Optical fiber assembly

Abstract

The invention relates to an optical assembly (50) comprising: an optical fiber (200), a support (51), a fiber positioning substrate (52), a beam splitter element (60), an optical component (100) forming a resonant array, and a cover plate. The substrate (52) rests on the support and has a housing for receiving the beam splitter element and the optical component. A groove (80), formed in the substrate (52) and the support (51) and opening into the housing, receives the optical fiber so that it is aligned with the beam splitter element. The arrangement of the constituent elements of the optical assembly relative to each other allows bidirectional transmission of signals with a light source / photodetector assembly arranged in a direction orthogonal to an optical axis of the optical fiber without requiring dynamic alignment of the elements. Figure 1

Description

Title of the invention: Optical fiber assembly Technical field of the invention

[0001] The present invention relates to an optical fiber assembly for the bidirectional transmission of optical signals from a light source to a photodetector. The present invention further relates to an optical assembly enabling the bidirectional transmission of signals from a light source to a photodetector, the light source / photodetector assembly being arranged in a direction substantially orthogonal to the optical axis of the optical fiber.

[0002] The invention finds an advantageous application in the aeronautical field, in particular for equipping an aircraft. Previous technique

[0003] In aircraft, optical fibers are increasingly used to interconnect equipment for communication purposes.

[0004] In the particular context of the distribution of Li-Fi (acronym for Light-Fidelity) type optical signals, optical fibers can be used to carry these optical signals bidirectionally from light sources to photodetectors, these light sources and photodetectors being housed at the level of the backs of the passenger seats.

[0005] These optical fibers run the entire length of the cabin, in areas that are difficult to access and have limited volume, generally in the ceiling, under the luggage compartments, and one of their ends arrives above the backs of the passenger seats.

[0006] An interface is then necessary between the end of an optical fiber, located above the backrest of a passenger seat, and the light source / photodetector assembly located at the level of said backrest of a passenger seat, to allow: - on the one hand, the optical coupling of a light beam, carrying optical signals, coming from the light source towards the optical fiber, - on the other hand, the optical coupling of a light beam, carrying optical signals, coming from the optical fiber to the photodetector.

[0007] 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 substantially orthogonal to this optical axis, which implies the use of an angle return of the order of 90°.

[0008] In the so-called downward flow direction, that is, 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 reflection, with a mirror for example, can suffice as an interface between the optical fiber and the photodetector.

[0009] However, in the so-called upward flow direction, that is, 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. A setup based on lenses and a prism or a mirror can, for example, achieve this optical coupling. However, such a setup requires meticulous implementation because the alignments between the different optical elements must be precise to obtain optimal coupling. Furthermore, such a setup is bulky, both in terms of weight and volume, expensive, and inefficient in terms of injection into the optical fiber, making it difficult to integrate into a highly constrained environment such as that of an aircraft. Presentation of the invention

[0010] The present invention aims to remedy the aforementioned drawbacks.

[0011] To this end, the present invention proposes an optical assembly comprising: - an optical fiber, comprising an optical axis, - a basic substrate, called a support, - a substrate known as a fiber positioning substrate, - a beam splitter element, - an optical component forming a resonant grating, called an optical component, - a cover plate,

[0012] the fiber positioning substrate resting on a main face of said support and having a lateral edge having a hollow profile forming a housing for receiving the beam splitter element and the optical component, a longitudinal groove being made in the fiber positioning substrate and the support and opening into the housing of said fiber positioning substrate, said longitudinal groove being dimensioned to receive the optical fiber, the optical fiber being positioned in the optical assembly so that a first end face of the optical fiber is opposite the beam splitter element, the cover plate resting on the fiber positioning substrate and pressing the optical fiber into the longitudinal groove, the optical component being configured to receive a light beam, said first incident beam,coming from a direction substantially perpendicular to the optical axis of the optical fiber, and to transmit this first incident beam towards the optical fiber, via the beam splitter element, , the beam splitter element being configured for: - allow the first incident beam to pass towards the optical fiber, - transmit a light beam, called the second incident beam, from the optical fiber out of the optical assembly, in a direction substantially perpendicular to the optical axis of the optical fiber.

[0013] The arrangement of the different constituent elements of the optical assembly with respect to each other advantageously allows the bidirectional transmission of signals with a light source / photodetector assembly arranged in a direction substantially orthogonal to the optical axis of the optical fiber without having to resort to a dynamic alignment of the elements with each other and with the light source and the photodetector.

[0014] The planar component advantageously allows for the collection of a maximum number of rays from the first incident beam originating from the light source and their transmission into the optical fiber, via the beam splitter element. The beam splitter element transmits the second incident beam, originating from the optical fiber, to the photodetector.

[0015] The optical assembly thus allows an efficient optical coupling of the first incident beam from the light source to the optical fiber, through the optical component and an efficient optical coupling of the second incident beam from the optical fiber to the photodetector, through the beam splitter element.

[0016] In particular embodiments, the optical device may further comprise one or more of the following characteristics, taken individually or in all technically possible combinations.

[0017] In particular embodiments, the optical fiber comprises a core with refractive index nc and diameter dc, and the optical component comprises a stack comprising: - a substrate with a refractive index ns substantially equal to the refractive index nc of the optical fiber core and a thickness es less than or equal to the diameter dc of the fiber core, said substrate comprising two faces, called first and second faces, - a semi-reflective layer with a refractive index nsr greater than the refractive index ns of the substrate, and of thickness esr, - a diffraction layer of thickness ed, comprising, throughout its thickness, a diffraction grating of period A, - a reflective layer,

[0018] the reflective layer resting on the main face of the support, 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 of the first incident beam, having a first given wavelength Xi and arriving on the first face of the substrate with a predetermined angle of incidence ai and defined relative to a direction normal to said first face of the substrate: - The thicknesses of the semi-reflective layer and the diffraction layer are determined to generate destructive interference of the reflected rays, - the diffraction grating is configured to allow the diffraction of the first incident ray in the limit of the first order of diffraction, and under a diffraction angle such that the diffracted ray propagates in the substrate, in an angular acceptance cone of the optical fiber, towards the beam splitter element and then towards the first face of the optical fiber.

[0019] The stacking of the three layers on the substrate, their arrangement, and their characteristic parameters (thickness, refractive index of the layers) enable the optical component to achieve efficient optical coupling of the first incident beam from the light source to the optical fiber. The natural divergence of the light beam emitted by the light source is counteracted.

