Diploma thesis

Material: KTP
Polarizations: y → y + z
775 nm → 1550 nm + 1550 nm
Λ: 68.40 µm
m: -1
Pump FWHM: 0.88 nm
Dimensions: 4 µm x 4 µm x 5 mm
Table 3.4: Proposed and investigated crystal parameters
Figure 3.38: Pump envelope x phasematching function = JSA of the
propsed PDC state
with the additional side peaks of the sinc in figure 3.39. These peaks lead to an
increased distinguishability and limit the minimal achievable amount of entanglement.
The minimum cooperativity parameter possible with this proposed setup is
K=1.20 (S=0.67). It is important to note that a precise control over the pump
width is crucial because already detunings of about 0.5 nm result in a considerable
increase of the frequency correlations (see Figure 3.40). Effects from spatial modes
pose no problem. The phasematching curves, for different spatial modes, are too
much apart as plotted in Figure 3.41, and could be filtered with ease. Additionally
it is unlikely for wavelengths around 1550 nm to propagate in higher spatial modes
in a waveguide of 4 µm x 4 µm. In the experiment we observed only single mode
propagations in this wavelength regime.
Compared with the already implemented group velocity matching in KDP [10, 11],
this proposal exhibits two main advantages. The use of waveguides will result in
a much brighter single photon source and the wavelength of 1550 nm is optimal to
distribute the heralded photons through optical fibers.
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