Surface grating coupler suitable for photonic devices, associated method and assembly with surface grating coupler

Abstract

The present invention relates to a surface grating coupler comprising a substrate, a sub-wavelength grating, and a prism adjacent to the sub-wavelength grating. The sub-wavelength grating comprises a core material pattern extending in two dimensions and formed by two or more pluralities of portions of core material having, in a direction transverse to the propagation direction and adjacent to one another, at least a first plurality of portions and at least a second plurality of portions extending in the propagation direction. Each pair of neighbouring portions of the first and second pluralities of portions is separated by a first distance and a second distance in the propagation direction, respectively. The second plurality of portions is arranged such that at least the portions from the second portion to the penultimate portion in the propagation direction would be respectively inside the separation between neighbouring portions of each first plurality of portions if the first and second pluralities of portions have a shared position in the transverse direction. Furthermore, the invention discloses an assembly comprising the surface grating coupler, and a method associated with the surface grating coupler.

Description

[0001] SURFACE GRID COUPLER SUITABLE FOR PHOTONIC DEVICES, ASSOCIATED METHOD AND JOINT WITH SURFACE GRID COUPLER

[0002] TECHNICAL SECTOR

[0003] The present invention relates to the technical field of photonics. More specifically, the present invention relates to the coupling of light between photonic devices characterized by different mode sizes, where the mode size of the photonic device to which the light is coupled is different from that of the photonic device from which the light originates.

[0004] BACKGROUND OF THE INVENTION

[0005] One of the most important problems in integrated optics is the ineffective coupling of light between photonic devices due to the difference in mode size between one photonic device and another; for example, coupling light from devices such as optical fibers to devices such as waveguides integrated on chips, especially those made of silicon-on-insulator (SOI), which are widely used, requires couplers and / or coupling techniques that can adapt the mode size of one device to that of the other for satisfactory coupling. Light coupling should preferably have an adequate bandwidth, with low optical power losses and low wavelength dispersion.

[0006] Some of the couplers typically used are surface-based grating couplers and edge-based couplers. Both types of couplers, however, have limitations. Edge-based couplers, for example, have good bandwidth, but require the device to which the light is coupled to have a polished facet connection, that is, with the edge of the chip polished, and they must be located at the edge of the chip, which imposes restrictions on waveguide routing. Surface-based grating couplers are more versatile in terms of positioning on the chip, but have poorer performance.In this regard, the coupling efficiency of surface-based grating couplers is typically less than -2.2 dB due to the poor directionality of the upward-coupling radiation direction and poor overlap between the radiated field and the fundamental mode of the optical fiber. Furthermore, the 1 dB bandwidth is typically below 50 nm.

[0007] Specifically, to improve the coupling efficiency of surface grating couplers, techniques have been designed that aim to improve both factors, such as increasing the directionality by reducing reflections towards the substrate and back and maximizing the overlap, as well as improving the bandwidth to 1 dB using, for example, metamaterials based on subwavelength grating (commonly called SWG) as in Yun Wang, Wei Shi, Xu Wang, Zeqin Lu, Michael Caverley, Richard Bojko, Lukas Chrostowski, and Nicolas AF Jaeger, "Design of broadband subwavelength grating couplers with low back reflection," Opt Lett. 40, 4647–4650 (2015).

[0008] Despite these attempts to improve light coupling, there is still a need to develop new couplers or new coupling techniques for coupling light between devices such as optical fibers and integrated waveguides on chips that improve the performance of the solutions described in the prior art. The versatility of surface grating couplers is a desirable advantage, although their performance needs to be improved.

[0009] OVERVIEW

[0010] A first aspect of the invention relates to a surface grating coupler. The surface grating coupler comprises: a substrate, a first subwavelength grating (i.e., a first SWG) of core material on the substrate over at least a portion of the substrate's length, and a prism adjacent to at least a portion of the first subwavelength grating.

[0011] The length of the substrate is defined along a propagation direction of light waves in the surface-coupled grating. The first subwavelength grating comprises a pattern of core material extending two-dimensionally along the propagation direction and a direction transverse to the propagation direction. The core material pattern of the first subwavelength grating is formed by a plurality of core material portions having, in the transverse direction and adjacent to one another or to one another, at least a first plurality of portions and at least a second plurality of portions, each of the first and second pluralities of portions extending in the propagation direction. Each pair of neighboring portions of the first plurality of portions is separated by a first distance in the propagation direction.Each pair of neighboring portions of the second plurality of portions is separated by a second distance in the propagation direction. The second plurality of portions is arranged such that at least the portions from the second to the second-to-last portions in the propagation direction would respectively lie within the separation between neighboring portions of each first plurality of portions if the first and second pluralities of portions shared a position in the transverse direction.

