DP-QPSK for Optical Inter-Satellite Links in a Broadband Constellation Network

This paper presents a spectral efficient dual polarization quadrature phase shift keying (DP-QPSK) modulation format in an optical inter-satellite link (OISL). The model is simulated to operate in a low Earth orbit (LEO) satellite broadband constellation network. Its’ performance is analyzed and compared to the QPSK and the non-return to zero (NRZ) intensity modulation format for ISL distances of 1000 km to 6000 km. At a bit rate of 20 Gbps, the DP-QPSK and QPSK are observed to require a minimum transmitter laser power of 27 dBm at the maximum LEO OISL distance of 6000 km whereas the NRZ requires 37 dBm. The DP-QPSK is further observed to be the more spectral efficient modulation format of the three. Keeping to a bit-error rate (BER) of 10-9 and at a constant transmitter power of 30 dBm, the DP-QPSK and QPSK sustains the maximum LEO OISL distance whilst the NRZ supports a link distance of 2400 km. The modelled DP-QPSK system is then simulated for a bit rate of 40 Gbps. The system is observed to double the capacity of the QPSK at a constant symbol rate of 10 Gbaud.