Patent Application
20220244452
The present invention relates to the field of electromagnetic waveguiding, in particular by the inhibited-coupling mechanism and in particular waves in the optical, terahertz and microwave domains.
The invention proposes a waveguide allowing single-mode guiding, and in some cases, preservation of the polarization of the electromagnetic wave in the waveguide.
Several types of hollow optical fibres are currently used or are the subject of research.
Among these types of optical fibres there are hollow-core photonic crystal fibres or hollow micro structured fibres, using Photonic Forbidden Band guidance, also known as PFB. Such fibres are beneficial in the fields of non-linear optics, conversion of optical frequencies, and spectroscopy. This type of fibres nevertheless has limitations, in particular in terms of:
The current hollow optical fibres guiding by an inhibited-coupling mechanism make it possible to guide the light over broad transmission bands with relatively low dispersion but with relatively high losses. The losses for this type of fibre are attenuated by using a core with a hypocycloid contour.
Current research aims to further reduce the losses for this type of optical fibre.
In addition, as the current optical fibres are intrinsically multimode, this limits their application in certain fields such as telecommunications, for example.
A subject of the present invention is an electromagnetic waveguide, based on the inhibited-coupling mechanism, comprising a hollow central portion the contour of which is at least partially defined by a first set of at least seven primary hollow tubes, distributed annularly around the central hollow portion, said primary hollow tubes being substantially of the same size, distant from one another. According to the invention, said waveguide also comprises a second set of tubes comprising at least one hollow secondary tube: when there are several of these secondary tubes they are positioned annularly around the primary tubes, the area of the at least one hollow secondary tube being comprised between 0.35 and 0.50 times the area of the central hollow portion.
The primary tubes can be fixed to the secondary tubes or to a wall of a cladding bearing the secondary tubes.
By area of the central hollow portion is meant the area of the circle inscribed within the annular arrangement of the first set of hollow tubes.
Advantageously, the ratio, or scaling law, between the area of the central hollow portion and the area of the at least one hollow secondary tube makes it possible to limit the losses of the waveguide according to the invention.
Advantageously, the waveguide according to the invention performs in particular single-mode waveguiding, for example by filtering the four first higher-order modes of the core in order to preserve only the fundamental mode of the core.
In a particularly advantageous embodiment, the at least one hollow secondary tube is positioned opposite a first hollow tube.
In another particularly advantageous embodiment, the at least one hollow secondary tube is positioned opposite a gap between two primary hollow tubes.
Advantageously, the primary tubes can exhibit a cross section having one of the following shapes:
Advantageously, the primary hollow tubes can exhibit a cross section composed of a first circle comprising at least one inscribed circle: in the case of several inscribed circles, these inscribed circles are distributed over the inner circumference of the first circle, said inscribed circles being distant from one another.
Advantageously, if the primary tubes exhibit a cross section in the shape of an ellipse, the long axis of said ellipse is positioned radially with respect to the centre of the hollow central portion, also called hollow core.
Advantageously, if the primary tubes exhibit a cross section in the shape of a barred ellipse, said ellipse is divided in two by a segment.
If the primary tubes exhibit a cross section in the shape of a barred ellipse, the segment dividing the cross section of the ellipse in two is situated on the short axis of said ellipse.
Advantageously, the at least one secondary tube can exhibit a cross section having one of the following shapes:
The secondary tubes can be distant from one another.
Alternatively, the secondary tubes can touch one another.
The cross sections of the secondary tubes can form a grid comprising at least one unitary element.
The grid can comprise several unitary elements of different shapes.
A unitary element can be in the shape of a polyhedron.
The cross sections of the secondary tubes can for example form a grid of hexagonal unitary elements.
The cross sections of the secondary tubes can for example form a grid of triangular unitary elements.
Alternatively, the cross sections of the secondary tubes can for example form a grid of substantially square unitary elements.
Alternatively, the cross sections of the secondary tubes can for example form a grid of rectangular unitary elements.
The secondary tubes can form a grid having more than one type of unitary element, arranged to form a mesh; triangular, hexagonal, square or a combination of these arrangements.
The secondary tubes the contour of which is composed of an arc of a circle and three sides of a polygon can be distributed so as to form at least one corolla surrounding the primary tubes. Each of the shapes composing the corolla can be contiguous with its neighbour.
In a particular embodiment of the invention, the waveguide can be an optical fibre.
The optical fibre can be a microstructured optical fibre.
The primary tubes and the secondary tubes can be made from dielectric material.
The first and secondary tubes can have walls of the same thickness, for example of a thickness comprised between 100 nm and 2000 nm.
