Abstract:
A connection for an underwater acoustics system connecting elements of an antenna embedded in a leaktight first block of the system and an electro-optical transmitter embedded in a separate leaktight second block of the system. The antenna is electrically connected to a first part of a divisible transformer, which is also arranged in the leaktight first block. The electro-optical transmitter (e.g., vertical cavity surface emitting laser) is electrically connected to a second part of the divisible transformer, which is also arranged in the leaktight second block. The first part and the second part are anatomically separated, as are the first and second blocks within which they are contained, but have cores that can magnetically communicate with one another. By this configuration, the divisible transformer can communicate signals from the antenna to the electro-optical transmitter without compromising the leaktightness of the first or second blocks, thereby protecting the components.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to connection systems linking undersea acoustic antennas to electronic devices for interpreting acoustic signals. The electronic devices are situated within the hull of a submarine, while the antennas are situated outside the hull. 
     2. Background Art 
     The receiving antennas of sonars are generally situated outside a carrying vessel, a submarine for example, and are conventionally linked to electronic racks, which interpret the signals sent and received by these antennas, by electrical connections passing through the hull of the vessel. This arrangement entails numerous drawbacks, including a loss of leaktightness in the region of the connectors, a substantial number of cables, junction boxes, and pressure hull penetrators (PHP&#39;s), very high wiring costs, a reduced reliability by reason of the large number of devices used to establish these electrical connections, and finally a risk of a rupturing the leaktightness of the hull when it is necessary to replace one of the sensors. 
     For example, if it were desired to link a cylindrical antenna including 128 columns of 16 hydrophones, i.e., 2048 channels, using them all to carry out processing in azimuth and in then it would be necessary, between the antenna and the PHPs, to use 128 connectors on the columns and on the cables, 128 cables formed by 18 screened pairs, and 128 connectors on the cables and on the PHPs, i.e., 512 submerged connectors in total. As regards the PHPs, it would also be necessary to use 32 cables of 18 screened pairs fitted with 2 times 32 sockets, each socket including 4 connectors, 32 electronics boxes for conditioning the signals, and 32 cables fitted with 2 times 32 sockets for linking these conditioning boxes to the electronic rack. 
     Such an embodiment cannot be implemented in practice, by reason of the cost of the cabling, of the weight of the cables and connectors, which would be of the order of 6 tons, and of the very large number of PHPs and submerged connectors. 
     SUMMARY OF THE INVENTION 
     In order to use an antenna of this type, which is very useful for fine position-fixing of the sources of acoustic noise, and in order to overcome these drawbacks, the invention proposes a connection system for underwater acoustics. The connection system includes: elements of an antenna embedded in a leaktight first block of the system; a first part of a divisible transformer embedded in the first block, the first part electrically connected to the elements of the antenna; a second part of the divisible transformer embedded in a leaktight second block of the system, the second part magnetically continuous with the first part; and an electro-optical transmitter embedded in the second block and electrically connected to the second part. The first and second blocks are separated from one another, and the divisible transformer communicates signals from the elements of the antenna to the electro-optical transmitter without compromising the leaktightness of the first or second block. 
     According to another aspect of the invention, the electro-optical transmitter is a vertical cavity surface emitting laser (VCSEL). 
