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A photonic nanojet (PNJ) is a highly confined light beam that focuses from the shadow side of microparticles. In $46.47\lambda $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 $46.47\lambda $ and subwavelength FWHM of $0.77\lambda $ 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.

Single dielectric microspheres can manipulate light focusing and collection to enhance optical interaction with surfaces. To demonstrate this principle, we experimentally investigate the enhancement of the Raman signal collected by a single dielectric microsphere, with a radius much larger than the exciting laser spot size, residing on the sample surface. The absolute microsphere-assisted Raman signal from a single graphene layer measured in air is more than a factor of two higher than that obtained with a high numerical aperture objective. Results from Mie’s theory are used to benchmark numerical simulations and an analytical model to describe the isolated microsphere focusing properties. The analytical model and the numerical simulations justify the Raman signal enhancement measured in the microsphere-assisted Raman spectroscopy experiments.

Overcoming the classical diffraction limit in optical microscopy is known to be achievable by a variety of far-field and near-field microscopy techniques. More recently, so-called micro-object-based optical super-resolution microscopy techniques have emerged. In this review, we provide an overview of the state-of-the-art of optical super-resolution imaging techniques. In the first section, far-field techniques are discussed, which can be considered as advanced classical optical microscopy methods that mostly operate with fluorescent samples. In the second section, near-field techniques are presented that achieve super-resolution by maintaining a close distance between a nanometric detection unit and the sample, such that evanescent waves can be captured and processed. Near-field methods typically involve some scanning procedure to be able to map a reasonably large area of the sample. In the third section, dielectricmicro-object-based techniques are discussed. These provide amore recent, practical and affordable alternative to the other super-resolution microscopies. Finally, we provide a comparison of the presented techniques in terms of performance and cost, pointing out the application-specific strength of each imaging method. (c) 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The photonic nanojet phenomenon is commonly used both to increase the resolution of optical microscopes and to trap nanoparticles. However, such photonic nanojets are not applicable to an entire class of objects. Here we present a new type of photonic nanojet in reflection mode with the possibility to control the modulation of the photonic nanojet by a standing wave. In contrast to the known kinds of reflective photonic nanojets, the reported one occurs when the aluminum oxide hemisphere is located at a certain distance from the substrate. Under illumination, the hemisphere generates a primary photonic nanojet directed to the substrate. After reflection, the primary nanojet acts as an illumination source for the hemisphere, leading to the formation of a new reflective photonic nanojet. We show that the distance between the hemisphere and substrate affects the phase of both incident and reflected radiation, and due to constructive interference, the modulation of the reflective photonic nanojet by a standing wave can be significantly reduced. The results obtained contribute to the understanding of the processes of photonic nanojet formation in reflection mode and open new pathways for designing functional optical devices.

A photonic nanojet (PNJ) is a high intensity light beam that has beam diameter of sub-micrometers and depth of focus of several micrometers. In order to improve the accuracy and resolution of laser ablation using a PNJ, a shock wave generated in laser ablation was focused on. The shock wave pressure depends on the distance from sample surface and the shape of the surface. Thus, detection of the shock wave makes it possible to estimate the processing state. The confocal system made it possible to detect the shock wave via the vibration of the microsphere. The vibration signals in the time domain were Fourier transformed in the frequency domain. After the laser irradiation, there was a frequency peak that was not seen before the laser irradiation. Therefore, it was demonstrated that the shock wave generated by laser ablation could be detected from the vibration of the microsphere.

The photonic nanojet (PNJ) produced by a vector Bessel beam irradiating a dielectric spheroidal particle is investigated using the Discrete Dipole Approximation. The influence of the beam center, beam order, beam polarization type, and half cone angle of the vector Bessel beam on the characteristics of PNJ is analyzed. Several characteristics of PNJ including maximum intensity, the focal length, the effective length, and full width at half maximum are considered. The results show that the characteristics of the PNJ can be controlled by changing the four parameters of the Bessel beam. We think it will help to enhance the application of Bessel beams in generating PNJ and provide new properties to generate PNJ.

