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    • 专利摘要:
    The invention relates to a photonic circuit (C1) comprising a structure for coupling to an external device, this structure comprising a main waveguide (WP1) and at least two secondary waveguides (WS11, WS12, WS13, WS14). , each secondary guide (WS11, WS12, WS13, WS14) having a first portion substantially parallel to the main guide (WP1) disposed in the vicinity of the main guide (WP1) so as to achieve an evanescent wave coupling between the main guide (WP1) and the secondary guide, the first portion being extended by a second portion whose end opposite the first portion defines a coupling face of the secondary guide, opening at an outer face of the circuit.
    公开号:FR3055427A1
    申请号:FR1657975
    申请日:2016-08-26
    公开日:2018-03-02
    发明作者:Salim Boutami；Christophe Jany
    申请人:Commissariat a lEnergie Atomique CEA；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA；
    IPC主号:
    专利说明:

    (57) The invention relates to a photonic circuit (C1) comprising a structure for coupling to an external device, this structure comprising a main waveguide (WP1) and at least two secondary waveguides (WS1- |, WS1 2 , WS1 3 , WSI4), each secondary guide (WS1- |, WS1 2 , WS1g, WSI4) having a first portion substantially parallel to the main guide (WP1) arranged in the vicinity of the main guide (WP1) so as to produce a coupling by evanescent wave between the main guide (WP1) and the secondary guide, the first portion being extended by a second portion, one end opposite to the first portion defines a coupling face of the secondary guide, opening at an external face of the circuit.
    Cl
    3_, y
    Gl- / WSl WSli- d Jk 4WS13 yWS14
    B15185 - DD17167HB
    COUPLING STRUCTURE OF A PHOTON CIRCUIT TO AN OUTDOOR DEVICE
    Field
    The present application relates to the field of integrated optical circuits or photonic circuits, and more particularly relates to a structure for coupling a photonic circuit to an external device.
    Presentation of the prior art
    In certain applications, it may be necessary to want to optically couple two separate photonic circuits, that is to say made on different chips. For example, we may want to couple an integrated laser source on a first photonic chip, for example made from III-V semiconductor materials, to a passive photonic circuit integrated on a second chip, for example made from silicon .
    There are mainly two methods in the literature for optically coupling two photonic circuits, evanescent wave coupling and end-to-end coupling.
    Evanescent wave coupling consists of superimposing
    0 the two circuits so as to have, at a relatively small distance but not zero, a portion of a first waveguide
    B15185 - DD17167HB integrated in the first circuit, and a substantially parallel (but not coaxial) portion of a second waveguide integrated in the second circuit. The conditions to be observed for coupling by evanescent wave between two waveguides are for example described in the articles entitled Electrically driven hybrid Si / III-V Fabry-Pérot lasers based on adiabatic mode transformers by B. Ben Bakir et al. , Opt Exp 19, 10317 (2011), and Adiabaticity criterion and the shortest adiabatic mode transformer in a coupled-waveguide System by X. Sun et al., Opt let 34, 280 (2009). Coupling by evanescent wave allows, when correctly carried out, to obtain good coupling performance, and in particular very low losses of light energy during the transfer of the signal between the two circuits. However, this type of coupling requires taking special precautions when assembling the circuits, in order to be able to precisely control the distance between the two parallel portions of superimposed guides and the quality of the interface between the two circuits. In practice, this type of coupling is therefore relatively difficult to implement.
    The butt coupling consists of juxtaposing the two circuits so as to abut, along the same optical axis, one end of a first waveguide integrated in the first circuit to one end of a second waveguide integrated in the second circuit. Examples of optical systems implementing an end-to-end coupling between a photonic circuit and an external device are for example described in the articles entitled Diode-laser-to-waveguide butt coupling by P. Karioja et al., Applied optics 35, 404 (1996), and Efficient Silicon-on-Insulator Fiber Coupler Fabricated Using 248-nm-Deep UV Lithography by G. Roelkens et al., Photonics technology letters 17, 2613 (2005). End-to-end coupling is widely used, particularly in the telecommunications field, because of its ease of implementation. However, end-to-end coupling has the disadvantage of being
    B15185 - DD17167HB relatively sensitive to alignment errors between the two guides, and therefore to provide uncertain coupling yields.
    There is a need for a structure for coupling a photonic circuit to an external device, this structure overcoming all or part of the drawbacks of known structures. summary
    Thus, one embodiment provides a photonic circuit comprising a structure for coupling to an external device, this structure comprising a main waveguide and at least two secondary waveguides, each secondary guide having a first portion substantially parallel to the guide. main arranged in the vicinity of the main guide so as to achieve a coupling by evanescent wave between the main guide and the secondary guide, the first portion extending by a second portion, one end opposite to the first portion defines a coupling face of the secondary guide , opening at an external face of the circuit.
    According to one embodiment, each secondary guide has a point termination on the side of its coupling face.
    According to one embodiment, the coupling coefficients between the main guide and each of the secondary guides are substantially identical.
    According to one embodiment, the first portions of the secondary guides are substantially equal distance from the main guide.
    According to one embodiment, the coupling structure comprises four secondary guides.
    According to one embodiment, the main guide has a rectangular cross section, the first portions of the four secondary guides being, in cross section, arranged around the main guide on the diagonal axes of symmetry of the main guide.
    According to one embodiment, the maximum center-to-center distance between two secondary guides at their coupling faces is substantially equal to twice the radius of the
    B15185 - DD17167HB light beam propagated by each secondary guide at its coupling face.
