No abstract

In the current space gravitational wave (GW) detection, satellites are separated by millions of kilometers. As a result, watts of laser from one satellite is attenuated to the picowatt level at the other end due to the Gaussian beam divergence and the finite aperture of the telescope. Establishing an effective interferometry with such weak-light is a major challenge. The key is to enhance the weak-light while preserving its phase information, which carries the actual GW signal. This can be accomplished by employing an optical phase-locked loop (PLL) to lock the phase of a local oscillator (LO) laser to the weak-light and then sending the power-amplified LO back to the interferometer on the other satellite. Although shot-noise-limited performance of the picowatt level weak-light PLL has been achieved for high frequencies, it remains elusive for frequencies below 0.1 Hz. Here, we propose a three-step experimental scheme to identify the main noise sources of the weak-light PLL, which turn out to be the low-frequency phase measurement noise, the weak-light shot noise, and the laser phase noise. In this paper, the first step experiment result shows that the out-loop phase noise can be suppressed to a level less than 6 × 10−6 rad/√Hz from 6 mHz to 1 Hz by first using the special pilot-tone technique in the PLL to directly reduce the sampling time jitter noise in the digital phasemeter. The out-loop phase noise is mainly limited by the signal amplitude variation and differential time jitter noise of the reference clock.

No abstract

For the application of a digital array signal processing system with a high sampling rate and large bandwidth, and considering the constraints of limited resources (performance, volume, power consumption, weight, etc.), this paper proposes a design and implementation method of broadband digital array signal processing system based on radio frequency system on a chip. The system focuses on multi-channel synchronization under a high sampling rate and multi-channel amplitude and phase calibration under large bandwidth to form an all-digital, low-power, multi-channel, high-speed, large bandwidth hardware platform suitable for broadband digital array signal processing. Through the implementation of the Multiple-Input Multiple-Output phased-array digital beamforming algorithm, the test conducted verifies that the system has superior signal processing performance of the broadband digital array.