Fig. 5: Sensitivity of advanced modulation formats in the 53 km FSO link.
From: Tbit/s line-rate satellite feeder links enabled by coherent modulation and full-adaptive optics
Bit-error ratio (BER) as a function of a ROP and b photon-per-bit (PPB) for polarization-multiplexed QAM modulation format at symbol-rates of 25 GBd. The 4D modulation formats PS-QSPK and 4D-BPSK are also investigated. We find that they need the lowest number of PPB for a given BER. This is in agreement with the theory (see Supplementary material). BER versus ROP at fixed line rates in the order of c 13.3 Gbit/s/λ and d 100 Gbit/s/λsee Methods section). 4D-BPSK shows to be the most power-efficient modulation format, with measured sensitivity advantage of 0.7 dB and 1.4 dB over PS-QPSK and PM 4QAM respectively at a BER of 1 ∙ 10−3. In combination with a low-noise amplifier optical coherent Rx front-end, it is capable to transmit at ROP as low as −51.3 dBm and −41.2 dBm respectively, only 1.4 dB from the ideal shot noise limit
