Latency measurement in optical networks

• US 8,180,216 B2
• Filed: 12/20/2007
• Issued: 05/15/2012
• Est. Priority Date: 12/20/2007
• Status: Active Grant

• Current Assignee: Verizon Patent and Licensing Incorporated (Verizon Communications Inc.)
• Original Assignee: Verizon Patent and Licensing Incorporated (Verizon Communications Inc.)
• Inventors: Xia, Tiejun J., Wellbrock, Glenn A., Pollock, Michael D.
• Primary Examiner(s): Bello, Agustin
• Application Number:
  US11/961,702
• Publication Number:
  US 20090162052A1
• Time in Patent Office: 1,608 Days
• Field of Search: 398 9- 38
• US Class Current: 398/25
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 43/0858 One way delays
• CPC Class Codes: H04L 43/50 Testing arrangements

Abstract

A device for measuring optical latency in a test path includes an optical source to generate an optical signal. An optical modulator modulates the optical signal based on a modulation signal. An output port outputs the modulated optical signal to the test path. An input port receives a return optical signal following propagation through the test path. Latency calculating logic calculates the optical latency for the test path based on the modulation signal and the return optical signal.

Claims

1. A device, comprising:

a tunable laser to generate an optical signal at a particular wavelength;

an optical modulator to modulate the optical signal based on a modulation signal;

an output port to output the modulated optical signal to a test optical path;

an input port to receive a return optical signal following propagation through the test optical path;

latency calculating logic to calculate an optical latency for the test optical path based on the modulation signal and the return optical signal; and

a controller to receive user selections for the tunable laser and the modulation signal and configured to initiate calculation of the optical latency by the latency calculating logic,

wherein the user selections for the modulation signal further comprise at least one of a pulse width associated with the modulation signal or a pulse period associated with the modulation signal,

wherein the pulse width or the pulse period is selected such that a maximum measurable latency is less than the pulse period.

2. The device of claim 1, where the optical modulator comprises one of an acousto-optic modulator or an electro-optic modulator.

3. The device of claim 2, where the electro-optic modulator comprises a Mach-Zehnder modulator.

4. The device of claim 1 further comprising:

a driver for generating the modulation signal,

where the modulation signal comprises one of a square wave signal, or a pulsed pattern signal.

5. The device of claim 4, where the modulation signal is a radio frequency (RF) signal and where the driver is a RF driver.

6. The device of claim 1, further comprising:

a photodetector for receiving the return optical signal, converting the return optical signal to a return electrical signal, and transmitting the return electric signal to the latency calculating logic.

7. The device of claim 6, further comprising:

a second photodetector for receiving the modulated optical signal prior to output of the modulated optical signal to the test optical path, converting the return optical signal to an output electrical signal, and transmitting the output electrical signal to the latency calculating logic,

where the latency calculating logic calculates the optical latency for the test optical path based on the output electrical signal and the return electrical signal.

8. The device of claim 6,

where the latency calculating logic receives the modulation signal, and

where the latency calculating logic calculates the optical latency for the test optical path based on the modulation signal and the return electrical signal.

9. The device of claim 1,

wherein the optical modulator comprises a short rise time optical modulator.

10. The device of claim 9, wherein a rise time of the optical modulator is approximately 0.5 microseconds.

11. The device of claim 1, further comprising:

an input device for receiving user selections for at least one of the tunable laser or the modulation signal; and

an output device for outputting the calculated optical latency.

12. The device of claim 11, where the output device comprises a display.

13. A system, comprising:

a latency measuring tool;

a optical path to be tested; and

a loop back jumper for connecting an outgoing channel in the optical path to a return channel in the optical path,

wherein the latency measuring tool, further comprises;

a tunable laser to generate an optical beam having a selected wavelength;

an optical modulator to modulate the optical beam based on a modulation signal;

an output port to output the modulated optical beam to the outgoing channel;

a controller to receive user selections for the tunable laser and the modulation signal,

an input port to receive a return optical beam from the return channel; and

latency calculating logic for calculating an optical latency for the optical path based on the modulation signal and the return optical beam,

wherein the controller is configured to initiate calculation of the optical latency by the latency calculating logic, and

wherein the user selections for the modulation signal comprise at least one of a pulse width associated with the modulation signal or a pulse period associated with the modulation signal,

wherein the pulse width or the pulse period is selected such that a maximum measurable latency is less than the pulse period.

14. The system of claim 13,

where the optical path to be tested includes a number of optical segments,

where the optical path includes a first add/drop multiplexer for receiving the modulated optical beam in the outgoing channel from the latency measuring tool, and

where the optical path includes a second add/drop multiplexer for outputting the return optical beam from the return channel to the latency measuring tool.

15. The system of claim 13, where the optical modulator comprises a short rise time optical modulator.

16. The system of claim 15, where the optical modulator comprises one of an acousto-optic modulator or an electro-optic modulator.

17. The system of claim 13, where the optical path includes at least one channel in a wavelength division multiplexing (WDM) fiber optic system.

18. A method, comprising:

generating an optical beam having a selected wavelength;

receiving user selections of a pulse period and a pulse width,

wherein the pulse width or the pulse periods are selected such that a maximum measurable latency is less than the pulse period;

generating a radio frequency (RF) signal based on the received pulse period and pulse width;

modulating the optical beam based on the RF signal, by a short rise time optical modulator, to generate a modulated optical beam;

outputting the modulated optical beam on an optical path;

receiving a return optical beam from the optical path;

calculating an optical latency of the optical path based on a reference RF signal associated with the RF signal and the return optical beam; and

outputting the calculated optical latency.