WO2004034092A2 - Optical waveguide with high index contrast and reduced losses due to roughness, and method of producing same - Google Patents

Optical waveguide with high index contrast and reduced losses due to roughness, and method of producing same Download PDF

Info

Publication number
WO2004034092A2
WO2004034092A2 PCT/FR2003/050084 FR0350084W WO2004034092A2 WO 2004034092 A2 WO2004034092 A2 WO 2004034092A2 FR 0350084 W FR0350084 W FR 0350084W WO 2004034092 A2 WO2004034092 A2 WO 2004034092A2
Authority
WO
WIPO (PCT)
Prior art keywords
core
layer
optical waveguide
heart
refractive index
Prior art date
Application number
PCT/FR2003/050084
Other languages
French (fr)
Other versions
WO2004034092A3 (en
Inventor
Pierre Labeye
Michel Heitzmann
Original Assignee
Commissariat A L'energie Atomique
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Commissariat A L'energie Atomique filed Critical Commissariat A L'energie Atomique
Publication of WO2004034092A2 publication Critical patent/WO2004034092A2/en
Publication of WO2004034092A3 publication Critical patent/WO2004034092A3/en

Links

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y20/00—Nanooptics, e.g. quantum optics or photonic crystals
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/1223—Basic optical elements, e.g. light-guiding paths high refractive index type, i.e. high-contrast waveguides
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/13—Integrated optical circuits characterised by the manufacturing method
    • G02B6/132—Integrated optical circuits characterised by the manufacturing method by deposition of thin films

Definitions

  • the present invention relates to the field of integrated optics and, more particularly, optical waveguides with large deviation, or contrast, of refractive index, as well as the manufacture of such waveguides.
  • the invention relates more precisely to an optical waveguide with high refractive index, this waveguide further having reduced roughness losses, as well as to a method of manufacturing this waveguide.
  • the invention applies in particular to optical interconnections, to intra-chip optical connections ("intra-chip”), to optical telecommunications as well as to integrated optical sensors and, more generally, to. field of integrated optics where the differences in index between core (“core”) and optical cladding (“optical cladding”) are large enough to make optical losses by roughness not negligible.
  • index jump guides Two main types of optical waveguides exist in the field of integrated optics: index jump guides (see FIG. 1A)
  • the core 2 of a jump index guide seen in cross section, is delimited by interfaces which separate it from two materials 4 and 6 or possibly from two zones of the same material, having different dopings.
  • the index distribution in this cross section has discontinuities.
  • index jump guides are generally obtained by deposits and etchings of thin dielectric layers on a substrate.
  • index distribution function is continuous when passing from the core 8 to the sheath 10 of the guide. There are no index discontinuities in such guides.
  • These guides can for example be formed by ionic diffusion on a glass substrate which is immersed in a molten salt (see document [1]).
  • These two types of guides each have their advantages and disadvantages.
  • the main advantage of gradient index guides is that they do not have an interface, therefore no losses by surface roughness.
  • Their main drawback is that the index difference which they make it possible to achieve remains relatively small (a few hundredths to a tenth) and cannot reach those which are observed for example in guides made of silicon surrounded by silica.
  • the safest way to reduce the size of the integrated optical devices is to use structures with a very large index difference between the core and the sheath.
  • the possible radii of curvature go from a few millimeters to a few micrometers.
  • optical guides with a very large index difference have a major drawback: they have a lot of losses by optical diffusion due to the roughness of the interfaces between the core and the cladding of such guides.
  • n x and n 2 are respectively 1.46 and 1.45. Consequently (rz 2 - rz 2 ) 2 is little different from 8,5xl0 "4 .
  • n x and n 2 are respectively 3.45 and 1.45.
  • Another known way of reducing roughness losses consists in forming the guides by chemical etching along the crystalline planes of the material constituting these guides.
  • NH 4 OH can for example be used to etch the silicon.
  • the object of the present invention is to remedy the above drawbacks. It offers an optical waveguide with a large refractive index difference, the roughness losses of which are, however, lower than those of known guides with large index difference.
  • the invention also provides a method of manufacturing such a guide.
  • the subject of the present invention is an optical waveguide comprising:
  • this optical waveguide being characterized in that it further comprises at least one intermediate layer which extends at least along the sides of the heart, between this heart and the first confinement layer, and which has a refractive index N3 adapted to the refractive index Ne of the core and to the refractive index NI of the first confining layer to minimize optical losses, this refractive index N3 being less than Ne and greater than NI.
  • the refractive index N3 is given by the following formula:
  • K ⁇ + K 2 K ⁇ + K 2
  • the heart is formed on the second confinement layer, this optical waveguide thus being an optical waveguide with index jump.
  • the intermediate layer extends along the core, between this core and the first confinement layer, and thus completely separates the core from the first layer containment.
  • the intermediate layer extends only along the sides of the heart, between this heart and the first confinement layer.
  • the optical waveguide which is the subject of the invention can comprise a plurality of intermediate layers, the respective refractive indices of which decrease from the heart. This embodiment allows an optimization of the refractive indices of the intermediate layers to minimize the optical losses.
  • the optical waveguide object of the invention is a guide with high index confinement.
  • high index confinement is meant a difference in index between the core and the first confinement layer which is greater than 0.1 and preferably greater than 0.5.
  • this type of guide can include a silicon core and a first silica confinement layer.
  • the present invention also relates to a method of manufacturing the optical waveguide which is the subject of the invention, this optical waveguide comprising:
  • the core which has a refractive index Ne, this core having sides, and the first and second confinement layers between which the core is located and which have respectively refractive indices NI and N2, these refractive indices NI and N2 being lower than the refractive index Ne of the heart, this process being characterized in that: - the heart is formed, at least one intermediate layer is formed on the heart, this intermediate layer extending at least along the sides of the core and having a refractive index N3 adapted to the refractive index Ne of the core and to the refractive index NI of the first confinement layer to minimize optical losses, this refractive index N3 being less than Ne and greater than NI, and we form the first containment layer.
  • the core is formed on the second confinement layer, the optical waveguide thus being an optical waveguide with index jump.
  • the intermediate layer along the core, between this core and the first confinement layer, so as to completely separate the core from the first confinement layer.
  • the intermediate layer is formed only along the sides of the heart, between this heart and the first confinement layer.
  • a plurality of intermediate layers can be formed, the respective refractive indices of which decrease from the core.
  • FIG. 1A is a view in schematic cross-section of a known optical waveguide, with index jump, and has already been described
  • FIG. 1B is a schematic cross-section view of a known optical waveguide, with gradient of clue, and has already been described
  • FIG. 2 is a schematic cross-sectional view of a particular embodiment of the optical waveguide object of the invention, comprising a single intermediate layer
  • FIG. 3 is a view in schematic cross-section of an embodiment particular of the optical waveguide object of the invention, comprising two intermediate layers
  • FIGS. 4 to 6 schematically illustrate steps of a particular mode of implementation of the method object of the invention
  • Figure 7 schematically illustrates a variant of the process illustrated by Figures 4 to 6, and Figures 8 to 10 schematically illustrate steps of another particular embodiment of the process object of one invention.
  • the invention aims to reduce the roughness losses of guides with a large index difference.
  • the core is coated with such a guide, after etching, with one or more very thin layers, made of dielectric materials whose optical refractive indices are intermediate between the index Ne of the core and 1 NI index of the confinement layer with which the core is then covered.
  • a index jump guide comprising a core 12 between an upper confinement layer 14, the optical index is denoted NI, and a lower confinement layer 16, whose optical index is denoted N2, as well as an additional continuous layer 18, whose optical index is denoted N3 and which extends between layers 14 and 16 and between layer 14 and core 12.
  • N3 P ⁇ K ⁇ (N c 2 -N3 2 ) 2 + K 2 (N3 2 -N1 2 ) 2
  • Ki and K 2 are factors of proportionality.
  • optical index N'3 of this other layer 20 is less than N3 and greater than NI.
  • the general idea is always to decrease the index difference at each of the interfaces in order to reduce the roughness losses at these interfaces.
  • the invention makes it possible to reduce the roughness losses of guides with a large index difference which are formed by photolithography and etching, using a very inexpensive technological step, and thus makes it possible to envisage optical devices. integrated very small, still retaining good optical performance.
  • the invention is compatible with all materials with a large index difference and can very well be combined with other methods of reducing roughness itself.
  • silicon where it is possible to reduce the roughness of the sides of the guides by an oxidation / deoxidation technique of silicon, as described in document [3], it is possible to use the both this technique and the present invention.
  • Insulator " whose structure is shown in Figure 4.
  • This SOI substrate comprises a monocrystalline substrate 22 in which a layer of silica 24 is buried, the latter being thus surmounted by a layer of monocrystalline silicon 26.
  • the layer of buried silica can have a thickness of between 0.7 ⁇ m and l ⁇ m and the upper layer of silicon can have a thickness between 0.2 ⁇ m and 0.5 ⁇ m.
  • the core 28 of the guide is then formed by photolithography and etching from the layer 26, and the structure of FIG. 5 is then obtained in cross section.
  • the width of the core 28 can range from 0.4 ⁇ m, if one wishes to have a single-mode guide, up to several micrometers if one wishes to have a multimode guide.
  • a material having a refractive index approaching this value (2.64) can for example be silicon carbide, diamond carbon, titanium dioxide, or even silicon nitride (not stoichiometric).
  • FIG. 6 The structure of FIG. 6 is then obtained, where we see the layer of silicon nitride 30, which covers the layer 24 and the core 28, and the layer of silica 32 which covers this layer 30.
  • two thin layers 34 and 36 of different materials can be successively deposited as shown in FIG. 7.
  • the materials must have indices between the index of silicon and that of silica, the index of the first layer 34, which covers the layer 24 and the core 28, having to be greater than the index of the second layer 36 which covers layer 34.
  • Ti0 2 with an index approximately equal to 2.4 is used for layer 34 and Si 3 N 4 with an index approximately equal to 2 for layer 36. A reduction in losses is then obtained. roughness of a factor approximately equal to 2.
  • the Ti0 2 layer can be deposited by evaporation or spraying and the Si 3 N 4 layer by LPCVD.
  • the roughness on the sides 38 and 40 of the heart 28 (FIG. 8), roughness which is due to photolithography and etching, is much greater than the roughness on the lower and upper edges 42 and 44 of the heart. . It is possible to produce the intermediate layers only on the sides 38 and 40 (lateral edges) of the core if desired.
  • FIG. 5 shows such a core 28 in the case of silicon on silica.
  • a thin layer 46 of Si 3 N 4 according to the invention is deposited by LPCVD and the structure of FIG. 8 is then obtained.
  • layer 46 covers layer 24 and core 28.
  • anisotropic etching of the layer 46 for example by the technique of reactive ion etching ("reactive ion etching") full plate (without photolithography step) and we obtain the structure of FIG. 9 where we see that the flanks of the core 28 are covered with zones of Si 3 N 4 , consisting of the portions of layer 46 which remain after the anisotropic etching.
  • a plurality can be formed so that the sides of the heart are then covered with portions of this plurality of layers.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Nanotechnology (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • General Physics & Mathematics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Biophysics (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Optical Integrated Circuits (AREA)

