Excess broadband noise at equal intensities in the interferometer arms

We report a theoretical and experimental study of the excess photocurrent noise in the detection of low-coherence radiation caused by the beats of the random components of the optical spectrum at equal intensities in the interferometer arms. It is shown that, in this case, the spectral density of photocurrent fluctuations is 1.5 times higher than when detecting radiation without interference. This result makes it possible to clarify the value of the limiting level of the total fundamental noise of low-coherence radiation during interference. Excess noise cannot be completely subtracted in balanced detection.