Optical waveguides – Planar optical waveguide
Reexamination Certificate
1998-03-03
2001-01-30
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Planar optical waveguide
C385S130000, C385S043000, C385S049000
Reexamination Certificate
active
06181860
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical waveguide having a structure which facilitates and improves its connection to an optical fiber.
STATE OF THE ART
One of the fundamental requirements in the construction of communication network systems comprising optoelectronic components is that a connection between components a single mode fiber should take place with as small a loss as possible. In general, most of a connection loss depends on the difference in size between the optical fiber and the waveguide. When the optical waveguide is made of a semiconductor material, the loss at the interface between the waveguide and the fiber can, in certain cases, be as much as 10 dB.
By increasing the dimension of the optical field of the waveguide a better correspondence with the optical field of the fiber is achieved, whereby the connection loss in the interface between waveguide and fiber is reduced. A number of different arrangements and processes to increase the optical field of the waveguide are known.
One way of converting the optical field in the waveguide is to arrange lenses in the interface between the fiber and the waveguide. This method is, however, rather impractical.
Another way of achieving the above mentioned converting is to transform the dimensions of the waveguide in the interface with the fiber. Said transformation is generally called tapering. Tapering can occur either through the dimension of the waveguide being increased or reduced in order to increase the optical field. Minimizing the dimension is, however, connected with practical difficulties when the dimension of the single mode waveguide is tremendously small to begin with. A more common way is therefore to increase the dimension of the waveguide. This increase in the dimension can take place laterally, vertically or laterally and vertically together, where the vertical tapering can comprise complicated process steps which make manufacturing relatively expensive.
SUMMARY OF THE INVENTION
In a transition from a waveguide, defined for example in a or some semiconductor materials or some polymer material, to an optical fiber, there are many factors which play a decisive role in maintaining the intensity of the light. One of these factors relates how the optical fields of the waveguide and now the optical fiber are adapted to each other.
The solutions which are available today often solve said problem through increasing the dimension of the waveguide in the connection to the fiber. Said increase in the dimension is required both laterally and vertically in relation to an optical axis defined in the waveguide in order for the adaption of the field to be satisfactory. From a process point of view said increase in the dimension of the waveguide is relatively complicated, especially in the vertical direction, which can be a problem.
The present invention tackles the above mentioned problem by arrangins the waveguide with a so-called tooth-structure in its connection with the fiber.
The structure of the waveguide in its connection with the fiber can thereby be said to be a combination of both a so-called up-tapering and a down-tapering. By up-tapering is meant that the dimension is increased in at least one orthogonal direction towards the so-called optical axis defined in the waveguide, and with down-tapering is meant that the dimension is miminized in at least one orthogonal direction towards said optical axis.
The physical effect of an up-tapering in an orthogonal direction in relation to the optical axis is that the optical field increases in the same direction as the up-tapering and that the optical field in the other orthogonal direction towards the optical axis remains relatively undisturbed.
The physical effect of a down-tapering in an orthogonal direction in relation to the optical axis is that the optical field increases in both the orthogonal directions towards the optical axis, if said down-tapering makes the cross-section of the waveguide become sufficiently small. The optical field increases, seen relatively, more in the tapered direction, in this case the narrowing direction, compared with the untapered.
By means of said structure, when connecting the wave guide to the fiber, an increase in the optical field in both orthogonal directions towards the optical axis is obtained without it being necessary for this purpose to change the dimension in both said orthogonal directions.
The purpose of the present invention is to increase the optical field in a waveguide in both orthogonal directions in relation to the optical axis through only rearranging the size and structure in one of said orthogonal directions.
An advantage of the present invention is that the connection loss can be held to a low level.
Another advantage of the present invention is that aligning the optical fiber and the optical waveguide can be facilitated.
Yet another advantage of the present invention is that production can be relatively cheap.
A further advantage of the present invention is that it can be applied to waveguides manufactured from semiconductor material, polymer material and quartz.
The invention will now be described in more detail with the help of preferred embodiments and with reference to the appended drawing.
REFERENCES:
patent: 4262995 (1981-04-01), Tangonan
patent: 5058978 (1991-10-01), Kondoh et al.
patent: 5838853 (1998-11-01), Jinnai et al.
patent: 5841919 (1998-11-01), Akiba et al.
patent: 5926298 (1999-10-01), Li
Granestrand Per Olov
Svensson Per Johan Olof
Sanghavi Hemang
Telefonaktiebolaget LM Ericsson
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