Optical wireless communication (OWC) is expected to play a crucial role in future wireless communication networks due to its several advantages, including a license-free spectrum, robustness to electromagnetic interference, and ultra-wide bandwidth that enables very high transmission data rates. In most OWC systems, the received light typically requires amplification in the optical domain using lenses or compound parabolic collectors (CPCs). However, these approaches are constrained by the conservation of étendue, which results in a limited field of view (FOV) of the optical receiver.

Recent studies have shown that fluorescent concentrators/antennas can effectively concentrate light without being limited by étendue. Since the concentration principle of these antennas is based on fluorescence, they can achieve both high concentration gain and a wide FOV. Nevertheless, the photoluminescence (PL) lifetime of these antennas introduces an additional bandwidth-limiting factor. Fortunately, advancements in materials science techniques have significantly reduced the PL lifetime to just a few nanoseconds or even lower, thereby supporting the transmission of data at a high rate . This talk reviews the recent trend of exploring new fluorescent concentrators in various OWC applications, including visible light communications (VLCs) and underwater OWCs. These concentrators include those made from commercially available fluorescent fibers, as well as organic and inorganic fluorescent materials.

Compared with conventional planar electromagnetic waves, vortex electromagnetic waves carrying orbital angular momentum (OAM) are unique beams with a helical phase structure and a toroidal amplitude field. Due to the infinity of OAM modes and orthogonality between different modes, a completely new degree of freedom independent of time, frequency, and polarization domains is provided. OAM waves have great potential in terms of channel expansion and improving spectral efficiency. And with the progress of research, how to transmit more information and have more channel capacity has been a hot issue. In this paper, a novel single-layer dual-band orbital angular momentum (OAM) multiplexed reflective metasurface array antenna is proposed. We firstly design a metasurface that can realize dual-band nearly 360° phase coverage at 7 and 12 GHz, and realize 2-bit coding metasurface cells by obtaining suitable geometrical parameters through simulation optimization, and then we obtain the position of each cell in the array away from the feed source by computing. Afterwards, the corresponding phase compensation and the phase gradient required for specific mode OAM beam generation are calculated from the position of each cell in the array, and a 30×30 reflective metasurface array is obtained, which can independently generate different modes of OAM beams in the C and Ku bands, and complete flexible beam control in each operating band, providing a new possibility for realizing more transmission frequency bands and larger channel capacity in communication applications.

Three-dimensional waveguide structure forming mode manipulating devices

Mode multiplexing technology is a promising technology to increase the optical communication capacity, where a 3D waveguide structure is a neat solution for manipulating the modes with their symmetry in horizontal and vertical direction or their combination. Three-dimensional photonic-integrated vertical directional couplers are applied to form the mode multiplexer, where the mode (de)multiplexer serves for spatial (de)multiplexing the spatial guide modes in a few-mode waveguide. These guide modes are the waveguide modes such as the E11, E21, and E12 modes. In addition, the directional couplers (either the horizontal directional couplers or the vertical directional couplers) can be formed by using adiabatic tapered waveguides. The usage of the tapered waveguide can be functioned as a wavelength expander. In addition, the fabrication of the 3D waveguide structure can be utilized by using the multi-step photolithography processing methodology. For example, we have demonstrated the fabrication of a hybrid-core planar waveguide forming mode multiplexer by using multi-step photolithography processing for the realization of a high-order-mode band-passed function. Also, the passive device can be further developed to be an active device for dynamically manipulating the guided modes. In conclusion, the 3D waveguide structure forming mode manipulating devices are powerful in a mode division multiplexing system for the optical communication.

