JPS63183644A - Magneto-optical recording and reproducing head - Google Patents

Abstract

PURPOSE:To miniaturize an optical system and to reduce the weight of a head, and to raise the utilization efficiency of a laser beam by using a multiple image element for the photodetector of magneto-optical reproduction, and using an astigmatism method for a servo-error signal optical system. CONSTITUTION:A luminous flux from a semiconductor laser 1 passes through a collimating lens 2, a beam splitter 4, and an objective lens 5, a part of the luminous flux is converged and projected onto a magneto-optical recording medium surface 6, and a part thereof is reflected by the medium surface 6, the signal component of 100% is reflected by the splitter 4, and also, a part of this signal component and a component whose polarized light surface is different by n/2 is reflected. These reflected light beams are rotated by n/4 by a 1/2 lambda plate 7 provided with a rotary mechanism, the axis of its column transmits through the cylindrical lens 8 of 45 deg. against the track direction and a spherical lens 9, and total three optical fluxes of two luminous fluxes which are polarized and split with a separation angle phi against the optical axis direction and the optical axis by a multiple image element 10 are led to a multi-split photodetector 11.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a magneto-optical recording/reproducing head using a magneto-optical recording medium, and in particular to an optical element having a configuration that allows the magneto-optical system to be made smaller and simpler. This relates to the mounted magneto-optical recording/reproducing head.

(Prior art and problems to be solved by the invention) When writing and reproducing information signals using an optical head, first of all, focal plane detection (detection of focus error signal) and track position detection (detection of track error signal) are performed. detection) is important. Conventionally, various methods have been devised for focal plane detection. Representative methods include the Naifetsu method, the astigmatism method,
Examples include the critical angle method. Among these, the astigmatism method related to the present invention will be briefly described. FIG. 8 shows a conceptual diagram of the astigmatism method. Astigmatism method uses cylindrical lens 2
5 and a spherical lens 26, 3 in the figure.
0 indicates a ray toward the spherical lens, and 31 indicates a ray toward the composite lens. In this method, the beam shape on the photodetector 29 surface is determined by the relative distance between the medium surface of the optical disk 27 and the focal position of the objective lens 28 as shown in FIGS. 9(a) and 9(b).

It changes as shown in (e). That is, FIG. 5A shows the case where the objective lens 28 is close to the medium surface, FIG. 2B shows the case where the objective lens 28 is at a focused point, and FIG. Therefore, the outputs of each photodetector are A and B.

In the case of C and D, the photodetector 29 is (A+D)-
By performing the calculation of (B + C), it becomes possible to detect the focus error signal. At the same time, (A+B)-(C
By performing the calculation +D), it is possible to detect the track error signal by capturing the diffracted light from the optical disc with the guide groove. Of course, at this time, the axis of the cylinder of the cylindrical lens 25 is arranged at an angle of 45° with respect to the track direction. Therefore, by using the above method, servo signal detection can be configured with one photodetector, and a servo device (not shown) is used to position the spot of the light beam on the recording medium surface of the optical disk, and performs recording and reproduction. It is possible to do so.

Conventionally, in write-once optical discs, information signals are recorded as physical changes in shape by drilling holes on the surface of the recording medium, and since the reproduction principle is the same for servo signal detection and information signals, the recording medium surface When reproducing the above recorded information signal, a method in which a servo signal photodetector and a reproduction signal photodetector are separately detected is not generally used. For example, the sum signal (A+B+
C+D) and uses the high frequency range of this signal to reproduce the recorded information signal. Therefore, the configuration is such that the servo signal and the recording information signal can be detected with one four-split photodetector.

