A photonic device comprising a glass substrate and an optical pattern placed on the substrate.

Abstract

The invention relates to a photonic device (1) comprising a glass substrate (S) incorporating an array of optical waveguides. This array comprises at least one waveguide (Gc), referred to as the "coupling waveguide," having a first portion flush with a face (Sa) of the substrate (S) and a second portion intersecting the edge (Sc) of the substrate (S). The photonic device (1) also comprises a first layer formed of a material capable of propagating light radiation. The first layer at least partially covers the first portion of the coupling waveguide. The first layer defines an optical pattern (M) optically coupled to the array of optical waveguides. Figure 1

Description

Title of the invention: PHOTONIC DEVICE COMPRISING A GLASS SUBSTRATE AND A OPTICAL PATTERN DISPLAYED ON THE SUBSTRATE FIELD OF INVENTION

[0001] The present invention relates to a photonic device and falls within the field of integrated photonics. Integrated photonics is a field of photonics that focuses on integrating multiple optical functions onto a single chip, in a manner analogous to how electronic integrated circuits integrate electronic components. TECHNOLOGICAL BACKGROUND OF THE INVENTION

[0002] The document by Broquin et al "Integrated Photonics on Glass: A Review of the lon-Exchange Technology Achievements" Applied Sciences 11, no. 10: 4472 recalls that integrated photonics does not rely on a single technological platform and that silicon photonics, IILV photonics, polymer photonics, LiNbO3 photonics and glass photonics coexist in parallel, each of them presenting its own disadvantages and advantages.

[0003] The use of a glass-based technology platform for photonic devices offers a multitude of advantages, primarily due to the inherent properties of this material. A glass substrate exhibits exceptional transparency over a broad spectrum of wavelengths, encompassing both visible and infrared regions, which is essential for a wide range of optical applications. This low optical loss ensures minimal attenuation of the optical signal, thus preserving its integrity during propagation within the device.

[0004] In addition to optical advantages, a glass substrate offers significant thermal and mechanical benefits. Its low coefficient of thermal expansion ensures dimensional stability, even under varying temperature conditions, thus preserving the performance and reliability of the device. The mechanical strength of glass substrates provides robust support for delicate photonic structures, protecting them from potential damage. Furthermore, glass can be easily fabricated and shaped using standard microfabrication techniques.

[0005] Another notable advantage of a glass-based technology platform is its compatibility with various photonic materials and processes, which facilitates the integration of various photonic components, such as waveguides, modulators, and detectors. More specifically, the compatibility of glass with Optical fibers, often made from similar materials, allow for efficient coupling and reduce insertion losses.

[0006] These numerous advantages make glass an ideal material for the development of advanced photonic devices and integrated photonic circuits. SUBJECT OF THE INVENTION

[0007] One object of the invention is to propose a photonic device taking advantage of the listed advantages of a glass platform. BRIEF DESCRIPTION OF THE INVENTION

[0008] To achieve this goal, the object of the invention proposes a photonic device comprising: - a glass substrate having a first face, a second face opposite the first face, a slice connecting the first face to the second face and incorporating an optical guide array including at least one waveguide, called a "coupling" waveguide, having a first portion flush with the first face and a second portion intersecting the slice of the substrate; - a first layer made of a material capable of propagating light radiation, arranged on the first face of the substrate and covering at least part of the first portion of the coupling waveguide, the layer defining, on this first face, an optical pattern optically coupled to the optical guide network.

