Photonic nanojets are highly concentrated beams of light generated by dielectric structures on the order of a few wavelengths in size. They can create a small focus many wavelengths away from the structure. Photonic nanojet generators rely on near-field diffraction and interference to achieve their unusual characteristics. Traditional structures used are spherical and cylindrical microstructures made of materials like silica. The length and other parameters of photonic nanojets depend on factors like the material and size of the structure, refractive indices of the structure and surrounding environment, and wavelength of light. Recent research optimizes structures and materials to achieve longer and more controlled photonic nanojets for applications in imaging, sensing and optical manipulation.

1. Photonic Nanojets
Rabiul Islam Sikder
Date: 28th February 2023

2. Photonic Nanojets
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• Photonic Nanojets:
Highly concentrated, propagating beams of light generated by certain
types of dielectric structures (commonly spherical and cylindrical ones)
on the order of a few wavelengths in size. Typically, the PNJ hotspot—
the
location of greatest intensity—is less than half a wavelength in width
and
extends more than a wavelength in length. In the case of the sunlit
droplets,
the concentrated energy created by each droplet has a typical intensity
of
10 to 50 times that of
the incident light.
• Most PNJ generators can create a small focus many wavelengths
away
• PNJ generator relies on near-field diffraction and interference
effects to achieve its unusual characteristics. Because of this, PNJ
generators need to be analyzed with wave optics, rather than the
ray

3. Photonic Nanojets
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• From ordinary microspheres to GRIN structures:
Traditionally, spherical and cylindrical dielectric microstructures have
been the geometries of choice for producing point-focused and line-
focused PNJs, respectively. A single-index (for example, silica)
microsphere is one of the easiest ways to generate a PNJ, and a self-
assembled layer of microspheres can be used to produce a 2D array
of PNJ hotspots, simplifying alignment.

4. The theory behind PNJ design
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5. Review paper on Photonic Nanojets
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6. Photonic Nanojets
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7. Photonic jet lens
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8. Photonic Nanojets (controlling side lobes)
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9. Nanophotonic structural colors
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10. Photonic Nanojets
• Common concepts
• Common techniques
• Problems
• Major breakthroughs
• Current trends
• Researcher
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11. Photonic Nanojets
• Parameters
- Full width at half-maximum (FWHM) :
- Jet length (JL): same as the diffraction length, through which the light intensity decays to 1/e of the peak value, that is the hot spot.
- Working distance (WD) : The distance between the intensity hot spot and the closest point on the surface of the PNJ generator
- Focal length (FL):
- Light wavelength
 Source characteristics: wavelength, polarization, intensity distribution, coherence
- Radius of the microsphere
- Refractive index of the microsphere
- Refractive index of the surrounding environment
- Field enhancement
- Structure geometry (particle size and shape)
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12. Extremely long nanojet formation from a ballpoint photonic pen
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Photonic nanojet length:
330λ
Source wavelength: 365
nm plane wave
illumination
Jet length can be tuned by
changing the environment,
tip, and barrel materials

13. Extremely long nanojet formation from a ballpoint photonic pen
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• Analyzed SiO2 (n = 1.48), polystyrene (n = 1.65),
and Al2O3 (n = 1.79) sphere with the diameter of 5
and 10 µm as a tip of the photonic pen.
• Barrel materials: PDMS (n = 1.456), silicon dioxide
(SiO2) (n = 1.48), poly(methyl methacrylate) PMMA
(n = 1.52), and SU-8 (n = 1.62) are mainly
considered as barrel
materials of the PPs
• Among those, an SiO2 sphere with the 10 µm
diameter (pen tip) partially immersed in a high-index
SU-8 barrel with index difference of n = 0.14
showed an extremely long PNJ with the length of
over 330λ in a water environment under 365 nm
plane-wave illumination.

14. Extremely long nanojet formation from a ballpoint photonic pen
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Physical structure of photonic
nanojet depends on:
i) The sphere diameter
ii) Refractive index of the
sphere
iii) Refractive index of the
background environment
Jet length depends on
another factor:
i) Refractive index difference
between the barrel and tip

15. 15

16. 16

17. Spatial control of photonic nanojets
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Cascaed asymmetrical silica microstructure and
produced a FWHM waist that approaches λ/4

18. Photonic nanojet
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19. Photonic nanojet
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Photonic nanojet waist: 160 nm
Photonic nanojet length: 400 nm

20. Photonic nanojet using a graded index microsphere
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Photonic nanojet length : 20λ

21. Elongated photonic nanojets
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Photonic nanojet length: 20 um
Six equally thick spherical shells are assumed
Refractive indices: n = 1.02, 1.04, 1.06, 1.08,
1.10 and 1.12

22. Elongated photonic nanojets
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Photonic nanojet length: 20 um
Six equally thick spherical shells are assumed
Refractive indices: n = 1.02, 1.04, 1.06, 1.08,
1.10 and 1.12

23. Ultralong photonic nanojet
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• Ultra-long photonic nanojet using glass
based two-layer microsphere
• Beam length: 22 wavelengths

24. Ultralong photonic nanojet
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• Ultra-long photonic nanojet using glass
based two-layer microsphere
• Beam length: 22 wavelengths

25. Optimization of photonic nanojets
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• Optimization of five-layer microcylinders
• Optimization of five radii and refractive
indices
• Beam length : 107.5λ
• Source wavelength = 632.8 nm
• Refractive index range: 1.377 to 3.4

26. Optimization of photonic nanojets
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• Optimization of five-layer microcylinders
• Optimization of five radii and refractive
indices
• Beam length : 107.5λ
• Source wavelength = 632.8 nm
• Refractive index range: 1.377 to 3.4

27. Photonic nanojet using integrated silicon photonic chip
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• The design consists of a silicon hemisphere
on a silicon substrate
• PNJ length exceeds 17λ

28. Geometric effect on photonic nanojet
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• High intensity photonic nanojet with long length and low
divergence is observed in the elliptical microcylinder

29. Photonic nanojet shaping
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30. Photonic nanojet shaping
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31. Photonic nanojet by polarization engineering
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32. Review paper on optical trapping, sensing and imaging using photonic nanojets
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