Generation of squeezed vacuum pulses using cascaded second-order optical nonlinearity of periodically poled lithium niobate in a Sagnac interferometer

Squeezed vacuum pulses up to -1.7 dB at telecom-band (∼1550 nm) is generated with femtosecond laser pulses using cascaded χ (2) optical nonlinearity in a periodically poled lithium niobate crystal placed in a Sagnac interferometer. In spite of group velocity mismatch at short laser pulse pumping, sufficient cascaded nonlinear wave mixing is obtainable at the wavelength shifted from the phase matching wavelength for second harmonic generation. The theoretical model prediction agrees well with the experimental results.