[0009] According to other advantageous and non-limiting features of the invention, taken alone or in any technically feasible combination: - the coupling waveguide is partially embedded within a thickness of the substrate; - the first layer is formed of a material chosen from the list consisting of silicon nitride, lithium niobate, silicon, aluminium oxide, indium phosphide; - the photonic device further comprises a protective cover having an assembly face, the protective cover being assembled to the first face of the substrate by its assembly face, the assembly face being provided with at least one recess to house the optical pattern; - the protective cover is made of the same material as the substrate or of a material with the same coefficient of thermal expansion; - the photonic device further includes an adhesive layer between the assembly face of the protective cover and the first face of the substrate; - the protective cover includes at least one complementary waveguide, the at least one complementary waveguide combining with the second portion of the coupling waveguide of the support; - the assembly face of the protective cover does not extend over the entire first face of the support, and leaves an exposed area of ​​this first face; - the protective cover is transparent and includes at least one optical element such as a lens; - the optical pattern has a tapered or segmented shape that at least partially overhangs the first portion of the coupling waveguide; - the optical pattern includes a banded or ribbed waveguide; - the optical pattern implements an optical function, such as a filter; - the optical guide network also includes at least one internal waveguide having a first portion and a second portion both flush with the first face and an intermediate portion buried in the substrate, the intermediate portion being disposed between the first portion and the second portion. - the optical pattern is formed of at least two non-contiguous parts and the optical guide array also includes an internal waveguide optically coupling the two non-contiguous parts; - the optical guide array also includes an internal waveguide entirely overhung by the optical pattern; - the substrate has a U or V shaped groove on the edge intersecting the second portion of the waveguide to receive the end of an optical fiber; - the optical pattern extends to an edge of the first face; - the optical guide array comprises a plurality of waveguides coupling, one part being disposed on one side of the substrate and another part being disposed on the opposite side of the substrate.

[0010] According to another aspect, the invention proposes a photonic system comprising an optical device as above described, and at least one optical fiber placed against the edge of the substrate opposite the second portion of the coupling waveguide. Brief description of the drawings

[0011] Other features and advantages of the invention will become apparent from the detailed description of the invention which will follow with reference to the accompanying figures in which:

[0012] [Fig.1]

[0013] Fig. 1 illustrates a photonic device according to the invention;

[0014] [Fig.2a]

[0015] Fig. 2a represents a substrate of a photonic device incorporating an array of optical guides in top view and according to section AA;

[0016] [Fig.2b]

[0017] Fig. 2b represents the substrate of Fig. 2a according to section BB of this figure;

[0018] [Fig.3]

[0019] Figure 3 illustrates two approaches to coupling an optical fiber to a photonic device according to the invention;

[0020] [Fig.4a]

[0021] [Fig.4b]

[0022] Figures 4a and 4b illustrate different modes of propagation of light radiation in an optical pattern of a device according to the invention;

[0023] [Fig.5a]

[0024] [Fig.5b]

[0025] [Fig.5c]

[0026] [Fig.5d]

[0027] Figures 5a, 5b, 5c, 5d represent photonic devices according to the invention and implementing a variety of optical functions;

[0028] [Fig.6]

[0029] Figure 6 illustrates an embodiment in which a protective cover of a photonic device according to the invention has a complementary waveguide;

[0030] [Fig.7]

[0031] [Fig.8]

[0032] Figures 7 and 8 illustrate other features of a photonic device according to the invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] Fig. 1 represents, by way of illustration, a photonic device 1 according to the invention.

[0034] This photonic device 1 first comprises a glass substrate S. This substrate is delimited by a first face Sa, a second face Sb opposite the first face Sa, and a slice Sc peripherally connecting the first face Sa to the second face Sb.

[0035] Without this constituting a limitation and by way of illustration only, the thickness of the substrate can be between 500 microns and 1 mm. It can extend in a plane and take on a rectangular shape in that plane, and extend over a surface typically ranging from a few mm² to a few cm².

[0036] The exact nature of the glass from which the substrate S is formed can be arbitrary, provided that this substrate can be treated by ion exchange to incorporate, as will be shown later, an array of optical guides. In general, the glasses from which the substrate S can be made are suitable for undergoing ion exchange, generally involving the replacement of smaller ions (e.g., sodium) by larger ions (e.g., potassium, silver, or thallium) from a bath, for example, a bath of molten salt. This ion exchange makes it possible to locally modify the refractive index profile to suit the guiding of light.

[0037] This may be an alkali-silicate glass and in particular a borosilicate glass. The glass may be doped with other elements such as Erbium for light amplification properties for example.

[0038] As shown in [Fig. 2a], the substrate S incorporates an array of optical guides. This array of optical guides is intended to propagate light radiation in the photonic device 1. In this illustration, the array of optical guides is formed from a plurality of waveguides, each waveguide being defined within the thickness of the substrate as a volume having a refractive index different from the rest of the substrate. This refractive index allows the propagation of light radiation to be guided in the substrate S.

