CWLaserTimeStepper

class photonforge.CWLaserTimeStepper(*, power=1, rel_intensity_noise=0, linewidth=0, frequency=None, chirp_bandwidth=0, chirp_period=0, chirp_waveform='sawtooth', phase=0, reflection=0, seed=None)

Time-stepper for a continuous-wave (CW) laser source.

This model generates a complex optical field with a constant average power. It can optionally include phase noise, modeled as a Lorentzian line width, and relative intensity noise (RIN) from a white noise process. The output field has the form:

\[A[k] = \sqrt{P[k]} e^{j\phi[k]}\]

The phase noise is modeled as a discrete-time Wiener process. The phase increment at each step is a Gaussian random variable with variance determined by the linewidth Δν as:

\[\text{Var}[\Delta\phi] = 2\pi \Delta\nu \Delta t\]

RIN is modeled as an additive white noise process on the optical power. The variance of the power fluctuations is derived from the RIN PSD, band-limited by the simulation’s Nyquist frequency, and clamped at zero:

\[\text{Var}[P] \approx \text{RIN} \frac{P_0^2}{2\Delta t}\]

A linear frequency chirp can be added on top, sweeping the instantaneous frequency over a band \(B\) centered on frequency, with period \(T\):

\[f[k] = f_0 + B d(k \Delta t / T)\]

in which \(d\) ramps from -1/2 to 1/2 over each period (sawtooth), or over each half period and back (triangle).

Parameters:

• power (Annotated[float, minimum=0, units='W']) – Mean optical output power.

• rel_intensity_noise (Annotated[float, minimum=0, units='1/Hz']) – One-sided relative intensity noise (RIN) power spectral density.

• linewidth (Annotated[float, minimum=0, units='Hz']) – Full-width at half-maximum (FWHM) of the laser’s Lorentzian shape.

• frequency (Annotated[float, minimum=0, units='Hz'] | None) – Absolute laser frequency. If None, equals the carrier frequency. If detuned from the carrier by Δf, the output envelope is \(e^{-j2\pi\Delta f\,t}\).

• chirp_bandwidth (Annotated[float, minimum=0, units='Hz']) – Total frequency excursion of a linear sweep, centered on frequency. Zero disables the chirp.

• chirp_period (Annotated[float, minimum=0, units='s']) – Duration of one complete sweep.

• chirp_waveform (Literal['sawtooth', 'triangle']) – Sweep shape. A sawtooth ramps the optical frequency up over the period and resets; a triangle ramps it up over the first half of the period and back down over the second.

• phase (Annotated[float, units='°']) – Starting phase of the output envelope.

• reflection (complex) – Reflection coefficient for incident fields.

• seed (Annotated[int, minimum=0] | None) – Random number generator seed to ensure reproducibility.

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 any internal state of the time stepper.
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.

setup_state(*, component, time_step, carrier_frequency, **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.

• kwargs (object) – Unused.

Return type:

None