CWLaserTimeStepper

class photonforge.CWLaserTimeStepper(*, power=1, rel_intensity_noise=0, linewidth=0, frequency=None, 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:

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

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 rotates at 2πΔf.

• 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.

Methods

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, time_index, ...)	Take a single time step on the given inputs.
update(*args, **kwargs)	Update this time stepper.

Attributes

parametric_function	Function used to update a parametric component.
parametric_kwargs	Keyword arguments used to update a parametric component.
properties	Object properties.
random_variables	Random variables associated to this modles's parameters.

reset()

Reset internal state.

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 – Unused.

step_single(inputs, time_index, update_state, shutdown)

Take a single time step on the given inputs.

Parameters:

• inputs (dict[str, complex]) – Dictionary containing inputs at the current time step, mapping port names to complex values.

• time_index (int) – Time series index for the current input.

• update_state (bool) – Whether to update the internal stepper state.

• shutdown (bool) – Whether this is the last call to the single stepping function for the provided TimeSeries.

Returns:

Outputs at the current time step.

Return type:

dict[str, complex]