[0039] The cross-section of a waveguide typically has a circular or ellipsoidal shape when embedded in the substrate, or a portion of a circle or ellipse when it is flush with the first face. The size of this cross-section, at its widest point, can be on the order of a micrometer or a few micrometers. The guided mode, at a wavelength of 1550 nm, can have a cross-section with a size on the order of 10 micrometers.

[0040] In the optical guide network, we distinguish between the so-called "coupling" waveguides Gc, whose volume of different refractive index intersects the slice Sc of the substrate S, and the so-called "internal" waveguides Gi, whose volume of different refractive index does not intersect the slice Sc of the substrate S.

[0041] A coupling waveguide Gc is intended to propagate light radiation to or from the environment external to the device. For this purpose, an optical fiber (or more generally, a photonic component) of a surrounding photonic system can be placed against the edge Sc of the substrate S, opposite the portion of the coupling waveguide that intersects the edge, in a butt-coupling configuration. This assembly can be facilitated by placing a piece on the first face Sa of the substrate that acts as a mechanical stop for the end of the fiber, thus facilitating the precise positioning and adhesion of this fiber, particularly when the The coupling waveguide is flush with the first face Sa of the substrate S. Alternatively, a U-shaped or V-shaped groove can be formed on the edge of the substrate, at the portion of the coupling waveguide that intersects the edge, this groove allowing the fiber to be precisely positioned so that its core is aligned with the coupling waveguide.

[0042] It should be noted that the coupling of an optical fiber to a glass substrate can be achieved particularly efficiently, by limiting optical coupling losses, since the fiber and the substrate are made of similar materials. This coupling efficiency constitutes a very particular advantage of a photonic device according to the invention.

[0043] The photonic device 1 does not, however, require optical fiber to operate, the light radiation being able to propagate in the photonic system in which the device takes place by simple propagation in free space.

[0044] Each waveguide Gc,Gi of the optical guide array includes at least one portion that is flush with the first face Sa of the substrate S. This flush portion allows the waveguide to be optically coupled with a first layer disposed on and overhanging the first face of the substrate, as will be detailed later. The cross-section of the waveguide at its flush portion has a general shape resembling a portion of an ellipse, as shown in [Fig. 2b].

[0045] Some waveguides in the optical waveguide array may consist entirely of a flush portion. Other waveguides may also have a buried portion, meaning that the volume with a different refractive index in this portion is entirely incorporated into the substrate and is located at a predetermined distance from the first face Sa of this substrate. As already shown, the cross-section of a waveguide at its buried portion generally has an elliptical, or possibly circular, shape, as shown in [Fig. 2b]. Burying a portion of the waveguide is advantageous for preserving the quality of any light that may propagate through it. This prevents the light from interacting with elements that might be present on the first face Sa of the substrate S during its propagation.

[0046] Figure 2a shows a Gel coupling waveguide consisting of a first exposed portion and a second buried portion, the latter intersecting the Sc slice of the substrate. Figure 2a also shows another coupling waveguide Gc2 and an internal waveguide Gi2 consisting of a single exposed portion. An internal waveguide Gi, when it has a buried portion, also has two exposed portions, arranged on either side of the buried portion.

[0047] The optical guide array incorporated in the substrate S can mix any type of waveguide, coupling and internal, with or without a buried portion, according to any arrangement which is suitable for the intended application. In any case, an optical guide network compatible with a photonic device 1 according to the invention comprises at least one coupling waveguide Gc, formed therefore of a portion flush with the first face and a portion intersecting the slice Sc of the substrate S. This portion intersecting the slice Sc can be flush or buried.

[0048] To fabricate the substrate S equipped with its array of optical waveguides, a well-known ion exchange technique can be used, described, for example, in detail in the technical document provided in the introduction to this application. In general terms, a glass substrate without any waveguides can be fitted with a mask on its first face, the mask having open areas defining the location of the waveguides forming the array. The ion exchange operation is then carried out at the open areas, for example by immersing the substrate in a molten salt bath. This operation generally involves replacing smaller ions (for example, sodium) in a surface region of the substrate at the open areas of the mask with larger ions (for example, potassium, silver, or thallium) from the bath. This ion exchange can be assisted by an electric field.This leads to the definition of surface regions in the volume of the substrate S exhibiting a refractive index different from the rest of the substrate S.

