When looking at optical and electrical signals above 13Ghz+ how does the oscilloscope trigger on these signals?

When looking at optical and electrical signals above 13Ghz+ how does the oscilloscope trigger on these signals?

The mainframes (CSA8000, TDS8000, etc) are not able to trigger on signals this fast. There are two alternatives:

1. Use a frequency divider, sufficient to provide a 12.5Ghz, or slower trigger signal.
2. Many signal generators have a clock output that has been divided down to a lower frequency. These outputs tend to be synced to the data output. This output is usually meets the trigger input requirements.