JPH04319552A - Optical head - Google Patents

Abstract

PURPOSE:To control the light quantity of light irradiating a recording medium, and also, to curtail the number of parts by forming a deflection hologram on the reverse side of a half mirror, and providing a photodetector in the rear thereof. CONSTITUTION:On the reverse side of a half mirror 2, a polarization hologram 2a for diffracting the light which transmits through the half mirror 2 is formed, and also, a photodetector 5 is provided so as to detect a diffracted light having the same polarization as light radiated to a recording medium 4, in the diffracted light in the polarization hologram. Accordingly, light from a light source 1 is reflected by the surface of the half mirror 2 and radiated to the recording medium 4. Subsequently, a return light reflected by the recording medium 4 is diffracted by a hologram element 6 and an information signal and an error signal are detected. On the other hand, light of the light source, which transmits through the surface of the half mirror 2 is diffracted by the deflection hologram 2a formed on the reverse side. In this diffracted light, the diffracted light having the same polarization as the light radiated to the recording medium 4 is detected by the photodetector 5.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an optical head used in an optical information recording/reproducing device such as a magneto-optical disk drive device, and more particularly to an optical head using a hologram element having polarization characteristics in its optical system. It is.

0002

[Prior Art] Optical heads used in magneto-optical disk drives are small and compact in order to shorten access time.
Weight reduction is necessary. In addition, since the magnetic Kerr effect is used for signal detection, a semiconductor laser with good polarization characteristics is required, and the amount of polarized component of the laser light irradiated onto the magneto-optical disk as a magneto-optical recording medium is monitored. Therefore, it is necessary to control the amount of light emitted from the semiconductor laser to be constant.

Therefore, in the conventional optical head, as shown in FIG. 8, the above-mentioned request has been met by using a hologram element 22 in the optical system.

That is, this optical head is equipped with a semiconductor laser 28 as a light source.
On the optical path between the magneto-optical disk 30 and the semiconductor laser 28 side, a PBS (polarizing beam splitter) is installed.
20 and an objective lens 29 are arranged.

[0005] Also, from the semiconductor laser 28 to the PBS 20
A polarizing plate 26 and a light-receiving element 27 are arranged at positions where they can receive the light incident on the semiconductor laser 28 and reflected there. , APC (automatic light amount control) is performed so that the amount of light irradiated onto the magneto-optical disk 30 is constant.

Further, the return light reflected by the magneto-optical disk 30 enters the PBS 20 again, and a four-divided light receiving element 24 is arranged at a position where it can receive the light reflected here, and the PBS 20 and the light receiving element 24 There is PBS20 between
A (1/2) wavelength plate 21, a hologram element 22 for detecting a servo signal, and a PBS 23 are arranged in order from the side. Also, place 2 at a position where it can receive the light reflected by PBS23.
Divided light receiving elements 25 are arranged.

In the above configuration, the magneto-optical disk 30
The return light reflected by PBS20 is then reflected by (1
/2) The light enters the wavelength plate 21, the plane of polarization is rotated, and the light enters the hologram element 22.

As shown in FIG. 9, this hologram element 22 has two diffraction holograms 2 with different hologram shapes.
2a and 22b, and a diffraction hologram 22
The light diffracted by a and the light diffracted by the diffraction hologram 22b are separated into a P-polarized component and an S-polarized component by the PBS 23, and then separated onto the four-split light-receiving element 24 and the two-split light-receiving element 25, respectively. converge at different positions. And 4
A focus error signal is detected based on the output of the divided light receiving element 24, and a tracking error signal is detected based on the output of the two divided light receiving element 25. Further, an information signal is detected based on the outputs of both light receiving elements 24 and 25.

[0009]

[Problems to be Solved by the Invention] However, in the above conventional configuration, two PB
S20, 23 and a (1/2) wavelength plate 21 are required, and a polarizing plate 26 is also required to monitor the amount of polarized component of the laser beam irradiated from the semiconductor laser 28 to the magneto-optical disk 30. Therefore, there is a problem that the number of component parts of the optical head increases.