Abstract

The invention relates to an optical waveguide with high index contrast and reduced losses due to roughness and to the method of producing said guide. The invention is particularly suitable for optical telecommunications. The inventive waveguide comprises a core (12) having a refractive index Nc, which is disposed between first and second confinement layers (14, 16) having refractive indices N1 and N2 which are less than Nc. Said waveguide also comprises at least one intermediate layer (18) which extends along at least the length of the sides of the core and which is disposed between the core and the first confinement layer. The refractive index N3 of the intermediate layer is adapted to the refractive index Nc of the core and to the refractive index N1 of the first confinement layer in order to minimise the optical losses, N3 being less than Nc and greater than N1.

Description

GUIDE D'ONDE OPTIQUE, A FORT CONTRASTE D'INDICE ET A PERTES PAR RUGOSITE REDUITES, ET PROCEDE DE FABRICATION OPTICAL WAVEGUIDE, WITH HIGH INDEX CONTRAST AND REDUCED ROUGHNESS LOSSES, AND MANUFACTURING METHOD
DE CE GUIDEFROM THIS GUIDE
DESCRIPTIONDESCRIPTION
DOMAINE TECHNIQUETECHNICAL AREA
La présente invention concerne le domaine de l'optique intégrée et, plus particulièrement, les guides d'ondes optiques à fort écart, ou contraste, d'indice de réfraction, ainsi que la fabrication de tels guides d'ondes.The present invention relates to the field of integrated optics and, more particularly, optical waveguides with large deviation, or contrast, of refractive index, as well as the manufacture of such waveguides.
L'invention concerne plus précisément un guide d'onde optique à fort contraste d'indice de réfraction, ce guide d'onde ayant en outre des pertes par rugosité réduites, ainsi qu'un procédé de fabrication de ce guide d'onde.The invention relates more precisely to an optical waveguide with high refractive index, this waveguide further having reduced roughness losses, as well as to a method of manufacturing this waveguide.
L'invention s'applique notamment aux interconnexions optiques, aux connexions optiques intra-puces ("intra-chip") , aux télécommunications optiques ainsi qu'aux capteurs optiques intégrés et, plus généralement, au. domaine de l'optique intégrée où les différences d'indice entre cœur ("core") et gaine optique ("optical cladding") sont suffisamment grandes pour rendre les pertes optiques par rugosité non négligeables.The invention applies in particular to optical interconnections, to intra-chip optical connections ("intra-chip"), to optical telecommunications as well as to integrated optical sensors and, more generally, to. field of integrated optics where the differences in index between core ("core") and optical cladding ("optical cladding") are large enough to make optical losses by roughness not negligible.
ETAT DE LA TECHNIQUE ANTERIEURESTATE OF THE PRIOR ART
On se reportera aux documents suivants : [1] R.V. Ramaswamy, R. Srivastava : "Ion- exchanged glass waveguides : a review" , J. of Light . Tech., 6, p. 984-1002, 1988Refer to the following documents: [1] RV Ramaswamy, R. Srivastava: "Ion- exchanged glass waveguides: a review", J. of Light. Tech., 6, p. 984-1002, 1988
[2] D. Marcuse : "Light Transmission Optics", Bell Lab Séries, Van Nostrand Reinhold Company, p. 3187-3215 : "Mode concersion caused by surface imperfections of a dielectrie slab waveguide"[2] D. Marcuse: "Light Transmission Optics", Bell Lab Series, Van Nostrand Reinhold Company, p. 3187-3215: "Concersion mode caused by surface imperfections of a dielectrie slab waveguide"
[3] K.K. Lee & al . : "Fabrication of ultralow-loss Si/Si02 waveguides by roughness réduction", Optics Letters, vol. 26, n°23, 1er décembre 2001, p. 1888-1890.[3] KK Lee & al. : "Fabrication of ultralow-loss Si / Si0 2 waveguides by roughness reduction", Optics Letters, vol. 26, n ° 23, December 1, 2001, p. 1888-1890.
Dans le domaine de l'optique intégrée comme dans celui de la microélectronique, la recherche de l'intégration maximale est extrêmement importante, car les dimensions des dispositifs obtenus influent de manière directe sur leur coût de fabrication.In the field of integrated optics as in that of microelectronics, the search for maximum integration is extremely important, because the dimensions of the devices obtained have a direct influence on their manufacturing cost.
Le domaine de l'optique intégrée a connu un premier essor avec le développement des télécommunications optiques. La priorité était alors de fabriquer des dispositifs optiques intégrés qui soient compatibles avec les fibres optiques utilisées, ce qui avait une incidence directe sur le choix des matériaux employés (par exemple la silice ou le verre) et sur les géométries utilisées pour les guides d'ondes. L'inconvénient majeur de telles structures est qu'il est très difficile de faire prendre à la lumière des "virages très serrés" (ayant typiquement des rayons de courbure de 1 ' ordre de quelques millimètres) . Ceci impose la réalisation de dispositifs de taille importante (plusieurs centimètres carrés) . Par exemple, les multiplexeurs/démultiplexeurs de longueurs d'ondes, fabriqués en utilisant la technologie "silice sur silicium", dépassent une dizaine de centimètres carrés, ce qui les rend onéreux.The field of integrated optics experienced a first boom with the development of optical telecommunications. The priority was then to manufacture integrated optical devices which were compatible with the optical fibers used, which had a direct impact on the choice of materials used (for example silica or glass) and on the geometries used for the guides. waves. The major drawback of such structures is that it is very difficult to make "very tight turns" take in the light (typically having radii of curvature of the order of a few millimeters). This requires the production of large devices (several square centimeters). For example, wavelength multiplexers / demultiplexers, manufactured using "silica on silicon" technology, exceed ten square centimeters, which makes them expensive.
Deux grands types de guides d'ondes optiques existent dans le domaine de l'optique intégrée : les guides à saut d'indice (voir la figure 1A)Two main types of optical waveguides exist in the field of integrated optics: index jump guides (see FIG. 1A)
- les guides à gradient d'indice (voir la figure 1B) .- the index gradient guides (see Figure 1B).
Le cœur 2 d'un guide à saut d'indice, vu en coupe transversale, est délimité par des interfaces qui le séparent de deux matériaux 4 et 6 ou éventuellement de deux zones d'un même matériau, présentant des dopages différents. La répartition d'indice dans cette coupe transversale présente des discontinuités.The core 2 of a jump index guide, seen in cross section, is delimited by interfaces which separate it from two materials 4 and 6 or possibly from two zones of the same material, having different dopings. The index distribution in this cross section has discontinuities.
Ces guides à saut d'indice sont généralement obtenus par des dépôts et des gravures de couches minces diélectriques sur un substrat.These index jump guides are generally obtained by deposits and etchings of thin dielectric layers on a substrate.
Dans un guide à gradient d'indice, vu en coupe transversale, la fonction de répartition d'indice est continue lorsque l'on passe du cœur 8 à la gaine 10 du guide. Il n'existe pas de discontinuités d'indice dans de tels guides.In an index gradient guide, seen in cross section, the index distribution function is continuous when passing from the core 8 to the sheath 10 of the guide. There are no index discontinuities in such guides.
Ces guides peuvent être par exemple formés par diffusion ionique sur un substrat de verre qui est plongé dans un sel fondu (voir le document [1] ) . Ces deux types de guides ont chacun leurs avantages et leurs inconvénients. Le principal avantage des guides à gradient d'indice est qu'ils ne présentent pas d'interface donc pas de pertes par rugosité de surface. Leur principal inconvénient est que l'écart d'indice qu'ils permettent d'atteindre reste assez faible (quelques centièmes à un dixième) et ne peut atteindre ceux que l'on observe par exemple dans les guides faits de silicium entouré de silice.These guides can for example be formed by ionic diffusion on a glass substrate which is immersed in a molten salt (see document [1]). These two types of guides each have their advantages and disadvantages. The main advantage of gradient index guides is that they do not have an interface, therefore no losses by surface roughness. Their main drawback is that the index difference which they make it possible to achieve remains relatively small (a few hundredths to a tenth) and cannot reach those which are observed for example in guides made of silicon surrounded by silica.
