Patent ID: 11942755
Assignee: NIPPON TELEGRAPH AND TELEPHONE CORPORATION
Field: Telecommunications (Electrical engineering)
Classification: CPC H | IPC H

Claim 7:
8. A method of reducing a filter penalty used in an optical transmission system, the optical transmission system including a first transponder unit on a transmitting side and a second transponder unit on a receiving side, configured to perform transmission and reception of an optical signal through an optical transmission line in which an optical filter having a multiplexing/demultiplexing function of the optical signal is interposed, the first transponder unit on the transmitting side and the second transponder unit on the receiving side each including a respective transmission unit and a respective reception unit, the transmission unit of the first transponder unit transmitting the optical signal that has been generated by modulating laser light emitted from a laser light source with an electric signal from a communication apparatus to the optical transmission line, the reception unit of the second transponder unit receiving the optical signal from the transmission unit of the first transponder unit through the optical transmission line and converting the received optical signal into an electric signal, the method comprising:
measuring, by the reception unit of the second transponder unit, a bit error rate (BER), based on a received signal of the second transponder unit on the receiving side, and feeding the measured BER back to the first transponder unit on the transmitting side;
performing, by the transmission unit of the first transponder unit, frequency shift control of shifting a center frequency of the laser light emitted from the laser light source in accordance with the fed back BER so that the center frequency approaches a center frequency of the optical signal received in the second transponder unit on the receiving side; and
performing, by the transmission unit, the frequency shift control so that a value of the fed back BER is minimized, wherein minimizing the value of the fed back BER comprises repeatedly shifting the center frequency of the laser light and measuring and recording the corresponding feedback BER until a minimal fed back BER is reached.