Absorption spectroscopy based on frequency-modulated continuous-wave (FMCW) technology is characterized by a wide measuring range, high detection sensitivity, and high sensing speed. These features enable sensing of multiple target points, and continuous real-time gas monitoring. In this article, an on-chip FMCW multichannel absorption spectrometer is designed for the simultaneous measurement of optical path and gas absorption spectra. The wide tuning range of FMCW facilitates the measurement of multiple absorption bands of gas molecules under test. Based on the characteristics of frequency division multiplexing, the gas absorption spectra corresponding to different points can be detected simultaneously. Frequency modulation nonlinearity is corrected by introducing an auxiliary interference optical path with a fixed delay of 4 m, and the dual-interference optical path of the system is integrated into a silicon chip. Three-way parallel sensing experiments are carried out to demonstrate the efficacy of the proposed spectrometer. The results show that the coherent average measurement accuracy of gas absorption peak wavelength is better than 0.002 nm, and the optical path measurement accuracy is better than 25 μm. The system offers several advantages such as excellent integrability, wide band operation, high precision and multichannel synchronous online measurement. Due to these features, this system has high practical value in the field of gas sensing.

Dissipative Kerr soliton (DKS) microcombs based on multi-mode Si3N4 waveguides turn into an ideal tool that is compact and has precision for optical communication, precision spectroscopy, and frequency metrology. However, spatial waveguide mode interaction leads to local disturbances of dispersion, which may hinder DKS microcombs formation. In this letter, we generate the DKS microcomb in a dual-mode interaction Si3N4 microresonator without suppressing spatial waveguide mode interaction. The spatial waveguide mode interaction is investigated in the dual-mode interaction Si3N4 microresonator with a cross-sectional area of 800 × 1700 nm2. DKS microcomb is deterministically generated in the microresonator using an auxiliary light heating method. Furthermore, an integrated microcomb frequency measurement system is designed based on the DKS microcomb for frequency metrology.

Since the dispersive interferometry (DPI) based on optical frequency combs (OFCs) was proposed, it has been widely used in absolute distance measurements with long-distance and high precision. However, it has a serious problem for the traditional DPI based on the mode-locked OFC. The error of measurements caused by using the fast Fourier transform (FFT) algorithm to process signals cannot be overcome, which is due to the non-uniform sampling intervals in the frequency domain of spectrometers. Therefore, in this paper, we propose a new mathematical model with a simple form of OFC to simulate and analyze various properties of the OFC and the principle of DPI. Moreover, we carry out an experimental verification, in which we adopt the Lomb–Scargle algorithm to improve the accuracy of measurements of DPI. The results show that the Lomb–Scargle algorithm can effectively reduce the error caused by the resolution, and the error of absolute distance measurement is less than 12 μm in the distance of 70 m based on the mode-locked OFC.

There is an increasing demand for high-precision gas absorption spectroscopy in basic research and industrial applications, such as gas tracking and leak warning. In this Letter, a novel, to the best of our knowledge, high-precision and real-time gas detection method is proposed. A femtosecond optical frequency comb is used as the light source, and a broadening pulse containing a range of oscillation frequencies is formed after passing through a dispersive element and a Mach–Zehnder interferometer. Four absorption lines of H¹³C¹⁴N gas cells are measured at five different concentrations within a single pulse period. A single scan detection time of only 5 ns is obtained along with a coherence averaging accuracy of 0.0055 nm. High-precision and ultrafast detection of the gas absorption spectrum is accomplished while overcoming complexities related to the acquisition system and light source that are encountered in existing methods.

Precise absolute distance measurements are crucial in both scientific and industrial fields. Among various techniques, dual-comb ranging stands out due to its high precision and fast acquisition rate. However, the inherent periodicity of the comb pulse train leads to the limited non-ambiguity range (NAR) and periodic measurement dead zones, thereby impeding its practical applications. Here, we propose and demonstrate an arbitrary absolute distance measurement system utilizing dual repetition rate parallel linear asynchronous optical sampling. Based on the broad spectrum of optical frequency combs and wavelength division multiplexing technology, two sets of pulse trains with different wavelength ranges and repetition rates are used as signal pulses for simultaneous distance measurement. This approach straightforwardly extends the NAR to tens of kilometers by leveraging the Vernier effect. Additionally, incorporating a variable optical delay line in the reference path eliminates the measurement dead zones, thus enabling continuous measurements. Experimental results demonstrate that our proposed ranging system exhibits an Allan deviation of approximately 0.32 μm at an averaging time of 440 ms. Compared to commercial interferometers, the ranging accuracy is better than 3.8 μm for a target mirror positioned about 7 m away. Overall, the proposed system provides a compact, fast, high-precision, and dead-zone-free long-distance ranging solution with significant practical value for various precision engineering applications.