[0049] To bury part of these surface regions and thus form the buried portions of the waveguides, a second ion exchange step is carried out, with sodium ions for example, by applying an electric field to the substrate whose profile, in the plane, locally defines the burial depth of the portions.

[0050] Other methods for manufacturing the waveguide array are of course possible for forming at least some of the waveguides that compose it. These waveguides, particularly when they reside on the surface of the first face of the substrate S, can thus be formed by laser treatment of this face.

[0051] Continuing the description of the photonic device 1 illustrated in [Fig. 1], it comprises a first layer disposed on and in contact with the first face Sa of the substrate S. The first layer covers at least part of the flush portion of the coupling waveguide Gc. More generally, the first layer covers at least part of the flush portions of the waveguides forming the optical guide array. The first layer defines, on the first face Sa of the substrate S, an optical pattern M optically coupled to the optical guide array, which means that light ray propagating in the optical guide array is also able to propagate in the optical pattern M.

[0052] The first layer is therefore made of a material capable of propagating light radiation. For example, this first layer may be made of nitride of silicon, lithium niobate, silicon, aluminum oxide, indium phosphide. The first layer can be deposited on the first face Sa of the substrate S by any suitable deposition technique. Alternatively, it can be transferred, by a layer transfer technique, onto the first face Sa of the substrate S, which notably allows for the provision of an optical pattern M made of a crystalline material.

[0053] It is not necessary that this first layer be composed of a single material, and in general the optical pattern can implement a plurality of materials, successively or simultaneously formed on the first face of the substrate S.

[0054] Nor is it necessary for the first layer to extend continuously over the first face of the substrate S. The optical pattern M formed by this first layer can thus be composed of non-contiguous parts separated from each other by gaps in the substrate S that are devoid of any layer. An internal waveguide Gci can be provided to optically couple the two non-contiguous parts of a pattern.

[0055] In all cases, the term "first layer" refers to the thickness of material(s) formed on and in contact with the first face Sa of the support S. This thickness is not necessarily uniform over its entire extent and the first layer may be structured to present areas of distinct thicknesses.

[0056] The optical pattern M is adapted to guide light radiation from or towards the optical guide array of the support. To this end, the optical pattern M advantageously has a tapered or segmented shape Ze overhanging at least a portion of the flush portions of the waveguides of the optical guide array.

[0057] Figures 4a and 4b illustrate different possible embodiments of the optical pattern M comprising such tapered shapes Ze. In [Fig. 4a], and as can be seen in the cross-section of this figure, light radiation propagates entirely guided and confined within the optical pattern M, i.e., within the thickness of the first layer. This optical pattern can thus comprise a band waveguide (left cross-section of [Fig. 4a]) or a ribbed waveguide (right cross-section of [Fig. 4a]). In the cross-section of [Fig. 4b], the light radiation is not entirely confined within the optical pattern M, and a portion of this radiation is weakly guided within the glass substrate S, in a surface thickness arranged directly beneath the optical pattern M.

[0058] It is noted that it is possible to configure the optical pattern M, in particular by defining the width (the dimension transverse to the direction of propagation of the light radiation) to confine the light radiation. Such confinement is advantageous in that it allows for more precise guidance of the light radiation, and in particular makes it possible to form a pattern with a very small radius of curvature, for example on the order of 100 micrometers or less, and in all cases well below the radius of curvature of the waveguides incorporated in the substrate S.

[0059] Advantageously, the optical pattern M, in combination with the optical guide array, can enable the implementation of an optical function, such as a filter. The photonic device is generally associated with optical fibers F, forming inputs / outputs of the device's optical function.

[0060] Thus, and as shown in the photonic devices of Figures 5a, 5b, 5c, the optical guide network can comprise a plurality of coupling waveguides, one part being arranged on one side of the substrate S to form inputs of the photonic device 1 and another part being arranged on the opposite side of the substrate S, and forming outputs of the device 1. It could naturally be envisaged to arrange these coupling waveguides differently, for example on two adjacent sides of the substrate S.

[0061] In [Fig. 5a], the optical motif M forms a ring resonator. As is well known, such a resonator enables the realization of a wavelength filtering function.

