Abstract

A theory of spontaneous emission noise is presented based on classical electromagnetic theory[1]. Unlike conventional theories of laser noise, this presentation is valid for open resonators. A local Langevin force is added to the wave equation to account for spontaneous emission. A general expression is found relating the diffusion coefficient of this force to the imaginary part of the dielectric function. The field of laser is found by solving the wave equation by the Green’s function method. The lasing mode is a resonant state associated with a pole in Green’s function. The Langevin rate equations for a Fabry-Perot laser with arbitrary facet reflectivities are derived. Optical feedback can be represented by a complex, frequency dependent, facet reflectivity r(ω)exp(iϕ(ω)). The effect of optical feedback is to reduce the adiabatic chirp by F and to reduce the Lorentzian linewidth by F², where and τ is the round trip time in the laser cavity and α is the linewidth parameter[2].

© 1987 Optical Society of America