Xiaoyang Lei

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.

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.

Optical carrier-suppressed single sideband (OCSSSB) signals are known for their easy detection, low noise, and high energy efficiency. Here, we develop a high-performance OCSSSB signal generation system utilizing an integrated TFLN inphase/quadrature (IQ) modulator, along with an automatic bias control (ABC) module. Our device can achieve a side-mode suppression ratio (SMSR) surpassed 20 dB, optimally reaching up to 29.53 dB, which covers a large electrical-optic bandwidth and central wavelength range. For long-term stability, the peak–to– peak fluctuation of SMSR was measured to be 1.79 dB, with an average SMSR value of 23.47 dB for nearly 8 hours. Furthermore, we successfully demonstrate that our device can be implemented in a frequency-modulated continuous-wave (FMCW) ranging detection, allowing the standard deviation no more than ±2.60 mm. Our system offers substantial potential for direct application in various chip-scale integrated fields, including LIDAR and microwave photonics.

Grating interferometers highly valued for high resolution, straightforward benchmark and insensitivity to environmental disturbances, have become one of the most mainstream methods for ultra-precision positioning. Traditional heterodyne grating interferometers which use a dual-frequency orthogonally polarized laser source suffer nanometer-level periodic nonlinear error due to frequency and polarization mixing, thus becoming incompetent to undertake sub-nanometer measurement. Based on the design of two separated laser beams with a small frequency difference for heterodyne beating, a wavelength-stabilized and quasi-common-path heterodyne grating interferometer is proposed. It incorporates a symmetrical oblique incidence structure where the residual dead path is calibrated and the laser source wavelength is stabilized to the rubidium atomic transition line, diminishing heterodyne phase errors resulted from the optical path difference. This approach not only significantly mitigates periodic nonlinear error to below 0.3 nm, but also enhances measurement resolution, repeatability and interference robustness. The proposed heterodyne grating interferometer is determined for ultra-precision positioning serving for precision machinery manufacturing and scanning beam interference lithography and so forth.