In the positioning and navigation field, it is essential to use the direction-finding system to obtain the signal direction of arrival (DOA) and target position. The amplitude comparison-based monopulse (ACM) DOA algorithm performs a few calculations, has a simple system structure, and is widely used. The traditional ACM DOA algorithm uses the first-order Taylor expansion to introduce the nonlinear errors, and the angle measurement range is limited. In response to this problem, this study establishes a neural network model for error compensation, and it optimizes the traditional algorithm to obtain a better angle estimation performance. In order to perform an experiment with the proposed algorithm, a novel experimental device was designed. Two measurements at different angles were obtained by rotating the antenna. The ACM angle estimation used only one directional antenna. The results verified the optimization algorithm. The experimental results demonstrated that in comparison with the traditional first-order and the improved third-order Taylor expansion ACM DOA algorithm, the mean absolute error of this method reduced by 81.62% and 72.62%, respectively.

High repetition rate dual-microcomb interferometry offers high-precision and fast acquisition, showing broad application prospects in rapid and precise ranging scenarios. In this study, a continuous-wave laser was coupled into two chip-based integrated silicon nitride microresonators to drive two dissipative Kerr soliton optical frequency combs. Their repetition rates, 24.96202 GHz and 24.96121 GHz, were locked to external reference RF sources. Using this dual-microcomb source, we conducted linear displacement experiments within a range of 150 millimeters, with residual errors less than 10 micrometers compared to a reference laser interferometer. In static measurements, the Allan deviation reached 1.6 nanometers at an averaging time of 40 milliseconds. Additionally, with an update rate exceeding 800 kHz, dynamic measurement capabilities were demonstrated by measuring the rapid rotating chopper. To the best of our knowledge, this study is the first to utilize a repetition-frequency-locked coherent dual-microcomb source for ranging experiments, significantly enhancing distance measurement accuracy to the nanometer level compared to free-running systems. The proposed system is of importance for future high-precision LiDAR and remote sensing applications based on dual microcombs, and holds potential in areas such as multi-satellite formation flying and microelectronic device manufacturing.

To solve the acquisition problem of the satellite-ground microwave link ranging of the China Space Station, iterative local search (ILS) is proposed. In this paper, an iterative-local-search-based acquisition strategy is presented, and a Doppler frequency and code phase transfer model is designed, which can accomplish acquisition by multiple rounds of two-dimensional search. The adaptability of the ILS improved traditional acquisition algorithm to a high dynamic and low signal-to-noise ratio (SNR) environment can be significantly improved without relying on prior information. For the classical parallel code phase acquisition algorithm, the performance of the ILS acquisition strategy was experimentally evaluated for high dynamic weak signals, and the results demonstrated the superiority of the proposed strategy. The computational complexity of the ILS improved parallel code phase acquisition algorithm was greatly reduced. The sensitivity of the parallel code phase acquisition algorithm improved by the ILS strategy to the acquisition of weak signals in a dynamic environment was significantly improved.

Soliton microcomb (SMC) arouses wide interest in high-precision distance measurement by virtue of its characteristics in high repetition rate and on-chip capability. However, the high repetition rate brings challenges to frequency locking and signal processing. In this study, we propose a microwave photonic mixing method to simplify the signal processing in SMC-based synthetic wavelength interferometry. In order to achieve this method and obtain the equivalent low-frequency signal, multi-order sidebands with the same frequency interval can be generated and subsequently mixed in the optical domain using an electro-optic modulator (EOM). The microwave photonic mixing method not only decreases the required modulation frequencies for injection locking and frequency-downshifting, but also enables the use of a low-bandwidth photodetector for detection. In the ranging demonstration, the residuals are less than 5 μm compared with a referenced laser interferometer (LI) over a 90 mm distance, and the stability test shows an Allan deviation of 868 nm at an average time of 10 s. It is believed that this microwave photonic mixing synthetic wavelength interferometry for SMC-based distance measurement showcases potential in LIDAR, micro-nano manufacturing, inter-satellite ranging, etc.

The high-repetition-rate dual-microcomb interferometry, characterized by its high precision, rapid measurement speed, and ease of integration, shows significant promise in applications such as precision spectroscopy and high-speed precision ranging. As dual-microcomb interferometry usually requires a specific difference in repetition rates, tuning the repetition rate of the microcomb is crucial for integrating dual-microcomb sources and enhancing the measurement performance, including the precision and the update rate. This work demonstrates a coherent dual-microcomb system driven by a single continuous-wave fiber laser at 1560.49 nm. The system employs a hybrid tuning method combing single-sideband (SSB) modulation for precision pump frequency control (enabling continuous repetition rate tuning across a 4.34 MHz range) with thermal control for coarse tuning. The linear dependence between the repetition rate and pump modulation frequency shows a measured coefficient of 143.58 kHz/GHz. This method enables dual microcombs with MHz-level repetition rate tuning, significantly relaxing the fabrication and pairing requirements for microresonators. The advancement is particularly valuable for dual-comb spectroscopy and ranging applications, including gas detection and satellite formation flying.