Optics: measuring and testing – Shape or surface configuration
Reexamination Certificate
2000-09-20
2004-07-27
Font, Frank G. (Department: 2877)
Optics: measuring and testing
Shape or surface configuration
C356S445000, C250S310000, C250S311000
Reexamination Certificate
active
06768556
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical probe to produce or to detect near-field light for use with a near-field optical microscope or a near-field optical recording/reproducing device.
An optical microscope employs a lens to collect or to condense light. In this system, resolution is restricted by a wavelength of the light. In contrast with this optical microscope, a near-field optical microscope uses a near-field optical probe which produces optical near-field location in the vicinity of the probe in place of the lens. The near-field optical probe is placed in the neighborhood of a sample to scan a surface of the sample. It is resultantly possible to measure a contour and optical characteristics of the sample with resolution determined by the size or dimension of the aperture. The near-field optical microscope has been recently applied to various fields such as a field of contour measurement and spectroscopic analysis of, for example, a sample of an organism, quantum structure of a semiconductor, and a macromolecular material as well as a field of high-density optical recording.
As the near-field optical probe, a pointed optical fiber (optical fiber probe) having a fine opening of a size less than a wavelength of light has been usually employed. To fabricate this fiber probe, a tip end section of an optical fiber is extended while being heated. Alternatively, the tip end section is tapered to a point by chemical etching. Thereafter, the optical fiber other than the tip end section is coated with metal. By introducing light to the optical fiber, near-field light can be generated in the proximity of an aperture formed in the tip end section.
However, this fiber probe is attended with a drawback of low light utilization efficiency. When light is incident to a fiber with a fiber probe of this kind having, for example, a diameter of 100 nm, intensity of light emitted from the tip end of the fiber is about 0.001% or less of that of light incident to the fiber. To overcome this problem, various probes have been proposed as follows. (1) Multi-step tapered fiber probe: A fiber probe having a tip end section which is tapered in two or three steps to a point (Applied Physics Letters, Vol. 68, No. 19, pp. 2612-2614, 1996 and Vol. 73, No. 15, pp. 2090-2092, 1998), (2) Metallic needle probe: A probe of a needle of STM. By emitting light to a tip end section of the needle, strong near-field light is produced in the vicinity of the tip end (JP-A-6-137847). (3) Fiber probe with small metallic particle in aperture: A fiber probe in which a very small metallic particle is disposed at a center of an aperture in a tip end section (JP-A-11-101809 proposed by the first inventor of the present invention). Light emitted from the aperture excites plasmon in the small metallic particle to produce strong near-field in the neighborhood of the small metallic particle. (4) Tetrahedral tip: A triangular prism of glass is coated with metal having a thickness of about 50 nm so that surface plasmon is excited on the metal film. The surface plasmon proceeds toward a top end or a vertex of the triangular prism to produce strong near-field light in the proximity of the vertex (Physical Review B, Vol. 55, No. 12, pp. 7977-7984, 1997). (5) Probe on glass substrate with metallic scatterer: A probe including a glass substrate and a metallic scatterer formed on a bottom surface of the glass substrate. This configuration generates strong near-field light in the proximity of the metallic scatterer (JP-A-11-250460).
In the near-field optical microscope, it is necessary to set distance between the aperture to generate near-field light and a surface of a sample to a value ranging from several nanometers to several tens of nanometers. consequently, when the probe including an optical fiber or a glass piece is used, a particular control system is required to control the distance between the tip end of the probe and the sample surface. In general, the distance is measured using interatomic force between the tip end of the probe and the sample surface, and the distance is adjusted by servo control using the measured value.
However, the servo control has a limited servo band and hence the probe scanning speed is limited. Particularly, in an optical recording/reading device to operate at a high data transfer speed, the probe must scan a surface of a recording disk at a high speed. This method cannot appropriately control deviation of an interval of a high frequency caused by distortion and inclination of the disk. To solve this problem, various probes have been proposed as follows. (1) Flat opening probe: A probe fabricated by disposing an opening in a silicon substrate by anisotropic etching (The Pacific Conference on Lasers and Electro-Optics, WL2, “Fabrication of Si planar apertured away for high speed near-field optical storage and readout”. Since a peripheral area of the aperture is flat, the distance between the probe and the sample can be kept fixed by pushing the probe against the sample. (2) Probe with aperture having pad: On a bottom surface of a glass substrate, a projection in the form of a quadrangular prism having an aperture in a tip end thereof is fabricated, and a pad is manufactured in a periphery of the projection (JP-A-11-265520). The pad keeps the distance between the probe tip end and a sample. (3) Surface emitting laser probe with small metallic tip: On a laser emitting end surface of a surface emitting laser probe, a small opening and a small metallic projection are fabricated (Applied Physics, Vol. 68, No. 12, pp. 1380-1383, 1999). Since the probe has a flat structure, the distance between the probe and a sample can be kept fixed by pressing the probe against the sample. The probe has a small metallic projection and a resonance structure, the probe expectedly operates with higher efficiency.
The near-field probe requires three points regarding performance as follows. (1) High light utilization efficiency, (2) High scanning, and (3) Reduced background light in light measured by the probe.
To increase the light utilization efficiency, various methods have been proposed as above. The fiber probe having a tip end with multiple taper angles has light utilization efficiency which is about ten times to about one hundred times that of a fiber probe generally used. However, this probe is not fully applicable to applications requiring high light utilization efficiency, for example, to the optical recording/reading requiring a light utilization efficiency of 10% or more. The probe uses an optical fiber and is mechanically fragile and cannot scan at a high speed. The metallic needle probe, the fiber probe with small metallic particle in aperture, the glass probe coated with metal, and the probe on glass substrate with metallic scatterer have increased light utilization efficiency by using characteristics of metal, and hence a high light utilization efficiency can be expected. However, each of these probes has a tip end section with a mechanically fragile contour and hence is not suitable for the high-speed scanning. Particularly, in operation of the metallic needle probe and the probe on glass substrate with metallic scatterer, light which does not hit the tip end section or the scatterer is also incident to the sample. This resultantly leads to a problem of detection of much background light.
Various probes capable of scanning at a high speed have been proposed as above. The flat opening probe and the probe with aperture having pad can achieve the high-speed scanning. However, these probes have low light utilization efficiency. The surface emitting laser probe with small metallic tip expectedly scans at a high speed with high light utilization efficiency and a low amount of background light. To generate strong near-field light using the small metallic projection, the contour of the small metallic projection must be optimized. However, description has not been given of the contour of the small metallic projection at all. Moreover, description has not been given of a method of manufa
Hosaka Sumio
Isshiki Fumio
Matsumoto Takuya
Shimano Takeshi
Antonelli Terry Stout & Kraus LLP
Font Frank G.
Hitachi , Ltd.
Punnoose Roy M.
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