Format

Constellation

—

Line rate

—

Received

—

Quality

MER

—

Symbols

—

Bit errors

—

Freq offset

—

Detected intensity

Levels

—

Oversampling

—

Traces

—

Note

An eye diagram is a direct-detection instrument: the photodiode squares the field, and one threshold on intensity decides the bit. A coherent receiver has no eye to show — its I and Q rails mean nothing until a carrier phase has been recovered, and by then the signal is one sample per symbol with no waveform left to fold. That is what the constellation is for.

Wavelength axis

Trace

Resolution

—

Span

—

Points

—

Readings

Peak

—

At

—

Total power

—

OSNR

—

Note

An OSA reports power per resolution bandwidth, which is why the trace is labelled in one. Widen the resolution and the ASE floor climbs decibel for decibel while the channels — already narrower than either setting — do not move at all. That asymmetry is the reason an OSNR figure means nothing without the bandwidth it was quoted in, and it is worth doing once on the block's own parameter.

Sweep

Plot

Block

Plot

Note

The block on its own, as its scattering matrix: every port to every port, across the window. A run shows what one signal made of a device; this shows the device. Empty ends take the block's own window -- a grating's line, a ring's resonances -- and group delay is −dφ/dω, which is where a grating's dispersion and a ring's slow light are, and a power trace does not show either.