Abstract:
An optical fiber connection arrangement includes an alignment sleeve for coaxially aligning optical fibers mounted in ferrules. A gap between the ends of the optical fibers allows some light to escape. A sensor responds to the leaked light, and the resulting signal is processed to determine whether light signal is present or absent.

Description:
FIELD OF THE INVENTION 
   This invention relates to sensors for use in conjunction with optical fiber systems, for aiding in monitoring and verification of signal flow. 
   BACKGROUND OF THE INVENTION 
   Many communication systems rely on optical fibers for carrying signals, because of the very high bandwidth of optical fibers. In complex systems, it may be desirable to be able to route signals on a particular optical fiber to a given one of a plurality of sources or sinks of optical signals. This could be the case, for example, in a shipboard environment in which communications are accomplished by means of such optical fibers, and the optical fibers themselves, and the sources and sinks of information, are subject to damage due to collision or hostile action. In such an event, it is desirable to be able to disconnect an optical fiber from a failed unit and to reconnect it to an operable unit of the same (or possibly of a different) type. 
     FIG. 1  represents a prior-art arrangement  10  for routing optical communications fibers among a plurality of sources and sinks of information. In  FIG. 1 , a first source, sink, or source/sink of optical signals is represented as a box or block  12 , and a second source, sink, or source/sink of such signals is represented as a box  14 . Similarly, boxes  16  and  18  represent sources/sinks of a particular type of optical communications signals. As illustrated in  FIG. 1 , an optical fiber  12   o  carries signals produced by block  12  to a through connector in the form of a bulkhead junction or bulkhead connector  20   a  of a patch panel  20 , and thence through another optical fiber  14   o  to optical signal source/sink  14 . Similarly, optical signals produced by source  18  are carried by an optical fiber  18   o  to a bulkhead junction or bulkhead connector  20   b , and thence by way of an optical fiber  16   o  to source/sink block  16 . Other optical fibers, illustrated together as a bundle  22 , extend from various junction connectors, such as exemplary junction connectors  20   c ,  20   d ,  20   f , and  20   g , through a bulkhead holder or wall  24  aperture  26 , where they connect to various sources and sinks of optical signal (not illustrated). Junction connectors  20   c ,  20   d ,  20   f , and  20   g  connect to various optical fibers  28   c ,  28   d ,  28   f , and  28   g , illustrated together as a bundle  28 , which leave the region to connect to various sources and sinks of optical signals. 
   It will be clear by considering  FIG. 1  that the various equipments  12 ,  14 ,  16 , and  18 , as well as the remote equipments, can be connected together in various ways to either bypass damaged or defective equipment, or to apply signals to various different types of processing as may be required or desired, simply by disconnecting a fiber from a junction or patch terminal of patch panel  20 , and reconnecting it by way of another junction or patch terminal which communicates with the desired functional block. This ready reconfiguration may be valuable in various contexts. 
   A disadvantage of the patch-panel routing suggested by  FIG. 1  is that troubleshooting is somewhat difficult, in that a problem is usually manifested as a failure of a system including at least a source of optical signals and a sink of optical signals, joined by at least two separate optical fibers and a junction connector. When a failure of such a system is suspected, it is initially not known whether the problem lies in the source, the sink, or the interconnecting optical fibers. The troubleshooting of such arrangements may be done in a multitude of ways. One possible way to troubleshoot a failed system is to divide it into two parts, by disconnecting one of the optical fibers at the bulkhead connector of the junction panel. For example, if the putatively failed system includes source or source/sink  12  and sink or source/sink  14  of  FIG. 1 , some information could be gleaned by separating optical fiber  14   o  from bulkhead connector  20   a , and placing a light-responsive meter on bulkhead connector  20   a . If source  12  is operating, and produces enough light to be displayed on an optical power meter, one may make an initial assumption that source  12  and optical fiber  12   o  are functional, and the system problem lies elsewhere. If the operating mode of source  12  is not readily controllable, and no light is perceived at bulkhead connector  20   a , it may be necessary to disconnect optical fiber  12   o  from optical source  12 , and to substitute a known test light source. With a test light source at the remote end of optical fiber  12   o , and an optically responsive meter attached to bulkhead connector  20   a , the state of optical fiber  12   o  can be established without question. Testing of optical fiber path  14   o  may involve disconnecting optical fiber  14   o  from bulkhead connector  20   a , and applying a light source to the remote side (not visible in  FIG. 1 ) of bulkhead connector  20   a , and disconnecting the connection of optical fiber  14   o  from equipment  14 , and placing an optically responsive meter at the near end of fiber  14   o.    
