18 quED Manual www.qutools.com
9. Repeat alignment of the coupling mode from step 6 for the second arm of the source.
10. When the coupling modes in both arms of the source are aligned, switch off the pump
laser. Switch off the fiber checker, unplug it and connect the fibers to the optical inputs
of the controller unit.
11. Remove the alignment helper plate.
12. Place the long-pass filters in front of the fiber couplers and fasten them with the M2
screws.
13. Install the white protective cover back on the pump beam assembly and secure it with
the M4 screw on the top.
14. Switch on the laser and increase the input current to the operating value. Observe the
detected single- and coincidence-count rates and optimize the pointing of the couplers
for maximum single count rates (2 DOF, use only the screws on the coupler).
15. Perform a vertical walk (4 DOF) in one arm in order to increase the coincidence rate.
16. Place the half wave plate and the polarizers back in the setup. The coupling is now
optimized for one crystal only, thus optimize the coupling as described in section 3.4.2
with diagonal polarizers. You might want to check the HH and VV coincidence rates to
be fairly equal for a better entanglement.
17. Check the entanglement as described in section 3.5.
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