Optical transmission system

• US 20070230967A1
• Filed: 10/04/2006
• Published: 10/04/2007
• Est. Priority Date: 03/31/2006
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Akiyama, Tomoyuki
• Granted Patent: US 7,443,574 B2
• Time in Patent Office: Days
• US Class Current: 398/160
• CPC Class Codes: H04B 10/299 Signal waveform processing, e.g. reshaping or retiming

Abstract

An optical transmission system includes an optical nonlinear element having nonlinear input/output characteristics, a power detector detecting a power of a specific frequency component related to an optical signal reproduced by the optical nonlinear element, and a variable amplifier amplifying or attenuating the optical signal inputted to the optical nonlinear element. Evaluation of an output waveform is performed based on the power of the specific frequency component detected by the power detector, and a gain of the variable amplifier is properly controlled, so that an input power of the optical signal inputted to the optical nonlinear element can be easily set such that a good output waveform can be obtained without directly measuring the inputted or outputted optical signal.

Claims

1. An optical transmission system, comprising:

an optical nonlinear element having nonlinear input/output characteristics and reproducing an optical signal;

a power detector photoelectrically converting an optical signal reproduced by said optical nonlinear element to detect a power of a specific frequency component from an obtained electrical signal; and

a variable amplifier amplifying or attenuating the optical signal inputted to said optical nonlinear element in response to a detection result by said power detector.

2. The optical transmission system according to claim 1, wherein said power detector comprises:

a photo detector converting the optical signal reproduced by said optical nonlinear element to the electrical signal;

a filter retrieving the specific frequency component from the electrical signal obtained by said photo detector; and

a power measuring device measuring the power of the specific frequency component retrieved by said filter.

3. The optical transmission system according to claim 1, wherein said power detector detects a power of a bit rate frequency component of the inputted optical signal.

4. The optical transmission system according to claim 3, wherein said power detector comprises:

a photo detector converting the optical signal reproduced by said optical nonlinear element to the electrical signal;

a band pass filter retrieving the bit rate frequency component from the electrical signal obtained by said photo detector; and

a power measuring device measuring the power of the bit rate frequency component retrieved by said band pass filter.

5. The optical transmission system according to claim 3, further comprising:

a control circuit controlling said variable amplifier such that the power of the bit rate frequency component becomes minimum, based on a detection result by said power measuring device.

6. The optical transmission system according to claim 5, wherein said control circuit makes a gain of said variable amplifier increase/decrease periodically in a minute range to perform gain control of said variable amplifier in response to variation of the power of the bit rate frequency component associated with minute variety of the gain.

7. The optical transmission system according to claim 6, wherein said control circuit makes the gain of said variable amplifier increase when the power of the bit rate frequency component varies in phase and makes the gain of said variable amplifier decrease when the power of the bit rate frequency component varies in reverse phase, in association with the minute variation of the gain.

8. The optical transmission system according to claim 3, wherein the inputted optical signal is an optical signal modulated in an NRZ (Non Return to Zero) format.

9. The optical transmission system according to claim 1, wherein said power detector detects a power of a bit rate frequency component and a power of a direct-current component of the inputted optical signal.

10. The optical transmission system according to claim 9, wherein said power detector comprises:

a photo detector converting the optical signal reproduced by said optical nonlinear element to the electrical signal;

a band pass filter retrieving the bit rate frequency component from the electrical signal obtained by said photo detector;

a low pass filter retrieving the direct-current component from the electrical signal obtained by said photo detector; and

a power detector respectively measuring the power of the bit rate frequency component and the power of the direct-current component retrieved by said band pass filter and said low pass filter.

11. The optical transmission system according to claim 9, further comprising:

a control circuit controlling said variable amplifier such that a rate of the power of the bit rate frequency component and the power of the direct-current component maintains a constant value, based on a detection result by said power detector.

12. The optical transmission system according to claim 9, wherein the inputted optical signal is an optical signal modulated in an RZ (Return to Zero) format.