Optical wavelength add-drop multiplexer

• US 20050226621A1
• Filed: 08/09/2004
• Published: 10/13/2005
• Est. Priority Date: 03/30/2004
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi Communication Technologies Limited (Hitachi, Ltd.)
• Inventors: Sasaki, Shinya, Kikuchi, Nobuhiko, Sekine, Kenro
• Granted Patent: US 7,653,311 B2
• Time in Patent Office: Days
• US Class Current: 398/83
• CPC Class Codes: H04J 14/021 Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
• CPC Class Codes: H04J 14/0212 using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04J 14/0221 Power control, e.g. to keep the total optical power constant
• CPC Class Codes: H04J 14/02216 by gain equalization
• CPC Class Codes: H04J 14/0227 Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation

Abstract

It was difficult to detect a wavelength error. Further, a wavelength error of an optical add signal is accompanied by a calculation error of the number of wavelengths of a wavelength division multiplexing signal, which causes a set value of an optical signal level to become abnormal, resulting in the degradation of the optical signal.

According to the present invention, part of an inputted optical add signal 118 is reflected by a mirror 117, and is thereby inputted into an optical wavelength multiplexer 105 in the reverse direction so that the optical add signal is returned to paths 115-1 through 115-16 corresponding to wavelengths λ1 through λ16. If the returned optical add signal is an optical add signal having a correct wavelength (in FIG. 1, λ16), the optical signal enters its corresponding backward direction optical detector 113-16. Accordingly, it is possible to check whether or not a wavelength of the optical add signal is correct.

Claims

1. An optical wavelength add-drop multiplexer placed in position in an optical fiber transmission line, said multiplexer comprising:

a function of inserting (adding) optical signals having desired wavelengths into an optical signal transmitted through the optical fiber transmission line, or a function of branching (dropping) optical signals having desired wavelengths from the optical fiber transmission line to extract said optical signals having the desired wavelengths; and

optical wavelength judgment means for judging whether or not the inserted optical signals which are inserted into the optical wavelength add-drop multiplexer are the optical signal having the desired wavelengths.

2. An optical wavelength add-drop multiplexer according to claim 1, further comprising:

display means for displaying the results of the judgments made by the optical wavelength judgment means.

3. An optical wavelength add-drop multiplexer according to claim 1, wherein:

a wavelength meter for measuring wavelengths of the inserted optical signals is used as the optical wavelength judgment means.

4. An optical wavelength add-drop multiplexer according to claim 3, further comprising:

an optical wavelength demultiplexer for demultiplexing a wavelength division multiplexed optical signal having a plurality of different wavelengths, which has been inputted from the optical fiber transmission line, into optical signals having respective different wavelengths;

an optical switch for extracting from the optical wavelength add-drop multiplexer an optical signal having a desired wavelength from among the demultiplexed optical signals, or for inserting an optical signal having a desired wavelength into the optical wavelength add-drop multiplexer; and

an optical wavelength multiplexer for multiplexing each of the optical signals, which have been demultiplexed by the optical wavelength demultiplexer, with the optical signal inserted through the optical switch;

wherein said optical wavelength judgment means is provided at a side where the optical wavelength multiplexer supplies its output.

5. An optical wavelength add-drop multiplexer according to claim 4, wherein:

said optical wavelength judgment means is provided at one end of a transmission line through which an optical signal branched and output from an optical coupler is transmitted, said optical coupler being placed in the input side of an optical switch that is used to insert an optical signal having the desired wavelength into the optical signal add-drop multiplexer.

6. An optical wavelength add-drop multiplexer according to claim 2, wherein:

said display means displays at least one of;

a measured value of a wavelength of the inserted optical signal measured by the wavelength meter;

the result of a judgment as to whether or not the wavelength of the inserted optical signal is a desired wavelength;

information that can be used to judge whether or not the wavelength of the inserted optical signal is correct;

information about the number of optical signals, each of which has been judged to be an optical signal having the desired wavelength, among the inserted optical signals; and

an alarm based on the result of the judgment made by the optical wavelength judgment means;

or

a remote operator is notified of at least one of the above items.

