In the rapidly changing moisture air, conventional relative humidity (RH) sensors are often difficult to respond in time and accurately due to the limitation of flow rate and non-uniform airflow distribution. In this study, we numerically demonstrate that humidity changes on micro-zones can be monitored in real time using a Bloch surface wave (BSW) ubiquitous in one-dimensional photonic crystals (1DPC). This phenomenon can be observed by leakage radiation microscope (LRM). After theoretically deriving the angular resolution limit of LRM, we obtained the minimum BSW angular change on a practical scheme that can be observed in the momentum space to complete the detection, and realized the dynamic real-time monitoring of small-scale humidity change in experiment for the first time. This monitoring method has extremely high figure of merit (FOM) without hysteresis, which can be used in humidity sensing and refractive index sensing as well as the research on turbulence.

Full Poincaré (FP) beams that present all possible states of fully polarized light across their transverse section have received great attention in recent years. However, compared with huge successful design in coherent case, attempts in partial coherent case seem to encounter considerable challenges. It is generally believed that the difficulty of polarization change upon propagation induced by correlation seems inevitable. With the help of a new degree of freedom–twist phase, the correlation-induced polarization change is successfully eliminated. A new class of propagation-invariant twisted partially coherent FP beams are derived under specific parameter conditions to ensure complete polarization. Similar to coherent FP beams, all the polarization states of the beams are retained and covers the entire surface of the Poincaré sphere, and the propagation corresponds to a rigid rotation of the sphere. Besides, the twist phase can also be used to modulate the rigid rotation speed of the Poincaré sphere and the far-field beam spot size. The result paves the way for the design of FP beams and fully polarized vector beams in partially coherent domain and opens up new opportunities for applications such as scattering, polarization measurement, and optical sensing.

The skillful confinement of light brought by the composite waveguide structure has shown great possibilities in the development of photonic devices. It has greatly expanded the application range of an on-chip system in dark-field imaging and confined the laser when containing an active medium. Here we experimentally proved a stable directional emission in an active waveguide composed of metal and photonic crystal, which is almost completely unaffected by the external environment and different from the common local light field that is seriously affected by the structure. When the refractive index of samples on the surface layer changes, it can ensure the constant emission intensity of the internal mode, while still retaining the external environmental sensitivity of the surface mode. It can also be used for imaging and sensing as a functional slide. This research of chip-based directional emission is very promising for various applications including quantitative detection of biological imaging, coupled emission intensity sensing, portable imaging equipment, and tunable micro lasers.

Full Poincaré (FP) beams that present all possible states of fully polarized light across their transverse section have received great attention in recent years. However, compared with huge successful design in coherent case, attempts in partial coherent case seem to encounter considerable challenges. It is generally believed that the difficulty of polarization change upon propagation induced by correlation seems inevitable. With the help of a new degree of freedom–twist phase, the correlation-induced polarization change is successfully eliminated. A new class of propagation-invariant twisted partially coherent FP beams are derived under specific parameter conditions to ensure complete polarization. Similar to coherent FP beams, all the polarization states of the beams are retained and covers the entire surface of the Poincaré sphere, and the propagation corresponds to a rigid rotation of the sphere. Besides, the twist phase can also be used to modulate the rigid rotation speed of the Poincaré sphere and the far-field beam spot size. The result paves the way for the design of FP beams and fully polarized vector beams in partially coherent domain and opens up new opportunities for applications such as scattering, polarization measurement, and optical sensing.