Apparatus for Guiding Light from an Input Side to an Output Side

Abstract

An apparatus (1) for guiding light and a method for producing a photonic lantern (2) are described. The apparatus (1) for guiding light from an input side (5) to an output side (6), comprises an input waveguide (3) at the input side (5) formed by at least two multi-mode fibres (7), an output waveguide (4) at the output side (7) formed by a single multi-mode fibre (5) and a photonic lantern (2) optically connecting the at least two multi-mode fibres (7) of the input waveguide to the single multi-mode fibre (8) of the output waveguide. The photonic lantern (2) is being designed such that, light transmitted by light guiding cores (9) of the at least two multi-mode fibres (7) of the input waveguide (3) is coupled into a light guiding core (10) of the single multi-mode fibre (8) of the output waveguide (4) and propagates through the light guiding core (10) of the single multi-mode fibre (8) of the output waveguide (4) and that claddings (11) surrounding the light guiding cores (9) of the at least two multi-mode fibres (7) of the input waveguide (3) are tapered down until they do at least almost not confine light.

Claims

1. Apparatus (1) for guiding light from an input side (5) to an output side (6), comprising an input waveguide (3) at the input side (5) formed by at least two multi-mode fibres (7), an output waveguide (4) at the output side (7) formed by a single multi-mode fibre (5) and a photonic lantern (2) optically connecting the at least two multi-mode fibres (7) of the input waveguide to the single multi-mode fibre (8) of the output waveguide, said photonic lantern (2) is being designed such that, light transmitted by light guiding cores (9) of the at least two multi-mode fibres (7) of the input waveguide (3) is coupled into a light guiding core (10) of the single multi-mode fibre (8) of the output waveguide (4) and propagates through the light guiding core (10) of the single multi-mode fibre (8) of the output waveguide (4) and that claddings (11) surrounding the light guiding cores (9) of the at least two multi-mode fibres (7) of the input waveguide (3) are tapered down until they do at least almost not confine light.

2. Apparatus according to claim 1, characterized in that the at least two multi-mode fibres (7) of the input waveguide are located inside a capillary (12).

3. Apparatus according to claim 2, characterized in that the capillary (12) forms the cladding of the single multi-mode fibre (8) of the output waveguide (4).

4. Apparatus according to claim 2, characterized in that the capillary (12) comprises fluorine doped silica glass.

5. Apparatus according to claim 1, characterized in that the multi-mode fibres (7) of the input waveguide (3) are arranged in a close packed arrangement in relation to a cross-sectional plane of the input waveguide (3).

6. Apparatus according to claim 1, characterized in that a ratio of a diameter of the light guiding core (9) of at least one of the multi-mode fibres (7) of the input waveguide (3) to its cladding (11) is between 1.05 and 1.15, preferably 1.1.

7. Apparatus according to claim 1, characterized in that the input waveguide (3) comprises 58 to 62 multi-mode fibres (7).

8. Apparatus according to claim 1, characterized in that the photonic lantern (2) is designed such that the diameter of the light guiding core (9) of at least one of the multi-mode fibres (7) of the input waveguide (3) tapers down by 94.5 to 95.5%.

9. Apparatus according to claim 1, characterized in that the light guiding core (9) of at least one multi-mode fibre (7) of the input waveguide (3) and/or the light guiding core (10) of the single multi-mode fibre (8) of the output waveguide (4) comprise pure silica.

10. Apparatus according to claim 1, characterized in that the refractive index of the light guiding core (9) of at least one multi-mode fibre (7) of the input waveguide (3) and/or the refractive index of the single multi-mode fibre (8) of the output waveguide (4) is 1.440 to 1.448, preferably 1.444 at a wavelength within a range of 1450 to 1650 nm, in particular at a wavelength of approximately or accurately 1550 nm.

11. Apparatus according to claim 2, characterized in that the refractive index of the capillary (12) is 1.425 to 1.430, preferably 1.428 at a wavelength within a range of 1450 to 1650 nm, in particular at a wavelength of approximately or accurately 1550 nm.

