Observation of amplitude squeezing from semiconductor lasers by balanced direct detectors with a delay line

Simultaneous measurement of the signal-noise level and the corresponding shot-noise level using balanced direct detectors with a delay line is demonstrated. We have observed 1.3-dB squeezing from a constant-current-driven semiconductor laser, which is consistent with 3-dB squeezed noise at the output of the laser when the detection efficiency is taken into account.