0010

[Means for Solving the Problems] An optical head according to the invention of claim 1 irradiates a recording medium with light from a light source reflected on the surface of a half mirror, and uses return light from the recording medium for detecting a servo signal. An optical head that detects an information signal and an error signal by diffracting it with a hologram element, and controls the amount of light by detecting light from a light source that has passed through the half mirror with a photodetector. A polarization hologram that diffracts the light transmitted through the half mirror is formed on the back surface, and a polarization hologram is formed to detect diffracted light having the same polarization as the light irradiated onto the recording medium, out of the diffracted light of the polarization hologram. It is characterized in that the above-mentioned photodetector is disposed at.

The optical head according to the second aspect of the invention irradiates a recording medium with light from a light source reflected on the surface of a half mirror, and diffracts the return light from the recording medium by a hologram element for detecting a servo signal. The optical head detects an information signal and an error signal, and controls the amount of light by receiving light from a light source that has passed through the half mirror, and the back surface of the half mirror is provided with a light that has passed through the half mirror. A polarization hologram that diffracts is formed, and the hologram element is integrally formed on the surface of the half mirror, and among the diffracted light of the polarization hologram,
It is characterized in that the photodetector is arranged to detect diffracted light having the same polarization as the light irradiated onto the recording medium.

0012

According to the structure of claim 1, the light from the light source reflected on the surface of the half mirror is irradiated onto the recording medium, and the return light from the recording medium is diffracted by the hologram element for detecting the servo signal to obtain information. detecting the signal and the error signal,
An optical head that controls the amount of light by detecting light from a light source that has passed through the half mirror with a photodetector, wherein a polarization hologram that diffracts the light that has passed through the half mirror is formed on the back surface of the half mirror; In addition, the photodetector is arranged to detect the diffracted light having the same polarization as the light irradiated onto the recording medium among the diffracted lights of the polarization hologram, so that the light from the light source is transmitted to the surface of the half mirror. is reflected and irradiated onto the recording medium. Then, the return light reflected by the recording medium is diffracted by the hologram element, and an information signal and an error signal are detected. On the other hand, the light from the light source that passes through the front surface of the half mirror is diffracted by a polarization hologram formed on the back surface. Of this diffracted light, the diffracted light having the same polarization as the light irradiated onto the recording medium is detected by a photodetector, so the amount of light irradiated onto the recording medium is controlled based on the output of this photodetector. becomes possible.

According to the second aspect of the present invention, the recording medium is irradiated with the light from the light source reflected on the surface of the half mirror, and the returning light from the recording medium is diffracted by the hologram element for detecting the servo signal to obtain information. An optical head that detects a signal and an error signal and controls the amount of light by receiving light from a light source that has passed through the half mirror, the back surface of the half mirror diffracting the light that has passed through the half mirror. In addition to forming a polarization hologram, the hologram element is integrally formed on the surface of the half mirror, and among the diffracted lights of the polarization hologram, diffracted light having the same polarization as the light irradiated onto the recording medium is transmitted. Since the photodetector is arranged for detection, the same effect as in claim 1 can be obtained, and the number of components of the optical head can be further reduced by one.

[0014]

[Embodiment] Figs. 1 to 3 regarding the first embodiment of the present invention
The explanation based on this is as follows.

The optical head of this embodiment is used in a magneto-optical disk drive device, and as shown in FIG. A hologram element 6 and an objective are provided between the half mirror 2 and the magneto-optical disk 4 in order from the side of the half mirror 2. It has a configuration in which a lens 3 is arranged.

A polarization hologram 2a is formed on the back surface of the half mirror 2, as shown in FIG. The polarization hologram 2a has a hologram pattern as shown in FIG. 3, and separates the two polarization components by diffracting the S polarization component of the incident light into the 0th order and diffracting the P polarization component into the ±1st order. do.

A light receiving element 5 (photodetector) 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 installed at a position to receive one of the ±1st-order diffracted lights that are transmitted through the half mirror 2 and diffracted by the polarization hologram 2a, out of the laser light emitted from the semiconductor laser 1. ing. As a result, the polarized light component incident on the light receiving element 5 becomes the same as the polarized light component (P polarized light component) incident on the magneto-optical disk 4, so the light receiving element 5
APC (automatic light amount control) can be performed based on the output.