The hollow central portion, the first and secondary tubes can be filled with a gas such as air for example.
The waveguide according to the invention guides the waves in particular by inhibited coupling.
The waveguide can guide waves from among:
The material of the secondary tubes can be a material having a low absorption coefficient such as Teflon™, having a refractive index greater than 1.2 times that of air.
Alternatively, the material of the secondary tubes can be a highly reflective material such as a metal like copper.
Alternatively, the material of the secondary tubes can be a material having a low absorption coefficient such as silica.
The material of the secondary tubes can be a transparent material of the silica type having a refractive-index step greater than 1.2 times the refractive index of the void.
In a particularly advantageous embodiment, the waveguide according to the invention can also comprise a set of rods, at least one rod being positioned between two primary tubes, at a distance from secondary tubes.
In such an embodiment, the waveguide maintains the polarization of the guided waves.
The at least one third tube can exhibit one of the following forms:
According to the invention, the secondary tubes can be produced in a cladding of the waveguide and the primary tubes can be fixed to the inner wall of said cladding.
In such a case for example, the distance δrr between the at least one secondary tube and the inner wall of the cladding is preferably less than 0.2*rtin for the case of a primary tube that is circular or less than 0.2*√(Areain/π) for a primary tube having an area equal to Areain.
According to the invention, each primary tube can be fixed to the wall of a secondary tube.
The invention thus provides for the case where the primary tubes are produced in the void but fixed to secondary tubes that can be produced partially or totally in the cladding or produced in the void but fixed to a wall of a jacket for example.
Other advantages and features of the invention will become apparent on reading the detailed description of implementations and embodiments that are in no way limitative, and from the following attached drawings:
An aim of the present invention is in particular to reduce the losses for a propagation mode of a given order, and to increase the losses for the higher-order propagation modes.
The purpose of the present invention is in particular to propose an electromagnetic waveguide having a hollow central portion delimited by a first set of tubes isolated from one another, borne by a first tubular structure, and ordered so as to form a ring, for example called inner ring or first ring, and a second annular structure or outer ring. The second annular structure can advantageously comprise a second set of tubes positioned around the ring formed by the tubes of the inner ring.
The present invention can be applied in different fields, in particular for guiding waves in the optical, terahertz and microwave domains
The waveguide 1 comprises a hollow central portion or hollow core 2 that can either be filled with air, or with an inert gas, or can even be a void. The hollow core 2 can have a minimum diameter 2Rc, Rc corresponding to a radius of the hollow core 2. Around the hollow core 2 is located a first ring 4 or cylindrical inner ring 4 or even first annular structure 4, contained in the void like the hollow core 2, extending over the whole length of the waveguide. The inner ring 4 has an inner radius Rc and outer radius Rst.
The inner ring 4 comprises several primary hollow tubes 8, 9, 10, 11, 12, 13, 14 distant from one another. For example, as shown in
Rc, rtin and δtt can be linked by the following relationship:
with N, the number of primary tubes of the inner ring 4.
For non-circular tubes, the relationship remains valid by replacing Rc, rtin respectively with 0.1 √{square root over (Areac/π)} and 0.1 √{square root over (Areain/π)}
A waveguide according to the invention advantageously comprises at least seven primary tubes. The waveguide can however comprise more than seven primary tubes.
For example, a waveguide comprising six primary tubes has a smaller core size than a waveguide comprising seven primary tubes. Use of at least seven primary tubes makes it possible to minimize losses, in particular owing to the fact that the size of the core is more substantial than with seven primary tubes.
The primary tubes can be borne by an inner wall 5 of a cladding 3.
For example the tubes 100, 101, 102 comprised in the primary tubes 19 can be distant from one another, and in contact with the inner surface of the primary tubes 19.
A fourth cross-section shape for the primary tubes can be an ellipsoid shape 103, 104 as shown in
It is also possible for the primary tubes to have a cross-section shape that differs from one to another.
As shown in
The interior of the outer ring 3 is formed from a solid material in which the at least one hollow secondary tube 6 is inserted.
The distance between the at least one secondary tube 6 and the outer surface of the inner ring 4 is δrr. δrr can be negative. Preferably, δrr<0.2rtin for the case of a circular tube or δrr<0.2 √{square root over (Areain/π)} for a tube having an area equal to Areain.
In
Advantageously, it is possible to have at least one secondary tube having a shape such as shown in
The secondary tubes having a circular cross section can be distant from one another.
