Method and device for receiving optical signals

• US 9,014,555 B2
• Filed: 12/24/2012
• Issued: 04/21/2015
• Est. Priority Date: 10/26/2012
• Status: Active Grant

• Current Assignee: Industrial Technology Research Institute
• Original Assignee: Industrial Technology Research Institute
• Inventors: Hsu, Dar-Zu, Chen, Jye-Hong, Wei, Chia-Chien, Chen, Hsing-Yu
• Primary Examiner(s): TRAN, DZUNG D
• Application Number:
  US13/726,229
• Publication Number:
  US 20140119726A1
• Time in Patent Office: 848 Days
• Field of Search: 398202-204, 398207-211
• US Class Current: 398/38
• CPC Class Codes: H04B 10/616 Details of the electronic signal processing in coherent optical receivers
• CPC Class Codes: H04B 10/6971 using equalisation

Abstract

A method for receiving optical signals and a device using the same method are provided herein. The method includes the elements of receiving an input signal which includes a signal component and an interference component, wherein the interference component is subcarrier to subcarrier intermixing interference (SSII). The input signal is first converted into a frequency domain signal. The interference component of the input signal is estimated based on a mathematical model according to at least a dynamic chirp component and a static chirp component. The interference component is then cancelled from the input signal to obtain an output signal.

Claims

1. A method of receiving optical signals for an optical communication device, the method comprising:

receiving from an optical receiver an input signal comprising a signal component and an interference component, wherein the interference component is subcarrier to subcarrier intermixing interference (SSII);

converting the input signal into a frequency domain input signal;

estimating the interference component according to at least a dynamic chirp component and a static chirp component; and

cancelling the interference component from the frequency domain input signal to obtain a second signal.

2. The method of claim 1, wherein the method further comprises:

performing an equalization for the second signal to produce an equalized second signal; and

performing a decision for the equalized second signal to produce an output signal.

3. The method of claim 2, wherein the element of estimating the interference component according to at least the dynamic chirp component and the static chirp component further comprising:

calculating the interference component according to the equalized second signal and the output signal.

4. The method of claim 3, wherein the element of estimating the interference component according to at least the dynamic chirp component and the static chirp component comprising:

reconstructing a first signal which is from a modulator;

calculating a theoretical SSII based on the first signal and the dynamic chirp component according to a mathematical model; and

performing an amplitude and a phase adjustment to the theoretical SSII to reconstruct the interference component.

5. The method of claim 4, wherein the element of calculating the theoretical SSII based on the first signal and the dynamic chirp component according to the mathematical model further comprises:

measuring an error power of the frequency domain input signal;

calculating a correlation between the error power and the theoretical SSII; and

outputting the theoretical SSII if the correlation is greater than a first threshold.

6. The method of claim 5 further comprising:

if the correlation is not greater than the first threshold,

determining if a change of the correlation from a previous correlation is smaller than a second threshold; and

if the change of the correlation from the previous correlation is smaller than the second threshold, outputting the theoretical SSII.

7. The method of claim 6 further comprising:

if the change of the correlation from the previous correlation is not smaller than the second threshold, adjusting the dynamic chirp component to become a selected dynamic chirp and repeating calculating the theoretical SSII based on the first signal and the dynamic chirp component according to the mathematical model.

8. The method of claim 1, wherein before the element of estimating the interference component according to at least the dynamic chirp component and the static chirp component;

the method further comprises;

initializing the dynamic chirp component from a randomly selected set of numbers between 0 and 1.

9. The method of claim 5, wherein the element of measuring the error power of the frequency domain input signal comprises:

obtaining the error power of the frequency domain input signal based on a difference between the output signal and the equalized second signal.

10. The method of claim 1, wherein the element of receiving from the optical receiver the input signal comprising the signal component and the interference component comprising:

receiving from the optical receiver an optical signal which travels through a fiber; and

performing a direct detection on the optical signal to obtain the input signal.

11. An optical communication device comprising:

a receiver receiving an input signal comprising a signal component and an interference component, wherein the interference component is subcarrier to subcarrier intermixing interference (SSII); and

a processing unit coupled to the receiver and is configured to perform the functions of converting the input signal into a frequency domain input signal, estimating the interference component according to at least a dynamic chirp component and a static chirp component, and cancelling the interference component from the frequency domain input signal to obtain a second signal.

12. The device of claim 11 wherein the processing unit is further configured to perform the function of performing an equalization for the second signal to produce an equalized second signal and performing a decision for the equalized second signal to produce an output signal.

13. The device of claim 12, wherein the processing unit is further configured to perform the function of:

calculating the interference component according to the equalized second signal and the output signal.

