JPH04311846A - Magneto-optical head - Google Patents

Abstract

PURPOSE:To contrive the miniaturization and high speed access by detecting a light quantity of irradiated laser beams by providing a specified hologram on the back surface of a half-mirror, also detecting a servo error signal and decreasing the number of the component. CONSTITUTION:The hologram 2a is formed on the back surface of the half- mirror 2 and laser beams from a semiconductor laser 1 are led to the magneto- optical disk 4 by the half-mirror 2. On the other hand, laser beams transmitted to the half-mirror 2 are diffracted by the hologram 2a and the + or -1st order diffracted light is made incident on a light receiving element 5. The + or -1st order diffracted light is the same as the polarized component of the light being irradiated on the disk 4, so the light quantity of the actual laser beams being irradiated based on the light amount of the light receiving element 5 can be detected. Also the returned light from the disk 4 is diffracted by the hologram 2a and is made incident on the light receiving element 6 and the magneto-optical signal and the servo error signal are detected, so the number of the optical parts can be decreased.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical head using a polarization hologram having polarization characteristics in its optical system.

0002

2. Description of the Related Art Magneto-optical heads used in magneto-optical disk drives cannot shorten access time unless they are made smaller and lighter. Furthermore, since the magnetic Kerr effect is used for signal detection, it is necessary to use a semiconductor laser with good polarization characteristics and to monitor the amount of polarized light component irradiated onto the recording medium.

Conventional magneto-optical heads have satisfied the above requirements by having the configurations shown in FIGS. 7 and 8. Here, a conventional magneto-optical head will be described below with reference to FIGS. 7 and 8.

This magneto-optical head, as shown in FIG.
A semiconductor laser 31 is provided as a light source, and a polarizing beam splitter (PBS) 40 and an objective lens 33 are arranged on an optical path between the semiconductor laser 31 and a recording medium 34.

[0005] Furthermore, in order to monitor the light amount of the polarized component of the semiconductor laser beam irradiated onto the recording medium 34, the magneto-optical head has a polarizing plate 42 and a light receiving element 35 at a position where the light reflected by the PBS 40 can be received. This is the arranged configuration.

Furthermore, the magneto-optical head has a polarization hologram 4.
1 and a light receiving element 36.

The light reflected by the recording medium 34 (return light) is reflected by the PBS 40 and enters the polarization hologram 41, where it is used for signal detection. When the light reflected by the PBS 40 enters the polarization hologram 41 at a predetermined angle (Bragg angle), astigmatism occurs, and as shown in FIG. 8, the light is guided to the light receiving element 36.

That is, of the light transmitted through the polarization hologram 41, the S-polarized component is 0th-order diffracted, and the P-polarized component is 1st-order diffracted.
The light is diffracted for the next time and enters the light receiving element 36. A magneto-optical signal is detected based on these 0th-order diffracted light and 1st-order diffracted light.

The light receiving element 36 is composed of a four-part light receiving element 36a and a two-part light receiving element 36b. The four-divided light receiving element 36a detects a focus error signal based on the incident first-order diffracted light, while the two-divided light receiving element 36b detects a radial error signal based on the incident zero-order diffracted light.

0010

[Problems to be Solved by the Invention] However, in the conventional optical system described above, as shown in FIG.
A polarizing plate 42 is required to monitor the amount of polarized component of the laser beam irradiated. Therefore, there is a problem that the number of component parts increases and the weight of the magneto-optical head increases, so that high-speed access cannot be performed.

[0011]

[Means for Solving the Problem] A magneto-optical head according to the invention of claim 1 is a one-beam magneto-optical head that includes a half mirror and records and reproduces information using a laser beam guided by the half mirror. In order to detect a magneto-optical signal, the return light from the recording medium is transmitted to give it polarization characteristics, and at the same time, optical diffraction is used to diffract laser light with the same polarization component as the polarization component irradiated onto the recording medium in a predetermined direction. It is characterized in that a means (hologram) is provided on the back surface of the half mirror.

