FR2792734A1 - Integrated photonic circuit for optical telecommunications and networks, has substrate mounted light guide and optical receiver-transmitter vertically disposed with intermediate vertical light guide coupler - Google Patents

Abstract

Integrated photon circuit has a substrate with a light guide section (4) integrated on. A resonant optical component (2) detecting or receiving light is mounted on top of the light guide and an intermediate coupling circuit (12) couples light vertically from the optical component to the light guide.

Description

INTEGRATED PHOTONIC CIRCUIT COMPRISING A COMPONENT

  RESONANT OPTICS AND METHODS OF MAKING SAME

CIRCUIT

DESCRIPTION

TECHNICAL AREA

  The present invention relates to circuits

integrated photonics.

  It applies in particular to integrated optical telecommunications systems and

optical interconnections.

STATE OF THE PRIOR ART

  It is known to optically couple, by means of a mirror for example, a light guide formed on a substrate, to a laser of the VCSEL type.

hybridized to this substrate.

STATEMENT OF THE INVENTION

  The present invention relates to an integrated photonic circuit in which a resonant optical component, for example a laser emitter, is optically coupled to a light guide formed on a substrate, with a coupling efficiency greater than that of the coupling mentioned above. , between the laser

  type VCSEL and the light guide.

  Specifically, the subject of the present invention is an integrated photonic circuit formed on a substrate and comprising at least one light guide integrated into this substrate, this circuit being characterized in that it further comprises at least one resonant optical component which is integrated into the substrate and intended to emit or detect light or both, this resonant optical component being placed above a part of the light guide, and means for vertical optical coupling between the resonant optical component and this part of the light guide, the latter being provided to ensure the transfer of light between the resonant optical component and the rest of the light guide by means of the coupling means

vertical optics.

  It should be noted that the vertical coupling used in the present invention allows precise adjustment of the coupling, while a conventional lateral coupling is much more difficult to set up.

technical work.

  According to a preferred embodiment of the integrated photonic circuit object of the invention, the vertical optical coupling means comprises a layer of a material which is transparent to light and whose optical index is lower than that of the light guide thus than the material of the component

resonant optics.

  Preferably, the light guide is made of silicon. The invention makes it possible to efficiently couple a resonant optical component to a silicon light guide whose small cross section, although it is compatible with the dimensions required by microelectronics on silicon, does not allow, when a method is used classic coupling, a

  sufficient light insertion efficiency.

  With this silicon light guide, use is preferably made, as a substrate, of a structure of silicon on insulator type or SOI structure.

(for "Silicon On Insulator").

  The possibility of this optical coupling between the resonant optical component and the silicon light guide allows the integration of this component with other electro-optical components and with passive micro-photonic devices which are achievable on silicon type structures. on insulator. Such structures are almost the only ones to allow the production of passive photonic circuits having dimensions compatible with microelectronics. It should indeed be noted that a strong confinement of the light in the silicon guides is obtained due to the high index contrast between the silicon and the insulator

consisting of silica.

  Preferably, the vertical optical coupling means comprises a layer of silica. Such a layer is well suited to the use of a silicon light guide and of a substrate having a

  silicon on insulator type structure.

  Preferably, the optical component

  resonant includes a microresonator.

  It should be noted that the use of a laser transmitter comprising a microresonator or resonant microcavity (resonator or resonant cavity whose dimensions are of the order of a few micrometers) makes it possible, by confining the photons produced, to promote the rate of spontaneous emission in the desired mode and therefore lower the stimulated emission threshold of the laser transmitter. It should also be noted that such a laser transmitter is compatible with the requirements of

  size of photonic integration on silicon.

  Preferably, it is made so that the density of photonic states of the laser mode is reinforced so that the photons are constrained to

occupy this mode.

  It will be recalled that this selective reinforcement of the spontaneous emission rate depends on the ratio Q / V o Q is the quality factor of the cavity and V the volume of the associated mode. If the quality factor of the microcavity is sufficient, this makes it possible to transfer a large percentage (a few tens of%)

  of spontaneous emission in laser mode.

  Preferably, the microresonator is a microdisk ("microdisk") or micro-ring ("microring") microresonator or else a microstructure based on a photonic crystal with one or

two dimensions.

