Adapter for coupling light from a photonic circuit

Abstract

Adapter for coupling light from a photonic circuit. This description relates to an optical adapter (100) intended to serve as an interface on an integrated optical circuit (101) to produce a broadened beam of light (108) and thus facilitate coupling with optical fibers (509) and / or an optical connector (505). The optical adapter (100) has a plane mirror on its upper face and a converging mirror on its lower face. The beam of light (108) propagates, broadening between the integrated optical circuit (101) and the converging mirror inside the transparent optical adapter (100), the path being folded by the upper plane mirror. Figure for the abstract: Fig. 5

Description

Title of the invention: Adapter for coupling light from a photonic circuit. Technical field

[0001] This description relates generally to the field of integrated optical circuits, also called photonic integrated circuits (PICs), and more particularly to the coupling of light, or optical coupling, between an integrated optical circuit and one or more optical fibers. Prior art

[0002] Integrated optical circuits, particularly silicon photonic circuits, can combine numerous functions on a single chip. This offers an advantage, especially in terms of reduced size and optical losses, compared to assemblies made by assembling discrete components. In integrated photonic circuits, light is conducted in small optical waveguides, typically less than a micrometer wide, which allows for dense circuits. Integrated optical circuits communicate by exchanging light with external systems, with the coupling of this light achieved by attempting to limit optical losses. The problem of optical coupling is particularly critical in the case of single-mode optical beams, intended, for example, to be coupled in single-mode optical fibers, due to the small diameter of the light beams involved.

[0003] In an integrated optical circuit, the coupling interfaces of optical guides are generally of two types: 1) Vertical grating couplers (VGCs) that operate by diffracting light on a periodic structure at the end of an optical waveguide to direct light upwards on the chip, specifically at an angle close to the chip's vertical, for example, an angle of 8° (the angle considered in a medium with a refractive index equal to that of silica glass). The coupling gratings allow the formation of a light beam with a diameter on the order of tens of micrometers, which is suitable for the single-mode optical fibers commonly used for optical communications; and 2) Edge couplers, typically located at the edge of the circuit, consist of an optical waveguide that terminates at the chip edge, with the light exiting along the extension of the waveguide. The terminal portion of the waveguide may also have a structure that widens the optical mode before it exits the chip. The size of The beam size is typically between two and ten micrometers. A variant of edge coupling may include a cavity, such as a well, formed in the top surface of the circuit to provide access to an output of the optical guide. A mirror located in the cavity opposite the end of the optical guide then extracts the light by reflecting it off the plane of the chip, typically in a near-vertical direction.

[0004] The two types of interfaces mentioned above make it possible to form single-mode light beams with a maximum diameter close to ten micrometers. In this case, direct coupling with optical fibers is possible, but the beam diameter remains small, requiring the optical fibers to be positioned with a positioning accuracy of less than ±2 pm to obtain an acceptable coupling ratio. This positioning accuracy is difficult to achieve and requires the use of dedicated, expensive, and slow machines.To facilitate coupling and increase positioning tolerance, it is desirable to widen the diameter of the light beam exiting the integrated optical circuit to several tens of micrometers, for example about 50 pm, which allows the positioning tolerance to be relaxed to plus or minus 10 pm and consequently makes assembly less delicate, thus allowing the use of less expensive and faster machines.

[0005] Several techniques have been proposed for coupling light between an integrated optical circuit and optical fibers with an expanded beam diameter. In all cases, a sufficiently long optical path is considered so that the light beam can expand to reach the desired size. The different techniques are distinguished by the optical scheme used and by the portion of the optical path over which the beam expands.

[0006] Furthermore, edge-coupling involves attaching the optical fiber to the chip edge, which is mechanically fragile. To avoid this drawback and attach the fiber to the top surface of the chip while maintaining an optical configuration similar to edge-coupling, a cavity can be formed from the top surface of the chip. This cavity has a vertical wall in front of the end of the optical guide, so that the beam exiting the optical guide passes through this wall and enters the cavity. Inside the cavity, a reflecting mirror is arranged to intercept the beam and deflect it upwards, causing it to exit through the top surface of the chip in a near-vertical direction. Manufacturing this reflecting mirror can be done using various techniques and presents an industrial challenge.

[0007] US patents US 9817193, US 10209442, US 10459163 and US 10690848 and French patent FR 3066615 describe integrated optical circuits where Beam expansion is achieved within the thickness of the chip substrate, where the back side of the chip incorporates an optical function, either a lens or a mirror. This solution allows the beam expansion function to be integrated inside the chip without additional components. However, a drawback is that, to traverse the chip thickness between the beam guide area and the back side of the substrate, the light must pass through the interface between the silica and the silicon. The significant refractive index contrast between these materials means that a considerable portion of the light, approximately 15%, is reflected at the interface and lost. For technological reasons, it is difficult and expensive to place an antireflective coating at this location. Another disadvantage is that the desired optical function (lens or mirror, as applicable) is implemented on the back side of the chips.However, carrying out processes on the back side implies a higher manufacturing cost because the front side must be protected and then unprotected afterwards. Another drawback is that the substrate thickness cannot be chosen independently of the desired mode diameter, because it is the path length in the substrate that determines the size of the emitted mode, the broadening being determined by the natural diffraction of the beam.

[0008] French patent application FR 3050832, previously filed by the applicant, describes an optical element that allows the beam to be extracted from a cavity, in the case of edge coupling, using a reflector acting as a turning mirror. However, the optical element described in the aforementioned application does not have the function of widening the light beam.

