JPH07201063A - Laser light source device and magneto-optical recording / reproducing device - Google Patents

Abstract

(57) [Summary] [Object] The present invention utilizes, in a laser light source device and a magneto-optical recording / reproducing device, effective first-order diffracted light by externally modulating the laser light intensity with a simple and short optical path length. [Structure] Acousto-optical modulator means for emitting 0th-order light and 1st-order diffracted light having a polarization direction perpendicular to 0th-order light is used, and 0th-order light is blocked by polarization separation means. By utilizing the above, the optical path length for spatially separating the 0th-order light and the 1st-order diffracted light becomes unnecessary, and the optical system can be downsized accordingly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser light source device and magneto-optical recording / reproducing, and can be applied to, for example, a device requiring optical intensity modulation used in magneto-optical recording / reproducing.

[0002]

2. Description of the Related Art Conventionally, in a magneto-optical recording / reproducing apparatus for performing magneto-optical recording / reproducing by a magnetic field modulation method, a magneto-optical disk is normally irradiated with unmodulated (DC) laser light. The intensity may be switched stepwise. It is necessary to switch the light intensity with a time constant of about 10 [μs].

However, the SHG (second harmonic generater) green laser, which is a short-wavelength light source most suitable for high-density magneto-optical recording, cannot switch the light intensity at a high speed. μs]
It takes some rise time. Therefore, when the SHG green laser is applied to magneto-optical recording, high-speed light intensity modulation by an external light intensity modulator is essential. Conventionally, as this external light intensity modulator, a longitudinal wave acousto-optic modulator (hereinafter referred to as longitudinal wave AOM) is also used.

That is, as shown in FIG. 2, in the magneto-optical recording / reproducing apparatus 1, the laser beam L emitted from the SHG green laser 2 is introduced into the longitudinal wave AOM 3. The 0th-order light L0 and the 1st-order diffracted light L1 having a constant diffraction angle are emitted from the longitudinal wave A0M3. Of these, the first-order diffracted light L1 is selected as the signal light by the aperture 4 and is launched by the folding mirror 7 through the beam expander optical system including the biconcave lens 5 and the collimator lens 6, and the grating 8 and the first beam splitter. 9. The magneto-optical disk 11 is irradiated through the objective lens 10.

The reflected light from the magneto-optical disk 11 is bent by the first beam splitter 9 through the objective lens 10 and is incident on the polarized beam splitter 14 through the second beam splitter 12 and the λ / 2 plate 13. . The polarized beam splitter 14 separates the reflected light into P component and S component, and through the focusing optical systems 15A and 15B in which focusing lenses and concave lenses are combined, respectively, the photo detectors 16A and 1A are provided.
6B. This enables the photo detector 16A.
The data recorded on the magneto-optical disk 11 is reproduced by performing signal processing on the received light outputs of 16 and 16B.

In the first beam splitter 9, a part of the signal light is bent and guided through a focusing optical system 17 to a photodetector 18 for APC (automatic power control) which controls the laser intensity. A part of the reflected light is bent by the second beam splitter 12, and is guided to the servo photodetector 20 through the condensing optical system 19. As a result, the laser intensity is controlled to be constant according to the received light output of the photodetector 18, and the received light output of the photodetector 20 is signal-processed to control the focus and tracking of the magneto-optical disc 11.

[0007]

By the way, in the magneto-optical recording / reproducing apparatus 1 using the longitudinal wave AOM 3 as described above, the 0th order light L0 is incident on the objective lens 10 and the optical spot on the magneto-optical disk 11. In order to prevent the formation of the light, it is necessary to insert the aperture 4 or use a lens having a small diameter to block the 0th order light L0. However, in the longitudinal wave AOM3, since the diffraction angle of the first-order diffracted light L1 is small,
A certain distance is required until the two beams are spatially separated. For example, drive frequency 200 [MHz], diffraction angle
In the case of 25 [mrad], a distance of about 50 [mm] is required until the 0th-order light L0 and the 1st-order diffracted light L1 are sufficiently separated.

As a result, from the longitudinal wave AOM3 to the objective lens 10
There is a problem in that the optical path length up to is long and the size is large as a whole. Further, it becomes difficult to form an optical system in a straight line from the SHG green laser 2 to the magneto-optical disk 11 in terms of size, and it is necessary to raise the beam by the folding mirror 7, and the adjustment of the spectral axis thereof becomes complicated. Further, since the diffraction angle is proportional to the drive frequency, it may be possible to drive at a high drive frequency in order to increase the diffraction angle of the longitudinal wave AOM3, but there is a problem that the drive circuit becomes complicated.

