Optical waveguides – With optical coupler – Particular coupling structure
Reexamination Certificate
1998-11-12
2001-04-03
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Particular coupling structure
C385S014000, C385S027000, C385S028000, C385S041000, C385S131000, C385S132000
Reexamination Certificate
active
06212319
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to devices suitable for use in optoelectronics, particularly those capable of distributing a propagating mode for a light wave between a plurality of pathways.
Devices of this kind are used particularly in the field of telecommunications where it is frequently necessary to transfer a light wave carrying data from one pathway (wave-guide) to one or more other pathways. The term transfer here refers to switching in which the light wave is integrally switched from one pathway to another, or an operation comprising distributing the light wave between at least two pathways. Optoelectronic components are particularly well adapted to this type of function as there is little space available and moreover the electricity consumption is limited.
Optical devices are already known, generally based on semiconductors, which operate by switching either by adiabatic transformation of modes of the light wave (known by the acronyms DOS or COSTA), or by total internal reflection (known by the English acronym TIR), or again by mode coupling (known by the English acronym EODC).
The invention relates more specifically to devices of the latter type (EODC), more particularly those which have a multilayer structure surmounted by two at least partially parallel primary lines arranged to define, in two regions, straight with the primary lines, two waveguides operating according to a first propagation mode, as well as electro-optical control means placed at a chosen location to vary the coupling between the two waveguides.
A device of this kind is described notably in the publication by M. Schienle, G. Wenger, S. Eichinger, J. Müller, L. Stoll and G. Müller, “One by eight InP/InGaAsP optical matrix switch with low insertion and high cross-talk suppression”, IEEE Journal of Lightwave technology, vol 14 No. 5, May 1995. It comprises more precisely a first line segment defining a first wave guide the “exit” end of which is enclosed by the “entry” ends of two other line segments, also defining waveguides and covered with a metallized portion forming the current supply electrode. The three line segments are parallel to one another. To transfer a wave from the first guide to one of the entrances of the other two guides at least one of the two electrodes has to be supplied with current.
Owing to its 1×2-type architecture, a device of this kind rapidly becomes a large consumer of current when the number of waveguides becomes substantial. Moreover, this device does not allow the wave to be distributed over two guides until the two electrodes placed at the end of the waveguide through which the lightwave arrives are supplied with current, thereby increasing the current consumption still further. Moreover, the wave initially circulating in the first waveguide cannot remain in it given that the line which defines it is broken off substantially level with the entrances of the two guides which frame it. As a result the device becomes bulky as it requires a “1×2”-type architecture for each waveguide through which a given wave arrives. Thus, in order to produce a switch of the 1×16 type, 4 levels of waveguide have to be used.
SUMMARY OF THE INVENTION
The invention therefore proposes to overcome all or some of the above-mentioned disadvantages.
To do this, it proposes an electro-optical device of the type comprising, in known manner, a multilayer structure surmounted by two at least partially parallel primary lines, and arranged to define in two regions two waveguides operating according to a first mode of propagation, and electro-optical control means placed at a location selected to vary the coupling between the two guides, the device being notable in that the electro-optical control means are placed between the two primary lines and arranged, on the one hand, to authorize locally a second propagation mode affecting the two regions together and, on the other hand, to control the transfer of the first mode between the two guides which enclose it, by acting principally on this second mode.
The term “multilayer structure” here denotes a stack comprising at least one so-called lower “confining” layer and a so-called upper “confining” layer placed on either side of a layer known as the “lightwave guiding” layer, the primary lines being placed on the upper confining layer, opposite the guide layer, and the materials and dimensions of the primary layers and lines being selected so as to define, substantially straight with the primary lines, two waveguides operating according to a first propagation mode.
From now on, a single electro-optical control means will be sufficient to pass a light wave from a first guide to a second nearby guide without the need to switch off said first guide. This makes it possible to produce a so-called “cascade” structure in which the electricity consumption and bulk are reduced.
Preferably, the first and second propagation modes of the light wave are of the symmetrical and antisymmetrical types, respectively, coupling between these two modes taking place when their total gives a nonzero contribution.
According to another feature of the invention, each electro-optical control means comprises an element which extends locally parallel to each of the primary lines which enclose it, in a region where they are parallel to each other, over a coupling length selected as a function of at least the wavelength of the lightwave and the actual optical indices of the structure in the regions of the waveguides, viewed by the first and second modes of this light wave, the indices being a function at least of the materials forming the structure and geometric characteristics of this structure.
More preferably, this coupling length is proportional to the ratio between the wavelength of the lightwave and a multiple of the difference between the effective optical indices of the structure in the regions of the waveguide, viewed respectively by the first mode and second mode of the lightwave.
According to yet another feature of the invention, each electro-optical control means is arranged to act on the second mode by reducing the effective optical indices of the structure, in the region which extends between the waveguides.
Thus, by adjusting the effective optical indices, it is possible to control the proportion of the lightwave which one wishes to transfer to an adjacent waveguide, or in other words the coupling between these two modes. This transfer or coupling may be partial or total.
Preferably, this reduction in the effective optical indices is achieved by injecting electric current (or in other words by “injection of carriers”) into the electro-optical control means.
Even more preferably, in the event of exceeding a current intensity threshold, the transfer of the first mode of a waveguide towards the adjacent waveguide is prevented, whereas in the event of zero current intensity, the transfer of the first mode of a waveguide to the adjacent waveguide is automatic and virtually integral. Between these two current values, there will be a distribution of the lightwave between the waveguide through which the wave arrives and the adjacent waveguide in question, the distribution in each of the two waveguides naturally being a function of the intensity of the current injected.
In an embodiment in which the intensity of the electric control current can only assume the value zero and a value substantially greater than or equal to the threshold, the device acts as an “all or nothing” switch.
With the aim of avoiding crosstalk problems, the element of the electro-optical control means is advantageously formed in the selected location at distances from the two primary lines surrounding it which are selected so that this element finds itself placed closer to the primary line below which the part of the first mode is to be at least partially transferred than to the primary line below which the part of the first mode is at least partially extracted.
In a preferred embodiment of the element of the electro-optical control means, the latter is formed by a seconda
Christie Parker & Hale LLP
Dassault Electronique
Healy Brian
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