Photonic Nanojet Generation Using Integrated Silicon Photonic Chip with Hemispherical Structures

Abstract

Photonic nanojet (PNJ) is a tightly focused diffractionless travelling beam generated by dielectric microparticles. The location of the PNJ depends on the refractive index of the material and it usually recedes to the interior of the microparticle when the refractive index is higher than 2, making high index materials unsuitable to produce useful PNJs while high index favours narrower PNJs. Here we demonstrate a design of CMOS compatible high index on-chip photonic nanojet based on silicon. The proposed design consists of a silicon hemisphere on a silicon substrate. The PNJs generated can be tuned by changing the radius and sphericity of the hemisphere. Oblate spheroids generate PNJs further away from the refracting surface and the PNJ length exceeds 17λ when the sphericity of the spheroid is 2.25 The proposed device can have potential applications in focal plane arrays, enhanced Raman spectroscopy, and optofluidic chips.

CMOS compatible design of photonic nanojet

“…PNJ is sensitive to the surrounding refractive index 5,8 . To understand the effect of surrounding refractive on the PNJ of proposed design, we have varied the refractive index of the surrounding medium from 1 to 2.1.…”

Sub-wavelength photonic hooks generated in photonic chips with asymmetric array of Si3N4 micropillars

“…The characteristics of the photonic nanojets, including their length, width and focusing ability depend on both the size and shape of the particle as well as the refractive index contrast between the particles and the surrounding medium [1]. Various designs have been proposed to harness the potential of photonic nanojets, ranging from spherical particles for precise focusing to layered cylinders for extended nanojets, and even micropillar and hemispherical domes for seamless integration into photonic chips [2].…”

Narrow nano-beam generation inside of silicon photonic chip with a hemi-cylinder

“…In [25], a silicon grating structure with silica as gaps filling medium was proposed to produce the ultra-narrow array PNJ, and the study provided the possibility of integrating PNJ into silicon chips. In [26], a design of CMOS compatible high index on-chip PNJ based on silicon was numerically demonstrated, however, the achieved PNJ had a beam waist larger than λ/2. In practice, the high refractive index of silicon could be utilized to generate a narrower nano-beam.…”