Quantum noise is uncertainty of some physical quantity due to its quantum origin.
In the case of number of particles (photons or electrons), the quantum noise is also called shot noise. Most optical communications use amplitude modulation. In this case, the quantum noise appears as shot noise only.
In the case of uncertainty of electric field in some lasers, the quantum noise is not just shot noise; uncertainties of both amplitude and phase contribute to the quantum noise. This issue becomes important in the case of noise of a quantum amplifier, which preserves the phase. The phase noise becomes important at the frequency modulation or phase modulation of waves with energy of quantum comparable to the energy of a signal (which is believed to be more robust with respect to additive noise than an amplitude modulation).
Read more about Quantum Noise: Origin of Quantum Noise, Coherent States and Noise of A Quantum Amplifier
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