The photonic nanojet (PNJ) generated by a shaped optical fiber tip is an attractive technology for laser micro-machining. The working distance has the same order of size as the fiber core diameter; therefore, multimode (MM) fibers are generally preferred. However, the PNJ is due to the fundamental mode and, therefore, the energy coupled on the high-order modes does not contribute to the process. We demonstrate the benefit of a large-mode-area (LMA) optical fiber in the generation of the PNJ. A homemade 40 μm mode field diameter LMA fiber is compared with a 100/140 MM-shaped fiber tip. Similar micro-peaks are obtained, and an energy gain is demonstrated. The coupled energy required was eight times less intense with the LMA fiber, which may open new possibilities for laser micro- and nano-processing.

Photonic nanojets formed in the vicinity of the cylindrical graded-index lens with different types of index grading are numerically investigated based on the finite-difference time-domain method. The cylindrical lens with 1600 nm diameter is assembled by eighty-seven hexagonally arranged close-contact nanofibers with 160 nm diameter. Simulation and analysis results show that it is possible to engineer and elongate the photonic nanojet. Using differently graded-index nanofibers as building elements to compose this lens, the latitudinal and longitudinal sizes of the produced photonic nanojet can be flexibly adjusted. At an incident wavelength of 532 nm, the cylindrical lens with index grading = 2 can generate a photonic nanojet with a waist about 173 nm (0.32 wavelength). This lens could potentially contribute to the development of a novel device for breaking the diffraction limit in the field of optical nano-scope and bio-photonics.

We simulate the image generated by a microsphere residing in contact on top of an exposed Blu-ray disk surface, when observed by a conventional microscope objective. While microsphere lenses have been used to focus light beyond the diffraction limit and to produce super-resolution images, the nature of the light-sample interaction is still under debate. Simulations in related articles predict the characteristics of the photonic nanojet (PNJ) formed by the microsphere, but so far, no data has been published on the image formation in the far-field. For our simulations, we use the open source package Angora and the commercial software RSoft FullWave. Both packages implement the Finite Difference Time Domain (FDTD) approach. Angora permits us to accurately simulate microscope imaging at the diffraction limit. The RSoft FullWave is able to record the steady-state complex electrical and magnetic fields for multiple wavelengths inside the simulation domain. A microsphere is simulated residing on top of a dielectric substrate featuring sub-wavelength surface features. The scattered light is recorded at the edges of the simulation domain and is then used in the near-field to far-field transformation. The light in the far field is then refocused using an idealized objective model, to give us the simulated microscope image. Comparisons between the simulated image and experimentally acquired microscope images verify the accuracy of our model, whereas the simulation data predicts the interaction between the PNJ and the imaged sample. This allows us to isolate and quantify the near-field patterns of light that enable super-resolution imaging, which is important when developing new micro-optical focusing structures.

Here we answer the comment by I.V. Minin and O.V. Minin [Optical Materials 112 (2021) 110770] on our paper “Functional dielectric microstructure for photonic nanojet generation in reflection mode” [Optical Materials 110 (2020) 110503]. The process of reflective photonic nanojet modulation by a standing wave is considered by numerical simulations and additional experimental data. The results confirm that the data presented in the paper mentioned above are reliable and correspond to the physics of the process of reflective photonic nanojet formation.

This work addresses the shortcomings of the recent paper by A. Sergeev and K. Sergeeva [Optical Materials 110 (2020) 110503], in which the authors attempted to analyze the extended photonic nanojet generated in reflection mode by an array of aluminum oxide hemispheres. In this contribution we show the nature and parameters of photonic nanojet in reflection mode obtained in simulations, do not correspond to the experimental conditions and contradict the physics of the phenomenon, and this is worth discussing. In fact, the authors of above cited work observed in simulations a formation of the photonic nanojet in reflection mode, but the interaction with the incident field was not taken into account, which led to the absence of modulation of the photonic nanojet by a standing wave, which does not correspond to the physics of the process. Therefore, the results of the simulations presented in Figure 3 are not reliable.