  A microdisk or micro-ring resonator, exploiting gallery modes (called "whispering gallery modes" in articles in English) allows to obtain a strong confinement of photons. It is the same for a microresonator constituted by a microstructure based on crystal

  one or two dimensional photonics.

  Regarding the latter, consult document [1] which, like the other documents cited below, is mentioned at the end of this document.

description.

  Preferably, the material of the resonant optical component is chosen from III-V semiconductor compounds which are among the materials

  most efficient transmitters and / or detectors.

  This material may be a III-V semiconductor heterostructure with quantum wells ("quantum

  wells ") or quantum boxes.

  This allows, in the case where the resonant optical component is a laser transmitter, to lower the threshold of this laser transmitter by increasing the confinement of the

excite in the latter.

  The stimulated emission is all the more

  favored that the density of states convoluted exciton-

  photon is important in the desired laser mode. A laser transmitter in one or two dimensions thus has a

very low threshold.

  It should be noted that quantum wells are simpler to form than quantum dots but that the latter allow a

optimal confinement of excitons.

  It should also be noted that a III-V semiconductor heterostructure based on quantum wells or quantum dots can emit at wavelengths which are in the range from 1.3 pm to 1.5 pm, lengths d wave to which

the silicon is transparent.

  It should also be noted that, in order to produce integrated photonic circuits, it is necessary to have light sources and passive optical components of micron dimensions. With regard to passive optical components, the "silicon on insulator" technology allows, thanks to the high contrast of optical index between, on the one hand, silicon and, on the other hand, silica and air, d '' ensure the strong confinement of light which is necessary for miniaturization

of these components.

  In addition, the production of microcavity light sources makes it possible to meet requirements for miniaturization and low electrical consumption while being compatible with the

  "silicon on insulator" technology.

  The present invention also relates to a method of manufacturing the integrated photonic circuit object of the invention, in which a substrate is formed comprising a first layer intended for the manufacture of the light guide and a second layer intended for the manufacture of the optical coupling means and a third layer or portion of layer is added to this second layer by a technique called wafer bonding, this third layer or portion of layer being intended for the manufacture of the resonant optical component or

including the latter.

  The present invention further relates to another method of manufacturing the integrated photonic circuit object of the invention, in which a substrate is formed comprising a first layer intended for the manufacture of the light guide and a second layer intended for the manufacture of the means of optical coupling and a heterostructure is formed on this second layer based on an active material comprising nanocrystals of InAs (forming quantum dots) in a matrix of Si or Si3N4, this heterostructure being intended for the manufacture of

resonant optical component.

BRIEF DESCRIPTION OF THE DRAWINGS

  The present invention will be better understood from

  reading the description of exemplary embodiments

  given below, purely by way of indication and in no way limiting, with reference to the appended drawings in which: * FIG. 1 is a schematic longitudinal section view of an integrated photonic circuit according to the invention, FIG. 2 is a schematic top view of a first particular embodiment of the integrated photonic circuit which is the subject of the invention, comprising a microdisc resonator of the microdisc type, * FIG. 3 is a schematic longitudinal section view of the circuit of FIG. 2, O the figure 4 is a schematic top view of a second particular embodiment of the integrated photonic circuit object of the invention, comprising a microresonator based on one-dimensional photonic crystal, * FIG. 5 is a schematic longitudinal section view of the circuit of Figure 4, and * Figure 6 is a schematic longitudinal sectional view of a structure used for the manufacture of a circuit according to the invention ntion.

  DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

  In the integrated photonic circuit according to the invention, which is schematically represented in FIG. 1, a laser microsource 2, with resonant microcavity, is associated with a light guide 4 so as to allow the transfer of the generated light

  by the microsource in this light guide.

  The latter can be optically connected to other passive optical components (not shown) of the photonic circuit, which then receive the light generated by the microsource and transmitted by the guide.

from light.

  The light guide 4 is formed, in the example shown, from a structure of silicon on insulator type. This structure comprises a silicon substrate 6, on which a layer of silica 8 has been formed, as well as a layer of silicon formed on this layer of silica 8 and treated for

form the light guide 4.

