"""
TiO2/SiO2 Bragg mirror
======================
"""

# %%
# TiO2/SiO2 Bragg mirror simulation
# ---------------------------------
#
# Authors: O. Castany, M.Müller
#
# This notebook simulates a Bragg mirror composed of alternating layers of TiO₂ and SiO₂, each a quarter-wavelength thick at a central wavelength of 1550 nm.
# The mirror contains 8.5 periods, with air as the incident medium and glass as the substrate.

# %%
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 all required materials with constant (non-dispersive) refractive indicies.
# Air as incidence material and glass as exit material. The Bragg mirror materials are SiO2 and TiO2.

air = elli.AIR
glass = elli.ConstantRefractiveIndex(1.5).get_mat()
SiO2 = elli.ConstantRefractiveIndex(1.47).get_mat()
TiO2 = elli.ConstantRefractiveIndex(2.23 + 1j * 5.2e-4).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.

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)


# %%
# Create layers and structure
# ---------------------------
# We now build the multilayer stack:
# Alternating layers of TiO2 / SiO2:
# - 8 full periods + 1 TiO2 layer at the end → "8.5 periods"
# - Placed between air (front) and glass (back)

# Define periodic stack
# Repeated layers: 8.5 periods: Parameters (Substructure, repetitions, number of layers before, number of layers after the stack)
layerstack = elli.RepeatedLayers([L_TiO2, L_SiO2], 8, 0, 1)

# Build full structure
s = elli.Structure(air, [layerstack], glass)

# %%
# Structure Graph: Visualization of the refractive index profile in z-direction.
# ------------------------------------------------------------------------------
elliplot.draw_structure(s)

# %%
# Optical calculation
# -------------------
# Calculation of the reflection and transmission of the structure at normal incidence (0°).
(lbda1, lbda2) = (1100, 2500)
lbda_list = np.linspace(lbda1, lbda2, 200)

data = s.evaluate(lbda_list, 0)

R = data.R
T = data.T

# %%
# Reflection and Transmission data
# --------------------------------
# The plot shows the high reflection in the stopband region around the design wavelength and the interference patterns around it.
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()