[0020] In particular embodiments, the diffraction grating takes the form of a plurality of concentric circular arcs centered at the first end face of the optical fiber. Such a circular arc shape of the diffraction grating advantageously allows the rays diffracted by said diffraction grating to converge towards the first end face of the optical fiber.

[0021] In particular embodiments, the support, the fiber positioning substrate and the cover plate are each made of a material that allows at least the wavelengths in the ultraviolet to pass through.

[0022] In particular embodiments, the beam splitter element is a separate part from the optical component and is disposed between the first end face of the optical fiber and the optical component, the beam splitter element and the optical component having a shape complementary to the housing of the fiber positioning substrate, so as to each take place in a complementary manner in the housing of said fiber positioning substrate.

[0023] In particular embodiments, the beam splitter element is a prism splitter, for example a splitter cube.

[0024] In particular embodiments, the optical component has a first lateral edge having an inclination substantially equal to 45° with respect to the optical axis of the optical fiber, and in which the beam splitter element is a dichroic filter attached to the first lateral edge of the optical component, the optical component having a shape complementary to the housing of the fiber positioning substrate, so as to take place in a complementary manner in the housing of said fiber positioning substrate, with the first lateral edge opposite the first end face of the optical fiber.

[0025] In particular embodiments, the first end face of the optical fiber is inclined at an angle substantially equal to 45° with respect to the optical axis of said optical fiber, such that the first end face of the optical fiber is attached to the dichroic filter attached to the first lateral edge of the optical component.

[0026] The invention also relates to an optical assembly comprising a light source, a photodetector, and an optical assembly as described above. The light source is arranged opposite the optical component and is configured to emit the first incident beam. The photodetector is arranged opposite the beam splitter element so as to receive the second incident beam.

[0027] The invention also relates to a method for manufacturing an optical assembly as described above, with the beam splitter element of the optical assembly forming a separate part from the optical component. The method comprises the steps of: - positioning of the fiber positioning substrate on the main face of the support, - creation of the longitudinal groove in the fiber positioning substrate and the support, - positioning of the beam splitter element and the optical component in the housing of the fiber positioning substrate, - positioning of the optical fiber in the longitudinal groove, - positioning of the cover plate.

[0028] The invention also relates to a method for producing an optical assembly as described above, with the optical component having a first lateral edge inclined at approximately 45° to the optical axis of the optical fiber, and with the beam splitter forming a dichroic filter attached to the first lateral edge of the optical component. The method comprises the steps of: - positioning of the fiber positioning substrate on the main face of the support, - creation of the longitudinal groove in the fiber positioning substrate and the support, - positioning of the optical component in the housing of the fiber positioning substrate, - positioning of the optical fiber in the longitudinal groove, - positioning of the cover plate. Brief description of the figures

[0029] The invention will be better understood upon reading the following description, given by way of non-limiting example, and made with reference to the figures which represent:

[0030] Figure [1] is a top view of an optical assembly according to a first embodiment,

[0031] [Fig.2] is a sectional view of the optical assembly of [Fig.1] along line AA,

[0032] Figure [Fig. 3] is a sectional view of the optical assembly of Figure [Fig. 1] along line BB,

[0033] Fig. 4 is a sectional view of the optical assembly of Fig. 1 along line AA with a focusing lens at the level of a beam splitter element of the optical assembly,

[0034] Figure 5 is a top view of an optical assembly according to a second embodiment,

[0035] Figure [Fig. 6] is a sectional view of the optical assembly of Figure [Fig. 5] along line AA,

[0036] Figure [Fig. 7] is a sectional view of an optical assembly according to an alternative embodiment of the second embodiment,

[0037] Figure 8 is a cross-sectional view of a first configuration of an optical component of the optical assembly, regardless of the embodiment of the optical assembly.

[0038] Figure 9 is a cross-sectional view of a second configuration of an optical component forming a resonant array of the optical assembly, regardless of the embodiment of the optical assembly.

[0039] Figure 10 illustrates the trajectory, in the optical component of Figure 8, of a light ray, in the direction of the upward flow.

[0040] Fig. 11 illustrates the trajectory, in the optical component of Fig. 9, of a light ray, in the direction of the upward flow. Description of the implementation methods

[0041] An optical assembly 50 according to a first embodiment is described in relation to figures I to 4 and I to 11.

[0042] First embodiment of the optical assembly

[0043] The optical assembly 50 according to the first embodiment comprises, as illustrated in Figures 1 to 4, the following constituent elements: - a 200 Mbps optical fiber, - a basic substrate, called support 51, - a substrate, called a fiber positioning substrate 52, - a beam splitter element 60, - an optical component forming a resonant array, called an optical component 100, - a cover plate 53.

[0044] In the following description, the optical assembly will be associated with an XYZ coordinate system. The indication of the X, Y, and Z axes helps to understand the optical assembly. The X-axis designates a longitudinal axis of the optical assembly and corresponds to a longitudinal dimension of said optical assembly. The Y-axis designates an axis perpendicular to the X-axis and corresponds to a transverse direction of the optical assembly. The Z-axis designates an axis perpendicular to the X and Y axes. As illustrated in [Fig. 1], the Z-axis designates the vertical axis. Thus, in summary, the optical assembly 50 has a length along the X-axis, a width along the Y-axis, and a height along the Z-axis. As used in the description, the terms "horizontal", "vertical", "left", "right", "top", "bottom", "lower", "superior", etc. refer, unless otherwise specified, to the orientation of the optical assembly in the figures.

[0045] Furthermore, unless otherwise indicated, the terms "approximately", "about", "in the order of" mean within 10%, and preferably within 5%.

[0046] In this first embodiment, the beam splitter element 60 is a physical part as such, distinct from the optical component 100.

[0047] The optical assembly 50 is intended to be associated with a light source 300 and a photodetector 400, both of which are arranged in directions substantially perpendicular to an optical axis 240 of the optical fiber. As illustrated in [Fig. 2], the light source 300 is intended to be arranged opposite the optical component 100 and the photodetector 400 is intended to be arranged opposite the beam splitter element 60. The optical assembly, the light source 300, and the photodetector 400 form an optical assembly 70.

[0048] The optical assembly 50 is advantageously designed and configured for, as illustrated in [Fig.2]: - on the one hand, to transmit a light beam, called the first incident beam 310, originating from the light source 300 in the optical fiber 200, via the optical component 100, and - on the other hand, transmit a light beam, called second incident beam 410, from the optical fiber 200 to the photodetector 400, via the beam splitter element 60.

[0049] The first incident beam 310 and the second incident beam 410, and their direction of propagation, are each schematically represented by an arrow on [Fig.2].

