High-Precision Miniaturized Demonstration System for Inter-Satellite Laser Interferometric Ranging

Objective A laser ranging interferometer is the core payload of the next-generation twin satellites of the earth gravitational detection and the mission of space-based gravitational wave detection. It is demanding to meet the requirement of the nanometer-level precision in the inter-satellite displacement measurement. For testing the key components and technologies on ground such as the ultra-stable optical bench, the flight phase meter, and the data post-processing algorithm, it is of high value to set up a high-precision miniaturized demonstration system for the development of a laser ranging interferometer. Methods The demonstration system is a prototype of the laser interferometer based on the phase-locking transponder scheme (Fig. 1). There are two solid-state lasers with the kHz linewidth in the system of polarization maintaining fibers, wherein one laser tracks another one in phase by the servo controller. The offset frequency is 10 MHz from the ultra-stable oscillator. PD1 and PD2 correspond to the detectors in the master satellite and the slave counterpart, respectively. The beating signals from the two detectors are sampled by the rate of 58 MHz and processed in the digital phase-locking loop after the open-loop capture, and the bandwidth of the digital filter is decreased to 1 Hz step by step. The test modules in the system can be the optical benches for evaluating the performance of the benches or the inter-satellite simulators for evaluating the dynamical adaptability of detectors and phase meters. Results and Discussions The miniaturized laser interferometer is set up based on the phase-locking transponder scheme. The linear spectral density of the measurement noise is 0.17 nm/Hz(1/2) at 0.1 Hz (Fig. 2) without inserting any test module, which is far below the ten-nanometer level of the noise requirement in the next-generation earth gravitational detection mission. In addition, the feasibility is demonstrated in the approach of data post-processing to suppress the optical phase-locking noise, and hence the system noise is decreased to 0.11 nm/Hz(1/2) (Fig. 3). Conclusions In this study, the miniaturized demonstration system shows the performance of the low noise background. By inserting specific test modules, it can be utilized to test and evaluate the key technologies towards the next-generation earth gravitational detection mission, such as the noise performance of an ultra-stable optical bench, the dynamical adaptability of the detector and the phase meter, and the data post-processing algorithm for the suppression of the optical phase locking. Therefore, the high-precision miniaturized demonstration system is a powerful tool in the future research of the space-based laser ranging interferometer.