INTERCONNECT time domain simulations can be used to characterize photonic circuits in
the time domain.
When a simulation runs, data flows from the output port of one element to one or more
input ports of other connected elements.
The data flow scheduler controls the flow of the data through the circuit.
Similar to the frequency domain solver, INTERCONNECT time domain simulations support an arbitrary
number of modes, giving designers the capability to simulate bidirectional, multimode and multichannel
When one or more time dependent sources are connected to the inputs of a circuit, INTERCONNECT
runs a time domain simulation.
Some common results obtained from time domain simulations are: eye diagrams, bit error rates,
and extinction ratios.
Data is represented as a stream of frames where each frame represents either a single
sample or a block of samples.
Each sample represents the value of the signal at a specific point in time.
For optical signals, a block of samples constitute a waveform, where the waveform defines the
complex envelope of the optical field.
Here the carrier frequency, omega_0, is the center frequency of the simulation band.
The optical power is the absolute value squared of the complex envelope.
Here the impedance is taken to be 1.
Two different signal processing approaches are available for time domain simulations:
Transient Sample Mode and Transient Block Mode.
The default option is the Transient Sample Mode.
In the Transient Sample Mode, a sample-by-sample processing method is used, where each invocation
of an element accepts one sample from each input port of the element and produces one
sample at each output port.
Elements in the circuit transfer samples bidirectionally during each iteration to simulate interactions
and resonances between multiple elements.
The Transient Sample Mode is recommended for bidirectional simulations of close coupled
circuits, such as resonant structures, circuits with feedback loops, traveling laser sections,
or photonic circuits where reflections must be considered.
Applications of time domain simulations using the Transient Sample Mode include: optical
transceivers and waveguide division multiplexers, as well as sub-circuits like ring resonator
modulators, Mach Zehnder modulators, and electroabsorption modulators.
In the Transient Block Mode, a waveform from each input port of an element is mapped to
a waveform at its output ports, where a waveform is defined as a block of N samples.
The simulation progresses element by element, using the default settings, each element calculates only
one block, meaning each element only runs once.
The Transient Block Mode is recommended for open-loop systems, such as unidirectional
simulations of optical system links, where the simulation progresses unidirectionally
from the transmitter to the receiver.
Running the transient simulation in Block Mode is required when optical fiber nonlinear
dispersive effects must be considered, but the propagation time delay isn't of interest.