     Other features and advantages of the invention will become clearly apparent from the following description, given by way of non-limiting example with regard to the annexed figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a theoretical diagram of a system according to the invention; 
     FIG. 2 is a diagram of one of the channels of FIG. 1; 
     FIG. 3 is a diagram of an optical connection of FIG. 2; 
     FIG. 4 is a cross-section of a layer of optical fiber used in the diagram of FIG. 2; 
     FIG. 5 is a sectional view of a system for connecting the optical fibers; 
     FIG. 6 is a front view of a system for connecting the optical fibers; 
     FIG. 7 is a top view of a set of supply sockets fixed onto the hull of a carrying vessel; 
     FIG. 8 is a sectional view of the cables of FIG. 7 between two plugs; and 
     FIG. 9 is a sectional view of the cables of FIG. 7 in the region of a plug. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a connection system of the invention, which links a cylindrical acoustic antenna  101  of the type set out above to a sonar rack  102 . By way of example, each antenna comprises 128 columns of 16 hydrophones, plus the amplifiers (PA), the analog/digital converters (ADC), the multiplexers (MUX), and the connections corresponding to each column. These connections are linked by an optical-coupling system  103  to 8 sets of 8 optical fibers  104 , which carry out the reception signals, and to 8 sets of 8 optical fibers  105 , which carry in the control signals for the antenna. The extremities of these sets of optical fibers, which form cables, are overmolded onto optical/electrical converters  106  for the output signals and onto electrical/optical converters  107  for the control signals. 
     These converters are linked to through-hull connectors PHP, respectively  108  and  109  for the converters  106  and  107 . These PHPs carry the signals within the thick hull  110  of a submarine. The PHPs  108  and  109  are then linked to the sonar rack  102  by way of cables  111  and  112 . 
     FIG. 2 illustrates the set of connection elements corresponding to a column formed from 16 hydrophones  201  molded with their accompanying elements into a block  202  of plastic, which is transparent to the acoustic waves and conventionally formed of polyurethane. To each hydrophone  201  is linked an amplifier (PA)  203 , itself linked to an analog/digital converter (ADC)  204 . The set of these analog/digital converters is linked to a multiplexer (MUX)  205 , which multiplexes the signals from all the hydrophones onto a single output  206 . In this example, these hydrophones form one column of a cylindrical-type antenna, but this could be an acoustic antenna of any type, e.g., a flank antenna panel for a submarine or a segment of a towed linear acoustic antenna. 
     In this embodiment, the set of electronic circuits  203 ,  204 , and  205  is enclosed in a metal box  207  which provides effective screening by being linked to earth via a leaktight earth coupling  208 . The electrical power supply arrives via a lateral plug  209 , itself leaktight. The box  207  is filled with a product that can withstand the hydrostatic pressure, for example an insulating mineral oil or a polyurethane like that which constitutes the block  202 . 
     The digital data output by the multiplexer are extracted from the block  202  by the use of the divisible pulse transformer. The divisible transformer transmits the pulses, featuring a short time constant, and can be separated into two pieces. One piece  210  remains embedded in the mass of polyurethane  202 . The other piece  211  remains outside this mass  202  and linked to the cable  217  for connection to the sonar rack  102 . By this configuration, the whole of the antenna column and its accompanying elements embedded in block  202  can be connected to and disconnected from the block  214  containing the optical coupling  216 , without rupturing the leaktightnes of either block  202  or block  214 . 
     To accomplish this, the divisible transformer includes a divisible core of both a first internal part  210 , which is embedded in the polyurethane block  202 , and a second external part  211 , which is embedded in the polyurethane block  214 . The faces of the junction between the internal part  210  and the external part  211  form a gap but are relatively flush with the surfaces of the block  202  and the block  214 , respectively. 
     A primary winding  212  is wound on the inner part  210  of the core. The winding  212  is fed by an amplifier  213 , which receives the data supplied by the multiplexer  205 . The second part  211  of the core is itself molded in polyurethane block  214 . This second block  214  can be of different size than block  202  and can be fixed to the surface of the first block  202  by fixing means, not shown, clips or screws for example, so that the magnetic communication between the two parts  210  and  211  of the core is achieved optimally. Under these conditions, the magnetic flux induced by the primary winding  212  further induces, in a secondary winding  215  wound on the second part  211  of the magnetic core, a voltage representative of the signals leaving the multiplexer  205 . This secondary winding  215  is linked to an electro-optical component  216 , which makes it possible to convert these electrical signals into optical signals. This optical component can be a Vertical Cavity Surface Emitting Laser (VCSEL) component, which makes it possible to emit the light signals perpendicularly to its surface. 
