"""
TiO2/SiO2 Bragg mirror
======================
"""
# %%
# Example of a TiO2/SiO2 Bragg mirror with 8.5 periods
# ----------------------------------------------------
#
# Authors: O. Castany, M.Müller

# %%
import elli
import elli.plot as elliplot
import matplotlib.pyplot as plt
import numpy as np

np.set_printoptions(suppress=True, precision=3)

# %%
# Material definition
# -------------------
# We define air as incidence material and glass as exit material.
# SiO2 and TiO2 are defined by simplified dispersion relations.
air = elli.AIR
glass = elli.ConstantRefractiveIndex(1.5).get_mat()

n_SiO2 = 1.47
n_TiO2 = 2.23 + 1j * 5.2e-4

SiO2 = elli.ConstantRefractiveIndex(n_SiO2).get_mat()
TiO2 = elli.ConstantRefractiveIndex(n_TiO2).get_mat()

# %%
# Create layers and structure
# ---------------------------
# The SiO2 and TiO2 layers are set to the thickness of an
# quarterwaveplate of the respective material at 1550 nm.
#
# The layers are then stacked alternatingly and put into the
# complete structure with air and the glass substrate.
lbda0 = 1550

d_SiO2 = elli.get_qwp_thickness(SiO2, lbda0)
d_TiO2 = elli.get_qwp_thickness(TiO2, lbda0)

print("Thickness of the SiO2 QWP: {} nm".format(d_SiO2))
print("Thickness of the TiO2 QWP: {} nm".format(d_TiO2))

L_SiO2 = elli.Layer(SiO2, d_SiO2)
L_TiO2 = elli.Layer(TiO2, d_TiO2)

# Repeated layers: 8.5 periods
layerstack = elli.RepeatedLayers([L_TiO2, L_SiO2], 8, 0, 1)

s = elli.Structure(air, [layerstack], glass)

# %%
# Calculation
# -----------
(lbda1, lbda2) = (1100, 2500)
lbda_list = np.linspace(lbda1, lbda2, 200)

data = s.evaluate(lbda_list, 0)

R = data.R
T = data.T


# %%
# Structure Graph
# ---------------
# Schema of the variation of the refractive index in z-direction.
elliplot.draw_structure(s)

# %%
# Reflection and Transmission Graph
# ---------------------------------
fig = plt.figure()
ax = fig.add_subplot(1, 1, 1)
ax.plot(lbda_list, T, label="$T$")
ax.plot(lbda_list, R, label="$R$")
ax.legend(loc="center right")
ax.set_xlabel(r"Wavelength $\lambda$ (nm)")
ax.set_ylabel(r"Power reflection $R$ or transmission $T$")
ax.set_title(r"Bragg mirror: Air/{TiO$_2$/SiO$_2$}x8/TiO$_2$/Glass")
plt.show()