[0009] French patent FR 3124001, previously granted to the applicant, describes an integrated optical circuit surmounted by a transparent chip in which the beam propagates while being broadened. The transparent chip has a plane mirror on its upper surface that allows the beam to be folded back towards a collimating mirror fabricated on the integrated optical circuit, to produce a broadened beam of light. The advantage of this solution is that the positioning tolerance of the transparent chip is relaxed compared to the ±2 pm required for direct coupling to optical fibers. In the case of edge coupling, this patent FR 3124001 describes the possibility of fabricating a reflecting mirror in the optical circuit opposite the output of the waveguide.However, manufacturing a reflecting mirror within the optical circuit, for example at the bottom of a cavity, can prove challenging, and manufacturers of integrated optical circuits may choose not to incorporate such a mirror into their manufacturing process.

[0010] US patent application US 2023 / 025139 filed by Teramount describes an optical scheme comprising a first optical element focusing light onto an optical fiber, and a second optical element focusing light into the optical port of an integrated optical circuit. This system makes it possible to establish a connection between the fiber and the optical circuit, benefiting from a relaxed positioning tolerance. Indeed, as described in relation to Figures 4A and 4B of the aforementioned application, a displacement of the upper block is compensated by a variation in the inclination of the rays between the first and second optical elements. For example, a displacement of the upper block to the right is compensated by an inclination of the rays that approaches the horizontal. This optical scheme requires two focusing optical elements. Furthermore, it is not intended to produce a broadened and collimated beam of light exiting the device upwards. Summary of the invention

[0011] There is a need to overcome all or part of the disadvantages of existing optical coupling devices between an optical circuit and one or more optical fibers.

[0012] To this end, one embodiment provides an optical adapter comprising: - a transparent region; - a converging mirror located on the side of a first face of the transparent region and turned towards a second face of the transparent region, opposite the first face; - a first flat mirror located on the side of the second face of the transparent region and turned towards the first face; - a first optical port located on the side of the first face and intended to be positioned opposite one end of a waveguide of an integrated optical circuit; and - a second optical port located on the side of the second face, the optical adapter being intended to ensure propagation of a light beam between said end of the waveguide and the second optical port, the first plane mirror and the converging mirror being arranged so that the light beam propagates between the first and second optical ports, through the transparent region, by reflection on the first plane mirror and on the converging mirror, the light beam having, at the level of the second optical port, a size greater than that which it has at the level of the first optical port.

[0013] According to one embodiment, the adapter further comprises a second plane mirror located on a part of the transparent region protruding from its first face, said part being intended to be inserted into a cavity of the integrated optical circuit.

[0014] According to one embodiment, the adapter is devoid of optical elements other than the transparent region, the first plane mirror and the converging mirror.

[0015] According to one embodiment, the transparent region further includes at least one mechanical positioning element of the adapter relative to the integrated optical circuit.

[0016] According to one embodiment, at least one mechanical positioning element forms a projection from the first face of the transparent region.

[0017] According to one embodiment, at least one mechanical positioning element includes at least one pad without optical function intended to bear against the integrated optical circuit.

[0018] According to one embodiment, said at least one mechanical positioning element further comprises at least one finger without optical function and intended to be inserted into a cavity of the integrated optical circuit.

[0019] According to one embodiment, the first and second optical ports are respectively adapted to receive and emit the light beam.

[0020] According to one embodiment, the first face of the transparent region is parallel to its second face, the first plane mirror being parallel to the second face.

[0021] According to one embodiment, the second optical port is intended to be positioned opposite an optical connector into which one end of an optical fiber terminates.

[0022] One embodiment provides an optical device comprising an integrated optical circuit and the optical adapter as described, the optical adapter being mechanically attached to the integrated optical circuit.

[0023] According to one embodiment, the optical adapter is fixed to the integrated optical circuit by a layer of optically transparent glue.

[0024] According to one embodiment, the device further comprises at least one optical connector positioned opposite the second optical port and into which the end of an optical fiber terminates. Brief description of the drawings

[0025] These features and advantages, as well as others, will be described in detail in the following description of particular embodiments, given by way of non-limiting example, in relation to the accompanying figures, among which:

[0026] [Fig.1] is a schematic and partial side and sectional view of an optical adapter assembled to an integrated optical circuit according to one embodiment, with an indication of the geometric notations used in the description;

[0027] [Fig.2] is a detailed view of the assembly of [Fig.1], at the level of a beam sampling area in a cavity;

[0028] [Fig.3] is a schematic and partial side and cross-sectional view of a variant of the optical adapter of [Fig.1], comprising supports;

[0029] [Fig.4] is a schematic and partial side and sectional view of another variant of the optical adapter of [Fig.1], comprising a curved mirror and a positioning element;

[0030] [Fig. 5] is a schematic and partial side and cross-sectional view of an optical device according to one embodiment, notably showing the use of an optical microconnector; and

[0031] [Fig.6] is a schematic and partial side and sectional view of a variant of the integrated optical circuit and optical adapter, in the case of a beam coupled to a vertical coupling array. Description of the implementation methods

[0032] The same elements have been designated by the same reference numerals in the different figures. In particular, the structural and / or functional elements common to the different embodiments may have the same reference numerals and may have identical structural, dimensional and material properties.

[0033] For the sake of clarity, only the steps and elements useful for understanding the described embodiments have been shown and are detailed. In particular, applications implementing integrated optical circuits and optical devices comprising such circuits have not been detailed, as the described embodiments are compatible with all or most applications implementing integrated optical circuits and optical devices comprising such circuits, possibly with adaptations within the grasp of a person skilled in the art upon reading this description.