7. An optical wavelength add-drop multiplexer according to claim 1, wherein:

if it is judged that a wavelength of the inserted optical signal differs from the desired wavelength, or if a wavelength of the inserted optical signal agrees with a wavelength of an optical through signal or wavelengths of the other inserted optical signals, which pass through an optical switch that is used to extract from the optical wavelength add-drop multiplexer an optical signal having a desired wavelength from among optical signals demultiplexed by the optical wavelength demultiplexer for demultiplexing, into wavelengths, a wavelength division multiplexed optical signal having a plurality of different wavelengths, which has been inputted from the optical fiber transmission line, or that is used to insert an optical signal having a desired wavelength into the optical wavelength add-drop multiplexer,

then said optical add signal is blocked, or after checking that a wavelength of the inserted optical signal is equivalent to the desired wavelength, the inserted optical signal is added to a wavelength division multiplexed optical signal having a plurality of different wavelengths, which has been inputted from the optical fiber transmission line, or the inserted optical signal having the desired wavelength is multiplexed with the optical through signal.

8. An optical wavelength add-drop multiplexer according to claim 1, wherein:

an optical wavelength demultiplexer for demultiplex a wavelength division multiplexed optical signal having a plurality of different wavelengths, which has been inputted from the optical fiber transmission line, into optical signals having respective different wavelengths, or an optical wavelength multiplexer for multiplexing with an inserted optical signal each of the optical signals demultiplexed by the optical wavelength demultiplexer, is also used for the measurement of a wavelength of the inserted optical signal, or the judgment as to whether or not the inserted optical signal has the desired wavelength.

9. An optical wavelength add-drop multiplexer according to claim 1, wherein:

a mirror is provided so that part of an optical signal, which is output from the optical wavelength add-drop multiplexer to an optical fiber transmission line, is reflected back to travel in the reverse direction into the optical wavelength add-drop multiplexer from the output side of an optical wavelength demultiplexer for demultiplexing a wavelength division multiplexed optical signal having a plurality of different wavelengths, which has been inputted from the optical fiber transmission line, into optical signals having respective different wavelengths;

the optical signal which has traveled in the reverse direction is separated into different paths on a wavelength basis by an optical wavelength multiplexer that multiplexes with an inserted optical signal each of the optical signals demultiplexed by the optical wavelength demultiplexer; and

the existence of an optical signal having each wavelength is detected by a backward direction optical detector for detecting an optical signal traveling in the reverse direction, said backward direction optical detector being placed in each path.

10. An optical wavelength add-drop multiplexer according to claim 1, wherein:

an optical wavelength multiplexer having a circular type wavelength multiplexing property is used as an optical wavelength multiplexer for multiplexing with an inserted optical signal each of the optical signals which have been demultiplexed by an optical wavelength demultiplexer that demultiplexes a wavelength division multiplexed optical signal having a plurality of different wavelengths, which has been inputted from the optical fiber transmission line, into optical signals having respective different wavelengths;

optical detectors are placed, respectively, at a plurality of unused output ports other than the output port that outputs a wavelength division multiplexed optical signal having a plurality of different wavelengths, which has been inputted from the optical fiber transmission line; and

said optical detector detects the existence of the inserted optical signal having the desired wavelength.

11. An optical wavelength add-drop multiplexer according to claim 1, wherein:

an optical filter for selectively passing an optical signal having the desired wavelength is placed in a transmission line through which an optical signal inserted by an optical switch is transmitted, said optical switch being used to extract from the optical wavelength add-drop multiplexer an optical signal having the desired wavelength from among the demultiplexed optical signals, said demultiplexed optical signals being demultiplexed by an optical wavelength demultiplexer for demultiplexing a wavelength division multiplexed optical signal having a plurality of different wavelengths, which has been inputted from the optical fiber transmission line, into optical signals having respective different wavelengths, or said optical switch being used to insert an optical signal having the desired wavelength into the optical wavelength add-drop multiplexer.