    According to one embodiment, along their first portions, the secondary guides gradually widen until they reach a maximum width at their second portions.
    According to one embodiment, along the first portions of the secondary guides, the main guide is gradually refined.
    According to one embodiment, the main guide stops before the external face of the circuit.
    According to one embodiment, the main waveguide and the secondary waveguides are made of silicon-germanium and are surrounded by silicon.
    According to one embodiment, the main waveguide and the secondary waveguides are made of amorphous silicon and are surrounded by silicon oxide.
    According to one embodiment, the main waveguide forms an extension of a waveguide internal to the circuit, the internal waveguide being made of crystalline silicon.
    According to one embodiment, the main waveguide and the secondary waveguides are made of silicon nitride and are surrounded by silicon oxide.
    According to one embodiment, the circuit further comprises an integrated laser source, the main waveguide being coupled to the laser source.
    Brief description of the drawings
    These characteristics and advantages, as well as others, will be explained in detail in the following description of particular embodiments made without implied limitation in relation to the attached figures, among which:
    FIGS. 1A and 1B illustrate an example of a structure for coupling a photonic circuit to an external device;
    B15185 - DD17167HB FIGS. 2A, 2B, 2C, 2D illustrate an example of an embodiment of a structure for coupling a photonic circuit to an external device;
    Figures 3A and 3B illustrate an advantage of the coupling structure of Figures 2A, 2B, 2C, 2D;
    Figure 4 illustrates an alternative embodiment of the coupling structure of Figures 2A, 2B, 2C, 2D;
    FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H, 51 illustrate steps of an example of a method of manufacturing a coupling structure of the type described in relation to FIG. 4;
    FIGS. 6A, 6B, 6C illustrate steps of another example of a method of manufacturing a coupling structure of the type described in relation to FIG. 4; and FIGS. 7A, 7B, 7C, 7D illustrate steps of another example of a method of manufacturing a coupling structure of the type described in relation to FIG. 4.
    detailed description
    The same elements have been designated by the same references to the different figures and, moreover, the various figures are not drawn to scale. For the sake of clarity, only the elements which are useful for understanding the embodiments described have been shown and are detailed. In particular, in the description which follows, only structures for coupling a photonic circuit to an external device are detailed. The other elements that a photonic circuit may include are not detailed, the embodiments described being compatible with all the usual components that can be found in a photonic circuit.
    In the following description, unless otherwise indicated, when referring to qualifiers of absolute position, such as the terms forward, backward, up, down, left, right, etc., or relative, such as the terms above , below, upper, lower, etc., or to orientation qualifiers, such as the terms horizontal, vertical, etc., reference is made to the orientation of the views
    B15185 - DD17167HB in section of the figures, it being understood that, in practice, the structures described can be oriented differently. Unless specified otherwise, the expressions approximately, substantially, and of the order of mean to the nearest 10%, preferably to the nearest 5%, or, when they refer to angular dimensions or orientations (horizontal, vertical, parallel, orthogonal , etc.), to the nearest 10 °, preferably to the nearest 5 °.
    Figures IA and IB illustrate an example of a structure for coupling a photonic circuit to an external device. More particularly, FIGS. 1A and 1B represent an assembly comprising two separate photonic circuits C1 and C2 optically coupled. Figure IA is a top view of the assembly, and Figure IB is a longitudinal sectional view along the plane B-B of Figure IA.
    The circuit C1 comprises a structure for coupling to an external device comprising a waveguide W1 in the form of a ribbon, for example of rectangular cross section. The waveguide W1 is made of a first transparent material, and is surrounded by a sheath G1 of a second transparent material with a refractive index lower than that of the first material. The sheath G1 is in contact with the entire outer surface of the guide W1 with the exception of its entry / exit faces, which correspond to the two faces orthogonal to the longitudinal axis of the guide. In the example shown, the longitudinal axis or optical axis of the waveguide W1 is substantially horizontal. The waveguide W1 opens at a side face of the circuit C1, that is to say that one of its input / output faces, called the coupling face, forms a portion of a face side of the circuit Cl. On the side of its coupling face, the waveguide W1 has a tip-shaped termination portion, that is to say in which its width decreases progressively until it reaches a minimum value at level of the coupling face. In this example, the waveguide W1 has a substantially constant thickness over its entire length.
    B15185 - DD17167HB
    In the example shown, the circuit C2 comprises a substantially symmetrical coupling structure, comprising a waveguide W2 in the form of a ribbon, one coupling face of which opens at a lateral face of the circuit C2, the guide W2 having a point termination on the side of its coupling face, and being surrounded by a sheath G2 made of a material with a lower refractive index.
    The coupling between the circuits Cl and C2 is an end-to-end coupling, that is to say that the circuits Cl and C2 are juxtaposed so as to attach the coupling face of the waveguide W1 against the coupling face of the waveguide W2, so that the optical axes of the guides W1 and W2 coincide at the level of the coupling zone.
