from the outside, and the amount of light transmitted through the optical element can be changed.

  Although a liquid is used as the electrolyte, there is no problem even if a solid electrolyte is used. In the case where a solid electrolyte is used as the electrolyte, the thickness of the optical element 3 can be made thinner than in the case where a liquid is used as the electrolyte.

(Embodiment 3)
In Embodiment 3, an example of the optical information device of the present invention will be described. The optical information apparatus according to the third embodiment is an apparatus that records and reproduces signals with respect to an optical recording medium.

  FIG. 10 schematically shows the configuration of the optical information device 40 according to the third embodiment. The optical information device 40 includes an optical head 41, a motor 42 that is a rotation driving unit, and a processing circuit 43 that is a control unit. The optical head 41 has been described in the first embodiment.

  Since the optical head 41 is the same as that described in the first embodiment, a duplicate description is omitted.

  Next, the operation of the optical information device 40 will be described.

  First, when the optical recording medium 9 is set in the optical information device 40, the processing circuit 43 outputs a signal for rotating the motor 42 to rotate the motor 42. Next, the processing circuit 43 drives the light source 1 to emit light, and controls the light amount of the light source 1 according to the output from the first photodetector 6. The processing circuit 43 controls the transmittance of the optical element 3 so that the transmittance of the optical element 3 becomes an optimum value at the time of reproduction and recording.

  The light emitted from the light source 1 is reflected by the optical recording medium 9 and enters the second photodetector 12. The second photodetector 12 outputs a focus error signal indicating the focused state of light on the optical recording medium 9 and a tracking error signal indicating the light irradiation position to the processing circuit 43. Based on these signals, the processing circuit 43 outputs a signal for controlling the objective lens 8, thereby condensing the light emitted from the light source 1 onto a desired track on the optical recording medium 9. Further, the processing circuit 43 reproduces information recorded on the optical recording medium 9 based on the signal output from the second photodetector 12.

  As described above, since the first optical head of the present embodiment is used as the optical head, the optical element 3 of the present invention is set while the power of the light source 1 is set to a power at which the quantum noise becomes sufficiently low during reproduction. By reducing the transmittance of the recording medium, it is possible to perform reproduction while suppressing the disk surface power to a low power that does not cause deterioration of the optical recording medium or data erasure. Thus, the optical information device 40 capable of recording using the power of the light source 1 as it is can be configured.

  In addition, since it is possible to reproduce the light source with less quantum noise, it is possible to construct an optical information apparatus that can obtain a stable control signal and reproduction signal.

  In addition, since the transmittance is switched by an electric signal from the outside, the optical head can be easily miniaturized, which is suitable for miniaturization of the optical information apparatus.

  Further, although the optical head of the first embodiment has been described as the optical head, there is no problem even if the optical head described in the second embodiment is used.

  Moreover, although the objective lens uses a single lens, there is no problem even if it is a combined lens having a high NA. Further, if a lens with a high NA is used, the density can be increased, and the stability of the reproduction signal against the noise of the light source becomes strict, so the present invention is very useful.

  The embodiments of the present invention have been described above by way of examples. However, the present invention is not limited to the above embodiments, and can be applied to other embodiments based on the technical idea of the present invention.

  In the above embodiment, an infinite optical head is shown. However, a finite optical head that does not use a collimator lens may be used.

  In the above embodiment, the optical recording medium that records information only by light has been described. However, the same effect can be obtained by using the optical element of the present embodiment for an optical recording medium that records information by light and magnetism. Needless to say, is obtained.

  In the above embodiment, the case where the optical recording medium is an optical disk has been described. However, the present invention can be applied to an optical information device that realizes a similar function, such as a card-like optical recording medium.

An optical head that written to the present invention, and the optical information equipment is a power of the light source, while setting the power of the quantum noise is sufficiently low, low not occur the board power such erasure of deterioration and the data of the optical disc power It is possible to perform reproduction while suppressing the recording power, and at the time of recording, it is possible to perform recording by using the power of the light source as it is, and it is suitable for downsizing of the optical head. It is useful for an optical element, an optical head, an optical information device, an optical head control method, and the like.

Schematic diagram illustrating an example of the optical head according to the first embodiment of the present invention. Sectional drawing which shows an example about the optical element in Embodiment 1 and 2 of this invention The figure which shows an example of the patterned ITO film | membrane used for the optical element in Embodiment 1 of this invention The figure which shows the voltage applied to the ITO film | membrane of the optical element in Embodiment 1 of this invention (A) The figure which shows the spatial distribution of the light from the light source before passing through the optical element using the patterned ITO film | membrane in Embodiment 1 of this invention (b) Patterning in Embodiment 1 of this invention Showing the spatial distribution of light from a light source after passing through an optical element using a made ITO film The figure which shows another example of the patterned ITO film | membrane used for the optical element in Embodiment 1 of this invention Schematic diagram showing an example of the optical head according to Embodiment 2 of the present invention. The figure which shows an example of the patterned ITO film | membrane used for the optical element in Embodiment 2 of this invention The figure which shows another example of the patterned ITO film | membrane used for the optical element in Embodiment 2 of this invention The schematic diagram which shows an example about the optical information apparatus in Embodiment 3 of this invention Schematic diagram showing an example of a conventional optical head