14. The device of claim 13, wherein the processing unit is configured to perform the function of estimating the interference component according to at least the dynamic chirp component and the static chirp component, the function comprising:

reconstructing a first signal which is from a modulator, calculating a theoretical SSII based on the first signal and the dynamic chirp component according to a mathematical model, and performing an amplitude and a phase adjustment to the theoretical SSII to reconstruct the interference component.

15. The device of claim 14, wherein the processing unit is configured to perform the function of calculating the theoretical SSII based on the first signal and the dynamic chirp component according to the mathematical model, the function further comprises:

measuring an error power of the frequency domain input signal, calculating a correlation between the error power and the theoretical SSII, and outputting the theoretical SSII if the correlation is greater than a first threshold.

16. The device of claim 15, wherein the processing unit is further configured to perform the function of:

if the correlation is not greater than the first threshold, determining if a change of the correlation from a previous correlation is smaller than a second threshold; and

if the change of the correlation from the previous correlation is smaller than the second threshold, outputting the theoretical SSII.

17. The device of claim 16, wherein the processing unit is further configured to perform the function of:

if the change of the correlation from the previous correlation is not smaller than the second threshold, adjusting the dynamic chirp component to become a selected dynamic chirp and repeating calculating the theoretical SSII based on the first signal and the dynamic chirp component according to the mathematical model.

18. The device of claim 11, wherein before the processing unit is configured to perform the function of estimating the interference component according to at least the dynamic chirp component and the static chirp component;

the processing unit is further configured for;

initializing the dynamic chirp component from a randomly selected set of numbers between 0 and 1.

19. The device of claim 15, wherein the processing unit is configured to perform the function of measuring the error power of the frequency domain input signal comprises:

obtaining the error power of the frequency domain input signal based on a difference the output signal and the equalized second signal.

20. The device of claim 11, wherein device further comprises an photo detector receiving an optical signal which travels through a fiber, and performing a direct detection on the optical signal to obtain the input signal.

21. An optical communication device comprising:

a receiver receiving an input signal comprising a signal component and an interference component, wherein the interference component is subcarrier to subcarrier intermixing interference (SSII);

a fourier transform unit coupled to the receiver and converts the input signal into a frequency domain input signal;

a SSII calculation unit coupled to the fourier transform unit and estimates the interference component according to at least a dynamic chirp component and a static chirp component; and

a canceling unit coupled to the SSII calculation unit and the fourier transform unit and cancels the interference component from the frequency domain input signal to obtain a second signal.

22. The device of claim 21 further comprising:

an equalizer unit coupled to the canceling unit and the SSII calculation unit and performs an equalization for the second signal to produce an equalized second signal; and

a decision unit coupled to the equalizer unit and the SSII calculation unit and performs a decision for the equalized second signal to produce an output signal.

23. The device of claim 22, wherein the SSII calculation unit further performs the function of:

calculating the interference component according to the equalized second signal and the output signal.

24. The device of claim 23, wherein the SSII calculation unit comprises

a TX signal reconstruction module which reconstructs a first signal which is from a modulator;

a theoretical SSII calculation module which calculates a theoretical SSII based on the first signal and the dynamic chirp component according to a mathematical model; and

a RX reconstruction module which performs an amplitude and a phase adjustment to the theoretical SSII to reconstruct the interference component.

25. The device of claim 24, wherein the theoretical SSII calculation module further comprises the function of measuring an error power of the frequency domain input signal, calculates a correlation between the error power and the theoretical SSII, and outputs the theoretical SSII if the correlation is greater than a first threshold.

26. The device of claim 25, wherein theoretical SSII calculation module further comprises the function of:

if the correlation is not greater than the first threshold, determining if a change of the correlation from a previous correlation is smaller than a second threshold; and

if the change of the correlation from the previous correlation is smaller than the second threshold, outputting the theoretical SSII.

27. The device of claim 26, wherein theoretical SSII calculation module further comprises the function of:

if the change of the correlation from the previous correlation is not smaller than the second threshold, adjusting the dynamic chirp component to become a selected dynamic chirp and repeating calculating the theoretical SSII based on the first signal and the dynamic chirp component according to the mathematical model.

28. The device of claim 25, wherein theoretical SSII calculation module further comprises the function of obtaining the error power of the frequency domain input signal based on a difference between the output signal and the equalized second signal.

29. The device of claim 21, wherein the SSII calculation unit further comprises the function of:

initializing the dynamic chirp component from a randomly selected set of numbers between 0 and 1.

30. The device of claim 21, wherein device further comprises an photo detector receiving an optical signal which travels through a fiber, and performing a direct detection on the optical signal to obtain the input signal.