Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Reexamination Certificate
2000-03-16
2004-05-18
Korzuch, William (Department: 2653)
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
C369S118000, C369S013330
Reexamination Certificate
active
06738338
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a near-field optical head that can be used as a near-field optical read/write head or as a probe head for a scanning near-field microscope and to a method of fabricating the optical head. More particularly, the invention relates to a near-field optical head having a microscopic aperture whose size can be changed and to a method of fabricating such a near-field optical head.
A known near-field optical head is shown in FIGS.
15
(
a
) and
15
(
b
), where the optical head is generally indicated by numeral
200
. FIG.
15
(
a
) is a cross-sectional view of the near-field optical head
200
. FIG.
15
(
b
) is a top plan view of the optical head
200
. This head
200
has a silicon substrate
201
provided with an inverted conical hole
202
. The top portion of this hole
202
forms a microscopic aperture
203
having a size b less than the wavelength of light. If propagating light is made to hit this microscopic aperture
203
, near-field light is generated near the aperture
203
opposite the illuminated side, because the size b is shorter than the wavelength of the light. The propagating light is laser light, for example.
Where the near-field optical head
200
is used as a near-field read/write head, near-field light produced near the microscopic aperture
203
is made to hit a recording medium so that the surface structure or material undergoes a local change. In this way, information is recorded. Otherwise, the local change of the surface structure or material is detected, thus reading information. On the other hand, where the near-field optical head
200
is used as a probe head for a scanning near-field microscope, near-field light produced near the microscopic aperture
203
is made to hit the surface of a sample, scattering the near-field light. This results in propagating light, which in turn is detected to measure the optical characteristics or topography of the sample surface.
With the above-described near-field optical head
200
, it has been difficult to form the microscopic aperture
203
with a size less than 100 nm reliably. Furthermore, it has been impossible to vary the size of the aperture
203
. Where the near-field optical head
200
is used as a near-field optical recording read/write head, it is necessary to move the heavy head assembly during tracking for reading signals. Therefore, it has been difficult to place the head in position accurately and quickly.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention has been made. It is an object of the present invention to provide a near-field optical head having a microscopic aperture whose size can be varied.
It is another object of the invention to provide a method of fabricating this near-field optical head.
A near-field optical head set forth in one aspect and achieving the above-described objects comprises a substrate provided with a hole whose top portion forms a microscopic aperture. An aperture-limiting means is located inside the hole. A moving means for moving the aperture-limiting means is mounted. The aperture-limiting means is moved to limit the size of the microscopic aperture.
In this near-field optical head, the aperture-limiting means is positioned inside the hole formed in the substrate. The aperture-limiting means is moved by the moving means, thereby changing the size of the microscopic aperture. Hence, the microscopic aperture can be modified to desired size.
A near-field optical head in another aspect and achieving the above-described objects comprises a substrate provided with a hole whose top portion forms a microscopic aperture and a pair of aperture-limiting means inside the hole. Moving means are mounted to move the aperture-limiting means, respectively. The size of the microscopic aperture is limited by moving the aperture-limiting means.
In this near-field optical head, the two limiting means are located symmetrically with respect to the microscopic aperture. The aperture-limiting means are moved by their respective moving means, thereby modifying the size of the aperture. Therefore, the microscopic aperture can be varied to a desired size. Since the aperture can be moved over a recording track formed on a recording medium while maintaining constant the size of the aperture by moving the limiting means in synchronism, tracking can be done.
A near-field optical head in another aspect is characterized in that the aforementioned aperture-limiting means has a bottom surface flush with the bottom surface of the microscopic aperture.
In this near-field optical head, the aperture-limiting means are so positioned that their bottom surface is flush with the bottom surface of the microscopic aperture. This permits either a recording medium or a sample to be moved toward the microscopic aperture.
A near-field optical head in another aspect is characterized in that the moving means described above is a piezoelectric actuator or an electrostatic actuator.
In this near-field optical head, the aperture-limiting means is moved using the piezoelectric or electrostatic actuator. Therefore, the microscopic aperture can be changed to a desired size easily and accurately.
A near-field optical head in another aspect comprises a substrate provided with a hole whose top portion form a microscopic aperture and an aperture-limiting means positioned inside the hole. The aperture-limiting means is heated and expanded to thereby limit the size of the microscopic aperture.
In this near-field optical head, the aperture-limiting means that expands on heating is located inside the hole formed in the substrate. On expansion, the aperture-limiting means blocks propagating light and so the size of the microscopic aperture can be modified to a desired size by expanding the aperture-limiting means. Note that the aperture-limiting means can be heated by illuminating it with propagating light, for example.
A near-field optical head in another aspect is characterized in that there is provided a heating means for heating the aperture-limiting means.
In this near-field optical head, the heating means for heating the aperture-limiting means is mounted. Therefore, the aperture-limiting means can be expanded easily and accurately. The microscopic aperture can be modified to a desired size.
A near-field optical head in another aspect is characterized in that the aforementioned aperture-limiting means consists of a high polymer having a high coefficient of thermal expansion or a high polymer sealed with a gas.
In this near-field optical head, the aperture-limiting means is a high polymer having a high coefficient of thermal expansion or a high polymer sealed with a gas. Therefore, the aperture-limiting means can be expanded efficiently with a small amount of heat. The microscopic aperture can be modified to desired size.
A method of fabricating a near-field optical head as set forth above and achieving the objects described above starts with preparing a substrate. A hole is formed in this substrate such that the top portion form a microscopic aperture. An aperture-limiting means is positioned in the hole. A moving means for moving the aperture-limiting means is mounted. The size of the aperture is limited by moving the aperture-limiting means. A support means for supporting the moving means is deposited on a surface of the substrate that faces away from the aperture. Then, a sacrificial film is deposited on the substrate and on the support means. A light-blocking film is deposited on the sacrificial film. The light-blocking film is patterned to form the aforementioned aperture-limiting means. The support means is exposed, and the moving means described above is formed on this exposed support means. Finally, the sacrificial film is removed except for its portion located inside the hole.
In this method of fabricating a near-field optical head, the hole is formed in the substrate. The support means is deposited on the substrate. The sacrificial film is deposited on the substrate and on the support means. The light-blocking film is deposited on the sacr
Chiba Norio
Ichihara Susumu
Kasama Nobuyuki
Kato Kenji
Maeda Hidetaka
Adams & Wilks
Chu Kim-Kwok
Korzuch William
Seiko Instruments Inc.
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