FR2473188A1 - Bidirectional T=connector for optical fibres - has two couplers allowing each transmitting-receiving station to be interconnected on common optical bus - Google Patents

Abstract

The bi-directional optical 'T' is for use in connecting a transmitting and receiving station into an optic-fibre bus. The 'T' overcomes problems of attenuation and parasitic signal generation normally encountered. The arrangement is based on the use of primary couplers (3) linking directly with the bus (2) and a second, preferably 3db, coupler interconnecting the transmit and receive station (E.R) into the primary. The primary coupler consists of an optical channel set in parallel with a section of the bus. This parallel channel has two terminals (8,9) which transmit and receive into the two terminations of a split channel in the second coupler. This in turn splits at the local station into two arms terminating at the station receive and transmit points. Both couplers are symmetrically constructed.

Description

Bi-directional optical tee
The present invention relates to the fiber optic links of several transceiver stations therebetween. It relates more particularly to the connection of each of these stations to an optical bus on optical fiber called the main information transfer fiber so as to allow all the stations to communicate with each other.

In known manner, in a program distribution installation from a transmitting station to receiving stations, the transfer of information is done by means of an optical bus formed from or from a main optical fiber to which is connected to the transmitting and branching stations on the optical bus to which the receiving stations are respectively connected.

Each of the branches is obtained by an optical coupler coupling between them the main fiber and a secondary fiber. Such an optical coupler constitutes an optical tee and defines on the main fiber two coupling ports, respectively for input and output of light energy and on the secondary fiber also two ports of which only one however constitutes, due to the directivity of the coupling, an energy output port to which the receiving source concerned is connected. Thus, at each branch, to the nearest coupling losses, the optical coupler distributes the light energy available on the input access on the main fiber, on the emitting source side, on the main fiber between the output access on the main fiber. and the exit access on the secondary fiber.

 In an installation of another type, in which all the stations are transceiver stations, the use of an optical bus, with main optical fiber, equipped with branches formed by the preceding couplers and to which the stations are respectively connected transceivers, by the two accesses on the secondary fiber of each coupler for each transmitting / receiving station, cannot, because of the directivity of these couplers, transfer information from any of these stations, then transmitting , to all the others: only the stations located on the same side of the station considered to be transmitting along the optical bus will receive the information transmitted.

For reception of this information transmitted by all the other stations, it is necessary to adopt a closed loop structure obtained by connecting the two ends of the optical bus. With such a structure, the information transmitted by any one of the stations then reaches successively the other stations by traversing in the same direction the closed loop, however this information transmitted although attenuated remains present on the loop and constitutes parasites from the first desired route completed.

The object of the present invention is to allow such transmitting-receiving stations to communicate with each other while avoiding this drawback.

It relates to a bi-directional optical tee for connection of a transceiver station to an optical bus formed by an optical fiber called the main information transfer fiber, characterized in that it comprises two optical couplers, the one, said first coupler, coupling between them the main fiber and a secondary optical fiber and defining two coupling ports on each of these fibers and the other, said second coupler, coupling between them two auxiliary optical fibers and also defining two access ports coupling on each of said auxiliary fibers, two of which accesses belonging to one and the other of said auxiliary fibers are connected respectively to said transceiver station and the other two to the accesses on said secondary fiber.

According to another characteristic of the invention, said second coupler is a 3 dB coupler.

 According to another characteristic, the two auxiliary fibers consist of the terminal portions of the secondary fiber extending beyond the coupling accesses which it has for the first coupler, the first and second couplers then having two common coupling accesses.

 The characteristics and advantages of the present invention will emerge from the description given below of the bi-directional tee according to the invention illustrated schematically in the single figure given in the attached drawing.

In the figure, there is illustrated the connection of a transceiver station 1 to an optical bus 2 formed by an optical fiber called the main fiber. This main optical fiber is intended to ensure the transfer of information between a plurality of transceiver stations such as station t, not shown in this figure and which are connected to the main optical fiber 2 in the same way as station 1 .

 The connection of the transceiver station 1 to the main optical fiber 2 is ensured by two optical couplers 3 and 4.

