Figure 1
From: Experimental filtering effect on the daylight operation of a free-space quantum key distribution
Experimental setup for measuring the effect of filtering techniques on the daylight operation of a free-space QKD system. The optical parts of the transmitter comprise four laser diodes, a silica-based polarization module, neutral density filters, a telescope, and components for signal synchronization. Real-time data processing was performed with an field-programmable gate array (FPGA) based system. In the receiver, a four-channel single-photon detector (SPD) was installed with a polarization-decoding module for the BB84 protocol. Additional optics for polarization control and filtering systems were used. Both transmitter and receiver were installed above gimbal systems, which allow elevation and azimuth control for beam alignment. FPGA, field programmable gate array; LD, laser diode; Sync. LD, synchronization laser diode; Sync. PD, synchronization photodiode; SPD, single-photon detector; DM, dichroic mirror; HWP, half-wave plate; ND filter, neutral density filter; PBS, polarization beam splitter; BS, beam splitter.