Or, la manière la plus sûre de réduire la taille des dispositifs optiques intégrés consiste à utiliser des structures à très fort écart d'indice entre le cœur et la gaine. Dans ce cas, les rayons de courbure possibles passent de quelques millimètres à quelques micromètres. On peut alors espérer fabriquer des puces optiques occupant une surface de l'ordre du millimètre carré.However, the safest way to reduce the size of the integrated optical devices is to use structures with a very large index difference between the core and the sheath. In this case, the possible radii of curvature go from a few millimeters to a few micrometers. We can then hope to manufacture optical chips occupying an area of the order of a square millimeter.
Cependant, les guides optiques à très fort écart d'indice ont un inconvénient majeur : ils présentent beaucoup de pertes par diffusion optique du fait de la rugosité des interfaces entre le cœur et la gaine de tels guides .However, optical guides with a very large index difference have a major drawback: they have a lot of losses by optical diffusion due to the roughness of the interfaces between the core and the cladding of such guides.
A titre indicatif, on sait que les pertes P par rugosité à une interface d'un guide plan sont notamment proportionnelles au carré de la différence des carrés des indices de réfraction respectifs ni et n2 des matériaux situés de part et d'utre de cette interface (voir le document [2] ) :
Figure imgf000006_0001
As an indication, it is known that the losses P by roughness at an interface of a planar guide are in particular proportional to the square of the difference of the squares of the respective refractive indices ni and n 2 of the materials located on either side of this interface (see document [2]):
Figure imgf000006_0001
Dans le cas d'une fibre optique ou d'un guide intégré en silice dopée ou en verre, nx et n2 valent respectivement 1,46 et 1,45. En conséquence (rz2 — rz2)2 est peu différent de 8,5xl0"4.In the case of an optical fiber or an integrated guide made of doped silica or glass, n x and n 2 are respectively 1.46 and 1.45. Consequently (rz 2 - rz 2 ) 2 is little different from 8,5xl0 "4 .
Au contraire, dans le cas d'un guide en silicium entouré de silice, nx et n2 valent respectivement 3,45 et 1,45.On the contrary, in the case of a silicon guide surrounded by silica, n x and n 2 are respectively 3.45 and 1.45.
En conséquence (ttf - n )2 est peu différent de 96. Par rapport au cas précédent, les pertes augmentent donc d'environ 5 ordres de grandeurs.Consequently (ttf - n) 2 is little different from 96. Compared to the previous case, the losses therefore increase by around 5 orders of magnitude.
Cet exemple met en évidence le gros inconvénient des guides à fort écart d'indice.This example highlights the major drawback of guides with a large index difference.
Des recherches ont bien entendu été menées pour réduire cette rugosité, en améliorant sans cesse les procédés de fabrication, notamment les procédés de photolithographie et de gravure des guides. Par exemple, d'après le document [3], des guides en silicium sont fabriqués par photolithographie et gravure puis subissent une étape d'oxydation puis une étape de désoxydation (en fait une étape de gravure d'oxyde généralement dans un bain de FH/FHN4) , ce qui a pour effet de réduire la rugosité. Cependant cette réduction a lieu au détriment des dimensions du guide.Research has of course been carried out to reduce this roughness, by constantly improving the manufacturing processes, in particular the photolithography and guide engraving processes. For example, according to document [3], silicon guides are produced by photolithography and etching, then undergo an oxidation step and then a deoxidation step (in fact an etching step of oxide generally in an FH bath / FHN 4 ), which has the effect of reducing roughness. However, this reduction takes place at the expense of the dimensions of the guide.
Une autre manière connue de réduire les pertes par rugosité consiste à former les guides par gravure chimique selon les plans cristallins du matériau constitutif de ces guides. On peut par exemple utiliser du NH4OH pour graver le silicium.Another known way of reducing roughness losses consists in forming the guides by chemical etching along the crystalline planes of the material constituting these guides. NH 4 OH can for example be used to etch the silicon.
Cependant, on est alors grandement limité par le fait que, d'une part, le matériau doit être cristallin et que, d'autre part, les guides doivent être dessinés dans la direction des plans cristallins. Il n'est alors plus possible d'envisager des parties courbes pour ces guides .However, it is then greatly limited by the fact that, on the one hand, the material must be crystalline and that, on the other hand, the guides must be drawn in the direction of the crystal planes. It is then no longer possible to envisage curved parts for these guides.
Le problème principal lié à la réduction de la rugosité par oxydation/désoxydation du silicium est double. D'une part, cette solution ne s'applique qu'au silicium et donc pas aux autres matériaux à fort écart d'indice comme les matériaux III-V.The main problem related to the reduction of roughness by oxidation / deoxidation of silicon is twofold. On the one hand, this solution only applies to silicon and therefore not to other materials with a large index difference such as III-V materials.
D'autre part, cette solution entraîne une importante perte de cote pour les guides. D'après le document [3], l'épaisseur d'un guide passe de 0,35μm à 0, 05μm.On the other hand, this solution leads to a significant loss of rating for the guides. According to document [3], the thickness of a guide goes from 0.35 μm to 0.05 μm.
Une légère perte de cote pourrait être facilement prise en compte lors de la conception du guide, mais une perte de cote de cette ampleur rend très délicate, voire impossible, la fabrication de certains dispositifs, par exemple des coupleurs de proximité dans lesquels on doit former deux guides colinéaires et très proches l'un de l'autre.A slight loss of dimension could easily be taken into account when designing the guide, but a loss of dimension of this magnitude makes it very difficult, if not impossible, to manufacture certain devices, for example proximity couplers in which one must form two collinear guides and very close to each other.
La solution préconisée dans le document [3] ne s'applique donc qu'à certains dispositifs.The solution recommended in document [3] therefore only applies to certain devices.
Dans le cas de la réduction des pertes par rugosité au moyen d'une gravure chimique, on est grandement limité par le fait que les guides doivent s'étendre suivant quelques directions privilégiées, sans qu'il soit possible de former des parties courbes.In the case of reduction of roughness losses by means of chemical etching, it is greatly limited by the fact that the guides must extend in a few preferred directions, without it being possible to form curved parts.
EXPOSÉ DE L'INVENTIONSTATEMENT OF THE INVENTION
La présente invention a pour but de remédier aux inconvénients précédents. Elle propose un guide d'onde optique à fort écart d'indice de réfraction, dont les pertes par rugosité sont toutefois plus faibles que celles des guides à fort écart d'indice connus. L'invention propose aussi un procédé de fabrication d'un tel guide.The object of the present invention is to remedy the above drawbacks. It offers an optical waveguide with a large refractive index difference, the roughness losses of which are, however, lower than those of known guides with large index difference. The invention also provides a method of manufacturing such a guide.
De façon précise, la présente invention a pour objet un guide d'onde optique comprenant :Specifically, the subject of the present invention is an optical waveguide comprising:
