JP2001283458A - Light beam condensing device and information recording/ reproducing system using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light beam condensing device capable of forming a fine light beam spot on an object without bringing the object on which light beams are condensed close to a head part. SOLUTION: Light from a light source 11 is irradiated on an opening 14 smaller than the wavelength of the light source 11, propagating light 15 emitted from the opening 14 is guided to a phase conjugate element 16 to be spatially inverted, and whereby light beams are condensed on the position of the opposite side of the opening 14 across the phase conjugate element 16 to form the fine light beam spot 17.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a light beam focusing device and an information recording / reproducing system such as an optical disk system using the same.

[0002]

2. Description of the Related Art Information recording / reproducing systems, such as optical disk systems, are required to have higher capacities. In order to increase the capacity of the optical disk system, a method using evanescent light is being studied in addition to a method of shortening the wavelength of the light source to reduce the spot size (spot diameter) of the light beam. For example, in an optical system using a normal objective lens, the spot size is about the same as the wavelength of the light source, but by using a solid immersion lens, the size can be reduced to half a wavelength or less using evanescent light. Spot size can be reduced.

FIG. 4 is a diagram showing the principle of an optical disk system using the latter method.
The evanescent light is generated from the minute aperture 43 by passing the light beam condensed by the lens 41 through the minute opening 43 having a smaller diameter than the light source wavelength formed on the metal plate 42 supported on the suspension 45. Is irradiated as a minute light beam spot 44 on a recording medium 46 which is an optical disk.

In the method using the evanescent light, the diameter of the light beam spot 44 on the recording medium 46 can be reduced to a wavelength or less, but the evanescent light is locally generated only at the light exit end of the minute aperture 43. , Small aperture 4
3 abruptly attenuates with distance from the
A large wall is that the recording medium 46 must be placed very close to the recording medium.

That is, when the recording medium 46 is to be brought close to the minute opening 43, the flatness of the surface of the recording medium 46 is strictly required in order to prevent the metal plate 42 from contacting the recording medium 46. Is almost completely eliminated, but it is technically difficult to satisfy these requirements, and even if it can be realized, the cost will increase significantly.

[0006]

As described above, in the prior art, when evanescent light is applied to an information recording / reproducing system, a recording medium must be placed close to a minute aperture for generating evanescent light. This has been a major factor hindering the practical use of a system using evanescent light.

An object of the present invention is to provide a light beam condensing device capable of forming an extremely small light beam spot having a wavelength equal to or less than the wavelength of a light source on an object without bringing the object on which the light beam is condensed close to the light condensing device. An object of the present invention is to provide an information recording / reproducing system using the information.

[0008]

In order to solve the above-mentioned problems, a light beam condensing device according to the present invention irradiates light from a light source to an opening smaller than the wavelength of the light source, and propagates light emitted from the opening. Is incident on the phase conjugate element and spatially inverted, thereby condensing the light beam at a position opposite to the opening with the phase conjugate element interposed therebetween.

According to this configuration, the distance between the aperture (small aperture) smaller than the wavelength of the light source and the phase conjugate element and the distance between the phase conjugate element and the condensing position of the light beam have substantially the same value. Since it can be made relatively large, it is possible to form a minute light beam spot on the object without bringing the object on which the light beam is condensed close to the light collecting device.

Further, another light beam condensing device according to the present invention irradiates light from a light source to an opening smaller than the wavelength of the light source, and makes propagation light emitted from this opening incident on a phase conjugate element, and By generating inverted phase conjugate light and further changing the traveling direction of the phase conjugate light, a light beam is condensed at a position distant from the phase conjugate element. Even with such a configuration, the distance between the light-collecting device and the light-beam condensing position can be increased.

In the present invention, it is preferable that the size of the minute aperture is set to approximately one half of the wavelength of the light source. In this way, the propagation light can be efficiently transmitted on the same principle as the radio wave emission from the antenna. Is radiated from the minute aperture.

The light beam condensing device of the present invention is applied to an optical head in an information recording / reproducing system so that a light beam is condensed on a recording medium such as an optical disk to record and reproduce information. This makes it possible to increase the distance between the optical head and the recording medium, eliminating the need for high precision in the flatness of the recording medium, and even if there is some dust or dirt on the surface of the recording medium. Thus, information can be recorded and reproduced stably.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows the configuration of a light beam condensing device according to a first embodiment of the present invention. In FIG. 1, a light source 11 is, for example, a red semiconductor laser having a wavelength of 650 nm. Light emitted from the light source 11 is condensed by a condenser lens 12 and enters a minute opening 14 formed in a metal plate 13. The minute aperture 14 has a length of one side smaller than the wavelength of the light source 11, preferably approximately ほ ぼ of the wavelength of the light source 11.
Of about 325 nm.

Since the minute aperture 14 is smaller than the wavelength of the light source 11, the light is emitted from the light source 11
The light incident on the minute aperture 14 through the aperture generates evanescent light near the light exit light end of the minute aperture 14. At this time, the propagation light 15 is simultaneously emitted from the minute aperture 14. The propagating light 15 forms a minute light beam spot near the light emitting end of the minute aperture 14,
The beam width increases as the distance from the beam increases.