[0034] Unless otherwise specified, when referring to two elements connected together, this means directly connected without intermediate elements other than conductors, and when referring to two elements coupled together, this means that these two elements can be connected or linked through one or more other elements.

[0035] In the following description, when reference is made to absolute position qualifiers, such as the terms "front", "back", "top", "bottom", "left", "right", etc., or relative position qualifiers, such as the terms "above", "below", "superior", "inferior", etc., or to orientation qualifiers, such as the terms "horizontal", "vertical", etc., reference is made, unless otherwise specified, to the orientation of the figures.

[0036] Unless otherwise specified, the expressions "approximately", "about", "substantially", and "in the order of" mean to within 10% or 10°, preferably to within 5% or 5°.

[0037] Unless otherwise specified, the expression "in contact with" means "in mechanical contact with".

[0038] The [Fig.1] is a schematic and partial side and sectional view of an optical adapter 100 assembled to an integrated optical circuit 101, also called an integrated photonic circuit 101 or photonic chip 101, according to one embodiment.

[0039] The integrated optical circuit 101 is, for example, a silicon-based photonic circuit, that is, an optical circuit formed on a silicon substrate 103. Alternatively, the substrate 103 may be made of a material other than silicon, for example, a III-V semiconductor material, silicon carbide, etc.

[0040] The integrated optical circuit 101 can implement one or more elementary functions (not detailed in the figures), chosen for example from: - an electro-optical light modulation function; - a photodetection function, for example using a photodiode; - a wavelength filtering function; - an optical routing function; and - an electrical conduction function.

[0041] In the example shown, the elementary function(s) are implemented by one or more elementary components formed in a transparent region 105 located on the surface of the integrated optical circuit 101. The transparent region 105 can be homogeneous, i.e., made of a single transparent material, or inhomogeneous, i.e., made of several different transparent materials, possibly including cavities or air pockets. The concept of transparency is considered at a working wavelength Xo of the integrated optical circuit 101. The material(s) of the transparent region 105 are, for example, chosen from silica glass, silicon nitride, polymers transparent at the working wavelength Xo, etc.

[0042] The elementary optical components are, for example, connected to each other by one or more optical guides typically comprising a central region, or optical core, surrounded by a peripheral region, or optical cladding, the peripheral region having a refractive index strictly lower than that of the central region. By way of example, the central region is made of silicon or silicon nitride and the peripheral region is made of silica glass. By way of alternative, other types of optical circuits 101 are conceivable, for example circuits comprising optical guides made of IILV semiconductor material.

[0043] An optical link between the integrated optical circuit 101 and the outside of the circuit is made using at least one vertical optical coupler with a diffraction grating and / or at least one edge optical coupler.

[0044] Figure 1 illustrates more particularly the case of edge coupling. By way of example, the mode diameter can advantageously be enlarged by transferring the light into a thin silicon nitride waveguide, for which the mode diameter di is, for example, about 9.0 pm. In the case of a single-mode beam, the term "mode diameter" means a diameter for which the intensity The light intensity is reduced by a factor of 1 / e², where "e" represents the exponential function, relative to the center of the beam. The beam is, for example, Gaussian in shape.

[0045] The transparent region 105 has, for example, a thickness chosen so as to completely contain the optical mode of the coupler. As an example, the beam axis is located at a depth hi equal to approximately 7.0 pm below the top surface of the integrated optical circuit. A cavity 107 is formed, for example, in front of the coupler edge-on to allow access to and collection of the beam. The cavity 107 has, for example, a depth h'i below the beam axis equal to approximately 7.0 pm. Pi is denoted as a point at the center of the beam at the edge-on end of the coupler, from which the light begins to diverge.

[0046] The optical adapter 100 is assembled on the optical circuit 101 and makes it possible to produce an enlarged and collimated beam of light 108 directed upwards, in the orientation of [Fig. 1]. In [Fig. 1], the beam 108 has an optical axis symbolized by a solid line and an envelope symbolized by two dashed lines located on either side of the optical axis of the beam 108. In the illustrated example, the adapter includes a sampling mirror 109 intended to be inserted into the cavity 107 to sample the beam exiting the coupler edge-on and orient it in a direction close to the vertical. The mirror 109 is, in this example, a plane mirror. In [Fig.[l] Let Mi be the point of intersection of the surface of mirror 109 with the optical axis of the beam 108 from the coupler, and consider an orientation of mirror 109 such that the optical axis PiMi, initially horizontal, is, after reflection on mirror 109, oriented at an angle 0 equal to approximately 16.0° with respect to the vertical. To obtain the angle 0, the sampling mirror 109 is inclined at an angle 0i equal to 45° - 0 / 2, that is to say, equal, in this example, to approximately 37.0°.

[0047] The mechanical and optical assembly of the adapter 100 onto the circuit 101 is, for example, achieved using a transparent optical adhesive. The adhesive preferably has a refractive index close to that of the transparent region 105, in order to limit unwanted reflections at the interfaces between the materials.

[0048] Furthermore, the adapter 100 is advantageously made of transparent materials having a refractive index close to that of the material of the transparent region 105, for example, silica glass. In the following description, for simplicity, the refractive indices seen by the light beam 108 are assumed to be all equal to that of silica glass. However, in practice, materials with different refractive indices can be used, taking into account the angles of refraction and the losses due to stray reflections at the interfaces. Optical simulation software tools, such as the software known by the trade name "Zemax," can, for example, be used for this purpose.

