Generation of bright squeezed light at 1.06 μ m using cascaded non-linearities in a triply resonant c.w. PPLN OPO

We have used an ultra-low threshold continuous-wave Optical Parametric Oscillator (OPO) to reduce the quantum fluctuations of the reflected pump beam below the shot noise limit. The OPO consisted of a triply resonant cavity containing a Periodically-Poled Lithium Niobate crystal pumped by a Nd:YAG laser and giving signal and idler wavelengths close to 2.12 microns and a threshold as low as 300 microwatts. We detected the quantum fluctuations of the pump beam reflected by the OPO using a slightly modified homodyne detection technique. The measured noise reduction was 30 % (inferred noise reduction at the output of the OPO 38 %).