[0012] The surface grating coupler described above has a coupling efficiency and bandwidth greater than those previously mentioned, for example, a coupling efficiency of up to -0.6 dB and a 1 dB bandwidth of up to 375 nm can be achieved. To this end, the coupler includes a SWG-based waveguide that presents the two-dimensional pattern described. The prism adjacent to the waveguide allows the propagated mode to exit through said prism, thus radiating it from the first SWG to another device.

[0013] The first SWG includes the dimensional pattern designed such that said SWG behaves as a homogeneous metamaterial. More specifically, the pattern of the first SWG has a plurality of portions such that the periodicities thereof are sub-wavelength for a light to be coupled, thus making the first SWG as little diffractive as possible, preferably not at all diffractive. The periodicities are defined as a function of the length, according to the propagation direction, of a portion of material and a portion of space without material, that is, the length from the start of one portion of material to the start of the next portion of material within the same plurality of portions. Such a pattern design imposes that the radiation be of zero order and, therefore, the radiation angle 0 is described according to the following equation: n B (TO)'

[0014] 0(A) = arcsin n P( ) where A is a wavelength of the light to be propagated by the grating coupler per surface, n B is the real part of the effective index of the Bloch-Floquet mode that supports the first SWG, and n P is the refractive index of the material to which the light is coupled, which is that of the prism of the grating coupler by surface and which, in preferred embodiments, has a value as high as possible to be much greater than n B In the surface grating coupler of the present invention, the effective index of the Bloch-Floquet mode has little wavelength dependence and thus the radiation angle 0 also has little wavelength dependence.

[0015] A second aspect of the invention relates to an assembly comprising the surface grating coupler according to the first aspect of the invention, and an optical fiber adjacent to the prism of the surface grating coupler, there being a separation between the optical fiber and the prism.

[0016] A third aspect of the invention relates to a method. The method comprises at least the following steps: disposing a first subwavelength grating of core material on a substrate over at least a portion of the substrate's length to produce a surface grating coupler; disposing a prism adjacent to at least a portion of the first subwavelength grating; and radiating at least one light wave via the surface grating coupler by coupling the at least one light wave into an input of the surface grating coupler and propagating the at least one light wave over at least part of a length of the first subwavelength grating, i.e., radiating said at least one light wave via the coupler by injecting it into an input port thereof and propagating it over the first subwavelength grating or part of said first grating.

[0017] The method has features of the surface grating coupler as described in the first aspect of the invention. Therefore, the method further provides the following. The length of the substrate is defined along a propagation direction of light waves in the surface grating coupler. The first subwavelength grating comprises a pattern of core material extending two-dimensionally along the propagation direction and a direction transverse to the propagation direction. The core material pattern of the first subwavelength grating is formed by a plurality of core material portions having, in the transverse direction and adjacent to one another or to one another, at least a first plurality of portions and a second plurality of portions, each of the first and second pluralities of portions extending in the propagation direction;Each pair of neighboring portions of the first plurality of portions is separated by a first distance in the propagation direction; Each pair of neighboring portions of the second plurality of portions is separated by a second distance in the propagation direction; and the second plurality of portions is arranged such that at least the second to second-last portions in the propagation direction are respectively within the separation between neighboring portions of each first plurality of portions if the first and second pluralities of portions shared a position in the transverse direction.

[0018] BRIEF DESCRIPTION OF THE DRAWINGS

[0019] To complement the description being made and in order to help better understand the characteristics of the invention, a set of drawings is attached as an integral part of said description, in which, for illustrative and non-limiting purposes, the following has been represented:

[0020] Figure 1.- Shows a perspective view of a surface grid coupler according to some embodiments.

[0021] Figure 2.- Shows a sectional view of an assembly with a grid coupler per surface according to some embodiments.

[0022] Figures 3, 4, 5, 6, 7 and 8.- Partially show, from a top view, grid couplers according to some embodiments.

[0023] DETAILED DESCRIPTION

[0024] The surface grating coupler 1 of the present disclosure at least includes a substrate 2, a first subwavelength grating 10 (first SWG 10) on the substrate 2, specifically on an insulating layer 3 such as, for example, silicon dioxide or buried oxide (commonly called BOX), and a prism 4 adjacent to at least a portion of the first SWG 10, as can be seen, for example, in the embodiments of Figures 1 and 2.