We experimentally report the geometric effect on photonic nanojet generated by dielectric microcylinders with non-cylindrical cross-sections. The non-cylindrical cross-sections include truncated microcylinders and elliptical microcylinders. The truncated microcylinder is formed with the cutting thickness. The elliptical microcylinder is defined by ratio of minor to major axes. The specific spatial electromagnetic fields for microcylinders with different non-cylindrical cross-sections are studied by using finite-difference time-domain calculation. The direct imaging of photonic nanojets for microcylinders with different non-cylindrical cross-sections are performed with a scanning optical microscope system. The field distribution and location of photonic nanojet depending on the various spatial shapes are experimentally demonstrated. The photonic nanojet with long focal length and low divergence could be used to scan over a target to obtain a large area image when the non-cylindrical micro-media are coupled with a conventional optical microscope.

This theoretical study is mainly focused on to show the behavior of photonic nanojet from highly intense to higher propagation produce from a set of purposed droplet type microstructures. Simulation result clearly indicated that the proposed combined structure of a hemisphere and a cone of equal radius can able to produce a photonic nanojet having the intensity larger than the conventional spherical microstructure. By decreasing the height offered by the spherical part of the micro structure gives an increased zigzag type response for the propagation length which was found to be maximum for cone. However the intensity of photonic nanojet decreases with decrease in height offered by spherical part of the proposed microstructure.

Dielectric microspheres with appropriate refractive index can image objects with super-resolution, that is, with a precision well beyond the classical diffraction limit. A microsphere is also known to generate upon illumination a photonic nanojet, which is a scattered beam of light with a high-intensity main lobe and very narrow waist. Here, we report a systematic study of the imaging of water immersed nanostructures by barium titanate glass microspheres of different size. A numerical study of the light propagation through a microsphere points out the light focusing capability of microspheres of different size and the waist of their photonic nanojet. The former correlates to the magnification factor of the virtual images obtained from linear test nanostructures, the biggest magnification being obtained with microspheres of similar to 6-7 mu m in size. Analyzing the light intensity distribution of microscopy images allows determining analytically the point spread function of the optical system and thereby quantifies its resolution. We find that the super-resolution imaging of a microsphere is dependent on the waist of its photonic nanojet, the best resolution being obtained with a 6 mu m empty set microsphere, which generates the nanojet with the minimum waist. This comparison allows elucidating the super-resolution imaging mechanism.

In this work, we thoroughly investigate the shape, size, and location of the photonic nanojets (PNJs) generated from the illuminated dome lens. The silk fiber is directly extracted from the cellar spider and used to form the dome lens by its liquid-collecting ability. The solidified dielectric dome lenses with different dimensions are obtained by using ultraviolet curing. Numerical and experimental results show that the long PNJs are strongly modulated by the dimension of the dome lens. The optimal PNJ beam shaping is achieved by using a mesoscale dielectric dome lens. The PNJ with a long focal length and a narrow waist could be used to scan over a target for large-area imaging. The silk fiber with a dome lens is especially useful for bio-photonic applications by combining its biocompatibility and flexibility.

Photonic Nanojets (PNJs) have attracted considerable research attention in the fields of super-resolution optical microscopy, nano-photolithography, and single molecule sensors because of their sub-wavelength near-field focusing properties. In this paper, we thoroughly studied how the polarizations and amplitude profiles of the incident beams affect the shape, size, and location of the PNJs generated from the illuminated microspheres. Numerical results showed that the PNJs generated by microspheres were strongly modulated by the polarizations and amplitude profiles of the illumination beams. Therefore, PNJs can be engineered according to the requirements of a specific application by designing the polarizations and amplitude profiles of the illumination light. Various fascinating properties of the PNJs generated with different illumination schemes were demonstrated and their implications for potential applications were discussed as well.

Photonic nanojet is a sub-wavelength focus generated by a dielectric microparticle, like microsphere and microcylinder. The formation of nanojet can be tuned by changing the refractive index distribution and geometrical parameters of the structure. Many applications based on photonic nanojet have been explored based on the special property of dielectric microparticles. In this letter, a graded-index structure that combines hemisphere and microcylinder is proposed, which can generate a sub-wavelength nanojet with a full width at a half maximum of 120.9 nm (0.24 λ with 500 nm illumination wavelength). The influences of refraction index distribution and the length of cylinder on the properties of photonic nanojet are simulated and discussed. Moreover, the sensitivity of fabrication errors is analyzed to verify the feasibility of this structure.

