Diploma thesis

This is the silliest stuff that ever I heard.
William Shakespeare
A Midsummer Night’s dream
5 Conclusion and Outlook
In the past year considerable progress has been made towards a pure heralded single
photon source. We were able to extend the analysis of wave propagation inside
a waveguide to spatial modal effects in collaboration with Thomas Lauckner and
Division 3. Effects that have just recently been observed in experiments by Kaisa
Laiho.
We analyzed different possibilities to produce pure heralded single photon states
inside a waveguide ranging from the first attempts with spectral filtering to crystal
engineering, where uncorrelated photon pairs are produced directly in the downconversion
process. The first setups employing this method are currently under
development in the laboratory. We pushed this approach even further by investigating
the possibility of generating uncorrelated counterpropagating photon pairs
inside a waveguide geometry. The inherent decorrelation and separation of photon
pairs inside the crystal may be a further step to the integration and miniaturization
of these single photon sources. Several groups are currently facing the challenge of
producing chips with a submicrometer grating period.
Our characterization of the id201 APDs provided knowledge of their noise properties.
The gained data will prove useful for future work with these single photon
detectors.
SHG proved to be a valuable tool to investigate the phasematching properties of
our crystal samples. We were able to identify all degenerate phasematching points
and to compare our modelling with actual data. There are still discrepancies between
theory and experiment, but only moderate fitting is necessary to reach a good
agreement. Despite all simplifications in the derivation of the two-photon-state, we
showed that our theoretical treatment is sufficient. Further improvement could be
made by a more precise model of the waveguiding structures.
Finally we used the SHG data to find a PDC process degenerate in frequency. First
results are very promising. We are looking forward to see a bright pure heralded
single photon source in the near future.
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