Optical path switching apparatus

Optical waveguides – With optical coupler – Switch

Reexamination Certificate

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C385S017000

Reexamination Certificate

active

06819827

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical path switching apparatus for switching at least one input optical path selectively into any one of output optical paths to permit a light beam to pass therethrough, and more particularly to an optical path switching apparatus available for a two-way optical communications system to have a plurality of communications devices selectively communicate with each other by switching at least one input optical path selectively into any one of output optical paths to permit a light beam to pass therethrough.
2. Description of the Related Art
Up until now, there have been proposed a wide variety of optical path switching apparatuses as will be seen for example from pages 442-423, vol. 16, No. 11 of ELECTRONICS LETTERS, published 22nd May 1980. The conventional optical path switching apparatus disclosed by the above ELECTRONICS LETTERS is shown in
FIGS. 7
to
10
. The conventional optical path switching apparatus thus shown comprises switching means
5
for switching input optical paths selectively into any one of the output optical paths, the switching means
5
having a plurality of switching paths to permit a plurality of light beams to respectively pass therethrough, inputting means
1
for inputting a plurality of light beams to the switching means
5
, the inputting means
1
having a plurality of input optical paths formed therein to have a plurality of light beams respectively pass therethrough, and outputting means
3
for outputting a plurality of light beams from the switching means
5
, the outputting means
3
having a plurality of output optical paths formed therein to have a plurality of light beams respectively pass therethrough.
The inputting means
1
is constituted by an optical fiber collimator array made of optical fibers and following input collimator lenses for converting each of incident light beams to paralleled light beams, respectively. The outputting means
3
is constituted by an optical fiber collimator array made of output collimator lenses respectively followed by output optical fibers for converting each of light beams to paralleled outputting light beams.
As shown in
FIGS. 7 and 8
, the switching means
5
has a housing
7
, a plurality of optical path switching elements
2
accommodated in the housing
7
in which each of the input optical paths is switched into any one of the output optical paths, and a plurality of actuation elements
4
to actuate respectively the corresponding optical path switching elements
2
. Each of the optical path switching elements
2
is actuated and moved by each of the actuation elements
4
to assume two different positions, i.e., a first position where each of the input optical paths of the inputting means
1
is switched to any one of the output optical paths of outputting means
3
and a second position where each of the input optical paths of the inputting means
1
is not switched to any one of the output optical paths of outputting means
3
.
In the conventional optical path switching apparatus, each of the optical path switching elements
2
of the switching means
5
is constituted by a pentagonal prism made of glass, and it is well known that the pentagonal prisms has excellent optical properties and functions as the optical path switching element. The pentagonal prism of the optical path switching element
2
is illustrated in
FIGS. 9 and 10
. The pentagonal prism has two reflection surfaces including a first reflection surface &egr; on which a light beam from the input optical path of the inputting means
1
is reflected and a second reflection surface &ggr; on which the light beam from the first reflection surface is reflected again to proceed toward the output optical path of the outputting means
3
. The optical path of the light beam in the optical path switching apparatus is indicated by arrow in the drawings. First and second reflection surfaces &ggr; and &egr; of the pentagonal prism are spaced apart from each other at an angle of 45 degrees to reflect at right angles the light beam from the inputting means
1
to the optical path of the outputting means
3
, as shown in FIG.
9
. The pentagonal prism also has two transmission surfaces including a first transmission surface &bgr; to have the light beam from the input optical path of the inputting means
1
transmit into the pentagonal prism and a second transmission surface &agr; to have the light beam reflected on the reflection surfaces transmit from inside of the pentagonal prism to the output optical path of the outputting means
3
.
In the pentagonal prism, an angle &phgr; between any input optical path and any output optical path. are constantly maintained at 90 degrees, even if a set-up angle &thgr; of the pentagonal prism is eventually fluctuated from a predetermined angle. This means that the input optical paths are precisely switched to any one of the output optical paths, at any time.
The pentagonal prism placed in the conventional optical path switching apparatus is usually prepared by a process that a glass block is cut and polished to form a pentagonal shape having surfaces &agr;, &bgr;, &ggr;, &egr; and &dgr;, as shown in
FIGS. 9 and 10
. The surfaces &ggr; and &egr; are coated with reflective multi layers and surfaces &agr; and &bgr; are coated with unreflective multi layers. With regard to the surface &dgr; of the pentagonal prism, any coating is not applied thereon because the surface &dgr; is independent from switching of optical paths.
As to the surfaces &ggr; and &egr;, a reflective coating is essential because, if any reflective coating is not applied thereon, an incident angle of the inputted light beam onto the surfaces is smaller than an internal reflection of glass and air, per se, and therefore the inputted light beam is hardly reflected there. So, the surfaces &ggr; and &egr; must be coated by reflective dielectric multi layers. On the other hand, the unreflective coatings on the surfaces &agr; and &bgr; are required, because, if any unreflective coating is not applied on the surfaces, it is not avoidable to reflect some amount of the inputted light beam on the each surface. For example, about 4% of the inputted light beam is reflected and lost at each of the surfaces &agr; and &bgr;, respectively, when reflection index of air is 1.0 and the same of glass is 1.5. Such reflections on the surfaces &agr; and &bgr; invite problems of back reflection of the inputted light beam, which a part of the introduced light beams returns to back truck, and cause to arise unstable signals in optical communications devices. It is, therefore, required to prevent from any reflection of the light beams on the surfaces &agr; and &bgr; by applying an unreflective coating of dielectric multi layers.
As a light having a broad range of wave length of 1.3 &mgr;m to 1.6 &mgr;m is generally used in optical communications technology, reflective coatings or unreflective coatings of the surfaces are extremely essential when the inputted light beam has such broad wave length. In order to meet above requirements, a coating of dielectric multi layers such as thin layers of SiO
2
and of TiO
2
are applied on the surfaces by vacuum deposition method or the like. The materials of such thin layers are selected in accordance with aims of the coating.
The pentagonal prism should be as small as possible in order to miniaturize the switching apparatus and to offer technical advantage thereby. Area of the each surfaces &agr;, &bgr;, &ggr; and &egr; on the pentagonal prism is preferable as small as 1 square millimeter or smaller than this. In order to manufacture such small sized pentagonal prism, however, high degree of polishing techniques for glass material and high degree of coating techniques to form reflective and unreflective layers are necessary. Further, it is needed to take a complicated manufacturing process, since such small surfaces &agr;, &bgr;, &ggr; and &egr; are able to be formed only by high-precision processing technology and they should be coated

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