On both sides of the semiconductor laser 1, there are a four-part light receiving element 7 for detecting an error signal and a four-part light receiving element 7 for detecting an information signal.
A divided light-receiving element 9 is arranged so that one of the ±1st-order diffracted light diffracted by the hologram element 6 is converged on the light-receiving element 7 and the other is converged on the light-receiving element 9.

The hologram element 6 (FIG. 1) is composed of two diffraction holograms 6a and 6b with different hologram shapes so that servo signals such as tracking error signals can be detected. The returned light is diffracted by the diffraction holograms 6a and 6b, reflected by the half mirror 2, and converged at different positions of the four-divided light receiving element 7. Note that the focus error signal is detected by applying the so-called Foucault method to the convergent light diffracted by either one of the diffraction holograms 6a and 6b.

Between the half mirror 2 and the light receiving element 9,
A polarizing hologram 8 is arranged obliquely with respect to the optical axis, and the first-order diffracted light diffracted by the diffraction holograms 6a and 6b of the hologram element 6 is separated into polarized components and guided to the four-divided light receiving element 9. , to detect magneto-optical signals as information signals.

In the above configuration, the laser beam emitted from the semiconductor laser 1 is reflected by the half mirror 2, but some of the light is transmitted and enters the polarization hologram 2a formed on the back surface of the half mirror 2. .

In the polarization hologram 2a, the S-polarized component of the incident light is diffracted in the 0th order, while the P-polarized component is diffracted in the ±1st order. Then, one of the ±1st order diffracted lights enters the light receiving element 5. Therefore, the light-receiving element 5 detects light of the P-polarized component, which is the same as the polarized component of the light irradiated onto the magneto-optical disk 4 . Therefore, based on the output of the light receiving element 5, APC can be performed so that the amount of light emitted from the semiconductor laser 1 is constant.

The light reflected by the above half mirror 2 is
The light (0th-order diffracted light) that is incident on the hologram element 6 and transmitted therethrough is focused onto the magneto-optical disk 4 by the objective lens 3 . The return light reflected by the magneto-optical disk 4 is condensed by the objective lens 3 and enters the hologram element 6 again.

The returned light is transmitted to the hologram element 6 at 0
The light is separated into second-order diffracted light and ±first-order diffracted light. These lights are then reflected by the half mirror 2, and the 0th order diffracted light returns to the semiconductor laser 1. Further, one of the ±1st-order diffracted lights is guided to the light receiving element 7, and the other is separated into polarized components by the polarization hologram 8 and then guided to the light receiving element 9.

At this time, one of the ±1st-order diffracted lights respectively diffracted by the two diffraction holograms 6a and 6b of the hologram element 6 converges on two different positions of the four-divided light-receiving element 7. Then, based on the four outputs of the light receiving element 7, a tracking error signal and a focus error signal are detected. In other words, the tracking error signal can be obtained by comparing the sum of the two outputs on the left and the sum of the two outputs on the right, and the focus error signal can be obtained by comparing the two outputs on the left (or right). I can get a signal.

Further, the other of the ±1st-order diffracted lights respectively diffracted by the two diffraction holograms 6a and 6b of the hologram element 6 is separated into polarization components by the polarization hologram 8, and is split into four polarization components of the four-divided light-receiving element 9. converge at different positions. Based on the four outputs of this light receiving element 9,
A magneto-optical signal is detected.

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

As a result, one of the ±1st-order diffracted lights transmitted through the half mirror 2 and diffracted by the polarization hologram 2a is received by the light receiving element 5, and based on the amount of the received light, the magneto-optical disk 4 It is possible to detect the amount of laser light irradiated to the area. Therefore, automatic light amount control can be performed based on the output of the light receiving element 5.

Furthermore, since the polarization hologram 2a is formed on the back surface of the half mirror 2, the number of optical parts can be reduced compared to the conventional one, and the overall size and weight can be reduced, and high-speed access can be achieved.

Next, regarding the second embodiment of the present invention, FIG.
The explanation will be as follows based on FIG. 7. For convenience of explanation, members having the same functions as those shown in the drawings of the above-described embodiments are denoted by the same reference numerals, and their explanations will be omitted.

The optical head of this embodiment is used in a magneto-optical disk drive, and its schematic configuration is shown in FIG. 4.