    The advantage of providing a tip-shaped termination portion at the coupling face has the advantage of improving the tolerance for alignment errors compared to a coupling structure with regular cross section. Indeed, the guiding of the light in the structure is carried out by index contrast between the region W1 (respectively W2), of higher index, and the region G1 (respectively G2), of lower index. When the section of the guide W1 (respectively W2) gradually refines until it disappears, we tend towards a homogeneous infinite sheath, transporting a plane wave of infinite extension. For a guide section W1 (respectively W2) reduced but not zero, a wider mode of propagation (or surface of the light beam in cross section) is therefore obtained. As a result, for a given alignment error, the reduction in the coupling coefficient linked to the misalignment of the guides W1 and W2 is reduced compared to a coupling structure with regular cross section. The coupling coefficient or rate is in fact linked to the spatial integral of overlap between the two modes, taking into account the misalignment.
    A limitation is that to achieve effective coupling, the size of the light propagation mode in the guide W1 and the size of the light propagation mode in
    B15185 - DD17167HB the guide W2 should preferably be substantially identical at the level of the coupling faces of the guides. In practice, to be able to control the size of the mode at the coupling face of the guide, the final width of the guide at the end of the tip must remain large enough to be able to be precisely controlled during manufacture. This reproducibility constraint constitutes a limit to the extension of accessible mode and therefore to the tolerance for alignment errors which can be reached.
    FIGS. 2A, 2B, 2C, 2D illustrate an example of an embodiment of a structure for coupling a photonic circuit to an external device. More particularly, FIGS. 2A, 2B, 2C, 2D represent an assembly comprising two distinct photonic circuits C1 and C2 optically coupled. Figure 2A is a top view of the assembly, Figures 2B and 2C are longitudinal sectional views along the planes BB and CC of Figure 2A, and Figure 2D is a cross-sectional view along the plane DD of Figure 2A.
    The circuit C1 comprises a structure for coupling to an external device comprising a main wave guide WP1, for example optically coupled to another component (not visible in the figures) of the circuit Cl, and two secondary wave guides WS1] _ and WSlg, for example substantially identical, not directly coupled to other components of the circuit. The main waveguide WP1 and the secondary waveguides WS1] _ and WSlg are for example in the form of ribbons, for example rectilinear, for example with rectangular cross sections (for example square). In this example, each of the guides WP1, WS1] _ and WSlg has a substantially constant thickness over its entire length. Each of the guides WP1, WS1] _ and WSlg is made of a first transparent material and is surrounded by a sheath of a second transparent material with a lower refractive index. For example, the guides WP1, WS1] _ and WSlg are made from the same first material, and are coated in the same continuous sheathing region G1 with a second material with a lower refractive index. The optical axes of the guides WP1, WS1] _ and WSlg are
    B15185 - DD17167HB for example substantially parallel, but not confused. In this example, the optical axes of the guides WP1, WS1] _ and WSI2 are substantially horizontal.
    Each secondary guide WS1] _, WSI2 comprises a first portion or coupling portion of optical axis substantially parallel to the optical axis of guide WP1, arranged in the vicinity of guide WP1 so as to allow coupling by evanescent wave between the main guide WP1 and the secondary guides WS1] _, WSI2 · The secondary guides WS1] _, WSI2 are preferably arranged so that the coupling coefficients between the main guide WP1 and each of the secondary guides WS1] _, WSI2 are substantially identical. For this, the secondary guides WS1] _, WSI2 can be arranged at substantially equal distance from the main guide WP1. The distance from optical axis to optical axis between the main guide WP1 and each of the secondary guides WS1] _, WSI2 is for example substantially constant over the entire length of the coupling portion between the main guide WP1 and the secondary guides WS1] _ , WSI2. The length of the coupling portion between the main guide WP1 and the secondary guides WS1] _, WSI2, and the distance between the main guide WP1 and the secondary guides WS1] _, WSI2 along this coupling portion, are chosen from so as to minimize coupling losses, for example according to the teachings described in the above-mentioned articles by B. Ben Bakir et al. and of X. Sun et al.
    In the example shown, along the coupling portion between the main guide WP1 and the secondary guides WS1] _, WSI2, the guide WP1 is progressively refined until it stops, while the guides WS1] _ and WSI2 gradually widen. This arrangement in inverted points of the guides WP1 and WS1] _, WSI2 makes it possible to improve the coupling between the guide WP1 and the guides WS1] _ and WSI2. This arrangement also makes it possible to make the coupling substantially independent of the length of the coupling portion, provided that the length of the coupling portion is greater than a minimum value which can be determined from the teachings of the abovementioned articles.
    B15185 - DD17167HB
    It will be noted that the final width of the tips formed by the terminations of the guides WP1, WS1] _ and WSI2 on the side of the coupling zone between the guide WP1 and the guides WS1] _ and WSI2 does not need to be precisely controlled , insofar as the points here do not have the function of precisely controlling the size of the modes for achieving end-to-end coupling as in the example of FIGS. IA and IB, but only of facilitating the transfer of light energy by evanescent wave between the main guide WP1 and the secondary guides WS1] _ and WSI2. Furthermore, the embodiments described are not limited to the particular case where the main guide WP1 and the secondary guides WS1] _, WSI2 have inverted-point shapes at the level of the coupling zone between the guide WP1 and the guides WS1 ] _, WSI2. As a variant, only the main guide WP1 can have a point termination, the secondary guides WS1] _, WSI2 having a regular cross section in the coupling zone between the guide WP1 and the guides WS1] _, WSI2. Alternatively, the main guide WP1 can have a regular section, while the secondary guides WS1] _, WSI2 can gradually widen in the coupling zone between the guide WP1 and the guides WS1] _, WSI2. As a variant, the main guide and the secondary guides WS1] _, WSI2 can all have a regular section in the coupling zone between the guide WP1 and the guides WS1] _, WSI2.