12. Method for producing a photonic lantern (2) suitable for an apparatus for guiding light from an input side (5) to an output side (6) comprising the steps of: providing at least two multi-mode fibres (7) comprising a light guiding core (9) and a cladding (11) surrounding the light guiding core (9), stacking the at least two multi-mode fibres (7) inside a capillary (12), heating and drawing the capillary (12) together with the multi-mode fibres (7) in such a way, (a) that the light guiding cores (9) of the at least two multi-mode fibres (7) become a light guiding core (10) of a single multi-mode fibre (8), at which the capillary (12) building the cladding of said single multi-mode fibre (8) and (b) that claddings (11) surrounding the light guiding cores (9) of the at least two multi-mode fibres (7) when stacked inside the capillary (12) are tapered down until they do at least almost not confine light.

13. Method according to claim 12, characterized in that the at least two multiple multi-mode fibres (7) comprising a light guiding core (9) and a cladding (11) surrounding the light guiding core (9) are stacked together in a close packed arrangement inside the capillary (12).

14. Method according to claim 12, characterized in that the diameter of the light guiding cores (9) of the at least two multi-mode fibres (7) are tapered down in such a way that a resulting diameter is 4.5 to 4.6% of the diameter before tapering.

15. Use of an apparatus (1) according to claim 1 for coupling light from multiple telescopes into a single spectrograph, for medical endoscopy and/or for guiding light from multiples laser sources to a laser cutting tool.

16. Use of a photonic lantern produced according to claim 12 for coupling light from multiple telescopes into a single spectrograph, for medical endoscopy and/or for guiding light from multiples laser sources to a laser cutting tool.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG. 1: Diagram of an apparatus according to the invention with multiple multi-mode fibres at the input side, a single multi-mode fibre at the output side, and a photonic lantern connecting the input and the output side,

[0042] FIG. 2 Cross- and longitudinal-sectional view of a waveguide comprising several multi-mode fibres in a close packed arrangement,

[0043] FIG. 3: Results of a first simulation with respect to the light distribution in the input and the output waveguide of an apparatus according to the invention,

[0044] FIG. 4; Results of a second simulation with respect to the light distribution in the input and the output waveguide of an apparatus according to the invention,

[0045] FIG. 5: Results of a third simulation with respect to the light distribution in the input and the output waveguide of an apparatus according to the invention,

[0046] FIG. 6: Curve showing the efficiency of light coupling with respect to the second simulation, and

[0047] FIG. 7: Curve showing the efficiency of light coupling with respect to the third simulation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0048] FIG. 1 shows in a longitudinal cross-section a schematic diagram of an apparatus 1 according to the invention, which allows an efficient coupling of light between several multi-mode fibres 7 and one single multi-mode fibre 8. Here, the apparatus 1 comprises a specific photonic lantern 2 building a transition region and connecting the input waveguide 3 with multiple multi-mode fibres 7 with one single multi-mode fibre 8 of the output waveguide 4.

[0049] Traditionally, photonic lanterns are produced by stacking a bundle of single-mode fibres inside a capillary and tapering them down to fuse into a single multi-mode fibre. The capillary becomes the cladding of the single multi-mode fibre, the cladding of the single-mode fibres become the core of the multi-mode fibre, and the cores of the single-mode fibres are reduced to the point, that they can no longer efficiently couple light. Multi-mode fibres cannot be drawn into a photonic lantern in the traditional way as their significantly larger cores would still be able to couple light even after tapering. Consequently, light does not propagate across a single fibre and may lead to erroneous spectroscopic measurements.

[0050] According to the invention, an apparatus 1 comprising a photonic lantern 2 as well as a method of producing such a photonic lantern 2 are provided as to make it possible to couple light from many multi-mode fibres 7 to a single multi-mode fibre 8. This coupling of light is obtained by stacking and tapering several multi-mode fibres 7 with high core to cladding ratios such that claddings 11, when tapered, become too thin to efficiently confine light. Unlike with traditional designs, the core 10 of the single multi-mode fibre 8 is formed by fusing the cores 9 of the many multi-mode fibres 7 with the cladding formed from the capillary 12.

[0051] As shown in FIG. 1, on the input side 5 a waveguide 3 is formed by multiple multi-mode fibres 7 guiding light in the direction of the photonic lantern 2 connecting the input waveguide 3 and the output waveguide 4, which only comprises one single multi-mode fibre 8 with a core 10 having large core diameter. In addition, the capillary 12 of the input waveguide 3 surrounding the multiple multi-mode fibres 7 becomes the cladding of the output waveguide 4, respectively the one single multi-mode fibre 8.

