Optical waveguides – Having particular optical characteristic modifying chemical... – Of waveguide core
Reexamination Certificate
1999-11-04
2001-05-22
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
Having particular optical characteristic modifying chemical...
Of waveguide core
C385S123000, C385S125000
Reexamination Certificate
active
06236797
ABSTRACT:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a light transmitting tube to be employed for illuminations, projectors, and the like and, more particularly, to light transmitting tube to be suitably employed in case that the tube is used in an environment where the tube is bent to have a small radius or is bent at many portions, or in case that a flexible tube surrounding an optical transmission tube has a small inner diameter.
A neon tube and a fluorescent tube have been used as a light emitting member for providing light in length of several meters. However, the neon tube and the fluorescent tube require high voltage. The neon tube or the fluorescent tube can not be used in water or at a place to be wet with rain or snow because dangers including electric shock and electrical leakage may occur. Furthermore, since the neon tube and the fluorescent tube are made of glass tube, these have drawback in their impact resistance, so the neon tube and the fluorescent tube can not be used at such a place that an object including a person or a vehicle may come in contact with the tube.
Another conventional light transmitting tube is formed by filling a transparent core liquid or flexible transparent polymer into a flexible tube. A further another light transmitting tube is prepared by twisting plastic optical fibers. Light generated from a light source is entered into each of the tubes through an end of the tube and emitted out of the surface of the tube over a length of dozens of meters so that the light source and the emitting portion are separately provided, thus reducing the danger of damage. Therefore, the light transmitting tube can be used in water, outdoors, or an environment having a possibility of explosion. In addition, since complex process including glass blowing is not required, the light transmitting tube can be easily manufactured and can provide good workability.
Conventionally, in the light transmitting tube having a liquid core, when bent as shown in
FIG. 3
, many light beams have angles of incidence relative to the outer surface of the tube, which are smaller than the critical angle, at the bent portion, thus increasing the optical leakage (optical loss) out of the core. This has been a problem. Therefore, materials have been selected to increase the difference between the respective reflective indexes and many structural designs have been made to reduce the optical loss at the bent portion as much as possible. However, it is difficult to select such materials because of requirement of transparency and it is also difficult to design structure for each of applications.
OBJECT AND SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above conventional problems and to provide a light transmitting tube which can reduce the optical loss at a bent portion and which allows the increase in the included angle of incident beams into the light transmitting tube without increasing the optical loss.
A light transmitting tube of a first aspect comprises a tubular cladding and a solid core made of material having reflection index higher than that of the material for the tubular cladding, wherein the cladding has rigidity higher than said core, and the core and said cladding are not bonded to each other.
It is preferable that the cladding is a thermoplastic tube and the core is flexible solid matter.
The light transmitting tube of the first aspect comprises the cladding and the transparent solid core having reflection index higher than that of the cladding. In this light transmitting tube, the cladding is made to have rigidity higher than that of the core, and the core and the cladding are not bonded to each other whereby the core and the cladding are separated from each other so as to appear a space (air layer) between the outer surface of the core and the inner surface of the cladding at a bent portion of the light transmitting tube. Since the difference in the reflection index between the core and the air layer is larger than the difference in the reflection index between the core and the cladding, the critical angle is reduced, thereby reducing the optical loss at the bent portion.
It should be noted that the term “not bonded” means a state that the cladding and the core do not adhere to each other such that the cladding and the core can be separated from each other at the interface therebetween.
An optical transmission tube according to a second aspect comprises tubular cladding made of thermoplastic material and a solid core made of material having reflection index higher than that of the material for the tubular cladding, wherein said cladding is expanded by heating whereby an air layer is produced between said core and said cladding.
It is preferable that the core is made of thermosetting material.
The light transmitting tube of the second aspect comprises the cladding made of thermoplastic material and the transparent solid core having reflection index higher than that of the cladding. In this light transmitting tube, said cladding is expanded by heating whereby the core and the cladding are separated so as to produce a space (air layer) between the outer surface of the core and the inner surface of the cladding. Since the difference in the reflection index between the core and the air layer is larger than the difference in the reflection index between the core and the cladding, the critical angle is reduced, thereby reducing the optical loss at the portion where the air layer is produced. This means the optical loss can be reduced at a bent portion of the light transmitting tube. The included angle of the incident beams into the light transmitting tube can be increased without increasing the optical loss.
REFERENCES:
patent: 5982969 (1999-11-01), Sugiyama et al.
Hotta Atsushi
Tanuma Itsuo
Terahama Tatsuo
Bridgestone Corporation
Kanesaka & Takeuchi
Palmer Phan T. H.
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