Add Fourier interferometers explicitly to Perceval

[anthonyrtw]

Fourier interferometers are possibly the most commonly used optical component/circuit that is not directly available in Perceval currently.

Here, I've defined a Fourier interferometer class UFT(Unitary) that can be immediately defined:

from perceval import *
fourier_circuit = Circuit(m) // UFT(m)

This saves the user from calculating the Matrix form of Fourier interferometers and then explicitly defining the matrix as a Unitary.

I have also made it available from root.

[Aubaert]

Hello, rather than creating a new class, I think this would make more sense as a new catalog component, whose builder would make a unitary

[anthonyrtw]

Hi,
I think adding the UFT to the components library is fairly minimal but is a lot more concise for someone coding than:

uft = catalog["fourier interferometer"].build(m)
circuit.add(1, uft)

As opposed to simply circuit.add(1, UFT(m))

Also catalog components are generally built up from many sub-components. This can of course be done for Fourier interferometers, but I've simply taken the matrix unitary.