Demonstration of daytime CubeSat-to-ground laser communication in OOK modulation with a dual-mode superconducting nanowire single-photon detector

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Single-photon detectors have been adopted in deep space laser communication to improve the sensitivity of the ground receiver. For low-earth-orbit (LEO) laser communication, a ground receiver with upgraded sensitivity offers several advantages, such as reducing the ground telescope aperture size for mobile applications, giving a large tolerance for atmosphere attenuation, and reducing the power requirement for the transmitter in space. On-off keying (OOK) is one of the most common intensity modulations in the LEO laser communications, but is not suitable for conventional single-photon detectors which output photon counting clicks. In this paper, we demonstrate an LEO cube-satellite (CubeSat) to ground communication with a dual-mode superconducting nanowire single-photon detector (SNSPD) that can both operate at single-photon counting regime and quasi-linear mode under 50 Mbps OOK modulation. The CubeSat-to-ground results show that the SNSPD can work well both during the day and at night, and cope effectively with the large fluctuation of optical power in satellite-to-ground links and the significant variation of background photon noise in a day. The optical power corresponding to bit error ratio less than 10−3 is estimated in a separate experiment, which is -45 dBm for low dark counts at night, and -35 dBm for high background noise in the daytime (∼10 Mcps upper limit). This work demonstrates the feasibility of adopting the modified dual-mode SNSPDs in the OOK format satellite-to-ground laser communications both at night and in the day.