     These light signals are then taken up by an optical fiber  217 , which is overmolded into the second polyurethane block  214  in such a way that its extremity is just opposite from where the light signals leave the electro-optical component  216 . The coupling between the fiber  217  and the component  216  can be achieved either directly, or by way of a waveguide, in order to facilitate manufacture of the assembly. With the material used to manufacture the second block  214  being transparent to light, there is no particular precaution to be taken, when overmolding, to avoid an interruption of the light-signal passage due to an infiltration of the overmolding product. The assembly thus forms a coupling between the column of hydrophones, equipped with its electronic matching elements, and the cable linking the assembly to the sonar rack  102 . 
     The use of a VCSEL component is particularly beneficial, since the output mode of the light from this component allows easy matching to the optical transmission fiber, as already set out above. Furthermore, this component operates in current mode, and the value of this current is of about 1 mA with a consumption of the order of one milliwatt. This low current is particularly well suited to the transmission capabilities of the transformer described above. Furthermore, the wavelengths likely to be used can vary between 650 nm and 1100 nm, which are well adapted to transmission by optical fiber. In one preferred embodiment, a wavelength of 850 nm will be used. For further information on these types of component, reference may be made to the  IEEE Spectrum publication of February  1998, page 43. 
     Even with a correct set-up, the dismantling of the blocks  202  and  214  cause a gap which is relatively large and exhibits fairly disperse characteristics, in particular as a consequence of the successive removal and refitting. The coupling between the primary winding  212  and secondary winding  215  of the transformer can therefore become relatively loose and not well defined. In order to make the electro-optical component  216  function with a modulation current adapted to these characteristics, a feedback system is used, including a feedback winding  224  wound on the first part  210  of the magnetic core of the transformer. This feedback winding  224 , by way of a matching circuit, including a rectification system for example, makes it possible to control the gain of the amplifier  213 . 
     The optical fibers  217  corresponding to the various columns of the antenna are then grouped together into cables, which are linked to the device for gathering the optical data and for optical/electrical conversion  106 . The invention produces these cables in the form of a flat cable, as represented in FIG. 4, which is formed by overmolding of the optical fibers  217  side-by-side in the form of a layer with a coating of polyurethane, to achieve continuity with the block  214 . The overmolding features grooves  402  and  403  between the various fibers on each of the faces of the flat cable. This makes it possible to easily separate the fibers, complete with their coating, so as to facilitate fitting to the devices  106  by forming loops of slack as required. 
     A set of control signals, such as clock, synchronization, gain-control, etc., are sent to the electronic units  203 - 205  linked to the hydrophones. To accomplish this, the invention transmits these control signals via optical fibers  218 , which are inserted into a blind hole  225  formed on one of the faces of the overmolding block  202  of the antenna. This hole  225  is situated facing a photodiode  220 , which is driven by the light signals originating from the fiber  218 . The electrical signals emitted by this diode  220  in response to these light signals are then decoded in a conditioning circuit  221 , which selects the various signals necessary both for the amplifiers  203 , the analog/digital converters  204 , and the multiplexers  205 . This selection takes place, for example, by decoding of a digital frame including all the necessary signals, according to a preestablished coding. 
     The fibers  218  originating from the device for electrical/optical conversion and distribution  107  of the optical signals are preferably assembled together in the form of a fiat cable, like the optical fibers  217 . In order to facilitate the coupling between the extremity of the fiber  218  and the photodiode  220 , the invention proposes to use a “large-core fiber,” which obtains a light beam  222  that is relatively wide, such that it can compensate for any defects in positioning and alignment between the extremity of the fiber  218  and the photodiode  220 . 