Ultrafast all-optical computing is essential for overcoming the speed and efficiency limitations of electronic systems, enabling rapid data processing and transmission with minimal energy consumption. The main challenges in all-optical computing include developing materials with strong, fast, and reversible nonlinear optical properties, as currently used materials often require high power and lack durability. Managing optical losses and maintaining signal integrity over distances and components is crucial, necessitating low-loss waveguides and efficient light confinement. Integrating nanoscale optical components with high precision and miniaturization demands advanced fabrication techniques and innovative designs for scalable all-optical circuits. Developing novel materials with enhanced nonlinear optical properties, including organic materials, graphene, plasmonic nanostructures, transition metal dichalcogenides, MXenes, and advanced metal–organic frameworks, can significantly improve the performance of optical switches and logic gates.

In this paper, we present a theoretical model and comprehensive analysis of ultrafast transitions between reverse saturable absorption and saturable absorption in CoTCPP surface-supported metal–organic framework (SURMOF) nanofilms with femtosecond (fs) laser pulses at 400 nm.

The effects of laser input intensity, thickness, concentration, and nonlinear absorption coefficients on transmittance have been studied to optimize all-optical switching in recently reported CoTCPP SURMOF nanofilms. We demonstrate ultralow-power and ultrahigh-contrast all-optical switching in SURMOF nanofilms and use the results to design all-optical fs AND, OR, NOT, universal NOR, and NAND logic gates. The percentage modulation of the Boolean all-optical NAND logic gate with CoTCPP SURMOF nanofilms is greater compared to MoTe₂ nanofilms and BODIPY derivative compound ZL-61. A passive photonic diode with CoTCPP/ZL-61 has also been designed, which results in a nonreciprocity of 17 dB.

Based on CoTCPP SURMOF nanofilms, various combinational circuits that include an adder, subtractor, multiplexer, and encoder can be designed and explored using ultrafast all-optical logic gates. The remarkable nonlinear optical properties of CoTCPP SURMOFs open exciting prospects for ultrafast all-optical computing.

Introduction

A methodology suitable for analyzing strong IBG (Integrated Bragg Grating) is presented using the Transfer Matrix Method (TMM) based on the translation of any waveguide's physical structure into a matrix of effective refractive indexes, n_eff, which is wavelength-dependent and describes the behavior of light in the IBG while avoiding the use of approximations like in Coupled Mode Theory.

IBGs have special characteristics that require a methodology that considers any tiny variation in geometry. These have a notable impact on the value of n_eff because of the high refractive index contrast of SOI (Silicon on Insulator) and therefore on the spectrum of the transfer function.

Method

Starting with a given IBG geometry, we mapped the waveguide structure into a matrix, N’, of effective refractive indices, which are functions of the wavelength and position along the IBG, n_eff(λ,z). Subsequently, the TMM was applied using N’ to characterize each layer and interface of the IBG. Finally, the reflectivity and phase spectra were obtained, i.e., the transfer function.

Using this methodology, four apodization methods (corrugation width, lateral delay, duty cycle, and periodic phase modulations) and different chirp methods are presented and compared. Also, the presence of additional Bragg orders is demonstrated as a result of the Fourier transform equivalence between the IBG apodization and its transfer function in reflection. To demonstrate the generality of the methodology, two technological platforms, SOI and Al₂O₃, are analyzed.

Results

Simulations allow us to obtain the reflectivity and phase spectra, i.e., the IBG transfer function. The goodness of each method is observed, as well as the second and third Bragg order spectra. The Al₂O₃ platform shows more robustness against fabrication errors.

Conclusions

TMM is the most suitable methodology for analyzing an IBG. Apodization, chirp methods, and higher Bragg orders are demonstrated to improve transfer functions.

