JPH01315052A - Magneto-optical head device - Google Patents

Abstract

PURPOSE:To eliminate the noises caused by the return light and to obtain a compact and light-weight magneto-optical head device by reflecting the linear polarized light received from a semiconductor laser by the light quantity higher than a specific ratio to obtain the rectangular reflected light and using this reflected light as the return light to the semiconductor laser. CONSTITUTION:An external resonance optical system 10 consists of a beam splitter 6 which reflects the incident parallel luminous flux 5 by the >=20% light quantity as the rectangular reflected light 5B and an external reflecting mirror 11. The outgoing linear polarized light 2 of a semiconductor laser 1 is turned into the parallel luminous flux 5. The flux 5 is partly (>=20%) reflected by the beam splitter 6 and turned into the rectangular reflected light 5B. The light 5B is reflected by the mirror 11 and fed back to the laser 1 as the return light 15A via a return optical path 15 consisting of the splitter 6, etc. Under such conditions, the laser 1 has the stable oscillation in a single mode. As a result, the back talk noises produced by the return light are eliminated. Thus it is possible to obtain a compact and light-weight magneto-optical magnetic head at the low cost without using a high frequency superposition circuit.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention relates to a magneto-optical head device in which information is erased and recorded by light irradiation and an external magnetic field, and information is reproduced by light irradiation. Regarding the configuration of the optical system.

[Conventional technology]

In a magneto-optical disk as a magneto-optical recording medium, the recording shape W
Since the magnetization directions of the information recording areas in the erasing state are opposite to each other, a magnetic field is applied in a direction corresponding to the magnetization direction in each state, and light focused on a minute spot with a diameter of approximately 1 μm is projected. Then, the temperature of the information recording section is raised to near the Chierly temperature, and the information recording section is magnetized in the direction of the magnetic field to record or erase information.

In addition, when reproducing information, the Kerr effect is used, in which when linearly polarized light is reflected by a magnetic material, the polarization direction of the reflected light rotates with respect to the polarization direction of the incident light, and the reflected light is passed through an analyzer. By doing this, the original strength signal corresponding to the rotation direction of the polarization direction, that is, the magnetization direction of the information recording section, is detected.

FIG. 3 is a configuration diagram of an optical system of a conventional magneto-optical head device. A semiconductor laser 1 serving as a light source projects linearly polarized light 2 whose polarization direction is perpendicular to the plane of the paper and is indicated by the symbol ■, and is converted into a parallel light beam by a collimating lens 3. Since the projection light from the semiconductor laser 1 has different expansion angles in the horizontal direction and the vertical direction, the cross section of the parallel light beam is an inertia circle. This parallel light beam is shaped by a beam distortion prism 4 into a parallel beam 5 having a circular cross section. This parallel beam 5 passes through a beam splitter 6 and a reflection mirror 7, and is focused by an objective lens 8 onto a minute spot 50 with a diameter of 1 μm on a magnetic recording portion (not shown) of a magneto-optical disk 9 as a magneto-optical recording medium. Projected.

The information track on which the magnetic recording section is provided is arranged in a direction parallel to the plane of the paper, and the direction of polarization of the projected light is approximately perpendicular to the direction of the information track. The projected light is reflected by a magnetic recording section (not shown), and this reflected light 5
The polarized light 1 changes its polarization direction according to the direction of magnetization of the magnetic recording section, passes through the objective lens 82 and reflection mirror 7 again, is reflected by the beam splitter 6, becomes detected reflected light 51A, and is guided to the reflected light detection system 41. . The reflected light detection system 41 includes a 1/2 wavelength plate 42. Polarizing beam splitter 46. Noise is removed from the optical path 46 consisting of the photodetector 44 and the optical path 47 which guides the light reflected by the beam splitter 43 to the photodetector 45 via the coupling lens 48 and the cylindrical lens 49. Converts information into electrical signals and outputs them.