The magneto-optical head according to the second aspect of the invention is a magneto-optical head that includes a half mirror and records and reproduces information using a laser beam guided by the half mirror, and detects a servo error signal. The grating is equipped with a grating that diffracts the incident laser beam and divides it into three beams and guides the three beams to the half mirror, and transmits the return light from the recording medium to detect the magneto-optical signal and polarizes the beam. The half mirror is characterized in that an optical diffraction means (hologram) is provided on the back surface of the half mirror to diffract a laser beam having the same polarization component as that irradiated onto the recording medium in a predetermined direction.

[0013]

According to the structure of claim 1, the laser beam irradiated from the light source is reflected by the half mirror and guided onto the recording medium, and is also transmitted through the half mirror.

The return light from the recording medium passes through the half mirror and enters the light diffraction means provided on the back surface of the half mirror. Of this incident light, the S-polarized light component is diffracted in the 0th order, and the P-polarized light components are diffracted in the ±1st order, and are guided to the light-receiving elements. A magneto-optical signal is detected based on these diffracted lights. Further, since the above-mentioned incident light enters the half mirror at a predetermined angle and has astigmatism, servo error signals such as a focus error signal and a radial error signal can be detected.

On the other hand, when the laser light emitted from the light source that has passed through the half mirror is incident on the light diffraction means, the P polarized component of the incident light is diffracted to the ±1st order. This is the same polarized light component that is incident on the recording medium. Therefore, the amount of laser light irradiated onto the recording medium can be detected based on the diffracted light of either one of the ±1st-order diffracted lights.

[0016] Automatic light amount control can be performed based on the detected laser light amount.

According to the second aspect of the present invention, the laser beam irradiated from the light source is divided into three beams by being diffracted by the zeroth order and ±1st order by the grating. These three beams are guided to a half mirror, reflected there, guided to a recording medium, and transmitted through the half mirror.

The return light from the recording medium passes through the half mirror and enters the light diffraction means provided on the back surface of the half mirror. Of the incident light, the S-polarized light component is diffracted in the 0th order, and the P-polarized light component is diffracted in the ±1st order and guided to the light receiving element. A magneto-optical signal and a servo error signal are detected based on these diffracted lights.

On the other hand, when the laser light emitted from the light source that has passed through the half mirror is incident on the light diffraction means, the P polarized component of the incident light is diffracted to the ±1st order. This is the same polarized light component that is incident on the recording medium. Therefore, the amount of laser light irradiated onto the recording medium can be detected based on the diffracted light of either one of the ±1st-order diffracted lights.

[0020] Automatic light amount control can be performed based on the detected laser light amount.

[0021]

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

The magneto-optical head according to the present invention includes a semiconductor laser 1 as a light source, as shown in FIG. This semiconductor laser 1 and a magneto-optical disk 4 as a recording medium
A half mirror 2 and an objective lens 3 are arranged between the optical paths.

A hologram 2a is provided on the back surface of the half mirror 2 (shown as a groove in FIG. 2 for convenience). The hologram 2a has a pattern as shown in FIG. 1, and is configured to diffract the S-polarized component of the incident light to the 0th order and to diffract the P-polarized component to the ±1st order.

A light receiving element 5 is arranged behind the half mirror 2, that is, on the opposite side of the half mirror 2 from the side where the semiconductor laser 1 is arranged. This light-receiving element 5 is configured to receive light that is transmitted through the half mirror 2 and diffracted by the hologram 2a among the laser light emitted from the semiconductor laser 1. The polarized light components incident on the light receiving element 5 are the same ±first-order diffracted light as the polarized light components (P polarized light components) incident on the magneto-optical disk 4 . Automatic light amount control can be performed using either one of the ±first-order diffracted lights.

The magneto-optical disk 4 is attached to the half mirror 2.
A light receiving element 6 is arranged on the opposite side. The light-receiving element 6 is composed of a four-part light-receiving element and a two-part light-receiving element. A focus error signal is detected by the 4-split light receiving element, and 2
A radial error signal is detected in the divided light receiving elements.

In this embodiment, the focus error is detected by the astigmatism method through a four-part light receiving element. That is, light incident on the half mirror 2 at a predetermined angle (Bragg angle) becomes circular on the four-split light receiving element when in focus, but becomes elliptical when out of focus. Therefore, 4
Of the signals detected by the four light-receiving elements of the split light-receiving element,
A focus error can be detected by summing the signals from the light receiving elements on the diagonal and then calculating the difference between the two sets of sum signals.

