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L o g i c 1 6 U s e r M a n u a l
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3.3
Device Features
3.3.1
Active Edge and Threshold Detection
A detection event occurs when the active edge of an input signal reaches the user-defined threshold
voltage. The threshold level and the active edge (rising or falling) can be adjusted for each input,
individually. Logic16 uses detection events to determine when to tag time or take a count.
3.3.2
Time Tagger Mode
In this mode, Logic16 outputs a time tag when a detection event occurs on an input channel. This feature
is useful in time correlated single photon counting especially where absolute time tags are required. This
mode can be used for g2 (cross and auto correlation measurements), timing histograms, time of arrival/
time of flight, also for coincidence counting post processing. This mode could be applied in quantum
communication, quantum cryptology, quantum key distribution (QKD) as well as LiDAR and other time
correlation experiments.
Time is stored in the device as multiples of its internal timing resolution 156.25 ps or 78.125 ps for
Configuration A or B, respectively. Note that in Logic16 there is no designated “start” channel - the
reference time is that of the first tag, regardless of which input it was detected on. In other words, the
first signal detected will be recorded as occurring at time = 0.
In Time Tagger Mode, Logic16 offers modifiable filtering and gating. Employing these features will improve
maximum event rate, which is the rate at which assigning time tags to detection events can occur. Data
transfer rate, the rate at which time tags can be sent across the USB interface, is limited to the USB
connection. As a result, maximum data transfer rate is always 11 MHz.
Table 3-I summarizes the use and rates of relevant for each filtering option.
Max. event
rate
Max. data
transfer rate
Use when
…
(MHz, across all inputs)
Continuous 11
11
-
All time tags must be recorded
Time Tag
Filter
190
11
-
Pump or trigger rate > 10 MHz, but only relevant
TOF tags are needed (trigger and signal)
-
Measuring for long periods of time (e.g., days)
and only multi-photon events are needed
Edge Gate
190
11
-
Heralding events by a <= 10 MHz source
Level Gate
190
11
-
Adjustable gate open with specific times