Upon illumination, a dielectric microsphere (μS) can generate a photonic nanojet (PNJ), which plays a role in the super-resolution imaging of a sample placed in the μS’s immediate proximity. Recent microscopy implementations pioneered this concept but, despite the experimental characterization and theoretical modeling of the PNJ, the key physical factors that enable optimization of such imaging systems are still debated. Here, we systematically analyzed the parameters that govern the resolution increase in the case of large-diameter (>20 µm) μS-assisted incoherent microscopy by studying both the illumination and the detection light paths. We determined the enhanced-resolution zone created by the μS, in which the detection system has a net resolution gain that we calculated theoretically and subsequently confirmed experimentally. Our results quantitatively describe the resolution enhancement mediated by the optical contrast between the μS and its surrounding medium, and provide concrete means for designing μS-enhanced imaging systems for several application requirements.

In the present paper the basic characteristics (length, peak intensity, and full-width half-maximum) of nanojets formed in the vicinity of dielectric core-shell cuboids with different types of index grading are investigated by finite-difference time domain method . The latitudinal and longitudinal sizes of a nanojet and its peak intensity depending on the optical contrast variation of cuboids core-shells are numerically investigated. It has been shown that it is possible to control and elongate the nanojet abnormally. It also was shown that graded cuboid with dimensions of 4 × 4 × 4 wavelength may has FWHM of a jet less than uniform cuboid with dimensions of 1 × 1 × 1 wavelength. At wavelength of 600 nm graded index cuboid with dimensions of 4 × 4 × 4 wavelength and index grading = 2 allow to form photonic jet with FWHM about 232 nm or 0.39 wavelength.

Results of numerical simulation of light wave scattering on conical dielectric micron particles shaped as axicons and on combined particles shaped as truncated cones with adjacent hemispheres in the near field (photonic nanojet) region are presented. The spatial dimensions and the intensity of the photonic nanojets from particles with different spatial orientations are investigated. It is first shown that a combination of spherical and conical focusing in combined particles allows highly localized photonic nanojets to be formed with the peak intensity exceeding by several times the peak intensity for isolated microaxicons.

The direct imaging of photonic nanojets in different dielectric microdisks illuminated by a laser source is reported. The SiO 2 and Si 3 N 4 microdisks are of height 650 nm with diameters ranging from 3 μm to 8 μm. The finite-difference time-domain calculation is used to execute the numerical simulation for the photonic nanojets in the dielectric microdisks. The photonic nanojet measurements are performed with a scanning optical microscope system. The photonic nanojets with high intensity spots and low divergence are observed in the dielectric microdisks illuminated from the side with laser source of wavelengths 405 nm, 532 nm and 671 nm. The experimental results of key parameters are compared to the simulations and in agreement with theoretical results. Our studies show that photonic nanojets can be efficiently created by a dielectric microdisk and straightforwardly applied to nano-photonics circuit.

Optical field parameters in a “photonic nanojet” formed near surfaces of dielectric spherical microparticles illuminated by a focused laser beam are studied theoretically. The influence of the beam waist on “photonic nanojet” parameters (length, width, and intensity) is analyzed.

The imaging properties of BaTiO3 glass (BTG) microspheres in the diameter range of 5-50 µm which are fully immersed in a polydimethylsiloxane layer are experimentally studied. Our experimental results show that for both Blu-ray disc samples and the single-layer hexagonally close-packed microsphere array samples, with the increase of the diameter of BTG microspheres, the range of focal image positions (RFIP) increases linearly. When the diameter of BTG microspheres increases from 5 to 50 μm, the RFIP changes from 4 to 25 μm. For the microsphere array samples, Talbot effect is observed, and both the position of Talbot images and the Talbot distance depend on the diameter of BTG microspheres. Numerical simulations indicate that the length of the photonic nanojet changes from 2.9 to 7.1 μm when the BTG microsphere size increases from 5 to 50 μm, and the calculated RFIP is between 6 and 24 μm. The calculated RFIPs match well with the experimental ones. Our researches reveal that the RFIP depends on the length of the photonic nanojet of the BTG microsphere.