However, in magneto-optical recording, the signal detection method is based on the principle as shown below, so in the write-once type method, the servo photodetector and the recording information signal photodetector cannot be shared. That is, in magneto-optical recording, since a thermomagnetic recording method is used to record information signals, the recorded information signals exist on the surface of the recording medium in the form of magnetic recording information rather than physical shape changes. Therefore, a method for reproducing magnetically recorded information from a magneto-optical recording medium utilizes magneto-optical effects called the Kerr effect and the Faraday effect. Figure 7(a), (
b) shows a conventional magneto-optical recording medium head that utilizes the Kerr effect. In the magneto-optical recording/reproducing head shown in FIG. 7(a), a laser beam emitted from a semiconductor laser 1 is converted into parallel light by a collimator lens 2, and a beam splitter 3,
The light passes through the beam splitter 4 and is narrowed down to a minute light spot by the objective lens 5 installed on the actuator.
The light is irradiated onto the surface of the magneto-optical recording medium 6 and reflected. At this time, the polarization state of the reflected light changes depending on the magnetization state of the irradiated magneto-optical recording medium. The reflected light from the magneto-optical recording medium passes through the objective lens 5 again, has its optical path bent by the beam splitter 4, and reaches a half-wave plate 7 with a rotating mechanism. At this time, the half-wave plate changes the polarization plane of the reflected light to n/
The light is rotated by 4 and sent to the analyzer 12, and is focused by the lens 9 onto the photodetectors B13a and 13b, a signal corresponding to the magnetization state of the medium is output, and a differential amplifier 17 forms a difference signal. At this time, a portion of the transmitted light from the beam splitter 4 is reflected by the beam splitter 3, and is guided to a servo optical system using an astigmatism method, which includes a cylindrical lens 14, a spherical lens, and a 4-split photodetector 16. A focus error signal and a track error signal were obtained to position the light beam on the surface of the magneto-optical recording medium.

The magneto-optical recording/reproducing head shown in FIG. 7(b) is an example in which the beam splitter 3 is provided in the optical path of the reflected light from the beam splitter 4, and the other configuration is the same as that in FIG. 7(a).

FIG. 6 is a diagram for explaining the reproducing principle of magneto-optical recording using the magnetic Kerr effect. R- represents the polarized light reflected from the magnetized region, and R- represents the polarized light reflected from the magnetized region above the medium film surface. Further, θ is called the Kerr rotation angle, and represents the amount by which the plane of polarization of light is rotated due to the magneto-optic effect.

At this time, when the reproducing light spot scans the alternately magnetized areas of the magneto-optical recording medium 6, the analyzer 12 is mechanically rotated by θ from the extinction position, with the light intensity incident on the analyzer 12 being P. The light intensity of the modulated light when

S = Psin2θksin2θ (Problem to be Solved by the Invention) In the magneto-optical recording/reproducing head shown in FIG. Because of this, not only does the efficiency of light utilization deteriorate, but also it is necessary to use two expensive beam splitters. On the other hand, Fig. 7 (b
), it is possible to use one beam splitter between the laser and the medium, but the number of beam splitters remains two, and the efficiency of the light on the recording information signal side deteriorates. Signal-to-noise ratio (SN) of recorded information signal
This leads to disadvantages such as deterioration of ratio). The conventional magneto-optical heads shown in FIGS. 7(a) and 7(b) use both transmitted light and reflected light from the analyzer, so they have a spatially large configuration. Further, there are disadvantages such as the necessity of using two photodetectors with the same characteristics, the small light-receiving area of the photodetectors, and the hassle of individually adjusting the light-receiving position. Additionally, in this case, the servo error signal is obtained using a separate optical system, resulting in a spatially large configuration.
This has been a major drawback in reducing the size and cost of the device.

An object of the present invention is to improve the above-mentioned drawbacks and provide a magneto-optical recording/reproducing head which can reduce the size and weight of the optical system for magneto-optical reproduction, and at the same time has an optical system configuration that is highly efficient in utilizing laser light. It is in.

(Means for Solving the Problems) The magneto-optical recording/reproducing head of the present invention includes a light source and a beam emitted from the light source that condenses and irradiates onto the surface of a magneto-optical recording medium, and extracts reflected light or transmitted light. a first optical system; a beam splitter provided in the optical path of the reflected light or transmitted light for dividing the amplitude of the reflected light or transmitted light; It is installed in the optical path, and the polarization plane is set to n/4.
a second optical system that rotates and polarizes the light beam in three directions: an optical axis direction and two different directions with separation angles with respect to the optical axis; and an information signal is generated from the polarized light beam in the three directions. It is characterized by being equipped with a multi-division photodetector that detects each.

