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HgCdTe APD detector modules telecommunication are developed at CEA/Leti for atmospheric LIDAR and free space optical (FSO). The development is driven by the design and manufacture of generic sub-assemblies that can be adapted in each detector module to meet the specific detector requirements of each application. The optimization of such subassemblies is detailed in perspective of the challenges that are set by the specifications for detector modules currently developed for atmospheric LIDAR, in the scope of an R&T CNES project for Airbus and an H2020 project HOLDON, and FSO, in the scope of an ESA project and in collaboration with Mynaric Lasercom GmbH. Two detector modules have recently been delivered to Airbus DS for extensive LIDAR simulation tests. Initial characterization of these modules shows that the input noise, NEP=10-15fW/√Hz (5 photons rms) have been reduced by a factor three compared to previously developed large area detectors although the bandwidth have been increased to 180 MHz in order to respond to the requirements of high spatial depth resolution. The temporal remanence was 10 -4 at 200 ns after the detection of short light impulse, which is compatible with demanding LIDAR applications such as bathymetric profiling.

The characterization results and analysis from the detection of meso-photonic laser pulses, characterized by zero to tens of photons per pulse, using an inhouse developed detector module based on HgCdTe avalanche photodiodes (APDs) are reported. In this detector module, HgCdTe APDs is hybridized to a specifically developed Si CMOS amplifier circuit with a low input noise and high bandwidth of 400 MHz that is shown to be capable of detecting single photon events at APD gain in excess of 100. The use of a Si CMOS amplifier with a high bandwidth is crucial to detect pulsed signals at high rates. With the present detector, this has enabled to detect temporally distinguishable single photon events up to a record rate of 500 MHz on a single solid-state detector. The capacity of the detector to characterize mesoscopic light states was demonstrated on an input state of an average of l= 1.6 photons using a fitting procedure to extract the timing and amplitude of each pulse. This analog approach to analyze the detection of meso-photonic light is shown to be efficient to estimate the attenuated photon state and to calibrate detector characteristics such as the event detection efficiency (87%), the multiplication gain distribution and corresponding excess noise factor (F = 1.33) and the timing jitter distribution with a full width half maximum of FWHM= 277 ps.

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In the present communication, the characterization results of an in-house developed four-quadrants detection module based on HgCdTe APDs and a Si-CMOS ROIC pre-amplifier is discussed. The module has been designed to be employed as high data rate ground-segment detector for 1.55 μm long-distance free-space optical communication links in the framework of a project funded by the European Space Agency. The detector is characterized by a multiplication gain in excess of M = 150, a ROIC input referred noise of Ne = 45 electrons rms and a measured bandwidth of BW = 450 MHz. These characteristics enable the linear-mode detection of meso-photonic states ranging from tens of photons per pulse down to the single-photon level at high count rates exceeding 500 MHz per quadrant (and 2 GHz if the signal is dispatched over all four-quadrants). For the present module, the performance for PPM and OOK modulation formats was estimated and its potentiality for long-distance free-space optical communications employing these modulation formats was validated. In particular, for the PPM format, a detection probability of 0.9 and a false alarm probability of 10 -2 , a minimum PPM slot width of 500 ps and a temporal jitter with a FWHM ~ 160 ps were estimated, for an incident photonic state with 10 photons/pulse. The potentiality of the detector for 625 Mbps OOK modulation format was also evaluated and compared with a quantum limited situation. In this case, a -3.9 dB penalty from the quantum limited BER was obtained. A new generation of detectors is currently in development, which is expected to further improve the performance.

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