Sub-shot-noise-limited optical heterodyne detection using an amplitude-squeezed local oscillator

We experimentally demonstrate a novel sub-shot-noise-limited heterodyne det ection scheme measure a weak optical signal field by employing amplitude-sq ueezed light as the local oscillator (LO) field. The amplitude-squeezed LO field at 428.8 nm is generated from a high efficiency single-pass second-ha rmonic generation in a KNbO3 crystal pumped by femtosecond (130 fs) pulses at 857.6 nm, and the signal field is combined with the generated squeezed L O field through the crystal. An enhancement of 0.7 dB (1.4 dB inferred) in signal-to-noise ratio beyond the shot-noise limit is directly observed.