[0049] According to one embodiment, the optical adapter 100 comprises a transparent region 111, a converging mirror 113, for example a concave mirror, located on the side of a first face 11 IB of the transparent region 111 (the lower face of the region 111, in the orientation of [Fig. 1]) and a plane mirror 115 located on the side of a second face 111T of the transparent region 111 (the upper face of the region 111, in the orientation of [Fig. 1]) opposite the face 11 IB. The plane mirror 115 and converging mirror 113 are arranged so that the beam 108 is reflected towards the face 11 IB by the plane mirror 115 and then reflected and collimated by the converging mirror 113 in the direction of the face 111T. We denote M2 the point of intersection of the optical axis of the beam 108 with the plane mirror 115 on the face 111T and M3 the point of intersection of the optical axis with the surface of the converging mirror 113.Between the coupler's edge exit and the converging mirror 113, the beam widens along its path over a total length L equal to PiMi + MiM2 + M2M3. .

[0050] The converging mirror 113 allows the beam 108 to be reflected and collimated. It also allows the inclination of the optical axis to be modified if it is manufactured so that the surface of the converging mirror 113 forms, with respect to the horizontal, an angle θ3 at point M3. The converging mirror is then said to be inclined at an angle θ3. In the example shown, we wish to obtain a beam directed perpendicularly to the face 111T. For this, we choose, for example, an inclination given by θ3 = 0 / 2 = 8.0°.

[0051] After reflection on the converging mirror 113, the collimated light beam exits the adapter 100 through its upper face. P2 denotes the point where the optical axis of the beam from the converging mirror intersects the face 111T of the adapter 100.

[0052] In the external optical medium, located above the adapter 100, P3 denotes the position of the center of the neck of the Gaussian beam 108 and d3 its diameter measured perpendicular to the optical axis. In the example shown, the optical medium above the adapter 100 is air. If the incident beam M3P2 is not perpendicular to the face 111T, then the refracted beam directed along the optical axis P2P3 undergoes a change of direction upon passing through this surface. In the illustrated example, the inclination of the converging mirror 113 is chosen to orient the beam perpendicular to the upper face 111T of the adapter 100, so that the optical axis remains perpendicular to this surface in the output medium above the adapter 100.Furthermore, referring to the concept of real and virtual images in optics, we can say that point P3 is a real image in the output medium if it is located above face 111T, and that it is a virtual image in the output medium if it is located below face 111T. In the embodiment shown in [Fig. 1], point P3 is a real image.

[0053] In the example shown, the adapter 100 has a first optical port 117, or light port 117, located on the side of face 11 IB and a second optical port 119 located on the side of face 111T. The optical port 117, called the lower optical port or light port, is defined by the surface centered on point Pi which propagates the beam 108 of diameter dp. The optical port 119, called the upper optical port or light port, is defined by the surface centered on point P3 which propagates the beam 108 of diameter d3. The adapter 100 ensures the propagation of the light beam 108 between the lower light port 117 and the upper light port 119. Propagation can occur from the lower port 117 to the upper port 119 or from the upper port 119 to the lower port 117 with the same beam shape, according to the principle of reverse light propagation.As an example, the upper port 119 has a diameter d3 at least five times greater than the diameter dH, for example, approximately 50 µm. This diameter is compatible with commercially available pluggable optical micro-connectors.

[0054] By way of example, the adapter 100 is manufactured on a silica glass wafer by implementing the following successive steps: a) manufacturing of the flat mirror 115 by photolithography then engraving of a metallic layer, for example in aluminium; b) protection of the plane mirror 115 by a layer of silica; c) turning the plate over and gluing it onto a temporary transfer substrate, or handle; d) thinning and polishing of the plate then creation of the three-dimensional shapes defining the converging mirror 113 and the sampling mirror 109; e) metallization of the surfaces of mirrors 113 and 109, for example by depositing a layer of aluminum on the side of face 11 IB followed by photolithography operations and then etching of this layer; and f) turning the wafer over on a soft adhesive support, removing the temporary transfer substrate and cutting the wafer into chips, each forming an optical adapter 100.

[0055] The technique used to define the three-dimensional shapes of the converging mirror 113 and the sampling mirror 109 is, for example, grayscale photolithography in a photosensitive resin, followed, for example, by transfer etching in silica glass. Alternatively, it is lithography employing a technique known as "Nano-Imprint Lithography" using a three-dimensional mold. Alternatively, it is direct laser etching followed by wet etching, a technique known as "Selective Laser Etching."

[0056] The assembly of the adapter 100 onto the integrated optical circuit 101 is, for example, carried out using chip transfer equipment, for example, of the "pick-and-place" type, and an optically transparent adhesive. An optical adhesive that polymerizes under the action of ultraviolet radiation is, for example, used to mechanically bond the assembly after it has been placed. Preferably, an adhesive is used that can subsequently withstand a temperature of around 250 °C for approximately 2 minutes, so that the assembly consisting of the optical circuit 101 and the adapter 100 can withstand passage through a solder reflow oven at 250 °C. The materials constituting the adapter 100 are preferably selected to withstand the same stresses.

[0057] An example of dimensioning is described below in relation to [Fig. 1]. This example is not, however, limiting, and other dimensioning methods are accessible to those skilled in the art from the indications in this description.

[0058] The calculations are presented for a working wavelength Xo = 1.310 pm (wavelength measured in a vacuum), but can be transposed to any other wavelength. We consider the situation where the materials traversed all have the refractive index n of silica glass at this wavelength, i.e., n = 1.447.