In this study, we explore the transmission of a high-speed 10Gbps optical signal over a hybrid Single-Mode Fiber (SMF) and Multi-Mode Fiber (MMF) system using Optisystem. The optical signal is initially transmitted over 5-20 kilometers of an SMF, ensuring minimal dispersion and loss while maintaining signal integrity. Following the SMF transmission, the signal is coupled into an MMF, which operates in the LP01 mode. The MMF generates 16 distinct modes, each carrying the optical field of the transmitted signal. The simulation outcomes demonstrate that the hybrid system can sustain high signal quality and low BER across different fiber spans, showing resilience against modal dispersion and attenuation. By optimizing parameters like laser wavelength, modulation format, and receiver sensitivity, we achieved efficient signal transmission suitable for high-speed applications. This research underscores the potential of hybrid SMF-MMF systems to meet the growing demand for high-bandwidth communication in contemporary optical networks, especially where integrating different fiber types can offer a more adaptable and scalable solution. In addition, this multimode transmission approach aims to leverage the capacity of MMFs to handle multiple modes. Future work will investigate advanced modulation techniques and the effects of environmental factors on system performance to further improve the reliability and efficiency of hybrid optical networks.

In recent years, heterojunctions formed by stacking two-dimensional (2D) materials have attracted considerable interest because of their outstanding electronic and optoelectronic characteristics. These have paved the way for new device structures and uses. The combination of black phosphorus (BP) and molybdenum disulfide (MoS₂) is particularly noteworthy for its potential in creating state-of-the-art optoelectronic devices. This research explores the dynamics between BP, MoS₂, and chromium (Cr) contacts, shedding light on the electrical characteristics of a BP/MoS₂ heterojunction that exhibits rectifying behavior, mainly n-type conduction, and a significant ON/OFF current ratio. The higher unexpected current observed in the presence of a negative bias applied to both the MoS₂ and BP sides is clarified through an energy band model that includes a type II heterojunction at the BP/MoS₂ interface. In this case, Cr makes a Schottky contact with MoS₂ and an ohmic contact with BP. The BP/MoS₂ heterojunction also shows a remarkable photoresponse, which increases linearly with the incident light power, reaching a responsivity of 100 µA/W to white light with an incident power of 50 µW. Time-resolved photocurrent experiments show a fast response, with rise times of less than 200 milliseconds. Moreover, the rectifying characteristics at lower pressure present a kink in the forward region revealing different conduction mechanisms, namely drift-diffusion and band-to-band tunnelling. The results of this work highlight the potential of BP/MoS2 heterostructures for applications in low-power electronics, high-performance transistors, photodetector, and sensitive pressure sensors [1,2,3].

[1] Viscardi, L.; et al., Dominant N-Type Conduction and Fast Photoresponse in BP/MoS₂ Heterostructures. Surfaces and Interfaces 2024, 49, 104445.
[2] Di Bartolomeo, A.; et al., Gated BP/MoS₂ heterostructure with temperature enhanced photocurrent. IEEE 24th International Conference on Nanotechnology (NANO) (2024).
[3] Durante, O.; et al., Pressure-Dependent Current Transport in vertical BP/MoS₂ heterostructures. Submitted on 2D Materials.

The creation and manipulation of quantum states are essential in developing quantum information theory and its applications. Such states can be applied in quantum communication, cryptography, and quantum computing. The states, defined in a finite-dimensional Hilbert space (truncated states), are relevant in this context. The physical systems in which finite-dimensional states can be generated, and the system's evolution can, thus, be limited to a certain number of n-photon states, are called quantum scissors [1]. For the cases of linear and nonlinear systems, we refer to them as linear and nonlinear quantum scissors, respectively.

In this communication, we consider a system consisting of two identical nonlinear Kerr-type quantum oscillators excited by a series of ultra-short pulses. The oscillators are coupled to each other, and the interaction between them is of the linear type. We discuss how the excitation influences the system's generation of strongly entangled states. In addition, we demonstrate that the effectiveness of creating maximally or almost maximally entangled states depends strongly on the applied excitation scheme and on the time between two subsequent pulses. In particular, we investigate how entanglement production depends on the frequencies of the excitations and on the fact that both subsystems are excited simultaneously or not [2,3].

