Abstract
A photonic nanojet (PNJ) is a highly confined light beam that focuses from the shadow side of microparticles. In <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$46.47\lambda $</tex-math></inline-formula> this work, we propose a PNJ with ultrahigh quality factor formed by dielectric truncated microtoroid. The key properties of PNJ, such as the maximum intensity, the length of PNJ, the full-width at half maximum (FWHM), are studied in detail using finite-difference time-domain (FDTD) analysis. The results show that a PNJ with an enhanced intensity of 55.21 times to the incident light, superlong length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$46.47\lambda $</tex-math></inline-formula> and subwavelength FWHM of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$0.77\lambda $</tex-math></inline-formula> is formed by semi-microtoroid, thus, an ultrahigh quality factor of 3308.68 is achieved. More importantly, the properties of the PNJ are tunable by changing the truncated proportions of the microtoroid. The structure we proposed has the advantages of compact structure and simple experimental operation, which is expected to apply in many research fields, including optical detection, optical data storage, super-resolution image, nanopattern, nanolithography, and so on.
Highlights
A PHOTONIC nanojet (PNJ) is a tightly focused light beam with a high-intensity peak, long length and subwavelength waist that emerges from the shadow surface of a transparent microparticle
The simulations of photonic nanojets generated by truncated microtoroid are employed by using the finite-difference time-domain (FDTD) method
The distribution of the PNJ along y axis is depicted in Fig. 3(c), which gives the subwavelength full-width at half maximum (FWHM) of the PNJ formed by the semi-microtoroid of 0.308 μm (0.77λ)
Summary
A PHOTONIC nanojet (PNJ) is a tightly focused light beam with a high-intensity peak, long length and subwavelength waist that emerges from the shadow surface of a transparent microparticle. Many demonstrations show that the key properties of the PNJ, including maximum intensity, the length of PNJ, and FWHM, depend on the geometric parameters (size, shape, etc.), refractive indices of the micro-particles and output wavelength of the incident light [16]–[20]. For these applications, the enhanced electric field intensity, the ultralong length of PNJ and narrow beam waist of PNJs are especially expected by researchers. Compare with the traditional microsphere and microcylinder structures, the PNJ generated from truncated microtoroid structure has long working distance and higher maximum intensity. What is worth mention that the truncated microtoroid is height-tunable compare with traditional microtoroid or microaxicon
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