GB2242754A - Optical fibre 1 to N splitter - Google Patents
Optical fibre 1 to N splitter Download PDFInfo
- Publication number
- GB2242754A GB2242754A GB9005013A GB9005013A GB2242754A GB 2242754 A GB2242754 A GB 2242754A GB 9005013 A GB9005013 A GB 9005013A GB 9005013 A GB9005013 A GB 9005013A GB 2242754 A GB2242754 A GB 2242754A
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- GB
- United Kingdom
- Prior art keywords
- fibre
- optical
- primary
- fibres
- cross
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
- G02B6/2821—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals
- G02B6/2826—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals using mechanical machining means for shaping of the couplers, e.g. grinding or polishing
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/24—Coupling light guides
- G02B6/26—Optical coupling means
- G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
- G02B6/2804—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers
- G02B6/2821—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals
- G02B6/2826—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals using mechanical machining means for shaping of the couplers, e.g. grinding or polishing
- G02B6/283—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals forming multipart couplers without wavelength selective elements, e.g. "T" couplers, star couplers using lateral coupling between contiguous fibres to split or combine optical signals using mechanical machining means for shaping of the couplers, e.g. grinding or polishing couplers being tunable or adjustable
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Mechanical Coupling Of Light Guides (AREA)
Abstract
An optical splitter comprises a primary optical fibre 36 which may have a D-shaped cross-section (D-fibre) which crosses at least two, e.g. three, secondary D-fibres 38, 40, 42 to form three cross-couplers by evanescent coupling of their cores. Equal splitting of an optical signal propagating along the primary fibre 36 is achieved by appropriate coupling constant of the cross-couplers achieved by fanning the secondary fibres 38, 40, 42 to provide different interaction lengths with the primary fibre 36. Another embodiment (Fig. 2) employs different separations of primary and secondary fibres to achieve the same result. <IMAGE>
Description
OPTICAL POWER SPLITTER
This invention relates to optical power splitters, and in particular to optical power splitters in which the optical signals propagate in optical fibres.
Architectures of optical communications systems have been proposed in which a downstream optical transmission from a primary station is broadcast via optical fibres to a number of secondary stations. This can be achieved by, for example, transmitting the signals down a primary optical fibre and extracting portions of the signal from this primary fibre by coupling it to a series of secondary fibres. These secondary fibres can be coupled directly to the secondary stations or be first subjected to further multiple splitting to form a tree structure.
Each of the optical splitter stages can be regarded as an 1 to N optical splitter in which the primary waveguide is coupled to (N-l) secondary waveguides, each of the primary and secondary waveguides being optically coupled to a secondary station or further optical splitter as appropriate.
A known method of forming such 1 to N optical splitters is to make (N-l) fused optical couplers and splice them in series each of which couples a portion of the signal in one fibre into another by evanescent coupling between the fibre cores. Generally, they will be formed with different coupling constants such that the optical power split to each of the (N-l) secondary fibres and that remaining in the primary fibre are substantially equal at some predetermined working wavelength, i.e. the first coupler has a coupling constant of 1 to 1/N, the second of 1 to l/(N-l) and so on.
It will be understood that the term primary optical fibre does not necessarily refer to a single distinct fibre but refers collectively to the sections of fibres coupled to the primary station which carry the larger portion of the signal between it and the various individual fused couplers of the assembly.
There are disadvantages associated with this approach to forming the 1 to N optical splitters. There are optical losses associated with each splice necessary to connect the individual couplers together and the assembly as a whole is relatively bulky. It is an object of the present invention to provide a 1 to N coupler which exhibits smaller losses and can be formed more compactly than hitherto possible.
Accordingly, an optical splitter comprises a primary optical fibre crossed by a least two secondary optical fibres fixed relative to the primary optical fibre, each evanescently coupled to the primary optical fibre to extract a portion only of an optical signal from the primary optical fibre.
