The Eye Diagram Perspective

In digital communications, we use an Eye Diagram to visualize signal quality. Jitter manifests as "thick" vertical lines at the crossing points, effectively closing the "eye" horizontally.

Calculating Bit Error Rate (BER)

BER is the ratio of corrupted bits to the total number of bits transmitted. It is a statistical probability often visualized on a Waterfall Curve.

For enterprise fiber (10G/40G/100G), the standard requirement is a BER of $10^{-12}$. This means only one bit error is allowed for every 1 trillion bits sent.

Sources of Jitter

1. Deterministic Jitter (Dj): Predictable timing errors caused by EMI, crosstalk, or impedance mismatches.
2. Random Jitter (Rj): Unpredictable noise typically following a Gaussian distribution, often caused by thermal noise in oscillators.

Forward Error Correction (FEC)

In 25G and 100G links, jitter is so prevalent that we can no longer rely on 'clean' physics. We use FEC—adding redundant parity bits—to allow the receiver to mathematically correct errors caused by jitter without requiring a retransmission.

Conclusion

Jitter is the enemy of throughput. As we push toward 400G and 800G, the engineering challenge shifts from "how do we send bits" to "how do we perfectly time the sampling of those bits" in a world of high-frequency noise.