Abstract:
An expansion network for increasing the number of subscriber terminations at a passive optical bus system comprising optical mixers is disclosed. The mixers are arranged in groups and the optical transmitters individually provided per subscriber are connected to the light receivers likewise individually provided per subscriber, being connected thereto in the manner of a mesh network via respectively only one of the mixers so that the attenuation of only one mixer is inserted into the optical path.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an expansion network for increasing the number of subscriber terminations at a passive optical bus system comprising optical mixers, for example, what referred to as star couplers. 
     2. Description of the Prior Art 
     Passive optical mixers, so-called star couplers, which are useable for the formation of an optical bus system have limited number of inputs and outputs. When one wishes to connect more subscribers, for example, sub-task computers in a multicomputer system, to the bus system, then a plurality of star couplers must be interconnected in a suitable manner to form a system. 
     One possibility for expanding coupler networks to be formed in such a manner is known from the German published application No. 31 23 445, fully incorporated herein by this reference This known expansion possibility has the advantage that opto-electrical amplifiers can be inserted into he appertaining, required light conductors between the star couplers with little expense, the opto-electric amplifiers regenerating the light signals and reducing the attenuation in the coupler network. With respect to transit times and subscriber connection, the meshed star couplers essentially behave in the manner that a correspondingly large coupler would behave when they are joined in close spatial proximity. For ideal optical components, the transmission loss is likewise the same as given a single coupler but, in practice, a few decibels of additional losses are added due to losses in the mixer and, under given conditions, in the required, optical plugs. The signal transit times and attenuations occurring, however, can be disadvantageous, particularly in multicomputer systems. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to provide an expansion network, which likewise permits the possibility of connecting a great number of subscribers, but which is more favorable then the known expansion solution in view of signal transit times and attenuations. 
     The above object is achieved, according to the present invention by an expansion network for increasing the number of subscriber terminations at a passive optical bus system comprising optical mixers, the expansion network being particularly characterized in that, for the connection of n·m subscribers, for example, sub-task computers in a multicomputer system, which are combined in m groups of n subscribers each, to the optical bus system, m·m mixers in the m groups of m mixers are each provided. Furthermore, m transmitter-side optical fibers optically operated in parallel extend from a light transmitter respectively individually arranged per subscriber, whereby, in each of the m groups the first optical fiber of these m transmitter-side optical fibers which departs from the first light transmitter of the appertaining group is respectively connected to a first optical input of the first mixer of this group, the second optical fiber is connected to a first optical input of the second mixer of the group and the m th  transmitter-side optical fiber of the m transmitter-optical fibers is connected to the first optical input of the m th  mixer of this group. In addition, m receiver-side optical fibers extend to a light receiver respectively individually arranged per subscriber, whereby, dependent on the appertaining group, for example, on the first group, the first receiver-side optical fiber of the m optical fibers which extends to the first light receiver of the appertaining group departs from a first optical output of the first mixer of this group, the second receiver-side optical fiber departs from a first optical output of the first mixer of the second group, and on down the line until the m th  optical fiber departs from the first optical output of the first mixer of the m th  group. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Other objects, features and advantages of the invention, its organization, construction and operation will be best understood from the following detailed description, taken in conjunction with the accompanying drawing, on which there is a single figure which is a block diagram illustration of a preferred exemplary embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The drawing schematically illustrates an arrangement of subscriber-associated light transmitters S for a plurality 
     of subscribers T1n 1  . . . T1n n  and T1n n  (m-1) 1 . . . t1n n ·m, subscriber-associated light receivers E for the subscribers T1n, optical mixers M 1  . . . M m , as well as transmitting-side optical fibers LLFS and receiving-side optical fibers LLFE. 
     For the connection of n·m subscribers T1n, for example, sub-job computers in a multicomputer system, to the optical bus system, the subscribers being combined in m groups G 1  . . . G m  of n subscribers T1n each, m·m mixers are provided in the m groups G 1  . . . G m  of m mixers M 1  . . . M m  each. A plurality m transmitting-side optical fibers LLFS 1  . . . LLFS m , LLFS 1  . . . LLFS m  . . . optically operated in parallel extend from the light transmitters S 1  . . . S n , S 1  . . . S n , . . . respectively individually arranged per subscriber Tln, whereby, in each of the m groups G 1  . . . G m , the first optical fibers LLFSl of the m transmitting-side optical fibers LLFS 1  . . . LLFS m  which departs from the first light transmitter S 1  of the appertaining group, for example, group G 1 , is respectively connected to a first optical input I1 of the first mixer M 1  of this group G 1 , the second optical fibers of the m transmitting-side optical fibers are connected to a first optical input of the second mixer of the group, . . . and the m th   transmitting-side optical fibers LLFS m  of the m transmitting-side optical fibers are connected to the first optical input I1 of the m th  mixer Mm of the group G 1 . 
