Controllable optical add/drop multiplexer

1. A method of a controllable selective add/drop channel in a fiber-optic communication system provided with 2 N of wavelength-division multiplexing channels, whose optical frequencies at a constant frequency separation Δv between adjacent two channels are retunable, the method comprising:

(a) inputting multi-channel optical signal in a N-stage structure, where each stage, at n=1, 2, . . . , N, contains an optical filter having one input or two inputs and two outputs and characterizing by transmission in form periodic function with spectral separation between two adjacent extremums Δv n =2 n−1 Δν and having a possibility of controllable tuning transmissions and to be connecting, optical filter in each stage except the first one, by input or one the two inputs with one of the outputs of optical filter of the previous stage, with one input of optical filter of the first stage being an input port of N-stage structure;

(b) choosing channel that is the subject of add/drop;

(c) tuning said optical filter of each stage in such a way that transmission from input to output, that are used in the connection of said optical filters described in (a), had maxima on the frequency of said chosen channel;

(d) transmitting the multi-channel optical signal through N-stage structure and dropping chosen channel on output of said optical filter of the last stage, which is a drop port in N-stage structure; and

(e) adding of a new channel on the frequency of the drop channel, multiplex new channel and all channels, except the dropped one, and return multiplexed channels to the optical network.

2. The method of claim 1 , wherein in the case of the optical filters that have two inputs, add of a new channel is done through an adding port of N-stage structure, connected with input of said optical filter of the last stage, that is not used in connection of said optical filters described in paragraph (a), multiplexing of a new channel and all channels, except the dropped one, is done by connecting of said output of the optical filter of each stage, except the first one, that is not used in connections of said optical filters described in (a), with input of said optical filter of the previous stage that is not used in connections of said optical filters that are described in (a), and return of the multiplexed channels to the optical network is done through the output of said optical filter of the first stage that had not been used in connection of said optical filters described in (a).

3. The method of claim 1 , wherein in the case of the optical filters that have one input, addition of a new channel is carried out through one of the inputs of an optical combiner, that has N+1 of inputs and one output, multiplexing of a new channel and all channels, except the dropped one, is done by connecting an output of the optical filter of each stage, that is not used in connections of filters that was described in (a), with one of the inputs of said optical combiner, at that through output of said optical combiner multiplexed channels return to the optical network.

4. A controllable optical add/drop multiplexer provided with 2 N of wavelength-division multiplexing channels, whose optical frequencies at a constant frequency separation Δv between adjacent two channels are retunable, that has one input port ( 71 ), one output port ( 72 ), one drop port ( 73 ) and one add port ( 74 ), comprising:

a N-stage structure, where each stage, at n=1, 2, . . . , N, contains an optical filter having two inputs (a,b) and two outputs (c,d) and characterizing by transmission in form periodic function with spectral separation between two adjacent extremums Δν n =2 n−1 Δν and having a possibility of controllable tuning transmissions; and

a controller ( 78 ) for tuning of transmission of said optical filters ( 75 - 1 , 75 - 2 , 75 - 3 ).

5. The controllable optical add/drop multiplexer of claim 4 , wherein in said N-stage structure:

said optical filter ( 75 - 2 , 75 - 3 ) of each stage, except the first one, by one of the inputs (a) and one of the outputs (c) is connected with one of the outputs (d) and one of inputs(b) of optical filter of the previous stage correspondingly;

said optical filter ( 75 - 1 ) of the first stage by the other input (a) is connected with the input port ( 71 );

said optical filter ( 75 - 1 ) of the first stage by the other output (c) is connected with the output port ( 72 );

said optical filter ( 75 - 3 ) of the last stage by the other output (d) is connected with the drop port ( 73 ); and

said optical filter ( 75 - 3 ) of the last stage by the other input (b) is connected with the add port ( 74 ).

6. The controllable optical add/drop multiplexer of claim 4 , wherein said optical filters ( 75 - 1 , 75 2 , 75 - 3 ) of each stages of said N-staged structure are single-stage nonsymmetrical Mach-Zehnder interferometers ( 20 ) and/or two-stage nonsymmetrical Mach-Zehnder interferometers ( 40 ).