The present invention has been made in consideration of the above points, and a laser light source device and magneto-optical recording capable of utilizing effective first-order diffracted light by simply and externally modulating the intensity of laser light with a short optical path length. It is intended to propose a playback device.

[0010]

In order to solve the above problems, according to the present invention, in a laser light source device that modulates the intensity of a laser light with an external light, the 0th-order light and the 0th light of the laser light emitted from the laser light source are used. An acousto-optic modulator that emits first-order diffracted light having a polarization direction perpendicular to the next-order light and a polarization separator that separates the zero-order light and the first-order diffracted light emitted from the acousto-optic modulator are provided. I did it.

Further, according to the present invention, in the magneto-optical recording / reproducing apparatus 1 which modulates the intensity of the laser light L by the external light, the laser light L emitted from the laser light source 2 is changed into the 0th order light L10 and the 0th order light L10. On the other hand, an acousto-optic modulator 31 that emits a first-order diffracted light L11 having a vertical polarization direction and a polarization separator 34 that separates the zero-order light L10 and the first-order diffracted light L11 emitted from the acousto-optic modulator 31 are provided. I decided to provide it.

[0012]

The acousto-optic modulator 31 serves as the 0th-order light L10 and the 1st-order diffracted light L having a polarization direction perpendicular to the 0th-order light L10.
By using the one that emits 11 and using the polarization separation means 34 to block the 0th-order light L10 and use only the 1st-order diffracted light L11, the 0th-order light L10 and the 1st-order diffracted light L11 are spatially separated. The optical path length for this is unnecessary, and the optical system can be downsized accordingly.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail with reference to the following drawings.

In FIG. 1, in which parts corresponding to those in FIG. 2 are designated by the same reference numerals, numeral 30 generally indicates the structure of a magneto-optical recording / reproducing apparatus according to the present invention. In this embodiment, a transverse wave is used as an external light intensity modulator. An acousto-optic modulator (hereinafter referred to as transverse wave AOM) 31 is used. In practice, the transverse wave AOM 31 is an acousto-optic modulator by a transducer that generates a transverse ultrasonic wave. The transverse wave AOM 31 is characterized in that the polarization of the first-order diffracted light is orthogonal to the polarization of the incident light and the zero-order light. A polarization beam splitter (hereinafter referred to as PBS) is used as a polarization separation device that separates 0th-order diffracted light.

In practice, the laser light L emitted from the SHG green laser 2 is incident on the transverse wave AOM 31. Transverse wave A
A beam expander optical system including a biconcave lens 32 and a collimator lens 33 is arranged near the exit end of the OM 31 on the axis of the first-order diffracted light L11, and the first-order diffracted light L11 is expanded and collimated. At this time, the 0th-order light L10 is also incident on the lenses 32 and 33 and enlarged.

As a result, the 0th-order light L10 and the 1st-order diffracted light L11 overlap with each other, but they do not interfere with each other because their polarization directions are orthogonal to each other. Beam expander optical system 32, 33
The output light from is incident on the PBS 34, and the 0th order light L10 is 90
[°] It is bent and only the first-order diffracted light L11 is transmitted.
The first-order diffracted light L11 transmitted from the PBS 5 illuminates the magneto-optical disk 11 through the grating 8, the beam splitter 9, and the objective lens 10.

In the above structure, the transverse wave AOM 31 is S
It is arranged at a position of about 5 mm from the emission end of the HG green laser 2. The transverse wave AOM 31 has a rising speed of several μs and exhibits a sufficiently high response speed as a light intensity switching element. Further, since the transverse wave AOM31 does not require spatial separation of the 0th-order light L10 and the 1st-order diffracted light L11, a small diffraction angle is acceptable. As a result, the transverse wave AOM3
No. 1 is driven at a driving frequency significantly lower than that of the longitudinal wave AOM3 shown in FIG.

The beam expander optical system has a radius of curvature of 2
It is composed of a biconcave lens 32 of [mm] and a collimator lens 33 of focal length 25 [mm]. Biconcave lens 32
Are arranged at a position of about 5 mm from the transverse wave AOM31. The collimator lens 33 is a double concave lens 32 to 20.
It is placed at a position of about [mm]. With such a configuration, the first-order diffracted light L11 becomes parallel light having a diameter of 6 [mm].
The 0th-order light L10 is also expanded and emitted from the beam expander optical systems 32 and 33.

