An object of the present invention is a modular optoelectronic connector that can be used especially when high transmission bit rates are encountered. High bit rates of this kind are encountered for example in the field of telecommunications, especially for the interconnection of SDH type telephone exchanges. Each channel of an exchange of this kind must indeed give a bit rate of 622 Mbits. The expected developments are such that these bit rates must be raised to 2.5 Gbits and then 10 Gbits. High bit rates of this kind are furthermore being encountered in more limited spaces, as for example in computer local area networks or in aircraft. The bit rate requirements may then be also high owing to transmissions of image signals. Furthermore, inside one and the same piece of equipment, for example for the connection between several electronic racks in one and the same electronic cabinet, it may be planned to have very high bit rates.
To provide for the transmission of information of this kind without being hampered by problems of crosstalk or electromagnetic noise, it is preferred to use optical links. The invention pertains in fact to all optical links in which, ultimately, information has to be conveyed at a high information bit rate.
The preparation of information in electrical form and its transmission in optical form requires the making of optoelectronic couplers. In a first approach, devices have been developed in which an electronic card comprises an optoelectronic coupler of this kind. In this case, the electronic board can be accessed from outside by an optical connector. However, such an approach dictates the reservation of space on such an electronic board to make the electro-optical conversions. With a view to miniaturization, another approach is becoming prevalent. In this other approach, the coupler is an integral part of a connector. With this type of development, harnesses are appearing for example on the market. Harnesses of this kind comprise a cable and optoelectronic connectors at each of its ends. In a harness, the connectors are mounted on a cable. In the invention, it is thus planned, if necessary, to make harnesses of this kind. However, more generally in the invention, it is provided that the connectors may be distributed separately from the cables.
An optoelectronic connector according to the invention then comprises an electronic port linked to a coupler that is itself connected to an optical port. A cable to be connected to the optical port is an optical cable. At another end of a link, a reverse conversion is done, and another connector is mounted. For the user, on either side of the cable, the links are electrical. The optoelectronic conversion is transparent to the user. The advantage of these approaches is of course a gain in space on the electrical cards which no longer has to incorporate a coupling function. Another advantage is simplicity of use. All that remains is a constraint relating to the electrical supply of the coupler but this is done through the electrical port.
An embodiment of this kind however has the drawback of being costly to manufacture. Indeed, the technologies implied in such a connector require strict compliance with various physical constraints. Thus, on the electrical port side, given the high information bit rates (for example in the range of several Gbits), it is necessary to act efficiently to counter radioelectrical noises. In the coupler, it is necessary to take account of the problems of thermal dissipation of the transducers used. Indeed, the known transducers, namely laser diodes, can consume up to 100 milliwatts per unit. The heat dissipation related to the working of the transducer prompts a heating of this transducer, resulting in a drift in its operating frequency.
Cost-related problems, for their part, lead to the making of multifiber sets. Indeed, since the mounting of a connector for a single optical fiber is costly, the cost is substantially reduced by providing for the connections of bundles of optical fibers, For example, there are known embodiments in which twenty optical fibers are connected to a connector. However, while an embodiment of this kind leads to a reduction in the cost price per optical fiber of the connector, it does not accurately correspond to requirements. With embodiments of this kind, the user may have access either to a connector with very many optical fibers or to a connector with a single optical fiber. However the cost is high in both cases. In the invention, optoelectronic links are sought wherein it is possible to make use of a modularity: the user, as required, can associate a desired number of optical fibers to meet his requirements.
The making of multifiber sets furthermore leads to specific difficulties. Indeed, owing to heat consumption, laser diodes have to be separated from one another by a substantial space inside the connector. Similarly, when the optoelectronic connector is mounted on an electronic card, the laser diodes are spaced out so that they can be mounted therein. Besides, in order to be able to get connected to this type of connector, it is necessary to get close to a termination of an optical fiber of the optical radiating element of the coupler. Now, the multifiber optical connectors have a standardized distribution of the optical terminations. In this standardized distribution, the terminations are close to each other. It is then necessary to create a waveguide in the optoelectronic connectors. This waveguide enables a geometrical matching between the necessarily big spacing between the laser diodes mounted in the optoelectronic connector and a close spacing close of the terminations of the optical fibers presented in a standardized optical connector. The making of a waveguide of this kind complicates the coupler. This waveguide itself must also comply with the above-mentioned constraints.
In practice, to make optoelectronic connectors of this kind, laser diodes using Vcsel technology are used. The term Vcsel refers to vertical cavity solid emitting lasers. With vertical cavity solid emitting lasers of this kind, the laser radiation is actually scattered in a scattering cone whose angular aperture is about 8° to 12°. It becomes easier to place an optical fiber termination in front of a cone of this kind to pick up the optical signal sent. However, the presence, of the waveguide mentioned here above implies the making of two optical interfaces. A first interface is located between the laser diode and the input of the waveguide. A second interface is located at the output of the waveguide and at the input of the optical connector. These two interfaces lead to insertion losses which are themselves curbed by improving the quality of the optical terminations of the fibers of the optical connector and/or of the waveguides. For example, these ends of the fibers are polished by means of a plane or spherical polishing. If the polishing is plane, preferably it is slightly inclined with respect to the incident direction of the optical transmission so as not to prompt any parasitic reflections, both on the side of the interface with the laser diode and on the side of the interface with the optical connector. Ultimately, the presence of this waveguide results in a complex and costly structure if it is sought to prevent if from being a generator of transmission losses.
Furthermore, the electrical port that conveys the data elements must be especially well protected to prevent electromagnetic parasites. This shielding may be conventionally obtained by arrangements of metal partition walls. However, this type of approach is not compatible with desired goals of miniaturization and modularity of an optoelectronic connector. Or else, the manufacturing equipment becomes so precise that handling it runs counter to the conditions of very large-scale production.
In short, the approaches used for the prior art optoelectronic connectors are costly, not modular and do not have as good a transmission quality as would be desired.