1. W. Leoński, A. Kowalewska-Kudłaszyk, Progress in Optics, Ed. E. Wolf, 56 (2011) 131.
2. J. K. Kalaga, A. Kowalewska-Kudłaszyk, M. W. Jarosik, R. Szczęśniak, W. Leoński, Nonlinear Dynamics, 97 (2019), 1619.
3. J. K. Kalaga, A. Kowalewska-Kudłaszyk, J. Opt. Soc. Am. B, 36 (2019), 2140.

The concept of high-dimensional multiphotonic gates has many potential applications. As an example, encoding qubit information in high-dimensional systems has significant advantages in terms of robustness against errors and can reduce quantum circuit complexities, and high-dimensional error-correction codes have shown advantages in terms of resources. Furthermore, high-dimensional multiphoton gates can be used for Bell-state or Greenberger–Horne–Zeilinger-state measurements, which are an essential requirement of quantum communication protocols. As a high-dimensional degree of freedom, the orbital angular momentum (OAM) of photons can be used for this purpose.

In this work, integrated high-dimensional quantum gates are proposed for the first time. The structure of the proposed integrated quantum gates includes properly designed multimode interference (MMI) waveguides. In MMI waveguides, an input field profile can be reproduced in single or multiple images at periodic intervals along the propagation direction of the waveguide. This property is called self-imaging. Using the beam propagation method (BPM) for simulating OAM modes in MMI waveguides, it has been shown that at the shortest length for self-imaging occurrence, the sign of the topological charge of the even OAM modes is reversed, while the odd OAM modes remain unchanged. The charge conversion property of the MMI waveguides for even higher-order OAM modes can be used to implement the integrated quantum gates in a simple way. For instance, for an input state of (-2, -1, 0, 1), the quantum logic gate of X can be implemented using the proposed MMI waveguide followed by a first-order spiral phase plate (SPP), in that the SPP adds +1 to the mode, leading to (-1,0,1,2). Afterwards, the MMI waveguide reverses the sign of the even modes without any change in the odd modes, which leads to the correct output modes: (-1,0,1, -2).

The emission enhancement of quantum emitters is crucial for the development of quantum technologies based on single-photon sources. Metallic nanoparticles have been initially considered with this aim due to their ability to produce strong electromagnetic energy concentrations (hot spots) at the emitters' position. However, metallic nanostructures suffer from high non-radiative losses. To address this, high-refractive-index dielectric (HRID) nanoparticles, characterized by exhibiting Mie resonances with negligible absorption in specific spectral ranges, have emerged as an alternative. Additionally, dielectric nanoparticles can exhibit magnetic responses despite being non-magnetic materials. The interference between electric and magnetic resonances can result in directional properties, potentially increasing the collection efficiency of scattered radiation. Despite these advantages, HRID nanoparticles do not enhance light emission as much as metallic ones. In contrast, hybrid metal–dielectric nanostructures can offer greater functionality and efficiency compared to purely metallic or dielectric nanoparticles.

Recently, moderate-refractive-index (MRI) dielectric nanoparticles have been numerically and experimentally demonstrated to enhance the emission of excitons in 2D materials. These MRI materials (n≈2.2) exhibit broadband Mie resonances, enabling the simultaneous enhancement of multiple excitons.

In this work, different dimer configurations are analyzed with the objective of enhancing the photoluminescence signal of a quantum dot located in the dimer gap. Dimers of pure metallic, pure HRID, pure MRI dielectric, and hybrid combinations of metallic and dielectric nanoparticles, either HRID or MRI, are numerically explored. For each case, the excitation enhancement, Purcell factor at the emission wavelengths, and directionality are studied by means of the Finite Element Method in COMSOL Multiphysics. Through the results obtained, we can conclude that the combination of MRI and HRID nanoparticles can provide large values of the photoluminescence signal (4–4.8 for MRI combinations and 5.4-7 for HRID) with low losses (with the ratio of the radiative to non-radiative power being between 0.63 and 0.7).