  The laser microsource 2 is formed above one end 10 of this light guide and an intermediate layer of silica 12 is interposed between the laser microsource and this end of the light guide. This produces vertical integration of an active part (laser microsource) of the photonic circuit and a passive part (light guide)

  of this circuit, the active part being positioned above

  above this passive part. The function of the intermediate layer 12 is to transfer the light emitted by the laser microsource to the end 10 of the light guide by vertical evanescent coupling, which is symbolized by the arrow

F1 in Figure 1.

  The end 10 of the waveguide, which is located below this intermediate layer, is

  intended to recover the light thus transferred.

  The latter then propagates in the rest 14 of the light guide (which is symbolized by the horizontal arrow F2) to be optionally sent to other passive components (not shown) of the

integrated photonic circuit.

  The use of the laser microsource with a resonant microcavity 2 and the silicon-on-insulator type structure makes light transfer from the microsource to the light guide particularly efficient due to the compatibility, in terms of optical confinement, of such a laser source and a

such structure.

  As will be seen below, the end of the waveguide intended to recover the light emitted by the laser microsource can be what is called a "photon collector" and it is then appropriate that the remainder 14 of the guide wave is sufficiently coupled to this photon collector to inhibit the resonant nature of the latter which would otherwise cause a

  additional light filtering (not desired).

  In the example of FIGS. 2 and 3, the laser microsource has a configuration of microdisk 2a type. We see in these figures the silicon-on-insulator type structure further comprising the silicon substrate 6, the silica layer 8 formed on the latter and, on this silica layer, the silicon light guide 4 whose end 10 constitutes

  then a photon collector (made of silicon).

  On this latter is the intermediate layer of silica 12. The microsource of microdisk 2a type is formed on this intermediate layer. As a purely indicative and in no way limitative, the width L of the light guide is 0.3 μm, the diameter D of the microdisc microsource is approximately 5 μm, the thickness E1 of the silica layer 8 is 0.5 μm, l thickness E2 of the silicon layer, from which the collector 10 and the rest 14 of the light guide are formed, is 0.2 μm, the thickness E3 of the intermediate silica layer 12 is 0.2 μm and the thickness E4 of the microdisc laser microsource

is 0.2 pm.

  In the example of FIGS. 4 and 5, the laser microsource comprises a resonator 2b based on a one-dimensional photonic crystal. We also see in these Figures 4 and 5 the silicon substrate 6 covered by the silica layer 8, itself surmounted by the guide

silicon light 4.

  In the case of FIGS. 4 and 5, the end of this light guide is straight and extends the

  rest 14 (itself rectilinear) of this light guide.

  This end is covered by the intermediate layer of silica 12, itself covered by the laser microsource 2 based on one-dimensional photonic crystal. As a purely indicative and in no way limitative, the length Ls of this microsource based on photonic crystal is approximately 3 μm, the width L of the light guide is 0.3 μm, the thickness El of the silica layer 8 is 0, 5 pm, the thickness E2 of the silicon layer, from which the end 10 and the rest 14 of the light guide are formed, is 0.2 pm, the thickness E3 of the intermediate layer 12 is 0, 2 pm and the thickness E4 of the microsource based

of photonic crystal is 0.2 pm.

  In the particular configuration of FIGS. 2 and 3 and in the other particular configuration of FIGS. 4 and 5 there are found the important elements of the diagram of FIG. 1, which are the resonant microcavity source, the intermediate evanescent coupling layer and the guide.

  light (in silicon in the examples considered).

  In the case of FIGS. 2 and 3, the evanescent coupling is carried out towards a photon collector which itself forms a disk strongly coupled to the rest of the

light guide.

  In the case of FIGS. 4 and 5, the evanescent coupling is carried out directly from the resonant cavity of the microsource to the light guide at

through the middle layer.

  Given the small dimensions given above by way of example for the circuits of FIGS. 2 to 5, the free spectral interval between the cavity modes is appreciable: in the case of FIGS. 2 and 3, the free spectral interval between two modes is of the order of a few tens of nanometers for a microdisk whose radius is worth a few micrometers (see document [2] on this subject) and, in the case of FIGS. 4 and 5, where a crystal is used one-dimensional photonics, this interval can exceed one hundred nanometers (see on this subject

document [3]).