[0027] Furthermore, the light incident on the two-split light-receiving element is
They partially overlap and interfere on the two light receiving elements. When the track shifts left and right with respect to the radial direction, a change in brightness occurs on the light receiving element. This change is detected as a differential output of the two-split light receiving element, and a radial error signal is detected.

According to the above configuration, the laser beam from the semiconductor laser 1 is incident on the half mirror 2. Of this incident light, the light reflected by the half mirror 2 is guided to a predetermined location on the magneto-optical disk 4 via the objective lens 3.

Return light collected from the magneto-optical disk 4 through the objective lens 3 passes through the half mirror 2 and enters a hologram 2a (light diffraction means) provided on the back surface of the half mirror. At this time, a predetermined angle (Bragg angle)
The incident light is incident on the hologram 2a.

In the hologram 2a, S of the incident light
The polarized light component is diffracted in the 0th order and guided to the two-split light receiving element of the light receiving element 6, and the P polarized light component is diffracted in the ±1st order. +
Either the first-order diffracted light or the -1st-order diffracted light (FIG. 2 shows the case of the +1st-order diffracted light) is guided to the four-split light-receiving element. These diffracted lights incident on the light receiving element 6 are converted into magneto-optical signals that change depending on the amount of incident light.

Further, a focus error is detected based on the +1st-order diffracted light by the astigmatism method. That is, when the diffracted light is in focus, it becomes circular on the four-split photodetector, but when it is out of focus, it becomes an ellipse, so the signals from the diagonal photodetectors are summed, and then the two sets of signals are summed. A focus error signal is detected by taking the difference between the sum signals.

Furthermore, a radial error detection signal is detected based on the 0th order diffracted light incident on the two-split light receiving element. In other words, the diffracted light partially overlaps and interferes on the two light-receiving elements, so when the track shifts left and right with respect to the radial direction, a change in brightness and darkness occurs on the light-receiving element, and this change is divided into two. The radial error signal is detected by detecting it as a differential output of the light receiving element.

On the other hand, out of the laser light emitted from the semiconductor laser 1, the light that has passed through the half mirror appears on the hologram 2.
When the light is incident on a point a, the P polarized light component of the incident light is diffracted by the ±1st order, and the S polarized light component is diffracted by the 0th order.

The +1st order diffracted light is incident on the light receiving element 5, and has the same polarization component as that incident on the magneto-optical disk 4. Therefore, the amount of laser light irradiated onto the magneto-optical disk 4 can be detected based on the amount of light incident on the light receiving element 5. It is possible to perform automatic light amount control based on the detected laser light amount.

As described above, the magneto-optical head according to this embodiment has a structure in which the hologram 2a is provided on the back surface of a half mirror, and the light receiving element 5 is provided behind it.

As a result, either the +1st-order diffracted light or the -1st-order diffracted light that is transmitted through the half mirror 2 and diffracted by the hologram 2a is received by the light receiving element 5, and the amount of the received light is Based on this, the actual amount of laser light irradiated onto the magneto-optical disk 4 can be detected. Therefore,
Based on this detected light amount, automatic light amount control can be performed.

Furthermore, the hologram 2a causes the S-polarized light component and the P-polarized light component of the return light from the magneto-optical disk 4 to undergo 0th-order diffraction and ±1st-order diffraction, respectively, and enter the light-receiving element 6. This allows the number of optical components to be reduced, making it possible to achieve smaller size, lighter weight, and faster access as a whole.

Another magneto-optical head according to the present invention will now be described with reference to FIGS. 3 and 4.

In this embodiment, two holograms having different patterns are provided on the back surface of the half mirror, and light receiving elements for detecting magneto-optical signals and for detecting servo error signals are configured accordingly. This embodiment differs from the previous embodiment in that

That is, the half mirror 1 according to this embodiment
2 has a first hologram 12a and a second hologram 12b (both optical diffraction means) on its back surface, as shown in FIG.
The structure is set up. Note that the other components and arrangement are the same as in the previous embodiment.

