To ensure transmission performance equivalent to 10G systems, Huawei's coherent systems use coherent receiver technology to leverage the chromatic dispersion (CD), polarization mode dispersion (PMD), OSNR tolerance, and system transmission capacity.
Coherent receiver technology uses a local oscillator (LO) laser that has the same frequency as the received signal and implements interference between the LO laser signal and the received signal to restore the amplitude, phase, and polarization state information from the received signal. In addition, the technology uses high-speed ***og-to-digital converter (ADC) and digital signal processing (DSP) techniques to compensate for CD and PMD on the line.
By using coherent receiver technology, a 40G/100G coherent system does not have to use a fixed dispersion compensation module (DCM) or a tunable DCM (TDCM), which is intended for fine-tuning the dispersion of a single wavelength in a traditional 40G system. A 40G/100G coherent system that uses this technology requires fewer optical amplifiers, does not require accurate measurement of fiber length and dispersion, reduces system configuration costs and labor, and improves fiber transmission network performance.
A coherent system has a higher CD and PMD tolerance than a traditional 10G/40G non-coherent system and extends the transmission reach to several thousand kilometers without dispersion compensation. This technology reduces the fiber transmission delay and enables large-capacity transmission with low delay. In a traditional non-coherent system, a TDCM module takes several minutes to implement dispersion compensation. In a coherent system, however, the high-speed digital signal processing (DSP) mechanism takes only milliseconds to implement dispersion compensation, which ensures fast wavelength rerouting in a dynamic optical network and therefore implements fully dynamic wavelength grooming.
A 40G/100G coherent system can transmit both coherent 40G/100G wavelengths and non-coherent 10G/40G wavelengths. This makes an upgrade from a traditional network with DCM modules to a coherent 40G/100G network possible.
