Tailoring aberration-free photonic nanojets through the illumination of dielectric cylinders using cylindrical vector beams.

This study explores the manipulation of photonic nanojets (PNJs) via axial illumination of cylindrical dielectric particles with cylindrical vector beams (CVBs). The edge diffraction effect of cylindrical particles is harnessed to achieve the near-field focusing of CVBs, minimizing the spherical aberration's impact on the quality of the PNJ. By discussing how beam width, refractive index, and particle length affect PNJs under radially polarized incidence, a simple and effective approach is demonstrated to generate rod-like PNJs with uniform transmission distances and super-diffraction-limited PNJs with pure longitudinal polarization. Azimuthal polarization, on the other hand, generates tube-like PNJs. These PNJs maintain their performance across scale. Combining edge diffraction with CVBs offers innovative PNJ modulation schemes, paving the way for potential applications in particle trapping, super-resolution imaging, photo-lithography, and advancing mesotronics and related fields.

Compact, low-loss, and high-polarized-extinction ratio terahertz TM-pass polarizer based on a hybrid plasmonic waveguide with a graphene ridge.

A compact, low-loss, and high-polarized-extinction ratio TM-pass polarizer based on a graphene hybrid plasmonic waveguide (GHPW) has been demonstrated for the terahertz band. A ridge coated by a graphene layer and the hollow HPW with a semiround arch (SRA) Si core is introduced to improve structural compactness and suppress the loss. Based on this, a TM-pass polarizer has been designed that can effectively cut off the unwanted TE mode, and the TM mode passes with negligible loss. By optimizing the angle of the ridge, the height of the ridge, air gap height, and the length of the tapered mode converter, an optimum performance with a high polarization extinction ratio of 30.28 dB and a low insert loss of 0.4 dB is achieved in the 3 THz band. This work provides a scheme for the design and optimization of polarizers in the THz band, which has potential application value in integrated terahertz systems.

Ultracompact parabolic sidewall-profiled hybrid plasmonic waveguide Bragg grating with optimized spectral properties of long-wavelength passband.

An ultracompact hybrid plasmonic waveguide Bragg grating (HPWBG) with improved spectral properties of long-wavelength passband is proposed. A hollow HPW is introduced to suppress the entire loss, and a parabolic profiled sidewall is designed to optimize the spectral properties for specific wave bands. The transfer matrix method and finite element method are combined to ensure the efficiency of numerical research. The results show that the parabolic profile effectively reduces the reflection and strengthens the resonance of the mode in the long-wavelength passband, suppressing the oscillations and realizing significant smoothness and improvement in transmission. The optimized transmittance is greater than 99%, and insertion loss is as low as 0.017 dB. A wide bandgap of 103 nm is also attained. The structure also has a compactness with a length of 3.4 µm and exhibits good tolerance. This work provides a scheme for designing and optimizing wavelength selecting devices and has potential application value in integrated photonic devices.

Compact and low-loss TM-pass polarizer based on a hybrid plasmonic waveguide with a semiround arch Si core.

A compact and low loss TM-pass polarizer based on a hybrid plasmonic waveguide (HPW) has been demonstrated. By introducing the hollow HPW with a semiround arch (SRA) Si core, the unwanted TE mode can be effectively cut off and the TM mode can pass through by hybrid plasmonic mode with excellent transmission characteristics. The hollow structure realizes lower index with n=1 due to the air region, and the SRA construction effectively suppresses the energy loss of the TM mode caused by the corner effect. Thus, TM modes pass through with negligible loss and exhibit the characteristic of strong mode limitation. By optimizing the width of metal, the width of the HPW, and the length of the tapered mode converter, an optimum performance with a high polarization extinction ratio of 67.87 dB and a low insert loss of 0.029 dB at the work wavelength=1550nm is achieved. Detailed analysis also proves that the proposed polarizer has a compact size of only 7 µm and a great fabrication tolerance. This work offers a simple and effective scheme of polarization control on-chip.

Focusing characteristics of cylindrical vector beams through a multi-focal all-dielectric grating lens.

A novel, to the best of our knowledge, type of multi-focal all-dielectric grating lens is proposed in this work, and focusing characteristics of cylindrical vector beams through the lens are investigated in detail. Based on the negative refraction mechanism of negative-first-order diffraction and Fermat's principle, a multi-focal lens is designed. By analyzing the diffraction effect of the grating, the essential factor that affects the focus quality is found. Through a two-step optimization process, secondary foci and the focal displacement of primary foci caused by high-order diffractions are overcome, and the quality of the focal field is significantly improved. This work provides a reference for micro-lens design for focus modulation, and the research results also have potential applications in the fields of light-field manipulation and optical tweezers.