[0050] The two incident light beams 310, 410 are advantageously configured to transmit an optical data transmission signal, for example a modulated optical signal of the Li-Fi type.

[0051] The optical assembly 50 is thus advantageously intended for the bidirectional transmission of optical signals: - in the direction known as the upward flow, that is to say from the light source 300 towards the optical fiber 200, - in a direction called downward flow, that is to say from optical fiber 200 to photodetector 400.

[0052] 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 Xp

[0053] In a preferred embodiment, the first incident beam 310 is at a wavelength of 940nm. In one embodiment, the first incident beam 310, exiting the light source 300, is a diverging beam and takes the form of a scattering cone (not shown in the figures). Alternatively, a lens (not shown in the figures) can be placed at the exit of the light source 300 to collimate the first incident beam.

[0054] Generally, any light source can be used for the light source 300, such as, for example, light-emitting diodes (LEDs) or laser sources, such as laser diodes or vertical-cavity surface-emitting laser diodes (VCSELs). However, the use of surface-emitting light sources, such as LEDs or VCSELs, is advantageously preferred.

[0055] The photodetector 400 is configured to detect the second incident beam 410.

[0056] The second incident beam 410 has a wavelength, called the second wavelength X2, distinct from that of the first incident beam.

[0057] In a preferred embodiment, the second incident beam 410 is at a wavelength of 850nm.

[0058] In a preferred embodiment, the photodetector 400 is a photodiode.

[0059] The optical assembly 50 according to the invention is configured such that its elements constituents are arranged in relation to each other in such a way as to allow bidirectional transmission of optical signals, without having to resort to dynamic alignment of the elements with each other and with the light source 300 and the photodetector 400.

[0060] The various elements constituting the optical assembly 50 and their arrangement in relation to each other are now described. 200 Optical Fiber

[0061] The optical fiber 200 preferably comprises, in a conventional manner, a core 210 and an optical cladding 220 surrounding the core 210, as illustrated in [Fig.3]. Core 210 has a refractive index nc and a diameter dc. Core 210 is preferably made of glass, silica-based. The optical cladding 220 surrounds the core 210 and has a refractive index lower than the refractive index nc of the core. Optical fiber 200 has a first end face 230. Preferably, the first end face 230 is straight, that is, perpendicular to the optical axis 240 of the optical fiber 200. 200 Mbps optical fiber can be single-mode or multi-mode. Preferably, the optical fiber is multi-mode.

[0062] In a preferred embodiment, the optical fiber 200 has a diameter of 430 µm, with a core diameter of 400 µm and a cladding thickness of 30 µm. The support

[0063] The support 51 is a transparent substrate, made for example of transparent glass. Preferably, as illustrated in [Fig.1], support 51 is in the form of a plate. The support 51 is preferably made of a material that allows at least ultraviolet wavelengths to pass through. By ultraviolet, we mean wavelengths between 100 nm and 400 nm. The support 51 has a main face 511 for receiving the fiber positioning substrate 52, the beam splitter element 60 and the optical component 100. Preferably, the main face 511 of the support 51 is flat and contained in an XY plane. The main face 511 of the support 51 defines a reference plane. The main face 511 receives the fiber positioning substrate 52, the element beam splitter 60 and optical component 100, it advantageously participates in the relative alignment, along the Z axis, of said fiber positioning substrate, said beam splitter element and said optical component.

[0064] The fiber positioning substrate

[0065] The fiber positioning substrate 52 is a transparent substrate, made for example of transparent glass. Preferably, as illustrated in Figures 1 and 2, the fiber positioning substrate 52 is in the form of a plate. The fiber positioning substrate 52 is preferably made of a material that allows at least wavelengths in the ultraviolet to pass through. Preferably, the fiber positioning substrate 52 is made of the same material as the support. The fiber positioning substrate 52 has a first main face 521, arranged against the main face 511 of the support 51. In other words, the first main face 521 of the fiber positioning substrate 52 and the main face 511 of the support 51 are in contact with each other. The fiber positioning substrate 52 has a second main face 522, opposite the first main face 521. The second main face 522 is intended for receiving the cover plate 53. Preferably, the first main face 521 and the second main face 522 of the fiber positioning substrate 52 are flat. The fiber positioning substrate 52 has a thickness ep, preferably constant, between the first and second main faces. The thickness ep is substantially less than the diameter dc of the optical fiber.

[0066] The fiber positioning substrate 52 further has a lateral edge 523 having a hollow profile forming a housing for receiving the beam splitter element 60 and the optical component 100. It is understood that the housing extends over the entire thickness ep of the fiber positioning substrate 52.

[0067] In the following description, by abuse of language, the housing formed by the lateral edge 523 of the fiber positioning substrate 52 will simply be referred to as the housing of the fiber positioning substrate 52.

[0068] The shapes of the optical component 100 and the beam splitter element 60 have a shape that is complementary to the housing of the fiber positioning substrate 52, so that each takes place in a complementary manner in the housing of said fiber positioning substrate 52. The beam splitter element 60 and the optical component 100 are thus each abutting against the lateral edge 523 of the housing of the fiber positioning substrate 52 when they are in position in the optical assembly 50.

[0069] The shape of the housing for the fiber positioning substrate 52 is advantageously adapted to allow self-centering of the beam splitter element 60 and the optical component 100.

[0070] In a preferred embodiment, the housing for the fiber positioning substrate 52 has, in an XY plane, a V-shaped form with the point of the V directed towards an opposite lateral edge, as illustrated in [Fig. 1]. The housing for the fiber positioning substrate 52 is thus delimited by two lateral walls forming the lateral edge 523, between which the beam splitter element 60 and the optical component 100 are positioned. The beam splitter element and the optical component each abut against the lateral walls forming the housing for the fiber positioning substrate 52 when they are in position within the optical assembly 50.

[0071] The beam splitter element 60 and the optical component 100 are preferably substantially the same thickness as the fiber positioning substrate 52.

[0072] A longitudinal groove 80 is made both in the fiber positioning substrate 52 and in the support 51 for receiving and holding in place the optical fiber 200 in the optical assembly 50.

[0073] The longitudinal groove 80 is made from the second main face 522 of the fiber positioning substrate 52 towards the support 51. The longitudinal groove 80 is through the thickness ep of the fiber positioning substrate 52 and penetrates part of a thickness of the support 51, as illustrated in [Fig.3].

[0074] The longitudinal groove 80, with longitudinal axis along the X axis, extends between the two lateral edges of the fiber positioning substrate 52. The longitudinal groove 80 thus opens into the housing of the fiber positioning substrate 52.