The coupler 3 ensures the coupling between the main optical fiber 1 and a secondary fiber referenced 5 and defines on the main fiber two coupling ports 6 and 7 and on the secondary fiber two other coupling ports 8 and 9. In the example illustrated the secondary fiber extends beyond the ports 8 and 9 of the first coupler 3.

 The coupler 4 ensures the coupling between the two terminal portions of the preceding secondary fiber 5 and defines on these terminal portions two coupling ports combined with the ports 8 and 9 of the first coupler and two other coupling ports 10 and 11 for the transmitting station. -receiver 1.

 Advantageously, the coupler 4 is a 3 dB coupler, the coupling being produced symmetrically between two optical fibers of the same characteristics, here two identical portions of the same fiber 5.

Of course, the coupler 4 can ensure the coupling between two auxiliary fibers, the two ports of this coupler and those of the coupler 3 on the secondary fiber, forming in the illustrated case the common ports 8 and 9 of the two couplers 3 and 4, will be then respectively connected by means of two suitable optical connectors.

 To explain the transfer of energy obtained by this connection, a transmitting part E connected to the access 10 and a receiving part R connected to the access 11 have been shown diagrammatically for the station 5.

When station 1 is considered to be transmitting, the useful transfer of lighted energy takes place from access 10 to accesses 8 and 9 then to accesses 6 and 7 on the main fiber. When the coupler 4 is a 3 dB coupler, the light power transfer takes place equally on the ports 8 and 9, this to the coupling losses of the coupler 4, these ports 8 and 9 then form two identical sources for the coupler 3 and the light powers at ports 6 and 7 are equal. This useful transfer of energy from access 10 to the two accesses 6 and 7 on the fiber, shown diagrammatically by the dotted lines in the direction of the arrows indicated, shows that this method of connection using two uni-directional couplers constitutes an optical tee. bi-directional connection of a station to a fiber for the "injection" of energy from the station on the main fiber.

 It will be noted that part of the light energy at ports 8 and 9 is returned by the coupler 3, respectively by ports 9 and 8 to station 1, this certainly constitutes a loss of energy transfer from port 10 towards accesses 6 and 7 but does not cause any disturbance in the operation of station 1 and is therefore not harmful for the distribution of information from station 1 to other similar stations located on either side of this station 1 along the main fiber 2. Of course, the characteristics of the coupler 3 will be such that the transfer of energy will take place essentially on the main fiber.

 Conversely, station 1 being considered to be receiving, by couplers 3 and 4 it can detect the light energy present at any of the ports 6 and 7. Thus, for example, the light energy at port 5, then access input is distributed, at losses of the coupler 3 close, between the access 7 from which it is transmitted to the other stations by the fiber 2 and the access 9 from which it is transmitted by the coupler 4 to the accesses 10 and 11. The energy present on access 11 is detected by station 1. Similarly, apart from the losses, the energy coming from access 7 is distributed between access 6 from where it is transmitted to other stations by fiber 2 and accesses 10 and 11, station 1 detecting the energy at access 11.

There is therefore also a bi-directional optical tee connecting a station to a fiber for Wltextraction "of energy from the fiber whatever the direction of transmission on the fiber.

Claims (3)

1 / Bi-directional optical tee for connection of a transceiver station to an optical bus formed by an optical fiber called the main information transfer fiber, characterized in that it comprises two optical couplers, one, called the first coupler , coupling the main fiber and a secondary optical fiber together and defining two coupling ports on each of these fibers and the other, said second coupler, coupling between them two auxiliary optical fibers and also defining two coupling ports on each of said fibers two of which accesses belonging to one and the other of said auxiliary fibers are respectively connected to said transceiver station and the other two to the accesses on said secondary fiber. 2 / bi-directional optical tee according to claim 1, characterized in that said second coupler is a 3 dB coupler. 3 / bi-directional optical tee according to one of claims 1 and 2, characterized in that said auxiliary fibers are constituted by end portions of said secondary fiber extending beyond said coupling ports it has, both coupling access belonging to said first coupler and the two coupling accesses belonging to said second coupler and connecting these couplers then forming two accesses common to said couplers.