Noise Figure and Homodyne Noise Figure

The traditional optical noise figure Fpnf of E. Desurvire takes as powers the squares and variances of photocurrents, proportional to 4th powers of amplitudes (fields). This is in conflict with the electrical noise figure Fe. which is defined for a linear system with 2 quadratures and power proportional to squared amplitudes. The optical in-phase and quadrature noise figure Fo,IQ avoids such contradictions. It is measured with a coherent I&Q receiver which has 2 available quadratures, like an electrical receiver. For an amplifier with high gain one gets the optimum noise figure Fo,IQ = 1, while all prior optical noise figures are equal to 2 in this case. Fe and Fo,IQ have been combined into one generalized noise figure FIQ for all frequencies. For homodyne receivers with 1 quadrature, the optical homodyne noise figure Fo,I has been derived. Here it is combined with the electrical homodyne noise figure Fe,I into a generalized homodyne noise figure FI. While Fo,IQ and Fo,I differ, Fe and Fe,I are identical. All this and the generalized noise figures Ffas and Fase of H. Haus are discussed.