     A plurality m receiver-side optical fibers LLFE 1  . . . LLFE m , LLFE 1  . . . LLFE m , . . . , lead to the light receivers E 1  . . . E n , E 1  . . . E n , . . . respectively individually arranged per subscriber whereby, dependent on the appertaining group G 1  . . . G m  for example, dependent on the first group Gl, the first receiver-side optical fibers LLFE 1  of the m optical fibers LLFE 1  . . . LLFE m  which lead to the first light receiver E 1  of the appertaining group, for example the group G 1 , extend from a first optical output O 1  of the first mixer M 1  of the group G 1 , the second receiver-side optical fibers extend from a first optical output of the first mixer M 1  of the second group, . . . and the m th  receiver-side optical fibers LLFE m  of the m optical fibers extend from the first optical output O 1  of the first mixer M 1  of the m th  group. 
     For example, in accordance with the feature of the invention, respectively m light-emitting diodes LED electrically connected in parallel are arranged in each of the n·m light transmitters S for optical parallel operation of the m transmitting-side optical fibers LLFS. 
     It can also be provided in accordance with the invention that respectively m light-emitting diodes LED electrically connected in series are arranged in each of the n·m light transmitters S for the optical parallel operation of the m transmitting side optical fibers LLFS. 
     Another feature of the invention provides that respectively m light-emitting diodes LED are arranged in each of the n·m light transmitters S for optical parallel operation of the m transmitting side optical fibers LLFS, these light-emitting diodes LED being divided into a number of groups, whereby the light-emitting diodes LED of respectively each group are connected electrically parallel to one another and the group arrangements formed in this manner are electrically connected in series. 
     A solution which is technically more simple, but more involved in terms of cost and space, provides that a respective m-fold arrangement of complete electro-optical transmission transducers is established in each of the n·m light transmitters S for the optical parallel operation of the transmitting-side optical fibers LLFS. 
     For the optical parallel operation of the transmitter-side optical fibers LLFS, it can also be provided in accordance with the invention that the m optical fibers LLFS 1  . . . LLFS m  in each of the n·m light transmitters S are optically coupled to a common light-emitting diode LED in a known manner by what are referred to as tapers, cf. Johnson et al, Appl. Phys. Lett., Vol. 35, No. 1, 1979, Page 479. 
     Finally, another feature of the invention is characterized in that, for optical parallel operation of the transmitting-side optical fibers LLFS, respectively one optical mixer is provided per subscriber Tln, optical signals from a common, subscriber-associated electro-optical transmission transducer being supplied thereto, these optical signals being transmitted through the optical mixer to the m transmitting-side optical fibers LLFS 1  . . . LLFS m   
     For the reception of optical signals via or more of the m receiving-side optical fibers LLFE 1  . . . LLFE m  per subscriber Tln by means of the appertaining light receiver E, respectively m photo-transistors connected electrically parallel can be arranged in each of the n·m light receivers in accordance with the invention. 
     In accordance with another feature of the invention, a respective m-fold arrangement of complete opto-electrical receiving transducers can be provided in each of the n·m light receivers E for the reception of optical signals via one or more of the m receiver-side optical fibers LLFE. 
     Alternatively thereto, it can also be provided for the reception of optical signals via one or more of the m receiver-side optical fibers LLFE that the m optical fibers LLFE 1  . . . LLFE m  in each of the n·m light receivers E are optically coupled to a common photo-transistor in a known manner by what are referred to as tapers. 
     Finally, it can also be provided in accordance with the invention that, for the reception of optical signals via one or more of the m receiver-side optical fibers LLFE 1  . . . LLFE m , respectively one optical mixer is provided per subscriber Tln, this optical mixer being supplied with optical signals via one or more of the m receiver-side optical fibers LLFE, these optical signals being transmitted by the optical mixer to a common, subscriber-associated opto-electric reception transducer. 
     In the arrangement shown on the drawing, all star couplers are connected in parallel, i.e. each light pulse traverses only one mixer if one leaves subscriber-associated mixers for light transmitters or, respectively, light transducers which may potentially be provided out of consideration. 
     The attenuation between a light transmitter and the light receiver is therefore established only by the division factor and losses of a single star coupler (plus line attenuation, plug attenuation, etc, as usual). This advantage cf the arrangement particularly comes to bear for purely passive networks having great numbers of subscribers and relatively short distances of the subscribers from the couplers. The number of connections to the light transmitters and light receivers is dependent on the expansion level of the network. 
     NUMERICAL EXAMPLE 1 
     In this example 64 subscribers are to be connected to the optical bus system. For this purpose, 16 star couplers and 8×64=512 optical fibers are required. Every transmission module must have four outputs and every receiving module must have four inputs. 
     The transmission loss of the coupler network (without optical cable) is composed of 12 dB for light division (1:16) plus the simple mixer losses (1 . . . 4 dB). 
     NUMERICAL EXAMPLE 2 
     In this example, 1024 subscribers are to be connected to the optical bus system. For this purpose, 16 subscriber groups having 64 subscribers per subscriber group are required. Also, 256 star couplers and 2×16×1024=2×16384 optical fibers are required for this purpose. 
     The transmission loss of the coupling network is defined by the division factor 1:64 (18.1 dB) plus the simple attenuation loss of the couplers (about 1 . . . 4 dB). 
     Although I have described my invention by reference to particular illustrative embodiments thereof, many changes and modifications of the invention may become apparent to those skilled in the art without departing from the spirit and scope of the invention. I therefore intend to include within the patent warranted hereon all such changes and modifications as may reasonably and properly be included within the scope of my contribution to the art.