Abstract:
A signal processing system ( 10 ) has a plurality of optical fibers ( 40, 42, 43 ) with their one ends ( 40 ) mounted in an array board ( 41 ) to receive electromagnetic radiation. A coupler ( 54 ) interconnects the other ends of the optical fibers ( 42, 43 ) in parallel such that electromagnetic radiation is first coupled together and then directed into two or more independent processing channels ( 45, 47 ).

Description:
This application is the U.S. national phase of international application PCT/GB04/04842 filed Nov. 16, 2004 which designated the U.S. and claims benefit of GB 0327037.8 and EP 03257338.8, dated Nov. 20, 2003, the entire content of each of which is hereby incorporated by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to an electromagnetic signal processing system and more specifically, but not exclusively, to a system of processing an optical signal. 
   2. Discussion of Prior Art 
   WO02/29436 teaches that a laser-radar receiver should comprise an array of optical fibres which are connected to at least one radiation detector, each optical fibre having different physical characteristics which result in known delays in the transmission time of pulsed electromagnetic radiation. Such delays are conveniently achieved by using optical fibres of differing lengths so that they operate as delay lines. Arrays of 3×3 optical fibres are taught, each optical fibre connected to single avalanche photo-diode (APD). 
   In our co-pending UK patent application number 0322564.6, we have taught that an electromagnetic signal processing system may comprise a plurality of optical fibre arrays, each optical fibre array having a cluster of optical fibres with their one ends oriented to receive electromagnetic radiation and arrange to transmit electromagnetic radiation to an array output, the array outputs being connected to transmit electromagnetic radiation in sequence to a signal detector input. In this co-pending application we have also taught various additional features for such signal processing systems. 
   SUMMARY OF THE INVENTION 
   According to the present invention a signal processing system has at least two independent processing channels, a plurality of optical fibres with their one ends oriented to receive electromagnetic radiation, and couplers interconnecting the other ends of the optical fibres in parallel such that electromagnetic radiation transmitted by the optical fibres will be coupled together and then directed into each of the independent processing channels. In this manner the same optical signal arriving at an array of optical fibres can be split into different independent channels for processing. 
   At least one of the independent processing channels preferably includes a processing board with an output to a signal detector. At least one of the processing boards may include electrical and/or optical signal processing components. 
   At least one of the independent processing channels is preferably arranged to transmit the electromagnetic radiation in sequence to a single detector input. This can be achieved as taught in our co-pending UK patent application 0322564.6. Preferably another independent processing channel may be arranged to transmit the electromagnetic radiation in sequence to another signal detector input, and the independent processing channels incorporate different optical delays to minimise any range/position ambiguity. 
   One of the independent processing channels may be arranged to transmit electromagnetic radiation in sequence to a signal detector unit, and another independent processing channel arranged to transmit the electromagnetic radiation to a processing board configured to assess the range and depth of a target. 
   By providing at least two independent processing channels, it is possible for each independent processing channel to contain different signal detectors. This enables the electromagnetic radiation to be assessed with different sensitivities for different tasks, for different wavelengths, and for other different physical characteristics. 
   By having at least two independent processing channels, the invention also enables one processing channel to feed signals into at least one of the other channels. This feature greatly enhances the processing of received electromagnetic radiation. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example only, with reference to the accompanying drawings in which: 
       FIG. 1  is a diagram illustrating our current technique of connecting optical fibres to a detector, 
       FIG. 2  is a diagram illustrating one embodiment of the present invention, and 
       FIG. 3  is a diagram illustrating a further embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
   With reference to  FIG. 1 , a signal processing system  10 , comprises an optical fibre cluster or array  11  having nine optical fibres, one end of each fibre being depicted by the small circles  40 . The set of nine fibres is positively located in predetermined relative positions in an array board  41  which, in use, would be mounted to face the direction from which an electromagnetic signal may be received. Although the array board  41  is show as being rectangular with optical fibres  40  arranged equally-spaced in a 3×3 matrix, the array board  41  may be of any convenient shape and its cluster of optical fibres  40  may be any required number arranged in any suitable manner to receive electromagnetic radiation. The optical fibre array  41  is depicted in a simplified manner with only two optical fibres  42 ,  43  for the right-hand column being drawn. It should be understood that all nine optical fibres of the array board  41  have different lengths, as shown in  FIG. 1 , so that there is an in-built time delay between the transmission by each optical fibre. The optical fibres  42 ,  43  are shown joined in parallel by a 2-in-to-1 coupler  44  to a single output  45 . The other optical fibres  40  forming the array board  41  would similarly be connected in parallel to the output  45  by respective couplers  44 . 