[0059] The lower light port 117 is considered to be centered on point Pi located at depth hi below the upper face of the integrated optical circuit 101, for example hi = 7.0 pm. The port 117 is considered to emit a circular Gaussian single-mode beam of diameter di = 9.0 pm. The Rayleigh length of this beam in a medium of refractive index n is zR = n ir (di / 2)2 / Xo - 70.3 pm. The total divergence of the beam, evaluated at 1 / e2 in intensity, is A0 di / zR 128 mrad 7.3°.

[0060] An inclination of angle 0 = 16.0° is chosen for the optical axis of the light beam 108 with respect to the vertical during its path between Mb M2 and M3.

[0061] The sampling mirror 109 is a plane mirror inclined at an angle θi = 45° - θ / 2 = 37.0°, such that the initially horizontal optical axis is reflected at an angle θ with respect to the vertical. A distance xi = 10 pm is chosen between Pi and Mb.

[0062] The adapter 100 is manufactured so that its upper face 111T is at an altitude h2 = 189.8 pm above the upper face of the integrated optical circuit 101. The plane mirror 115 which folds the light beam 108 is located on the face 111T.

[0063] The converging mirror 113 is manufactured with an inclination 03 = 0 / 2 = 8.0°, so that the optical axis of the beam 108 is perpendicular to the upper surface of the adapter along the path M3P2 after reflection. An altitude h3 = 8.3 pm above the surface of the integrated optical circuit 101 is chosen for point M3. In this case, the length of the optical path between Pi and M3 is L = PiMi + MiM2 + M2M3 = xi + (2 h2 + hi - h3) / cos(0) 403.5 pm. The horizontal distance between Mi and M2 is x2 = (h2 + hi) tan(0) 56.4 pm and that between M2 and M3 is x3 = (h2 - h3) tan(0) 52.0 pm.

[0064] A converging mirror 113 is chosen, spherically shaped with a focal length f = 394.0 pm, corresponding to a radius of curvature R = 2f - 788.0 pm. The distance, along the optical axis, between the source point Pi and the object focal point of the converging mirror is denoted by ôs, ôs = L - f = 9.5 pm. The image of the lower light port 117 formed by the converging mirror 113 in the medium above the adapter 100 has a throat with a diameter of: d3 = di f (zR2 + ôs2) 1 / 2 50.0 pm. This beam diameter of 50 pm is compatible with pluggable optical micro-connectors available from connector manufacturers. The total divergence of the beam exiting the air, estimated at 1 / e2 in intensity, is given by A03 = 4 Xo / (jt d3) 33 mrad 1.9°. We therefore obtain a wider beam, increasing from 9 to 50 pm in diameter, and a lower divergence, decreasing from 7.3 to 1.9°.

[0065] For greater precision, it can be taken into account that the light beam strikes the converging mirror 113 at an oblique angle of incidence 0 / 2 with respect to the axis of the mirror 113. Thus, as an alternative, an ellipsoidal surface of radius Ri = 2f / cos(0 / 2) in the plane of incidence (plane of [Fig. 1]) and R2 = 2f cos(0 / 2) in the sagittal plane (perpendicular to the plane of incidence and containing the optical axis) can be chosen for the mirror 113. Generally, a person skilled in the art is able to determine the ideal surface using optical design software.

[0066] In the situation described, the neck of the beam 108 seen in the silica after the converging mirror 113 is located on the optical axis after the center M3 of the mirror 113 at a distance s' = l / ( 1 / f - 1 / (L + zR2 / ôs)) 689 pm. The altitude h5 of the neck of the beam seen in air above the upper surface of the adapter is deduced: h5 = (s'- h2 + h3) / n + h2 540 pm. This value is the altitude of the upper light port 119, centered on point P3, above the upper face 111T of the adapter 100. In this case, if a micro-optical connector is assembled, it is positioned so that its light inlet coincides with the upper light port 119 of the adapter 100.

[0067] Furthermore, the overall dimensions of the geometric shapes are designed to allow the adapter 100 to be assembled onto the integrated optical circuit 101 without collisions between surfaces. For the sampling mirror 109, Wi and Hi denote respectively the width and height of the portion of the mirror 109 to the left of point Mb. Hi = 5.0 pm is chosen to leave a margin h'i - Hi = 2.0 pm between the bottom of the sampling mirror 109 and the integrated optical circuit 101. Wi = Hi / tan(0i) = 6.6 pm. For the portion of the mirror 109 to the right of point Mb, there is no geometric constraint if the cavity 107 is sufficiently wide, that is, if it is wider than xi + hi / tan(0i) = 16.6 pm. In this case, the sampling mirror 109 can be more extensive to the right of Mi than to the left. For example, a cavity 107 wider than 20 pm is chosen.

[0068] For the converging mirror 113, W3 and H3 denote respectively the width and height of the portion of the mirror 113 to the left of point M3. The diameter of the light beam 108 arriving at the converging mirror 113 is given by: d33 = di (1 + (L / zR)2 )1 / 2 - 52.5 pm. To reflect the majority of the incident beam, W3 = 1.5 d3 / 2 = 37.5 pm is chosen. Therefore, H3 = W3 tan(03) = 5.3 pm. The margin between the bottom of the converging mirror 113 and the face 11 IB of the adapter 100 is h3 - H3 = 3.0 pm, which avoids a collision with the surface 11 IB. The part of the converging mirror 113 to the right of point M3 is higher and therefore there is no risk of collision with the integrated optical circuit 101. By choosing a distance h4 = 15.0 pm between the lower surface 11 IB of the adapter 100 and the upper face of the integrated optical circuit 101, the width of the mirror 113 to the right of point M3 can be (h4-h3) / tan(03) 47.7 pm.The converging mirror 113 can therefore be more extended to the right of M3 than to the left.

