Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
2002-02-08
2004-06-01
Ullah, Akm Enayet (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S147000
Reexamination Certificate
active
06744952
ABSTRACT:
The invention relates to a connecting device for connecting optical waveguides, in particular for connecting waveguides of different refractive index in a low-reflection fashion.
Glass fiber networks that are distinguished by high data transmission rates play a key role in telecommunication. Optical data telecommunications with the aid of glass fibers require amplifiers at regular intervals for this purpose. The previously used electronic amplifiers with electronic converters are increasingly being replaced in this case by optical amplifiers, in particular by optical fiber amplifiers. It is possible by using such optical devices to implement transmission rates that are higher by several orders of magnitude than the transmission rates that can be realized with the aid of electronic amplifiers.
However, there is the problem in this regard that the core refractive indexes of the optical amplifiers and of the generally used monomode fibers for data transmission differ markedly as a rule. The coupling of fibers of different refractive indexes is attended, however, by undesired effects owing to reflection losses, and by signal distortions and ghost signals owing to multiple reflections. Also particularly disturbing are reflections in or at surfaces of emergence of optical fiber amplifiers, where undesired resonances can occur inside the amplifier because of the reflections. The end faces of the waveguides can be bevelled in order to avoid instances of coupling into the amplifier, that are caused by reflection, and reflection losses, or at least to reduce them.
Such a coupling of waveguides is disclosed, for example, in European Patent EP 0 194 325, in the case of which the fibers to be coupled to one another are ground at the same angle. However, if the fibers have different core refractive indexes, when light is coupled into the second fiber this leads to an angular offset between the optical axis of the output fiber and the optical axis of the input fiber. Consequently, in the case of such an arrangement, the optical axis of the input fiber must run obliquely to the optical output axis. Such arrangements are, however, difficult to adjust and therefore expensive to fabricate.
Again, EP 0 858 976 A2 discloses a device for coupling optical fibers, in the case of which the end faces of glass fibers of different refractive indexes respectively have different lead or grinding angles. Again, in the case of this embodiment of a waveguide connector the glass fibers are coupled to one another in such a way that the end faces of the fibers are aligned parallel to one another. However, the result of this is that the optical axes of the two glass fibers are necessarily at an angle to one another. A substantial outlay on adjustment and mounting also results from these embodiments.
The present invention has therefore addressed the object of providing an improved coupling between waveguides of different refractive indexes. The aim here is not to restrict this solution to fiber amplifiers, but rather that it can be applied for surface waveguides or waveguides in three-dimensional space, for example.
This aim is already achieved in a most surprisingly simple way with the aid of a connecting device for connecting at least two optical waveguides having the features of claim 1.
In the case of the connecting device according to the invention for connecting at least two optical waveguides, a first optical waveguide is held relative to a second optical waveguide, an end face of the first waveguide running obliquely to the optical axis of the first waveguide, and an end face of the second waveguide running obliquely to the optical axis of the second waveguide. The refractive index of at least one light-guiding region of the first optical waveguide differs in this case from the refractive index of a light-guiding region of the second optical waveguide, and the above described problems of the prior art are avoided, since the end face of the first optical waveguide and the end face of the second optical waveguide are inclined such that the optical axis of the first and of the second optical waveguides are arranged substantially parallel to one another.
This particular arrangement of the waveguides permits an extremely simple design of the connecting device according to the invention, in the case of which the waveguides meet one another not obliquely, but in a straight line in the plug-in direction, additionally rendering possible low-reflection coupling of waveguides of different refractive indexes of the light-guiding regions.
The result of this is a lower space requirement by comparison with the coupling with the aid of fibers that meet one another obliquely, particularly also whenever a plurality of connections are to be arranged next to one another. Moreover, axial play between the waveguides, or a slight axial maladjustment is substantially less critical.
It is advantageous for the purpose of low-reflection coupling of optical signals into the second optical waveguide when, furthermore, the connecting device according to the invention is designed in such a way that a wave that is being guided in the first optical waveguide emerges, owing to refraction at the end face of the first optical waveguide, from the first optical waveguide at an angle a obliquely to the optical axis of the first optical waveguide, and enters the second optical waveguide obliquely to the second optical axis of the second optical waveguide and, owing to refraction at the end face of the second optical waveguide, propagates in the second optical waveguide substantially parallel to the optical axis of the second optical waveguide.
This has the advantage, furthermore, of thereby rendering possible a very precise fine adjustment of the fibers. Light exits more obliquely relative to the optical axis owing to the aligned or rectilinear arrangement of the waveguides relative to one another, and to the oblique arrangement of the end faces. Consequently, an axial displacement of the fibers relative to one another causes a displacement of the point where the signal is incident on the fiber, into which the signal is launched again, in the radial direction. However, this displacement is reduced by the factor of the sine of the angle &agr; between the optical axis and the direction of light propagation in the gap between the waveguides. This factor renders an exact fine adjustment possible, since at small angles of the end face normal to the optical axis a relative displacement in the axial direction causes only a radial displacement of the point of incidence that is reduced by this sine factor.
In the connecting device according to the invention, the core of the first optical waveguide preferably has a different refractive index than the core of the second optical waveguide.
It is, moreover, advantageous for the transmission properties of the connecting device in accordance with the present invention when the spacing of the end face of the first optical waveguide from the end face of the second optical waveguide varies in the direction of the optical axis of the first optical waveguide along the direction perpendicular to this optical axis. Disturbing resonance phenomena can be reduced to a large extent by this arrangement. Consequently, ghost signals produced by the varying spacing, in particular by multiple reflection, are further damped.
The invention can be used with particular advantage for coupling optical waveguides with optical amplifiers that generally have a different refractive index than the waveguide for signal transmission. Consequently, in a practical way at least one of the two optical waveguides comprises an optically amplifying material in a practical way for such an embodiment of the connecting device.
The optical waveguide for the optical amplification can, in particular, also have a region doped with rare-earth elements.
In accordance with a preferred embodiment of the invention, the first optical waveguide comprises a fiber waveguide, and the second optical waveguide comprises an amplifier fiber doped with erbium.
For l
Brinkmann Matthias
Kobayashi Noboru
Reichel Steffen
Millen White Zelano & Branigan P.C.
Schot Glas
Ullah Akm Enayet
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