[0025] The first SWG 10 includes a pattern of core material 7 extending two-dimensionally by means of two or more pluralities of core material portions 7. With reference to Figures 1 and 2, the two dimensions of the pattern correspond to the X and Z axes, the Z axis being the direction of propagation of light waves in the surface grating coupler 1, and the X axis being a direction transverse to this; obviously, the blocks of core material 7 of the pattern have a third dimension, corresponding to the Y axis, which determines the height of the blocks of core material. Hereinafter, the terms portions and blocks are used interchangeably.The two or more pluralities of blocks include one or more first pluralities of portions or blocks 11a, which will hereinafter also be referred to as pluralities of odd portions or blocks 11a for the sake of clarity, and one or more second pluralities of portions or blocks 11b, which will hereinafter also be referred to as pluralities of even portions or blocks 11b for the sake of clarity. Each plurality of even blocks 11b is arranged adjacent to one or two pluralities of odd blocks 11a, and likewise each plurality of odd blocks 11a is arranged adjacent to one or two pluralities of even blocks 11b. In preferred embodiments, there are two or more pluralities of odd blocks 11a, and / or two or more pluralities of even blocks 11b.

[0026] The pluralities of blocks 11a, 11b each include multiple portions 12 of core material spaced apart from one another along the direction of propagation, i.e., along the illustrated Z axis. Thus, between each pair of neighboring portions 12a of each odd plurality of portions 11a there is a separation 13a, referred to as the first distance or di, and between each pair of neighboring portions 12b of each even plurality of portions 11b there is also a separation 13b, referred to as the second distance or d2. In some embodiments, di is equal to d2. In the spaces between portions 12, a void is provided which may expose the insulating layer 3, or which may be filled with an insulating material such as epoxy or silicon dioxide.

[0027] Each of the one or more pluralities of even portions 11b is arranged in the pattern of the first SWG 10 such that at least its second to second-last portions 12 (although it could also be the first and / or last) in the propagation direction would respectively lie within the spacing 13, corresponding to the first distance (di), between neighboring portions 12 of each of the one or more pluralities of odd portions 11a if the first and second pluralities of portions 11a, 11b shared position in the transverse direction.Preferably, the same occurs vice versa, i.e. each of the one or more pluralities of odd portions 11a is arranged in the pattern of the first SWG 10 such that at least its second to penultimate portions 12 (although it could also be the first and / or the last) in the propagation direction would respectively lie within the spacing 13, corresponding to the second distance (d2), between neighboring portions 12 of each of the one or more pluralities of even portions 11b if the odd and even pluralities of portions 11a, 11b shared position in the transverse direction.This can be seen, for example, in Figure 4, where, for illustrative purposes, it is shown with shading how the portions 12b' of a plurality of even portions 11 b would be in the separations between neighboring portions of a plurality of odd portions 11a if the plurality of even portions 11 b were in the same position as the plurality of odd portions 11a on the X axis. It can also be seen, for example, in Figure 5, where various portions 12b' of a plurality of odd portions 11 b are shown with a dashed edge that would be within the space between neighboring portions of a plurality of even portions 11a if they were in the same transverse position.With reference to Figure 4, it can be seen that, in this example, the portions defining the start of the first SWG 10 (the leftmost part of the first SWG 10, i.e., with the lowest Z coordinate) are those of the pluralities of odd portions 11a, so the first portions of the pluralities of even portions 11b would also be within the spacings 13 of the portions of the pluralities of odd portions 11a but not vice versa. In the same example, the last portions of the pluralities of odd portions 11a would also be within the spacings 13 of the portions of the pluralities of even portions 11b, but not vice versa since the portions defining the end of the first SWG 10 (the rightmost part of the first SWG 10, i.e., with the highest Z coordinate) are those of the pluralities of even portions 11b.The start and end portions of the first SWG 10 could be the other way around: the portions of the pluralities of odd portions 11b at the start and those of the pluralities of even portions 11a at the end. Separately, in other examples, such as those in Figures 5 and 7, the same pluralities of portions, whether even or odd, define the start and end of the first SWG 10, in which case the first and last portions of the other pluralities of portions would also be within the gaps 13 if both pluralities of portions shared a transverse position.

[0028] In relation to the above, it can be seen, for example, in the embodiments of Figure 6, that the position according to the direction of propagation of blocks of a plurality of blocks, in this case those of the plurality of even blocks 11 b, may be different within each respective separation 13 a. Thus, some blocks are closer to the previous block (to the left of the first SWG 10) than to the following block (to the right of the first SWG 10), according to the direction of propagation, of the other plurality of blocks, while other blocks are closer to the following block than to the previous block. Although not illustrated, the same may occur in the transverse direction.

[0029] Each portion of the second plurality of even blocks has a length L2, according to the propagation direction, less than or equal to the first distance, di, so that there is no overlap between portions of blocks of even and odd pluralities if they share a position in the transverse direction. When L2=di, there could be contact between edges on both sides (according to the propagation direction) of blocks in the case that the even and odd pluralities are in the same position according to the transverse direction, while if l_2 <di, puede haber contacto o no en uno de los lados de los bloques si compartiesen posición transversal. La elección de L2 a partir de di , particularmente si es igual o menor, puede realizarse en función de la precisión de la técnica de fabricación empleada para el primer SWG, o del valor de periodicidad o ciclo de trabajo deseado para el acoplador de rejilla por superficie 1 en cuestión.The fabrication of the surface grating coupler may be more economical if L2 is smaller than di , although the performance in terms of coupling efficiency and bandwidth are generally higher the closer L2 is to di , which also applies to Li>d2. In this respect, it has been observed that the closer the length is to the separation distance, the lower the effective mode index in the first SWG 10. Likewise, the closer the length is to the separation distance, the smaller the wavelength dispersion and, therefore, the wider the bandwidth, although it may not always be preferable to increase the bandwidth excessively since this may cause the radiation with a Gaussian field profile to be smaller.The lengths Li, L2 and the distances di, d2 do not necessarily have to be constant along the first SWG 10; thus, for example, in embodiments such as those in Figure 8, there may be variation in the lengths and / or distances of one or both of the plurality of odd blocks 11a and even blocks 11b, while in the specific case of Figure 8 there are greater lengths and distances in the pairs of blocks closest to the end of the first SWG 10 (the rightmost part of the first SWG 10).

[0030] In some embodiments, such as those in Figure 5, each pair of first pluralities of odd-numbered blocks 11a neighboring in the transverse direction are separated by a distance dw.i equal to or greater than a width W2 of the portions of the plurality of even-numbered blocks 11 b along the transverse direction. The choice of dw.i relative to W2, particularly whether it is equal to or greater, can also be made by the same criteria explained above for L2; by means of these values, the minimum pattern size (i.e., portion and / or distance) of the first SWG 10 can be adjusted and thus facilitate its mass production with techniques such as deep ultraviolet lithography. This also applies to the width of the blocks of the pluralities of odd-numbered blocks 11a and the distance between pluralities of odd-numbered blocks 11a along the transverse direction. There are also embodiments having distances dw.i, dw,2 and widths W1, W2 in the pluralities of odd blocks 11 a and / or even blocks 11 b, as in Figure 8, where the blocks of the pluralities of odd blocks 11 a have a width Wi, and the blocks of the pluralities of even blocks 11 b have widths W2 and W3.

[0031] In some embodiments, portions of each plurality of odd portions 11a have the same two-dimensional geometry along the propagation and transverse directions; and / or portions of the second plurality of even portions 11b have the same two-dimensional geometry along the propagation and transverse directions. Optionally, the two-dimensional geometry of the portions of the pluralities of odd and even portions 11a, 11b are the same. For example, in some embodiments, the two-dimensional geometry of the portions of the first plurality(ies) of portions 11a and / or of the portions of the second plurality(ies) of portions 11b is square or rectangular, as in Figures 1 , 3 and 4 , including rectangular two-dimensional geometry without corners (i.e., with rounded edges), as in Figure 8 , while in some other embodiments it is elliptical, as in Figure 5 .In embodiments such as those in Figure 7, each plurality of portions 11a, 11b has its own two-dimensional geometry. The two-dimensional geometry of the portions impacts the coupling efficiency and bandwidth; a compromise may be made between these parameters and the manufacturing complexity of the surface-grid coupler 1 or the precision of the manufacturing technique to use one geometry or another. For example, elliptical geometries tend to have a simpler manufacturing process than square or rectangular geometries; generally, square geometries also tend to be simpler to manufacture than rectangular geometries. Rectangular geometries, on the other hand, generally manage to provide a greater bandwidth that can be achieved, for example, by having lower dispersion compared to other geometries.

[0032] In some embodiments, the portions of the first plurality(ies) of portions 11a have a length L1 along the same propagation direction, and a width W1 along the same transverse direction; and / or the portions of the second plurality(ies) of portions 11b have a length L2 along the same propagation direction, and a width W2 along the same transverse direction. Optionally, the length L1, L2 of the portions of the first and second pluralities of portions 11a, 11b are the same and / or the width W1, W2 of the portions of the first and second pluralities of portions 11a, 11b are the same. In some embodiments, such as, for example, those of Figures 1 , 3-7, the first distance, di , is equal to the second distance, d2.

[0033] In some embodiments, the first and second pluralities of portions 11a, 11b are arranged such that at least the second to penultimate portions 12a in the propagation direction of one or more second pluralities of portions 11a from the second to penultimate in the transverse direction have a single point of contact with four portions 12b of the first pluralities of portions 11b. That is, the first SWG 10 can be designed such that various portions 12 of the pluralities of even portions 11 b, as well as of the odd portions 11 a, are surrounded by portions 12 of pluralities of odd portions 11 a (or even portions 11 b in the case of the portions 12 of the pluralities of odd portions 11 a), such that the only point of contact with the portions 12 b is at points on the contour, optionally the corners on said contour, of each portion 12.Thus, a checkerboard-type pattern can be generated, with 12 portions with two-dimensional geometry such as square, rectangular or even elliptical, among others.

[0034] In some embodiments, such as those of Figures 2 and 3, the grating adapter 1 further includes a second subwavelength grating 20 (i.e., a second SWG 20) adjacent the first SWG 10; for clarity, the second SWG 20 is most easily identified by the length Ls illustrated in Figures 2 and 3. The second SWG 20 comprises a pattern of core material 7 extending two-dimensionally in both the propagation direction and the transverse direction and is formed from a plurality of core material portions 22 having, in the transverse direction and adjacent to each other, at least a third plurality of portions 21a and at least a fourth plurality of portions 21b, each of the third and fourth pluralities of portions 21a, 21b extending in the propagation direction.This second SWG 20 helps to adapt the mode that propagates through the surface grid coupler 1 , either from a port 9 that serves as input towards the first SWG 10, or vice versa, from the first SWG 10 towards the port 9 that serves as output. In the absence of the second SWG, the surface grid coupler 1 may have the port 9 connected in any manner known in the art to the first SWG 10, preferably by means of a mode adapter 6.

[0035] In some embodiments, such as those of Figures 2 and 3, each pair of neighboring blocks 22a of the third plurality(ies) of blocks 21a is separated by a distance in the propagation direction that is greater for each pair of neighboring blocks 22a that are closer to the first SWG 10. Each pair of neighboring blocks 22b of the fourth plurality(ies) of blocks 21b is separated by a distance in the propagation direction that is greater for each pair of neighboring blocks 22b that are closer to the first SWG 10. The blocks 22b of the fourth plurality(ies) of blocks 21b have a portion in contact with blocks 22a of the third plurality(ies) of blocks 21a and another portion in contact with gaps between neighboring blocks 22a of the third plurality(ies) of blocks 21a.And the blocks 22a of the third plurality / ies of blocks 21a have a part in contact with blocks 22b of the fourth plurality / ies of blocks 21b and another part in contact with separations between neighboring blocks 22b of the fourth plurality / ies of blocks 21b.

[0036] In some embodiments, such as those in Figure 3, portions 22a of each third plurality of portions 21a have a length along the propagation direction and / or a width along the transverse direction that is smaller for portions 22a closer to the first subwavelength grating 10; and / or portions 22b of each fourth plurality of portions 21b have a length along the propagation direction and / or a width along the transverse direction that is smaller for portions 21b closer to the first subwavelength grating 10. That is, the length of the portions becomes shorter and / or the width of the portions becomes narrower as the corresponding portion is closer to a side adjacent to the first SWG 10 than to an opposite side; however, it is not necessary that each portion closer to one side or the other has a change in length and / or width.Adjusting the length and / or width in this manner improves mode adaptation from port 9 to its propagation to the first SWG 10, and vice versa, thus allowing for lower optical power losses.

[0037] As with the portions of the first SWG 10 in some embodiments, the portions 22a of the third plurality(ies) of portions 21a may have the same two-dimensional geometry along the propagation and transverse directions and / or the portions 22b of the fourth plurality(ies) of portions 21b have the same two-dimensional geometry along the propagation and transverse directions in some embodiments. Indeed, the two-dimensional geometry of the portions 22a, 22b of the third and fourth pluralities of portions are the same in some embodiments. The second SWG 20 has, in some embodiments, a width along the transverse direction that is greater at one end or side than at an opposite end or side, while in other embodiments such widths are equal at both ends or sides.The end or side with the smallest width is, in some embodiments, adjacent to the first SWG 10, while in other embodiments it is the side opposite and not adjacent to the first SWG 10. Changes in width of the second SWG 20, if any, which are preferably made progressively according to the length Ls of the second SWG 20, assist in mode adaptation.

[0038] In some embodiments, the grating adapter 1 further includes a modal adapter 6 disposed between the port 9 or input of the surface grating coupler 1 and the first subwavelength grating 10; for the sake of clarity, the modal adapter 6 is most easily identified by the length LM illustrated in Figures 2, 3 and 8. The width of the modal adapter 6 in the transverse direction may, in some embodiments, be greater at an end or side closest to the first subwavelength grating 10 than at an opposite end or side, i.e., at the end or side closest to the port 9.

[0039] In some embodiments where the surface grid coupler 1 includes the second SWG 20, preferably one end of the modal adapter 6 is connected to the port 9 or inlet of the surface grid coupler 1 and another end of the modal adapter 6 is connected to the second SWG 20, as in Figures 2 and 3. In embodiments where the coupler does not include the second SWG 20, preferably one end of the modal adapter 6 is connected to the port 9 or inlet of the surface grid coupler 1 and another end of the modal adapter 6 is connected to the first SWG 10, as in Figure 8.

[0040] The coupling efficiency of the surface grating coupler 1 may be higher because the prism 4 is arranged, in some embodiments, in such a way that it forms an angle 8b, 0, with respect to the first SWG 10 such that: 0 = arctan(T / L c) ± 10%, where T is the distance between the prism 4 and a first portion 22a, 22b of one of the pluralities of odd or even portions 21a, 21b that is closest to a port 9 or inlet of the grating coupler by surface 1, and L cis the length of the first SWG 10 in the propagation direction, as illustrated in Figures 2 and 3. The separation between the first SWG 10 and the prism 6, inclined in such a way that the separation becomes smaller as one advances in the propagation direction, makes it possible to radiate an almost Gaussian field profile with an overlap level of up to 95%; In some embodiments, the prism 6 is in contact with the first SWG 10 at least at one end of the first SWG 10 furthest from the port 9 or inlet of the grating coupler by surface 1. Such separation may be by means of a medium such as air or, as in some embodiments, be caused by the inclusion, in the grating adapter 1, of a cover between at least a portion of the first SWG 10 and the prism 6. Likewise, in some embodiments, the prism 4 may include an anti-reflective coating 5 to reduce or prevent reflections at the interface between the prism 4 and the air.

[0041] The radiation angle, Q, can also be configured by means of the characteristics of the prism 6, for example, the angle 8a. Thus, the radiation angle Q can comply with the following: 6 = 0 + 0. When, for example, an optical fiber 30 is available, as in the assembly 40 of Figure 2, the light coupling is to be done in a controlled manner to couple the light to the optical fiber 30 (with a core 31 in a sheath 32), and vice versa.

[0042] In some embodiments, the grid adapter 1 is adapted for radiation of light waves of at least one predetermined wavelength A. A periodicity, in the propagation direction, of the portions 22a of the one or more pluralities of odd portions 21a and / or of the portions 22b of the one or more pluralities of even portions 21b satisfies the relation A < A / (2 • n e7 ), where A is the periodicity, A is the predetermined wavelength and n e7is the effective refractive index of a mode of the grating coupler per surface 1. The periodicity A is the same for the pluralities of odd and even portions 11a, 11b.

[0043] In this text, the words "comprise", "include" and their variants (such as "comprising", "including", etc.) should not be interpreted in an exclusive manner, that is, they do not exclude the possibility that what is described includes other elements, steps, etc. Furthermore, apart from having used the words "first", "second", "third", etc., it will be understood that these words have only been used to distinguish one element or parameter from another for the sake of clarity; however, none of these words could have been used or other words could have been used; for example, the first plurality of portions could have been called the second plurality of portions and the second plurality of portions could have been called the first plurality of portions.

[0044] Furthermore, the invention is not limited to the specific embodiments described above, but also encompasses, for example, variations that can be realized by the average person skilled in the art (for example, in terms of the choice of materials, dimensions, components, configuration, etc.), within the meaning of the claims.

Claims

CLAIMS 1. A surface grating (1) comprising: a substrate (2), a first subwavelength grating (10) of core material (7) in at least a portion of the substrate (2) along its length, and a prism (4) adjacent to at least a portion of the first subwavelength grating (10); the length of the substrate being defined along a propagation direction (Z) of light waves in the surface grating; the first subwavelength grating comprises a pattern of core material extending two-dimensionally along the propagation direction and a direction transverse (X) to the propagation direction;characterized in that: the core material pattern of the first subwavelength grating is formed by two or more pluralities of core material portions (11 a, 11 b) having, in the transverse direction and adjacent to one / the other, at least a first plurality of portions (11 a) and at least a second plurality of portions (11 b), each of the first and second pluralities of portions extending in the propagation direction; each pair of neighboring portions (12 a) of the first plurality of portions is separated by a first distance ( d i ) in the propagation direction; each pair of neighboring portions (12 b) of the second plurality of portions is separated by a second distance ( d 2 ) in the propagation direction;and each second plurality of portions is arranged such that at least the portions from the second to the penultimate portion in the propagation direction would respectively be within the separation between neighboring portions of each first plurality of portions if the first and second pluralities of portions shared a position in the transverse direction.; 2. The surface grid coupler (1) of claim 1, wherein each portion (12b) of the second plurality of portions (11b) has a length (L2) according to the propagation direction (Z) less than or equal to the first distance (di).

3. The surface grid coupler (1 ) of any of the preceding claims, wherein each pair of first pluralities of portions (11a) neighboring in the transverse direction (X) are separated by a distance (dw.i) equal to or greater than a width (W2) of the portions (12b) of the second plurality of portions (11 b) according to the transverse direction.

4. The surface grating coupler (1 ) of any one of the preceding claims, wherein the portions (12a) of the first plurality of portions (11a) have the same two-dimensional geometry along the propagation (Z) and transverse (X) directions; the portions (12b) of the second plurality of portions (11b) have the same two-dimensional geometry along the propagation and transverse directions; and, optionally, the two-dimensional geometry of the portions of the first and second pluralities of portions is the same.

5. The surface grid coupler (1) of claim 4, wherein the two-dimensional geometry of the portions (12a) of the first plurality of portions (11a) and / or the portions (12b) of the second plurality of portions (11b) is square, rectangular, or elliptical.

6. The surface grid coupler (1 ) of any one of the preceding claims, wherein the portions (12a) of the first plurality of portions (11a) have a length (Li) along the propagation direction (Z) that is equal, and a width (Wi) along the transverse direction (X) that is equal; the portions (12b) of the second plurality of portions (11b) have a length (L2) along the propagation direction that is equal, and a width (W2) along the transverse direction that is equal; and optionally, the lengths of the portions of the first and second pluralities of portions are the same and / or the widths of the portions of the first and second pluralities of portions are the same.

7. The surface grid coupler (1) of any of the preceding claims, wherein the first distance (di) is equal to the second distance (d2).

8. The surface grid coupler (1 ) of any of the preceding claims, wherein the first and second pluralities of portions (11a, 11b) are arranged such that at least the second to penultimate portions (12b) in the propagation direction (Z) of each second plurality of portions (11b) from the second to penultimate in the transverse direction (X) have a single point of contact with four portions (12a) of the first pluralities of portions.

9. The surface grating coupler (1) of any one of the preceding claims, further comprising a second subwavelength grating (20) in a portion of the substrate (2) along its length and which is contiguous with the first subwavelength grating (10); the second subwavelength grating (20) comprises a pattern of core material (7). which extends two-dimensionally along the propagation direction (Z) and the transverse direction (X) and is formed by a plurality of core material portions (21a,21b) having, in the transverse direction and adjacent to each other, at least a third plurality of portions (21a) and at least a fourth plurality of portions (21b), each of the third and fourth pluralities of portions extending in the propagation direction; each pair of neighboring portions (22a) of the third plurality of portions is separated by a distance in the propagation direction that is greater for each pair of neighboring portions closer to the first subwavelength grating; each pair of neighboring portions (22b) of the fourth plurality of portions is separated by a distance in the propagation direction that is greater for each pair of neighboring portions closer to the first subwavelength grating;the portions of the fourth plurality of portions have a portion in contact with portions of the third plurality of portions and another portion in contact with separations between neighboring portions of the third plurality of portions; and the portions of the third plurality of portions have a portion in contact with portions of the fourth plurality of portions and another portion in contact with separations between neighboring portions of the fourth plurality of portions.

10. The surface grating coupler (1) of claim 9, wherein the portions (22a) of the third plurality of portions (21a) have a length along the propagation direction (Z) and / or a width along the transverse direction (X) that is smaller for portions closer to the first subwavelength grating (10); and / or the portions (22b) of the fourth plurality of portions (21b) have a length along the propagation direction and / or a width along the transverse direction that is smaller for portions closer to the first subwavelength grating.