[0052] Depending whether the photonic lantern 2 arranged in the transition region of the apparatus 1 shown in FIG. 1 is used as a beam combiner or splitter light is directed from the input waveguide 3 into the output waveguide 4 or from the output waveguide 4 into the input waveguide 3. If the photonic lantern 2 is used to combine light guided by different multi-mode fibres 7 into the input end on the input side 5, e.g. for coupling light from multiple telescopes into a single spectrograph, light guided by at least two multi-mode fibres 7 is combined by the photonic lantern 2, and then propagates through the core 10 of the single multi-mode fibre 8 with a large diameter. According to the invention and shown in FIG. 1 the claddings 11 of the several multi-mode fibres 7 become too thin to efficiently confine light and the original cladding of the input waveguide 3 formed by a capillary 12 becomes the cladding of the single multi-mode fibre 8 of the output waveguide 4. Thus, the core 10 of the single multi-mode fibre leaving the apparatus 1 at its output end on the side 6 is formed by fusing the cores 9 of multiple multi-mode fibres 7 entering the apparatus 1 on its input side 5. As already mentioned, light coupling can take place in either direction, combining light from many multi-mode fibres 7 into a single multi-mode fibre 8 or splitting light from a single multi-mode fibre 8 into multiple multi-mode fibres 7.

[0053] The apparatus 1 according to the invention and the photonic lantern 2 produced by the inventive method, as shown in FIG. 1 can be used preferably in the field of astrophysics, where light from multiple telescopes can be coupled into a single spectrograph. Furthermore, this technical solution is advantageous for medical endoscopy and/or surgery and can also be used in the field of industrial manufacturing, particularly where light from a cutting laser is divided between multiple output points whilst maintaining sufficient power. Of course, the inventive technical solution is also suitable for telecommunication and Internet applications, especially for multichannel bidirectional data transfer.

[0054] FIG. 2 shows in a cross-sectional view, cf. FIG. 2a, as well as in a longitudinal-sectional view, cf. FIG. 2b, of a photonic lantern 2 produced according to the invention. Multiple multi-mode fibres 7 are arranged in a closed packed arrangement 13. According to the specific embodiment shown in FIG. 2 a bundle of multi-mode fibres 7, each with a core diameter of 23 μm and core-to-cladding ration of 1:1.1, are stacked together in a hexagonal packing, whereat this packing is arranged inside a capillary 12 with an internal diameter of 219 μm, and a refractive index of 1.440533 at a wavelength of 1550 nm. The diameter of the cladding 11 of each multi-mode fibre 7 is about 25 μm, so that its thickness is about 1 μm.

[0055] The photonic lantern 2 shown in FIG. 2 was produced by pre-tapering larger multi-mode fibres 7 with high core-to-cladding rations.

[0056] According to this embodiment 61 multi-mode fibres 7 are used because of the number of desired telescopes as well as the current maximum optical fibre successfully drawn into a photonic lantern 2 as known from “D. Noordegraaf et. al., Multi-mode to single-mode conversion in a 61 port Photonic Lantern, Optics Express, 18(5), pp 4673-4678, 2010”. Core and cladding diameters are chosen to ensure, that the claddings 11 of the several multi-mode fibres 7 become thin enough to allow multi-mode behaviour in the combined single multi-mode fibre 8.

[0057] The internal diameter of the capillary 12 selected to allow optimal packing arrangements 13 of the 61 multi-mode fibres 7 in the input waveguide 3. Here, algorithm known from “R. L. Graham et. al., Dense packings of congruent circles in a circle, Discrete Mathematics 181, pp. 139-154, 1998” are used to determine the most effective packing. The refractive index is selected to allow multi-mode behaviour in the fused section, respectively the single multi-mode fibre 8 with a numerical aperture of 0.1.

[0058] For the manufacturing, the stack is heated and tempered with a glass processing unit in such a way, that the fused single multi-mode fibre has a core diameter of approximately 80 μm, and a numerical aperture of 0.1.