- un cœur qui a un indice de réfraction Ne, ce cœur ayant des flancs, et des première et deuxième couches de confinement entre lesquelles se trouve le cœur et qui ont respectivement des indices de réfraction NI et N2 , ces indices de réfraction NI et N2 étant inférieurs à l'indice de réfraction Ne du coeur, ce guide d'onde optique étant caractérisé en ce qu'il comprend en outre au moins une couche intermédiaire qui s'étend au moins le long des flancs du cœur, entre ce cœur et la première couche de confinement, et qui a un indice de réfraction N3 adapté à l'indice de réfraction Ne du cœur et à l'indice de réfraction NI de la première couche de confinement pour minimiser les pertes optiques, cet indice de réfraction N3 étant inférieur à Ne et supérieur à NI . Selon un mode de réalisation particulier du guide d'onde optique objet de l'invention, l'indice de réfraction N3 est donné par la formule suivante :a core which has a refraction index Ne, this core having sides, and first and second confinement layers between which the core is located and which have respectively refractive indices NI and N2, these refractive indices NI and N2 being lower than the refractive index Ne of the heart, this optical waveguide being characterized in that it further comprises at least one intermediate layer which extends at least along the sides of the heart, between this heart and the first confinement layer, and which has a refractive index N3 adapted to the refractive index Ne of the core and to the refractive index NI of the first confining layer to minimize optical losses, this refractive index N3 being less than Ne and greater than NI. According to a particular embodiment of the optical waveguide object of the invention, the refractive index N3 is given by the following formula:
N3 = * c ? N3 = * c?
Kλ + K2 où Kl et K2 sont des paramètres liés à la géométrie du guide d'onde optique.K λ + K 2 where Kl and K2 are parameters related to the geometry of the optical waveguide.
Selon un mode de réalisation préféré de l'invention, le cœur est formé sur la deuxième couche de confinement, ce guide d'onde optique étant ainsi un guide d'onde optique à saut d'indice.According to a preferred embodiment of the invention, the heart is formed on the second confinement layer, this optical waveguide thus being an optical waveguide with index jump.
Selon un premier mode de réalisation particulier du guide d'onde optique objet de l'invention, la couche intermédiaire s'étend le long du cœur, entre ce cœur et la première couche de confinement, et sépare ainsi totalement le cœur de la première couche de confinement.According to a first particular embodiment of the optical waveguide which is the subject of the invention, the intermediate layer extends along the core, between this core and the first confinement layer, and thus completely separates the core from the first layer containment.
Selon un deuxième mode de réalisation particulier, la couche intermédiaire s'étend seulement le long des flancs du cœur, entre ce cœur et la première couche de confinement.According to a second particular embodiment, the intermediate layer extends only along the sides of the heart, between this heart and the first confinement layer.
Le guide d'onde optique objet de l'invention peut comprendre une pluralité de couches intermédiaires dont les indices de réfraction respectifs vont en décroissant à partir du cœur. Ce mode de réalisation permet une optimisation des indices de réfraction des couches intermédiaires pour minimiser les pertes optiques.The optical waveguide which is the subject of the invention can comprise a plurality of intermediate layers, the respective refractive indices of which decrease from the heart. This embodiment allows an optimization of the refractive indices of the intermediate layers to minimize the optical losses.
Selon un mode de réalisation avantageux de l'invention, le guide d'onde optique objet de l'invention est un guide à fort confinement d'indice. Par « fort confinement d'indice », on entend une différence d' indice entre le cœur et la première couche de confinement qui est supérieure à 0,1 et de préférence supérieure à 0,5. A titre d'exemple, ce type de guide peut comprendre un cœur en silicium et une première couche de confinement en silice.According to an advantageous embodiment of the invention, the optical waveguide object of the invention is a guide with high index confinement. By "high index confinement" is meant a difference in index between the core and the first confinement layer which is greater than 0.1 and preferably greater than 0.5. By way of example, this type of guide can include a silicon core and a first silica confinement layer.
La présente invention concerne également un procédé de fabrication du guide d'onde optique objet de l'invention, ce guide d'onde optique comprenant :The present invention also relates to a method of manufacturing the optical waveguide which is the subject of the invention, this optical waveguide comprising:
- le cœur qui a un indice de réfraction Ne, ce cœur ayant des flancs, et les première et deuxième couches de confinement entre lesquelles se trouve le cœur et qui ont respectivement des indices de réfraction NI et N2 , ces indices de réfraction NI et N2 étant inférieurs à l'indice de réfraction Ne du coeur, ce procédé étant caractérisé en ce que : - on forme le cœur, on forme au moins une couche intermédiaire sur le cœur, cette couche intermédiaire s'étendant au moins le long des flancs du cœur et ayant un indice de réfraction N3 adapté à l'indice de réfraction Ne du cœur et à l'indice de réfraction NI de la première couche de confinement pour minimiser les pertes optiques, cet indice de réfraction N3 étant inférieur à Ne et supérieur à NI, et on forme la première couche de confinement .the core which has a refractive index Ne, this core having sides, and the first and second confinement layers between which the core is located and which have respectively refractive indices NI and N2, these refractive indices NI and N2 being lower than the refractive index Ne of the heart, this process being characterized in that: - the heart is formed, at least one intermediate layer is formed on the heart, this intermediate layer extending at least along the sides of the core and having a refractive index N3 adapted to the refractive index Ne of the core and to the refractive index NI of the first confinement layer to minimize optical losses, this refractive index N3 being less than Ne and greater than NI, and we form the first containment layer.
Selon un mode de mise en œuvre préféré du procédé objet de l'invention, on forme le cœur sur la deuxième couche de confinement, le guide d'onde optique étant ainsi un guide d'onde optique à saut d'indice. Selon un premier mode de mise en œuvre particulier du procédé objet de l'invention, on forme la couche intermédiaire le long du cœur, entre ce cœur et la première couche de confinement, de manière à séparer totalement le cœur de la première couche de confinement . Selon un deuxième mode de mise en œuvre particulier, on forme la couche intermédiaire seulement le long des flancs du cœur, entre ce cœur et la première couche de confinement.According to a preferred embodiment of the method which is the subject of the invention, the core is formed on the second confinement layer, the optical waveguide thus being an optical waveguide with index jump. According to a first particular mode of implementation of the process which is the subject of the invention, the intermediate layer along the core, between this core and the first confinement layer, so as to completely separate the core from the first confinement layer. According to a second particular embodiment, the intermediate layer is formed only along the sides of the heart, between this heart and the first confinement layer.
Dans le procédé objet de l'invention, on peut former une pluralité de couches intermédiaires dont les indices de réfraction respectifs vont en décroissant à partir du cœur.In the process which is the subject of the invention, a plurality of intermediate layers can be formed, the respective refractive indices of which decrease from the core.