The cross sections of the secondary tubes can form a grid comprising at least one unitary element having one of the cross-section shapes shown in
In general terms, the cross sections of the secondary tubes can form a grid comprising more than one unitary element, said unitary elements being arranged to form a mesh; triangular, hexagonal, square or a combination of these arrangements.
In
Advantageously, such a waveguide makes it possible to preserve quite low energy losses for the mode to be propagated and to increase losses for the higher-order modes. In fact, the higher-order modes can leak via the gaps between two consecutive primary tubes when they are not placed opposite the secondary tubes. Alternatively, the higher-order modes can leak via the secondary tubes when these are in contact with the primary tubes.
The second waveguide 20, like the first waveguide 1, comprises a core 29 surrounded by a first ring 24 constituted by eight primary tubes 200, 201, 202, 203, 204, 205, 206, 207. The eight primary tubes 200, 201, 202, 203, 204, 205, 206, 207 are supported by the inner wall 27 of a cladding 25 forming an outer ring.
The second waveguide 20 also comprises two secondary tubes 21, 22 forming part of an outer ring 25. The two secondary tubes 21, 22 are positioned opposite the core 2 and two gaps between two consecutive primary tubes 200, 201 and 204, 205.
The configuration of the secondary tubes opposite an interstice between two primary tubes is particularly suitable when the distance between two consecutive primary tubes is relatively large.
A second tubular structure 26 can form a jacket of the waveguide according to the invention. The secondary tubes 21, 22 can be borne by the second tubular structure 26.
The second waveguide 30, like the first waveguide 1, comprises a core 38 surrounded by a first ring 39 constituted by eight primary tubes 300, 301, 302, 303, 304, 305, 306, 307. The eight primary tubes 300, 301, 302, 303, 304, 305, 306, 307 are supported by the inner wall 37 of a cladding 35 forming an outer ring.
The second waveguide 30 also comprises four secondary tubes 31, 32, 33, 34 forming part of a second ring 35. The four secondary tubes 31, 32, 33, 34 are positioned opposite an interstice between two of the primary tubes of the first ring 39. In
A second tubular structure 36 can form a jacket of the waveguide according to the invention. The secondary tubes 31, 32, 33, 34 can be borne by the second tubular structure 36.
The fourth waveguide 40, like the third waveguide 30, comprises a core 41 surrounded by a first ring 42 constituted by eight primary tubes 400, 401, 402, 403, 404, 405, 406, 407. The eight primary tubes 400, 401, 402, 403, 404, 405, 406, 407 are supported by the inner wall 44 of a cladding 43 forming an outer ring. The eight primary tubes 400, 401, 402, 403, 404, 405, 406, 407 are for example, but not necessarily, regularly distributed within the first ring 42. The fourth waveguide 40 also comprises two secondary tubes 47, 48 forming part of a second ring 43. The two secondary tubes 47, 48 are positioned opposite one of the primary tubes of the first ring 42.
A second tubular structure 45 can form a jacket of the waveguide according to the invention. The secondary tubes 47, 48 can be borne by the second tubular structure 45.
Advantageously, the alignment of the primary tubes 47, 48 with the secondary tubes 402, 406 makes it possible to allow leakage of the unwanted propagation modes. This type of waveguide architecture is particularly suitable when the spaces between the primary tubes are relatively small.
The fifth waveguide 50 comprises eight primary tubes 501, 502, 503, 504, 505, 506, 507, 508, distributed over a first ring 57 around the core 56. The primary tubes 501, 502, 503, 504, 505, 506, 507, 508 can be borne by the inner wall 59 of a cladding 55 forming an outer ring.
The fifth waveguide 50 also comprises a second ring 55 comprising secondary tubes 51, 53, 52, 54. The secondary tubes are situated respectively opposite the primary tubes 502, 504, 506, 508. The secondary tubes 502, 504, 506, 508 can be distant from one another.
A second tubular structure 58 can form a jacket of the waveguide according to the invention. The secondary tubes 51, 53, 52, 54 can be borne by the second tubular structure 58.
The sixth waveguide 80 comprises eight primary tubes 84, 85, 86, 87, 88, 89, 800, 801, distributed over a first ring 82 around the core 81. The sixth waveguide 80 also comprises a second ring 83 comprising eight secondary tubes 802, 803, 804, 805, 806, 807, 808, 809. The secondary tubes 802, 803, 804, 805, 806, 807, 808, 809 are situated respectively opposite the primary tubes 84, 85, 86, 87, 88, 89, 800, 801. In
The seventh waveguide 90 can comprise a first ring 92 comprising for example eight primary tubes 95, 96, 97, 98, 99, 900, 901, 902 surrounding the hollow core 91. Moreover, the seventh waveguide 90 can comprise four rods 904, 905, 906, 907 positioned in the first ring 92. For example, a first rod 904 can be inserted between a primary tube 95 and a next primary tube 96 on the first ring 92, turning in the clockwise direction. A second rod 905 can be inserted between a primary tube 97 and a primary tube 98. A third rod 906 can be inserted between a primary tube 99 and a primary tube 900. The gap between the primary tubes 902 and 95, 96 and 97, 98 and 99, 900 and 901 does not comprise a rod.