[0075] Preferably, the longitudinal groove 80 and the housing are arranged relative to each other so that the tip of the V of the housing coincides with the longitudinal axis of the longitudinal groove 80. It is understood that the tip of the V of the housing of the fiber positioning substrate 52 is truncated by the longitudinal groove 80.

[0076] The shape and / or dimension of the longitudinal groove 80 is preferably adapted to the diameter of the optical fiber 200.

[0077] The longitudinal groove 80 preferentially has, in a YZ plane, a V-shaped section, as illustrated in [Fig.3].

[0078] Preferably, the longitudinal groove 80 is dimensioned so that the lower part of the core 210 of the optical fiber 200 is flush with the main face 511 of the support 51. Thus, the core 210 of the optical fiber 200 is opposite the beam splitter element 60 and the optical component 100, i.e. that the core 210 The optical fiber 200 is at the same height, along the Z-axis, as the beam splitter element 60 and the optical component 100. The optical fiber 200 can substantially exceed the second main face 522 of the fiber positioning substrate 52.

[0079] Advantageously, the housing of the positioning substrate 52 is dimensioned so that the opening angle of the V-shape of the housing formed by the lateral edge of the fiber positioning substrate 52 corresponds substantially to the numerical aperture of the optical fiber 200. The cover plate

[0080] The cover plate 53 is a transparent substrate, made for example of transparent glass. Preferably, as illustrated in figures 1 and 3, the cover plate 53 is in the form of a plate. The cover plate 53 is preferably made of a material which allows at least the wavelengths in the ultraviolet to pass through. The cover plate 53 is positioned against the second main face 522 of the fiber positioning substrate 52, to advantageously slightly compress the optical fiber 200 in the longitudinal groove 80.

[0081] The cover plate 53 is arranged so as not to cover the housing of the fiber positioning substrate 52. The beam splitter element

[0082] The beam separator element 60 has a main face 61 attached to the main face 511 of the support 51.

[0083] As explained previously, the beam separator element 60 has a shape complementary to a part of the housing of the positioning support 52.

[0084] In a preferred embodiment, when the housing has a V-shaped section in an XY plane, the beam separator element 60 has a truncated V-shaped section in the same plane. The beam splitter element 60 has a first edge 62 attached to the first end face 230 of the optical fiber 200 and a second opposite edge 63 attached to the optical component 100.

[0085] The beam splitter element 60 has two longitudinal edges 64, each being attached to a part of one of the side walls of the housing of the fiber positioning substrate 52.

[0086] The beam splitter element 60 is configured to pass or reflect a light beam passing through it depending on the wavelength of said light beam.

[0087] More specifically, the beam splitter element 60 is configured to: - allow the first incident beam 310 from the light source 300, and from the optical component 100, to pass towards the optical fiber 200, and - reflect the second incident beam 410 coming from the optical fiber 200 towards the photodetector 400.

[0088] The beam splitter element 60 is thus preferably configured to be reflective to the wavelengths of light beams associated with the direction of downward flow and transparent to the wavelengths of light beams associated with the direction of upward flow.

[0089] In the preferred example where the wavelength of the first incident beam 310 is 940nm and the wavelength of the second incident beam 410 is 850nm, the beam splitter element is configured for example to be reflective at wavelengths below 900nm and transparent at wavelengths above 900nm.

[0090] In a preferred embodiment, the beam splitter element 60 is designed as a prism splitter, in particular as a splitter cube.

[0091] The beam splitter element 60 is preferably made of a material having a refractive index substantially equal, preferably equal, to the refractive index nc of the core 210 of the optical fiber 200.

[0092] In a particular embodiment, as illustrated in [Fig. 4], the optical assembly 50 may include a lens 90 attached to a face of the beam splitter 60, opposite the main face 61 of said beam splitter. Such a lens 90 advantageously allows the second incident beam 410 to be focused onto the photodetector 400, particularly when the size of the spot of said second light beam is greater than that of the photodetector.

[0093] The beam splitter element 60 is thus configured to direct the second incident beam 410, that coming from the optical fiber 200, towards the photodetector 400, as illustrated in [Fig. 2]. More precisely, the beam splitter element 60 is configured to direct the second incident beam 410 out of the optical assembly, in a direction substantially perpendicular to the optical axis 240 of the optical fiber 200.

[0094] In other words, the beam splitter element 60 advantageously allows an angle of approximately 90° to be referred to the photodetector 400.

[0095] As illustrated in [Fig.2], the photodetector 400 is preferentially positioned relative to the beam splitter element 60, and at a distance from said beam splitter element, so that a maximum of the rays forming the second incident beam 410, and deflected by the beam splitter element 60, is received in whole, or in part, by said photodetector.

[0096] Such an arrangement of the optical assembly 50 vis-à-vis the photodetector 400 allows the transmission of the second incident beam 410 into the photodetector 400 with optimal coupling. The optical component forming a resonant array

[0097] The optical component 100 has a first main face 101 attached to the main face 511 of the support 51.

[0098] As explained previously, the optical component 100 has a shape complementary to a part of the housing of the positioning support 52.

[0099] In a preferred embodiment, when the housing has a V-shaped section in an XY plane, the optical component 100 has a truncated V-shaped section in the same plane.

[0100] The optical component 100 has a first lateral edge 103 attached to the second edge 63 of the beam splitter element 60. The optical component 100 has a second lateral edge 104 opposite said first lateral edge 103 of the optical component 100.

[0101] The optical component 100 has two longitudinal edges 105, each being attached to a part of one of the side walls of the housing of the fiber positioning substrate 52.

[0102] The optical component 100 is advantageously dedicated to the direction of the upward flow.

[0103] The optical component 100 is advantageously configured to receive the first incident beam 310 and transmit this first incident beam 310 to optical fiber 200, via beam splitter element 60.

[0104] The light source 300 is intended to be positioned opposite a second main face 102, which is opposite the first main face 101 of the optical component. The light source 300 is preferably placed at a distance from the optical component 100.

[0105] 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.

[0106] The optical component 100 comprises, as illustrated in Figures 8 and 9, a successive stack comprising: a substrate 110, a layer, called a semi-reflective layer 120, one layer, called diffraction layer 130, one layer, called reflective layer 140.

[0107] The stacking order of the three layers 120, 130, 140 on the substrate 110 is not necessarily that stated above. Nevertheless, the semi-reflective layer 120 and the diffraction layer 130 are necessarily located between the substrate 110 and the reflective layer 140. Thus, the optical component 100 can have two configurations.