BRÈVE DESCRIPTION DES DESSINS La présente invention sera mieux comprise à la lecture de la description d'exemples de réalisation donnés ci -après, à titre purement indicatif et nullement limitatif, en faisant référence aux dessins annexés sur lesquels : - la figure 1A est une vue en coupe transversale schématique d'un guide d'onde optique connu, à saut d'indice, et a déjà été décrite, la figure 1B est une vue en coupe transversale schématique d'un guide d'onde optique connu, à gradient d'indice, et a déjà été décrite, la figure 2 est une vue en coupe transversale schématique d'un mode de réalisation particulier du guide d'onde optique objet de l'invention, comprenant une seule couche intermédiaire, - la figure 3 est une vue en coupe transversale schématique d'un mode de réalisation particulier du guide d'onde optique objet de l'invention, comprenant deux couches intermédiaires, les figures 4 à 6 illustrent schématiquement des étapes d'un mode de mise en œuvre particulier du procédé objet de l'invention,BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be better understood on reading the description of exemplary embodiments given below, by way of purely indicative and in no way limiting, with reference to the appended drawings in which: - Figure 1A is a view in schematic cross-section of a known optical waveguide, with index jump, and has already been described, FIG. 1B is a schematic cross-section view of a known optical waveguide, with gradient of clue, and has already been described, FIG. 2 is a schematic cross-sectional view of a particular embodiment of the optical waveguide object of the invention, comprising a single intermediate layer, - FIG. 3 is a view in schematic cross-section of an embodiment particular of the optical waveguide object of the invention, comprising two intermediate layers, FIGS. 4 to 6 schematically illustrate steps of a particular mode of implementation of the method object of the invention,
- la figure 7 illustre schématiquement une variante du procédé illustré par les figures 4 à 6, et les figures 8 à 10 illustrent schématiquement des étapes d'un autre mode de réalisation particulier du procédé objet de 1 ' invention.- Figure 7 schematically illustrates a variant of the process illustrated by Figures 4 to 6, and Figures 8 to 10 schematically illustrate steps of another particular embodiment of the process object of one invention.
EXPOSÉ DÉTAILLÉ DE MODES DE RÉALISATION PARTICULIERSDETAILED PRESENTATION OF PARTICULAR EMBODIMENTS
Comme on l'a vu, l'invention a pour but de diminuer les pertes par rugosité des guides à fort écart d'indice.As we have seen, the invention aims to reduce the roughness losses of guides with a large index difference.
Selon un aspect de l'invention, on enrobe le coeur d'un tel guide, après gravure, d'une ou plusieurs couches très minces, faites de matériaux diélectriques dont les indices de réfraction optiques sont intermédiaires entre 1 ' indice Ne du coeur et 1 ' indice NI de la couche de confinement dont on recouvre ensuite le coeur.According to one aspect of the invention, the core is coated with such a guide, after etching, with one or more very thin layers, made of dielectric materials whose optical refractive indices are intermediate between the index Ne of the core and 1 NI index of the confinement layer with which the core is then covered.
Ceci est schématiquement illustré par l'exemple de la figure 2 où l'on voit, en coupe transversale, un guide à saut d'indice conforme à l'invention, comportant un cœur 12 entre une couche de confinement supérieure 14, dont l'indice optique est noté NI, et une couche de confinement inférieure 16, dont l'indice optique est noté N2 , ainsi qu'une couche supplémentaire continue 18, dont l'indice optique est noté N3 et qui s'étend entre les couches 14 et 16 et entre la couche 14 et le cœur 12.This is schematically illustrated by the example of FIG. 2 in which we see, in cross section, a index jump guide according to the invention, comprising a core 12 between an upper confinement layer 14, the optical index is denoted NI, and a lower confinement layer 16, whose optical index is denoted N2, as well as an additional continuous layer 18, whose optical index is denoted N3 and which extends between layers 14 and 16 and between layer 14 and core 12.
Les pertes P par rugosité, pour un guide plan incluant une seule couche mince supplémentaire, dont l'indice est noté N3 , sont approximativement données par la formule suivante :The losses P by roughness, for a planar guide including a single additional thin layer, the index of which is noted N3, are approximately given by the following formula:
P≈Kα (Nc 2-N32) 2+K2 (N32-N12) 2 où Ki et K2 sont des facteurs de proportionnalité . Dans ce cas, il est facile de montrer que les pertes sont minimales pour une valeur de N3 qui est donnée par la formule suivante :P≈K α (N c 2 -N3 2 ) 2 + K 2 (N3 2 -N1 2 ) 2 where Ki and K 2 are factors of proportionality. In this case, it is easy to show that the losses are minimal for a value of N3 which is given by the following formula:
N32 _ K1NC 2 + K2N12 κ1 +κ2 N32 _ K 1 N C 2 + K 2 N1 2 κ 1 + κ 2
Ces calculs sont approchés et la valeur de l'indice de réfraction de la couche supplémentaire, ou couche intermédiaire, peut être affinée à l'aide de logiciels commercialement disponibles, permettant le calcul numérique de la propagation optique dans le guide, ces logiciels mettant en œuvre la méthode BPM (pour "Beam Propagation Method") ou même la méthode FDTD (pour "Finite Différence Time Domain") .These calculations are approximated and the value of the refractive index of the additional layer, or intermediate layer, can be refined using commercially available software, allowing the numerical calculation of the optical propagation in the guide, this software putting in place implements the BPM method (for "Beam Propagation Method") or even the FDTD method (for "Finite Difference Time Domain").
Il est possible d'améliorer ce résultat en augmentant le nombre de couches intermédiaires comme le montre la figure 3.It is possible to improve this result by increasing the number of intermediate layers as shown in Figure 3.
L'exemple que l'on voit sur cette figure 3 résulte simplement de l'ajout d'une autre couche intermédiaire continue 20 à l'exemple de la figure 2, cette autre couche 20 s ' étendant entre la couche intermédiaire 18 et la couche 14.The example that can be seen in this FIG. 3 simply results from the addition of another continuous intermediate layer 20 to the example of FIG. 2, this other layer 20 extending between the intermediate layer 18 and the layer 14.
On précise que l'indice optique N'3 de cette autre couche 20 est inférieur à N3 et supérieur à NI.It is specified that the optical index N'3 of this other layer 20 is less than N3 and greater than NI.
L'idée générale est toujours de diminuer l'écart d'indice à chacune des interfaces afin de diminuer les pertes par rugosité en ces interfaces.The general idea is always to decrease the index difference at each of the interfaces in order to reduce the roughness losses at these interfaces.
Dans ce cas, il convient d'utiliser des logiciels de calcul numérique pour optimiser les indices des couches que l'on ajoute.In this case, numerical calculation software should be used to optimize the indices of the layers that are added.
Des avantages de 1 ' invention sont donnés ci-après .Advantages of the invention are given below.
L'invention permet de réduire les pertes par rugosité des guides à fort écart d'indice que l'on forme par photolithographie et gravure, à l'aide d'une étape technologique très peu coûteuse, et permet ainsi d'envisager des dispositifs optiques intégrés de très petite taille, conservant tout de même de bonnes performances optiques.The invention makes it possible to reduce the roughness losses of guides with a large index difference which are formed by photolithography and etching, using a very inexpensive technological step, and thus makes it possible to envisage optical devices. integrated very small, still retaining good optical performance.
L'invention est compatible avec tous les matériaux à fort écart d'indice et peut très bien être combinée à d'autres méthodes de réduction de la rugosité elle-même. Par exemple, dans le cas particulier du silicium où il est possible de réduire la rugosité des flancs des guides par une technique d'oxydâtion/désoxydation du silicium, comme cela est décrit dans le document [3] , on peut mettre en œuvre à la fois cette technique et la présente invention. On donne maintenant des exemples de procédés de fabrication de guides d'ondes optiques conformes à l'invention.The invention is compatible with all materials with a large index difference and can very well be combined with other methods of reducing roughness itself. For example, in the specific case of silicon where it is possible to reduce the roughness of the sides of the guides by an oxidation / deoxidation technique of silicon, as described in document [3], it is possible to use the both this technique and the present invention. We now give examples of methods of manufacturing optical waveguides according to the invention.
Dans le cas de guides à fort écart d'indice en silicium, la fabrication de tels guides a lieu bien souvent en partant d'un substrat SOI (pour "Silicon OnIn the case of guides with a large silicon index difference, the manufacture of such guides very often takes place starting from an SOI substrate (for "Silicon On