International audience; We demonstrate the key role of the laser injection into a multimode fiber to obtain a photonic jet (PJ). PJ, a high concentrated propagating beam with a full width at half maximum smaller than the diffraction limit, is here generated with a shaped optical fiber tip using a pulsed laser source (1064~nm, 100~ns, 35~kHz). Three optical injection systems of light are compared. For similar etched marks on silicon with diameters around 1~$\mu$m, we show that the required ablation energy is minimum when the injected light beam is close to the fundamental mode diameter of the fiber. Thus, we confirm experimentally that to obtain a PJ out of an optical fiber, light injection plays a role as important as that of the tip shape, and therefore the role of the fundamental mode in the process.

Super-resolution photonic nanojet interferometry is a new modality for 3D label-free super-resolution imaging. We present a comparative study of the photonic nanojet interaction with a polymer sample. We use numerical modelling to understand the interaction between a microsphere-induced photonic nanojet and the polymer sample. The numerical model employs the same set of input parameters (melamine formaldehyde microsphere with a diameter of 11 μm and a refractive index of 1.68), as in our experiments. The interaction is described using the Finite-Difference Time-Domain method applied on a finely discretized mesh. The knowledge gained using the verified and validated model, will be used to conduct numerical simulations in a wider parameter space. This enables optimizing the design of 3D-interferometric super-resolution microscopes. © 2017 SPIE.

The generations of localized photonic nanojets using core-shell diffraction gratings working in the visible light region are demonstrated numerically. The power flow patterns for the core-shell diffraction gratings are simulated by using the finite-difference time-domain method. The focusing qualities of localized photonic nanojets are evaluated in terms of focal length and transversal width along propagation and transversal directions. Due to surface plasmon polaritons, it has been demonstrated that the metallic shell is critical for power enhancement of photonic nanojet. The high-resolution imaging of the core-shell diffraction grating can be expected from the high-intensity photonic nanojet. The photonic nanojet could be operated in a wide range imaging for nano-scale targets through the core-shell diffraction grating.

Label-free photoacoustic microscopy (PAM) with nanometric resolution is important to study cellular and sub-cellular structures, microcirculation systems, micro-vascularization, and tumor angiogenesis etc. But, the lateral resolution of a conventional microscopy is limited by optical diffraction. The photonic nanojet generated by silica microspheres can break this diffraction limit. Single silica sphere can provide narrow photonic jet, however its short length and short working distance limits its applications to surface imaging. It is possible to increase the length of the photonic nanojet and its working distance by optimizing the sphere design and its optical properties. In this work, we will present various sphere designs to achieve ultra-long and long-working distance photonic nanojets for far-field imaging. The nanojets thus generated will be used to demonstrate super-resolution photo-acoustic imaging using k-wave simulations. The study will provide new opportunities for many biomedical imaging applications that require finer resolution. MOE (Min. of Education, S’pore) Published version

We compare the focusing of Gaussian and plane wave illumination for a cascaded asymmetric microstructure. Although the Gaussian beam generates a longer and wider photonic nanojet, it can still focus efficiently for non-optimal microstructure geometries.

The photonic nanojet shaping effect in the dielectric non-spherical microparticles is reported. The specific spatial electromagnetic field is studied by using finite-difference time-domain calculation which constitutes the so-called photonic nanojet. The dielectric non-spherical microparticle is truncated by the cutting thickness. The latitudinal and longitudinal dimensions of the photonic nanojet and its peak intensity depending on the variation of cutting thickness are numerically researched. The shape dependence of the photonic nanojet in the non-spherical microparticles has been investigated by quality criterion. The practical results are drawn concerning the possible procedures to gain the control over the properties of photonic nanojet in the non-spherical microparticles. The shaping mechanism has a significant impact on the use of photonic nanojet to distinguish nanoscale specimens.