12. An optical wavelength add-drop multiplexer according to claim 1, wherein:

an optical detector for detecting the existence of an optical signal inserted by an optical switch, or for branching part of the inserted optical signal to detect the branched optical signal, is placed through an optical filter for selectively passing an optical signal having the desired wavelength, said optical switch being used to extract from the optical wavelength add-drop multiplexer an optical signal having the desired wavelength from among the demultiplexed optical signals, said demultiplexed optical signals being demultiplexed by an optical wavelength demultiplexer for demultiplexing a wavelength division multiplexed optical signal having a plurality of different wavelengths, which has been inputted from the optical fiber transmission line, into optical signals having respective different wavelengths, or said optical switch being used to insert an optical signal having the desired wavelength into the optical wavelength add-drop multiplexer.

14. An optical wavelength add-drop multiplexer according to claim 1, wherein:

said optical wavelength add-drop multiplexer has a broadcast type configuration in which an optical add signal and an optical through signal are coupled by an optical coupler before outputting the coupled signal to an optical fiber transmission line, and has inside the optical wavelength add-drop multiplexer a path for wavelength-demultiplexing an optical through signal into signals on a wavelength basis, and also has a configuration in which all optical add signals are temporarily combined by an optical coupler before demultiplexing the combined signal into different paths on a wavelength basis by an optical wavelength demultiplexer; and

between the path of the demultiplexed optical through signal and the path of the demultiplexed optical add signal, one of paths having the same wavelength is selected and inputted into an optical wavelength multiplexer, and then either transmitting an optical through signal to output the optical through signal, or selecting an optical add signal to output the optical add signal, is selected.

13. An optical wavelength add-drop multiplexer that is provided in position in an optical fiber transmission line, and that has a function of inserting (adding) an optical signal having a desired wavelength into an optical signal transmitted through the optical fiber transmission line, or a function of branching (dropping) an optical signal having a desired wavelength from the optical fiber transmission line to extract said optical signal having the desired wavelength, said multiplexer comprising:

means that has a broadcast type configuration in which an optical coupler combines an inserted optical signal, which is inserted into the optical wavelength add-drop multiplexer, with an optical through signal passing through the optical wavelength add-drop multiplexer, before outputting the combined optical signal to an optical fiber transmission line, and that demultiplexes the optical through signal on a wavelength basis, and then transmits the demultiplexed signals into the optical wavelength add-drop multiplexer; and

means for;

combining a plurality of inserted optical signals by use of an optical coupler;

inputting the combined optical signal from an optical wavelength multiplexer placed on the output side of the optical wavelength add-drop multiplexer;

demultiplexing the inputted optical signal into different paths on a wavelength basis by the optical wavelength multiplexer; and

then, for each wavelength path, selecting either totally reflecting an inserted optical signal traveling in the reverse direction to output the optical signal in the forward direction, or transmitting the optical through signal to output the optical through signal in the forward direction.

15. An optical network having a plurality of nodes, each comprising an optical wavelength add-drop multiplexer comprising:

a function of inserting (adding) optical signals having desired wavelengths into an optical signal transmitted through the optical fiber transmission line, or a function of branching (dropping) optical signals having desired wavelengths from the optical fiber transmission line to extract said optical signals having the desired wavelengths; and

optical wavelength judgment means for judging whether or not the inserted optical signals which are inserted into the optical wavelength add-drop multiplexer are the optical signal having the desired wavelengths;

wherein other nodes are notified of at least one of;

a measured value of a wavelength of an inserted optical signal obtained at one node;

the result of a judgment as to whether or not the wavelength of the added optical signal is a desired wavelength;

information that can be used to judge whether or not the wavelength of the added optical signal is correct;

information about the number of optical signals, each of which has been judged to be an optical signal having the desired wavelength, among the added optical signals; and

an alarm based on the result of the judgment made by the optical wavelength judgment means.