   While the described testing is tedious but reasonably efficient, the difficulties become greater when the equipments to which the optical fibers are connected lie at remote locations relative to the patch panel  20  of  FIG. 1 . This would be the case if equipments connected and interacting through optical fiber bundle  22 , one or more of bulkhead connectors  20   c ,  20   d ,  20   e , and or  20   f , and optical fiber bundle  28 , were to cease to function correctly. In that case, testing would require traveling to at least one of the remote locations to break a connection, and another trip to reestablish the connection. In addition, either the connections and tests would have to be performed seriatim by one person, or the connection/disconnection would have to be coordinated by some form of communications other than the optical fiber in question. In complex systems with hundreds of optical fibers, the testing may result in long down times. 
   Prior methods for addressing the problems of testing of complex communication systems take forms such as repeater junction boxes, as described in U.S. Pat. No. 6,243,510, issued Jun. 5, 2001 in the name of Rauch, and automatic analysis systems such as that described in U.S. Pat. No. 4,837,856 issued Jun. 6, 1989 in the name of Glista, Jr. In general, the repeater or junction boxes have relatively limited bandwidth, and are complex and expensive, and the automatic analysis arrangements are complex and expensive. The automatic analysis system uses a bypass fiber, and its manufacturing is complex. Another arrangement is described in U.S. Pat. No. 5,793,481, issued Aug. 11, 1998 in the name of Leali, which samples the signals at a location using a splitter/bypass, and processes them to produce an indication of the presence or absence of signals, which is complex. 
   Improved or alternative arrangements optical fiber status indicators or sensors are desired. 
   SUMMARY OF THE INVENTION 
   A sensor according to an aspect of the invention, for use in conjunction with light flow through a junction or gap between first and second optical fibers, comprises an alignment sleeve including first and second ends. The first and second ends of the alignment sleeve are dimensioned to accommodate ends of first and second optical fiber ferrules, respectively. The alignment sleeve, when assembled with the ferrules, coaxially aligns the associated first and second optical fibers, respectively, to thereby facilitate the flow of light across a gap between the first and second optical fibers. The sensor includes an optical sensor located adjacent the gap, for generating an electrical signal representative of light leaking from the gap. An indication arrangement is responsive to the electrical signal for providing an indication of light flow through the gap. 
   In a particular embodiment of the invention, the indication arrangement comprises a visual indicator, which may be a light-emitting solid-state device. In another particular embodiment, the indicator may be a digital electrical network interface, or may include both. In the case of a digital electrical network interface, the indication means may include a serial data bus interface, which may be an Inter-Integrated Circuit (I 2 C) bus connection. 
   A system according to another aspect of the invention is for monitoring light flow through plural junctions between pairs or sets of optical fibers. Each of the sets of optical fibers includes first and second optical fibers. The system comprises a plurality of sensors, each of which comprises (a) an alignment sleeve including first and second ends, with the first and second ends of the alignment sleeve being dimensioned to accommodate ends of first and second optical fiber ferrules. The alignment sleeve, when assembled with the ferrules, coaxially align the associated first and second optical fibers, respectively, of one of the plural sets of optical fibers, to thereby facilitate the flow of light across a gap between the first and second optical fibers of the one of the sets of optical fibers. The system also includes (b) an optical sensor located adjacent the gap, for generating an electrical signal representative of light leaking from the gap, (c) an address generator for generating a unique address for each of the sensors, (d) a bus connection arrangement responsive to the electrical signal and to the address, for generating a bus signal including information relating to the light flow through the gap and the identity of the sensor, and (e) a bus coupled to the bus connection means of each of the sensors and to utilization means. In a particular embodiment of this aspect of the invention, the bus connection arrangement generates the bus signal according to a first bus protocol, and the system further includes protocol conversion means coupled to the bus, for converting the first bus protocol to a second bus protocol. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a simplified diagram in perspective or isometric view of a prior-art optical fiber connection system, illustrating a patch panel; 