(Function) By simplifying the optical system, it is possible not only to make the magneto-optical head more compact and weigh more, but also to increase the efficiency of using the light from the light source, thereby reducing the burden on the light source. Therefore, increasing the rotation speed of the magneto-optical disk can alleviate the problem of the burden of optical power during recording, and as a result, the rotation speed of the magneto-optical disk can be increased and the data transfer speed can be improved. It becomes possible. At the same time, it is also possible to significantly shorten the access time of the magneto-optical disk system itself. On the other hand, since only one photodetector is required, the effort required for adjustment can be significantly reduced.

(Example) Next, the present invention will be explained with reference to the drawings.

FIG. 1 shows a first embodiment of the magneto-optical recording/reproducing head of the present invention. This magneto-optical recording/reproducing head uses a semiconductor laser 1
and a collimating lens 2) that condenses and irradiates the light beam emitted from the semiconductor laser onto the surface of the magneto-optical recording medium. A half-wave plate 7 with a rotation mechanism that rotates the polarization plane of the reflected light by n/4, a cylindrical lens 8, and a spherical lens 9, which direct the light beam in two different directions with a separation angle in the optical axis direction and in the optical axis direction. and a multi-segment photodetector 11 that detects information signals from the light beam transmitted in the optical axis direction and from both the light beams polarized and split at the separation angle. There is.

The light beam emitted from the semiconductor laser 1 is passed through the collimating lens 2
) The beam passes through the beam splitter 4 in this order, and is focused and irradiated onto the magneto-optical recording medium surface 6 by the objective lens 5 installed on the actuator. A part of the focused luminous flux is magneto-optical a
Reflected by self-recorded media.

The reflected light beam is split by a beam splitter 4. At this time, the beam splitter 4 is configured to reflect 100% of the recorded information signal component on the magneto-optical recording medium, and to reflect part of the component whose polarization plane differs by 11/2 from the recorded information signal component. I'll keep it. The light reflected from the magneto-optical recording medium by the beam splitter 4 has its plane of polarization rotated by r1/4 by a half-wave plate 7 equipped with a rotation mechanism. Next, this reflected light passes through a cylindrical lens 8 whose cylinder axis has an angle of 45° with respect to the track direction, and a spherical lens 9, and is transmitted by the double image element 10 according to the present invention.
A total of three light fluxes, ie, two light fluxes that are polarized and split in the optical axis direction and with a separation angle φ with respect to the optical axis, are guided to the multi-split photodetector 11 .

FIG. 2 shows a configuration example of the multi-division photodetector 11 according to the present invention. The light beam transmitted in the optical axis direction is detected by the multi-split photodetector 1.
1, and outputs a focus error signal FO and a tracking error signal Tr using the astigmatism method in the prior art. On the other hand, the other two light fluxes are guided to the photodetecting sections 11b and llc. At this time, the configuration is such that the recording information signal S recorded on the medium surface is obtained by performing differential calculation between the signals of the photodetector 11B and the photodetector 11c. In the multi-division light detection 511, the light detection section 11b
In order to perform differential amplification between the photodetector 11c and the photodetector 11c, the same amount of light needs to be incident on both photodetectors. For this purpose, the half wavelength plate 7 with a rotation mechanism is rotated around the optical axis for adjustment. Of course, if the optical axis of the half-wave plate 7 is designed in advance so as to theoretically rotate the plane of polarization by r114, a rotation mechanism is not required, but in reality, due to mechanical misalignment or environmental conditions, Since the characteristics may change, it is better to provide a rotation mechanism.

