OPTICAL MONITORING IN AN OPTICAL COMMUNICATIONS NETWORK

• US 20160149638A1
• Filed: 06/18/2013
• Published: 05/26/2016
• Est. Priority Date: 06/18/2013
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Bruno, Gianmarco, Deho, Alberto
• Granted Patent: US 9,641,246 B2
• Time in Patent Office: Days
• CPC Class Codes: H04B 10/07 Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
• CPC Class Codes: H04B 10/079 using measurements of the data signal
• CPC Class Codes: H04B 10/85 Protection from unauthorised access, e.g. eavesdrop protection

Abstract

A communications network element comprises a network element input, a network element output and a monitoring port. An optical splitting device taps a portion of an input optical signal or an output optical signal to form a first signal. An optical signal transforming apparatus applies an optical transfer function to the first signal to form the optical monitoring signal applied to the monitoring port. The optical transfer function preserves the spectral property of the first signal and applies a time-domain obfuscation to the tapped signal. The optical signal transforming apparatus comprises an optical through signal path, an optical splitting device positioned in the optical through signal path and an optical combining device positioned in the optical through signal path. An optical feedback path is connected to the optical splitting device and the optical combining device. The optical splitting device is arranged to tap off a portion of a signal passing along the through signal path and apply it to the feedback path, and the optical combining device is arranged to recombine at least part of the tapped portion of the signal with the signal passing along the through signal path.

Claims

1. A communications network element comprising:

a network element input arranged to receive an input optical signal having a first spectral property;

a network element output arranged to output an output optical signal having a second spectral property;

a monitoring port arranged to output an optical monitoring signal;

a first optical splitting device arranged to tap a portion of one of the input optical signal and the output optical signal to form a first signal having one of the first spectral property and the second spectral property;

optical signal transforming apparatus having an input and an output, the input arranged to receive the first signal and to apply an optical transfer function to the first signal to form the optical monitoring signal, the optical transfer function being arranged to preserve the spectral property of the first signal and to apply a time-domain obfuscation to the tapped signal, the optical signal transforming apparatus being further arranged to provide the optical monitoring signal to the output and to the monitoring port, the optical signal transforming apparatus comprising;

an optical through signal path between the input and the output;

a second optical splitting device positioned in the optical through signal path;

an optical combining device positioned in the optical through signal path;

an optical feedback path connected to the second optical splitting device and the optical combining device, wherein the second optical splitting device is arranged to tap off a portion of a signal passing along the through signal path and apply it to the feedback path, and the optical combining device is arranged to recombine at least part of the tapped portion of the signal with the signal passing along the through signal path.

2. A communications network element according to claim 1 wherein the optical transfer function of the optical signal transforming apparatus is variable.

3. A communications network element according to claim 1 wherein the first spectral property and the second spectral property comprise one of optical power, power spectral density, wavelength, frequency, and optical signal-to-noise ratio.

4. A communications network element according to claim 1, further comprising an optical signal processing apparatus arranged to receive the input optical signal and to form the output optical signal, wherein the first optical splitting device is positioned on at least one of:

the network element input side of the optical signal processing apparatus;

the network element output side of the optical signal processing apparatus.

5. A communications network element according to claim 1, wherein the optical signal transforming apparatus further comprises a delay element.

6. A communications network element according to claim 1, wherein the optical combining device is located in the optical through signal path at a position which is nearer to the input than the second optical splitting device.

7. A communications network element according to claim 1, wherein the optical signal transforming apparatus comprises a four-port coupler comprising:

a first input port and a first output port coupled to the optical through signal path;

a second input port and a second output port coupled to the optical feedback path.

8. A communications network element according to claim 7 wherein the four-port coupler has a variable coupling ratio.

9. A communications network element according to claim 7 wherein the four-port coupler has a coupling ratio of 50:

50.

10. A communications network element according to claim 1, wherein the optical signal transforming apparatus comprises:

a first mirror positioned in the optical through signal path, the first mirror being transparent on a first side so as to pass an optical signal along the through signal path;

a second mirror at a spaced apart position from the first mirror along the optical through signal path, the second mirror being partially reflective and arranged to pass a first portion of light passing along the through signal path and to reflect a second portion of light passing along the through signal path to the optical feedback path; and

at least a third mirror at a position offset from the first mirror and the second mirror to form the optical feedback path, wherein the first mirror is reflective on a second side so as to direct light from the optical feedback path along the optical through signal path.

11. A communications network element according to claim 10 wherein the optical transfer function of the optical signal transforming apparatus is variable by at least one of:

a variable length of the optical feedback path;

a variable reflectivity of the second mirror.

15. An optical communications network comprising a communications network element according to claim 1.

12. A method of monitoring an optical signal in a communications network element, the method comprising:

receiving an optical signal having a spectral property;

splitting off a part of the optical signal to form a tapped signal having a spectral property;

applying an optical transfer function to the tapped signal to form an optical monitoring signal, the optical transfer function being arranged to preserve the signal property of the tapped signal and to apply a time-domain obfuscation to the tapped signal; and

providing the optical monitoring signal to a monitoring port of the communications network element,

wherein the step of applying the optical transfer function comprises;

providing an optical through signal path;

splitting off a portion of a signal passing along the optical through signal path and applying the signal portion to an optical feedback path;

recombining at least part of the signal portion from the optical feedback path with the through signal path.

13. A method according to claim 12 wherein the optical transfer function is variable.

14. A method according to claim 12 which is performed on at least one of:

a network element input side of an optical signal processing apparatus at the communications network element;

a network element output side of an optical signal processing apparatus at the communications network element.