    As shown in FIGS. 2A, 2B and 2C, at the end of the coupling portion between the main guide WP1 and the secondary guides WS1] _, WSI2, the main guide WP1 is interrupted, while each of the secondary guides WS1 ] _, WSI2 is extended by a second portion opening out at a lateral face of the circuit C1. In other words, each of the secondary guides WS1] _, WSI2 has an input / output face or coupling face to an external device forming a portion of a lateral face of the circuit C1. As in the example described above in relation to FIGS. IA and IB, each secondary guide WS1] _, WSI2 has, on the side of its coupling face to a device
    B15185 - DD17167HB exterior, a tip-shaped termination portion, that is to say in which its width decreases progressively until it reaches a minimum value at the coupling face, so as to increase the size of the modes at the level coupling faces while retaining a sufficiently large guide width to be able to be reproduced with good precision. By way of example, the width of the secondary guides WS1] _, WSI2 at the level of the coupling face of the circuit C1 is between 0.1 and 0.5 μm. Preferably, the length of the tip is greater than 100 times the wavelength of the light intended to be transmitted by the coupling structure.
    Thus, the structure described makes it possible to optically couple the main guide WP1 to an external device, by evanescent coupling between the guide WP1 and the guides WS1] _, WSI2, then by end-to-end coupling between the guides WS1] _, WSI2 and the external device.
    In the example shown, the circuit C2 comprises a substantially symmetrical coupling structure, comprising a main waveguide WP2, and two secondary waveguides WS2] _ and WS22 surrounded by a cladding material G2 of lower index of refraction. The waveguides WP2, WS2] _ and WS22 are arranged so as to achieve on the one hand a coupling by evanescent waves between the main guide WP2 and the secondary guides WS2] _ and WS22, and on the other hand to allow a end-to-end coupling between the secondary guides WS2] _ and WS22 and an external device, in a similar way to what has been described for the circuit Cl. The coupling between the circuits Cl and C2 is an end-to-end coupling, it is ie the circuits C1 and C2 are juxtaposed so as to attach the coupling face of the guide WS1] _ against the coupling face of the guide WS2] _ and the coupling face of the guide WSI2 against the coupling face of the guide WS22, so that the optical axes of the guides WS1] _ and WS2] _ on the one hand, and WSI2 and WS22 on the other hand, are merged at the level of the coupling zone.
    B15185 - DD17167HB
    Figures 3A and 3B illustrate an advantage of the coupling structure of Figures 2A, 2B, 2C, 2D compared to the coupling structure of Figures IA, IB.
    FIG. 3A comprises a first diagram, on the left-hand side of the figure, representing, for the coupling structure of FIGS. 1A, 1B, the distribution of the light energy I carried by the guides W1 and W2 in a direction x transverse to the guides , for example a vertical direction in the orientation of Figure IA. This first diagram comprises a curve 101 in solid line corresponding to the distribution of the light energy carried by the guide W1 at the level of the coupling face of the guide W1, and a curve 103 in broken line corresponding to the distribution of energy light carried by guide W2 at the coupling face of guide W2. We place ourselves here in the case where there is an alignment error e in the direction x between the guides Wl and W2, that is to say that the optical axes or central axes of the guides Wl and W2 are offset by a distance e in the direction x at the level of the coupling zone. As shown in the figure, in this example, the distributions 101 and 103 are substantially Gaussian, and have generally identical general shapes. However, due to the alignment error e between the guides W1 and W2, the distributions 101 and 103 are not aligned. In the example shown, the overlap area between the curves 101 and 103 is very limited, which results in a particularly low coupling coefficient between the guides W1 and W2.
    FIG. 3A also comprises a second diagram, on the right-hand side of the figure, representing, for the coupling structure of FIGS. 2A, 2B, 2C, 2D, the distribution of the light energy I carried by the guides WS1] _ and WSlg on the one hand, and WS2] _ and WS2g on the other hand, in a direction x transverse to the guides, that is to say a vertical direction in the orientation of FIG. 2A. This second diagram includes a curve 201 in solid line corresponding to the distribution of the light energy carried by the guides WS1] _ and WSlg at the level of the coupling face.
    B15185 - DD17167HB of circuit C1, and a curve 203 in broken lines corresponding to the distribution of the light energy carried by the guides WS2] _ and WS22 at the level of the coupling face of circuit C2. We place ourselves here in the case where there is, between circuits C1 and C2, an alignment error e in the direction x of the same value as in the first diagram, that is to say that the optical axes of the guides WS1] _ and WS2] _ on the one hand, and WSI2 and WS22 on the other hand are offset by the distance e in the direction x at the level of the coupling zone. As shown in the figure, in this example, each of the distributions 201 and 203 corresponds substantially to a sum of two Gaussians offset along the x axis by a distance equal to the distance from optical axis to optical axis between the guides WS1 ] _ and WSI2 on the one hand (for distribution 201) and WS2] _ and WS22 on the other hand (for distribution 203). As a result, the distributions 201, respectively 203 of the coupling structure of FIGS. 2A, 2B, 2C, 2D, are much more extensive than the distributions 101, respectively 103 of the coupling structure of FIGS. IA, IB. In particular, for the same alignment error e, the overlap area between curves 201 and 203 is significantly greater than the overlap area between curves 101 and 103. Thus, for the same alignment error e, the coupling coefficient between circuits C1 and C2 is higher with the coupling structure of FIGS. 2A, 2B, 2C, 2D than with the coupling structure of FIGS. IA, IB. The coupling structure of FIGS. 2A, 2B, 2C, 2D therefore makes it possible to increase the tolerance for alignment errors in the direction x with respect to the coupling structure of FIGS. IA, IB.
