LIGHT POWER ADJUSTING METHOD, OPTICAL TRANSMITTER, AND OPTICAL RECEIVER

Abstract

The present invention provides provide a light power adjusting method, an optical transmitter, and an optical receiver suitable for ensuring high data transmission quality by preventing the rapid increase in SBS which occurs when the light power exceeds a predetermined value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an overview of occurrence of SBS.

FIG. 2 illustrates an example configuration in which reflected light is measured by an optical transmitter.

FIG. 3 illustrates a relationship between the power of incident light incident on an optical transmission line and the power of reflected light returned from the optical transmission line.

FIG. 4 illustrates a light power threshold calculation method according to an embodiment of the present invention.

FIG. 5 illustrates an optical transmitter according to an embodiment of the present invention.

FIG. 6 illustrates an operation flow of a light power threshold calculation operation (1).

FIG. 7 illustrates an operation flow of a light power threshold calculation operation (2).

FIGS. 8A to 8D illustrate an overview of influence of a low-frequency amplitude modulation applied to light.

FIG. 9 is a graph representing a pattern of changes of the light power threshold caused by application of the low-frequency amplitude modulation.

FIG. 10 illustrates an operation flow of a light power adjustment operation (1) using application of the low-frequency amplitude modulation.

FIG. 11 illustrates an operation flow of a light power adjustment operation (2) using application of the low-frequency amplitude modulation.

FIG. 12 is a graph illustrating a relationship of the reflected light power with the incident light power with respect to types of optical fibers forming the optical transmission line.

FIG. 13 illustrates an operation flow of an operation of identifying the type of the optical fiber forming the optical transmission line.

FIG. 14 illustrates an example configuration of an optical receiver according to an embodiment of the present invention.

FIGS. 15A and 15B are graphs illustrating the concept of a dispersion slope.

Claims

1. A method of adjusting light power of light incident on an optical transmission line, comprising: measuring light power of reflected light returned from the optical transmission line with respect to light incident on the optical transmission line at first light power;measuring light power of reflected light returned from the optical transmission line with respect to light incident on the optical transmission line at second light power, the second light power being larger than the first light power at a predetermined increment;calculating a first difference between the measured values of light power of the reflected light corresponding to the light incident on the optical transmission line at the first light power and at the second light power;determining a light power threshold to be the first light power with which an amount of change of the first difference reaches a predetermined value; andsetting light power of light incident on the optical transmission line at a value equal to or smaller than the light power threshold.

2. The method of claim 1, further comprising: changing the predetermined increment on the basis of a measured value of light power of reflected light returned from the optical transmission line.

3. The method of claim 1, further comprising: measuring light power of reflected light returned from the optical transmission line with respect to light incident on the optical transmission line at third light power, the third light power being larger than the second light power at a predetermined increment;calculating a second difference between the measured values of light power of the reflected light corresponding to the light incident on the optical transmission line at the first light power and at the third light power;determining a light power threshold to be the first light power with which an amount of change of the calculated first difference and an amount of change of the calculated second difference reach the predetermined value.

4. The method of claim 1, further comprising: applying a frequency modulation to light incident on the optical transmission line; andadjusting the light power threshold by changing a frequency of the frequency modulation to be applied.

5. The method of claim 4, further comprising: transmitting light from an optical transmitter side to an optical receiver side through the optical transmission line;detecting light power of light received at the optical receiver side;transmitting notification information from the optical receiver side to the optical transmitter side when the light power detected at the optical receiver side is lower than a specified value;increasing the light power threshold by applying the frequency modulation to light incident on the optical transmission line at the optical transmitter side; andincreasing light power of light incident on the optical transmission line up to a value equal to or less than the light power threshold increased;

6. The method of claim 4, further comprising: transmitting light from an optical transmitter side to an optical receiver side through the optical transmission line;detecting light power of light received at the optical receiver side;transmitting light power information from the optical receiver side to the optical transmitter side, the light power information indicating a insufficient amount of light power with respect to a specified value; andsetting a light power of light incident on the optical transmission line, at a value equal to or less than the light power threshold and at the value obtained by adding the insufficient amount of light power to light power of light currently incident on the optical transmission line.