  Such characteristics are in agreement with the performances which are generally required for optical telecommunications for example

  (currently 30 nm of useful spectral range).

  For the manufacture of the structures of Figures 2 to 5 we can start by developing the active material of the laser microsource (we will come back to this later) then define this laser microsource, for example by electronic lithography then reactive ion etching ("reactive ion etching ") and then define the passive components (likely to be on the substrate 6) and the light guide 4 as well as any other light guides for example by optical or electronic lithography or by

dry and / or wet etching.

  The laser microsource can be pumped either optically or electrically but pumping optically is easier to implement than pumping electrically because the latter requires the deposition of metal layers (to form electrical contacts) as well than doping semiconductor materials. The integrated photonic circuits of FIGS. 2 to 5 have the advantage of allowing the exploitation of electro-optical materials, such as InP, which have high refractive indices and are in contact with air and with materials, such as for example silica, which have low refractive indices, which ensures excellent optical confinement. Therefore it is not necessary to make very thick components (several micrometers thick) or to suspend these components

  above an air gap by means of micro-machining.

  In particular, this solves the manufacturing and mechanical reliability problems which are generally observed in the case of suspended microlasers of the resonant microdisc type (see on this subject).

document [4]).

  In addition, the methods of manufacturing the active and passive parts of the integrated photonic circuits of FIGS. 2 to 5 are sufficiently independent to preserve all the achievements of the techniques of manufacturing photonic circuits on

  silicon on insulator type structures.

  In what follows, we return to the manufacturing of the laser microsource. More precisely, we now consider the integration, with the rest of the circuit, of the active material from which is formed.

this laser microsource.

  As active material, a III-V semiconductor compound having a direct gap is preferably used, a material which is perfectly mastered for manufacturing the lasers conventionally used in the field of optical telecommunications at 1.3 μm and

1.55 pm.

  Two ways are possible and indicated in

what follows.

  According to a first particular embodiment, a structure of silicon on insulator type is manufactured comprising a silicon substrate 6, on which a layer of silica 8 is formed, as well as a layer of silicon 16 formed on this layer of silica 8 , or we use a structure commercially

available like this.

  A layer of silica 18, intended for the formation of the intermediate layer 12, is then formed on the silicon layer 16, then a complete layer or a portion of a layer of a semiconductor compound.

  III-V, for example InP, on this layer of silica 18.

  This layer 20 or this layer portion of InP is applied to this layer of silicone 18 by the technique called wafer bonding ("wafer

bonding ").

  When a layer portion of InP is used, this portion therefore only extends over a

part of layer 18.

  The laser microsource 2 is then produced from this layer 20 in InP, by epitaxy of InP / GaInAsP and known techniques for manufacturing laser microsources, so as to obtain a GaInAsP / InP heterostructure (with quantum wells or with

quantum dots).

  The intermediate vertical coupling layer 12 is then produced from the silica layer 18 and then the light microguide 4 (including the end 10 of the latter which is located under the layer 12) is produced from the layer of silicon 16 of

the silicon on insulator structure.

  Instead of forming the laser microsource by epitaxy from the layer 20 or the layer portion in InP, it is also possible to transfer, onto the silicon on insulator type structure provided with the silica layer 18, a complete laser structure formed at from InP, this transfer still taking place

  by the plate bonding technique.

  The second particular embodiment also uses a silicon type substrate

on insulator.

  On this substrate, a layer of silica is formed intended for the formation of the intermediate coupling layer and, on this layer of silica, a chemical vapor deposition is produced and epitaxy a heterostructure based on 'an active material, called SIA material and made up of nanocrystals of InAs distributed in a matrix of Si or Si3N4. This SIA material is manufactured by a combination of chemical vapor deposition techniques, to obtain the Si or Si2N4 matrix, and molecular beam epitaxy

  epitaxy "), to obtain the nanocrystals of InAs.

  Regarding such SIA material we can

see document [5].

  After the production of the heterostructure, the intermediate vertical coupling layer 12 and the light guide 4 (y

  including end 10 of the latter).

  Additional details are given below on the manufacture of circuits.

  integrated photonics according to the invention.

  SOI substrates (Si / SiO2 / Si) called "Unibond" are commercially available from

SOITEC.

