Optical thin film synthesis program based on the use of
J. A. Dobrowolski and D. Lowe
In Sossi's formulation of the Fourier transform method of optical multilayer design the refractive-index pro-
file is derived for an inhomogeneous layer of infinite extent having the desired spectral transmittance.
layer is then approximated by a finite system of discrete homogeneous layers. Because it does not make any
assumptions about the refractive indices, thicknesses, or number of layers, it is the most powerful analytical
method proposed so far. The method has been programmed for a computer and combined with other nu-
merical design procedures. With the program it is possible to design filters with almost any desired trans-
mittance characteristics using realistic refractive indices.
There exist two basic approaches to the synthesis
of optical multilayer systems with irregular spectral
The numerical synthesis meth-
search, evolution, substractive
method-do not make any assumptions about the
thicknesses or refractive indices of the layers which may
be absorbing or dispersive. The construction param-
eters can be easily constrained to be within reasonable
limits. Generally any property of the multilayer that
can be evaluated can be specified.
But in some in-
stances considerable expenditure of computer time is
needed to obtain a satisfactory solution.
In the analytical synthesis methods3'4 a series ex-
pansion of the desired spectral transmittance or re-
flectance curve is solved for the construction parameters
of the required multilayer system. To make solution
possible certain simplifying assumptions have to be
made about either the thicknesses or refractive indices
of the nonabsorbing, nondispersive layers. Solutions
can be obtained quickly, but they sometimes call for
refractive indices that cannot be realized in practice.
One particular analytical method of thin film syn-
thesis is based on the use of Fourier transforms (FT).
Delano 5' 6