[Problem that the invention seeks to solve]

In the conventional device, reflected light 51 reflected by the information recording section
is not reflected by the beam splitter 6 toward the reflected light detection system 41 side to become the detected reflected light 51A, but a part of it becomes the return light 51B that passes through the beam splitter 6. The light passes through the collimating lens 6 and returns to the semiconductor laser 1 . In this way, when a part of the emitted light from the semiconductor laser 1 is returned from the external reflector to the semiconductor laser as the return light 51B, large noise may be generated even if this is a weak light amount of several percent or less. Known Tail (commonly known as Back Ta1k No1se, abbreviated as BT)
N). In order to prevent the return light 51B, a known method is to provide a 1/4 wavelength plate between the beam splitter 6 and the reflection mirror 7 to form an isolator. However, since the material of the magneto-optical disk has birefringence, this isolator cannot sufficiently suppress the returned light 51B. Further, in a method such as a magneto-optical recording method that reads changes in the polarization plane of light, it is impossible to use such an isolator.

FIG. 4 is an operating characteristic diagram showing a method of driving a semiconductor laser to prevent BTN, 61 is an output light-current characteristic curve of the semiconductor laser, and DC bias current 62 is the driving current of the semiconductor laser. By superimposing a high frequency current 64 on the order of several QQ MHz on the laser beam and modulating the drive current so that it falls below the threshold value 63, the semiconductor laser is configured to oscillate in multiple modes, and the return light 5 for the optical output waveform 60 is modulated.
The influence of 1B is reduced.

However, K which modulates a semiconductor laser at a frequency of several hundred MHz or higher
In this case, the high frequency superimposing circuit must be placed as close to the semiconductor laser as possible, and the high frequency superimposing circuit must be mounted inside the magneto-optical head device, resulting in a large device as a whole. In addition, high-frequency superimposition circuits have many variations in output level and are not compatible with individual semiconductor lasers, so in order to modulate semiconductor lasers so as to cut the threshold, they must be connected and driven individually. There is a problem in that the adjustment work becomes complicated, such as having to select those having the following characteristics.

The purpose of the present invention is to obtain a magneto-optical head device that does not require a high frequency superimposition circuit and is therefore small and inexpensive by using the return f:J element inversely and eliminating BTN. .

[Means for resolving issues]

In order to solve the above problems, according to the present invention, linearly polarized light emitted from a semiconductor laser is formed into a parallel beam, and is projected as a minute spot onto a magneto-optical recording medium via a beam splitter, a reflecting mirror, and an objective lens, thereby generating an external magnetic field. The beam splitter records and erases information as well as detects reflected light that is reflected from a magneto-optical recording medium and is separated by the beam splitter to reproduce information. At least 20% of the light intensity of the parallel beam
The above-described light is reflected as ta-angle reflected light, and includes an external resonant optical system for the semiconductor laser that reflects the right-angle reflected light in the opposite direction and generates a return light directed toward the semiconductor laser via the beam splitter. shall be.

[Effect]

In the above means, at least 20% or more of the light amount of the parallel light beam emitted from the semiconductor laser, shaped into a parallel light beam by the collimating lens and the beam shaping prism, and incident on the beam splitter, is separated as right-angled reflected light from the beam splitter. By providing an external resonant optical system that returns the orthogonally reflected light to the semiconductor laser as return light, the semiconductor laser is externally modulated at high speed by strong optical feedback, and stable single mode emission is achieved. Return from magnetic disk 9
Light effects (BTN) are eliminated and noise is reduced. Therefore, there is no need for a high frequency superimposition circuit for eliminating BTN, and the magneto-optical head device can be made smaller and more quantifiable.

〔Example〕

This UA will be explained below based on an example.

FIG. 1 is a configuration diagram showing an optical system of an apparatus according to an embodiment of the present invention, and detailed explanation will be omitted by using the same reference numerals for parts having the same configuration and two functions as the conventional apparatus. In the figure, an external resonant optical system 10 includes a beam splitter 6 that reflects 20% or more of the amount of incident parallel light beam 5 as orthogonally reflected light 5B, and an external reflection mirror 11 that reflects the orthogonally reflected light 5B.

In the embodiment device, the linearly polarized light 2 emitted from the semiconductor laser 1 is transmitted through a collimating lens 3 and a piece shaping prism 4t.
- A part (20% or more) of the parallel light beam 5 having a circular cross section is reflected by the parallel beam splitter 6 and becomes a right angle reflected light 5B.

