SNSPD Calibrations

Andrew Muller and I have completed our calibrations for the new SNSPD system which utilizes a Yokogawa frame controller. The results can be seen in the first attached image. On the left side of the table we list the numbers achieved on the older system and on the right the Yokogawa. These values include Dark Count (DC), Theoretical or computed number of expected photons/second, maximum and minimum achieved photon rate (as a percentage of theoretical rate), as well as the applied bias voltage on the SNSPD. The results for the dark count are varied between the two systems as the older unit had shielded fiber optic cables and the new system had not received this upgrade yet thus we saw an increase in dark counts by an order of magnitude. Both systems were given the same target rate of 100k photons/second and through calibrations made in python that are seen in the code "photonrate.py" and the newer "photonrate_yokogawa.py" a theoretical maximum photon rate (109k) was calculated based on the readouts on the power meter while cycling through each attenuator module to in order to account for differences or fiber loss. The code then automatically sets and attempts to achieve the desired rate. The efficiencies are then calculated by the resultant photon rate, with respect the the theorized rate, readout by the counter (seen as item 1 in the second image). Maximum and minimum values represent that of the highest and lowest achieved rates when adjusting the polarization of the optical fiber exiting from the laser which affects the rate readout on the counter (but not the power meter). Our results showed that the newer Yokogawa system was capable of achieving very similar and slightly higher efficiencies than the older unit which came in about roughly 72% and 71% respectively. The Thorlabs power meter is shown as item 2 in the second image, followed by the older attenuator and switch modules as item 3, and the new Yokogawa system, item 4. The Yokogawa frame controller has a number of compatible modules which include an in unit laser, power meter, switch and attenuators. The Yokogawa power meter seems to have a broad range of power input (larger than the Thorlabs meter) and more tests will be done to test its accuracy and limits. Code will be uploaded to git this Tuesday.