Entangled Photons Recombination from Broadband Parametric Down-Conversion

Conclusions: In this thesis, a study on the dependence of the peak-to-background ratio in the SFG spectrum on the number of frequency modes in PDC has been carried out. Particularly, a theoretical analysis for the optical elements to be utilized in the experimental setup has been performed. For example, the most suitable nonlinear crystal to generate the broadest PDC spectral bandwidth with the higher parametric gain. As a result of this analysis, BBO crystal with 5mm length has been chosen. Also the optimal material of the prisms has been chosen with the most practical geometry of the dispersion compensator to compensate for all the positive GVD in PCD. 

Moreover, an experimental setup has been built to study the dependence of the peak-to-background ration on the GVD compensation and the number of frequency modes. The most important results are summarized as follows:

  • An efficient pump reconstruction has been observed. The highest measured peak-to-background ration is 20 +/-1.0 for pump power 200 mW using a high resolution monochromator. In addition, the spectral bandwith of the peak coincides with the pump bandwidth. 
  • The peak-to-background ration demonstrates a high dependence on the time delay, which is caused by the GVD, between signal and idler beams. The peak-to-background ratio increases when the GVD is compensated and it reaches its maximum with zero GVD. Positive and negative GVD have the same effect on the peak-to-background ratio. 
  • The thesis demonstrates the dependence of the measured peak-to-background ratio on the number of the frequency modes in PDC. The peak-to-background ratio increases with increasing the number of the frequency modes in the PDC, similarly to the Fedorov ratio, which is commonly used operational measure of entanglement. Such dependence reveals a new method for the PDC entanglement characterization. 

Finally, the experimental setup can be further improved using spatial light modulator (SLM) with spectral-physe holograms to compensate for the higher order dispersion or to modulate the phases of the signal and idler and study their effect on the reconstructed pump spectrum and the peak-to-background ratio.