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.
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。