   An optical system  46  is used to direct incoming electromagnetic signals on to the ends of the optical fibres  40 . 
   The present invention is illustrated by  FIG. 2  in which the same reference numerals have been used to indicate equivalent features. The primary difference is that the coupler  44  of  FIG. 1  has been replaced by a 2-in-to-2 coupler  54  which couples the optical fibres  42  and  43  together, but then directs the combined signal into two separate, and therefore independent, processing channels defined by the output  45  and a second output  47 . This configuration enables the independent processing channels  45 ,  47  to feed the electromagnetic radiation into different signal processors. One of the independent processing channels  45 ,  47  may be provided with a processing board with an output to a signal detector, the processing board including electrical and/or optical signal processing components. 
   The other independent processing channel  47  or  45  can be arranged to transmit the electromagnetic radiation in sequence to a signal detector input as taught by our aforesaid co-pending UK patent application. 
   In  FIG. 3 , two array boards  41  and  141  are provided with electromagnetic radiation through the same optical system  46 . The optical fibres  42  and  43  are connected in parallel by a 2-in-to-1 connector  44  to an optical fibre  50 , whereas optical fibres  142  and  143  from array board  141  are connected in parallel by a 2-in-to-1 connector  144  to an optical fibre  150 . 
   It will be noted that the optical fibre  50  is longer than the optical fibre  150  whereby any signal transmitted by optical fibre  50  to coupler  154  will be delayed relative to a signal through the shorter optical fibre  150 . This cascading of the optical fibres  50  and  150  enables the respective signals to be differentiated by a signal detector. 
   However, the coupler  154  serves to split the combined signal into the two independent processing channels  45  and  47  for separate processing in the same manner as has been described with reference to  FIG. 2 . 
   Instead of using 2-in-to-2 couplers, N-in-to-M couplers may be used so that any number of inputs can be combined together and then split into any number of independent processing channels. 
   A primary advantage of the invention is that the same optical signal arriving at an array board  41 , or  141 , will be split into different independent processing channels. 
   In the real system there would be many other fibres feeding into the independent processing channels  45  and  47 . Typically, multiple array boards  41  or  141  would be individually mounted to face a direction from which an electromagnetic signal might be received. They may face either in the same direction or may be oriented to receive electromagnetic radiation from different directions. Instead of being mounted in the array boards, the optical fibres  40  could be mounted directly through any convenient support structure. 
   In addition to directing the electromagnetic signal into two or more independent processing channels  45 ,  47 , this approach also enables signals to be fed back from a stage in one channel to a stage in another channel, and vice versa, whereby detection of a signal characteristic in one processing channel can be used to affect the processing of the same signal in another channel. This enables the formation of very complex processing architectures. 
   In one example, one of the independent processing channels could have a cascaded structure as taught in our aforesaid co-pending UK patent application, whilst another independent processing channel could include a processing board incorporating electrical and/or optical components to process signals, the processing board being fed with all fibres from the array (not just from one cluster) into the signal detector. In this manner the detector would receive a series of pulses which would permit the range and depth of a target to be deduced. The depth of the target being the difference between the front and the back edges of the signal. 
   In another example, two independent processing channels could have cascaded structures as taught in our aforesaid co-pending UK patent application, but with the channels using different time delays. This configuration enables issues, such as the “range/position ambiguity” to be minimised or eliminated. 
   In a further example, the independent processing channels could contain different detectors, for instance with different sensitivities for different tasks, different wavelengths, and other differing parameters.