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator lens 3 Optical element of this invention 4 Polarization beam splitter 5 1st condensing lens 6 1st photodetector 7 1/4 wavelength plate 8 Objective lens 9 Optical recording medium 10 Cylindrical lens 11 2nd collection Optical lens 12 Second photodetector 22 First ITO film 23 Ni (OH) ₂ film 24 KCl solution 25 Second ITO film 27 Sealing layer 41 Optical head 42 Motor 43 Processing circuit

Claims (6)

A laser light source for emitting laser light;
An objective lens for condensing the laser light emitted from the laser light source onto an optical recording medium;
An optical element disposed between the light source and the optical recording medium, the transmittance of which varies according to an applied voltage;
A collimator lens that is disposed between the objective lens and the laser light source and converts the laser light emitted from the laser light source into parallel light;
The voltage applied to the optical element is such that the transmittance of the optical element is lower when the signal is reproduced from the optical recording medium than when the signal is recorded on the optical recording medium. Switching between when recording a signal and when reproducing a signal from the optical recording medium,
And, the voltage applied to the optical element is switched by the region of the optical element so that the transmittance of the central part of the optical element is lower than that of the peripheral part of the optical element,
The optical element is
An electrochromic material layer whose transmittance changes according to the applied voltage;
An electrolyte disposed on one side of the electrochromic material layer;
A first transparent electrode disposed on the other surface of the electrochromic material layer;
A second transparent electrode disposed on a surface of the electrolyte opposite to the electrochromic material layer,
At least one of the first transparent electrode and the second transparent electrode is an optical element having a plurality of electrodes capable of applying different voltages to the electrochromic material layer,
The plurality of electrodes include a circular first electrode and a second electrode disposed so as to surround the first electrode,
The optical element is disposed on the objective lens side with respect to the collimator lens,
The voltage and the voltage of the second electrode of the first electrode, the transmittance of the portion of the electrochromic material layer corresponding to the first electrode, the electrochromic material layer corresponding to the second electrode in proportions such that lower than the transmittance of the portion of the, which is applied to the electrochromic material layer,
When recording a signal on the optical recording medium, the ratio of the voltage of the first electrode applied to the central portion of the optical element and the voltage of the second electrode applied to the peripheral portion of the optical element;
When reproducing a signal from the optical recording medium, the ratio of the voltage of the first electrode applied to the central part of the optical element and the voltage of the second electrode applied to the peripheral part of the optical element is:
Optical head characterized by being equal . Before SL plurality of electrodes, the first, further comprising an electrode the electrode of one or more concentric circles between said second electrode, according to claim 1 optical head according. A laser light source for emitting laser light;
An objective lens for condensing the laser light emitted from the laser light source onto an optical recording medium;
An optical element disposed between the light source and the optical recording medium, the transmittance of which varies according to an applied voltage;
A collimator lens that is disposed between the objective lens and the laser light source and converts the laser light emitted from the laser light source into parallel light;
The voltage applied to the optical element is such that the transmittance of the optical element is lower when the signal is reproduced from the optical recording medium than when the signal is recorded on the optical recording medium. Switching between when recording a signal and when reproducing a signal from the optical recording medium,
And, the voltage applied to the optical element is switched by the region of the optical element so that the transmittance of the central part of the optical element is lower than that of the peripheral part of the optical element,
The optical element is
An electrochromic material layer whose transmittance changes according to the applied voltage;
An electrolyte disposed on one side of the electrochromic material layer;
A first transparent electrode disposed on the other surface of the electrochromic material layer;
A second transparent electrode disposed on a surface of the electrolyte opposite to the electrochromic material layer,
At least one of the first transparent electrode and the second transparent electrode is an optical element having a plurality of electrodes capable of applying different voltages to the electrochromic material layer,
The plurality of electrodes include an elliptical first electrode and a second electrode disposed so as to surround the first electrode,
The optical element is disposed on the laser light source side with respect to the collimator lens,
The voltage and the voltage of the second electrode of the first electrode, the transmittance of the portion of the electrochromic material layer corresponding to the first electrode, the electrochromic material layer corresponding to the second electrode in proportions such that lower than the transmittance of the portion of the, which is applied to the electrochromic material layer,
When recording a signal on the optical recording medium, the ratio of the voltage of the first electrode applied to the central portion of the optical element and the voltage of the second electrode applied to the peripheral portion of the optical element;
When reproducing a signal from the optical recording medium, the ratio of the voltage of the first electrode applied to the central part of the optical element and the voltage of the second electrode applied to the peripheral part of the optical element is:
Optical head characterized by being equal . The optical head according to claim 3 , wherein the plurality of electrodes further include one or a plurality of concentric elliptical electrodes between the first electrode and the second electrode. The laser wavelength of the light source is a 420nm from 390 nm, according to claim 1 or 3 optical head according. An optical information apparatus for recording or reproducing a signal with respect to an optical recording medium,
Rotation driving means for rotating the optical recording medium;
An optical head for recording or reproducing a signal on the optical recording medium,
An optical information device using the optical head according to claim 1 or 3 as the optical head.

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