Scontel has developed and characterized a new type of single-photon receiver, which can operate at wavelengths up to 2.5
microns.
System characteristics:
Spectral range: up to 2.5 µm
QE at 2 µm: >5 %
Timing jitter: ≤ 50 ps
Dark counts rate: ≤ 700 cps
Dead time: ≤ 20 ns
No afterpulsing
Fiber coupling (no misalignment)
Operation in a continuous mode
The first graph presents two spectral dependencies of quantum efficiency for the selected SSPD coupled with
SM2000 fiber (See below).
The lower curve (blue) corresponds to the case when we apply standard fiber cold filter. Here you can see that the
quantum efficiency very sharply decreases with wavelength increasing
The second curve (red) corresponds to the case without any cold filter. Here decline of spectral dependence of
quantum efficiency is much more flat that allows to obtain quantum efficiency about 1% up to a wavelength of 2.3
micrometers.
However, the absence of cold filter increases dark counts level.
See the second graph. Here are the dependencies of the quantum efficiency of SSPD vs. bias current and two
dependencies of dark counts (in case of presence cold filter and without it)
The spectral dependencies shown on first graph was measured at 25 microamps bias current whith corresponds
approximately 700 cps of false counts for "no filter" and below 10 cps for "filter"
As shown on the second graph slope of dependencies increase at wavelength increasing.
Thus, we have created and characterized a new type of single-photon detector system which allows to have singlephoton response at wavelengths up to 2.5 microns
The task of lowering the level of dark counts currently seems to be insolubile at the moment.
However, under some conditions of using this system level of dark counts can be significantly reduce and for my
opinion possible to reach dark counts level almost as for corresponds case of filter application. This could be achieved
if the light source location will be at cold conditions. For example, it may be quantum dot emitted photons with
wavelength in the range of 2-2,5 microns and located at a low temperature (4.2 K, or at least 77).