Long-term mutual coherence is a key factor that affects the signal-to-noise ratio and resolution of a dual-comb interferometer. To realize a phase-stable dual-comb interferometer configuration, tightly phase-locked loop systems or digital error correction methods with external optical reference are commonly used. This paper presents a self-referencing digital error correction method based on the short-term spectral characteristics of interferograms to reduce the cost and complexity of the phase-stable dual-comb interferometer configuration. In our experiment, fully mutual coherence of a dual-comb interferometer is reconstructed and 1 Hz theoretical linewidth in 1 s acquisition time is achieved by digitally compensating for time jitter, center frequency jitter, and carrier-envelope-phase jitter, offering an effective technique for advanced dual-comb applications.

In this paper, a novel optical encoder enabling the simultaneous measurement of displacement and the position of precision stages is presented. The encoder is composed of an improved single-track scale grating and a compact two-probe reading head. In the scale grating, multiple reference codes are physically superimposed onto the incremental grooves, in contrast to conventional designs, where an additional track is necessary. The distribution of the reference codes follows a specific mathematical algorithm. For the reading head, a two-probe structure is designed to identify the discrete reference codes by means of the superimposition of the codes with a stationary mask and to read the continuous incremental grooves by means of a grating interferometry, respectively. A prototype encoder was designed, constructed and evaluated, and experimental results show that the distance code precision achieved is 0.5 μm, while the linearity error of the linear displacement measurement is less than 0.06%.

Dual-comb system parameters have significant impacts on the ranging accuracy. We present a theoretical model and a numerical simulation method for the parameter optimization of a dual-comb ranging system. With this method we investigate the impacts of repetition rate difference, repetition rate, and carrier-envelope-offset frequency on the ranging accuracy. Firstly, the simulation results suggest a series of discrete zones of repetition rate difference in an optimal range, which are consistent with the experimental results. Secondly, the simulation results of the repetition rate indicate that a higher repetition rate is very favorable to improve the ranging accuracy. Finally, the simulation results suggest a series of discrete optimal ranges of the carrier-envelope-offset frequency for the dual-comb system. The simulated results were verified by our experiments.

Chromatic confocal technology (CCT) is one of the most promising methods for the contactless and accurate measurement of structure profiles. Based on the principles of chromatic dispersion and confocal theory, a dispersion probe is proposed and optimized with several commercial and cheap refractive index lenses. The probe provides 0.3× magnification and a dispersion range of 400 μm with a commercial LED source with an effective bandwidth of ca. 450–623 nm. Since the noise fluctuation can affect the extraction stability of the focal wavelength, a modification to the centroid peak extraction algorithm is proposed in this paper, where several virtual pixels are interpolated among the real pixels of the spectrometer before thresholding. In addition, a series of experiments were carried out to test the system’s displacement measurement performance. The results clearly show that stability is improved by the modified algorithm, and the calibration repeatability is ±0.3 μm in the full measurement range with a linear stage. The standard deviation at the fixed position has an optimal value of 0.009 μm. The section profile of a Fresnel lens is measured by the CCT system to demonstrate its high feasibility and efficiency.

Periodic microscale array structures play an important role in diverse applications involving photonic crystals and diffraction gratings. A polarized holographic lithography system is proposed for patterning high-uniformity microscale two-dimensional crossed-grating structures with periodic tunability. Orthogonal two-axis Lloyd’s mirror interference and polarization modulation produce three sub-beams, enabling the formation of two-dimensional crossed-grating patterns with wavelength-comparable periods by a single exposure. The two-dimensional-pattern period can also be flexibly tuned by adjusting the interferometer spatial positioning. Polarization states of three sub-beams, defining the uniformity of the interference fringes, are modulated at their initial-polarization states based on a strict full polarization tracing model in a three-dimensional space. A polarization modulation model is established considering two conditions of eliminating the unexpected interference and providing the desired identical interference intensities. The proposed system is a promising approach for fabricating high-uniformity two-dimensional crossed gratings with a relatively large grating period range of 500–1500 nm. Moreover, our rapid and stable approach for patterning period-tunable two-dimensional-array microstructures with high uniformity could be applicable to other multibeam interference lithography techniques.

Snapshot spectral imaging technology enables the capture of complete spectral information of objects in an extremely short period of time, offering wide‐ranging applications in fields requiring dynamic observations such as environmental monitoring, medical diagnostics, and industrial inspection. In the past decades, snapshot spectral imaging has made remarkable breakthroughs with the emergence of new computational theories and optical components. From the early days of using various spatial‐spectral data mapping methods, they have evolved to later attempts to encode various dimensions of light, such as amplitude, phase, and wavelength, and then computationally reconstruct them. This review focuses on a systematic presentation of the system architecture and mathematical modeling of these snapshot spectral imaging techniques. In addition, the introduction of metasurfaces expands the modulation of spatial‐spectral data and brings advantages such as system size reduction, which has become a research hotspot in recent years and is regarded as the key to the next‐generation snapshot spectral imaging techniques. This paper provides a systematic overview of the applications of metasurfaces in snapshot spectral imaging and provides an outlook on future directions and research priorities.