     In order to connect the optical fibers  217  to the device  106 , a small device is used like the one represented in longitudinal section in FIG. 5, and in transverse section in FIG.  6 . This small device comprises a rectangular flat box  501  into which is inserted a piece  502  forming a fiber-clamping vice. This piece  502  comprises V-shaped longitudinal furrows, which hold the fibers  217  in the material  401  forming the flat cable after separation at the furrows  402  and  403 . As this coating is soft, it molds into the furrows, which ensures leaktightness of the assembly in this region. The optical/electrical conversion system is formed by photodiodes  504  fixed on to the inner and lower face of the internal cavity delimited by the box  501 . If appropriate, these photodiodes are assembled together into an Application Specific Integral Circuit (ASIC), which can integrate into this device a certain number of supplementary functions, thereby allowing, for example, amplification and/or multiplexing of the signals. To couple the fibers to the photodiodes, a mirror  505  may be used that is, for example, inclined at 45° and arranged between the extremity of the fibers and the input faces of the photodiodes. 
     The whole of the cavity is filled with a transparent, dielectric gel or an oil, in order to withstand the pressure outside the hull. This gel is inserted through an orifice, which is then closed off by a stopper  506 . The electrical signals leave via screened pairs  507 . 
     In another embodiment, this ASIC is produced in monolithic form, which makes it possible to use a waveguide integrated into the substrate of the ASIC, thereby making it further possible to couple the fibers directly to this waveguide. In this way, the mirror and the oil filling can be dispensed with. 
     In a similar fashion, the device for electrical/optical conversion and distribution of the optical control signals to the fibers  218  is produced with a device similar to that of FIGS. 5 and 6. The difference relates to the replacement of the receiving photodiodes by light-emitting diodes. In one preferred embodiment, components of the VCSEL type will be used in place of light-emitting diodes, such as the components  216  of FIG.  2 . 
     In order to obtain redundancy of the system, which allows for fault tolerance, the invention also proposes, as represented in FIG. 3, to use two optical transmitters  226  and  236 , e.g., DVCSELs wired in parallel on the terminals of the secondary winding  215 . These components  226  and  236  are wired head-to-tail, such that the failure of one does not impair the operation of the other. These two components  226  and  236  are linked respectively to two optical fibers  227  and  237 , which terminate on optical duplexers  301  and  302 . Each of these duplexers are linked, respectively, to two pickup devices  306  and  316 , which provide complete redundancy by always having the output signals from the transformer available on one of these two devices  306  and  316 . 
     Finally, in order to obtain a system entirely without electrical contacts and entirely removable, the invention proposes to feed each antenna element  202  via an induction system, by means of a removable transformer, as represented in FIGS. 7,  8  and  9 . To do that, the plug  209  of FIG. 2 is replaced by a part  901  of a magnetic core. The core includes this part  901  and a second part  902 , which loop the magnetic circuit. The part  901  is U-shaped and embedded in the polyurethane block  202 , while the part  902  is linear and closes the magnetic circuit. This part  902  is fixed onto a spacing piece  903 , which itself is fixed to the hull  110  on to which the antenna is fixed. Thus, dispersion of the magnetic flux in this hull is avoided. 
     A secondary winding  904  wound on the part  901  of the magnetic circuit feeds the electronic elements embedded in the block  202 . To feed the transformer, a primary winding is used, formed from multi-strand cables  905  that form loops, which pass through the hollow interior of the magnetic circuit  901 / 902  and are looped as represented in FIG.  7 . These cables  905  are supplied with electrical energy from a junction box  906  which, in leaktight fashion, brings out the electrical energy from inside the hull  110 . This junction box is preferably situated above the flotation line of the carrying vessel to facilitate repairs at this region. This flotation line, in the case of a submarine, being that in existence when the submarine is on the surface. 
     In order to have sufficient coupling, multi-strand cables, each strand of which is traversed by the same current, can be used, two in the case represented in the figures. In order to minimize the losses between the transformers, which form contactless electrical plugs, these cables are assembled together between these plugs, in the manner represented in FIG.  8 .