Insulator") dont la structure est représentée sur la figure 4.Insulator ") whose structure is shown in Figure 4.
Ce substrat SOI comprend un substrat monocristallin 22 dans lequel est enterrée une couche de silice 24, cette dernière étant ainsi surmontée d'une couche de silicium monocristallin 26.This SOI substrate comprises a monocrystalline substrate 22 in which a layer of silica 24 is buried, the latter being thus surmounted by a layer of monocrystalline silicon 26.
Afin de former une structure qui soit monomode aux longueurs d'onde utilisées dans les télécommunications (de l'ordre de l,55μm), la couche de silice enterrée peut avoir une épaisseur comprise entre 0,7μm et lμm et la couche supérieure en silicium peut avoir une épaisseur comprise entre 0,2μm et 0,5μm.In order to form a structure which is single-mode at the wavelengths used in telecommunications (of the order of 1.55 μm), the layer of buried silica can have a thickness of between 0.7 μm and l μm and the upper layer of silicon can have a thickness between 0.2μm and 0.5μm.
Le cœur 28 du guide est ensuite formé par photolithographie et gravure à partir de la couche 26, et l'on obtient alors, en coupe transversale, la structure de la figure 5.The core 28 of the guide is then formed by photolithography and etching from the layer 26, and the structure of FIG. 5 is then obtained in cross section.
La largeur du cœur 28 peut aller de 0,4μm, si l'on désire avoir un guide monomode, jusqu'à plusieurs micromètres si l'on désire avoir un guide multimode.The width of the core 28 can range from 0.4 μm, if one wishes to have a single-mode guide, up to several micrometers if one wishes to have a multimode guide.
En reprenant la formule mentionnée plus haut et en supposant que le champ électromagnétique varie peu entre les deux interfaces de la couche mince intermédiaire que l'on veut ajouter, on a :By taking up the formula mentioned above and assuming that the electromagnetic field varies little between the two interfaces of the intermediate thin layer that we want to add, we have:
Nc=3, 5 Nl=l , 45 K1=K2 N c = 3, 5 Nl = 1.45 K 1 = K 2
N3 peu différent de 2,64.N3 little different from 2.64.
Un matériau présentant un indice de réfraction se rapprochant de cette valeur (2,64) peut par exemple être du carbure de silicium, du carbone diamant, du dioxyde de titane, ou encore du nitrure de silicium (non stoechiométrique) .A material having a refractive index approaching this value (2.64) can for example be silicon carbide, diamond carbon, titanium dioxide, or even silicon nitride (not stoichiometric).
Si l'on dépose une très fine couche d'un matériau ayant un tel indice, on diminue les pertes d'un facteur peu différent deIf a very thin layer of a material having such an index is deposited, the losses are reduced by a factor little different from
(Ne 2 - 2)2 (NC 2 - N32)2 + (N32 -N12)2 c'est à dire peu différent de 2. Si l'on utilise du nitrure de silicium stoechiométrique dont l'indice est approximativement égal à 2, on obtient une diminution des pertes d'un facteur environ égal à 1,5.(N e 2 - 2 ) 2 (N C 2 - N3 2 ) 2 + (N3 2 -N1 2 ) 2 i.e. little different from 2. If stoichiometric silicon nitride is used whose index is approximately equal to 2, a reduction in losses is obtained by a factor approximately equal to 1.5.
On peut donc former une fine couche de nitrure de silicium de quelques dizaines de nanomètres d'épaisseur, par exemple par LPCVD, avant de recouvrir la structure d'une couche de silice (couche de confinement supérieure) par exemple par PECVD.It is therefore possible to form a thin layer of silicon nitride a few tens of nanometers thick, for example by LPCVD, before covering the structure with a layer of silica (upper confinement layer) for example by PECVD.
On obtient alors la structure de la figure 6 où l'on voit la couche de nitrure de silicium 30, qui recouvre la couche 24 et le cœur 28, et la couche de silice 32 qui recouvre cette couche 30.The structure of FIG. 6 is then obtained, where we see the layer of silicon nitride 30, which covers the layer 24 and the core 28, and the layer of silica 32 which covers this layer 30.
Au lieu de déposer une seule couche (couche 30) , on peut déposer successivement deux couches minces 34 et 36 de matériaux différents comme le montre la figure 7. Les matériaux doivent avoir des indices compris entre l'indice du silicium et celui de la silice, l'indice de la première couche 34, qui recouvre la couche 24 et le cœur 28, devant être supérieur à l'indice de la deuxième couche 36 qui recouvre la couche 34.Instead of depositing a single layer (layer 30), two thin layers 34 and 36 of different materials can be successively deposited as shown in FIG. 7. The materials must have indices between the index of silicon and that of silica, the index of the first layer 34, which covers the layer 24 and the core 28, having to be greater than the index of the second layer 36 which covers layer 34.
A titre d'exemple, on utilise du Ti02 d'indice environ égal à 2,4 pour la couche 34 et du Si3N4 d'indice environ égal à 2 pour la couche 36. On obtient alors une diminution des pertes par rugosité d'un facteur environ égal à 2.By way of example, Ti0 2 with an index approximately equal to 2.4 is used for layer 34 and Si 3 N 4 with an index approximately equal to 2 for layer 36. A reduction in losses is then obtained. roughness of a factor approximately equal to 2.
La couche de Ti02 peut être déposée par évaporation ou pulvérisation et la couche de Si3N4 par LPCVD . Dans bien des cas, la rugosité sur les flancs 38 et 40 du cœur 28 (figure 8) , rugosité qui est due à la photolithographie et à la gravure, est bien supérieure à la rugosité sur les bords inférieur et supérieur 42 et 44 du coeur. II est possible de ne réaliser les couches intermédiaires que sur les flancs 38 et 40 (bords latéraux) du coeur si on le désire.The Ti0 2 layer can be deposited by evaporation or spraying and the Si 3 N 4 layer by LPCVD. In many cases, the roughness on the sides 38 and 40 of the heart 28 (FIG. 8), roughness which is due to photolithography and etching, is much greater than the roughness on the lower and upper edges 42 and 44 of the heart. . It is possible to produce the intermediate layers only on the sides 38 and 40 (lateral edges) of the core if desired.
Pour cela, on part du cœur formé par gravure sur son subtrat. La figure 5 montre un tel cœur 28 dans le cas du silicium sur silice.For this, we start from the heart formed by engraving on its substrate. FIG. 5 shows such a core 28 in the case of silicon on silica.
Ensuite, on dépose une fine couche 46 en Si3N4 selon l'invention par LPCVD et l'on obtient alors la structure de la figure 8. On voit que la couche 46 recouvre la couche 24 et le cœur 28. Ensuite, on effectue une gravure anisotrope de la couche 46, par exemple par la technique de gravure ionique réactive ("reactive ion etching") pleine plaque (sans étape de photolithographie) et l'on obtient la structure de la figure 9 où l'on voit que les flancs du cœur 28 sont recouverts de zones en Si3N4, constituées des portions de la couche 46 qui subsistent après la gravure anisotrope.Then, a thin layer 46 of Si 3 N 4 according to the invention is deposited by LPCVD and the structure of FIG. 8 is then obtained. We see that layer 46 covers layer 24 and core 28. Then, we performs anisotropic etching of the layer 46, for example by the technique of reactive ion etching ("reactive ion etching") full plate (without photolithography step) and we obtain the structure of FIG. 9 where we see that the flanks of the core 28 are covered with zones of Si 3 N 4 , consisting of the portions of layer 46 which remain after the anisotropic etching.
Il ne reste plus alors qu'à recouvrir entièrement la structure obtenue d'une couche 48 en Si02, par exemple par PECVD, pour obtenir le guide d'onde optique à saut d'indice de la figure 10.It then remains only to completely cover the structure obtained with a layer 48 of Si0 2 , for example by PECVD, in order to obtain the optical waveguide with index jump of FIG. 10.
Comme précédemment, au lieu d'une seule couche intermédiaire (couche 46) , on peut en former une pluralité de sorte que les flancs du cœur sont alors recouverts de portions de cette pluralité de couches. As before, instead of a single intermediate layer (layer 46), a plurality can be formed so that the sides of the heart are then covered with portions of this plurality of layers.