[0108] In a first embodiment of the optical component 100, represented in the [Fig.8] cross-sectional view, said optical component comprises the successive stacking described above.

[0109] In a second embodiment of the optical component 100, shown in cross-sectional view in [Fig.9], said optical component comprises the following successive stacking: - the substrate 110, - the 130 diffraction layer, - the 120 semi-reflective layer, - the 140 reflective layer.

[0110] When the optical component 100 is in position in the optical assembly, the reflective layer 140 is attached to the main face 511 of the support 51. The substrate 110 of the optical component is intended to be opposite the light source 300.

[0111] Regardless of the configuration of the optical component 100, the substrate 110 has a first face 113 and a second opposite face 114.

[0112] As can be understood, and as illustrated in Figures 8 and 9, the first face 113 of the substrate 110 and the second main face 102 of the optical component 100 form a single face. Thus, the light source 300 is intended to be positioned opposite the first face 113 of the substrate 110 of the optical component 100.

[0113] The substrate 110 of the optical component 100 has, between its first face 113 and its second face 114, a thickness es substantially less than or equal to the diameter dc of the core 210 of the optical fiber 200.

[0114] The substrate 110 of the optical component 100 is made of a material having a refractive index ns appreciably equal, preferably equal, to the refractive index nc of the core 210 of the optical fiber 200.

[0115] Regardless of the configuration of the optical component 100, the three layers 120, 130, 140 of the optical component each have the following characteristics.

[0116] The semi-reflective layer 120 has a thickness esr. It is made of a material having a refractive index nsr greater than the refractive index ns of the substrate 110. The material is transparent to the first wavelength Xi of the first incident beam 310. In one embodiment example, the semi-reflective layer 120 is made of silicon nitride (Si3N4).

[0117] The reflective layer 140 has a thickness er. It is made of a material with a refractive index nr. It is configured to reflect the first wavelength Xi of the first incident beam 310. In a preferred embodiment example, the reflective layer 140 is a metallic layer, for example gold or silver, or several dielectric layers.

[0118] The diffraction layer 130 has a thickness ed. It includes a 131 diffraction grating, with a spatial period A. The 131 diffraction grating is made throughout the thickness of the 130 diffraction layer. The diffraction grating 131 is advantageously dimensioned according to the first wavelength Xidu first incident beam 310, according to Bragg's law.

[0119] The diffraction grating 131 is preferably designed for a wavelength range including the first wavelength Xidu first incident beam 310. Preferably, the diffraction grating 131 is designed for a wavelength range extending ± 5 nm around the first wavelength / .,of the first incident beam 310. The diffraction grating 131 is made of materials with two different refractive indices. The diffraction grating 131 is preferentially formed from the materials of the layers located throughout the diffraction layer 130.

[0120] Thus, in the first configuration of the optical component 100, the diffraction grating 131 is made of a material having a refractive index corresponding to the refractive index nsr of the semi-reflective layer 120 and a refractive index corresponding to the refractive index nr of the reflective layer 140. The diffraction grating 131 is made for example by etching the material of the semi-reflective layer 120 and then depositing the material constituting the reflective layer 140.

[0121] In the second configuration of the optical component, the diffraction grating 131 is made of a material having a refractive index corresponding to the refractive index ns of the substrate 110 and a refractive index corresponding to the refractive index nsr of the semi-reflective layer 120. The diffraction grating 131 is made for example by etching in the material of the substrate 110 and then depositing the material of the semi-reflective layer 120.

[0122] The diffraction grating 131 is periodic along a longitudinal axis of the optical assembly.

[0123] In a preferred embodiment, as illustrated in [Fig. 1], the diffraction grating 131 takes the form of a plurality of concentric circular arcs.

[0124] The circular arcs are arranged so that their focal points coincide and are located at the first end face 230 of the optical fiber 200. The The circular arcs extend approximately within the same angular range and exhibit periodically increasing radii of curvature, as illustrated in [Fig. 1] (top view). The angular range corresponds preferentially to the numerical aperture of optical fiber 200.

[0125] The optical component 100, in particular the three layers 120, 130, 140, is advantageously dimensioned according to the first wavelength Xi of the first incident beam 310 passing through it and an angle of incidence ai of a ray of said first incident beam, called the first incident ray. The angle of incidence ai is defined relative to the direction normal to the diffraction grating 131, therefore to the direction normal to the first face 113 of the substrate 110.

[0126] According to the invention, the angle of incidence ai of the first incident ray is preferably close to zero, for example within a range of values ​​between 0 and 20°. This range of values ​​for the angle of incidence ai is given here by way of illustration only and should not be considered limiting. The range of values ​​is variable and depends, among other things, on the first wavelength Xi of the first incident beam 310, the materials constituting the different layers 120, 130, 140 constituting the optical component 100, the characteristics of the semi-reflective layer 120 and the diffraction layer 130.

[0127] According to the invention, regardless of the configuration of the optical component 100, for each first incident ray, with first wavelength Xi and angle of incidence aB, the thicknesses of the semi-reflective layer 120 and the diffraction layer 130 are dimensioned so as to generate, in the substrate 110, 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.

[0128] The combination of the semi-reflective layer 120 and the reflective layer 140 with the diffraction grating 131 makes it advantageous to create a resonant grating which cancels the rays reflected in the substrate 110.

[0129] As a reminder, for two rays to interfere destructively, they must be in opposite phase and in the same direction.

[0130] The calculations of the thicknesses of the semi-reflective layer 120 and the diffraction layer 130 to form a resonant network, is within the reach of a person skilled in the art.

[0131] Furthermore, according to the invention, and regardless of the configuration of the optical component 100, for each first incident ray, of first wavelength Xi and of an angle of incidence ab, the diffraction grating 131 is configured to allow the diffraction of the first incident ray from the light source 300 within the limit of the first order of diffraction, and under a diffraction angle such that a ray diffracted by said diffraction grating 131 then propagates in the substrate 110, in an angular acceptance cone of the optical fiber, in the direction of the first edge of the substrate.

[0132] More specifically, the spatial period A of the diffraction grating 131 is chosen such that the first incident ray from the light source 300 is diffracted in the limit of the first order of diffraction. To obtain a ray diffracted in the limit of the first order of diffraction by the diffraction grating 131, the spatial period of said diffraction grating is advantageously chosen to be on the order of the first wavelength Xi of the first incident beam 310.

[0133] The spatial period A of the diffraction grating 131 is chosen such that the diffracted rays of order 1 can be refracted into the substrate.

