We present a novel method for generating an extremely confined nanoscale light field using an all-dielectric conical nanotip coupled to a microfiber. By launching a radially polarized TM01 mode into the tip, we achieve constructive interference of longitudinal electric field components at the apex, resulting in a highly localized optical hotspot with sub-10 nm dimensions and a mode volume as small as 10-7 λ3. This approach overcomes the limitations of conventional dielectric tips and rivals plasmonic superfocusing without incurring ohmic losses. Numerical simulations reveal that the focal spot features a high intensity enhancement ratio (> 3500), strong peak-to-background contrast (> 30 dB), and circular symmetry. Furthermore, we demonstrate the ability to shape the light field into arbitrary nanoscale patterns by modifying the tip geometry. These findings open new avenues for low-loss, high-precision light confinement in applications such as optical nano tweezers, nanoscopy, nano lasers, and nanoparticle spectroscopy.

We propose a new, to the best of our knowledge, surface-illuminated Si photodetector (PD) structure with slanted surface-relief grating that solves issues of low sensitivity to near-infrared (NIR) light and a trade-off between absorption layer thickness and high-speed response. The slanted grating, composed of tilted Si and SiO2 arrays, efficiently deflects normally incident photons. When coupled with the lateral quasi-propagating mode in the absorption layer with a circular resonator shape, the photon lifetime is dramatically extended, resulting in increased absorption of NIR photons. Simulations have confirmed that even an absorption layer as thin as 300 nm can achieve an extremely high absorption of 29.2% at a wavelength of 1012 nm. We believe this innovative design can play a crucial role in the design of thin and high-speed PDs.

We propose a new, to the best of our knowledge, surface-illuminated Si photodetector (PD) structure with slanted surface-relief grating that solves issues of low sensitivity to near-infrared (NIR) light and a trade-off between absorption layer thickness and high-speed response. The slanted grating, composed of tilted Si and SiO2 arrays, efficiently deflects normally incident photons. When coupled with the lateral quasi-propagating mode in the absorption layer with a circular resonator shape, the photon lifetime is dramatically extended, resulting in increased absorption of NIR photons. Simulations have confirmed that even an absorption layer as thin as 300 nm can achieve an extremely high absorption of 29.2% at a wavelength of 1012 nm. We believe this innovative design can play a crucial role in the design of thin and high-speed PDs. (c) 2025 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.

Deep Reinforcement Learning (DRL) is regarded as an effective methos to solve the problems of Routing, Modulation, Spectrum, and Core Allocation (RMSCA) in Space-Division Multiplexing Elastic Optical Networks (SDM-EONs). An excellent design of the reward function can guide the agents of DRL to achieve rapid learning. Therefore, in combination with the SDM-EON scenario characteristic, we propose a Multi-link Fragmentation-aware and Inter-core Crosstalk-aware DRL-based RMSCA Algorithm (MIDRL-RMSCA). In MIDRL-RMSCA, a network fragmentation metric based on multiple links is introduced to measure the distribution of global spectrum resources. Furthermore, for the SDM-EON scenario, the inter-core resource adjacency degree is introduced to achieve space-frequency joint resource perception. Simulation results show that our algorithm outperforms reference algorithms in both blocking rate and spectrum resource utilization. Specifically, it achieves blocking rate reductions of 24.85% and 28.01%, as well as resource utilization improvements of 17.66% and 19.05%, in the NSFNET and Cost- 239 networks, respectively.

We numerically demonstrated a surface-illuminated Si PIN photodiode (PD) structure with a metasurface composed of etched isosceles triangle pillars that can enhance sensitivity in the near-infrared wavelength range (NIR) by enabling directional scattering (DS) of photons. The metasurface is designed to act as a deflector to increase the absorption efficiency by extending the photon dwell time. This is particularly effective in thin intrinsic layers (i-layers) of silicon, surpassing the capabilities of conventional omnidirectional scattering gratings. Our results show a 3.5-fold increase in internal quantum efficiency over wavelengths above 0.9 µm compared to the structure without metasurface. The absorption enhancement brought about by directional scattering is not limited to thin i-layers; it can potentially improve a wide range of photodiode geometries and structures. Furthermore, the proposed structure, consisting of an all-Si layer and a simple geometric etching process, makes it compatible with foundry fabrication methods and opens up new possibilities for expanding applications of Si PDs.