The cross-over of each secondary fibre with the primary fibre defines a cross-coupler having an interaction region where there is evanescent field coupling between the fibre cores of some predetermined strength. The strength of the coupling and the length of the interaction region determines the coupling constant of cross-coupler i.e. the proportion of an optical signal which is coupled out of the primary fibre into the secondary fibre at some predetermined working the wavelength. Nany such cross-couplers can be formed close to each other by fixing the secondary fibres close together across the primary fibre thus allowing the formation of a compact 1 to N splitter whilst eliminating the need for splices between the individual cross-couplers.
Further, as will be explained in detail below, the coupling constants of the cross-couplers can be readily made to have the same value, or the different values required for equal portions to be coupled from the primary fibre. In particular, the secondary fibres may be fixed so they all cross the primary fibre at the same angle, the differences in coupling constant being determined by the differences in the separation of the cores of the primary and secondary fibres. This can be achieved through the use of different sized spacers located between the fibres or by forming the secondary fibres from appropriate sections of a fibre having a tapered cladding, the fibres all being in direct contact with the primary fibre.
An alternative arrangement is to fix the secondary fibres so their cores are the same distance from the primary fibre core but that they cross the primary fibre at different angles. This can be readily achieved by forming the secondary fibre into a fan of fibres across which crosses a straight, primary fibre. Other arrangements for varying the angle of cross-over are possible - for example a curved primary fibre can cross a parallel array of secondary fibres.
Preferably the optical fibres are D-fibres, i.e.
optical fibres having a D-shaped cross-section with their cores very close to their flat section, as long lengths are readily made by polishing off a sector of the preform in the otherwise conventional method of manufacturing optical fibres.
Embodiments of the present invention and its principle of operation will now be described by way of example only with reference to the accompanying drawings in which
Figure 1 is a perspective view of a cross coupler;
Figure 2 is an optical splitter according to the present invention in which the differences in coupling constants of the cross-couplers are determined by the differences in spacing of the fibres; and
Figure 3 is a graph showing the coupling length as a function of core separation for various values of surrounding index;
Figure 4 and 5 are further embodiments of the present invention in which the differences in coupling constants of the cross-couplers are determined by the interaction angles of the cross-couplers.
Referring to Figure 1 a cross-coupler 2 comprises a primary optical D-fibre 4 having a core 6 and a flat cladding portion 8 across which is fixed a secondary optical D-fibre 10 having a core 12 and flat cladding portion 14. The cores 6 and 12 are sufficiently close to the surfaces of the fibres at the respective flat portions 8 and 14 that an optical signal propagating in one core is evanescently coupled to the other core along a coupling region 16 of some characteristic length (interaction length) L which is dependant on the core width and is proportional to the cross-over or interaction angle e.
The angle e has been exaggerated in Figure 1 for clarity.
It is, in practice, of the order of 10.
The strength of the evanescent coupling can be denoted by a coupling length Zc which is the physical length in which optical power in one fibre completely couples into the other. In a length of 2Zc the power will have coupled back into the original fibre. The proportion of power coupled into the second fibre by a coupler of coupling length Zc having a coupling region of length L is given by P = (1 - COS (rL/Zc))/2 (1)
Referring now to Figure 2, a 1 to 4 optical splitter 20 according to the present invention comprising a primary optical D-fibre 22 fixed in contact across three parallel secondary optical D-fibres 24, 26 and 28 to form three cross-couplers 30, 32 and 34 respectively, each as shown in Figure 1.Each cross-coupler has an interaction angle of 0.920 (again this angle is exaggerated in Figure 2 for clarity) and an interaction length L of imam.
The cross-couplers 30, 32, 34 have couplings constants p, of 1/4, 1/3 and 1/2 respectively so that an optical signal entering the fibre 22 from the left of
Figure 2 is apportioned into four substantially equally portions between the right hand ends of fibres 22, 24, 26 and 28. The different coupling constants are obtained by different spacings of cores calculated as follows.
