Cascaded χ(2) nonlinearity in QND measurement

 QND measurement schemes often use Kerr nonlinearity to couple the intensity fluctuations of the signal beam to the phase fluctuations of the probe beam by means of the cross-phase modulation effect. Such schemes use materials with intrinsic χ⁽³⁾nonlinearity. However, it has already been shown that Kerr-effect-like correlation between two light waves may be achieved through cascaded χ⁽²⁾: χ⁽²⁾ processes. The value of the nonlinearity induced by cascading χ⁽²⁾ can, in many cases, be much higher than fibre χ⁽³⁾. The authors point out the possibility of using the cascaded χ⁽²⁾ nonlinearity instead of intrinsic χ⁽³⁾ nonlinearity in the scheme which resembles the well-known photon number QND measurement scheme. The non-degenerate second-harmonic generation (SHG) with a large phase mismatch is considered. The harmonic wave influence on the measurements is shown. High QND measurement characteristics can be achieved with the use of an appropriate set of parameters. Received: 6 April 1996