The difference between this optical head and the optical head of the previous embodiment lies in the half mirror 12. That is, in the half mirror 12 of the optical head of this embodiment, as shown in FIG. 5, not only a polarizing hologram 12a is formed on the back surface, but also a hologram 12b ( A hologram element) is formed, thereby reducing the number of components of the optical head.

The polarization hologram 12a has the same hologram shape as the embodiment described above (see FIG. 3 of the embodiment described above). Moreover, as shown in FIG. 6, the hologram 12b is
Two diffraction holograms 12c with different hologram shapes.
The return light reflected by the magneto-optical disk 4 is diffracted by the diffraction holograms 12c and 12d, and then converged at different positions of the four-divided light receiving elements 7 and 9 (FIG. 4). It has become.

Other configurations of the optical head of this embodiment are as follows:
This is the same as the previous embodiment.

In the above configuration, the laser light emitted from the semiconductor laser 1 is reflected by the hologram 12b formed on the surface of the half mirror 2, but some of the light is 0th-order diffracted (transmitted) by the hologram 12b. , half mirror 2
The light enters a polarizing hologram 12a formed on the back surface of the hologram.

In the polarization hologram 12a, the S-polarized component of the incident light is diffracted in the 0th order, while the P-polarized component is diffracted in the ±1st order. Then, as shown in FIG. 7, one of the ±1st order diffracted lights enters the light receiving element 5. therefore,
The light receiving element 5 detects the amount of light of the P-polarized light component, which is the same as the polarized light component of the light irradiated onto the magneto-optical disk 4 . Therefore, based on the output of the light receiving element 5, APC can be performed so that the amount of light emitted from the semiconductor laser 1 is constant.

Note that 0 shown in FIGS. 5 and 7
The -0th order light is the 0th order diffracted light of the hologram 12b that is 0th order diffracted by the polarization hologram 12a, and the 0-1st order light is the 0th order diffracted light of the hologram 12b that is 1st order diffracted by the polarization hologram 12a. It shows the light.

On the other hand, light emitted from the semiconductor laser 1 and reflected by the hologram 12b formed on the surface of the half mirror 2 is focused onto the magneto-optical disk 4 by the objective lens 3. The return light reflected by the magneto-optical disk 4 is condensed by the objective lens 3, and then returned to the half mirror 2.
incident on .

The hologram 12b of the half mirror 2 separates the returned light into 0th-order diffracted light (reflected light) and ±1st-order diffracted light (reflected diffracted light). The 0th order diffracted light then returns to the semiconductor laser 1. Further, one of the ±1st-order diffracted lights is guided to the light receiving element 7, and the other is separated into polarized components by the polarization hologram 8 and then guided to the light receiving element 9.

At this time, one of the ±1st-order diffracted lights respectively diffracted by the two diffraction holograms 12c and 12d of the hologram 12b converges on two different positions of the four-divided light-receiving element 7. Then, based on the four outputs of the light receiving element 7, a tracking error signal and a focus error signal are detected. That is, a tracking error signal is obtained by comparing the sum of the two outputs on the left and the sum of the two outputs on the right. Also, by comparing the two outputs on the left side (or right side), a focus error signal can be obtained.

Further, the other of the ±1st-order diffracted lights diffracted by the two diffraction holograms 12c and 12d of the hologram 12b is separated into polarization components by the polarization hologram 8, and is divided into four different polarization components of the four-divided light-receiving element 9. Converge on position. Then, based on the four outputs of the light receiving element 9, a magneto-optical signal is detected.

As described above, in the optical head according to this embodiment, the hologram 12b for detecting servo signals is formed on the front surface of the half mirror 2, and the polarization hologram 12a is formed on the back surface, and the polarization hologram 12a is formed on the back surface of the half mirror 2. This is a configuration in which a light receiving element 5 is provided.

As a result, one of the ±1st-order diffracted lights transmitted through the half mirror 2 and diffracted by the polarization hologram 2a is received by the light receiving element 5, and based on the amount of the received light, the magneto-optical disk 4 It is possible to detect the amount of laser light irradiated to the area. Therefore, automatic light amount control can be performed based on the output of the light receiving element 5.