7. A controllable optical add/drop multiplexer for fiber-optic communication system provided with 2 N of wavelength-division multiplexing channels, whose optical frequencies at a constant frequency separation Δv between adjacent two channels are retunable, that have one input port ( 81 ), one output port ( 82 ), one drop port ( 83 ) and one add port ( 84 ), comprising:

a N-stage structure, where each stage, at n=1, 2, . . . , N, contains an optical filter having one input (g or a) and two outputs (p, k or e, f) and characterizing by transmission in form periodic function with spectral separation between two adjacent extremums Δv n =2 n−1 Δν and having a possibility of controllable tuning transmissions;

an optical combiner ( 86 ), that have N+1 inputs and one output, connected with output port ( 82 ); and

a controller ( 89 ) for tuning of transmission of said optical filters [ 85 - 1 , . . . , 85 - 6 ].

8. The controllable optical add/drop multiplexer of claim 7 , wherein in said N-stage structure:

said optical filter [ 85 - 1 , . . . , 85 - 5 ] of each stage except the last one that is connected with input of said optical filter of the next stage by one of the outputs (p or e), and by the other output (k or f) is connected with one of the inputs of said optical combiner;

said optical filter ( 85 - 1 ) of the first stage is connected by own input (g) with input port ( 81 );

said optical filter ( 85 - 6 ) of the last stage that is connected with the other input of said optical combiner by one output (f), and that is connected with the drop port ( 83 ) by the other output (e); and

said optical combiner ( 86 ) is connected by one input that is not used in the connections that had been described above with the add port ( 84 ).

9. The controllable optical add/drop multiplexer of claim 7 , wherein said optical filters [ 85 - 1 , . . . , 85 - 6 ] of N-stage structure are multi-stage nonsymmetrical Mach-Zehnder interferometers ( 60 ).

10. A controllable selective add/drop channel apparatus for a fiber-optic communication system provided with 2 N of wavelength-division multiplexing channels, whose optical frequencies at a constant frequency separation Δv between adjacent two channels are retunable, comprising:

(a) a multi-channel optical signal N-stage structure, where each stage, at n=1, 2, . . . , N, contains an optical filter having one input or two inputs and two outputs and a transmission in form periodic function with spectral separation between two adjacent extremums Δv n =2 n−1 Δν and having a controllable tuning transmission, and further comprising an optical filter in each stage except a first stage, the one input or one of the two inputs connected with one of the outputs of optical filter of the previous stage, with the one input of the optical filter of the first stage being an input port of the N-stage structure;

(b) providing channel that is the subject of add/drop;

(c) said optical filter of each stage being tuned in such a way that the transmission from the input to the output, that are used in the connection of said optical filters described in (a), had maxima on the frequency of said channel;

(d) the multi-channel optical signal being transmitted through the N-stage structure and the output of said optical filter of the last stage, further comprising a drop port in the N-stage structure; and

(e) a new channel added on the frequency of the dropped channel, and the new channel and all channels, except the dropped channel, being return multiplexed channels in the N-stage structure.

11. The apparatus of claim 10 , further comprising an adding port of N-stage structure, connected with the input of said optical filter of the last stage, that is not used in connection of said optical filters described in paragraph (a), wherein the multiplexing of a new channel and all channels, except the dropped one, further comprises connecting one of the outputs of the optical filter of each stage, except the first one, which output is not used in connections of said optical filters described in (a), being connected with one of the inputs of said optical filter of the previous stage that is not used in connections of said optical filters that are described in (a), and return of the multiplexed channels to the optical network is done through the output of said optical filter of the first stage that had not been used in connection of said optical filters described in (a).

12. The apparatus of claim 10 , further comprising an optical combiner, that has N+1 of inputs and one output, wherein in the case of the optical filters that have one input, addition of a new channel is carried out through one input of the optical combiner, and wherein multiplexing of a new channel and all channels, except the dropped one, is done by connecting an output of the optical filter of each stage, that is not used in connections of filters that was described in (a), with one of the inputs of said optical combiner, and the output of said optical combiner combines the multiplexed channels and is connected to an output of the N-stage structure for return to an optical network.