FR2859795A1 - Elector-optical converter for bidirectional electro-optical connection device, has optical circulator receiving modulated and continuous optical signals from respective electro-optical transducers, and providing modulated optical signal - Google Patents

Abstract

The converter has an electro-optical transducer (2) providing at its output (4) an optical signal modulated by a modulating electrical signal received at its input (3). Another electro-optical transducer (7) provides a continuous optical signal at its output (8). An optical circulator (11) has two inputs (12, 13) receiving the signals from the respective outputs (4, 8), and an output (17) delivering the modulated optical signal. An independent claim is also included for a bidirectional type electro-optical connection device having an electro-optical converter.

Description

Electro-optical converter and type connection device

  bidirectional having such a converter

  The present invention relates to an electro-optical converter and a bidirectional connection device comprising such a converter. The connection device is of the type used in the field of optical fiber transmissions, in particular but not only for connecting an end of an optical fiber to an electronic circuit for detecting or emitting light rays.

  An optical fiber is used essentially as an information transport medium, in the form of light signals, normally digitized. This means of transport has the advantage of effectively resisting noise, especially electromagnetic, and also allow very high information rates. Such flows are required on the one hand in long distance transmissions, but for some time, in transmissions between drawers superimposed or contiguous of the same electronic cabinet. For example, rates of 10 Gigabits per second over distances of the order or less than one meter can be better provided by an optical link. However, the processing in the current computing devices being of electronic type, it is important to make an optoelectronic conversion of the light signals to be processed, the input and the output of the optical fiber. In addition, the optical fibers can be butted to each other, it is important to be able to connect effectively.

  Various solutions have been devised to solve these conversion and / or connection problems.

  In some solutions, it has been imagined to manufacture harnesses. In these harnesses, the optical fiber or a sheet of optical fibers is provided at its two ends (or at least at one of its ends), in a fixed manner, with an optoelectronic conversion device. In this case, the optical fiber delivers at one end or both electrical or electronic signals while it can deliver optical signals at another end. The disadvantage presented by this type of solution is on the one hand the cost generated by this integration of means. On the other hand the maneuverability of the fiber is greatly reduced. Indeed, it is easy to understand that the length of the fiber can not be adjusted as easily as one would like, especially if it is provided on either side of electronic conversion circuits crimped at the ends of the fibers. In this case, it is not possible at all to lengthen or shorten it. It only remains to exchange for another harness of different size, but high cost too. Moreover, the presence of the electronic conversion circuit leads to producing at the end of the optical fiber a tip whose size is awkward if it is necessary to thread the fiber in narrow orifices to conduct the signals from one place to another. .

  To solve this problem, it is possible to provide optoelectronic connection and conversion devices, that is to say having optical input input ports on the one hand and electrical (electronic) output and input ports. 'somewhere else. These connection and / or conversion devices are connected on the one hand to optical fibers. On the other hand, they are connected to electronic circuits.

  Moreover, the mode of transmission in the optical fibers may depend on the monomode or multimode nature of the fiber and or the device for injecting light rays into the fiber. Then, during the injection or extraction of the light rays of an optical fiber, it is important to concentrate these rays at the maximum on the core of the fiber, whose diameter is of the order of ten micrometers for a fiber monomode (while they are of the order of 50 or 62.5 micrometers for multimode fibers). In practice, there is then a volume loss, the light rays being dispersed in a wide aperture cone, typically of the order of twenty degrees. Only the light rays located in a solid angle under which, from the heart of an optical fiber, one sees a sensitive area of an optoelectronic detector, or vice versa, are used. This partition in the solid angle reduces the injected or sampled power. Considerable losses are thus encountered during the optoelectronic conversion, or even when connecting a plurality of optical fibers abutting each other.

  To solve these problems, it is known, in particular in the document US Pat. No. 5,168,537, to place lenses that focus on the path of the light rays so as to concentrate the energy on the useful zones: the core of the fiber or the sensitive area of the detector. The implementation of these focusing lenses is however, industrially, a disadvantage because it requires manipulations of microscopic objects for which, moreover, the implementation must be rigorous given the tolerances mentioned above. As a result, the devices presented in this document can only be used in the laboratory, not on a large scale.