Furthermore, since not only the polarizing hologram 12a is formed on the back surface of the half mirror 2, but also the hologram 12b is formed on the front surface, the number of optical parts can be further reduced than in the first embodiment, and the overall As a result, further compactness, weight reduction, and high-speed access are possible.

In the above embodiments, an optical head used in a magneto-optical disk drive device has been described, but the present invention can also be applied to an optical head of a magneto-optical card device, a magneto-optical tape device, etc.

[0046]

As described above, in the optical head according to the invention of claim 1, a polarization hologram for diffracting light transmitted through the half mirror is formed on the back surface of the half mirror, and the diffraction of the polarization hologram is A photodetector is arranged to detect diffracted light having the same polarization as the light irradiated onto the recording medium.

[0047] Accordingly, based on the output of the photodetector,
It is possible to control the amount of light irradiated to the recording medium, and it also has fewer parts than conventional optical heads, making it possible to create a compact and lightweight optical head, which has the effect of achieving high-speed access. play.

As described above, in the optical head according to the second aspect of the invention, a polarization hologram for diffracting light transmitted through the half mirror is formed on the back surface of the half mirror, and a polarization hologram is formed on the surface of the half mirror. A configuration in which a hologram element is integrally formed, and a photodetector is arranged to detect diffracted light having the same polarization as the light irradiated onto the recording medium, out of the diffracted light of the polarization hologram. It is.

[0049] Accordingly, based on the output of the photodetector,
It is possible to control the amount of light irradiated onto the recording medium, and furthermore, it is possible to realize a compact and lightweight optical head with a smaller number of parts than the optical head of claim 1 above.
This has the effect that faster access can be achieved.

[Brief explanation of drawings]

FIG. 1 shows a first embodiment of the present invention, and is a schematic configuration diagram of an optical head.

FIG. 2 is an explanatory diagram showing the configuration of the half mirror in FIG. 1;

FIG. 3 is an explanatory diagram showing a hologram shape of a polarization hologram formed on the back surface of the half mirror in FIG. 1;

FIG. 4 shows a second embodiment of the present invention, and is a schematic configuration diagram of an optical head.

FIG. 5 is an explanatory diagram showing the configuration of the half mirror shown in FIG. 4;

6 is an explanatory diagram showing a hologram shape of a hologram formed on the surface of the half mirror shown in FIG. 4. FIG.

7 is an explanatory diagram showing the positional relationship between the 0-0 order light and the 0-1 order light diffracted by the half mirror of FIG. 5 and a light receiving element; FIG.

FIG. 8 is a schematic configuration diagram of a conventional optical head.

FIG. 9 is an explanatory diagram showing detection of an error signal in the optical head of FIG. 8;

[Explanation of symbols]

1 Semiconductor laser (light source) 2 Half mirror 2a Polarizing hologram 4 Magneto-optical disk (recording medium) 5 Light receiving element (photodetector) 6 Hologram element 6a Diffraction hologram 6b Diffraction hologram 12 Half mirror 12a Polarization hologram 12b Hologram (hologram element) 12c Diffraction hologram 12d Diffraction hologram

Claims (2)

[Claims] 1. Light from a light source reflected on the surface of a half mirror is irradiated onto a recording medium, and the returned light from the recording medium is diffracted by a hologram element for detecting a servo signal to detect an information signal and an error signal. At the same time, the optical head controls the amount of light by detecting the light from the light source that has passed through the half mirror with a photodetector, and the back surface of the half mirror has a polarization hologram that diffracts the light that has passed through the half mirror. and the photodetector is arranged to detect diffracted light having the same polarization as the light irradiated onto the recording medium, out of the diffracted light of the polarization hologram. optical head. 2. Light from a light source reflected on the surface of a half mirror is irradiated onto a recording medium, and the returned light from the recording medium is diffracted by a hologram element for detecting a servo signal to detect an information signal and an error signal. In addition, the optical head controls the amount of light by receiving light from a light source that has passed through the half mirror, and a polarization hologram that diffracts the light that has passed through the half mirror is formed on the back surface of the half mirror. Also, the hologram element is integrally formed on the surface of the half mirror, and the hologram element is configured to detect diffracted light having the same polarization as the light irradiated onto the recording medium, out of the diffracted light of the polarization hologram. An optical head characterized in that the above-mentioned photodetector is disposed in the optical head.