Here, in the present embodiment, the minute aperture 1
A phase conjugate element 16 is disposed facing the light emitting end side of No. 4, and the propagation light 15 emitted from the minute aperture 14 enters the phase conjugate element 16. In this embodiment, the phase conjugate element 16 is a transmission type element.
The propagating light 15 incident on the light source is spatially inverted. That is, the propagating light 15 incident on the phase conjugate element 16 exits from the surface on the side opposite to the incident side.

The spatially inverted propagation light is applied to the minute aperture 1
When the light propagates by the same distance as that between the phase conjugate element 4 and the phase conjugate element 16, the light beam spot 17 becomes a small light beam spot 17 having almost the same size as that immediately after the light exits the small aperture 14. Thus, the minute light beam spot 17 can be formed at a position sufficiently distant from the minute aperture 14 and the phase conjugate element 16.

Specifically, the distance L1 between the minute aperture 14 and the phase conjugate element 16 is, for example, about 0.3 mm, and the distance L2 between the phase conjugate element 16 and the position where the minute light beam spot 17 is formed is also L2. , And L2 = approximately 0.
3 mm.

As described above, in the light beam condensing device according to the present embodiment, the light from the light source 11 is applied to the minute aperture 14 smaller than the wavelength, and the propagating light 1
5 is guided to the phase conjugate element 16 and spatially inverted, so that the light beam can be focused as a small light beam spot 17 smaller than the wavelength of the light source 11 at a position opposite to the small opening 14 with the phase conjugate element 16 interposed therebetween. it can.

In this case, as described above, the distance between the minute aperture 14 and the phase conjugate element 16 is substantially the same as the distance between the phase conjugate element 16 and the formation position of the minute light beam spot 17 which is the beam condensing position. These distances are, for example, 0.
Since it can be as large as about 3 mm, a minute light beam can be projected on the object without bringing the object irradiated with the focused light beam close to the phase conjugate element 16 which is the head of the light collecting device. A spot can be formed.

Further, according to the present embodiment, the size of the small aperture 14 is set to 波長 of the wavelength of the light source 11, so that the small aperture 14 is formed according to the same principle as the radio wave emission from the antenna used in the telecommunication. , The propagation light 15 can be efficiently emitted.

Further, even if the beam shape of the light emitted from the light source 11 is disturbed, the light emitted from the minute aperture 14 is shaped into a beam shape with good symmetry, and this is collected as a light beam spot 17 on the object. Since light is emitted, when the light beam focusing device of the present embodiment is applied to an information recording / reproducing system described later, there is also an advantage that recording / reproducing characteristics are improved.

(Second Embodiment) FIG. 2 shows a second embodiment of the present invention.
1 shows a configuration of a light beam focusing device according to the embodiment. FIG.
, The light source 11, the condenser lens 12, the metal plate 13, and the minute aperture 14 are the same as those of the light beam focusing device of the first embodiment. That is, the light source 11 has a wavelength of about 650, for example.
The condensing lens 12 condenses the light emitted from the light source and makes the light enter the minute opening 14 formed in the metal plate 13.

In the present embodiment, unlike the first embodiment, the propagation light emitted from the minute aperture 14 is guided to the phase conjugate element 22 via the beam splitter 21. That is, the point that the phase conjugate element 22 is disposed at a position opposite to the condenser lens 12 with respect to the metal plate 13 is the same as in the first embodiment, but the phase conjugate plate 22 is The distance L3 from the light emitting end of the small aperture 14 formed in the above is disposed at a position of, for example, about 1 mm.

The phase conjugate element 22 is a reflection type element made of, for example, a photorefractive crystal in the present embodiment, whereas the phase conjugate element 16 used in the first embodiment is a transmission type element. The incident light emitted from the minute aperture 14 and transmitted through the beam splitter 21 is time-reversed to generate phase conjugate light 23 traveling in the direction opposite to the direction of the incident light. The phase conjugate light 3 is condensed in the converted traveling direction by the beam splitter 21 changing its traveling direction by about 90 °, and is a minute light having a diameter of about half the wavelength of the light source 11. Beam spot 2
4 is formed.

As described above, according to the present embodiment, the light source 11
Irradiating the light from the micro aperture 14 smaller than the wavelength,
The propagation light 15 emitted from the minute aperture 14 is guided to the phase conjugate element 22 via the beam splitter 21 and time-reversed to generate the phase conjugate light 23, and the traveling direction of the phase conjugate light 23 is changed by the beam splitter 21. By converting and condensing the light, the light beam is formed as a small light beam spot smaller than the wavelength of the light source 11 on the object without bringing the object close to the head of the light condensing device as in the first embodiment. Light can be collected.

Also in this embodiment, the minute opening 14 is formed.
Is set to の of the wavelength of the light source 11,
It is possible to increase the radiation efficiency of the propagation light 15 from the minute aperture 14.