7. The method of claim 1, further comprising: storing tolerance range information including a tolerance range of a light power threshold associated with each of optical fiber types;comparing the light power threshold with each of tolerance ranges included in the tolerance range information; andidentifying the optical fiber type associated with the tolerance range including the light power threshold as a actual optical fiber type of the optical transmission line.

8. The method of claim 7, further comprising: transmitting the actual optical fiber type from the optical transmitter side to the optical receiver side; andperforming dispersion compensation to each of a wavelength of signal light received from the optical transmission line at the optical receiver side on the basis of the actual optical fiber type.

9. An optical transmitter for transmitting light, comprising: means for setting light power of light incident on an optical transmission line;means for generating light incident on the optical transmission line at first light power;means for generating light incident on the optical transmission line at second light power, the second light power being larger than the first light power at a predetermined increment;means for measuring light power of reflected light returned from the optical transmission line with respect to light incident on the optical transmission line;means for calculating a first difference between the measured values of light power of the reflected light corresponding to the light incident on the optical transmission line at the first light power and at the second light power;means for determining a light power threshold to be the first light power with which an amount of change of the first difference reaches a predetermined value; andmeans for setting light power of light incident on the optical transmission line at a value equal to or smaller than the light power threshold.

10. The optical transmitter of claim 9, further comprising: means for changing the predetermined increment on the basis of a measured value of light power of reflected light returned from the optical transmission line.

11. The apparatus of claim 9, further comprising: means for generating light incident on the optical transmission line at third light power, the third light power being larger than the second light power at a predetermined increment;means for calculating a second difference between the measured values of light power of the reflected light corresponding to the light incident on the optical transmission line at the first light power and at the third light power;means for determining the light power threshold to be the first value with which an amount of change of the first difference and an amount of change of the second difference reach the predetermined difference value.

12. The optical transmitter of claim 9, further comprising: means for applying a frequency modulation to light incident on the optical transmission line; andmeans for adjusting the light power threshold by changing a frequency of the frequency modulation to be applied.

13. The optical transmitter of claim 12, further comprising: means for receiving notification information transmitted from the optical receiver side, the notification information indicating that light power detected at the optical receiver side is lower than a specified value;means for increasing the light power threshold by applying the frequency modulation to light incident on the optical transmission line; andmeans for increasing light power of light incident on the optical transmission line up to a value equal to or less than the light power threshold increased;

14. The optical transmitter of claim 12, further comprising: means for receiving light power information from the optical receiver side, the light power information indicating a insufficient amount of light power of light received at the optical receiver side with respect to a specified value;means for setting a light power of light incident on the optical transmission line, at a value equal to or less than the light power threshold and at the value obtained by adding the insufficient amount of light power to light power of light currently incident on the optical transmission line.

15. The optical transmitter of claim 9, further comprising: means for storing tolerance range information including a tolerance range of a light power threshold associated with each of optical fiber types;means for comparing the light power threshold with each of tolerance ranges included in the tolerance range information;means for identifying the optical fiber type associated with the tolerance range including the light power threshold as a actual optical fiber type of the optical transmission line; andmeans for sending the actual optical fiber type to the optical receiver side through the optical transmission line.

16. An optical receiver for receiving light, comprising: means for storing dispersion information associated with each of optical fiber types;means for receiving the actual optical fiber type sent from the optical transmitter side through the optical transmission line; andmeans for performing dispersion compensation to each of a wavelength of signal light received from the optical transmission line on the basis of the actual optical fiber type and the dispersion information.

17. The optical receiver of claim 16, wherein the dispersion information includes chromatic dispersion values of respective wavelengths corresponding to the associated optical fiber type.

18. The optical receiver of claim 16, wherein the dispersion information includes a chromatic dispersion value of a predetermined wavelength and dispersion slope value corresponding to the associated optical fiber type.