PE1-2.5 Optical System Design
You can design a point-to-point link by constructing link power and rise-time budgets with worked numbers, choose components against those budgets, and describe WDM and its applications.
This is the unit that turns the course into engineering: two budgets, one for power and one for speed, and a design passes only if both close. The rise-time budget is the one students under-rate — a link with plenty of power margin can still fail because the dispersion and component rise times add in quadrature to more than the bit period. WDM is the idea that made the installed fibre plant last: send many wavelengths down one fibre and capacity multiplies without digging.
Work through these
Point-to-point links
The basic link, which is what most of this subject has been building towards. Everything above becomes a component choice here.
Component choice and considerations
Picking the source, fibre and detector against the requirement. It is a systems decision and the constraints pull against each other.
Link power budget with a worked example
Adding up the losses and checking there is light left over. Doing the worked example carefully is the single most useful exercise in the subject.
Rise time budget with a worked example
The other budget, which checks the link is fast enough rather than strong enough. A link can pass one and fail the other, which is why both exist.
Wavelength division multiplexing (WDM)
Sending several wavelengths down one fibre, which multiplies capacity without new cable. It is the reason installed fibre kept up with demand.
Applications of WDM
What the technique above is used for, and the components it needs. It closes the subject on the technology that made long haul capacity affordable.
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