[0069] Since the sampling mirror 109 is truncated at the bottom, some of the light is lost because it is not reflected. The truncation occurs at a distance xn = Xi - Wi 3.4 pm from the source point Pb, a distance at which the diameter of the light beam 108 is: du = di (1 + (xn / zR)2 )1 / 2 9.0 pm. The truncation at the distance Hi below the point Mi therefore causes an optical loss given by: Ici = 1 / 2 (1 + crlï-^2 (2 Hi) / dn)) 1.3%, where "erf" is the Gaussian error function.

[0070] Similarly, the light beam 108 arriving at the converging mirror 113 is truncated on the left at a distance W3 from point M3, causing an optical loss lc3 1 / 2 (1 + erf(-^2 (2 W3) / d33)) 0.2% (the effect of the inclination 03 of the converging mirror 113 is negligible in this calculation). Since the portion of the converging mirror 113 located to the right of M3 is larger than the portion to the left, the light loss to the right of the converging mirror 113 is smaller and is, in this case, negligible.

[0071] The folding of the light beam 108 is done by reflection on the plane mirror 115 located on the upper face 111T of the adapter 100. The optical axis intersects the plane mirror 115 at point M2 and the propagation distance between Pi and M2 is: L2 = Xi + (h2 + hi ) / cos(0) 215 pm. The diameter of beam 108 is then given by d2 = di (1 + (L2 / z R)2 y / 2 ~ 28.9 |jm. Its length in the horizontal direction is d22 = d2 / cos(0) 30.1 pm. The plane mirror 115 can be extended to the left of M2 without immediate limitation. However, it cannot be extended to the right of M2 without limitation because it would block part of the beam exiting the adapter 100 after reflection on the converging mirror 113. We then choose a width W2 = 20.5 pm for the edge of the plane mirror 115 to the right of point M2. In this situation, part of the light is not reflected by the plane mirror 115, which results in a loss lc2 = 1 / 2 (1 + erf(-^2 (2 W2) / d22)) - 0.3%. At the same time, part of the light exiting through the upper face 111T is blocked by the plane mirror 115, resulting in a loss of lc4 1 / 2 (1 + crlï-^2 (2 (x3-W2 ) / d3)) 0.6% (the diameter of the beam 108 on the upper face 111T has been approximated by d3, so as not to complicate the notations).

[0072] In total, the geometric losses mentioned amount to 3 + lc2 + lc3 + lc4 = 2.4%, which is very low for most applications. Added to this are the losses due to reflection from the mirror metal, which are on the order of 3.1% for a reflection from an aluminum surface. For three reflections, the cumulative loss is 9.3%. The use of a metal that reflects light better, such as gold or silver, makes it possible to reduce the value of these losses.

[0073] Moreover, the total footprint in the x direction to realize the whole optical system is: Xi + x2 + x3 + d3 / 2 144 pm, which is compact.

[0074] The sensitivity of the optical system to variations in the geometry of the adapter 100 and its positioning on the integrated optical circuit 101 is detailed below in relation to [Fig. 1]. An adapter 100 is considered that propagates light between the integrated optical circuit 101 and an optical micro-connector (not detailed in [Fig. 1]), and the tolerance allowing a transmission of more than 90% for each error taken individually is determined.

[0075] In the case of a translation of the adapter 100 relative to the integrated optical circuit 101, the lower optical port 117 connected to the adapter 100 shifts relative to the light port present in the integrated optical circuit 101. Depending on the shifts in the three spatial directions x, y, and z, the light transmission coefficient is given by T (1 + ôx² / (2 zR)²) exp(-4 (ôy² + ôz²) / di²). It is assumed in this expression that ôx is much smaller than zR, which is a condition easily met in practice. It follows that the positioning tolerances are ôy(90%) = ôz(90%) = 1.5 pm and ôx(90%) = 47 pm. It can be seen that the positioning is more critical in the y and z directions. Depending on the y direction, proper alignment can be aided by positioning elements such as fingers or tabs designed to fit into complementary cavities extending into the thickness of the integrated optical circuit 101 from its top face.According to the z direction, correct positioning can be ensured by supports whose height is chosen so that the lower light port 117 of the adapter 100 is at the same height as the light port of the integrated optical circuit 101.

[0076] An error in the angle 0i is mainly reflected by an inclination of the lower optical port by an angle of 2 ô0i with respect to the vertical, so that the transmission coefficient is T = exp(- 4 (2 ô01 / A0)2). From this we deduce ô0i(90 %) = 10.3 mrad = 0.59°.

[0077] An error in angle 03 can be taken into account by considering the offset ôz = 2 L Ô03 of the lower light port 117 relative to the integrated optical circuit. We have T exp(- 4 (2 L ô03 / di)2) and we deduce ô03(90%) = 1.8 mrad = 0.10°. Such precision in the fabrication of the reflecting mirror 109 is achievable, for example, by the grayscale photolithography technique, by the "Nano-Imprint Lithography" technique, or by the "Selective Laser Etching" technique.

[0078] An error in the thickness h2 of the adapter results in an offset ôz = 2 L ôh2 sin(0) of the lower light port 117 relative to the integrated optical circuit 101. We have T exp(- 4 (2 ôh2 sin(0) / di)2) and we deduce ôh2(90%) = 2.6 pm. In practice, it is possible to thin and polish a silica glass wafer by controlling the thickness with a precision better than this tolerance.

