new dispersion_parameter parameter

src/scgenerator/evaluator.py

@@ -559,6 +559,7 @@ envelope_rules = default_rules + [
     Rule("c_to_a_factor", pulse.c_to_a_factor),
     # Dispersion
     Rule("beta2_coefficients", fiber.auto_dispersion_coefficients),
+    Rule("beta2_coefficients", fiber.handle_dispersion_paramter),
     Rule("beta2_arr", fiber.dispersion_from_coefficients),
     Rule("beta2", lambda beta2_coefficients: beta2_coefficients[0]),
     Rule("beta2", lambda beta2_arr, w0_ind: beta2_arr[w0_ind]),

src/scgenerator/parameter.py

@@ -325,6 +325,8 @@ class Parameters:
     he_mode: tuple[int, int] = Parameter(int_pair)
     fit_parameters: tuple[int, int] = Parameter(float_pair)
     beta2_coefficients: Iterable[float] = Parameter(num_list)
+    dispersion_parameter: float = Parameter(type_checker(*number))
+    dispersion_slope: float = Parameter(type_checker(*number))
     dispersion_file: DataFile = Parameter(DataFile.validate)
     model: str = Parameter(
         literal("pcf", "marcatili", "marcatili_adjusted", "hasan", "custom"),

src/scgenerator/physics/fiber.py

@@ -14,6 +14,7 @@ from scgenerator.physics import units
 from scgenerator.physics.units import c, pi
 
 pipi = 2 * pi
+pi2c = 2 * pi * c
 T = TypeVar("T")
 
 
@@ -46,14 +47,29 @@ def is_dynamic_dispersion(pressure=None):
     return out
 
 
-def beta2_to_D(beta2, l):
-    """returns the D parameter corresponding to beta2(l)"""
-    return -(pipi * c) / (l**2) * beta2
+def beta2_to_dispersion_parameter(beta2: float, wavelength: T) -> T:
+    return -(pipi * c) / (wavelength**2) * beta2
 
 
-def D_to_beta2(D, l):
-    """returns the beta2 parameters corresponding to D(l)"""
-    return -(l**2) / (pipi * c) * D
+def dispersion_parameter_to_beta2(dispersion_parameter: float, wavelength: T) -> T:
+    return -(wavelength**2) / (pipi * c) * dispersion_parameter
+
+
+def dispersion_slope_to_beta3(
+    dispersion_parameter: float, dispersion_slope: float, wavelength
+) -> float:
+    return (wavelength**2 / pi2c) ** 2 * (
+        dispersion_slope + 2 * dispersion_parameter / wavelength
+    )
+
+
+def handle_dispersion_paramter(
+    wavelength: float, dispersion_parameter: float, dispersion_slope: float | None = None
+) -> list[float]:
+    coeffs = [dispersion_parameter_to_beta2(dispersion_parameter, wavelength)]
+    if dispersion_slope is not None:
+        coeffs.append(dispersion_slope_to_beta3(dispersion_parameter, dispersion_slope, wavelength))
+    return coeffs
 
 
 def find_zdw(l: np.ndarray, beta2_arr: np.ndarray) -> list[float]:
@@ -629,7 +645,7 @@ def load_custom_dispersion(
     wl_file = units.normalize_wavelengths(wl_file)
 
     ind = np.where((l >= wl_file.min()) & (l <= wl_file.max()))[0]
-    out[ind] = np.interp(l[ind], wl_file, D_to_beta2(D, wl_file))
+    out[ind] = np.interp(l[ind], wl_file, dispersion_parameter_to_beta2(D, wl_file))
     return out, ind
 
 

tests/test_parameters.py

@@ -1,3 +1,13 @@
 import pytest
 
 import scgenerator as sc
+
+
+def test_dispersion_logic():
+    params = sc.Parameters(wavelength=1550e-9, dispersion_parameter=5e-6)
+    assert params.compute("beta2_coefficients") == pytest.approx([-6.3772409974749684e-27])
+
+    params = sc.Parameters(wavelength=1550e-9, dispersion_parameter=5e-6, dispersion_slope=25)
+    assert params.compute("beta2_coefficients") == pytest.approx(
+        [-6.3772409974749684e-27, 5.116448086629504e-41]
+    )