With the new advanced modulation schemes that enable transmission of high-speed optical signals over fiber, research centers, network equipment manufacturers (NEMs)—and eventually carriers—need new test instruments to properly characterize these signals.
Like EXFO’s recognized PSO-100 Series Optical Sampling Oscilloscopes, the PSO-200 Optical Modulation Analyzer uses optical sampling, allowing complete characterization of random or repetitive digital signals up to 100 Gbit/s.
One of the crucial elements to take into account when characterizing or optimizing transmitters and modulators is the recovery of perfect signals and waveforms. A distortion-free signal recovery is precisely what the optical sampling technique used in the PSO-200 brings when compared to electrical sampling. With the PSO-200, there are no bandwidth limitations—no impedance mismatch.
With high bandwidth and low distortions the PSO-200 is able to measure constellation diagrams with very high fidelity without the need for equalization or DSP enhancement.
The PSO-200’s flexible design makes it a future-proof tool to characterize—without distortion—any optical signal. Its effective bandwidth is broad enough to support constellation and eye-diagram analysis of signals at rates beyond 1 Tbit/s.
Thanks to detailed and accurate amplitude and phase patterns, the PSO-200 then performs in-depth pulse shape analysis for transmitter testing both in R.-D. and manufacturing environments.
Advanced modulation formats in which the information is encoded—not only in the intensity but also in the phase of the signal—require a much more detailed and complex analysis of the signals and waveforms that include new measurements such as the error vector magnitude, polarization unbalance, quadrature error, etc. The PSO-200 offers the full flexibility for users to select the best views and measurements required to meet their needs.
Important information about the quality of the signal transmitted can be recovered from the constellation diagram. The PSO-200 offers powerful analysis capabilities to identify issues such as quadrature errors, imbalance between the I and Q branches of the modulators, signal-to-noise ratio (SNR) issues, etc. The large bandwidth of the PSO-200 allows precise recovery of constellation diagrams, including the transition information. Each polarization can also be analyzed as two I and Q eye diagrams or using time-domain patterns (e.g., as in the case of QPSK or DQPSK). What’s more, these diagrams provide additional information about the signal quality, such as information on skew, jitter and other timing issues.
The quality of the transmitted signal can also be established by looking at the error vector magnitude, which compares the recovered signal to an ideal signal. The PSO-200 not only provides the value of the EVM but also its evolution over time.
The unique time-resolved error vector magnitude (EVM) analysis, developed by EXFO, allows user to quickly identify Tx impairments and apply masks for fast and precise pass/fail decision in manufacturing.
In addition to providing extremely accurate signal analysis, the PSO-200 offers bit error-rate (BER) measurement capabilities that are normally only found in real-time sampling systems. When using any PRBS up to 216-1 or user-defined sequence of equivalent length, the PSO-200’s powerful algorithms can perform smart analysis of the data recovered to estimate the BER. Additionally, a powerful gearbox, an error summary and a visual representation of all errors in all graphs allow users to identify potential error sources faster.
Once the transmitter seems fully optimized, it can be interesting to see the impact of bandwidth-limited network elements, such as the receiver front-end on the signal. This can be simulated by applying a digital filter on the recovered signal. Butterworth, Bessel-Thomson and Chebyshev filters of any bandwidth and order up to eight are available in the PSO-200 and can be applied to the recovered signal.
Now with the PSO-200, it has never been this easy to re-process the data acquired offline to perform more advanced analysis or validate the transmission parameters or quality, using customer-specific algorithms. With a touch of the Save function, EXCEL- and MatLAB-compatible files, including the raw data acquired, can easily be exported. Acquired traces are also stored in the PSO-200 proprietary format. All the files stored include the acquired traces and online analysis data, and since the PSO-200 software can be installed on any PC; this means that acquired traces and signals can be re-opened offline for further analysis—as if working on the instrument itself.