Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1998-12-14
2001-01-30
Lee, John D. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S024000
Reexamination Certificate
active
06181845
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to an optical switch matrix comprising n input channels, branching means for dividing the input channels up into a total of p branched channels, merging means for merging p branched channels into m output channels, and optical fibres for connecting the output channels of the branching means with the input channels of the merging means, wherein n, m, and p are natural numbers greater than or equal to 2.
BACKGROUND OF THE INVENTION
Such optical switch matrices are known. On Feb. 10, 1995, during a workshop of Eindhoven University of Technology in the Netherlands Siemens presented an 8×8 optical switch matrix named “8×8 Modulaufbau,” which consists of an array of sixteen juxtaposed 1×8 switches on a long rectangular InP-substrate and optical fibres (embedded in a product of AT&T called “Optiflex™” and bent through an angle of 180°) for connecting the switches. Eight of said 1×8 switches are each used as an input channel which branches into in eight channels. Each of these branched channels is connected to one of the merging channels of the remaining eight 1×8 switches (or, more accurately, 8×1 switches), in such a manner that an input signal in one of the input channels can be switched to any one of the output channels.
Said optical switch matrix has a length of more than 300 mm and a width of at least 50 mm, which is very large, especially in an industry where small size is, in many cases, of the essence. A reason for these considerable dimensions is that the optical fibres, which are usually made of glass, can only be bent to a certain extent. The minimal bending radius for glass fibres is about 25 mm. If smaller radii are used, the glass fibre may break or the optical loss within the fibre may increase to an unacceptably high level. As mentioned, in said optical switch matrix the fibres are bent through an angle of 180°. Consequently, the minimum width of the matrix exceeds 50 mm.
SUMMARY OF THE INVENTION
The present invention has for its object to provide an n×m optical switch matrix which is relatively small in size. To this end, an optical switch matrix as described in the first paragraph is provided wherein the branching means, the optical fibres (preferably p in all), and the merging means are each attached to a separate substrate or a separate group of substrates, which substrates are optically aligned.
Surprisingly, it has been found that the present invention allows a size reduction of the order of 80%. The use of a separate substrate for the optical fibres enables very efficient placement thereof, resulting in a considerable size reduction both in the longitudinal and the transverse direction, especially if the substrate with the branching means and the substrate with the merging means are on opposite sides of the substrate to which the optical fibres are attached. Further, owing to the compactness and rigidity of the elements of the optical switch matrix according to the invention, said elements can be aligned accurately with relatively little effort and do not suffer from tensions induced by movement of the optical fibres during operation (as can be the case with structures such as “Optiflex™”).
Usually, switch matrices are packaged in a hermetically sealed unit to protect them from corrosion. Said small size of the matrices according to the invention allows the use of a single package unit or box for packaging the entire switch matrix. In consequence, only n+m fibres have to be fed through the walls of the package. Up until now, the branching means and the merging means were each packaged in one or more separate boxes, and the optical fibres emerging from these boxes were spliced together one by one. In that case, the total number of fibre feedthroughs amounts to n+m+2p.
For a 8×8 switch matrix, the invention makes it possible to reduce the total number of fibre feedthroughs from 144 (i.e., 8+8+(2×64)) to 16 (i.e., 8+8), which since the hermetic feedthroughs are responsible for the greater part of total packaging costs, is a major advantage. Also, instead of the interconnect fibres and the fibres extending from the merging/branching means being spliced together one by one, the substrates according to the invention (provided with the interconnect fibres and the merging/branching means, respectively) can be optically aligned in a few automated process steps using conventional equipment.
Further, the invention solves another problem inherent to the above mentioned “8×8 Modulaufbau” which resides in the fact that the dimensions of the substrates carrying the switches or optical fibres are, of course, limited by the dimensions of the wafers of which the substrates are made. If, for instance, InP-wafers are used, the maximum length of the InP-substrates is 2 inches at most because InP-wafers have (at present) a maximum diameter of 2 inches. Since 8 1×8 switches need a total length of about 1 inch, the number of juxtaposed 1”switches on a single substrate cannot exceed 16. Consequently, larger matrices, e.g., 16×16 matrices which would comprise 32 juxtaposed switches, cannot be manufactured using the “8×8 Modulaufbau,” whereas they can be manufactured using the present invention.
It will be understood that, apart from the above example, the invention allows the construction of larger matrices with at least a double switch capacity irrespective of the material used.
The terms “branching means” and “merging means” include both active means (e.g., switches) and passive means. Since the invention pertains to a switch matrix, the total number (and the position) of the switches in the branching means and the merging means should be such that at least two input channels can selectively be connected (for a certain wavelength) to one of at least two output channels.
Optical switch matrices wherein n (the number of inputs) and m (the number of outputs) are equal or wherein n equals 2m or m/2 are preferred. Such matrices can be mass-produced, are very versatile, and, more importantly, are basic building blocks in telecommunications and Clos networks. Preferred are those optical switch matrices wherein n equals 2
i
, “i” being an integer (preferably in the range of 2-8, at present more preferably 2-5), and/or wherein said branching means and said merging means consist of a cascade or tree of 1×2 and 2×1 switches, respectively.
It should be noted that although it is, in some cases, preferred to integrate all branching or merging means on a single substrate (which allows simple production and optical alignment of the separate substrates), the invention does not exclude the use of more than one substrate for each of said means. For example, a 4×4 matrix comprising 4 branching means (4 1×4 switches) each on a separate substrate, an interconnect chip provided with 16 optical fibres, and 4 merging means (4 4×1 switches) arranged in twos on two substrates, is also within the scope of the present invention. By doing so, defective switches can be disposed of individually instead of in combination with the sound switches on the same substrate. Thus, the production yield is improved.
In a preferred embodiment, the optical fibres are attached to a substrate with at least p grooves on two opposing sides. This can be achieved, for instance, by providing short grooves on both sides or by providing grooves which run the length of the substrate. The substrates can be manufactured using conventional methods and enable automated and accurate placement of the fibres, again using conventional techniques. In principle, the substrates can be made of any material suitable for supporting a polymeric waveguide structure or optical fibres. In connection with the alignment of the optical fibres with the channels of the switches, it is preferred to use rigid materials. Examples are thermoset polymers (in which the desired grooves can be made, e.g., by shaping techniques such as injection moulding), glass, or other inorganic materi
De Dobbelaere Peter M. C.
Horsthuis Winfried H. G.
Connelly-Cushwa Michelle R.
Greene Kevin E.
JDS Uniphase Photonics C.V.
Lacasse Randy W.
Lacasse & Associates
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