The right angle reflected light 5B is reflected by the external reflection mirror 11 and returns to the beam splitter 6. Beam shaping prism 4. The returned light is returned to the semiconductor laser 1 via an optical path 15 formed by the collimating lens 3 . At this time, the distance between the semiconductor laser 1 and the external reflection mirror 11 is constant, and by forming an external resonator that returns the strong return light 15A, which is 205 times the amount of emitted light, at a period determined by the distance, The semiconductor laser 1 is externally modulated at high speed and stably emits in a single mode. Therefore, the semiconductor laser 1, which was oscillating in multiple modes due to the return light 51B which is a part of the reflected light from the magneto-optical disk 9 as a magneto-optical recording medium (reflected light 51 in Figure Mc3), is far more The signal is converted into a single mode by external high-speed modulation using the strong return light 15, and the BTN caused by the return light 51B is eliminated.

FIG. 2 is a block diagram showing a different embodiment of the present invention, in which the external resonant optical system 20 is a polarizing beam splitter 26.
1/4 wavelength plate 24. and an external reflection mirror 21, which differs from the previous embodiment in nine points. Since the polarizing beam splitter 26 has a reflectance R8 of about 100% for S-polarized light (symbol -) and a reflectance Rp of about 50% for p-polarized light (symbol O), the straight line projected from the semiconductor laser 1 Polarized light (
About 50% of the p-polarized light is reflected by the beam splitter 26 and becomes a circularly polarized light beam by passing through the quarter-wave plate 24. The circularly polarized light beam is reflected by the external reflection mirror 21 and passes through the quarter-wave plate again, thereby becoming an S-polarized linearly polarized light beam. Approximately 100% of the S-polarized light flux is reflected by the polarization beam splitter 26 and returns to the semiconductor laser 1 as reflected light 25A.However, since it does not go to the reflected light detection system 41, it is reflected light from the reflection mirror 21. The influence on the detection system 41 is eliminated. Also,
Since the amount of light returning to the semiconductor laser 1 corresponds to approximately 40% of the amount of linearly polarized light 2 emitted from the semiconductor laser 1,
The semiconductor laser 1 is externally modulated at high speed by the strong return light 25A from the external resonant optical system 20, and oscillates in a stable single mode, thereby allowing the laser diode to emit light from the magneto-optical disk 9 as an information recording medium. The influence of BTN due to returned light can be eliminated.

〔Effect of the invention〕

As described above, the present invention focuses linearly polarized light emitted from a semiconductor laser into a minute spot and projects the linearly polarized light onto an information recording section of a magneto-optical recording medium by a beam splitter disposed in a projection optical system. An external resonant optical system is provided which reflects at least 20% of the amount of light into right angle reflected light, converts it into light returned to the semiconductor laser, and outputs it.

As a result, the semiconductor laser is externally high-speed modulated by the strong return light and stably oscillates in a single mode, so the return light from the magneto-optical disk increases the noise in the emitted light beam of the semiconductor laser.BTN is eliminated, and therefore B
The high frequency superimposing circuit conventionally used to eliminate the influence of TN is no longer necessary, and a magneto-optical head device that is smaller and lighter in weight can be economically advantageously provided.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an optical system of an embodiment of the present invention;
Fig. 2 is a configuration diagram showing the optical system of the apparatus of different embodiments;
This figure is a block diagram showing the optical system of a conventional device, and FIG. 4 is a diagram for explaining the operation of the conventional device of high frequency superposition type. 1... Semiconductor laser, 2... Outgoing linearly polarized light, 3...
... Collimating lens, 4... Beam shaping prism,
6...Beam splitter, 7...Reflection mirror, 8.
...Objective lens, 9...Magneto-optical recording medium (magneto-optical disk), 10, 20...External resonance optical system, 11.2
1... External reflection mirror, 24... 1/4 wavelength plate, 2
6... Polarizing beam splitter, 41... Reflected light detection system, 51... Reflected light, 51B... Return light (BTN)
, 5... Incoming parallel light flux, 15A, 25A... Return from external resonant optical system Fig. 2

Claims (1)

[Claims] 1) Linearly polarized light emitted from a semiconductor laser is made into a parallel beam and projected as a minute spot onto a magneto-optical recording medium via a beam splitter, reflection mirror, and objective lens, and information is recorded and erased by combining with an external magnetic field. In addition, in a device that reproduces information by detecting reflected light reflected from a magneto-optical recording medium and separated by the beam splitter, the beam splitter converts at least 20% or more of the light amount of the incident parallel beam into orthogonally reflected light. The light is characterized by comprising an external resonant optical system for the semiconductor laser that reflects the orthogonally reflected light in the opposite direction and generates a return light directed toward the semiconductor laser via the beam splitter. magnetic head device.