Hello Sathya

Fourier series is a periodic series. Which mostly used for donotes any kind of wave forms. For example if I want to record your voice for one second saying something, It will be found. It is a fourier series. Which may look something like this.

Voice= sin(x) + 1/10 sin(2x) + 1/100 sin(3x)

WiFi modulation uses orthogonal combinations of amplitude and phase to encode every bit in a stream, and even makes room for redundant data to counter the loss due to fading, reflections, multi-path, etc. All this is synthesised in a DSP engine using FFT and IFFT.

You can take your periscope and take the light that comes from the surface and put it all back together underneath the water so you can see enemies while submerged.