Microlenses and microlens arrays are one of the indispensable components in modern optical systems ranging from imaging and beam shaping to polarization control and switchable 2D/3D displays. Among them, the liquid crystal microlenses (LCMs) with size below 1 mm have attracted more and more attention due to their stimuli‐responsiveness and tunability in focal length and polarization. Compared with microlenses based on inorganic binary optics, diffractive optical elements, or metasurface, LCMs are more cost‐effective and can be easily tuned. In this paper, an in‐depth review of the design principles, fabrication techniques, emerging applications, and recent advances of LCMs and arrays is presented, aiming to clarify the characteristics, limitations, and challenges in LCMs design and fabrication. This review may provide directions for solving those challenges, and expand the applications of LCMs.

In this paper, a surface-enhanced Raman scattering (SERS) sensor with a giant field enhancement factor based on the coupling of surface plasmon polaritons (SPPs) is designed and studied theoretically. The proposed sensor adopts a metal-dielectric layered hybrid slot waveguide structure, combining thin metal (gold) layers and silicon nitride strip waveguides. Unlike other similar sensors, the silicon nitride waveguide structure does not serve as an excitation signal channel, conventionally loaded with the guided modes, but as an auxiliary layer, making it easier to concentrate the light field in the slot. Therefore, the sensor has a higher enhancement factor compared to the pure metal or dielectric slot structure. The results exhibit that we can obtain a maximum enhancement factor exceeding 10^6 under the compact configuration of 510 × 300 × 225nm^3 at the wavelength of 785 nm. By analyzing the dependence of the sensor performance on the structural parameters, we show that the structure of such sensor can directly be applied to SERS spectroscopic analysis as well as integrated with micro-and nano-photonic platform to perform on-chip detection system.

Threshold conditions to realize electric field enhancement and energy confinement in the low-refractive-index core of nanoscale waveguides are studied by solving the field function. When the incident lightwave meets the relation of special thresholds, we observe the enhanced electric field and a concentrated light energy in the core. The electric field enhancement and the confined light power are highly dependent on the light wavelength. When the core width is 30 nm, for a wavelength of 1.55 µm, we achieve a power confinement factor above 40%. As the basis for a growing number of potential applications, the threshold conditions discovered in this work will find significant applications in many fields, such as optical sensors and optical communication components.