[0079] The integrated optical circuit 101 equipped with the adapter 100 according to the present invention can be used with a fiber optic connector designed to accept an enlarged beam of light. This could be, for example, a connector with microlenses at the ends of the optical fibers (available from Senko) or a ferrule that deflects the light from the optical fibers using a curved reflector, acting both as a right-angle reflector and for beam collimation (available from USConec). Depending on the geometry of the optical connector envisaged, its orientation relative to the adapter 100 and the integrated optical circuit 101 is adapted so that the optical axes are aligned.

[0080] The present invention allows the use of any type of optical connector. It is sufficient to dimension the thickness of the adapter 100 and its converging mirror 113 to produce an expanded beam with a diameter equal to the nominal mode diameter of the optical connector envisaged and positioned at the altitude required by this connector.

[0081] In summary, the adapter 100 exhibits low optical losses and can be used with various commercially available connectors, without being tied to a specific connector during the design phase other than by the diameter and position of the beam throat expected by that connector. Furthermore, the use of the optical adapter 100 simplifies the design and implementation of the integrated optical circuit 101, since the optical functions related to beam widening are integrated exclusively within the adapter 100.

[0082] Fig. 2 is a detail view of the assembly of the optical connector 100 of Fig. 1 with the integrated optical circuit 101.

[0083] In the example shown, the cavity 107 is formed in the integrated optical circuit 101 by etching the transparent region 105 down to the substrate 103, which serves as a stop layer for the etching process. This example is not, however, limiting; the etching process can, alternatively, be stopped before reaching the substrate 103, the cavity 107 presenting then a depth strictly less than the thickness of the transparent region 105. The transparent region 111 of the optical adapter 100 includes a portion 111S projecting from the lower face 11 IB of the region 111, the portion 111S being intended to be inserted into the cavity 107. The mirror 109 is located on the projecting portion 111S. This allows for edge coupling of a waveguide 201 formed in the transparent region 105 of the circuit 101. In the example shown, the waveguide 201 comprises a central region 20IC, or core, surrounded by a peripheral region, or sheath, formed by the transparent region 105. The central region 20IC has a refractive index strictly greater than that of the peripheral region 105.Furthermore, in this example, another waveguide 203 is located on and directly above one end of the waveguide 201 to allow light to be transferred from the waveguide 201 to an output port 205 of the integrated optical circuit 101 located opposite the sampling plane mirror 109 of the optical adapter 100. Similar to the waveguide 201, the waveguide 203 comprises a central region 203C, or core, surrounded by a peripheral region, or sheath, formed by the transparent region 105. The waveguide 203 differs, for example, from the waveguide 201 in that it propagates a mode of larger diameter. As an alternative, the waveguide 203 may be omitted.

[0084] In the illustrated example, a transparent region 207, for example obtained by polymerization of a layer of glue interposed between the integrated optical circuit 101 and the adapter 100, fills the free spaces extending between the upper face of the circuit 101 and the lower face 100B of the adapter 100.

[0085] Fig. 3 is a schematic and partial side and sectional view of a variant of the optical adapter 100 of Fig. 1.

[0086] In the example shown, the transparent region 111 further includes mechanical positioning elements 301, for example pads without optical function, projecting from the lower face 11 IB of the region 111 and intended to bear against the upper face of the circuit 101. This allows adjustment of the distance separating the adapter 100 from the circuit 101 along the vertical axis "z".

[0087] Furthermore, in this example, the transparent region 111 comprises a lower portion 303 facing the upper face of the circuit 101 and an upper portion 305 opposite the lower portion 303 and facing outwards. By way of example, the portion 305 is a silica glass plate and the portion 303 is a polymer shaped by grayscale photolithography or by the "Nano-Imprint Lithography" technique. Alternatively, the portions 303 and 305 are made of the same transparent material, for example silica glass, and the surfaces are formed, for example, by the "Selective Laser Etching" technique.

[0088] In the example shown, the integrated optical circuit 101 has the optical output port 205 located on the end side of the waveguide 203 opposite the cavity 107.

[0089] Fig. 4 is a schematic and partial side and sectional view of another variant of the optical adapter 100 of Fig. 1.

[0090] According to this embodiment, the transparent region 111 comprises a portion 401 without optical function, projecting from the lower face 111B of the adapter 100 and intended to be inserted into a cavity 403 of the integrated optical circuit 101. The portion 401 has, for example, a tooth, finger or tab shape, and acts as a mechanical positioning element of the optical adapter 100 relative to the integrated optical circuit 101. The portion 401 makes it possible to facilitate and / or improve the alignment of the adapter 100 with respect to the circuit 101, in particular alignment along the horizontal axis "x" or alignment in the horizontal plane "xy".

[0091] In the example shown, the part 401 devoid of optical function is formed in the part 303 of the region 111.

[0092] Although only one part 401 has been shown in [Fig.4], this example is not limiting and the adapter 100 can of course, as an alternative, include more parts 401 without optical function intended to fit into cavities previously formed in the upper face of the circuit 101.

[0093] Fig. 5 is a schematic and partial side and cross-sectional view of an optical device 500 according to one embodiment.

[0094] In the example shown, the optical device 500 comprises the assembly previously described in relation to [Fig. 4] including the integrated optical circuit 101 and the optical adapter 100. The optical device 500 further comprises a socket 501, or receptacle, or base, integral with the upper face of the integrated optical circuit 101 and surrounding the optical adapter 100. The socket 501 has, in particular, the function of allowing the mechanical placement of a micro-connector at the appropriate location above the optical adapter 100. In this example, the socket 501 has an opening located opposite the upper light port 119 of the optical adapter 100. The opening 503 allows the light beam 108 propagated by the adapter 100 to pass through.

