Laser noise considerations for phase modulated links

Photonic links employing intensity modulation with direct detection are typically unaffected by laser phase noise without a mechanism to convert that phase noise into intensity noise. Such mechanisms in long links include chromatic dispersion and double-Rayleigh scattering, the latter of which introduces multi-path interference (MPI). However, these processes are generally not a concern in short links for avionic platforms except when reflections from fiber optic connectors produce strong MPI. Phase modulated links provide distinct advantages over intensity modulation for digital and analog applications; however, they are severely impacted by laser phase noise. Here we describe considerations for a phase modulated link employing an asymmetric Mach-Zehnder interferometer (MZI).