Near-field scanning optical microscopy (NSOM), with nanoscale spatial resolution, is a powerful tool for studying intriguing phenomena in micro/nano-photonic devices on a chip. However, the full potential of this technique is hindered by two main challenges: first, how to significantly eliminate phase drift caused by environmental fluctuations (such as temperature and vibrations), and second, how to expand the characterization area beyond a single scanning field (~100μm) without losing accuracy and flexibility. Furthermore, the integration of fiber-optic-based systems has greatly enhanced the practicality of NSOM, making it more accessible for broader use. Therefore, solving these two problems, particularly in all-fiber NSOM systems, is of great significance and a promising research direction.

Our research group has developed several all-fiber reflection-based NSOM systems using a common-path interferometer, which effectively eliminates phase drift accumulated in fiber transmission lines. Additionally, we have implemented active feedback compensation for phase drift caused by the relative sliding of the scanning probe and the substrate on the sample stage. With these compensation techniques, we aim to achieve stable near-field data acquisition over long periods (e.g., overnight), with a phase drift rate of <0.001º/s, improving upon existing records by 1-2 orders of magnitude.

On the other hand, by combining optical frequency domain reflectometry (OFDR) with NSOM, and utilizing the spectral scanning capability of narrow-linewidth lasers, we can quickly and accurately measure the distance between two points outside a single scanning field. This enables distributed (in situ) characterization of various physical quantities (such as loss, dispersion, etc.) at different measurement points. This provides unique optical characterization capabilities for studying photonic integrated circuits at the millimeter or centimeter scale. Compared to traditional real-space scanning methods, the frequency-domain scanning technique (based on precise phase resolution) is faster and not affected by the shape and positioning of the photonic circuits on the sample.

After overcoming these two technical challenges, we will endow NSOM with the essential features of high precision and scalability, unlocking its full potential in studying novel and complex nano-photonic devices with high spatial complexity, such as those exhibiting topological and multi-mode functionalities. This will pave the way for new directions in the experimental characterization of nano-photonics.

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近场光学显微镜（NSOM）具有纳米级空间分辨能力，能够精确研究片上微纳光子器件中的各种新奇效应。然而，要充分发挥这项技术的潜力，还需要解决两个主要问题：首先，如何显著消除由环境波动（如温度变化和振动）引起的相位漂移；其次，如何扩展纳米探针的表征区域，使其能够灵活跨越单个扫描场（约100μm）而不失精度和灵活性。此外，采用全光纤化设备的光学系统大大提高了NSOM技术的操作便利性，可以极大推动这项技术的广泛应用。因此，解决上述两个问题，尤其是在全光纤NSOM中，将具有重要的意义，是一个值得深入探索的研究方向。

我们课题组开发的多款全光纤反射型NSOM，采用共光路干涉仪基础架构，有效消除了光纤传输线路中相位漂移的影响。同时，我们还通过主动反馈补偿技术，消除了样品测试台上扫描探针与基底之间相对滑移所带来的相位漂移。基于这些补偿技术，我们期望在极长的操作时间（例如过夜）内实现稳定的近场信息记录（相位漂移速度<0.001º/s，比现有技术提高了1-2个数量级）。

另一方面，通过将光频域反射测量（OFDR）技术与NSOM结合，利用窄线宽激光器的频谱扫描能力，我们能够快速、准确地对单个扫描场外的两个点进行距离测量，从而实现对不同测量点的物理量（如损耗、色散等）的分布式（原位）表征。这为研究毫米至厘米尺度的片上集成光子回路提供了独特的光学表征能力。与传统的实空间扫描方法相比，我们采用的频域扫描测量方法（基于精确的相位分辨能力）不仅速度更快，而且不受样品光子回路形状和摆放姿态等因素的影响。

在克服上述两个技术难题后，我们将赋予NSOM技术“高精度与可扩展性”这一重要特性，全面释放其在研究具有高空间复杂度的“拓扑”与“多模复用”片上光子器件中的潜力，从而开辟纳米光子学实验表征的新方向。