FIG. 3 shows an embodiment of the half-wave plate 7 with a rotating mechanism. FIG. 3(a) is a front view, and FIG. 3(b) is a side view. The rotation mechanism includes a support base 18, on which a rotatable support column 20 is supported. At one end of the support column,
The gear 19 is fixed, and the support column 20 and the gear 19
A through hole 21 is provided therethrough. A half wavelength plate 22 is fixed within this through hole. According to this half-wave plate with a rotating mechanism, the gear 19
By rotating the half-wave plate 22, the half-wave plate 22 is rotated.

FIG. 4 is a diagram illustrating the optical properties of the double image element according to the present invention. The double image element is constructed by, for example, polishing quartz crystals into wedge shapes of the same shape and bonding them together. Conventionally, a Wallaston prism is formed by pasting together wedges whose optical axes are parallel to and perpendicular to the plane of incidence.
The separation angle Φ was determined by the apex angle of the wedge. In the double image element according to the present invention, the optical axis of the wedge on the incident light side is set at an arbitrary angle as shown in the figure, and the light beam is divided into two parts using the birefringence of crystal, and each light beam is divided into two according to the apex angle of the wedge. The beam is divided into two by the difference, and the light beam is transmitted through the next wedge and exits.

Here, basically, four light beams are formed. By setting the optical axis and the apex angle of the wedge so that two of the formed light beams overlap, the light beam is essentially spread in three directions. It is possible to divide.

The ratio of the amount of light divided into three directions can be determined, for example, by setting the optical axis on the exit side to an arbitrary capacity, and the separation angle φ is determined by the apex angle of the wedge. Therefore, the separation width d of the multi-division photodetector 11 is set in advance to match the separation width calculated from the separation angle φ. Further, the optimum light amount ratio is set in consideration of the S/N ratio of the recording information signal and the S/N ratio of the servo error signal.

FIG. 5 shows a second embodiment of the magneto-optical recording/reproducing head of the present invention. This magneto-optical recording/reproducing head uses a semiconductor laser 1 as a light source, as in the first embodiment of the present invention, and condenses and irradiates the light beam emitted from the light source onto the surface of a magneto-optical recording medium 6.
A beam splitter 4 is disposed in the optical path of the reflected light to split the amplitude, and a cylindrical lens 8 and a spherical lens 9 are arranged in the optical path of the reflected light to divide the light beam into two different beams in the optical axis direction and at a separation angle with respect to the optical axis. a double image element 10a that splits polarized light in three directions, a multi-segment photodetector 11 that detects information signals from the light beam transmitted in the optical axis direction, and the two light beams polarized and split at the separation angle. We are prepared.

In the first embodiment described above, the double image element according to the present invention is arranged in a fixed state, and the plane of polarization is set to n/4 using a half-wave plate.
By rotating the double image element, the amount of each light that is polarized and split by the separation angle Φ was equalized, but in the second embodiment, the half-wave plate was removed and the double image element itself was placed in a rotating mechanism, and the optical axis was centered. The structure is such that the same effect can be obtained by rotating it. At this time, since the direction of separation by the double-image element changes rotationally as the double-image element rotates, it is possible to always stably send the light flux to each photodetector by fixing the photodetector to the double-image element, for example. Configure it to reach it.

In the above embodiments, an example of a basic optical system was shown, but the influence of retardation occurring in optical elements and magneto-optical recording media can be suppressed by inserting a phase compensation plate having a phase compensation effect into the reproduction optical system. Good too. In addition, in the above embodiment, the reflected light from the magneto-optical recording medium is divided by the beam splitter and the reflected light from the beam splitter is used to obtain an information signal, but by changing the optical configuration of the beam splitter, the transmitted light It is also possible to use a configuration in which signal detection is performed. In this case, the configuration is such that the light from the light source is reflected by the beam splitter and focused on the magneto-optical recording medium. Furthermore, although the above embodiments have a configuration in which information signals are detected using reflected light from a magneto-optical recording medium, a configuration may also be adopted in which light transmitted through the magneto-optical recording medium is used.

