Excess Quantum Noise Is Colored

Whereas quantum noise in a laser is essentially white, we show that excess quantum noise is colored. The coloring is determined by both the geometry (nonorthogonality) and the dynamics (eigenvalues) of the eigenmodes of the laser resonator. Experimentally, we demonstrate these concepts by using nonorthogonal polarization modes. We also show that the induced correlations between the modes can be used to greatly reduce the excess quantum noise.