Two stage optical amplifier

1. A system comprising a pair of two stage amplifiers arranged at two spatially separate modules, for respectively serving two opposite directions of bi-directional optical transmission comprising one or more informational channels each serving exclusively for transmitting optical traffic and not performing supervisory channel functions, wherein

each of the two-stage optical amplifiers comprises a 1 st stage, a 2 nd stage and a mid-stage formed between said two stages, and serves one of the two opposite transmission directions, and wherein

each stage of said two stages is formed by at least one optical amplifying unit and is located at a spatially separate module, so that each of the two spatially separate modules accommodates the 1 st stage of one of said amplifiers and the 2 nd stage of the other of said amplifiers;

the system comprises at least two Optical Add Drop Multiplexers (OADMs) connected in the mid-stages of said two-stage optical amplifiers and adapted to add and drop said one or more informational channels.

2. The system of claim 1 , wherein said OADMs are connected in such a manner that each of the two transmission directions is separately served by one or more of said OADMs by adding/dropping the one or more information channels in said transmission direction.

3. The system of claim 1 , wherein said OADMs are connected in such a manner that at least one of the OADMs is switched into both of the two transmission directions and serves both of them, said at least one OADM is switched so as to allow redirecting the optical traffic from one direction to another when required, by interconnecting a 1 st stage and a 2 nd stage of the same spatially separate module but of different said two-stage amplifiers.

4. The system according to claim 1 , wherein each of said amplifiers

is provided with a control-communication circuit comprising a control-communication channel arranged between the two stages of the amplifier, for controlling said 1 st and 2 nd stages so as to match at least one optical characteristics of one stage to respective at least one characteristics of the other stage among the two stages, and

to prevent automatic shutting down of one of the stages whenever the other of the stages is shut down,

said control-communication circuit further comprising a micro-controller of the two-stage amplifier and connection means for interconnecting said 1 st and 2 nd stages of the two-stage amplifier.

5. The system according to claim 4 , wherein said two stages are matched to one another in respect and wherein said control-communication channel serves for controlling at least one parameter of the amplifying units of said stages, selected from a list comprising: gain, gain flatness and gain tilt.

6. The system according to claim 5 , wherein the optical connection and the control-communication channel between the stages is arranged to externally interconnect said modules.

7. The system according to claim 1 , wherein each of said modules is designed as a universal two-stage optical amplifier assembly, comprising said 1 st stage and a 2 nd stage being preliminarily matched to one another in respect of at least one optical characteristics,

input of the assembly being connected to input of the 1 st stage,

output of the 2 nd stage being connected to output of the assembly, output of the 1 st stage and input of the 2 nd stage are respectively connected to a pair of mid-stage contacts of the assembly; said universal assembly being provided with a control-communication circuit adapted to form a control-communication channel between the two stages, and control said two stages so as to match at least one optical characteristics of one stage to respective at least one characteristics of the other stage among the two stages, and to prevent automatic shutting down of one of the stages whenever the other of the stages is shut down;

while said control-communication circuit is also adapted to alternatively form an alternative control-communication channel between any of the stages of said universal assembly and a complementary stage located on another similar universal assembly;

wherein in said system, any of the two OADMs is connected between any of the stages of said universal assembly and a complementary stage of another similar universal assembly, using the mid-stage contacts located at the different universal assemblies, and

said control-communication circuit forms the alternative control-communication channel between at least one of the stages of said universal assembly and a complementary stage located on another similar universal assembly.

8. The system according to claim 7 , wherein the 1 st stage and the 2 nd stage are preliminarily matched so that the is stage of the universal assembly is preliminarily adjusted to match to a set of characteristics designed for the 2 nd stage, while the 2 nd stage of the universal assembly is preliminarily adjusted to match to a set of characteristics designed for the 1 st stage, thereby any of the 1stage and the 2 nd stage of said universal assembly approximately matches to a complementary stage of said universal assembly or of another similar universal assembly.

9. The system according to claim 7 , wherein the control-communication circuit is capable of dynamically matching any of the 1 st stage and the 2 nd stage of said universal assembly to a complementary stage of said universal assembly or of another similar universal assembly.

10. The system according to claim 7 , wherein the control-communication circuit is divided into two separate portions respectively suitable for being connected to corresponding separate portions of a control-communication circuit of another similar universal assembly, so as to form a control-communication channel between a 1 st stage of one assembly and a 2 nd stage of the other assembly and vice versa.