Article

Spontaneous polarization induced by natural thermalization of incoherent light.

Institut Carnot de Bourgogne, UMR 5209 CNRS-Université de Bourgogne, Dijon Cedex, France.
Optics Express (impact factor: 3.59). 11/2008; 16(22):17171-85. pp.17171-85
Source: PubMed

ABSTRACT We analyze theoretically the polarization properties of a partially coherent optical field that propagates in a nonlinear Kerr medium. We consider the standard model of two resonantly coupled nonlinear Schrödinger equations, which account for a wave-vector mismatch between the orthogonal polarization components. We show that such a phase-mismatch is responsible for the existence of a spontaneous repolarization process of the partially incoherent optical field during its nonlinear propagation. The repolarization process is characterized by an irreversible evolution of the unpolarized beam towards a highly polarized state, without any loss of energy. This unexpected result contrasts with the commonly accepted idea that an optical field undergoes a depolarization process under nonlinear evolution. The repolarization effect can be described in details by simple thermodynamic arguments based on the kinetic wave theory: It is shown to result from the natural tendency of the optical field to approach its thermal equilibrium state. The theory then reveals that it is thermodynamically advantageous for the optical field to evolve towards a highly polarized state, because this permits the optical field to reach the ???most disordered state???, i.e., the state of maximum (nonequilibrium) entropy. The theory is in quantitative agreement with the numerical simulations, without adjustable parameters. The physics underlying the reversible property of the repolarization process is briefly discussed in analogy with the celebrated Joule???s experiment of free expansion of a gas. Besides its fundamental interest, the repolarization effect may be exploited to achieve complete polarization of unpolarized incoherent light without loss of energy.

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Keywords

celebrated Joule??
 
coherent optical field
 
complete polarization
 
free expansion
 
fundamental interest
 
incoherent optical field
 
kinetic wave theory
 
nonlinear Kerr medium
 
nonlinear Schrödinger equations
 
optical field undergoes
 
orthogonal polarization components
 
polarization properties
 
polarized state
 
quantitative agreement
 
simple thermodynamic arguments
 
spontaneous repolarization process
 
standard model
 
thermal equilibrium state
 
unexpected result contrasts
 
unpolarized incoherent light