Using 3D finite-difference time-domain modeling, a microsphere-generating nanojet and gold nanoantenna gap are optimized to achieve 3D nanojet confinement to a subwavelength volume of about 0.009 µm3 (wherein the edges of the volume are defined at 1/e2 of the maximum electric-field intensity) for an incident wavelength of 633 nm. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2700–2706, 2014

A photonic nanojet (PNJ) is a tightly focused beam that emerges from the shadow surface of microparticles. Due to its high peak intensity and subwavelength beam waist, the PNJ has increasingly attracted attention, with potential applications in optical imaging, nanolithography, and nanoparticle sensing. A variety of ways have been demonstrated to further shrink the beam waist of PNJs, such as engineering the microparticle geometry and optimizing a multilayer structure. In this simulation work, we report the realization of an ultranarrow PNJ, which is formed by an engineered two-layer microcylinder of high refractive-index materials. Finite element analysis shows that under 632.8 nm illumination, the full width at half maximum of the beam waist can reach 87 nm (~λ/7.3). As far as we know, this is the narrowest PNJ ever reported. Using the backscattering intensity as a contrast mechanism, we also demonstrated the imaging resolution and capability of the ultranarrow PNJ through numerical simulations. We anticipate that this ultranarrow PNJ will open new possibilities in a variety of research areas, including nanoparticle detection, biomedical imaging, and nanolithography.

A tunable photonic nanojet achieved using a core–shell microcylinder with nematic liquid crystal is reported. The core–shell microcylinder can be obtained by the infiltration of liquid crystal into the air core of a microcylinder. The refractive indices of the liquid crystals can be changed by rotating the directors of the liquid crystals. Therefore, we were able to control the flow direction of the photonic nanojet in two-dimensional core–shell microcylinder structures. Using high resolution finite-difference time-domain simulation, we demonstrate that the photonic nanojet can be continuously tuned in the core–shell microcylinder. The horizontal and vertical shifts of photonic nanojet depend strongly on the director of the liquid crystals. Such a mechanism of nanojet adjustment should open up a new application for using visible light to detect nanoparticles, optical gratings, and single molecules with subwavelength spatial resolution.

The characteristics of photonic nanojets are analyzed by changing the parameters, such as the wavelength, refractive index of the surroundings, diameter and refractive index of the microsphere, in this paper. Quadratic functions are used to describe the relation between the above parameters and photonic nanojets’ characteristics. Several techniques are proposed to control the photonic nanojets.

A core-shell structure based on three-dimensional micro-cuboids connected by photonic nanojets is proposed with the aim for power enhancement of surface plasmon polaritons. The performance of the core-shell micro-cuboid is evaluated and compared with the dielectric micro-cuboid. The dependence of the power enhancement with the metallic shell is also evaluated and demonstrated that the metallic shell is critical for engineering photonic nanojet. The subwavelength focusing is obtained from the photonic nanojet. The significant effect of core-shell micro-cuboids can be used to distinguish nano-scale objects.

Nano-photonics, where optical structures can manipulate light at the sub-wavelength scale, is making important advances towards optical communications, imaging and sensing. A novel platform suitable for fundamental investigations of light propagation through micro- and nano-structures will be discussed. This platform is based on a dielectric multilayer that sustains Bloch surface waves (BSWs). We experimentally and theoretically investigate components including a disk resonator and a photonic nanojet, which are fabricated on a Bloch surface wave platform.

The ultra-high transmission of photonic nanojet induced modes in chains of core–shell microcylinders illuminated by a plane wave is reported. Using high resolution finite-difference time-domain simulation, the periodical focusing of lightwave in straight chains of touching core–shell microcylinders is characterized with the periodicity of photonic nanojets corresponding to the diameter of two microcylinders. The core–shell microcylinders are efficiently coupled to the collimated incident lightwaves. We observe the lightwave with high optical transport of 3 dB in the maxima of transmission spectra for a chain of core–shell microcylinders. The chains of core–shell microcylinders can be assembled inside hollow waveguide and used in a variety of microscopy techniques, biomedical applications, and optical microprobes with subwavelength spatial resolution.

The main characteristics of “photonic nanojets” (the cross-section size, length, and peak intensity) formed in the vicinity of micron-sized composite particles consisting of a core and several shells with different refractive indices are considered. It is shown that it is possible to manipulate the parameters of a “photonic nanojet”, in particular, extend its size or increase its peak intensity by changing the refractive index of the neighboring shells in the composite spherical microparticles.