[0041] In the same manner as in the embodiment described above, detection of the magneto-optical signal and detection of the amount of laser light irradiated onto the magneto-optical disk 14 are performed. However, the detection of the servo error signal is different from the previous embodiment. The reason why the hologram is divided into the first and second holograms 12a and 12b as described above and the light receiving element 17 is configured as shown in FIG. 3 is because the focus error signal is detected by the Foucault method and the radial error signal is This is because the detection is performed using the push-pull method.

According to the configuration of this embodiment, the semiconductor laser 1
The laser beam from 1 is incident on the half mirror 12. Of this incident light, the light reflected by the half mirror 12 is guided to a predetermined location on the magneto-optical disk 14 (recording medium) via the objective lens 13.

Return light collected from the magneto-optical disk 14 through the objective lens 13 passes through the half mirror 12,
The light is incident on first and second holograms 12a and 12b provided on the back surface of the half mirror.

In the first hologram 12a, the S-polarized component of the incident light is diffracted to the 0th order and divided into two light receiving elements in the light receiving element 17 (in FIG. 3, the upper half of the light receiving element 17
The P-polarized light component is guided to the left-hand light-receiving element (of the divided light-receiving elements), and the P-polarized light component is subjected to ±1st-order diffraction, and either one of the ±1st-order diffracted lights is guided to the 4-split light-receiving element ( In FIG. 3, the light is guided to the left two light-receiving elements among the four-divided light-receiving elements in the lower half of the light-receiving element 17.

Similarly, in the second hologram 12b,
The S-polarized component of the incident light is diffracted to the 0th order and passes through the light receiving element 17.
The P polarized light component is guided to the inner two-split light receiving element (the right one of the two split light receiving elements in the upper half of the light receiving element 17 in FIG. 3), and the P polarized light component is diffracted by the ±1st order, and the ±1st order diffracted light is One of the diffracted lights is guided to the four-part light-receiving element in the light-receiving element 17 (in FIG. 3, the right two light-receiving elements among the four-part light-receiving elements in the lower half of the light-receiving element 17).

These diffracted lights are incident on the light receiving element 17,
It is converted into a magneto-optical signal that changes depending on the amount of incident light.

A focus error is detected by the Foucault method based on the +1st-order diffracted light.

That is, when the diffracted light is in focus, the amount of light incident on each of the four-split light-receiving elements is equal, but when the focus is shifted, the amount of light incident on the two light-receiving elements on the left of the four-split light-receiving element is equal. The amount of incident light becomes unbalanced, and the amount of incident light also becomes unbalanced between the two right light receiving elements.

In other words, by calculating the sum of the signals of the two light-receiving elements at both ends of the four light-receiving elements and the sum of the signals of the two light-receiving elements in the middle, and then calculating the difference between the two sets of sum signals, the focus error signal is obtained. is detected.

Furthermore, a radial error detection signal is detected by the push-pull method based on the 0th order diffracted light incident on the two-split light receiving element. In other words, when the track shifts to the left or right in the radial direction due to the intensity distribution of the 0th-order diffracted light, the amount of light incident on each light receiving element changes, and by detecting this change as the differential output of the two divided light receiving elements, A radial error signal is adapted to be detected.

On the other hand, when the light transmitted through the half mirror 12 among the laser light emitted from the semiconductor laser 11 is incident on the holograms 12a and 12b, P of the incident light is
The polarized light components are each subjected to ±1st-order diffraction, and the S-polarized light components are each subjected to 0th-order diffraction. One of the ±1st-order diffracted lights (FIG. 3 shows the +1st-order diffracted light) is incident on the light receiving element 15, but the polarization component is the same as the polarization component that is incident on the magneto-optical disk 4. be. Therefore, based on the amount of light incident on the light receiving element 15, the magneto-optical disk 14
It is possible to detect the amount of laser light irradiated to the area. It is possible to perform automatic light amount control based on the detected laser light amount.

As described above, in the magneto-optical head according to this embodiment, the first and second holograms 12a and 12b with different patterns are provided on the back surface of the half mirror 12, and the light receiving element 15 is provided behind them. The configuration is as follows.