[0134] The previously described arc-shaped diffraction grating 131 advantageously allows the rays diffracted by the diffraction grating 131 to converge towards the first end face 230 of the optical fiber 200, passing through the beam splitter element, as illustrated in [Fig.2].

[0135] Thus, the optical component 100 advantageously allows a maximum of the rays from the first incident beam 310 coming from the light source 300 to be collected, deflected and injected into the optical fiber 200, after passing through the beam splitter element, as illustrated in [Fig.2].

[0136] The light source 300 is arranged with respect to the first face of the substrate such that a maximum of the rays of the first incident beam 310 enter the substrate, from the first face 113 of the substrate 110, and pass through said substrate in order to be diffracted by the diffraction grating 131 and then transmitted in the optical fiber 200.

[0137] Such an arrangement of the optical component 100, 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, after passing through the beam splitter element.

[0138] As an example of dimensioning, the ratio between the total thickness of the three layers 120, 130 and 140 of the optical component 100 and the thickness of the substrate 110 of the optical component 100 is 1 to 400. The thickness of optical component 100 is on the order of the thickness of the fiber positioning substrate 52.

[0139] By way of illustration only, Figures 10 and 11 show an example of the trajectory of a ray of the first incident beam in the optical component for both configurations of the optical component. Only a ray 10 of the first incident beam 310 is shown for clarity. In this instance, and without limitation, the ray shown 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 ([Fig. 10])#

[0140] When the ray 10 reaches the first face 113 of the substrate 110, at an angle of incidence ai, the ray 10 generates a refracted ray 11 propagating in the substrate 110. Said ray also generates a reflected ray, not shown in [Fig.10].

[0141] When the refracted ray 11 reaches the second face 114 of the substrate 110, the refracted ray 11 generates: - a refracted ray 12 propagating in the semi-reflective layer 120, - a reflected ray 13 in the substrate 110.

[0142] The refracted ray 12 propagates through the semi-reflective layer 120 and reaches the diffraction grating 131. The refracted ray 12 then generates: - a diffracted ray 14 according to the first order of diffraction, - a reflected ray 15.

[0143] The diffracted ray 14 propagates in the semi-reflective layer 120 and is then refracted in the substrate 110 and travels towards the first lateral edge 103 of the optical component 100, passes through the beam splitter element 60, the first end face 230 of the optical fiber 200, and is then transmitted in the optical fiber 200 along a propagation direction 16. Since the refractive index of the substrate 110 of the optical component 100 and that of the beam splitter element 60 are substantially equal to that of the core 210 of the optical fiber 200, the diffracted ray 14 propagating in the substrate 110 then propagates in the beam splitter element 60, and then in the optical fiber 200, without refraction and without loss by reflection.

[0144] The reflected ray 15 propagates in the semi-reflective layer 120 and then, when it reaches the second face 114 of the substrate 110, generates a refracted ray 17 in the substrate 110. The refracted ray 17 propagates in the same direction of propagation as the reflected ray 13.

[0145] The reflected ray 15 is also reflected by the second face 114 of the substrate 110 towards the diffraction grating 131.

[0146] The various characteristic parameters (thicknesses, refractive index of the layers) of the optical component 100 according to the invention being determined so that the phase shift between the reflected ray 13 and the refracted ray 17 (coming from the reflected ray 15) is substantially equal to II and that these two rays 13, 17 propagate in the same direction of propagation, there then results in a destructive interference between these two rays 13, 17, decreasing the luminous intensity propagating along the direction of reflection, and consequently increasing the luminous intensity of the diffracted ray 14 propagating along the direction of propagation 16 towards the beam splitter element and then the optical fiber.

[0147] The optical component 100 thus forms a resonant array, by repeating the process of destructive interference of the different rays reflected in the substrate 110, and further enhancing the light intensity of the diffracted rays propagating along the propagation direction 16 towards the optical fiber. a. Second configuration of the optical component ([Fig. 11])#

[0148] When the ray 20 reaches the first 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.11].

[0149] When the refracted ray 21 reaches the second face 114 of the substrate 110 and the diffraction grating 131, the refracted ray 21 generates: - a diffracted ray 22 according to the first order of diffraction, - a refracted ray 24 propagating in the semi-reflective layer 120, - a reflected ray 23 in the substrate 110.

[0150] The diffracted ray 22 propagates in the substrate 110 and travels towards the first lateral edge 103 of the optical component, passes through the beam splitter element 60, the first end face 230 of the optical fiber 200, and is then transmitted in the optical fiber 200 along a propagation direction 30. Since the refractive index of the substrate 110 and that of the beam splitter element 60 are substantially equal to that of the core of the optical fiber 200, the diffracted ray 22 is transmitted in the optical fiber 200 without refraction and without loss by reflection.

[0151] The refracted ray 24 propagates through the semi-reflective layer 120 and reaches the reflective layer 140. The refracted ray 24 generates a reflected ray 25. The reflected ray 25 propagates through the semi-reflective layer 120 and then generates, upon reaching the diffraction grating 131: - a diffracted ray 28, according to the first order of diffraction, - a refracted ray 27 in the substrate 110, - a reflected ray 26 in the semi-reflective layer 120.

[0152] The diffracted ray 28 propagates in the substrate 110 and travels towards the first lateral edge 103 of the optical component 100, passes through the beam splitter element 60, the first end face 230 of the optical fiber 200, and is then transmitted in the optical fiber 200 along the same propagation direction 30 as the diffracted ray 22.

[0153] The refracted ray 27 propagates in the same direction of propagation as the reflected ray 23.

[0154] The various characteristic parameters (thicknesses, refractive index of the layers) of the optical component 100 according to the invention being determined such that the phase shift between the reflected ray 23 and the refracted ray 27 (originating from the reflected ray 25) is substantially equal to II and that these two rays 23, 27 propagate in the same direction of propagation, a destructive interference then results between these two rays 23, 27, reducing the light intensity propagating along the direction of reflection, and consequently increasing the light intensity of the diffracted rays 22, 28 propagating along the direction of propagation 30 towards the optical fiber 200.

[0155] The optical component 100 thus forms a resonant network, by repeating the process of destructive interference of the different rays reflected in the substrate of the optical component, and further strengthening the luminous intensity of the diffracted rays propagating along the direction of propagation 30 towards the optical fiber 200.

