Effect of Mode Nonorthogonality on Light Coherence In F-P and DFB Lasers

Abstract

In this paper we extend a theory of the light coherence^1,2 to take into account the nonorthogonal nature of the laser modes that leads to the excess noise factor^3,4. The coherence properties of light presented by correlation functions are determined by means of the time dependent solutions of the Fokker-Planck equation. In our approach, the problem of calculating the correlation functions has been reduced to an eigenvalue problem of the Sturm-Liouville equation². It is worth noting, that in contrast to the standard theory the correlation functions are modified by the excess noise factor dependent on the spatial distributions of the laser modes. Numerical result obtained for F-P as well as for DFB lasers reveal the difference between the standard approach (for orthogonal laser modes) and the more realistic model (mode nonorthogonality included). We find, that the coherence properties of light from lasers strongly depend on the changes of the geometry of the laser structure (having the same Q-factor).