2. Photonic Nanojets
2
• 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
3
• 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.
10. Photonic Nanojets
• Common concepts
• Common techniques
• Problems
• Major breakthroughs
• Current trends
• Researcher
10
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)
11
12. Extremely long nanojet formation from a ballpoint photonic pen
12
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
13
• 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
14
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
21. Elongated photonic nanojets
21
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
22
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
23
• Ultra-long photonic nanojet using glass
based two-layer microsphere
• Beam length: 22 wavelengths
24. Ultralong photonic nanojet
24
• Ultra-long photonic nanojet using glass
based two-layer microsphere
• Beam length: 22 wavelengths
25. Optimization of photonic nanojets
25
• 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
26
• 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
27
• The design consists of a silicon hemisphere
on a silicon substrate
• PNJ length exceeds 17λ
28. Geometric effect on photonic nanojet
28
• High intensity photonic nanojet with long length and low
divergence is observed in the elliptical microcylinder