For P = 1/2, equation (1) gives
cos (rL/ZC) = 0, from which we have sL/Zc = n.r/2, n an integer; and
Zc' = 2n.L
For n = 1, Zc = 2L = 2mm
In this example the refractive index of the cladding of the fibres is 1.442 so reference to the graph of Figure 3, which shows the dependance of coupling length Zc with core separation for various intervening refractive indices, shows the required core-to-core separation to be 9.35;m.
In a similar way, the core-to-core separations required for P = 1/3 and 1/4 are found to be 9.66um and 9.83m respectively.
In any particular embodiment the dependance of coupling length with core separation can be readily determined in known manner for the particular optical fibres to be used and the corresponding calculations made to determine the necessary separations.
These required separations can be obtained by chosing suitable D-fibre cross-sections such that the cores of the secondary fibre are appropriately spaced when in contact with the primary fibre 22.
A method of obtaining a suitable range of D-fibre cross-sections is to remove a tapered section from the
D-fibre pre-form by polishing so that the fibre pulled from it has a core covered by a varying thickness of cladding. Sections from such a tapered D-fibre can be selected which have the required cladding thickness for the desired separation.
Other methods of varying the spacing may be used, for example the use of variable thickness spacers.
In this example the graph of Figure 3 relates to operation at 1.3;m.
Referring now to Figure 4, a 1 to 4 optical splitters comprises a primary optical D-fibre 36 fixed in contact with a fan of three diverging secondary D-fibres 38, 40 and 42 to form cross couplers 44, 46 and 48 respectively.
In this embodiment, the coupling length Zc is the same for each cross-coupler, different coupling constants being obtained by providing different interaction angles and hence interaction lengths, L, for each coupler.
In this particular example it was found that for the fibre used complete coupling first occurred at 0.320.
Equation (1) shows that for P = 1/2 6 = 0.640, for P = 0 0 1/2 8 = 0.80 and for P = 1/4 @ e = 0.91 .
The angles could also be varied by fixing a curved primary fibre across a parallel array of secondary fibres.
Specific means of fixing the fibres relative to each other have not been shown for reasons of clarity. It will be appreciated many methods may be employed.
One convenient method of fixing the primary and secondary fibres in place is to embed them in a thermoplastic blocks by the method described in the applicants co-pending application GB 8813668.4 namely heating a substrate of a thermoplastic material such as polystyrene until it is deformable by a fl-fibre when pressed by an optically flat former. The former is pressed against the fibres which are forced into the substrate until the flat surfaces are flush with the top surface of the substrate. The former is them removed and the substrate allowed to cool. The complete optical splitter is then formed by fixing the two blocks together.
It will be clear that other cross-sections of optical fibre may be used to form the optical splitter and that splitters for N greater than four can be readily constructed.
The core end of each of the secondary fibres and each end of the primary fibre may be spliced to "pigtails" of communication fibre to provide a package readily spliced to communications fibres of a communications network.
Although this requires additional splices there is still a net benefit over known couplers because of the elimination of inter-coupler splicers. In the case of D-fibres fixed in thermoplastic blocks, the pigtail splices can also be embeded in the block.
Claims (8)
1. An optical 1 to N splitter comprising a primary optical fibre crossed by a least two secondary optical fibres fixed relative to the primary optical fibre, the core of each being evanescently coupled to the core of primary optical fibre to extract a portion only of an optical signal from the primary optical fibre.
2. An optical splitter as claimed in claim 2 in which each secondary fibre couples substantially l/Nth of the optical power initially entering the primary optical fibre at a predetermined working wavelength by providing that each has a suitable, different coupling constant with the primary optical fibre.
3. An optical splitter as claimed in claim 2 in which secondary fibres are fixed so they all cross the primary fibre at the same angle, the differences in coupling constant being determined by the differences in the separation of the cores of the primary and secondary fibres.
4. An optical splitter as claimed in claim 3 in which the spacing between the primary and secondary fibres is determined by spacers.