[0156] All the constituent elements of said optical assembly 50, and where applicable the lens 90, are advantageously held in place relative to each other, for example by gluing. The glue used to hold the various elements together, in particular the holding of the optical fiber 200 in the longitudinal groove 80, the holding of the fiber positioning substrate 52 against the support 51, the holding of the cover plate 53 against the fiber positioning substrate 52, the holding of the beam splitter element 60 and the optical component 100 in the housing of the fiber positioning substrate 52 and against the support 51, is, for example, of the same refractive index as that of the optical cladding 220 of the optical fiber 200.

[0157] Furthermore, since the materials of the support 51, the fiber positioning substrate 52 and the cover plate 53 are transparent, their assembly can advantageously be carried out using an adhesive suitable for polymerizing with light radiation in the ultraviolet, for example within the range of 300nm to 400nm.

[0158] Second embodiment of the optical assembly

[0159] An optical assembly 50 according to a second embodiment is described in relation to figures 5 to 7.

[0160] In this second embodiment, the optical assembly 50 comprises all the constituent elements of the optical assembly according to the first embodiment. The differences between the two embodiments relate to the beam splitter element 60 and the geometric shape of the optical component 100. In this second embodiment, the beam splitter element 60 is not a separate part as such. The beam splitter element 60 is in the form of a dichroic filter affixed to the first lateral edge 103 of the optical component. As with the first embodiment of the optical assembly 50, the beam splitter element 60, in the form of a dichroic filter, is configured to: - allow the first incident beam 310 from the light source 300, and from the optical component 100, to pass towards the optical fiber 200, and - reflect the second incident beam 410 from the optical fiber 200 towards the photodetector 400.

[0161] The dichroic filter 60 is configured to direct the second incident beam 410 out of the optical component 110, in a direction substantially perpendicular to the optical axis 240 of the optical fiber 200 towards the photodetector 400, as illustrated in [Fig. 6]. The dichroic filter 60 advantageously provides an angle reflection of substantially 90° towards the photodetector 400. The dichroic filter 60 behaves transparently for the first incident beam 310 and allows the first incident beam 310 from the light source 300 to pass through to the optical fiber 200.

[0162] The first lateral edge 103 of the optical component 100 has an angle substantially equal to 45° with respect to the optical axis 240 of the optical fiber 200, as illustrated in [Fig.6].

[0163] The first lateral edge 103 of the optical component 100 is partially attached to the first end face 230 of the optical fiber 200, as illustrated in [Fig.6].

[0164] The remainder of the description associated with the various constituent elements of the optical assembly 50 according to the first embodiment, their characteristics and the mode of operation of the optical assembly also apply to the second embodiment.

[0165] The various examples and variants according to the first embodiment of the optical assembly 50 can also be applied to the second embodiment.

[0166] In an alternative embodiment of the second embodiment of the optical assembly, illustrated in [Fig.7], the first end face 230 of the optical fiber 200 is inclined at an angle substantially equal to 45° with respect to the optical axis 240 of said optical fiber, such that the entire first end face of the optical fiber is in contact with the dichroic filter of the optical component. Method for manufacturing optical assembly

[0167] A method for manufacturing an optical assembly 50 is now described, by way of non-limiting example. The method will be described in the case of the first embodiment of the optical assembly.

[0168] The fiber positioning substrate 52 is positioned on the support 51.

[0169] The fiber positioning substrate 52 has been prepared beforehand. The housing, In particular, its shape is achieved, for example, by classic micromachining techniques.

[0170] The fiber positioning substrate 52 is positioned on the support 51 so that its first main face 521 is placed against the main face 511 of the support 51.

[0171] The fiber positioning substrate 52 is held in place on the support 51 for example by gluing.

[0172] Preferably, the fiber positioning substrate 52 and the support 51 being made of transparent material, the adhesive used can be an adhesive suitable for polymerizing with light radiation in the ultraviolet.

[0173] Once the fiber positioning substrate 52 is positioned on the support 51, the longitudinal groove 80 is made in the fiber positioning substrate 52 and the support 51.

[0174] The longitudinal groove 80, in particular its shape and depth, is produced for example by conventional micromachining techniques, or by laser engraving or by means of a diamond saw.

[0175] Once the longitudinal groove 80 has been made, the beam splitter element 60 and the optical component 100 are positioned in the housing of the fiber positioning substrate 52.

[0176] The beam splitter element 60 is first positioned in the housing until it abuts against the lateral edge 523 of the fiber positioning substrate. Then the optical component 100 is positioned in the housing until it abuts against the lateral edge 523 of the fiber positioning substrate 52 and the beam splitter element 60.

[0177] More specifically, the beam splitter element 60 is positioned in the housing until its longitudinal edges 64 come abutting against the lateral walls of the lateral edge 523 of the fiber positioning substrate 52. Then the optical component 100 is positioned in the housing until its longitudinal edges 105 come abutting against the lateral walls of the lateral edge 523 of the fiber positioning substrate 52 and its first lateral edge 103 comes abutting against the second edge 63 of the beam splitter element 60.

[0178] The beam splitter element 60 and the optical component 100 are held in place in the housing and on the support, for example by gluing.

[0179] Next, the optical fiber 200 is positioned in the longitudinal groove 80.

[0180] The optical fiber 200 is arranged in the longitudinal groove 80 so that the first end face 230 of the optical fiber 200 comes against the first edge 62 of the beam splitter element 60.

[0181] The optical fiber 200 is held in place in the longitudinal groove 80 for example by gluing.

[0182] Once the optical fiber 200 is positioned in the longitudinal groove, the cover plate 53 is positioned.

[0183] The cover plate 53 is arranged in the assembly so as to rest only on the second main face 522 of the fiber positioning substrate 52, covering the optical fiber 200 in the longitudinal groove 80.

[0184] The cover plate 53 is held in place on the fiber positioning substrate 52, for example, by adhesive. Preferably, since the fiber positioning substrate 52 and the cover plate 53 are made of transparent material, the adhesive used can be one suitable for curing with ultraviolet light.

[0185] When the optical assembly is carried out according to the second embodiment, the embodiment process differs in that the step of positioning the beam splitter element 60 and the optical component 100 in the housing of the optical component consists only of a step of positioning the optical component 100 in the housing of the fiber positioning substrate 52.

[0186] The optical component 100 is prepared beforehand. The first lateral edge 103 of the optical component is polished to achieve an inclination angle of approximately 45°. The overall shape of the optical component and the polishing of the first lateral edge are achieved, for example, by conventional micromachining techniques.

[0187] The optical component 100 is positioned in the housing until it comes against the lateral edge 523 of the fiber positioning substrate 52.

[0188] More specifically, the optical component 100 is positioned in the housing until its longitudinal edges 105 come into contact with the lateral walls of the lateral edge 523 of the fiber positioning substrate 52.