In this work, we numerically study the focusing of a linearly polarized laser beam of wavelength λ = 633 nm using microcubes of heights 0.4 µm, 0.6 µm, and 0.8 µm and width varying from 0.4 µm to 0.8 µm fabricated of silica (refractive index n = 1.46) on a substrate. The minimal focal spot was obtained for microcube with height of 0.6 µm and width of 0.58 µm. The diameters of photonic nanojet in this case were equal to FWHM min = 0.39λ and FWHM max = 0.67λ.

We report on the new optical tool for precise manipulation of various microobjects. This tool is referred to as a “photonic nanojet” (PJ) and corresponds to specific spatially localized and high-intensity area formed near micron-sized transparent spherical dielectric particles illuminated by a visible laser radiation The descriptive analysis of the morphological shapes of photonic nanojets is presented. The PJ shape characterization is based on the numerical calculations of the near-field distribution according to the Mie theory and accounts for jet dimensions and shape complexity.

Previously (Chen et al., 2004), it was shown that dielectric cylinder can form focal spots with small diameters and long depth. This type of focal spot was called photonic nanojet. In this paper, it was shown that dielectric cylinder of radius 595 nm (1.12 of wavelength) forms near the surface a photonic nanojet with diameter equal to 0.31 of wavelength and depth of focus equal to 0.57 of wavelength. Adding truncated concentric rings with radiuses equal to radiuses of zone plate to the cylinder increases the depth of focus to 1.18 of the wavelength. The diameter and intensity of focal spot near the cylinder surface remain unchanged.

In the field of optical imaging, the conventional imaging resolution is about 200 nm due to the diffraction limit. The higher resolution is urgently needed for further developing scientific research. Therefore, how to break through this limitation to acquire high quality and high resolution image has become a hot research topic. The microspheres with the size of tens of micrometers exhibit the ability to improve the imaging resolution of the conventional optical microscope by locating them directly on the sample surface. Due to its simplicity, the microsphere optical nanoscope technology is widely studied. This paper introduces the research background of the optical microscope and the research progress of microsphere optical nanoscope technology. At the same time, approaches to adjusting the photonic nanojet generated by the microspheres by fabricating concentric ringing, central mask, and surface coating of microspheres are reviewed. The possible reasons for this improved resolution are discussed. The applications and development of the microsphere ultra-microscopic technology in the future are discussed.

Since Chen et al. reported on the photonic nanojet (PNJ), many researches have been carried out from various viewpoints such as fundamental physics and device applications. We have numerically analyzed, based on the finite-difference time-domain (FDTD) method, generation of PNJ from microcylinders incorporating the liquid crystals (LCs) with radial hedgehog and tangential alignments, in which the director of LC molecules is perpendicular or parallel to the LC/matrix interface. For the radial hedgehog alignment of LC molecules, the PNJ from LC microcylinders is separated into two beams. For the tangential alignment of LC molecules, we show that the PNJ from LC microcylinders are uniquely polarized reflecting birefringence of LCs, which cannot be obtained using optically isotropic microdroplets or microcylinders. By using the LC micro-systems, we may obtain a rich variety of PNJ with electrical tunability.

We present a comprehensive review on the latest research activities that explore the Gouy phase and indicate the recent experimental progresses for its observations in studies that rely on a longitudinal-differential interferometer. The latter is a far-field instrument that measures light fields in amplitude and phase in the entire three-dimensional space. We outline in detail why such technique is superior to measure directly the Gouy phase anomaly, i.e., the difference of the phase in a wave field with respect to a referential plane wave. This only became possible in conjunction with suitable sample designs that provide simultaneous phase information on a referential plane wave. Beyond outlining a fundamental theory of the Gouy phase in general optics, we put emphasis on discussing the peculiar features of the Gouy phase in a new-domain of optics, i.e., micro-optics. In this domain, micro- and eventually nano-structured materials allow to control and to localize light on sub-wavelength spatial domains; and deeper understanding of the amplitude and phase evolution is crucial for many applications. We discuss phase anomalies in light fields generated by various micro-optical systems, such as in the 2D and 3D foci of small-size microlenses, in the spot of Arago that appears behind circular obstacles, in light fields behind periodic objects such as amplitude grating, and in photonic nanojets that emerge directly behind dielectric microspheres. With our work we shed new light on an effect that is presumably understood since long time; and indicate the implications for a diverse range of future applications.

