Linear optical amplifiers are described quantum mechanically by a linear differential equation with Langevin operator noise sources. Even if the gain medium is composed of fermions, in the limit when the amplifier is a linear amplifier, the noise sources must have bosonlike commutation relations. I show in detail how the Tomonaga approximation produces the bosonic commutators of the noise sources.
© 2001 Optical Society of America
(060.4510) Fiber optics and optical communications : Optical communications
(140.3280) Lasers and laser optics : Laser amplifiers
(140.3550) Lasers and laser optics : Lasers, Raman
(140.4480) Lasers and laser optics : Optical amplifiers
(270.2500) Quantum optics : Fluctuations, relaxations, and noise
H. A. Haus, "Linearity of optical amplifiers and the Tomonaga approximation," J. Opt. Soc. Am. B 18, 1777-1779 (2001)