[londons_explore]

A laser that transmits data at 100Gbps can also transmit at 1 bit per second with an additional path loss of 110 decibels.

You'd normally achieve this by transmitting a well-known pseudorandom sequence. You also need clock stability into the ppb range.

A path loss of 110 decibels is huge. It can easily account for your lenses being hugely off axis.

[sneak]

What books or webpages do I read to learn how to understand the why of your first sentence?

[londons_explore]

This is from the Shannon-Hartley theorem, the 'power limited case':

https://en.wikipedia.org/wiki/Shannon%E2%80%93Hartley_theore...