[0059] Through the system shown in FIG. 2 light from 61 multi-mode fibres 7 can be combined into a single multi-mode fibre 8. For the intended application light from multiple telescopes pointed at the same astronomical object such as a star or galaxy, can be combined into a single multi-mode fibre 8 to be fed into a spectrograph. Thus, a more sensitive measurement can be taken. An alternative application combines light from multiple high-power lasers together into a single multi-mode fibre 8 for surgical or manufacturing uses.

[0060] The technical solution shown in FIG. 2 differs from prior art in that traditional photonic lanterns combine many single-mode fibres into one multi-mode fibre. Single-mode fibres, while having other advantages, are harder to launch light into. In contrast, multi-mode fibres inputs allow light to be more efficiently launched into them allowing more light to be combined into a single multi-mode fibre.

[0061] FIG. 3 shows the results of a first simulation regarding the light coupling between multiple multi-mode fibres 7 and one single multi-mode fibre 8 being coupled with the help of an apparatus 1, respectively a photonic lantern 2 according to the invention. FIG. 3 a) shows in a cross-sectional view the light distribution in a bundle of several multi-mode fibres 7 of the input waveguide 3, whereat FIG. 3 b) shows, also in a cross-sectional, view the light distribution in the single multi-mode fibre 8 of the output waveguide 4, having a comparatively large core diameter.

[0062] It can be seen very clearly from FIG. 3 a) and b), that although light is guided into the photonic lantern 2 connecting the input and the output waveguide 3, 4 by several multi-mode fibres 7 being irregularly distributed within the input waveguide 3, the light distribution over the cross-section of the one single multi-mode fibre 8 is very uniform, as shown in FIG. 3 b). Furthermore, light losses caused by the light coupling are minimized.

[0063] In addition, FIG. 4 shows the results of a second simulation. Here, seven multi-mode fibres 7 of the input waveguide 3 guiding light into the photonic lantern 2 are arranged in a hexagonal packing, as shown in FIG. 4 a). In contrast to FIG. 3 b) FIG. 4 b) shows the light distribution within the photonic lantern 2 in a longitudinal-sectional view. Again, the light distribution in the one single multi-mode fibre 8 of the output waveguide 4 is very uniform compared to the light distribution within the input waveguide 3 comprising seven separate multi-mode fibres 7.

[0064] According to a third simulation, whose results are shown in FIG. 5, the light guiding multi-mode fibres 7 of the input waveguide 3 are arranged in-line. The light distribution within the input waveguide 3 can be seen in FIG. 5 a). As a result, FIG. 5 b) clearly shows that the light distribution within the single multi-mode fibre 8 of the output waveguide 4 is very uniform again. The photonic lantern 2 connecting the input and the output waveguide 3, 4 combines the light propagating through the different multi-mode fibres 7 of the input waveguide 3 in a very efficient way.

[0065] In addition to FIGS. 4 and 5, FIGS. 6 and 7 show the light transmission efficiency along the propagating path of the light through an apparatus 1, respectively a photonic lantern 2 according to the invention. FIG. 6 shows the efficiency of the light coupling in case the incoming light is distributed over the input waveguide 3 as shown FIG. 4 a) and FIG. 7 shows the efficiency of the light coupling in case the incoming light is distributed over the input waveguide 3 as shown FIG. 5 a). It clearly can be seen, that the efficiency of the light coupling realized by the photonic lantern 2 according to the invention, hence the ratio of luminous intensity in the output waveguide 4 to the luminous intensity in the input waveguide 3 is between 0.88, in FIGS. 6 and 0.87 in FIG. 7. The results show, that using an apparatus 1, respectively a photonic lantern 2 according to the invention a very efficient light coupling between multiple multi-mode fibres 7 and a single multi-mode fibre 8, whereby light coupling can take place in either direction, can be realized.

LIST OF REFERENCE NUMERALS

[0066] 1 apparatus connecting several multi-mode fibres with a single multi-mode fibre [0067] 2 photonic lantern [0068] 3 input waveguide [0069] 4 output waveguide [0070] 5 input side [0071] 6 output side [0072] 7 multi-mode fibre of the input waveguide [0073] 8 single multi-mode fibre of the input waveguide [0074] 9 core of a multi-mode fibre of the input waveguide [0075] 10 core of the single multi-mode fibre of the input waveguide [0076] 11 claddings of a multi-mode fibre of the input waveguide [0077] 12 capillary [0078] 13 close packing arrangement