Optical waveguides – With optical coupler
Reexamination Certificate
1998-12-04
2001-10-02
Font, Frank G. (Department: 2877)
Optical waveguides
With optical coupler
Reexamination Certificate
active
06298179
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an optical detector which is generally used in optical communication, and to an optical information apparatus, optical measurement, an analysis apparatus and the like.
Heretofore, the devices which have been most generally used as light-to-current converters are photomultipliers, charged coupled devices (“CCDs”), and photodiodes.
With respect to photomultipliers, an advantage thereof is that the photomultiplier responds to very weak light and hence the amplification factor thereof is large, while a disadvantage thereof is that the response speed is low, i.e., on the order of microseconds, the conversion current is small, i.e., on the order of microamperes, and the correlation between light intensity and current density varies to some degree whereby both the dark current and the noise levels are large.
In addition, the CCD does not directly convert light into current, but temporarily converts light into electric charge and then converts the electric charge into current in the stage of reading the electric charge. For this reason, the CCD has an advantage in that the correlation between light intensity and current is extremely high, while it has a disadvantage in that the response speed is low due to the two stages of the conversion process. In addition, the conversion mechanism of the CCD is complicated.
Further, with respect to the photodiode, it is an advantage that the bandwidth is wide, i.e., 20 GHz, while it is a disadvantage that the range of operation temperatures is narrow, i.e., in the range of 10 to 40° C.
It is an object of the present invention to provide an optical pumping field emission type light-to-current converter which utilizes field emission so that the amount of field emission current is increased to realize a response speed on the order of picoseconds (10
−12
seconds) and having a structure that is simplified.
SUMMARY OF THE INVENTION
An optical pumping field emission type light-to-current converter according to the present invention utilizes field emission in order to solve the above-described problems associated with the prior art.
The basic principles will hereinafter be described. When applying a negative bias voltage to the sharp tip of a needle-like structure made of a conductive material, a high electric field is generated at the sharp tip of the needle-like structure to reduce the potential barrier against electrons which are shut in the surface of the sharp tip of the needle-like structure. As a result, there is an increased probability that the electrons in the surface are emitted to the outside on the basis of Heisenberg's uncertainty principle. This phenomenon is referred to as field emission. In the needle-like structure of the conductor made of metal or the like, the amount of emission current varies greatly depending on the electric field strength at the sharp tip of the needle-like structure, and does not respond to light which is incident on the sharp tip of the needle-like structure. However, in the semiconductor, in particular, a semiconductor material which has electrical characteristics close to that of an insulator, or an insulating material, when light is incident on the sharp tip of the needle-like structure, the optical conductivity is increased momentarily so that the amount of field emission current becomes extremely large. A device in which such principles are applied is referred to herein as an optical pumping field emission type light-to-current converter.
An optical pumping field emission type light-to-current converter according to the present invention is constructed by joining an optical waveguide material through which light is propagated, a conductive transparent film, a semiconductor material or an insulating material, and a conductor material to each other, and the light emission side of the optical waveguide material has a sharpened shape, whereby the intensity of light which has been made incident on the optical wave guide material is detected at high sensitivity and at high-speed response.
REFERENCES:
patent: 5362972 (1994-11-01), Yazawa et al.
patent: 0209643 (1989-08-01), None
Nakajima Kunio
Nishikawa Osamu
Adams & Wilks
Font Frank G.
Nguyen Tu T.
Seiko Instruments Inc.
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