       FIG. 2   a  is a simplified representation of the juxtaposition of the ends of two optical fibers, illustrating transverse misalignment of the axes, and  FIG. 2   b  is a simplified representation similar to that of  FIG. 2   a , illustrating skew misalignment; 
       FIG. 3  is a simplified cross-sectional view of a partially completed optical fiber mounted in a ferrule; 
       FIG. 4  is a simplified cross-section of the juxtaposition of two optical fibers, each mounted in a ferrule, with the aid of an alignment sleeve; 
       FIG. 5  is a simplified cross-section similar to that of  FIG. 4 , illustrating a light sensor arrangement extending into the region near the gap between the optical fibers in the alignment sleeve; 
       FIG. 6  is a simplified perspective or isometric view, partially exploded to show details, of a fault-detection/optical-fiber-coupling which can be used as a bulkhead connector; 
       FIG. 7  is a simplified representation of a fault-detection/optical-fiber-connector, illustrating details of a possible placement of microchips on a printed circuit board; 
       FIG. 8  is a simplified diagram in schematic and block form, illustrating a possible electrical/electronic layout; and 
       FIG. 9   a  is a simplified perspective or isometric view, partially exploded, showing a patch panel using fault-detection/optical-fiber-couplings in a network context, and  FIG. 9   b  is a simplified perspective or isometric view of a portion thereof. 
   

   DESCRIPTION OF THE INVENTION 
   One way optical fibers are connected is by butting together flat end faces of the optical fibers.  FIGS. 2   a  and  2   b  illustrate two possible types of optical fiber misalignment, as described at page 154 in the text FIBER OPTICS AND OPTOELECTRONICS, second edition, by Peter K. Cheo, published 1990 by Prentice-Hall, ISBN 0-13-315045-3. In  FIG. 2   a , the axis  12   x  of optical fiber  12   o  is offset by a distance x from the axis  14   x  of optical fiber  14   o , so the gap  210  between the ends of the fibers has constant thickness or spacing. In  FIG. 2   b , the front faces  12   ff  and  14   ff  of optical fibers  12   a  and  14   a , respectively, are skewed by an angle designated Θ to create a gap  212  of varying width. 
   The skewing or offset of the two fibers as described in conjunction with  FIGS. 2   a  and  2   b  tends to cause some of the light traveling through the gap between the leak, so that the receiving optical fiber receives less light than might otherwise be expected. Also, some of the light arriving at the gap from a fiber may be reflected by the gap, and return through the fiber toward the source of the light. Both reflection and leakage cause attenuation of the signal coupled from one fiber to another through a gap between fibers. A conventional solution to these potential misalignments and losses is described in the text FIBER OPTIC COMMUNICATIONS, second edition, by Joseph C. Palais, published 1984, 1988 by Prentice-Hall, ISBN 0-13-314527-1. Attachment of an optical fiber to a ferrule is described therein.  FIG. 3  represents the attachment of an optical fiber to a ferrule in the manner described by Palais. In  FIG. 3 , an optical fiber cable  310  including a cover  314  and an optical fiber proper  316  is inserted into an axial bore  318  in a ferrule  320 , with the bare optical fiber  316  extending through an aperture  322  in a front face  324  of the ferrule  320 . Cavity  318  between the optical fiber cover  314  and the inner surface of cavity  318  of the ferrule  324  is filled with epoxy  326 . The bare fiber  316  extending from front face  324  is broken off or removed, and the front face  324 , with the optical fiber, is polished flat. Two optical fibers can be juxtaposed with their front faces  324  adjoining to allow light to flow between the fibers, but this is still subject to attenuation attributable to the misalignments described in conjunction with  FIGS. 2   a  and  2   b.    