    FIG. 3B is a diagram representing the evolution of the coupling coefficient k (value without unit between 0 and 1) as a function of the alignment error e (in pm), for a coupling structure of the type described in relation with FIGS. 1A, 1B (curve 301 in FIG. 3B, in dotted lines), and for a coupling structure of the type described in relation to FIGS. 2A to 2D (curve 303 in FIG. 3B, in solid line). Like this
    B15185 - DD17167HB appears in Figure 3B, when the alignment error e increases, the coupling coefficient k decreases more strongly for the structure of Figures IA and IB (curve 301) than for the structure of Figures 2A to 2D (curve 303). The coupling structure of Figures 2A to 2D therefore has better tolerance to alignment errors than the coupling structure of Figures IA, IB.
    The distance between the secondary guides WS1] _ and WSlg (respectively WS2] _ and WS2g) at the level of the coupling face of the circuit C1 (respectively C2) is preferably chosen sufficiently small so that the beams carried by the secondary guides overlap partially at the coupling face of the structure. For example, for a given width of the secondary guides at the level of the coupling face (for example the minimum reproducible width in the technology considered), the beam carried by each secondary guide can be assimilated to the level of its coupling face. to a Gaussian beam of radius R, that is to say such that the light intensity I at the level of the coupling face is defined by the relation (x 2 + y 2
    I = x and y being the coordinates in the plane of the coupling face of the guide, in an orthogonal coordinate system centered on the optical axis of the guide. The center to center distance between the secondary guides WS1] _ and WSlg at the level of the coupling face of the structure is for example between R and 3R, and preferably of the order of 2R.
    FIG. 4 illustrates an alternative embodiment of the coupling structure of FIGS. 2A, 2B, 2C, 2D. In Figure 4, only a cross section of the circuit C1 in the same section plane as that of Figure 2D has been shown. The structure of Figure 4 differs from the structure of Figures 2A, 2B, 2C, 2D mainly in that it includes not two, but four secondary guides WS1] _, WSlg, WSI3, WSI4, for example
    B15185 - DD17167HB substantially identical, coupled by evanescent coupling with the main guide WP1 and emerging on a lateral face of the circuit Cl. In the structure of FIG. 4, at the level of the coupling face of the circuit Cl, the optical axes of the secondary guides WSly and WSI3 on the one hand, and WSI2 and WSI4 on the other hand define two substantially orthogonal planes. As a result, the coupling structure of FIG. 4 makes it possible to improve the tolerance for alignment errors not only in the x direction, but also in a y direction orthogonal to the x direction and orthogonal to the direction of propagation of the light at the coupling area. As in the example of FIGS. 2A, 2B, 2C, 2D, the maximum distance between two secondary guides of the structure of FIG. 4 is preferably chosen sufficiently small so that the beams carried by the guides partially overlap at the level of the coupling face of the structure. For example, if R is called the radius of the beams (assimilated to Gaussian beams) carried by the secondary guides at the level of the coupling face of the structure, the maximum center-to-center distance between two secondary guides at the level of the face of coupling can be of the order of 2R.
    FIG. 4 represents a preferred configuration in which the guides WP1, WSly, WSI2, WSI3 and WSI4 are of rectangular section, and in which, at the level of the coupling zone between the guide WP1 and the guides WSly, WSI2, WSI3 and WSI4 , the guides WSly, WSI2, WSI3 and WSI4 are placed at equal distance from the guide WP1, and are located, in cross section, respectively at the four corners of the guide WP1. In other words, in the example of FIG. 4, in cross section, the optical axes of the secondary guides WSly and WSI3 are located on either side of the guide WP1 on a first diagonal of the guide WP1, and the axes optics of the secondary guides WSI2 and WSI4 are located on either side of the guide WP1 on the second diagonal of the guide WP1. An advantage of this configuration is linked to the fact that, in a waveguide of rectangular section, the light is generally
    B15185 - DD17167HB polarized. The arrangement of the secondary guides on the diagonal axes of symmetry of the main guide allows the coupling between the main guide and the secondary guides to be carried out in substantially the same way in the four secondary guides, that is to say that the coefficients coupling between the main guide and the four secondary guides are substantially the same.
    Examples of the method of manufacturing a coupling structure of the type described above will now be described.
    FIGS. 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H, 51 illustrate steps of an example of a method for manufacturing a coupling structure of the type described in relation to FIG. 4.
    It is considered in this example that the coupling structure is integrated in a photonic circuit using silicon-germanium (SiGe) as high index material and silicon (Si) as low index material. This type of circuit can for example be used in the spectral range of the infrared medium, for example for processing optical signals of wavelengths ranging from 3 to 12 μm. As a variant, for this same range of wavelengths, a similar manufacturing process could be implemented to produce a coupling structure using germanium as the high index material (core) and silicon-germanium as the low index (sheath).
    Figures 5A, 5B, 5C, 5D, 5E, 5F, 5G, 5H, 51 each include, in the left part of the figure, a top view of the structure, and, in the right part of the figure, a sectional view according to the plan aa of FIG. 5A.
