SUB-POISSONIAN LIGHT AND PHOTOCURRENT SHOT-NOISE SUPPRESSION IN CLOSED OPTOELECTRONIC LOOP

Photocurrent shot-noise suppression is observed in closed optoelectron ic loop below the limit (1 - eta) of standard shot-noise level (SNL) i mposed by conventional theory of photodetector with quantum efficiency eta. Experimental results on photocurrent noise are presented for dif ferent values of feedback strength and quantum efficiency eta of in-lo op photodiode. It is shown that at fixed feedback strength the suppres sion factor does not depend on eta. Minimum noise spectral density is observed below the SNL by a factor 17.8 (- 12.5 dB). Such large suppre ssion cannot be explained in terms of an ordinary sub-Poissonian light state in the loop. We suggest the concept of an anticorrelation light state, where the light in the loop is described as a non-stationary s tate with Poissonian quantum fluctuations, and superimposed anticorrel ated classical fluctuations. While the degree of noise reduction in th e photocurrent can be arbitrary large, the degree of anticorrelation b etween the classical and quantum fluctuations in the light beam remain s limited by the quantum efficiency of the feedback photodiode. Calcul ations based on this concept are in good agreement with experimental d ata on super-shot-noise power, obtained for the beam extracted from th e loop by a beam splitter.