A near-field sub-nanometer optical field is generated by confining a radially polarized fiber mode at a non-metallic cone shaped nanotip that is connected to the output end of a nanofiber.

We present a novel photodetector concept that involves the metasurface-induced scattering of a vertically incident photon beam wave front toward desired direction, facilitating guided light propagation, and resulting in enhanced detection efficiency in an ultra-thin photo absorption layer. The higher absorption efficiency is enabled by an enhanced photon density of states while substantially reducing the optical group velocity of light and extending the photon material interaction time compared to the traditional semiconductor photodetectors without an integrated metasurface. We have demonstrated a surface-illuminated Si PIN photodiode (PD) structure with a metasurface composed of etched isosceles triangle pillars using Finite Difference time Domain numerical simulation that can enable photon beam steering and guided light propagation. This increases the absorption efficiency in devices with very small diameter (<10 mu m), surpassing the capabilities of conventional omnidirectional scattering diffraction patterns. Our results show a 3.5-fold increase in internal quantum efficiency over wavelengths above 900 nm compared to the structure without metasurface. The absorption enhancement brought about by directional scattering is not limited to thin i-layers; it can potentially improve a wide range of photodiode geometries and structures.

We proposed a simple but unprecedented approach for suppressing power crosstalk (XT) between closely spaced optical fiber cores. Unlike the conventional method, used for image fibers and based on the arrangement of cores of different shapes and refractive indices, our method suppresses XT using optical fibers with a random core or cladding refractive index (RI) distribution. The results showed that RI fluctuations of approximately ±3% caused significant XT reduction at core spacings greater than ~5 times the core radius. We believe that the proposed method can contribute to the easy fabrication of ultrafine image fibers with high resolutions.

A new fiber optic capillary structure for single-end-controlled nanoparticle transport was proposed by adjusting incident wavelengths. Two bowtie cores combined with the capillary allow for the confinement of light intensity inside an ultrasmall area.

We propose a flexibly tunable and low-loss optical burette with an all-dielectric bowtie core capillary structure, where nanoparticle arrays can be transported bidirectionally with incident light from one end. Multiple hot spots, acting as optical traps, are periodically distributed at the center of the bowtie cores along the propagation direction because of the mode interference effect of guided lights. By adjusting the beam waist position, the hot spots continuously move across the entire capillary length; thus, trapped nanoparticles also transfer with the hot spots. The bidirectional transfer can be realized simply by changing the beam waist in the forward or backward direction. We confirmed that nanosized polystyrene spheres can be bidirectionally moved along a capillary length of ≈ 20 μm. Furthermore, the magnitude of the optical force can be adjusted using the incident angle and beam waist width, whereas the trapping period can be adjusted using the incident wavelength. These results were evaluated using the finite-difference time-domain method. We believe that this new approach can be extensively used in the field of biochemical and life sciences because of the properties of an all-dielectric structure, bidirectional transportation, and single incident light.

This research proposes a graded-index multilayer dielectric microsphere lens to elongate and control the beam shape of the photonic nanojets (PNJs). To find the optimal set of material and structural parameters, the genetic algorithm (GA) was applied. Our work achieved the ultralong PNJ of $\boldsymbol{129.21\lambda}$ long in water environment with a beam FWHM of $\sim \boldsymbol{2.73 \lambda}$ , which are top performances to the best of our knowledge. We believe that this simple optical probe could contribute to particle trapping and transport nanoparticles such as biomolecules.

We present an optical burette with an all-dielectric bowtie core capillary structure that can transport nanoparticles bidirectionally with incident light from one end. We confirm that nanosized particles can be moved along a capillary length of $\approx$20$\mu$m simply by adjusting the focus position of the input light.

An optical conveyor belt is designed based on a stepped anti-reflection strip which is capable of capturing and transporting a large number of high-refractive-index (HRI) and low-refractive-index (LRI) nanoparticles, simultaneously. The bidirectional transportation can be achieved easily by switching the incident wavelength. The transmission success rate can be flexibly adjusted by changing the light power, and the maximum can reach 99.9% with an incident power of $100 \text{mW}/\mu \mathrm{m}^{2}$ . This design also has the potential of separating HRI and LRI particles by making the difference in their transmission success rate. This proposal with simple structure, easy operation and various functions is expected to be widely used in nanoparticle transmission and manipulation.

