Optical signal performances simulation¶
This section describes ENP tool capabilities for the simulation of the physical layer optical performances of the optical channels (OCh) in the network.
Optical signal performances simulated¶
Per OCh-path metrics¶
ENP is able to compute the following optical performances for each Optical Channel (OCh) path:
- Optical power at reception (dBm).
- Optical Signal-to-Noise Ratio (OSNR) (dB).
- Chromatic Dispersion (CD) (ps/nm).
- Polarization Mode Dispersion (PMD) (ps).
Additionally, the per-OCh-path evolution of the previously shown metrics can be observed in the 'View optical performance information' right-click option.
Per optical link aggregated metrics¶
ENP is able to compute aggregated metrics from the per-OCh metrics described above:
- Total optical power at fiber start (dBm).
- Total optical power at fiber end (dBm).
- Ratio max/min power among OCh paths at fiber start (dB). This is a measure of how uniform is the power, among the OCh paths traversing a fiber: that ratio (in dB) between the power of the OCh path of highest power, and the one of lower power. A value of 0 dB means perfect power equalization.
- Ratio max/min power among OCh paths at fiber end (dB).
Per-OCh performance tolerances¶
ENP permits defining different tolerance metrics that should be satisfied at the reception side of OCh paths and visually informs the user if such tolerances are not met. Performance tolerances refer to maximum and minimum power at reception, maximum CD, PMD, or OSNR.
Additionally, the different nodes in the network can generate other warnings if the optical performances are outside their own operational ranges. For instance, nodes implementing optical amplification can generate warnings if their total input power is above the saturation range. For information on the warnings and checks implemented by different node types, please see the per-node documentation information.
Optical impairments model¶
The optical impairments model adopted by ENP follows the state-of-the-art guidelines for optical performance estimation. The computation of the per-OCh performances depends on the characterization of:
- Per-node optical signal modifications. Each node in the network that is capable of optically propagating an input signal to its output port, at least for one input/output node pair, is required to implement the ISimpleNodeCapableOpticalSignalPropagation interface. The implementation requires specifying what is the effect in the optical signal when traversing the node. For instance, an implementation of an optical amplifier will modify the optical power, PMD, CD, and OSNR of the signal in each OCh depending on node parameters like its noise figure (that may be input power and gain dependent), etc.
- Per-fiber span optical signal modifications. The effects in the per-OCh optical signals when traversing a fiber are computed as a function of a set of per-fiber user-configurable values, like frequency-dependent attenuation and chromatic dispersion coefficients, PMD design values, or other physical parameters of the fiber, of importance for calculating the OSNR degradation caused by nonlinear effects.
Nonlinear impairments impact in OSNR¶
ENP implements state-of-the-art algorithms for estimating the impact of nonlinear optical signal impairments in the OSNR when traversing the optical fibers, of significant importance in heavily loaded links with high injection powers. These algorithms are based on different variants of the so-called Gaussian Noise Model method, suitable for a broad range of coherent modulations, and have been validated against reference scenarios in the scientific literature.