     FIG. 4  illustrates the juxtaposition (butting) of two optical fiber cables  410   a  and  410   b , each mounted in a ferrule  420   a  and  420   b , respectively, as described in conjunction with  FIG. 3 . An alignment sleeve  430  defines a through aperture  432  with first and second open ends  434   a  and  434   b , into which ferrules  420   a  and  420   b , respectively, are inserted. A gap alignment lip  436   a ,  436   b  associated with the alignment sleeve  430  provides an abutment surface or stop against which corresponding surfaces of ferrules  420   a ,  420   b , respectively, can be placed. The positions of the alignment lips on the ferrules and the alignment sleeve are selected so that the adjacent ends of optical fibers  416   a  and  416   b  are separated by a gap  408  of known dimension. The alignment sleeve  430  holds coaxial the ferrules  420   a  and  420   b , and the associated ends of the optical fibers  416   a ,  416   b , to thereby tend to minimize the misalignments described in conjunction with  FIGS. 2   a  and  2   b . The alignment sleeve and associated ferrules may have any sort of gap alignment lip. The alignment sleeve may be threaded or unthreaded, and if threaded, the associated ferrules may include a guide ring  440  for a screw-on cap. 
   According to an aspect of the invention, the light leaking from the gap  408  of  FIG. 4  is sensed to produce an indication of the light flowing through the optical fibers  416   a  and  416   b . The resulting structure performs much the same function as the directional or star coupler arrangement of the Leali patent, but is much less complex and expensive.  FIG. 5  is a cross-sectional view similar to that of  FIG. 4 , illustrating the principle of the invention. In  FIG. 5 , elements corresponding to those of  FIG. 4  are designated by like alphanumerics. The arrangement of  FIG. 5  differs from that of  FIG. 4 , in that the alignment sleeve  430  defines an aperture  530  extending through one side at a location aligned with the gap  408 . A light-responsive sensor  510  is inserted into this aperture  530 , so as to receive light leaked from gap  408  when light is traversing the optical junction between the two optical fibers. Light-responsive sensor  510  produces an electrical signal which is applied to an indicator arrangement illustrated as an amplifier  512  and a light emitting device  514 , represented as a light bulb. Those skilled in the art know that solid-state light emitters are preferred to ordinary light bulbs because of their efficiency and long life. Other forms of indicators may be used. Preferred indicators include solid-state devices such as light emitting diodes (LEDs). 
   It will be apparent that the arrangement described in conjunction with  FIG. 5  amounts to an inline fault detector for optical fibers. The amount of light or the light power passing between the optical fibers must be of a magnitude such that the leaked light is sufficient to cause the light sensor  510  to produce a signal. Thus, there is a tradeoff between the requisite amount of leakage light at the gap and the sensitivity of the light responsive sensor. A more sensitive sensor allows inline fault detection with less light traversing the fibers or with a lower-loss gap, or both. Those skilled in the art know how to handle this tradeoff. As described in the literature, a gap such as  408  is not too critical for power loss. 
   A major advantage of an aspect of the invention over arrangements which detect the light to produce an electrical signal, perform the fault detection, and then remodulate the light for transmission further down the fiber, is that of bandwidth. The presence of a demodulator/remodulator in a signal transmission path can significantly limit the effective bandwidth of the transmission path, whereas according to aspects of the invention the optical fibers are coupled as directly as possible, without demodulation or remodulation of the signals traversing the signal path. 
     FIG. 6  illustrates a structure  600  including an alignment sleeve similar to that of  FIG. 5 , fitted with a flange to provide facility for bulkhead mounting. In  FIG. 6 , elements corresponding to those of  FIG. 5  are designated by the same alphanumerics. The alignment sleeve is designated  430 , and the alignment lip as  436   b . A mounting flange  630  is affixed or integral with alignment sleeve  430 , and projects in a plane orthogonal to alignment axis  608 . Flange  630  defines a plurality of screw clearance apertures, some of which are designated  632 , by which the flange can be affixed to a bulkhead panel through which a portion of the alignment sleeve  430  projects. Thus, the inline fault detector can be a combination bulkhead connector/fault detector. 
     FIG. 7  is a symbolic representation of an inline fault detector, showing the use of both a local indicator and a network connection. In  FIG. 7 , elements corresponding to those of  FIG. 5  are designated by like reference alphanumerics. As illustrated in  FIG. 7 , the light sensing device  510  may be mounted on a printed-circuit board  710  at a location adjacent gap  408 . A light-emitting diode  514  provides local indication, and  512  is the amplifier. A multicontact connector  712  provides for interconnection with a mating connector  714  and associated cable  716 , which includes signal conductors as well as conductors for providing power to the printed circuit board  710  and its associated electrical/electronic elements. 
