Phase-resolved & polarization-resolved near-field scanning optical microscopy (NSOM), which has nanoscale resolving capability, is a powerful tool for studying intriguing phenomena in micro/nano-photonic devices on a chip. However, the full power of this technique is hindered by two major issues: 1) how to significantly eliminate the phase drift caused by environment fluctuations (such as temperature and stress), and 2) how to expand the characterization area outside a single scanning field (~100μm) without losses of accuracy and flexibility. Additionally, with the employment of fiber optics in its setup, the resultant vulgarization has made NSOM very close to convenient usages, namely implementation outside lab. Therefore, it will be greatly expected to solve the above two problems in an all-fiber NSOM.

By using a common path interferometer in a reflection-based scattering-NSOM, we can passively eliminate the phase drift accumulated in a fiber circuit. The remainder phase drift from the measurement stage can also be actively compensated by feedback loops. In this way, we have chances to realize ultra-stable phase-resolving (by 1-2 orders of magnitude) over ultra-long operation time (e.g. over-night).

On the other hand, by exploiting the frequency resource in a narrow-linewidth tunable laser, we can combine the optical frequency domain reflectometer technique and NSOM to carry out measurements across two points outside a single scanning field. A flexible and accurate calibration of the distance of arbitrary two points is very useful in investigating large-scale (e.g. mm or cm) photonic integrated circuits. And the frequency-sweeping method has one remarkable advantage over spatially-tracing approaches with the convenience in measuring those distributed quantities, such as propagation loss and dispersion.

Generally, after overcoming aforementioned two technique challenges, we should be able to endow NSOM a very useful feature, say “accuracy & extendable”, therefore fully liberating its potential in study of novel and complex nano-photonic devices on a chip, such as the ones having topological and multi-mode functionalities.

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振幅/相位/偏振可表征的近场光学显微镜（NSOM）具有十纳米量级的空间分辨能力，是精确研究片上微纳光子器件各种新奇效应的重要工具。不过，要想彻底释放出这项技术的全部潜力还需要解决如下两方面的问题。首先，我们需要显著降低环境扰动（温度、振动）造成的相位漂移噪声，大大延长系统的可操作时间；其次，我们要让探针的表征区域可以灵活跨越单个扫描场（~100μm），而不丢失测量的准确性。此外，一套全光纤化的光路可以大大提高NSOM技术的便利性，可以推动该技术的普及化（现场）应用。因此，在全光纤NSOM中克服上述两项困难将具有格外重要的意义，是一个非常值得探索的研究方向。

我们组开发的多款全光纤反射型NSOM具有共光路干涉仪的基础框架，可以有效消除环境在光纤链路中产生的相位漂移。同时，我们对样品测试台上扫描探针与基底相对滑移造成的相位漂移也进行了主动反馈补偿。利用这些相位补偿技术，我们希望在极长的操作时间（over-night）内可以实现极稳定的近场信息记录（相位漂移速度<0.001º/s，比现有记录提高1-2个数量级）。

另一方面，将光频域反射测量（OFDR）技术与NSOM结合起来，我们可以利用窄线宽激光器的频谱扫描能力，快速的对单个NSOM扫描场外的两个点进行精确的距离测量，可以在不同的测量点上进行各种物理量（损耗、色散等）的分布式（原位）表征。这为研究毫米/厘米规模的片上集成光子回路提供了独有的光学观测能力。我们采用的频域扫描测量方法（基于精确的相位分辨能力）与传统的实空间扫描测量方法相比，更加快速，而且不受测量样品的光子回路形状和摆放姿态等实际因素的影响。

总之，在克服上述两个困难之后，我们将赋予NSOM技术“高精确性+可扩展性”(small & scalable)的独特性能。我们的测量系统将在研究具有高空间复杂度的“拓扑”和“多模复用”片上光子器件中发挥独特的纳米光学表征能力。