Optical pulses are subject to distortion and stretching as they pass through optical filters and optical fibers over long distances.
(https://github.com/tacticstactics/Optical-pulse-broadening/blob/4f1e0422b0de5515737d8783b0ee29195dfa3780/optical_pulse_broadening_optical_filter.ipynb)
The optical filter is an Infinite Impulse Response (IIR) composed of a dielectric coating.
The transmitted light and the reflected light are subjected to phase difference, which causes the light pulse to be deformed.
When light passes through an optical material, it is subjected to a phase difference according to the wavelength dependence of the refractive index.
In materials with large dispersion, the longer the distance, the longer the pulse.