Elastic Optical Network (EON), which adopts a flexible grid, is a promising solution for next-generation optical networks. EONs face the problem of poor spectrum utilization due to the generation of spectrum fragmentation. In order to improve the performance of EONs, spectrum management is necessary. In this paper, a Load Balancing and Time-Frequency (LB-TF) fragmentation awareness algorithm is proposed. This algorithm performs spectrum allocation by comparing spectrum continuity and service duration. The simulation results show that, compared with the reference algorithms, the LB-TF algorithm can improve the spectrum utilization by 6.0% and reduce the request blocking rate by 37.8%. In different network models with different requests bandwidth distributions, the LB-TF algorithm performs well.

Optical multiple-input multiple-output (MIMO) technology is introduced into optical space division multiplexing (SDM) communication as an effective solution for the crosstalk issue. Unfortunately, this application is limited because all the channel information over the transmission link must be transmitted to MIMO receivers for complete crosstalk compensation, which indicates difficulty in applying MIMO to the transmission path via optical switches. We newly propose that one of the solutions to this limitation is a ring network because all channel information can be maintained in the ring. In particular, a typical ring network model comprising optical add-drop multiplexers (OADMs) and multicore fibers (MCFs) is introduced, and the ability of MIMO to compensate for capacity degradation because of the inter-core crosstalk is investigated. Moreover, the protection function, which is essential for the ring network, is also evaluated under the fiber and fiber core failures. As per the simulation results, although the protection operation affects the transmission capacity, the capacity loss is suppressed in the event of a failure to < 5%. We believe that these results provide useful information for designing SDM-based optical networks.

We have previously shown that space division multiplexing (SDM) based optical ring network consisting of multicore fibers (MCFs) and optical switch nodes such as optical add-drop multiplexers (OADMs) can be a promising application of optical multiple-input multiple-output (MIMO) technique. This network model is effective in avoiding the degradation of MIMO channel capacity due to route switching by nodes. In this paper, we proposed a new ring protection scheme for this ring network model by applying MIMO processing. It was found that this proposed method can prevent signal interruption even without switching at the nodes, especially in the fully coupled environment.

Multiple-input and multiple-output (MIMO) signal processing technique has been introduced to eliminate the interference caused by crosstalk along Space Division Multiplexing (SDM) links. In optical networks, optical paths are set between end-to-end nodes via several switches. Optical switches connect light signals using appropriate switching rules. Consequently, different combinations of light signals transmitted through several coupled Multi-Core Fibers (MCFs) along an end-to-end optical path. In turn, this type of optical transmission results in an increased complexity with respect to the MIMO signal processing at the receiver and also in a reduced transmission capacity of the entire communication system. To analyze this issue in detail, an optical MIMO network model with MCFs and optical switch was considered, and the eigenvalue distribution of channel matrix along with average capacity of MCF links was discussed. The analysis showed that the optical switch disperses the eigenvalue distribution of channel matrix and reduces the capacity by approximately 15% for SDM network with MCFs. This degradation rate is increased noticeably for larger crosstalk in MCF links and is increased moderately with an increasing number of switches.

The focus of this study was mainly on the birefringence of nanosized bowtie-shaped slot core fibers that can transport ultrasmall optical spots. Here we showed large birefringence for the fibers reaching as high as 0.33, which is three orders of magnitude greater than normal-sized birefringent fibers, the main cause of which being the impact of geometrical birefringence arising from significant differences between the orthogonal modal distributions. Moreover, we investigated the polarization maintaining property for acute-angled bending in a 5-mu m fiber and demonstrated slight degradations of less than 5 dB for the extinction ratio in a 180. bend, which was several orders of magnitude lower than the ratio for the fiber without bending. We used computer simulations for the estimates presented in this study. We believe that the high-polarization maintaining performance presented herein will be required for nanosized optical sensing probes and interconnections in photonic integrated circuits.

In this study, we propose a novel silicon-core optical fiber with a bowtie-shaped slot core structure for ultrasmall light-spot transmission. Our simulations show that this dielectric structure creates a nanosized optical spot with the high intensity and transmits it with the low loss. As an example, we obtained an optical spot with the full width at half maximum of 5 nm × 5 nm and a peak power density 167 times higher than that of the surrounding areas. The optical loss because of the scattering in the waveguides and the material absorption was estimated to be 0.58 dB/cm, which is a thousand times less than the optical losses in typical plasmonic waveguides. We believe our proposed structure will contribute to research studies in the field of near-field sensing systems. It also has application potential in nanolithography with high-power lasers.