OSNR has long been recognized as a key performance indicator in wavelength-division multiplexing (WDM) networks, because it provides a multichannel assessment of signal quality in a very short period of time. In addition, OSNR can predict bit error rate (BER) within just a few minutes, while typical BER tests must run for hours or days.
The IEC 61280-2-9 standard defines OSNR measurement as the power ratio between the signal power and the noise at half the distance between the peaks. However, in ROADM or 40 Gbit/s systems, this method may lead to incorrect results, because the noise level between the peaks is no longer directly correlated with the noise level at the channel wavelength. EXFO’s in-band OSNR is the answer to this challenge.
For Pol-Mux signals at 40G and 100G, neither the IEC nor the in-band method work. This calls for a new measurement method: Pol-Mux OSNR.
EXFO’s Pol-Mux OSA is the first third-party instrument for Pol-Mux OSNR measurements that is not limited to any specific system vendor. The new commissioning assistant, which is the key feature of the new Pol-Mux OSA, is perfect for Pol-Mux OSNR measurements during turn-up. Based on the channel shutdown method, it provides highly accurate amplified spontaneous emission (ASE) OSNR measurements.
The commissioning assistant can be utilized after the user has first taken a measurement at the receiver with all of the channels turned on, and then acquired a series of traces, each taken with one channel turned off. The Pol-Mux OSA then performs the Pol-Mux OSNR calculations via a user-friendly wizard.
The commissioning assistant therefore greatly accelerates OSNR measurements based on the channel shutdown method, and drastically reduces potential human errors. In addition, two standards-compliant calculation approaches are available in the commissioning assistant: one compliant with the IEC-61282-12 standard (under revision), and the other compliant with the China Communications Standards Association (CCSA) method YD/T 2147-2010.
WDM networks are becoming increasingly complex, with new technologies being deployed (tighter channel spacing, polarization-multiplexed signals, etc.) that increase the number of potential causes for failure. While past impairment types were relatively
few and well-known (excessive loss, high dispersion, excessive ASE noise, etc.), these newly deployed technologies give rise to previously uncommon impairments, such as crosstalk and nonlinear effects.
This is now possible with EXFO’s WDM Investigator, which provides detailed information about the signal and noise for each channel. The WDM Investigator provides information on link characteristics, such as the presence of polarization-multiplexed signals or the
presence of carved noise due to filters or ROADMs. It also checks the presence of several types of impairments (crosstalk, non-linear effects, carrier leakage and PMD pulse spreading), and gives an assessment of their severity (OK, warning, risk).
With 33 pm (or ~4.5 GHz) resolution bandwidth defined as the FWHM of the OSA filter shape, the IQS-5240BP can analyze all densely spaced signals, including important 25 GHz ITU-grid WDM signals, and any high-speed modulated lasers/emitters.
Combined with a very sharp rejection ratio (–35 dBc at 0.1 nm), the optical signal-to-noise ratio (OSNR) and modulated band profile can be measured with high accuracy. To ensure accurate noise and broad signal power measurements, the noise-equivalent bandwidth (NEB) of the OSA is calibrated at many points from 1250 nm to 1650 nm.