  Regarding microdisc or microdisc laser microsources, we will also consult

documents [6], [7] and [8].

  About photonic crystals, we

see also document [9].

  Instead of coupling a laser microsource like those in FIGS. 1 to 5 to one end of a light guide according to the invention, it is possible to couple this laser microsource to any part of a light guide ( always via an intermediate coupling layer), by adapting, if necessary, this part to the microsource (for example by giving this part a configuration of light collector in the case where the laser microsouce is microdisk type

or micro-ring).

  Furthermore, the invention is not limited to the integration of a laser microsource: an integrated microresonator according to the invention can be used not only as a laser emitter but also as a light amplifier or as a resonant photodetector or even as a laser emitter and resonant photodetector,

alternating these two uses.

  The documents cited herein

description are as follows:

  [1] T. Baba, IEEE J. Select. Topics. In Quantum Electron. 3 no 3 (1997) p.808 [2] B.E. Little et al., J. of Lightwave Technol. 15 no 6 (1997) p.998 [3] J.S. Foresi et al., Lett. To Nature 390 (1997) p.143 [4] D.Y. Chu et al., Appl. Phys. Lett. 65 no 25 (1994) [5] J. Shi et al., Appl. Phys. Lett. 70 (1997) 2586 [6] S.I. McCall et al., Appl. Phys. Lett. 60 (1992) 289 [7] J.P. Zhang et al., Phys. Rev. Lett. 75 (1995) 2678 [8] T. Baba et al., IEEE Photon. Technol. Lett. 9

(1997) 878

  [9] E. Yablonovitch, Phys. Lett. 58, 2059 (1987).

Claims (12)

  1. Integrated photonic circuit formed on a substrate and comprising at least one light guide (4) integrated into this substrate, this circuit being characterized in that it further comprises at least one resonant optical component (2) which is integrated into the substrate and intended to emit or detect light or   two, this resonant optical component being placed above   above a part (10) of the light guide, and means (12) for vertical optical coupling between the resonant optical component and this part of the light guide, the latter being provided to ensure the transfer of light between the optical component resonant and the rest (14) of the light guide by   through the vertical optical coupling means.   2. Integrated photonic circuit according to claim 1, in which the vertical optical coupling means comprises a layer (12) of a material which is transparent to light and whose optical index is lower than that of the light guide thus   than that of the material of the resonant optical component.   3. Integrated photonic circuit according to one   any of claims 1 and 2, wherein the   light guide (4) is made of silicon.   4. Integrated photonic circuit according to claim 3, in which the substrate is a   silicon on insulator type structure.   5. Integrated photonic circuit according to one   any of claims 1 to 4, wherein the   vertical optical coupling means comprises a layer silica (12).   6. Integrated photonic circuit according to one   any of claims 1 to 5, wherein the   resonant optical component (2) comprises a microresonator. 7. Integrated photonic circuit according to claim 6, in which the microresonator is a   microdisc or micro-ring microresonator (2a).   8. Integrated photonic circuit according to claim 6, in which the microresonator is a microstructure based on a photonic crystal (2b) with one or two dimensions.   9. Integrated photonic circuit according to one   any of claims 1 to 8, wherein the   material of the resonant optical component (2) is chosen   among III-V semiconductor compounds.   10. Integrated photonic circuit according to claim 9, in which the material of the resonant optical component (2) is a III-V semiconductor heterostructure with quantum wells or boxes. quantum.   11. Method for manufacturing the integrated photonic circuit according to any one of   claims 1 to 10, wherein a substrate is formed   comprising a first layer (16) intended for the manufacture of the light guide and a second layer (18) intended for the manufacture of the optical coupling means and a third layer or portion of layer (20) is added to this second layer by a so-called wafer bonding technique, this third layer or portion of layer being intended for the manufacture of the resonant optical component (2) or including the latter.   12. Method of manufacturing the integrated photonic circuit according to any one of   claims 1 to 10, wherein a substrate is formed   comprising a first layer (16) intended for the manufacture of the light guide and a second layer (18) intended for the manufacture of the optical coupling means and a heterostructure based on a material is formed on this second layer active comprising nanocrystals of InAs in an Si or Si3N4 matrix, this heterostructure being intended for the   manufacture of the resonant optical component (2).