Unbalanced Optical Modulation for Satellite Laser Links

Intersatellite and ground-to-satellite laser links are stepping into the new era with increasing demands for ranging and communication. It is a strong demand to flexibly allocate the link power for the two functions in free-space applications. To our best knowledge, unbalanced modulation for ranging and communication has not been reported in the field of optics, while the corresponding technology has been widely applied in a variety of satellite microwave links. In this work, we propose a scheme of unbalanced dual binary phase shift keying (UD-BPSK) in which the optical carrier is modulated by the mixed signal composed of the high-power communication baseband and the low-power ranging baseband. The power allocation for the two functions can be adjusted by setting the baseband power ratio. The traditional modulator for laser communication is theoretically and experimentally demonstrated in the scheme of UD-BPSK, and the picosecond level of precision is verified under the condition that the ranging signal only consumes 1% of the total power. Furthermore, dual one-way ranging is performed and the result shows the stability of 5 × 10 –17/day for the time-frequency transfer, meeting the synchronization demand of state-of-the-art microwave clocks in orbit. The scheme of UD-BPSK opens a gate to the multifunctional laser link with different baseband signals modulating on the unified carrier for specific functions in the future.