5. An optical splitter as claimed in claim 3 in which the secondary fibres have different minimum cladding thicknesses which determine the difference in the separation of core of the primary fibre and the cores of the secondary fibres.
6. An optical splitter as claimed in claim 2 in which identical secondary fibres are fixed so they all cross the primary fibre with the same separation, the differences in coupling constant being determined by the differences in the angle at which the primary and secondary fibres cross.
7. An optical splitter as claimed in any preceding claim in which the optical fibres are fl-fibres.
8. An optical splitter as claimed in any preceding claim in which one end of each of the secondary fibre and each end of the primary fibre is spliced to a portion of communications fibre.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9005013A GB2242754A (en) | 1990-03-06 | 1990-03-06 | Optical fibre 1 to N splitter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9005013A GB2242754A (en) | 1990-03-06 | 1990-03-06 | Optical fibre 1 to N splitter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9005013D0 GB9005013D0 (en) | 1990-05-02 |
| GB2242754A true GB2242754A (en) | 1991-10-09 |
Family
ID=10672102
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9005013A Withdrawn GB2242754A (en) | 1990-03-06 | 1990-03-06 | Optical fibre 1 to N splitter |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2242754A (en) |
Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4021097A (en) * | 1976-03-08 | 1977-05-03 | Sperry Rand Corporation | Distributive tee coupler |
| US4054366A (en) * | 1976-07-12 | 1977-10-18 | Hughes Aircraft Company | Fiber optics access coupler |
| GB2045458A (en) * | 1979-03-19 | 1980-10-29 | Hicks J W | Coupled communications fibres |
| US4307933A (en) * | 1980-02-20 | 1981-12-29 | General Dynamics, Pomona Division | Optical fiber launch coupler |
| EP0093460A1 (en) * | 1982-03-22 | 1983-11-09 | Koninklijke Philips Electronics N.V. | Method of manufacturing a fibre-optical coupling element |
| EP0147168A2 (en) * | 1983-12-19 | 1985-07-03 | Litton Systems, Inc. | Three port coupler |
| US4673270A (en) * | 1985-06-28 | 1987-06-16 | Amp Incorporated | Channel add/drop filter-coupler |
| EP0250151A2 (en) * | 1986-06-16 | 1987-12-23 | Shiley Incorporated | Multi-channel optical transmission system |
| EP0287252A1 (en) * | 1987-04-02 | 1988-10-19 | BRITISH TELECOMMUNICATIONS public limited company | A method of forming an optical fibre junction |
-
1990
- 1990-03-06 GB GB9005013A patent/GB2242754A/en not_active Withdrawn
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4021097A (en) * | 1976-03-08 | 1977-05-03 | Sperry Rand Corporation | Distributive tee coupler |
| US4054366A (en) * | 1976-07-12 | 1977-10-18 | Hughes Aircraft Company | Fiber optics access coupler |
| GB2045458A (en) * | 1979-03-19 | 1980-10-29 | Hicks J W | Coupled communications fibres |
| US4307933A (en) * | 1980-02-20 | 1981-12-29 | General Dynamics, Pomona Division | Optical fiber launch coupler |
| EP0093460A1 (en) * | 1982-03-22 | 1983-11-09 | Koninklijke Philips Electronics N.V. | Method of manufacturing a fibre-optical coupling element |
| EP0147168A2 (en) * | 1983-12-19 | 1985-07-03 | Litton Systems, Inc. | Three port coupler |
| US4673270A (en) * | 1985-06-28 | 1987-06-16 | Amp Incorporated | Channel add/drop filter-coupler |
| EP0250151A2 (en) * | 1986-06-16 | 1987-12-23 | Shiley Incorporated | Multi-channel optical transmission system |
| EP0287252A1 (en) * | 1987-04-02 | 1988-10-19 | BRITISH TELECOMMUNICATIONS public limited company | A method of forming an optical fibre junction |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9005013D0 (en) | 1990-05-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |