Fibre-optic optical device

Abstract

The invention relates to an optical device comprising: - an optical fibre, - an optical component comprising: o a substrate, o a stack of three layers arranged on one face of the substrate:  a semi-reflective layer,  a diffraction layer comprising a diffraction grating,  a reflective layer, o an optical element (600). The optical component is arranged and dimensioned to form an interface between the optical fibre and a light source / photodetector assembly arranged in directions perpendicular to an optical axis of the optical fibre. The stack of the three layers and their characteristic parameters (thicknesses, refractive index of the layers) enable the optical component to optically couple a first incident beam from the light source to the optical fibre. The optical element enables the optical component to efficiently optically couple a second incident beam from the optical fibre to the photodetector.

Description

[0001] Fiber optic device

[0002] Technical field of the invention

[0003] The present invention relates to a fiber optic optical device for the bidirectional transmission of optical signals from a light source and / or to a photodetector. The present invention relates in particular to an optical device for the bidirectional transmission of signals from a light source and / or to a photodetector arranged in a direction substantially orthogonal to the optical axis of the optical fiber.

[0004] The invention finds an advantageous application in the aeronautical field, in particular for equipping an aircraft.

[0005] Prior art

[0006] In aircraft, optical fibers are increasingly used to interconnect equipment for communications purposes.

[0007] In the specific context of the distribution of Li-Fi (Light-Fidelity) type optical signals, optical fibers can be used to route these signals bidirectionally from light sources to photodetectors located in the backs of passenger seats.

[0008] These optical fibers run all along the cabin, in areas that are difficult to access and have limited space, generally in the ceiling, under the luggage compartments, and one of their ends reaches above the backs of the passenger seats.

[0009] An interface is then necessary between the end of an optical fiber, located above the back of a passenger seat and the light source / photodetector assembly arranged at the level of said back of a passenger seat, to allow:

[0010] - on the one hand the optical coupling of a light beam, carrying optical signals, coming from the light source to the optical fiber,

[0011] - on the other hand the optical coupling of a light beam, carrying optical signals, coming from the optical fiber to the photodetector.

[0012] Optical couplings are all the more complex as they must be made, not in a direction of the optical axis of the optical fiber, but in a direction orthogonal to this optical axis, which implies the use of an angle return of the order of 90°.

[0013] In the so-called downward flow direction, i.e. from the optical fiber to the photodetector, optical coupling can, for example, simply rely on the natural divergence of the light beam. A simple angle deflection, with a mirror for example, may be sufficient as an interface between the optical fiber and the photodetector. However, in the so-called upward flow direction, i.e. from the light source to the optical fiber, the natural divergence of the light beam emitted by the light source must be counteracted, in order to capture the entire light beam emitted by the light source and then inject it into the optical fiber. An assembly based on lenses and a prism or a mirror can achieve this optical coupling. However, such an assembly requires careful implementation because the alignments must be precise to obtain optimal coupling.Furthermore, such an assembly is cumbersome, both in terms of weight and volume, expensive and inefficient in terms of injection into the optical fiber, therefore difficult to integrate into a very constrained environment such as that of an airplane.

[0014] Presentation of the invention

[0015] The present invention aims to remedy the aforementioned drawbacks.

[0016] To this end, the present invention proposes an optical device comprising:

[0017] - an optical fiber comprising a core, of refractive index n c and of diameter of, and having a first end face,

[0018] - an optical component comprising: o a substrate with refractive index n s substantially equal to the refractive index n c of the core of the optical fiber and thickness e s substantially less than or equal to the diameter of the core of the fiber, said substrate:

[0019] ■ comprising two faces, called the first and second faces,

[0020] ■ extending between two opposite edges, called first and second edges,

[0021] ■ having a first longitudinal portion starting from the first edge and a second longitudinal portion starting from the second edge, o a stack of three layers arranged on the second face of the substrate, at the level of the first longitudinal portion of said substrate: ■ a semi-reflecting layer of refractive index n S r greater than the refractive index n s of the substrate, and of thickness e S r,

[0022] ■ a diffraction layer, of thickness ed, comprising, throughout its thickness, a diffraction grating of period A,

[0023] ■ a reflective layer, o an optical element, at its second longitudinal portion, the optical fiber being arranged opposite the optical component so that the first end face of said optical fiber is attached to the first edge of the substrate, the semi-reflective layer and the diffraction layer being arranged between the substrate and the reflective layer, the semi-reflective layer being arranged between the substrate and the diffraction layer or between the diffraction layer and the reflective layer, for a first incident ray, having a first given wavelength λi and arriving on the first face of the substrate with a predetermined angle of incidence λai and defined relative to a direction normal to said first face of the substrate: o the thicknesses of the semi-reflective layer and of the diffraction layer are determined to generate destructive interference of the reflected rays,o the diffraction grating is configured to allow diffraction of the first incident ray within the limit of the first diffraction order, and at a diffraction angle such that the diffracted ray propagates in the substrate, in an acceptance cone of the optical fiber, towards the first face of the optical fiber, for a second incident ray coming from the optical fiber, having a second wavelength λ2 distinct from the first wavelength λi, the optical element is configured to direct said second incident ray out of the substrate, perpendicular to the first face of the substrate.,

[0024] The optical component advantageously forms an interface between the first end face of the optical fiber and a light source / photodetector assembly arranged in a direction substantially perpendicular to an optical axis of the optical fiber.

[0025] The optical component advantageously allows: - on the one hand, to collect a maximum of the first incident rays forming the first incident beam from the light source and to transmit them into the optical fiber, and

[0026] - on the other hand, to collect a maximum of the second incident rays forming the second incident beam coming from the optical fiber and to transmit them to the photodetector.

[0027] The stacking of the three layers, their arrangement and their characteristic parameters (thicknesses, refractive index of the layers) allow the optical component to achieve efficient optical coupling of the first incident beam coming from the light source to the optical fiber. The natural divergence of the light beam emitted by the light source is counteracted.

[0028] The optical element enables the optical component to achieve efficient optical coupling of the second incident beam from the optical fiber to the photodetector.

[0029] In particular embodiments, the optical device may further comprise one or more of the following characteristics, taken individually or in all technically possible combinations.

[0030] In particular embodiments, the diffraction grating is in the form of a plurality of concentric circular arcs, centered on the first edge of the substrate, at the first face of the optical fiber. Such a circular arc shape of the diffraction grating advantageously makes it possible to converge the rays diffracted by said diffraction grating towards the first end face of the optical fiber.

[0031] In particular embodiments, the circular arcs extend over the same angular range corresponding to a numerical aperture of the optical fiber. In particular embodiments, the diffraction grating has materials whose refractive indices are identical to the materials of the layers arranged on either side of the diffraction layer.

[0032] In particular embodiments, the second edge of the substrate of the optical component has an inclination of an angle substantially equal to 45° relative to a longitudinal axis of said substrate and the optical element is a mirror attached to said second edge of the substrate. The invention also relates to an optical assembly comprising a light source, a photodetector and an optical device according to at least one of its embodiments. The light source is arranged facing the first face of the substrate, at the first longitudinal portion, and is configured to emit the first incident ray. The photodetector is arranged facing the first face of the substrate, at the second longitudinal portion, and is arranged relative to the optical element so as to receive the second incident ray.

[0033] Brief description of the figures

[0034] The invention will be better understood by reading the following description, given as a non-limiting example, and made with reference to the figures which represent:

[0035] Figure 1 is a perspective view of an optical device according to the invention comprising, in exploded view, an optical component according to a first configuration, Figure 2 is a sectional view of the optical device with the first configuration of the optical component, and illustrating the trajectory, in the optical component, of a light ray, in the direction of the upward flow,

[0036] Figure 3 is a sectional view of the optical device with a second configuration of the optical component, and illustrating the trajectory, in the optical component, of a light ray, in the direction of the upward flux,

[0037] Figure 4 illustrates the path of a light beam in the optical device in the upward direction, regardless of the configuration of the component,

[0038] Figure 5 illustrates the path of a light beam in the optical device in the downward flow direction,

[0039] Figure 6 illustrates a top view of a diffraction layer of the optical device, with a diffraction grating in the form of concentric circular arcs.

[0040] Description of the embodiments

[0041] Figure 1 illustrates an example of an optical device 500 according to the invention. Said optical device comprises an optical fiber 200 and, in semi-exploded perspective, an optical component 100 forming a resonant network, called an optical component.

[0042] The optical device 500 advantageously forms part of an optical assembly 700 further comprising a light source 300 and a photodetector 400.

[0043] The light source 300 and the photodetector 400 are arranged in directions substantially perpendicular to an optical axis of the optical fiber 200. According to the invention, the optical component 100 of the optical device is advantageously intended for and configured to:

[0044] - on the one hand, transmitting a light beam, called the first incident beam 310, coming from the light source 300 into the optical fiber 200, as illustrated in Figure 4, and

[0045] - on the other hand, transmit a light beam, called second incident beam 410, coming from the optical fiber 200 to the photodetector 400, as illustrated in figure 5.

[0046] Each light beam 310, 410 is advantageously configured to transmit an optical data transmission signal, for example a modulated optical signal of the Li-Fi type.

[0047] The optical component 100 is thus advantageously intended for the bidirectional transmission of optical signals:

[0048] - in a so-called upward flow direction, from the light source 300 to the optical fiber 200,

[0049] - in a so-called downward flow direction, from the optical fiber 200 to the photodetector 400.

[0050] The light source 300 is preferably a quasi-monochromatic source. The first incident beam 310 is for example emitted at a wavelength, called the first wavelength λi.

[0051] In an exemplary embodiment, the first incident beam 310, at the output of the light source 300, is a divergent beam and is in the form of a diffusion cone, as illustrated in FIG. 4. In a variant not shown, a lens may be arranged at the output of the light source 300, to collimate the first incident beam.

[0052] Generally, any light source may be used for the light source 300, such as, for example, light-emitting diodes (known by the acronym LED) or laser sources, such as laser diodes or vertical-cavity surface-emitting laser diodes, commonly known by the acronym VCSEL (for "Vertical-Cavity Surface-Emitting Laser"). However, the use of surface-emitting light sources, such as LEDs or VCSELs, will be advantageously preferred.

[0053] The photodetector 400 is configured to detect the second incident beam 410. The second incident beam 410 has a wavelength, called the second wavelength λ2, distinct from that of the first incident beam.

[0054] In an exemplary embodiment, the photodetector 400 is a photodiode.

[0055] The optical fiber 200 of the optical device 500 preferably comprises, in a conventional manner, a core 210 and an optical cladding 220, as illustrated in FIGS. 2 and 3.

[0056] The 210 core has a refractive index n c and a diameter of. The core 210 is preferably made of glass, based on silica.

[0057] The optical cladding 220 surrounds the core 210 and has a refractive index lower than the refractive index n c of the heart.

[0058] The optical fiber 200 has a first end face 230 intended to come against the optical component 100.

[0059] The optical fiber 200 may be a single-mode optical fiber or a multi-mode optical fiber. Preferably, the optical fiber is a multi-mode optical fiber.

[0060] The optical component 100 of the optical device 500 comprises a substrate 110.

[0061] Said substrate has a first face, called lower face 113, and a second opposite face, called upper face 114.

[0062] The substrate 110 has, between said lower face and said upper face, a thickness e s substantially less than or equal to, preferably less than, the diameter of the core 210 of the optical fiber 200.

[0063] The substrate 110 has a first edge 111 intended to be attached to the first end face 230 of the optical fiber 200, as illustrated in FIGS. 1 to 5. The substrate 110 and the optical fiber 200 are preferably held together by gluing. The glue used to hold the first end face 230 of the optical fiber 200 against the first edge 111 of the substrate 110 preferably has the same refractive index as that of the core 210 of the optical fiber 200.

[0064] The substrate 110 further has a second edge 112 opposite said first edge. The substrate 110 is made of a material having a refractive index n s substantially equal, preferably equal, to the refractive index n c of the core 210 of the optical fiber 200.

[0065] The substrate 110 extends longitudinally between the first and second edges 111, 112. The substrate 110 has two distinct longitudinal portions, called first 115 and second 116 longitudinal portions. The first longitudinal portion 115 extends from the first edge 111 and the second longitudinal portion 116 extends from the second edge 112.

[0066] By extension, the first longitudinal portion 115 of the substrate will be likened to a first longitudinal portion of the optical component 100. Similarly, the second longitudinal portion 116 of the substrate will be likened to a second longitudinal portion of the optical component 100.

[0067] The first longitudinal portion of the optical component 100 is advantageously dedicated to the direction of the upward flow and the second longitudinal portion is dedicated to the direction of the downward flow. Thus, the light source 300 is intended to be positioned opposite the lower face 113 of the substrate, at the level of said first longitudinal portion, and the photodetector 400 is intended to be positioned opposite the lower face 113 of the substrate 110, at the level of said second longitudinal portion. The light source 300 and the photodetector 400 are preferably placed at a distance from the lower face 113 of the substrate.

[0068] The first longitudinal portion 115 of the optical component 100 is preferably sized to collect a maximum of the rays constituting the first incident beam 310 coming from the light source 300.

[0069] The optical component 100 comprises, at its first longitudinal portion, a stack of three layers from the upper face 114 of the substrate 110, as illustrated in FIGS. 1 to 3:

[0070] - a layer, called semi-reflective layer 120,

[0071] - a layer, called diffraction layer 130,

[0072] - a layer, called reflective layer 140.

[0073] The optical component 100 comprises, at its second longitudinal portion, an optical element 600, as illustrated in FIGS. 1 to 3.

[0074] The following description will describe, firstly, the operating principle of the optical component 100 in the direction of the upward flow and then, secondly, in the direction of the downward flow.

[0075] Upward flow direction

[0076] At the first longitudinal portion 115, the stacking order of the three layers 120, 130, 140 on the substrate 110 is not necessarily that stated above. Nevertheless, the semi-reflective 120 and diffraction 130 layers are necessarily included between the substrate 110 and the reflective layer 140. Thus, the optical component 100 can have two configurations at the level of said first longitudinal portion.

[0077] In a first embodiment configuration of the optical component, shown in Figures 1 and 2, said optical component comprises, from the upper face 114 of the substrate 110, the successive stack previously described. The optical component is shown in Figure 1 in exploded perspective in order to better understand the stack of the different layers constituting it. Figure 2 represents a sectional view of the optical component 100.

[0078] In a second configuration for producing the optical component, shown in FIG. 3 in sectional view, said optical component comprises the following successive stack, from the upper face 1 14 of the substrate:

[0079] - the diffraction layer 130,

[0080] - the semi-reflective layer 120,

[0081] - the reflective layer 140.

[0082] Regardless of the configuration of the optical component 100, the three layers of the optical component stack each have the following characteristics. The semi-reflective layer 120 has a thickness e S r.

[0083] It is made of a material with a refractive index n S r greater than the refractive index n s of the substrate 1 10. The material is transparent to the first wavelength Xi of the first incident beam 310.

[0084] In a preferred embodiment, the semi-reflective layer 120 is made of silicon nitride (SiaIXk).

[0085] The reflective layer 140 has a thickness e r .

[0086] It is made of a material with a refractive index n r . It is configured to reflect the first wavelength Xi of the first incident beam 310.

[0087] In a preferred embodiment, the reflective layer 140 is a metallic layer, for example gold or silver, or several dielectric layers. The diffraction layer 130 has a thickness ed.

[0088] It comprises a diffraction grating 131, of spatial period A. The diffraction grating 131 is produced throughout the thickness of the diffraction layer.

[0089] The diffraction grating 131 is advantageously sized as a function of the first wavelength Xi of the first incident beam 310, according to Bragg's law. The diffraction grating 131 is preferably designed for a wavelength range comprising the first wavelength Xi of the first incident beam 310. Preferably, the diffraction grating 131 is designed for a wavelength range extending by ± 5 nm around the first wavelength Xi of the first incident beam 310.

[0090] The diffraction grating 131 is made with materials having two different refractive indices. The diffraction grating is preferably formed from the materials of the layers located on either side of the diffraction layer 130. Thus, in the first configuration, the diffraction grating 131 is made from a material having a refractive index corresponding to the refractive index n Sr of the semi-reflecting layer 120 and a refractive index corresponding to the refractive index n r of the reflective layer 140. The diffraction grating 131 is produced for example by etching the material of the semi-reflective layer 120 then depositing the material constituting the reflective layer 140.

[0091] In the second configuration, the diffraction grating 131 is made of a material having a refractive index corresponding to the refractive index n s of the substrate 110 and a refractive index corresponding to the refractive index n S r of the semi-reflective layer 120. The diffraction grating 131 is produced for example by etching in the material of the substrate 110 then depositing the material of the semi-reflective layer 120.

[0092] The diffraction grating 131 is periodic along a longitudinal axis of the substrate corresponding to the extension of the optical axis of the optical fiber.

[0093] In a preferred embodiment, as illustrated in FIG. 1, the diffraction grating 131 is in the form of a plurality of concentric circular arcs. The circular arcs are arranged so that their focal points coincide and are located at the first end face 230 of the optical fiber. The circular arcs extend substantially in the same angular range and have periodically increasing radii of curvature, as illustrated in FIG. 6. FIG. 6 is a top view of the diffraction layer. The angular range preferably corresponds to the numerical aperture of the optical fiber 200.

[0094] In the first longitudinal portion 115, the optical component 100, in particular the three layers, is advantageously sized as a function of the first wavelength λi of the first incident beam 310 passing through it and of an angle of incidence αi of a ray of said first incident beam, called the first incident ray. The angle of incidence αi is defined relative to the direction normal to the diffraction grating 131, therefore to the normal direction of the lower face 113 of the substrate 110.

[0095] According to the invention, the angle of incidence ai of the first incident ray is preferably close to zero, for example in a range of values ​​between 0 and 20°. This range of values ​​for the angle of incidence ai is given here for illustrative purposes only and should not be considered as limiting. The range of values ​​is variable and depends, among other things, on the first wavelength λi of the first incident beam 310, the constituent materials of the different layers constituting the optical device, the characteristics of the semi-reflecting layer 120 and the diffraction layer 130.

[0096] According to the invention, whatever the configuration of the optical component, for each first incident ray, of first wavelength λi and an angle of incidence λi, the thicknesses of the semi-reflecting layer 120 and of the diffraction layer 130 are dimensioned so as to generate, in the substrate 110, a destructive interference of the rays reflected by the two layers. The reflected rays correspond to the reflection of the first incident ray on each of the layers.

[0097] The combination of the semi-reflective layer 120 and the reflective layer 140 with the diffraction grating 131 makes it possible to advantageously create a resonant grating making it possible to cancel the rays reflected in the substrate 110.

[0098] As a reminder, for two rays to interfere destructively, they must be in phase opposition and in the same direction.

[0099] The calculations of the thicknesses of the semi-reflecting layer 120 and of the diffraction layer 130 to form a resonant grating are within the reach of those skilled in the art. In addition, according to the invention, and whatever the configuration of the optical component, for each first incident ray, of first wavelength λi and an angle of incidence λi, the diffraction grating 131 is configured to allow the diffraction of the first incident ray coming from the light source 300 within the limit of the first diffraction order, and at a diffraction angle such that a ray diffracted by said diffraction grating 131 then propagates in the substrate 110, in an acceptance cone of the optical fiber 200, in the direction of the first edge of the substrate.

[0100] More precisely, the spatial period A of the diffraction grating 131 is chosen such that the first incident ray coming from the light source 300 is diffracted within the limit of the first diffraction order. To obtain a ray diffracted within the limit of the first diffraction order by the diffraction grating 131, the spatial period of said diffraction grating is advantageously chosen to be of the order of the first wavelength λi of the first incident beam 310.

[0101] The spatial period A of the diffraction grating 131 is also chosen such that the diffracted rays of order 1 can be refracted in the substrate 110.

[0102] The previously described arcuate shape of the diffraction grating 131 advantageously makes it possible to converge the rays diffracted by the diffraction grating 131 towards the first end face 230 of the optical fiber 200, as illustrated in FIG. 6. The dotted circle in FIG. 6 represents the shape of the first incident beam 310, coming from the light source 300, and arriving on the diffraction grating 131.

[0103] Thus, the optical component 100 advantageously makes it possible, at the level of the first longitudinal portion 115, to collect a maximum of the rays of the first incident beam 310 coming from the light source 300, to deflect them and to inject them into the optical fiber 200, as illustrated in FIG. 4.

[0104] The light source 300 is arranged relative to the first face of the substrate such that a maximum of the rays of the first incident beam 310 penetrates into the substrate, from the lower face 113 of the substrate 110, and passes through said substrate in order to be diffracted by the diffraction grating 131 then transmitted into the optical fiber 200.

[0105] Such an arrangement of the optical component, whatever its configuration, thus allows the transmission of the first incident beam 310 from the light source 300 into the optical fiber 200 with optimal coupling.

[0106] By way of illustration, Figures 2 and 3 represent an example of the trajectory of a ray of the first incident beam in the optical component for the two configurations of the optical component. Only a ray 10 of the first incident beam 310 is represented for the sake of clarity. In this case, and in a non-limiting manner, the ray represented is that located on a central axis of said first incident beam. An arrow indicates the direction of propagation of this ray. a) First configuration of the optical component (Figure 2)

[0107] When the ray 10 reaches the lower face 1 13 of the substrate 1 10, at an angle of incidence ai, the ray 10 generates a refracted ray 1 1 propagating in the substrate 1 10. Said ray also generates a reflected ray, not shown in FIG. 2.

[0108] When the refracted ray 1 1 reaches the upper face 114 of the substrate 1 10, the refracted ray 1 1 generates:

[0109] - a refracted ray 12 propagating in the semi-reflecting layer 120,

[0110] - a reflected ray 13 in the substrate 1 10.

[0111] The refracted ray 12 propagates in the semi-reflecting layer 120 and reaches the diffraction grating 131. The refracted ray 12 then generates:

[0112] - a diffracted ray 14 according to the first order of diffraction,

[0113] - a reflected ray 15.

[0114] The diffracted ray 14 propagates in the semi-reflecting layer 120 then is refracted in the substrate 110 and heads towards the first edge 111 of the substrate, towards the first end face 230 of the optical fiber, then in the optical fiber in a propagation direction 16. The refractive index of the substrate being substantially equal to that of the core of the optical fiber 200, the diffracted ray 14 propagating in the substrate then propagates in the optical fiber, without refraction and without loss by reflection.

[0115] The reflected ray 15 propagates in the semi-reflecting layer 120 then generates, when it reaches the upper face 114 of the substrate 110, a refracted ray 17 in the substrate 110. The refracted ray 17 propagates in the same direction of propagation as the reflected ray 13.

[0116] The reflected ray 15 is also reflected by the upper face 114 of the substrate 110 towards the diffraction grating.

[0117] The various characteristic parameters (thicknesses, refractive index of the layers) of the optical component 100 according to the invention being determined in such a way that the phase shift between the reflected ray 13 and the refracted ray 17 (coming from the reflected ray 15) is substantially equal to n and that these two rays 13, 17 propagate in the same direction of propagation, this then results in a destructive interference between these two rays 13, 17, reducing the light intensity propagating in the direction of reflection, and consequently increasing the light intensity of the diffracted ray 14 propagating in the direction of propagation 16 towards the optical fiber. The optical component 100 thus forms a resonant network, by repeating the process of destructive interference of the different rays reflected in the substrate, and further reinforcing the light intensity of the diffracted rays propagating in the direction of propagation 16 towards the optical fiber.b) Second configuration of the optical component (figure 3).

[0118] When the ray 20 reaches the lower face 113 of the substrate 110, at an angle of incidence ai, the ray 20 generates a refracted ray 21 propagating in the substrate 110. Said ray also generates a reflected ray, not shown in FIG. 3.

[0119] When the refracted ray 21 reaches the upper face 114 of the substrate 110 and the diffraction grating 131, the refracted ray 21 generates:

[0120] - a diffracted ray 22 according to the first order of diffraction,

[0121] - a refracted ray 24 propagating in the semi-reflecting layer 120,

[0122] - a reflected ray 23 in the substrate.

[0123] The diffracted ray 22 propagates in the substrate 110 and heads towards the first edge 111 of the substrate, towards the first end face 230 of the optical fiber, then in the optical fiber in a propagation direction 30. The refractive index of the substrate being substantially equal to that of the core of the optical fiber 200, the diffracted ray 22 is transmitted in the optical fiber, without refraction and without loss by reflection.

[0124] The refracted ray 24 propagates in the semi-reflecting layer 120 and reaches the reflecting layer 140. The refracted ray 24 generates a reflected ray 25. The reflected ray 25 propagates in the semi-reflecting layer 120 and then generates, when it reaches the diffraction grating 131:

[0125] - a diffracted ray 28, according to the first order of diffraction,

[0126] - a refracted ray 27 in the substrate 1 10,

[0127] - a reflected ray 26 in the semi-reflecting layer 120.

[0128] The diffracted ray 28 propagates in the substrate 110 and heads towards the first edge 111 of the substrate, towards the first end face 230 of the optical fiber, then in the optical fiber in the same direction of propagation 30 as the diffracted ray 22.

[0129] The refracted ray 27 propagates in the same direction of propagation as the reflected ray 23.

[0130] The various characteristic parameters (thicknesses, refractive index of the layers) of the optical component 100 according to the invention being determined in such a way that the phase shift between the reflected ray 23 and the refracted ray 27 (coming from the reflected ray 25) is substantially equal to n and that these two rays 23, 27 propagate in the same direction of propagation, this then results in destructive interference between these two rays 23, 27, reducing the light intensity propagating in the direction of reflection, and consequently increasing the light intensity of the diffracted rays 22, 28 propagating in the direction of propagation 30 towards the optical fiber 200.

[0131] The optical component 100 thus forms a resonant network, repeating the process of destructive interference of the different rays reflected in the substrate, and further reinforcing the light intensity of the diffracted rays propagating in the propagation direction 30 towards the optical fiber.

[0132] Downward flow direction

[0133] At the second longitudinal portion 116, the optical component 100 comprises the optical element 600.

[0134] The optical element 600 is advantageously configured to direct the second incident beam 410, that coming from the optical fiber 200, towards the photodetector 400, as illustrated in FIG. 5. More precisely, the optical element 600 is configured to direct the second incident beam 410 out of the substrate 110, in a direction substantially perpendicular to the lower face 113 of said substrate.

[0135] In other words, the optical element 600 advantageously allows an angle return of substantially 90° towards the photodetector 400.

[0136] As illustrated in FIG. 5, the photodetector 400 is preferably positioned relative to the optical element 600 of the optical component 100, and at a distance from the lower face 113 of the substrate 110, so that a maximum of the rays forming the second incident beam 410 and deflected by the optical element 600 is received in full, or in part, by said photodetector.

[0137] In an exemplary embodiment of the optical element 600, said optical element is a mirror attached to the second edge 112 of the substrate 110. The second edge 112 of the substrate has an inclination of a predefined angle relative to the longitudinal axis of the substrate.

[0138] In a preferred embodiment of the optical element 600, as illustrated in FIGS. 2 and 3, the second edge 112 of the substrate has an inclination of an angle substantially equal to 45° relative to the longitudinal axis of the substrate.

[0139] In another exemplary embodiment of the optical element 600, said optical element is a prism, for example a glass prism. The shape of the prism is advantageously adapted such that the second incident beam 410 is oriented towards the photodetector 400.

[0140] In another exemplary embodiment of the optical element 600, said optical element comprises a stack of layers as described in the first longitudinal portion 115. The characteristic parameters of the different layers (thicknesses, refractive indices, period of the diffraction grating) of this stack of layers are, in this case, advantageously adapted to the second wavelength λ2 of the second incident beam.

[0141] Thus, regardless of the optical element 600 used, the second incident beam 410, coming from the optical fiber, passes through the substrate to the optical element 600, is deflected by the optical element 600 and is directed towards the photodetector 400. The diffraction grating 131 located in the first longitudinal portion 115, being configured to be insensitive to the second wavelength λ2 of the second incident beam coming from the optical fiber, said second incident beam is not deflected by this diffraction grating 131.

[0142] Such an arrangement of optical component 100 with respect to the photodetector 400 allows the transmission of the second incident beam 410 into the photodetector 400 with optimal coupling.

[0143] The invention thus proposes an optical device with an optical component of compact size, advantageously allowing the bidirectional transmission of optical signals, via light beams, from a light source 300 and / or towards a photodetector 400, both arranged in a direction substantially perpendicular to the optical axis of the optical fiber 200, with optimal coupling.

[0144] The use of a compact and substantially flat optical component allows installation of the optical device in environments constrained in terms of volume or dimension, such as in aircraft.

[0145] Thus, in a preferred application, the optical assembly 700 is disposed in an aircraft. The optical device 500 is disposed in an aircraft cabin, with the optical component 100 disposed above a passenger seat. The light source 300 and the photodetector 400 are disposed in the passenger seat.

[0146] The optical component 100 can be placed near equipment such as equipment known by the acronym PSU (“Passenger Service Unit”, in English terminology), allowing in particular a passenger to trigger calls to the commercial flight crew or to turn on / off a reading light.

[0147] The optical module may advantageously be intended for data transmission, via Li-Fi technology (acronym for “Light Fidelity”). The light source 300 of the optical assembly 700 is thus configured to emit the first incident beam 310 with the first wavelength λ located in the infrared range. By infrared range, we mean the range of wavelengths between 780 nm and 2 pm. The photodetector of the optical module is, for its part, configured to detect the second incident beam with the second wavelength λ also located in the infrared range.

Claims

Claims Claim 1. Optical device (500) comprising: - an optical fiber (200) comprising a core (210), of refractive index n c and of diameter of, and having a first end face (230), - an optical component (100) comprising: o a substrate (110) of refractive index n s substantially equal to the refractive index n c of the core of the optical fiber and thickness e s substantially less than or equal to the diameter of the fiber core (200), said substrate: ■ comprising two faces, called first (1 13) and second (1 14) faces, ■ extending between two opposite edges, called first (1 11 ) and second (1 12) edges, ■ having a first longitudinal portion (1 15) starting from the first edge (11 1) and a second longitudinal portion (1 16) starting from the second edge (1 12), o a stack of three layers arranged on the second face (1 14) of the substrate (110), at the level of the first longitudinal portion (1 15) of said substrate: ■ a semi-reflective layer (120) of refractive index n S r greater than the refractive index n s of the substrate, and thickness esr, ■ a diffraction layer (130), of thickness ed, comprising, throughout its thickness, a diffraction grating (131) of period A, ■ a reflective layer (140), o an optical element (600), at its second longitudinal portion (1 16), the optical fiber (200) being arranged opposite the optical component (100) so that the first end face (230) of said optical fiber is attached to the first edge (11 1) of the substrate (1 10), the semi-reflecting layer (120) and the diffraction layer (130) being arranged between the substrate (110) and the reflective layer (140), the layer semi-reflecting layer (120) being arranged between the substrate (1 10) and the diffraction layer (130) or between the diffraction layer (130) and the reflective layer (140), for a first incident ray, having a first given wavelength λi and arriving on the first face (1 13) of the substrate (110) with a predetermined angle of incidence λi and defined relative to a direction normal to said first face of the substrate: o the thicknesses of the semi-reflecting layer (120) and of the diffraction layer (130) are determined to generate destructive interference of the reflected rays, o the diffraction grating (131) is configured to allow the diffraction of the first incident ray within the limit of the first diffraction order, and at a diffraction angle such that the diffracted ray propagates in the substrate (1 10), in an acceptance cone of the optical fiber (200), towards the first side of the optical fiber,for a second incident ray coming from the optical fiber, having a second wavelength λ2 distinct from the first wavelength λi, the optical element (600) is configured to direct said second incident ray out of the substrate (1 10), perpendicular to the first face (1 13) of the substrate., Claim 2. Optical device (500) according to claim 1 wherein the diffraction grating (131) is in the form of a plurality of concentric circular arcs, centered on the first edge (111) of the substrate, at the level of the first face (230) of the optical fiber (200). Claim 3. Optical device (500) according to the preceding claim in which the circular arcs extend over the same angular range corresponding to a numerical aperture of the optical fiber (200). Claim 4. Optical device (500) according to one of the preceding claims in which the diffraction grating (131) has materials whose refractive indices are identical to the materials of the layers arranged on either side of the diffraction layer (130). Claim 5. Optical device (500) according to one of the preceding claims in which the second edge (1 12) of the substrate (1 10) of the optical component (100) has an inclination of an angle substantially equal to 45° relative to a longitudinal axis of said substrate and in which the optical element (600) is a mirror attached to said second edge of the substrate. Claim 6. Optical assembly (700) comprising a light source (300), a photodetector (400) and an optical device (500) according to one of the preceding claims, said light source being arranged opposite the first face (1 13) of the substrate (1 10), at the first longitudinal portion (1 15), and configured to emit the first incident ray, said photodetector being arranged opposite the first face (1 13) of the substrate (1 10), at the second longitudinal portion (1 16), and arranged relative to the optical element (600) so as to receive the second incident ray.

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