    FIG. 5A illustrates an initial step during which one starts from a substrate 501 of crystalline silicon, on the upper face of which a layer of silicon-germanium 503 is deposited, for example by epitaxy.
    FIG. 5B illustrates a step subsequent to the step of FIG. 5A, during which the lower secondary guides WSI4 and WSI3 of the structure of FIG. 4 are
    B15185 - DD17167HB delimited in the silicon-germanium layer 503, for example by lithography and etching.
    FIG. 5C illustrates a step of depositing, for example by epitaxy, a layer of silicon 505 of thickness greater than the thickness of the layer of silicon-germanium 503, on the upper face of the structure obtained at the end of the step of FIG. 5B. The silicon layer 505 can then be planarized, for example by mechanical-chemical planarization (CMP). At the end of this step, the silicon layer 505 fills the space laterally surrounding the secondary guides WSI4 and WSI3 and completely covers the upper faces of the secondary guides WSI4 and WSI3.
    FIG. 5D illustrates a step subsequent to the step of FIG. 5C, during which a layer of silicon germanium 507 is deposited, for example by epitaxy, on the upper face of the layer 505.
    FIG. 5E illustrates a step subsequent to the step of FIG. 5D, during which the main guide WP1 of the structure of FIG. 4 is delimited in the silicon-germanium layer 507, for example by lithography and etching.
    FIG. 5F illustrates a step of depositing, for example by epitaxy, a silicon layer 509 of thickness greater than the thickness of the silicon-germanium layer 507, on the upper face of the structure obtained at the end of the step of FIG. 5E. The silicon layer 509 can then be planarized, for example by mechanical-chemical planarization (CMP). At the end of this step, the silicon layer 509 fills the space laterally surrounding the main guide WP1, and completely covers the upper face of the main guide WP1.
    FIG. 5G illustrates a step subsequent to the step of FIG. 5F, during which a layer of silicon germanium 511 is deposited, for example by epitaxy, on the upper face of the layer 509.
    FIG. 5H illustrates a step subsequent to the step of FIG. 5G, during which the secondary guides
    B15185 - DD17167HB upper WS1] _ and WSlg of the structure of FIG. 4 are delimited in the silicon-germanium layer 511, for example by lithography and etching.
    FIG. 51 illustrates a step of depositing, for example by epitaxy, a layer of silicon 513 of thickness greater than the thickness of the layer of silicon-germanium 511, on the upper face of the structure obtained at the end of the step in Figure 5H. The silicon layer 513 can then be planarized, for example by mechanical-chemical planarization (CMP). At the end of this step, the silicon layer 513 fills the space laterally surrounding the secondary guides WS1] _ and WSlg, and completely covers the upper face of the secondary guides WS1] _ and WS1 2 .
    At the end of the step of FIG. 51, a coupling structure similar to that of FIG. 4 is obtained, the silicon layers 501, 505, 509 and 513 forming the sheath of material of low index G1 of the structure .
    For the near infrared range, for example for optical signals with wavelengths between 0.8 and 2 μm, a similar method can be implemented using silicon oxide as the low index material, and amorphous silicon as a higher index material. Alternatively, for this same range of wavelengths or for visible light (for example in the wavelength range from 0.3 to 0.8 µm), a similar manufacturing process can be implemented using silicon nitride (SiN) as the high index material and silicon oxide as the low index material.
    FIGS. 6A, 6B, 6C illustrate steps of another example of a method for manufacturing a coupling structure of the type described in relation to FIG. 4.
    FIGS. 6A, 6B, 6C each comprise, in the upper left part of the figure, a top view of the structure, in the upper right part of the figure, a view in cross section along the plane a- a of FIG. 6A, and partly
    B15185 - DD17167HB lower left of the figure, a view in longitudinal section along the plane β-β in FIG. 6A.
    In this example, we consider a photonic circuit produced in SOI technology (silicon on insulator), to which we wish to add a coupling structure of the type described in relation to FIG. 4.
    FIG. 6A illustrates a starting structure comprising a support substrate 601 made of silicon, surmounted by a layer of silicon oxide 603. A waveguide W internal to the photonic circuit, made of crystalline silicon, is arranged on the face upper layer of the silicon oxide layer 603. The waveguide 603 is surrounded laterally and on the side of its upper face by a layer of planarized silicon oxide 605.
    FIG. 6B illustrates a step of forming, from the upper face of the structure of FIG. 6A, a cavity or recess 607 at the level of a peripheral zone of the circuit in which it is desired to produce the coupling structure. The cavity 607 extends, in depth, to the upper face of the silicon substrate 601. The cavity 607 is located so that the internal waveguide W opens into the cavity 607.
    FIG. 6C illustrates a step of forming, in the cavity 607, a coupling structure of the type described in relation to FIG. 4, by successive depositions of layers of silicon oxide (as material of lower index) and of layers of amorphous silicon (as material of higher index), for example according to a process similar to that which has been described in relation to FIGS. 5A to 51. As a variant, the material of high index may be silicon nitride and the low index material can be silicon oxide. In this example, care is taken, during this step, to align the main guide WP1 of the coupling structure with the internal guide W of the photonic circuit, so that the guide WP1 forms an extension of the internal guide W. terms, in the example shown, one face of the internal guide W opening into the cavity 607 is attached to the face of the main guide WP1 opposite the region of
    B15185 - DD17167HB coupling between the main guide WP1 and the secondary guides WS1] _, WSlg, WSI3 and WSI4. Thus, the structure produced makes it possible to couple the internal guide W of the photonic circuit to an external device.