   The arrangement of  FIG. 7  also includes a chip or solid-state network processor  718  which interacts with a unique address generator  720  and with sensor  510  to communicate through cable  716  with an external network. The unique address generator produces an address which allows the location of a fault to be localized. The sensor  510  information is processed by processor  718  and reported to the network. In one embodiment of the invention, the cable  716  uses four conductors, namely a common, a power conductor to carry operating power from the remote network to the device  700 , and two more conductors for I 2 C data and clock signals. 
     FIG. 8  is a simplified schematic and block diagram illustrating details of one possible embodiment  800  of the electronics of the invention. In  FIG. 8 , an integrated optical detector  810  includes a sensor  812  responsive to light  814  for producing an electrical indication. A bias voltage source  816  provides operating bias. The electrical indication, together with the bias, is applied to the terminals of a feedback  822  amplifier  818  to produce an analog signal related to the amplitude of the leakage light  814  reaching the sensor  812 . The analog signal is applied from the output of the amplifier  818  to a microprocessor (μP)  824  incorporating an integral 8-bit analog-to-digital converter (ADC)  826  for converting the analog output signal from amplifier  818  into digital form which can be processed by μP  824 . Processor  824  processes the local identification or address signal from an ID chip  828 , together with the light-power-representative digital signal, to produce I 2 C-format digital data signals for transmission over a conductor  830   a  associated with terminal or connector strip  830 . Clock signals are coupled between μP  824  and conductor  830   b . Power for operating the various components of structure  800  of  FIG. 8  is provided by a VCC conductor  830   c  and ground conductor  830   d . A light-emitting diode (LED)  832  is connected to μP  824 . 
   In operation of structure  800  of  FIG. 8 , the amount of optical leakage power  814  detected by the optical detector  812  is converted to analog electric voltage (or possibly a current), which is digitized in ADC  826 . The digital signal is then processed, and controls the indicator LED, and also controls network transmission of the I 2 C-format (or any other desired format) digital data signals. If the amount of light power corresponds to one consistent with normal light transmission through the optical fibers, the LED will be ON or lit, and exhibit a green color, otherwise the LED will be OFF or dark. If the LED is of the dual-color type, it will turn red rather than OFF. The data stream constantly transmits the measured power level, together with the ID of the inline sensor. A central computer can monitor the power level, and use calibration to identify those power levels which can be considered to represent ordinary operation and fault conditions. 
   In operation of the arrangement of  FIG. 8 , microprocessor  824  generates one static signal for controlling the LED  832 , and also produces two dynamic signals, which are the clock and data signals, in this cased corresponding to the standard two-wire I 2 C bus. Microprocessor  824  compares the light power as indicated by the optical detector  810  with a standard, and produces the required LED control signals. All the elements of the arrangement of  FIG. 8  are commercial off-the-shelf (COTS) items. The microprocessor may contain internal FLASH (nonvolatile) memory to store calibration data, or use external FLASH memory. 
   The described inline detector arrangement is no more lossy, in principle, than an ordinary optical fiber connector bulkhead. The losses of such bulkheads are generally in the order of 1 to 2 dB. 
   In order to keep the cost of the arrangement of  FIG. 7  or  8  low, it is desirable not to require too much processing in each fault-detection/optical fiber coupling. If the remote network is a complex network with extensive syntax requirements, the cost of each fault-detection/optical fiber coupling may grow. It would be advantageous to reduce the need for complex processing in each individual fault-detection/optical fiber coupling. 
     FIG. 9   a  is a simplified partial perspective or isometric view, partially exploded to show details, of a patch panel arrangement  900  according to an aspect of the invention. In  FIG. 9   a , A designates a patch panel with a printed-circuit board (PCB) designated M on the reverse side, which can be seen in  FIG. 9   b . A plurality of identical (except for the ID chip, not illustrated) inline fault detector/optical fiber couplings are illustrated, one of which is designated C. A plurality of LEDs arranged for inline fault detection are illustrated, one of which is designated B, and each of which is associated with a fault detector coupling C. Designation D represents a local network cable corresponding to  716  of  FIG. 7 , extending from the associated inline fault detector/coupling through patch panel A to the remote side thereof, where the cable D is connected to conductive traces (not illustrated) on the PC board. The conductive traces on the pc board lead to an electronics module designated H, which multiplexes and converts the digital signal from each individual fault-detection/optical fiber coupling. More particularly, module H multiplexes the signals from each fault-detection/optical fiber coupling, so that they do not interfere, and also converts the syntax from a simple one associated with the individual fault-detection/optical fiber coupling to a more complex one associated with the remote network, accessible by way of path I. Path I also provides for power to the patch panel. 