Claims

REVENDICATIONS
1. Guide d'onde optique comprenant :1. Optical waveguide comprising:
- un cœur (12, 28) qui a un indice de réfraction Ne, ce cœur ayant des flancs (38, 40) , et des première et deuxième couches de confinement (14-16, 32-24, 48-24) entre lesquelles se trouve le cœur et qui ont respectivement des indices de réfraction NI et N2 , ces indices de réfraction NI et N2 étant inférieurs à l'indice de réfraction Ne du coeur, ce guide d'onde optique étant caractérisé en ce qu'il comprend en outre au moins une couche intermédiaire (18, 18-20, 30, 34-36, 46) qui s'étend au moins le long des flancs du cœur, entre ce cœur et la première couche de confinement (14, 32, 48), et qui a un indice de réfraction N3 adapté à l'indice de réfraction Ne du cœur et à l'indice de réfraction NI de la première couche de confinement pour minimiser les pertes optiques, cet indice de réfraction N3 étant inférieur à Ne et supérieur à NI.- a core (12, 28) which has a refractive index Ne, this core having sides (38, 40), and first and second confinement layers (14-16, 32-24, 48-24) between which is the heart and which have respectively refractive indices NI and N2, these refractive indices NI and N2 being lower than the refractive index Ne of the heart, this optical waveguide being characterized in that it comprises in in addition to at least one intermediate layer (18, 18-20, 30, 34-36, 46) which extends at least along the sides of the heart, between this heart and the first confinement layer (14, 32, 48) , and which has a refractive index N3 adapted to the refractive index Ne of the core and to the refractive index NI of the first confinement layer to minimize optical losses, this refractive index N3 being less than Ne and greater to NI.
2. Guide d'onde optique selon la revendication! , dans lequel l'indice de réfraction N3 est donné par la formule suivante :2. Optical waveguide according to claim! , in which the refractive index N3 is given by the following formula:
N22 _ KXNC 2 + K2N κ1 +κ2 où Kl et K2 sont des paramètres liés à la géométrie du guide d'onde optique. N22 _ K X N C 2 + K 2 N κ 1 + κ 2 where Kl and K2 are parameters related to the geometry of the optical waveguide.
3. Guide d'onde optique selon l'une quelconque des revendications 1 et 2 , dans lequel le cœur (28) est formé sur la deuxième couche de confinement (24), ce guide d'onde optique étant ainsi un guide d'onde optique à saut d'indice.3. Optical waveguide according to any one of claims 1 and 2, in which the heart (28) is formed on the second layer of confinement (24), this optical waveguide thus being an optical waveguide with index jump.
4. Guide d'onde optique selon l'une quelconque des revendications 1 à 3, dans lequel la couche intermédiaire (18, 18-20, 30, 34-36) s'étend le long du cœur (28) , entre ce cœur et la première couche de confinement (32) , et sépare ainsi totalement le cœur de la première couche de confinement.4. Optical waveguide according to any one of claims 1 to 3, in which the intermediate layer (18, 18-20, 30, 34-36) extends along the heart (28), between this heart and the first confinement layer (32), and thus completely separates the core from the first confinement layer.
5. Guide d'onde optique selon l'une quelconque des revendications 1 à 3, dans lequel la couche intermédiaire (46) s'étend seulement le long des flancs (38, 40) du cœur, entre ce cœur et la première couche de confinement (48) .5. Optical waveguide according to any one of claims 1 to 3, in which the intermediate layer (46) extends only along the sides (38, 40) of the heart, between this heart and the first layer of containment (48).
6. Guide d'onde optique selon l'une quelconque des revendications 1 à 5, comprenant une pluralité de couches intermédiaires (18-20, 34-36) dont les indices de réfraction respectifs vont en décroissant à partir du cœur (28) .6. Optical waveguide according to any one of claims 1 to 5, comprising a plurality of intermediate layers (18-20, 34-36) whose respective refractive indices are decreasing from the heart (28).
7. Guide d'onde optique selon l'une quelconque des revendications 1 à 6, dans lequel le guide d'onde optique est un guide à fort confinement d' indice .7. Optical waveguide according to any one of claims 1 to 6, wherein the optical waveguide is a guide with high index confinement.
8. Procédé de fabrication du guide d'onde optique selon l'une quelconque des revendications 1 à 7, ce guide d'onde optique comprenant : le cœur (28) qui a un indice de réfraction Ne, ce cœur ayant des flancs (38, 40) , et les première et deuxième couches de confinement (32-24, 48-24) entre lesquelles se trouve le cœur et qui ont respectivement des indices de réfraction NI et N2 , ces indices de réfraction NI et N2 étant inférieurs à l'indice de réfraction Ne du coeur, ce procédé étant caractérisé en ce que : - on forme le cœur (28) , on forme au moins une couche intermédiaire (30, 34-36, 46) sur le cœur, cette couche intermédiaire s 'étendant au moins le long des flancs du cœur et ayant un indice de réfraction N3 adapté à l'indice de réfraction Ne du cœur et à l'indice de réfraction NI de la première couche de confinement pour minimiser les pertes optiques, cet indice de réfraction N3 étant inférieur à Ne et supérieur à NI, et on forme la première couche de confinement (32, 48) .8. A method of manufacturing the optical waveguide according to any one of claims 1 to 7, this optical waveguide comprising: the core (28) which has a refractive index Ne, this core having flanks (38 , 40), and the first and second confinement layers (32-24, 48-24) between which the core is located and which respectively have indices of refraction NI and N2, these refractive indices NI and N2 being lower than the refractive index Ne of the core, this process being characterized in that: - the core is formed (28), at least one intermediate layer is formed (30 , 34-36, 46) on the heart, this intermediate layer extending at least along the sides of the heart and having a refractive index N3 adapted to the refractive index Ne of the heart and to the refractive index NI of the first confinement layer to minimize optical losses, this refractive index N3 being less than Ne and greater than NI, and the first confinement layer (32, 48) is formed.
9. Procédé selon la revendication 8,, dans lequel on forme le cœur (28) sur la deuxième couche de confinement (24), le guide d'onde optique étant ainsi un guide d'onde optique à saut d'indice. 9. The method of claim 8, wherein the heart is formed (28) on the second confinement layer (24), the optical waveguide thus being an optical waveguide index jump.
10. Procédé selon l'une quelconque des revendications 8 et 9, dans lequel on forme la couche intermédiaire (30, 34-36) le long du cœur (28), entre ce cœur et la première couche de confinement (32, 48), de manière à séparer totalement le cœur de la première couche de confinement.10. Method according to any one of claims 8 and 9, in which the intermediate layer (30, 34-36) is formed along the core (28), between this core and the first confinement layer (32, 48). , so as to completely separate the core from the first containment layer.
11. Procédé selon l'une quelconque des revendications 8 et 9, dans lequel on forme la couche intermédiaire (46) seulement le long des flancs (38, 40) du cœur (28) , entre ce cœur et la première couche de confinement (48) . 11. Method according to any one of claims 8 and 9, in which the intermediate layer (46) is formed only along the sides (38, 40) of the heart (28), between this heart and the first confinement layer ( 48).
12. Procédé selon l'une quelconque des revendications 8 à 11, dans lequel on forme une pluralité de couches intermédiaires (34, 36) dont les indices de réfraction respectifs vont en décroissant à partir du cœur (28) . 12. Method according to any one of claims 8 to 11, in which a plurality of intermediate layers (34, 36) is formed, the respective refractive indices of which decrease from the core (28).
PCT/FR2003/050084 2002-10-10 2003-10-09 Optical waveguide with high index contrast and reduced losses due to roughness, and method of producing same WO2004034092A2 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR02/12592 2002-10-10
FR0212592A FR2845775B1 (en) 2002-10-10 2002-10-10 OPTICAL WAVEGUIDE GUIDE WITH HIGH INDEX CONTRAST AND REDUCED RUGOSITY LOSSES, AND METHOD FOR MANUFACTURING THE SAME

