Functions of a DCM

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After an optical signal is transmitted over a specific distance, the optical signal pulse is widened because of the positive dispersion accumulated in the system. As a result, the system transmission performance is seriously affected. A DCM is a passive device using a dispersion compensation fiber (DCF). With a DCM, signal pulses are compressed because a DCM has inherent negative dispersion that can offset the positive dispersion of the transmission fiber.
According to implementation principles, DCMs are classified into two types: DCMs using a DCF fiber and DCMs using fiber Bragg grating (FBG).

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Functions of a DCM
After an optical signal is transmitted over a specific distance, the optical signal pulse is widened because of the positive dispersion accumulated in the system. As a result, the system transmission performance is seriously affected. A DCM is a passive device using a dispersion compensation fiber (DCF). With a DCM, signal pulses are compressed because a DCM has inherent negative dispersion that can offset the positive dispersion of the transmission fiber. According to implementation principles, DCMs are classified into two types: DCMs using a DCF fiber and DCMs using fiber Bragg grating (FBG).

Working principle of a DCM
After an optical signal is transmitted over a specific distance, the optical signal pulse is widened because of the positive dispersion accumulated in the system. As a result, the system transmission performance is seriously affected. A DCM is a passive device using a dispersion compensation fiber (DCF). With a DCM, signal pulses are compressed because a DCM has inherent negative dispersion that can offset the positive dispersion of the transmission fiber. According to implementation principles, DCMs are classified into two types: DCMs using a DCF fiber and DCMs using fiber Bragg grating (FBG).

Methods for remotely verifying the installation of DCMs
1. It is time- and labor-consuming to verify the installation of DCMs onsite. You can verify whether DCMs are correctly installed by remotely checking the optical power at each point of the OAU board. The OAU board provides five optical ports for reporting the optical power. Port 3 (RDC optical port) detects the intermediate input optical power. Port 5 (TDC optical port) detects the intermediate output optical power. 2. Query the optical power of the OAU from east to west to calculate the optical power difference between optical port 5 and optical port 3, which is 1.6 dB. Query the optical power of the OAU from west to east to calculate the optical power difference between optical port 5 and optical port 3, which is 5.3 dB. These indicate that the DCM (C1) is installed from east to west and DCM (C3) is installed from west to east. Both DCMs are correctly installed and no onsite rectification is required. 3. Training must be provided to hardware installation personnel before the installation. Installation personnel must install DCM modules according to the cabinet fiber connection diagram of the engineering design, and pay attention to the pigtails from subracks in the DCM frame at the bottom of the cabinet. These pigtails have been labeled with the type of DCM modules they are to be connected to.

Position of the DCM module on an NE
If only one OBU board is configured on the NE, the DCM/DCU must be placed between a VOA and the OBU on the line. If only one OAU board is configured on the NE, the DCM/DCU must be placed between the TDC and RDC ports of the OAU board on the line. If OAU+OBU or OPU+OBU are configured on the NE, the DCM/DCU must be placed between the two OA boards.

DCM/DCU connection on a line
If only OBU is configured on the line, connect the DCM/DCU between a variable optical attenuator and the OBU. If only OAU is configured on the line, connect the DCM/DCU between the TDC and RDC ports on the OAU. If both OAU and OBU are configured on the line, connect the DCM/DCU between the two OA boards.

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