    Once the guides WP1, WSI4, WSlg, WSI3 and WSI4 of the coupling structure have been produced, the structure obtained can be cut, for example by cleavage, according to a vertical cutting plane passing through the coupling faces of the secondary guides WSI4, WSlg , WSI3 and WSI4, so as to open the coupling faces of the secondary guides WSI4, WSlg, WSI3 and WSI4 on a side face of the photonic circuit.
    FIGS. 7A, 7B, 7C, 7D illustrate steps of another example of a method of manufacturing a coupling structure of the type described in relation to FIG. 4.
    Figures 7A, 7B, 7C, 7D each comprise, in the upper left part of the figure, a top view of the structure, in the upper right part of the figure, a cross-sectional view along the plane α-a of the figure 7A, and in the lower left part of the figure, a view in longitudinal section along the plane β-β in FIG. 7A.
    In this example, the photonic circuit in which the coupling structure is formed is an active circuit integrating a laser source.
    FIG. 7A illustrates a starting structure comprising a support substrate 701 made of indium phosphide (InP), surmounted by a buffer layer 703, also made of indium phosphide. The buffer layer 703 is surmounted by an active stack of laser diodes, for example a stack of quantum wells based on indium gallium arsenide (InGaAs), in which the laser source is formed (not visible in the figure) of the circuit, as well as, coupled to the laser source, a waveguide corresponding to the main waveguide WP1 of the coupling structure. The active stack is surmounted by an upper layer 705 of indium phosphide, which surrounds the waveguide WP1 laterally and on the side of its upper face.
    B15185 - DD17167HB
    FIG. 7B illustrates a step of forming, from the upper face of the structure of FIG. 7A, two trenches or cavities 707a and 707b extending vertically in the structure up to the upper face of the substrate 701. In top view , the trench 707a has substantially the shape of the secondary guides WSI4 and WSI4 of the coupling structure that one seeks to produce, and the trench 707b has substantially the shape of the secondary guides WSlg and WSI3 of the coupling structure that one seeks to achieve.
    FIG. 7C illustrates a step of depositing a passivation layer 709, for example made of silicon oxide, on the upper surface of the structure obtained at the end of the step of FIG. 7B, followed by a step of localized removal of layer 709 at the bottom of trenches 707a, 707b. At the end of this step, the layer 709 covers substantially the entire upper surface of the circuit, as well as the side walls of the trenches 707a, 707b, but leaves the upper surface of the substrate 701 accessible at the bottom of the trenches 707a, 707b.
    FIG. 7D illustrates a step subsequent to the step of FIG. 7C, during which are successively deposited in the trenches 707a, 707b, for example by epitaxy, a first layer of indium-gallium arsenide 711 forming the guides of lower secondary waves WSI4 and WSI3 of the coupling structure respectively in the trenches 707a and 707b, a layer of indium phosphide 713, and a second layer of indium-gallium arsenide 715 forming the secondary waveguides upper WSI4 and WSlg of the coupling structure respectively in trenches 707a and 707b.
    Particular embodiments have been described. Various variants and modifications will appear to those skilled in the art. In particular, the embodiments described are not limited to the examples of dimensions and materials described above.
    In addition, the embodiments described are not limited to the examples described above in which the structure of
    B15185 - DD17167HB coupling includes two or four secondary guides. More generally, an increase in the tolerance for alignment errors can be obtained as soon as the coupling structure comprises at least two secondary guides.
    In addition, the embodiments described are not limited to the above-mentioned examples in which the coupling structure comprises waveguides of rectangular section. More generally, the embodiments apply regardless of the shape of the waveguides of the coupling structure.
    By way of example, the waveguides of the coupling structure can be of circular or elliptical section.
    Furthermore, although only examples have been described in which the proposed coupling structure is used to couple the photonic circuit to which it is integrated with another photonic circuit, the embodiments described are not limited to this particular application . Indeed, the coupling structures described can be used to couple a photonic circuit to another optical device, for example an optical fiber.
    B15185 - DD17167HB
    权利要求:
    Claims (15)
    [1" id="c-fr-0001]
    1. Photonic circuit (Cl) comprising a structure for coupling to an external device, this structure comprising a main waveguide (WP1) and at least two secondary waveguides (WS1] _, WSlg, WSI3, WSI4), each secondary guide (WSI4, WSlg, WSI3, WSI4) having a first portion substantially parallel to the main guide (WP1) arranged in the vicinity of the main guide (WP1) so as to achieve a coupling by evanescent wave between the main guide (WP1) and the secondary guide, the first portion extending by a second portion, one end opposite to the first portion defines a coupling face of the secondary guide, opening at an external face of the circuit.
    [2" id="c-fr-0002]
    2. The circuit as claimed in claim 1, in which each secondary guide (WSI4, WSlg) has a point termination on the side of its coupling face.
    [3" id="c-fr-0003]
    3. The circuit of claim 1 or 2, wherein the coupling coefficients between the main guide (WP1) and each of the secondary guides (WSI4, WSlg, WSI3, WSI4) are substantially identical.
    [4" id="c-fr-0004]
    4. Circuit according to any one of claims 1 to 3, wherein the first portions of the secondary guides (WSI4, WSlg, WSI3, WSI4) are substantially equidistant from the main guide (WP1).