We report on the generation of photonic nanojets, which resemble optical bottle beams. They are realized by manipulating the illumination of dielectric microspheres. As illumination we use the outer region of deliberately truncated Bessel-Gauss beam or a focused Gaussian beam with intentionally induced spherical aberrations. For the Bessel-Gauss beam possessing a single side lobe only, the nanojet spot resembles an optical bottle beam with a strong confinement due to the nanojet effect. When multiple side lobes of the aberrated focal spot are used, a chain of 3D optical bottle beams appears. We show the 3D intensity distributions close to the spot and discuss the main characteristics of such optical bottle beams.

The imaging resolution of a conventional optical microscope is limited by diffraction to ~200 nm in the visible spectrum. Efforts to overcome such limits have stimulated the development of optical nanoscopes using metamaterial superlenses, nanoscale solid immersion lenses and molecular fluorescence microscopy. These techniques either require an illuminating laser beam to resolve to 70 nm in the visible spectrum or have limited imaging resolution above 100 nm for a white-light source. Here we report a new 50-nm-resolution nanoscope that uses optically transparent microspheres (for example, SiO₂, with 2 μmdiameter9 μm) as far-field superlenses (FSL) to overcome the white-light diffraction limit. The microsphere nanoscope operates in both transmission and reflection modes, and generates magnified virtual images with a magnification up to ×8. It may provide new opportunities to image viruses and biomolecules in real time.

Optical resolution photoacoustic microscopy (ORPAM) is important for various biomedical applica-tions, such as the study of cellular structures, microcirculation systems, and tumor angiogenesis. However, thelateral resolution of a conventional ORPAM is limited by optical diffraction. In this work, we report a simulationstudy to achieve subdiffraction-limited super-resolution in ORPAM using microspheres. Laser radiation isfocused through a microsphere to generate a photonic nanojet, which provides the possibility to break the dif-fraction limit in ORPAM by reducing the size of the excitation volume. In our simulations using microspheres, weobservedimprovementinthelateralresolutionupto∼fourfoldcomparedtoconventionalORPAM.Themethodissimple, cost effective, and can provide far-field resolution. This approach may provide new opportunities formany biomedical imaging applications that require finer resolution. © 2014 Society of Photo-Optical InstrumentationEngineers (SPIE) [DOI: 10.1117/1.JBO.19.11.116003]

We discuss the usage of the photonic nanojet to detect deeply subwavelength pits in a metal substrate for the purpose of high-density optical data storage. Three-dimensional finite-difference time-domain (FDTD) computational solutions of Maxwell's equations are used to analyze and design the system. We find that nanojet-illuminated pits having lateral dimensions of only 100×150 nm2 yield a 40-dB contrast ratio. The FDTD simulation results show that pit-depth modulation and pit-width modulation can significantly increase the optical data-storage capacity.

Microsized spheres can focus light into subwavelength spatial domains, a phenomenon called photonic nanojet. Even though well studied in three-dimensional (3D) configurations, only a few attempts have been reported to observe similar phenomena in two-dimensional (2D) systems. This, however, is important to take advantage of photonic nanojets in planar optical systems. Usually, surface plasmon polaritons are suggested for this purpose, but they suffer notoriously from rather low propagation lengths due to 2 3 4 5 6 7 8 9 intrinsic absorption. Here, we solve this problem and explore, numerically and experimentally, the use of Bloch surface waves sustained by a suitably structured all-dielectric media to enable subwavelength focusing in a planar optical system. Since only a low-index contrast can be achieved while relying on Bloch surface waves, we perceive a new functional element that allows a tight focusing and the observation of a photonic nanojet on top of the surface. We experimentally demonstrate a spot size of 0.662 lambda in the effective medium. Our approach paves the way to 2D all-dielectric photonic chips for nanoparticle manipulation in fluidic devices and sensing applications.