(Effects of the Invention) As explained above, the magneto-optical recording medium head of the present invention has the following features:
By using a double image element as an analyzer for magneto-optical reproduction and using an astigmatism method in a servo error signal optical system, a recorded information signal and a servo error signal can be obtained by a single multi-segment photodetector. The optical system could be made smaller and lighter in weight. Furthermore, since the servo error signal optical system and the recording information signal optical system are integrated, the efficiency of using light from the light source can be increased. Therefore, the load on the light source can be reduced, and by increasing the rotational speed of the disk, the data transfer speed can be improved as a result. At the same time, it is also possible to significantly shorten the access time of the magneto-optical disk system itself. On the other hand, since only one photodetector is required, the effort required for adjustment can be significantly reduced.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a first embodiment of the magneto-optical recording/reproducing head of the present invention, FIG. 2 is a diagram showing an example of the configuration of a multi-division photodetector according to the present invention, and FIG. FIG. 4 is a diagram for explaining the optical properties of the double image element according to the present invention, and FIG. 5 is a diagram for explaining the optical properties of the double image element according to the present invention. FIG. 6 is a diagram showing an embodiment of the present invention, and FIG. 7(a) is a diagram for explaining the reproduction principle of magneto-optical recording using the magnetic Kerr effect. (b) is a diagram showing the basic configuration of a conventional magneto-optical recording/reproducing head, FIG. 8 is a conceptual diagram of the astigmatism method, and FIG. 9 (a). (b) and (c) are diagrams for explaining the operating principle of the astigmatism method. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Collimator lens, 3.4... Beam splitter, 5.28... Objective lens, 6... Magneto-optical recording medium, 7... 2 minutes with rotation mechanism 1 wavelength plate, 8.14.25
...Cylindrical lens, 9.15.26...Spherical lens, 10.10a...Double image element, 11...Multi-segment photodetector, 12...Analyzer, 13a, 13b-... Photodetector, 16... Quadrant photodetector, 17... Differential amplifier, 18... Support stand, 19... Gear, 20... Support column, 21... Through hole, 22 ... Half wavelength plate, 27 ... Optical disk, 29 ... Photodetector, 30 ... Spherical lens direction rays Fig. 1 Fig. 2 Fig. 3 Fig. 4 Double image element Fig. 5 ↑ 1～? Figure 6↑ 1~-1? - Figure 8 Figure 9

Claims (5)

[Claims] (1) A light source, a first optical system that condenses and irradiates the light flux emitted from the light source onto the surface of the magneto-optical recording medium, and extracts the reflected light or transmitted light; a beam splitter that divides the amplitude of the reflected light or the transmitted light, and a beam splitter that is installed in the optical path of the transmitted light of the beam splitter or the reflected light from the beam splitter, rotates the plane of polarization by n/4, and in the optical axis direction and in two different directions with separation angles from the optical axis.
1. A magneto-optical recording/reproducing head comprising: a second optical system that splits polarized light in three directions; and a multi-divided photodetector that detects information signals from the polarized light beams in three directions. (2) In the magneto-optical recording/reproducing head according to claim 1, the second optical system includes a half-wave plate that rotates the plane of polarization by n/4, and a cylindrical lens.
1. A magneto-optical recording/reproducing head comprising a spherical lens and a double image element that polarizes a light beam into three directions: in the optical axis direction and in two different directions at separation angles with respect to the optical axis. (3) In the magneto-optical recording/reproducing head according to claim 1, the second optical system includes a cylindrical lens, a spherical lens, and a cylindrical lens, a spherical lens, and a cylindrical lens that directs the light beam in the optical axis direction and at a separation angle with respect to the optical axis. 1. A magneto-optical recording/reproducing head comprising a double image element with a rotating mechanism that divides polarized light into two different directions and three directions. (4) The magneto-optical recording/reproducing head according to claim 1, wherein the multi-division photodetector outputs a recording information signal at the same time as a servo error signal. (5) A magneto-optical recording and reproducing head according to any one of claims 1 to 4, wherein the light source is a laser.