Publications (2)

Publication Number Publication Date
WO2004034092A2 true WO2004034092A2 (en) 2004-04-22
WO2004034092A3 WO2004034092A3 (en) 2004-07-29

Family

ID=32039602

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/FR2003/050084 WO2004034092A2 (en) 2002-10-10 2003-10-09 Optical waveguide with high index contrast and reduced losses due to roughness, and method of producing same

Country Status (2)

Country Link
FR (1) FR2845775B1 (en)
WO (1) WO2004034092A2 (en)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114400504A (en) * 2021-12-07 2022-04-26 中国航空工业集团公司北京长城计量测试技术研究所 Preparation method of low-loss silicon nitride waveguide

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR3105455A1 (en) * 2019-12-20 2021-06-25 Commissariat A L'energie Atomique Et Aux Energies Alternatives Waveguide manufacturing process

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0358414A2 (en) * 1988-09-03 1990-03-14 Gec-Marconi Limited Optical waveguide
US5057022A (en) * 1989-03-20 1991-10-15 Miller Robert O Method of making a silicon integrated circuit waveguide
US5143577A (en) * 1991-02-08 1992-09-01 Hoechst Celanese Corporation Smooth-wall polymeric channel and rib waveguides exhibiting low optical loss
US5825524A (en) * 1994-10-25 1998-10-20 Commissariat A L'energie Atomique Transverse electric mode electro-optic cell for a modulator and process for producing such a cell
US6157765A (en) * 1998-11-03 2000-12-05 Lucent Technologies Planar waveguide optical amplifier

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0358414A2 (en) * 1988-09-03 1990-03-14 Gec-Marconi Limited Optical waveguide
US5057022A (en) * 1989-03-20 1991-10-15 Miller Robert O Method of making a silicon integrated circuit waveguide
US5143577A (en) * 1991-02-08 1992-09-01 Hoechst Celanese Corporation Smooth-wall polymeric channel and rib waveguides exhibiting low optical loss
US5825524A (en) * 1994-10-25 1998-10-20 Commissariat A L'energie Atomique Transverse electric mode electro-optic cell for a modulator and process for producing such a cell
US6157765A (en) * 1998-11-03 2000-12-05 Lucent Technologies Planar waveguide optical amplifier

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
LEE K K ET AL: "Fabrication of ultralow-loss Si/SiO/sub 2/ waveguides by roughness reduction" OPTICS LETTERS, 1 DEC. 2001, OPT. SOC. AMERICA, USA, vol. 26, no. 23, pages 1888-1890, XP002244938 ISSN: 0146-9592 cité dans la demande *
RIDDER DE R M ET AL: "SILICON OXYNITRIDE PLANAR WAVEGUIDING STRUCTURES FOR APPLICATION IN OPTICAL COMMUNICATION" IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, IEEE SERVICE CENTER, US, vol. 4, no. 6, novembre 1998 (1998-11), pages 930-937, XP000801339 ISSN: 1077-260X *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114400504A (en) * 2021-12-07 2022-04-26 中国航空工业集团公司北京长城计量测试技术研究所 Preparation method of low-loss silicon nitride waveguide

Also Published As

Publication number Publication date
FR2845775B1 (en) 2005-01-07
FR2845775A1 (en) 2004-04-16
WO2004034092A3 (en) 2004-07-29

Similar Documents

Publication Publication Date Title
US6690871B2 (en) Graded index waveguide
JP5170792B2 (en) Planar optical waveguide and optical device
US7397995B2 (en) Multiple-core planar optical waveguides and methods of fabrication and use thereof
EP0129463B1 (en) Integrated optical polarising device and process for its manufacture
EP0323317B1 (en) Method of manufacturing micro light guides having a low optical propagation loss by depositing multiple layers
EP3287822B1 (en) Photonic circuit comprising a structure to couple to an external device
US8000565B2 (en) Buried dual taper waveguide for passive alignment and photonic integration
EP1918744B1 (en) Process for manufacturing a slot waveguide
EP2169436A1 (en) Light coupler between an optical fibre and a waveguide made on an SOI substrate
FR2633401A1 (en) SEMICONDUCTOR DEVICE COMPRISING AN INTEGRATED LIGHT GUIDE WHICH HAS AT LEAST ONE RECTILINE AND A CURVED PART
EP2141520A1 (en) Coupling device with compensated birefringence
US20200150338A1 (en) Photonic Apparatus for Controlling Polarization
WO2004097464A2 (en) Multiple-core planar optical waveguides and methods of fabrication and use thereof
CN107329208A (en) A kind of silicon photon spot-size converter of refractive index gradient change
Pearson et al. Arrayed waveguide grating demultiplexers in silicon-on-insulator
EP0668517B1 (en) Procedure of realising an optical guide, and an optical guide obtained by this procedure
EP0324694B1 (en) Integrated-optics device for the separation of the polarization components of an electromagnetic field, and method for manufacturing it
EP0811863B1 (en) Vertical positioning of an optoelectronical component on a carrier relative to an optical conductor integrated on this carrier
EP3022593A1 (en) Optical coupler provided with an intermediate waveguide
EP3491438B1 (en) Multi-spectral optical coupler with low receive losses
EP2648025A1 (en) A process for manufacturing a photonic circuit
WO2004034092A2 (en) Optical waveguide with high index contrast and reduced losses due to roughness, and method of producing same
EP0736786A1 (en) Polarisation-independant multi-wavelength filter and manufacturing process
EP1058138A1 (en) Multiplexer/demultiplexer having three waveguides
Janz Silicon-based waveguide technology for wavelength division multiplexing

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A2

Designated state(s): JP US

AL Designated countries for regional patents

Kind code of ref document: A2

Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LU MC NL PT RO SE SI SK TR

121 Ep: the epo has been informed by wipo that ep was designated in this application
122 Ep: pct application non-entry in european phase
NENP Non-entry into the national phase

Ref country code: JP

WWW Wipo information: withdrawn in national office

Country of ref document: JP