[0053] As a result, among the laser light incident from the semiconductor laser 11, the first and second holograms 12a,
+1st order diffracted light (or -1st order diffracted light) diffracted by 12b
is received by the light receiving element 15, and the actual amount of laser light irradiated onto the magneto-optical disk 14 can be detected based on the amount of received light. Furthermore, automatic light amount control can be performed based on the detected light amount.

[0054] Also, the first and second holograms 12a and 1
2b, the S-polarized light component and the P-polarized light component of the return light from the magneto-optical disk 14 are respectively subjected to 0th-order diffraction and ±1st-order diffraction and are incident on the light receiving element 17. Therefore, the number of optical parts can be reduced, and the overall As a result, smaller size, lighter weight, and faster access are possible.

Another magneto-optical head of the present invention will now be described with reference to FIGS. 5 and 6.

In this embodiment, a grating for generating three beams is placed in front of the semiconductor laser, and light receiving elements for detecting magneto-optical signals and servo error signals are configured accordingly. This embodiment differs from the first embodiment in this point.

That is, in the magneto-optical head according to this embodiment, as shown in FIG. 5, a grating 28 is arranged between the optical path of the semiconductor laser 21 and the half mirror 22. In the grating 28, the incident light is separated into 0th-order diffracted light and ±1st-order diffracted light. Note that the other components and arrangement are the same as in the previous embodiment.

Similar to the embodiment described above, the detection of the magneto-optical signal and the amount of laser light irradiated onto the magneto-optical disk 24 are performed in the light receiving element 29. In this embodiment, the focus error signal is detected by the astigmatism method, and the radial error signal is detected by the three-beam method.

According to the configuration of this embodiment, the semiconductor laser 2
Laser light from 1 is incident on grating 28. The grating 28 diffracts the incident light and separates it into three beams: 0th-order diffracted light and ±1st-order diffracted light. These three beams are incident on the half mirror 22. The three beams reflected by the half mirror 22 pass through the objective lens 23
They are each guided to predetermined locations on the magneto-optical disk 24 (recording medium) via the magneto-optical disk 24 (recording medium).

Return light collected from the magneto-optical disk 24 through the objective lens 23 passes through the half mirror 22,
The light is incident on a hologram 22a provided on the back surface of the half mirror. At this time, the incident light is incident on the hologram 22a at a predetermined angle (Bragg angle).

In the hologram 22a, the S-polarized component of the incident light is 0th-order diffracted, and the P-polarized component is diffracted by ±1
The light is then diffracted and guided to the light receiving element 29, where it is converted into a magneto-optical signal that changes depending on the amount of incident light.

Based on the incident light guided to the light-receiving element 29, a focus error is detected via the four-part light-receiving element in the light-receiving element 29 by the astigmatism method as described above.

Furthermore, a radial error detection signal is detected based on the ±1st-order diffracted light among the returned light from the magneto-optical disk 24. In other words, when the track shifts left and right with respect to the radial direction, the amount of ±1st-order diffracted light incident on the corresponding light receiving element changes, and by detecting this change as a differential output, a radial error signal is detected. It has become.

On the other hand, when the light (main beam) transmitted through the half mirror 22 out of the laser light emitted from the semiconductor laser 21 is incident on the hologram 22a, the P polarized light component of the incident light is diffracted in the ±1st order ( Main beam ±1
(order diffracted light), and the S-polarized light component is also subjected to 0th-order diffraction (0th-order diffracted light of the main beam). Either the +1st-order diffracted light or the -1st-order diffracted light (FIG. 5 shows the case of the +1st-order diffracted light) is incident on the light receiving element 25, but the polarized light that is incident on the magneto-optical disk 4 is Since the components are the same, the amount of laser light irradiated onto the magneto-optical disk 24 can be detected. It is possible to perform automatic light amount control based on the detected laser light amount.

Note that the 0th-order diffracted light of the main beam and the +1st-order diffracted light of the main beam have a relationship as shown in FIG. There is.

As described above, in the magneto-optical head according to this embodiment, the grating 28 is provided in front of the semiconductor laser 21, the hologram 22a is provided on the back surface of the half mirror 22, and the hologram 22a is provided on the back surface of the half mirror 22. This is a configuration in which a light receiving element 25 is provided.