   In  FIG. 9   a , F represents a first optical fiber cable, and E represents a connector therefore, such as a ferrule. Items K and L in  FIG. 9   a  also represent an optical fiber cable and connector therefor. Item J represents an electrical connector corresponding to  714  of  FIG. 7 , but on the opposite side of cable  716 . Item J plugs into the printed circuit board mounted on panel A. 
   As mentioned, the invention can be used in optical fiber coupling situations where an unthreaded alignment sleeve is used, or with a threaded alignment sleeve, with a bulkhead-connectible alignment sleeve, and can also be used with a flanged adaptor having a fiber optic connector on one side and a coupling on the other side. 
   A sensor ( 500 ) according to an aspect of the invention, for use in conjunction with light flow through a junction or gap ( 408 ) between first ( 410   a ) and second ( 410   b ) optical fibers, comprises an alignment sleeve ( 430 ) including first ( 430   a ) and second ( 430   b ) ends. The first ( 430   a ) and second ( 430   b ) ends of the alignment sleeve ( 430 ) are dimensioned to accommodate ends of first ( 420   a ) and second ( 420   b ) optical fiber ferrules, respectively. The alignment sleeve ( 430 ), when assembled with the ferrules ( 420   a ,  420   b ), coaxially aligns the associated first ( 410   a ) and second ( 410   b ) optical fibers, respectively, to thereby facilitate the flow of light across a gap ( 408 ) between the first ( 410   a ) and second ( 410   b ) optical fibers. The sensor ( 500 ) includes an optical sensor ( 510 ) located adjacent the gap ( 408 ), for generating an electrical signal representative of light leaking from the gap ( 408 ). An indication arrangement ( 512 ,  514 ), which may be static, dynamic, or both, is responsive to the electrical signal for providing an indication of light flow through the gap ( 408 ). 
   In a particular embodiment of the invention, the indication arrangement ( 512 ,  514 ) comprises a visual indicator ( 514 ), which may be a light-emitting solid-state device. Alternatively, the indication arrangement ( 512 ,  514 ) may be a digital electrical network interface ( 712 ), or both. In the case of a digital electrical network interface ( 712 ), the indication means may include a serial data bus interface ( 824 ), which may be an I 2 C bus connection. 
   A system ( 900 ) according to another aspect of the invention is for monitoring light flow through plural junctions between pairs or sets of optical fibers (K, F). Each of the sets (K, F) of optical fibers includes first (K) and second (F) optical fibers. The system ( 900 ) comprises a plurality of sensors ( 500 , C), each of which comprises (a) an alignment sleeve ( 430 ) including first and second ends, with the first and second ends of the alignment sleeve ( 430 ) being dimensioned to accommodate ends of first and second optical fiber ferrules. The alignment sleeve ( 430 ), when assembled with the ferrules, coaxially align the associated first (K) and second (F) optical fibers, respectively, of one of the plural sets of optical fibers, to thereby facilitate the flow of light across a gap ( 408 ) between the first (K) and second (F) optical fibers of the one (K&lt;F) of the sets of optical fibers. The system also includes (b) an optical sensor ( 510 ) located adjacent the gap ( 408 ), for generating an electrical signal representative of light leaking from the gap ( 408 ), (c) an address generator ( 720 ) for generating a unique address for each of the sensors ( 500 ), (d) a bus connection arrangement ( 824 ,  828 ) responsive to the electrical signal and to the address, for generating a bus signal including information relating to the light flow through the gap ( 408 ) and identity of the sensor ( 500 ), and (e) a bus ( 712 ,  716 ,  830 , H, I) coupled to the bus connection arrangement ( 824 ,  828 ) of each of the sensors ( 500 ) and to utilization means. In a particular embodiment of this aspect of the invention, the bus connection arrangement ( 824 ,  828 ) generates the bus signal according to a first bus protocol, and the system further includes protocol conversion means (H) coupled to the bus, for converting the first bus protocol to a second bus protocol.