import numpy as np
[docs]def directional_coupler_lc(wavelength_nm, n_eff_1, n_eff_2):
'''
Calculates the coherence length (100% power transfer) of a
directional coupler.
Args:
wavelength_nm (float): The wavelength in [nm] the
directional coupler should operate at.
n_eff_1 (float): n_eff of the fundamental (even)
supermode of the directional coupler.
n_eff_2 (float): n_eff of the first-order (odd)
supermode of the directional coupler.
Returns:
float: The length [um] the directional coupler
needs to be to achieve 100% power transfer.
'''
wavelength_m = wavelength_nm * 1.e-9
dn_eff = (n_eff_1 - n_eff_2).real
lc_m = wavelength_m / (2. * dn_eff)
lc_um = lc_m * 1.e6
return lc_um
[docs]def grating_coupler_period(wavelength,
n_eff,
n_clad,
incidence_angle_deg,
diffration_order=1):
'''
Calculate the period needed for a grating coupler.
Args:
wavelength (float): The target wavelength for the
grating coupler.
n_eff (float): The effective index of the mode
of a waveguide with the width of the grating
coupler.
n_clad (float): The refractive index of the cladding.
incidence_angle_deg (float): The incidence angle
the grating coupler should operate at [degrees].
diffration_order (int): The grating order the coupler
should work at. Default is 1st order (1).
Returns:
float: The period needed for the grating coupler
in the same units as the wavelength was given at.
'''
k0 = 2. * np.pi / wavelength
beta = n_eff.real * k0
n_inc = n_clad
grating_period = (2.*np.pi*diffration_order) \
/ (beta - k0*n_inc*np.sin(np.radians(incidence_angle_deg)))
return grating_period
[docs]def loss(n, wavelength):
kappa = n.imag
alpha = 4.34 * 4 * np.pi * np.abs(
kappa) / wavelength # 4.34 = 10*np.log10(np.e) -> [dB/m] = 4.34 [/m]
return alpha # [db/um] if working in [um]
[docs]def qpm_wavenumber(pmp_n,
pmp_l,
sig_n,
sig_l,
idl_n,
idl_l,
period_qpm,
type='forward'):
pi2 = np.pi * 2
k_pmp = pmp_n * pi2 / pmp_l
k_sig = sig_n * pi2 / sig_l
k_idl = idl_n * pi2 / idl_l
k_qpm = pi2 / period_qpm
if type == 'forward':
sgn_1 = 1
sgn_2 = 1
elif type == 'forward_backward':
sgn_1 = 1
sgn_2 = -1
elif type == 'backward':
sgn_1 = -1
sgn_2 = -1
k_mismatch = k_idl * sgn_1 + k_sig * sgn_2 + k_qpm - k_pmp
return k_mismatch
[docs]def qpm_period(pmp_n, pmp_l, sig_n, sig_l, idl_n, idl_l, type='forward'):
pi2 = np.pi * 2
k_pmp = pmp_n * pi2 / pmp_l
k_sig = sig_n * pi2 / sig_l
k_idl = idl_n * pi2 / idl_l
if type == 'forward':
sgn_1 = 1
sgn_2 = 1
elif type == 'forward_backward':
sgn_1 = 1
sgn_2 = -1
elif type == 'backward':
sgn_1 = -1
sgn_2 = -1
k_qpm = k_pmp - k_idl * sgn_1 - k_sig * sgn_2
l_qpm = pi2 / k_qpm
return l_qpm