AmplitudeModTimeStepper

class photonforge.AmplitudeModTimeStepper(*, a0=0, a1, a2, a3, z0=None, insertion_loss=0, extinction_ratio=None, chirp=0, dloss_dv=, dloss_dv2=, f_3dB=0, mesh_refinement=None, verbose=True)

Time-stepper for a uniform electro-optic amplitude modulator.

This model implements a two-port optical amplitude modulator with a single electrical drive. It maps an electrical input voltage to an optical amplitude scaling factor through a static polynomial transfer function. The model also includes voltage-dependent loss, chirp, and an optional first-order low-pass filter to simulate a finite electro-optic bandwidth. The final amplitude is clipped by an envelope defined by the insertion loss and extinction ratio.

The scaling factor applied to the optical signal before losses and clamping is:

\[s_0 = a_0 + a_1 V + a_2 V^2 + a_3 V^3\]

The chirp-induced phase shift is proportional to the logarithm of the final amplitude scaling relative to the maximum amplitude (derived from the insertion loss):

\[\Delta\phi = -C \ln \frac{s_\text{total}}{s_\text{max}}\]

In the \(e^{-j\omega t}\) convention this phase makes the instantaneous frequency of the output follow its power, \(\delta\nu = (C/4\pi)\,{\rm d}\ln P/{\rm d}t\).

Parameters:

• a0 (Annotated[float, _]) – Constant gain coefficient.

• a1 (Annotated[float, units='1/V']) – Linear electro-optic gain coefficient.

• a2 (Annotated[float, units='1/V²']) – Quadratic electro-optic gain coefficient.

• a3 (Annotated[float, units='1/V³']) – Cubic electro-optic gain coefficient.

• z0 (Annotated[complex, units='Ω'] | Interpolator | None) – Characteristic impedance of the electrical port used to convert the input field amplitude to voltage. If None, derived from port impedance, calculated by mode-solving, or set to 50 Ω.

• insertion_loss (Annotated[float, minimum=0, units='dB']) – Optical propagation loss.

• extinction_ratio (Annotated[float, minimum=0, units='dB'] | None) – Optical extinction ratio.

• chirp (float) – Chirp parameter \(C\) as quoted on modulator datasheets: the output frequency deviates by \(\delta\nu = (C/4\pi)\,{\rm d}\ln P/{\rm d}t\). Positive values blue-shift the rising optical edge and red-shift the falling one.

• dloss_dv (Annotated[float, units='dB/μm/V']) – Linear voltage-dependent optical loss coefficient.

• dloss_dv2 (Annotated[float, units='dB/μm/V²']) – Quadratic voltage-dependent optical loss coefficient.

• f_3dB (Annotated[float, minimum=0, units='Hz']) – -3 dB frequency cutoff for bandwidth limiting. Only active for positive values.

• mesh_refinement (Annotated[float, exclusiveMinimum=0] | None) – Minimal number of mesh elements per wavelength used for mode solving.

• verbose (bool) – Flag setting the verbosity of mode solver runs.

Important

The electrical input \(A\) is converted to a voltage signal through the port impedance:

\[V = \Re\{A\} \sqrt{\Re\{Z_0\}}\]

Notes

The total loss is clamped at 0 dB to avoid gain.

Note

PhotonForge uses the \(e^{-j\omega t}\) time convention, so an envelope \(e^{-j2\pi\Delta f\,t}\) is light at \(f_c + \Delta f\), with \(f_c\) the carrier frequency. The instantaneous frequency deviation of an output envelope a is therefore \(-(1/2\pi)\,{\rm d}\arg a/{\rm d}t\), for example -numpy.gradient(numpy.unwrap(numpy.angle(a)), time_step) / (2 * numpy.pi), and the frequency axis of a numpy.fft spectrum must be reversed.

Methods

bind_native(step, keys[, state, cstate, context])	Bind a compiled step function.
reset()	Reset internal state.
setup(component, time_step, *[, ...])	Initialize the time stepper.
setup_state(*, component, time_step, ...[, ...])	Initialize internal state.
step([inputs, steps, time_step, show_progress])	Compute the outputs of this time stepper, given inputs.
step_single(inputs, outputs, time_index, ...)	Take a single time step on the given inputs.
update(*args, **kwargs)	Update this time stepper.
write_verilog_a(path, *[, backend, ...])	Write this configured time stepper as one Verilog-A module.

Attributes

parametric_function	Function used to update the time stepper.
parametric_kwargs	Keyword arguments used to update the time stepper.
path_delays	Minimum delay in time steps of each (input key, output key) signal path; missing pairs have no path and None means every input reaches every output within the time step.
properties	Object properties.
random_variables	Random variables associated to the time stepper's parameters.
status

reset()

Reset internal state.

Return type:

None

setup_state(*, component, time_step, carrier_frequency, verbose=None, **kwargs)

Initialize internal state.

Parameters:

• component (Component) – Component representing the laser source.

• time_step (Annotated[float, minimum=0, units='s']) – The interval between time steps (in seconds).

• carrier_frequency (Annotated[float, minimum=0, units='Hz']) – The carrier frequency used to construct the time stepper. The carrier should be omitted from the input signals, as it is handled automatically by the time stepper.

• verbose (bool | None) – If set, overrides the time stepper’s verbose attribute.

• kwargs (object) – Unused.

Return type:

object