  In general, the quality of the injection and the optoelectronic conversion conditions the flow of the signals transmissible by the optical fibers. A problem stems from the fact that the optical fiber used is either a monomode fiber or a multimode type fiber. Indeed, if the type of light injection is multimode type, inexpensive, several propagation modes are present simultaneously in the fiber. However, these modes, different, have propagation speeds or phase rotations such that, depending on the distance between the sampling location and the injection site, destructive interference may occur. As a result, a digital type signal of all or nothing type, with sudden transitions, will be transmitted in the form of a signal with a rise time much longer than the rise time of the excitation optical signal. . Indeed, some spectral components undergo these interferences. As a result, the transmission bandwidth of the optical fiber, in terms of Gigabits per second, can be reduced due to injection or optical transmission deficits.

  The object of the invention is to solve these flow problems by adopting a solution not including microscopic assemblies that mechanically require too great precision to be implemented industrially at lower cost. According to the invention, in emission, a double optical injection is used. In practice, the electronic signal to be transmitted is converted by a first electro-optical transducer, for example a diode of the VCSEL type, into an optical signal. The optical signal thus produced is then amplified, optically, by the production of another optical signal, continuous, powerful, which is also injected into the optical transmission fiber. The two optical signals are coupled by an optical coupler, in one example a circulator. Such a circulator makes it possible to modulate the powerful continuous optical signal by the modulated optical signal emitted by the first transducer.

  By doing so, we have a resulting optical signal much better formatted, which has much better form qualities. These much higher form qualities allow, for example, to ensure a required bit rate while choosing optical fibers of lesser quality, for example of the multimode type. Or, such an arrangement can be satisfied with an optical coupling, the transmission fiber inserted into the converter, which is of lower quality. Or the invention allows to extend distances between repeaters.

  In the state of the art, the form quality of the optical signal is normally increased by increasing the bias voltage of the transducers. This increase in bias voltage leads to more strongly solicit these transducers, and to reduce correspondingly the service life. With the invention, the modulating transducer is not solicited so strongly, its life is well increased.

  The subject of the invention is therefore an electro-optical converter comprising a first electro-optical transducer receiving as input an electrical signal modulating and producing as output an optical signal modulated by the electrical signal, characterized in that it comprises a second electro-transducer -optic, outputting a continuous optical signal, and an optical circulator receiving on a first input the optical output of the first transducer and on a second input the optical output of the second transducer, and outputting on an optical output the optical signal modulated by the electrical signal.

  The invention further relates to a bi-directional electrooptic connection device comprising a converter as above, characterized in that it further comprises an optoelectronic transducer receiving as input a modulated optical signal and outputting a modulated electrical signal.

  The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These are presented only as an indication and in no way limitative of the invention. The figures show: FIG. 1: a representation of a converter provided with an optical coupling device according to the invention; - Figure 2: a representation of a practical embodiment of such a converter or such a device; - Figure 3: a representation of a practical embodiment of a device according to the invention for complete assembly on a printed circuit.

  Figure 1 shows an electro-optical converter 1 according to the invention. This electro-optical converter 1 comprises a first electro-optical transducer 2 receiving at input 3 an electrical, electronic, modulating signal.

  The first transducer 2 produces at output 4 an optical signal modulated by the electrical signal. Normally, this signal available at the output 4 is taken by a termination 5 of an optical fiber 6 and is routed to its final destination. In the invention, the converter comprises a second electro-optical transducer 7 which is not modulated. The electro-optical transducer 7 produces at its output 8 a continuous optical signal. Transducer 7 is called an electro-optical transducer because, in practice, it is electrically powered, in one way or another, to produce the continuous optical signal. As for the first transducer 2, an optical fiber 9 removes the continuous optical signal at its termination.