[0189] The optical component 100 is held in place in the housing and on the support, for example by gluing.

[0190] The optical fiber is then positioned in the longitudinal groove 80 so that its first end face 230 comes against the first lateral edge 103 of the optical component 100.

[0191] The invention thus proposes a compact optical assembly that advantageously enables the bidirectional transmission of optical signals, via light beams, from a light source to a photodetector, both arranged in a direction substantially perpendicular to the optical axis of the optical fiber, with optimal coupling. The optical assembly is configured to ensure self-centering of the beam splitter element and the optical component with respect to the optical fiber to guarantee efficient bidirectional transfer. The optical assembly eliminates the need for a dynamic alignment step between the beam splitter element, the optical component, the optical fiber, the light source, and the photodetector.

[0192] The use of a compact and substantially flat optical assembly allows its installation in environments constrained in terms of volume or dimension, such as in aircraft.

[0193] Thus, in a preferred application, the optical assembly 70 is arranged in an aircraft. The optical assembly is located in an aircraft cabin positioned above a passenger seat. The light source and the photodetector are located in the passenger seat.

[0194] The optical assembly 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 a reading light on / off.

[0195] The optical assembly can advantageously be used for data transmission via Li-Fi (Light Fidelity) technology. The light source 300 of the optical assembly 70 is thus configured to emit the first incident beam 310 with the first wavelength Xi located in the infrared range. By infrared range, we mean the range of wavelengths between 780 nm and 2 pm. The photodetector is, for its part, configured to detect the second incident beam with the second wavelength also located in the infrared range.

Claims

1. Demands Optical assembly (50) comprising: - an optical fiber (200), comprising an optical axis (240) and a core (210) of refractive index nc and diameter dc, - a basic substrate, called support (51), - a substrate called a fiber positioning substrate (52), - a beam splitter element (60), - an optical component forming a resonant grating, called optical component (100), - a cover plate (53), the fiber positioning substrate (52) resting on a main face (511) of said support (51) and comprising a lateral edge (523) having a hollow profile forming a housing for receiving the beam splitter element (60) and the optical component (100), a longitudinal groove (80) being made in the fiber positioning substrate (52) and the support (51) and opening into the housing of said fiber positioning substrate, said longitudinal groove being dimensioned to receive the optical fiber (200), the optical fiber (200) being positioned in the optical assembly (50) such that a first end face (230) of the optical fiber (200) is opposite the beam splitter element (60), the cover plate (53) resting on the fiber positioning substrate and pressing the optical fiber into the longitudinal groove, the optical component (100) being configured to receive a light beam, called the first incident beam (310), coming from a direction substantially perpendicular to the optical axis (240) of the optical fiber (200), and to transmit this first incident beam (310) to the optical fiber (200), via the beam splitter element (60), the beam splitter element (60) being configured for: - allow the first incident beam (310) to pass towards the optical fiber (200), - transmit a light beam, called the second incident beam (410), coming from the optical fiber (200) out of the optical assembly, in a direction substantially perpendicular to the optical axis (240) of the optical fiber (200), characterized in that the optical component (100) comprises a stack including: - a substrate (110) with a refractive index ns substantially equal to the refractive index nc of the optical fiber core and a thickness es less than or equal to the diameter dc of the fiber core (200), said substrate having two faces, called first (113) and second (114) faces, - a semi-reflective layer (120) with a refractive index nsr greater than the refractive index ns of the substrate, and of thickness esr, - a diffraction layer (130), of thickness ed, comprising, throughout its thickness, a diffraction grating (131) of period A, - a reflective layer (140), the reflective layer (140) resting on the main face (511) of the support (51), the semi-reflective layer (120) and the diffraction layer (130) being disposed between the substrate (110) and the reflective layer (140), the semi-reflective layer (120) being disposed between the substrate (110) and the diffraction layer (130) or between the diffraction layer (130) and the reflective layer (140), for a first incident ray of the first incident beam (310), having a first given wavelength Xi and arriving on the first face (113) of the substrate (110) with a predetermined angle of incidence ai and defined relative to a direction normal to said first face of the substrate (110): - the thicknesses of the semi-reflective layer (120) and the diffraction layer (130) are determined to generate destructive interference of the reflected rays, - the diffraction grating (131) is configured to allow the diffraction of the first incident ray within the limit of the first order diffraction, and under a diffraction angle such that the diffracted ray propagates in the substrate (110), in an angular acceptance cone of the optical fiber (200), towards the beam splitter element and then towards the first face of the optical fiber.

2. Optical assembly (50) according to claim 1 in which the diffraction grating (131) is in the form of a plurality of concentric circular arcs, centered at the first end face (230) of the optical fiber (200).

3. Optical assembly (50) according to any one of the preceding claims wherein the support (51), the fiber positioning substrate (52) and the cover plate (53) are each made of a material that allows at least wavelengths in the ultraviolet to pass through.

4. Optical assembly (50) according to any one of the preceding claims wherein the beam splitter element (60) is a separate part of the optical component (100) and is disposed between the first end face (230) of the optical fiber (200) and the optical component, the beam splitter element (60) and the optical component (100) having a shape complementary to the housing of the fiber positioning substrate (52), so as to each fit in a complementary manner in the housing of said fiber positioning substrate.

5. Optical assembly (50) according to the preceding claim in which the beam splitter element is a prism splitter, for example a splitter cube.

6. An optical assembly (60) according to any one of claims 1 to 3, wherein the optical component (100) has a first lateral edge (103) having an inclination substantially equal to 45° with respect to the optical axis (240) of the optical fiber, and wherein the beam splitter element (60) is a dichroic filter attached to the first lateral edge (103) of the optical component (100), the optical component (100) having a shape complementary to the housing of the fiber positioning substrate (52), so as to fit complementaryly into the housing of said fiber positioning substrate, with the first lateral edge (103) opposite the first end face (230) of the optical fiber (200).

7. Optical assembly (50) according to the preceding claim wherein the first end face (230) of the optical fiber (200) is inclined at an angle substantially equal to 45° with respect to the optical axis (240) of said optical fiber, such that the first end face (230) of the optical fiber is attached to the dichroic filter attached to the first lateral edge (103) of the optical component (100).

8. Optical assembly (70) comprising a light source (300), a photodetector (400) and an optical assembly (50) according to any one of the preceding claims, said light source being arranged opposite the optical component and configured to emit the first incident beam, said photodetector being arranged opposite the beam splitter element so as to receive the second incident beam.

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