The rods 904, 905, 906, 907, like the first tubes 95, 96, 97, 98, 99, 900, 901, 902, are borne by an inner wall of a cladding 93 surrounding the first ring 92.
Advantageously, the positioning of the rods 904, 905, 906, 907 in one in two interstices separating the primary tubes makes it possible to maintain the polarization of the wave propagating in the seventh waveguide.
The eighth waveguide 110 as shown in
The eighth waveguide 110 comprises a hollow core 111 surrounded by a first ring 112. The first ring 112 comprises eight primary tubes 1120, 1121, 1122, 1123, 1124, 1125, 1126, 1127. A rod 1128, 1129, 1130, 1131 is inserted in one in two gaps between two consecutive primary tubes. For example, a first rod 1128 can be inserted between two primary tubes 1120, 1121, a second rod 1129 can be inserted between two primary tubes 1122 and 1123, a third rod 1130 can be inserted between two primary tubes 1124 and 1125, a fourth rod 1131 can be inserted between two primary tubes 1126 and 1127.
Moreover, the eighth waveguide 110 comprises a second ring 113 comprising four secondary tubes 116, 117, 118, 119. The secondary tubes can for example be positioned opposite the gaps between the primary tubes 1121 and 1122, 1123 and 1123, 1125 and 1126, 1127 and 1120, between which no rod has been inserted.
Advantageously, the positioning of the rods 1128, 1129, 1130, 1131 in one in two interstices separating the primary tubes 1120, 1121, 1122, 1123, 1124, 1125, 1126, 1127 makes it possible to maintain the polarization of the wave propagating in the waveguide according to the invention. The positioning of the secondary tubes 116, 117, 118, 119 facing a second interstice of two separating the primary tubes, said second interstices not comprising rods, makes it possible to increase the losses for the higher-order modes greater than the mode preferably guided in the core of the waveguide according to the invention.
In
The first ring 112 can comprise nine primary tubes 123. The primary tubes 123 can have one of the shapes shown in
The first ring 122 is surrounded by a second ring 125. The second ring 125 can comprise secondary tubes 126 in the shape of petals 109, as shown in
In
The secondary tubes 126 are borne by a cladding or jacket 127 surrounding the second ring 125.
In
The first ring 132 comprises by way of example nine primary tubes 133. The primary tubes 133 can have one of the shapes shown in
The first tubes 133 can be supported by a grid 134.
The tenth waveguide 130 also comprises a second ring 135 comprising secondary tubes 136 forming a grid 134 with a squared unitary pattern. The grid is cut out in such a way as to form the second ring 135 around the first ring 132 and so as to have an outer contour 137 that is circular in shape.
In
The hollow core 141 is surrounded by a first ring 142 comprising primary hollow tubes 143. By way of example,
The primary hollow tubes 143 can have one of the shapes shown in
The first hollow tubes 143 can be borne by a first tubular structure 145.
The eleventh waveguide 140 also comprises a second ring 146. The secondary tubes of the second ring 146 are arranged so as to form a grid with a hexagonal unitary pattern such as a Kagome structure, for example. The grid with a hexagonal unitary pattern is cut out in order to have circular inner and outer contours.
In general terms, the secondary tubes forming the second ring can form a grid comprising at least one unitary element. The unitary element can exhibit a cross section having one of the shapes shown in
Alternatively, the grid can be composed of several different unitary patterns from among the shapes shown in
Thus, the secondary tubes can form a grid of triangular, or substantially square, or rectangular, unitary elements.
In
By way of example,
By way of example
By way of example,
The bar 183 of the ellipse 182 can be arranged in the ellipse 182 along its short diameter for example.
Of course, the various characteristics, forms, variants and embodiments of the invention can be combined together in various combinations inasmuch as they are not incompatible or mutually exclusive. In particular, all the variants and embodiments described above can be combined together.
| Number | Date | Country | Kind |
|---|---|---|---|
| FR1908906 | Aug 2019 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/071732 | 7/30/2020 | WO | 00 |