  According to the invention, the two fibers 6 and 9 are connected at the input of an optical circulator 11, on inputs 12 and 13, respectively. The circulator 11 is a conventional circulator, in one example a three-way circulator, of the rotator type. Faraday or delay plate circulator, or having a polarization beam splitter, a birefringent crystal, a prism, a mirror or a lens. The circulator 11 thus has two inputs 14 and 15 in relation to the ports 12 and 13, and an output 16 in connection with an output port 17.

  The operation of a circulator is such that the optical wave can propagate in only one direction, for example that shown by the arrow 18. The direction 18 leads in particular the continuous wave transmitted by the optical fiber 9 to to be modulated optically by the modulated optical wave transmitted by the fiber 6. In this way, on the output 16 and the port 17, there is a more powerful modulated optical wave.

  The operation of the circulator is also also such that the modulation produced by the transducer 2 does not disturb the operation of the continuous optical wave transducer 7. If necessary, an optical isolator 19 is placed on the optical path between two strands of the optical fiber 9. This insulator 19 allows me to propagate the optical wave only from the output port 8 to the input port 13 of the circulator 11. In one example, the insulator 19 is made by a Bragg grating cell.

  The operation of circulators can be better understood by reading the article: Effect of Relatively Strong Light Injection on the Chirpto Power Ratio and the 3db Bandwidth of Directly Modulated Semiconductors of Gnitabouré Yabre Lasers, IEEE Journal of Lightwave Technology, Volume 14, number 10, October 1996, pages 2367 and following. Its interest can also be deduced from the article Reduction of Nonlinear Distortion in Directly Modulated Semiconductor Lasers by Coherent Light Injection by Gnitabouré Yabre and Jean Le Bihan, IEEE Journal of Quantum Electronics, Volume 33, Number 7, July 1997, pages 1132. and following. Finally, the improvement of the modulated bandwidth can be understood by the article Enhanced Modulation Bandwidth in Injection-Locked Semiconductor Lasers due to Simpson T.B. and Liu J.M. and published in IEEE Photonics Technology Letters, volume 9, number 10, October 1997.

  The optical circulator 11 thus receives on its first input 12 the optical output of the first transducer 2 and on its second input 13 the optical output of the second transducer 7. The circulator 11 delivers on its optical output 17 the optical signal modulated by the electrical signal. An optical transmission fiber 20 with its terminations 21 and 22 is more particularly used to route the optical signal thus amplified from one electro-optical converter to another converter located in another device (for example a distance of some meters) but the inverse type, optoelectronic.

  In this respect, FIG. 1 shows a complete device comprising, on the one hand, the transmission channel that has just been described so far, and on the other hand a reception channel. The reception channel comprises, like the optical output port 17, an input optical port 23 into which is connected a termination 24 of a reception optical fiber 25. The reception optical port 23 is a reception port a third transducer 26, here of optoelectronic type producing on an electrical output 27 an electrical reception signal.

  It can therefore be seen that at the location of the optical injection there is a doubling of the optical injection and a combination in the circulator 11 of the injected optical waves.

  FIG. 2 shows a practical representation of the electro-optical connection device shown in FIG. 1. In a preferred example, this device comprises two disjoint but associated assemblies. A first set comprises a plane electronic circuit 28 essentially provided with the first and second electro-optical transducers 2 and 7, as well as with the third optoelectronic transducer 26. These transducers 2, 7 and 26 are for example connected and deposited on the circuit 28 by precise surface mount technology, in particular wherein the transducers are mounted by solder ball connections. At the time of the reflow of these solder balls, the transducers occupy on the circuit 28 a very precisely designated place and corresponding to a screen printing of this circuit 28.

  The device also comprises a second assembly 29 which is an optical structure, optically connected to the circuit 28. For example, this optical connection is obtained by a precise display, in particular also by solder balls such as 30 and 31, ports 12 and 13 of the circulator 11 with the transducers 2 and 7. The optical structure 29 therefore comprises in this respect three sections of optical fiber, 30 to 32, respectively connecting the port 12 to the input 14, the port 13 to entrance 15 and exit 16 to port 17.