11. The surface grating coupler (1) of any of claims 9-10, wherein the portions (22a) of the third plurality of portions (21a) have the same two-dimensional geometry along the propagation (Z) and transverse (X) directions; the portions (22b) of the fourth plurality of portions (21 b) have the same two-dimensional geometry along the propagation and transverse directions; and, optionally, the two-dimensional geometry of the portions of the third and fourth pluralities of portions is the same.

12. The surface grating coupler (1) of any of the preceding claims, further comprising a modal adapter (6) disposed between a port (9) of the surface grating coupler (1) and the first subwavelength grating (10).

13. The surface grating coupler (1) of claim 12, when depending on any one of claims 9-11, wherein one end of the modal adapter (6) is connected to the port (9) of the surface grating coupler (1) and another end of the modal adapter is connected to the second subwavelength grating (20).

14. The surface grating coupler (1) of any one of the preceding claims, wherein the prism (4) is arranged at an angle <p respecto a la primera rejilla sub longitud de onda (10) tal que: 0 = arctan(T / L) ± 10%, donde T es la distancia entre el prisma y una primera porción (22a, 22b) de una de las primeras y segundas pluralidades de porciones (21a, 21 b) que está más próxima a un puerto (9) del acoplador de rejilla por superficie (1), y L es una longitud (Le) de la primera rejilla sub longitud de onda en la dirección de propagación (Z).

15. The surface grating coupler (1) of claim 14, wherein the prism (4) is in contact with the first subwavelength grating (10) at least at one end of the first subwavelength grating furthest from the port (9) of the surface grating coupler (1).

16. The surface grating coupler (1) of any one of the preceding claims, further comprising a cover between at least a portion of the first subwavelength grating (10) and the prism (4).

17. The surface grating coupler (1) of any one of the preceding claims, which is adapted for radiation of light waves of at least one predetermined wavelength A; wherein a periodicity (A), in the propagation direction (Z), of the portions (22a, 22b) of the first plurality of portions (21a) and / or of the portions of the second plurality of portions (21b) satisfies < A / (2 • n e7), where A is the periodicity, A is the predetermined wavelength and n e7 is the effective refractive index of a mode of the grating coupler per surface.

18. An assembly (40) comprising the surface grating coupler (1) of any one of the preceding claims, and an optical fiber (30) adjacent to the prism (4) of the surface grating coupler.

19. A method, comprising: disposing a first subwavelength grating (10) of core material (7) on at least a portion of a substrate (2) along its length to produce a surface grating (1); disposing a prism (4) adjacent to at least a portion of the first subwavelength grating; and radiating at least one light wave through the surface grating by coupling the at least one light wave into a port (9) of the surface grating or the prism and propagating the at least one light wave over at least part of a length of the first subwavelength grating; the length of the substrate is defined along a propagation direction (Z) of light waves in the surface grating; the first subwavelength grating comprises a pattern of core material extending two-dimensionally along the propagation direction and a direction transverse (X) to the propagation direction;characterized in that: the first subwavelength grating comprises a core material pattern formed by a plurality of core material portions (11 a, 11 b) having, in the transverse direction and adjacent to one another, at least a first plurality of portions (11 a) and a second plurality of portions (11 b), each of the first and second pluralities of portions extending in the propagation direction; each pair of neighboring portions (12 a) of the first plurality of portions is separated by a first distance ( d i ) in the propagation direction; each pair of neighboring portions (12 b) of the second plurality of portions is separated by a second distance ( d 2 ) in the propagation direction;and each second plurality of portions is arranged such that at least the portions from the second to the penultimate portion in the propagation direction are respectively within the separation between neighboring portions of each first plurality of portions if the first and second pluralities of portions shared a position in the transverse direction.; 20. The method of claim 19, wherein a periodicity (A), in the propagation direction (Z), of the portions (12a, 12b) of the first plurality of portions (11a) and / or of the portions of the second plurality of portions (11b) satisfies A < 2 / (2 • n e ), where A is the periodicity, A is the wavelength of the at least one light wave and n e7 is the effective refractive index of a mode of the grating coupler per surface (1).

21. The method of any one of claims 19-20, further comprising arranging the surface grating coupler (1) adjacent to a photonic device (30). to couple the at least one light wave from the grating coupler per surface to the photonic device or vice versa.

22. The method of any one of claims 19-21, wherein the surface grid coupler (1) is a surface grid coupler according to any one of claims 2-17.

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