As a result, the +1st-order diffracted light of the main beam diffracted by the hologram 22a or the -1st-order diffracted light of the main beam
One of the next diffracted lights is received by the light receiving element 25, and based on the amount of the received light, the magneto-optical disk 24
The actual amount of laser light irradiated on the area can be detected. Therefore, automatic light amount control can be performed based on the detected light amount.

Further, the hologram 22a causes the S-polarized light component and the P-polarized light component of the return light from the magneto-optical disk 24 to undergo 0th-order diffraction and ±1st-order diffraction, respectively, and reach the light receiving element 29.
The number of optical components can be reduced because
Overall, it enables smaller size, lighter weight, and faster access.

[0069]

Effects of the Invention The magneto-optical head according to the invention of claim 1 has the following features:
As described above, in order to detect a magneto-optical signal, the return light from the recording medium is transmitted to give it polarization characteristics, and the laser beam with the same polarization component as that irradiated onto the recording medium is diffracted in a predetermined direction. The optical diffraction means is provided on the back surface of the half mirror.

Therefore, the return light from the recording medium is diffracted by the optical diffraction means provided on the back surface of the half mirror, and a magneto-optical signal and a servo error signal are detected. The number of parts can be reduced, making it smaller, lighter, and faster accessible.

[0071] Furthermore, when the light transmitted through the half mirror among the laser light emitted from the light source is incident on the light diffraction means, the P polarized light component of the incident light is diffracted to the ±1st order. This is the same polarized light component that is incident on the recording medium. Therefore, the amount of laser light irradiated onto the recording medium can be detected based on the diffracted light of either one of the ±1st-order diffracted lights. Therefore, it is also possible to perform automatic light amount control based on the detected laser light amount.

Further, as described above, the magneto-optical head according to the second aspect of the invention detects the servo error signal.
comprising a grating that diffracts the incident laser light, divides it into three beams, and guides the three beams to the half mirror,
Optical diffraction means (hologram ) is provided on the back surface of the half mirror.

Therefore, in addition to the effect of claim 1, since the laser beam irradiated from the light source is divided into three beams by being diffracted by the 0th order and ±1st order by the grating, high accuracy can be achieved by the three beam method. This has the effect that radial errors can be detected.

[Brief explanation of drawings]

FIG. 1 is a rear view showing a hologram pattern of the present invention.

FIG. 2 is a block diagram showing the configuration of the magneto-optical head of the present invention.

FIG. 3 is a block diagram showing the configuration of another magneto-optical head of the present invention.

FIG. 4 is a rear view showing another hologram pattern of the present invention.

FIG. 5 is a block diagram showing the configuration of still another magneto-optical head of the present invention.

FIG. 6 is an explanatory diagram showing the relationship between the 0th-order diffracted light and the +1st-order diffracted light of the main beam when the amount of laser light irradiated onto the recording medium is detected using the magneto-optical head having the configuration shown in FIG. be.

FIG. 7 is a block diagram showing the configuration of a conventional magneto-optical head.

8 is an explanatory diagram showing in detail the main parts of the magneto-optical head shown in FIG. 7; FIG.

[Explanation of symbols]

1 Semiconductor laser 2 Half mirror 2a Hologram (light diffraction means) 4 Magneto-optical disk (recording medium) 5 Light receiving element

Claims (2)

[Claims] Claim 1: A device comprising a half mirror and recording and reproducing information using a laser beam guided by the half mirror.
In a beam-type magneto-optical head, the return light from the recording medium is passed through so as to detect a magneto-optical signal, giving it polarization characteristics, and a laser beam with the same polarization component as that irradiated onto the recording medium is directed in a predetermined direction. A magneto-optical head characterized in that a light diffraction means for diffracting light is provided on the back surface of the half mirror. 2. A magneto-optical head that includes a half mirror and records and reproduces information using a laser beam guided by the half mirror, in which the incident laser beam is diffracted to detect a servo error signal. Divide into three beams
The laser beam is equipped with a grating that guides the beam to the half mirror, and transmits the return light from the recording medium so as to detect a magneto-optical signal, giving it polarization characteristics, and the laser beam has the same polarization component as that irradiated onto the recording medium. A magneto-optical head characterized in that a light diffraction means for diffracting light in a predetermined direction is provided on the back surface of the half mirror.