超 精 密 嵌 入 式 光 纤 微 探 头 干 涉 测 量 技 术 与 仪 器(特 邀)

Significance Achieving accurate and high-speed measurement of dynamic motion remains a major technical challenge for both scientific research and industrial applications. Ultra^-precision laser interferometry, which utilizes the optical wavelength as an intrinsic metric, is established as the most precise method for displacement measurement. It plays a pivotal role in diverse applications such as the online monitoring of complex surfaces in high^-end equipment manufacturing, mirror displacement detection in gravitational wave observation, geophysical measurement in fundamental research, and nanometer^-scale stage positioning in precision lithography. However, traditional ultra^-precision laser interferometers rely on complex bulk^-optic mirror configurations, leading to a bulky overall structure that fails to meet the growing demand for measurement in limited spaces. To overcome these limitations, the fiber^-optic microprobe interferometer (FMI) has emerged as a highly promising solution, offering unparalleled flexibility and an ultra^-compact structure. Despite these significant advantages, this technology still faces three core challenges: 1) signal undetectability, stemming from the lack of a comprehensive optical^-field propagation model for fiber^-optic microprobes; 2) measurement inaccuracy, caused by the severe degradation or loss of frequency lock in laser frequency stabilization during dynamic modulation; 3) precision limitations, resulting from the failure of error compensation mechanisms when complex nonlinear characteristics deviate from standard elliptical trajectories. Consequently, a systematic review of the solutions to these bottlenecks, along with a summary of the current research status of fiber^-optic microprobe interferometry, will provide crucial theoretical and technical references for researchers in the field of laser metrology. Progress To comprehensively discuss fiber^-optic microprobe interferometry, the core content of this review is organized into three main aspects. 1) Principles of fiber^-optic microprobe interferometry. We systematically introduce the operational principles of the FMI. The core configuration of the FMI is divided into three functional units: the microprobe sensing unit, the tunable laser frequency stabilization unit, and the high-precision signal demodulation unit. In addition, the primary factors influencing measurement speed and range are thoroughly analyzed, establishing that the laser modulation frequency f and the object motion frequency f_s must satisfy f ≥ 2f_s to avoid spectral aliasing. Finally, a comprehensive comparison with conventional homodyne and heterodyne interferometry is presented to highlight the FMI's unique characteristics. 2) Research status of FMI technologies. This section reviews the state^-of^-the^-art developments across three key technical dimensions. First, regarding fiber^-optic micro^-sensors, we review the development of sensors based on Michelson and Fabry-Perot (F-P) interferometric principles. F-P cavity microprobes are inherently compact, yet their measurement range is typically limited to the micrometer level due to fiber beam divergence. To address this, structural enhancements (e.g., tapered fiber ends, GRIN lenses, and folded F-P cavities) have been developed to extend the detectable range to the millimeter or even hundred^-millimeter scale. In parallel, Michelson microprobes employ micro^-prisms to mitigate high^-order intrinsic errors. Second, concerning high-precision laser frequency stabilization under tuning conditions, we analyze the influence of frequency stability on displacement accuracy. For semiconductor lasers, active stabilization methods lock the laser frequency to an external high-stability reference (such as molecular absorption lines, F-P cavities, or optical combs) to achieve superior precision compared with passive methods. To address the requirements for rapid, wide^-range tuning in FMIs, our team employed a stabilization method based on the linear absorption spectrum of acetylene molecules. The utilized DFB laser demonstrated a relative expanded uncertainty better than 5×10⁻⁸ (k = 2) within 3 h. Third, regarding high-precision displacement demodulation methods, we review the relationship between the phase modulation depth (PMD) and the measurement range. To prevent SINAD degradation, the PMD must be precisely locked at 2.63 rad, where the first^- and secondorder Bessel functions of the first kind are equal (i.e., J₁(C) = J₂(C). We discuss typical PMD control schemes, analyze the mechanisms underlying periodic nonlinear errors, and summarize existing error suppression techniques. Furthermore, an adaptive PGC method and a two-stage fusion method for nonlinear error elimination developed by our team are introduced. 3) Instrument integration and applications. We systematically introduce the instrumentation integration and practical applications of the FMI. The achievements of our team in instrument integration are summarized. Specifically, key challenges in achieving nanometer precision over large measurement ranges and eliminating nonlinear errors have been successfully addressed. Furthermore, a series of FMI products has been developed. The minimum dimensions of the microprobes have been reduced to ∅3.4 mm×20 mm, and a resolution of 0.1 nm has been achieved. The practical applications of these instruments include the measurement of lowreflectivity objects, large^-range linear displacement tracking, and testing within vacuum environments. Conclusions and Prospects Fiber^-optic microprobe laser interferometers represent a highly promising next-generation technology, characterized by transformative advantages over traditional systems, including ultra^-miniaturization, thermal isolation, and embedded measurement capabilities. These instruments have been successfully applied in aerospace component stress and vibration testing, as well as material deformation measurement and other fields. Additionally, as reported in Nature, the first observation of phonon quadrupole topological insulators was facilitated by these devices. To provide benchmark^-level embedded metrology for high^-end equipment, future research must be strictly focused on scientific breakthroughs regarding measurement range and measurement speed.