    [5" id="c-fr-0005]
    5. Circuit according to any one of claims 1 to 4, wherein the coupling structure comprises four secondary guides (WSl !, WS1 2 , WS1 3 , WS1 4 ).
    [6" id="c-fr-0006]
    6. The circuit as claimed in claim 5, in which the main guide (WP1) is of rectangular cross section, the first portions of the four secondary guides (WSI4, WSlg, WSI3, WSI4) being, in cross section, arranged around the main guide ( WP1) on the diagonal axes of symmetry of the main guide.
    [7" id="c-fr-0007]
    7. Circuit according to any one of claims 1 to 6, in which the maximum center-to-center distance between two
    B15185 - DD17167HB secondary guides (WS1] _, WSlg, WSI3, WSI4) at the level of their coupling faces is substantially equal to twice the radius of the light beam propagated by each secondary guide at the level of its coupling face.
    [8" id="c-fr-0008]
    8. Circuit according to any one of claims 1 to 7, in which, along their first portions, the secondary guides (WSI4, WSlg, WSI3, WSI4) gradually widen until they reach a maximum width at the level of their second portions.
    [9" id="c-fr-0009]
    9. Circuit according to any one of claims 1 to 8, in which, along the first portions of the secondary guides, the main guide (WP1) is gradually refined.
    [10" id="c-fr-0010]
    10. Circuit according to any one of claims 1 to 9, wherein the main guide is interrupted before the outer face of the circuit (Cl).
    [11" id="c-fr-0011]
    11. Circuit according to any one of claims 1 to 10, in which the main waveguide (WP1) and the secondary waveguides (WSI4, WSlg, WSI3, WSI4) are made of silicon germanium and are surrounded by silicon.
    [12" id="c-fr-0012]
    12. Circuit according to any one of claims 1 to 10, in which the main waveguide (WP1) and the secondary waveguides (WSI4, WSlg, WSI3, WSI4) are made of amorphous silicon and are surrounded by silicon oxide.
    [13" id="c-fr-0013]
    13. Circuit according to any one of claims 1 to 10, in which the main waveguide (WP1) and the secondary waveguides (WSI4, WSlg, WSI3, WSI4) are made of silicon nitride and are surrounded by 'silicon oxide.
    [14" id="c-fr-0014]
    14. The circuit of claim 12 or 13, wherein the main waveguide (WP1) forms an extension of a waveguide (W) internal to the circuit (Cl), the internal waveguide (W) being of crystalline silicon.
    [15" id="c-fr-0015]
    15. Circuit according to any one of claims 1 to 10 comprising an integrated laser source, the main waveguide (WP1) being coupled to the laser source.
    B 15185 DD17167HB
    1/8
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    同族专利:
    公开号 | 公开日
    EP3287822A1|2018-02-28|
    US20180059329A1|2018-03-01|
    EP3287822B1|2019-03-13|
    US10191217B2|2019-01-29|
    FR3055427B1|2019-05-10|
    引用文献:
    公开号 | 申请日 | 公开日 | 申请人 | 专利标题
    GB2369449A|2000-11-28|2002-05-29|Bookham Technology Plc|Optical waveguide device with tapered branches|
    US20130170807A1|2011-12-28|2013-07-04|Nec Corporation|Spot size converter, optical transmitter, optical receiver, optical transceiver, and method of manufacturing spot size converter|
    US20150010266A1|2013-07-03|2015-01-08|Cisco Technology, Inc.|Photonic integration platform|
    JP5335654B2|2009-12-04|2013-11-06|キヤノン株式会社|Mode conversion element|
    US9261647B1|2013-08-28|2016-02-16|Sandia Corporation|Methods of producing strain in a semiconductor waveguide and related devices|
    JP6262597B2|2014-05-12|2018-01-17|日本電信電話株式会社|Spot size converter|
    EP3206062A1|2016-02-12|2017-08-16|Huawei Technologies Co., Ltd.|Waveguide structure for optical coupling|FR3053479B1|2016-06-30|2019-11-01|StmicroelectronicsSas|JOINT REGION BETWEEN TWO WAVEGUIDES AND METHOD OF MANUFACTURING THE SAME|
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    US11215755B2|2019-09-19|2022-01-04|GenXComm, Inc.|Low loss, polarization-independent, large bandwidth mode converter for edge coupling|
    法律状态:
    2017-08-31| PLFP| Fee payment|Year of fee payment: 2 |
    2018-03-02| PLSC| Search report ready|Effective date: 20180302 |
    2018-08-30| PLFP| Fee payment|Year of fee payment: 3 |
    2019-08-30| PLFP| Fee payment|Year of fee payment: 4 |
    2021-05-07| ST| Notification of lapse|Effective date: 20210405 |
    优先权:
    申请号 | 申请日 | 专利标题
    FR1657975|2016-08-26|
    FR1657975A|FR3055427B1|2016-08-26|2016-08-26|STRUCTURE FOR COUPLING A PHOTONIC CIRCUIT TO AN EXTERNAL DEVICE|FR1657975A| FR3055427B1|2016-08-26|2016-08-26|STRUCTURE FOR COUPLING A PHOTONIC CIRCUIT TO AN EXTERNAL DEVICE|
    EP17185641.2A| EP3287822B1|2016-08-26|2017-08-09|Photonic circuit comprising a structure to couple to an external device|
    US15/677,198| US10191217B2|2016-08-26|2017-08-15|Structure for coupling a photonic circuit to an external device|
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