def Ez_to_H(Ez, omega, dL, npml):
""" Converts the Ez output of mode solver to Hx and Hy components
"""
N = Ez.size
matrices = compute_derivative_matrices(omega, (N, 1), [npml, 0], dL=dL)
Dxf, Dxb, Dyf, Dyb = matrices
# save to a dictionary for convenience passing to primitives
info_dict = {}
info_dict['Dxf'] = Dxf
info_dict['Dxb'] = Dxb
info_dict['Dyf'] = Dyf
info_dict['Dyb'] = Dyb
Hx, Hy = Ez_to_Hx_Hy(Ez)
return Hx, Hy
def get_modes(eps_cross, omega, dL, npml, m=1, filtering=True):
""" Solve for the modes of a waveguide cross section
ARGUMENTS
eps_cross: the permittivity profile of the waveguide
omega: angular frequency of the modes
dL: grid size of the cross section
npml: number of PML points on each side of the cross section
m: number of modes to solve for
filtering: whether to filter out evanescent modes
RETURNS
vals: array of effective indeces of the modes
vectors: array containing the corresponding mode profiles
"""
k0 = omega / C_0
N = eps_cross.size
matrices = compute_derivative_matrices(omega, (N, 1), [npml, 0], dL=dL)
Dxf, Dxb, Dyf, Dyb = matrices
diag_eps_r = sp.spdiags(eps_cross.flatten(), [0], N, N)
A = diag_eps_r + Dxf.dot(Dxb) * (1 / k0)**2
n_max = np.sqrt(np.max(eps_cross))
vals, vecs = solver_eigs(A, m, guess_value=4 * n_max)
if filtering:
filter_re = lambda vals: np.real(vals) > 0.0
# filter_im = lambda vals: np.abs(np.imag(vals)) <= 1e-12
filters = [filter_re]
vals, vecs = filter_modes(vals, vecs, filters=filters)
if vals.size == 0:
raise BaseException("Could not find any eigenmodes for this waveguide")
vecs = normalize_modes(vecs)
return vals, vecs