  The structure 29 also comprises another optical fiber section 33 connecting an input port 34 to an output port 35, the latter position precisely opposite the optoelectronic transducer 26.

  The structure 29 can be made in different ways. For example a base of glass or other transparent material may be grooved at the location of the sections 30 to 33 and receive in an intermediate cavity the circulator 11. The latter, especially if it comprises a Bragg grating is passive type . It does not require power supply. The base can also be covered with another transparent structure thus forming sections 30 to 33. These sections are optionally filled with a transparent material of refractive index adapted to play the role of optical fiber.

  On the one hand, the structure 29 thus comprises the ports 12, 13 and 35 opposite the circuit 28, and on the other hand it comprises the ports 17 and 34 opposite two terminations 36 and 37 of two optical fibers 38 and 39 transmission and reception respectively. The structure 29, in particular by the presence of the sections 30 to 33 makes it possible to adapt the standardized gap to exist between the terminations 36 and 37 of optical fiber at much finer spacings corresponding to the position of the transducers 2, 7 and 26.

  FIG. 3 shows a more complete embodiment of the bidirectional connection device of FIG. 2. In this, the assembly 29 and the circuit 28 are associated on the one hand with each other, and on the other hand with an electronic circuit of FIG. connection (and also processing) 40. The circuit 40 present in the form of a wafer is placed at right angles to the circuit 28. The circuit 40 is flat and is surmounted by a radiator 41. A sole 42 radiant heat is connected to firstly to the radiator 41 and secondly to the circuit 40 and the circuit 28. The sole serves to efficiently collect the thermal energy produced by the transducers 2.7 and 26 mounted on the circuit 28. The device of FIG. is intended to be mounted, for example by a surface mount technology or by a wire bonding technology on a receiver printed circuit, parallel to the plane of the circuit 40. The assembly thus recommended is particularly interesting because, of the fa it doubling the emission, in particular by the presence of the transducer 26 with continuous optical emission, the dissipated heat may be greater. It is thus shown that, in the present case, the dissipated heat is important without, moreover, increasing the polarization voltage of the modulating transducer 2. It is only increased because of the presence of the second optical transducer 7. The polarization voltages of these two transducers may be weaker. Their behavior in time is better ensured, provided an effective dissipation of the heat produced.

Claims (1)

9 CLAIMS   1 - Electro-optical converter comprising a first electro-optical transducer receiving as input an electrical signal modulating and producing as output an optical signal modulated by the electrical signal, characterized in that it comprises a second electro-optical transducer, producing as output a continuous optical signal, and an optical circulator receiving on a first input the optical output of the first transducer and on a second input the optical output of the second transducer, and delivering on an optical output the optical signal modulated by the electrical signal.   2 - Converter according to claim 1, characterized in that the circulator comprises a directional optical isolator placed between the second transducer and a three-way circulator.   3 - Converter according to one of claims 1 to 2, characterized in that the circulator comprises a Faraday rotator, a circulator with trays delay, a polarization beam splitter, a birefringent crystal, a prism, a mirror or a lens.   4 - bidirectional type electro-optical connection device comprising a converter according to one of claims 1 to 3, characterized in that it further comprises an optoelectronic transducer receiving as input a modulated optical signal and outputting an electrical signal module.   5 - Device according to claim 4, characterized in that it comprises, in two disjoint sets but associated, - a first electronic circuit provided with a first and a second electro-optical transducers and a third optoelectronic transducer, and an optical structure connected to this circuit comprising, on the one hand, a first and a second output port for receiving an optical signal from the first and second electro-optical transducers and an input port for injecting an optical signal. in the third optoelectronic transducer, and on the other hand an optical fiber output termination and an optical fiber input termination, the two output ports and the output termination being optically connected to the circulator, the input port and the input termination being directly connected to each other.   6 - Device according to one of claims 4 to 5, characterized in that it comprises a first electronic circuit at right angles to a second electronic circuit, the second electronic circuit being flat and being surmounted by a radiator, a radiant sole thermally connected to the radiator for dissipating thermal energy and the second circuit being intended to be mounted on a printed circuit.