[0062] Figure 5b shows a photonic device 1 implementing a multiplexing / demultiplexing function. This application example takes advantage of the ability to form patterns M with very small radii of curvature to constitute the central pattern Ml, thus reducing the size of the device 1. It also takes advantage of the weakly guided nature of the propagation of light radiation in the glass substrate S, which allows light radiation to be injected into the multitude of guides constituting the central pattern Ml with low light loss, in particular the light located between two guides of the central pattern Ml.

[0063] Figure 5c shows another example of a photonic device 1, allowing, for example, the adjustment of the distance between the optical fibers Fe of an input optical fiber bundle and the distance between output optical guides Fs. These output guides can, for example, be used for coupling the photonic device with a photonic component, for example, a photonic component of the silicon photonic chip type. It can be seen in this figure that it is possible to configure the waveguides of the optical guide array to guide the light radiation not only in the depth of the substrate S, but also in the plane of this substrate, along any possible path.

[0064] In the highly schematic example of [Fig. 5d], the optical pattern is composed of three optical sub-patterns Ma, Mb, Mc formed from layers of different materials. A wide variety of functions can be integrated onto the same substrate by mixing the materials composing the layers of the sub-patterns.

[0065] Thus, a first material (for example silicon nitride) can be used to form a first sub-motif Ma intended to constitute passive waveguides, a second material (for example lithium niobate) to form a second sub-motif Mb intended to constitute a modulator, and a third material Mc, for example based on A12O3, to form a third motif Mc intended to constitute an amplifier.

[0066] It is noted that metallic tracks Pe can be provided extending between contact pads PI and an electrically conductive layer Ce formed on the first layer constituting one of the sub-patterns. In general, a photonic device according to the invention can thus provide for a conductive layer, formed of an electrically conductive material, disposed on the first layer.

[0067] Following the description of the photonic device 1 in [Fig. 1], this device may optionally include a protective cover C. The protective cover has an assembly face G by which it is assembled to the first face of the substrate S. The assembly face Cl is provided with at least one recess E to accommodate the optical motif M. This assembly may be optical in nature (by molecular adhesion and without the need for adhesive) or, alternatively, a layer of adhesive may be provided between the assembly face Cl of the protective cover C and the first face Sa of the substrate S.

[0068] The protective cover C and the substrate S may have identical dimensions at their respective mounting faces. However, advantageously, the mounting face Cl of the protective cover C does not extend over the entire first face Sa of the substrate S. The protective cover C exposes a surface area of ​​the first face Sa of the substrate S. This exposed surface area of ​​the first face Sa of the substrate S can be used to position contact pads PI, connected to a conductive layer formed on a pattern M of the device, as shown in relation to [Fig. 5d]. Thus, when the photonic device 1 is integrated into a more complex system, it can be easily connected electrically to electronic components of that system, even when this photonic device 1 has a protective cover C.

[0069] Advantageously, for reasons of thermal robustness, the protective cover is made of the same material as that constituting the substrate S, in the same glass or in a material having the same coefficient of thermal expansion.

[0070] The protective cover C may have functions other than protecting the fragile parts of the photonic device 1. It can thus be provided that the protective cover C includes at least one complementary waveguide Gc, the at least one complementary waveguide combining with the waveguide of the support, in particular with a coupling waveguide Gc. This configuration is that shown in Figure 6 shows the existing assembly interface IA between the protective cover C and the substrate S. The complementary waveguide Gp is ​​arranged in the protective cover C opposite a flush portion of the coupling guide Gc when these two parts are properly joined at their bonding interfaces. This facilitates the coupling of an optical fiber F by providing a combined cross-section of the complementary waveguide Gp and the coupling guide Gc that more closely resembles the shape of the fiber core.

[0071] When the protective cover C is transparent to light radiation, it can be treated to form an optical element such as a lens L. The optical pattern M can include, beneath this optical element, a surface grating enabling, for example, the guidance of light radiation passing through the optical element into the first layer defining the pattern or, conversely, the guidance of light radiation propagating in the first layer defining the pattern towards the optical element. This optional aspect is illustrated in the implementation example in [Fig. 7].

[0072] This [Fig. 7] also illustrates the feature whereby a protective cover C can provide more than one recess E to protect the optical pattern M, particularly when the latter is composed of a plurality of non-contiguous parts. The spaces separating these non-contiguous parts, which separate the parts of the optical pattern from one another, can allow internal pillars of the protective cover to bear against the first face of the support.

