Dynamic information storage or retrieval – Storage or retrieval by simultaneous application of diverse... – Magnetic field and light beam
Reexamination Certificate
1999-12-03
2002-06-04
Hudspeth, David (Department: 2651)
Dynamic information storage or retrieval
Storage or retrieval by simultaneous application of diverse...
Magnetic field and light beam
C369S300000, C369S044230, C369S126000, C250S234000
Reexamination Certificate
active
06400655
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an apparatus of recording and reproducing a data onto/from a recording medium, and more particularly to a near field optical recording/reproducing head and a near field optical recording/reproducing apparatus employing the same that are adaptive for writing an information onto a recording medium or reading an information recorded on the recording medium by irradiating a near field light onto the recording medium and converting the near field light reflected from the recording medium into electrical signals.
2. Description of the Conventional Art
Generally, an information recording medium includes an optical recording medium or an opto-magnetic recording medium that is accessed by means of a far field optical system. As for the optical recording medium, there has been developed a DVD-RAM (digital versatile disc-random access memory) that is capable of recording at most 4.7 GB data larger than a recording capacity of a CD (compact disc) on a disc having a diameter of 120 mm. As for an opto-magnetic recording medium adopting the magnetic field modulation recording system, there has been suggested a standard for an advanced storage magneto optical (ASMO) device having a recording capacity of 6.1 GB level. There has been actively done a study for providing such information recording media having a high density in compliance with a high capacity of information such as a moving picture. However, the existent optical recording system or opto-magnetic recording system failed to arrive at a satisfying level of recording capacity due to its optical and physical limit. For instance, a DVD-RAM having a diameter of 120 mm and a recording capacity of 2.6 GB that is commercially available can not accommodate a picture with a resolution corresponding to a high density television, hereinafter referred to as “HDTV”, more than two hours. Furthermore, a driving apparatus for the optical recording/reproducing system or the opto-magnetic recording/reproducing system has more and more serious vibration and noise as it goes into a higher multiple speed. As a result, it is difficult to operate the existent driving apparatus for the optical recording/reproducing system or opto-magnetic recording/reproducing system at a high speed beyond a certain limit so that a servo control can be performed.
In order to enlarge a recording capacity of a recording medium adopting the existent optical recording/reproducing system or opto-magnetic recording/reproducing system, a pit(or recording mark) size and a track width must become small to that extent. However, since the size of an optical spot for forming the pit or the mark can not be smaller than so-called “diffraction limit value”, a limit exists in improving the recording density. In the case of a far field optical system, the size of an optical spot can not be smaller than a diffraction limit value proportional to &lgr;/NA in which “&lgr;” represents a wavelength of a light source and “NA” does a numerical aperture of an objective lens. In other words, to make a laser diode into a short wavelength and make an objective lens into a high numerical aperture, have encountered a physical limit. Accordingly, there has been done a study for shortening the wavelength &lgr; or enlarging the numerical aperture NA so as to reduce the size of a light spot in the far field optical system. Nowadays, a blue laser with a wavelength of 450 nm has been commercially available, but it is basically impossible to reduce a light spot within the wavelength of a light.
In light of a trend toward a high density of an information, a novel optical recording/reproducing system able to overcome a limit in the recording/reproducing apparatus employing the current far field optical system is required. Accordingly, a growing interest has been taken in a near field optical recording/reproducing system utilizing a near field.
The near field optical recording/reproducing system is to record and reproduce information cells in hundreds of angstrom(Å) unit using a near field optics technology and a micro electro-mechanical system (MEMS) technology. Accordingly, the near field optical recording/reproducing system can improve the recording capacity dramatically in comparison to the existent optical recording/reproducing system or opto-magnetic recording/reproducing system. For instance, it is expected that, if a near field is used, then a HDTV level image data more than 20 Gbytes can be stored in one surface of a disc having a diameter of 3 cm. In this case, an image with a HDTV level resolution can be viewed for more than two hours at a picture quality of MPEG2 (moving picture experts group 2) with a sheet of disc with a diameter of 3 cm. Thus, when the near field is used, a recording medium can have a high capacity and an extremely small size. A data recording/reproducing apparatus of such a near field recording/reproducing system consists of a nano-scale of optical tip, and a system capable of driving the optical tip with a very high accuracy and at a high speed. The optical tip keeps a focus length within tens of nm from the recording medium to irradiate a near field light or an evanescent wave onto the recording medium, thereby forming a light spot into a micro size of tens of nm which is less than the wavelength of a light.
In the recording medium of near field optical recording/reproducing system as described above, a light spot has a micro size smaller than the wavelength of a light, so that pits and marks formed on the recording medium become small to that extent to record a high density of information. Since a light intensity is exponentially decayed as a light reflected from the recording medium becomes distant from the surface of the recording medium at the time of reproduction, the optical tip should keep a focus length of tens of nm from the recording medium likewise. During the reproduction, the optical tip receives a reflected light and converts the received reflected light into electrical signals. Since a near light signal can not be detected when the optical tip is a long distance from the recording medium and an intensity of the detected near light is reduced in inverse proportion to a distance between the tip and the recording medium, it is desirable that the tip comes into close to the recording medium as far as possible.
However, because the present study as to the near field optical recording/reproducing system stays at a principle level yet, improvements in many fields such as the servo control, the recording speed, the resolution, the convenience, the portability, the data transfer rate and so on are required. For instance, the conventional optical recording/reproducing system makes use of an actuator for driving the objective lens in two axis directions(i.e., tracking direction and focusing direction) to thereby carry out the tracking and focusing controls with a Lorenz force generated by a magnetic circuit of the actuator. However, a recording medium of near field optical recording/reproducing system can not make use of the existent actuator because pits and tracks are formed into a micro size smaller than an operation range of the actuator. In other words, since the near field optical recording/reproducing apparatus jumps tens to hundreds of tracks even in a minimum operation range of the actuator, it can not perform the tracking and focusing control by means of the existing actuator.
Accordingly, in order to implement the near field optical recording/reproducing apparatus, a development of a head driving device should be preceded such that the optical tip can keep a near-field distance from the recording medium and can access the recording medium at a random basis. Also, a light transfer device for transferring a light to the optical tip as well as a recording/reproducing signal processor is needed.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a near field recording/reproducing head that is adaptive for the near field recording and reproducti
Birch & Stewart Kolasch & Birch, LLP
Chu Kim-Kwok
Hudspeth David
LG Electronics Inc.
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