[0095] In the illustrated example, the optical device 500 further comprises an optical connector 505, for example a micro-optical connector, inserted into the opening 503 of the support 501. In the example shown, the optical connector 505 includes a converging mirror 507, for example a concave mirror, for reflecting the light from the optical adapter 100 to an optical fiber 509, one end of which terminates in the optical connector 505. In this example, the conjugate optical port 119 optics via converging mirror 507 is located on the end of optical fiber 509.

[0096] An advantage of the optical device 500 is that the use of an expanded light beam 108 at the optical port 119 increases the positioning tolerance of the optical connector 505, so that it is possible to use a plug-in optical connector in the receptacle 501 positioned on the integrated optical circuit 101. Assembling the optical adapter 100 with the integrated optical circuit 101 makes it possible to obtain said expanded light beam.

[0097] Fig. 6 is a schematic and partial side and cross-sectional view of a variant of the integrated optical circuit 101.

[0098] In the example shown, the optical coupling between the waveguide 201 of the integrated optical circuit 101 and the optical adapter 100 is achieved by means of a diffraction grating located at the end of the waveguide 201 and formed, for example, by partially etching a periodic structure in the core 201C of the waveguide. This diffraction grating constitutes an optical port 205 for receiving or emitting a light beam 108.

[0099] In this case, the integrated optical circuit 101 is devoid of the cavity 107 and the optical adapter 100 is devoid of the part 111S of the transparent region 111 protruding from the face 11 IB and of the plane reflecting mirror 109. By way of example, the optical adapter 100 does not include any optical function other than that implemented by the plane mirrors 115 and converging mirrors 113 and the transparent region 111.

[0100] Various embodiments and variants have been described. Those skilled in the art will understand that certain features of these various embodiments and variants could be combined, and other variants will become apparent to those skilled in the art. In particular, adapting the optical device 500 to the case of diffraction grating coupling as previously described in relation to [Fig. 6] is within the grasp of those skilled in the art based on the indications in this description.

[0101] Finally, the practical implementation of the described embodiments and variants is within the reach of a person skilled in the art, based on the functional indications given above. In particular, the described embodiments are not limited to the specific examples of materials and dimensions mentioned in this description.

Claims

Demands

1. Optical adapter (100) comprising: - a transparent region (111); - a converging mirror (113) located on the side of a first face (11 IB) of the transparent region (111) and facing a second face (111T) of the transparent region (111), opposite the first face (11 IB); - a first plane mirror (115) located on the side of the second face (111T) of the transparent region (111) and facing the first face (11 IB); - a first optical port (117) located on the side of the first face (11 IB) and intended to be positioned opposite one end of a waveguide (201; 203) of an integrated optical circuit (101); and - a second optical port (119) located on the side of the second face (111T), the optical adapter (100) being intended to ensure propagation of a light beam (108) between said end of the waveguide (201;203) and the second optical port (119), the first plane mirror (115) and the converging mirror (113) being arranged so that the light beam (108) propagates between the first (117) and second (119) optical ports, through the transparent region (111), by reflection on the first plane mirror (115) and on the converging mirror (113), the light beam (108) having, at the level of the second optical port (119), a size (d3) greater than that (di) which it has at the level of the first optical port (117).;

2. Adapter (100) according to claim 1, further comprising a second plane mirror (109) located on a portion (111S) of the transparent region (111) projecting from its first face (11 IB), said portion (111S) being intended to be inserted into a cavity (107) of the integrated optical circuit (101).

3. Adapter (100) according to claim 1, wherein the adapter (100) is devoid of optical elements other than the transparent region (111), the first plane mirror (115) and the converging mirror (113).

4. Adapter (100) according to any one of claims 1 to 3, wherein the transparent region (111) further comprises at least a mechanical positioning element (301; 401) of the adapter (100) relative to the integrated optical circuit (101).

5. Adapter (100) according to claim 4, wherein said at least one mechanical positioning element (301; 401) protrudes from the first face (11 IB) of the transparent region (111).

6. Adapter (100) according to claim 4 or 5, wherein said at least one mechanical positioning element (301; 401) comprises at least one pad (301) without optical function intended to bear against the integrated optical circuit (101).

7. Adapter (100) according to any one of claims 4 to 6, wherein said at least one mechanical positioning element (301; 401) further comprises at least one finger (401) devoid of optical function and intended to be inserted into a cavity (403) of the integrated optical circuit (101).

8. Adapter (100) according to any one of claims 1 to 7, wherein the first (117) and second (119) optical ports are respectively adapted to receive and emit the light beam (108).

9. Adapter (100) according to any one of claims 1 to 8, wherein the first face (11 IB) of the transparent region (111) is parallel to its second face (111T), the first plane mirror (115) being parallel to the second face (111T).

10. Adapter (100) according to any one of claims 1 to 9, wherein the second optical port (119) is intended to be positioned opposite an optical connector (505) into which one end of an optical fiber (509) terminates.

11. Optical device (500) comprising an integrated optical circuit (101) and the optical adapter (100) according to any one of claims 1 to 10, the optical adapter (100) being mechanically attached to the integrated optical circuit (101).

12. Device (500) according to claim 11, wherein the optical adapter (100) is fixed to the integrated optical circuit (101) by an optically transparent layer of adhesive (207).

13. Device (500) according to claim 11 or 12, further comprising at least one optical connector (505) positioned opposite the second optical port (119) and into which the end of an optical fiber (509) terminates.

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