[0073] In [Fig.7] also, the support 1 includes an internal waveguide Gi entirely overhung by the optical pattern M. This internal waveguide Gi can contribute to passively realizing an optical function of the photonic device 1.

[0074] The last three features, although represented on the same [Fig.7] for reasons of conciseness, can naturally be integrated independently of each other in a photonic device according to the invention.

[0075] According to another optional feature of a photonic device according to the invention, shown in [Fig.8], the optical pattern M can be provided to extend to an edge of the first face of the support S. In this way, this optical pattern M can be directly coupled to an optical fiber F or to an optical component, without going through a coupling waveguide.

[0076] Of course the invention is not limited to the modes of implementation described and alternative embodiments can be made without departing from the scope of the invention as defined by the claims.

Claims

Demands

1. Photonic device (1) comprising: - a glass substrate (S) having a first face (Sa), a second face (Sb) opposite the first face (Sb), a slice (Sc) connecting the first face (Sa) to the second face (Sb) and incorporating an optical guide array comprising at least one waveguide (Gc), called "coupling waveguide", having a first portion flush with the first face (Sa) and a second portion intersecting the slice of the substrate (Sc); - a first layer formed of a material suitable for propagating light radiation disposed on the first face (Sa) of the substrate (S) and covering at least part of the first portion of the coupling waveguide (Gc), the layer defining, on this first face (Sa), an optical pattern (M) optically coupled to the optical guide array.

2. Photonic device (1) according to the preceding claim in which the coupling waveguide (Gc) is partially embedded in a thickness of the substrate (S).

3. Photonic device according to any one of the preceding claims wherein the first layer is formed of a material selected from the list consisting of silicon nitride, lithium niobate, silicon, aluminum oxide, indium phosphide.

4. Photonic device (1) according to any one of the preceding claims further comprising a protective hood (C) having an assembly face (Cl), the protective hood (C) being assembled to the first face (Sa) of the substrate (S) by its assembly face (Cl), the assembly face (Cl) being provided with at least one recess (E) to house the optical pattern (M).

5. Photonic device (1) according to the preceding claim further comprising an adhesive layer between the assembly face (Cl) of the protective cover (C) and the first face (Sa) of the substrate (S).

6. Photonic device (1) according to any one of claims 4 and 5 wherein the protective cover (C) comprises at least one complementary waveguide (Gp), the at least one complementary waveguide combining with the second portion of the coupling waveguide (Gc).

7. Photonic device (1) according to any one of claims 4 to 6 wherein the assembly face (Cl) of the protective cover (C) does not extend over the entire first face (Sa) of the support (S), and leaves an exposed area of ​​this first face (Sa).

8. Photonic device (1) according to any one of claims 4 to 7 wherein the protective cover is transparent and includes at least one optical element such as a lens.

9. Photonic device (1) according to any one of the preceding claims wherein the optical pattern (M) has a tapered or segmented shape overhanging at least in part the first portion of the coupling waveguide (Gc).

10. Photonic device (1) according to any one of the preceding claims wherein the optical guide array also comprises at least one internal waveguide (Gi) having a first portion and a second portion both flush with the first face (Sa) and an intermediate portion buried in the substrate (S), the intermediate portion being disposed between the first portion and the second portion.

11. Photonic device (1) according to the preceding claim wherein the optical pattern (M) is formed of at least two non-contiguous parts and the optical guide array also includes an internal waveguide (Gi) optically coupling the two non-contiguous parts.

12. Photonic device (1) according to any one of claims 10 and 11 wherein the optical guide array also includes an internal waveguide (Gi) entirely overridden by the optical pattern (M).

13. Photonic device (1) according to any one of the preceding claims wherein the substrate (S) has a U-shaped or V-shaped groove at the edge (Sc) intersecting the second portion of the coupling waveguide (Gc).

14. Photonic device (1) according to any one of the preceding claims wherein the optical pattern (M) extends to an edge of the first face (Sa).

15. A photonic system comprising a photonic device (1) according to any one of the preceding claims, and at least one optical fiber (F) or a photonic component placed against the edge (Sc) of the substrate (S) opposite the second portion of the coupling waveguide (Gc).

Images