Optical waveguides – Optical fiber waveguide with cladding
Reexamination Certificate
2003-01-30
2004-09-28
Robinson, Mark A. (Department: 2872)
Optical waveguides
Optical fiber waveguide with cladding
C385S124000, C385S031000
Reexamination Certificate
active
06798961
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical-fiber wiring board and an optical-fiber wiring assembly for optically interconnecting optical elements, optical circuits or optical apparatuses, and more particularly to an optimal optical fiber for the optical-fiber wiring board.
BACKGROUND ART
Conventionally, an optical-fiber wiring board is used to optically interconnect optical elements, optical circuits or optical apparatuses. The optical-fiber wiring board is constructed to include a plurality of optical fibers routed on a substrate in a predetermined pattern. Generally, a communication-dedicated single mode optical fiber having an outside diameter of 250 &mgr;m is used as an optical fiber that is routed on the optical-fiber wiring board. For example, Japanese Unexamined Patent Publication No. 2000-66035 discloses an optical fiber having an outside diameter of 125 &mgr;m for an optical-fiber wiring board.
In the optical-fiber wiring board, a number of portions in which the optical fibers are bent and routed. As such, the bending loss of the optical fibers is increased, and the performance of the optical-fiber wiring board is thereby lowered. Hence, for the optical-fiber wiring board, the optical fibers need to be routed not to increase the bending loss. However, a problem arises in that such a routing manner makes it difficult to implement the miniaturization of the optical-fiber wiring board.
In more specific, on the optical-fiber wiring board, linear portions where the optical fibers are routed to be linear on the substrate and curved portions where the optical fibers are bent and routed to be curved. In order to prevent the increase in the bending loss of the optical fiber in the curved portion, the curved portion needs to be formed to have a minimum radius of curvature, specifically, a radius of curvature greater than a minimum radius of curvature allowable with respect to the bending loss. However, in order to form the curved portion with the radius of curvature greater than the minimum radius of curvature, the area of the substrate needs to be proportionally increased. Consequently, the size of the optical-fiber wiring board is enlarged.
In addition, on the optical-fiber wiring board, crossover sections are formed in each of which two optical fibers are routed such that the one optical fiber (upper optical fiber) crosses over the other optical fiber (lower optical fiber) routed in contact with the surface of the substrate. In this crossover section, the upper optical fiber is routed to be bendable. In order to reduce the bending loss of the upper optical fiber, the upper optical fiber needs to be routed to have a radius of curvature greater than the minimum radius of curvature. However, when the upper optical fiber is routed to have a radius of curvature greater than the minimum radius of curvature, mutual interference occurs between the upper optical fiber and other optical fibers routed adjacent to the lower optical fiber routed on the substrate. In order to prevent the interference, the wiring density of the optical fibers on the substrate needs to be reduced. In order to achieve the reduction, however, the area of the substrate needs to be enlarged, which consequently leads to enlargement of the size of the optical-fiber wiring board.
When the number of the crossover sections formed on the optical-fiber wiring board is reduced, the bending loss on the overall optical-fiber wiring board is reduced. However, the reduction in the number of the crossover sections cannot be implemented unless otherwise the area of the substrate is enlarged. As such, the size of the optical-fiber wiring board needs to be enlarged to reduce the number of the crossover sections.
Thus, with ordinary communication-dedicated optical fibers used with a device such as an optical-fiber wiring board on which the fibers are bent and routed, the bending loss is increased. When the optical fibers are routed considering the bending loss to prevent the problem, another problem arises in that the size of the device using the optical fibers is enlarged.
The present invention is made in view of the above-described circumstances, and an object thereof is to provide an optical fiber suitable for use in an environment including many portions where the optical fiber is bent. More particularly, the present invention is to provide an optical fiber that is optimal for use with an optical-fiber wiring board, and an optical-fiber wiring board and an optical-fiber wiring assembly that use the optical fiber.
DISCLOSURE OF INVENTION
In order to achieve the above-described object, the present invention has been accomplished by paying attention to the fact that an optical fiber used with an optical-fiber wiring board or the like has an overall length of about 0.5 to 1 m, which is considerably small in comparison with the length of an optical fiber used for communication. Specifically, the present invention has been accomplished by paying attention to the fact that dissimilar to an ordinary communication-dedicated single mode optical fiber, such as a communication-dedicated single mode optical fiber according to the ITU (International Telecommunication Union) standards, since the length of the optical fiber used with the aforementioned optical-fiber wiring board or the like is short, the dispersion need not be taken into consideration as a design parameter.
In specific, a first aspect of the present invention is intended for an optical fiber of a single mode type including a core and a cladding.
As characteristics, a relative refraction index difference of the core and the cladding is increased to be greater than a relative refraction index difference of a communication-dedicated single mode optical fiber, and a core diameter is increased to be larger than a core diameter of the communication-dedicated single mode optical fiber. Thereby, a mode field diameter is set to be substantially the same as a mode field diameter of the communication-dedicated single mode optical fiber.
By thus increasing the relative refraction index difference of the core and the cladding to be greater than the relative refraction index difference of the communication-dedicated single mode optical fiber, confinement of light into the core is enhanced. Consequently, when the optical fiber is bent, it is suppressed that light in the core transmit to the cladding. As such, in comparison to the communication-dedicated optical fiber, the optical fiber reduces the bending loss. That is, the minimum radius of curvature of the optical fiber is less than the minimum radius of curvature of the communication-dedicated optical fiber.
However, when the relative refraction index difference of the optical fiber is increased to be greater than that of the communication-dedicated single mode optical fiber, the mode field diameter thereof becomes smaller than the mode field diameter of the communication-dedicated single mode optical fiber. As such, when the optical fiber is connected to the ordinary communication-dedicated single mode optical fiber, the connection loss is increased.
For this reason, according to the optical fiber of the first aspect of the present invention, the core diameter is increased to be larger than the core diameter of the communication-dedicated single mode optical fiber, whereby the mode field diameter is set to be substantially the same as the mode field diameter of the communication-dedicated single mode optical fiber. This arrangement prevents the connection loss from being increased when the optical fiber is connected to the communication-dedicated single mode optical fiber.
As described above, according to the optical fiber of the first aspect of the present invention, the bending loss is reduced, and the connection loss is not increased even when it is connected to the communication-dedicated single mode optical fiber. As such, the optical fiber is suitable to an environment including many portions where it is bent; and it can be optimally used with, for example, an optical-fiber wiring board.
It is noted that the f
Kondo Katsuaki
Yoshida Minoru
Amari Alessandro
Mitsubishi Cable Industries Ltd.
Nixon & Peabody LLP
Robinson Mark A.
Studebaker Donald R.
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