(Third Embodiment) FIG. 3 shows a third embodiment of the present invention.
1 shows a configuration of an information recording / reproducing system using a light beam condensing device of the present invention as an embodiment.

In the information recording / reproducing system of this embodiment,
The light source 11, the condenser lens 12, described in the first embodiment,
Metal plate 13 having minute opening 14 and phase conjugate element 16
Is used for an optical head (also referred to as an optical pickup) 31. This optical head 3
1 is supported by a suspension 32, and its tip (phase conjugate element 16) is, for example, 0.3 mm from the recording medium 33.
The recording medium 33 is disposed so as to be located at a distance of mm.

The suspension 32 moves the optical head 31 in the radial direction of the recording medium 33 by a head actuator (not shown) while supporting the optical head 31.
The light beam from the optical head 31 is moved to a position on the recording medium 33 where recording or reproduction is to be performed.

The recording medium 33 is a disk-shaped recording medium capable of optically recording (writing) / reproducing (reading) information, that is, an optical disk. For example, a medium of a phase change type, a magneto-optical type or a write-once type is used. Used. The recording medium 33 may be capable of both recording and reproduction, or may be capable of reproduction only. The recording medium 33 is rotated by a spindle motor (not shown) during recording / reproduction.

Taking the case where the recording medium 33 is a phase change type medium or the like as an example, when recording information on the recording medium 33, the optical head 31 is used as an optical head for recording. The light from the semiconductor laser, which is the light source 11 in the optical head 31, is intensity-modulated in accordance with the information signal to be recorded, and is minutely focused on the recording medium 33 via the condenser lens 12, the minute aperture 14, and the phase conjugate element 16. By irradiating as a beam spot, a recording mark such as a phase change area of information is formed on the recording medium 33.

On the other hand, when reproducing the information recorded on the recording medium 33, the optical head 31 is used as a reproducing optical head, and the optical head 321 irradiates the recording medium 33 with a light beam. Then, the reflected light from the recording medium 33 is detected by a photodetector (not shown), and is further subjected to arithmetic processing, whereby information recorded as a recording mark such as a phase change area on the recording medium 33 is reproduced.

As described above, in the information recording / reproducing system of this embodiment, since the light beam condensing device described in the first embodiment is used for the optical head 31, an extremely small light beam spot is formed on the recording medium 33. To perform recording / reproduction at a very high density.

Further, the distance between the optical head 31 and the recording medium 33 can be made longer than when the conventional evanescent light is used. According to the example described in the first embodiment, the distance is about 0. 3 mm. If the distance between the optical head 31 and the recording medium 33 is at this level, the requirement for the flatness accuracy of the recording medium 33 is greatly relaxed as compared with the conventional method using evanescent light, and the recording medium 3
Even if some dust and dirt adhere to the surface of the recording medium 3, the recording / reproducing operation can be performed stably without causing a writing error or a reading error. There is no problem.

Further, since the system of this embodiment has such advantages, it is suitable as a so-called removable disk system in which the recording medium 33 can be attached to and detached from a drive device, like many conventional optical disk systems. I have.

The present invention is not limited to the embodiments described above. For example, the material of the base material on which the minute openings are provided is not limited to metal, and may be a nonmetallic material such as plastic. Further, the phase conjugate element can be replaced with a hologram element having the same effect.

[0037]

As described above, according to the light beam condensing device of the present invention, the propagation light obtained by passing the light from the light source through the small aperture smaller than the wavelength of the light source is transmitted to the phase conjugate element. By condensing the light beam by spatial inversion or time inversion, an extremely small light beam spot having a wavelength equal to or less than the wavelength of the light source can be formed on the object without bringing the object close to the light collecting device.

Therefore, if this light beam condensing device is applied to, for example, an information recording / reproducing system, it is possible to realize an extremely high-density recording / reproducing, excellent operation reliability, and low-cost system. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a light beam focusing device according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a light beam focusing device according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of an information recording / reproducing system according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional information recording / reproducing system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Light source 12 ... Condensing lens 13 ... Metal plate 14 ... Micro aperture 15 ... Propagation light 16 ... Phase conjugate element 17 ... Micro light beam spot 21 ... Beam splitter 22 ... Phase conjugate element 23 ... Phase conjugate light 24 ... Micro light beam Spot 31: Optical head (optical pickup) 32: Suspension 33: Recording medium (optical disk)

Claims (3)

[Claims] 1. A light from a light source is applied to an opening smaller than the wavelength of the light source, and propagation light emitted from the opening enters a phase conjugate element and is spatially inverted, so that the phase conjugate element is interposed therebetween. A light beam focusing device for focusing a light beam at a position opposite to an opening. 2. The method according to claim 1, further comprising: irradiating light from a light source to an opening smaller than the wavelength of the light source, and propagating light emitted from the opening to a phase conjugate element to generate time-reversed phase conjugate light; A light beam condensing device, wherein a light beam is condensed at a position distant from the phase conjugate element by changing a traveling direction of light. 3. An information recording / reproducing system, comprising: condensing the light beam on a recording medium by the light beam condensing device according to claim 1; and performing at least one of recording and reproduction of information.