The PBS 34 is a beam expander optical system 3
It is placed immediately after 2, 33. The PBS 34 transmits the polarization component of the first-order diffracted light L11 by 100% and crosses it at 0 °.
The polarized component of the next light L10 is reflected by 100%. This result 1
Only the next-order diffracted light L11 is selected, and the magneto-optical disk 11 is irradiated through the grating 8, the beam splitter 9, and the objective lens 10 to form an optical spot. On the other hand, PBS3
The 0th order light L10 reflected by 4 is blocked by the light blocking member 35.

According to the above construction, it is not necessary to insert an aperture or a lens after the beam is skipped over a long distance in order to separate the two light beams of the 0th order light L10 and the 1st order diffracted light L11. Therefore, the size of the optical system can be significantly reduced. Incidentally, according to the experiment, the distance from the output end of the SHG green laser 2 to the objective lens 10 is 60
It can be shortened to around [mm]. This is about half the distance of the optical system using the conventional longitudinal wave AOM3. As a result, from the SHG green laser 2 to the magneto-optical disk 11
It becomes possible to make the optical system in a straight line, and it becomes easy to adjust the optical axis.

In the above embodiment, the PBS is arranged immediately after the beam expander optical system, but the arrangement of the PBS is not limited to this, and it may be arranged in the beam expander optical system. With this, the optical path length can be further shortened, and the entire configuration can be downsized.

In the above embodiment, the transverse wave AOM is used.
The case where the polarization beam splitter is used as the polarization separation means for separating the 0th-order light and the 1st-order diffracted light emitted further has been described, but the invention is not limited to this, and two light beams including mutually orthogonal components can be polarization-separated. Various optical elements such as a polarizing prism and a sheet polarizer may be used as long as they are optical elements.

Further, in the above embodiment, the case where the present invention is applied to the magneto-optical recording / reproducing apparatus has been described.
The present invention is not limited to this, and is suitable for being widely applied to various laser light application devices as a laser light source device in the case of modulating the external light intensity of laser light.

[0024]

As described above, according to the present invention, when the effective 1st-order diffracted light is obtained by modulating the external light intensity of the laser light, the acousto-optic modulator is used for the 0th-order light and the 0th-order light. A first order diffracted light having a vertical polarization direction is used, and the 0th order light is blocked by the polarization separating means so that only the first order light is used. It is possible to realize a laser light source device and a magneto-optical recording / reproducing device that can reduce the size of the optical system by that amount, because the optical path length for physically separating them becomes unnecessary.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical system showing a configuration of an embodiment of a magneto-optical recording / reproducing apparatus according to the present invention.

FIG. 2 is a block diagram of an optical system showing a configuration of a conventional magneto-optical recording / reproducing apparatus.

[Explanation of symbols]

1, 30 ... Magneto-optical recording / reproducing apparatus, 2 ... SHG green laser, 3 ... Longitudinal wave acousto-optic modulator, 4 ... Aperture, 5, 32 ... Biconcave lens, 6, 33 ... Collimator lens, 7 ...... Rising mirror, 8 …… Grating, 9,12 …… Beam splitter, 10 …… Objective lens, 11 …… Magnetic disk, 13 …… λ / 2 plate, 1
4, 34 ... Polarized beam splitter (PBS), 15,
17, 19 ... Condensing optical system, 16, 18, 20 ... Photo detector, 31 ... Transverse wave acousto-optic modulator.

Claims (4)

[Claims] 1. A laser light source device for modulating the external light intensity of a laser light, wherein a 0th-order light and a 1st-order diffracted light having a polarization direction perpendicular to the 0th-order light are emitted from the laser light emitted from the laser light source. A laser light source device comprising: an acousto-optic modulator that emits light; and a polarized light separator that separates the 0th-order light and the 1st-order diffracted light emitted from the acousto-optic modulator. 2. A laser light source device according to claim 1, wherein a transverse wave acousto-optic modulator is used as the acousto-optic modulator. 3. A magneto-optical recording / reproducing apparatus which modulates the intensity of a laser beam with an external light, wherein the laser beam emitted from a laser light source has a zero-order light and a first-order polarization direction perpendicular to the zero-order light. A magneto-optical recording / reproducing apparatus comprising: an acousto-optic modulator that emits broken light; and a polarization splitter that separates the 0th-order light and the 1st-order diffracted light emitted from the acousto-optic modulator. 4. A magneto-optical recording / reproducing apparatus according to claim 1, wherein a transverse wave acousto-optic modulator is used as the acousto-optic modulating means.