To improve the data rate in laser communication systems, a new modulation scheme, which uses the photon polarisation property, is proposed. Performance analysis and Monte-Carlo simulation are made, considering both non-turbulent and heavy-turbulent atmospheric conditions. The simulation results show that the data rate is twice as much as that of pulse-position modulation in a broad range of optical link efficiency.Introduction: Optical communication technology is under rapid development in many fields, especially in inter-satellite and deep-space communications [1]. However, the limited transmitting power and the energy attenuation between two remote sides make the received laser power very weak. The avalanche photodiode (APD) as the receiver can largely improve the optical link efficiency. Pulse-position modulation (PPM) can further raise the power usage, but it would reduce the data rate [2,3]. Motivated by this background, we present a new communication system, which utilises the photon polarisation property to improve the achievable data rate. We analyse the capacity performance of the scheme, with photon counts modelled as a Poisson distribution and the impact of scintillations described by an exponential function for heavy turbulence [4]. The simulation results verify the feasibility of optical communication of higher data rate than that of PPM in turbulent conditions.